Western University Scholarship@Western Electronic Thesis and Dissertation Repository 6-21-2012 12:00 AM Neuroplasticity in the Mesolimbic System Induced by Sexual Experience and Subsequent Reward Abstinence Kyle Pitchers The University of Western Ontario Supervisor Lique M. Coolen The University of Western Ontario Graduate Program in Anatomy and Cell Biology A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Kyle Pitchers 2012 Follow this and additional works at: https://ir.lib.uwo.ca/etd Recommended Citation Pitchers, Kyle, "Neuroplasticity in the Mesolimbic System Induced by Sexual Experience and Subsequent Reward Abstinence" (2012). Electronic Thesis and Dissertation Repository. 592. https://ir.lib.uwo.ca/etd/592 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. NEUROPLASTICITY IN THE MESOLIMBIC SYSTEM INDUCED BY SEXUAL EXPERIENCE AND SUBSEQUENT REWARD ABSTINENCE (Spine Title: Sex, Drugs and Neuroplasticity) (Thesis Format: Integrated Article) By Kyle Kevin Pitchers Graduate Program in Anatomy and Cell Biology A thesis submitted in partial fulfillment of the requirements for degree of Doctor of Philosophy The School of Graduate and Postdoctoral Studies The University of Western Ontario London, Ontario, Canada © Kyle K. Pitchers, 2012 THE UNIVERSITY OF WESTERN ONTARIO SCHOOL OF GRADUATE AND POSTDOCTORAL STUDIES CERTIFICATE OF EXAMINATION Supervisor Examiners Dr. Lique Coolen Dr. Steven Laviolette Dr. Marco Prado Dr. Stan Leung Dr. John Yeomans The thesis by Kyle Kevin Pitchers entitled: Neuroplasticity in the mesolimbic system induced by sexual experience and subsequent reward abstinence is accepted in partial fulfillment of the requirements for degree of Doctor of Philosophy Date Chair of the Thesis Examination Board ii ABSTRACT Drugs of abuse are hypothesized to usurp brain reward circuits by causing neuroplasticity that contributes to the development and expression of addiction. However, little is known about how these brain circuits are altered in response to natural reward experience. Using male rodent sexual behavior, the goal of my thesis was to determine whether natural reward experience produces neural alterations in the mesolimbic dopamine system, that in turn, regulate incentive motivation for natural as well as drug reward. First, it was determined that male rat sexual experience causes facilitation of sexual behavior, sensitized amphetamine reward, and increased dendritic spines in the nucleus accumbens (NAc). Second, it was found that levels of the transcription factor deltaFosB were increased by sexual experience in several reward-related brain regions, notably the NAc. Blocking deltaFosB activity in the NAc using viral vector-mediated gene transfer attenuated long-term effects of sexual experience on sexual behavior, drug reward, and dendritic spines on NAc neurons. Then, we determined that NAc deltaFosB accumulation and sensitized drug reward caused by sexual experience were dependent on D1, but not D2, dopamine receptor activation during mating. Next, we demonstrated sex experience- induced neuroplasticity in the ventral tegmental area, consisting of an immediate but transient decrease in soma size of dopamine neurons, and reduced tonic dopamine input to NAc. This reduction in soma size was shown to be dependent on endogenous opioids, and critical for morphine reward tolerance, facilitation of sexual behavior, deltaFosB accumulation in the NAc, and mating cue-induced neuronal activity. Finally, sexual experience was found to cause short and long-term increases in NNMDA and AMPA receptor subunit expression/trafficking respectively. Moreover, sexual experience caused iii an immediate and long-lasting reduction in AMPA/NMDA ratio of synaptic currents in PFC-responding NAc shell neurons. Together, these studies begin to fill an important gap in our knowledge concerning the molecular/cellular basis for natural reward and extend our understanding of the underlying mechanisms of substance abuse. Keywords: sexual behavior, neuroplasticity, deltaFosB, endogenous opioid, mesolimbic, nucleus accumbens, ventral tegmental area, medial prefrontal cortex, dopamine, glutamate, dendritic spines, substance abuse, psychostimulant, opiate, reward memory, incentive motivation. iv CO-AUTHORSHIP Chapter 1 entitled “Mixing pleasures: Review of the effects of drugs on sexual behavior in humans and animal models” was written by Kyle K. Pitchers and Karla S. Frohmader with inputs by Dr. Lique M. Coolen, experimental data included was completed by Kyle K. Pitchers, Karla S. Frohmader, and Margaret E. Balfour. Chapter 2 entitled “Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence” was written by Kyle K. Pitchers with inputs by all co-authors. Study design was by Kyle K. Pitchers and Dr. Lique M. Coolen with intellectual input by Drs. Neil M. Richtand, Lei Yu, and Michael N. Lehman. Experimental procedures and data analysis were performed by Kyle K. Pitchers and Margaret E. Balfour. Chapter 3 entitled “deltaFosB in the nucleus accumbens is critical for reinforcing effect of sexual reward” was written by Kyle K. Pitchers with input by all co-authors. Study design was by Kyle K. Pitchers and Dr. Lique M. Coolen with intellectual input by Drs. Michael N. Lehman and Eric J. Nestler. Experimental procedures and data analysis were performed by Kyle K. Pitchers and Karla S. Frohmader. Drs. Vincent Vialou and Eric J. Nestler, and Ezekiell Mouzon provided experimental tools (viral vectors). Chapter 4 entitled “DeltaFosB and dopamine receptor activity in the nucleus accumbens is critical for increased amphetamine reward and nucleus accumbens spine density following loss of natural reward in sexually experienced male rats” was written by Kyle K. Pitchers with input by all co-authors. Study design by Kyle K. Pitchers and Dr. Lique M. Coolen with intellectual input by Drs. Michael N. Lehman and Eric J. Nestler. Experimental procedures and data analysis were performed by Kyle K. Pitchers. Drs. Vincent Vialou and Eric J. Nestler provided viral vectors. Chapter 5 entitled “Endogenous opioid- v induced neuroplasticity of dopaminergic neurons in the ventral tegmental area mediates reinforcement of natural reward” was written by Kyle K. Pitchers with input by all co- authors. Study design was by Kyle K. Pitchers, Caroline M. Coppens, and Dr. Lique M. Coolen. Experimental procedures and data analysis were performed by Kyle K. Pitchers, Caroline M. Coppens, Jonathan Fuller, Sandy Van, and Karla S. Frohmader. Chapter 6 entitled “Natural reward experience alters AMPA and NMDA receptor distribution and function in the nucleus accumbens” was written by Kyle K. Pitchers with inputs by all co-authors. Study design by Kyle K. Pitchers and Dr. Lique M. Coolen with intellectual input by Drs. Susanne Schmid, Michael N. Lehman and Steven R. Laviolette, and Andrea Di Sebastiano. Experimental procedures and data analysis were performed by Kyle K. Pitchers, Xu Wang, Andrea R. Di Sebastiano, and Dr. Susanne Schmid. vi ACKNOWLEDGEMENTS First and foremost, I would like to thank my supervisor, Dr. Lique Coolen, for being a great mentor, teacher, friend, and sometimes even lab partner. She pushed me to be a better scientist every day. I am grateful for all her valuable advice, her enthusiasm, and her passion for research. My admiration for her cannot be overstated. I can only hope one day to be half the supervisor she has been (and continues to be) to me. I would also like to thank members of my advisory committee, Drs. Michael Lehman, Walter Rushlow, and Stephen Ferguson, for their advice and support throughout the progression of my degree. One of the main reasons I loved working in the Coolen laboratory was the people that comprised it. I would like to thank former and present members of the Coolen and Lehman laboratories for creating a great work environment. I especially want to thank Karla ‘K Fro’ Frohmader, Roberto Caratun, Ricky Baby Baltazar, Ian ‘Spider’ Webb, Mandrea Di Sebastiano, Xu Wang, and Cleusa De Oliveira for all of their help and friendship over the years. I cannot imagine better group of people to work with. On a personal level, I am grateful for all the love and support I have received from my family and friends. Thank you very much. vii TABLE OF CONTENTS TITLE i ABSTRACT iii CO-AUTHORSHIP v ACKNOWLEDGEMENTS vii TABLE OF CONTENTS viii LIST OF TABLES xv LIST OF FIGURES xvi LIST OF APPENDICES xviii LIST OF ABBREVIATIONS xix CHAPTER 1: INTRODUCTION Mixing pleasures: Review of the effects of drugs on sexual behavior in humans and animal models 1.1 INTRODUCTION 2 1.2 Animal studies: Sexual performance and motivation 2 1.2.1 Psychostimulants 3 1.2.2 Opiates 9 1.3 Brain sites of drug action 10 1.3.1 Mesolimbic system 11 1.3.2 Neural activation by sex and drugs in the mesolimbic system 21 1.3.3 Drug-induced neuroplasticity in the mesolimbic system 22 1.3.4 Effects of experience on the locomotor-inducing effects of 24 amphetamine 1.3.5 Effects of sexual experience on drug reward 25 1.4 SUMMARY 26 1.5 THESIS RATIONALE AND OBJECTIVES 26 1.5.1 Rationale 27 1.5.2 Hypothesis 27 1.5.3 Objectives 27 1.6 REFERENCES 29 viii CHAPTER 2: Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence