Biphasic Effects of D₃-Receptor Agonists, 7-OH-DPAT and PD 128907, on the D₁-Receptor Agonist-Induced Hyperactivity in Mice

Abstract

Effects of D₃-receptor agonists, 7-OH-DPAT and PD128907, on the D₁-receptor agonist SKF81297-induced hyperactivity in mice were examined. 7-OH-DPAT and PD128907 significantly suppressed the SKF81297-induced hyperactivity at low doses, but significantly potentiated the hyperactivity at high doses. These D₃-agonists alone had no effect on the motor activity. A κ-receptor agonist that reduces dopamine release had no effect on the SKF81297-induced hyperactivity. These results suggest that lower doses of 7-OH-DPAT and PD128907 may negatively influence the D₁-receptor mediated behaviors via post synaptic D₃-receptors. On the other hand, higher doses of these compounds may positively influence these behaviors via D₂ or D₃-receptors.