Clinical correlates to assist with chronic traumatic encephalopathy diagnosis: Insights from a novel rodent repeat concussion model

INTRODUCTION: Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease linked to repetitive head injuries. Chronic traumatic encephalopathy symptoms include changes in mood, behavior, cognition, and motor function; however, CTE is currently diagnosed only postmortem. Using a rat model of recurrent traumatic brain injury (TBI), we demonstrate rodent deficits that predict the severity of CTE-like brain pathology. METHODS: Bilateral, closed-skull, mild TBI was administered once per week to 35 wild-type rats; eight rats received two injuries (2 x TBI), 27 rats received five injuries (5 x TBI), and 13 rats were sham controls. To determine clinical correlates for CTE diagnosis, TBI rats were separated based on the severity of rotarod deficits and classified as mild or severe and further separated into acute, short, and long based on age at euthanasia (90, 144, and 235 days, respectively). Brain atrophy, phosphorylated tau, and inflammation were assessed. RESULTS: All eight 2 x TBI cases had mild rotarod deficiency, 11 5 x TBI cases had mild deficiency, and 16 cases had severe deficiency. In one cohort of rats, tested at approximately 235 days of age, balance, rearing, and grip strength were significantly worse in the severe group relative to both sham and mild groups. At the acute time period, cortical thinning, phosphorylated tau, and inflammation were not observed in either TBI group, whereas corpus callosum thinning was observed in both TBI groups. At later time points, atrophy, tau pathology, and inflammation were increased in mild and severe TBI groups in the cortex and corpus callosum, relative to sham controls. These injury effects were exacerbated over time in the severe TBI group in the corpus callosum. CONCLUSIONS: Our model of repeat mild TBI suggests that permanent deficits in specific motor function tests correlate with CTE-like brain pathology. Assessing balance and motor coordination over time may predict CTE diagnosis. Copyright (C) 2017 American Association for the Surgery of Trauma. All rights reserved.)