Within the CNS, endothelial cells acquire a set of protective properties (the so-called blood-brain barrier) limiting the penetration of blood-borne substances and pathogens into the brain parenchyma and maintaining brain homeostasis. Dysfunction of the blood-brain barrier is a common trait of many CNS disorders, including epilepsy, stroke and neurodegenerative diseases. Conversely, through its protective role, the barrier precludes therapeutic or diagnostic drugs to accumulate in effective concentrations at their target site within the CNS.