FMRFamide: an endogenous peptide with marked inhibitory effects on opioid-induced feeding behavior

The peptide FMRFamide (Phe-Met-Arg-Phe-NH2), which displays a broad phylogenetic distribution, is considered to have important regulatory influences on basic functions in invertebrates. Extensive FMRFamide-like immunoreactive neuropeptides have also been demonstrated in the mammalian central nervous system, suggesting a possible physiological role for these peptides in mammals. There is evidence that FMRFamide, and/or related neuropeptides, may modulate opioid-mediated responses. Intracerebroventricular (ICV) administrations of FMRFamide inhibit in a dose-dependent manner (0.01-10 micrograms) mu- (morphine) and kappa- (U-50,488H) opiate-induced feeding in the laboratory mouse. In deer mice, FMRFamide inhibits the display of exogenous opiate-induced components of natural feeding behavior, such as food hoarding and food ingestion. In addition, ICV administrations of FMRFamide also antagonize endogenous opioid-mediated, stress-induced feeding in mice. These observations suggest that FMRFamide, or FMRFamide-like peptides present in the mammalian brain, may have important roles in the control of opioid-mediated feeding.