[Neuritic degeneration in Alzheimer-type dementia, with special reference to the presence of dark neurites]

Abstract

Four cases of neuritic degeneration in the cerebral cortex of Alzheimer-type dementia patients have been examined by routine and Gallyas-silver electron microscopy. This examination has revealed neuritic changes described below. (1) Dendrites and axons with an increased electron density (dark neurites) were found scattered throughout the neuropils, these dark neurites thought to be either degraded neurites resulting from simple neuronal atrophy or retrograde and/or transsynaptic degeneration due to an axonal injury within the senile plaques. (2) Both dystrophic neurites and neuropil threads were found scattered throughout the neuropils and showed some similarities in producing abnormal substances in their processes and in their manner of aggregating, especially within the senile plaque region. These degenerated neurites may have been caused by neurotoxicity of the amyloid. On Gallyas electron microscopic inspection, neurites often are found to have small fibrous and sometimes tubular structures on which silver particles are deposited. This finding may represent the initial stage of a neurofibrillary change. (3) The regeneration of neurites though such ultrastructures is not known, but such concept is believed by many authors and is discussed.