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 nucleus accumbens (nAcc), we visualized the cellular and subcellular distribution of DA receptors on postnatal nAcc neurons in culture using fluoroprobe derivatives of DA receptor ligands. Previously, we have shown that rhodamine-N-(p-aminophenethyl)-spiperone (NAPS) (10 nM), a derivative of the D2 antagonist spiperone, labels D2-like receptors on living nAcc neurons. We now show that rhodamine-Sch-23390 (30 nM), a derivative of the D1 antagonist, labels D1-like receptors. Putative specific membrane labeling reached a plateau after about 20 min. Labeling was stereospecific, as it was unaffected by competition with (-)-butaclamol, but blocked with (+)-butaclamol. We found that 52 +/- 7% of nAcc medium-sized neurons showed D1 labeling, which extended onto the dendrites. Labeling was also seen on presynaptic terminals, often abutting D1-positive and D1-negative cell bodies, consistent with a presynaptic modulatory role for D1 receptors. Larger neurons, which may be GABAergic or cholinergic interneurons, were also labeled. By sequential labeling first with rhodamine-Sch-23390 and then rhodamine-NAPS, we found that 38 +/- 6% of medium-sized neurons express both D1- and D2-like receptors, indicating that D1-D2 interactions may occur at the level of single postsynaptic neurons.