EFFECT OF OPIOID AGONISTS SELECTIVE FOR 3 SUBCLASSES OF OPIOID RECEPTORS AND ONE SIGMA-RECEPTOR AGONIST ON DOPAMINE STIMULATED ADENYLATE-CYCLASE IN RAT CAUDATE-NUCLEUS

The adenylate cyclase in rat caudate nucleus homogenate could be stimulated by dopamine and less potently by the dopamine D1 receptor specific agonist SKF38393. Agonists selective for mu[D-Ala2, MePhe4Gly(ol)5]enkephalin (DAGO) and delta-opioid receptors [D-Pen2, D-Pen5]enkephalin (dPen-dPen), inhibited the dopamine but not the dopamine D1 stimulated adenylate cyclase. The kappa-opioid agonist, U69593, had no effect, probably due to low kappa receptor contents in rat caudate nucleus. 10(-4) M of the sigma-receptor specific agonist, 1,3-di-o-tolylguanidine (DTG), potentiated the dopamine as well as the dopamine D1 stimulated adenylate cyclase while lower concentrations of DTG had no effect.