Thromboxane receptor deficiency attenuates platelet accumulation in the outer shell region of hemostatic plugs in vivo. Laser-induced injury was performed in cremaster muscle arterioles of wild-type (blue) or TP^−/− (red) mice as described in “Materials and methods.” (A-B) Total platelet accumulation following laser injury was measured by quantifying the CD41-positive area over time. (A) Graph showing the CD41-positive area over time (mean ± standard error of the mean [SEM]). (B) Graph showing the area under the CD41 vs time curve (AUC). Data points represent AUCs of individual hemostatic plugs. The line and error bars show the median and interquartile range. (C-D) α-Granule secretion following laser injury was used as a measure of platelet activation by quantifying the P-selectin–positive area over time. (C) Graph showing the P-selectin–positive area over time (mean ± SEM). (D) Graph showing the area under the P-selectin vs time curve. Data points represent AUCs of individual hemostatic plugs. The line and error bars show the median and interquartile range. Wild-type, n = 32 injuries in 4 mice; TP^−/−, n = 39 injuries in 4 mice. NS, not significant; WT, wild-type.