Degtyarenko A M, Simon E S, Burke R E
Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4455, USA.
J Neurophysiol. 1998 Dec;80(6):3284-96. doi: 10.1152/jn.1998.80.6.3284.
Locomotor modulation of disynaptic EPSPs from the mesencephalic locomotor region in cat motoneurons. J. Neurophysiol. 80: 3284-3296, 1998. When low-frequency tetanization of the mesencephalic locomotor region (MLR) produce fictive locomotion in unanesthetized, decerebrate cats, each MLR stimulus produces a distinctive cord dorsum potential (CDP) and oligosynaptic excitatory postsynaptic potentials (EPSPs) in many lumbosacral motoneurons. The average segmental latency from the initial CDP wave [mean delay from stimulus: 4.3 +/- 0.9 (SD) ms] to the onset of detectable MLR EPSPs was 1.6 +/- 0.4 ms, suggesting a disynaptic segmental connection. In gastrocnemius/soleus, flexor hallucis longus, flexor digitorum longus, tibialis anterior, and posterior biceps-semitendinosus motoneurons (35/38 cells), MLR EPSPs either appeared or were enhanced during the phase of fictive stepping in which the target motoneurons were depolarized and the motor pool was active (the phase), with parallel changes between EPSP amplitudes and membrane depolarization. In contrast, MLR stimulation produced small (1/10) or no EPSPs in extensor digitorum longus (EDL) motoneurons, with no phase enhancement (4/10) or oligosynaptic inhibitory postsynaptic potentials during the phase (5/10). Eight of 10 flexor digitorum longus (FDL) cells exhibited membrane depolarization in the early flexion phase of fictive stepping, and five of these showed parallel enhancement of disynaptic MLR EPSPs during early flexion. Three cases were studied when the FDL motor pool exhibited exclusively extensor phase firing. In these cases, the disynaptic MLR EPSPs were enhanced only during the extensor phase, accompanied by membrane depolarizations. We conclude that the last-order interneurons that produce disynaptic MLR EPSPs may well participate in producing the depolarizing locomotor drive potentials (LDPs) found in hindlimb motoneurons during fictive locomotion. However, the absence of linkage between MLR EPSP enhancement and LDP depolarizations in EDL motoneurons suggests that other types of excitatory interneurons also must be involved at least in some motor pools. We compared these patterns with the modulation of disynaptic EPSPs produced in FDL cells by stimulation of the medial longitudinal fasciculus (MLF). In all seven FDL motoneurons tested, disynaptic MLF EPSPs appeared only during the extension phase, regardless of when the FDL motoneurons were active. The fact that the modulation patterns of MLR and MLF disynaptic EPSPs is different in FDL motoneurons indicates that the two pathways do not converge on common last-order interneurons to that motor pool.
猫运动神经元中来自中脑运动区的双突触兴奋性突触后电位的运动调节。《神经生理学杂志》80: 3284 - 3296, 1998年。当中脑运动区（MLR）的低频强直刺激在未麻醉、去大脑的猫中产生虚拟运动时，每个MLR刺激在许多腰骶运动神经元中产生独特的脊髓背电位（CDP）和多突触兴奋性突触后电位（EPSP）。从初始CDP波[刺激的平均延迟：4.3±0.9（标准差）毫秒]到可检测到的MLR EPSP开始的平均节段潜伏期为1.6±0.4毫秒，提示双突触节段连接。在腓肠肌/比目鱼肌、拇长屈肌、趾长屈肌、胫骨前肌和肱二头肌-半腱肌运动神经元（35/38个细胞）中，MLR EPSP在虚拟踏步阶段出现或增强，在该阶段目标运动神经元去极化且运动神经元池活跃（该阶段），EPSP幅度与膜去极化之间存在平行变化。相比之下，MLR刺激在趾长伸肌（EDL）运动神经元中产生小的（1/10）或无EPSP，在该阶段无相位增强（4/10）或多突触抑制性突触后电位（5/10）。10个趾长屈肌（FDL）细胞中有8个在虚拟踏步的早期屈曲阶段表现出膜去极化，其中5个在早期屈曲期间双突触MLR EPSP平行增强。研究了3例FDL运动神经元池仅表现出伸展相放电的情况。在这些情况下，双突触MLR EPSP仅在伸展相增强，伴有膜去极化。我们得出结论，产生双突触MLR EPSP的最后一级中间神经元很可能参与产生在虚拟运动期间在后肢运动神经元中发现的去极化运动驱动电位（LDP）。然而，EDL运动神经元中MLR EPSP增强与LDP去极化之间缺乏联系表明，其他类型的兴奋性中间神经元也必须至少参与一些运动神经元池。我们将这些模式与通过刺激内侧纵束（MLF）在FDL细胞中产生的双突触EPSP的调节进行了比较。在所有测试的7个FDL运动神经元中，双突触MLF EPSP仅在伸展相出现，而与FDL运动神经元何时活跃无关。FDL运动神经元中MLR和MLF双突触EPSP的调节模式不同这一事实表明，这两条通路不会汇聚到该运动神经元池的共同最后一级中间神经元上。
