Optimizing respiratory plasticity with chronic cervical SCI

摘要 颈髓损伤(CSCI)扰乱了通往脊髓呼吸运动神经元的神经通路，导致 呼吸受损，甚至死亡。迫切需要新的治疗策略来改善呼吸 CSCI后的能力。由于大多数CSCI是不完全的，因此通过利用工具可以诱导有意义的功能恢复 神经可塑性的内在能力，强化了备用神经通路对呼吸运动神经元的作用。 反复急性间歇低氧是一种简单、安全、有效的呼吸运动诱导方法 急性脊髓损伤啮齿动物模型的可塑性和改善呼吸能力。不幸的是，适度的Raih 对慢性CSCI有效。因此，与慢性(非急性)CSCI相关的未知因素损害了Raih 功效。候选者包括腺苷依赖可塑性的相互竞争机制的串扰抑制， 持续性神经炎和年龄相关的性二形症。在这个项目中，我们的根本目标是 是：1)了解限制AIH诱导的膈运动可塑性的因素；2)利用这一理解 开发优化慢性CSCI治疗效果的改良RAIH方案。 AIH引起多种不同的膈运动促进机制，包括：1)5-羟色胺依赖 由颈动脉化学感受器激活启动的Q通路；2)腺苷依赖的S通路 膈神经运动核局部缺氧。虽然如果单独激活每个通路都有治疗潜力， 共激活导致途径竞争，甚至PMF取消。我们假设慢性CSCI转移 平衡趋于等Q&S通路激活，破坏了RAIH的治疗效果。最小化脊椎 通过缩短AIH低氧发作和腺苷积累来改善功能 通过解除腺苷对可塑性的限制而产生的结果。因为炎症会破坏5-羟色胺(而不是 腺苷依赖的PMF，我们还将检验抗炎药物改善RAIH疗效的假说 患有慢性CSCI。最后，由于AIH诱导的膈运动可塑性表现出深刻的年龄依赖性 我们将比较Raih在中年雄性大鼠和雌性大鼠中的疗效。通过使用两个已建立的模型 对于慢性(&gt；8周)CSCI(C2半切和C4脊柱挫伤)，我们预计会有更有力的结论 因为每种模式都有独特的优势/局限性。提出了五个目标来检验假设：1) CSCI降低脊髓PO2，增加腺苷对PMF的约束；2)AIH低氧发作时间较短 减少组织缺氧和腺苷蓄积，优化PMF；3)优化RAIH改善雄性大鼠 呼吸能力超过“常规”的RAIH；4)抗炎药物增强RAIH的疗效；5) 优化的Raih对中年雌性大鼠的呼吸能力的改善比对雄性大鼠更大。每个目标都得到支持 通过激动人心的初步数据论证了可行性和概念论证。通过优化重复的AIH- 诱导可塑性改善呼吸能力，我们获得新的机械洞察力，并更接近 在患有慢性CSCI呼吸障碍的人类中进行全面的临床试验。

ABSTRACT Cervical spinal cord injury (cSCI) disrupts neural pathways to spinal respiratory motor neurons, causing respiratory impairment and even death. New treatment strategies are desperately needed to improve breathing ability after cSCI. Since most cSCI are incomplete, meaningful functional recovery can be induced by harnessing the intrinsic capacity for neuroplasticity, strengthening spared neural pathways to respiratory motor neurons. Repetitive acute intermittent hypoxia (rAIH) is a simple, safe and effective means to induce respiratory motor plasticity and improve breathing ability in rodent models of acute cSCI. Unfortunately, moderate rAIH is less effective with chronic cSCI. Thus, unknown factors associated with chronic (not acute) cSCI undermine rAIH efficacy. Candidates include cross-talk inhibition from competing mechanisms of adenosine-dependent plasticity, persistent neuroinflammation and age-dependent sexual dimorphisms. In this project, our fundamental goals are: 1) to understand factors limiting AIH-induced phrenic motor plasticity; and 2) use that understanding to develop refined rAIH protocols that optimize therapeutic efficacy with chronic cSCI. AIH elicits multiple distinct mechanisms of phrenic motor facilitation (pMF), including: 1) serotonin-dependent Q pathway initiated by carotid chemoreceptor activation; and 2) adenosine-dependent S pathway initiated by local hypoxia in the phrenic motor nucleus. Although each pathway has therapeutic potential if activated alone, co-activation leads to pathway competition and even pMF cancellation. We hypothesize that chronic cSCI shifts the balance towards equal Q & S pathway activation, undermining rAIH therapeutic efficacy. Minimizing spinal hypoxia and adenosine accumulation by shortening AIH hypoxic episodes is predicted to improve functional outcomes by removing the adenosine constraint to plasticity. Since inflammation undermines serotonin (not adenosine)-dependent pMF, we will also test the hypothesis that anti-inflammatory drugs improve rAIH efficacy with chronic cSCI. Finally, since AIH-induced phrenic motor plasticity exhibits profound age-dependent sexual dimorphisms, we will compare rAIH efficacy in middle-aged male vs female rats. By using two established models of chronic (> 8 weeks) cSCI (C2 hemisection and C4 spinal contusion), we anticipate more robust conclusions since each model has unique advantages/limitations. Five aims are proposed to test the hypotheses that: 1) cSCI decreases spinal PO2, increasing the adenosine constraint to pMF; 2) AIH with shorter hypoxic episodes lessens tissue hypoxia and adenosine accumulation, optimizing pMF; 3) in male rats, optimized rAIH improves breathing capacity more than “conventional” rAIH; 4) anti-inflammatory drugs enhance rAIH efficacy; and 5) optimized rAIH improves breathing capacity more in middle-aged female versus male rats. Each aim is supported by exciting preliminary data demonstrating feasibility and proof of concept. By optimizing repetitive AIH- induced plasticity to improve breathing ability, we gain new mechanistic insights and move closer to comprehensive clinical trials in humans suffering from impaired breathing due to chronic cSCI.