Behavioral and biochemical studies in monkeys made hemiparkinsonian by MPTP.

Monkeys were required to press a lever rapidly for food, using either the right or the left hand. After stable baseline performance was established, MPTP (N-methyl-4-phenyl-2,3,5,6-tetrahydropyridine) was injected into the internal carotid of one side via a transfemoral catheter. The onset and time course of clinically severe, Parkinson-like symptoms were paralleled by a significant decrease of bar-pressing activity in the side contralateral to injection, while the forelimb in the unaffected side continued normal pressing. The unilaterality of effects was confirmed biochemically after sacrifice by a 95% drop in striatal dopamine (DA) levels of the injected compared to the uninjected hemisphere. The results show that hemiparkinsonism achieved by carotid injection is very stable; that normal motor behavior is maintained on the unaffected side and that goal-achieving strategies remain active, but that the affected side is unable to execute the task unless extrinsic levodopa is provided.