Discrepancy between tau immunoreactivity and argyrophilia by the Bodian method in neocortical neurons of corticobasal degeneration.

To clarify different features of cytoskeletal pathology in neocortical neurons between corticobasal degeneration (CBD) and Alzheimer's disease (AD), the relationship between neurofibrillary tangles (NFTs), which are defined as a fibrillary structure stained by the Bodian method, and tau-immunopositive neurons in layers II-III of the premotor cortex was assessed by sequential staining for tau immunohistochemistry followed by the Bodian method on the same section. In AD brains, tau-like immunoreactivity in neurons was uniformly colocalized with Bodian-positive NFTs. In CBD brains, however, tau-immunopositive neurons could be classified into three different types: (1) those not stained at all by the Bodian method (diffuse cytoplasmic type), which represented the majority of these immunopositive neurons, (2) some partly stained by the Bodian method (mixed type), and (3) a few for which argyrophilia demonstrated by the Bodian method was completely colocalized with immunoreactivity (NFT type). This discrepancy between tau-like immunoreactivity and Bodian method is characteristic of CBD and suggests that the tau molecule is less liable to form argyrophilic fibrils in neocortical neurons of CBD.