Different conformation of neuronal tau deposits distinguished by double immunofluorescence with ATS and thiazin red combined with Gallyas method

Different kinds of tau deposits were quantitatively investigated with thiaz in red (TR), a fluorochrome that binds to fibrillary structures like neurof ibrillary tangles (NFTs), in brains obtained at autopsy from patients with Alzheimer's disease (AD), Pick body (PB) disease, corticobasal degeneration (CBD) or diffuse NFTs with calcification (DNTC). After recording double-la beling fluorescence images with anti-paired helical filament tau (AT8) and TR, the sections were subjected to Gallyas method (GAL). This enabled three different staining properties to be compared on the identical neuron. AT8- positive neocortical neurons of AD and DNTC were fibrillary and uniformly p ositive for TR and GAL, consistently forming NFTs. NFTs lacking AT8 immunor eactivity (IR) were more frequent in DNTC than in AD, suggesting that evolu tion of NFTs is more accelerated in DNTC. Scarce TR staining in tau-positiv e neocortical neurons of CBD suggests their paucity of fibrillary structure . Since the affinity of TR for PB was not consistent, this may be dependent not only on the amount but also the characteristics of fibrillary structur es. PBs were further characterized by the scarcity of GAL staining. This ap proach, which quantitatively clarifies differences between AT8-IR, TR and G AL, provides a morphological basis for further investigations of the differ ent conformational states of tau from its deposition to fibril formation of various types.