Alzheimer-type pathology in melanin-bleached sections of substantia nigra.

Bleaching of melanin prior to Gallyas staining enabled us to detect an unexpectedly large number of neurofibrillary tangles (NFTs; 62 and 50 NFTs in the upper and the lower substantia nigra, respectively, mostly in the neuronal cytoplasm of the medial zona compacta) in brains of patients who had had Alzheimer's disease. Amyloid-like deposits were quite scarce. In Alzheimer's disease it has been commonly observed that other subcortical nuclei projecting widely to the cerebral cortex also contain a large number of NFTs, although they have few amyloid deposits. In these subcortical nuclei retrograde degeneration may initially affect intraneuronal processes, leading to the preferential development of NFTs in the neuronal cytoplasm.