Spreading Depolarizations and Post-Ischemic Injury

描述（由申请人提供）：目前缺血性中风的临床治疗方案非常有限，非常需要能够在中风发作后几小时内安全给药并最大限度地减少神经元损失的干预措施。人们早就知道，动物中风模型中会出现扩张性去极化（SD）重复波（类似于皮质扩张性抑制），但直到最近才有令人信服的证据表明，SD在人类缺血性脑损伤后非常普遍。SDs在神经元和胶质细胞中产生大量离子重分布，需要消耗代谢能量来恢复体内平衡。缺血后的重复SDs对已经因局部血流量减少而受损的脑组织产生了严重的额外代谢需求。因此，预防这些缺血后SD事件的发生和进展，甚至限制其有害后果的方法，可能会在临床医学中产生实质性的积极结果。我们发现Zn2+在SD的发生中起着重要的作用，并且在每次SD事件发生后突触释放大量的Zn2+。Zn2+先前已被证明对神经元和神经胶质都有毒性，我们的总体假设是，与SD相关的Zn2+增加对缺血后的损伤有重要作用。我们认为这是由于Zn2+在神经元和星形胶质细胞中的积累，这反过来1)降低了SD事件启动的阈值，2)作为Ca2+兴奋性毒性的上游触发。Aim 1的研究利用小鼠海马切片来评估Zn2+在单个神经元和星形胶质细胞群中的释放和积累机制。目的2研究Zn2+促进海马切片SD发生的机制，包括抑制星形细胞摄取功能和上调神经元NMDA受体功能。目的3验证了Zn2+在SD后Ca2+解除调控的上游的假设，并验证了目的1和2中确定的干预是否能显著改善脑切片和体内的神经元活力。突触结构和功能的切片研究将辅以小鼠局灶性缺血的体内研究。每个目标都应该为该领域提供重要的新信息，当这些机制研究结合在一起时，应该提出限制缺血性脑损伤巩固和扩散的新方法。

DESCRIPTION (provided by applicant): Current options for clinical treatment of ischemic strokes are currently very limited and there is a great need for interventions that can be safely administered during a period of several hours following the onset of a stroke and minimize neuronal loss. It has long been known that repetitive waves of spreading depolarizations (SD) (analogous to cortical spreading depression) occur in animal stroke models, but only recently has it been convincingly shown that SDs are very prevalent following human ischemic brain injuries. SDs produce massive ionic redistributions in neurons and glia, requiring the expenditure of metabolic energy to restore homeostasis. The repetitive SDs following ischemia place a severe additional metabolic demand on brain tissue that is already compromised by reductions in local blood flow. Thus approaches to prevent the onset and progression of these post-ischemic SD events, or even to limit their deleterious consequences, are likely to have substantial positive outcomes in clinical medicine. We have discovered that Zn2+ can play an important role in initiation of SD, and that Zn2+ release from synapses is substantial following each SD event. Zn2+ has previously been demonstrated to be toxic to both neurons and glia, and our overall hypothesis is that Zn2+ increases associated with SD make a significant contribution to injury following ischemia. We propose that this is due to Zn2+ accumulation in both neurons and astrocytes, which in turn 1) lowers the threshold for initiation of SD events and 2) serves as an upstream trigger for Ca2+ excitotoxicity. Studies in Aim 1 utilize hippocampal slice preparations from mice to evaluate the mechanisms of Zn2+ release and accumulation in single neurons and populations of astrocytes. Aim 2 examines mechanisms by which Zn2+ can facilitate the onset of SD in hippocampal slices, including inhibition of astrocyte uptake function and up-regulation of neuronal NMDA receptor function. Aim 3 tests the hypothesis that Zn2+ is upstream of Ca2+ deregulation following SD, and tests whether interventions that disrupt the processes identified in Aims 1&2 provide significant improvements in neuronal viability in brain slice and in vivo. Slice studies of synaptic structure and function will be complemented by in vivo studies of focal ischemia in mice. Each aim should independently provide significant new information for the field, and when taken together, these mechanistic studies should suggest novel approaches to limit the consolidation and spread of ischemic brain injury. PUBLIC HEALTH RELEVANCE: This project is designed to identify new approaches to limit the deleterious consequences of a stroke. Following a stroke, aberrant waves of brain activation contribute to the spread of injury. This project is designed to identify new approaches to limit the onset, or consequences, of these spreading waves of activation and thereby improve functional recovery.