M. Srour1, G. Barmparas1, N. K. Dhillon1, N. Cho1, M. Alkaslasi1, E. J. Smith1, E. J. Ley1, G. M. Thomsen1 1Cedars-Sinai Medical Center,Los Angeles, CA, USA
Introduction: NFL athletes sustain acute head trauma with no perceived motor deficit although sidelines analysis appears to indicate altered mental status. It has been hypothesized that repeat mild traumatic brain injury (TBI) induces tolerance that may lead to quicker recovery, although this has not been definitively demonstrated clinically or in vivo. We studied the time to regain consciousness following mild TBI in a rodent model to better understand how repeat injury alters the acute recovery.
Methods: Righting time for 44 wild type (WT) rats and 17 WT mice were examined over a 5-week period. Rodents were administered repeat, bilateral, closed skull TBI with a controlled cortical impact device using varying injury parameters to deliver mild or moderate concussion. Starting at postnatal day 60, rats were administered either once weekly moderate injury (n=16 TBI, 16 sham) or 3x per week mild injury (n=7 TBI, 5 sham). Mice (aged >360 days) were administered mild repeat injury (n=11 TBI, 6 sham) once per week for 5 weeks. Righting time, defined as the length to turn over from supine to prone on all four paws after removal from anesthesia, was assessed following TBI or sham procedure.
Results: Rats administered a mild, 3x per week, concussion exhibited a delay in righting time after the first week of injuries that significantly decreased over time (Figure). Similarly, in mice that received a mild concussion once per week for 5 weeks, righting time significantly decreased over time (not shown). Rats that received a more moderate concussion once per week for 5 weeks demonstrated significantly longer righting times relative to sham that did not decrease over time (not shown).
Conclusion: Although cumulative incidence of mild TBI may lead to permanent long-term deficits in motor and balance, the acute recovery after each episode may unexpectedly decrease. Clinically our findings suggest that the expected symptoms after repeat blows to the head may diminish over time, which may complicate both the concussion diagnosis and prevention of long-term damage.
