Argyrophilic grains of Braak: occurrence in dendrites of neurons containing hyperphosphorylated tau protein
Abstract
Braak's argyrophilic grains (ArGs) are spindle-shaped neuropil structures originally found in patients afflicted with adult onset dementia. We recently observed that tau protein is hyperphosphorylated in most nerve cells in areas rich in ArGs, suggesting that these grains may be a morphological expression of tau protein pathology in local neurons. The aim of this study was therefore to determine in three cases with ArGs whether grains are associated with individual neurons containing hyperphosphorylated tau. A combination of Gallyas silver staining and AT8 immunocytochemistry was used. AT8 is a monoclonal antibody that recognizes tau in a phosphorylation-dependent manner. Up to 80% of pyramidal cells of sector CA1 showed diffuse AT8 staining of their cell bodies and dendrites. Most grains were freely scattered throughout the neuropil. However, some were clearly located in side-branches of apical dendrites of AT8 immunoreactive pyramidal neurons. Dendritic branches often formed bush-like ramifications containing clusters of ArGs. Other dendrites consisted of a single stump containing one or two large grains at their tips. Spheroidal enlargements of dendritic branches, with a size corresponding to ArGs, were also found in Golgi C...Continue Reading
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