Role of dopamine D1 receptors in the striatal and cortical fos expression induced by the muscarinic agonist pilocarpine.

Injections of the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg) induced pronounced expression of the immediate early gene (IEG) product Fos in the striatum and cortex of rats. Pretreatment with the dopamine D1 receptor antagonist 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-H-3-benzazepine hydrochloride (SCH-23390; 0.2-2.0 mg/kg) drastically attenuated the pilocarpine response in the striatum, but had no effect in the cortex. In contrast, the muscarinic receptor antagonist scopolamine (0.75-3.00 mg/kg) virtually abolished the Fos response at both sites. These results suggest that stimulation of dopamine D1 receptors may mediate the effects of muscarinic agonists on Fos expression in the striatum, but not the cortex.