AQP4 and Parkinson disease: Following the establishment of a 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced Parkinson's disease (PD) model, AQP4‐deficient (AQP4−/−) mice displayed significantly stronger microglial inflammatory responses and remarkably greater losses of tyrosine hydroxylase (TH+)‐positive neurons than did wild‐type AQP4 (AQP4+/+) controls.