Dopamine D1- and D2-receptor interaction in turning behaviour induced by dopamine agonists in 6-hydroxydopamine-lesioned rats.

The selective dopamine D2-antagonist sulpiride potentiated contralateral circling behaviour induced by the D1-agonist CY 208-243 in rats with unilateral lesions of substantia nigra, but reduced the effects of the selective D2-agonist bromocriptine. Similarly, the D1-antagonist SCH 23390 tended to increase the effects of bromocriptine but markedly inhibited CY 208-243 induced turning. The mixed D1/D2-antagonist fluphenazine was effective in reducing circling behaviour induced by either agonist, whereas pimozide (D1/D2) inhibited only the actions of bromocriptine. These results indicate that the actions of CY 208-243 and bromocriptine are mediated via distinct but interacting receptor subtypes.