大鼠耳蜗传出神经系统发育中降钙素基因相关肽和乙酰胆碱酯酶的时空分布

Growth and Development Process of Calcitonin Gene-related Peptide and Acetylcholinesterase in Rat Cochlear Efferent Nervous System

目的探讨耳蜗发育过程中传出神经的发育分布。方法应用Tublin免疫组织化学方法标记出生后3~15天以及出生后4个月大鼠耳蜗基底膜上所有传入和传出神经纤维及其末梢的分布;应用酶组织化学或免疫组织化学方法观察出生后不同时间耳蜗基底膜上降钙素基因相关肽(calcitonin gene-related peptide,CGRP)和乙酰胆碱脂酶(AchE)的表达和分布。结果耳蜗传入神经纤维及末梢在大鼠出生后当天已经与内、外毛细胞建立起突触联系;从出生后第五天开始CGRP出现在内毛细胞周围及底部,但AchE标记的传出神经尚未进入Corti器,出生后第七天AchE才开始与CGRP同时出现在内侧螺旋束和隧道螺旋束的耳蜗传出神经纤维及末梢。结论 CGRP和乙酰胆碱出现在Corti器的时间均明显早于耳蜗传出神经末梢在耳蜗靶细胞的就位;在大鼠耳蜗发育早期出现在内毛细胞区域的CGRP和乙酰胆碱或许是由内毛细胞及其周围支持细胞分泌的一种诱导耳蜗传出神经纤维朝着耳蜗螺旋器趋向性生长的引导信号。

Objective To study the developmental distribution of efferent nerves during cochlear development by evaluating the spatiotemporal distribution of efferent nerve markers, acetylcholinesterase(AchE) and calcitonin gene related peptide(CGRP) in rat cochlea from postnatal day to 15 days and 4 months after birth.Methods The innervation and distribution of afferent and efferent nervous system in the cochlear basilar membrane at different times after birth were assessed by Tublin immunochemistry. The enzyme histochemical and immunocytochemical techniques were also used to observe the expression and distribution of CGRP and AchE in cochlear efferent nerve fibers and synapse at different times after birth.Results The cochlear afferent nerve fibers and terminals had established synaptic connections with the inner and outer hair cells on the day after birth.CGRP began to appear in the region surrounding the inner hair cells on the fifth day after birth. However, AchE-labeled efferent nerve fibers had not entered the organ of Corti yet on the fifth day after birth. Unlike the CGRP, AchE appears expression was obserred simultaneously in the cochlear efferent fibers and terminals in both internal spiral bundle and tunnel spiral bundle from the seventh day after birth. It could be seen that CGRP and AchE appeared in the organ of Corti significantly later than the cochlear afferent innervation in the cochlear target cells in place. Conclusion The early expression of CGRP and acetylcholine in the region of inner hair cells may be guiding signals secreted by inner hair cells and surrounding support cells to induce the directional growth of efferent nerve fibers to the organ of Corti.