Two automated locomotor activity tests for dopamine autoreceptor agonists

Abstract

In the first test (exploratory activity), pretreated rats explored a novel environment in the dark. The potential autoreceptor agonists apomorphine HCl, N-n-propylnorapomorphine (NPA), and N-n-propyl-3-(3-hydroxyphenyl)-piperidine (3-PPP) and its enantiomers decreased the total distance travelled while at the same time paradoxiacally increasing the number of discrete movements. This is a very different pattern from that of the typical antipsychotic drugs haloperidol HCl and chlorpromazine HCl, and the atypical antipsychotic drug clozapine, which also decreased the total distance travelled but decreased the number of movements. Both groups decreased the distance/movement. In the second test, rats were habituated to the monitors in the light and then treated with test drug and stimulant (d-amphetamine sulfate or apomorphine HCl). Apomorphine HCl, NPA, and (+)3-PPP antagonized amphetamine-stimulated locomotor behavior (total distance) without antagonizing apomorphine-stimulated behavior, suggesting a presynaptic dopamine autoreceptor agonism. EMD 23448 gave equivocal activity. On the other hand, haloperidol HCl, chlorpromazine HCl, and clozapine decreased both amphetamine- and apomorphine-stimulated behavior, suggesting a postsynaptic dopamine antagonism. 3-PPP and (−)3-PPP showed neither pattern in this test.