EXPRESSION OF D-1 RECEPTOR MESSENGER-RNA IN PROJECTIONS FROM THE FOREBRAIN TO THE VENTRAL TEGMENTAL AREA

In situ hybridization was combined with Fluoro-Gold retrograde labelin g to determine if cells projecting from the forebrain to the ventral t egmental area (VTA) express D-1 receptor mRNA. Cell counts were made i n the prefrontal cortex, shell of the nucleus accumbens, and ventral p allidum to estimate the percentage of neurons projecting to the VTA th at express D-1 receptor mRNA. Retrogradely labeled cells were observed in the infralimbic and prelimbic regions of the prefrontal cortex, an d up to 37% of the retrogradely labeled cells expressed D-1 receptor m RNA. Double-labeled cells constituted up to 89% of retrogradely labele d neurons in the rostral shell and up to 68% in the caudal shell of th e nucleus accumbens. The number of retrogradely labeled cells in the v entral pallidum that were double-labeled ranged from 13% in the rostra l to less than 10% in the caudal portions. These data provide anatomic al support for a role of D-1 receptors in the reciprocal innervation b etween the forebrain and VTA. (C) 1997 Wiley-Liss, Inc.