Postnatal development of the juxtaoral organ as a muscle receptor of masticatory muscles

采用电生理和形态学方法研究了大鼠颌旁器官功能与结构的发育关系。为了进行功能分析，从10天至10周的Wistar大鼠分离的近颌器官中记录了对斜坡和保持拉伸反应的持续放电。10 ~ 12日龄大鼠在动态拉伸期结束时，各感觉单元均出现短暂放电现象。持续放电的邻旁器官拉伸阈值在10天和3周之间显著下降，在5周龄时达到成人值。另一方面，静态敏感性在出生后2 - 4周明显增加。电镜检查显示，出生后2至4周，由于外囊完成，囊腔明显扩大。此外，在1周龄至4周龄之间，在感觉单元的前末端分支数量、末端轴突的静脉曲张样肿胀大小以及核心结构周围的胶原和弹性纤维密度上观察到年龄依赖性的增加。免疫组化检查显示，囊腔内、外囊腔内含有透明质酸离子。当用透明质酸酶去除囊腔中的透明质酸离子时，器官的持续放电消失。在洗浴液中加入6 mM-KCl后，再次出现持续放电。这些结果表明，带负电荷的透明质酸离子在近端器官的包膜空间有助于感觉终端膜的去极化，导致该器官的兴奋性增加。

The developmental relationship between function and structure of the juxtaoral organ in rats was investigated using the electrophysiological and morphological techniques. For functional analysis, sustained discharges in response to ramp-and-hold stretches were recorded from the juxtaoral organs isolated from Wistar rats aged 10 days to 10 weeks. All sensory units of the animals of 10-12 days old showed nothing but brief discharges at the end of the dynamic phase of stretch. The threshold amplitude of stretch of the juxtaoral organ for a sustained discharge fell significantly between 10 days and 3 weeks reaching adult values at 5 weeks of age. On the other hand, the static sensitivity increased conspicuously between 2 and 4 weeks after birth.Electron microscopic examination revealed a conspicuous expansion of the capsular space caused by completion of the outer capsule between 2 and 4 weeks after birth. Moreover, between 1 and 4 weeks of age, age-dependent increases were observed in the number of preterminal branches in a sensory unit, in the size of the varicose-like swellings along the terminal axon, and in the density of collagen and elastic fibers around the core structure. Immunohistochemical investigation showed that the capsular space between inner and outer capsules contained hyaluronate ions. When hyaluronate ions in the capsular space were removed with a treatment of hyaluronidase, the sustained discharge of the organ was disappeared. The sustained discharge was appeared again by addition of 6 mM-KCl in the bathing solution.These results suggested that the negatively charged hyaluronate ions in the capsular space of the juxtaoral organ contributed to the depolarization of sensory terminal membranes resulting in an increase in the excitability of this organ.