Hair cell force generation does not amplify or tune vibrations within the chicken basilar papilla.

Anping Xia,Patrick D Raphael,Xiaofang Liu,John S Oghalai,Brian E Applegate

doi:10.1038/ncomms13133

Anping Xia, Patrick D Raphael + Show 3 more

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https://doi.org/10.1038/ncomms13133

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Abstract

Frequency tuning within the auditory papilla of most non-mammalian species is electrical, deriving from ion-channel resonance within their sensory hair cells. In contrast, tuning within the mammalian cochlea is mechanical, stemming from active mechanisms within outer hair cells that amplify the basilar membrane travelling wave. Interestingly, hair cells in the avian basilar papilla demonstrate both electrical resonance and force-generation, making it unclear which mechanism creates sharp frequency tuning. Here, we measured sound-induced vibrations within the apical half of the chicken basilar papilla in vivo and found broadly-tuned travelling waves that were not amplified. However, distortion products were found in live but not dead chickens. These findings support the idea that avian hair cells do produce force, but that their effects on vibration are small and do not sharpen tuning. Therefore, frequency tuning within the apical avian basilar papilla is not mechanical, and likely derives from hair cell electrical resonance.

Highlights

Frequency tuning within the auditory papilla of most non-mammalian species is electrical, deriving from ion-channel resonance within their sensory hair cells
We show that mechanical properties of the chicken peripheral auditory system do not match previously published measures of frequency tuning in chicken hair cells and auditory nerves
Our finding that mechanical tuning is much broader than previously measured electrical and neural tuning is consistent with the concept that frequency tuning in birds derives from the electrical characteristics of their hair cells and not the underlying mechanical response of the basilar membrane (BM)

Summary

Introduction

Frequency tuning within the auditory papilla of most non-mammalian species is electrical, deriving from ion-channel resonance within their sensory hair cells. Frequency tuning within the apical avian basilar papilla is not mechanical, and likely derives from hair cell electrical resonance. The inner ear transduces the mechanical energy of sound into electrochemical signals that are encoded within the auditory nerve This originates when sound-induced pressure waves deflect stereociliary bundles at the apical poles of sensory hair cells. The active force generation properties of OHCs are commonly thought to locally amplify and sharpen the spatial extent of the BM vibrations This is termed cochlear amplification and it improves auditory sensitivity to quiet sounds and frequency selectivity[6,18]. Turtles and lizards, bird hair cells are arrayed in a plane, are surrounded by a non-specialized supporting cells layer that supports hair cell regeneration, and have electrical tuning[28]

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