Noise-induced damage in the zebrafish inner ear endorgans: evidence for higher acoustic sensitivity of saccular and lagenar hair cells

Abstract The three otolithic endorgans of the inner ear are known to be involved in sound detection in different teleost fishes, yet their relative roles for auditory-vestibular functions within the same species remain unclear. In zebrafish (Danio rerio), saccule and utricle are thought to play key functions in encoding auditory and vestibular information, respectively, but the biological function of lagena is not clear. We hypothesized that the saccule is the main auditory endorgan and lagena might serve an auditory function given its connectivity to the saccule and dominant vestibular function of the utricle in this species. We investigated the acoustic sensitivity of the three otolithic endorgans in adult zebrafish by comparing the impact of acoustic trauma (continuous white noise at 168 dB for 24 h) on their sensory epithelia. Noise treatment caused hair cell loss in both the saccule and lagena, but not in the utricle. This effect was identified immediately after acoustic treatment and did not increase 24h post trauma. Furthermore, hair cell loss was accompanied by a reduction in presynaptic activity measured based on Ribeye b expression but mainly in the saccule, supporting its main contribution for noise-induced hearing loss. Our findings support the hypothesis that the saccule plays a major role in hearing and that lagena is also acoustically affected but with less sensitivity most likely extending the species hearing dynamic range. Summary statementNoise-treated zebrafish showed higher hair cell loss and synaptopathy in the inner ear saccule and, to some extent, in the lagena, confirming their higher sensitivity and contribution for hearing loss compared to utricle.