Corticotropin-releasing factor is a downstream mediator of the beta-melanocyte-stimulating hormone-induced anorexigenic pathway in chicks

Proopiomelanocortin (POMC, a precursor of anorexigenic neuropeptides) neurons in hypothalamus suppresses food intake in both mammals and chickens. In mammals, several lines of evidence suggest that POMC-derived anorexigenic peptides upregulate mRNA levels of anorexigenic peptides such as corticotropin-releasing factor (CRF) and thyrotropin-releasing factor and downregulate mRNA levels of orexigenic peptides such as orexin and melanin-concentrating hormone. However, the POMC-induced anorexigenic pathway in chickens has not been well characterized. In the present study, we investigated how POMC neurons regulate mechanisms of food intake using an anorexigenic peptide, beta-melanocyte-stimulating hormone (β-MSH), derived from the post-transcriptional cleavage of POMC. Central administration of β-MSH in chicks significantly suppressed food intake, and importantly, this suppression was accompanied by a significant upregulation of CRF mRNA levels. Furthermore, the CRF type 2 receptor antagonist alpha-helical CRF significantly reversed the anorexigenic action of β-MSH. These findings indicate that CRF and its receptor, CRF type 2 receptor, act as the major mediators in β-MSH-induced anorexigenic action in chicks. β-MSH significantly increased orexin mRNA levels and did not alter mRNA levels of thyrotropin-releasing factor and melanin-concentrating hormone in chicks, suggesting that the β-MSH-induced anorexigenic pathway in chicks is different from that in mammals. Increases in orexin mRNA levels were accompanied by significant decreases in plasma glucose concentration, suggesting that orexin mRNA might be stimulated by β-MSH-induced hypoglycemia. Thus, this study demonstrates the direct evidence that CRF is a critical downstream target in the β-MSH-induced anorexigenic pathway in chicks.