Neuronal Mechanisms of Cerebral Cortex Controlling Trigeminal Mesencephalic Spindle Atfetents for Smooth Mastication

在亚灵长类动物中，从大脑皮层到三叉运动核（Vmo）的投射被认为不是直接的，而是通过脑干的前运动神经元间接的。然而，皮质直接投射到运动前神经元的投射模式尚未得到很好的研究。然而，Vmo的前运动神经元包括中脑核（Vmes）神经元，它们是初级传入神经，其细胞体位于大脑中。因此，本研究对大鼠的投影模式进行了形态学研究。首先，我们通过向Vmo注射逆行示踪剂来检测Vmo运动前神经元的分布。运动前神经元分布于注射部位同侧的Vmes、三叉神经口核和主核、臂旁核、叉上核、Vmo周围的旁细胞网状结构（pRF）和三叉神经感觉核内侧的pRF，并以注射部位同侧为主。然后，我们通过在第一个实验中标记运动前神经元的脑干中注射逆行示踪剂，检查了直接投射到Vmo运动前神经元的皮质神经元的分布。在初级和次级运动皮层、初级体感皮层、岛叶和边缘皮层分别发现了向Vmo周围网状结构、三叉神经口核和Vmes核投射的皮质神经元。目前的研究表明，从不同的皮层区域通过运动前神经元（包括Vmes神经元）到Vmo的几个强投射，这些神经元是地形组织的。本研究有助于揭示复杂的神经元机制在皮层控制下颚运动。

In subprimates, projections from the cerebral cortex to the trigeminal motor nucleus (Vmo) are considered to be not direct, but indirect through premotoneurons in the brainstem. However, the projection patterns of the corticofugal direct projections to the premotoneurons have not been examined well. Whereas, the premotoneurons for the Vmo include the mesencephalic nucleus (Vmes) neurons that are primary afferents whose cell bodies are located in the brain. Therefore the present study was conducted to examine the projection patterns morphologically in the rat. At first, we examined the distribution of the premotoneurons for the Vmo by making an injection of a retrograde tracer into the Vmo. The premotoneurons were found in the Vmes ipsilateral to the injection site, and in the trigeminal oral and principal nucleus, parabrachial nucleus, supratrigeminal nucleus, parvocellular reticular formation (pRF) surrounding the Vmo, and pRF medial to the trigeminal sensory nuclei bilaterally with an ipsilateral predominance to the injection site. Then, we examined the distribution of cortical neurons projecting directly to the premotoneurons for the Vmo, by making an injection of the retrograde tracer into the brainstem where the premotoneurons were labeled in the first experiment. The cortical neurons projecting to the reticular formation around the Vmo, the trigeminal oral nucleus, and the Vmes nucleus were found in the primary and secondary motor cortex, the primary somatosensory cortex, and the insular and limbic cortex, respectively.The present study demonstrated several, strong projections from the distinct cortical areas to the Vmo through premotoneurons including the Vmes neurons, which are topographically organized. The present study contributed to reveal complex neuronal mechanisms in the cortical control of jaw movements.