Regional quantitative study of formation process of neurofibrillary tangles in the hippocampus of non-demented elderly brains: comparison with late-onset Alzheimer's disease brains.

We quantitatively investigated the formation process of neurofibrillary tangles (NFT) in the hippocampus of 32 brains from non-demented elderly persons using tau-immunohistochemistry, compared with 13 brains from patients with late-onset Alzheimer's disease (AD). The 32 non-demented elderly brains were classified into 16 brains in group I and 16 brains in group II mainly based on the distribution of tau-positive neurons in the hippocampus. Tau-positive neurons were found predominantly in the CA2 in group I, while they were found predominantly in the subiculum-pre-CA1 in group II. Most late-onset AD brains showed a distribution of tau-positive neurons similar to that in group II. In addition, the distribution pattern of tau-positive neurons in the hippocampus was closely related to degeneration of the perforant pathway with the accumulation of tau. These findings suggest that NFT occur first in the CA2 and extend to the subiculum-pre-CA1 in group I, while they occur first in the subiculum-pre-CA1 and extend to the CA2 later in group II, and that the NFT occurring in the subiculum-pre-CA1 are mainly related to degeneration of the perforating route and in the CA2 are related to the degeneration of the non-perforating route.