Neuropeptide Y mediates ghrelin-induced feeding in the goldfish, Carassius auratus.

Intracerebroventricular (ICV) and intraperitoneal (IP) administration of n-octanoic acid-modified ghrelin stimulates food intake in the goldfish. We examined the involvement of neuropeptide Y (NPY) in the orexigenic action of ghrelin using a NPY Y1-receptor antagonist, BIBP-3226. Food intake induced by ICV or IP injection of ghrelin was suppressed by ICV preinjection of BIBP-3226 for 1 h. We then examined whether ghrelin affects the expression of NPY mRNA in the goldfish brain using a real-time PCR method. ICV, but not IP, administration of ghrelin at a dose sufficient to stimulate food intake increased the expression of brain NPY mRNA obtained from 2 h after treatment. These results indicate that the orexigenic action of central ghrelin is mediated by the release of NPY in the brain with stimulating NPY synthesis, and that peripheral ghrelin also stimulates food intake via brain NPY pathway.