EFFECTS OF SEX AND PRENATAL STRESS ON VULNERABILITY TO DRUGS by Mark B. Thomas A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Psychology) in The University of Michigan 2012 Doctoral Committee: Professor Jill B. Becker, Chair Professor Margaret E. Gnegy Professor Theresa M. Lee Professor Terry E. Robinson 1 © Mark B. Thomas 2012 i To my parents, who surely sacrificed many of their dreams through the years to provide me with the resources to pursue my own. It is my dad in particular that I have thought of most during the writing of this dissertation. Sadly, he has been battling terminal cancer for the majority of this process. Though I know he would never let me, I would gladly trade in all of my accomplishments for a cure. ii ACKNOWLEDGEMENTS I wish to thank Dr. Jill Becker for the invaluable guidance she has provided during my graduate studies. Without her unwavering support, none of the work described here would have been possible. My other committee members, Dr. Terry Robinson, Dr. Theresa Lee, and Dr. Margaret Gnegy, also deserve special recognition. All provided insightful comments that played a critical role in the preparation of this dissertation. Lastly, just as I am indebted to members of the committee, I also wish to thank Dr. Seema Bhatnagar for first sparking my interest in pursuing a research career. Despite moving to a different university, she has continued to play an active role in my development, and has directly contributed to some of the work presented here. iii TABLE OF CONTENTS DEDICATION ………………………………………………………………...……...…ii ACKNOWLEDGEMENTS …………………………………………………...……….iii LIST OF FIGURES ……………………………………………………………...……vii LIST OF TABLES ………………………………………………….…………………..x LIST OF APPENDICES ………………………………………………………………vi CHAPTER I. INTRODUCTION ………………………………………………………….…1 1. Fetal programming …………………………………………………3 1.1. “Fetal origins” hypothesis …………..…..……………......…3 1.2. Rodent models of prenatal undernourishment …..……....3 1.3. Prenatal stress in humans ……………….………………....5 1.4. Preclinical models of prenatal stress ………….……...…...6 1.5. The influence of PS on reproductive behaviors ………….7 2. Rat neural development ………………………………………..…9 2.1. Embryonic period ……………………….…………………...9 2.2. Fetal period ………….…………………………………...…10 2.3. Striatal development – dorsal component ………..…..…11 2.4. Striatal development – ventral component ……….…......11 2.5. Striatal development – dopamine receptors ………….…12 3. Stress regulation ……………………………………………...…..14 3.1. The hypothalamic-pituitary-adrenal (HPA) axis ………...14 3.2. Ontogeny of corticoid receptors …..…………………..….16 3.3. The influence of PS on HPA axis activity …..………..….17 3.4. Prenatal and postnatal components of PS ….……….....19 4. Drug addiction ………………………………………………….....21 iv 4.1. Definition and symptomology …..……………………...….21 4.2. Mechanisms of drug addiction ………………….……...…22 4.3. Preclinical paradigms of drug abuse and addiction vulnerability…...…………………………………..………......24 4.3.1. Operant self-administration …………………….…..24 4.3.1.1. Acquisition ………………………….…………..25 4.3.1.2. Maintenance …………………………..…….....25 4.3.1.3. Reinstatement …………………….……………26 4.3.2. Non-operant self-administration of ethanol ..…..…27 4.3.3. Drug-induced sensitization ……………….…...…...29 4.3.4. Conditioned place preference (CPP) ……...……...29 4.4. Individual differences in drug addiction ……….…….......29 4.5. Sex differences in drug abuse and addiction ….…….....30 4.6. Prenatal stress and drug responsiveness …..………..…36 5. Specific aims …………………………………………………...…38 II. SEX-SPECIFIC EFFECTS OF PRENATAL STRESS ON STEADY- STATE EXTRACELLULAR DOPAMINE IN THE NUCLEUS ACCUMBENS AND DORSAL STRIATUM …………………………...44 Introduction …………………………………………………………………....44 Methods ………………………………………………………………………..47 Results …………………………………………………………………………52 Discussion ……………………………………………………………………..53 III. SEX-SPECIFIC SUSCEPTIBILITY TO COCAINE IN RATS WITH A HISTORY OF PRENATAL STRESS …………...……...…………………..61 Introduction …………………………………………………………...……….61 Methods ………………………………………………...……………………..62 Results ……………………………………………………...…………………68 Discussion …………………………………………………...…………....…..72 IV. SEX DIFFERENCES IN PRENATAL STRESS EFFECTS ON COCAINE PURSUIT …………………………..………..……………...84 Introduction ……………………………………………………………...….…84 v Methods ………………………………………………………………………..86 Results ………………………………………....………………………………91 Discussion ……………………………………………………………………..94 V. CONCLUSIONS ………………………………………………………...106 1. Summary of findings and working hypotheses ……………...106 2. Possible mechanisms responsible for sex-dependent effects of PS ………………………………………………………………...108 3. Conclusions and overall hypothesis ……...…………………..114 APPENDICES ……………………………………………………………….118 REFERENCES ………………………………………………………………134 vi LIST OF FIGURES Figure 1.1 Approximate timeline of early-life neurogenesis for a selection of rat brain regions, based on and modified from the work of Bayer et al. (1993) ….…41 1.2 Schematic representation of the factors implicated in rat HPA axis regulation …………………………….………….…………………………..……42 1.3 Hormonal fluctuations across the female rat’s 4-day estrous cycle ……….43 2.1 Mean (+ SEM) steady-state extracellular dopamine (DA) concentrations in the nucleus accumbens (a; NAc) and dorsal striatum (b) of females with (PS) and without (No PS) a history of prenatal ……………………………….56 2.2 The mean (+ SEM) slope of the curve used to determine extracellular dopamine concentrations in the nucleus accumbens (a; NAc) and dorsal striatum (b) of females with (PS) and without (No PS) a history of prenatal stress ………………………………………………………...………………...…57 2.3 Mean (+ SEM) steady-state extracellular dopamine (DA) concentrations in male and female rats with (PS) and without (No PS) a history of prenatal stress …………………………………………………………………………......58 2.4 The mean (+ SEM) slope of the curve used to determine extracellular dopamine concentrations in males and females (oil and estradiol-treated subjects combined) with (PS) and without (No PS) a history of prenatal stress ………………………………………………………..…………………….59 3.1 Mean (± SEM) amount of cocaine (mg/kg/session/week) self-administered at a constant low dose (0.2 mg/kg/infusion) by male (a) and female (b) rats with (PS; male n = 14; female n = 15) and without (No PS; male n = 9; female n = 9) a history of prenatal stress ………………………………….....76 3.2 Figure 3.2 Mean (+ SEM) amount of cocaine (0.2 mg/kg dose) per session self-administered across the entire 3-week study ………………………...…77 vii 3.3 Mean (+ SEM) number of 1-hour sessions of self-administration needed for male and female rats with (PS; male n = 14; female n = 15) and without (No PS male n = 9; female n = 9) a history of prenatal stress to acquire self- administration at a constant low dose (0.2 mg/kg/infusion) of cocaine …...78 3.4 Mean (± SEM) amount of cocaine (mg/kg/session) self-administered at all three drug doses ………………………………………………………………...79 3.5 The rate of acquisition on the escalating-doses regimen of self- administration …………………………………………………………...…….…80 3.6 The mean peak (± SEM) in distance traveled during session 1 of locomotor recording ………………………………………………………………………….81 3.7 The summed peaks in distance traveled after the first 2 injections of cocaine (5 and 10 mg/kg; a, c) or saline (1 ml/kg; b, d) during sessions 1 and 12 for rats subjected to prenatal stress (PS) or no prenatal stress (No PS) …………………………………………………………………………...82 3.8 The percentage of each group exceeding a 125% increase in stereotyped head movements from session 1 to 12 in response to the final injection of cocaine (20 mg/kg) or saline (1 ml/kg) ………………………………………..83 4.1 The inter-infusion interval (III; mean ± SEM) of male and female rats for each of the first 9 self-administration sessions …….………….……………..97 4.2 The mean (+ SEM) inter-infusion interval (III) of male and female rats with (PS) and without (No PS) a history of prenatal stress during session 34 of self-administration testing ………………..………………………………….....98 4.3 Drug seeking in the absence of reinforcement, as measured by active nose pokes during periods of signaled drug inaccessibility (“no drug” active pokes) ……...…………………………………………………………….……….99 4.4 Motivation for cocaine, as determined by breaking point (BP) scores on a progressive ratio (PR) schedule ……………………………………………...100 4.5 The mean (+ SEM) breaking point (BP) score of males and females with (PS) and without (No PS) a history of prenatal stress, following a natural log (ln) transformation ……………………………………….……………….........101 4.6 Overall severity of drug pursuit, as indicated by the sum of normalized viii scores for 3 addiction-like traits ………………………………………………102 4.7 The percentage of each group that was positive for 0, 1, 2, and 3 addiction-like traits ……………………………………………………………..103 4.8 The number of addiction-like traits satisfied by rats that did (n = 8) and did not (n = 66) develop a “bursting” pattern of cocaine intake …………...….104 5.1 The hypothesized relationship between maternal stress (Mat. Stress), pup- directed licking/grooming (LG) bouts, and males’ drug seeking in the absence of reinforcement (“no drug” active pokes) ………………...…......116 5.2 An overview of changes in sexual dimorphisms as a consequence of prenatal stress (PS) ………………………………………………………...…117 ix LIST OF TABLES Table 2.1 A comparison of litters derived from repeatedly-stressed (Stress; n = 9) and non-stressed (No Stress; n = 10) mothers ………………………………60 4.1 A comparison of litters derived from repeatedly-stressed (Stress; n = 13) and non-stressed (No Stress; n = 12) mothers …………………………….105 x LIST OF APPENDICES Appendix