Lack of toxicity of human neuromelanin to rat brain dopaminergic neurons.

Neuromelanin extracts from the substantia nigra of a parkinsonian and a non-parkinsonian case were injected into the substantia nigra and caudate-putamen of rat brains. Rats were sacrificed at periods ranging from 3 days to 8 months. Substantial amounts of neuromelanin remained at both injection sites even after 8 months, indicating a very slow rate of phagocytosis. No differences were seen in the reaction to control or parkinsonian melanin, and no neurotoxicity attributable to the melanin was observed. These data fail to support the hypothesis of neurotoxicity of melanin as a cause of Parkinson's disease.