Figure 2.

A. Diagrammatic representation of perivascular clearance of solutes, normally entering the walls (basement membranes) of capillaries and then arteries, but not of veins. B. Cross section through a human artery at the surface of the brain. The tissue has been immunostained for collagen IV (a marker of basement membranes, shown here in blue), smooth muscle cells (immunostaining for smooth muscle actin, shown in green) and amyloid‐β (Aβ), using anti‐4G8 antibody, shown here in red. Note the presence of Aβ surrounding the smooth muscle cells, leaving the endothelial basement membrane (blue) free of Aβ. There is some Aβ accumulating at the surface of the brain, with the collagen IV present in glia limitans. Confocal microscopy. Scale bar: 20 μm.