GRIA1 and concussion: In addition, after brain injury the N-terminal of the GluA1 subunits of AMPARs is cleaved by extracellular proteases and released into the bloodstream through the compromised blood–brain barrier.33 This GluA1 peptide was recently shown to be acutely and significantly elevated after concussion in club sport athletes,30 and serum GluA1 peptide values correlate with acute computerized concussion testing (Immediate Post-Concussion Assessment and Cognitive Testing [ImPACT]) after concussion.30