Repeated treatment with imipramine potentiates the locomotor effect of apomorphine administered into the hippocampus in rats.

The effect of apomorphine, injected into the dorsal hippocampus, on the locomotor activity of imipramine-treated rats was studied. The rats were chronically implanted with cannulae 1 week before imipramine treatment. Imipramine was given in a dose of 10 mg/kg per os, acutely, or twice a day for 14 days. Intrahippocampal injection of apomorphine induced a dose-dependent increase in locomotor activity. This effect was antagonized by pretreatment with pimozide (2 mg/kg). Repeated, but not single, administrations of imipramine significantly enhanced the apomorphine-induced locomotor hyperactivity in rats. This effect was observed at 2, 48 and 96 h after the last dose of imipramine. The results obtained indicate that repeated administration of imipramine increases the responsiveness of the hippocampal dopaminergic system.