Injection of SCH 23390, but not 7-hydroxy-DPAT, into the ventral tegmental area blocks the acute motor-stimulant response to cocaine

The present studies examined the effects of intra-ventral tegmental area (VTA) injection of SCH 23390, a dopamine (DA) D1 receptor antagonist or 7-OH-DPAT, a DA D2/3 receptor agonist, on cocaine-stimulated motor activity. Intra-VTA SCH 23390 (1.5-15 nmol/side) dose-dependently blocked cocaine-induced motor activity. Thus, 15 nmol/side SCH 23390 completely blocked, while 5 nmol/side attenuated, the motor-stimulant response to cocaine. These doses of SCH 23390 did not alter basal motor activity, suggesting the effects on the motor-stimulant response to cocaine were not the result of a generalized suppression of activity. In contrast to previous studies, intra-VTA 7-OH-DPAT did not alter basal motor activity at any of the doses tested (0.5-15 nmol/side). In addition, intra-VTA 7-OH-DPAT (1.5-15 nmol/side) pretreatment did not significantly alter the motor-stimulant response to cocaine. These data suggest that DA D1 receptors in the VTA may play a role in psychostimulant-induced motor activity. However, the role DA D2/3 receptors in the VTA may have in cocaine-induced motor activity remains unclear.