Abstract
In mammals, neural encoding of sounds is mediated by ribbon-type synapses between inner ear hair cells (IHCs) and postsynaptic spiral ganglion neurons. These specialized connections are arranged along the IHC basolateral surface with gradient changes in morphology and electrophysiological properties, which are essential for the level coding of sound intensity. Large synaptic ribbons, which predominantly reside on the modiolar IHC face, are responsive to loud sounds and more susceptible to acoustic insults. Selective loss of them is the major cause for reduced cochlear audible range. However, other than fewer ribbons after noise exposure, the consequential presynaptic reorganization in the IHCs remains less characterized. Here, by means of volume electron microscopy and artificial intelligence-assisted image analysis, we investigated noise exposure-related changes in the mouse IHCs. Apart from morphological changes of the ribbon-type active zones, our quantifications reveal differential synaptic reorganization in the IHCs with staggered basolateral pole orientations as well as reduced spatial correlation between ribbons and proximal mitochondria. Together, these results argue for putative presynaptic mechanisms underlying activity-dependent structural changes in the sensory epithelial cells.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Conflicts of interest The authors declare no competing financial interests.
minor correction in the figure and text