The RB photothrombotic stroke model induces platelet aggregates and responds to tPA-lytic treatment poorly. (A) Single vessel-directed RB photothrombosis induced a train of initially unstable platelet clots that transformed into rapidly expanding platelet aggregates, as shown by intravital microscopy using DyLight488-conjugated anti-GPIbβ antibody (arrow indicates the site of 20-μm diameter laser photoactivation; also see supplemental Video 1). Scale bar, 50 μm. (B) Tracing of the size of 3 photoactivation-induced platelet aggregates under single-vessel RB-PTS over time. The initial platelet clots were repeatedly flushed away by the blood flow until the later clot adhered to the endothelial wall and expanded in size rapidly (n = 3). (C) Intravenous application of 10 mg/kg tPA at 30 minutes after the proximal MCA branch-directed RB-PTS failed to reduce the infarct size. The TTC-unstained infarcted area (indicated by arrows) was 18 ± 1.95 mm³ in tPA-treated mice (n = 10) and 18 ± 2.80 mm³ in the vehicle-treated mice (n = 6) at 24 hours recovery. P > .05 by unpaired Student t test. Shown are the mean ± standard error of the mean. NS, not significant.