Nociceptin: Proteins and Enzymes

Nociceptin (Orphanin FQ, OFQ), a heptadecapeptide peptide, has been designated as an endogenous ligand for the ORL1 receptor. The amino acid sequence of nociceptin hashomology with other opioid peptides, especially the prodynorphin fragment dynorphin A, suggesting a close evolutionary relationship between the precursors. A diffuse distribution throughout the brain is seen with binding studies and in situ hybridization suggesting an extensive role for nociceptin in a multitude of CNS functions. Immunocytochemical localizations in rat spinal cord have demonstrated nociceptin abundance in superficial dorsal horn, lateral spinal nucleus and the region dorsal to the central canal. Nociceptin immunoreactivity was not affected by dorsal rhizotomy, indicating that in spinal cord the peptide is produced by central rather than primary afferent neurons. The localization is supported by its function in processing of nociceptive signals.