Figure 2. Aquaporin expression in the nervous system.

a | In the retina, aquaporin 4 (AQP4) is expressed in its vitreous-facing ciliary epithelium and in perivascular processes of Müller cells. b | In the olfactory epithelium, AQP4 is expressed in olfactory epithelium support cells. c | In the inner ear, AQP4 can be detected in the inner sulcus, and in Claudius and Hensen cells in the cochlea, and AQP1 can be found in intermediate cells and fibrocytes of the spiral ligament. d | In the brain, AQP4 is primarily expressed in astrocyte processes of the glia limitans externa and perivascular astrocyte foot processes. AQP4 is also expressed in the basolateral cell plasma membrane of ependymal cells and in subependymal astrocyte processes of the glia limitans externa. AQP1 is expressed in the cerebrospinal fluid (CSF)-facing plasma membrane of the choroid plexus epithelium. The sites of AQP9 expression remain unclear. e | In the spinal cord, AQP1 is expressed in non-myelinated dorsal root ganglion (DRG) neurons, whereas AQP4 is expressed in astrocyte processes of the glia limitans externa and in perivascular astrocyte foot processes. f | In the enteric nervous system, AQP1 is expressed in glia, whereas AQP4 is found in neurons and glia of the submucosal and myenteric plexuses. g | In the spine, AQP9 is expressed in osteoclasts within the vertebrae, and AQP1 and AQP3 are found in nucleus pulposus cells.