Embryonic Raphe Cell Transplant and Cervical Spinal Cord Injury

描述（由申请人提供）：呼吸损伤是颈脊髓损伤（SCI）后发病和死亡的主要原因。因此，确定提高呼吸能力的治疗方法是当务之急。我们正在通过研究使用胚胎细胞移植的神经元替代策略来解决这一目标。这种移植为研究受损脊髓内“供体”神经元的功能整合提供了机会。5-羟色胺（5-hydroxytryptamine; 5-HT）在颈脊髓损伤后呼吸恢复中起重要作用。例如，脊髓损伤后的呼吸恢复与膈运动神经元（PhrMNs）的5-HT免疫反应性相关，5-HT受体激动剂也能促进恢复。同样，5-羟色胺拮抗剂或5-羟色胺能中缝神经元的消融会损害或破坏膈恢复。先前的脊髓损伤后运动恢复研究使用5-HT细胞移植来增强腰椎运动池的5-HT神经支配。这些5-羟色胺移植物可以建立适合地形的连接，并与改善运动有关。由于5-HT对脊髓损伤后的呼吸恢复至关重要，并且在启动膈运动可塑性方面也起着重要作用，我们建议研究颈椎5-HT细胞移植对脊髓损伤后呼吸运动恢复的影响。我们假设胚胎中缝细胞移植将激活存活的phrmn，并通过依赖5- ht的机制改善膈运动输出。颈椎（C2）半切病变（C2HS）后，同侧球脊髓通路被破坏，导致phrmn失活并使同侧半膈瘫痪。对侧膈运动神经元由于完好的球脊髓投射而保持活跃。C2HS同侧的膈运动神经元可以通过穿过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强，导致先前瘫痪的同侧半膈部分恢复。我们建议使用C2HS模型结合宫颈缝细胞移植来验证我们的假设。很少有明确的证据表明，在细胞替换后，功能恢复是通过明确的机制发生的。因此，这些研究是对表型确定的胚胎细胞移植（即5-HT）增强颈椎脊髓损伤后呼吸恢复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.