EXPRESSION OF D-1 RECEPTOR, D-2 RECEPTOR, SUBSTANCE-P AND ENKEPHALIN MESSENGER-RNAS IN THE NEURONS PROJECTING FROM THE NUCLEUS-ACCUMBENS

In situ hybridization was combined with FluoroGold retrograde labellin g to determine the distribution of messenger RNAs for the D-1 dopamine receptor, D-2 dopamine receptor, beta-preprotachykinin or preproenkep halin in the neurons projecting from the nucleus accumbens to the vent ral pallidum and the ventral tegmental area. Neurons were quantified i n both the core and the shell of the nucleus accumbens to estimate the proportion of neurons projecting to the ventral pallidum or ventral t egmental area that contain transcripts for D-1 receptors, D-2 receptor s, beta-preprotachykinin or preproenkephalin. Following the deposition of FluoroGold into the central ventral pallidum, both the core and th e shell of the nucleus accumbens were retrogradely labelled, while dep osits into the ventral tegmental area selectively labelled cells in th e shell. A high percentage of nucleus accumbens neurons innervating th e ventral tegmental area expressed messenger RNAs for D-1 receptors (7 2%) and beta-preprotachykinin (62%), while less than 3% of the neurons contained messenger RNAs For preproenkephalin or D-2 receptors. The n eurons projecting to the ventral pallidum did not show the discrete di stribution of transcripts as was observed in the accumbens-ventral teg mental area projection. Preproenkephalin messenger RNA was identified in 46% of the neurons innervating the ventral pallidum, and D-2 recept or messenger RNA was found in approximately 40% of the cells. A large minority of neurons projecting from the nucleus accumbens to the ventr al pallidum also expressed messenger RNAs for D-1 receptors (37%) and beta-preprotachykinin (35%). While a higher percentage of D-1 receptor , and beta-preprotachykinin messenger RNA expressing cells were locate d in the shell than in the core of the nucleus accumbens, the percenta ge tended to be higher in the core for cells expressing D-2 receptors or preproenkephalin messenger RNA. These data indicate that messenger RNAs for D-2 receptors and enkephalin are selectively expressed in the accumbens-pallidal projection while transcripts encoding D-1 receptor s and substance P are contained in the efferent projections to both th e ventral pallidum and ventral tegmental area. The presence of D-1 rec eptor and beta-preprotachykinin messenger RNAs in both mesencephalic a nd pallidal projections contrasts output from the striatum where the e xpression of D-1 receptor and beta-preprotachykinin messenger RNAs is primarily restricted to the mesencephalic projection. (C) 1997 IBRO. P ublished by Elsevier Science Ltd.