Central administration of melanin-concentrating hormone increases alcohol and sucrose/quinine intake in rats.
BACKGROUND
Alcohol is a caloric compound that can contribute to energy intake. Therefore, peptides that regulate energy balance likely modify the motivation to consume alcohol. Melanin-concentrating hormone (MCH) regulates energy homeostasis and has been implicated in other behaviors that impact alcohol consumption (i.e., anxiety, fluid balance, and reward). We tested the hypothesis that MCH would decrease the motivation to consume alcohol secondarily to reducing anxiety.


METHODS
Rats were trained to drink 10% ethanol or an isocaloric concentration of sucrose with use of a sucrose-fading technique. MCH (1, 5, or 10 microg) or its saline vehicle was administered into the third cerebral ventricle (i3vt), and intake of ethanol or sucrose and chow was assessed for 2 hr. Alcohol-naïve rats were evaluated in an elevated plus maze after i3vt MCH (10 microg), neuropeptide Y, or saline administration.


RESULTS
Contrary to the hypothesis, MCH dose-dependently increased alcohol intake: saline = 0.7 +/- 0.1 g/kg, 1 microg MCH = 1.0 +/- 0.1 g/kg, 5 microg MCH = 1.2 +/- 0.1 g/kg, and 10 microg MCH = 1.8 +/- 0.3 g/kg (p < 0.01), and this was true whether water was simultaneously available or not. MCH also significantly increased sucrose intake (saline = 1.0 +/- 0.3 g/kg, 10 mug MCH = 1.4 +/- 0.5 g/kg; p < 0.05). MCH had no effect on time spent in the open arms (54.3 +/- 11.5 sec) relative to saline (58.2 +/- 23.8 sec), whereas neuropeptide Y, a known anxiolytic, increased time spent on the open arms (119.2 +/- 22 sec, p < 0.05).


CONCLUSIONS
We conclude that MCH nonspecifically increases ingestive behavior. Furthermore, MCH had no apparent effect on anxiety. The ability of MCH to increase alcohol and/or sucrose intake may be explained by the effect of MCH on energy balance and/or reward processes.
Duncan
Elizabeth A
EA
Department of Psychiatry, University of Cincinnati, Cincinnati, Ohio 45237, USA. duncanea@ucmail.uc.edu
Proulx
Karine
K
Woods
Stephen C
SC
D000428:Alcohol Drinking / Q000378:metabolism*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D004326:Drinking / Q000187:drug effects* / Q000502:physiology; D004734:Energy Metabolism / Q000187:drug effects; D000431:Ethanol / Q000378:metabolism*; D007028:Hypothalamic Hormones / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D007276:Injections, Intraventricular; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D008543:Melanins / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D010907:Pituitary Hormones / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D011803:Quinine / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D012201:Reward; D012646:Self Administration; D013395:Sucrose / Q000378:metabolism*
D007028:Hypothalamic Hormones; D008543:Melanins; D010907:Pituitary Hormones; D000431:Ethanol; D013395:Sucrose; C019463:melanin-concentrating hormone; D011803:Quinine