Seasonally inappropriate body weight induced by food restriction: Effect on hypothalamic gene expression in male Siberian hamsters

Male Siberian hamsters undergo physiological weight change in changing phot operiod. Weight loss was induced by food restriction in long days to mimic short-day weight loss, or by food restriction superimposed on short-day-wei ght loss, to test the hypothesis that the hypothalamus differentiates betwe en weight change induced by imposed negative energy balance (inappropriate body weight) and seasonal, appropriate, body weight change, even when these are of similar magnitude. Short-day weight loss was accompanied by reduced POMC and leptin receptor (OB-Rb) mRNA in the arcuate nucleus but elevated cocaine- and amphetamine-regulated transcript. Melanocortin 3-receptor gene expression was reduced in the arcuate nucleus but elevated in the ventrome dial. nucleus compared with ad libitum-fed long-day controls. Weight loss i n long-day restricted animals generated a gene expression profile typical o f negative energy balance with low cocaine- and amphetamine-regulated trans cript mRNA and elevated OB-Rb. Melanocortin 3-receptor mRNA levels were ind istinguishable in short-day and long-day food-restricted hamsters. The hypo thalamic correlates of food restriction in short days included up-regulated anabolic neuropeptides and increased OB-Rb mRNA. Low plasma leptin is inte grated differently in short-day and long-day restricted animals, and season ally-inappropriate body weight in either photoperiod engages the compensato ry neuropeptide systems involved in the defense of body weight.