• Nucleolar volume and melanin pigment were measured in nerve cells of the substantia nigra in cases of idiopathic Parkinson's disease and in other cases of parkinsonism associated with cerebrovascular disease. In cerebrovascular parkinsonism, nucleolar volume is reduced by 16%, whereas melanin content is unchanged, reflecting local deficiencies in circulation on function of nerve cells, otherwise normal for age. In idiopathic parkinsonism, remaining cells are atrophied, and nucleolar volume is reduced by 16%. Melanin content is decreased by 22% because of preferential loss of the highly pigmented cells. The pathogenesis of idiopathic parkinsonism may lie with a secondary aggravation of changes that occurs, as part of the "normal process of aging," in relation to the cytotoxic effects of dopamine metabolism and melanin accumulation.
Mann DMA, Yates PO. Pathogenesis of Parkinson's Disease. Arch Neurol. 1982;39(9):545–549. doi:10.1001/archneur.1982.00510210015004
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