Cerebral I/R induces an AT1aR-dependent leukocyte recruitment response that is mediated by vascular wall-associated AT1aR in normotensive mice, while blood cell-associated AT1aR mediates the response in Ang II hypertensive mice. Focal brain ischemia (45 min) and reperfusion (4 hrs) were induced by occluding the middle cerebral artery using the intraluminal filament method. Leukocyte-endothelial cell adhesion in cerebral venule was monitored through a cranial window by fluorescence intravital videomicroscopy. Angiotensin (2000 ng/kg/min)(Panel B) or an equal volume of saline (Panel A) was infused over a 2 wk period in WT, AT1aR-/-, WT→WT BM chimeric, and AT1aR-/-→WT BM chimeric mice. Leukocytes were labeled in vivo with Rhodamin 6G for fluorescence. Data are shown as mean ± SE with 5-7 mice per group. * denotes p < 0.05 relative to corresponding non-ischemic WT mice. † denotes p < 0.05 relative to corresponding WT mice + I/R. ‡ denotes p < 0.05 relative to corresponding WT→WT BM chimeras.