Although the physiological blood brain barrier major role in the regulation of water circulation, several studies have proposed the theory of the cerebral glymphatic system. The suggestion of this system's involvement evoked considerable discussions regarding the regulations of water circulations in the brain. Aquaporine 4, a water protein, plays a central roles in this regulation process. Some interpretations of water regulation in the brain suggest that the circulations of the interstitial fluids is causally linked to Cerebral edema or various cerebral diseases, such as Alzheimer's disease and acute disseminated encephalomyelitis for example.