Concussive Injury before or after Controlled Cortical Impact Exacerbates Histopathology and Functional Outcome in a Mixed Traumatic Brain Injury Model in Mice

Traumatic brain injury (TBI) may involve diverse injury mechanisms (e. g., focal impact vs. diffuse impact loading). Putative therapies developed in TBI models featuring a single injury mechanism may fail in clinical trials if the model does not fully replicate multiple injury subtypes, which may occur concomitantly in a given patient. We report development and characterization of a mixed contusion/concussion TBI model in mice using controlled cortical impact (CCI; 0.6mm depth, 6 m/sec) and a closed head injury (CHI) model at one of two levels of injury (53 vs. 83 g weight drop from 66 in). Compared with CCI or CHI alone, sequential CCI-CHI produced additive effects on loss of consciousness (p < 0.001), acute cell death (p < 0.05), and 12-day lesion size (p < 0.05) but not brain edema or 48-h contusion volume. Additive effects of CHI and CCI on post-injury motor (p < 0.05) and cognitive (p < 0.005) impairment were observed with sequential CCI-CHI (83 g). The data suggest that concussive forces, which in isolation do not induce histopathological damage, exacerbate histopathology and functional outcome after cerebral contusion. Sequential CHI-CCI may model complex injury mechanisms that occur in some patients with TBI and may prove useful for testing putative therapies.