Johnson Michael D, Frigon Alain, Hurteau Marie-France, Cain Charlette, Heckman C J
Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois;
Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
J Neurophysiol. 2017 May 1;117(5):2065-2074. doi: 10.1152/jn.00981.2016. Epub 2017 Mar 1.
In this study we evaluate temporal summation (wind-up) of reflexes in select distal and proximal hindlimb muscles in response to repeated stimuli of the distal tibial or superficial peroneal nerves in cats 1 mo after complete spinal transection. This report is a continuation of our previous paper on reflex wind-up in the intact and acutely spinalized cat. To evaluate reflex wind-up in both studies, we recorded electromyographic signals from the following left hindlimb muscles: lateral gastrocnemius (LG), tibialis anterior (TA), semitendinosus (ST), and sartorius (Srt), in response to 10 electrical pulses to the tibial or superficial peroneal nerves. Two distinct components of the reflex responses were considered, a short-latency compound action potential (CAP) and a longer duration bout of sustained activity (SA). These two response types were shown to be differentially modified by acute spinal injury in our previous work (Frigon A, Johnson MD, Heckman CJ. 590: 973-989, 2012). We show that these responses exhibit continued plasticity during the 1-mo recovery period following acute spinalization. During this early chronic phase, wind-up of SA responses returned to preinjury levels in one muscle, the ST, but remained depressed in all other muscles tested. In contrast, CAP response amplitudes, which were initially potentiated following acute transection, returned to preinjury levels in all muscles except for Srt, which continued to show marked increase. These findings illustrate that spinal elements exhibit considerable plasticity during the recovery process following spinal injury and highlight the importance of considering SA and CAP responses as distinct phenomena with unique underlying neural mechanisms. This research is the first to assess temporal summation, also called wind-up, of muscle reflexes during the 1-mo recovery period following spinal injury. Our results show that two types of muscle reflex activity are differentially modulated 1 mo after spinal cord injury (SCI) and that spinal reflexes are altered in a muscle-specific manner during this critical period. This postinjury plasticity likely plays an important role in spasticity experienced by individuals with SCI.
在本研究中，我们评估了猫在完全脊髓横断1个月后，对胫神经远端或腓浅神经的重复刺激，所选后肢远端和近端肌肉中反射的时间总和（wind-up）。本报告是我们之前关于完整和急性脊髓损伤猫反射增强的论文的延续。为了在两项研究中评估反射增强，我们记录了左后肢以下肌肉的肌电信号：外侧腓肠肌（LG）、胫骨前肌（TA）、半腱肌（ST）和缝匠肌（Srt），以响应胫神经或腓浅神经的10次电脉冲。反射反应的两个不同成分被考虑在内，一个是短潜伏期复合动作电位（CAP），另一个是持续时间更长的持续活动（SA）。在我们之前的研究中（Frigon A，Johnson MD，Heckman CJ. 590：973 - 989，2012），这两种反应类型被证明会因急性脊髓损伤而受到不同程度的改变。我们表明，这些反应在急性脊髓损伤后的1个月恢复期内表现出持续的可塑性。在这个早期慢性阶段，SA反应的增强在一块肌肉（ST）中恢复到损伤前水平，但在所有其他测试肌肉中仍受到抑制。相比之下，急性横断后最初增强的CAP反应幅度，在除Srt之外的所有肌肉中都恢复到损伤前水平，而Srt继续显示出明显增加。这些发现表明，脊髓元件在脊髓损伤后的恢复过程中表现出相当大的可塑性，并强调了将SA和CAP反应视为具有独特潜在神经机制的不同现象的重要性。本研究首次评估了脊髓损伤后1个月恢复期内肌肉反射的时间总和，也称为增强。我们的结果表明，脊髓损伤（SCI）1个月后，两种类型的肌肉反射活动受到不同程度的调节，并且在这个关键时期脊髓反射以肌肉特异性方式发生改变。这种损伤后可塑性可能在脊髓损伤个体经历的痉挛中起重要作用。
