Cerebral I/R elicits AT1aR dependent platelet recruitment, with vascular wall-associated AT1aR mediating the response in both normotensive and Ang II-induced hypertensive mice. Focal brain ischemia (45 min) and reperfusion (4 hrs) were induced by occluding the middle cerebral artery using the intraluminal filament method. Platelet 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. Platelets were labeled ex vivo with CFDSE. 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. n = 5-7 mice per group.