Neuropeptide VF-associated satiety involves mu and kappa but not delta subtypes of opioid receptors in chicks

Neuropeptide VF (NPVF) induces satiety through hypothalamic interactions; however, the central mechanism that mediates these effects is poorly understood. Therefore, this study was conducted to explore some possible opioid receptor associated mechanisms of NPVF-induced satiety using chicks as models. Co-injection of NPVF and a mu opioid receptor antagonist (beta-funaltrexamine, FNA) did not have an additive suppressive effect on food intake compared to NPVF and FNA when injected alone. Contrary, co-injection of NPVF and a delta opioid receptor antagonist (ICI-174,864, ICI) caused a greater reduction in food intake than when both were injected alone. Co-injection of NPVF and a kappa opioid receptor antagonist (nor-binaltorphimine, BNI) did not cause an additive suppressive effect on food intake than when the two were injected alone. A reversal of neuropeptide Y and β-endorphin induction of food intake occurred when NPVF was co-injected. These results support that NPVF-induced satiety is mediated through mu and kappa but not delta subtypes of opioid receptors, and their ligands including neuropeptide Y and β-endorphin. Thus, NPVF-associated anorexia may be mediated via modulation of the chick's innate opioid-associated orexigenic system.