Ultrastructural and permeability features of microvessels in the periventricular area of senescence-accelerated mice (SAM)

Brain transfer of intravenously injected horseradish peroxidase (HRP) and t he ultrastructural features of the vessels were examined in periventricular areas in senescence-accelerated mice (SAMP8), which show age-related defic its in learning and memory, and senescence-accelerated resistant mice (SAMR 1), which do not show age-related deficits. In all mice examined with light microscopy, staining reaction for HRP was seen in the periventricular area adjacent to the medial side of the lateral ventricle. Electron microscopic examination in the periventricular area of young and old mice of both stra ins showed that the staining reaction for HRP appeared in the vesicular pro files of the endothelial cytoplasm, the cytoplasm of the perivascular cells , the basal lamina, and the adjoining extracellular spaces of the white mat ter, suggesting an incomplete blood-brain barrier (BBB) in the periventricu lar white matter. In addition, irregularly thickened endothelial cell cytop lasm, membranous;Inclusions within the basal lamina, and electron-dense end othelial cell cytoplasm were occasionally seen in aged SAMP8 mice. These fi ndings were not observed in 3-month-old SAMP8 mice and 3- and 13-month-old SAMR1 mice. Perivascular collagen deposits were also frequently seen in age d SAMP8 mice. These findings Indicate that the endothelial cells and pericy tes in the periventricular white matter in aged SAMP8 mice have an ultrastr ucture with damaged BBB function. Intravascular substances can easily penet rate the periventricular white matter and the BBB of the vessels in the are a can be deteriorated with aging in SAMP8 mice. (C) 2001 Wiley-Liss, Inc.