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The regulation of alcohol intake by melanin-concentrating hormone in rats
Elizabeth A Duncan1, Therese R Rider, Ronald J Jandacek
1Department of Psychiatry, University of Cincinnati, USA. duncanel@mail.nih.gov
Abstract:
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 microg 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.
Insights
Melanin-concentrating hormone (MCH) appears to increase alcohol consumption by enhancing its rewarding effects. However, MCH does not seem to regulate alcohol drinking naturally, though this finding is tentative.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
Background:
- Melanin-concentrating hormone (MCH) is known to influence alcohol consumption, but the underlying mechanisms and physiological significance remain largely unknown.
- This study investigates the role of MCH in modulating alcohol intake and its reinforcing properties.
Purpose of the Study:
- To determine if endogenous MCH enhances alcohol consumption.
- To ascertain if MCH increases the reinforcing value of alcohol.
- To explore the potential role of the MCH receptor 1 (MCHR1) in these effects.
Main Methods:
- Rats were trained to consume 10% alcohol using a sucrose fading method.
- Central administration of an MCHR1 antagonist or saline was performed before MCH or saline administration.
- Alcohol intake was measured, and a separate cohort of rats was trained on a progressive ratio schedule to assess alcohol's reinforcing properties following MCH administration.
Main Results:
- Blocking MCHR1 did not reduce alcohol intake or attenuate MCH-induced alcohol drinking.
- MCH administration increased total lever presses for alcohol on a progressive ratio schedule, indicating enhanced reinforcing properties.
- MCH did not affect the breakpoint for alcohol acquisition.
Conclusions:
- Melanin-concentrating hormone (MCH) augments alcohol consumption, likely by increasing alcohol's reinforcing value.
- Endogenous MCH does not appear to regulate alcohol drinking, although this conclusion is tentative due to the antagonist's limited efficacy.
- Further research is needed to fully elucidate the role of MCH in alcohol use and addiction.
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