Counter S A, Aldskogius H, Borg E
Neurology Department, Harvard University, Cambridge, MA.
Acta Otolaryngol. 1993 Jan;113(1):43-7. doi: 10.3109/00016489309135765.
The brain stem position, organization and number of motoneurons innervating the rabbit tensor tympani muscle (TTM) were determined by retrograde axonal transport of cholera toxin B/horseradish peroxidase conjugate (CTB-HRP) and wheat germ agglutinin HRP conjugate (WGA-HRP) tracers. The synaptic input to the TTM motoneurons was examined with WGA-HRP. The results show the motoneurons of the TTM to be localized in a cluster ventro-lateral to the outer margin of the ipsilateral trigeminal motor nucleus (VMN) and dorso-lateral to the superior olive. The number of labeled cells was greater in the combined CTB-HRP/WGA-HRP injected cases. The TTM motoneurons were triangular and elongated in shape and smaller than those of the VMN. An extensive network of dendritic branches was present ventro-laterally in the vicinity of the superior olive. Similar, but less extensive collections of dendritic processes were observed to course dorso-medially, rostrally and caudally. Axons were observed to project first dorsally or laterally, towards the trigeminal motor root, then after a sharp turn coursed ventrally within the trigeminal motor root (VMR). Transneuronal transport of the WGA-HRP was not accomplished in any preparation, suggesting among other things, system or species differences in the effectiveness of the WGA-HRP conjugate as a transynaptic tracer. It is concluded that the TTM acoustic reflex in rabbits and other mammals, its threshold, prolonged contraction capacity, and its influence on middle ear sound transmission may be related to its demonstrated extensive synaptic field in the reflex chain, particularly in the area of the superior olive, while its many other physiological functions may be made possible by the number, location, and multi-dimensional orientation of its motoneurons and dendrites.
通过霍乱毒素B/辣根过氧化物酶复合物（CTB-HRP）和小麦胚凝集素HRP复合物（WGA-HRP）示踪剂的逆行轴突运输，确定了支配家兔鼓膜张肌（TTM）的脑干位置、运动神经元的组织结构和数量。用WGA-HRP检测了TTM运动神经元的突触输入。结果显示，TTM运动神经元位于同侧三叉神经运动核（VMN）外缘腹外侧和上橄榄背外侧的一个簇中。在联合注射CTB-HRP/WGA-HRP的病例中，标记细胞的数量更多。TTM运动神经元呈三角形且细长，比VMN的运动神经元小。在上橄榄附近的腹外侧存在广泛的树突分支网络。在背内侧、 Rostral和尾侧也观察到了类似但不太广泛的树突过程集合。观察到轴突首先向背侧或外侧投射，朝向三叉神经运动根，然后在急转弯后在三叉神经运动根（VMR）内腹侧走行。在任何制剂中都未完成WGA-HRP的跨神经元运输，这表明除其他因素外，WGA-HRP复合物作为跨突触示踪剂的有效性存在系统或物种差异。得出的结论是，家兔和其他哺乳动物的TTM听觉反射、其阈值、延长的收缩能力及其对中耳声音传导的影响，可能与其在反射链中显示的广泛突触场有关，特别是在上橄榄区域，而其许多其他生理功能可能由其运动神经元和树突的数量、位置和多维取向实现。
