Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Centre de recherche du Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, QC, Canada.
Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA.
J Physiol. 2024 Nov;602(22):6225-6258. doi: 10.1113/JP286808. Epub 2024 Sep 27.
In quadrupeds, such as cats, cutaneous afferents from the forepaw dorsum signal external perturbations and send inputs to spinal circuits to co-ordinate the activity in muscles of all four limbs. How these cutaneous reflex pathways from forelimb afferents are reorganized after an incomplete spinal cord injury is not clear. Using a staggered thoracic lateral hemisections paradigm, we investigated changes in intralimb and interlimb reflex pathways by electrically stimulating the left and right superficial radial nerves in seven adult cats and recording reflex responses in five forelimb and ten hindlimb muscles. After the first (right T5-T6) and second (left T10-T11) hemisections, forelimb-hindlimb co-ordination was altered and weakened. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-, mid- and long-latency homonymous and crossed reflex responses in forelimb muscles and their phase modulation remained largely unaffected after staggered hemisections. The occurrence of homolateral and diagonal mid- and long-latency responses in hindlimb muscles evoked with left and right superficial radial nerve stimulation was significantly reduced at the first time point after the first hemisection, but partially recovered at the second time point with left superficial radial nerve stimulation. These responses were lost or reduced after the second hemisection. When present, all reflex responses, including homolateral and diagonal, maintained their phase-dependent modulation. Therefore, our results show a considerable loss in cutaneous reflex transmission from cervical to lumbar levels after incomplete spinal cord injury, albeit with preservation of phase modulation, probably affecting functional responses to external perturbations. KEY POINTS: Cutaneous afferent inputs co-ordinate muscle activity in the four limbs during locomotion when the forepaw dorsum contacts an obstacle. Thoracic spinal cord injury disrupts communication between spinal locomotor centres located at cervical and lumbar levels, impairing balance and limb co-ordination. We investigated cutaneous reflexes from forelimb afferents during quadrupedal locomotion by electrically stimulating the superficial radial nerve bilaterally, before and after staggered lateral thoracic hemisections in cats. We showed a loss/reduction of mid- and long-latency homolateral and diagonal reflex responses in hindlimb muscles early after the first hemisection that partially recovered with left superficial radial nerve stimulation, before being reduced after the second hemisection. Targeting cutaneous reflex pathways from forelimb afferents projecting to the four limbs could help develop therapeutic approaches aimed at restoring transmission in ascending and descending spinal pathways.
在四足动物（如猫）中，来自前脚背的皮肤传入信号会感知外部干扰，并向脊髓回路发送输入信号，以协调四肢肌肉的活动。不完全性脊髓损伤后，来自前肢感觉传入的这些皮肤反射通路如何重新组织尚不清楚。使用交错的胸外侧半切模型，我们通过电刺激 7 只成年猫的左右桡浅神经，并记录 5 个前肢和 10 个后肢肌肉的反射反应，研究了同侧和对侧肢体反射通路的变化。第一次（右 T5-T6）和第二次（左 T10-T11）半切后，前肢和后肢的协调性发生改变，运动减弱。第二次半切后，猫需要平衡辅助才能进行四足运动。短、中、长潜伏期同侧和交叉反射反应在前肢肌肉中基本保持不变，相位调制也基本保持不变。用左、右桡浅神经刺激引起的后肢肌肉同侧和对角中、长潜伏期反应，在第一次半切后即刻显著减少，但第二次左桡浅神经刺激时部分恢复。这些反应在第二次半切后消失或减少。当存在时，所有反射反应，包括同侧和对角反应，都保持其相位依赖性调制。因此，我们的结果表明，不完全性脊髓损伤后，从颈段到腰段的皮肤传入反射传递有相当大的损失，尽管保留了相位调制，可能影响对外界干扰的功能反应。关键点：当前脚背接触障碍物时，皮肤传入输入信号协调四肢的运动。胸段脊髓损伤破坏了位于颈段和腰段的脊髓运动中枢之间的通讯，损害了平衡和肢体协调。我们通过双侧电刺激桡浅神经，在猫的交错胸外侧半切前后，研究了四足运动中来自前肢传入的皮肤反射。我们发现，第一次半切后早期，后肢肌肉的中、长潜伏期同侧和对角反射反应减少/降低，左侧桡浅神经刺激后部分恢复，但第二次半切后减少。针对前肢传入投射到四肢的皮肤反射通路，可能有助于开发旨在恢复上行和下行脊髓通路传输的治疗方法。
