Does the brain's gatekeeper falter in aging?

The brain's gatekeeper, the blood-brain barrier (BBB), may undergo pathologic changes associated with the aging process. Substrate transport through the brain capillary endothelium, which makes up the BBB in vivo, is controlled by dynamic inputs from three other cells (astrocyte, pericyte, and neuron) that form direct physical contacts with the capillary endothelium. Thus, aging-related changes in any of these three cells may cause abnormalities in blood-brain barrier transport in the aged brain or in Alzheimer's disease.