VISUALIZATION OF ANTIPSYCHOTIC DRUG-BINDING TO LIVING MESOLIMBIC NEURONS REVEALS D2 RECEPTOR, ACIDOTROPIC, AND LIPOPHILIC COMPONENTS

To examine the binding of antipsychotic drugs to living neurons, we ap plied fluoroprobe derivatives of the D2 antagonist spiperone to mesoli mbic system neurons in postnatal culture, We found that rhodamine-N-(p -aminophenethyl) spiperone (rhodamine-NAPS) stereospecifically labele d the plasma membranes of 38 +/- 6% of ventral tegmental area neurons, 22 +/- 7% of which were dopaminergic, and 50 +/- 6% of medium-sized p utatively GABAergic nucleus accumbens neurons, with a time constant of similar to 8 min, In contrast, the BODIPY derivative of NAPS rapidly labeled intracellular sites in all neurons in a punctate pattern, cons istent with acidotropic uptake, Native antipsychotics also show acidot ropic uptake, which we visualized by their displacement of the fluores cent weak base vital dye acridine orange from acidic intracellular com partments, We found that acidotropic uptake correlated best with the p artition coefficients of the drugs. With a time constant of 23 min, rh odamine-NAPS labeled all neurons in a pattern suggestive of lipophilic solvation, Thus, initially rhodamine-NAPS makes possible visualizatio n of D2 receptors on living neurons; however, acidotropic uptake and l ipophilic solvation obscure receptor labeling and may account for time -dependent factors in the action of antipsychotic drugs, as well as af fect their use as radioreceptor ligands.