Figure 7.

The basal lamina physically separates all three cell types of the blood-brain barrier. A, Double immunolabeling against laminin (white) and RECA (red) of a large cortical vessel. The basal lamina consists of an outer thick lamina intensively immunoreactive for laminin and an inner lamina that displays weaker staining for laminin. The inner lamina contains pockets, which often are shaped as tunnels running perpendicular to the length of the vessel (white arrows). Inset, High-power image of a laminin-stained vessel wall illustrating the two laminas. B, Large vessel stained against laminin (white) and GFAP (green). GFAP-positive astrocytic end feet cover the basal lamina. C, Desmin-positive pericytes (red) are localized in pockets of the basal lamina (laminin; white). D, High-power view of desmin-positive pericytes. E, An antibody directed against actin smooth muscle (pericyte specific) demonstrates that only large vessels are surrounded by pericytes. Pericytes are absent from the capillary wall, and only weak expression is observed in medium-size vessels (white arrows). Scale bar: A, 20 μm; B, 30 μm; C, 20 μm; D, 40 μm; E, 100 μm.