AQP4 and ischemia: In accordance, AQP4-deficient mice are less prone to develop cytotoxic edema in experimental ischemia and bacterial meningitis.56,57 However, the consequences of AQP4 deficiency vary depending on the type of brain edema studied, as AQP4-null mice are more prone to develop vasogenic edema.58 In studies of TBI models, there have been reports of both increased59–61 and reduced41,62 AQP4 protein expression.