Neurobiological Mechanisms Involved in MDMA-Seeking Behaviour and Relapse M. Juliana Orejarena PhD thesis Barcelona, 2010 Neurobiological Mechanisms Involved in MDMA-Seeking Behaviour and Relapse Maria-Juliana Orejarena Serrano Memoria` presentada per optar al grau de Doctor en Biologia per la Universitat Pompeu Fabra. Aquesta Tesi Doctoral ha estat realitzada sota la direccio´ de la Dra. Patricia Robledo i del Dr. Rafael Maldonado al Departament de Ciencies` Experimentals i de la Salut de la Universitat Pompeu Fabra Barcelona, 2010 A mi mama y mis hermanas, A Karolos Contents Contents vii List of Figures ix Abstract xi Resumen xiii 1 Introduction3 1.1 Motivation and Reward ..................... 3 1.1.1 The Brain Reward Pathways .............. 4 1.1.2 Role of Dopamine in Reward.............. 6 1.1.2.1 The Hedonic Hypothesis........... 6 1.1.2.2 The Learning Hypothesis........... 7 1.2 Drug Addiction.......................... 10 1.2.1 Theories of Drug Addiction............... 13 1.2.1.1 The Opponent Process Theory . 13 1.2.1.2 The Allostasis Theory............. 14 1.2.1.3 The Incentive Sensitization Theory . 16 1.2.2 Neurocircuitry of Addiction............... 17 1.3 Animal Models of Addiction .................. 22 1.3.1 Intra-Cranial Self Stimulation ............. 22 1.3.2 Conditioned Place Preference ............. 23 1.3.3 Operant Intravenous Drug Self-administration . 24 1.3.3.1 Acquisition................... 26 1.3.3.2 Extinction.................... 28 1.3.3.3 Reinstatement to Drug Seeking Behaviour . 29 1.3.3.4 The Yoked Control-Operant Paradigm . 29 1.3.4 Complementary Biochemical and Genetic Methods Used in Our Studies ................... 31 1.3.4.1 Microarray................... 31 1.3.4.2 Microdialysis.................. 34 1.4 MDMA............................... 35 vii viii CONTENTS 1.4.1 History........................... 36 1.4.2 Pharmacodynamics.................... 37 1.4.3 Pharmacokinetics and Neurotoxicity.......... 38 1.4.4 Abuse and Addiction .................. 42 1.4.5 Use Pattern: Relevance of Acute and Chronic Toler- ance ............................ 43 1.4.6 Acute Pharmacological Effects in Humans . 46 1.4.7 Acute Pharmacological Effects in Animals . 47 1.5 Mechanisms Involved in MDMA Reinforcement and Relapse 49 1.5.1 Participation of the Dopaminergic System . 49 1.5.2 Participation of the Serotonergic System . 50 1.5.2.1 5-HT2A Receptors............... 51 1.5.2.2 5-HT2AR: Structure, Second Messenger Ac- tivation Pathway and Distribution in the Brain 51 1.5.2.3 5-HT2AR Modulation of Dopamine . 54 1.5.2.4 5-HT2AR and MDMA-Induced Reinforcement .......................... 55 1.6 Neuroadaptive Changes Following Active versus Passive Drug- Administration .......................... 57 1.6.0.5 Gene Expression Changes .......... 58 1.6.0.6 Changes in Dopamine ............ 60 1.6.0.7 Changes in Receptor Binding Sites . 62 2 Working Hypothesis 67 3 Objectives 69 4 Results 73 4.1 Article 1, Trigo et al 2009..................... 73 4.2 Article 2, Orejarena et al 2009 .................. 81 4.3 Article 3, Fernandez-Castillo` et al 2009 (submitted) . 92 4.4 Article 4, Orejarena et al 2010 (submitted) . 124 5 Discussion 165 5.1 Passive versus Active MDMA Administration . 165 5.2 Involvement of 5-HT2AR in MDMA-Induced Reinforcement 172 5.3 Involvement of 5-HT2AR in Relapse to MDMA-Seeking Be- haviour............................... 175 6 Conclusions 181 References 213 Acknowledgements 215 Appendices 217 A Supplementary Material for Article 3 219 B Supplementary Material for Article 4 241 C List of Abbreviations 249 Index 255 Glossary 255 List of Figures 1.1 Brain Reward Pathways..................... 5 1.2 Opponent-Process Theory.................... 14 1.3 Allostasis Theory......................... 15 1.4 The Spiralling Distress Cycle of Addiction........... 15 1.5 Neurocircuitry of Addiction................... 18 1.6 Conditioned Place Preference Paradigm............ 23 1.7 The Yoked Control-Operant Paradigm............. 30 1.8 Microarray Expression Analysis................. 32 1.9 Microdialysis ........................... 34 1.10 MDMA Structure and Steroisomers............... 35 1.11 Pathways of MDMA Metabolism in Rats and Humans. 39 1.12 5-HT2AR Second Messenger Activation Pathway . 52 1.13 CNS distribution of the 5-HT2AR................ 53 1.14 5-HT2AR Modulation of Dopamine............... 55 1.15 Gene Expression Changes in Active vs Passive Drug Admin- istration............................... 61 5.1 Heat Map: Active vs Passive MDMA Administration . 169 ix Abstract (+) 3,4-methylenedioxymethamphetamine (MDMA), commonly known as “ecstasy”, is currently a highly consumed drug with liability to produce ad- diction in some individuals. MDMA induces unique psychoactive effects that clearly distinguish it from hallucinogenic or psychostimulant drugs. MDMA mainly enhances the activity of both the serotonergic and the do- paminergic system in the mesolimbic brain reward pathways. However, the neurobiological mechanisms underlying its possible addictive prop- erties are still not fully understood. In the present work, we have con- tributed to this subject by establishing that the serotonin 5-HT2A receptor, in contrast to what has been observed for other drugs of abuse, is critical for MDMA-induced reinforcement. Moreover, the pharmacological block- ade of this receptor can prevent cue-induced relapse. This effect is pos- sibly mediated by its excitatory control over basal and MDMA-induced increase in midbrain dopamine, as supported by our microdialysis data. Furthermore, we have also shown that MDMA can act as an interocep- tive cue to induce relapse to cocaine-seeking behaviour. Additionally, we demonstrated differential changes at the level of the dopaminergic brain reward pathway and gene expression changes in different brain areas, fol- lowing self-administered MDMA in comparison to passive administration. These results underpin the impact of a learning component in the reward- ing/reinforcing properties of MDMA, and provide new evidence for the serotonergic involvement in MDMA-seeking behavior and relapse. xi xii Abstract Resumen (+) 3,4-metilendioximetanfetamina (MDMA), popularmente conocida como “´extasis”, es una droga susceptible de producir adiccin en algunos individuos. Actualmente es consumida principalmente por adolescentes y jovenes.´ Los particulares efectos psicoactivos inducidos por la MDMA, permiten distinguirlo de manera clara de otros psicoestimulantes o com- puestos alucinogenos.´ Esta droga actua´ principalmente activando el sis- tema dopaminergico´ y serotonergico´ en los circuitos neurales de placer. Sin embargo, los mecanismos neurobiologicos´ implicados en las propiedades adictivas de esta droga no han sido aun´ esclarecidos. El trabajo presentado en esta Tesis Doctoral ha puesto de manifiesto algunos aspectos claves de estos procesos que eran desconocidos hasta el momento. Hemos encontrado que el receptor de serotonina 5-HT 2A par- ticipa de forma cr´ıtica en las propiedades reforzantes de la MDMA, con- trario a lo observado en el caso de otros psicoestimulantes. Ademas,´ el blo- queo farmacologico´ de este receptor puede prevenir la reinstauracion´ de la busqueda´ de la MDMA, desencadenada por un est´ımulo o clave previa- mente asociado a su consumo. Estos efectos pueden ser debidos al bloqueo del control excitatorio que normalmente ejercen estos receptores sobre los niveles de dopamina en estructuras mesol´ımbicas, como ha sido revelado en nuestros estudios de microdialisis.´ Hemos demostrado tambien´ que la MDMA puede actuar como clave interoceptiva y desencadenar la reca´ıda a la busqueda´ y consumo de coca´ına. Adicionalmente, nuestros estudios han mostrado que tanto la activacion´ del sistema dopaminergico´ mesol´ımbico, como los cambios en la expresion´ genica´ en diferentes areas´ cerebrales que ocurren tras la administracion´ de la MDMA, dependen de si el sujeto par- ticipa de manera activa en el consumo de esta droga, o si por el contrario xiii xiv Resumen la recibe de forma pasiva. En conclusion,´ este trabajo resalta la importancia de los procesos de aprendizaje y memoria sobre las propiedades reforzantes/recompensantes de la MDMA. Ademas,´ nuestras investigaciones aportan nuevas eviden- cias en relacion´ a la participacion´ del sistema serotonergico´ en la busqueda´ y reca´ıda al consumo de esta droga. Resumen 1 2 Resumen CHAPTER 1 Introduction 1.1 Motivation and Reward Motivation is an internal response of an individual that is the sum re- sult of a variety of neurophysiological factors that initiate, sustain and di- rect behaviour. In its most primary form, it involves homeostatic processes related to hunger, thirst and temperature regulation. Homeostasis occurs thanks to coordinated and self-regulated processes, that allow an organ- ism to achieve a dynamic equilibrium and maintain stability while adjust- ing to changing conditions. The result of these homeostatic processes are instances of motivation, called drive states. Drive states are characterized by tension and discomfort due to a physiological need followed by relief when that need is satisfied. They are related to activities that enhance sur- vival or will ultimately support a given level of reproductive success such as eating, drinking and sexual behaviour. Thus, rewarding stimuli are now recognized as hedonic incentives, causing neural representations that elicit motivation and goal pursuit (Kandel, 2000). This, in turn, has resulted in the evolution of an oriented sequence of behaviours either toward specific 3 4 1. Introduction