A study of toxic effect of amyloid substance in brain

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Toxic effect of amyloid substances against tissue was investigated. Diffuse type of senile plaques are thought to be an initial step of amyloid-formation. beta-amyloid or preamyloid in diffuse plaque was observed by electron microscopy applying immunohistochemical and methemanine-silver impregnation methods. The amyloid substance in this structure consisted of fine short fibrillar bundle and was partially amorphic. Most of the preamyloid deposited between small processes. The membrane of these processes showed unclear appearance in comparison to the same structure in other portion without preamyloid. This finding may indicate that the preamyloid induce the degeneration of the surrounding tissue due to its toxic effect.Another important abnormal protein with amyloid nature, the neurofibrillary tangles (NFT) , was also investigated to elucidate its toxic effect. Extracellular NFT was, differ from intraneuronal NFT,surrounded by degenerated neuronal processes and invaded by numerous astrocytic processes and microglia. The Immunohistochemical and ultrastructural alteration of extracellular NFT was also noticed. A series of these findings may be the evidence of toxic effect of NFT against the surrounding tissue.