AQP4 and Parkinson disease: In our previous studies, compared with AQP4+/+ mice, AQP4−/− mice were significantly more prone to MPTP‐induced neurotoxicity and subsequently exhibited significantly stronger microglial responses in the midbrain and more severe PD symptoms.26, 27, 28 However, the mechanisms underlying hyperactive microglial responses and more severe clinical symptoms in PD after administration of MPTP in AQP4‐deficient mice remain unclear.