APOMORPHINE AND AMPHETAMINE PRODUCED DIFFERENTIAL-EFFECTS ON THE SPEED AND SUCCESS OF REACTION-TIME RESPONDING IN THE RAT

Apomorphine, a nonselective, direct-acting dopamine agonist, and amphe tamine, a nonselective indirect-acting dopamine agonist, were compared for their effects on the reaction time response in rats. Animals were shaped to release a lever in response to an auditory/visual stimulus to avoid mild foot shock. The characteristics of the reaction time res ponse of primary interest were percent successful avoidance and respon se latency. Apomorphine (0, 1, and 5 mg/kg, IP) significantly decrease d successful avoidance, but had no effect on response latencies. Thus, the decrease in successful avoidance was not a direct result of longe r latencies. Amphetamine (0, 0.5, and 1 mg/kg, IP) produced a differen t pattern of effects on the reaction time response. Successful avoidan ce was not affected by amphetamine treatment. However, response latenc ies were dose-dependently decreased in response to amphetamine. These results demonstrate that dopamine receptor stimulation by different do pamine agonists produces a different pattern of effects on the charact eristics of the reaction time response. In addition, these results dem onstrate that successful avoidance can be modulated independently of r esponse latencies.