In summary, we report that unlike cortical grey matter astrocytes, which exhibit decreased perivascular Aqp4 and unchanged Aqp4 abundance following ischemia, subcortical white matter astrocytes exhibit greatly increased perivascular Aqp4, plasmalemmal Aqp4, and Aqp4 abundance; this molecular heterogeneity may underlie the relatively greater propensity for tissue swelling exhibited by subcortical white matter. This evidence concerns the gene AQP4 and ischemia.