Fig. 4

Anti-neurodegenerative effects of the fetal thymus graft on SG cells of the cochlea. SG cells in Groups A (a), B (b), C (c), and D (d) were histopathologically examined. Representative findings. H&E staining (original magnification x100). Several cells showed degeneration in the spiral ganglion of Group B aged 6 months old and the development of these findings in Group C aged 12 months old as aging. On the other hand, thymus-grafted Group D revealed no remarkable changes in SG cells, compared with Group A aged 2 months old. e) To evaluate degeneration of the auditory neurons, the nuclei of SG cells in the apical, middle, or basal turns of the cochlea were quantified. Although no significant difference of density of the nuclei/10,000 μm² was observed between Group B aged 6 months old and Group C aged 12 months old at the apical turn (p = 0.065), age-related devastation of the density of SGs between Groups B and C was found in the other turns (p < 0.005–0.0005), and significant recovery of the density in thymus-grafted Group D in comparison with that in Group B at all turns (p < 0.01–0.00005) was observed. The significant recovery of neurodegeneration in Group D was insufficient to reach the level of Group A in the middle turn (p = 0.033); however, no significant difference in comparison with Group A was observed in any other turns (p > 0.05). NS: no significance. n = 5 for Groups A-C and 10 for Group D (mean ± SD)