Embryonic Raphe Cell Transplant and Cervical Spinal Cord Injury

描述（由申请人提供）：呼吸系统损害是颈脊髓损伤（SCI）后发病率和死亡率的主要原因。因此，识别增强呼吸能力的治疗是高度优先的。我们正在解决这个目标，通过检查使用胚胎细胞移植的神经元替代策略。这种移植提供了一个机会，研究功能整合的“供体”神经元在受损的脊髓。5-羟色胺（5-HT）在颈脊髓损伤后呼吸恢复中起重要作用。例如，SCI后呼吸恢复与膈运动神经元（PhrMN）上的5-HT免疫反应性相关，5-HT受体激动剂也可促进恢复。同样，膈神经的恢复也会被5-HT拮抗剂或肾上腺素能中缝神经元的消融所损害或消除。以前的研究脊髓损伤后的运动恢复使用5-HT细胞移植，以加强5-HT神经支配的腰椎运动池。这些5-HT移植物可以建立拓扑学上适当的连接，并与改善运动有关。由于5-HT是脊髓损伤后呼吸恢复的关键，也起着重要的作用，在启动膈运动可塑性，我们建议检查颈部5-HT细胞移植对呼吸运动恢复颈部脊髓损伤后的影响。我们假设胚胎中缝细胞移植将支配存活的PhrMN，并通过5-HT依赖性机制改善膈运动输出。在颈部（C2）半切损伤（C2 HS）后，同侧球脊髓通路被破坏，导致PhrMN失活，并麻痹同侧半膈。由于完整的球脊髓投射，外侧膈运动神经元保持活跃。C2 HS同侧的膈运动神经元可以通过穿过损伤尾侧脊髓中线的球脊髓通路（即交叉脊髓通路）募集。这些通路最初是无效的，但它们的突触功效在数周至数月的时间内逐渐增加，导致先前麻痹的同侧半横膈膜的部分恢复。我们建议使用C2 HS模型结合颈中缝细胞移植来验证我们的假设。已经有一些明确的证据表明，通过确定的机制发生的细胞替代后的功能恢复。因此，这些研究是对表型确定的胚胎细胞移植（即5-HT）促进颈脊髓损伤后呼吸恢复的潜力的原理验证探索。

DESCRIPTION (provided by applicant): Respiratory compromise is the leading cause of morbidity and mortality following cervical spinal cord injury (SCI). Accordingly, identifying treatments to enhance the ability to breathe is a high priority. We are addressing this goal by examining neuronal replacement strategies using embryonic cell transplants. Such transplants offer an opportunity to study the functional integration of "donor" neurons within the injured spinal cord. Serotonin (5-hydroxytryptamine; 5-HT) plays an important role in recovery of breathing after cervical SCI. For example, respiratory recovery after SCI correlates with 5-HT immunoreactivity on phrenic motoneurons (PhrMNs) and 5-HT receptor agonists also enhance recovery. Similarly, phrenic recovery is impaired or abolished by 5-HT antagonists or ablation of serotonergic raphe neurons. Previous studies of locomotor recovery after SCI have used 5-HT cell transplants to enhance 5-HT innervation of lumbar motor pools. These 5-HT grafts can establish topographically appropriate connections and are associated with improved locomotion. Because 5-HT is critical to recovery of breathing after SCI, and also plays an essential role in initiating phrenic motor plasticity, we propose to examine the impact of cervical 5-HT cell transplant on respiratory motor recovery after cervical SCI. We hypothesize that embryonic raphe cell transplants will innervate surviving PhrMNs and improve phrenic motor output via 5-HT-dependent mechanisms. Following a cervical (C2) hemisection lesion (C2HS), ipsilateral bulbospinal pathways are disrupted leading to inactivation of PhrMNs and paralyzing the ipsilateral hemidiaphragm. Contralateral phrenic motoneurons remain active due to intact bulbospinal projections. Phrenic motoneurons ipsilateral to C2HS can be recruited via bulbospinal pathways that cross the spinal midline caudal to the injury (i.e. crossed-spinal pathways). These pathways are initially ineffective, but their synaptic efficacy gradually increases over a period of weeks to months, resulting in a partial recovery of the previously paralyzed ipsilateral hemi- diaphragm. We propose to use the C2HS model in conjunction with cervical raphe cell transplants to test our hypothesis. There have been few unequivocal demonstrations of functional recovery following cell replacement that occur via defined mechanisms. Accordingly, these studies are a proof-of-principle exploration of the potential for a phenotypically defined embryonic cell transplant (i.e. 5-HT) to enhance respiratory recovery after cervical SCI.