Ultrastructural study of senile plaques and microvessels in the brain with Alzheimer's disease and Down's syndrome.

This study examined the relation between amyloid fibrils and senile plaques in brains of patients with Alzheimer's disease. All the senile plaques contained some amyloid fibrils, which seemed to be produced in the basement membranes of capillary endothelial cells and projecting into surrounding parenchyma. Even when amyloid fibrils could not be seen in senile plaques using light microscopy, at least one degenerate capillary containing amyloid fibrils was found when serial sections were examined by electron microscopy. Amyloid fibrils consisted of hollow rods and were composed of filaments arranged as a tightly coiled helix, each turn comprising five globular subunits. Many capillaries and microvessels showed degenerative changes. Many terminal arterioles had smooth muscle cells with an irregular shape and arrangement, often showing a series of focal constrictions. The findings suggest that the capillary degeneration with the formation of amyloid fibrils may be a primary change in the genesis of senile plaques. Furthermore, degenerative changes in the microvessels may also be an important factor in the loss of neurons in the brain of subjects with Alzheimer's disease.