Interactive effects of stimulation of D1 and D2 dopamine receptors on fos-like immunoreactivity in the normosensitive rat striatum.

Systemic administration of the selective, full, D1 dopamine agonist A-77636 [(1R,3S)3-(1'-adamantyl)-1-aminomethyl-3,4- dihydro-5,6-dihydroxy-1H-2-benzopyran hydrochloride] (0.36-2.9 mg/kg) led to a dose-dependent induction of Fos-like immunoreactivity (FLI) in the striatum. Quantitative analysis of the sections indicated that immunoreactive cells were more numerous in the medial than the lateral striatum and, within these regions, appeared to be randomly distributed. The staining produced by A-77636 could be abolished by pretreatment with the selective D1 antagonist SCH-23390. The selective D2 dopamine agonist quinpirole (3 mg/kg) had no effect on striatal FLI when given by itself, but markedly potentiated the weak striatal staining produced by low doses of A-77636. When combined with the highest dose of A-77636, which produced substantial staining by itself, quinpirole produced an increase in the number of immunoreactive cells seen in the lateral striatum but actually decreased the number present in the medial striatum. Statistical analysis of the distribution of immunoreactive cells demonstrated that, in both regions, quinpirole converted the relatively homogeneous staining seen after A-77636 alone into a markedly patchy pattern. These findings indicate that stimulation of D2 receptors produces both stimulatory and inhibitory effects on the D1-mediated expression of Fos in the striatum and that the interaction between D1 and D2 receptor stimulation must, therefore, be more complex than the simple synergism suggested by previous studies.