α-Melanocyte-stimulating hormone mediates melanin-concentrating hormone-induced anorexigenic action in goldfish

In goldfish, intracerebroventricular (ICV) administration of melanin-concentrating hormone (MCH) inhibits feeding behavior, and fasting decreases hypothalamic MCH-like immunoreactivity. However, while MCH acts as an anorexigenic factor in goldfish, in rodents MCH has an orexigenic effect. Therefore, we examined the involvement of two anorexigenic neuropeptides, α-melanocyte-stimulating hormone (α-MSH) and corticotropin-releasing hormone (CRH), in the anorexigenic action of MCH in goldfish, using an α-MSH receptor antagonist, HS024, and a CRH receptor antagonist, α-helical CRH(9–41). ICV injection of HS024, but not α-helical CRH(9–41), suppressed MCH-induced anorexigenic action for a 60-min observation period. We then examined, using a real-time PCR method, whether MCH affects the levels of mRNAs encoding various orexigenic neuropeptides, including neuropeptide Y (NPY), orexin, ghrelin and Agouti-related peptide (AgRP), in the goldfish diencephalon. ICV administration of MCH at a dose sufficient to inhibit food consumption decreased the expression of mRNAs for NPY and ghrelin, but not for orexin and AgRP. These results indicate that the anorexigenic action of MCH in the goldfish brain is mediated by the α-MSH signaling pathway and is accompanied by inhibition of NPY and ghrelin synthesis.