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 6

The 3D-reconstructed images and the numbers of NMDARs and AMPARs at the nerve fibers around the IHCs. Postsynaptic AMPARs, NMDARs, and nerve fibers around the IHCs were identified by immunostaining for GluA2 (red), GluN1 (cyan), and neurofilament (NF) (green). Nuclei were labeled with DAPI (blue). (a, b, c) In the study, we define the “IHC basal pole region” and the “IHC nuclei region” in every single IHC. The changed tendency in location of AMPARs and NMDARs was observed at the afferent dendrites around the adjacent IHC in the 3D-reconstructed images. (a) The locations of NMDARs and AMPARs at the afferent dendritic terminals in the normal cochlea. (b) AMPARs and NMDARs essentially switched locations on SGN dendrites after gentamicin treatment for 7 days. (c) The gentamicin-induced translocation of AMPARs and NMDARs was almost completely blocked after coinjection of MK801 and gentamicin for 4 days. (d, f, h) The numbers of GluN1-positive NMDARs. (e, g) The numbers of GluA2-positive AMPARs. (i) The numbers of colocalized AMPARs and NMDARs at the basal poles of the IHCs. GM 4 d, 7 d: gentamicin treatment for 4 days or 7 days; GM + MK 4d, 7d: combined treatment of gentamicin and MK801 for 4 days or 7 days; IHC: inner hair cell. .