Figure 1: The blood-brain and the blood-cerebrospinal fluid barriers. A schematic diagram of the two barriers that represent the largest interface between blood and brain extracellular fluids: the brain endothelium forming the blood-brain barrier (BBB), also referred to as the neurovascular unit, and the choroid plexus epithelium forming the blood-cerebrospinal fluid (CSF) barrier. The neuroependymal surface lining of the ventricular system (inner CSF-brain barrier) is unique to the fetal brain and is not present in the adult. The neuroependymal cells are connected by “strap junctions” that prevent exchange of large molecules such as proteins between the CSF and brain [31]. Tight junctions and adherens junctions limit paracellular pathway endothelium and epithelium permeability. The neurovascular unit consists of specialized endothelial cells interconnected by tight junctions surrounded by basal lamina in which pericytes are embedded, with an outer ensheathment of astrocytic perivascular endfeet. Mast cells are located at perivascular locations in apposition with astrocytic and neuronal processes [27]. Inflammation may result in disruption of tight junctions and adherens junctions leading to paracellular passage of cytokines.