Inhibition and stimulation of adenylyl cyclase by opioid and D1 dopamine or A2a adenosine agonists, respectively, were characterized in the caudate putamen of rats. D1 dopamine receptors have been reported to be localized preferentially on striatonigral neurons and A2a adenosine receptors on striatopallidal neurons. The aim of the present study was to evaluate the effects of mu-[Tyr-D-Ala-Gly-(N-Me)Phe-Gly-ol (DAMGO)], delta 1-[Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE)], and delta 2- ([D-Ala2]deltorphin-II [DT-II]) opioid agonists on the D1 dopamine receptor- and A2a adenosine receptor-stimulated adenylyl cyclase in membranes from rat caudate putamen. The results show that DAMGO, DPDPE, and DT-II inhibit forskolin-stimulated adenylyl cyclase [selectively antagonized by D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP; mu antagonist), 7-benzylidenenaltrexone (BNTX; delta 1 antagonist), and naltriben (NTB; delta 2 antagonist), respectively], but only mu- and delta 2-opioid agonists inhibit D1 dopamine-stimulated adenylyl cyclase (antagonized by CTOP and NTB, respectively). Furthermore, DT-II and DPDPE inhibit A2a adenosine-stimulated adenylyl cyclase (antagonized by NTB and BNTX, respectively), whereas DAMGO did not inhibit A2a adenosine-stimulated adenylyl cyclase activity. These results suggest that mu-, delta 1-, and delta 2-opioid receptors display differential localization and provide neurochemical evidence suggesting the differential location of the delta 1 and delta 2 subtypes. mu-Opioid receptors may be preferentially expressed by striatonigral neurons, delta 1-by striatopallidal neurons, and delta 2-by these two striatal efferent neuron populations.