Degenerating neurofibrils (DNF), which are composed of paired helical filaments (PHF) and
amyloid fibrils (AF), are the 2 characteristic pathological fibrillar deposits in Alzheimer cortex. These fibrils were simultaneously studied by 2 techniques: The immunolabelling with a specific antiserum raised against PHF and elective
thioflavine S staining of AF. In neuronal perikaryons, neurofibrillary tangles (NFT) consist of 3 populations: firstly, strongly immunolabelled tangles were weakly
thioflavine-stained. Secondly, less dense tangles were weakly immunolabelled but strongly
thioflavine-stained. Thirdly, ghost tangles which correspond to extracellular NFT were exclusively
thioflavine-stained. Thus, it is likely that NFT are degraded to form extracellular AF. Around
neuritic plaques and some vessels with
amyloid angiopathy, immunolabelled neurites,
thioflavine-stained neurites and transition figures were also observed. On the other hand, the central core of plaques and pathological vessel walls were strongly
thioflavine-stained but were never immunoreactive. In conclusion, these observations favour catabolism of PHF bundles found in NFT and in degenerating neurites into an
amyloid substance. This
amyloid substance seems different from other
amyloid deposits found in the central core of
neuritic plaques and vessel walls.