大鼠口面部本体觉传导通路中二级神经元的形态学研究

The mesencephalic trigeminal nucleus (MTN) contains the somata of primary afferent neurons that innervate muscle spindles in masticatory muscles and mechanoreceptors in the periodontal ligaments. More and more studies have showed that the central axons of Vme neurons descended along Probst' tract and gave off axon collaterals to a lot nuclei in the pons, medulla and even C1-3 segment. Now, the function of so widespread connections of the Vme neurons is still unknown because the second-order neurons receiving Vme afferents have not been well revealed owing to the limitation of tracing techniques. Recently, we successfully labeled the afferent axon terminals of MTN neurons by injection of subunit B of cholera toxin (CTb) into masseter nerve or by injection of wheat germ agglutinin-horseradish peroxidase （WGA-HRP）into the trigeminal motor root. Studies using these techniques provided detailed immunofluorescence staining of Vme central terminals and showed four stable areas always with dense terminals of Vme neurons. Further studies by combining these technniques and retrograde fluorecent labeling showed that four classes of projection neuron including the neurons projecting to the contralateral thlamus, to the contralateral trigiminal transition zone, to ipisilateral cerebellum or to bilateral cerebellum, were respectively located in one of these areas. The present study will extend the examination of the features of these second-order neurons by combining more other morphological techniques.

三叉神经中脑核（MTN）由支配咀嚼肌肌梭和牙周膜机械感受器的初级传入神经元组成。这些神经元的中枢突沿Probst束下行途径脑桥、延髓并抵达第三颈髓节段，沿途发出大量侧支，广泛投射。尽管以往进行了大量的研究，但MTN众多投射区的功能目前仍然多数不清楚。其中主要原因是受方法学限制难以对接受MTN传入的二级神经元进行可靠定位。 近年，我们先后将霍乱毒素B亚单位（CTb）注射至咬肌神经或将麦芽凝集素结合的辣根过氧化物酶（WGA-HRP）注射至三叉神经运动根均成功标记了MTN神经元的中枢突，并且实现了与逆行追踪联合标记及荧光染色。这一进步使得定位口面部本体觉通路中的二级神经元变得既容易又可靠，初步研究即发现：MTN广泛投射区中有4个恒定的密集投射区，它们分别聚集着向对侧丘脑、对侧三叉神经过渡区、同侧小脑或双侧小脑投射的神经元。本研究将在此基础上综合多种形态学方法对这些二级神经元进行深入研究。

三叉神经中脑核（MTN）由支配咀嚼肌肌梭和牙周膜机械感受器的初级传入神经元组成，专职口面部本体觉信息的传递。以往大量研究表明MTN神经元的中枢突在脑干内投射广泛。众多的投射如何划区、各区域负责何种功能，目前仍然不清楚。此外，由于方法学的限制，支配大鼠牙周膜机械感受器的MTN神经元的投射目前尚未明确。. 鉴于以上问题，本研究对以下四方面问题进行了形态学研究：1）将四甲基罗丹明（TMR-DA）注射至三叉神经运动根（m5）进行跨节追踪，并根据分布模式对MTN神经元的投射终末进行分区；2）采取TMR-DA注射至m5联合CTB注射至下牙槽神经，双重跨节追踪，研究支配牙周膜机械感受器的MTN神经元的投射；3）采取TMR-DA注射至m5联合荧光金（FG）注射至小脑下脚（或小脑上脚或三叉神运动核或丘脑腹后内侧核（VPM））对跨节标记终末与逆行标记终末的重叠分布进行研究，有重叠分布者进一步观察电镜水平下的突触联系； 4）采取TMR-DA注射至m5联合跨单突触病毒注射至丘脑，观察二者重叠分布及联系。. 经过以上研究，取得多方面认识。最重要的认识是MTN的内众多的投射区域中存在一个特别核区专门负责将口面部本体觉信息向高级中枢传递。其余的包括首次对支配大鼠牙周膜机械感受器MTN神经元的投射进行了揭示；意外发现延髓线核头部接受MTN的投射。