Bromocriptine induces marked locomotor stimulation in dopamine-depleted mice when D-1 dopamine receptors are stimulated with SKF38393.

In mice pretreated with reserpine plus alpha-methyl-p-tyrosine, neither the D-2 selective agonist bromocriptine, nor the D-1 selective agonist SKF38393, produced any measurable increase in locomotion in mice. However, the combination of the two agonists produced a marked and dose-dependent increase in co-ordinated locomotor activity. In mice with their dopamine stores and dopamine synthesis intact, SKF38393 was inactive by itself, but significantly enhanced the stimulant effect produced by bromocriptine. The data suggest that bromocriptine requires concomitant stimulation of D-1 receptors for the full expression of its behavioural stimulant effects.