ANTAGONISM BY 8-OH-DPAT, BUT NOT RITANSERIN, OF CATALEPSY INDUCED BY SCH-23390 IN THE RAT

In the present experiments, it was shown that the catalepsy induced by the dopamine D1 antagonist SCH23390 (0.2 mg kg-1 sc), was completely antagonised by the administration of 8-OH-DPAT (0.1 mg kg-1 sc) for the duration of the effect of SCH 23390 (approx. 120 min). Neither the catalepsy induced by raclopride (16 mg kg-1 sc) nor that induced by SCH23390 (0.2 mg kg-1 sc) could be antagonised by treatment with the 5-HT2 receptor antagonist ritanserin (0.13-2.0 mg kg-1 sc). Administration of SCH23390 (0.0 125-0.2 mg kg-1 sc) produced a significant suppression of avoidance behavior at all doses, and also produced a significant decrease in the number of intertrial crosses. At the higher doses, 0.05 and 0.2 mg kg-1 sc, there were also escape failures. In contrast to the finding in our previous report that raclopride and 8-OH-DPAT in a synergistic manner produce a suppression of conditioned avoidance behavior, no such interaction was found between 8-OH-DPAT (0.1 mg kg-1 sc) and SCH 23390 (6-mu-g kg-1 sc) in the present study.