Comparison of four staining methods on the detection of neuritic plaques

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Abstract
The sensitivities of four staining methods for detecting the presence of neuritic plaques in the normal aging. Alzheimer disease (AD) and Down's syndrome (DS) brains were compared. The Bielschowsky method and immunostaining with monoclonal antibody (4G8, IgG2b) to β-amyloid revealed the highest numbers of plaques. The thioflavin S-staining method showed about 38%–70% of plaques as shown by the Bielschowsky method. The Bodian method is the least sensitive method revealing about 26%–39% of plaques as compared with the Bielschowsky method. In the first part of this study, serial sections (6 μm) of the plaques from AD and DS brains were cut and stained with Bielschowsky, thioflavin S and Bodian methods, respectively. In the second part, Bielschowsky and immunostaining methods were used to stain serial sections (6 μm) of plaques from the same block of brain tissue. A Zeiss Axiophot fluorescence microscope, coupled with the Cambridge Quantiment 970 and Zeiss Videoplan computerized image analyzers, was used to quantify the number of plaques. Both Bielschowsky and immunostaining methods revealed the presence of both the peripheral zone (halo) and the central core of a classical plaque and resulted in the highest plaque counts. The central core of the thioflavin S-stained plaques were still clearly present, but the peripheral zone was barely visible. In Bodian stain, however, both central core and peripheral zone were poorly stained and not detectable by computer. They were quantified by human eye observation. The Bielschowsky method and immunostaining with pretreatment with formic acid are, therefore, the most sensitive methods showing the highest contrast of plaque image and thus facilitate the quantification of plaque by computer. However, Bielschowsky method is not a specific method for plaques. It stains neurofibrillary tangles and blood vessels regardless of whether they have amyloid deposits or not. Immunostaining is a sensitive and specific method for amyloid and exhibits low background staining. It confirmed that all Bielschowsky-stained plaques contained amyloid deposit.

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