Hair cell exocytosis
Auditory sensory hair cells release glutamate onto the afferent nerve fibers to refine the ascending auditory pathways during development and to transduce incoming sound-stimulation in adulthood. Here, we examine the mechanism underlying the autonomous and evoked synaptic release before and after the onset of hearing, respectively.
Synaptic release in the hair cells. Inner hair cell synapse harbors a synaptic ribbon, a large organelle, which tethers a halo of glutamate-filled synaptic vesicles. In response to sound stimulation, hair cell depolarizes. The calcium influx through the voltage-gated calcium channels triggers the fusion of synaptic vesicles to the plasma membrane. Glutamate, released into the synaptic cleft, activates the postsynaptic glutamate receptors from the afferent auditory nerve fibers.
Wiring and activity of the auditory nerve fibers
To achieve a sound-coding over a large range of frequencies and intensities, the auditory nerve fibers differ in their activation threshold and in their distribution along the cochlear tonotopic axis. Here, we combine electrophysiology and computational modeling to determine the wiring and the weight of the fibers in the auditory nerve. This will enable to develop electrophysiological probes to map the distribution of the fibers in the auditory nerve and hence to detect hidden auditory loss.
Computational simulation of the auditory nerve firing. Computational modeling of the sound-evoked firing of 807 fibers distributed along the tonotopic axis. At low-level of stimulation, basilar membrane response is sharply frequency-tuned and activates ANFs of a narrow band corresponding to sound probe frequency. In contrast, responses to intense stimuli are poorly tuned and recruit additional ANFs from broadband region with predominance toward the basal region of the cochlea.
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- Sharon Kujawa, Harvard University, USA
- Marci Lesperance, Michigan University, USA
- Ruben Vidal, Indianapolis University, USA
- Peter Heil, Würzburg University, Germany
- Michèle Studer, Nice Sophia Antipolis University, France