Corticotropin-releasing hormone mediates α-melanocyte-stimulating hormone-induced anorexigenic action in goldfish

α-Melanocyte-stimulating hormone (α-MSH) and corticotropin-releasing hormone (CRH) both suppress food intake, and the α-MSH- or CRH-signaling pathway has possible potency to mediate anorexigenic actions induced by most other neuropeptides in goldfish. Therefore, using specific receptor antagonists, we examined whether the anorexigenic actions of α-MSH and CRH mutually interact. The inhibitory effect of ICV injection of the α-MSH agonist, melanotan II (MT II), on food intake was abolished by treatment with a CRH 1/2 receptor antagonist, α-helical CRH(9–41), whereas the anorexigenic action of ICV-injected CRH was not affected by treatment with a melanocortin 4 receptor antagonist, HS024. This led us to investigate whether α-MSH-containing neurons in the goldfish brain have direct inputs to CRH-containing neurons, using confocal laser scanning microscopy. α-MSH- and CRH-like immunoreactivities were distributed throughout the brain, especially in the diencephalon. α-MSH-containing nerve fibers or endings lay in close apposition to CRH-containing neurons in a region of the hypothalamus, the nucleus posterioris periventricularis (NPPv). These results indicate that, in goldfish, α-MSH-induced anorexigenic action is mediated by the CRH-signaling pathway, and that CRH plays a crucial role in the regulation of feeding behavior as an integrated anorexigenic neuropeptide in this species.