Fig. 3

Representative electron micrographs obtained from areas of FITC-albumin extravasation of 4 h pMCAO animals illustrating different patterns of endothelial alterations. For comprehensibility, endothelial cells (E) are transparently highlighted in yellow. Vascular basement membranes are transparently highlighted in red. Insets show native image sections devoid of coloring. a Score 0: endothelial cells appear unaffected with a dense and compact cytoplasm. An extravasation of FITC-albumin is not observed. b Score 1: endothelial cells show a less electron dense cytoplasm indicative of an endothelial edema. Electron dense DAB-grains showing FITC-albumin remain restricted to the vascular lumen (L). If sectioned, TJ strands remain detectable (arrow). c Score 2: electron dense FITC-albumin-related DAB grains are found within the endothelial layer, but do not reach beyond the vascular basement membrane. Again, endothelial TJ remain detectable (arrow). d & e Score 3: FITC-albumin related DAB grains are not restricted to the endothelial layer, but reach the adjacent compartments of the neuropil, beyond the vascular basement membrane. Here, the endothelial integrity is lost, showing discontinuous plasma membranes of the endothelial layer (d). Often, parts of the endothelial cell are detached from the underlying basement membrane (e). f Score 4: in rare cases, erythrocytes are found to extravasate into the neuropil, not being associated to the vascular compartment. Scale bars: each 1 μm