Department of Medecine, University of Fribourg, Chemin du Musée 5, 1700, Fribourg, Switzerland.
Eur J Neurosci. 2017 Jun;45(11):1379-1395. doi: 10.1111/ejn.13576. Epub 2017 May 2.
Corticospinal and corticobulbar descending pathways act in parallel with brainstem systems, such as the reticulospinal tract, to ensure the control of voluntary movements via direct or indirect influences onto spinal motoneurons. The aim of this study was to investigate the corticobulbar projections from distinct motor cortical areas onto different nuclei of the reticular formation. Seven adult macaque monkeys were analysed for the location of corticobulbar axonal boutons, and one monkey for reticulospinal neurons' location. The anterograde tracer BDA was injected in the premotor cortex (PM), in the primary motor cortex (M1) or in the supplementary motor area (SMA), in 3, 3 and 1 monkeys respectively. BDA anterograde labelling of corticobulbar axons were analysed on brainstem histological sections and overlapped with adjacent Nissl-stained sections for cytoarchitecture. One adult monkey was analysed for retrograde CB tracer injected in C5-C8 hemispinal cord to visualise reticulospinal neurons. The corticobulbar axons formed bilateral terminal fields with boutons terminaux and en passant, which were quantified in various nuclei belonging to the Ponto-Medullary Reticular Formation (PMRF). The corticobulbar projections from both PM and SMA tended to end mainly ipsilaterally in PMRF, but contralaterally when originating from M1. Furthermore, the corticobulbar projection was less dense when originating from M1 than from non-primary motor areas (PM, SMA). The main nuclei of bouton terminals corresponded to the regions where reticulospinal neurons were located with CB retrograde tracing. In conclusion, the corticobulbar projection differs according to the motor cortical area of origin in density and laterality.
皮质脊髓和皮质延髓下行通路与脑干系统（如网状脊髓束）平行作用，通过直接或间接影响脊髓运动神经元，确保对随意运动的控制。本研究旨在研究来自不同运动皮质区的皮质延髓投射到网状结构的不同核团。对 7 只成年猕猴进行了皮质延髓轴突末梢位置的分析，对 1 只猕猴进行了网状脊髓神经元位置的分析。在 3 只、3 只和 1 只猕猴中，分别将逆行示踪剂 BDA 注射到前运动皮层（PM）、初级运动皮层（M1）或辅助运动区（SMA）。在脑干组织学切片上分析 BDA 顺行标记的皮质延髓轴突，并与相邻的尼氏染色切片重叠，以观察细胞构筑。对一只成年猕猴进行了 C5-C8 半脊髓注射 CB 逆行示踪剂，以观察网状脊髓神经元。皮质延髓轴突形成双侧终末场，有末梢和中途终末，在属于桥脑延髓网状结构（PMRF）的各种核团中进行了定量分析。来自 PM 和 SMA 的皮质延髓投射倾向于主要在同侧 PMRF 结束，但起源于 M1 时则在对侧结束。此外，起源于 M1 的皮质延髓投射比起源于非初级运动区（PM、SMA）的皮质延髓投射密度更低。末梢终末的主要核团与用 CB 逆行示踪剂定位的网状脊髓神经元相对应。总之，皮质延髓投射的密度和偏侧性因起源的运动皮质区而异。
