Immunoelectron microscopy of TPD brain with AT8 and immunogold labeling. A: in the Acb, the immunogold labeling in neurons was mostly localized to the granular structures (indicated by circles). Paired-helical filaments (PHF) were rare. Scale bar = 1.0 μm. B: sparse bundles of PHF were scattered in the neuronal cytoplasm. Scale bar = 200 nm. C: in the hippocampal CA1 region, prominent bundles of AT8 positive PHF were seen. Scale bar = 500 nm.