EVIDENCE FOR DELTA-OPIOID RECEPTOR SUBTYPES REGULATING ADENYLYL-CYCLASE ACTIVITY IN RAT-BRAIN

Opioid agonists selective for mu- or delta opioid receptors inhibit ad enylyl cyclase in membranes from rat caudate-putamen and nucleus accum bens. The presence of subtypes of delta opioid receptors has been sugg ested. In both brain regions we have found that the inhibition of aden ylyl cyclase by DPDPE was more readily antagonized by 7-benzylidenenal trexone (BNTX), than by naltriben. in contrast, the inhibitory effects of deltorphin-II and DSLET were more readily antagonized by naltriben , than by BNTX. Neither naltriben nor BNTX significantly antagonized t he effect of a mu selective agonist. These results suggest that inhibi tion of adenylyl cyclase in caudate-putamen and nucleus accumbens is r egulated by two forms of delta-opioid receptor with ligand selectiviti es similar to those two forms proposed to mediate analgesic effect.