Abnormal neuritic architecture identified by Di-I in Pick's disease.

The fluorescent stain Di-I combined with confocal microscopy identified an abnormal neuritic pattern in the cortices of frontal and anterior temporal lobes in postmortem tissues from patients with Pick's disease (PD). Focal, dense neuritic aggregates 50 to 200 microns in diameter were scattered throughout all cortical layers. The three-dimensional analysis provided by confocal microscopy revealed the neuritic clusters to consist of enlarged, randomly arrayed, dystrophic neurites that were not associated with amyloid deposits, astrocytic processes or capillaries. In the intervening neuropil, there were fewer neurites compared to controls. The occipital cortex, which is unaffected in PD, showed a neuritic architecture comparable to normal controls as did affected brain tissues from patients with Alzheimer's disease or remote, ischemic infarction. This neuritic pattern is, thus far, unique to PD and may reflect the loss of specific subpopulations of cortical neurons and proliferation of neurites of the remaining neurons.