Journal
INTERNATIONAL JOURNAL OF NEUROPSYCHOPHARMACOLOGY
Volume 16, Issue 9, Pages 2067-2079Publisher
OXFORD UNIV PRESS
DOI: 10.1017/S1461145713000333
Keywords
Ethanol; orexin 2 receptor; reinstatement; TCS-OX2-29
Funding
- National Health and Medical Research Council of Australia [1021227]
- Besen Family Foundation
- Victorian Government's Operational Infrastructure Support Program
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Orexins are hypothalamic neuropeptides which bind to two G-protein-coupled receptors, orexin-1 (OX1R) and orexin-2 (OX2R) receptor. While a role for OX1R has been established in both ethanol reinforcement and ethanol-seeking behaviour, the role of OX2R in these behaviours is relatively less-studied. The aim of this study was to determine the role of central OX2R in ethanol-taking and ethanol-seeking behaviour. Indiana ethanol-preferring rats were trained to self-administer ethanol (10% w/v) or sucrose (0.7-1% w/v) in the presence of reward-associated cues before being implanted with indwelling guide cannulae. The selective OX2R antagonist TCS-OX2-29 was administered i.c.v. to assess its effect on operant self-administration and cue-induced reinstatement following extinction. Following i.c.v. injection TCS-OX2-29 reduced self-administration of ethanol, but not sucrose. Despite reducing ethanol self-administration, TCS-OX2-29 had no impact on cue-induced reinstatement of ethanol seeking. To determine where in the brain OX2R were acting to modulate ethanol self-administration, TCS-OX2-29 was microinjected into either the shell or core of the nucleus accumbens (NAc). Intra-NAc core, but not shell, infusions of TCS-OX2-29 decreased responding for ethanol. Importantly, the doses of TCS-OX2-029 used were non-sedating. Collectively, these findings implicate OX2R in the NAc in mediating the reinforcing effects of ethanol. This effect appears to be drug-specific as antagonism of central OX2R had no impact on sucrose self-administration. Thus, OX2R in addition to OX1R may represent a potential therapeutic target for the treatment of ethanol-use disorders. However, unlike OX1R, no impact of OX2R antagonism was observed on cue-induced reinstatement, suggesting a more prominent role for OX2R in ethanol self-administration compared to cue-conditioned ethanol-seeking.
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