Localization of orphanin FQ (nociceptin) peptide and messenger RNA in the central nervous system of the rat

Orphanin FQ (OFQ) is the endogenous agonist of the opioid receptor-like rec eptor (ORL-1). It and its precursor, prepro-OFQ, exhibit structural feature s suggestive of the opioid peptides. A cDNA encoding the OFQ precursor sequ ence in the rat recently has been cloned, and the authors recently generate d a polyclonal antibody directed against the OFQ peptide. In the present st udy, the authors used in situ hybridization and immunohistochemistry to exa mine the distribution of OFQ peptide and mRNA in the central nervous system of the adult rat. OFQ immunoreactivity and prepro-OFQ mRNA expression corr elated virtually in all brain areas studied. In the forebrain, OFQ peptide and mRNA were prominent in the neocortex endopiriform nucleus, claustrum, l ateral septum, ventral forebrain, hypothalamus, mammillary bodies, central and medial nuclei of the amygdala, hippocampal formation, paratenial and re ticular nuclei of the thalamus, medial habenula, and zona incerta. No OFQ w as observed in the pineal or pituitary glands. In the brainstem, OFQ was pr ominent in the ventral tegmental area, substantia nigra, nucleus of the pos terior commissure, central gray, nucleus of Darkschewitsch, peripeduncular nucleus, interpeduncular nucleus, tegmental nuclei, locus coeruleus, raphe complex, lateral parabrachial nucleus, inferior olivary complex, vestibular nuclear complex, prepositus hypoglossus, solitary nucleus, nucleus ambiguo us, caudal spinal trigeminal nucleus, and reticular formation. In the spina l cord, OFQ was observed throughout the dorsal and ventral horns. The wide distribution of this peptide provides support for its role in a multitude o f functions, including not only nociception but also motor and balance cont rol, special sensory processing, and various autonomic and physiologic proc esses. J. Comp. Neurol. 406:503-547, 1999. (C) 1999 Wiley-Liss, Inc.