Light and electron microscopic studies of pigment in human and rhesus monkey substantia nigra and locus coeruleus

Neuromelanin pigment of the substantia nigra and locus coeruleus from nine human autopsy cases and from four rhesus monkeys was studied. Melanin and lipofuscin pigments from other anatomical sites were also observed for the purpose of comparison with the substantia nigra‐locus coeruleus pigment. Ultrastructurally, the neuromelanin pigment granule was composed of three distinct components. The first was a finely granular, medium dense matrix which occasionally had linear configurations very similar to those of neuronal lipofuscin granules from human cerebral cortex. The second component was a very dense, coarsely granular material which appeared to to be deposited on the finely granular matrix. This very dense component was apparently the reducing part of the neuromelanin granule, as it was the site of localization of silver deposits in formalin‐fixed tissue which had been stained with diamine silver prior to post‐osmication and examination in the electron microscope. No evidence of silver reduction was noted in lipofuscin pigment. The third component of the neuromelanin granule was a lipid globule which was not preserved in glutaraldehyde or formol‐permanganate fixed tissue. A lipid globule was not observed in melanin granules from the skin, eye, or pia mater.