Ultrastructure of Paired Helical Filaments of Alzheimerʼs Neurofibrillary Tangle

Abstract
Isolated paired helical filaments (PHF) of Alzheimer's disease and senile dementia of the Alzheimer type (AD/SDAT) were studied by negative stain techniques and electron microscopy (EM). The helical structure of the PHF was confirmed by tilt analysis of negatively stained isolated PHF. A substructure of four protofilaments, each 3–5 nm in diameter, was also observed. A comparison of PHF substructure, neurofilaments and microtubules, revealed no similarity among the three structures.