The Blood-Brain Barrier in the Aging Brain

Homeostasis of the extracellular microenvironment in the neural tissue of the brain as well as its protection against neurotoxic compounds and variations in the composition of the blood are important for normal function of the neurons. It is warranted by a structure formed between blood and brain which is therefore called the blood-brain barrier (BBB). This barrier has been postulated in earlier decades by experiments using dyes which directly visualized both the protection of the brain if injected into the vasculature, and free access of the brain if injected into the cerebrospinal fluid. Since in the first experiment some areas of the brain around the ventricle were stained and in the second experiment the identical areas were not, the barrier necessarily had to be separated into a BBB and a blood-cerebrospinal fluid barrier.