GPVI activation induces the formation of gaps in joints via release of serotonin. Nonarthritic mice (treated or not with fluoxetine for 21 days) were injected intravenously with CRP (40 μg/kg) or its diluent PBS. Thirty minutes after the CRP injection, the 0.45-μm fluorescent microspheres were injected. Two minutes after the microsphere injections, the fluorescence in ankle joints was evaluated using an in vivo imaging system. The radiant efficiency quantifications in the ankle joints for all mice and representative results are presented. ***P < .0001; **P = .0019.