The neural mechanisms underlying levodopa-induced dyskinesia in Parkinson's disease.

Treatment-related dyskinesias are the major limitation of dopamine replacement therapies such as levodopa in Parkinson's disease (PD). Recent studies in parkinsonian, nonhuman primates have highlighted abnormalities in neural functioning that might underlie the generation of dyskinetic symptoms in patients with PD who have received prolonged dopaminergic therapy. This article reviews studies on metabolic activity in subregions of the basal ganglia which suggest that profound abnormalities in basal ganglia output may underlie levodopa-induced dyskinesia. Such abnormalities may result from changes within basal ganglia circuitry and may include either overt changes in average firing rate or modulation of the pattern of cell-cell communication within subregions of the basal ganglia circuitry. An appreciation of abnormalities in the mechanisms responsible for modulating synaptic transmission in the basal ganglia may suggest novel therapeutic approaches to the problem of dyskinesia.