The regulation of alcohol intake by melanin-concentrating hormone in rats

Given into the brain, melanin-concentrating hormone (MCH) increases alcohol consumption, but the mechanism and physiological relevance of this effect are unclear. We hypothesized that endogenous MCH will enhance alcohol drinking and that MCH increases alcohol's reinforcing properties. An MCH receptor 1 (MCHR1) antagonist, or saline was administered centrally alone, or preceding MCH or saline to rats trained to drink 10% alcohol using sucrose fading. Blocking MCHR1 neither reduced alcohol intake (saline = 0.4 ± 0.1 g, 30 μg MCHR1 antagonist = 0.4 ± 0.1 g/kg alcohol), nor attenuated MCH-induced alcohol drinking (MCHR1 antagonist/saline = 0.7 ± 0.1 g/kg, MCHR1 antagonist/MCH = 0.9 ± 0.1 g/kg alcohol). Another cohort of rats was trained to lever press for alcohol on a progressive ratio schedule. MCH or saline was administered centrally and lever presses were measured. MCH had no effect prior to the break point, but increased total responding during the session (saline = 87.2 ± 32.0, MCH = 315.4 ± 61.0 presses). In conclusion, these data suggest that MCH augments alcohol drinking partly by enhancing the drug's reinforcing value. Further, endogenous MCH does not seem to regulate alcohol drinking, however because the antagonist failed to attenuate MCH-induced alcohol intake this conclusion is tentative.