Silver stains distinguish tau-positive structures in corticobasal degeneration/progressive supranuclear palsy and in Alzheimer’s disease—Comparison between Gallyas and Campbell-Switzer methods

Possible differences in silver-staining profiles and their relation to tau-like immunoreactivity were investigated on cortical sections from corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), Down’s syndrome (DS) and Alzheimer’s disease (AD). Pairs of mirror sections were double-fluorolabeled with an anti-PHF tau (AT8) antibody and thiazin red (TR), a fluorochrome that labels fibrillary structures such as neurofibrillary tangles (NFTs). Subsequently, one of the pair was stained with Gallyas method (GAL), and the other with Campbell-Switzer method (CS). Identification of the same structure on the corresponding microscopic fields enabled a comparison of four different profiles of each structure: AT8 immunoreactivity, and affinity to TR, GAL and CS. NFTs of DS/AD, containing three- and four-repeat tau, were positive for TR, GAL and CS. AT8-immunoreactive structures of CBD/PSP, containing mainly four-repeat tau, were positive for GAL, but negative for CS and TR. This discrepancy is explainable if the argyrophilia with GAL is related to deposits containing four-repeat tau, while that with CS is linked to those containing three-repeat tau. The lack of CS labeling may also be related to poor TR staining, possibly representing scarcity of fibrillary structure in CBD/PSP. The absence of CS staining is characteristic of tau-positive structures of CBD/PSP, which is readily distinguishable from NFTs of DS/AD, hence is of potential pathological and diagnostic relevance.