Reelin labeling in endothelial cells. A) Low magnification electron microscopy image of a reelin-labeled endothelial cell in the cortex. This endothelial cell presents a thin cytoplasm, which is clearly delimited by the basement membrane (white arrowheads) in the abluminal side. The nucleus (n) occupies most of the cell body of the endothelial cell. B-C) Details of the areas marked with dashed-lined boxes in A. In B, a reelin-labeled transcytosis vesicle (outlined black arrow) is located in a narrow cytoplasm area between the nucleus (n) and the cell membrane (white arrowheads). In C, a small cluster of reelin-labeled caveolar vesicles is shown (outlined black arrows), with one of them presenting the open neck towards the capillary lumen (outlined black arrowhead). Note also that the abluminal side (white arrowheads) is devoid of labeling. D) Reelin labeling in a small brain capillary in the cortex. This capillary is formed by the almost-continuous thin cytoplasm of a reelin-labeled endothelial cell. Note also the lack of labeling in myelinated processes (m) located in the vicinity of this capillary. E-F) Detail images of the areas indicated by dashed-line boxes in D. Reelin-labeled caveolar vesicles are present in different stages. A labeled caveolar vesicle in E (outlined black arrow) presents a well-delineated oval shape, while a labeled caveolar vesicle in F that is located in close proximity to the luminal side of the capillary is about to form the open neck (outlined black arrowhead). Note also the presence of reelin labeling in the luminal side of the membrane (outlined black stars), and the lack of labeling in the abluminal side (white arrowheads). m: myelinated process; n: nucleus. Scale bars: 2 microns in A, D; 0.5 microns in B-C and E-F.