Hair Cell Afferent Synapses: Function and Dysfunction

Abstract

To provide a meaningful representation of the auditory landscape, mammalian cochlear hair cells are optimized to detect sounds over an incredibly broad range of frequencies and intensities with unparalleled accuracy. This ability is largely conferred by specialized ribbon synapses that continuously transmit acoustic information with high fidelity and sub-millisecond precision to the afferent dendrites of the spiral ganglion neurons. To achieve this extraordinary task, ribbon synapses employ a unique combination of molecules and mechanisms that are tailored to sounds of different frequencies.Here we review the current understanding of how the hair cell's presynaptic machinery and its postsynaptic afferent connections are formed, how they mature, and how their function is adapted for an accurate perception of sound.

Protection of Cochlear Ribbon Synapses and Prevention of Hidden Hearing Loss

“…However, the extracellular transport of synaptic vesicles in the IHCs ceases completely [ 47 ] ( Figure 2(c) ). Otoferlin operates as a Ca 2+ sensor at the IHC synapse [ 57 ]. In Otoferlin knockout mice, the rapid phase of exocytosis is abolished in IHCs and is not reversed by fast Ca 2+ influx or Ca 2+ uncaging [ 58 ].…”

Pathophysiological changes in inner hair cell ribbon synapses in the ageing mammalian cochlea

“…2014; Johnson et al . 2017, 2019). Each postsynaptic type I SGN forms only one synapse with an adult IHC (Pujol et al .…”

Biophysical and morphological changes in inner hair cells and their efferent innervation in the ageing mouse cochlea

“…In the adult mammalian cochlea, sound-induced displacement of the hair cell stereociliary bundles regulates the gating of mechanoelectrical transducer (MET) channels located at the tips of the shorter rows of stereocilia (Beurg et al 2009). The depolarizing MET current, which is mainly carried by K + but also by Ca 2+ ions, generates a receptor potential that modulates the release of glutamate from IHC ribbon synapses onto the spiral ganglion afferent terminals (Marcotti, 2012;Johnson et al 2019). IHC membrane repolarization is then achieved by the activation of two characteristic basolateral membrane K + channels, which carry the negatively activating K + current I K,n , and the large-conductance Ca 2+ -activated K + current I K,f (Marcotti et al 2003;Oliver et al 2003).…”

“…The depolarizing MET current, which is mainly carried by K + but also by Ca 2+ ions, generates a receptor potential that modulates the release of glutamate from IHC ribbon synapses onto the spiral ganglion afferent terminals (Marcotti, 2012; Johnson et al . 2019). IHC membrane repolarization is then achieved by the activation of two characteristic basolateral membrane K + channels, which carry the negatively activating K + current I K,n , and the large‐conductance Ca 2+ ‐activated K + current I K,f (Marcotti et al .…”