Object With the recent increasing interest in outcomes after repetitive mild traumatic brain injury (rmTBI; e.g., sports concussions), several models of rmTBI have been established. Characterizing these models in terms of behavioral and histopathological outcomes is vital to assess their clinical translatability. The purpose of this study is to provide an in-depth behavioral and histopathological phenotype of a clinically relevant model of rmTBI. Methods We utilized a previously published weight drop model of rmTBI (7 injuries in 9 days) in 2–3 month old mice that produces cognitive deficits without persistent loss of consciousness, seizures, gross structural imaging or microscopic evidence of structural brain damage. Injured and sham injured (anesthesia only) mice were subjected to a battery of behavioral testing including tests of balance (rotorod), spatial memory (Morris water maze), anxiety (open field plus maze,), and exploratory behavior (holeboard). After behavioral testing, brains were assessed for histopathological outcomes including brain volume, microglial and astrocyte immunolabeling. Results Compared with sham mice, mice subjected to rmTBI showed increased exploratory behavior, had impaired balance, and worse spatial memory that persisted up to 3 months after injury. Long-term behavioral deficits were associated with chronic increased astrocytosis and microgliosis but no volume changes. Conclusions We demonstrate that our rmTBI model results in a characteristic behavioral phenotype that correlates with the clinical syndrome of concussion and repetitive concussion. This model offers a platform from which to study therapeutic interventions for rmTBI.

Acutely after concussion, single-task and dual-task stride-length alterations were present among youth athletes compared with a control group. Although single-task gait alterations were not detected after symptom resolution, dual-task gait differences persisted, suggesting that dual-task gait alterations may persist longer after concussion than single-task gait or objective quiet-stance alterations. Dual-task gait assessments may, therefore, be a useful component in monitoring concussion recovery after symptom resolution.

OBJECTIVE Traumatic brain injury (TBI) is a leading cause of death and severe morbidity for otherwise healthy full-term infants around the world. Currently, the primary treatment for infant TBI is supportive, as no targeted therapies exist to actively promote recovery. The developing infant brain, in particular, has a unique response to injury and the potential for repair, both of which vary with maturation. Targeted interventions and objective measures of therapeutic efficacy are needed in this special population. The authors hypothesized that MRI and serum biomarkers can be used to quantify outcomes following infantile TBI in a preclinical rat model and that the potential efficacy of the neuro-reparative agent erythropoietin (EPO) in promoting recovery can be tested using these biomarkers as surrogates for functional outcomes. METHODS With institutional approval, a controlled cortical impact (CCI) was delivered to postnatal Day (P)12 rats of both sexes (76 rats). On postinjury Day (PID)1, the 49 CCI rats designated for chronic studies were randomized to EPO (3000 U/kg/dose, CCI-EPO, 24 rats) or vehicle (CCI-veh, 25 rats) administered intraperitoneally on PID1–4, 6, and 8. Acute injury (PID3) was evaluated with an immunoassay of injured cortex and serum, and chronic injury (PID13–28) was evaluated with digitized gait analyses, MRI, and serum immunoassay. The CCI-veh and CCI-EPO rats were compared with shams (49 rats) primarily using 2-way ANOVA with Bonferroni post hoc correction. RESULTS Following CCI, there was 4.8% mortality and 55% of injured rats exhibited convulsions. Of the injured rats designated for chronic analyses, 8.1% developed leptomeningeal cyst–like lesions verified with MRI and were excluded from further study. On PID3, Western blot showed that EPO receptor expression was increased in the injured cortex (p = 0.008). These Western blots also showed elevated ipsilateral cortex calpain degradation products for αII-spectrin (αII-SDPs; p < 0.001), potassium chloride cotransporter 2 (KCC2-DPs; p = 0.037), and glial fibrillary acidic protein (GFAP-DPs; p = 0.002), as well as serum GFAP (serum GFAP-DPs; p = 0.001). In injured rats multiplex electrochemiluminescence analyses on PID3 revealed elevated serum tumor necrosis factor alpha (TNFα p = 0.01) and chemokine (CXC) ligand 1 (CXCL1). Chronically, that is, in PID13–16 CCI-veh rats, as compared with sham rats, gait deficits were demonstrated (p = 0.033) but then were reversed (p = 0.022) with EPO treatment. Diffusion tensor MRI of the ipsilateral and contralateral cortex and white matter in PID16–23 CCI-veh rats showed widespread injury and significant abnormalities of functional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD); MD, AD, and RD improved after EPO treatment. Chronically, P13–P28 CCI-veh rats also had elevated serum CXCL1 levels, which normalized in CCI-EPO rats. CONCLUSIONS Efficient translation of emerging neuro-reparative interventions dictates the use of age-appropriate preclinical models with human clinical trial–compatible biomarkers. In the present study, the authors showed that CCI produced chronic gait deficits in P12 rats that resolved with EPO treatment and that chronic imaging and serum biomarkers correlated with this improvement.

Traumatic brain injury (TBI) is a major public health issue, with recent increased awareness of the potential long-term sequelae of repetitive injury. While TBI is common, objective diagnostic tools with sound neurobiological predictors of outcome are lacking. Indeed, such tools could help identify those at risk for more severe outcomes after repetitive injury and improve understanding of biological underpinnings to provide important mechanistic insights. We tested the hypothesis that acute and subacute pathological injury, including the microgliosis that results from repeated, mild closed head injury, is reflected in susceptibility-weighted magnetic resonance imaging (SWI) and diffusion-tensor imaging (DTI) microstructural abnormalities. Using a combination of high-resolution magnetic resonance imaging (MRI), stereology and qPCR, we studied the pathophysiology of male mice that sustained 7 consecutive mild traumatic brain injuries over 9 days in acute (24 hour) and subacute (1 week) time periods. Repetitive mild closed head injury induced focal cortical microhemorrhages and impaired axial diffusivity at one week post-injury. These microstructural abnormalities were associated with a significant increase in microglia. Notably, microgliosis was accompanied by a change in inflammatory microenvironment, defined by robust spatiotemporal alterations in tumor necrosis factor alpha (TNFα) receptor mRNA. Together, these data contribute novel insight on the fundamental biological processes associated with repeated mild brain injury concomitant with subacute imaging abnormalities in a clinically relevant animal model of repeated mild TBI. These findings suggest new diagnostic techniques can be used as biomarkers to guide the use of future protective or reparative interventions.