The endothelial blood-brain barrier (BBB) and the epithelial blood-cerebrospinal fluid barrier (BCSFB) at the level of the choroid plexus (CP) comprise the brain barriers. They protect the central nervous system (CNS) from changes in the blood thus ensuring CNS homeostasis, which is prerequisite for proper function of neurons. The anatomical basis of these barriers is represented by unique intercellular protein complexes formed in between BBB endothelial cells and the BCSFB epithelial cells, respectively, inhibiting paracellular diffusion of water soluble molecules. In addition BBB endothelial cells keep out unwanted compounds from the brain by their lack of fenestrae and low pinocytotic activity. To meet the high demand of the neuronal cells for energy and drive efflux of toxic metabolites at the same time, BBB endothelial and BCSFB epithelial cells express unique combinations of enzymes and transport molecules. Brain barrier cells are thus unique and….