ORPHANIN FQ NOCICEPTIN-IMMURAOREACTIVE NERVE-FIBERS PARALLEL THOSE CONTAINING ENDOGENOUS OPIOIDS IN RAT SPINAL-CORD/

ANTISERA Were developed that specifically recognize orphanin FQ/nocice ptin, the 17 amino acid peptide reported to be the endogenous ligand f or the orphan opioid receptor. Immunocytochemical localizations in rat spinal cord demonstrated that orphanin FQ /nociceptin-immunoreactivit y (-ir) was abundant in superficial dorsal horn, lateral spinal nucleu s and the region dorsal to the central canal, areas that also exhibit prominent enkephalin- and dynorphin-ir. Orphanin FQ/nociceptin-ir was not affected by dorsal rhizotomy, indicating that in spinal cord the p eptide is produced by central rather than primary afferent neurons. Th us, the distribution of orphanin FQ/nociceptin-ir appeared in neuronal circuits that parallel those containing enkephalin- and dynorphin-ir, with only modest co-existence of these peptides.