MMP9 and concussion: In TBI animal models, increased expression of MMP-9 has been reported with concomitant disruption in the BBB (79) and in clinical studies increased expression of MMP-9 were reported in CSF of mTBI patients compared to controls within 72 h following injury, as well as in SMs engaged in heavy weapons training with repetitive exposures to blast both acutely and chronically following blast exposure (80, 81).