Department of Physiology, Teikyo University School of Medicine, Tokyo, Japan.
Department of Cell Biology and Neuroscience, Juntendo University Graduate School of Medicine, Tokyo, Japan.
J Comp Neurol. 2022 Aug;530(11):1950-1965. doi: 10.1002/cne.25313. Epub 2022 Mar 15.
Although corticospinal neurons are known to be distributed in both the primary motor and somatosensory cortices (S1), details of the projection pattern of their fibers to the lumbar cord gray matter remain largely uncharacterized, especially in rodents. We previously investigated the cortical area projecting to the gray matter of the fourth lumbar cord segment (L4) (L4 Cx) in mice. In the present study, we injected an anterograde tracer into multiple sites to cover the entire L4 Cx. We found that (1) the rostromedial part of the L4 Cx projects to the intermediate and ventral zones of the lumbar cord gray matter, (2) the lateral part projects to the medial dorsal horn, and (3) the caudal part projects to the lateral dorsal horn. We also found that the border between the rostromedial and caudolateral parts corresponds to the border between the agranular and granular cortex. Analysis of the somatotopic patterns formed by the cortical projection cells and the primary sensory neurons innervating the skin of the hindlimb and its related area suggests that the lateral part corresponds to the S1 hindlimb area and the caudal part to the S1 trunk area. Examination of thalamic innervation by the L4 Cx revealed that the caudolateral L4 Cx focally projects to the ventrobasal complex (VB) and the posterior complex (PO), while the medial L4 Cx widely projects to the PO but little to the VB. These findings suggest that the L4 Cx is parceled into subregions defined by the cytoarchitecture and subcortical projection.
虽然已知皮质脊髓神经元分布于初级运动和体感皮层（S1）中，但它们的纤维向腰骶髓灰质的投射模式的细节在很大程度上仍未得到描述，尤其是在啮齿动物中。我们之前研究了投射到小鼠第四腰椎段（L4）灰质的皮质区域（L4 Cx）。在本研究中，我们将顺行示踪剂注射到多个部位以覆盖整个 L4 Cx。我们发现：（1）L4 Cx 的前内侧部分投射到腰骶髓灰质的中间和腹侧区；（2）外侧部分投射到背侧角的内侧部；（3）尾侧部分投射到背侧角的外侧部。我们还发现，前内侧和尾外侧部分之间的边界对应于无颗粒和颗粒皮质之间的边界。对皮质投射细胞和支配后肢及其相关区域皮肤的初级感觉神经元形成的躯体感觉图谱的分析表明，外侧部分对应于 S1 后肢区，尾侧部分对应于 S1 躯干区。对 L4 Cx 向丘脑的神经支配的检查表明，尾侧 L4 Cx 局部投射到腹侧基底核复合体（VB）和后复合体（PO），而内侧 L4 Cx 广泛投射到 PO，但投射到 VB 的很少。这些发现表明，L4 Cx 被划分为由细胞构筑和皮质下投射定义的子区域。
