Abstract
Blast exposure is an increasingly significant health hazard and can have a range of debilitating effects, including auditory dysfunction and traumatic brain injury. To assist in the development of effective treatments, a greater understanding of the mechanisms of blast-induced auditory damage and dysfunction, especially in the central nervous system, is critical. To elucidate this area, we subjected rats to a unilateral blast exposure at 22 psi, measured their auditory brainstem responses (ABRs), and histologically processed their brains at 1 day, 1 month, and 3-month survival time points. The left and right auditory cortices was assessed for astrocytic reactivity and axonal degenerative changes using glial fibrillary acidic protein immunoreactivity and a silver impregnation technique, respectively. Although only unilateral hearing loss was induced, astrocytosis was bilaterally elevated at 1 month post-blast exposure compared to shams, and showed a positive trend of elevation at 3 months post-blast. Axonal degeneration, on the other hand, appeared to be more robust at 1 day and 3 months post-blast. Interestingly, while ABR threshold shifts recovered by the 1 and 3-month time-points, a positive correlation was observed between rats’ astrocyte counts at 1 month post-blast and their threshold shifts at 1 day post-blast. Taken together, our findings suggest that central auditory damage may have occurred due to biomechanical forces from the blast shockwave, and that different indicators/types of damage may manifest over different timelines.
Highlights
Blast exposure, which can be characterized by high wave pressure change and high energy impulse noise, as well as the related traumatic brain injury (TBI), has become a common threat in modern war theaters
To shed light on putative injury changes in the central auditory system following blast exposure, we evaluated auditory brainstem responses (ABRs) thresholds, astrocytosis and axonal integrity in the auditory cortex (AC)
These findings confirm that blast exposure impacts the peripheral and central auditory system, and may suggest that brain compression and shearing forces from the blast itself play a predominant role in related auditory impairment
Summary
Blast exposure, which can be characterized by high wave pressure change and high energy impulse noise, as well as the related traumatic brain injury (TBI), has become a common threat in modern war theaters. Studies have found that up to 15.8% of combat-injured participants had TBI [1], and that blast exposure was the predominant cause for their TBI [2]. Individuals with blast-related TBI can experience a range of disability, including motor deficits, cognitive decline, and notably, auditory dysfunction. Blast-induced injury in the auditory cortex especially important considering that up to 67% of blast-exposed individuals with mild TBI have significant hearing threshold shifts and 59% develop tinnitus [3]. There are no universally-effective treatments for individuals suffering from these problems
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