Neuromelanin and RNA in cells of substantia nigra.

We have found that with accumulation of neuromelanin granules within cell bodies of neurones of the human substantia nigra there is a reduction in cytoplasmic RNA and a decrease in nucleolar volume. These observations imply a gradual decrease in the functional capacity of the cell such that eventually, the cell is unable to produce sufficient protein to maintain its metabolic economy with atrophy and death ensuing. This reduction in protein synthesis may result from the mechanical displacement and disruption of the endoplasmic reticulum by the accumulated pigment granules.