Blast-Induced Tinnitus and Hearing Loss in Rats: Behavioral and Imaging Assays

Abstract

The current study used a rat model to investigate the underlying mechanisms of blast-induced tinnitus, hearing loss, and associated traumatic brain injury (TBI). Seven rats were used to evaluate behavioral evidence of tinnitus and hearing loss, and TBI using magnetic resonance imaging following a single 10-msec blast at 14 psi or 194 dB sound pressure level (SPL). The results demonstrated that the blast exposure induced early onset of tinnitus and central hearing impairment at a broad frequency range. The induced tinnitus and central hearing impairment tended to shift towards high frequencies over time. Hearing threshold measured with auditory brainstem responses also showed an immediate elevation followed by recovery on day 14, coinciding with behaviorally-measured results. Diffusion tensor magnetic resonance imaging results demonstrated significant damage and compensatory plastic changes to certain auditory brain regions, with the majority of changes occurring in the inferior colliculus and medial geniculate body. No significant microstructural changes found in the corpus callosum indicates that the currently adopted blast exposure mainly exerts effects through the auditory pathways rather than through direct impact onto the brain parenchyma. The results showed that this animal model is appropriate for investigation of the mechanisms underlying blast-induced tinnitus, hearing loss, and related TBI. Continued investigation along these lines will help identify pathology with injury/recovery patterns, aiding development of effective treatment strategies.

Blast Exposure Induces Post-Traumatic Stress Disorder-Related Traits in a Rat Model of Mild Traumatic Brain Injury

“…52 The studies reported here, which were conducted using general anesthesia, however, suggest that a blast-related mTBI exposure can induce PTSD-related traits independent of exposure to a PTSD stressor. Unlike in some other studies, 5,26,31,33,34,36,38,43,[47][48][49][50] we did not see cognitive effects. No deficits were present in a Morris water maze or in a win-shift task, a relatively challenging test of working memory.…”

“…23 Animals have been exposed to various forms of blast ranging from direct exposure to live explosives to controlled blast waves produced by compressed-air generators (reviewed in Elder et al 1 ) with activity in this area increasing dramatically in rodent models in recent years. 5, A number of studies have begun to look at the behavioral effects of blast across a range of blast exposures 5,26,31,33,34,36,38,43,[47][48][49][50] using blast alone or blast in combination with repeated stress 36 or other factors such as transportation or anesthesia. 33 These studies have documented a variety of, at least, short-term effects, suggesting that blast can be associated with anxiety as well as impairments in a variety of learning and memory tasks.…”

“…5,26,31,34,36,43,47,49,50 One study also reported impairments in prepulse inhibition immediately after blast exposure, changes that had mostly recovered by 90 days after exposure. 38 We utilized a rat model of mTBI in which adult male rats were exposed to a controlled blast overpressure injury in a shock tube. Prior studies using this system established that exposures up to 74.5 kPa (equivalent to 10.8 psi) while representing a level of blast that is transmitted to the brain, 7 lead to no persistent neurological …”

Mapping Tinnitus-Related Brain Activation: An Activation-Likelihood Estimation Metaanalysis of PET Studies

“…Considering that the LGB, the primary relay center for visual information, has never correlated with tinnitus in the literature, we speculate that our result may indicate the MGB rather than the LGB because of the possible spatial resolution problems with PET. Previous research on the MGB in murine tinnitus models has already elucidated changes in the spontaneous firing rates at a single-cell level, cell density reductions in all subdivisions by immunohistochemical staining, and significant damage and compensatory plastic changes using diffusion tensor imaging (26). Because of the anatomic subcortical location, the MGB has never been mentioned in tinnitus studies using qEEG or magnetoencephalography.…”

Preliminary studies on differential expression of auditory functional genes in the brain after repeated blast exposures

“…Auditory/vestibular injuries from blast traumatic brain injury (TBI) can cause increased incidence of tinnitus and hearing loss, which worsens over time if not treated [1][2][3][4]. Shock waves generated from explosive blasts are reported to be destructive to both gas-and fluid-filled structures of the body, including the lungs, intestines, brain, eyes, nose, and middle ear [5][6][7][8][9].…”