ABSTRACT
Properties of the Blood-Brain Barrier Katerina Dorovini-Zis1,* and Sukriti Nag2
In all mammals the neuronal and glial microenvironment of the brain and spinal cord is regulated and maintained by two central nervous system (CNS) barriers, a bloodbrain barrier (BBB) and a blood-cerebrospinal fl uid barrier (BCSFB). The BBB is formed by endothelial cells (EC) lining the cerebral capillaries and the BCSFB by the specialized epithelial cells of the choroids plexus. The CNS has an extensive capillary network with a large surface area of approximately 240 cm2 per 1 g of brain tissue (Crone 1963), which, in the human brain provides an average of 12 cm2 of capillary endothelial surface area (Nag and Begley 2005) for the rapid exchange of O2, CO2 and metabolites between blood and brain. Capillary density is greater in the gray than in the white matter and there are regional variations in capillary density and surface area among different areas of the gray matter (Gross et al. 1986). In general, areas with high neuronal activity and high concentration of synapses are most richly vascularized. The BBB is a highly specialized, dynamic, regulatory selective permeability barrier with important morphological, metabolic, functional and immunological properties, which are critical for the normal function of the CNS and the generation of responses to injury. The physical barrier is formed by tight junctional complexes that seal the lateral surfaces of adjacent EC, so that EC form a continuous cell layer with the
1 Department of Pathology and Laboratory Medicine, The University of British Columbia, Vancouver General Hospital, 855 West 12th Avenue, Vancouver, Canada, V5Z-1M9.
