Dystonia is predictive of subsequent altered dopaminergic responsiveness in a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine+3-nitropropionic acid model of striatonigral degeneration in monkeys.

We conducted a new chronic sequential 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 3-nitropropionic acid (3NP) intoxication paradigm in two female monkeys in order to reproduce the striatonigral degeneration type of levodopa-unresponsive parkinsonism. A comparison was made with MPTP-, 3NP-intoxicated and control monkeys. A levodopa-responsive parkinsonism emerged in all MPTP-treated monkeys. During subsequent 3NP intoxication, one of the two MPTP +3NP monkeys exhibited hindlimb dystonia concomitantly with a reduced levodopa response. All MPTP-monkeys had severe cell loss in the substantia nigra pars compacta (>70%), but 3NP-induced discrete lesioned areas and cell loss predominantly in the putamen appeared only in the dystonic and levodopa-unresponsive animal. We propose that the appearance of dystonia after 3NP intoxication following dopaminergic striatal denervation is the key symptom predictive of the loss of dopaminergic response.