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。脊髓完全横断的大鼠可以学习保持后肢在屈曲位置，如果腿部电击时，腿是延长（响应-应急休克）。使用这种简单的准备，我们已经表明，刺激以双向方式改变脊髓学习的能力。伴随反应的电击训练促进了以后的脊髓学习。相反，不依赖于腿部位置的伤害性刺激（不可控制的休克或外周爪损伤）抑制未来的脊髓学习并损害挫伤性脊髓损伤（SCI）后的运动恢复。先前的工作已经发现，脊髓学习中的这些损伤依赖于谷氨酸介导的可塑性的适应不良形式，其损害脊髓中未来的使用依赖性可塑性。调节这种可塑性的可塑性（“元可塑性”）的细胞机制还没有很好地理解。 我们的假设是，脊髓内的细胞因子肿瘤坏死因子（TNF α）在不可控制的刺激后脊髓学习障碍中起着关键的机制作用。TNF α在SCI或伤害性刺激后以升高的水平释放。最近发现TNF α通过增加谷氨酸AMPA受体（AMPAR）向脊髓神经元质膜的运输来改变受损脊髓内的突触可塑性。 初步数据表明，TNF α诱导的AMPAR运输可能有助于脊髓损伤后的学习障碍。鞘内递送AMPAR激动剂或TNFa损害脊髓学习。相反，TNFa抑制剂促进脊髓学习。目的1建立这些TNF α介导的作用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等方法，检测不可控刺激后脊髓中TNF α mRNA和蛋白水平的变化。目的3用生物化学和共聚焦显微镜方法检测TNF诱导的AMPAR向脊髓神经元质膜的运输。目的4测试TNFa 1抑制剂促进挫伤性SCI后使用依赖性可塑性和功能恢复的治疗潜力。 我们的长期目标是解开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不良可塑性。通过确定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，促进脊髓损伤后的学习和神经康复。 公共卫生相关性：项目叙述/公共卫生相关性声明脊髓损伤（SCI）产生一种破坏性综合征，其特征是运动控制和活动能力丧失，以及感觉功能障碍和疼痛。该项目探讨了调节脊髓学习的细胞机制，这种学习被认为有助于SCI后功能的恢复。这些研究可能为改善SCI后的恢复提供新的靶点。

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.