Fig. 15.

Perivascular microglia and vascular degeneration. a–f Electron micrographs of a perivascular microglial cell (M) adjoining a degenerating arteriole. Perivascular astrocytic feet (As, arrow) exhibit lack of ribosomes and altered mitochondria including swollen mitochondria (sm, panel c), mitochondria with disorganized cristae (arrowhead in c) and completely dystrophic mitochondria (* in c). The intimal endothelial cells (EC, panels a–c) are partially dislodged from the basal lamina with free processes protruding into the lumen. The abnormal endothelial cells exhibit a high density of small osmiophilic vescicles. Note the lack of definition of the basal lamina between endothelial and smooth muscle (SM) cells (arrow in c). The perivascular microglial cell a, b, d–f shows lysosomal cholesterol crystals (cc in panels b and d), a lipofuscin body (lf in panels b and c) and enlarged endoplasmic reticulum cisternae (er) characteristic of the “dark” microglial phenotype e. Arrowheads in panel d show abnormal enhanced interstitial spaces in the neuropil neighboring the perivascular microglial cell. Arrowhead in panel f indicates remnants of an astrocytic foot process next to a microglial process. m, mitochondria; tj, tight junction. Scale bars, 2.5 µm a; 1 µm b; 0.2 µm c; 0.4 µm d, e; 0.8 µm f