大脑皮层通过调节中间神经元支配脊髓前角的运动神经元。目前,神经追踪,免疫组织化学,和免疫电子显微镜用于探索和确认皮质脊髓束(CST)和颈脊髓钙视网膜素(Cr)中间神经元之间的突触连接特征。我们的形态学结果表明,(1)来自大脑皮层的生物素化右旋糖酐胺标记(BDA)纤维主要表现为对侧脊髓分布,腹角(VH)的分布比背角(DH)的分布更密集。电子显微镜(EM)显示BDA末端与脊髓神经元形成不对称突触,它们的平均标记率在DH和VH之间没有差异。(2)Cr免疫反应性(Cr)神经元在整个脊髓灰质中分布不均,并且在VH中比在DH中更致密和更大。在单标记电子显微镜(EM)水平,VH中Cr+枝晶的标记率高于DH,其中Cr+树突主要接受不对称的突触输入,在VH和DH之间。(3)免疫荧光三重标记在BDA+末端间有明显的配位点,突触素和Cr+树突,在VH中比在DH中具有更高的密度。(4)EM中的双重标记,BDA+终端和Cr+枝晶呈现相同的模式,BDA末端与Cr树突或Cr负(Cr-)树突形成不对称突触,和Cr树突接收BDA+末端或BDA-突触输入。VH中靶向Cr枝晶的BDA末端的平均百分比高于DH中的平均百分比,但是靶向Cr枝晶的BDA末端的百分比明显高于靶向Cr枝晶的百分比。BDA+末端大小没有差异。Cr+枝晶接受BDA+终端输入的百分率低于接受BDA-终端输入的百分率,BDA+末端尺寸大于Cr+枝晶接收的BDA-末端尺寸。目前的形态学结果表明,脊髓Cr中间神经元参与了皮质脊髓途径的调节过程。
The cerebral cortex innervates motor neurons in the anterior horn of the spinal cord by regulating of interneurons. At present, nerve tracing, immunohistochemistry, and immunoelectron microscopy are used to explore and confirm the characteristics of synaptic connections between the corticospinal tract (CST) and cervical spinal calretinin (Cr) interneurons. Our morphological results revealed that (1) biotinylated dextran amine labeled (BDA+) fibers from the cerebral cortex primarily presented a contralateral spinal distribution, with a denser distribution in the ventral horn (VH) than in the dorsal horn (DH). An electron microscope (EM) showed that BDA+ terminals formed asymmetric synapses with spinal neurons, and their mean labeling rate was not different between the DH and VH. (2) Cr-immunoreactive (Cr+) neurons were unevenly distributed throughout the spinal gray matter, and were denser and larger in the VH than in the DH. At the single labeling electron microscope (EM) level, the labeling rate of Cr+ dendrites was higher in the VH than in the DH, in which Cr+ dendrites mainly received asymmetric synaptic inputs, and between the VH and DH. (3) Immunofluorescence triple labeling showed obvious apposition points among BDA+ terminals, synaptophysin and Cr+ dendrites, with a higher density in the VH than in the DH. (4) Double labeling in EM, BDA+ terminals and Cr+ dendrites presented the same pattern, BDA+ terminals formed asymmetric synapses either with Cr+ dendrites or Cr negative (Cr-) dendrites, and Cr+ dendrites received either BDA+ terminals or BDA- synaptic inputs. The average percentage of BDA+ terminals targeting Cr+ dendrites was higher in the VH than in the DH, but the percentage of BDA+ terminals targeting Cr- dendrites was prominently higher than that targeting Cr+ dendrites. There was no difference in BDA+ terminal size. The percentage rate for Cr+ dendrites receiving BDA+ terminal inputs was lower than that receiving BDA- terminal inputs, and the BDA+ terminal size was larger than the BDA- terminal size received by Cr+ dendrites. The present morphological results suggested that spinal Cr+ interneurons are involved in the regulatory process of the cortico-spinal pathway.