The orexins and appetitive motivation in the rat Shaun Khoo A thesis in fulfillment of the requirements for the degree of Doctor of Philosophy School of Psychology Faculty of Science July 2017 PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Khoo First name: Shaun Other name/s: Yon-Seng Abbreviation for degree as given in the University calendar: PhD School: Psychology Faculty: Science Title: The orexins and appetitive motivation in the rat Abstract 350 words maximum: (PLEASE TYPE) Addiction is a chronic relapsing disorder characterised by compulsive drug seeking that persists despite adverse consequences. One popular, and widely heralded therapeutic target, is the orexin system, a hypothalamic neuropeptide system involved in arousal, appetite and reward. The motivational activator theory, the first coherent account of orexin’s role in appetitive motivation, predicts that orexin contributes to appetitive behaviour, including drug seeking, when the reinforcer is highly salient, available under a high unit-cost, or when reward seeking cue- driven. The present study used the dual orexin receptor antagonist, TCS 1102, a commercially available compound related to the clinically approved insomnia drug, suvorexant. TCS 1102 was administered intracerebroventricularly to rats trained to self-administer food, 4% alcohol beer or intravenous nicotine in a variety of self-administration and relapse-like paradigms. While TCS 1102 was able to reduce orexin-A-induced increases in consumption of normal grain pellets, it did not affect FR1, FR5, or FR10 self-administration of palatable food or cue+prime reinstatement of palatable food seeking. Orexin neuron activation measured by c-Fos/orexin-A immunohistochemistry showed that while orexin neurons were robustly recruited under behavioural testing conditions, there was no specific activation of these neurons during cue-induced reinstatement. For alcoholic beer self-administration, TCS 1102 did not affect FR1 self-administration or reacquisition of alcoholic beer. For nicotine self adminstration, FR1 self-administration, cue- induced and nicotine-primed reinstatement was not affected by TCS 1102. However, there was a small, transient effect on cue+prime nicotine reinstatement after a chronic, but not brief, period of self-administration. These results show that TCS 1102 is not effective in reducing appetitive motivation for palatable food, alcoholic beer or nicotine. Moreover, orexin neurons may be recruited by operant or appetitive contexts, but may not be necessary for appetitive motivation. This is the first time that the effects of a dual orexin receptor antagonist have been examined over a range of conditions of reinforcement in accordance with specific predictions of the motivational activator theory. Furthermore, these results suggest that orexin receptor antagonism is unlikely to be an effective addiction pharmacotherapy. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. 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Table of Contents Acknowledgements ........................................................................................................... ii Abbreviations ................................................................................................................... iii List of Figures ................................................................................................................. vii List of Tables ................................................................................................................... ix Chapter 1. Introduction ..................................................................................................... 1 1. The Orexin/Hypocretin System ................................................................................. 3 2. The Orexins and Animal Models of Addiction ....................................................... 21 3. Selecting Orexin Antagonists for Behavioural Studies ........................................... 42 4. Aims and Hypotheses .............................................................................................. 58 Chapter 2. Methods and Results ..................................................................................... 61 Experiment 1. Orexin-A-induced Feeding ...................................................................... 61 Experiment 2. TCS 1102 and Orexin-A-induced Feeding .............................................. 68 Experiment 3. Palatable Food Self-Administration and Reinstatement.......................... 73 Experiment 4. Varied Unit Costs for Palatable Food ...................................................... 80 Experiment 5. Neuronal Activation During Reinstatement ............................................ 89 Experiment 6. Beer Self-Administration and Reacquisition ........................................... 98 Experiment 7. Nicotine Self-Administration and Reinstatement .................................. 107 Experiment 8. Cue/Prime Compound Reinstatement and FR5 ..................................... 120 Chapter 3. General Discussion ...................................................................................... 126 References ..................................................................................................................... 154 i Acknowledgements I would like to acknowledge my supervisor, Prof. Gavan McNally, who believed in my project even when I didn’t. My unofficial supervisor, Dr Kelly Clemens, welcomed me into her lab to run the nicotine and some food experiments and always tried to help me be a better scientist. I am grateful to my co-supervisor and Head of School, Prof. Simon Killcross, who was very supportive of the PhD student community in the School. I would like to thank my colleagues and friends in the McNally Lab for being there all the time: Dr Asheeta Prasad, Dr Joanna Yau (especially for help with microscopy and photoshop), Dr Auntora Sengupta, Dr Philip Jean-Richard Dit Bressel, Eun A (Lucy) Choi (especially for help with immunohistochemistry), and Gabrielle Gibson. In the Clemens/Westbrook-Holmes Lab, I would like to thank: Dr