Embryonic Raphe Cell Transplant and Cervical Spinal Cord Injury

描述(由申请人提供)：呼吸障碍是颈髓损伤(SCI)后发病率和死亡率的主要原因。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-羟色胺；5-羟色胺)在颈椎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上的5-羟色胺免疫反应有关，5-羟色胺受体激动剂也可以促进恢复。类似地，5-羟色胺拮抗剂或消融5-羟色胺能中缝神经元可损害或消除膈神经的恢复。以前关于脊髓损伤后运动恢复的研究使用了5-羟色胺细胞移植来增强腰椎运动池的5-羟色胺神经支配。这些5-羟色胺移植物可以在局部建立适当的连接，并与改善运动能力有关。由于5-羟色胺是脊髓损伤后呼吸恢复的关键，也是启动膈运动可塑性的关键因素，我们建议研究颈椎5-羟色胺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通过5-羟色胺依赖的机制来神经支配存活的PhrMns并改善膈运动输出。在颈椎(C2)半横断损伤(C2HS)后，同侧球脊髓通路被扰乱，导致PhrMns失活，并使同侧半球瘫痪。对侧膈运动神经元由于球脊髓投射完整而保持活跃。与C2HS同侧的膈运动神经元可以通过穿过脊髓中线尾侧至损伤处的球脊髓通路(即交叉脊髓通路)招募。这些通路最初是无效的，但它们的突触效力在几周到几个月的时间里逐渐增加，导致先前瘫痪的同侧半横肌部分恢复。我们建议将C2HS模型与宫颈中缝细胞移植结合使用来检验我们的假设。很少有明确的证据表明，通过明确的机制发生细胞置换后的功能恢复。因此，这些研究是对表型明确的胚胎细胞移植(即5-羟色胺)促进颈椎脊髓损伤后呼吸恢复的可能性的原则验证探索。

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.