Opioid receptor-like (ORL1) receptor distribution in the rat central nervous system: Comparison of ORL1 receptor mRNA expression with I-125-[(14)Tyr]-orphanin FQ binding

The recently discovered neuropeptide orphanin FQ (OFQ), and its opioid rece ptor-like (ORL1) receptor, exhibit structural features suggestive of the mu , kappa, and delta opioid systems. The anatomic distribution of OFQ immunor eactivity and mRNA expression has been reported recently. In the present an alysis, we compare the distribution of orphanin receptor mRNA expression wi th that of orphanin FQ binding at the ORL1 receptor in the adult rat centra l nervous system (CNS). By using in vitro receptor autoradiography with I-1 25-[(14)Tyr]-OFQ as the radioligand, orphanin receptor binding was analyzed throughout the rat CNS. Orphanin binding sites were densest in several cor tical regions, the anterior olfactory nucleus, lateral septum, ventral fore brain, several hypothalamic nuclei, hippocampal formation, basolateral and medial amygdala, central gray, pontine nuclei, interpeduncular nucleus, sub stantia nigra, raphe complex, locus coeruleus, vestibular nuclear complex, and the spinal cord. By using in situ hybridization, cells expressing ORL1 mRNA were most numerous throughout multiple cortical regions, the anterior olfactory nucleus, lateral septum, endopiriform nucleus, ventral forebrain, multiple hypothalamic nuclei, nucleus of the lateral olfactory tract, medi al amygdala, hippocampal formation, substantia nigra, ventral tegmental are a, central gray, raphe complex, locus coeruleus, multiple brainstem motor n uclei, inferior olive, deep cerebellar nuclei, vestibular nuclear complex, nucleus of the solitary tract, reticular formation, dorsal root ganglia, an d spinal cord. The diffuse distribution of ORL1 mRNA and binding supports a n extensive role for orphanin FQ in a multitude of CNS functions, including motor and balance control, reinforcement and reward, nociception, the stre ss response, sexual behavior, aggression, and autonomic control of physiolo gic processes. J. Comp. Neurol. 412:563-605, 1999. (C) 1999 Wiley-Liss, Inc .