Ultrastructural Study of Senile Plaques and Microvessels in the Brain in Alzheimer’s Disease

Summary

Several kinds of senile plaques were examined by light and electron microscopy.

Amyloid masses around capillaries formed the cores of typical senile plaques. All the senile plaques contained at least some amyloid fibrils, and these seemed to be produced at the basement membranes of capillary endothelial cells and projected into the surrounding parenchyma. Even when the senile plaques themselves appeared with light microscopy to lack amyloid fibrils, at least one degenerable capillary with amyloid fibrils was demonstrated when serial sections were examined ultrastructurally. The capillaries producing amyloid fibrils showed degeneration and some of them were destroyed.

The findings described above suggest that the amyloid fibrils which form the cores of several kinds of senile plaques seem to be produced at the basement membrane of the endothelial cell. It is speculated that the capillary degeneration with formation of amyloid fibrils may be a primary change in the genesis of senile plaques.

On the other hand, endothelial cells of many microvessels showed swelling or atrophy, and the basement membranes were hypertrophic and irregular in shape. Considering the described findings above, it might be suggested that the microcirculatory disturbance due to degeneration of the microvessels, including amyloid angiopathy, is very important in the changes in the brain with Alzheimer’s disease.

Finally, amyloid fibrils appeared as a rod which was hollow in the center and was composed of a filament arranged as a tightly coiled helix, each turn of which consisted of five globular subunits. This finding showed a new ultrastructure of amyloid fibrils in the brain.