Contribution of Microglia to Axonal Injury following Repetitive Concussion in Mou

描述(申请人提供)：据估计，每年有160-380万例与运动相关的脑震荡。人类脑震荡通常不会导致CT或MRI可见的宏观损害，但多发性脑震荡可导致轴突损伤、长期认知障碍和神经系统疾病。这些长期的变化在职业运动员中得到了最好的描述，拳击手被称为“拳击性痴呆症”，其他运动员被称为慢性创伤性脑病。对这些人的研究表明，在轴突损伤区域的创伤性脑损伤后，大脑的常驻免疫细胞小胶质细胞被激活。在尸检样本中，脑震荡后脑白质中的小胶质细胞也被激活。这种反应是否有助于持续的轴突损伤，防止进一步的损伤，或者在脑震荡中是中性的，目前尚不清楚。为了填补这一知识空白，我们的实验室开发了一种重复性的小鼠脑震荡损伤模型，类似于Longhi和他的同事(NeuroSurgery 2005)。在该模型中，两次相隔24小时的闭合颅骨撞击导致一致的轴突变性和小胶质细胞激活模式，而不会造成神经细胞丢失。这一设想的中心假设是，小鼠反复脑震荡损伤后持续的小胶质细胞激活导致轴突变性和电生理妥协。为了解决这一假设，我们将对白质内小胶质细胞的表型进行跨时间点的比较。将给予一种小胶质细胞特异性毒素，以确定消除小胶质细胞在急性和慢性损伤阶段对轴突变性的影响。如果成功，这些实验将极大地增加我们对激活的小胶质细胞在重复性脑震荡创伤小鼠模型轴突损伤中的作用的了解。这些结果可能加深我们对导致脑震荡患者认知障碍的病理过程的理解，并可能对治疗学产生重要影响。在这些实验中，申请者将接受多种技术的培训，包括小动物外科手术、免疫组织化学、体视学、流式细胞术、定量聚合酶链式反应、细胞外脑片电生理学和定量数据的统计分析。

DESCRIPTION (provided by applicant): There are an estimated 1.6-3.8 million sports-related concussions each year. Human concussions do not usually cause macroscopic lesions visible by CT or MRI, but multiple concussions can lead to axonal injury, long-term cognitive impairments, and neurological disease. These long- term changes are best described in professional athletes, termed "dementia pugilistica" in boxers and chronic traumatic encephalopathy in other athletes. Studies in these individuals have shown that activation of the brain's resident immune cells, microglia, occurs after traumatic brain injury in areas of axonal injury. Microglial activation in white matter has also been noted after concussion in post- mortem-samples. Whether this response contributes to ongoing axonal injury, protects against further damage, or is neutral in concussion is not known. To fill this knowledge gap, our lab has developed a reproducible model of repetitive concussive injury in mouse similar to Longhi and colleagues (Neurosurgery 2005). In this model, two closed-skull impacts delivered 24 hours apart result in a consistent pattern of axon degeneration and microglial activation without neuronal cell loss. The central hypothesis of this proposal is that persistent microglial activatio following repetitive concussive injury in mouse results in axon degeneration and electrophysiological compromise. To address this hypothesis, the phenotype of microglia within white matter will be compared across time points. A microglial-specific toxin will be administered to determine how elimination of microglia effects axonal degeneration in both the acute and chronic injury phase. If successful, these experiments will greatly increase our knowledge of the role of activated microglia in axonal injury in this mouse model of repetitive concussive trauma. These results may deepen our understanding of the pathological processes that cause cognitive impairments in concussed individuals and could have important implications for therapeutics. For these experiments the applicant will be trained in multiple techniques including small animal surgery, immunohistochemistry, stereology, flow cytometry, qPCR, extracellular brain slice electrophysiology, and statistical analysis of quantitative data.