Differential expression of cocaine- and amphetamine-regulated transcript and agouti related-protein in chronically food-restricted sheep

Abstract

Recently, much attention has focused on the role of the melanocortin system in the regulation of energy homeostasis, especially the satiety effects of the pro-opiomelanocortin (POMC)-derived peptide α-melanocyte stimulating hormone (α-MSH). We have found that POMC mRNA levels are similar in fat and thin sheep and the current study sought to further characterize the effects of nutritional status on the melanocortin system. To this end, we studied the expression of agouti-related peptide (AGRP) (an endogenous antagonist of α-MSH) and cocaine- and amphetamine-regulated transcript (CART), which is co-localized within POMC cells of the arcuate nucleus (ARC) in rodents. Twelve ovariectomized ewes were randomly divided into two groups and fed a maintenance ( n=6) or restricted diet ( n=6). At the time of experimentation, the animals had significantly ( P<0.0001) different bodyweights (53.4±2.2 kg, ad libitum vs. 30.4±1.2 kg, food-restricted), which was largely due to altered body fat deposits. In situ hybridization was used to study the expression of POMC, AGRP and CART. The expression of POMC in the ARC was similar in ad libitum and food-restricted animals but the expression of AGRP was profoundly increased in the food-restricted group. The expression of CART was abundant throughout the hypothalamus but was not found in the ARC. In food-restricted animals, the expression of CART was lower in the retrochiasmatic nucleus ( P<0.01), paraventricular nucleus ( P<0.001), the dorsomedial nucleus and the lateral hypothalamic area ( P<0.05), but was higher ( P<0.01) in the posterior hypothalamic area. Thus, long-term changes in nutritional status have profound effects on the expression of AGRP and CART in the hypothalamus.