S1PR2 and brain edema: As shown in Fig. 1a–c, S1pr2−/− mice exhibited a dramatic decrease in both infarct ratio (wild-type 0.324± 0.053 versus S1pr2 null 0.084±0.017, 74% reduction, P<0.05, one-way analysis of variance (ANOVA) followed by Newman–Keuls test) and total cerebral oedema ratio (wild-type 0.121± 0.011 versus S1pr2−/− 0.047±0.008, 61.2% reduction, P<0.05, one-way ANOVA followed by Newman–Keuls test), which is the sum of cytotoxic and vasogenic oedema.