Response of neuropeptide Y-induced feeding to μ-, δ- and κ-opioid receptor antagonists in the neonatal chick

It is known that opioid antagonists reduce the orexigenic effect of neropeptide Y (NPY) in mammals. We studied the effect of three opioid antagonists on NPY-induced feeding in male broiler chicks. β-Funaltrexamine (β-FNA), naloxonazine (NAL), ICI-174,864 (ICI) or nor-binaltorphimine (nor-BNI), antagonists of μ-, μ1-, δ- or κ-receptors, and NPY were co-injected in chicks. Food intake was measured 30 min after treatment. Co-injection of β-FNA or NAL was effective in reducing NPY-induced feeding, whereas ICI and nor-BNI had little effect on NPY-induced feeding. These data suggest that the μ-opioid receptor, especially the μ1-opioid has some relation to NPY-induced feeding, and implies that an endogenous ligand, such as β-endorphin, participates in the orexigenic effect of NPY in neonatal chicks.