The neuronal mechanism underlying parkinsonism and dyskinesia, and differential roles of the putamen and caudate nucleus.

The basal ganglia were manipulated pharmacologically by using GABA antagonists and also 1-methyl-14-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rats, cats, and monkeys, and neuronal activities were recorded from the basal ganglia. It was concluded that (a) in parkinsonism, neuronal activities of the caudate nucleus decreased, those of the pars reticulata of the substantia nigra and internal segment of the globus pallidus increased, and those of the ventromedial nucleus of the thalamus depressed markedly; (b) in dyskinesia, periodical discharges of the caudate-putamen complex were the primary event in rodents, resulting in activation of the thalamus; and (c) the caudate nucleus was involved in the manifestation or driving of locomotion, while the putamen was related to regulation of tonus in contralateral muscles with proximal dominancy.