Schmidt B J, Meyers D E, Tokuriki M, Burke R E
Laboratory of Neural Control, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, MD 20892.
Exp Brain Res. 1989;77(1):57-68. doi: 10.1007/BF00250567.
We examined modulation of transmission in short-latency, distal hindlimb cutaneous reflex pathways during fictive locomotion in 19 decerebrate cats. Fictive stepping was produced either by electrical stimulation of the mesencephalic locomotor region (MLR) or by administration of Nialamide and 1-DOPA to acutely spinalized animals. Postsynaptic potentials (PSPs) produced by electrical stimulation of low threshold afferents (less than 2.5 times threshold) in the superficial peroneal (SP), sural, saphenous or medial plantar nerves were recorded intracellularly from various extensor (n = 28) and flexor (n = 24) motoneurons and averaged throughout the step cycle, together with voltage responses to intrasomatic constant current pulses (in order to monitor relative cell input resistance). Each motoneuron studied displayed rhythmic background oscillations in membrane potential and correlated variations in input resistance. The average input resistance of extensor motoneurons was lowest during mid-flexion, when the cells were relatively hyperpolarized and silent. Conversely, average input resistance of flexor motoneurons was highest during mid-flexion, when they were depolarized and active. The amplitude of the minimum-latency excitatory components of PSPs produced by cutaneous nerve stimulation were measured from computer averaged records representing six subdivisions of the fictive step cycle. Oligosynaptic EPSP components were consistently modulated only in the superficial peroneal responses in flexor motoneurons, which exhibited enhanced amplitude during the flexion phase. With the other skin nerves tested (sural, saphenous, and plantar), no consistent patterns of modulation were observed during fictive locomotion. We conclude that transmission through some, but not all, oligosynaptic excitatory cutaneous pathways is enhanced by premotoneuronal mechanisms during the flexion phase of fictive stepping in several cat hindlimb motor nuclei. The present results suggest that the patterns of interaction between the locomotor central pattern generator and excitatory cutaneous reflex pathways depend on the source of afferent input and on the identity of the target motoneuron population.
我们在19只去大脑猫的虚拟运动过程中，研究了短潜伏期、后肢远端皮肤反射通路中的传递调制。通过电刺激中脑运动区（MLR）或向急性脊髓损伤动物施用尼亚酰胺和左旋多巴来产生虚拟踏步。从不同的伸肌（n = 28）和屈肌（n = 24）运动神经元细胞内记录由腓浅神经（SP）、腓肠神经、隐神经或足底内侧神经中低阈值传入纤维（小于阈值的2.5倍）的电刺激产生的突触后电位（PSP），并在整个步周期内进行平均，同时记录对体细胞内恒流脉冲的电压响应（以监测相对细胞输入电阻）。所研究的每个运动神经元在膜电位上都表现出节律性背景振荡以及输入电阻的相关变化。伸肌运动神经元的平均输入电阻在屈曲中期最低，此时细胞相对超极化且无活动。相反，屈肌运动神经元的平均输入电阻在屈曲中期最高，此时它们去极化且活跃。通过代表虚拟步周期六个细分的计算机平均记录来测量由皮肤神经刺激产生的PSP的最短潜伏期兴奋性成分的幅度。仅在屈肌运动神经元的腓浅神经反应中，寡突触兴奋性突触后电位成分持续受到调制，在屈曲阶段其幅度增强。对于所测试的其他皮肤神经（腓肠神经、隐神经和足底神经），在虚拟运动期间未观察到一致的调制模式。我们得出结论，在几只猫后肢运动核的虚拟踏步屈曲阶段，通过一些但并非所有的寡突触兴奋性皮肤通路的传递通过运动前神经元机制得到增强。目前的结果表明，运动中枢模式发生器与兴奋性皮肤反射通路之间的相互作用模式取决于传入输入的来源和目标运动神经元群体的身份。
