Severe long-term 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in the vervet monkey ( Cercopithecus aethiops sabaeus)

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces parkinsonian neurochemical and functional deficits in human and non-human primates. The utility of MPTP-induced parkinsonism in monkeys as an animal model of Parkinson's disease would be greater if it produced a persistent and stable behavioural syndrome so that the effects of novel therapeutic treatments can be accurately assessed. Further, the claim that many species including primates spontaneously recover from MPTP is a significant difference from idiopathic Parkinson's disease. This experiment focused on the long-term (six months) persistence of behavioural deficits in severely and moderately parkinsonian monkeys. The severity of the syndrome was based on a quantitative and objective measure of parkinsonism. Adult male African green (vervet) monkeys ( Cercopithecus aethiops sabaeus) were treated with MPTP (cumulative dose 2.5 mg/kg over five days), and six were saline-control treated. MPTP-treated subjects were examined in two groups: those that were severely parkinsonian (“severe” group, n=11) and those that were moderately impaired (“moderate” group, n=5) the month after treatment. Summary factor scores were examined reflecting abnormal (“parkinsonian”) behaviour and normal “healthy” behaviour. Subjects that displayed severe parkinsonism the month after MPTP were found to show stable and severe parkinsonism for the time period studied. In contrast, the group of animals that initially were moderately parkinsonian did not show a stable deficit during the study. These data suggest that the initial severity of the deficit is an important predictor of outcome. None the less, stable parkinsonism can be observed in severely parkinsonian subjects despite variability in the severity of the impairment in response to MPTP treatment. Two moderately and three severely affected subjects were studied for more than six months and they appeared to show equivalent scores at six months compared with between 11 to 19 months after MPTP administration. MPTP-treatment in the vervet monkey can result in persistent long-term deficits and therefore provides an excellent phenomenological as well as neuropathological model of Parkinson's disease.