Côté Marie-Pascale, Gossard Jean-Pierre
Centre de Recherche en Sciences Neurologiques, Département de Physiologie, Faculté de Médecine, Université de Montréal, Montréal, Québec, H3C 3J7 Canada.
J Neurosci. 2004 Dec 15;24(50):11317-27. doi: 10.1523/JNEUROSCI.1486-04.2004.
Plasticity after spinal cord injury can be initiated by specific patterns of sensory feedback, leading to a reorganization of spinal networks. For example, proprioceptive feedback from limb loading during the stance phase is crucial for the recovery of stepping in spinal-injured animals and humans. Our recent results showed that step training modified transmission from group I afferents of extensors in spinal cats. However, cutaneous afferents are also activated during locomotion and are necessary for proper foot placement in spinal cats. We therefore hypothesized that step training would also modify transmission in cutaneous pathways to facilitate recovery of stepping. We tested transmission in cutaneous pathways by comparing intracellular responses in lumbar motoneurons (n = 136) in trained (n = 11) and untrained (n = 7) cats spinalized 3-5 weeks before the acute electrophysiological experiment. Three cutaneous nerves were stimulated, and each evoked up to three motoneuronal responses mediated by at least three different pathways. Overall, of 71 cutaneous pathways tested, 10 were modified by step training: transmission was reduced in 7 and facilitated in 3. Remarkably, 6 of 10 involved the medial plantar nerve innervating the plantar surface of the foot, including two of the facilitated pathways. Because the cutaneous reflexes are exaggerated after spinalization, we interpret the decrease in most pathways as a normalization of cutaneous transmission necessary to recover locomotor movements. Overall, the results showed a high degree of specificity in plasticity among cutaneous pathways and indicate that transmission of skin inputs signaling ground contact, in particular, is modified by step training.
脊髓损伤后的可塑性可由特定模式的感觉反馈引发，从而导致脊髓网络的重组。例如，站立期肢体负重产生的本体感觉反馈对于脊髓损伤动物和人类恢复行走至关重要。我们最近的研究结果表明，阶梯训练改变了脊髓猫中伸肌I类传入纤维的信号传递。然而，皮肤传入纤维在运动过程中也会被激活，并且对于脊髓猫正确的足部放置是必需的。因此，我们推测阶梯训练也会改变皮肤通路中的信号传递，以促进行走恢复。我们通过比较在急性电生理实验前3 - 5周进行脊髓横断的训练猫（n = 11）和未训练猫（n = 7）的腰段运动神经元（n = 136）的细胞内反应，来测试皮肤通路中的信号传递。刺激三条皮肤神经，每条神经可诱发由至少三种不同通路介导的多达三种运动神经元反应。总体而言，在测试的71条皮肤通路中，有10条因阶梯训练而发生改变：7条通路的信号传递减少，3条通路的信号传递增强。值得注意的是，10条通路中有6条涉及支配足底表面的足底内侧神经，其中包括两条信号传递增强的通路。由于脊髓横断后皮肤反射会增强，我们将大多数通路中信号传递的减少解释为恢复运动所需的皮肤信号传递的正常化。总体而言，结果显示皮肤通路之间的可塑性具有高度特异性，并表明特别是传递地面接触信号的皮肤输入的信号传递会因阶梯训练而改变。
