Figure 4.

Pathophysiological changes of glial cells in the auditory nerve of fB knockout mice. (A–H) Electron micrographs of Rosenthal’s canal in adult WT (A,A’,C,I) and fB^−/− (B,B′,D–H,J) mice. (A’) is the high magnification of the enclosed areas in the WT (A) auditory nerve revealing tight associations between the myelin of satellite glial cells (g) and type I (I) SGNs. (B′) is the high magnification of the enclosed area in (B) showing abnormal swirling of myelin sheaths around type I SGNs (black arrowheads) of fB^−/− mice. Similar changes in myelination of SGNs were seen in type I SGNs of the other young adult fB^−/− mice (C,D). Arrowheads point out myelin whorls in the myelination surrounding SGNs in (C). (E–G) Electron micrographs of axons in the osseous spiral lamina (OSL) of WT (E) and fB^−/− (F,G) mice. The majority of myelinating glial cells around the axon appear relatively normal in the fB knockout mice (F). Enlarged space between the glial cells and the axon of the auditory nerve in an fB^−/− mouse (G). (H) Pathological changes were also seen in the non-myelinating glial cells around type II (II) SGNs. (I,J) Similar myelin pathological changes were also seen in the postnatal fB^−/− mice (P14) (J), although the development of SGNs shows no abnormalities (I). (K) Confocal images showing Na,K-ATPase immunoreactivity in satellite glial cells surrounding SGNs in young adult WT (the top panel) and fB^−/− (bottom panel) mice. Confocal images of both WT and fB^−/− mice were obtained using the same microscope acquisition settings. Images in the top-right of the right panel are enlarged images of boxed areas in the center. A reduced Na,K-ATPase immunoreactivity is seen between WT and fB^−/− mouse samples. Images were taken from the basal portion of the mouse cochleas. (L,M) Neuron densities are significantly reduced in the apical and basal portions but not in the middle portion in fB^−/− mouse cochleae. Confocal images of NF200⁺ neurons in the middle turn of young adult WT (the top panel) and fB^−/− (the bottom panel) mice. Propidium iodide (PI) was used to counterstain cell nuclei. Scale bar = 20 μm. Quantification of SGNs in WT and fB^−/− mice revealed significant decreases of SGNs in the apical and basal portions of the auditory nerve and no significant loss of SGNs (M). Data bars represent mean density; error bars represent SEM; Data were analyzed by Mann-Whitney U test with statistical significance defined as a *p value of ≤ 0.05 (see detailed information in the Result section).