Quantification of hair cell number, ribeye b and nuclei in the zebrafish inner ear endorgans

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 the lagena is not clear. We hypothesized that the zebrafish saccule serves as a primary auditory endorgan, making it more vulnerable to noise exposure, and that lagena might have an auditory function given its connectivity to the saccule and dominant vestibular function of the utricle.

In this study, we compared the impact of acoustic trauma (continuous white noise at 168 dB for 24 h) between the sensory epithelia of the three otolithic endorgans. 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 24 h post trauma. Furthermore, hair cell loss was accompanied by a reduction in presynaptic activity measured based on Ribeye b presence 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 sound detection and that lagena is also acoustically affected extending the species hearing dynamic range.