Blast Exposure Causes Long-Term Degeneration of Neuronal Cytoskeletal Elements in the Cochlear Nucleus: A Potential Mechanism for Chronic Auditory Dysfunctions

Abstract

Blast-induced auditory dysfunctions including tinnitus are the most prevalent disabilities in service members returning from recent combat operations. Most of the previous studies were focused on the effect of blast exposure on the peripheral auditory system and not much on the central auditory signal-processing regions in the brain. In the current study, we have exposed rats to single and tightly coupled repeated blasts and examined the degeneration of neuronal cytoskeletal elements using silver staining in the central auditory signal-processing regions in the brain at 24 h, 14 days, 1 month, 6 months, and 1 year. The brain regions evaluated include cochlear nucleus, lateral lemniscus, inferior colliculus, medial geniculate nucleus, and auditory cortex. The results obtained indicated that a significant increase in degeneration of neuronal cytoskeletal elements was observed only in the left and right cochlear nucleus. A significant increase in degeneration of neuronal cytoskeletal elements was observed in the cochlear nucleus at 24 h and persisted through 1 year, suggesting acute and chronic neuronal degeneration after blast exposure. No statistically significant differences were observed between single and repeated blasts. The localized degeneration of neuronal cytoskeletal elements in the cochlear nucleus suggests that the damage could be caused by transmission of blast shockwaves/noise through the ear canal and that use of suitable ear protection devices can protect against acute and chronic central auditory signal processing defects including tinnitus after blast exposure.

Blast Traumatic Brain Injury Induces Long-Term Alterations in Inflammatory Gene Expression in Chinchilla Brains

“…Any level of blast exposure leads to long-term degeneration of the auditory pathway and results in chronic auditory dysfunctions such as hearing loss, tinnitus, central auditory processing disorders, and poor speech intelligibility [29,56]. Interestingly, evidence is evolving that tinnitus can trigger cognitive impairment and early-onset dementia [57,58], which could be affiliated with unresolved neuroinflammation.…”