Dynamics of platelet thrombus formation in vivo. Mesenteric arterioles of rats were injured via photoactivation of systemically administered rose bengal, and platelet interactions with growing thrombi were visualized by DIC microscopy. (A) This single image (representative of 12) highlights the ability of this imaging technique to resolve single platelets during thrombus formation in vivo (see Video S2 for analysis of thrombus development in real time). (B) Representative example of a newly recruited platelet translocating over the thrombus surface with a sliding motion, maintaining maximal surface area contact (Video S2). (C) A single adherent platelet (dotted outline) extending and recoiling from a fixed point of contact over the surface of another stationary adherent platelet. Such behavior was often induced by transient contacts made with other translocating platelets (0.02 seconds, dotted outline) (Video S3). (D) Platelets within the superficial layer of thrombi were loosely packed such that platelets often detached from the thrombus surface in clusters (Video S2). White scale bar = 5 μM; black scale bar = 10 μM.