N-Methyl-D-Aspartate Receptors Involvement in the Gentamicin-Induced Hearing Loss and Pathological Changes of Ribbon Synapse in the Mouse Cochlear Inner Hair Cells

Figure 2

Spatial distribution of cochlear ribbons in IHCs and their relationship with inner spiral bundles in the normal mouse mature cochlea. The HCs, presynaptic ribbons, and nerve fibers were identified by immunostaining for myosin 7a (red), Ctbp2 (magenta), and neurofilament (NF) (green), respectively. Nuclei were labeled with DAPI (blue). (a) Ctbp2-positive ribbons (magenta puncta) were distributed at the basal poles of the IHCs and below the IHC nuclei. The IHC nuclei are marked with a red arrow. (b) NF staining showed that the ISBs appeared as nets of nerve fibers that include radially directed dendritic terminals of type I ANFs and efferent fibers of the olivocochlear system. (c) Merged images of (a) and (b). The IHC basal poles were surrounded by ISBs. (d, e) The 3D-reconstructed images showing the spatial relation among IHCs, presynaptic ribbons, and ISBs. (d) View from the modiolar side to the pillar side. (e) View from the pillar side to the modiolar side. IHC: inner hair cell; OHC: outer hair cell; ISBs: inner spiral bundles; ANFs: afferent nerve fibers. Scar bar = 10 μm.