Metaplasticity and Recovery After Spinal Cord Injury: Cellular Mechanisms

描述（由申请人提供）：先前的研究表明，脊髓内的神经元对反应-结果（工具）关系敏感。完全脊髓横断的大鼠在腿伸展时，如果腿部受到电击，可以学会保持后肢屈曲的姿势（反应-偶发性休克）。使用这个简单的准备，我们已经证明刺激以双向方式改变脊髓学习的能力。反应偶发电击训练促进后来的脊柱学习。相反，与腿部位置无关的伤害性刺激（不可控的电击或外周爪损伤）会抑制未来的脊柱学习，并损害挫伤脊髓损伤（SCI）后的运动恢复。先前的研究发现，脊髓学习的这些损伤依赖于谷氨酸介导的可塑性的不适应形式，这种可塑性损害了脊髓未来的使用依赖性可塑性。调控这种可塑性的细胞机制（“元可塑性”）尚不清楚。我们的假设是脊髓内的细胞因子肿瘤坏死因子a （TNFa）在不可控刺激后的脊髓学习障碍中起着关键的机制作用。在脊髓损伤或伤害性刺激后，TNFa的释放水平升高。最近发现TNFa通过增加谷氨酸AMPA受体（AMPAR）到脊髓神经元质膜的运输来改变损伤脊髓内的突触可塑性。初步数据表明，tnfa诱导的AMPAR贩运可能导致脊髓损伤后的脊柱学习障碍。鞘内注入AMPAR激动剂或TNFa会损害脊柱学习能力。相反，TNFa抑制剂促进脊柱学习。目的1建立这些tnfa介导效应的剂量反应和时间特征。目的2采用qRT-PCR、ELISA、原位杂交和免疫荧光法检测不可控刺激后脊髓中TNFa mRNA和蛋白水平。目的3通过生化和共聚焦显微镜方法检测在不可控刺激后，tnf诱导AMPARs向脊髓神经元质膜运输。目的4测试TNFa1抑制剂在促进挫伤性脊髓损伤后使用依赖性可塑性和功能恢复方面的治疗潜力。我们的长期目标是揭示调节适应性脊柱可塑性的机制，使患者能够重建基本功能，同时限制可能导致痉挛或顽固性疼痛的适应性可塑性不良。通过明确脊髓学习和功能恢复的关键机制，我们希望提供新的治疗靶点，促进脊髓损伤后的脊髓学习和神经康复。

DESCRIPTION (provided by applicant): Prior research has shown that neurons within the spinal cord are sensitive to response-outcome (instrumental) relationships. Rats with complete spinal cord transections can learn to maintain the hindlimb in a flexed position if leg shock is delivered when the leg is extended (response- contingent shock). Using this simple preparation, we have shown that stimulation alters the capacity for spinal learning in a bidirectional manner. Training with response-contingent shock promotes later spinal learning. Conversely, nociceptive stimulation that is independent of leg position (uncontrollable shock or peripheral paw injury) inhibits future spinal learning and impairs locomotor recovery after contusive spinal cord injury (SCI). Prior work has found that these impairments in spinal learning depend on a maladaptive form of glutamate-mediated plasticity that impairs future use-dependent plasticity in the spinal cord. The cellular mechanisms regulating this plasticity of plasticity ("metaplasticity") are not well-understood. Our hypothesis is that the cytokine tumor necrosis factor a (TNFa) within the spinal cord plays a critical mechanistic role in spinal learning impairments after uncontrollable stimulation. TNFa is released in elevated levels after SCI or nociceptive stimulation. TNFa has recently been found to alter synaptic plasticity within the injured spinal cord by increasing trafficking of the glutamate AMPA receptor (AMPAR) to the plasma membrane of spinal neurons. Preliminary data suggest that TNFa-induced AMPAR trafficking may contribute to spinal learning impairments after SCI. Intrathecal delivery of an AMPAR agonist or TNFa impairs spinal learning. Conversely a TNFa inhibitor promotes spinal learning. Aim 1 establishes the dose-response and temporal features of these TNFa-mediated effects. Aim 2 evaluates TNFa mRNA and protein levels in the spinal cord after uncontrollable stimulation using qRT-PCR, ELISA, in situ hybridization and immunofluorescence. Aim 3 examines TNF-induced trafficking of AMPARs to the plasma membrane of spinal neurons after uncontrollable stimulation by biochemical and confocal microscopy methods. Aim 4 tests the therapeutic potential of a TNFa1 inhibitor for promoting use-dependent plasticity and recovery of function after contusive SCI. Our long-term goal is to unravel the mechanisms that regulate adaptive spinal plasticity, allowing patients to re-establish essential functions, while limiting the maladaptive plasticity that can lead to spasticity or intractable pain. By defining key mechanisms that disable spinal cord learning and recovery of function, we hope to provide novel therapeutic targets that promote spinal cord learning and neurorehabilitation after SCI. PUBLIC HEALTH RELEVANCE: Project Narrative/Public Health Relevance Statement Spinal cord Injury (SCI) produces a devastating syndrome that is characterized by loss of motor control and mobility, as well as sensory dysfunction and pain. The proposed project explores cellular mechanisms that regulate a form of spinal cord learning that is thought to contribute to recovery of function after SCI. These studies may provide a novel target for improving recovery after SCI.