Autoradiographic localization of [H-3]nociceptin binding sites in the rat brain

The binding sites of nociceptin (also named orphanin FQ), the endogenous li gand of ORL1 (opiate receptor like 1), were localized in rat brain, using a n autoradiographic procedure. High levels of binding were observed in the c ingulate, retrosplenial, perirhinal, insular and occipital cortex, anterior and posteromedial cortical amygdaloid nuclei, basolateral amygdaloid nucle us, amygdaloid complex, posterior hippocampus, dorsal endopiriform, central medial thalamic, paraventricular, rhomboid thalamic, suprachiasmatic, vent romedial hypothalamic nuclei, mammillary complex, superficial gray layer of the superior colliculus, locus coeruleus, dorsal raphe nucleus. More moder ate labelling was observed in the prefrontal, fronto-parietal, temporal, pi riform cortex, dentate gyrus, anterior olfactory nucleus, olfactory tubercl e, shell of nucleus accumbens, claustrum, lateral septum, laterodorsal thal amic, medial habenular, subthalamic, reuniens thalamic nuclei, subiculum, p eriaqueductal grey matter and pens. A lower binding site density was observ ed in the anterior and medial hippocampus, olfactory bulb, caudate putamen, the core of the nucleus accumbens, medial septum, ventrolateral, ventropos terolateral and mediodorsal thalamic nuclei, lateral and medial geniculate nuclei, hypothalamic area, substantia nigra, ventral tegmentum area and int erpedoncular nucleus. A moderate and similar labelling was found in the dor sal and ventral horn of the spinal cord. No labelling was apparent in the c orpus callosum. Thus, it appears that the ORL1 receptor is particularly abu ndant in the cerebral cortex, limbic system of the rat brain and some areas involved in pain perception. (C) 2000 Elsevier Science B.V. AU rights rese rved.