Ultrastructural abnormalities in the cerebral neocortex and hippocampus associated with Alzheimer's disease and aging.

Lesions of the frontal and temporal neocortices and hippocampus typically found in Alzheimer's disease were looked for with the electron microscope in 119 autopsy cases whose ages ranged from 24-93 years. By light microscopy 11 of the cases over the age of 60 had large numbers of plaques and neurofibrillary tangles, whereas the remaining cases had few or none. From the age frequency distribution of the electron microscopic lesions in these two categories of cases amyloid fibrils and abnormal neurites, both components of plaques, were first seen at approximately the same time. This suggests that amyloid is unlikely to precede the neurites in their formation. The abnormal neurites were thought, due to the small numbers of synapses in their walls, to be largely derived from degenerating neuronal processes and not synaptic boutons.