Eisdorfer Jaclyn T, Sobotka-Briner Hannah, Schramfield Susan, Moukarzel George, Chen Jie, Campion Thomas J, Smit Rupert, Rauscher Bradley C, Lemay Michel A, Smith George M, Spence Andrew J
Department of Bioengineering, College of Engineering, Temple University, Philadelphia, PA, United States.
Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ, United States.
Front Mol Neurosci. 2022 Aug 26;15:872634. doi: 10.3389/fnmol.2022.872634. eCollection 2022.
Neuromodulatory therapies for spinal cord injury (SCI) such as electrical epidural stimulation (EES) are increasingly effective at improving patient outcomes. These improvements are thought to be due, at least in part, to plasticity in neuronal circuits. Precisely which circuits are influenced and which afferent classes are most effective in stimulating change remain important open questions. Genetic tools, such as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), support targeted and reversible neuromodulation as well as histological characterization of manipulated neurons. We therefore transduced and activated lumbar large diameter peripheral afferents with excitatory (hM3Dq) DREADDs, in a manner analogous to EES, in a rat hemisection model, to begin to trace plasticity and observe concomitant locomotor changes. Chronic DREADDs activation, coupled with thrice weekly treadmill training, was observed to increase afferent fluorescent labeling within motor pools and Clarke's column when compared to control animals. This plasticity may underlie kinematic differences that we observed across stages of recovery, including an increased and less variable hindquarters height in DREADDs animals, shorter step durations, a more flexed ankle joint early in recovery, a less variable ankle joint angle in swing phase, but a more variable hip joint angle. Withdrawal of DREADDs agonist, clozapine--oxide (CNO) left these kinematic differences largely unaffected; suggesting that DREADDs activation is not necessary for them later in recovery. However, we observed an intermittent "buckling" phenomenon in DREADDs animals without CNO activation, that did not occur with CNO re-administration. Future studies could use more refined genetic targeted of specific afferent classes, and utilize muscle recordings to find where afferent modulation is most influential in altering motor output.
脊髓损伤（SCI）的神经调节疗法，如硬膜外电刺激（EES），在改善患者预后方面越来越有效。这些改善被认为至少部分归因于神经回路的可塑性。究竟哪些回路受到影响，以及哪些传入神经类别在刺激变化方面最有效，仍然是重要的悬而未决的问题。基因工具，如仅由设计药物激活的设计受体（DREADDs），支持靶向和可逆的神经调节以及对被操纵神经元的组织学特征分析。因此，我们在大鼠半切模型中，以类似于EES的方式，用兴奋性（hM3Dq）DREADDs转导并激活腰段大直径外周传入神经，以开始追踪可塑性并观察伴随的运动变化。与对照动物相比，观察到慢性DREADDs激活与每周三次的跑步机训练相结合，可增加运动神经元池和克拉克柱内的传入荧光标记。这种可塑性可能是我们在恢复阶段观察到的运动学差异的基础，包括DREADDs动物的后肢高度增加且变异性降低、步幅持续时间缩短、恢复早期踝关节更弯曲、摆动期踝关节角度变异性降低，但髋关节角度变异性更大。停用DREADDs激动剂氯氮平 - 氧化物（CNO）后，这些运动学差异基本未受影响；这表明在恢复后期，DREADDs激活对它们并非必要。然而，我们在未激活CNO的DREADDs动物中观察到一种间歇性的“屈曲”现象，重新给予CNO时这种现象未出现。未来的研究可以使用更精细的针对特定传入神经类别的基因靶向方法，并利用肌肉记录来确定传入神经调制在改变运动输出方面最具影响力的部位。
