ORPHANIN FQ NOCICEPTIN IN THE VENTROMEDIAL NUCLEUS FACILITATES LORDOSIS IN FEMALE RATS/

THE localization of opioid receptor-like (ORL-1) orphan receptor in th e ventromedial nucleus of the hypothalamus (VMH) suggested a role for this opioid system in the regulation of lordosis behavior. Recently, t he ligand for ORL-1, orphanin FQ/nociceptin (OFQ/N), has been characte rized and also demonstrated to be present in the VMH. The present expe riments examined whether OFQ/N in the VMH facilitates lordosis behavio r in estrogen-primed, sexually unreceptive female rats, and whether es trogen regulates ORL-1 levels in the VMH. Estrogen was shown to increa se ORL-1 immunoreactivity in the VMH, and microinfusions of OFQ/N into the VMH facilitated lordosis behavior in a dose-dependent manner.