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既往的研究证明，由支配咬肌的三叉神经中脑核神经元到丘脑腹后内侧核存在着一条由四级神经元组成的传递本体觉信号的中枢通路．此通路的第二级神经元位于三叉神经脊束核吻测亚核背内侧部和邻接的小细胞网状核的一部分，第三级神经元存在于沿三又神经感觉主核内缘伸延的“带状区”。本研究将ＰＨＡ－Ｌ注入第二级神经元所在区域，不仅在“带状区”发现有很多标记终末，而且在三叉神经中脑核区域内也发现较密集的ＰＨＡ－Ｌ阳性终末，许多终末与中脑核神经无形成密切接触．对这种材料又向咬肌神经内注入ＨＲＰ，观察到有一些ＨＲＰ标记的中脑核神经元与ＰＨＡ－Ｌ标记终末接触．本研究结果提示，在三叉神经本体感觉通路中，由第二级神经元的核区向初级传入神经元发出有回返投射，并对其机能意义进行了讨论．
Previous studies have shown that there is a central pathway through the masseter muscle of the trigeminal nucleus pulposus neurons to the ventral thalamic ventral nucleus to transmit the body sensory signals composed of four levels of neurons. The second neuron of this pathway is located in the dorsolateral part of the subnucleus submandibular nucleus and part of the adjacent small cell reticular nucleus. The third neuron exists in the inner edge of the main nuclear nucleus “Ribbon.” In this study, we injected PHA-L into the region of second neurons, not only found many terminal markers in “zone”, but also found more dense PHA-L positive terminal in the nucleus of trigeminal nerve, Many terminals have no direct contact with the nucleus pulposus. In turn, HRP was injected into the masseter nerve, and some HRP-labeled mesencephalic neurons were observed to be in contact with the terminal PHA-L marker. The results of this study suggest that in the trigeminal sensory pathway, retrograde projection is given to the primary afferent neurons by the nuclear region of the second neuron and its functional significance is discussed.