Differential effects of dopamine agonists on locomotion in intact and reserpine-treated mice.

1. Apomorphine and bromocriptine induced a dose-dependent locomotion in mice. The responses of both drugs were decreased by SCH 23390 or sulpiride pretreatment. 2. Locomotor activity induced by apomorphine was increased and that of bromocriptine was decreased by reserpine. 3. SKF 38393 or quinpirole also induced locomotion. The response of SKF 38393 was decreased by reserpine. 4. Combination of SKF 38393 with bromocriptine induced a significant locomotor activity different from that of SKF 38393 or bromocriptine in reserpinized animals. 5. Combination of quinpirole with bromocriptine even decreased the response of bromocriptine in intact animals. 6. In conclusion, bromocriptine needs intact dopaminergic neurons and activation of D-1 receptor for expression of locomotion. High doses of quinpirole may induce locomotor activity possibly through D-1/D-2 receptor activation and quinpirole may potentiate the effect of bromocriptine on autoreceptor for inducing sedation.