Turning behavior in rats with unilateral lesions of the subthalamic nucleus: synergism between D1 and D2 receptors.

Rats with unilateral kainic acid lesion of the subthalamic nucleus showed a dose dependent rotational response to the lesioned side (ipsilateral) after systemic administration of the non-selective dopaminergic agonist apomorphine. Both D2 and D1 selective antagonists ((-)sulpiride and SCH23390) inhibited the response to apomorphine in these rats. Selective D2 and D1 agonists (quinpirole and SKF38393) were unable to induce turning behavior. However, an ipsilateral circling response was obtained after the simultaneous application of both agonists. The interaction mechanism between dopaminergic receptor subtypes seems to be similar to that of other normosensitive models of turning previously studied (Barone et al., 1986; Robertson and Robertson, 1986; Arnt and Perregard, 1987; Asim et al., 1990; Pazo et al., 1993). It is proposed that the ipsilateral turning response to dopaminergic agonists in rats with subthalamic nucleus lesion results from an impaired behavioral expression of the action of dopaminergic agonists on one side, leading the rats to turn away from the intact hemisphere.