Paper Title
Investigating Hearing Loss and Recovery: Insights from The Zebrafish Model

Abstract
The increasing levels of environmental noise due to growing urban aggregations have created a serious hazard to the auditory system leading to noise-induced hearing loss (NIHL) and Temporary Threshold Shifts (TTS). The mechanisms underlying such impairment are not fully understood, and limited information is available on vertebrates such as fishes that share homologous inner ear structures to mammals and the ability to regenerate hair cells. The zebrafish (Danio rerio) has become an important model organism to study human sensorineural dysfunctions such as deafness, genetic causes of inner ear deficits and mechanisms of hair cell regeneration. Here, we investigated the effects of noise exposure on TTS and functional recovery in zebrafish, as well as the associated morphological damage and regeneration of the inner ear saccular hair cells. Specimens were exposed to white noise continuously for 24h at different amplitude levels (130, 140 or 150 dB re 1 μPa) versus quiet lab conditions. The auditory sensitivity was assessed through the auditory evoked potential (AEP) recording technique, which measures the overall neural activity synchronized with tone stimuli presentation. Recovery from acoustic trauma was evaluated at 3, 7 and 14 days post treatment. Results revealed significant TTS within the best hearing range of the species. Increasing noise levels elicited a significant delay in the auditory response and higher TTS. At 130 dB and 140 dB, full recovery was achieved after 3 days with thresholds from all frequencies returning to baseline levels; while at 150 dB, thresholds only returned to baseline after 14 days. Hearing loss was accompanied by structural damage of the saccular sensory hair cells but this effect was only significant at 150 dB. This study established an important assay to investigate in greater detail the mechanisms of noise-induced changes in the vertebrate auditory system at both functional and structural levels.