Presence of reactive microglia in monkey substantia nigra years after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration

This report describes the presence of reactive microglia, the accumulation of extracellular melanin, and the extensive loss of dopaminergic neurons in the substantia nigra of monkeys administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) 5 to 14 years before death. This evidence of chronic neuroinflammation years after MPTP exposure is similar to that previously reported in humans. The monkeys were drug free for at least 3 years before death, indicating that a brief exposure to MPTP had instituted an ongoing inflammatory process. The mechanism is unknown but could have important implications regarding the cause of Parkinson's disease and possible approaches to therapy.