Identification of an aging-related spherical inclusion in the human brain.

Inclusions, such as corpora amylacea, axonal spheroids and ubiquitin-positive granular structures, are present in aged brains. We found a phosphorylated tau-positive inclusion in brain tissues obtained from 13 non-demented subjects and five patients with Alzheimer's disease. This inclusion was spherical and 3–20 µm in size. It was most frequently detected in the hippocampal CA1 region and in the prosubiculum but was not present in the white matter. The density of this inclusion increased significantly with aging and decreased after the occurrence of neurofibrillary tangles. The presence of the inclusion was confirmed using immunoelectron microscopy. These findings show a possibility that the inclusion is a novel aging-related structure in the human brain.