Ultrastructural studies of amyloid fibrils and senile plaques in human brain.

Amyloid fibrils and senile plaques in brains with Alzheimer's disease, senile dementia and Down's syndrome were examined by light and electron microscopy. In addition, replicas of amyloid fibrils, made by a quick freezing method from a brain with Down's syndrome, were examined. All amyloid masses forming the cores of senile plaques consisted of numerous amyloid fibrils spreading from the walls of small blood vessels to the surrounding parenchyma. The amyloid fibrils ran in various directions, forming bundle-like groups in a geometrical array. They appeared as rods with hollow structures consisting of an array of globular units in the replicas, while they showed bead-like structure in the tissue specimens of 500-nm thick sections. The ultrastructure of replicas reveals a new finding on the structure of amyloid fibrils in the human brain.