VISUALIZATION OF D1 DOPAMINE-RECEPTORS ON LIVING NUCLEUS-ACCUMBENS NEURONS AND THEIR COLOCALIZATION WITH D2 RECEPTORS

To examine the substrate for dopamine (DA) synaptic action in the nucl eus accumbens (nAcc), we visualized the cellular and subcellular distr ibution of DA receptors on postnatal nAcc neurons in culture using flu oroprobe derivatives of DA receptor ligands, Previously, we have shown that rhodamine-N-(p-aminophenethyl)-spiperone (NAPS) (10 nM), a deriv ative of the D2 antagonist spiperone, labels D2-like receptors on livi ng nAcc neurons. We now show that rhodamine-Sch-23390 (30 nM), a deriv ative of the D1 antagonist, labels D1-like receptors. Putative specifi c membrane labeling reached a plateau after about 20 min. Labeling was stereospecific, as it was unaffected by competition with (-)-butaclam ol, but blocked with (+)-butaclamol. We found that 52 +/- 7% of nAcc m edium-sized neurons showed D1 labeling, which extended onto the dendri tes. Labeling was also seen on presynaptic terminals, often abutting D 1-positive and D1-negative cell bodies, consistent with a presynaptic modulatory role for D1 receptors, Larger neurons, which may be GABAerg ic or cholinergic interneurons, were also labeled. By sequential label ing first with rhodamine-Sch-23390 and then rhodamine-NAPS, we found t hat 38 +/- 6% of medium-sized neurons express both D1- and D2-like rec eptors, indicating that D1-D2 interactions may occur at the level of s ingle postsynaptic neurons.