Study of the neural basis of circling behavior induced by L-dopa in lesioned entopeduncular cats

Experiments were carried out in cats bearing unilateral electrolytic lesion of the entopeduncular nucleus. The animals were tested for circling 1-2 weeks after surgery. Postoperatively the cats displayed transient spontaneous ipsiversive turning. The administration i.p. of L-DOPA (80 mg/kg) plus CarbiDOPA (30 mg/kg), suspended in 10% Tween 80, induced rotational behavior toward the lesioned side. This effect began about 26 min after drug administration and reached its maximum 40-110 min after the injection. Electrolytic lesions placed in the superior colliculus, strionigral pathway or pedunculopontine nucleus, contralateral to the lesioned entopeduncular nucleus did not modify the circling behavior induced by L-DOPA. Similar results were observed following unilateral lesion of the sensorimotor cortex or the VL thalamic nucleus. These results suggest that the circus movements induced by L-DOPA, in animals with unilateral lesion of the entopeduncular nucleus, is not mediated by the classic outflow of the striopallidal system.