The D2 dopamine receptor agonist LY171555 induces catalepsy in the mouse

The dopamine agonist LY171555 (quinpirole), a specific D2 receptor agonist, induces catalepsy in mice at doses ranging from 0.3 to 10 mg/kg. The effects of an intermediate dose of this compound (1 mg/kg SC) were antagonized by 25 mg/kg of the selective D2 antagonist (-)-sulpiride (IP) injected 20 min before LY171555. SCH 23390, a selective D1 antagonist, administered (0.3 mg/kg IP) 20 min before LY171555 (1 mg/kg) enhanced the cataleptic effects of this compound. Finally, when the D1 dopamine receptor agonist SKF 38393 (20 mg/kg SC) was administered immediately beforehand, the cataleptic effects of 1 mg/kg of LY171555 were markedly reduced. These results suggest that there is a functional interaction between D1 and D2 dopamine receptors in the modulation of catalepsy.