ORPHANIN FQ, AGONIST OF ORPHAN OPIOID RECEPTOR ORL1, STIMULATES FEEDING IN RATS

IT has long been known that opioids, whether administered exogenously or released endogenously, play a role in feeding behavior, and that bl ockade of opioid receptors with various antagonists can inhibit feedin g. Recently, the orphan opioid receptor, ORL1, and its presumed ligand , orphanin FQ, have been identified in human and rodent brain, and sho w structural similarity to classical opioid receptors and peptides, re spectively. While it has been shown that central administration of orp hanin FQ induces hyperalgesia, the effects of this peptide on food int ake have not been studied. In the present study, we report that centra l injection of orphanin FQ induces feeding in satiated rats and that t his effect can be blocked by peripheral administration of the opioid a ntagonist naloxone.