Dopamine agonists: Their effect on locomotion and exploration

The results of two experiments are reported in which animals were simultaneously tested for locomotion and exploration after systemic injections of dopaminergic agonists. The testing apparatus was an open field in which 16 holes were made in the floor. Locomotion was measured by movement in the open field. Exploration was measured by investigation of the holes in the floor. In the first experiment the effects of apomorphine and ET 495 at three dose levels were compared in male rats that had been adapted to the testing situation for 21 days. In these animals, both drugs reduced exploration but only apomorphine reduced locomotion. In the second experiment, male and female rats with little prior experience in the apparatus were tested under three doses of apomorphine. In general the females were more sensitive to the drug, showing decreases in exploration at lower doses than did the males. Furthermore, the apomorphine failed to reduce locomotor activity in either sex except under the highest dose of apomorphine used (10 mg/kg) at which time stereotyped behavior was frequently observed.