D-1- and D-2-like dopamine receptors are co-localized on the presynaptic varicosities of striatal and nucleus accumbens neurons in vitro

The neuromodulatory actions of dopamine in the striatum and nucleus accumbe ns are likely to depend on the distribution of dopamine receptors on indivi dual postsynaptic cells. To address this, we have visualized D-1- and D-2-l ike receptors on living medium-spiny GABAergic neurons in cultures from the striatum and nucleus accumbens using receptor antagonist fluoroprobes. We labeled D-1-like receptors with rhodamine-SCH23390, D-2-like receptors with rhodamine-N-(p-aminophenethyl)spiperone and synaptic sites with K+-stimula ted uptake of the activity-dependent endocytic tracer FM-143. The fluoropro bes were applied in sequence to assess co-localization. We found that D-1- or D-2-like receptors were present on about two-thirds of the cells, and co -localized on 22 +/- 3% (mean +/- S.E.M.) of striatal and 38 +/- 6% of nucl eus accumbens cells. On either D-1 or D-2 labeled cells, postsynaptic label ing continuously outlined the cell body membrane and extended to proximal d endrites, but not axons. About two-thirds of synaptic varicosities showed D -1 or D-2 labeling. D-1- and D-2-like receptors were co-localized on 21 +/- 4% of striatal and 27+/-3% of nucleus accumbens varicosities. Presynaptic labeling was typically more intense than postsynaptic labeling. The distrib ution of presynaptic dopamine receptors contrasted with that of postsynapti c GABA, receptors, which were clustered in longer patches on neighboring po stsynaptic membranes. The extensive presence of D-1- and D-2-like receptors on presynaptic varico sities of medium-spiny neurons suggests that the receptors are likely to pl ay an important and interacting role in the presynaptic modulation of inhib itory synaptic transmission in the striatum and nucleus accumbens. The sign ificant overlap in labeling suggests that D-1-D-2 interactions, which occur at the level of individual postsynaptic cells, the circuit level and the s ystems level, may also be mediated at the presynaptic level. Finally, the a bility to visualize dopamine, as well as GABA(A), receptors on the individu al synapses of living neurons now makes possible physiological studies of i ndividual mesolimbic system synapses with known receptor expression, (C) 19 98 IBRO. Published by Elsevier Science Ltd.