Presence and characterization of nociceptin (orphanin FQ) receptor binding in adult rat and human fetal hypothalamus.

High affinity and saturable nociceptin (orphanin FQ) receptors were detected and characterized in adult rat and human fetal hypothalamic membranes, utilizing [125I]Tyr12-nociceptin as ligand. Nociceptin bound with picomolar affinity, dynorphin A with nanomolar affinity, naloxone and dynorphan A(1-8) with micromolar while des-Tyr1-dynorphin (dynorphin A(2-17)), several other opioids, morphine and benzomorphans failed to compete for binding at 1-10 microM. Gpp(NH)p together with sodium ion markedly decreased binding, consistent with involvement of a G protein-linked receptor.