Cocaine and dopaminergic actions in rat neostriatum

Electrophysiological experiments were conducted in vivo to characterize the involvement of dopamine in effects of cocaine at the cellular level. L-DOPA (preceded by carbidopa) evoked excitation and depression equally at 0.25 mg/kg; however, at 0.5 and 1.0 mg/kg depression in the basal rate of discharge predominated. Cocaine evoked similar responses. At 0.25 and 0.5 mg/kg excitation and depression were elicited in about equal proportion, while at 1.0 mg/kg depression was predominant. Cocaine-induced neuronal changes were reversible by haloperidol. In experiments with specific dopamine antagonists, cocaine-induced neuronal depression was blocked with the D1 antagonist, SCH 23390 at a dose of 0.25 mg/kg. The D2 antagonist, eticlopride, did not alter cocaine-induced depression in any specific manner. Excitation, following cocaine, was not altered by intervention with SCH 23390, yet it was blocked with the D2 antagonist eticlopride at a dose of 0.25 mg/kg. The duration of these changes was consistent with the observed duration of the psychotropic actions of cocaine.