Gossard J P, Rossignol S
Centre de Recherche en Sciences Neurologiques, Faculté de Médecine, Université de Montréal, Que., Canada.
Brain Res. 1990 Dec 24;537(1-2):1-13. doi: 10.1016/0006-8993(90)90333-7.
To help elucidate the role of presynaptic mechanisms in the control of locomotor movements, the transmission of PAD pathways was investigated by recording dorsal root potentials (DRPs) evoked by electrical stimulation of cutaneous and muscle nerves of both hindlimbs at various phases of the fictive step cycle. Fictive locomotion occurred spontaneously in decorticate cats or by stimulating the mesencephalic locomotor region (MLR) as well as in low spinal cats injected with nialamide and L-DOPA. Evoked DRPs were superimposed on a fluctuating DRP accompanying the fictive locomotor rhythm (locomotor DRP) which typically consisted of two peaks of depolarization per cycle, the largest peak occurring during the flexor phase. The amplitude of evoked DRPs was substantially modulated throughout the locomotor cycle and followed a similar modulation pattern for all stimulated nerves whether ipsilateral (i-) or contralateral (co-). The amplitude of evoked DRPs decreased at the beginning of the flexor phase, dropped to a minimum later in the flexor phase and then increased during the extensor phase where it became maximum. Results were comparable in decorticate and spinal preparations and for L6 and L7 rootlets with cutaneous and muscle nerve stimulation. It is noteworthy that the modulation pattern for a given rootlet was similar for i- and co- stimulation, even though the bilateral locomotor DRPs fluctuate out-of-phase with each other, subjecting the stimulated fibres to opposite presynaptic polarization changes. This suggests that the modulation may depend more on the presynaptic mechanisms of the receiving fibres than on those of the stimulated fibres. These results demonstrate that the transmission in spinal pathways involved in primary afferent depolarization (PAD) is phasically modulated by the activity in the spinal locomotor network. It is further suggested that the presynaptic inhibition associated with PAD evoked by movement-related sensory feedback during real locomotion could be modulated in a similar way.
为了帮助阐明突触前机制在控制运动行为中的作用，通过记录在虚构步周期的不同阶段对双侧后肢的皮肤神经和肌肉神经进行电刺激所诱发的背根电位（DRP），研究了PAD通路的传递。在去皮质猫中自发出现虚构运动，或通过刺激中脑运动区（MLR）以及在注射了尼亚酰胺和左旋多巴的低位脊髓猫中出现虚构运动。诱发的DRP叠加在伴随虚构运动节律的波动DRP（运动DRP）上，该运动DRP通常每个周期由两个去极化峰组成，最大的峰出现在屈肌期。诱发DRP的幅度在整个运动周期中受到显著调制，并且对于所有受刺激的神经，无论是同侧（i-）还是对侧（co-），都遵循相似的调制模式。诱发DRP的幅度在屈肌期开始时降低，在屈肌期后期降至最低，然后在伸肌期增加并达到最大值。在去皮质和脊髓标本中以及对L6和L7神经根进行皮肤和肌肉神经刺激时，结果是可比的。值得注意的是，即使双侧运动DRP彼此异相波动，使受刺激的纤维经历相反的突触前极化变化，给定神经根的调制模式对于i-和co-刺激也是相似的。这表明调制可能更多地取决于接受纤维的突触前机制，而不是受刺激纤维的突触前机制。这些结果表明，参与初级传入去极化（PAD）的脊髓通路中的传递受到脊髓运动网络活动的相位调制。进一步表明，在实际运动过程中与运动相关的感觉反馈所诱发的与PAD相关的突触前抑制可能以类似的方式受到调制。
