FIG. 6.

Ultrastructural analysis of E12.5 αv^−/− cerebral microvessels. (A) Expanded vascular lumen contains a nucleated red blood cell; endothelial cells line the lumen and are closed by normal interendothelial cell junctions (solid arrowheads). Although pericyte cell bodies were absent in this section, pericyte processes in contact with the endothelium were seen (arrows). Numerous round brain parenchymal cells (N/G) and their foot processes are visible in the perivascular sheath. Some of the foot processes contact a pericyte process; very few contact endothelial cells. There is an extensive space surrounding the entire vessel. (B) Extravasated red blood cell rests among brain parenchymal cells (N/G) beneath the endothelium with closed interendothelial cell junctions (arrows). An enlarged endothelial cell (E) is protruding into the vascular lumen (L) and undergoing mitosis (solid arrowhead marks a chromosome). Magnification: (A) 6,000×; (B) 13,000×. Abbreviations: E, endothelial cells; N/G, brain parenchymal cells.