Levodopa-induced dyskinesia: facts and fancy. What does the MPTP monkey model tell us?

Levodopa-induced dyskinesia, one of the most frequent long-term side effects of antiparkinsonian therapy, is often attributed to denervation supersensitivity of dopamine receptors and perhaps more specifically the D-1 receptor. The available evidence based not only on clinico-pathological studies in patients but also on results of experiments performed on methyl-phenyl-tetrahydropyridine (MPTP)-treated monkeys suggests that the mechanisms may be more complex than heretofore believed. Thus it appears that no single receptor is the sole culprit, that some form of denervation supersensitivity is probably involved but not in the form of increased density of dopamine receptors. Moreover, other neurotransmitter systems must be considered such as GABA, excitatory aminoacids and peptides. The MPTP monkey model remains very useful for predicting the potential of new drugs for inducing dyskinesia. Such trials however must be performed in drug-naive animals.