Development of a stable, early stage unilateral model of Parkinson's disease in middle-aged rhesus monkeys.

An important issue raised in testing new neuroprotective/restorative treatments for Parkinson's disease (PD) is the optimal stage in the disease process to initiate therapy. Current palliative treatments are effective in the early disease stages raising ethical concerns about substituting an experimental treatment for a proven therapy. Thus, we have endeavored to create a stable 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) nonhuman primate model of early PD. The new model was created by controlling for dose and route administration of MPTP (unilateral intracarotid infusion), and age of the animals (middleaged, 16-19 years old) in 27 female rhesus monkeys. All animals showed stable parkinsonian features lasting for up to 12-month as per behavioral evaluation. Compared with late-stage PD animals, postmortem analysis demonstrated that more dopaminergic neurons remained in the substantia nigra pars compacta, and more fibers were found in the striatum. In addition, tissue levels of striatal dopamine and its metabolites were also higher. Our results support that a milder but stable PD model can be produced in middle-aged rhesus monkeys.