Furthermore, while AQP1 is not detected in astrocytes in the healthy brain, it appears to be upregulated within astrocytomas in humans [58,59] and also in astrocytes following a subarachnoid haemmorage and following brain stab injury in rats [60], which is an effect that has been shown by cell culture studies to probably occur in response to hypertonicity via a hypertonicity-response element in the AQP1 gene [86,87]. Here, AQP1 is linked to astrocytoma (excluding glioblastoma).