The blood-brain barrier in vitro: Ten years of research on microvessels isolated from the brain.

The cerebral microvessels represent a distinctive compartment in the brain with unique physiological, biochemical and morphological properties. The barrier which separates the general circulation from the central nervous system is a complex mechanism that has a relative impermeability to a number of blood-borne substances, but-at the same time-operates with several specific carriers for the various compounds needed in the brain. Morphologically, the presence of tight interendothelial junctions, the paucity of pinocytotic vesicles in the endothelium and the absence of fenestrations are the hallmarks of this barrier.