Handbook of Blood Brain Barrier Peptides and Amino Acids

The interstitial fluid (rSF) of the brain is separated from the blood by theblood-brain barrier (BBB). This barrier must not be thought of as a singleentity or as an absolute restriction to all molecules but as a multiple structurelocated at several sites within the brain. The first of these interfaces is locatedat the endothelium of the brain capillaries. Secondly there is a potential sitefor interchange on the outer linings of the brain between the dura and thearachnoid membranes. Thirdly there are the choroid plexuses and thecerebrospinal fluid (CSF) which is in contact with the very permeable internalependymal lining of the brain. Finally there are areas of the brainwhich lack a blood-brain barrier. These areas constitute the circumventricularorgans and have leaky capillaries with a barrier at the ependyma whichlimits the spread of molecules from those regions. Each of theseBBB sites has its own characteristic permeability and transport functions. Wewill now consider the properties of each of these barrier sites between theblood and the brain.