ANATOMICAL DISTRIBUTION OF MU-OPIOID, DELTA-OPIOID, AND KAPPA-OPIOID AND NOCICEPTION ORPHANIN FQ-STIMULATED [S-35] GUANYLYL-5'-O-(GAMMA-THIO)-TRIPHOSPHATE BINDING IN GUINEA-PIG BRAIN/

An in vitro autoradiographic technique has recently been developed to visualize receptor-activated G-proteins by using agonist-stimulated [S -35]guanylyl-5'-O-(gamma-thio)-triphosphate ([S-35]GTP gamma S) bindin g in the presence of excess guanosine 5'-diphosphate. This technique w as used to localize opiaid-activated G-proteins in guinea pig brain, a species that contains the three major types of opioid receptors. This study used selective mu, delta and kappa opioid agonists as well as n ociceptin or orphanin FQ (N/OFQ) peptide, an endogenous ligand for an orphan opioid receptor-like (ORL1) receptor, to stimulate [S-35]GTP ga mma S binding in guinea pig brain sections. Opioid receptor specificit y was confirmed by blocking agonist-stimulated [S-35] GTP gamma S bind ing with the appropriate antagonists. In general, the distribution of agonist-stimulated [S-35]GTP gamma S binding correlated with previous reports of receptor binding autoradiography although quantitative diff erences suggest regional variations in receptor coupling efficiency. M u, delta, and kappa opioid-stimulated [S-35]GTP gamma S binding was fo und in the caudate-putamen, nucleus accumbens, amygdala, and hypothala mus. Mu-stimulated [S-35]GTP gamma S binding predominated in the hypot halamus, amygdala, and brainstem, whereas K-stimulated [S-35]GTP gamma S binding was particularly high in the substantia nigra and cortex an d was moderate in the cerebellum. N/OFQ-stimulated [S-35]GTP gamma S b inding was highest in the cortex, hippocampus, and hypothalamus and ex hibited a unique anatomical distribution compared with opioid-stimulat ed [S-35]GTP gamma S binding. The present study extends previous repor ts on opioid and ORL1 receptor localization by anatomically demonstrat ing functional activity produced by mu, delta, and kappa opioid and OR L1 receptor activation of G-proteins. (C) 1997 Wiley-Liss, Inc.