Deficits in behavioral initiation and execution processes in monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism.

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to two monkeys led to hypokinesia, tremor, rigidity, adipsia and aphagia. Quantitative assessment of hypokinesia revealed increased reaction time, delayed onset of muscle activity and prolonged movement time in a forelimb reaching task after selective degeneration of the nigrostriatal dopamine (DA) system sparing mesocortical dopamine neurons. The losses of pars compacta cells of substantia nigra, of striatal [3H]mazindol binding and of striatal DA content (more than 90%) quantitatively paralleled the severity of behavioral deficits. Additional monoamine systems were affected with stronger MPTP effects.