FIGURE 4.

Major structural and cellular components of the capillary NVU. Endothelial cells that line the capillary lumen form tight junctions which oppose the movement metabolites and proteins into the brain. Pericytes located in the endothelial basement membrane control capillary diameter. Astrocyte endfeet that surround the parenchymal basement sense increases in neuronal activity and respond by releasing vasoactive factors. Nerve terminals, found in proximity with astrocyte endfeet, release neurotransmitters that influence capillary diameter. Oligodendrocyte progenitor cells interact with cellular components of the NVU to regulate the formation and function of capillaries. Microglia send processes into the NVU that allow them to communicate with pericytes and endothelial cells. (See section “6.1. Structure and function of the NVU” for details).