AQP4 and brain ischemia: However, AQP4 expression changes depend on the model used; for example, in the rodent model of transient focal brain ischemia, peaks of swelling and AQP4 expression, particularly the M1 isoform, were observed at 1- and 48-hr after ischemia (Ribeiro Mde et al., 2006; Hirt et al., 2009).