BIPHASIC EFFECTS OF D-3-RECEPTOR AGONISTS, 7-OH-DPAT AND PD128907, ONTHE D-1-RECEPTOR AGONIST-INDUCED HYPERACTIVITY IN MICE

Effects of D-3-receptor agonists, 7-OH-DPAT and PD128907, on the D-1-r eceptor agonist SKF81297-induced hyperactivity in mice were examined. 7-OH-DPAT and PD128907 significantly suppressed the SKF81297-induced h yperactivity at low doses, but significantly potentiated the hyperacti vity at high doses. These D-3-agonists alone had no effect on the moto r activity. A kappa-receptor agonist that reduces dopamine release had no effect on the SKF81297-induced hyperactivity. These results sugges t that lower doses of 7-OH-DPAT and PD128907 may negatively influence the D-1-receptor mediated behaviors via post synaptic D-3-receptors. O n the other hand, higher doses of these compounds may positively influ ence these behaviors via D-2- Or D-3-receptors.