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.