EXCITOTOXICITY IN CIRCULATORY ARREST BRAIN INJURY

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。该项目的长期目标是明确低温循环骤停(HCA)引起的兴奋性毒性神经元损伤的机制，并开发预防方法。在Baumgartner博士的犬HCA存活模型中，复制了心脏手术期间的临床经验，狗在18xC下经历了2小时的循环停止，表现出一致的神经功能缺陷和选择性神经元死亡的组织学模式。鲍姆加特纳博士最初表明，在HCA前后给予选择性谷氨酸受体拮抗剂可以减少神经元坏死。最近，鲍姆加特纳博士的研究小组表明，神经元死亡可以通过细胞凋亡或坏死机制发生。HCA后谷氨酸的释放会导致一氧化氮(NO)的积累，而一氧化氮(NO)可介导神经元的死亡，而抑制神经元型一氧化氮合酶(NOS)可减少脑内NO的产生并防止细胞凋亡在本项目的最新更新中有待检验的主要假说是，线粒体功能障碍决定了HCA后通过细胞凋亡或坏死导致迟发性兴奋毒性神经元损伤的机制，缺血预适应(IPC)可以防止神经元凋亡，其药理上是通过开放线粒体内膜上依赖于ATP的钾通道来实现的。进一步推测，NO可能在IPC对神经元的损伤和保护中起中介作用。在初步实验中，鲍姆加特纳博士的团队已经证明，二氮嗪，一种依赖于ATP的钾通道开放剂，可以产生药理上的IPC，并且这种药物可以防止作用于线粒体内膜的心肌细胞的凋亡。在他们的犬模型中，二氮嗪显示出在HCA后几乎完全消除了神经功能障碍，并减少了选定的神经元群体中的细胞凋亡。他们还表明，缺氧可以通过诱导i-NOS和NO的产生来激活HIF-1，这是IPC晚期的一种可能的分子途径。现在，这项建议的目的是利用1H和31P磁共振成像(以及用于检测缺血变化的扩散和灌注加权成像)测量脑代谢来扩展这些观察，作为体内线粒体功能障碍的替代标志，并将这些测量与神经元存活、凋亡和坏死相关联。这些测量将在未经治疗的HCA中进行，也将在使用二氮卓的药理性IPC动物中进行。拟议资源将以服务能力与该项目互动，因为所需技术(灌注(和扩散)成像--TRD1、质子和磷MRSI-TRD2)已经开发并可用。这个项目将实施定制的数据采集协议，用于灌注和扩散磁共振成像，以及犬的1H和31P磁共振成像。KKI磁铁的大口径、短长度和开放式设计特别适合这种特殊的大型动物准备，在麻醉期间需要仔细的生理监测。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The long-term goal of the project is to define the mechanisms of excitotoxic neuronal injury caused by hypothermic circulatory arrest (HCA), and to develop the means to prevent it. In Dr Baumgartner's canine survival model of HCA, replicating clinical experience during cardiac operations, dogs subjected to 2 hours of circulatory arrest at 18xC sustain a consistent neurological deficit and histological pattern of selective neuronal death. Dr Baumgartner originally showed that administration of selective glutamate receptor antagonists before and after HCA reduced the neuronal necrosis. More recently, Dr Baumgartner's group have shown that neuronal death can occur by apoptopic or necrotic mechanisms. Glutamate release after HCA results in accumulation of nitric oxide (NO), which mediates neuronal death, and that inhibition of neuronal nitric oxide synthase (NOS) reduces production of NO in the brain and prevents apoptosis The main hypothesis to be tested in the latest renewal of this project is that mitochondrial dysfunction determines the mechanism of delayed excitotoxic neuronal injury after HCA by apoptosis or necrosis, and that neuronal apoptosis can be prevented by ischemic preconditioning (IPC), achieved pharmacologically by opening ATP-dependent potassium channels on the inner mitochondrial membrane. It is further hypothesized that NO may act as a mediator both of neuronal injury and neuronal protection by IPC. In preliminary experiments, Dr Baumgartner's group have shown that diazoxide, an ATP-dependent potassium channel opener, can produce pharmacologic IPC, and that this agent can prevent apoptosis in cardiomyocytes acting on the inner mitochondrial membrane. In their canine model, diazoxide has shown near total elimination of neurological deficit following HCA, with reduction in apoptosis in select neuronal populations. They have also showed that hypoxia can activate HIF-1 with induction of i NOS and production of NO, a putative molecular pathway of the late form of IPC. The purpose of this proposal is now to extend these observations using measurements of cerebral metabolism by 1H and 31P MRSI (as well as diffusion and perfusion-weighted imaging for the detection of ischemic changes) as surrogate markers of mitochondrial dysfunction in vivo, and to correlate these measures with neuronal survival, apoptosis and necrosis. These measurements will be made both in untreated HCA, and in animals with pharmacologic IPC with diazoxide. The proposed resource will interact with this project in a service capacity, since the required techniques (perfusion (and diffusion) imaging - TRD 1, proton and phosphorus MRSI - TRD 2) are already developed and available. Customized data acquisition protocols for perfusion and diffusion MRI, and for 1H and 31P MRSI in canine will be implemented for this project. The wide bore, short length and open design of the KKI magnet is particularly well suited for this particular large animal preparation which requires careful physiological monitoring during anesthesia.