Central orexin (hypocretin) 2 receptor antagonism reduces ethanol self-administration, but not cue-conditioned ethanol-seeking, in ethanol-preferring rats

Int J Neuropsychopharmacol. 2013 Oct;16(9):2067-79. doi: 10.1017/S1461145713000333. Epub 2013 Apr 22.

Abstract

Orexins are hypothalamic neuropeptides which bind to two G-protein-coupled receptors, orexin-1 (OX(1)R) and orexin-2 (OX(2)R) receptor. While a role for OX(1)R has been established in both ethanol reinforcement and ethanol-seeking behaviour, the role of OX(2)R in these behaviours is relatively less-studied. The aim of this study was to determine the role of central OX(2)R 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 OX(2)R 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 OX(2)R 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 OX(2)R in the NAc in mediating the reinforcing effects of ethanol. This effect appears to be drug-specific as antagonism of central OX(2)R had no impact on sucrose self-administration. Thus, OX(2)R in addition to OX(1)R may represent a potential therapeutic target for the treatment of ethanol-use disorders. However, unlike OX(1)R, no impact of OX(2)R antagonism was observed on cue-induced reinstatement, suggesting a more prominent role for OX(2)R in ethanol self-administration compared to cue-conditioned ethanol-seeking.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alcohol Drinking / metabolism
  • Alcohol Drinking / physiopathology
  • Alcohol Drinking / prevention & control*
  • Alcohol Drinking / psychology
  • Animals
  • Behavior, Animal / drug effects*
  • Brain / drug effects*
  • Brain / metabolism
  • Brain / physiopathology
  • Conditioning, Psychological / drug effects*
  • Cues*
  • Drug-Seeking Behavior / drug effects*
  • Ethanol / administration & dosage*
  • Isoquinolines / pharmacology*
  • Male
  • Motor Activity / drug effects
  • Orexin Receptor Antagonists*
  • Orexin Receptors / metabolism
  • Pyridines / pharmacology*
  • Rats
  • Reward
  • Self Administration
  • Sucrose / administration & dosage

Substances

  • 1-(3,4-dihydro-6,7-dimethoxy-2(1H)-isoquinolinyl)-3,3-dimethyl-2-((4-pyridinylmethyl)amino)-1-butanone
  • Hcrtr2 protein, rat
  • Isoquinolines
  • Orexin Receptor Antagonists
  • Orexin Receptors
  • Pyridines
  • Ethanol
  • Sucrose