Characterization of nociceptin-stimulated in situ [35S]GTPgammaS binding in comparison with opioid agonist-stimulated ones in brain regions of the mice.

We studied the characterization of receptor-mediated G protein activity by nociceptin throughout brain regions, using in situ GTPgammaS binding autoradiography. Nociceptin-stimulated GTPgammaS binding was markedly observed in amygdala, hippocampal pyramidal cell layers, temporal and entorhinal cortex, infralimbic organ, anterior olfactory nucleus, and rostral part of thalamus. These nociceptin-stimulated activities were not affected by naloxone, naltrindol nor norbinaltorphimine which completely blocked mu-, delta- or kappa-opioid agonist-stimulated GTPgammaS binding, respectively. In addition, the distribution of nociceptin-stimulated activities throughout brain regions was found to be different from such opioid receptor-mediated ones.