Molecular physiology and pathophysiology of tight junctions in the blood-brain barrier.

Disruption of the tight junctions (TJs) of the blood-brain barrier (BBB) is a hallmark of many CNS pathologies, including stroke, HIV encephalitis, Alzheimer's disease, multiple sclerosis and bacterial meningitis. Furthermore, systemic-derived inflammation has recently been shown to cause BBB tight junctional disruption and increased paracellular permeability. The BBB is capable of rapid modulation in response to physiological stimuli at the cytoskeletal level, which enables it to protect the brain parenchyma and maintain a homeostatic environment. By allowing the "loosening" of TJs and an increase in paracellular permeability, the BBB is able to "bend without breaking"; thereby, maintaining structural integrity.