LOW-DOSES OF APOMORPHINE SUPPRESS OPERANT MOTOR-PERFORMANCE IN RATS

The purpose of this study was to examine the effects of low doses of a pomorphine on motor performance. Six rats were rewarded with sugar wat er on a partial reinforcement schedule for pressing force-sensitive be ams with a minimum force of 1 g. The kinetics of individual responses and the temporal characteristics of response sequences were measured; open field locomotor activity was also measured in a separate apparatu s. Apomorphine (APO), amphetamine (AMP), and haloperidol (HAL) were ad ministered systemically. It was found that low doses of APO (0.03 and 0.1 mg/kg, SC) produced weaker and longer beam presses. These decrease s in response peak force resulted from decreases in the rate of rise o f force. APO also caused disproportionate lengthening of beam release time. In addition, the low doses of APO increased the time intervals b etween consecutive components of response sequences. These low doses o f APO are known to decrease dopaminergic tone. Hence, the observed pat tern of motor dysfunctions produced by APO is similar to the bradykine sia seen in human Parkinson's disease.