Less than a decade ago, the term blood–brain barrier underwent a major conceptual change when it was recognized that the cerebrovasculature was anything, but passive in its structure and function. Instead of a layer of bricks separated by heavy mortar, the brain endothelial cell became one of a complement of cell types performing together as a dynamic, integrated unit and functioning as a major contributor to brain homeostasis. Today, this assembly is known as the neurovascular unit (NVU) and consists of endothelial cells, pericytes, astroctyes, and neurons with critical roles for microglia, circulating immune cells and smooth muscle cells as well (Abbott et al, 2010; Neuwelt et al, 2011). As a unit, these cells form a permeability barrier; regulate blood flow, neuronal development, and immune function; and conduct surveillance of neural signaling and cellular activity. The NVU is now implicated in many neurologic disease conditions because a damaged or dysfunctional NVU will lead to dysfunction of the surrounding brain cells and their integrated neurologic functions (Neuwelt et al, 2011; Zlokovic, 2011). Thus, the NVU may be either a cause of neurologic disease or a major, therapy requiring, complicating condition associated with a primary disease.