Optimizing respiratory plasticity with chronic cervical SCI

摘要 颈脊髓损伤（cSCI）破坏了脊髓呼吸运动神经元的神经通路， 呼吸障碍甚至死亡。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是不完整的，有意义的功能恢复可以诱导利用 神经可塑性的内在能力，加强备用神经通路呼吸运动神经元。 反复急性间歇性缺氧（rAIH）是一种简单、安全、有效的诱导呼吸运动的方法 可塑性和改善急性cSCI啮齿动物模型的呼吸能力。不幸的是，中度rAIH 对慢性脊髓损伤有效。因此，与慢性（非急性）cSCI相关的未知因素破坏了rAIH 功效候选者包括来自腺苷依赖性可塑性的竞争机制的串扰抑制， 持续性神经炎症和年龄依赖性两性异形。在这个项目中，我们的基本目标 是：1）了解限制AIH诱导的膈运动可塑性的因素; 2）使用这种理解 开发完善的rAIH方案，优化慢性cSCI的治疗效果。 AIH诱发了多种不同的膈神经运动易化机制，包括：1）降钙素依赖性 由颈动脉化学感受器激活启动的Q途径;和2）由腺苷依赖性S途径启动的腺苷依赖性S途径。 膈神经运动核局部缺氧。虽然每种途径如果单独激活都有治疗潜力， 共激活导致途径竞争，甚至pMF取消。我们假设慢性颈脊髓损伤 Q & S通路激活平衡，破坏了rAIH治疗效果。最小化脊柱 通过缩短AIH缺氧发作，预测缺氧和腺苷积累可改善功能性 通过消除腺苷对可塑性的限制，由于炎症会破坏血清素（而不是 腺苷）依赖性pMF，我们还将检验抗炎药改善rAIH疗效的假设 慢性脊髓损伤最后，由于AIH诱导的膈运动可塑性表现出深刻的年龄依赖性性别差异， 二型性，我们将比较rAIH在中年雄性与雌性大鼠中的功效。通过使用两个已建立的模型 对于慢性（> 8周）cSCI（C2半切和C4脊髓挫伤），我们预计会得出更有力的结论 因为每个模型都有独特的优点/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的限制; 2）AIH伴较短缺氧发作 减少组织缺氧和腺苷积累，优化pMF; 3）在雄性大鼠中，优化的rAIH改善 呼吸能力超过"常规" rAIH; 4）抗炎药增强rAIH疗效;和5） 优化的rAIH在中年雌性大鼠中比雄性大鼠更能改善呼吸能力。每个目标都得到支持 通过令人兴奋的初步数据证明可行性和概念验证。通过优化重复的AIH- 诱导可塑性，以提高呼吸能力，我们获得了新的机制的见解，并更接近 在患有慢性cSCI导致的呼吸受损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.