Robbins A, Pfaff D W, Schwartz-Giblin S
Rockefeller University, Laboratory of Neurobiology and Behavior, New York, NY 10021.
Exp Brain Res. 1992;92(1):46-58. doi: 10.1007/BF00230382.
These experiments tested hypotheses about the logic of reticulospinal and reticuloreticular controls over deep back muscles by examining descending efferent and contralateral projections of the sites within the medullary reticular formation (MRF) that evoke EMG responses in lumbar axial muscles upon electrical stimulation. In the first series of experiments, retrograde tracers were deposited at gigantocellular reticular nucleus (Gi) sites that excited the back muscles and in the contralateral lumbar spinal cord. The medullary reticular formation contralateral to the Gi stimulation/deposition site was examined for the presence of single- and double-labeled cells from these injections. Tracer depositions into Gi produced labeled cells in the contralateral Gi and Parvocellular reticular nucleus (PCRt) whereas the lumbar injections retrogradely labeled cells only in the ventral MRF, indicating that separate populations of medullary reticular cells project to the opposite MRF and the lumbar cord. In the second series of experiments the precise relationships between the location of neurons retrogradely labeled from lumbar spinal cord depositions of the retrograde trace, Fluoro-Gold (FG) and effective stimulation tracks through the MRF were examined. The results indicate that the Gi sites that are most effective for activation of the back muscles are dorsal to the location of retrogradely labeled lumbar reticulospinal cells. To verify that cell bodies and not fibers of passage were stimulated, crystals of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) were deposited at effective stimulation sites in the Gi. NMDA decreased the ability of electrical stimulation to activate back muscles at 5 min postdeposition, indicating a local interaction of NMDA with cell bodies at the stimulation site. In the third series of experiments, electrical thresholds for EMG activation along a track through the MRF were compared to cells retrogradely labeled from FG deposited into the cervical spinal cord. In some experiments, Fast Blue was also deposited into the contralateral lumbar cord. Neurons at low threshold points on the electrode track were labeled following cervical depositions, indicating a direct projection to the cervical spinal cord. The lumbar depositions, again, labeled cells in MRF areas that were ventral to the locations of effective stimulation sites, primarily on the opposite side of the medulla. In addition, the lumbar depositions back-filled cells in the same cervical segments to which the Gi neurons project. These results suggest that one efferent projection from effective stimulation sites for back muscle activation is onto propriospinal neurons in the cervical cord, which in turn project to lumbar cord levels.(ABSTRACT TRUNCATED AT 400 WORDS)
这些实验通过检测延髓网状结构（MRF）内一些位点的下行传出纤维和对侧投射，来验证有关网状脊髓和网状网状结构对深部背部肌肉控制逻辑的假说，这些位点在电刺激时会引起腰椎轴肌的肌电图（EMG）反应。在第一组实验中，逆行示踪剂被注射到激发背部肌肉的巨细胞网状核（Gi）位点以及对侧腰脊髓中。检查了与Gi刺激/注射位点相对侧的延髓网状结构，以寻找这些注射产生的单标记和双标记细胞。向Gi注射示踪剂在对侧Gi和小细胞网状核（PCRt）中产生了标记细胞，而向腰段注射示踪剂仅逆向标记了腹侧MRF中的细胞，这表明延髓网状细胞的不同群体分别投射到对侧MRF和腰脊髓。在第二组实验中，研究了从逆行示踪剂氟金（FG）注入腰脊髓后逆向标记的神经元位置与通过MRF的有效刺激轨迹之间的确切关系。结果表明，对激活背部肌肉最有效的Gi位点位于逆向标记的腰网状脊髓细胞位置的背侧。为了验证被刺激的是细胞体而不是通过的纤维，将兴奋性氨基酸激动剂N-甲基-D-天冬氨酸（NMDA）的晶体注射到Gi中的有效刺激位点。NMDA在注射后5分钟降低了电刺激激活背部肌肉的能力，表明NMDA在刺激位点与细胞体发生了局部相互作用。在第三组实验中，将沿MRF轨迹进行EMG激活的电阈值与从注入颈脊髓的FG逆向标记的细胞进行了比较。在一些实验中，快蓝也被注入对侧腰脊髓。在颈段注射后，电极轨迹上低阈值点的神经元被标记，表明其直接投射到颈脊髓。同样，腰段注射标记了MRF区域中位于有效刺激位点位置腹侧的细胞，主要在延髓的对侧。此外，腰段注射使与Gi神经元投射到的相同颈段中的细胞发生了回充。这些结果表明，用于激活背部肌肉的有效刺激位点的一种传出投射是到颈脊髓中的脊髓 propriospinal 神经元上，而这些神经元又投射到腰脊髓水平。（摘要截断于400字）
