EXCITOTOXICITY IN CIRCULATORY ARREST--BRAIN INJURY

循环骤停中的兴奋性毒性——脑损伤

• 批准号: 2609644
• 负责人: WILLIAM Anthony BAUMGARTNER
• 金额: $ 31.56万
• 依托单位: JOHNS HOPKINS UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-12-01 至 2000-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2609644
• 关键词: NMDA receptors; apoptosis; aspartate; brain injury; corpus striatum; disease /disorder model; dizocilpine; dogs; enzyme activity; glutamate receptor; glutamates; glycine; heart arrest; hippocampus; immunocytochemistry; induced hypothermia; inhibitor /antagonist; isozymes; microdialysis; neuroprotectants; neurotransmitter metabolism; neurotransmitter receptor; nitric oxide synthase; receptor expression; reperfusion

The goal of this project is to define the mechanisms of excitatory neurotransmitter mediated neuronal death during hypothermic circulatory arrest (HCA) and to develop a pharmacologic strategy to prevent it. We established a canine survival model of HCA that closely simulates clinical practice in cardiovascular surgery. Dogs subjected to 2 hours of circulatory arrest at a brain temperature of 18 degrees C suffer a consistent neurologic deficit and histopathologic pattern of selective neuronal necrosis and changes in neurotransmitter specific receptors. In the current period of the grant, we found that the NMDA antagonist, dizocilpine, prevented most of the injury when given before and over 20 hours after HCA. The AMPA antagonist NBQX was also protective even though it was administrated after rewarming from HCA at a time when electroencephalographic (EEG) changes associated with neuronal death had developed. These observations indicate the majority of glutamate mediated damage from HCA evolves in the reperfusion period and that the events mediating damage can be blocked with medications. Preliminary experiments utilizing in vivo brain microdialysis indicate that large extracellular increases in the excitatory amino acid neurotransmitters glutamate and glycine precede a 12-fold rise in the conversion of arginine to citrulline by nitric oxide synthase (NOS) during the postoperative reperfusion period. Using immunocytochemistry, we observed that the expression of neuronal NOS (nNOS) activity increases substantially after 6-18 hours of reperfusion in areas of the brain enriched in glutamate receptors such as the hippocampus, basal ganglia and cerebellum. Concomitant with this increased enzymatic activity is an accumulation of nitric oxide (NO) metabolites in the serum and urine that are effectively reduced by NOS inhibitors. Preliminary data also suggest that neuronal death following HCA occurs due to both apoptosis and necrosis during the period when nNOS is activated. NO may be directly responsible for such programmed cell death since we can reliably inhibit the apoptosis with NOS inhibitors. To explore the cascade of events that mediate brain injury following HCA we propose to: (1) determine the pattern and sequence of neurotransmitter release as well as the regulation of neurotransmitter receptor expression; (2) examine the role of NO in mediating neurotoxicity after HCA; (3) determine the relationship between excitatory neurotransmitters and NO activity; (4) examine the occurrence of both apoptosis and necrosis following HCA and the inhabitation of cell death with NOS inhibitors; (5) determine how and when manipulating NO production affects the neurologic outcome of dogs. The proposed research will expedite the clinical use of glutamate receptor antagonists, and may develop a novel therapeutic approach to neuroprotection based on the use of isoform specific NOS inhibitors. The ability to provide cerebral protection could result in better patient outcomes after circulatory arrest during cardiothoracic procedures.

这个项目的目标是确定兴奋性的机制， 低温循环中神经递质介导的神经元死亡 HCA，并制定预防HCA的药理学策略。我们 建立了HCA犬生存模型， 心血管外科实习 犬接受2小时的 循环停止在18摄氏度的大脑温度遭受 一致的神经功能缺损和选择性 神经元坏死和神经递质特异性受体的变化。 在 我们发现NMDA拮抗剂， 地佐环平，防止了大部分的伤害时，给予之前和超过20 HCA后几小时 AMPA拮抗剂NBQX也具有保护作用， 在HCA复温后给药， 与神经元死亡相关的脑电图（EEG）变化 开发 这些观察结果表明，大多数谷氨酸介导的 HCA的损伤在再灌注期发生， 介导的损害可以用药物阻断。 利用体内脑微透析的初步实验表明， 细胞外兴奋性氨基酸大量增加 神经递质谷氨酸和甘氨酸的含量比正常人高12倍， 一氧化氮合酶（NOS）将精氨酸转化为瓜氨酸 术后再灌注期。 使用免疫细胞化学，我们 观察到神经元NOS（nNOS）活性表达增加 基本上在脑区域再灌注6-18小时后 富含谷氨酸受体，如海马，基底神经节和 小脑 伴随着酶活性的增加， 一氧化氮（NO）代谢物在血清和尿中的积累， NOS抑制剂可有效降低。 初步数据还表明， HCA后的神经元死亡是由于细胞凋亡和坏死 在nNOS被激活期间。 NO可能直接负责 因为我们可以可靠地抑制细胞凋亡， 一氧化氮合酶抑制剂 为了探索HCA后介导脑损伤的级联反应，我们 建议：（1）确定神经递质的模式和顺序 释放以及调节神经递质受体的表达; (2)探讨NO在HCA后神经毒性中的作用;（3） 确定兴奋性神经递质和NO之间的关系 活性;（4）检测细胞凋亡和坏死的发生 HCA后和用NOS抑制剂抑制细胞死亡;（5） 确定如何以及何时操纵NO产生影响神经系统 狗的结局 这项研究将加速谷氨酸受体的临床应用 拮抗剂，并可能开发一种新的治疗方法， 基于使用同种型特异性NOS抑制剂的神经保护。 的 提供脑保护的能力可以使患者 心胸外科手术期间循环停止后的结局。