DIFFERENTIAL-EFFECTS OF DOPAMINE-D2 AGONIST QUINPIROLE UPON THE DORSAL IMMOBILITY RESPONSE IN RATS

The effects of various dose levels of systemically injected quinpirole upon the dorsal immobility response (DIR) over a time course was investigated in male rats. A low dose of quinpirole (0.01 mg/kg) significantly attenuated the duration of the DIR following the 10-min interval, whereas the highest dose (1.0 mg/kg) had a biphasic effect so that at the 10-min interval the duration of the DIR was significantly potentiated and at the 60-min interval the duration of the DIR was significantly attenuated. The intermediate dose (0.1 mg/kg) had intermediate behavioral effects. The data support the growing evidence that quinpirole has differential effects upon behavior over time as a function of the dose levels. The present data were discussed in reference to presynaptic and postsynaptic dopamine D2 receptor theory.