Abstract

Fasting activates orexigenic neuropeptide Y neurons in the hypothalamic arcuate nucleus (ARC) of mice, which is reversed by 2h refeeding with standard chow. Here we investigated the contribution of diet-derived macronutrients and anorectic hormones to the reversal of the fasting-induced ARC activation during 2h refeeding. Refeeding of 12h-fasted mice with a cellulose-based, non-caloric mash induced only a small reduction in c-Fos expression. Refeeding with diets, containing carbohydrates, protein or fat alone reversed it similar to chow, however this effect depended on the amount of intake. The fasting-induced ARC activation was unchanged by subcutaneously injected amylin, CCK (both 20 microg/kg), insulin (0.2U/kg and 0.05U/kg) or leptin (2.6mg/kg). Insulin and leptin had no effect on c-Fos expression in neuropeptide Y or proopiomelanocortin containing ARC neurons. Interestingly, CCK but not amylin reduced the ghrelin-induced c-Fos expression in the ARC in ad libitum fed mice suggesting that endogenous CCK may inhibit orexigenic ARC neurons when acting together with other feeding-related signals. We conclude that all three macronutrients and also non-nutritive, ingestion-dependent signals contribute to an inhibition of orexigenic ARC neurons after refeeding. Similar to the previously demonstrated inhibitory in vivo action of peptide YY, CCK may be a postprandial mediator of ARC inhibition. Key words: c-Fos, insulin, leptin, amylin.