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Pharmacological and Environmental Factors in the Development of Contingent Tolerance to Cocaine in Pigeons

Permanent Link: http://ufdc.ufl.edu/UFE0022416/00001

Material Information

Title: Pharmacological and Environmental Factors in the Development of Contingent Tolerance to Cocaine in Pigeons
Physical Description: 1 online resource (118 p.)
Language: english
Creator: Marusich, Julie
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: cocaine, operant, pigeon, tolerance
Psychology -- Dissertations, Academic -- UF
Genre: Psychology thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of effects of repeated cocaine administration on operant behavior in humans and nonhumans. Previous research with rats and monkeys has shown that tolerance to behavioral effects of cocaine develops if the drug is administered before behavioral test sessions but does not if it is administered after sessions, an outcome which is referred to as contingent tolerance. Many experiments have found contingent tolerance, except a recent experiment using pigeons. The results of that study suggested that pigeons might develop tolerance to effects of cocaine regardless of whether the drug was administered before or after behavioral test sessions. The current set of experiments focused on environmental and pharmacological factors in the development of contingent tolerance to cocaine in pigeons by examining various relations between time of drug administration and the conduct of behavioral test sessions. Experiment 1 examined if cocaine administered immediately before or immediately after the behavioral session led to the development of tolerance to effects of cocaine during the behavioral session. The results showed that pre-session administration of cocaine reliably led to tolerance, and post-session administration of cocaine led to tolerance in half the subjects. Experiment 2 examined whether eating under effects of cocaine in the home cage, which occurs if the drug is given post-session, contributed to the development of tolerance to effects of cocaine on key pecking during the behavioral session. In this experiment, some subjects were administered cocaine after the behavioral session and immediately before being fed their post-session food ration, and other subjects were fed their post-session food ration immediately after the session and were administered cocaine one hour later. Results of Experiment 2 found that eating in the home cage under the effects of cocaine was not necessary for tolerance to develop to effects of cocaine during the behavioral session, and that the majority of subjects developed tolerance from post-session cocaine administration. Experiment 3 examined whether mere exposure to cocaine in the home cage without exposure to an experimental session led to tolerance to effects of cocaine during a behavioral session. Mere drug exposure did not reliably produce tolerance during the behavioral session. Experiment 4 examined if daily cocaine administration during dose-response curve redetermination was necessary for tolerance to develop. The results showed that tolerance from post-session cocaine administration was readily observed even when chronic dosing was discontinued during dose-response curve assessment. Therefore, the combined results showed that pigeons often develop tolerance to effects of cocaine during the behavioral session when cocaine is administered post-session. Some aspect of exposure to the experimental session or experimental context on a regular basis was necessary for tolerance to develop, yet this exposure did not have to occur while subjects were under effects of the drug. These results indicate that not-contingent tolerance may be common in pigeons, and therefore questions the generality of contingent tolerance to cocaine.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Julie Marusich.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Branch, Marc N.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022416:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022416/00001

Material Information

Title: Pharmacological and Environmental Factors in the Development of Contingent Tolerance to Cocaine in Pigeons
Physical Description: 1 online resource (118 p.)
Language: english
Creator: Marusich, Julie
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: cocaine, operant, pigeon, tolerance
Psychology -- Dissertations, Academic -- UF
Genre: Psychology thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of effects of repeated cocaine administration on operant behavior in humans and nonhumans. Previous research with rats and monkeys has shown that tolerance to behavioral effects of cocaine develops if the drug is administered before behavioral test sessions but does not if it is administered after sessions, an outcome which is referred to as contingent tolerance. Many experiments have found contingent tolerance, except a recent experiment using pigeons. The results of that study suggested that pigeons might develop tolerance to effects of cocaine regardless of whether the drug was administered before or after behavioral test sessions. The current set of experiments focused on environmental and pharmacological factors in the development of contingent tolerance to cocaine in pigeons by examining various relations between time of drug administration and the conduct of behavioral test sessions. Experiment 1 examined if cocaine administered immediately before or immediately after the behavioral session led to the development of tolerance to effects of cocaine during the behavioral session. The results showed that pre-session administration of cocaine reliably led to tolerance, and post-session administration of cocaine led to tolerance in half the subjects. Experiment 2 examined whether eating under effects of cocaine in the home cage, which occurs if the drug is given post-session, contributed to the development of tolerance to effects of cocaine on key pecking during the behavioral session. In this experiment, some subjects were administered cocaine after the behavioral session and immediately before being fed their post-session food ration, and other subjects were fed their post-session food ration immediately after the session and were administered cocaine one hour later. Results of Experiment 2 found that eating in the home cage under the effects of cocaine was not necessary for tolerance to develop to effects of cocaine during the behavioral session, and that the majority of subjects developed tolerance from post-session cocaine administration. Experiment 3 examined whether mere exposure to cocaine in the home cage without exposure to an experimental session led to tolerance to effects of cocaine during a behavioral session. Mere drug exposure did not reliably produce tolerance during the behavioral session. Experiment 4 examined if daily cocaine administration during dose-response curve redetermination was necessary for tolerance to develop. The results showed that tolerance from post-session cocaine administration was readily observed even when chronic dosing was discontinued during dose-response curve assessment. Therefore, the combined results showed that pigeons often develop tolerance to effects of cocaine during the behavioral session when cocaine is administered post-session. Some aspect of exposure to the experimental session or experimental context on a regular basis was necessary for tolerance to develop, yet this exposure did not have to occur while subjects were under effects of the drug. These results indicate that not-contingent tolerance may be common in pigeons, and therefore questions the generality of contingent tolerance to cocaine.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Julie Marusich.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Branch, Marc N.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022416:00001


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9614297b9823e7fd9e32ba8d6dc7ee243df19b10







PHARMACOLOGICAL AND ENVIRONMENTAL FACTORS IN THE DEVELOPMENT OF
CONTINGENT TOLERANCE TO COCAINE IN PIGEONS




















By

JULIE A. MARUSICH


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2008


































2008 Julie A. Marusich









ACKNOWLEDGMENTS

I thank my advisor, Marc Branch, for his guidance, support, and encouragement, and for

always being available for discussion. I also thank him for great help in developing my writing,

teaching me to think critically, and teaching me how to design experiments properly. I thank

Jesse Dallery for providing helpful comments throughout my graduate career, enduring aid in

statistical and graphical analyses, and always being a source of positive reinforcement. I thank

Tim Hackenberg for teaching me what it means to be a radical behaviorist. I thank my graduate

student colleagues Brian Kangas, Anne Macaskill, Dave Maguire, Michelle Miller, Jon Pinkston,

Matt Weaver, and Jin Yoon for their help in running sessions, technical support, and always

being available for conceptual discussions. I thank my other committee members H. Jane

Brockmann, Brian Iwata, and Alan Spector for their many contributions to this project and help

in shaping me into a better scientist. Lastly, I would like to thank my family and friends,

especially Phil, Bethany, Erin and Rachelle for their care and support throughout this process.









TABLE OF CONTENTS

page

A C K N O W LE D G M EN T S ..................................................................... ............................... ...

LIST OF TABLES ......... ..... .... ......... .................................... 6

LIST O F FIG U RE S .................................................................8

A B S T R A C T ............................................ ...................................................... 10

CHAPTER

1 IN TR O D U C T IO N .................................12.............................

2 EX PER IM EN T 1 .............................................................................. ........ 19

M e th o d ............................................................................................................1 9
S u b j e c ts ................................ ...................................................................................... 1 9
A pparatu s .................................................. .... .................. .. ....... ... .. ........... 19
Procedure ......... .. ...... ........ .... .... .. ........... ........ .. 20
R esu lts an d D iscu ssio n ...................................................................................................... 2 3

3 EXPERIMENT 2 ........................................................................... 44

M e th o d ................................ ..........................................................................4 5
S u b je cts ................... ...................4...................5..........
A p p aratu s ................................................... ....................... 4 5
P ro c e d u re ............. ............................ .. .........................................................4 5
R esu lts an d D iscu ssio n ...................................................................................................... 4 7

4 E X P E R IM E N T 3 .................................................................57

M e th o d ................................ ..........................................................................5 8
S u b j e cts ................... ...................5...................8..........
A p p aratu s ................................................... ....................... 5 8
P ro c e d u re ............. ............................ .. .........................................................5 8
R esu lts an d D iscu ssio n ...................................................................................................... 6 0

5 EXPERIMENT 4 ........................................................................... 80

M e th o d ................................ .......................................................................... 8 0
S u bj e cts ................... ...................8...................0..........
A p p aratu s ................................................... ....................... 8 1
P procedure ......... ...... ........ ...... .... ..... ..... .......... .. 8 1
Results and Discussion .................... ............................ ...... 83




4









6 G E N E R A L D ISC U SSIO N ........... .......... .........................................................................10 1

L IST O F R E FE R E N C E S ................................................................................................. 115

B IO G R A PH IC A L SK E T C H ............................... ................. .................................................. 118









LIST OF TABLES


Table page

2-1 Number of administrations of each dose of cocaine during acute dose-response curve
determination for Experim ent 1...... ........................... ........................................ 30

2-2 Number of administrations of each dose of cocaine during dose-response curve
determination following the first chronic regimen for Experiment 1...............................31

2-3 Number of administrations of each dose of cocaine during dose-response curve
determination following the second chronic regimen for Experiment 1. ........................32

2-4 Key pecks per minute following each administration of saline-vehicle for
E x p erim ent 1 ..............................................................................33

2-5 ED50s for each subject for each phase of Experiment 1....... .... ................................... 34

3-1 Number of administrations of each dose of cocaine for each subject during acute
dose-response curve determination for Experiment 2. ........................... .................. 50

3-2 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following the chronic drug regimen for Experiment 2. .....51

3-3 Key pecks per minute following each administration of saline-vehicle for
E x p erim en t 2 ........................................................................... 5 2

3-4 ED50s for each subject for each phase of Experiment 2. ..................................................53

4-1 Number of administrations of each dose of cocaine for each subject during acute
dose-response curve determination for Experiment 3. ........................ ................... 65

4-2 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 30 administrations of saline in the home
cage for E xperim ent 3 .................................................................. .. .......... ............... 66

4-3 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 30 administrations of cocaine in the home
cage for Experim ent 3 ........ .............. .. .................................. ............... 67

4-4 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 60 administrations of cocaine in the home
cage for E xperim ent 3 ...... .. .......................... .. ........... ............. .. ...... ......................68

4-5 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following the pre-session chronic drug regimen for
Experim ent 3 .............. .............. ............................ ............ ...... ............. .69









4-6 Key pecks per minute following each administration of saline-vehicle for
E x p erim ent 3 ............................................................................................................. ........ 70

4-7 ED50s for each subject for each phase of Experiment 3 ........... ...................................71

5-1 Number of administrations of each dose of cocaine for each subject during acute
dose-response curve determination for Experiment 4. ................... ................... .......... 86

5-2 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following post-session chronic administration with
saline administered on intervening days for Experiment 4 ......................... ............87

5-3 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following post-session chronic administration with
cocaine administered on intervening days for Experiment 4 ................ ...............88

5-4 Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following pre-session chronic administration for
E x p erim en t 4 ........................................................................... 8 9

5-5 Key pecks per minute following each administration of saline-vehicle for
E x p erim en t 4 ........................................................................... 9 0

5-6 ED50s for each subject for each phase of Experiment 4. ................... ...................92









LIST OF FIGURES


Figure page

2-1 Effects of cocaine during acute and pre-session administration for the Pre-post group
in E x perim ent 1 ............................................................................35

2-2 Effects of cocaine during acute and post-session administration for the Pre-post
group in Experiment 1. ................................................ .............36

2-3 Effects of cocaine during pre-session and post-session administration for the Pre-post
group in Experiment 1. ................................................ .............37

2-4 Effects of cocaine during acute and post-session administration for the Post-pre
group in Experiment 1. ................................................ .............38

2-5 Effects of cocaine during acute and pre-session administration for the Post-pre group
in E x perim ent 1 ............................................................................39

2-6 Effects of cocaine during pre-session and post-session administration for the Post-
pre group in Experim ent 1 ................................. ...........................................40

2-7 Group-average data for both groups showing effects of cocaine during acute
administration and the first chronic regimen in Experiment 1. .......................................41

2-8 Group-average data for both groups showing effects of cocaine during acute
administration and the second chronic regimen in Experiment 1...................................42

2-9 Group-average data for both groups showing effects of cocaine during the first and
second chronic regimen in Experiment 1.................... .......... ................................ 43

3-1 Effects of cocaine during acute and post-session administration for the Immediate-
D rug group in E xperim ent 2. ..................................................................... .................. 54

3-2 Effects of cocaine during acute and post-session administration for the Delayed-Drug
group in Experim ent 2. ......................... ........................ .. ............. .. ...... 55

3-3 Group-average data for both groups in Experiment 2, comparing effects of acute
cocaine administration and post-session administration............... .............................56

4-1 Effects of cocaine during acute administration and following 30 days of saline
administration in the home cage for Experiment 3.................................... ............72

4-2 Effects of cocaine during acute administration and following 30 days of cocaine
administration in the home cage for Experiment 3......... .................... ....... ............73

4-3 Effects of cocaine during acute administration and following 60 days of cocaine
administration in the home cage for Experiment 3............................ ....................74









4-4 Effects of cocaine during acute and pre-session administration for Experiment 3............75

4-5 Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 30 days of saline administered in the
h om e cag e. ............................................................. ................ 7 6

4-6 Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 30 days of cocaine administered in
the hom e cage. .......................................................... ................. 77

4-7 Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 60 days of cocaine administered in
the hom e cage. .......................................................... ................. 78

4-8 Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of pre-session cocaine. ........... ................... ........... ........ 79

5-1 Effects of cocaine during acute administration and post-session administration with
saline administered on intervening days for Experiment 4.............................................93

5-2 Effects of cocaine during acute administration and post-session administration with
cocaine administered on intervening days for Experiment 4 .......................... ..........94

5-3 Effects of cocaine during post-session administration with saline or cocaine
administered on intervening days for Experiment 4. ......................... ............... ......95

5-4 Effects of cocaine during acute administration and pre-session administration for
E x p erim en t 4 ........................................................................... 9 6

5-5 Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and post-session administration with saline administered on
intervening days. ............................................................................97

5-6 Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and post-session administration with cocaine administered on
intervening days. ............................................................................98

5-7 Group-average data for Experiment 4 comparing effects of cocaine during post-
session administration with saline or cocaine administered on intervening days..............99

5-8 Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and pre-session administration.................... .... ...................... 100









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

PHARMACOLOGICAL AND ENVIRONMENTAL FACTORS IN THE DEVELOPMENT OF
CONTINGENT TOLERANCE TO COCAINE IN PIGEONS

By

Julie A. Marusich

August 2008

Chair: Marc Branch
Major: Psychology

Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of

effects of repeated cocaine administration on operant behavior in humans and nonhumans.

Previous research with rats and monkeys has shown that tolerance to behavioral effects of

cocaine develops if the drug is administered before behavioral test sessions but does not if it is

administered after sessions, an outcome which is referred to as contingent tolerance. Many

experiments have found contingent tolerance, except a recent experiment using pigeons. The

results of that study suggested that pigeons might develop tolerance to effects of cocaine

regardless of whether the drug was administered before or after behavioral test sessions. The

current set of experiments focused on environmental and pharmacological factors in the

development of contingent tolerance to cocaine in pigeons by examining various relations

between time of drug administration and the conduct of behavioral test sessions. Experiment 1

examined if cocaine administered immediately before or immediately after the behavioral

session led to the development of tolerance to effects of cocaine during the behavioral session.

The results showed that pre-session administration of cocaine reliably led to tolerance, and post-

session administration of cocaine led to tolerance in half the subjects. Experiment 2 examined

whether eating under effects of cocaine in the home cage, which occurs if the drug is given post









session, contributed to the development of tolerance to effects of cocaine on key pecking during

the behavioral session. In this experiment, some subjects were administered cocaine after the

behavioral session and immediately before being fed their post-session food ration, and other

subjects were fed their post-session food ration immediately after the session and were

administered cocaine one hour later. Results of Experiment 2 found that eating in the home cage

under the effects of cocaine was not necessary for tolerance to develop to effects of cocaine

during the behavioral session, and that the majority of subjects developed tolerance from post-

session cocaine administration. Experiment 3 examined whether mere exposure to cocaine in the

home cage without exposure to an experimental session led to tolerance to effects of cocaine

during a behavioral session. Mere drug exposure did not reliably produce tolerance during the

behavioral session. Experiment 4 examined if daily cocaine administration during dose-response

curve redetermination was necessary for tolerance to develop. The results showed that tolerance

from post-session cocaine administration was readily observed even when chronic dosing was

discontinued during dose-response curve assessment. Therefore, the combined results showed

that pigeons often develop tolerance to effects of cocaine during the behavioral session when

cocaine is administered post-session. Some aspect of exposure to the experimental session or

experimental context on a regular basis was necessary for tolerance to develop, yet this exposure

did not have to occur while subjects were under effects of the drug. These results indicate that

not-contingent tolerance may be common in pigeons, and therefore questions the generality of

contingent tolerance to cocaine.









CHAPTER 1
INTRODUCTION

Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of

repeated drug exposure (Carlton, 1983; Wolgin, 1989). Tolerance is often viewed as an

adjustment to a disturbance caused by initial drug effects, and its development may depend on

the original drug effect, and the frequency of drug administration. With repeated intermittent

drug administration, as opposed to constant administration, tolerance often develops to drug

effects that disrupt behavior (Stewart & Badiani, 1993). The experiments described in this

dissertation are focused on tolerance to behavioral effects of cocaine.

Clinical reports on cocaine abuse in humans usually point to tolerance as an

accompaniment to abuse (Johanson & Fischman, 1989). Specifically, because tolerance to both

reinforcing and aversive effects of cocaine has been demonstrated in humans, it has been

suggested that the development of tolerance can lead to the administration of larger doses of the

drug, and can therefore lead to the development of substance dependence (Johanson &

Fischman, 1989). Because of its association with drug abuse, tolerance is one of the criteria for

substance dependence according to the Diagnostic and Statistical Manual of Mental Disorders-

IV (DSM-IV).

Tolerance has been found to develop to the subjective and physiological effects of cocaine

in humans (Fischman, Schuster, Javaid, Hatano, & Davis, 1985; Mendelson, Sholar, Mello,

Teoh, & Sholar, 1998). Tolerance can also develop to the reinforcing effects of cocaine

(Emmett-Oglesby, Peltier, Depoortere, Pickering, Hooper, Gong, & Lane, 1993), and is a

common observation in drug effects on nonhuman operant behavior (e.g., Smith, 1990; Wolgin

& Hertz, 1995; Woolverton, Kandel, & Schuster, 1978). Because much human behavior can be









viewed as operant (e.g., Skinner, 1953), the study of effects of drugs on operant behavior of

nonhuman animals may have relevance to the human condition.

Tolerance can be demonstrated by a shift in the dose-effect curve away from acute effects

of the drug and toward baseline levels of behavior. This generally results in a shift in the dose-

response curve in the direction of higher doses (Carlton, 1983). Although drug tolerance can be

based on a variety of processes, the present research focuses on one particular type of process

involved in tolerance, behavioral processes. Tolerance based on behavioral processes is often

referred to as behavioral tolerance (Carlton, 1983; Wolgin, 1989). Behavioral tolerance is a

behavioral compensation for the original effects of a drug. In this type of tolerance, behavioral

processes are thought to play a key role in determining whether or not tolerance develops.

Behavioral tolerance can develop as a result of Pavlovian conditioning or operant

conditioning (Siegel, 1989; Wolgin, 1989). In the operant-conditioning account (the account of

interest here), tolerance may develop to the effects of a drug when the drug originally decreases

the amount of reinforcement obtained. In this situation, the subject's behavior will be altered to

obtain the original amount of reinforcement. If the drug initially enhances the subjects's behavior

so that it receives reinforcement more frequently than originally or does not affect the frequency

of reinforcement, tolerance is not predicted (Wolgin, 1989). The view that tolerance occurs

through a behavioral change to compensate for a loss of reinforcement is often referred to as the

reinforcement-loss hypothesis or the reinforcement-density hypothesis (Schuster, Dockens, &

Woods, 1966).

Contingent tolerance is a form of behavioral tolerance associated with operant behavior.

Contingent tolerance refers to tolerance that is dependent on the relationship between the time of

drug administration and behavioral testing (Carlton & Wolgin, 1971). Specifically, contingent









tolerance is tolerance that develops only when drug is administered before the behavioral

session, and not when drug is administered after the behavioral session or with no temporal

association with the behavioral session (Carlton & Wolgin, 1971). Contingent tolerance can be

accounted for by the reinforcement-loss hypothesis (Schuster, et al., 1966) because the drug

usually needs to be administered before the behavioral session to decrease reinforcement

obtained. The subject's behavior then adjusts, over the course of continued drug exposure, to

obtain the original amount of reinforcement. Basically, the idea is that the subject relearns, while

under the influence of the drug, to emit behavior that is effective in garnering reinforcement. If

the drug is repeatedly administered after the session, then there is often no disruption in

reinforcement obtained, as well as no opportunity to relearn while drugged, and therefore

tolerance is not predicted. Contingent tolerance is likely relevant to human drug taking, given the

operant nature of much human behavior, and may explain some instances of the development of

drug tolerance in humans.

Many past experiments have investigated whether contingent tolerance develops to effects

of psychoactive drugs. The first experiment to investigate contingent tolerance examined

tolerance to ethanol in rats (Chen, 1968). One group of subjects was administered ethanol daily,

for three consecutive days, before being placed in a circular maze, and the other group was

administered the drug immediately after exposure to the circular maze, also for three consecutive

days. On the fourth day, all subjects were administered ethanol before exposure to the maze to

test for tolerance. The group repeatedly administered ethanol before the session had developed

tolerance to the accuracy decreasing effects of ethanol, whereas the group repeatedly

administered ethanol after the session did not show tolerance, indicating that contingent

tolerance had developed to effects of ethanol on maze running in rats (Chen, 1968).









A similar experiment examined contingent tolerance to amphetamine in rats (Carlton &

Wolgin, 1971). In this experiment, the Amphetamine-saline group was repeatedly administered

amphetamine before 30 min access to sweetened condensed milk in the home cage, and

administered saline after milk access each day. The Saline-amphetamine group was repeatedly

administered saline before access to milk in the home cage, and amphetamine after milk

presentation. Only subjects in the Amphetamine-saline group developed tolerance to the milk-

intake decreases produced by amphetamine. When the Saline-amphetamine group was switched

to amphetamine administration before each milk-drinking session, subjects developed tolerance

to the milk-intake decreases, indicating that contingent tolerance had developed to effects of

amphetamine on milk drinking in rats (Carlton & Wolgin, 1971).

Campbell and Seiden (1973) sought to examine if contingent tolerance would develop to

effects of amphetamine on a typical operant task. In this experiment, rats were administered

amphetamine repeatedly before or after daily exposure to a Differential Reinforcement of Low

rates 17.5 s (DRL 17.5") schedule of reinforcement (i.e., a procedure in which reinforcement

occurred only for responses that occurred 17.5 s or more apart). When the group repeatedly

administered amphetamine before the session showed tolerance to the rate-increasing (and

therefore reinforcement-rate decreasing) effects of the drug, the group administered the drug

after the session, in which subjects had not yet shown tolerance, was switched to pre-session

administration. Then subjects in this group also developed tolerance to the rate-increasing

effects, indicating that contingent tolerance had developed to effects of amphetamine on lever

pressing in rats (Campbell & Seiden, 1973).

Two methodologically similar studies examined the development of contingent tolerance

to cocaine (Bowen, Fowler, & Kallman, 1993; Woolverton et al., 1978). Rats were repeatedly









administered cocaine before or after daily periods of 15 min access to sweetened condensed milk

in the home cage. Cocaine initially produced dose-dependent decreases in milk intake.

Subsequent dose-response analyses revealed that subjects administered cocaine before milk

access developed tolerance to the milk-intake decreases, whereas subjects administered cocaine

after milk access showed sensitization (i.e., an increased response to the drug) to the milk-intake

decreases. Therefore contingent tolerance developed to effects of cocaine on a milk-drinking task

in rats (Bowen et al., 1993; Woolverton et al, 1978).

An additional study examined the development of contingent tolerance in primates (Branch

& Sizemore, 1988). Squirrel monkeys were repeatedly administered cocaine after a behavioral

session in which they pressed a sequence of colored keys for food reinforcement. Food

reinforcement was presented on a second-order schedule in which the completion of three to five

responses on the colored keys in the correct order was reinforced on a Variable Ratio 2 schedule

meaning every two times on average [second order VR 2 (Fixed Ratio 3, 4, or 5: S]. Post-session

administration of cocaine did not produce tolerance to the rate-decreasing or accuracy-decreasing

effects of cocaine. When cocaine was later administered repeatedly before the session, tolerance

developed to the accuracy-decreasing effects of the drug, indicating that contingent tolerance had

developed to effects of cocaine on a key pressing task in monkeys (Branch & Sizemore, 1988).

Another experiment examined the development of contingent tolerance in rats with

different operant tasks (Smith, 1990). Rats were exposed to three sessions daily. The first session

each day consisted of free-operant shock avoidance with head movement as the operant. Shocks

were presented on regular intervals unless subjects moved their heads in a particular location.

Each head movement postponed shock for a fixed time interval so that all shocks could be

avoided if head movements occurred before the interval expired. In the second session of the









day, subjects lever pressed on a Fixed Interval (FI) schedule in which a response was reinforced

by food presentation after a specified interval of time had passed, and in the third session,

subjects nose poked on a Fixed Ratio (FR) schedule in which reinforcement was presented after

a particular number of responses was made. Each of the three types of sessions was conducted in

a different, distinct chamber. Cocaine was then administered daily for four-week blocks at a

particular time in relation to the sessions. First cocaine was administered after the third session of

the day, then before the third session, then before the second session, and then before the first

session. Tolerance to effects of cocaine during the FI and FR session only developed when

cocaine was administered before that particular session. Thus contingent tolerance was found to

effects of cocaine on lever pressing and nose poking in rats (Smith, 1990).

Most past research on contingent tolerance has been conducted with rats (Bowen et al.,

1993; Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Chen, 1968; Poulos, Wilkinson,

Cappell, 1981; Wenger, Tiffany, Bombardier, Nicholls, & Woods, 1981; Woolverton et al.,

1978), and one experiment used monkeys (Branch & Sizemore, 1988), but until recently no

research was conducted using pigeons to the best of my knowledge. Pinkston and Branch (2004)

sought to examine contingent tolerance to cocaine in pigeons that pecked on a multiple FR FR

(mult FR FR) schedule of reinforcement. Therefore the two FR schedules had distinct key colors

associated with them, and alternated after four reinforcers were earned on a particular schedule.

Subjects were exposed to three different chronic drug regimens, with order of the regimens

counterbalanced across subjects. The drug regimens consisted of repeated administration of a

relatively small dose of cocaine before the session, a small dose of cocaine after the session, and

a large dose of cocaine after the session. The majority of subjects developed tolerance to the rate

decreasing effects of cocaine when a small dose was administered either before or after the









session regardless of the order in which subjects proceeded through the chronic drug regimens.

Hence this study found not-contingent tolerance to effects of cocaine on key pecking in pigeons

(Pinkston & Branch, 2004). Because it involved a within-subject design and was more

complicated than past experiments investigating contingent tolerance to cocaine, the Pinkston

and Branch study did not provide for a direct test of whether contingent tolerance had developed.

The purpose of the present experiment was to investigate if tolerance to the effects of

cocaine is contingent on the relationship between the time of drug administration and the

experimental session in pigeons. More specifically, the experiment aimed to examine the effects

of cocaine on FR responding when administered pre-session and post-session in a between-

groups (initially) design.









CHAPTER 2
EXPERIMENT 1

Method

Subjects

Subjects were 12 male, White Carneau pigeons (Double "T" Farm, Glenwood, IA). Six

subjects (Cohort 1) were experimentally experienced and ranged in age from five months to one

year and five months at the beginning of the experiment. The remaining subjects (Cohort 2) were

experimentally naive and aged approximately seven months at the beginning of the experiment.

Cohorts were run in succession. All were drug naive. Subjects were housed in individual home

cages in a windowless colony room on a 16.5/7.5 hr light/dark cycle (lights on at 7am). The

colony room was maintained between 19.4'C and 22.80C. Subjects had access to vitamin-

enriched water at all times in the home cage, and were maintained at 80% of their free-feeding

body weight by post session feeding (Purina ProGrains for Pigeons) delivered immediately after

each session if needed.

Apparatus

Experimental sessions were conducted in a BRS/LVE Inc. (Model PIP 010 016)

standard three-key operant test chamber with interior dimensions measuring 31.0 cm by 36.5 cm

by 35.0 cm. The center key in each chamber measured 2.5-cm in diameter, and was located on

the panel 8.7 cm from the ceiling, equidistant from both sidewalls. To register a response, the

key required approximately 0.11 N. A 28-V DC houselight was centered 2.2 cm from the ceiling

at the center of the panel, and illuminated the chamber during the experimental session. Mixed

grain could be made available through a 5.5 cm by 5.0 cm aperture centered near the base of the

panel 20.0 cm from the ceiling.









A speaker in the experimental room produced white noise (95 db) to mask extraneous

sounds. Experimental events were arranged and recorded by EC-BASIC (Palya, Walter, & Chu,

1995) software on a computer located in another room. A cumulative recorder in another room

recorded responses as a function of time during daily sessions.

Procedure

Training. All subjects in Cohort 1 had previous experience pecking a key on a fixed ratio

(FR) schedule of reinforcement. Subjects required one to three days of an FR 1 schedule of

reinforcement to adjust to the new experimental chamber and white key light. Key pecks were

reinforced with 3 s access to mixed grain. The key light and houselights were extinguished

during food presentation. After all subjects reliably pecked the key, subjects were put on baseline

conditions.

Subjects in Cohort 2 were trained to peck a white key light through reinforcement of

successive approximations. This method was not successful for one subject (43) that was later

trained to peck the key through autoshaping (Brown & Jenkins, 1968). After all subjects reliably

pecked the key, subjects were put on an FR 1 for one to four 40-reinforcement sessions until

subjects responded 40 times in the session with minimal pause. Subjects then underwent ratio

training. Ratio training began with an FR 1. The program incremented the ratio requirement by

two responses per reinforcer after four ratios were completed with less than 1 s pause within each

ratio, excluding post reinforcement pause (PRP). Ratio requirements incremented across sessions

beginning with the last ratio requirement from the previous session until FR 20 was successfully

completed four times with less than 1 s pause within each ratio, excluding PRP. Ratio training

took two to four sessions. Throughout training and baseline, pecks were reinforced with 3 s

access to mixed grain. After ratio training was complete, subjects were run on baseline

conditions.









Baseline. Experimental sessions began with a 5-min blackout during which key pecking

had no consequence, followed by an FR 20 schedule of reinforcement for 20 min or until 40

reinforcers were obtained, whichever came first. Responding was determined to be stable by

visual inspection of cumulative records and graphs of daily session-wide response rates after 30-

40 sessions. One subject (4991) did not maintain reliable key pecking during this period. This

subject's 80% weight was reassessed and determined to be 100 g less than previously

determined, so its body weight was adjusted accordingly. Reliable key pecking was achieved on

baseline following the second weight determination. Sessions were conducted seven days a week

at approximately the same time each day.

Drug regimen. After responding was judged to be stable both within and across sessions,

acute effects of cocaine were assessed. Acute effects of cocaine were determined by

administration of the drug once per week. Saline and cocaine doses of 10.0 mg/kg, 5.6 mg/kg,

3.0 mg/kg, and 1.0 mg/kg were administered in descending order, with each dose being given

twice. A fixed order of dosing was used to aid in revealing systematic differences across repeated

determinations of effects of each dose (cf. Sidman, 1960), and there were no such differences. A

descending dose order as opposed to an ascending order was used because the first

administration of cocaine often produces a substantial decrease in rate of responding regardless

of the dose magnitude. This decrement in responding is usually replicated at large doses but not

at small doses, therefore descending dose order leads to reliable drug effects, whereas ascending

dose order does not. Following the first two replications of each dose, any dose that produced

effects judged to be too variable across two assessments (e.g. one assessment produced complete

suppression of responding, and the other assessment produce no effect) was repeated until the

mean effects was judged to be representative of all administrations. If more than one dose









produced variable effects, these doses were generally administered in alternating order. Some

subjects were also administered 4.2 mg/kg or 7.4 mg/kg cocaine if none of the doses in the

original set produced approximately a 50% decrease in rate of responding. Table 2-1 shows the

number of administrations of each dose.

After acute effects of cocaine were determined, subjects were divided into two groups

based on each subject's initial dose response curve, with an attempt to produce two groups each

containing subjects with similar drug effects. Each subject was then administered a dose of

cocaine, which originally produced approximately a 50% decrease in rate on FR responding,

chronically (i.e., once per day) for 30 sessions. If there was no dose that produced approximately

a 50% decrease in rate, then generally the dose that was 1/8 or 1/4 of a log unit smaller than the

smallest dose that produced complete response suppression was used. The Pre-post group was

administered cocaine immediately before the session, and saline immediately after the session.

The Post-pre group was administered saline immediately before the session, and cocaine

immediately after the session. All subjects in Cohort 1 were administered 5.6 mg/kg chronically.

Chronic doses for subjects in Cohort 2 included 5.6 mg/kg, 7.4 mg/kg, and 10.0 mg/kg cocaine.

Effects of cocaine were then redetermined. Subjects continued to be administered their

chronic dose everyday except once weekly when administered one of their initial acute doses of

cocaine or saline pre-session. All test doses were followed by post-session saline administration.

Some subjects were administered 13.0 mg/kg or 17.0 mg/kg if none of the original series of

doses produced complete suppression of responding after the original series of doses was

determined twice. One subject in the Pre-post group (4991) pecked very little during chronic pre-

session administration and during dose-response curve redetermination. This subject was then

administered saline pre-session once every four sessions, with pre-session cocaine administered









before intervening sessions (cf. Miller & Branch, 2004). This regimen continued until key

pecking resumed on days when cocaine was administered pre-session (approximately 50

sessions). The dose-response curve was then redetermined for this subject, with data excluded

from when key pecking was suppressed. Table 2-2 shows the number of administration of each

dose during this assessment. The large numbers of administrations for the doses given

chronically indicate the number of administrations that were used to calculate the mean effects

that are shown in the figures.

Following dose-response redetermination, subjects in the Post-pre group were switched to

pre-session drug administration. These subjects received their chronic dose immediately pre-

session and saline immediately post-session for 30 sessions. Subjects in the Pre-post group were

switched to post-session administration of their chronic dose and pre-session saline

administration for 30 sessions. The dose-response curve was then redetermined as described

above (i.e., in the context of continued daily drug administration; Table 2-3 shows how many

times each dose was tested).

Drug Procedure. Cocaine hydrochloride (obtained from the National Institute on Drug

Abuse) was dissolved in sterile 0.9% sodium chloride solution. Doses were determined by the

weight of the salt, and the injection volume was 1 mL/kg. Drug was administered via

intramuscular (IM) injections in the breast muscle. During daily administration, injections

alternated sides of the breast.

Results and Discussion

Figure 2-1 displays average key pecking response rate within a session for the Pre-post

group in Experiment 1, calculated as the percent of saline vehicle rate of responding, plotted as a

function of dose of cocaine. Percent saline values were determined on an individual-subject basis

by dividing the average response rate under effects of a particular dose for a subject by the









average response rate during saline vehicle for that subject and multiplying this value by 100.

Table 2-4 shows the response rate following each saline vehicle administration for all subjects

during each phase of the experiment. During acute cocaine administration, all subjects showed

dose-dependent decreases in rate of key pecking.

Dose-response curves following chronic administration were determined by averaging the

response rate following each administration of each dose and dividing this value by the average

saline response rate during the period of daily administration. Values for the chronic doses were

determined by averaging the response rate from sessions preceded by administrations of the

chronic dose that occurred the day prior to a test dose, and dividing this value by the average

saline response rate. Therefore, many more values for effects of the chronic dose (or saline for

the Post-pre group) were included in the dose-response curve determination than determinations

of other doses. Following 30 sessions of pre-session administration of cocaine, all subjects in the

Pre-post group showed some amount of tolerance, as predicted, to the rate-decreasing effects of

cocaine, as indicated by higher response rates under effects of larger doses of cocaine as

compared to that during acute administration as displayed in Figure 2-1. Subject 592 showed a

decrease in control rate of responding (Table 2-4) as well as an increase in variability particularly

following administration of saline, but still showed tolerance to rate-decreasing effects of

cocaine when the data were normalized based on the saline vehicle control. Subject 40 also

showed an increase in variability of key pecking rate following administration of saline, but still

showed tolerance.

Figure 2-2 shows effects of cocaine after chronic dosing was switched from pre-session to

post-session. Some subjects (754, 36, 4991) continued to show varying degrees of tolerance to

effects of cocaine, and one subject showed a loss of tolerance (40). For those subjects









administered a larger chronic dose (7.4 mg/kg or 10.0 mg/kg), post-session administration

produced a substantial decrease in rate of responding during saline vehicle to near zero (Table 2-

4). Subject 49 continued to respond when pre-session drug doses were administered, with large

percentage increases because of the very low rates when drug was not given, whereas Subject

592 rarely responded when any dose (including saline) was administered. This suppression of

responding made it difficult to determine whether these subjects were still tolerant to the rate-

decreasing effects of cocaine.

Figure 2-3 compares effects of cocaine administered pre-session and post-session for the

Pre-post group. For some subjects administered a moderate dose of cocaine chronically (754, 36,

4991), the dose effects were, for the most part, unchanged when cocaine was repeatedly

administered post-session rather than pre-session. Subject 40 showed less tolerance from post-

session administration as compared to pre-session. Those subjects administered larger chronic

doses (Subjects 49, 592) pecked very little when saline was administered before the session, with

occasional pecking when other doses of drug were administered mainly for Subject 49. Overall,

the switch from pre-session to post-session administration did not produce additional tolerance

for any subject, and was associated with a slight loss of tolerance for some subjects (36, 4991,

40).

Figure 2-4 shows average key pecking rate within a session as a function of saline vehicle

rate of responding for subjects in the Post-pre group. Acute administration of cocaine produced

dose-related decreases in key pecking for all subjects that were of similar magnitude to the rate-

decreases seen for subjects in the Pre-post group. After cocaine was administered post-session

for 30 sessions, three of six subjects (45, 35, 43) surprisingly showed notable tolerance to the

rate-decreasing effects of cocaine. Subjects 727 and 752 showed little change in drug effects,









although for both subjects effects of 5.6 mg/kg were attenuated. Subject 596, which was

administered post-session 10.0 mg/kg cocaine, showed near zero response rates following

cocaine and saline administrations (Table 2-4), similar to that seen when subjects in the Pre-post

group were given large doses of cocaine post-session. Subjects 35 and 752 also occasionally

showed response suppression, but generally continued to respond during the chronic post-session

cocaine regimen.

Following the first 30 sessions after the switch from post-session to pre-session

administration of cocaine, some of the subjects in the Post-pre group that had previously

developed tolerance (45, 43) continued to show varying degrees of tolerance as displayed in

Figure 2-5. Subject 35 showed a loss of tolerance. Subject 727 showed little change in drug

effects as compared to the post-session condition. Subject 596 continued to have a very low

saline vehicle control rate, and occasionally pecked at a slow rate when cocaine was

administered. Subject 752, which did not develop notable tolerance following post-session

dosing, did show substantial tolerance following pre-session administration of cocaine.

Figure 2-6 compares effects of cocaine administered post-session and pre-session for the

Post-pre group. For those subjects that developed tolerance following post-session dosing

(Subjects 45, 35, 43) pre-session drug administration produced a slight increase (Subject 45) or

decrease (Subjects 35, 43) in the amount of tolerance produced by post-session dosing. The

switch from post-session to pre-session administration of cocaine produced tolerance for Subject

752 that had not previously developed much tolerance.

Similar results were found for subjects in the Pre-session and Post-pre group when data

were analyzed at the group-average level. Figure 2-7 shows group average data from acute

administration and following the first chronic regimen for both groups. Percent saline values for









the group average were determined by calculating the average response rate during saline vehicle

administrations averaged across all administrations of saline for all subjects, and then dividing

the response rate under effects of a particular dose averaged across each administration of that

dose across all subjects by the average response rate during saline vehicle for all subjects and

multiplying this value by 100. Only doses experienced by all subjects were included in the graph.

Acute administration of cocaine produced dose-dependent decreases in rate of responding that

were similar at the group-average level for both groups. Both pre-session and post-session drug

administration produced tolerance at the group-average level. Note that data from subjects that

showed response suppression during chronic-post-session-administration sessions were excluded

for all graphs and analyses of group-average data. That is, data are presented only for subjects

that continued to key peck during the repeated-administration phases.

To provide ancillary analyses, the effective dose 50 (ED50; dose that produced a 50%

decrease in response rate) was calculated for each subject for each drug regimen based on a

straight-line fit to the data for each individual pigeon. The ED50 was calculated by fitting a

straight line to the percent of vehicle control data as a function of the log dose of cocaine. A

straight line (as opposed to a curve) was chosen because it is the most parsimonious function,

and because it could be fit to a line with values of zero. The straight line was fit to the

descending portion of the dose-response curve. If the largest dose of cocaine did not completely

suppress responding, an additional data point was added for a dose that was 1/8 of a log unit

larger than the largest dose used with a response rate of zero. This allowed better estimation of

ED50s when curves did not reach zero, and is a conservative method because it did not

overestimate the amount of tolerance. If anything, it underestimated the amount of tolerance.

ED50s were not calculated when subjects showed response suppression due to the poor fit of the









line. ED50s are shown in Table 2-5. For the Pre-post group, all subjects showed an increase in

ED50 from acute administration to that following pre-session administration. Similarly, subjects

in the Post-pre group all showed an increase in ED50 from acute administration to post-session

administration, except for the subject that showed response suppression; however, the change

was minimal for subjects 727 and 752. These data corroborate the view that the majority of

subjects in both groups developed tolerance.

Figure 2-8 displays group average data comparing effects of cocaine during acute

administration, and following the second chronic drug regimen. Data from both groups continued

to show tolerance when pre-session drug administration was switched to post-session, and when

post-session administration was switched to pre-session. This is supported by examination of

individual-subject ED50s for both groups (Table 2-5). The majority of subjects (3 of 4) from the

Pre-post group that did not show response suppression continued to show an ED50 that was

larger than that from acute administration when chronic dosing was switched to post-session. For

subjects in the Post-pre group, the majority of subjects (4 of 5) that did not show response

suppression also had a larger ED50 when switched to pre-session administration as compared to

acute administration.

Figure 2-9 compares data from pre-session and post-session cocaine administration for

both groups at the group average level. The group average data from the Pre-post group show

slightly more tolerance from pre-session administration as compared to post-session

administration. All subjects that did not show response suppression had a larger ED50 from pre-

session dosing than that from post-session dosing (Table 2-5). Data from the Post-pre group

show no change in the amount of tolerance when pre-session and post-session dosing was

compared. Three of five subjects that did not show response suppression had a larger ED50 from









post-session administration as compared to pre-session administration, while the other two

subjects had a larger ED50 from pre-session administration (Table 2-5).

When cocaine was administered pre-session first, as predicted, all subjects developed

tolerance to effects of cocaine during the behavioral session. Surprisingly, however, when

cocaine was initially administered post-session, half of the subjects developed notable tolerance.

Switching subjects from pre-session to post-session administration did not produce any more

tolerance than that previously developed, and switching subjects from post-session to pre-session

administration rarely produced additional tolerance if tolerance had already developed. Only one

subject (752) showed the classic contingent-tolerance effect in that it did not develop tolerance

when cocaine was administered post-session, but it did develop tolerance when cocaine was

subsequently administered pre-session. It is not possible to determine if some other subjects

would have shown this effect if their behavior had not been suppressed due to post-session

dosing. The regimen of post-session administration of larger doses of cocaine (7.4 mg/kg and

10.0 mg/kg) reliably produced near zero response rates and generally was associated with

suppressed responding following pre-session cocaine administrations as well. Possible reasons

for response-suppression in sessions followed by large doses will be presented in the General

Discussion (Chapter 6).









Table 2-1. Number of administrations of each dose of cocaine administered during acute dose-
response curve determination for Experiment 1.

Acute Subject
Dose 592 49 4991 754 36 40 45 35 43 727 596 752
Sal 3 4 2 3 2 2 4 2 6 2 4 2
1.0 2 2 2 2 2 2 2 2 2 2 2 2
3.0 2 2 2 3 3 4 2 4 2 2 2 4
4.2 2 2 1 1 2 2
5.6 5 4 5 5 4 5 3 4 3 4 2 4
7.4 3 2 2 -
10.0 2 4 2 2 2 3 3 3 2 2 3 3
13.0 -
17.0









Table 2-2. Number of administrations of each dose of cocaine administered during dose-response
curve determination following the first chronic regimen for Experiment 1. Note that
the number of cocaine administrations for each subject's chronic dose reflects the
number of administrations used in dose-response curve determination, rather than the
total number of administrations of that dose.

Chronic 1 Subject
Dose 592 49 4991 754 36 40 45 35 43 727 596 752
Sal 3 3 2 2 2 4 14 18 11 11 11 11
1.0 2 2 2 4 2 2 2 2 2 2 2 2
3.0 2 2 2 2 2 3 2 3 2 2 2 2
4.2 2 2 2 4 2 2
5.6 2 3 9 14 14 15 2 5 3 3 2 3
7.4 13 3 3 -
10.0 2 13 2 2 3 3 3 4 2 2 3 2
13.0 2 1 2 2
17.0 1 2 2 1 -









Table 2-3. Number of administrations of each dose of cocaine administered during dose-response
curve determination following the second chronic regimen for Experiment 1. Details
are as in Table 2-2.

Chronic 2 Subject
Dose 592 49 4991 754 36 40 45 35 43 727 596 752
Sal 12 10 10 14 13 13 2 3 2 2 3 3
1.0 2 2 2 2 2 2 2 4 2 2 2 2
3.0 2 2 2 2 2 2 2 3 3 3 2 2
4.2 2 2 2 2 2 3
5.6 2 2 2 3 2 2 2 15 12 11 2 14
7.4 2 2 12 -
10.0 2 2 2 3 2 3 2 3 3 2 11 4
13.0 2 2 2 2 2
17.0 2 2 3 2 -










Table 2-4. Key pecks per minute following each administration of saline-vehicle for each phase
of the experiment for Experiment 1. The mean shown in italics was used to calculate
percent saline values for Figures 2-1-2-9.

Subject
Phase 592 49 4991 754 36 40 45 35 43 727 596 752
Acute 156.2 118.7 160.2 231.3 144.4 187.2 51.4 115.6 182.4 163.1 173.8 183.6
125.2 132.0 153.6 246.2 156.4 172.7 51.1 104.0 169.3 153.8 218.1 175.6
152.2 141.8 189.3 66.9 94.8 173.9
164.8 75.7 133.9 203.5
113.6
150.7
Mean 144.6 139.3 156.9 222.3 150.3 180.0 61.3 109.8 140.8 158.45 192.3 179.6

Chronic 76.6 127.1 137.2 212.6 150.7 46.0 84.6 0.0 139.8 140.6 0.0 184.5
1 33.1 101.4 143.0 206.8 145.6 125.5 81.4 0.0 121.5 150.2 0.0 202.0
0.0 97.8 160.6 75.4 0.0 127.8 157.0 0.0 161.5
203.6 76.3 3.1 126.0 163.6 1.0 201.7
101.9 113.0 137.4 163.4 2.1 187.3
86.2 119.1 144.6 156.6 0.0 174.3
106.6 51.5 135.5 165.7 0.0 0.7
91.8 9.0 116.4 165.3 0.0 104.1
78.9 82.3 125.2 158.9 0.0 184.1
84.6 130.3 126.1 167 0.0 197.1
93.4 129.4 117.0 158.5 0.0 179.3
92.5 145.7
97.9 143.0
108.5 142.9
15.0
5.0
128.8
140.4
Mean 36.6 108.8 140.1 209.7 148.15 133.9 90.0 75.5 128.8 158.8 0.3 161.5

Chronic 72.2 45.2 159.2 198.0 151.9 219.4 66.5 120.3 67.0 146.4 11.0 74.2
2 21.0 0.0 153.2 205.9 164.4 179.9 57.6 84.7 33.1 154.9 0.0 213.9
71.3 0.0 152.4 203.6 156.4 157.5 71.9 2.0 182.1
0.0 0.0 151.2 224.1 154.1 199.3
10.2 0.0 156.2 202.9 152.8 172.7
0.0 81.0 167.8 205.4 154.8 230.9
0.0 0.0 155.6 148.7 160.1 206.7
0.0 0.0 172.5 199.0 157.5 223.3
0.0 0.0 141.7 190.2 154.8 200.7
0.0 0.0 125.8 203.2 158.5 211.6
0.0 212.3 150.1 181.0
0.0 218.1 159.9 212.6
200.9 169.4 201.8
214.4
Mean 14.6 12.6 153.6 201.9 157.3 199.8 62.1 92.3 50.1 150.65 4.3 156.7









Table 2-5. ED50s (mg/kg) for each subject for each phase of Experiment 1.

Phase
Subject Acute Pre-session Post-session
592 3.45 13.02
49 8.01 11.44
4991 3.53 15.63 11.51
754 3.91 6.11 5.71
36 4.63 11.79 9.36
40 5.18 8.22 4.86
Pre-post Mean 4.79 11.04 7.86

45 5.08 14.42 14.30
35 5.07 4.41 7.89
43 2.43 7.31 12.90
727 2.50 2.69 3.35
596 10.26
752 4.08 8.76 4.29
Post-pre Mean 3.83 12.64 8.55












Pre-session > Post-session


250 7.4

200 -

150-

100 -


592


S1S2 1 3 5.6 10


250 10.0


-*- Acute
A-- Chronic Pre-session


250 5.6


200

150

100 A

50


S1S2 1 3 5.6 10 17


250 5.6
5.6


150


S1S2 1 3 5.6 10


4991


100 A

50


S1S2 1 3 5.6 10 17


250 5.6
5.6


200


150 T


100 A

50

0


1(


S1S2 1 3 5.6 10 17
Dose of Cocain


00 A

50 -

0
S1S2 1 3 5.6 10 17
e (mg/kg)


Figure 2-1. Effects of cocaine during acute and pre-session administration for the Pre-post group
in Experiment 1. Each graph shows data from an individual subject. Response rate is
plotted as a function of dose (log scale) of cocaine for the Pre-post group in
Experiment 1. Data are plotted as percent of values obtained after administration of
saline vehicle. Circles display the effects of cocaine during acute administration, and
triangles show the effects of 30 days of pre-session cocaine administration. The
points above "S" indicate the average effects of saline vehicle control, with error bars
displaying the range of effects of saline vehicle. Numbers centered above each graph
identify the subjects. Numbers to the right of the y-axes identify the dose of cocaine
administered chronically for each subject.


100

50


250

200












Pre-session -: Post-session


2507.4
7.4


50

0
S1S3 1 3 5.6 10


250
10.(


100 J


S1S3


1 3 5.6 10


250 5.6


-*- Acute
--- Chronic Post-session


100 -

50


S1S3 1 3 5.6 10 17


250 5.6


100 -* i

50-


S1S3 1 3 5.6 10 17


250 5.6
5.6


100 -

50

0 -


100 -

50

0 -


S1S3 1 3 5.6 10 17 S1S3
Dose of Cocaine (mg/kg)


1 3 5.6 10 17


Figure 2-2. Effects of cocaine during acute and post-session administration for the Pre-post
group in Experiment 1. Each graph shows data from an individual subject. Response
rate as a percent of control is plotted as a function of dose of cocaine for the Pre-post
group in Experiment 1. Circles display the effects of cocaine during acute
administration, and squares show the effects of 30 days of post-session cocaine
administration. All other details are as in Figure 2-1.












Pre-session > Post-session


592


-A- Chronic Pre-session
--- Chronic Post-session


250 5.6


754


1 3 5.6 10


200

150

100 -A

50


S2S3 1 3 5.6 10 17


250 36
5.6

200

150

100 -A i

50


S2S3 1 3 5.6 10 17
S2S3 1 3 5.6 10 17


250 5.6
15.6


200


100 -A t

50

0 -


150 -

100 -

50-


S2S3 1 3 5.6 10 17 S2S3
Dose of Cocaine (mg/kg)


1 3 5.6 10 17


Figure 2-3. Effects of cocaine during pre-session and post-session administration for the Pre-post
group in Experiment 1. Each graph shows data from an individual subject. Response
rate as a percent of control is plotted as a function of dose of cocaine for the Pre-post
group in Experiment 1. Triangles display effects of cocaine following 30 days of pre-
session cocaine administration, and squares show the effects of 30 days of post-
session cocaine administration. All other details are as in Figure 2-1.


100 -A M


S2S3 1 3 5.6 10


250 11
IO.b


100


S2S3


250

200











--- Acute
Post-session > Pre-session -- Chronic Post-session


250 7.4 45 250 5.6 727

200- 200

150- 150

1004 100 -a f

50 50-

0- 0
S1S2 1 3 5.6 10 S1S2 1 3 5.6 10


35 596
S250 5. 250 10.
5.6
0
o
S200- 200

S150- 150

S 100 100 -

50- 50

0 0 0
S1S2 1 3 5.6 10 S1S2 1 3 5.6 10


2505.6 43 250 5.6 752
5.6 5.6

200- 200

150- 150

100 100 -

50 50

0 // 0 /
S1S2 1 3 5.6 10 S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 2-4. Effects of cocaine during acute and post-session administration for the Post-pre
group in Experiment 1. Each graph shows data from an individual subject. Response
rate as a percent of control is plotted as a function of dose of cocaine for the Post-pre
group in Experiment 1. Circles display the effects of cocaine during acute
administration, and triangles show the effects of 30 days of post-session cocaine
administration. All other details are as in Figure 2-1.













Post-session > Pre-session


250

200


--- Acute
-E- Chronic Pre-session


250

200


100 4 -i

50

50 -
S1S3 1 3 5.6 10


100 U

50

S3 1 3 5.6 10
S1S3 1 3 5.6 10


250 110.C
10.C


150


100 d i


3 5.6 10


S1S3 1 3 5.6 10


250 5.6

200

150
T


1(


S1S3 1 3 5.6 10
Dose of Cocaine


)0 -

50


S1S3 1 3 5.6 10
(mg/kg)


Figure 2-5. Effects of cocaine during acute and pre-session administration for the Post-pre group
in Experiment 1. Each graph shows data from an individual subject. Response rate as
a percent of control is plotted as a function of dose of cocaine for the Post-pre group
in Experiment 1. Circles display the effects of cocaine during acute administration,
and squares show the effects of 30 days of pre-session cocaine administration. All
other details are as in Figure 2-1.


250
5.6
200

150

100 -

50

0-
S1 S3


2505.6
5.6

200

150

100












Post-session > Pre-session


250 7.4
7.4


-- Chronic Post-session
-0- Chronic Pre-session


250 5.6
5.6


100 -

50


S2S3 1 3 5.6 10


100 -

50

0 S3 1 3 5.6 10
S2S3 1 3 5.6 10


250 1i.C


596


1007 *


1 3 5.6 10


43


S2S3 1 3 5.6 10


250 5.6


200

150


3 5.6 10


100-

50-


S20S3 1 3 5.6 10
S2S3 1 3 5.6 10


Dose of Cocaine (mg/kg)


Figure 2-6. Effects of cocaine during pre-session and post-session administration for the Post-pre
group in Experiment 1. Each graph shows data from an individual subject. Response
rate as a percent of control is plotted as a function of dose of cocaine for the Post-pre
group in Experiment 1. Triangles display effects of cocaine following 30 days of
post-session cocaine administration, and squares show the effects of 30 days of pre-
session cocaine administration. All other details are as in Figure 2-1.


250


200 -

150 -

100


S2S3


250 5.6
5.6


200


150

100 -

50

0 -S
S2S3











-*- Acute
A- Chronic 1

S250 A Pre-post 250 B Post-pre

S200 200
a(D
( 150 150

.E 100 100

I 50 50

0 0
S1S2 1 3 5.6 10 S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 2-7. Group-average data for both groups showing effects of cocaine during acute
administration and the first chronic regimen in Experiment 1. Response rate as a
percent of control is plotted as a function of dose of cocaine for Experiment 1. Data
are averaged across all subjects in a group. Circles display the effects of cocaine
during acute administration, and triangles display effects of cocaine following the
first chronic regimen (pre-session drug for the Pre-post group, and post-session drug
for the Post-pre group). The points above "S" indicate the average effects of saline
vehicle control, with inner error bars displaying the standard deviation, and outer
error bars displaying the range of effects of saline vehicle. Data from Subject 596 are
not included in the group average from the first chronic regimen for the Post-pre
group. A) Data from the Pre-post group. B) Data from the Post-pre group.










-*- Acute
-U- Chronic 2


Pre-post


A


c 250
0
0
- 200
C'--

_ 150
U,
. 100
,,
0 50
0


250 1 B


200 -

150 -

100 -

50-

0-


S1S3


Post-pre


1 3 5.6 10


Dose of Cocaine (mg/kg)


Figure 2-8. Group-average data for both groups showing effects of cocaine during acute
administration and the second chronic regimen in Experiment 1. Response rate as a
percent of control is plotted as a function of dose of cocaine for Experiment 1. Circles
display the effects of cocaine during acute administration, and squares display effects
of cocaine following the second chronic regimen (post-session drug for the Pre-post
group, and pre-session drug for the Post-pre group). All other details are as in Figure
2-7. Data from Subject 596 are not included in the group average from the second
chronic regimen for the Post-pre group, and data from Subjects 592 and 49 are not
included in the group average from the second chronic regimen for the Pre-post
group. A) Data from the Pre-post group. B) Data from the Post-pre group.


S1S3 1 3 5.6 1C









-- Chronic 1
--- Chronic 2

P 250 A Pre-post 250 BPost-pre

200 200


0)
.100 100

't 50 50 -


S2S3 1 3 5.6 10 S2S3 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 2-9. Group-average data for both groups showing effects of cocaine during the first and
second chronic regimen in Experiment 1. Response rate as a percent of control is
plotted as a function of dose of cocaine for Experiment 1. Triangles display effects of
cocaine following the first chronic regimen (pre-session drug for the Pre-post group,
and post-session drug for the Post-pre group), and squares display effects of cocaine
following the second chronic regimen (post-session drug for the Pre-post group, and
pre-session drug for the Post-pre group). All other details are as in Figure 2-7. Data
from Subject 596 are not included in the group average from the first and second
chronic regimen for the Post-pre group, and data from Subjects 592 and 49 are not
included in the group average from the second chronic regimen for the Pre-post
group. A) Data from the Pre-post group. B) Data from the Post-pre group.









CHAPTER 3
EXPERIMENT 2

The results of Experiment 1 were not consistent with past research on contingent tolerance

to cocaine (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al.,

1978), except for experiments conducted using pigeons (Pinkston & Branch, 2004). The one

experiment using pigeons found not-contingent tolerance to cocaine (Pinkston & Branch, 2004),

whereas experiments employing other species have found contingent tolerance to cocaine

(Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978). Although

there are many procedural differences in the experiments conducted with pigeons compared to

those conducted with other species, one particular procedural aspect of Experiment 1 potentially

contributed to the not-contingent tolerance seen in that experiment, and to the inter-subject

variability in effects for the Post-pre group. Subjects in the Post-pre group were fed in their home

cage immediately after the session and immediately after post-session cocaine administration if

they weighed below their 80% weight. Some subjects were consistently fed after the session

because their weight was low, and some were rarely fed after the session because they were at or

above their 80% weight. Those that were consistently fed after the session also were the ones

that developed tolerance to effects of cocaine during the session when cocaine was administered

post-session. Those subjects that were not regularly fed after the session did not show tolerance

to effects of cocaine following post-session administration.

This correlation suggested that eating under effects of cocaine in the home cage might have

contributed to the development of tolerance to effects of cocaine during the behavioral session.

Eating in the home cage, that is, pecking at grain, involves similar behavior as key pecking in the

operant chamber. Therefore, subjects who often eat under effects of cocaine in the home cage

might develop tolerance to effects of cocaine on eating, and this tolerance might generalize to









behavior associated with key pecking during the behavioral session. Hence, the purpose of

Experiment 2 was to investigate whether eating under effects of cocaine in the home cage can

contribute to the development of tolerance to key pecking during the behavioral session.

Method

Subjects

Subjects were 12 adult male, White Carneau pigeons (Double "T" Farm, Glenwood, IA).

All subjects were experimentally and drug naive, and aged approximately seven months at the

beginning of the experiment. Subjects were housed and maintained as in Experiment 1.

Apparatus

Experimental sessions were conducted in two similarly constructed BRS/LVE Inc. (Model

PIP 010 016) standard three-key operant test chambers measuring 31.0 cm by 36.5 cm by

35.0 cm. To register a response, the key required approximately 0.07 N for one chamber, and

0.11 N for the other chamber. All other details are described in Experiment 1.

Procedure

Training. Subjects were trained, through the method of successive approximations, to

peck the center key when it was illuminated white. After all subjects reliably pecked the key,

they were exposed to FR 1 for one session. Sessions ended after 30 min or 20 grain

presentations, whichever came first. Subjects then underwent ratio training as described in

Experiment 1. Ratio training took two to seven sessions. One subject began ratio training and did

not exceed FR 1 for two consecutive sessions. It then continued exposure to FR 1 for two more

sessions, followed by ratio training. Key pecks were reinforced with 3 s access to mixed grain

throughout training. The key light and houselights were extinguished during food presentation.

After ratio training was complete, subjects were placed on baseline conditions.









Baseline. Sessions began with a 5-min blackout, during which key pecking had no

programmed consequence. This was followed by an FR 20 schedule of reinforcement for 20 min

or until 40 reinforcers were obtained, whichever came first. After 34-42 sessions, responding was

determined to be stable by visual inspection of graphs of daily session-wide response rates and of

cumulative records. Sessions were conducted seven days a week at approximately the same time

everyday for each pigeon. Pecks were initially reinforced with 3-s access to mixed grain, a

duration that was then titrated to shorter times until a duration was found for each subject such

that post-session body weights were approximately 10-15 g under 80% weight everyday. The

final grain access durations ranged from 1.2-2.5 s. Hopper durations were adjusted over a period

of 54 sessions.

Drug regimen. After responding was determined to be stable with the final hopper-access

durations in place, acute effects of cocaine were assessed as described in Experiment 1, except

that injections occurred every four days and every dose was administered a minimum of two

times (Table 3-1). Doses of 13.0 mg/kg and 17.0 mg/kg cocaine were also assessed for some

subjects when no dose in the initial range of doses produced complete suppression of responding

following determination of the original set of doses. One subject died at the beginning of the

acute dosing phase due to unknown causes. Therefore no data will be shown for this subject, nor

will any of its data be included in the analyses.

Following acute dosing, subjects were divided into two matched groups based on initial

dose-response curves. Each subject was then administered, chronically for 30 consecutive

sessions, a dose of cocaine that originally produced a moderate rate-decreasing effect on FR

responding. This dose was chosen based on the same criteria used to select a chronic dose in

Experiment 1. Subjects in both groups were administered saline immediately before each session









during the chronic drug regimen. The Immediate-Drug group was administered cocaine

immediately after the session, as had been the Post-pre group of Experiment 1, and the Delayed-

Drug group was administered drug 60 min after the session. The 60-min delay was chosen

because previous research has shown that behavioral effects of cocaine in pigeons generally last

about 60 min (Marusich & Branch, 2008). Both groups were fed their post-session ration of food

in the home cage within 5 min of session termination. Post-session rations were calculated as the

difference between the subject's post-session weight and the subject's 80% weight, with a

minimum of 5 g fed if the subject was near or above its 80% weight. Therefore the Immediate-

Drug group was administered drug, and then given its post-session ration, while the Delayed-

Drug group was given its post-session ration and then administered drug approximately 60 min

later.

Following 30 days of this chronic drug regimen, the dose response curve was

redetermined. The chronic drug regimen continued except once every four days, when subjects

were administered one of their initial acute doses of cocaine pre-session. All test doses were

followed by post-session saline administered at the same time each subject was normally injected

drug based on group assignment. Each dose was administered a minimum of two times. Any

dose that produced variable effects was repeated until effects were replicated. Doses of 13.0

mg/kg and 17.0 mg/kg cocaine were also assessed for some subjects when no dose in the initial

range of doses produced a consistent decrease in rate of responding. Table 3-2 indicates the

number of administrations of each dose.

Drug Procedure. The drug procedure was the same as that used in Experiment 1.

Results and Discussion

Figure 3-1 displays average key pecking response rate within a session for the Immediate-

Drug group in Experiment 2, calculated as the percent of saline vehicle rate of responding,









plotted as a function of dose of cocaine. Table 3-3 shows the response rate following each saline

vehicle administration for all subjects during each phase of the experiment. During acute cocaine

administration, all subjects showed dose-dependent decreases in rate of key pecking. Following

30 sessions of cocaine administered immediately after the session, two of five subjects (648,

244) showed tolerance to the rate-decreasing effects of cocaine as indicated by the dose-response

curve shifted to the right. Subject 634 showed little change in drug effects. Subjects 2173 and

606 that were administered 10.0 mg/kg cocaine immediately post-session showed near zero

saline vehicle control rates, and pecked little following pre-session drug administration making it

difficult to determine if tolerance had developed. Similarly, Pigeon 634, which received 5.6

mg/kg, also showed disrupted responding during sessions, as indicated by the wide range of

effects of pre-session saline. Overall, effects in this group replicate those seen with the Post-pre

group of Experiment 1.

Figure 3-2 shows key pecking calculated as the percent of saline vehicle control rate

plotted as a function of dose of cocaine for the Delayed-Drug group. Acute administration of

cocaine produced dose-related decreases in key pecking for all subjects although the decreases

were modest for Subject 582. Thirty sessions of cocaine administered 60 min after the session

ended produced some amount of tolerance for all subjects in the Delayed-Drug group. The

administration of 10.0 mg/kg cocaine (to 3 of the pigeons) 60 min after the session ended did not

produce the response suppression that was seen in the Immediate-Drug group and in Experiment

1 when large doses of cocaine were administered immediately after the session.

Figure 3-3 shows group-average data for both the Immediate-Drug and Delayed-Drug

groups. Data were excluded from all graphs and analyses from subjects that showed response

suppression during the phases the suppression was observed. This figure compares data during









acute administration and following the chronic post-session drug regimens. Data from both

group averages indicate that tolerance developed from post-session administration immediately

after the session and 60 min after the session completed. This was supported by an analysis of

ED50s from acute and chronic administration. All subjects in the Immediate-Drug group that did

not commonly show response suppression had a larger ED50 following chronic administration,

although the change was minimal for subject 634. Similarly, all subjects in the Delayed-drug

group showed an increase in ED50 following chronic administration (Table 3-4) indicating that

all subjects in both groups that did not show response suppression developed tolerance.

Post-session administration of cocaine produced tolerance in most subjects regardless of

whether cocaine was administered immediately or 60 min after the session ended, except when

larger doses were administered immediately after the session. Post-session administration of 10.0

mg/kg cocaine administered immediately after the session generally produced response

suppression similar to that seen in Experiment 1 when the same drug regimen was used. Subjects

that ate in the home cage under effects of cocaine (Immediate-Drug group) showed similar if not

lower levels of tolerance to effects of cocaine in the behavioral session as compared to subjects

that did not eat under effects of cocaine in the home cage (Delayed-Drug group). Therefore

eating under effects of cocaine in the home cage probably contributed little if any to the

development of tolerance to the rate-decreasing effects of cocaine in the behavioral session for

subjects in Experiments 1 and 2. Additionally, giving the Delayed-Drug group the drug one-hour

after the session and after they had eaten resulted in no within-session suppression of key

pecking, suppression that could mask the development of tolerance. All six of the subjects in the

Delayed-Drug group showed tolerance.









Table 3-1. Number of administrations of each dose of cocaine for each subject during acute dose-
response curve determination for Experiment 2.

Acute Subject
Dose 648 634 2173 244 606 582 21 604 544 6110 653
Sal 4 4 3 4 3 3 3 4 3 4 3
1.0 2 3 3 3 2 2 2 3 3 2 2
3.0 2 2 4 3 2 2 2 3 2 2 2
5.6 2 3 4 2 3 3 4 4 3 3 2
10.0 3 2 4 2 3 2 3 2 2 3 3
13.0 3 3 -
17.0 4









Table 3-2. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following the chronic drug regimen for Experiment 2.
Note that the number of saline administrations reflects the number of saline
administrations used in dose-response curve determination, rather than the total
number of saline administrations.

Chronic Subject
Dose 648 634 2173 244 606 582 21 604 544 6110 653
Sal 15 15 14 12 12 18 18 15 15 14 14
1.0 2 3 2 2 2 4 2 2 2 2 2
3.0 2 2 2 2 2 2 2 2 2 2 2
5.6 2 4 2 2 2 2 2 4 4 3 3
10.0 2 2 2 2 2 2 5 3 3 3 3
13.0 3 2 2 3 -
17.0 2









Table 3-3. Key pecks per minute following each administration of saline-vehicle for each phase
of the experiment for Experiment 2. The mean shown in italics was used to calculate
percent saline values for Figures 3-1-3-3.

Subject
Phase 648 634 2173 244 606 582 21 604 544 6110 653
Acute 175.3 182.1 256.8 39.6 171.5 214.9 191.2 114.6 181.8 89.5 183.6
204.3 176.3 258.1 89.5 184.6 214.5 175.7 136.8 193.5 140.4 162.5
187.4 171.7 264.0 49.9 178.9 207.2 141.2 144.1 186.3 130.1 200.6
218.3 176.0 61.6 200.6 110.6
Mean 196.3 176.5 259.6 60.15 178.3 212.2 169.4 149.0 187.2 117.65 182.2

Chronic 185.4 168.8 0.0 62.8 0.6 229.9 156.4 105.8 174.1 181.1 217.4
176.6 143.8 0.0 48.4 0.0 218.2 121.3 111.2 170.8 172.2 194.2
174.7 160.6 0.0 65.2 0.0 227.2 150.7 117.5 182.1 191.8 193.1
151.2 126.4 0.0 51.4 0.0 235.9 127.0 111.9 169.5 179.3 203.0
186.0 142.8 0.0 78.2 0.0 200.9 163.4 124.1 183.1 200.9 221.9
192.8 148.8 0.0 77.8 0.0 212.6 176.6 96.6 179.2 201.5 199.9
178.2 126.4 0.0 67.9 0.0 218.0 174.1 112.2 172.8 200.9 187.8
174.2 138.8 0.0 61.3 0.6 230.2 174.4 129.0 182.0 178.1 192.9
168.7 21.4 0.0 57.8 0.0 234.1 187.6 131.0 174.0 195.5 182.0
156.6 0.0 0.0 66.0 0.0 206.8 189.9 71.2 177.5 200.5 220.9
186.7 126.1 0.0 77.6 0.2 250.3 191.0 116.8 177.8 203.2 203.1
192.4 90.6 0.0 78.6 0.0 237.3 189.5 105.1 175.7 192.5 205.5
194.1 118.8 0.0 235.1 166.6 136.3 175.6 197.5 197.5
187.3 50.1 0.0 217.2 152.7 91.0 169.6 197.4 187.1
159.6 83.8 222.3 162.3 119.4 158.2
233.2 138.3
234.4 174.3
200.5 159.4
Mean 177.6 110.5 0.0 66.1 0.2 224.7 164.8 111.9 174.8 192.3 200.5









Table 3-4. ED50s (mg/kg) for each subject for each phase of Experiment 2.

Phase
Subject Acute Chronic
648 3.96 14.38
634 3.28 4.01
2173 12.42
244 2.12 5.91
606 5.28
Immediate-Drug Mean 5.41 8.10

582 12.86 15.99
21 4.94 11.81
604 2.58 6.68
544 3.37 6.23
6110 4.48 7.36
653 3.75 7.54
Delayed-Drug Mean 5.33 9.27












Immediate-Drug


-*- Acute
-- Chronic


180 15.6


180 3.0


90 -

60

30 -
0

S1S2 1 3 5.6 10


180 5.6 634

150

120 -

90

60

30

S1S2 1 3 5.6 10
S1 S2 1 3 5.6 10


180 10.0


S1S2
S1 S2


244











1 3 5.6 10


606


S1S2 1 3 5.6 10


2173


0 I // A A A
S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 3-1. Effects of cocaine during acute and post-session administration for the Immediate-
Drug group in Experiment 2. Each graph shows data from an individual subject.
Response rate is plotted as a function of dose of cocaine for the Immediate-Drug
group in Experiment 2. Data are plotted as percent of values obtained after
administration of saline vehicle. Circles display the effects of cocaine during acute
administration, and triangles show the effects of 30 days of cocaine administered
immediately after the session. All other details are as in Figure 2-1.











Delayed-Drug


180 10.0
150-
120-
90-


-*- Acute
-- Chronic


582





:::7


180 15.6


90 *


0 1 .. 1
S1S2 1 3 5.6 10 17


90 -
60

30-
0
S1S2 1 3 5.6 10


SS1 -S2
S1S2


1 3 5.6 10


6110


30 -
30 -
0-
S1S2 1 3 5.6 10


180 13.0


180 15.6


S30
0 /
S1S2 1 3 5.6 10 S1S2
Dose of Cocaine (mg/kg)


1 3 5.6 10


Figure 3-2. Effects of cocaine during acute and post-session administration for the Delayed-Drug
group in Experiment 2. Each graph shows data from an individual subject. Response
rate is plotted as a function of dose of cocaine for the Delayed-Drug group in
Experiment 2. Data are plotted as percent of values obtained after administration of
saline vehicle. Circles display the effects of cocaine during acute administration, and
triangles show the effects of 30 days of cocaine administered 60 min after the session
ended. All other details are as in Figure 2-1.










-*- Acute
-- Chronic
180 A Immediate-Drug 180 B Delayed-Drug

0 150 150

2 120 120 -

90 90-

I 60 -- 60 -

3 30 30

0 0 0 0 ---
S1S2 1 3 5.6 10 S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 3-3. Group-average data for both groups in Experiment 2, comparing effects of acute
cocaine administration and post-session administration. Response rate as a percent of
control is plotted as a function of dose of cocaine for Experiment 2. Data are averaged
across all subjects in a group. Circles display the effects of cocaine during acute
administration, and triangles display effects of cocaine following the chronic regimen
(immediate post-session drug for the Immediate-Drug group, and 60 min post-session
drug for the Delayed-Drug group). The points above "S" indicate the average effects
of saline vehicle control, with inner error bars displaying the standard deviation, and
outer error bars displaying the range of effects of saline vehicle. Data from Subjects
2173 and 606 are not included in the group average from the chronic regimen for the
Immediate-Drug group. A) Data from the Immediate Drug group. B) Data from the
Delayed Drug group.









CHAPTER 4
EXPERIMENT 3

The results of Experiments 1 and 2 suggest that pigeons often develop tolerance to effects

of cocaine during a behavioral session when cocaine is repeatedly administered after the session.

That is, tolerance developed even though no opportunity to "practice" the required response

while the drug was active occurred. Tolerance developed for most subjects administered cocaine

post-session except those administered a large dose (e.g., 7.4 mg/kg or 10.0 mg/kg) immediately

after the session, a result similar to the findings of Pinkston and Branch (2004). Based on the

large number of subjects that developed tolerance from post-session administration of a moderate

dose of cocaine (e.g., 5.6 mg/kg or 3.0 mg/kg) in the present experiments and in the experiment

by Pinkston and Branch (2004), it is likely that if all subjects were administered moderate doses

of cocaine post-session, the majority would have shown tolerance. Key pecking or eating under

effects of cocaine was not necessary for tolerance to develop to the rate-decreasing effects of

cocaine during the session. It was also unnecessary for cocaine to be closely temporally related

or contextually related to the behavioral session because subjects administered cocaine in the

colony room 60 min after the session ended still showed tolerance to effects of cocaine during

the behavioral session. These results suggest that behavioral factors might not be important in the

development of tolerance to effects of cocaine during the behavioral session. Therefore, the

purpose of Experiment 3 was to examine if mere drug exposure in the home cage without

exposure to experimental sessions or the experimental context would lead to the development of

tolerance to effects of cocaine during the behavioral session.









Method


Subjects

Subjects were 6 adult male, White Carneau pigeons (Double "T" Farm, Glenwood, IA).

All subjects were experimentally and drug naive and aged approximately eight months at the

beginning of the experiment. All were maintained at 83% of their free-feeding body weight (The

local IACUC mandated the change in this fixed parameter from the 80% level in the previous

experiments) by post session feeding. Subjects were housed and maintained as in Experiment 1.

Apparatus

Experimental sessions were conducted in a BRS/LVE Inc. (Model PIP 010 016)

standard three-key operant test chamber measuring 31.0 cm by 36.5 cm by 35.0 cm. The center

key in each chamber measured 2.5-cm in diameter, and was located on the panel 8.7 cm from the

ceiling, equidistant from both sidewalls. To register a response, the key required approximately

0.09 N. All other details are described in Experiment 1.

Procedure

Training. Subjects were trained as in Experiment 2. Ratio training took three to five

sessions. Key pecks were reinforced with 3 s access to mixed grain throughout training and

baseline. The key light and houselights were extinguished during food presentation. After ratio

training was complete, subjects were exposed to baseline conditions.

Baseline. Sessions began with a 5-min blackout, during which key pecking had no

programmed consequence. This was followed by an FR 20 schedule of reinforcement for 20 min

or until 40 reinforcers were obtained, whichever came first. After 50-53 sessions, responding was

determined to be stable by visual inspection of graphs of daily session-wide response rates.

Sessions were conducted seven days a week at approximately the same time everyday. One









subject died due to unknown causes during baseline conditions. Therefore no data will be shown

for this subject, nor will any of its data be included in any analyses.

Drug regimen. After responding was determined to be stable, acute effects of cocaine

were assessed as described in Experiment 2. Doses of 13.0 mg/kg cocaine were also assessed for

some subjects when no dose in the initial range of doses produced complete suppression of

responding. Table 4-1 shows the number of administration of each dose during this assessment.

Following acute dosing, all subjects were exposed to 30 daily administrations of saline,

with no exposure to the experimental chamber. Subjects were weighed and fed up to their 83%

weight between 10:00 am-10:30 am, and were injected with saline between 11:30 am-12:00 pm.

The purpose of this phase was to examine if prolonged time away from the experimental

chamber had any effect. Then daily sessions resumed, and the dose-response curve was

redetermined. Acute doses of cocaine and saline were administered once every four days in

descending order with no injection occurring on intervening days. Each dose was administered a

minimum of two times. Any dose that produced variable effects was repeated until effects were

replicated. See Table 4-2 for the number of administrations of each dose given.

In the second phase, all subjects were exposed to 30 daily administrations of 5.6 mg/kg

cocaine, with no exposure to the experimental chamber. That is, another 30-day period without

exposure to the FR schedule occurred. The 5.6 mg/kg dose was chosen because it was commonly

used as a chronic dose in Experiments 1 and 2 because it produced a moderate to large decrease

in rate of responding for most subjects, and because it generally has resulted in tolerance whether

given before or after sessions. Subjects were fed and administered drugs at the times specified in

the previous phase, but otherwise remained in their home cages. Exposure to the FR schedule

was then re-initiated, and the dose-response curve was then redetermined as described in the first









phase. No injections occurred on days intervening acute doses to minimize the amount of pairing

of the drug and the experimental context, and to minimize the amount of exposure to the

experimental contingencies while under effects of the drug. Redetermination of the dose-

response curve took place over approximately 100 sessions. The numbers of administrations of

each dose are displayed in Table 4-3.

The third phase of the experiment was identical to the second, that is, no sessions were

conducted, except that chronic dosing continued for 60 days. The same chronic dose was used

for this phase. Exposure to the FR schedule then re-commenced, and the dose-response curve

was then redetermined again as described in the first phase with no injections on days

intervening acute dosing days. Redetermination of the dose-response curve took place over

approximately 40-90 sessions depending on the variability of dose effects. Table 4-4 shows the

number of administration of each dose during this assessment.

During the fourth and final phase of the experiment, subjects were exposed to daily

sessions and daily administration of 5.6 mg/kg cocaine immediately before the behavioral

session for 30 days. Then the dose-response curve was redetermined as described in previous

phases except 5.6 mg/kg cocaine continued to be administered on days between test doses. Table

4-5 shows how many times each dose was tested.

Drug Procedure. The drug procedure was the same as that used in Experiment 1.

Results and Discussion

Figure 4-1 displays average key pecking response rate within a session in Experiment 3,

calculated as the percent of saline vehicle rate of responding, plotted as a function of dose of

cocaine. Table 4-6 shows the rate of responding following saline vehicle administrations for all

subjects during each phase of the experiment, which stayed relatively constant across all phases

of the experiment except for Subject 965, whose rates under saline after the first 30-day









"vacation" were lower than at other times in the study. During acute cocaine administration, all

subjects showed dose-dependent decreases in rate of key pecking. Thirty sessions in the home

cage with saline administration was followed by a slight shift in the dose-response curve to the

right, suggesting that time off from experimental sessions itself was associated with modest

changes, at best, in the dose-response function. Due to the small change in drug effects from

acute administration to that following 30 days away from the session, the data from these two

drug regimens were averaged for each subject by taking the average of each administration of

each dose across both phases for individual subjects, and were used as a comparison for the

subsequent drug regimens. Therefore acute administration refers to the average of the initial

acute administration and that following 30 days of saline administration for the remainder of this

section.

When cocaine was administered daily in the home cage for 30 consecutive sessions, that

regimen produced a variety of drug effects across subjects as compared to drug effects during

acute administration shown in Figure 4-2. Subjects 740 and 945 developed tolerance following

this regimen, whereas 965 developed sensitization. Subject 881 showed little effect of this drug

regimen, and Subject 808 skipped this drug regimen due to illness.

Because tolerance did not develop in all subjects following 30 administrations of cocaine

in the home cage, subjects were administered an additional 60 daily administrations of cocaine in

the home cage with no exposure to experimental sessions, with this regimen beginning about 100

days after cessation of the previous 30-day period of administration without sessions. The results

of that exposure compared to acute effects are displayed in Figure 4-3. This drug regimen had

little effect for most subjects, with no additional tolerance developing for the two subjects that

had shown tolerance after a 30-day regimen. In fact, Subject 740, which previously developed









tolerance, showed less tolerance following 60 additional cocaine administrations in the home

cage. Subject 965 continued to show sensitization.

Cocaine (5.6 mg/kg) was then administered pre-session for 30 days to see if any additional

tolerance would develop for those subjects already showing tolerance, and to see if those that did

not previously show tolerance would develop it. Effects of cocaine administered acutely as

compared to those after a regimen of daily pre-session administration are displayed in Figure 4-

4. Daily pre-session cocaine administration led to additional tolerance in Subjects 740 and 945,

the emergence of modest tolerance for Subject 881 and not much effect for 808. Subject 965

continued to show sensitization to effects of large doses of cocaine, and showed increases in rate

of responding under effects of small doses of cocaine.

The examination of data at the group-average level showed drug effects similar to the data

from individual subjects. Figure 4-5 compares group-average data during initial acute

administration and following 30 days in the home cage with saline administered daily. The group

average data shows a slight change in drug effects following 30 days away from the session, with

all subjects showing a slight increase in ED50 from initial acute administration to following 30

sessions of saline administration in the home cage (Table 4-7). Because this increase in ED50

was small, the group-average data for the following drug regimens was compared to the data

averaged from the initial acute administration and that following 30 days of saline

administration. The ED50 for the average of the initial acute and 30 days of saline administration

was calculated by fitting a straight line to the data averaged from the two sets of determinations.

Figure 4-6 compares group-average data from acute administration and following 30 days

of cocaine administered in the home cage with no exposure to the experimental session. While it

appears that drug exposure in the home cage produced a slight amount of tolerance at the group









average level, ED50 did not increase for all subjects, and increases were relatively small (Table

4-7). Note that data from Subject 808 were excluded from this analysis because this subject

skipped this phase of the experiment.

Figure 4-7 shows group-average data from acute administration and 60 days of cocaine

administration in the home cage with no exposure to the experimental chamber. Visual

inspection shows very little change in drug effects between acute administration and 60 days of

cocaine administration in the home cage. It should be noted that the group-mean effect is not

particularly representative of the individual-animal data (Compare Figure 4-3). Examination of

changes in ED50 show that three subjects had a slightly higher ED50 following 60 days of

cocaine administration as that compared to acute administration, but the other two subjects

showed a slight decrease in ED50 from acute administration to that following 60 days of cocaine

administration (Table 4-7). Interestingly, the group-average ED50 after this condition was close

to the value from the initial acute dose-effect assessments.

Figure 4-8 displays group average data from acute administration and pre-session cocaine

administration. When cocaine was administered pre-session with daily experimental sessions,

tolerance developed at the group average level; however, only two subjects (740 and 945; Table

4-7) showed a large increase in ED50 following acute administration as compared to that

following pre-session administration. Two other subjects showed a slight increase in ED50 (881

and 808) following pre-session administration, and one subject showed a decrease in ED50

(965).

Overall, time away from experimental sessions with cocaine administered in the home

cage had no consistent influence on drug effects. The tolerance developed during home cage

cocaine administrations was neither consistent across subjects nor consistent within subject.









These results suggest that mere cocaine exposure in the home cage is unlikely to produce notable

tolerance to effects of cocaine during the behavioral session. Because mere drug exposure in the

home cage, which eliminates many behavioral factors, did not reliably lead to tolerance to effects

of cocaine during the behavioral session, it is therefore likely that some behavioral or contextual

factors associated with experimental sessions do play a role in the development of tolerance to

effects of cocaine during the behavioral session.

When drug administration occurred before each session, three of the five subjects showed

reliable tolerance, as predicted, but two others did not, with one (965) actually showing

sensitization to effects of large doses. Effects of smaller doses (3 and 5.6 mg/kg) for 965,

however, did change as a function of pre-session dosing. Previous experience with the drug had

resulted in those doses having rate-decreasing effects (Figure 4-3), but after pre-session chronic

dosing, those doses resulted in increases in response rate.









Table 4-1. Number of administrations of each dose of cocaine for each subject during initial
acute dose-response curve determination for Experiment 3.


Acute Subject
Dose 740 945 881 808 965
Sal 3 3 3 6 3
1.0 2 3 2 2 2
3.0 4 2 3 3 2
5.6 4 4 3 5 2
10.0 4 3 3 3 4
13.0 2
17.0









Table 4-2. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 30 administrations of saline in the home cage
for Experiment 3.


30 Days Sal Subject
Dose 740 945 881 808 965
Sal 4 4 4 2 2
1.0 2 2 2 2 2
3.0 2 2 2 2 2
5.6 2 3 2 8 2
10.0 3 2 3 2 2
13.0 2
17.0









Table 4-3. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 30 administrations of cocaine in the home
cage for Experiment 3.


30 Days Coc Subject
Dose 740 945 881 808 965
Sal 2 2 2 2
1.0 2 2 2 2
3.0 2 2 2 2
5.6 3 3 3 2
10.0 6 4 4 3
13.0 3
17.0 -









Table 4-4. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following 60 administrations of cocaine in the home
cage for Experiment 3.


60 Days Coc Subject
Dose 740 945 881 808 965
Sal 2 2 2 2 2
1.0 2 2 2 2 2
3.0 2 2 2 4 2
5.6 3 3 3 7 3
10.0 2 3 2 5 3
13.0 3 2
17.0 --









Table 4-5. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following the pre-session chronic drug regimen for
Experiment 3. Note that the number of cocaine administrations of the chronic dose
reflects the number of administrations used in dose-response curve determination,
rather than the total number of administrations of that dose.


Pre-session Subject
Dose 740 945 881 808 965
Sal 2 2 3 4 2
1.0 2 2 4 4 2
3.0 2 2 5 2 2
5.6 15 18 16 16 11
10.0 4 7 6 4 2
13.0 3 3 3 2 3
17.0 2 2 -









Table 4-6. Key pecks per minute following each administration of saline-vehicle for each phase
of the experiment for Experiment 3. The mean shown in italics was used to calculate
percent saline values for Figures 4-1-4-8.


Subject
Phase 740 945 881 808 965


Acute


Mean

30 Days Sal



Mean

30 Days Coc



Mean

60 Days Coc

Mean

Pre-session




Mean


174.6 155.9 118.3 189.8
164.3 144.3 125.5 205.2
174.3 137.1 120.2 206.5
205.0
194.3
206.1
171.0 145.8 121.3 201.1


205.8
196.0
179.3
200.0
195.1

181.4
182.7


135.9
141.4
132.6
122.5
133.1

132.1
101.0


128.5
112.0
111.8
126.2
120.0

140.6
113.5


201.0
204.4


202.7


182.1 116.5 127.0


206.4
184.7
195.5


121.1
126.1
123.6


124.7
93.7
109.2


200.6
193.1
196.8


170.9 95.3 100.7 201.0
153.8 112.0 107.7 224.6
107.5 170.1
169.8
162.4 103.6 105.3 191.4


136.7
147.0
118.2


134.0

91.2
97.7


94.4

121.4
131.4


126.4

159.9
123.9
141.9

122.0
101.1


111.6









Table 4-7. ED50s (mg/kg) for each subject for each phase of Experiment 3.


Phase
Subject Acute 30 Days Sal Acute + Sal 30 Days Coc 60 Days Coc Pre-session
740 4.47 8.25 4.81 7.26 6.39 23.79
945 3.53 4.22 3.80 6.90 7.07 14.06
881 3.88 6.93 3.99 4.59 4.27 4.14
808 4.41 8.95 5.05 4.44 7.11
965 9.48 9.82 9.85 5.14 3.78 4.04
Mean 5.15 7.63 5.50 4.86 5.19 10.63











-*- Acute
-- 30 Days Off + Sal


160-
140
120
100
80-
60-
40-
20
0-


1 3 5.6 10 17


160
140
120
100 -
80
60
40
20
0--
S1S2 1 3 5.6 10
965
160
140
120
100-
80
60
40
20
0S 1 3
$1S2 1 3 5.6 10


S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-1. Effects of cocaine during acute administration and following 30 days of saline
administration in the home cage for Experiment 3. Each graph shows data from an
individual subject. Response rate is plotted as a function of dose (log scale) of
cocaine for Experiment 3. Data are plotted as percent of values obtained after
administration of saline vehicle. Circles display the effects of cocaine during acute
administration, and triangles show the effects of 30 days of saline administration with
no exposure to the session. All other details are as in Figure 2-1.


S1S2 1 3 5.6 10 17











-*- Acute and Sal
-- 30 Days Off + Coc

740 808
160- 160
140- 140
120- 120
100 100 -
80- 80
60- 60-
40- 40-
20- 20
0 0
S1S3 1 3 5.6 10 17 S1S3 1 3 5.6 10
945 965
2 160- 160
o 140- 140
o 120- 120
S100- 100- U
a 80- 80
U)
60 60
40- 40
8 20- 20
0_ 0
S1S3 1 3 5.6 10 17 S1S3 1 3 5.6 10
881
160
140
120
100-
80
60
40
20
0 -
S1S3 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 4-2. Effects of cocaine during acute administration and following 30 days of cocaine
administration in the home cage for Experiment 3. Each graph shows data from an
individual subject. Response rate is plotted as a function of dose (log scale) of
cocaine for Experiment 3. Data are plotted as percent of values obtained after
administration of saline vehicle. Circles display the effects of cocaine averaged from
during acute and saline administration, and squares show effects of 30 days of
cocaine administration (5.6 mg/kg/day) with no exposure to the session. All other
details are as in Figure 2-1.











-*- Acute and Sal
--- 60 Days Off + Coc


160-
140
120
100
80-
60-
40-
20
0-


S1S4 1 3 5.6 10 17


1 3 5.6 10 17


160
140
120
100 *
80
60
40
20
0--
S1S4 1 3 5.6 10
965
160
140
120 -
100-
80
60
40
20
0
S1S4 1 3 5.6 10
$1S4 1 3 5.6 10


S1S4 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-3. Effects of cocaine during acute administration and following 60 days of cocaine
administration in the home cage for Experiment 3. Each graph shows data from an
individual subject. Response rate is plotted as a function of dose (log scale) of
cocaine for Experiment 3. Data are plotted as percent of values obtained after
administration of saline vehicle. Circles display the effects of cocaine averaged from
during acute and saline administration, and diamonds show effects of 60 days of
cocaine administration (5.6 mg/kg/day) with no exposure to the session. All other
details are as in Figure 2-1.










-*- Acute and Sal
-X- Pre-Session Coc


0 S 1 .
$1S5 1 3 5.6 10 17


S1S5 1 3 5.6 10 17


S1S5 1 3 5.6 10


S1S5 1 3 5.6 10


S1S5 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-4. Effects of cocaine during acute and pre-session administration for Experiment 3.
Each graph shows data from an individual subject. Response rate is plotted as a
function of dose (log scale) of cocaine for Experiment 3. Data are plotted as percent
of values obtained after administration of saline vehicle. Circles display the effects of
cocaine averaged from during acute and saline administration, and X's show effects
of 30 sessions of pre-session cocaine administration with daily experimental sessions.
All other details are as in Figure 2-1.


160-
140
120
100
80-
60-
40-
20
0


~,""-~~











Group Average


-- Acute
--- 30 Days Off + Sal


160 -
140
120
100
80 -
60 -
40 -
20
0 -


S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-5. Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 30 days of saline administered in the
home cage. Response rate as a percent of control is plotted as a function of dose of
cocaine for Experiment 3. Data are averaged across all subjects. Circles display the
effects of cocaine during acute administration, and triangles show the effects of 30
days of saline administration with no exposure to the session. The points above "S"
indicate the average effects of saline vehicle control, with inner error bars displaying
the standard deviation, and outer error bars displaying the range of effects of saline
vehicle.










-*- Acute and Sal
Group Average -- 30 Days Off + Coc
2 160
O
O 140
S120
^ 100
0 80
60-
40-
o 20
~ 0
>, 0 _ _,,_
S1S3 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-6. Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 30 days of cocaine administered in
the home cage. Response rate as a percent of control is plotted as a function of dose
of cocaine for Experiment 3. Data are averaged across all subjects. Circles display the
effects of cocaine averaged from during acute and saline administration, and squares
show effects of 30 days of cocaine administration with no exposure to the session. All
other details are as in Figure 4-5.











Group Average


-- Acute and Sal
--- 60 Days Off + Coc


S1S4 1 3 5.6 10
Dose of Cocaine (mg/kg)


Figure 4-7. Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of cocaine following 60 days of cocaine administered in
the home cage. Response rate as a percent of control is plotted as a function of dose
of cocaine for Experiment 3. Data are averaged across all subjects. Circles display the
effects of cocaine averaged from during acute and saline administration, and
diamonds show effects of 60 days of cocaine administration with no exposure to the
session. All other details are as in Figure 4-5.












Group Average


-- Acute and Sal
-x- Pre-session Coc


-5
, 160
0
o 140 -
4--
0
S120 -
100 -
-
S80-
- 60-
40-
8 20-
> 0-
&


Figure 4-8. Group-average data for Experiment 3 comparing effects of acute cocaine
administration and effects of pre-session cocaine. Response rate as a percent of
control is plotted as a function of dose of cocaine for Experiment 3. Data are averaged
across all subjects. Circles display the effects of cocaine averaged from during acute
and saline administration, and X's show effects of 30 sessions of pre-session cocaine
administration with daily experimental sessions. All other details are as in Figure 4-5.


S1S5 1 3 5.6 10
Dose of Cocaine (mg/kg)









CHAPTER 5
EXPERIMENT 4

Results of Experiment 3 showed that mere drug exposure in the home cage without

exposure to the behavioral session was not sufficient to produce consistent tolerance to effects of

cocaine during the behavioral session. Experiments 1 and 2 suggested that behavioral factors

such as eating or key pecking under effects of cocaine are not necessary for the development of

tolerance to effects of cocaine during the behavioral session. Yet when behavioral factors were

mostly eliminated in Experiment 3, tolerance did not consistently develop. This combination of

results makes it difficult to determine if behavioral or pharmacological variables, or both, played

a role in the development of tolerance to effects of cocaine during the behavioral session.

When subjects were exposed to daily administration of cocaine in the home cage in

Experiment 3, daily administration was discontinued when sessions resumed, in order to prevent

additional pairings of cocaine and the behavioral session. Although subjects in Experiment 3 did

not reliably show tolerance to effects of cocaine during the behavioral session, it is possible that

tolerance had developed during the chronic drug regimen, but the tolerance was diminished or

not expressed during dose-response curve redetermination because daily cocaine administration

was discontinued. Therefore, the purpose of Experiment 4 was to determine if daily cocaine

administration was necessary during dose-response curve redetermination for tolerance to

develop or be expressed. Experiment 4 used daily behavioral sessions because that procedure

was associated with the development of tolerance in Experiments 1 and 2.

Method

Subjects

Subjects were 6 adult male, White Carneau pigeons (Double "T" Farm, Glenwood, IA).

All subjects were experimentally and drug naive, and aged approximately seven months at the









beginning of the experiment. All were maintained at 83% of their free-feeding body weight by

post session feeding when needed. Subjects were housed and maintained as in Experiment 1.

Apparatus

Experimental sessions were conducted a BRS/LVE Inc. (Model PIP 010 016) standard

three-key operant test chamber measuring 31.0 cm by 36.5 cm by 35.0 cm. To register a

response, the key required approximately 0.07 N. All other details are described in Experiment 1.

Procedure

Training. Subjects were trained as in Experiment 2. Ratio training took four to eight

sessions except for one subject. This subject reached, but did not exceed FR 11 after 11 sessions.

The FR value was then incremented by two responses per reinforcer for each session for this

subject until FR 20 was reached. Key pecks were reinforced with 3 s access to mixed grain

throughout training and baseline. The key light and houselights were extinguished during food

presentation. After ratio training was complete, subjects were exposed to baseline conditions.

Baseline. Sessions began with a 5-min blackout, during which key pecking had no

programmed consequence. This was followed by an FR 20 schedule of reinforcement for 20 min

or until 40 reinforcers were obtained, whichever came first. After 51-64 sessions, responding was

determined to be stable by visual inspection of graphs of daily session-wide response rates.

Sessions were conducted seven days a week at approximately the same time every day. One

subject died due to unknown causes during baseline conditions. Therefore no data will be shown

for this subject, nor will any of its data be included in any analyses.

Drug regimen. After responding was determined to be stable, acute effects of cocaine

were assessed as described in Experiment 2. Table 5-1 shows how many times each dose was

tested during this phase. Following acute dosing, each subject was administered 5.6 mg/kg

cocaine 60 min after the session ended for 60 consecutive sessions. This dose was chosen









because it was commonly used as a chronic dose in Experiments 1 and 2, was the only chronic

dose used in Experiment 3, and because it initially produced some decrease in rate of responding

for all subjects. Subjects were administered saline everyday immediately before the session

during the chronic drug regimen, and were fed their post-session ration within 5 min after the

session if needed. Therefore all subjects were given their post-session ration and then

administered drug approximately 60 min later.

Following this chronic drug regimen, the dose-response curve was redetermined. Once

every four days subjects were administered one of their initial acute doses of cocaine pre-session.

On intervening days, subjects were administered saline before the session. Post-session saline

was administered 60 min after the session on acute dosing days and intervening days. Each dose

was administered a minimum of two times. Any dose that produced variable effects was repeated

until effects were replicated. Doses of 13.0 mg/kg cocaine were also assessed for all subjects.

Table 5-2 shows the number of administrations of each dose.

Once dose-response curve redetermination was complete, redetermination began again as

described above, except that 5.6 mg/kg cocaine was administered 60 min post-session on

intervening days rather than saline. Saline was administered before the session on intervening

days, and 60 min post-session on acute dosing days. See Table 5-3 for the number of

administrations of each dose during this phase.

Then subjects were administered 5.6 mg/kg cocaine immediately before each session with

saline administered 60 min after the session for 30 consecutive sessions. The dose-response

curve was then redetermined as described above, with 5.6 mg/kg cocaine administered pre-

session on intervening days. Saline was administered 60 min post-session on acute dosing days

and intervening days. The number of administrations of each dose is displayed in Table 5-4.









Drug Procedure. The drug procedure was the same as that used in Experiment 1.

Results and Discussion

Figure 5-1 displays average key pecking response rate within a session in Experiment 4,

calculated as the percent of saline vehicle rate of responding, plotted as a function of dose of

cocaine. Table 5-5 shows the rate of responding following each saline vehicle administration for

all phases of the experiment. Rates following vehicle administration were generally stable across

all phases of the study, although those for Pigeon 279 were more variable than those of the other

subjects. During acute cocaine administration, all subjects showed dose-dependent decreases in

rate of key pecking. Following 60 sessions of daily cocaine administrations 60 min after the

session ended, the dose-response curve was redetermined with saline administered on

intervening days. This procedure led to some amount of tolerance for all subjects at least for

some doses of cocaine as indicated by a shift in the dose-response curve to the right (Figure 5-1),

although the change was minimal for subject 811. Notably, doses that initially eliminated key

pecking no longer did so, a change evident for all 5 subjects. These results replicate the findings

of Experiment 2 in which post-session dosing resulted in tolerance when the post-session

administration occurred 60 min post session.

Figure 5-2 shows effects of acute cocaine administration as compared to effects of post-

session cocaine administration with chronic dosing on days intervening between probe doses.

When daily post-session administration resumed and dose-response curve redetermination

continued, all subjects continued to show tolerance to varying degrees, but the amount of

tolerance was small for subject 811. Effects of post-session administration of cocaine with and

without post-session drug administered on intervening days are displayed in Figure 5-3. One

subject, 961, showed slight additional tolerance at the largest dose when daily cocaine

administration resumed, while two other subjects, 811 and 286, showed a slight shift of the









function back to the left. For 109, the two curves are virtually identical, and 279's function

showed an increase in rate at 3.0 mg/kg.

Figure 5-4 compares effects of acute cocaine administration and effects after a regimen of

pre-session cocaine administration. When cocaine was administered daily pre-session, and

continued to be so during dose-response assessments, the tolerance produced by post-session

administration was maintained for two subjects (811, 286), and additional tolerance, as compared

to that after post-session administration, was evident for the three other subjects (279, 961, 109).

Figure 5-5 shows group-average data comparing effects of cocaine during acute

administration and following post-session administration when saline was administered on

intervening days. The group-average data show that slight tolerance had developed; however the

change in ED50 was small for all subjects (Table 5-6). Four of five subjects showed an increase

in ED50 and one subject showed a very slight decrease in ED50 (811) from acute administration

to post-session administration with saline administered on intervening days.

Figure 5-6 compares group average data from acute administration and following post-

session administration with cocaine administered (post-session) on intervening days during the

dose-response assessment. These data show that the small amount of tolerance previously

developed was maintained when post-session injections on intervening days switched from

saline to cocaine. All subjects had a larger ED50 when cocaine was administered post-session

with drug administered on intervening days as compared to that during acute administration

(Table 5-6).

Figure 5-7 displays group average data from post-session administration when saline was

administered on intervening days, and when cocaine was administered on intervening days. The

group average data show that the switch from saline on intervening days to cocaine on









intervening days did not alter the dose-effect curve, with both drug regimens producing very

similar functions. Note as well that the ED50 values (Table 5-6) for the two conditions were

similar, also suggesting that changing what occurred between dose assessments resulted in little

change in drug effects.

Figure 5-8 shows group average data from acute administration and after/during a regimen

of daily pre-session cocaine administration. These data show that tolerance was observed at the

group-average level when cocaine administration was switched from post-session to pre-session.

Comparison of Figure 5-8 with Figures 5-5 and 5-6 show that pre-session administration of

cocaine produced more tolerance as that compared to post-session administration at the group

average level. Examination of ED50s showed that three of five subjects (109, 279, 961) showed

a larger ED50 for pre-session administration as compared to post-session administration

regimens (Table 5-6), and the other two subjects (811, 286) showed ED50s that were similar to

that during acute administration, indicating pre-session administration produced more tolerance

than post-session administration for some, but not all, of the subjects.

These results indicate that daily cocaine administration between test doses is not necessary

for tolerance developed during post-session administration to be expressed. When daily

administration of cocaine resumed, it did not consistently produce additional tolerance,

suggesting that daily cocaine administration during dose-response curve redetermination likely

does not contribute to the development of tolerance. These results strengthen the results of

Experiment 3 in that subjects in Experiment 3 would have likely shown the same drug effects if

daily cocaine administration was continued during dose-response curve redetermination.

Therefore the tolerance, or lack of tolerance shown during dose-response curve redetermination

in Experiment 3 was probably indicative of the actual amount of tolerance that developed.









Table 5-1. Number of administrations of each dose of cocaine for each subject during acute dose-
response curve determination for Experiment 4.


Acute Subject
Dose 811 286 109 279 961
Sal 4 5 4 4 5
1.0 3 3 3 4 3
3.0 3 3 3 3 3
5.6 3 5 4 5 4
10.0 4 3 3 4 3
13.0 -









Table 5-2. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following post-session chronic administration with
saline administered on intervening days for Experiment 4. Note that the number of
saline administrations reflects the number of administrations used in dose-response
curve determination, rather than the total number of administrations of saline.


Post, sal/sal Subject
Dose 811 286 109 279 961
Sal 15 15 16 16 16
1.0 2 2 2 2 2
3.0 2 2 2 2 2
5.6 4 3 5 4 3
10.0 5 5 5 6 7
13.0 3 3 2 2 2









Table 5-3. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following post-session chronic administration with
cocaine administered on intervening days for Experiment 4. Other details are as in
Table 5-2.


Post, sal/coc Subject
Dose 811 286 109 279 961
Sal 16 16 16 16 16
1.0 2 2 2 2 2
3.0 2 2 2 2 2
5.6 4 3 5 4 2
10.0 5 5 5 5 5
13.0 3 4 2 3 4









Table 5-4. Number of administrations of each dose of cocaine for each subject during dose-
response curve determination following pre-session chronic administration for
Experiment 4. Note that the number of cocaine administrations of the chronic dose
reflects the number of administrations used in dose-response curve determination,
rather than the total number of administrations of that dose.


Pre-session Subject
Dose 811 286 109 279 961
Sal 2 2 2 3 2
1.0 2 2 2 2 2
3.0 2 2 2 3 2
5.6 15 15 15 14 15
10.0 6 6 5 3 3
13.0 3 3 4 3 6









Table 5-5. Key pecks per minute following each administration of saline-vehicle for each phase
of the experiment for Experiment 4. The mean shown in italics was used to calculate
percent saline values for Figures 5-1-5-8.


Subject
Phase 811 286 109 279 961
Acute 133.0 125.7 136.9 109.5 174.0


Mean

Post, sal/sal

















Mean

Post, sal/coc


132.7 138.1
157.9 132.0
163.2 153.0
165.2
146.7 142.8


156.4 154.4 161.6
191.7 136.0 166.7
194.0 167.1 158.9
176.2 177.2 148.1
183.8 180.5 156.1
187.8 175.5 159.5
167.1 175.2 164.3
168.1 177.4 153.7
164.4 169.1 154.9
172.7 187.0 166.8
158.5 173.2 171.3
172.1 180.0 160.5
152.4 187.3 153.9
174.5 174.3 164.9
173.5 189.0 155.7
156.8
173.8 172.9 159.6


161.7
176.3
162.4
158.0
168.3
161.1
170.8
167.2
180.8
188.5
18.2
180.5
158.4
172.1
145.3


185.5
193.5
178.5
182.7
192.5
180.4
184.0
183.1
126.1
186.0
172.6
185.2
163.5
165.0
132.6


161.9
159.7
162.4
160.4
168.9
165.1
160.9
157.0
171.8
153.1
175.2
153.6
134.7
140.6
142.0


148.8 105.6 174.8
130.2 113.9 186.2
140.6 94.1 199.5
194.4
139.1 105.7 183.8


57.8
111.6
96.0
105.7
102.9
117.3
109.6
111.4
116.0
103.3
113.4
118.5
92.4
109.0
100.1
122.0
105.4

109.1
77.9
116.3
121.0
114.9
128.0
112.8
98.5
126.1
112.6
115.1
96.3
40.9
64.1
87.3


201.0
171.3
202.6
196.7
196.7
196.0
201.4
189.7
196.8
196.5
197.7
185.3
193.8
202.1
193.0
200.9
195.1

209.1
197.6
180.8
204.0
218.9
217.3
196.5
187.3
200.7
204.1
198.2
197.3
184.6
173.5
116.4









Table 5-5. Continued.


Subject
Phase 811 286 109 279 961
172.3 112.2 148.8 48.5 12.0
Mean 169.5 170.1 157.3 98.1 181.1

Pre-session 171.6 177.5 102.5 56.1 195.3
161.1 178.1 137.2 103.9 191.0
89.6
Mean 166.4 177.8 119.9 83.2 193.2









Table 5-6. ED50s (mg/kg) for each subject for each phase of Experiment 4.

Phase
Subject Acute Post, sal/sal Post, sal/coc Pre-session
811 5.99 5.51 6.53 5.92
286 5.86 8.82 6.93 5.69
109 3.74 5.48 5.50 10.44
279 3.41 5.73 8.45 8.97
961 5.13 6.46 6.37 13.29
Mean 4.83 6.40 6.76 8.86











-- Acute
-- Chronic, sal/sal intervening


811 279
160- 160
140- 140
120 120
100- T\ 100 -
80 80-
60 60 -
40 40-
20 20
0 0
S1S2 1 3 5.6 1013 S1S2 1 3 5.6 1013


g 286 961
E 160 160
0
0 140- 140
0
S120- 120
100 100 -
a 80 1 80
c 60- 60
4 40 40
8 20 20
> 0- --_ o 0
SS1S2 1 3 5.6 1013 S1S2 1 3 5.6 1013


109
160
140
120
100 -
80
60
40
20-
0 I
S1S2 1 3 5.6 1013
Dose of Cocaine (mg/kg)

Figure 5-1. Effects of cocaine during acute administration and post-session administration with
saline administered on intervening days for Experiment 4. Each graph shows data
from an individual subject. Response rate is plotted as a function of dose of cocaine
for Experiment 4. Data are plotted as percent of values obtained after administration
of saline vehicle. Circles display the effects of cocaine during acute administration,
and triangles show the effects of 60 days of cocaine administered 60 min after the
session ended with saline administered on intervening days. All other details are as in
Figure 2-1.











-*- Acute
-U- Chronic, sal/5.6 intervening


811
160
140
120-
100 -
80-
60
40
20
0
S1S3 1 3 5.6 1013


286
160-
140-
120 -
100- I
80-
60-
40
20-
0 -
S1S3 1 3 5.6 1013


S1S3 1 3 5.6 1013


S1S3 1 3 5.6 1013
S1 S3 1 3 5.6 1013


109
160
140
120
100 -
80-
60-
40-
20-
0-
0 ii ------------
S1S3 1 3 5.6 1013
Dose of Cocaine (mg/kg)

Figure 5-2. Effects of cocaine during acute administration and post-session administration with
cocaine administered on intervening days for Experiment 4. Each graph shows data
from an individual subject. Response rate is plotted as a function of dose of cocaine
for Experiment 4. Data are plotted as percent of values obtained after administration
of saline vehicle. Circles display the effects of cocaine during acute administration,
and squares show effects of one-hour-post-session cocaine with cocaine administered
on intervening days. All other details are as in Figure 2-1.











A- Chronic, sal/sal intervening
-0- Chronic, sal/5.6 intervening


S2S3 1 3 5.6 1013


286
160
140
120
100
80
60-
40-
20-

S2S3 1 3 5.6 1013


S2S3 1 3 5.6 1013


961
160
140
120 -
100 -
80-
60-
40
20-
0
S2S3 1 3 5.6 1013


109
160
140
120 -
100 -
80
60-
40-
20
0 -
S2S3 1 3 5.6 1013
Dose of Cocaine (mg/kg)

Figure 5-3. Effects of cocaine during post-session administration with saline or cocaine
administered on intervening days for Experiment 4. Each graph shows data from an
individual subject. Response rate is plotted as a function of dose of cocaine for
Experiment 4. Data are plotted as percent of values obtained after administration of
saline vehicle. Triangles show the effects of 60 days of cocaine administered 60 min
after the session ended with saline administered on intervening days, and squares
show effects of one-hour-post-session cocaine with cocaine administered on
intervening days. All other details are as in Figure 2-1.











-*- Acute
--- Chronic pre-session


811
160
140
120-
100 *
80-









286
160
140
120
100 -
80-
60-
40-
20
0 -
S1S4 1 3 5.6 1013


160
140
120
100-
80
60
40
20
0SS
S1 S4


S1S4 1 3 5.6 1013


961
160
140
120
100 -
80
60-
40-
20-
0
S1 S4 1 3 5.6 1013


1 3 5.6 1013
Dose of Cocaine (mg/kg)


Figure 5-4. Effects of cocaine during acute administration and pre-session administration for
Experiment 4. Each graph shows data from an individual subject. Response rate is
plotted as a function of dose of cocaine for Experiment 4. Data are plotted as percent
of values obtained after administration of saline vehicle. Circles display the effects of
cocaine during acute administration, and diamonds show effects of 30 days of pre-
session cocaine administration. All other details are as in Figure 2-1.










S-*- Acute
E Group Average -- Chronic, sal/sal intervening
0
O 160
4--
S140
120
n 100
80 -
60 -
40
n_ 20-
20 -

S1S2 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 5-5. Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and post-session administration with saline administered on
intervening days. Response rate as a percent of control is plotted as a function of dose
of cocaine for Experiment 4. Data are averaged across all subjects. Circles display the
effects of cocaine during acute administration, and triangles show the effects of post-
session administration with saline administered on intervening days. The points above
"S" indicate the average effects of saline vehicle control, with inner error bars
displaying the standard deviation, and outer error bars displaying the range of effects
of saline vehicle.










-- Acute
E Group Average Chronic, sal/5.6 intervening
0
O 160
4--
S140-
| 120
o 100 -
80 -
60
40

S20
S1S3 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 5-6. Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and post-session administration with cocaine administered on
intervening days. Response rate as a percent of control is plotted as a function of dose
of cocaine for Experiment 4. Data are averaged across all subjects. Circles display the
effects of cocaine during acute administration, and squares show the effects of post-
session administration with cocaine administered on intervening days. All other
details are as in Figure 5-5.










2- Chronic, sal/sal intervening
1 Group Average Chronic, sal/5.6 intervening
0
0 160 -
S140
S120
.- 100
S80 -
60
40-
_(D 2 -
0
._ -20

S2S3 1 3 5.6 10
Dose of Cocaine (mg/kg)
Figure 5-7. Group-average data for Experiment 4 comparing effects of cocaine during post-
session administration with saline or cocaine administered on intervening days.
Response rate as a percent of control is plotted as a function of dose of cocaine for
Experiment 4. Data are averaged across all subjects. Triangles display effects of post-
session administration with saline administered on intervening days, and squares
show the effects of post-session administration with cocaine administered on
intervening days. All other details are as in Figure 5-5.










S-*- Acute
16 Group Average --- Pre-session
0
0 160 -
S140
120
a- 100 -
80 -
60
40
S20
0
S1S4 1 3 5.6 10
Dose of Cocaine (mg/kg)

Figure 5-8. Group-average data for Experiment 4 comparing effects of cocaine during acute
administration and pre-session administration. Response rate as a percent of control is
plotted as a function of dose of cocaine for Experiment 4. Data are averaged across all
subjects. Circles display the effects of cocaine during acute administration, and
diamonds show the effects of pre-session administration. All other details are as in
Figure 5-5.









CHAPTER 6
GENERAL DISCUSSION

The main conclusion of the current experiments was that not-contingent tolerance was

observed in pigeons. The majority of subjects in all experiments administered post-session

cocaine developed tolerance. Experiment 1 found that post-session administration of cocaine in

pigeons could result in tolerance to effects of cocaine during the behavioral session. Half of the

subjects administered cocaine after the session developed tolerance. Experiment 2 also examined

effects of post-session drug administration. Eating under the effects of cocaine was controlled,

and nearly all the subjects developed tolerance to the drug's within-session effects regardless of

whether or not they ate under the effects of the drug. The only exceptions were subjects that

received a relatively large dose immediately post-session and as a result exhibited response

suppression throughout the session. Results of Experiments 1, 2, and 4 combined therefore show

that post-session administration of cocaine often led to tolerance to effects of cocaine during the

behavioral session. For subjects in Experiments 1, 2 and 4 that never showed response

suppression, 16 of 18 subjects (all subjects except 727 and 752) developed notable tolerance

from chronic post-session cocaine administration. A paired t-test comparing the ED50 from

acute administration and the ED50 from the first post-session dosing regimen across subjects in

all experiments was significant [t (17) = 4.97; p < .01; average acute ED50 = 4.52; average post-

session ED50 = 8.37]. This indicates that tolerance was a common outcome from post-session

cocaine administration across this series of experiments. Most of the instances in which post-

session drug administration did not lead to tolerance were accompanied by suppression of key

pecking that was associated with chronic administration of relatively large doses of cocaine (7.4

mg/kg or 10.0 mg/kg) immediately post-session. It is possible that had all subjects been

chronically administered moderate doses of cocaine (3.0 mg/kg or 5.6 mg/kg) post-session that









those that showed behavioral suppression would have instead shown tolerance. The fact that

post-session administration of cocaine usually led to tolerance in the pigeons suggests that

tolerance to cocaine's effects on operant behavior in pigeons is not contingent on the time of

drug administration in relation to the time of the behavioral session, an outcome that suggests

that cocaine exposure alone is sufficient to produce tolerance in this species.

When mere drug exposure was examined in Experiment 3, however, it did not reliably lead

to the development of tolerance. A few subjects showed small amounts of tolerance when

cocaine was repeatedly administered while the pigeon remained in its the home cage (i.e.,

operant-response sessions were not conducted), but this tolerance was not consistently found

across subjects or within subject when a second, longer exposure period was examined.

Experiment 4 was conducted to see if the fact that dose-response determinations in

Experiment 3 were made under conditions where no drug was administered between test doses

might have contributed to the lack of development of tolerance. Experiment 4, which involved

post-session cocaine administration, showed again that post-session dosing can result in

tolerance and also that the discontinuation of chronic dosing during dose-response curve

redetermination did not prevent the observation of tolerance that had developed during chronic

post-session dosing. Therefore it is unlikely that the cessation of chronic dosing in Experiment 3

during dose-response curve redetermination prevented the expression of any tolerance that had

developed when cocaine was administered in the home cage.

The results of the current research are not consistent with much past research on contingent

tolerance, except research conducted with pigeons. Pinkston and Branch (2004) found not-

contingent tolerance to cocaine in pigeons, but Bowen et al. (1993), Branch and Sizemore

(1988), Smith (1990), and Woolverton et al. (1978) all found contingent tolerance to cocaine









when squirrel monkeys or rats were used as subjects. Therefore the majority of research

conducted using cocaine has found that post-session cocaine administration does not lead to

tolerance (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978),

and some has even found that post-session administration of cocaine leads to sensitization

(Bowen et al., 1993; Woolverton et al., 1978). Contingent tolerance has also been a common

finding in rats with other psychoactive drugs such as ethanol (Chen, 1968; Wenger et al., 1981)

and amphetamine (Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Poulos et al., 1981).

The finding of tolerance resulting from post-session drug administration is also not

consistent with the reinforcement-loss hypothesis (Schuster et al., 1966). The reinforcement-loss

hypothesis states that subjects will develop tolerance if the initial drug effect produces a loss in

reinforcement obtained. Initial administration of cocaine pre-session did produce a loss of

reinforcement because response rate was decreased, whereas initial administration of cocaine

post-session had no effect on the amount of reinforcement obtained. Had contingent tolerance

been found, then the reinforcement-loss hypothesis would have been supported because only the

subjects with an initial decrease in reinforcement obtained (Pre-post group) would have shown

tolerance. Therefore the reinforcement-loss hypothesis cannot be used to explain how or why

subjects in the present set of experiments developed tolerance as a result of post-session drug

administration. Although the reinforcement-loss hypothesis can account for the results of many

experiments that have found tolerance (e.g., Bowen et al., 1993; Branch & Sizemore, 1988;

Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Poulos et al., 1981; Smith, 1990;

Woolverton et al., 1978), this is not the first experiment to demonstrate that behavioral tolerance

can develop without reinforcement loss (e.g., Pinkston & Branch, 2004; Smith, 1986).









Throughout Experiments 1 and 2, it was common for subjects administered larger doses of

cocaine (7.4 mg/kg or 10.0 mg/kg) immediately after the session to show response suppression

during the session. Such suppression was also commonly seen in the study by Pinkston and

Branch (2004) when large doses of cocaine were administered 20 min after the session.

Additionally, large doses of amphetamine have also been found to produce response suppression

of food maintained behavior when administered post-session (Glowa & Barrett, 1983). Though

the present experiment was not designed to investigate why response suppression is associated

with large doses of cocaine administered immediately after the session, the Pinkston and Branch

(2004) study found that replacing post-session administrations of cocaine with post-session

administrations of saline was followed by recovery of key pecking. This indicated that preceding

drug administration with the session might have caused the behavioral suppression, meaning the

suppression was likely due to Pavlovian associations between the session and the drug. The drug

was never administered, however, without exposure to the behavioral session, therefore one can

only tentatively conclude that Pavlovian processes were responsible for the response suppression

(cf Pinkston & Branch, 2004).

The response suppression seen when large doses of cocaine were administered

immediately after the session in Experiments 1 and 2 was not observed for subjects in the

Delayed-Drug group in Experiment 2. Three subjects in this group were administered 10.0

mg/kg daily 60 min after the session. None of these subjects showed response suppression, and

all developed tolerance. These results suggest that failure to observe tolerance with post-session

large doses in Experiment 1 and for subjects in the Immediate-Drug group in Experiment 2 was a

result of the tolerance being masked by the apparently Pavlovian processes that resulted in

within-session suppression. When the 60-min delay between post-session cocaine administration









and the session obviated the Pavlovian processes, the administration of large chronic doses

resulted in tolerance. Therefore, the combination of size of chronic dose, and when the dose was

administered in relation to the behavioral session played a role in whether or not tolerance

developed. Subjects administered moderate chronic doses of cocaine (3.0 mg/kg or 5.6 mg/kg)

often developed tolerance regardless of if the drug was administered before the session,

immediately after the session, or 60 min after the session. Subjects administered larger chronic

doses of cocaine (7.4 mg/kg or 10.0 mg/kg) commonly showed tolerance when the drug was

administered before the session, or 60 min after the session, but not when the drug was

administered immediately after the session.

While the contrast between the current findings and examinations of contingent tolerance

with other species may appear to be evidence of a species difference in contingent tolerance to

cocaine, it remains possible that experimental differences produced the differences in outcomes,

rather than a species difference. Even though pigeons showed not-contingent tolerance with the

current experimental preparation and in the one other experiment that examined contingent

tolerance to cocaine in pigeons (Pinkston & Branch, 2004), many experimental differences need

to be considered before concluding that pigeons do not show contingent tolerance to cocaine.

One potentially important variable in the development of contingent tolerance to cocaine is

the length of the chronic drug regimen, which has varied across experiments. Experiments that

have found contingent tolerance to cocaine have used chronic regimens ranging from 20-45

sessions (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978).

Experiments that have found contingent tolerance to other psychoactive drugs have used chronic

regimens ranging from 3-28 sessions (Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Chen,

1968; Poulos et al., 1981; Wenger et al., 1981). The present set of experiments generally used 30









sessions as the original length of the chronic regimen except for a few exceptions when 60

sessions were used, so the current regimens were relatively long. Tolerance to drug effects is

usually a product of repeated drug administration (Carlton, 1983; Wolgin, 1989); therefore a

minimum of drug exposure is often necessary for the development of tolerance. In order for

contingent tolerance to be observed, a particular length of chronic dosing may be required.

Carlton and Wolgin (1971) found that seven days of chronic administration produced tolerance

in subjects administered the drug pre-session, but not for subjects administered the drug post-

session. Subjects in the Post-pre group were then switched to pre-session drug administration,

which led to the development of tolerance.

It is possible that tolerance from post-session dosing may take longer to develop than

tolerance from pre-session administration. No experiments have examined this directly by

systematically using different lengths of chronic regimens. The present set of experiments used

chronic regimens of similar length but slightly longer than the average of those that have found

contingent tolerance. Within the first 30 days of chronic administration, four of six subjects (36,

40, 592, 752) in the Pre-post group in Experiment 1 developed tolerance. Key pecking rates were

similar to saline vehicle control rates after 4-18 days for these subjects, indicating that tolerance

often develops quickly when cocaine is administered pre-session. What has not been determined

is exactly how long a chronic regimen must be to produce tolerance from post-session cocaine

administration. Being that previous experiments that found contingent tolerance to cocaine used

chronic regimens ranging from 20-45 sessions (Bowen et al., 1993; Branch & Sizemore, 1988;

Smith, 1990; Woolverton et al., 1978) it is possible that these chronic regimens were not long

enough to capture the tolerance that may have developed had post-session dosing continued.

While the chronic regimens in the present set of experiments were 30 consecutive days, the









chronic dose was actually administered over much longer span (a minimum of 24 additional

administrations) while the dose-response curve was redetermined, providing ample time for

tolerance to develop. Consequently, it is possible that if shorter chronic drug regimens were used

in the present set of experiments then contingent tolerance may have been observed. Future

experiments could manipulate the length of the chronic regimen for post-session administration

of cocaine to determine if the length of the chronic regimen is a factor in the development of

contingent tolerance.

Another variable that may be important in the development of contingent tolerance is the

behavioral task employed. The behavioral task used has varied across experiments investigating

contingent tolerance. Previous experiments that have found contingent tolerance to cocaine have

used milk drinking (Bowen et al., 1993; Woolverton et al., 1978), lever pressing (Smith, 1990),

nose poking (Smith, 1990), and key pressing (Branch & Sizemore, 1988) as the operant task.

Both the present set of experiments and the study by Pinkston and Branch (2004) used key

pecking as the operant task.

While key pecking is a prototypical operant task for pigeons (Schwartz & Gamzu, 1977), it

may not be equivalent to other operant tasks used with other species such as lever pressing in

rats. Research showing that pigeons are more likely to key peck than treadle press when response

independent food is presented (Green & Holt, 2003), and are more likely to peck a vertical than

horizontal surface (Burs & Malone, 1992) suggests that key pecking in pigeons may be

controlled by Pavlovian processes as well as operant contingencies. Some research has found

that there are two topographically distinguishable types of key pecks. Mere response-

independent presentation of food engenders key pecks of short duration, whereas contingent food

presentation maintains key pecks of longer duration (Schwartz, 1977; Schwartz & Williams,









1972). This suggests that some key pecks are operant whereas others are respondent (Schwarz,

1977). Therefore pecking in pigeons is sometimes viewed as a Pavlovian rather than operant

response.

Another factor that may determine whether or not contingent tolerance develops is if the

operant task used is related to foraging in the subject's natural environment. Treadle pressing in

pigeons is not a foraging related response (as opposed to pecking which is foraging related) and

is sensitive to operant contingencies. Therefore treadle pressing for food in pigeons may be a

more prototypical operant as compared to key pecking because treadle pressing is an arbitrary

response that is not used by pigeons to obtain food in their natural environment. If the current set

of experiments had been conducted with treadle pressing as the operant, a more prototypical

operant than key pecking, it is possible that contingent tolerance may have been observed. Yet

whether or not the operant task is foraging related may not be the key factor because contingent

tolerance to cocaine has been found in rats with licking a spout as the operant task (Bowen et al.,

1993; Woolverton et al., 1978), which is a foraging related behavior. The operant task used,

regardless of its relationship to foraging, may be the key factor. Therefore future studies could

replicate Experiment 1 using treadle pressing as the operant task to investigate if the topography

of the operant task is a factor in the development of contingent tolerance to cocaine.

One limitation of the present set of experiments is that they did not point to a mechanism

that prevented the development or expression of contingent tolerance or explain why tolerance

from post-session administration commonly developed. Due to the fact that previous experiments

on contingent tolerance have all had procedural differences, it is difficult to determine which, if

any procedural differences may be important factors in determining whether or not contingent

tolerance develops. One variable that has changed across experiments investigating contingent









tolerance is the schedule of reinforcement used. Contingent tolerance to cocaine has been found

when using an FR 40 and FI 5 min schedule of reinforcement (Smith, 1990). Another experiment

found contingent tolerance using a VR 2 (FR 3, 4, or 5: S) schedule of reinforcement (Branch &

Sizemore, 1988). Several contingent-tolerance experiments have used milk drinking as the

operant, which is reinforced on an FR 1 if each lick is counted as a response (Bowen et al., 1993;

Carlton & Wolgin, 1971; Poulos et al., 1981; Woolverton et al., 1978). The present set of

experiments used an FR 20 schedule of reinforcement, and Pinkston and Branch (2004) used a

mult FR 5 FR 100 schedule of reinforcement. While the few experiments that have found not-

contingent tolerance to cocaine used FR schedules of reinforcement (Pinkston & Branch, 2004;

present experiment), experiments that have found contingent tolerance have used a variety of

schedules of reinforcement including FR (Bowen et al., 1993; Branch & Sizemore, 1988; Smith,

1990; Woolverton et al., 1978). Based on the reinforcement-loss hypothesis, tolerance should

have developed to effects of cocaine on pecking on an FR schedule when cocaine was

administered pre-session because cocaine initially decreased the amount of reinforcement

obtained when administered pre-session. The reinforcement-loss hypothesis also predicts that

tolerance will not develop to effects of cocaine on key pecking on an FR schedule if cocaine is

administered post-session because initial post-session administration of cocaine did not affect the

amount of reinforcement obtained. Therefore the reinforcement-loss hypothesis predicts that

behavior under response-dependent schedules of reinforcement should show contingent tolerance

as long as the initial drug effect produces a reduction in reinforcement rate.

An additional potential factor in the development of contingent tolerance is the context in

which the drug is experienced. The present set of experiments found that neither eating nor key

pecking under the effects of cocaine was necessary for tolerance to develop to effects of cocaine









during the behavioral session. When these behavioral factors were omitted and subjects were

also not exposed to the experimental context during the chronic regimen in Experiment 3,

subjects did not develop notable tolerance. That is, mere drug exposure was not sufficient to

result in notable tolerance. In Experiment 3 subjects were not exposed to the experimental

context at all during chronic dosing. It is therefore possible that daily exposure to the

experimental context during the chronic dosing regimen is an important factor in the

development of tolerance to effects of cocaine during the behavioral session. The present set of

experiments, however, did not explicitly examine drug-paired cues in the context (e.g., the room

where injections were administered, the experimental context in which the drug was

experienced) that may have been involved in drug tolerance. Past research has shown that drug-

paired cues play a large role in determining whether or not tolerance will develop (Seigel, 1989).

The results of the present set of experiments showed that experiencing drug effects in the

experimental context was not necessary for tolerance to develop, but some regular exposure to

the experimental context during chronic dosing was necessary for notable tolerance to develop.

A future experiment could investigate the importance of the experimental context by replicating

Experiment 3 except that during the chronic regimen, subjects would be placed in the operant

chamber without consequences for key pecking. The results of this experiment compared to the

results of Experiment 3 would help illuminate whether the context in which the drug is

experienced is important.

A comparison of the results of Experiments 1, 2, and 4 with Experiment 3 show that some

factor (or factors) associated with behavioral sessions was (were) important in the development

of tolerance. Subjects in Experiments 1, 2, and 4 usually developed tolerance when exposed

daily to the experimental session even when given their chronic dose after the daily session.









Experiment 3 found that not exposing subjects to the experimental session during the chronic

dosing regimen produced little tolerance. Therefore exposure to the experimental session may

have been a key factor in the development of tolerance. Not identified in the present set of

experiments was the frequency at which subjects need to be exposed to experimental sessions in

order for tolerance to develop. Future experiments could examine if exposure to the experimental

session every other day, or even once a week during the chronic dosing regimen is sufficient to

produce tolerance.

A further potentially important variable in the development of contingent tolerance is the

association of drug administration and the behavioral session. During the chronic dosing

regimens in Experiments 1, 2, and 4 it was always the case that either drug administration

predicted the experimental session (pre-session administration), or the experimental session

predicted drug administration (post-session administration). Therefore the drug administration

and the behavioral session were always associated with each other, albeit at a substantial delay

when the drug administration occurred an hour after the session. If drug administration could be

completely disassociated with the behavioral session by administering the drug at random times

with respect to the session during the chronic regimen it might prevent the development of

tolerance. Future experiments investigating the association between drug administration and the

behavioral session may illuminate if it is the association between the drug and the session that

produces tolerance rather than the ability to engage in the target behavior while under effects of

the drug.

Another possibility is that the apparent tolerance from post-session dosing was a product of

some aspect of the experimental procedure other than post-session administration. During

Experiments 1, 2 and 4, subjects that were administered chronic cocaine post-session were also









given repeated exposure to the drug pre-session during dose-response curve assessments.

Intermittent pre-session administration of cocaine was necessary to determine if tolerance had

developed from post-session dosing, but it is possible that the intermittent pre-session exposure

to the drug produced tolerance rather than the chronic post-session administration. A previous

experiment examined the effects of repeated dose-response curve assessments in the

development of tolerance to cocaine in pigeons with acute doses administered at a variety of

intervals. This experiment found that dose-response curves were stable after eight determinations

of the dose-response curve indicating that tolerance is unlikely to develop during dose-response

curve assessment (Marusich & Branch, 2006). It was also the case that dose-response curves

within any particular phase of an experiment in the current set of experiments were relatively

stable. Each dose-response curve was determined a minimum of two times, so if intermittent pre-

session dosing produced some amount of tolerance, it would have been detected by a shift in the

dose-response curve while it was being determined, which did not happen. Therefore it is

unlikely that the intermittent pre-session administration of cocaine in the present set of

experiments contributed to the tolerance seen following chronic post-session administration.

The reinforcement-loss hypothesis appears applicable as a reasonable account of what

might occur when the drug is given pre-session, but a major puzzle created by the current results

concerns how experience during daily sessions could possibly interact with repeated post-session

drug administration. Tolerance was minimal when the drug was administered daily while no

sessions were scheduled, but was consistently produced when the same drug regimen, one

administration per day, occurred when sessions were also held daily, an hour before the drug was

given. No evidence of change in operant performance was evident during the period of daily

drug administration, yet only when daily operant-response sessions were conducted did tolerance









consistently develop. One possibility is that the extra experience with the operant contingencies

during the period of drug administration made the operant performance more resistant to the rate-

decreasing effects of cocaine, so the apparent tolerance was simply a result of more experience

with the FR schedule. That possibility, however, is not consistent with the results of Experiments

1 and 4 in which in many cases extended experience resulted in no changes in dose-response

functions. Subjects in Experiments 1 and 4 had considerably more exposure to the FR

contingency than subjects in Experiment 2 due to the length of the experiments, but subjects in

Experiments 1 and 4 did not show more tolerance on average than subjects in Experiment 2.

Therefore there is no data from the current set of experiments to suggest that extended exposure

to the FR schedule contributed to the development of tolerance. Future experiments could

examine this factor by exposing subjects to an FR contingency for a prolonged time, but without

chronic dosing, and then redetermining the dose-response curve to see if tolerance developed.

Another possibility is that the lack of opportunity to "practice" the target behavior (key

pecking) occurred in Experiment 3 such that tolerance that had developed was canceled out by

the lack of opportunity to peck under exposure to the operant contingency. That possibility,

however, is difficult to reconcile with the fact that in Experiment 3 when the saline vehicle was

administered daily during a 30-day hiatus from the operant contingencies no substantial changes

occurred in cocaine's effects.

In summary, the present set of experiments suggests that, under the conditions arranged,

tolerance to effects of cocaine during the behavioral session in pigeons was not dependent on

drug administration prior to the behavioral session. The majority of subjects administered drug

immediately after the session or 60 min after the session still developed tolerance to effects of

cocaine during the behavioral session, indicating that it is not necessary for subjects to engage in









the target behavior while under effects of the drug in order for them to develop tolerance to

effects of the drug on the target behavior. When behavioral factors were removed during the

period of repeated administration (Experiment 3), subjects no longer reliably showed tolerance.

Therefore some aspect of exposure to the experimental session or experimental context on a

regular basis was necessary for tolerance to develop, yet this exposure did not have to occur

while subjects were under effects of the drug. Although contingent tolerance to cocaine

previously appeared to be a reliable finding (Bowen et al., 1993; Branch & Sizemore, 1988;

Smith, 1990; Woolverton et al., 1978), results of the present experiment combined with those of

Pinkston and Branch (2004) suggest that not-contingent tolerance to cocaine is common in

pigeons. These results therefore question the generality of contingent tolerance to cocaine.

Even though research has found that it is common for humans to develop tolerance to

many effects of cocaine (Fischman, et al., 1985; Mendelson et al., 1998), none of that research

has examined post-session cocaine administration. Due to the paucity of data on contingent

tolerance to cocaine in humans, it is not yet known if humans would show contingent tolerance

to cocaine.









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Campbell, J. C. & Seiden, L. S. (1973). Performance influence on the development of tolerance
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Carlton, P. L. (1983). A Primer of Behavioral Pharmacology. New York: W. H. Freeman & Co.

Carlton, P. L. & Wolgin, D. L. (1971). Contingent tolerance to the anorexigenic effects of
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Chen, C. S. (1968). A study of the alcohol-tolerance effect and an introduction of a new
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Glowa, J. R. & Barrett, J. E. (1983). Response suppression by visual stimuli paired with
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Pharmacological Reviews, 41, 3-52.

Marusich, J. A. & Branch, M. N. (2006). Stability of cocaine dose-response functions at different
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BIOGRAPHICAL SKETCH

Julie Mamsich grew up in Washington State, where she attended Washington State

University for her undergraduate education. There, she was first exposed to behavior analysis

and behavioral pharmacology under the direction of Dr. Frances McSweeney. Julie completed

her Bachelor of Science degree in 2002. She then continued her education at the University of

Florida under the tutelage of Dr. Marc Branch. There, she continued her studies in behavior

analysis and behavioral pharmacology. Julie received her Master of Science degree in 2005 and

her PhD in 2008, both from the University of Florida. In the future, Julie plans to continue

conducting research in behavioral pharmacology and serve as a faculty member in a university

setting.





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1 PHARMACOLOGICA L AND ENVIRONMENTAL FACTORS IN THE DEVELOPMENT OF CONTINGENT TOLERANCE TO COCAINE IN PIGEONS By JULIE A. MARUSICH A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008

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2 2008 Julie A. Marusich

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3 ACKNOWLEDGMENTS I thank my advisor, Marc Branch, for his guidance, support, and encouragement, and for always being available for discussion. I also thank him for great help in developing my writing, teaching me to think critically, and teaching me how to design experiments properly. I thank Jesse Dallery for providing helpful comments throughout my graduate career, en during aid in statistical and graphical analyses, and always being a source of positive reinforcement. I thank Tim Hackenberg for teaching me what it means to be a radical behaviorist. I thank my graduate student colleagues Brian Kangas, Anne Macaskill, Da ve Maguire, Michelle Miller, Jon Pinkston, Matt Weaver, and Jin Yoon for their help in running sessions, technical support, and always being available for conceptual discussions. I thank my other committee members H. Jane Brockmann, Brian Iwata, and Alan S pector for their many contributions to this project and help in shaping me into a better scientist. Lastly, I would like to thank my family and friends, especially Phil, Bethany, Erin and Rachelle for their care and support throughout this process.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 3 LIST OF TABLES ................................ ................................ ................................ ........................... 6 LIST OF FIGURES ................................ ................................ ................................ ......................... 8 ABSTRACT ................................ ................................ ................................ ................................ ... 10 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 12 2 EXPERIMENT 1 ................................ ................................ ................................ .................... 19 Method ................................ ................................ ................................ ................................ .... 19 Subjects ................................ ................................ ................................ ............................ 19 Apparatus ................................ ................................ ................................ ......................... 19 Procedure ................................ ................................ ................................ ......................... 20 Results and Discussion ................................ ................................ ................................ ........... 23 3 EXPERIMENT 2 ................................ ................................ ................................ .................... 44 Method ................................ ................................ ................................ ................................ .... 45 Subjects ................................ ................................ ................................ ............................ 45 Apparatus ................................ ................................ ................................ ......................... 45 Procedure ................................ ................................ ................................ ......................... 45 Results and Discussion ................................ ................................ ................................ ........... 47 4 EXPERIMENT 3 ................................ ................................ ................................ .................... 57 Method ................................ ................................ ................................ ................................ .... 58 Subjects ................................ ................................ ................................ ............................ 58 Apparatus ................................ ................................ ................................ ......................... 58 Procedure ................................ ................................ ................................ ......................... 58 Results and Discussion ................................ ................................ ................................ ........... 60 5 EXPERIMENT 4 ................................ ................................ ................................ .................... 80 Method ................................ ................................ ................................ ................................ .... 80 Subjects ................................ ................................ ................................ ............................ 80 Apparatus ................................ ................................ ................................ ......................... 81 Procedure ................................ ................................ ................................ ......................... 81 Results and Disc ussion ................................ ................................ ................................ ........... 83

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5 6 GENERAL DISCUSSION ................................ ................................ ................................ ... 101 LIST OF REFERENCES ................................ ................................ ................................ ............. 115 BIOGRA PHICAL SKETCH ................................ ................................ ................................ ....... 118

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6 LIST OF TABLES Table page 2 1 Number of administrations of each dose of cocaine during acute dose response cur ve determination for Experiment 1. ................................ ................................ ........................ 30 2 2 Number of administrations of each dose of cocaine during dose response curve determination following the first chronic regimen for Experiment 1. ............................... 31 2 3 Number of administrations of each dose of cocaine during dose response curve determination following the second chronic regimen for Experiment 1. .......................... 32 2 4 Key pecks per minute following each administration of saline vehicle for Experiment 1. ................................ ................................ ................................ ..................... 33 2 5 ED50s for each subject for each phase of Experiment 1. ................................ .................. 34 3 1 Number of administrations of each dose of cocaine for each subject during acute dose response curve determination for Experiment 2. ................................ ...................... 50 3 2 Number of administrations of each dose of cocaine for each subject during dose response curve determination following the chronic drug regimen for Experiment 2. ..... 51 3 3 Key pecks per minute f ollowing each administration of saline vehicle for Experiment 2. ................................ ................................ ................................ ..................... 52 3 4 ED50s for each subject for each phase of Experiment 2. ................................ .................. 53 4 1 Number of administrations of each dose of cocaine for each subject during acute dose response curve determination for Experiment 3. ................................ ...................... 65 4 2 Number of administrations of each dose of cocai ne for each subject during dose response curve determination following 30 administrations of saline in the home cage for Experiment 3. ................................ ................................ ................................ ....... 66 4 3 Number of administrations of each dose of cocaine for each subject during dose response curve determination following 30 administrations of cocaine in the home cage for Experiment 3. ................................ ................................ ................................ ....... 67 4 4 Number of administrations of each dose of cocaine fo r each subject during dose response curve determination following 60 administrations of cocaine in the home cage for Experiment 3. ................................ ................................ ................................ ....... 68 4 5 Number of administrations of each dose of cocaine for each subject during dose response curve determination following the pre session chronic drug regimen for Experiment 3. ................................ ................................ ................................ ..................... 69

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7 4 6 Key pecks per minute following each administration of saline vehic le for Experiment 3. ................................ ................................ ................................ ..................... 7 0 4 7 ED50s for each subject for each phase of Experiment 3. ................................ .................. 71 5 1 Number of administrations of each dose of cocaine for each subject during acute dose response curve determination for Experiment 4. ................................ ...................... 86 5 2 Number of administrations of each dose of cocaine for each subject during dose response cur ve determination following post session chronic administration with saline administered on intervening days for Experiment 4. ................................ ............... 87 5 3 Number of administrations of each dose of cocaine for each subject during dose response curve determination following post session chronic administration with cocaine administered on intervening days for Experiment 4. ................................ ............ 88 5 4 Number of administrations of each dose of cocaine for each subject during dose response curve determination following pre session chronic administration for Experiment 4. ................................ ................................ ................................ ..................... 89 5 5 Key pecks per minute following each admi nistration of saline vehicle for Experiment 4. ................................ ................................ ................................ ..................... 90 5 6 ED50s for each subject for each phase of Experiment 4. ................................ .................. 92

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8 LIST OF FIGURES Figure page 2 1 Effects of cocaine during acute and pre session administration for the Pre post group in Experiment 1. ................................ ................................ ................................ ................. 35 2 2 Effects of c ocaine during acute and post session administration for the Pre post group in Experiment 1. ................................ ................................ ................................ ...... 36 2 3 Effects of cocaine during pre session and post session administration for the Pre post group in Experiment 1. ................................ ................................ ................................ ...... 37 2 4 Effects of cocaine during acute and post session administration for the Post pre group in Experiment 1. ................................ ................................ ................................ ...... 38 2 5 Effects of cocaine during acute and pre session administration for the Post pre group in Experiment 1. ................................ ................................ ................................ ................. 39 2 6 Effects of cocaine during pre session and post session adminisitration for the Post pre group in Experiment 1. ................................ ................................ ................................ 40 2 7 Group average data for both groups showing effects of cocaine during acute administration and the first chronic regimen in Experiment 1. ................................ ......... 41 2 8 Group average data for both groups showing effects of cocaine during acute administration and the second chronic regimen in Experiment 1. ................................ ..... 42 2 9 Group average data for both groups showing effects of cocaine during the first and second chronic regimen in Experiment 1. ................................ ................................ .......... 43 3 1 Effects of cocaine during acute and post session a dministration for the Immediate Drug group in Experiment 2. ................................ ................................ ............................. 54 3 2 Effects of cocaine during acute and post session administration for the Delayed Drug group in Experiment 2. ................................ ................................ ................................ ...... 55 3 3 Group average data for both groups in Experiment 2, comparing effects of acute cocaine administration and post session administration. ................................ ................... 56 4 1 Effects of cocaine during acute administration and following 30 days of saline administration in the home cage for Experiment 3. ................................ ........................... 72 4 2 Effects of cocaine during acute administration and f ollowing 30 days of cocaine administration in the home cage for Experiment 3. ................................ ........................... 73 4 3 Effects of cocaine during acute administration and following 60 days of cocaine administration in the home cage for Experiment 3. ................................ ........................... 74

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9 4 4 Effects of cocaine during acute and pre session administration for Experiment 3. ........... 75 4 5 Group aver age data for Experiment 3 comparing effects of acute cocaine administration and effects of cocaine following 30 days of saline administered in the home cage. ................................ ................................ ................................ ......................... 76 4 6 Group average data for Expe riment 3 comparing effects of acute cocaine administration and effects of cocaine following 30 days of cocaine administered in the home cage. ................................ ................................ ................................ ................... 77 4 7 Group average data for Experiment 3 compari ng effects of acute cocaine administration and effects of cocaine following 60 days of cocaine administered in the home cage. ................................ ................................ ................................ ................... 78 4 8 Group average data for Experiment 3 comparing effects of ac ute cocaine administration and effects of pre session cocaine. ................................ ............................ 79 5 1 Effects of cocaine during acute administration and post session administration with saline administered on intervening day s for Experiment 4. ................................ ............... 93 5 2 Effects of cocaine during acute administration and post session administration with cocaine administered on intervening days for Experiment 4. ................................ ............ 94 5 3 Effects of cocaine during post session administration with saline or cocaine administered on intervening days for Experiment 4. ................................ ......................... 95 5 4 Effects of cocaine during acute administration and pre session administration for Experiment 4. ................................ ................................ ................................ ..................... 96 5 5 Group average data for Experiment 4 comparing effects of cocaine during acute administration and post session administration with saline administered on intervening days. ................................ ................................ ................................ ................ 97 5 6 Group average data for Experiment 4 comparing effects of cocaine during acute administration and post session a dministration with cocaine administered on intervening days. ................................ ................................ ................................ ................ 98 5 7 Group average data for Experiment 4 comparing effects of cocaine during post session administration with saline or cocaine a dministered on intervening days. ............. 99 5 8 Group average data for Experiment 4 comparing effects of cocaine during acute administration and pre session administration. ................................ ................................ 100

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10 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PHARMACOLOGICAL AND ENVIRONMENTAL FA CTORS IN THE DEVELOP MENT OF CONTINGENT TOLERA NCE TO COCAINE IN PI GEONS By Julie A. Marusich August 2008 Chair: Marc Branch Major: Psychology Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of effects of repeated cocaine administration on operant behavior in hum ans and nonhumans. Previous research with rats and monkeys has shown that tolerance to behavioral effects of cocaine develops if the drug is administered before behavioral test sessions but does not if it is administered after sessions, an outcome which is referred to as contingent tolerance. Many experiments have found contingent tolerance, except a recent experiment using pigeons. The results of that study suggested that pigeons might develop tolerance to effects of cocaine regardless of whether the drug was administered before or after behavioral test sessions. The current set of experiments focused on environmental and pharmacological factors in the development of contingent tolerance to cocaine in pigeons by examining various relations between time of d rug administration and the conduct of behavioral test sessions. Experiment 1 examined if cocaine administered immediately before or immediately after the behavioral session led to the development of tolerance to effects of cocaine during the behavioral ses sion. The results showed that pre session administration of cocaine reliably led to tolerance, and post session administration of cocaine led to tolerance in half the subjects. Experiment 2 examined whether eating under effects of cocaine in the home cage, which occurs if the drug is given post

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11 session, contributed to the development of tolerance to effects of cocaine on key pecking during the behavioral session. In this experiment, some subjects were administered cocaine after the behavioral session and im mediately before being fed their post session food ration, and other subjects were fed their post session food ration immediately after the session and were administered cocaine one hour later. Results of Experiment 2 found that eating in the home cage und er the effects of cocaine was not necessary for tolerance to develop to effects of cocaine during the behavioral session, and that the majority of subjects developed tolerance from post session cocaine administration. Experiment 3 examined whether mere exp osure to cocaine in the home cage without exposure to an experimental session led to tolerance to effects of cocaine during a behavioral session. Mere drug exposure did not reliably produce tolerance during the behavioral session. Experiment 4 examined if daily cocaine administration during dose response curve redetermination was necessary for tolerance to develop. The results showed that tolerance from post session cocaine administration was readily observed even when chronic dosing was discontinued during dose response curve assessment. Therefore, the combined results showed that pigeons often develop tolerance to effects of cocaine during the behavioral session when cocaine is administered post session. Some aspect of exposure to the experimental session or experimental context on a regular basis was necessary for tolerance to develop, yet this exposure did not have to occur while subjects were under effects of the drug. These results indicate that not contingent tolerance may be common in pigeons, and the refore questions the generality of contingent tolerance to cocaine.

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12 CHAPTER 1 INTRODUCTION Drug tolerance, a loss of drug effect relative to initial impact, is a common outcome of repeated drug exposure (Carlton, 1983; Wolgin, 1989). Tolerance is often viewed as an adjustment to a disturbance caused by initial drug effects, and its development may depend on the original drug effect, and the frequency of drug administration. With repeated intermittent drug administration, as opposed to constant administra tion, tolerance often develops to drug effects that disrupt behavior (Stewart & Badiani, 1993). The experiments described in this dissertation are focused on tolerance to behavioral effects of cocaine. Clinical reports on cocaine abuse in humans usually po int to tolerance as an accompaniment to abuse ( Johanson & Fischman, 1989) Specifically, because tolerance to both reinforcing and aversive effects of cocaine has been demonstrated in humans, it has been suggested that the development of tolerance can lead to the administration of larger doses of the drug, and can therefore lead to the development of substance dependence (Johanson & Fischman, 1989). Because of its association with drug abuse, tolerance is one of the criteria for substance dependence accord ing to the Diagnostic and Statistical Manual of Mental Disorders IV (DSM IV). Tolerance has been found to develop to the subjective and physiological effects of cocaine in humans ( Fischman, Schuster, Javaid, Hatano, & Davis, 1985; Mendelson, Sholar, Mello, Teoh, & Sholar, 1998). Tolerance can also develop to the reinforcing effects of cocaine ( Emmett Oglesby Peltier Depoortere Pickering Hooper Gong & Lane, 1993) and is a common observation in drug effects on nonhuman operant behavior (e.g., Smith, 19 90; Wolgin & Hertz, 1995; Woolverton, Kandel, & Schuster, 1978). Because much human behavior can be

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13 viewed as operant (e.g., Skinner, 1953), the study of effects of drugs on operant behavior of nonhuman animals may have relevance to the human condition. To lerance can be demonstrated by a shift in the dose effect curve away from acute effects of the drug and toward baseline levels of behavior. This generally results in a shift in the dose response curve in the direction of higher doses (Carlton, 1983). Altho ugh drug tolerance can be based on a variety of processes, the present research focuses on one particular type of process involved in tolerance, behavioral processes. Tolerance based on behavioral processes is often referred to as behavioral tolerance (Car lton, 1983; Wolgin, 1989). Behavioral tolerance is a behavioral compensation for the original effects of a drug. In this type of tolerance, behavioral processes are thought to play a key role in determining whether or not tolerance develops. Behavioral tol erance can develop as a result of Pavlovian conditioning or operant conditioning (Siegel, 1989; Wolgin, 1989). In the operant conditioning account (the account of interest here), tolerance may develop to the effects of a drug when the drug originally decre ases the amount of reinforcement obtained. In this situation, the so that it receives reinforcement more frequently th an originally or does not affect the frequency of reinforcement, tolerance is not predicted (Wolgin, 1989). The view that tolerance occurs through a behavioral change to compensate for a loss of reinforcement is often referred to as the reinforcement loss hypothesis or the reinforcement density hypothesis (Schuster, Dockens, & Woods, 1966). Contingent tolerance is a form of behavioral tolerance associated with operant behavior. Contingent tolerance refers to tolerance that is dependent on the relationship b etween the time of drug administration and behavioral testing (Carlton & Wolgin, 1971). Specifically, contingent

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14 tolerance is tolerance that develops only when drug is administered before the behavioral session, and not when drug is administered after the behavioral session or with no temporal association with the behavioral session (Carlton & Wolgin, 1971). Contingent tolerance can be accounted for by the reinforcement loss hypothesis (Schuster, et al., 1966) because the drug usually needs to be administer ed before the behavioral session to decrease reinforcement obtain the original amount of reinforcement. Basically, the idea is that the subject relearns, while un der the influence of the drug, to emit behavior that is effective in garnering reinforcement. If the drug is repeatedly administered after the session, then there is often no disruption in reinforcement obtained, as well as no opportunity to relearn while drugged, and therefore tolerance is not predicted. Contingent tolerance is likely relevant to human drug taking, given the operant nature of much human behavior, and may explain some instances of the development of drug tolerance in humans. Many past expe riments have investigated whether contingent tolerance develops to effects of psychoactive drugs. The first experiment to investigate contingent tolerance examined tolerance to ethanol in rats (Chen, 1968). One group of subjects was administered ethanol da ily, for three consecutive days, before being placed in a circular maze, and the other group was administered the drug immediately after exposure to the circular maze, also for three consecutive days. On the fourth day, all subjects were administered ethan ol before exposure to the maze to test for tolerance. The group repeatedly administered ethanol before the session had developed tolerance to the accuracy decreasing effects of ethanol, whereas the group repeatedly administered ethanol after the session di d not show tolerance, indicating that contingent tolerance had developed to effects of ethanol on maze running in rats (Chen, 1968).

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15 A similar experiment examined contingent tolerance to amphetamine in rats (Carlton & Wolgin, 1971). In this experiment, the Amphetamine saline group was repeatedly administered amphetamine before 30 min access to sweetened condensed milk in the home cage, and administered saline after milk access each day. The Saline amphetamine group was repeatedly administered saline before access to milk in the home cage, and amphetamine after milk presentation. Only subjects in the Amphetamine saline group developed tolerance to the milk intake decreases produced by amphetamine. When the Saline amphetamine group was switched to amphetamine administration before each milk drinking session, subjects developed tolerance to the milk intake decreases, indicating that contingent tolerance had developed to effects of amphetamine on milk drinking in rats (Carlton & Wolgin, 1971). Campbell and Seide n (1973) sought to examine if contingent tolerance would develop to effects of amphetamine on a typical operant task. In this experiment, rats were administered amphetamine repeatedly before or after daily exposure to a Differential Reinforcement of Low ra occurred only for responses that occurred 17.5 s or more apart). When the group repeatedly administered amphetamine before the session showed tolerance to the rate i ncreasing (and therefore reinforcement rate decreasing) effects of the drug, the group administered the drug after the session, in which subjects had not yet shown tolerance, was switched to pre session administration. Then subjects in this group also deve loped tolerance to the rate increasing effects, indicating that contingent tolerance had developed to effects of amphetamine on lever pressing in rats (Campbell & Seiden, 1973). Two methodologically similar studies examined the development of contingent to lerance to cocaine (Bowen, Fowler, & Kallman, 1993; Woolverton et al., 1978). Rats were repeatedly

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16 administered cocaine before or after daily periods of 15 min access to sweetened condensed milk in the home cage. Cocaine initially produced dose dependent d ecreases in milk intake. Subsequent dose response analyses revealed that subjects administered cocaine before milk access developed tolerance to the milk intake decreases, whereas subjects administered cocaine after milk access showed sensitization (i.e., an increased response to the drug) to the milk intake decreases. Therefore contingent tolerance developed to effects of cocaine on a milk drinking task in rats (Bowen et al., 1993; Woolverton et al, 1978). An additional study examined the development of c ontingent tolerance in primates (Branch & Sizemore, 1988). Squirrel monkeys were repeatedly administered cocaine after a behavioral session in which they pressed a sequence of colored keys for food reinforcement. Food reinforcement was presented on a secon d order schedule in which the completion of three to five responses on the colored keys in the correct order was reinforced on a Variable Ratio 2 schedule meaning every two times on average [second order VR 2 (Fixed Ratio 3, 4, or 5: S]. Post session admin istration of cocaine did not produce tolerance to the rate decreasing or accuracy decreasing effects of cocaine. When cocaine was later administered repeatedly before the session, tolerance developed to the accuracy decreasing effects of the drug, indicati ng that contingent tolerance had developed to effects of cocaine on a key pressing task in monkeys (Branch & Sizemore, 1988). Another experiment examined the development of contingent tolerance in rats with different operant tasks (Smith, 1990). Rats were exposed to three sessions daily. The first session each day consisted of free operant shock avoidance with head movement as the operant. Shocks were presented on regular intervals unless subjects moved their heads in a particular location. Each head movem ent postponed shock for a fixed time interval so that all shocks could be avoided if head movements occurred before the interval expired. In the second session of the

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17 day, subjects lever pressed on a Fixed Interval (FI) schedule in which a response was rei nforced by food presentation after a specified interval of time had passed, and in the third session, subjects nose poked on a Fixed Ratio (FR) schedule in which reinforcement was presented after a particular number of responses was made. Each of the three types of sessions was conducted in a different, distinct chamber. Cocaine was then administered daily for four week blocks at a particular time in relation to the sessions. First cocaine was administered after the third session of the day, then before the third session, then before the second session, and then before the first session. Tolerance to effects of cocaine during the FI and FR session only developed when cocaine was administered before that particular session. Thus contingent tolerance was found to effects of cocaine on lever pressing and nose poking in rats (Smith, 1990). Most past research on contingent tolerance has been conducted with rats (Bowen et al., 1993; Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Chen, 1968; Poulos, Wilkinson, Ca ppell, 1981; Wenger, Tiffany, Bombardier, Nicholls, & Woods, 1981; Woolverton et al., 1978), and one experiment used monkeys (Branch & Sizemore, 1988), but until recently no research was conducted using pigeons to the best of my knowledge. Pinkston and Bra nch (2004) sought to examine contingent tolerance to cocaine in pigeons that pecked on a multiple FR FR (mult FR FR) schedule of reinforcement. Therefore the two FR schedules had distinct key colors associated with them, and alternated after four reinforce rs were earned on a particular schedule. Subjects were exposed to three different chronic drug regimens, with order of the regimens counterbalanced across subjects. The drug regimens consisted of repeated administration of a relatively small dose of cocain e before the session, a small dose of cocaine after the session, and a large dose of cocaine after the session. The majority of subjects developed tolerance to the rate decreasing effects of cocaine when a small dose was administered either before or after the

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18 session regardless of the order in which subjects proceeded through the chronic drug regimens. Hence this study found not contingent tolerance to effects of cocaine on key pecking in pigeons (Pinkston & Branch, 2004). Because it involved a within subj ect design and was more complicated than past experiments investigating contingent tolerance to cocaine, the Pinkston and Branch study did not provide for a direct test of whether contingent tolerance had developed. The purpose of the present experiment wa s to investigate if tolerance to the effects of cocaine is contingent on the relationship between the time of drug administration and the experimental session in pigeons. More specifically, the experiment aimed to examine the effects of cocaine on FR respo nding when administered pre session and post session in a between groups (initially) design.

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19 CHAPTER 2 EXPERIMENT 1 Method Subjects subjects (Cohort 1) were experiment ally experienced and ranged in age from five months to one year and five months at the beginning of the experiment. The remaining subjects (Cohort 2) were experimentally nave and aged approximately seven months at the beginning of the experiment. Cohorts were run in succession. All were drug naive. Subjects were housed in individual home cages in a windowless colony room on a 16.5/7.5 hr light/dark cycle (lights on at 7am). The colony room was maintained between 19.4 C and 22.8 C. Subjects had access to vi tamin enriched water at all times in the home cage, and were maintained at 80% of their free feeding body weight by post session feeding (Purina ProGrains for Pigeons) delivered immediately after each session if needed. Apparatus Experimental sessions we re conducted in a BRS/LVE Inc. (Model PIP 010 016) standard three key operant test chamber with interior dimensions measuring 31.0 cm by 36.5 cm by 35.0 cm. The center key in each chamber measured 2.5 cm in diameter, and was located on the panel 8.7 cm from the ceiling, equidistant from both sidewalls. To register a response, the key required approximately 0.11 N. A 28 V DC houselight was centered 2.2 cm from the ceiling at the center of the panel, and illuminated the chamber during the experimental ses sion. Mixed grain could be made available through a 5.5 cm by 5.0 cm aperture centered near the base of the panel 20.0 cm from the ceiling.

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20 A speaker in the experimental room produced white noise (95 db) to mask extraneous sounds. Experimental events were arranged and recorded by EC BASIC (Palya, Walter, & Chu, 1995) software on a computer located in another room. A cumulative recorder in another room recorded responses as a function of time during daily sessions. Procedure Training All subjects in Cohor t 1 had previous experience pecking a key on a fixed ratio (FR) schedule of reinforcement. Subjects required one to three days of an FR 1 schedule of reinforcement to adjust to the new experimental chamber and white key light. Key pecks were reinforced wit h 3 s access to mixed grain. The key light and houselights were extinguished during food presentation. After all subjects reliably pecked the key, subjects were put on baseline conditions. Subjects in Cohort 2 were trained to peck a white key light throug h reinforcement of successive approximations. This method was not successful for one subject (43) that was later trained to peck the key through autoshaping (Brown & Jenkins, 1968). After all subjects reliably pecked the key, subjects were put on an FR 1 f or one to four 40 reinforcement sessions until subjects responded 40 times in the session with minimal pause. Subjects then underwent ratio training. Ratio training began with an FR 1. The program incremented the ratio requirement by two responses per rein forcer after four ratios were completed with less than 1 s pause within each ratio, excluding post reinforcement pause (PRP). Ratio requirements incremented across sessions beginning with the last ratio requirement from the previous session until FR 20 was successfully completed four times with less than 1 s pause within each ratio, excluding PRP. Ratio training took two to four sessions. Throughout training and baseline, pecks were reinforced with 3 s access to mixed grain. After ratio training was complet e, subjects were run on baseline conditions.

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21 Baseline Experimental sessions began with a 5 min blackout during which key pecking had no consequence, followed by an FR 20 schedule of reinforcement for 20 min or until 40 reinforcers were obtained, whicheve r came first. Responding was determined to be stable by visual inspection of cumulative records and graphs of daily session wide response rates after 30 40 sessions. One subject (4991) did not maintain reliable key pecking during this period. This s 80% weight was reassessed and determined to be 100 g less than previously determined, so its body weight was adjusted accordingly. Reliable key pecking was achieved on baseline following the second weight determination. Sessions were conducted seven days a week at approximately the same time each day. Drug regimen After responding was judged to be stable both within and across sessions, acute effects of cocaine were assessed. Acute effects of cocaine were determined by administration of the drug once per week. Saline and cocaine doses of 10.0 mg/kg, 5.6 mg/kg, 3.0 mg/kg, and 1.0 mg/kg were administered in descending order, with each dose being given twice. A fixed order of dosing was used to aid in revealing systematic differences across repeated determin ations of effects of each dose (cf. Sidman, 1960), and there were no such differences. A descending dose order as opposed to an ascending order was used because the first administration of cocaine often produces a substantial decrease in rate of responding regardless of the dose magnitude. This decrement in responding is usually replicated at large doses but not at small doses, therefore descending dose order leads to reliable drug effects, whereas ascending dose order does not. Following the first two repl ications of each dose, any dose that produced effects judged to be too variable across two assessments (e.g. one assessment produced complete suppression of responding, and the other assessment produce no effect) was repeated until the mean effects was jud ged to be representative of all administrations. If more than one dose

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22 produced variable effects, these doses were generally administered in alternating order. Some subjects were also administered 4.2 mg/kg or 7.4 mg/kg cocaine if none of the doses in the original set produced approximately a 50% decrease in rate of responding. Table 2 1 shows the number of administrations of each dose. After acute effects of cocaine were determined, subjects were divided into two groups response curve, with an attempt to produce two groups each containing subjects with similar drug effects. Each subject was then administered a dose of cocaine, which originally produced approximately a 50% decrease in rate on FR responding, chronically (i .e., once per day) for 30 sessions. If there was no dose that produced approximately a 50% decrease in rate, then generally the dose that was 1/8 or 1/4 of a log unit smaller than the smallest dose that produced complete response suppression was used. The Pre post group was administered cocaine immediately before the session, and saline immediately after the session. The Post pre group was administered saline immediately before the session, and cocaine immediately after the session. All subjects in Cohort 1 were administered 5.6 mg/kg chronically. Chronic doses for subjects in Cohort 2 included 5.6 mg/kg, 7.4 mg/kg, and 10.0 mg/kg cocaine. Effects of cocaine were then redetermined. Subjects continued to be administered their chronic dose everyday except onc e weekly when administered one of their initial acute doses of cocaine or saline pre session. All test doses were followed by post session saline administration. Some subjects were administered 13.0 mg/kg or 17.0 mg/kg if none of the original series of dos es produced complete suppression of responding after the original series of doses was determined twice. One subject in the Pre post group (4991) pecked very little during chronic pre session administration and during dose response curve redetermination. Th is subject was then administered saline pre session once every four sessions, with pre session cocaine administered

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23 before intervening sessions (cf. Miller & Branch, 2004). This regimen continued until key pecking resumed on days when cocaine was administe red pre session (approximately 50 sessions). The dose response curve was then redetermined for this subject, with data excluded from when key pecking was suppressed. Table 2 2 shows the number of administration of each dose during this assessment. The larg e numbers of administrations for the doses given chronically indicate the number of administrations that were used to calculate the mean effects that are shown in the figures. Following dose response redetermination, subjects in the Post pre group were swi tched to pre session drug administration. These subjects received their chronic dose immediately pre session and saline immediately post session for 30 sessions. Subjects in the Pre post group were switched to post session administration of their chronic d ose and pre session saline administration for 30 sessions. The dose response curve was then redetermined as described above (i.e., in the context of continued daily drug administration; Table 2 3 shows how many times each dose was tested). Drug Procedure Cocaine hydrochloride (obtained from the National Institute on Drug Abuse) was dissolved in sterile 0.9% sodium chloride solution. Doses were determined by the weight of the salt, and the injection volume was 1 mL/kg. Drug was administered via intramuscula r (IM) injections in the breast muscle. During daily administration, injections alternated sides of the breast. Results and Discussion Figure 2 1 displays average key pecking response rate within a session for the Pre post group in Experiment 1, calculated as the percent of saline vehicle rate of responding, plotted as a function of dose of cocaine. Percent saline values were determined on an individual subject basis by dividing the average response rate under effects of a particular dose for a subject by t he

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24 average response rate during saline vehicle for that subject and multiplying this value by 100. Table 2 4 shows the response rate following each saline vehicle administration for all subjects during each phase of the experiment. During acute cocaine adm inistration, all subjects showed dose dependent decreases in rate of key pecking. Dose response curves following chronic administration were determined by averaging the response rate following each administration of each dose and dividing this value by th e average saline response rate during the period of daily administration. Values for the chronic doses were determined by averaging the response rate from sessions preceded by administrations of the chronic dose that occurred the day prior to a test dose, and dividing this value by the average saline response rate. Therefore, many more values for effects of the chronic dose (or saline for the Post pre group) were included in the dose response curve determination than determinations of other doses. Following 30 sessions of pre session administration of cocaine, all subjects in the Pre post group showed some amount of tolerance, as predicted, to the rate decreasing effects of cocaine, as indicated by higher response rates under effects of larger doses of cocai ne as compared to that during acute administration as displayed in Figure 2 1. Subject 592 showed a decrease in control rate of responding (Table 2 4) as well as an increase in variability particularly following administration of saline, but still showed t olerance to rate decreasing effects of cocaine when the data were normalized based on the saline vehicle control. Subject 40 also showed an increase in variability of key pecking rate following administration of saline, but still showed tolerance. Figure 2 2 shows effects of cocaine after chronic dosing was switched from pre session to post session. Some subjects (754, 36, 4991) continued to show varying degrees of tolerance to effects of cocaine, and one subject showed a loss of tolerance (40). For those s ubjects

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25 administered a larger chronic dose (7.4 mg/kg or 10.0 mg/kg), post session administration produced a substantial decrease in rate of responding during saline vehicle to near zero (Table 2 4). Subject 49 continued to respond when pre session drug do ses were administered, with large percentage increases because of the very low rates when drug was not given, whereas Subject 592 rarely responded when any dose (including saline) was administered. This suppression of responding made it difficult to determ ine whether these subjects were still tolerant to the rate decreasing effects of cocaine. Figure 2 3 compares effects of cocaine administered pre session and post session for the Pre post group. For some subjects administered a moderate dose of cocaine chr onically (754, 36, 4991), the dose effects were, for the most part, unchanged when cocaine was repeatedly administered post session rather than pre session. Subject 40 showed less tolerance from post session administration as compared to pre session. Those subjects administered larger chronic doses (Subjects 49, 592) pecked very little when saline was administered before the session, with occasional pecking when other doses of drug were administered mainly for Subject 49. Overall, the switch from pre sessio n to post session administration did not produce additional tolerance for any subject, and was associated with a slight loss of tolerance for some subjects (36, 4991, 40). Figure 2 4 shows average key pecking rate within a session as a function of saline vehicle rate of responding for subjects in the Post pre group. Acute administration of cocaine produced dose related decreases in key pecking for all subjects that were of similar magnitude to the rate decreases seen for subjects in the Pre post group. Aft er cocaine was administered post session for 30 sessions, three of six subjects (45, 35, 43) surprisingly showed notable tolerance to the rate decreasing effects of cocaine. Subjects 727 and 752 showed little change in drug effects,

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26 although for both subje cts effects of 5.6 mg/kg were attenuated. Subject 596, which was administered post session 10.0 mg/kg cocaine, showed near zero response rates following cocaine and saline administrations (Table 2 4), similar to that seen when subjects in the Pre post grou p were given large doses of cocaine post session. Subjects 35 and 752 also occasionally showed response suppression, but generally continued to respond during the chronic post session cocaine regimen. Following the first 30 sessions after the switch from p ost session to pre session administration of cocaine, some of the subjects in the Post pre group that had previously developed tolerance (45, 43) continued to show varying degrees of tolerance as displayed in Figure 2 5. Subject 35 showed a loss of toleran ce. Subject 727 showed little change in drug effects as compared to the post session condition. Subject 596 continued to have a very low saline vehicle control rate, and occasionally pecked at a slow rate when cocaine was administered. Subject 752, which d id not develop notable tolerance following post session dosing, did show substantial tolerance following pre session administration of cocaine. Figure 2 6 compares effects of cocaine administered post session and pre session for the Post pre group. For tho se subjects that developed tolerance following post session dosing (Subjects 45, 35, 43) pre session drug administration produced a slight increase (Subject 45) or decrease (Subjects 35, 43) in the amount of tolerance produced by post session dosing. The s witch from post session to pre session administration of cocaine produced tolerance for Subject 752 that had not previously developed much tolerance. Similar results were found for subjects in the Pre session and Post pre group when data were analyzed at t he group average level. Figure 2 7 shows group average data from acute administration and following the first chronic regimen for both groups. Percent saline values for

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27 the group average were determined by calculating the average response rate during salin e vehicle administrations averaged across all administrations of saline for all subjects, and then dividing the response rate under effects of a particular dose averaged across each administration of that dose across all subjects by the average response ra te during saline vehicle for all subjects and multiplying this value by 100. Only doses experienced by all subjects were included in the graph. Acute administration of cocaine produced dose dependent decreases in rate of responding that were similar at the group average level for both groups. Both pre session and post session drug administration produced tolerance at the group average level. Note that data from subjects that showed response suppression during chronic post session administration sessions wer e excluded for all graphs and analyses of group average data. That is, data are presented only for subjects that continued to key peck during the repeated administration phases. To provide ancillary analyses, the effective dose 50 (ED50; dose that produced a 50% decrease in response rate) was calculated for each subject for each drug regimen based on a straight line fit to the data for each individual pigeon. The ED50 was calculated by fitting a straight line to the percent of vehicle control data as a func tion of the log dose of cocaine. A straight line (as opposed to a curve) was chosen because it is the most parsimonious function, and because it could be fit to a line with values of zero. The straight line was fit to the descending portion of the dose res ponse curve. If the largest dose of cocaine did not completely suppress responding, an additional data point was added for a dose that was 1/8 of a log unit larger than the largest dose used with a response rate of zero. This allowed better estimation of E D50s when curves did not reach zero, and is a conservative method because it did not overestimate the amount of tolerance. If anything, it underestimated the amount of tolerance. ED50s were not calculated when subjects showed response suppression due to th e poor fit of the

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28 line. ED50s are shown in Table 2 5. For the Pre post group, all subjects showed an increase in ED50 from acute administration to that following pre session administration. Similarly, subjects in the Post pre group all showed an increase i n ED50 from acute administration to post session administration, except for the subject that showed response suppression; however, the change was minimal for subjects 727 and 752. These data corroborate the view that the majority of subjects in both groups developed tolerance. Figure 2 8 displays group average data comparing effects of cocaine during acute administration, and following the second chronic drug regimen. Data from both groups continued to show tolerance when pre session drug administration was switched to post session, and when post session administration was switched to pre session. This is supported by examination of individual subject ED50s for both groups (Table 2 5). The majority of subjects (3 of 4) from the Pre post group that did not sh ow response suppression continued to show an ED50 that was larger than that from acute administration when chronic dosing was switched to post session. For subjects in the Post pre group, the majority of subjects (4 of 5) that did not show response suppres sion also had a larger ED50 when switched to pre session administration as compared to acute administration. Figure 2 9 compares data from pre session and post session cocaine administration for both groups at the group average level. The group average da ta from the Pre post group show slightly more tolerance from pre session administration as compared to post session administration. All subjects that did not show response suppression had a larger ED50 from pre session dosing than that from post session do sing (Table 2 5). Data from the Post pre group show no change in the amount of tolerance when pre session and post session dosing was compared. Three of five subjects that did not show response suppression had a larger ED50 from

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29 post session administration as compared to pre session administration, while the other two subjects had a larger ED50 from pre session administration (Table 2 5). When cocaine was administered pre session first, as predicted, all subjects developed tolerance to effects of cocaine du ring the behavioral session. Surprisingly, however, when cocaine was initially administered post session, half of the subjects developed notable tolerance. Switching subjects from pre session to post session administration did not produce any more toleranc e than that previously developed, and switching subjects from post session to pre session administration rarely produced additional tolerance if tolerance had already developed. Only one subject (752) showed the classic contingent tolerance effect in that it did not develop tolerance when cocaine was administered post session, but it did develop tolerance when cocaine was subsequently administered pre session. It is not possible to determine if some other subjects would have shown this effect if their behav ior had not been suppressed due to post session dosing. The regimen of post session administration of larger doses of cocaine (7.4 mg/kg and 10.0 mg/kg) reliably produced near zero response rates and generally was associated with suppressed responding foll owing pre session cocaine administrations as well. Possible reasons for response suppression in sessions followed by large doses will be presented in the General Discussion (Chapter 6).

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30 Table 2 1. Number of administrations of each dose of cocaine administered during acute dose response curve determination for Experiment 1. Acute Subject Dose 592 49 4991 754 36 40 45 35 43 727 596 752 Sal 3 4 2 3 2 2 4 2 6 2 4 2 1.0 2 2 2 2 2 2 2 2 2 2 2 2 3.0 2 2 2 3 3 4 2 4 2 2 2 4 4.2 2 2 1 1 2 2 5.6 5 4 5 5 4 5 3 4 3 4 2 4 7.4 3 2 2 10.0 2 4 2 2 2 3 3 3 2 2 3 3 13.0 17.0

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31 Table 2 2. Number of administrations of each dose of cocaine administered during dose re sponse curve determination following the first chronic regimen for Experiment 1. Note that number of administrations used in dose response curve determination, rather than t he total number of administrations of that dose. Chronic 1 Subject Dose 592 49 4991 754 36 40 45 35 43 727 596 752 Sal 3 3 2 2 2 4 14 18 11 11 11 11 1.0 2 2 2 4 2 2 2 2 2 2 2 2 3.0 2 2 2 2 2 3 2 3 2 2 2 2 4.2 2 2 2 4 2 2 5.6 2 3 9 14 14 15 2 5 3 3 2 3 7.4 13 3 3 10.0 2 13 2 2 3 3 3 4 2 2 3 2 13.0 2 1 2 2 17.0 1 2 2 1

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32 Table 2 3. Number of administrations of each dose of cocaine administered during dose response curve det ermination following the second chronic regimen for Experiment 1. Details are as in Table 2 2. Chronic 2 Subject Dose 592 49 4991 754 36 40 45 35 43 727 596 752 Sal 12 10 10 14 13 13 2 3 2 2 3 3 1.0 2 2 2 2 2 2 2 4 2 2 2 2 3.0 2 2 2 2 2 2 2 3 3 3 2 2 4.2 2 2 2 2 2 3 5.6 2 2 2 3 2 2 2 15 12 11 2 14 7.4 2 2 12 10.0 2 2 2 3 2 3 2 3 3 2 11 4 13.0 2 2 2 2 2 17.0 2 2 3 2

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33 Table 2 4. Key pecks per minute following each administration of saline vehicle for each phase of the experiment for Experiment 1. The mean shown in italics was used to calculate percent saline values for Figures 2 1 2 9. Subject Phase 592 49 4991 754 36 40 45 35 43 727 596 752 Acute 156.2 11 8.7 160.2 231.3 144.4 187.2 51.4 115.6 182.4 163.1 173.8 183.6 125.2 132.0 153.6 246.2 156.4 172.7 51.1 104.0 169.3 153.8 218.1 175.6 152.2 141.8 189.3 66.9 94.8 173.9 164.8 75.7 133.9 203.5 113.6 150.7 Mean 144.6 139.3 156.9 222.3 150.3 180.0 61.3 109.8 140.8 158.45 192.3 179.6 Chronic 76.6 127.1 137.2 212.6 150.7 46.0 84.6 0.0 139.8 140.6 0.0 184.5 1 33.1 101.4 143.0 206.8 145.6 125.5 81.4 0.0 121.5 150.2 0.0 202.0 0.0 97.8 160.6 75.4 0.0 127.8 157.0 0.0 161.5 203.6 76.3 3.1 126.0 163.6 1.0 201.7 101.9 113.0 137.4 163.4 2.1 187.3 86.2 119.1 144.6 156.6 0.0 174.3 106.6 51.5 135.5 165.7 0.0 0.7 91.8 9.0 116.4 165.3 0.0 104.1 78.9 82.3 125.2 158.9 0.0 184.1 84.6 130.3 126.1 167 0.0 197.1 93.4 129.4 117.0 158.5 0.0 179.3 92.5 145.7 97.9 143.0 108.5 142.9 15.0 5.0 128.8 140.4 Mean 36.6 108.8 140.1 209.7 148 .15 133.9 90.0 75.5 128.8 158.8 0.3 161.5 Chronic 72.2 45.2 159.2 198.0 151.9 219.4 66.5 120.3 67.0 146.4 11.0 74.2 2 21.0 0.0 153.2 205.9 164.4 179.9 57.6 84.7 33.1 154.9 0.0 213.9 71.3 0.0 152.4 203.6 156.4 157.5 71.9 2.0 182.1 0.0 0.0 151.2 224 .1 154.1 199.3 10.2 0.0 156.2 202.9 152.8 172.7 0.0 81.0 167.8 205.4 154.8 230.9 0.0 0.0 155.6 148.7 160.1 206.7 0.0 0.0 172.5 199.0 157.5 223.3 0.0 0.0 141.7 190.2 154.8 200.7 0.0 0.0 125.8 203.2 158.5 211.6 0.0 212.3 150.1 181.0 0.0 218.1 159.9 212.6 200.9 169.4 201.8 214.4 Mean 14.6 12.6 153.6 201.9 157.3 199.8 62.1 92.3 50.1 150.65 4.3 156.7

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34 Table 2 5. ED50s (mg/kg) for each subject for each phase of Exp eriment 1. Phase Subject Acute Pre session Post session 592 3.45 13.02 49 8.01 11.44 4991 3.53 15.63 11.51 754 3.91 6.11 5.71 36 40 4.63 11.79 9.36 5.18 8.22 4.86 Pre post Mean 4.79 11.04 7.86 45 5.08 14.42 14.30 35 5.07 4.41 7.89 43 2.4 3 7.31 12.90 727 2.50 2.69 3.35 596 10.26 752 4.08 8.76 4.29 Post pre Mean 3.83 12.64 8.55

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35 Figure 2 1. Effects of cocaine during acute and pre session administration for the Pre post group in Experiment 1. Each graph shows data from an indivi dual subject. Response rate is plotted as a function of dose (log scale) of cocaine for the Pre post group in Experiment 1. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and triangles show the effects of 30 days of pre session cocaine administration. The displaying the range of effects of saline vehicle. Numbers centered above each graph identify the subjects. Numbers to the right of the y axes identify the dose of cocaine administered chronically for each subject.

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36 Figure 2 2. Effects of cocaine during acute and post session administration for the Pre post gro up in Experiment 1. Each graph shows data from an individual subject. Response rate as a percent of control is plotted as a function of dose of cocaine for the Pre post group in Experiment 1. Circles display the effects of cocaine during acute administrati on, and squares show the effects of 30 days of post session cocaine administration. All other details are as in Figure 2 1.

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37 Figure 2 3. Effects of cocaine during pre session and post session administration for the Pre post group in Experiment 1. Each gr aph shows data from an individual subject. Response rate as a percent of control is plotted as a function of dose of cocaine for the Pre post group in Experiment 1. Triangles display effects of cocaine following 30 days of pre session cocaine administratio n, and squares show the effects of 30 days of post session cocaine administration. All other details are as in Figure 2 1.

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38 Figure 2 4. Effects of cocaine during acute and post session administration for the Post pre group in Experiment 1. Each graph shows data from an individual subject. Response rate as a percent of control is plotted as a function of dose of cocaine for the Post pre group in Experiment 1. Circles display the effects of cocaine during acute administration, and triangles show the effe cts of 30 days of post session cocaine administration. All other details are as in Figure 2 1.

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39 Figure 2 5. Effects of cocaine during acute and pre session administration for the Post pre group in Experiment 1. Each graph shows data from an individual s ubject. Response rate as a percent of control is plotted as a function of dose of cocaine for the Post pre group in Experiment 1. Circles display the effects of cocaine during acute administration, and squares show the effects of 30 days of pre session coc aine administration. All other details are as in Figure 2 1.

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40 Figure 2 6. Effects of cocaine during pre session and post session administration for the Post pre group in Experiment 1. Each graph shows data from an individual subject. Response rate as a p ercent of control is plotted as a function of dose of cocaine for the Post pre group in Experiment 1. Triangles display effects of cocaine following 30 days of post session cocaine administration, and squares show the effects of 30 days of pre session coca ine administration. All other details are as in Figure 2 1.

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41 Figure 2 7. Group average data for both groups showing effects of cocaine during acute administration and the first chronic regimen in Experiment 1. Response rate as a percent of control is plo tted as a function of dose of cocaine for Experiment 1. Data are averaged across all subjects in a group. Circles display the effects of cocaine during acute administration, and triangles display effects of cocaine following the first chronic regimen (pre session drug for the Pre post group, and post session drug for the Post vehicle control, with inner error bars displaying the standard deviation, and outer error bars displaying the ra nge of effects of saline vehicle. Data from Subject 596 are not included in the group average from the first chronic regimen for the Post pre group. A) Data from the Pre post group. B) Data from the Post pre group.

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42 Figure 2 8. Group average data for both groups showing effects of cocaine during acute administration and the second chronic regimen in Experiment 1. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 1. Circles display the effects of cocaine du ring acute administration, and squares display effects of cocaine following the second chronic regimen (post session drug for the Pre post group, and pre session drug for the Post pre group). All other details are as in Figure 2 7. Data from Subject 596 ar e not included in the group average from the second chronic regimen for the Post pre group, and data from Subjects 592 and 49 are not included in the group average from the second chronic regimen for the Pre post group. A) Data from the Pre post group. B) Data from the Post pre group.

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43 Figure 2 9. Group average data for both groups showing effects of cocaine during the first and second chronic regimen in Experiment 1. Response rate as a percent of control is plotted as a function of dose of cocaine f or Experiment 1. Triangles display effects of cocaine following the first chronic regimen (pre session drug for the Pre post group, and post session drug for the Post pre group), and squares display effects of cocaine following the second chronic regimen ( post session drug for the Pre post group, and pre session drug for the Post pre group). All other details are as in Figure 2 7. Data from Subject 596 are not included in the group average from the first and second chronic regimen for the Post pre group, an d data from Subjects 592 and 49 are not included in the group average from the second chronic regimen for the Pre post group. A) Data from the Pre post group. B) Data from the Post pre group.

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44 CHAPTER 3 EXPERIMENT 2 The results of Experiment 1 were not consistent with past research on contingent tolerance to cocaine (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978), except for experiments conducted using pigeons (Pinkston & Branch, 2004). The one experiment using pig eons found not contingent tolerance to cocaine (Pinkston & Branch, 2004), whereas experiments employing other species have found contingent tolerance to cocaine (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978). Although t here are many procedural differences in the experiments conducted with pigeons compared to those conducted with other species, one particular procedural aspect of Experiment 1 potentially contributed to the not contingent tolerance seen in that experiment, and to the inter subject variability in effects for the Post pre group. Subjects in the Post pre group were fed in their home cage immediately after the session and immediately after post session cocaine administration if they weighed below their 80% weig ht. Some subjects were consistently fed after the session because their weight was low, and some were rarely fed after the session because they were at or above their 80% weight. Those that were consistently fed after the session also were the ones that de veloped tolerance to effects of cocaine during the session when cocaine was administered post session. Those subjects that were not regularly fed after the session did not show tolerance to effects of cocaine following post session administration. This co rrelation suggested that eating under effects of cocaine in the home cage might have contributed to the development of tolerance to effects of cocaine during the behavioral session. Eating in the home cage, that is, pecking at grain, involves similar behav ior as key pecking in the operant chamber. Therefore, subjects who often eat under effects of cocaine in the home cage might develop tolerance to effects of cocaine on eating, and this tolerance might generalize to

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45 behavior associated with key pecking duri ng the behavioral session. Hence, the purpose of Experiment 2 was to investigate whether eating under effects of cocaine in the home cage can contribute to the development of tolerance to key pecking during the behavioral session. Method Subjects Subjects All subjects were experimentally and drug nave, and aged approximately seven months at the beginning of the experiment. Subjects were housed and maintained as in Experiment 1. Appa ratus Experimental sessions were conducted in two similarly constructed BRS/LVE Inc. (Model PIP 010 016) standard three key operant test chambers measuring 31.0 cm by 36.5 cm by 35.0 cm. To register a response, the key required approximately 0.07 N for one chamber, and 0.11 N for the other chamber. All other details are described in Experiment 1. Procedure Training Subjects were trained, through the method of successive approximations, to peck the center key when it was illuminated white. After all su bjects reliably pecked the key, they were exposed to FR 1 for one session. Sessions ended after 30 min or 20 grain presentations, whichever came first. Subjects then underwent ratio training as described in Experiment 1. Ratio training took two to seven se ssions. One subject began ratio training and did not exceed FR 1 for two consecutive sessions. It then continued exposure to FR 1 for two more sessions, followed by ratio training. Key pecks were reinforced with 3 s access to mixed grain throughout trainin g. The key light and houselights were extinguished during food presentation. After ratio training was complete, subjects were placed on baseline conditions.

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46 Baseline Sessions began with a 5 min blackout, during which key pecking had no programmed conseque nce. This was followed by an FR 20 schedule of reinforcement for 20 min or until 40 reinforcers were obtained, whichever came first. After 34 42 sessions, responding was determined to be stable by visual inspection of graphs of daily session wide response rates and of cumulative records. Sessions were conducted seven days a week at approximately the same time everyday for each pigeon. Pecks were initially reinforced with 3 s access to mixed grain, a duration that was then titrated to shorter times until a d uration was found for each subject such that post session body weights were approximately 10 15 g under 80% weight everyday. The final grain access durations ranged from 1.2 2.5 s. Hopper durations were adjusted over a period of 54 sessions. Drug regimen After responding was determined to be stable with the final hopper access durations in place, acute effects of cocaine were assessed as described in Experiment 1, except that injections occurred every four days and every dose was administered a minimum of two times (Table 3 1). Doses of 13.0 mg/kg and 17.0 mg/kg cocaine were also assessed for some subjects when no dose in the initial range of doses produced complete suppression of responding following determination of the original set of doses. One subject died at the beginning of the acute dosing phase due to unknown causes. Therefore no data will be shown for this subject, nor will any of its data be included in the analyses. Following acute dosing, subjects were divided into two matched groups based on in itial dose response curves. Each subject was then administered, chronically for 30 consecutive sessions, a dose of cocaine that originally produced a moderate rate decreasing effect on FR responding. This dose was chosen based on the same criteria used to select a chronic dose in Experiment 1. Subjects in both groups were administered saline immediately before each session

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47 during the chronic drug regimen. The Immediate Drug group was administered cocaine immediately after the session, as had been the Post p re group of Experiment 1, and the Delayed Drug group was administered drug 60 min after the session. The 60 min delay was chosen because previous research has shown that behavioral effects of cocaine in pigeons generally last about 60 min (Marusich & Branc h, 2008). Both groups were fed their post session ration of food in the home cage within 5 min of session termination. Post session rations were calculated as the min imum of 5 g fed if the subject was near or above its 80% weight. Therefore the Immediate Drug group was administered drug, and then given its post session ration, while the Delayed Drug group was given its post session ration and then administered drug app roximately 60 min later. Following 30 days of this chronic drug regimen, the dose response curve was redetermined. The chronic drug regimen continued except once every four days, when subjects were administered one of their initial acute doses of cocaine p re session. All test doses were followed by post session saline administered at the same time each subject was normally injected drug based on group assignment. Each dose was administered a minimum of two times. Any dose that produced variable effects was repeated until effects were replicated. Doses of 13.0 mg/kg and 17.0 mg/kg cocaine were also assessed for some subjects when no dose in the initial range of doses produced a consistent decrease in rate of responding. Table 3 2 indicates the number of admin istrations of each dose. Drug Procedure The drug procedure was the same as that used in Experiment 1. Results and Discussion Figure 3 1 displays average key pecking response rate within a session for the Immediate Drug group in Experiment 2, calculated as the percent of saline vehicle rate of responding,

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48 plotted as a function of dose of cocaine. Table 3 3 shows the response rate following each saline vehicle administration for all subjects during each phase of the experiment. During acute cocaine administr ation, all subjects showed dose dependent decreases in rate of key pecking. Following 30 sessions of cocaine administered immediately after the session, two of five subjects (648, 244) showed tolerance to the rate decreasing effects of cocaine as indicated by the dose response curve shifted to the right. Subject 634 showed little change in drug effects. Subjects 2173 and 606 that were administered 10.0 mg/kg cocaine immediately post session showed near zero saline vehicle control rates, and pecked little fo llowing pre session drug administration making it difficult to determine if tolerance had developed. Similarly, Pigeon 634, which received 5.6 mg/kg, also showed disrupted responding during sessions, as indicated by the wide range of effects of pre session saline. Overall, effects in this group replicate those seen with the Post pre group of Experiment 1. Figure 3 2 shows key pecking calculated as the percent of saline vehicle control rate plotted as a function of dose of cocaine for the Delayed Drug group. Acute administration of cocaine produced dose related decreases in key pecking for all subjects although the decreases were modest for Subject 582. Thirty sessions of cocaine administered 60 min after the session ended produced some amount of tolerance fo r all subjects in the Delayed Drug group. The administration of 10.0 mg/kg cocaine (to 3 of the pigeons) 60 min after the session ended did not produce the response suppression that was seen in the Immediate Drug group and in Experiment 1 when large doses of cocaine were administered immediately after the session. Figure 3 3 shows group average data for both the Immediate Drug and Delayed Drug groups. Data were excluded from all graphs and analyses from subjects that showed response suppression during the p hases the suppression was observed. This figure compares data during

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49 acute administration and following the chronic post session drug regimens. Data from both group averages indicate that tolerance developed from post session administration immediately aft er the session and 60 min after the session completed. This was supported by an analysis of ED50s from acute and chronic administration. All subjects in the Immediate Drug group that did not commonly show response suppression had a larger ED50 following ch ronic administration, although the change was minimal for subject 634. Similarly, all subjects in the Delayed drug group showed an increase in ED50 following chronic administration (Table 3 4) indicating that all subjects in both groups that did not show r esponse suppression developed tolerance. Post session administration of cocaine produced tolerance in most subjects regardless of whether cocaine was administered immediately or 60 min after the session ended, except when larger doses were administered imm ediately after the session. Post session administration of 10.0 mg/kg cocaine administered immediately after the session generally produced response suppression similar to that seen in Experiment 1 when the same drug regimen was used. Subjects that ate in the home cage under effects of cocaine (Immediate Drug group) showed similar if not lower levels of tolerance to effects of cocaine in the behavioral session as compared to subjects that did not eat under effects of cocaine in the home cage (Delayed Drug g roup). Therefore eating under effects of cocaine in the home cage probably contributed little if any to the development of tolerance to the rate decreasing effects of cocaine in the behavioral session for subjects in Experiments 1 and 2. Additionally, givi ng the Delayed Drug group the drug one hour after the session and after they had eaten resulted in no within session suppression of key pecking, suppression that could mask the development of tolerance. All six of the subjects in the Delayed Drug group sho wed tolerance.

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50 Table 3 1. Number of administrations of each dose of cocaine for each subject during acute dose response curve determination for Experiment 2. Acute Subject Dose 648 634 2173 244 606 582 21 604 544 6110 653 Sal 4 4 3 4 3 3 3 4 3 4 3 1. 0 2 3 3 3 2 2 2 3 3 2 2 3.0 2 2 4 3 2 2 2 3 2 2 2 5.6 2 3 4 2 3 3 4 4 3 3 2 10.0 3 2 4 2 3 2 3 2 2 3 3 13.0 3 3 17.0 4

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51 Table 3 2. Number of administrations of each dose of cocaine for each subjec t during dose response curve determination following the chronic drug regimen for Experiment 2. Note that the number of saline administrations reflects the number of saline administrations used in dose response curve determination, rather than the total nu mber of saline administrations. Chronic Subject Dose 648 634 2173 244 606 582 21 604 544 6110 653 Sal 15 15 14 12 12 18 18 15 15 14 14 1.0 2 3 2 2 2 4 2 2 2 2 2 3.0 2 2 2 2 2 2 2 2 2 2 2 5.6 2 4 2 2 2 2 2 4 4 3 3 10.0 2 2 2 2 2 2 5 3 3 3 3 13.0 3 2 2 3 17.0 2

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52 Table 3 3. Key pecks per minute following each administration of saline vehicle for each phase of the experiment for Experiment 2. The mean shown in italics was used to calculate percent saline values for Figures 3 1 3 3. Subject Phase 648 634 2173 244 606 582 21 604 544 6110 653 Acute 175.3 182.1 256.8 39.6 171.5 214.9 191.2 114.6 181.8 89.5 183.6 204.3 176.3 258.1 89.5 184.6 214.5 175.7 136.8 193.5 140.4 162.5 187.4 171.7 264.0 49.9 17 8.9 207.2 141.2 144.1 186.3 130.1 200.6 218.3 176.0 61.6 200.6 110.6 Mean 196.3 176.5 259.6 60.15 178.3 212.2 169.4 149.0 187.2 117.65 182.2 Chronic 185.4 168.8 0.0 62.8 0.6 229.9 156.4 105.8 174.1 181.1 217.4 176.6 143.8 0.0 48.4 0.0 218.2 12 1.3 111.2 170.8 172.2 194.2 174.7 160.6 0.0 65.2 0.0 227.2 150.7 117.5 182.1 191.8 193.1 151.2 126.4 0.0 51.4 0.0 235.9 127.0 111.9 169.5 179.3 203.0 186.0 142.8 0.0 78.2 0.0 200.9 163.4 124.1 183.1 200.9 221.9 192.8 148.8 0.0 77.8 0.0 212.6 176.6 96.6 179.2 201.5 199.9 178.2 126.4 0.0 67.9 0.0 218.0 174.1 112.2 172.8 200.9 187.8 174.2 138.8 0.0 61.3 0.6 230.2 174.4 129.0 182.0 178.1 192.9 168.7 21.4 0.0 57.8 0.0 234.1 187.6 131.0 174.0 195.5 182.0 156.6 0.0 0.0 66.0 0.0 206.8 189.9 71.2 177 .5 200.5 220.9 186.7 126.1 0.0 77.6 0.2 250.3 191.0 116.8 177.8 203.2 203.1 192.4 90.6 0.0 78.6 0.0 237.3 189.5 105.1 175.7 192.5 205.5 194.1 118.8 0.0 235.1 166.6 136.3 175.6 197.5 197.5 187.3 50.1 0.0 217.2 152.7 91.0 169.6 197.4 187.1 159. 6 83.8 222.3 162.3 119.4 158.2 233.2 138.3 234.4 174.3 200.5 159.4 Mean 177.6 110.5 0.0 66.1 0.2 224.7 164.8 111.9 174.8 192.3 200.5

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53 Table 3 4. ED50s (mg/kg) for each subject for each phase of Experiment 2. Phase Subject Acute Chronic 648 3.96 14.38 634 3.28 4.01 2173 12.42 244 2.12 5.91 606 5.28 Immediate Drug Mean 5.41 8.10 582 12.86 15.99 21 4.94 11.81 604 2.58 6.68 544 3.37 6.23 6110 4.48 7.36 653 3.75 7.54 Delayed Drug Mean 5.33 9.27

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54 Figure 3 1. Effects of cocaine during acute and post session administration for the Immediate Drug group in Experiment 2. Each graph shows data from an individual subject. Response rate is plotted as a function of dose of cocaine for the Immediate Drug group in Experiment 2. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and triangles show the effects of 30 days of cocaine administered immediately after the session. All other details are as in Figure 2 1.

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55 Figure 3 2. Effects of cocaine during acute and post session administration for the Delayed Drug group in Experiment 2. Each graph shows data from an individual subject. Response rate is plotte d as a function of dose of cocaine for the Delayed Drug group in Experiment 2. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and triangles show the effects of 30 days of cocaine administered 60 min after the session ended. All other details are as in Figure 2 1.

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56 Figure 3 3. Group average data for both groups in Experiment 2, comparing effects of acute cocaine administration and post session adminis tration. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 2. Data are averaged across all subjects in a group. Circles display the effects of cocaine during acute administration, and triangles display effects of cocaine following the chronic regimen (immediate post session drug for the Immediate Drug group, and 60 min post session drug for the Delayed of saline vehicle control, with inner error bar s displaying the standard deviation, and outer error bars displaying the range of effects of saline vehicle. Data from Subjects 2173 and 606 are not included in the group average from the chronic regimen for the Immediate Drug group. A) Data from the Immed iate Drug group. B) Data from the Delayed Drug group.

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57 CHAPTER 4 EXPERIMENT 3 The results of Experiments 1 and 2 suggest that pigeons often develop tolerance to effects of cocaine during a behavioral session when cocaine is repeatedly administered after the session. while the drug was active occurred. Tolerance developed for most subjects administered cocaine post session except those administered a large dose (e.g ., 7.4 mg/kg or 10.0 mg/kg) immediately after the session, a result similar to the findings of Pinkston and Branch (2004). Based on the large number of subjects that developed tolerance from post session administration of a moderate dose of cocaine (e.g., 5.6 mg/kg or 3.0 mg/kg) in the present experiments and in the experiment by Pinkston and Branch (2004), it is likely that if all subjects were administered moderate doses of cocaine post session, the majority would have shown tolerance. Key pecking or eati ng under effects of cocaine was not necessary for tolerance to develop to the rate decreasing effects of cocaine during the session. It was also unnecessary for cocaine to be closely temporally related or contextually related to the behavioral session beca use subjects administered cocaine in the colony room 60 min after the session ended still showed tolerance to effects of cocaine during the behavioral session. These results suggest that behavioral factors might not be important in the development of toler ance to effects of cocaine during the behavioral session. Therefore, the purpose of Experiment 3 was to examine if mere drug exposure in the home cage without exposure to experimental sessions or the experimental context would lead to the development of to lerance to effects of cocaine during the behavioral session.

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58 Method Subjects All subjects were experimentally and drug nave and aged approximately eight months at the begin ning of the experiment. All were maintained at 83% of their free feeding body weight (The local IACUC mandated the change in this fixed parameter from the 80% level in the previous experiments) by post session feeding. Subjects were housed and maintained a s in Experiment 1. Apparatus Experimental sessions were conducted in a BRS/LVE Inc. (Model PIP 010 016) standard three key operant test chamber measuring 31.0 cm by 36.5 cm by 35.0 cm. The center key in each chamber measured 2.5 cm in diameter, and was located on the panel 8.7 cm from the ceiling, equidistant from both sidewalls. To register a response, the key required approximately 0.09 N. All other details are described in Experiment 1. Procedure Training Subjects were trained as in Experiment 2. R atio training took three to five sessions. Key pecks were reinforced with 3 s access to mixed grain throughout training and baseline. The key light and houselights were extinguished during food presentation. After ratio training was complete, subjects were exposed to baseline conditions. Baseline Sessions began with a 5 min blackout, during which key pecking had no programmed consequence. This was followed by an FR 20 schedule of reinforcement for 20 min or until 40 reinforcers were obtained, whichever cam e first. After 50 53 sessions, responding was determined to be stable by visual inspection of graphs of daily session wide response rates. Sessions were conducted seven days a week at approximately the same time everyday. One

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59 subject died due to unknown ca uses during baseline conditions. Therefore no data will be shown for this subject, nor will any of its data be included in any analyses. Drug regimen After responding was determined to be stable, acute effects of cocaine were assessed as described in Expe riment 2. Doses of 13.0 mg/kg cocaine were also assessed for some subjects when no dose in the initial range of doses produced complete suppression of responding. Table 4 1 shows the number of administration of each dose during this assessment. Following acute dosing, all subjects were exposed to 30 daily administrations of saline, with no exposure to the experimental chamber. Subjects were weighed and fed up to their 83% weight between 10:00 am 10:30 am, and were injected with saline between 11:30 am 12: 00 pm. The purpose of this phase was to examine if prolonged time away from the experimental chamber had any effect. Then daily sessions resumed, and the dose response curve was redetermined. Acute doses of cocaine and saline were administered once every f our days in descending order with no injection occurring on intervening days. Each dose was administered a minimum of two times. Any dose that produced variable effects was repeated until effects were replicated. See Table 4 2 for the number of administrat ions of each dose given. In the second phase, all subjects were exposed to 30 daily administrations of 5.6 mg/kg cocaine, with no exposure to the experimental chamber. That is, another 30 day period without exposure to the FR schedule occurred. The 5.6 mg/ kg dose was chosen because it was commonly used as a chronic dose in Experiments 1 and 2 because it produced a moderate to large decrease in rate of responding for most subjects, and because it generally has resulted in tolerance whether given before or af ter sessions. Subjects were fed and administered drugs at the times specified in the previous phase, but otherwise remained in their home cages. Exposure to the FR schedule was then re initiated, and the dose response curve was then redetermined as describ ed in the first

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60 phase. No injections occurred on days intervening acute doses to minimize the amount of pairing of the drug and the experimental context, and to minimize the amount of exposure to the experimental contingencies while under effects of the dr ug. Redetermination of the dose response curve took place over approximately 100 sessions. The numbers of administrations of each dose are displayed in Table 4 3. The third phase of the experiment was identical to the second, that is, no sessions were cond ucted, except that chronic dosing continued for 60 days. The same chronic dose was used for this phase. Exposure to the FR schedule then re commenced, and the dose response curve was then redetermined again as described in the first phase with no injection s on days intervening acute dosing days. Redetermination of the dose response curve took place over approximately 40 90 sessions depending on the variability of dose effects. Table 4 4 shows the number of administration of each dose during this assessment. During the fourth and final phase of the experiment, subjects were exposed to daily sessions and daily administration of 5.6 mg/kg cocaine immediately before the behavioral session for 30 days. Then the dose response curve was redetermined as described in previous phases except 5.6 mg/kg cocaine continued to be administered on days between test doses. Table 4 5 shows how many times each dose was tested. Drug Procedure The drug procedure was the same as that used in Experiment 1. Results and Discussion F igure 4 1 displays average key pecking response rate within a session in Experiment 3, calculated as the percent of saline vehicle rate of responding, plotted as a function of dose of cocaine. Table 4 6 shows the rate of responding following saline vehicle administrations for all subjects during each phase of the experiment, which stayed relatively constant across all phases of the experiment except for Subject 965, whose rates under saline after the first 30 day

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61 the study. During acute cocaine administration, all subjects showed dose dependent decreases in rate of key pecking. Thirty sessions in the home cage with saline administration was followed by a slight shift in the dose response curve to the right, sugges ting that time off from experimental sessions itself was associated with modest changes, at best, in the dose response function. Due to the small change in drug effects from acute administration to that following 30 days away from the session, the data fro m these two drug regimens were averaged for each subject by taking the average of each administration of each dose across both phases for individual subjects, and were used as a comparison for the subsequent drug regimens. Therefore acute administration re fers to the average of the initial acute administration and that following 30 days of saline administration for the remainder of this section. When cocaine was administered daily in the home cage for 30 consecutive sessions, that regimen produced a variety of drug effects across subjects as compared to drug effects during acute administration shown in Figure 4 2. Subjects 740 and 945 developed tolerance following this regimen, whereas 965 developed sensitization. Subject 881 showed little effect of this dru g regimen, and Subject 808 skipped this drug regimen due to illness. Because tolerance did not develop in all subjects following 30 administrations of cocaine in the home cage, subjects were administered an additional 60 daily administrations of cocaine i n the home cage with no exposure to experimental sessions, with this regimen beginning about 100 days after cessation of the previous 30 day period of administration without sessions. The results of that exposure compared to acute effects are displayed in Figure 4 3. This drug regimen had little effect for most subjects, with no additional tolerance developing for the two subjects that had shown tolerance after a 30 day regimen. In fact, Subject 740, which previously developed

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62 tolerance, showed less toleran ce following 60 additional cocaine administrations in the home cage. Subject 965 continued to show sensitization. Cocaine (5.6 mg/kg) was then administered pre session for 30 days to see if any additional tolerance would develop for those subjects already showing tolerance, and to see if those that did not previously show tolerance would develop it. Effects of cocaine administered acutely as compared to those after a regimen of daily pre session administration are displayed in Figure 4 4. Daily pre session cocaine administration led to additional tolerance in Subjects 740 and 945, the emergence of modest tolerance for Subject 881 and not much effect for 808. Subject 965 continued to show sensitization to effects of large doses of cocaine, and showed increase s in rate of responding under effects of small doses of cocaine. The examination of data at the group average level showed drug effects similar to the data from individual subjects. Figure 4 5 compares group average data during initial acute administratio n and following 30 days in the home cage with saline administered daily. The group average data shows a slight change in drug effects following 30 days away from the session, with all subjects showing a slight increase in ED50 from initial acute administra tion to following 30 sessions of saline administration in the home cage (Table 4 7). Because this increase in ED50 was small, the group average data for the following drug regimens was compared to the data averaged from the initial acute administration and that following 30 days of saline administration. The ED50 for the average of the initial acute and 30 days of saline administration was calculated by fitting a straight line to the data averaged from the two sets of determinations. Figure 4 6 compares gro up average data from acute administration and following 30 days of cocaine administered in the home cage with no exposure to the experimental session. While it appears that drug exposure in the home cage produced a slight amount of tolerance at the group

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63 a verage level, ED50 did not increase for all subjects, and increases were relatively small (Table 4 7). Note that data from Subject 808 were excluded from this analysis because this subject skipped this phase of the experiment. Figure 4 7 shows group avera ge data from acute administration and 60 days of cocaine administration in the home cage with no exposure to the experimental chamber. Visual inspection shows very little change in drug effects between acute administration and 60 days of cocaine administra tion in the home cage. It should be noted that the group mean effect is not particularly representative of the individual animal data (Compare Figure 4 3). Examination of changes in ED50 show that three subjects had a slightly higher ED50 following 60 days of cocaine administration as that compared to acute administration, but the other two subjects showed a slight decrease in ED50 from acute administration to that following 60 days of cocaine administration (Table 4 7). Interestingly, the group average ED 50 after this condition was close to the value from the initial acute dose effect assessments. Figure 4 8 displays group average data from acute administration and pre session cocaine administration. When cocaine was administered pre session with daily exp erimental sessions, tolerance developed at the group average level; however, only two subjects (740 and 945; Table 4 7) showed a large increase in ED50 following acute administration as compared to that following pre session administration. Two other subje cts showed a slight increase in ED50 (881 and 808) following pre session administration, and one subject showed a decrease in ED50 (965). Overall, time away from experimental sessions with cocaine administered in the home cage had no consistent influence on drug effects. The tolerance developed during home cage cocaine administrations was neither consistent across subjects nor consistent within subject.

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64 These results suggest that mere cocaine exposure in the home cage is unlikely to produce notable toleran ce to effects of cocaine during the behavioral session. Because mere drug exposure in the home cage, which eliminates many behavioral factors, did not reliably lead to tolerance to effects of cocaine during the behavioral session, it is therefore likely th at some behavioral or contextual factors associated with experimental sessions do play a role in the development of tolerance to effects of cocaine during the behavioral session. When drug administration occurred before each session, three of the five subj ects showed reliable tolerance, as predicted, but two others did not, with one (965) actually showing sensitization to effects of large doses. Effects of smaller doses (3 and 5.6 mg/kg) for 965, however, did change as a function of pre session dosing. Prev ious experience with the drug had resulted in those doses having rate decreasing effects (Figure 4 3), but after pre session chronic dosing, those doses resulted in increases in response rate.

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65 Table 4 1. Number of administrations of each dose of cocaine for each subject during initial acute dose response curve determination for Experiment 3. Acute Subject Dose 740 945 881 808 965 Sal 3 3 3 6 3 1.0 2 3 2 2 2 3.0 4 2 3 3 2 5.6 4 4 3 5 2 10.0 4 3 3 3 4 13.0 2 17.0

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66 Table 4 2. Number of administrations of each dose of cocaine for each subject during dose response curve determination following 30 administrations of saline in the home cage for Experiment 3. 30 Days Sal Subject Dose 740 945 881 808 965 Sal 4 4 4 2 2 1.0 2 2 2 2 2 3.0 2 2 2 2 2 5.6 2 3 2 8 2 10.0 3 2 3 2 2 13.0 2 17.0

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67 Table 4 3. Number of administrations of each dose of cocaine for each subject during dose response curve determination following 30 admini strations of cocaine in the home cage for Experiment 3. 30 Days Coc Subject Dose 740 945 881 808 965 Sal 2 2 2 2 1.0 2 2 2 2 3.0 2 2 2 2 5.6 3 3 3 2 10.0 6 4 4 3 13.0 3 17.0

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68 Table 4 4. Number of administ rations of each dose of cocaine for each subject during dose response curve determination following 60 administrations of cocaine in the home cage for Experiment 3. 60 Days Coc Subject Dose 740 945 881 808 965 Sal 2 2 2 2 2 1.0 2 2 2 2 2 3.0 2 2 2 4 2 5.6 3 3 3 7 3 10.0 2 3 2 5 3 13.0 3 2 17.0

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69 Table 4 5. Number of administrations of each dose of cocaine for each subject during dose response curve determination following the pre session chronic drug regimen for Exper iment 3. Note that the number of cocaine administrations of the chronic dose reflects the number of administrations used in dose response curve determination, rather than the total number of administrations of that dose. Pre session Subject Dose 740 945 881 808 965 Sal 2 2 3 4 2 1.0 2 2 4 4 2 3.0 2 2 5 2 2 5.6 15 18 16 16 11 10.0 4 7 6 4 2 13.0 3 3 3 2 3 17.0 2 2

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70 Table 4 6. Key pecks per minute following each administration of saline vehicle for each phase of the experiment for Experiment 3. The mean shown in italics was used to calculate percent saline values for Figures 4 1 4 8. Subject Phase 740 945 881 808 965 Acute 174.6 155.9 118.3 189.8 136.7 164.3 144.3 125.5 205.2 147.0 174.3 137.1 120.2 206.5 118.2 205.0 194.3 206.1 Mean 171.0 145.8 121.3 201.1 134.0 30 Days Sal 205.8 135.9 128.5 201.0 91.2 196.0 141.4 112.0 204.4 97.7 179.3 132.6 111.8 200.0 122.5 126.2 Mean 195.1 133.1 120.0 202.7 94.4 30 Days Coc 181.4 132.1 140.6 121.4 18 2.7 101.0 113.5 131.4 Mean 182.1 116.5 127.0 126.4 60 Days Coc 206.4 121.1 124.7 200.6 159.9 184.7 126.1 93.7 193.1 123.9 Mean 195.5 123.6 109.2 196.8 141.9 Pre session 170.9 95.3 100.7 201.0 122.0 153.8 112.0 107.7 224.6 101.1 107.5 170.1 169.8 Mean 162.4 103.6 105.3 191.4 111.6

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71 Table 4 7. ED50s (mg/kg) for each subject for each phase of Experiment 3. Phase Subject Acute 30 Days Sal Acute + Sal 30 Days Coc 60 Days Coc Pre session 740 4.47 8.25 4.81 7.26 6.39 23.79 945 3.53 4.22 3.80 6.90 7.07 14.06 881 3.88 6.93 3.99 4.59 4.27 4.14 808 4.41 8.95 5.05 4.44 7.11 965 Mean 9.48 9.82 9.85 5.14 3.78 4.04 5.15 7.63 5.50 4.86 5.19 10.63

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72 Figure 4 1. Effects of cocaine during acute administration and follo wing 30 days of saline administration in the home cage for Experiment 3. Each graph shows data from an individual subject. Response rate is plotted as a function of dose (log scale) of cocaine for Experiment 3. Data are plotted as percent of values obtaine d after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and triangles show the effects of 30 days of saline administration with no exposure to the session. All other details are as in Figure 2 1.

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73 Fig ure 4 2. Effects of cocaine during acute administration and following 30 days of cocaine administration in the home cage for Experiment 3. Each graph shows data from an individual subject. Response rate is plotted as a function of dose (log scale) of cocai ne for Experiment 3. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine averaged from during acute and saline administration, and squares show effects of 30 days of cocaine administ ration (5.6 mg/kg/day) with no exposure to the session. All other details are as in Figure 2 1.

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74 Figure 4 3. Effects of cocaine during acute administration and following 60 days of cocaine administration in the home cage for Experiment 3. Each graph show s data from an individual subject. Response rate is plotted as a function of dose (log scale) of cocaine for Experiment 3. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine average d from during acute and saline administration, and diamonds show effects of 60 days of cocaine administration (5.6 mg/kg/day) with no exposure to the session. All other details are as in Figure 2 1.

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75 Figure 4 4. Effects of cocaine during acute and pre se ssion administration for Experiment 3. Each graph shows data from an individual subject. Response rate is plotted as a function of dose (log scale) of cocaine for Experiment 3. Data are plotted as percent of values obtained after administration of saline v ehicle. Circles display the effects of of 30 sessions of pre session cocaine administration with daily experimental sessions. All other details are as in Figure 2 1.

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76 Figur e 4 5. Group average data for Experiment 3 comparing effects of acute cocaine administration and effects of cocaine following 30 days of saline administered in the home cage. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 3. Data are averaged across all subjects. Circles display the effects of cocaine during acute administration, and triangles show the effects of 30 indicate the average effects of saline vehicle control, with inner error bars displaying the standard deviation, and outer error bars displaying the range of effects of saline vehicle.

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77 Figure 4 6. Group average data for Experiment 3 comparing effects of acut e cocaine administration and effects of cocaine following 30 days of cocaine administered in the home cage. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 3. Data are averaged across all subjects. Circles d isplay the effects of cocaine averaged from during acute and saline administration, and squares show effects of 30 days of cocaine administration with no exposure to the session. All other details are as in Figure 4 5.

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78 Figure 4 7. Group average data for Experiment 3 comparing effects of acute cocaine administration and effects of cocaine following 60 days of cocaine administered in the home cage. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 3. Data are averaged across all subjects. Circles display the effects of cocaine averaged from during acute and saline administration, and diamonds show effects of 60 days of cocaine administration with no exposure to the session. All other details are as in Figur e 4 5.

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79 Figure 4 8. Group average data for Experiment 3 comparing effects of acute cocaine administration and effects of pre session cocaine. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 3. Data are averaged across all subjects. Circles display the effects of cocaine averaged from during acute session cocaine administration with daily experimental sessions. All other details are as in Figure 4 5.

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80 CHAPTER 5 EXPERIMENT 4 Results of Experiment 3 showed that mere drug exposure in the home cage without exposure to the behavioral session was not sufficient to produce consistent tolerance to effects of cocaine during the behavio ral session. Experiments 1 and 2 suggested that behavioral factors such as eating or key pecking under effects of cocaine are not necessary for the development of tolerance to effects of cocaine during the behavioral session. Yet when behavioral factors we re mostly eliminated in Experiment 3, tolerance did not consistently develop. This combination of results makes it difficult to determine if behavioral or pharmacological variables, or both, played a role in the development of tolerance to effects of cocai ne during the behavioral session. When subjects were exposed to daily administration of cocaine in the home cage in Experiment 3, daily administration was discontinued when sessions resumed, in order to prevent additional pairings of cocaine and the behavi oral session. Although subjects in Experiment 3 did not reliably show tolerance to effects of cocaine during the behavioral session, it is possible that tolerance had developed during the chronic drug regimen, but the tolerance was diminished or not expres sed during dose response curve redetermination because daily cocaine administration was discontinued. Therefore, the purpose of Experiment 4 was to determine if daily cocaine administration was necessary during dose response curve redetermination for toler ance to develop or be expressed. Experiment 4 used daily behavioral sessions because that procedure was associated with the development of tolerance in Experiments 1 and 2. Method Subjects Glenwood, IA). All subjects were experimentally and drug nave, and aged approximately seven months at the

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81 beginning of the experiment. All were maintained at 83% of their free feeding body weight by post session feeding when needed. Subjects were housed and maintained as in Experiment 1. Apparatus Experimental sessions were conducted a BRS/LVE Inc. (Model PIP 010 016) standard three key operant test chamber measuring 31.0 cm by 36.5 cm by 35.0 cm. To register a response, the key required approximatel y 0.07 N. All other details are described in Experiment 1. Procedure Training Subjects were trained as in Experiment 2. Ratio training took four to eight sessions except for one subject. This subject reached, but did not exceed FR 11 after 11 sessions. T he FR value was then incremented by two responses per reinforcer for each session for this subject until FR 20 was reached. Key pecks were reinforced with 3 s access to mixed grain throughout training and baseline. The key light and houselights were exting uished during food presentation. After ratio training was complete, subjects were exposed to baseline conditions. Baseline Sessions began with a 5 min blackout, during which key pecking had no programmed consequence. This was followed by an FR 20 schedule of reinforcement for 20 min or until 40 reinforcers were obtained, whichever came first. After 51 64 sessions, responding was determined to be stable by visual inspection of graphs of daily session wide response rates. Sessions were conducted seven days a week at approximately the same time every day. One subject died due to unknown causes during baseline conditions. Therefore no data will be shown for this subject, nor will any of its data be included in any analyses. Drug regimen After responding was de termined to be stable, acute effects of cocaine were assessed as described in Experiment 2. Table 5 1 shows how many times each dose was tested during this phase. Following acute dosing, each subject was administered 5.6 mg/kg cocaine 60 min after the sess ion ended for 60 consecutive sessions. This dose was chosen

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82 because it was commonly used as a chronic dose in Experiments 1 and 2, was the only chronic dose used in Experiment 3, and because it initially produced some decrease in rate of responding for all subjects. Subjects were administered saline everyday immediately before the session during the chronic drug regimen, and were fed their post session ration within 5 min after the session if needed. Therefore all subjects were given their post session rati on and then administered drug approximately 60 min later. Following this chronic drug regimen, the dose response curve was redetermined. Once every four days subjects were administered one of their initial acute doses of cocaine pre session. On intervening days, subjects were administered saline before the session. Post session saline was administered 60 min after the session on acute dosing days and intervening days. Each dose was administered a minimum of two times. Any dose that produced variable effects was repeated until effects were replicated. Doses of 13.0 mg/kg cocaine were also assessed for all subjects. Table 5 2 shows the number of administrations of each dose. Once dose response curve redetermination was complete, redetermination began again as described above, except that 5.6 mg/kg cocaine was administered 60 min post session on intervening days rather than saline. Saline was administered before the session on intervening days, and 60 min post session on acute dosing days. See Table 5 3 for the number of administrations of each dose during this phase. Then subjects were administered 5.6 mg/kg cocaine immediately before each session with saline administered 60 min after the session for 30 consecutive sessions. The dose response curve was then rede termined as described above, with 5.6 mg/kg cocaine administered pre session on intervening days. Saline was administered 60 min post session on acute dosing days and intervening days. The number of administrations of each dose is displayed in Table 5 4.

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83 D rug Procedure The drug procedure was the same as that used in Experiment 1. Results and Discussion Figure 5 1 displays average key pecking response rate within a session in Experiment 4, calculated as the percent of saline vehicle rate of responding, plot ted as a function of dose of cocaine. Table 5 5 shows the rate of responding following each saline vehicle administration for all phases of the experiment. Rates following vehicle administration were generally stable across all phases of the study, althoug h those for Pigeon 279 were more variable than those of the other subjects. During acute cocaine administration, all subjects showed dose dependent decreases in rate of key pecking. Following 60 sessions of daily cocaine administrations 60 min after the se ssion ended, the dose response curve was redetermined with saline administered on intervening days. This procedure led to some amount of tolerance for all subjects at least for some doses of cocaine as indicated by a shift in the dose response curve to the right (Figure 5 1), although the change was minimal for subject 811. Notably, doses that initially eliminated key pecking no longer did so, a change evident for all 5 subjects. These results replicate the findings of Experiment 2 in which post session dos ing resulted in tolerance when the post session administration occurred 60 min post session. Figure 5 2 shows effects of acute cocaine administration as compared to effects of post session cocaine administration with chronic dosing on days intervening betw een probe doses. When daily post session administration resumed and dose response curve redetermination continued, all subjects continued to show tolerance to varying degrees, but the amount of tolerance was small for subject 811. Effects of post session a dministration of cocaine with and without post session drug administered on intervening days are displayed in Figure 5 3. One subject, 961, showed slight additional tolerance at the largest dose when daily cocaine administration resumed, while two other su bjects, 811 and 286, showed a slight shift of the

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84 showed an increase in rate at 3.0 mg/kg. Figure 5 4 compares effects of acute cocaine administration and effect s after a regimen of pre session cocaine administration. When cocaine was administered daily pre session, and continued to be so during dose response assessments, the tolerance produced by post session administration was maintained for two subjects (811, 2 86), and additional tolerance, as compared to that after post session administration, was evident for the three other subjects (279, 961, 109). Figure 5 5 shows group average data comparing effects of cocaine during acute administration and following post session administration when saline was administered on intervening days. The group average data show that slight tolerance had developed; however the change in ED50 was small for all subjects (Table 5 6). Four of five subjects showed an increase in ED50 an d one subject showed a very slight decrease in ED50 (811) from acute administration to post session administration with saline administered on intervening days. Figure 5 6 compares group average data from acute administration and following post session ad ministration with cocaine administered (post session) on intervening days during the dose response assessment. These data show that the small amount of tolerance previously developed was maintained when post session injections on intervening days switched from saline to cocaine. All subjects had a larger ED50 when cocaine was administered post session with drug administered on intervening days as compared to that during acute administration (Table 5 6). Figure 5 7 displays group average data from post sess ion administration when saline was administered on intervening days, and when cocaine was administered on intervening days. The group average data show that the switch from saline on intervening days to cocaine on

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85 intervening days did not alter the dose ef fect curve, with both drug regimens producing very similar functions. Note as well that the ED50 values (Table 5 6) for the two conditions were similar, also suggesting that changing what occurred between dose assessments resulted in little change in drug effects. Figure 5 8 shows group average data from acute administration and after/during a regimen of daily pre session cocaine administration. These data show that tolerance was observed at the group average level when cocaine administration was switched f rom post session to pre session. Comparison of Figure 5 8 with Figures 5 5 and 5 6 show that pre session administration of cocaine produced more tolerance as that compared to post session administration at the group average level. Examination of ED50s show ed that three of five subjects (109, 279, 961) showed a larger ED50 for pre session administration as compared to post session administration regimens (Table 5 6), and the other two subjects (811, 286) showed ED50s that were similar to that during acute ad ministration, indicating pre session administration produced more tolerance than post session administration for some, but not all, of the subjects. These results indicate that daily cocaine administration between test doses is not necessary for tolerance developed during post session administration to be expressed. When daily administration of cocaine resumed, it did not consistently produce additional tolerance, suggesting that daily cocaine administration during dose response curve redetermination likely does not contribute to the development of tolerance. These results strengthen the results of Experiment 3 in that subjects in Experiment 3 would have likely shown the same drug effects if daily cocaine administration was continued during dose response cur ve redetermination. Therefore the tolerance, or lack of tolerance shown during dose response curve redetermination in Experiment 3 was probably indicative of the actual amount of tolerance that developed.

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86 Table 5 1. Number of administrations of each dose o f cocaine for each subject during acute dose response curve determination for Experiment 4. Acute Subject Dose 811 286 109 279 961 Sal 4 5 4 4 5 1.0 3 3 3 4 3 3.0 3 3 3 3 3 5.6 3 5 4 5 4 10.0 4 3 3 4 3 13.0

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87 Table 5 2. Number of administrations of each dose of cocaine for each subject during dose response curve determination following post session chronic administration with saline administered on intervening days for Experiment 4. Note that the number of saline administ rations reflects the number of administrations used in dose response curve determination, rather than the total number of administrations of saline. Post, sal/sal Subject Dose 811 286 109 279 961 Sal 15 15 16 16 16 1.0 2 2 2 2 2 3.0 2 2 2 2 2 5.6 4 3 5 4 3 10.0 5 5 5 6 7 13.0 3 3 2 2 2

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88 Table 5 3. Number of administrations of each dose of cocaine for each subject during dose response curve determination following post session chronic administration with cocaine administered on interv ening days for Experiment 4. Other details are as in Table 5 2. Post, sal/coc Subject Dose 811 286 109 279 961 Sal 16 16 16 16 16 1.0 2 2 2 2 2 3.0 2 2 2 2 2 5.6 4 3 5 4 2 10.0 5 5 5 5 5 13.0 3 4 2 3 4

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89 Table 5 4. Number of adminis trations of each dose of cocaine for each subject during dose response curve determination following pre session chronic administration for Experiment 4. Note that the number of cocaine administrations of the chronic dose reflects the number of administrat ions used in dose response curve determination, rather than the total number of administrations of that dose. Pre session Subject Dose 811 286 109 279 961 Sal 2 2 2 3 2 1.0 2 2 2 2 2 3.0 2 2 2 3 2 5.6 15 15 15 14 15 10.0 6 6 5 3 3 13.0 3 3 4 3 6

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90 Table 5 5. Key pecks per minute following each administration of saline vehicle for each phase of the experiment for Experiment 4. The mean shown in italics was used to calculate percent saline values for Figures 5 1 5 8. Subject Phase 811 286 109 279 961 Acute 133.0 125.7 136.9 109.5 174.0 132.7 138.1 148.8 105.6 174.8 157.9 132.0 130.2 113.9 186.2 163.2 153.0 140.6 94.1 199.5 165.2 194.4 Mean 146.7 142.8 139.1 105.7 183.8 Post, sal/sal 156.4 154.4 161.6 57.8 201.0 191.7 1 36.0 166.7 111.6 171.3 194.0 167.1 158.9 96.0 202.6 176.2 177.2 148.1 105.7 196.7 183.8 180.5 156.1 102.9 196.7 187.8 175.5 159.5 117.3 196.0 167.1 175.2 164.3 109.6 201.4 168.1 177.4 153.7 111.4 189.7 164.4 169.1 154.9 116.0 196.8 172.7 18 7.0 166.8 103.3 196.5 158.5 173.2 171.3 113.4 197.7 172.1 180.0 160.5 118.5 185.3 152.4 187.3 153.9 92.4 193.8 174.5 174.3 164.9 109.0 202.1 173.5 189.0 155.7 100.1 193.0 156.8 122.0 200.9 Mean 173.8 172.9 159.6 105.4 195.1 Post, sal/coc 1 61.7 185.5 161.9 109.1 209.1 176.3 193.5 159.7 77.9 197.6 162.4 178.5 162.4 116.3 180.8 158.0 182.7 160.4 121.0 204.0 168.3 192.5 168.9 114.9 218.9 161.1 180.4 165.1 128.0 217.3 170.8 184.0 160.9 112.8 196.5 167.2 183.1 157.0 98.5 187.3 180 .8 126.1 171.8 126.1 200.7 188.5 186.0 153.1 112.6 204.1 18.2 172.6 175.2 115.1 198.2 180.5 185.2 153.6 96.3 197.3 158.4 163.5 134.7 40.9 184.6 172.1 165.0 140.6 64.1 173.5 145.3 132.6 142.0 87.3 116.4

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91 Table 5 5. Continued. Subject Phase 8 11 286 109 279 961 172.3 112.2 148.8 48.5 12.0 Mean 169.5 170.1 157.3 98.1 181.1 Pre session 171.6 177.5 102.5 56.1 195.3 161.1 178.1 137.2 103.9 191.0 89.6 Mean 166.4 177.8 119.9 83.2 193.2

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92 Table 5 6. ED50s (mg/kg) for eac h subject for each phase of Experiment 4. Phase Subject Acute Post, sal/sal Post, sal/coc Pre session 811 5.99 5.51 6.53 5.92 286 5.86 8.82 6.93 5.69 109 3.74 5.48 5.50 10.44 279 3.41 5.73 8.45 8.97 961 Mean 5.13 6.46 6.37 13.29 4.83 6.40 6.76 8. 86

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93 Figure 5 1. Effects of cocaine during acute administration and post session administration with saline administered on intervening days for Experiment 4. Each graph shows data from an individual subject. Response rate is plotted as a function of do se of cocaine for Experiment 4. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and triangles show the effects of 60 days of cocaine administered 60 min after the session ended with saline administered on intervening days. All other details are as in Figure 2 1.

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94 Figure 5 2. Effects of cocaine during acute administration and post session administration with cocaine administered on intervening days fo r Experiment 4. Each graph shows data from an individual subject. Response rate is plotted as a function of dose of cocaine for Experiment 4. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and squares show effects of one hour post session cocaine with cocaine administered on intervening days. All other details are as in Figure 2 1.

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95 Figure 5 3. Effects of cocaine during post session administration w ith saline or cocaine administered on intervening days for Experiment 4. Each graph shows data from an individual subject. Response rate is plotted as a function of dose of cocaine for Experiment 4. Data are plotted as percent of values obtained after admi nistration of saline vehicle. Triangles show the effects of 60 days of cocaine administered 60 min after the session ended with saline administered on intervening days, and squares show effects of one hour post session cocaine with cocaine administered on intervening days. All other details are as in Figure 2 1.

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96 Figure 5 4. Effects of cocaine during acute administration and pre session administration for Experiment 4. Each graph shows data from an individual subject. Response rate is plotted as a functio n of dose of cocaine for Experiment 4. Data are plotted as percent of values obtained after administration of saline vehicle. Circles display the effects of cocaine during acute administration, and diamonds show effects of 30 days of pre session cocaine ad ministration. All other details are as in Figure 2 1.

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97 Figure 5 5. Group average data for Experiment 4 comparing effects of cocaine during acute administration and post session administration with saline administered on intervening days. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 4. Data are averaged across all subjects. Circles display the effects of cocaine during acute administration, and triangles show the effects of post session administration with saline administered on intervening days. The points above displaying the standard deviation, and outer error bars displaying the range of effects of saline vehicle.

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98 F igure 5 6. Group average data for Experiment 4 comparing effects of cocaine during acute administration and post session administration with cocaine administered on intervening days. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 4. Data are averaged across all subjects. Circles display the effects of cocaine during acute administration, and squares show the effects of post session administration with cocaine administered on intervening days. All other detai ls are as in Figure 5 5.

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99 Figure 5 7. Group average data for Experiment 4 comparing effects of cocaine during post session administration with saline or cocaine administered on intervening days. Response rate as a percent of control is plotted as a function of dose of cocaine for Experiment 4. Data are averaged across all subjects. Triangles display effects of post session administration with saline administered on intervening days, and squares show the effects of post session administration with coc aine administered on intervening days. All other details are as in Figure 5 5.

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100 Figure 5 8. Group average data for Experiment 4 comparing effects of cocaine during acute administration and pre session administration. Response rate as a percent of c ontrol is plotted as a function of dose of cocaine for Experiment 4. Data are averaged across all subjects. Circles display the effects of cocaine during acute administration, and diamonds show the effects of pre session administration. All other details a re as in Figure 5 5.

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101 CHAPTER 6 GENERAL DISCUSSION The main conclusion of the current experiments was that not contingent tolerance was observed in pigeons. The majority of subjects in all experiments administered post session cocaine developed tolerance. Experiment 1 found that post session administration of cocaine in pigeons could result in tolerance to effects of cocaine during the behavioral session. Half of the subjects administered cocaine after the session developed tolerance. Experiment 2 also examined effects of post session drug administration. Eating under the effects of cocaine was controlled, session effects regardless of whether or not they ate under the effects of the drug. The only exceptions were subjects that received a relatively large dose immediately post session and as a result exhibited response suppression throughout the session. Results of Experiments 1, 2, and 4 combined therefore show that post session administration of cocaine often led to tolerance to effects of cocaine during the behavioral session. For subjects in Experiments 1, 2 and 4 that never showed response suppression, 16 of 18 subjects (all subjects except 727 and 752) developed notable toler ance from chronic post session cocaine administration. A paired t test comparing the ED50 from acute administration and the ED50 from the first post session dosing regimen across subjects in all experiments was significant [ t (17) = 4.97; p < .01; average acute ED50 = 4.52; average post session ED50 = 8.37]. This indicates that tolerance was a common outcome from post session cocaine administration across this series of experiments. Most of the instances in which post session drug administration did not lea d to tolerance were accompanied by suppression of key pecking that was associated with chronic administration of relatively large doses of cocaine (7.4 mg/kg or 10.0 mg/kg) immediately post session. It is possible that had all subjects been chronically adm inistered moderate doses of cocaine (3.0 mg/kg or 5.6 mg/kg) post session that

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102 those that showed behavioral suppression would have instead shown tolerance. The fact that post session administration of cocaine usually led to tolerance in the pigeons suggest s that drug administration in relation to the time of the behavioral session, an outcome that suggests that cocaine exposure alone is sufficient to produce toler ance in this species. When mere drug exposure was examined in Experiment 3, however, it did not reliably lead to the development of tolerance. A few subjects showed small amounts of tolerance when cocaine was repeatedly administered while the pigeon remai ned in its the home cage (i.e., operant response sessions were not conducted), but this tolerance was not consistently found across subjects or within subject when a second, longer exposure period was examined. Experiment 4 was conducted to see if the fac t that dose response determinations in Experiment 3 were made under conditions where no drug was administered between test doses might have contributed to the lack of development of tolerance. Experiment 4, which involved post session cocaine administratio n, showed again that post session dosing can result in tolerance and also that the discontinuation of chronic dosing during dose response curve redetermination did not prevent the observation of tolerance that had developed during chronic post session dosi ng. Therefore it is unlikely that the cessation of chronic dosing in Experiment 3 during dose response curve redetermination prevented the expression of any tolerance that had developed when cocaine was administered in the home cage. The results of the cu rrent research are not consistent with much past research on contingent tolerance, except research conducted with pigeons. Pinkston and Branch (2004) found not contingent tolerance to cocaine in pigeons, but Bowen et al. (1993), Branch and Sizemore (1988), Smith (1990), and Woolverton et al. (1978) all found contingent tolerance to cocaine

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103 when squirrel monkeys or rats were used as subjects. Therefore the majority of research conducted using cocaine has found that post session cocaine administration does no t lead to tolerance (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978), and some has even found that post session administration of cocaine leads to sensitization (Bowen et al., 1993; Woolverton et al., 1978). Contingent to lerance has also been a common finding in rats with other psychoactive drugs such as ethanol (Chen, 1968; Wenger et al., 1981) and amphetamine (Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Poulos et al., 1981). The finding of tolerance resulting from post session drug administration is also not consistent with the reinforcement loss hypothesis (Schuster et al., 1966). The reinforcement loss hypothesis states that subjects will develop tolerance if the initial drug effect produces a loss in reinforcemen t obtained. Initial administration of cocaine pre session did produce a loss of reinforcement because response rate was decreased, whereas initial administration of cocaine post session had no effect on the amount of reinforcement obtained. Had contingent tolerance been found, then the reinforcement loss hypothesis would have been supported because only the subjects with an initial decrease in reinforcement obtained (Pre post group) would have shown tolerance. Therefore the reinforcement loss hypothesis can not be used to explain how or why subjects in the present set of experiments developed tolerance as a result of post session drug administration. Although the reinforcement loss hypothesis can account for the results of many experiments that have found tol erance (e.g., Bowen et al., 1993; Branch & Sizemore, 1988; Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Poulos et al., 1981; Smith, 1990; Woolverton et al., 1978), this is not the first experiment to demonstrate that behavioral tolerance can develop wi thout reinforcement loss (e.g., Pinkston & Branch, 2004; Smith, 1986).

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104 Throughout Experiments 1 and 2, it was common for subjects administered larger doses of cocaine (7.4 mg/kg or 10.0 mg/kg) immediately after the session to show response suppression dur ing the session. Such suppression was also commonly seen in the study by Pinkston and Branch (2004) when large doses of cocaine were administered 20 min after the session. Additionally, large doses of amphetamine have also been found to produce response su ppression of food maintained behavior when administered post session (Glowa & Barrett, 1983). Though the present experiment was not designed to investigate why response suppression is associated with large doses of cocaine administered immediately after th e session, the Pinkston and Branch (2004) study found that replacing post session administrations of cocaine with post session administrations of saline was followed by recovery of key pecking. This indicated that preceding drug administration with the ses sion might have caused the behavioral suppression, meaning the suppression was likely due to Pavlovian associations between the session and the drug. The drug was never administered, however, without exposure to the behavioral session, therefore one can on ly tentatively conclude that Pavlovian processes were responsible for the response suppression (cf. Pinkston & Branch, 2004). The response suppression seen when large doses of cocaine were administered immediately after the session in Experiments 1 and 2 was not observed for subjects in the Delayed Drug group in Experiment 2. Three subjects in this group were administered 10.0 mg/kg daily 60 min after the session. None of these subjects showed response suppression, and all developed tolerance. These result s suggest that failure to observe tolerance with post session large doses in Experiment 1 and for subjects in the Immediate Drug group in Experiment 2 was a result of the tolerance being masked by the apparently Pavlovian processes that resulted in within session suppression. When the 60 min delay between post session cocaine administration

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105 and the session obviated the Pavlovian processes, the administration of large chronic doses resulted in tolerance. Therefore, the combination of size of chronic dose, an d when the dose was administered in relation to the behavioral session played a role in whether or not tolerance developed. Subjects administered moderate chronic doses of cocaine (3.0 mg/kg or 5.6 mg/kg) often developed tolerance regardless of if the drug was administered before the session, immediately after the session, or 60 min after the session. Subjects administered larger chronic doses of cocaine (7.4 mg/kg or 10.0 mg/kg) commonly showed tolerance when the drug was administered before the session, o r 60 min after the session, but not when the drug was administered immediately after the session. While the contrast between the current findings and examinations of contingent tolerance with other species may appear to be evidence of a species difference in contingent tolerance to cocaine, it remains possible that experimental differences produced the differences in outcomes, rather than a species difference. Even though pigeons showed not contingent tolerance with the current experimental preparation and in the one other experiment that examined contingent tolerance to cocaine in pigeons (Pinkston & Branch, 2004), many experimental differences need to be considered before concluding that pigeons do not show contingent tolerance to cocaine. One potentiall y important variable in the development of contingent tolerance to cocaine is the length of the chronic drug regimen, which has varied across experiments. Experiments that have found contingent tolerance to cocaine have used chronic regimens ranging from 2 0 45 sessions (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978). Experiments that have found contingent tolerance to other psychoactive drugs have used chronic regimens ranging from 3 28 sessions (Campbell & Seiden, 1973; Carlton & Wolgin, 1971; Chen, 1968; Poulos et al., 1981; Wenger et al., 1981). The present set of experiments generally used 30

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106 sessions as the original length of the chronic regimen except for a few exceptions when 60 sessions were used, so the current re gimens were relatively long. Tolerance to drug effects is usually a product of repeated drug administration (Carlton, 1983; Wolgin, 1989); therefore a minimum of drug exposure is often necessary for the development of tolerance. In order for contingent tol erance to be observed, a particular length of chronic dosing may be required. Carlton and Wolgin (1971) found that seven days of chronic administration produced tolerance in subjects administered the drug pre session, but not for subjects administered the drug post session. Subjects in the Post pre group were then switched to pre session drug administration, which led to the development of tolerance. It is possible that tolerance from post session dosing may take longer to develop than tolerance from pre s ession administration. No experiments have examined this directly by systematically using different lengths of chronic regimens. The present set of experiments used chronic regimens of similar length but slightly longer than the average of those that have found contingent tolerance. Within the first 30 days of chronic administration, four of six subjects (36, 40, 592, 752) in the Pre post group in Experiment 1 developed tolerance. Key pecking rates were similar to saline vehicle control rates after 4 18 day s for these subjects, indicating that tolerance often develops quickly when cocaine is administered pre session. What has not been determined is exactly how long a chronic regimen must be to produce tolerance from post session cocaine administration. Being that previous experiments that found contingent tolerance to cocaine used chronic regimens ranging from 20 45 sessions (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978) it is possible that these chronic regimens were not long enough to capture the tolerance that may have developed had post session dosing continued. While the chronic regimens in the present set of experiments were 30 consecutive days, the

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107 chronic dose was actually administered over much longer span (a minim um of 24 additional administrations) while the dose response curve was redetermined, providing ample time for tolerance to develop. Consequently, it is possible that if shorter chronic drug regimens were used in the present set of experiments then continge nt tolerance may have been observed. Future experiments could manipulate the length of the chronic regimen for post session administration of cocaine to determine if the length of the chronic regimen is a factor in the development of contingent tolerance. Another variable that may be important in the development of contingent tolerance is the behavioral task employed. The behavioral task used has varied across experiments investigating contingent tolerance. Previous experiments that have found contingent to lerance to cocaine have used milk drinking (Bowen et al., 1993; Woolverton et al., 1978), lever pressing (Smith, 1990), nose poking (Smith, 1990), and key pressing (Branch & Sizemore, 1988) as the operant task. Both the present set of experiments and the s tudy by Pinkston and Branch (2004) used key pecking as the operant task. While key pecking is a prototypical operant task for pigeons ( Schwartz & Gamzu, 1977 ), it may not be equivalent to other operant tasks used with other species such as lever pressing in rats. Research showing that pigeons are more likely to key peck than treadle press when response independent food is presented (Green & Holt, 2003), and are more likely to peck a vertical than horizontal surface (Burns & Malone, 1992) suggests that key pecking in pigeons may be controlled by Pavlovian processes as well as operant contingencies. Some research has found that there are two topographically distinguishable types of key pecks. Mere response independent presentation of food engenders key pecks of short duration, whereas contingent food presentation maintains key pecks of longer duration (Schwartz, 1977; Schwartz & Williams,

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108 1972). This suggests that some key pecks are operant whereas others are respondent (Schwarz, 1977). Therefore pecking in pi geons is sometimes viewed as a Pavlovian rather than operant response. Another factor that may determine whether or not contingent tolerance develops is if the in pigeons is not a foraging related response (as opposed to pecking which is foraging related) and is sensitive to operant contingencies. Therefore treadle pressing for food in pigeons may be a more prototypical operant as compared to key pecking because treadle pressing is an arbitrary response that is not used by pigeons to obtain food in their natural environment. If the current set of experiments had been conducted with treadle pressing as the operant, a more prototypical operant than key pecking, it is possible that contingent tolerance may have been observed. Yet whether or not the operant task is foraging related may not be the key factor because contingent tolerance to cocaine has been found in rats with licking a spout as the operant task (Bowen e t al., 1993; Woolverton et al., 1978), which is a foraging related behavior. The operant task used, regardless of its relationship to foraging, may be the key factor. Therefore future studies could replicate Experiment 1 using treadle pressing as the opera nt task to investigate if the topography of the operant task is a factor in the development of contingent tolerance to cocaine. One limitation of the present set of experiments is that they did not point to a mechanism that prevented the development or exp ression of contingent tolerance or explain why tolerance from post session administration commonly developed. Due to the fact that previous experiments on contingent tolerance have all had procedural differences, it is difficult to determine which, if any procedural differences may be important factors in determining whether or not contingent tolerance develops. One variable that has changed across experiments investigating contingent

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109 tolerance is the schedule of reinforcement used. Contingent tolerance to cocaine has been found when using an FR 40 and FI 5 min schedule of reinforcement (Smith, 1990). Another experiment found contingent tolerance using a VR 2 (FR 3, 4, or 5: S) schedule of reinforcement (Branch & Sizemore, 1988). Several contingent tolerance experiments have used milk drinking as the operant, which is reinforced on an FR 1 if each lick is counted as a response (Bowen et al., 1993; Carlton & Wolgin, 1971; Poulos et al., 1981; Woolverton et al., 1978). The present set of experiments used an FR 20 schedule of reinforcement, and Pinkston and Branch (2004) used a mult FR 5 FR 100 schedule of reinforcement. While the few experiments that have found not contingent tolerance to cocaine used FR schedules of reinforcement (Pinkston & Branch, 2004; prese nt experiment), experiments that have found contingent tolerance have used a variety of schedules of reinforcement including FR (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978). Based on the reinforcement loss hypothesis, tolerance should have developed to effects of cocaine on pecking on an FR schedule when cocaine was administered pre session because cocaine initially decreased the amount of reinforcement obtained when administered pre session. The reinforcement loss hyp othesis also predicts that tolerance will not develop to effects of cocaine on key pecking on an FR schedule if cocaine is administered post session because initial post session administration of cocaine did not affect the amount of reinforcement obtained. Therefore the reinforcement loss hypothesis predicts that behavior under response dependent schedules of reinforcement should show contingent tolerance as long as the initial drug effect produces a reduction in reinforcement rate. An additional potential factor in the development of contingent tolerance is the context in which the drug is experienced. The present set of experiments found that neither eating nor key pecking under the effects of cocaine was necessary for tolerance to develop to effects of c ocaine

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110 during the behavioral session. When these behavioral factors were omitted and subjects were also not exposed to the experimental context during the chronic regimen in Experiment 3, subjects did not develop notable tolerance. That is, mere drug expos ure was not sufficient to result in notable tolerance. In Experiment 3 subjects were not exposed to the experimental context at all during chronic dosing. It is therefore possible that daily exposure to the experimental context during the chronic dosing re gimen is an important factor in the development of tolerance to effects of cocaine during the behavioral session. The present set of experiments, however, did not explicitly examine drug paired cues in the context (e.g., the room where injections were admi nistered, the experimental context in which the drug was experienced) that may have been involved in drug tolerance. Past research has shown that drug paired cues play a large role in determining whether or not tolerance will develop (Seigel, 1989). The re sults of the present set of experiments showed that experiencing drug effects in the experimental context was not necessary for tolerance to develop, but some regular exposure to the experimental context during chronic dosing was necessary for notable tole rance to develop. A future experiment could investigate the importance of the experimental context by replicating Experiment 3 except that during the chronic regimen, subjects would be placed in the operant chamber without consequences for key pecking. The results of this experiment compared to the results of Experiment 3 would help illuminate whether the context in which the drug is experienced is important. A comparison of the results of Experiments 1, 2, and 4 with Experiment 3 show that some factor (or factors) associated with behavioral sessions was (were) important in the development of tolerance. Subjects in Experiments 1, 2, and 4 usually developed tolerance when exposed daily to the experimental session even when given their chronic dose after the d aily session.

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111 Experiment 3 found that not exposing subjects to the experimental session during the chronic dosing regimen produced little tolerance. Therefore exposure to the experimental session may have been a key factor in the development of tolerance. Not identified in the present set of experiments was the frequency at which subjects need to be exposed to experimental sessions in order for tolerance to develop. Future experiments could examine if exposure to the experimental session every other day, or even once a week during the chronic dosing regimen is sufficient to produce tolerance. A further potentially important variable in the development of contingent tolerance is the association of drug administration and the behavioral session. During the ch ronic dosing regimens in Experiments 1, 2, and 4 it was always the case that either drug administration predicted the experimental session (pre session administration), or the experimental session predicted drug administration (post session administration) Therefore the drug administration and the behavioral session were always associated with each other, albeit at a substantial delay when the drug administration occurred an hour after the session. If drug administration could be completely disassociated w ith the behavioral session by administering the drug at random times with respect to the session during the chronic regimen it might prevent the development of tolerance. Future experiments investigating the association between drug administration and the behavioral session may illuminate if it is the association between the drug and the session that produces tolerance rather than the ability to engage in the target behavior while under effects of the drug. Another possibility is that the apparent tolerance from post session dosing was a product of some aspect of the experimental procedure other than post session administration. During Experiments 1, 2 and 4, subjects that were administered chronic cocaine post session were also

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112 given repeated exposure to th e drug pre session during dose response curve assessments. Intermittent pre session administration of cocaine was necessary to determine if tolerance had developed from post session dosing, but it is possible that the intermittent pre session exposure to t he drug produced tolerance rather than the chronic post session administration. A previous experiment examined the effects of repeated dose response curve assessments in the development of tolerance to cocaine in pigeons with acute doses administered at a variety of intervals. This experiment found that dose response curves were stable after eight determinations of the dose response curve indicating that tolerance is unlikely to develop during dose response curve assessment (Marusich & Branch, 2006). It was also the case that dose response curves within any particular phase of an experiment in the current set of experiments were relatively stable. Each dose response curve was determined a minimum of two times, so if intermittent pre session dosing produced s ome amount of tolerance, it would have been detected by a shift in the dose response curve while it was being determined, which did not happen. Therefore it is unlikely that the intermittent pre session administration of cocaine in the present set of exper iments contributed to the tolerance seen following chronic post session administration. The reinforcement loss hypothesis appears applicable as a reasonable account of what might occur when the drug is given pre session, but a major puzzle created by the current results concerns how experience during daily sessions could possibly interact with repeated post session drug administration. Tolerance was minimal when the drug was administered daily while no sessions were scheduled, but was consistently produce d when the same drug regimen, one administration per day, occurred when sessions were also held daily, an hour before the drug was given. No evidence of change in operant performance was evident during the period of daily drug administration, yet only when daily operant response sessions were conducted did tolerance

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113 consistently develop. One possibility is that the extra experience with the operant contingencies during the period of drug administration made the operant performance more resistant to the rate decreasing effects of cocaine, so the apparent tolerance was simply a result of more experience with the FR schedule. That possibility, however, is not consistent with the results of Experiments 1 and 4 in which in many cases extended experience resulted in no changes in dose response functions. Subjects in Experiments 1 and 4 had considerably more exposure to the FR contingency than subjects in Experiment 2 due to the length of the experiments, but subjects in Experiments 1 and 4 did not show more toleran ce on average than subjects in Experiment 2. Therefore there is no data from the current set of experiments to suggest that extended exposure to the FR schedule contributed to the development of tolerance. Future experiments could examine this factor by ex posing subjects to an FR contingency for a prolonged time, but without chronic dosing, and then redetermining the dose response curve to see if tolerance developed. pecking) occurred in Experiment 3 such that tolerance that had developed was canceled out by the lack of opportunity to peck under exposure to the operant contingency. That possibility, however, is difficult to reconcile with the fact that in Experiment 3 when the saline vehicle was administered daily during a 30 day hiatus from the operant contingencies no substantial changes In summary, the present set of experiments suggests that, under the conditions arranged, tolerance t o effects of cocaine during the behavioral session in pigeons was not dependent on drug administration prior to the behavioral session. The majority of subjects administered drug immediately after the session or 60 min after the session still developed tol erance to effects of cocaine during the behavioral session, indicating that it is not necessary for subjects to engage in

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114 the target behavior while under effects of the drug in order for them to develop tolerance to effects of the drug on the target behavi or. When behavioral factors were removed during the period of repeated administration (Experiment 3), subjects no longer reliably showed tolerance. Therefore some aspect of exposure to the experimental session or experimental context on a regular basis was necessary for tolerance to develop, yet this exposure did not have to occur while subjects were under effects of the drug. Although contingent tolerance to cocaine previously appeared to be a reliable finding (Bowen et al., 1993; Branch & Sizemore, 1988; Smith, 1990; Woolverton et al., 1978), results of the present experiment combined with those of Pinkston and Branch (2004) suggest that not contingent tolerance to cocaine is common in pigeons. These results therefore question the generality of contingent tolerance to cocaine. Even though research has found that it is common for humans to develop tolerance to many effects of cocaine ( Fischman, et al., 1985; Mendelson et al., 1998) none of that research has examined post session cocaine administration. Due to the paucity of data on contingent tolerance to cocaine in humans, it is not yet known if humans would show contingent tolerance to cocaine.

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115 LIST OF REFERENCES Bowen, S. E., Fowler, S. C., & Kallman, M. J. (1993). Effects of variation in chroni c dose of cocaine on contingent tolerance as assessed in a milk drinking task. Psychopharmacology 113, 67 75. Branch, M. N., & Sizemore, G. M. (1988). Behavioral tolerance to cocaine in squirrel monkeys: Acute and chronic effects on complex operant behavi or. Pharmacology, Biochemistry, & Behavior, 30, 737 748 Brown, P. L. & Jenkins, H. M. (1968). Auto peck. Journal of the Experimental Analysis of Behavior 11, 1 8. performance, and choice. Journal of the Experimental Analysis of Behavior, 58, 399 413. Campbell, J. C. & Seiden, L. S. (1973). Performance influence on the development of tolerance to amphetamine. Pharmacology, Biochemistry & Behavior 1, 703 708. Carlton, P. L. (1983). A Primer of Behavioral Pharmacology New York: W. H. Freeman & Co. Carlton, P. L. & Wolgin, D. L. (1971). Contingent tolerance to the anorexigenic effects of amphetamine. Physiology and Behavior 7, 221 223. Chen, C. S. (1968). A study of the alcohol tolerance effect and an introduction of a new behavioral technique. Psychopharmacologia, 27, 265 274. Diagnostic and Statistical Manual of Mental Disorders, 4 th Ed., 1994, American Psychiatric Association. Emmett Oglesby, M. W ., Peltier, R. L ., Depoortere, R. Y ., Pickering, C. L ., Hooper, M. L ., Gong, Y. H ., & Lane, J. D (1993). Tolerance to self administration of cocaine in rats: time course and dose response determination using a multi dose method. Drug and Alc ohol Dependence, 32, 247 256. Fischman, M. W. (1978). Cocaine and amphetamine effects on repeated acquisition in humans. Federation Proceedings 37, 618. Fischman, M. W., Schuster, C. R., Javaid, J., Hatano, Y., & Davis, J. (1985). Acute tolerance developm ent to the cardiovascular and subjective effects of cocaine. Journal of Pharmacology and Experimental Therapeutics 235, 677 682. Glowa, J. R. & Barrett, J. E. (1983). Response suppression by visual stimuli paired with postsession d amphetamine injections in the pigeon. Journal of the Experimental Analysis of Behavior, 39, 165 173. Green, L. & Holt, D. D. (2003). Economic and biological influences on key pecking and treadle pressing in pigeons. Journal of the Experimental Analysis of Behavior, 80, 43 58.

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116 Jo hanson, C. E. & Fischman, M. W. (1989). The pharmacology of cocaine related to its abuse. Pharmacological Reviews, 41, 3 52. Marusich, J. A. & Branch, M. N. (2006). Stability of cocaine dose response functions at different inter dose intervals. Pharmacolog y, Biochemistry, and Behavior 84 360 369. Marusich, J. A. & Branch, M. N. (2008). Differences in the behavioral time course of effects of rate increasing and rate decreasing doses of cocaine in pigeons. Pharmacology, Biochemistry, & Behavior 89 150 159 Miller, M. L. & Branch, M. N. (2004). Tolerance to response disruptive effects of cocaine is facilitated by opportunity to respond in the absence of drug. Pharmacology, Biochemistry, and Behavior 79, 43 54. Mendelson, J. H., Sholar, M., Mello, N. K., Te oh, S. K., & Sholar, J. W. (1998). Cocaine Tolerance: Behavioral, Cardiovascular, and Neuroendocrine Function in Men. Neuropsychopharmacology, 18, 263 271. Palya, W. L., Walter, D. E., & Chu, J. Y. M. (1995). An inexpensive 1 millisecond experiment control interface for IBM PCs and its user friendly control language. Behavior, Research Methods, Instruments, & Computers, 27, 129 30. Pinkston, J. W. & Branch, M. N. (2004). Repeated post or presession cocaine administration: Roles of dose and fixed ratio sche dule. Journal of the Experimental Analysis of Behavior, 81, 169 188. Poulos, C. X., Wilkinson, D. A., & Cappell, H. (1981). Homeostatic regulation and Pavlovian conditioning in tolerance to amphetamine induced anorexia. Journal of Comparative and Physiolog ical Psychology 95, 735 746. Schuster, C. R., Dockens, W. S., & Woods, J. H. (1966). Behavioral variables affecting the development of amphetamine tolerance. Psychopharmacologia 9, 170 182. Schwartz, B. (1977). Studies of operant and reflexive key pecks in the pigeon. Journal of the Experimental Analysis of Behavior, 27, 301 313. Schwartz, B. & Gamzu, E. (1977). Pavlovian control of operant behavior: An analysis of autoshaping and its implications for operant conditioning. In Honig, W. K. & Staddon, J. E. R. (Eds.) Handbook of Operant Behavior (pp. 53 97). Englewood Cliffs, NJ: Prentice Hall. Schwartz, B. & Williams, D. R. (1972). Two different kinds of key peck in the pigeon: some properties of responses maintained by negative and positive response reinfo rcer contingencies. Journal of the Experimental Analysis of Behavior, 18, 201 216. Sidman, M. (1960). Tactics of Scientific Research. New York: Basic Books.

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117 Siegel, S. (1989). Pharmacological conditioning and drug effects. In Goudie, A. J. & Emmett Oglesby M. W. (Eds.) Psychoactive Drugs: Tolerance and Sensitization (pp. 115 180). New Jersey: Humana Press. Skinner, B. F. (1953). Science and Human Behavior New York: The Free Press. Smith, J. B. (1986). Effects of chronically administered d amphetamine on spaced responding maintained under multiple and single component schedules. Psychopharmacology 88, 296 300. Smith, J. B. (1990). Situational specificity of tolerance to decreased operant responding by cocaine. Pharmacology, Biochemistry, and Behavior 36, 473 477. Stewart, J. & Badiani, A. (1993). Tolerance and sensitization to behavioral effects of drugs. Behavioural Pharmacology 4, 289 312. Wenger, J. R., Tiffany, T. M., Bombardier, C., Nicholls, K., & Woods, S. C. (1981). Ethanol tolerance in the rat i s learned. Science 213, 575 577. Wolgin, D. L. (1989). The role of instrumental learning in behavioral tolerance to drugs. In Goudie, A. J. & Emmett Oglesby, M. W. (Eds.) Psychoactive Drugs: Tolerance and Sensitization (pp. 17 114). New Jersey: Humana Pre ss. Wolgin, D. L. & Hertz, J. M. (1995). Effects of acute and chronic cocaine on milk intake, body weight, an activity in bottle and cannula fed rats. Behavioural Pharmacology 6, 746 753. Woolverton, W. L., Kandel, D., & Schuster, C. R. (1978a). Toleran ce and cross tolerance to cocaine and d amphetamine. Journal of Pharmacology & Experimental Therapeutics 205, 525 535.

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118 BIOGRAPHICAL SKETCH Julie Marusich grew up in Washington State, where she attended Washington State University for her undergra duate education. There, she was first exposed to behavior analysis and behavioral pharmacology under the direction of Dr. Frances McSweeney. Julie completed her Bachelor of Science degree in 2002. She then continued her education at the University of Flori da under the tutelage of Dr. Marc Branch. There, she continued her studies in behavior analysis and behavioral pharmacology. Julie received her Master of Science degree in 2005 and her PhD in 2008, both from the University of Florida. In the future, Julie plans to continue conducting research in behavioral pharmacology and serve as a faculty member in a university setting.