QUANTITATIVE BEHAVIORAL-STUDY OF THE ACUTE AND LONG-TERM EFFECTS OF 2-STAGE BILATERAL 6-OHDA-INDUCED LESIONS OF THE NIGROSTRIATAL DOPAMINERGIC SYSTEM IN MONKEYS

Bilateral lesions of the nigrostriatal dopaminergic system (2-stage le sions separated by 5-6 months) were induced in 3 monkeys trained to in itiate forelimb-reaching movements toward a visual target. After each lesion, analysis of the task performance over several months of regula r testing showed that the latency to initiate the movement was permane ntly prolonged in monkeys showing 90% or more striatal dopamine deplet ion, whereas animals with less severe depletion completely recovered t he task performance. Several months after a unilateral nigrostriatal d amage, a lesion on the other side produced impairments only on the sid e of the body contralateral to that second lesion and did not reinstat e the deficits on the side previously affected by the first lesion. Th is suggests that the remaining intact nigrostriatal dopaminergic syste m may not be involved in the long-term behavioral recovery observed in monkeys with a unilateral lesion.