Dopaminergic regulation of immediate-early gene expression in the central nervous system.

Alterations in dopaminergic neurotransmission have profound effects on neuronal expression of the putative activity marker, Fos, in both the dorsal and ventral striatum. In the dorsal striatum, D1-like receptor agonists elevates Fos-like immunoreactivity predominantly in neurons projecting to the midbrain (substantia nigra), whereas D2-like receptor antagonist enhances Fos-like immunoreactivity principally in neurons projecting to the pallidum (globus pallidus). Since the nucleus accumbens (largest component of the ventral striatum) also sends projections to the midbrain (ventral tegmental area and substantia nigra) and pallidum (ventral pallidum), the present study utilized retrograde tract tracing techniques to determine if there was a similar segregation of D1-like receptor agonist- and D2-like receptor antagonist-induced $\rm Fos\sb{2{-}16}$-like immunoreactivity in these accumbal projections. Like in the dorsal striatum, D1-like receptor agonists but not D2-like receptor antagonists, increased $\rm Fos\sb{2{-}16}$-like immunoreactivity in accumbal neurons projecting to the midbrain. Also like in the dorsal striatum, D2-like receptor antagonist-induced $\rm Fos\sb{2{-}16}$-like immunoreactivity was located preferentially in accumbal neurons projecting to the pallidum (ventral pallidum). However, unlike in the dorsal striatum where the vast majority of neurons which display D1-like receptor agonist-induced $\rm Fos\sb{2-16}$-like immunoreactivity project to the midbrain, nearly 50% of those neurons in the nucleus accumbens which were $\rm Fos\sb{2{-}16}$ immunoreactive after d-amphetamine or CY 208-243 administration projected to the ventral pallidum. Thus, a similar number of accumbal neurons which expressed D1-like receptor agonist-induced $\rm Fos\sb{2{-}16}$-like immunoreactivity were retrogradely labelled from the midbrain and ventral pallidum. (Abstract shortened by UMI.