内耳毛细胞再生的前体细胞及其发育调调控基因

自从在鸟类等非哺乳脊椎动物中发现毛细胞再生现象至今已有20年,人们对毛细胞再生的研究也取得了丰硕的成果,而且有可能从试验性研究向临床应用性研究发展.目前对内耳毛细胞再生方面的研究,尤其是再生毛细胞的前体细胞和再生机制的探讨日益增多.本文将对毛细胞再生的前体细胞进行简单介绍,并对参与内耳毛细胞形成的相关蛋白,Notch信号途径及Math1基因进行综述,以进一步了解毛细胞产生的机制.

三甲基锡的神经毒性和耳毒性

有机锡化合物环境污染对人类健康造成很大的危害。众多有机锡化合物中三甲基锡（TMT）对人体有较强的神经毒性和耳毒性。TMT神经毒性可选择性破坏大脑边缘结构尤其是海马神经元以及听神经系统的神经元。TMT之所以选择性损害某些敏感神经元，其原因是因为这些神经元富含一种被称为Stannin的蛋白质，而Stannin蛋白正是TMT攻击的特异性靶目标。由于这种蛋白同样存在于线粒体，因此富含线粒体的细胞比线粒体贫乏的细胞更容易遭受有机锡化合物的攻击。TMT与Stannin产生不可逆性结合之后进而破坏线粒体的结构和功能，终导致线粒体损害，细胞色素C释放，从而启动细胞凋亡程序。TMT耳毒性主要表现在用药后迅速发生的高频听力损失，其早期功能改变表现为听神经动作电位的反应阈升高，随后逐渐出现耳蜗微音器电位振幅的降低。因此，TMT对听觉系统的急性损伤部位很可能早是发生在从内毛细胞到I型螺旋神经节的听神经末梢及其神经纤维，随着用药后时间的延长才会逐渐累及外毛细胞。TMT对周边听觉系统的损害作用包括兴奋性氨基酸毒性，氧化应激，细胞内钙超载，线粒体破坏，神经纤维脱髓鞘病变等多重损害机制，因此TMT模型可能有助于模拟和研究听神经病的多重损害模式。

噪声暴露引起耳蜗损伤机制的研究

噪声是常见的职业性伤害和听力致残因素，预防噪声性耳聋的发生及降低其听觉损害的程度一直是我们研究的重要课题。近年的研究发现噪声暴露可引起耳蜗内活性氧、活性氮自由基及金属蛋白酶增加,毛细胞内DNA损伤，Caspase-3激活，AIF及EndoG的转移等一系列变化，终导致毛细胞死亡，以凋亡为主。噪声损伤机制的研究为预防和治疗噪声性耳聋开辟了新的思路。

The purpose of the present study was to determine protectivie effects of basic fibroblast growth factor (bFGF) on cochlear neurons and hair cells in vitro and in vivo. In experiment I, cultured spiral ganglion neurons (SGNs) prepared from P3 mice were exposed to 20mM glutamate for 2 hours before the culture medium was replaced with fresh medium containing 0, 25, 50, and 100 ng/ml bFGF, respectively. Fourteen days later, all cultures were fixed with 4% paraformaldehyde, and stained with 1% toluidine blue. The number of surviving SGNs were counted and the length of SGNs neurites were measured. Exposure to 20 mM glutamate for 24 hours resulted in an inhibition on neurite outgrowth of SGNs and elevated cell death. Treatment of the cultures with bFGF led to promotion of neurite outgrowth and elevated number of surviving SGNs. Effects of bFGF were dose dependent with the highest potency at 100 ng/ml. In experiment Ⅱ, in vivo studies were carried out with guinea pigs in which bFGF or artificial perilymph was perfused into the cochlea to assess possible protective effects of bFGF on cochlear hair cells and compound action potentials(CAP). The CAPs were measured before, immediatly and 48 hours after exposure to noise. Significant differences in CAP were observed (p＜0. 05 ) among the bFGF perfused group, control group(t =3. 896 ) and artificial perilymph perfused group (t =2. 520) at 48 hours after noise exposure, Cochleae were removed and hair cell Loss was analyzed in surface preparations prepared from all experimental animals. Acoustic trauma caused loss of 651 and 687 inner hair cells in the control and artificial perilymph perfused group, respectively. In sharp contrast, only 31 inner hair cells were lost in the bFGF perfused ears. Similarly, more outer hair cells died in the control and perilymph perfuesed group (41830 and 41968, respectively) than in the group treated with bFGF (34258). Our results demonstrate that bFGF protected SGNs against glutmate neurotoxicity in vitro. In addition, treatment with bFGF also protected hair cells from acoustic trauma.

Cochlear outer hair cells (OHCs) are involved in a mechanical feedback loop in which the fast somatic motility of OHCs is required for cochlear amplification. Alternatively, amplification is thought to arise from active hair bundle movements ob-served in non-mammalian hair cells. We measured the voltage-evoked hair bundle motions in the gerbil cochlea to determine if such movements are also present in mammalian OHCs. The OHCs displayed a large hair bundle movement that was not based on mechanotransducer channels but based on somatic motility. Significantly, bundle movements were able to generate radial motion of the tectorial membrane in situ. This result implies that the motility-associated hair bundle motion may be part of the cochlear amplifier.

大鼠内耳胚胎和出生后的组织学研究（英）

The mouse labyrinth is an excellent model for study-ing the morphogenesis and cytodifferentiation of the mam-malian inner ear' s postnatal developmental periods andthe availability of numerous genetic mutants with a variety of inner ear abnormalities. There are many genes affectingthe inner ear of the mouse, and some of these lead to le-sions which resemble lesions occurring in man.