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 ar ea (VTA) injection of SCH 23390, a dopamine (DA) D1 receptor antagonis t or 7-OH-DPAT, a DA D2/3 receptor agonist, on cocaine-stimulated moto r activity. Intra-VTA SCH 23390 (1.5-15 nmol/side) dose-dependently bl ocked cocaine-induced motor activity. Thus, 15 nmol/side SCH 23390 com pletely blocked, while 5 nmol/side attenuated, the motor-stimulant res ponse to cocaine, These doses of SCH 23390 did not alter basal motor a ctivity, suggesting the effects on the motor-stimulant response to coc aine 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 addit ion, intra-VTA 7-OH-DPAT (1.5-15 nmol/side) pretreatment did not signi ficantly alter the motor-stimulant response to cocaine. These data sug gest that DA D1 receptors in the VTA may play a role in psychostimulan t-induced motor activity, However, the role DA D2/3 receptors in the V TA may have in cocaine-induced motor activity remains unclear.