老年大鼠耳蜗毛细胞死亡方式观察

Death modes of cochlea hair cells in aged rats

目的观察老年大鼠耳蜗毛细胞核的形态学变化,探讨老年大鼠耳蜗毛细胞的死亡方式。方法Wistar大鼠32只,分为两组。老年实验组20只,22～23月龄;青年对照组12只,2～3月龄。应用电位反应测听仪检测不同频率短纯音(4、10和20kHz)诱发的老年和青年Wistar大鼠双耳听性脑干反应阈值(ABR)。经听觉功能测试后,动物断头,解剖取出双耳听泡,固定耳蜗组织,分离耳蜗基底膜。采用细胞核DNA染料碘化丙锭(PI)标记不同年龄大鼠耳蜗基底膜毛细胞,荧光显微镜下自耳蜗顶部到底部观察老年大鼠耳蜗基底膜毛细胞核的形态学变化,判断老年大鼠耳蜗毛细胞死亡方式。结果老年实验组大鼠不同频率听性脑干反应阈值均高于青年对照组(P=0.001)。细胞核荧光染色发现老年实验组大鼠耳蜗基底膜毛细胞核存在核固缩、核肿胀和核缺失3种形态学变化,损伤的毛细胞主要存在于耳蜗基底膜的顶回和底回。结论凋亡和坏死为老年Wistar大鼠耳蜗毛细胞死亡的两种方式。

Objective To examine the age-related morphological changes in hair cell nuclei,and explore the death modes of cochlea hair cells in aged rats.Methods Thirty-two Wistar rats were used in present experiment.The animals were assigned to one of the two groups,rats in aged group（n=20）were 22-23 months of age,and those in young group（n=12）were 2-3 months of age.The auditory brainstem response（ABR）thresholds of both ears elicited with tone bursts at 4,10 and 20 kHz were measured in both young and aged Wistar rats.Upon completion of the auditory test,animals were decapitated and both left and right bullae were exposed.Following fixation,whole specimens comprising the basilar membrane with Corti＇s organ were separated from the modiolus.Propidium iodide（PI）,a popular DNA intercalating fluorescent probe,was used to trace the morphological changes in cochlea hair cell nuclei in the aged rats.Each Corti＇s organ was thoroughly inspected from the apical to the basal turns of cochlea with fluorescence microscopy.According to the morphological changes in the nuclei,the death modes of cochlea hair cell were determined.Results There were significant differences on ABR thresholds（P=0.001）at all tested frequencies between the young and aged rats.Three types of cochlea hair cell pathology appeared in the aged rats,including karyopyknosis,nuclear swelling and denucleation.A large number of loss or degenerated hair cells were present in the apical and basal end of cochlea in aged rats.Conclusion The present study indicates that apoptosis and necrosis are the death modes of cochlea hair cells in aged Wistar rats.