Mechanisms of Blast-Induced Vestibular Injury

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Project Summary Primary blast overpressure, such as that produced by explosive devices, has become an increasing cause of injury in both military and civilian populations. Dizziness and imbalance are frequent complaints of blast victims. However, few studies addressed the impact of blast overpressure on the vestibular system, representing an important knowledge gap in developing effective prevention, diagnosis and treatment programs of vestibular deficits in blast victims. To fill the knowledge gap, the goal of the application is to elucidate the mechanisms of blast-induced vestibular injuryin a rat model. The application is built upon our newly developed blast injury device that delivers blast waves directly into the external ear canal of rats. This model allows us investigate impact of primary blast on the vestibular system while avoiding damage to other air-filled organs. The blast-induced vestibular injury model was validated by our preliminary studies that assess vestibular hair cell histology, single vestibular afferent activity and vestibulo-ocular reflex(VOR). Results fromthe preliminary studies suggested that blast-induced vestibular injury is complex in nature and involves a combination of acute and progressive injury at all levels spanning from the periphery to the central vestibular system. The preliminary results lead to our hypothesis that blast exposure triggers degenerative processes in the Type I hair cell mediated pathways and the vestibular function reflects interactions of injury progression and compensatory processes. Current application will take advantage of the novel blast injury model to identify acute-to-chronic morphological, physiological and behavioral biomarkers of the vestibular deficits caused by exposure to blast overpressure waves with different intensities. Aim 1 is to investigate blast-induced structural damage to the vestibular system. We will investigate whether different end organs, types of vestibular hair cells or types of nerve endings exhibit different levels of susceptibility to blast exposure and different recovery over a period of 6 hours to 12 months. We will also investigate injury progression in the vestibular nuclei by analyzing biomarkers of inflammation, axonal damage and apoptosis. In addition, a 3D biomechanical model will be constructed to simulate blast energy propagation through the inner ear to quantify mechanical effects. Aim 2 is to employ single unit recording to assess injury progression in vestibular afferents following blast exposure. Spontaneous discharge and dynamic responses of different subgroups of afferents from the canals and otoliths will be studied. Aim 3 is to assess blast-induced vestibular injury progression by measuring the rotational and translational VORs. Both steady state and transient VORs will be measured to assess integrative outcomes of vestibularinjury progression and compensatory processes and identify the optimal VOR paradigms for diagnosis of blast-induced vestibular injury. Results from the study will elucidate the mechanisms underlying blast-induced vestibular deficits and provide essential information for early diagnosis and targets for intervention.