Efferent Activity Controls Hair Cell Response to Mechanical Overstimulation

The efferent pathway strengthens the auditory system for optimal performance by fine-tuning the response and protecting the inner ear from noise-induced damage. Although it has been well documented that efference helps defend against hair cell and synaptic extinction, the mechanisms of its otoprotective role have still not been established. Specifically, the effect of efference on an individual hair cell's recovery from mechanical overstimulation has not been demonstrated. In the current work, we explored the impact of efferent stimulation on this recovery using in vitro preparations of hair cells situated in the sacculi of American bullfrogs (Rana catesbeiana). In the absence of efferent stimulus, exposure of a hair bundle to high-amplitude mechanical deflection detuned it from its oscillatory regime, with the extent of detuning dependent on the applied signal. Efferent actuation concomitant with the hair bundle's relaxation from a high-amplitude deflection notably changed the recovery profile and often entirely eliminated the transition to quiescence. Our findings indicate that the efferent system acts as a control mechanism that determines the dynamic regime in which the hair cell is poised.