A Military-Relevant Model of Closed Concussive Head Injury: Longitudinal Studies Characterizing and Validating Single and Repetitive mTBI

Background: Closed-head concussive injury is one of the most common causes of traumatic brain injury (TBI). While single concussions result in short-term neurologic dysfunction, multiple concussions can result in cumulative damage and increased risk for neurodegenerative disease. Despite the prevalence of concussion, knowledge about what occurs in the brain following this injury is limited, in part due to a limited number of appropriate animal research models.Objectives: To study clinically relevant concussion, we recently developed a simple, non-invasive rodent model of closed-head projectile concussive impact (PCI) TBI. The overall goal of the current proposal is to conduct longitudinal studies on the Walter Reed Army Institute of Research PCI model following a 'SINGLE' or 'REPEATED' PCI injury in order to develop a more thorough understanding of the changes taking place at the cellular level following these concussive events and to establish how those changes relate to clinically relevant mild TBI (mTBI) pathological (i.e., biomarkers, EEG) and neurobehavioral (i.e., neurofunction, i.e., motor/balance), psychological (i.e., cognition), and emotional outcome metrics.Specific Aims: Phase I (SOW 1) studies will fully characterize the pathological and neurobehavioral changes following a 'SINGLE' PCI injury. The data generated in Phase 1 will be used to develop a 'healing profile' demonstrating the time it takes for the brain to return to 'normal' based on the associated neuropathological, molecular, and neurobehavioral changes. This healing profile will serve as the foundation to guide the experimental design for assessing the cumulative effects of repeated PCI in Phase 2 studies. Phase II (SOW 2) studies will evaluate the cumulative effects of 'REPEATED' PCI injuries occurring either before or after resolution of the healing profile established in Phase I (SOW 1).Study Design: PCI Model: To induce mild PCI injury, anesthetized rats are fitted with a custom-designed Kevlar-type helmet and placed on a platform positioned above a torque-sealed microcentrifuge tube packed with fixed amounts of dry ice. Upon heating, rapid sublimation of dry ice produces a build-up of compressed CO2 that triggers an eruptive force causing the cap to launch as an intact 'projectile,' resulting in a targeted PCI head injury. To control for potential effects of pressure wave itself, a highly perforated metal plate is inserted between the rat's head and the PCI device, allowing for the pressure wave to pass through but effectively blocking the projectile from impacting the rat's head. The helmet is implemented to protect the head from bruising, yet allowing the brain to sustain a mild PCI event. Experimental groups will consist of sham (anesthesia only), pressure wave controls, and PCI injury. After exposure to PCI injury, animals will be studied to evaluate the regional and temporal profiles of cellular, molecular, or bioenergetic changes in brain tissue as well as protein biomarker changes in cerebrospinal fluid and serum. Additional groups of animals will be evaluated for neurobehavioral (sensorimotor, cognitive, and affective) and qEEG (quantitative EEG) profiles in response to injury. Once the longitudinal effects of a single PCI across these outcome parameters has been established, the same processes will be repeated to evaluate the changes associated with repeated PCI injuries.Innovation: This proposal will deliver a safe, novel, cost-effective, high-throughput model of closed-head (no manipulation of the scalp or skull) injury induced by a PCI.Impact: The establishment of this model will provide knowledge about the changes that occur in the brain following concussive impacts. The knowledge will be used to advance the field of TBI regarding its diagnosis and treatment, including understanding of the pathological changes associated with multiple TBIs taking place at the cellular level. In addition to knowledge, the end product of this proposal will provide a platform for preclinical studies evaluating diagnostic modalities and therapies for the treatment of mTBI.