Photographs showing AQP4 distribution in normal rat brain assessed by immunofluorescent confocal microscopy. Aquaporins (AQPs) are a family of transmembrane proteins that selectively allow the passage of water through the plasma membranes, and AQP4, the predominant form in brain, is highly expressed in astrocytic endfeets near capillaries and in ependymal cells. AQP4 is expressed in subpial glial limitans (A), pericapillary astrocytic foot processes (B), and ependymal cells (C,D).