Disappearance of afferent and efferent nerve terminals in the inner ear of the chick embryo after chronic treatment with beta-bungarotoxin
Disappearance of afferent and efferent nerve terminals in the inner ear of the chick embryo after chronic treatment with beta-bungarotoxin
复制标题
长期使用β-银环蛇毒素治疗后鸡胚内耳传入和传出神经末梢消失
作者：
N. Hirokawa
从孵化第4天开始，将β-银环蛇毒素(β-Bt)每隔3天给雏鸡胚胎注射一次，以观察长期大量应用β-Bt的效果，并用电子显微镜观察毛细胞-神经在发育内耳中的关系。孵育第10天，神经末梢已与正在分化的毛细胞接触，但听前庭神经节细胞数量仅为对照组的1/3。至第14天，大部分神经节细胞变性、消失，神经上皮内仅见少量神经末梢。此时，大多数毛细胞缺乏与神经末梢的突触接触；但它们的突触前特化保持完好，并显示出持续分化的证据。第17天，听前庭神经节细胞完全消失。所有的毛细胞都没有传入和传出神经，但在第21天完全分化。研究发现，β-BT对培养的脊神经节细胞也有类似的破坏作用。目前的研究表明，β-BT在发育过程中长期大量应用时，会杀死听觉前庭和脊髓神经细胞。此外，毛细胞的分化正常进行，当神经末梢在发育后期缺失时，毛细胞的突触前特化保持不变。
Beta-Bungarotoxin(beta-BT) was applied to chick embryos at 3-day intervals beginning on the 4th day of incubation to see the effect of chronically and massively applied beta-BT, and to investigate the hair cell-nerve relationship in the developing inner ear by electron microscopy. On the 10th day of incubation, nerve terminals had achieved contact with differentiating hair cells, but the acoustico-vestibular ganglion cells of treated animals were decreased in number to one-third of those of the control. By the 14th day, most of the ganglion cells degenerated and disappeared, and only a few nerve terminals were seen in the neuroepithelium. At this time, most of the hair cells lacked synaptic contacts with nerve terminals; but their presynaptic specialization remained intact and they showed evidence of continuing differentiation. On the 17th day, the acoustico-vestibular ganglion cells were completely absent. All the hair cells were devoid of afferent and efferent innervation but were fully differentiated on the 21st day. Beta-BT was found to have a similar destructive effect on cultured spinal ganglion cells. The present study shows that beta-BT kills acoustico-vestibular and spinal nerve cells when applied chronically and massively during development. Furthermore, the differentiation of hair cells proceeds normally, and their presynaptic specializations are maintained when nerve terminals are absent during later developmental stages.