神经生长因子减轻噪声性阈移的透射电镜观察

Amelioration of nerve growth factor against noise-induced threshold shift: a transmission electron microscope observation

目的 探讨神经生长因子 (nervegrowthfactor,NGF)对豚鼠噪声性听力损伤的防治作用。方法 豚鼠每天暴露 115dB(A)白噪声连续 6d (45min/d) ,在暴露全部结束后不同时间 (1h、1d、2d、3d和 6d)分别测试皮层反应阈 ,并用透射电镜观察耳蜗螺旋器细胞内变化。结果 A(每日肌内注射NGF 10 0 0U/kg体重 )、B(每日肌内注射NGF 2 0 0 0U /kg体重 )和C(每日肌内注射NGF 30 0 0U/kg体重 ) 3个实验组动物听反应阈偏移幅度均小于生理盐水对照组 (每日肌内注射 1ml/kg体重 ) ,差异有非常显著性意义 (方差分析 ,P值均 <0 0 1) ;实验B、C两组动物在噪声暴露后 3d听反应阈已基本恢复 ,而对照组动物在噪声暴露后 6d仍有 (16 43± 6 91)dB( x±s)的阈移。透射电镜观察显示 ,对照组耳蜗病变在 3排外毛细胞 ,以底回末段损伤最重 ,主要有纤毛内微丝解聚、线粒体肿大和毛细胞轻度水肿 ;外毛细胞表面下池和传出神经末梢也有轻度肿胀的表现。实验A组耳蜗病变程度比对照组轻 ,多局限在第 3排外毛细胞。而实验B、C两组动物内耳损伤甚微。结论 在慢性声损伤中 ,外源性NGF能够减轻噪声对耳蜗毛细胞的损害 ,对噪声性听力损伤具有较明显的保护作用。

Objective To study the protective effects of nerve growth factor(NGF) on noise-induced hearing damage in guinea pigs Methods NGF injected Guinea pigs were consecutively exposed to white noise of 115 dB(A) for 6 days continually (45 min·d -1 ) Auditory thresholds were measured using auditory cortex evoked response to tone bursts in different post-exposure intervals (1 h, 1 d, 2 d, 3 d and 6 d) The ultrastructural changes within hair cells were also observed by a transmission electron microscope(TEM) Results The auditory threshold shifts in test group A(NGF:1 000 U·kg -1 ·d -1 , im ), B(NGF:2 000 U·kg -1 ·d -1 ,im ) and C( NGF:3 000U·kg -1 ·d -1 ,im ) were significantly fewer than that in the control group(Saline:1 ml·kg -1 ·d -1 ,im). Threshold shifts almost recovered in test group B and C 3 days after the exposure; while a threshold shift of (16 43±6 91) dB was present 6 days after the exposure in the control group TEM showed that all three rows of the outer hair cells(OHCs) of the basal turn in the control group displayed significant pathological changes Depolymerization of actin filiaments within stereocilia, swelling of submembraneous cistern and the efferent nerve-ending and slight edema of hair cells were evident In test group A, the hair cells display slight pathological changes, which are confined in the third row of OHCs in a local position of the basal turn In group B and C hair cells have nearly normal appearance Conclusion NGF is able to reduce threshold shift, and promote the recovery of auditory threshold in acoustic trauma This factor can, to some extent, protect against noise-induced hearing damage