Cytoarchitecture and innervation of the mouse cochlear amplifier revealed by large-scale volume electron microscopy.

In mammalian cochlea, sound-induced vibration is amplified by a three-row lattice of Y-shaped microstructures consisting of electromotile outer hair cell and supporting Deiters cell. This highly organized structure is thought to be essential for hearing of low-level sounds. Prior studies reported differences in geometry and synaptic innervation of the outer hair cells between rows, but how these fine features are achieved at subcellular level still remains unclear. Using serial block-face electron microscopy, we acquired few-hundred-micron-sized cytoarchitecture of mouse organ of Corti at nanometer resolution. Structural quantifications were performed on the Y-shapes as well as afferent and efferent projections to outer hair cells (OHCs). Several new features, which support the previously observed inter-row heterogeneity, are described. Our result provides structural bases for the gradient of mechanical properties and diverse centrifugal regulation of OHC rows.