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1 School of Biomedical Sciences, University of Nottingham, Nottingham NG7 2UH; 2 Neurobiology Division, Laboratory of Molecular Biology, Medical Research Council Centre, Cambridge CB2 2QH; and 3 Molecular Neuroendocrinology Group, The Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, United Kingdom
We investigated the role of the hypothalamic melanocortin system in the regulation of food intake in the Siberian hamster, which shows a profound seasonal decrease in food intake and body weight in short photoperiod (SP). In male hamsters maintained in long photoperiod (LP), intracerebroventricular injection of melanotan II (MTII) just before lights off significantly decreased food intake relative to vehicle treatment over the 6-h observation period. Similar effects were observed in age-matched hamsters after exposure to a short daylength for 9 wk, when body weight had significantly decreased. There was no clear difference in either the magnitude of response or the dose required for half-maximal inhibition of food intake in hamsters in SP compared with those in LP. MTII significantly increased grooming in both LP and SP. Our results indicate that the melanocortin system is a potent short-term regulator of food intake. However, the lack of differential response or sensitivity to MTII treatment in the obese (LP) vs. lean (SP) states does not support the hypothesis that changes in this melanocortin pathway underlie the long-term decrease in food intake that occurs in this seasonal model.
feeding; behavior; hypothalamus; body weight; seasonal rhythms; pro-opiomelanocortin; melanocortin-4 receptor; melanotan II
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