Amyloid beta protein (Abeta) starts to deposit as plasma membrane-bound form in diffuse plaques of brains from hereditary cerebral hemorrhage with amyloidosis-Dutch type, Alzheimer disease and nondemented aged subjects.

[hereditary cerebral hemorrhage with amyloidosis]

To clarify where and how beta -amyloid begins to deposit in senile plaques , we examined the ultrastructural localization of amyloid beta protein (Abeta ) in diffuse plaques of brains with hereditary cerebral hemorrhage with amyloidosis -Dutch type . Alzheimer disease (AD ), and from nondemented aged subjects . Serial ultrathin sections of osmium-plastic blocks were immunogold-labeled for Abetax-42 (Abeta 42 ), and sections on grids were observed under the electron microscope (EM ) after observing the exact localization of the diffuse plaques in sections on glass slides by the reflection contrast microscope . Abeta 42 deposition , which was decollated with gold particles , appeared in 3 forms in all subjects under the EM : 1 ) Scattered small bundles of amyloid fibrils between cell processes , frequently seen in the densely stained area of diffuse plaques . 2 ) Scattered small foci of nonfibrillar materials between cell processes as a relatively minor form . 3 ) Abeta 42 on a part of the cell surface plasma membrane of normal appearing cell processes , a major form in weakly immunostained areas . The last form was not associated with degenerative neurites or reactive glia . Abeta 42 deposition on the cell surface plasma membrane appears to be an initial event in diffuse plaques , and then it develops into amorphous /fibrillar amyloid between cell processes .