This project is aimed at understanding the biochemistry, biology and molecular pathologenesis of Alzheimer's disease (AD). In this disorder, the main histopathological lesion is the presence of neurofibrillary tangles and neuritic plaques in the cerebrum. Alzheimer's neurofibrillary tangles (ANT) have been found to contain unique antigenic determinants and determinants in common with several normal cytoskeletal components. The relationship between ANT and neurofilaments (NF) will be examined further by identifying the topographical distribution of NF-ANT determinants in the NF molecules. The techniques to be used are limited proteolysis, chemical cleavage of NF proteins and immunoblots. Three proteins in normal and AD brain homogenates of molecular weight 58-70kd have recently been shown to react with monoclonal anti-ANT antibodies. The distribution of these proteins in normal and AD brain and their relation to ANT accumulation will be studied by ELISA and immunoblotting technique. Two NF-ANT common antigenic determinants have been found to be sensitive to phosphatase. To find out if ANT consist of phosphorylated proteins, we will purify ANT from autopsy brains of subjects who died of senile dementia of the Alzheimer type. The purified samples will be studied for phosphate content. In addition they will be assayed for calcium and aluminum which are present at high concentration in tangle bearing neurons. The metal elements will be determined by energy disperse x-ray fluorescence. Our attention will also focus on the morphological and biochemical properties of ANT antigens in fine neuronal processes. Electron microscopy and immunoelectron microscopy will be used to determine if the antigens are distributed in a filamentous structure similar to PHF. We also plan to determine if the antigen bearing structures are as resistant to solubilization as the PHF. The last specific aim is to investigate the relationship between rodent and human PFH, and to study the cytoskeletal changes proceeding the accumulation of PHF in animal tissue. Histochemistry, electron microscopy and immunoelectron microscopy will be used.