Luo P F, Li J S
Department of Anatomy, Fourth Military Medical University, Xi'an, People's Republic of China.
Brain Res. 1991 Sep 20;559(2):267-75. doi: 10.1016/0006-8993(91)90011-j.
In order to confirm the monosynaptic connections of muscle spindle-mediated jaw stretch reflexes, 8 neurons of trigeminal mesencephalic nucleus innervating masseteric muscle spindles were identified electrophysiologically and stained intracellularly with horseradish peroxidase. These axon terminals projected to ipsilateral dorsal and dorsolateral divisions of trigeminal motor nucleus and extensive premotor areas. Under electron microscope, labeled terminals made monosynaptic contacts predominantly with dendrites in the jaw-closing motoneuron pools. One labeled and many non-labeled terminals were frequently observed to converge simultaneously on one dendrite in the area. However, it was of particular interest that 28% of the labeled terminals constituted the intermediate component of axo-axodendritic synaptic triads. The present study confirmed, for the first time, monosynaptic connections between jaw-closing muscle spindle afferents and jaw-closing motoneurons. These findings also provided ultrastructural evidence for the monosynaptic excitation of muscle spindle-mediated jaw stretch reflexes which received presynaptic and postsynaptic inhibitions of the premotor neurons from other sources.
为了证实肌梭介导的下颌伸展反射的单突触连接，通过电生理学方法鉴定了8个支配咬肌肌梭的三叉神经中脑核神经元，并用辣根过氧化物酶进行细胞内染色。这些轴突终末投射到三叉神经运动核的同侧背侧和背外侧部以及广泛的运动前区。在电子显微镜下，标记的终末主要与下颌闭合运动神经元池中的树突形成单突触联系。在该区域经常观察到一个标记终末和许多未标记终末同时汇聚到一个树突上。然而，特别有趣的是，28%的标记终末构成了轴-轴-树突触三联体的中间成分。本研究首次证实了下颌闭合肌梭传入纤维与下颌闭合运动神经元之间的单突触连接。这些发现也为肌梭介导的下颌伸展反射的单突触兴奋提供了超微结构证据，该反射受到来自其他来源的运动前神经元的突触前和突触后抑制。
