MECHANISMS OF INCREASED EXCITATORY AMINOACID IN ISCHEMIA

中枢神经系统损伤的一个主要假设是， 兴奋性氨基酸（EAA）水平，发生后，这种伤害造成 神经元内钙水平增加，由于过度激活 谷氨酸受体，导致神经元损伤和死亡。该方案 有几条证据支持，例如， 谷氨酸受体阻滞剂或抑制EAA水平的增加， 体内有保护作用。与大量关于 EAA水平增加的影响，细胞来源和 但对增加的骨密度的机制研究很少。双双增长 释放和吸收减少将有助于EAA增加。 令人惊讶的是，在最近的微透析研究中， 已经发现在缺血动物模型中观察到的水平是Ca 2 + 不敏感，表明从神经末梢的胞吐释放是 不是EAA水平升高的主要原因，其他 必须考虑机制和来源。 缺血时细胞外K+明显增加，两种Ca ~（2+）非依赖性 已经在体外鉴定了EAA的释放机制， 受K+升高的刺激。这些是谷氨酸转运体的逆转 在突触体和培养的神经元和星形胶质细胞中观察到， 在星形胶质细胞中观察到的EAA的诱导释放。 我们将学习小学 星形胶质细胞培养物和来自海马的突触体， 培养的小脑颗粒细胞进行体外研究，因为有 没有海马神经元培养物提供足够量的 用于运输研究的细胞。通过确认在 不同的体外制剂，我们将看看它们是否有不同的 反转特性另一个主要原因是增加了监管局 水平将是抑制摄取和星形胶质细胞具有非常活跃， 星形胶质细胞特异性EAA摄取系统。我们将研究EAA的抑制 在体外星形胶质细胞中增加介质K+的摄取。使用数据 在体外不同的系统上获得，我们将确定它们的 通过微透析增加体内EAA水平的贡献 在大鼠海马可逆性全脑缺血的实验中。在 此外，我们将用胶质毒素产生星形胶质细胞的局部耗竭， 和神经元的红藻氨酸，并确定这些影响 对缺血诱导的EAA释放的程序。了解 EAA释放或吸收受损的不同来源和机制， 它们各自对缺血时EAA水平升高的贡献， 其他病理状态对于解释当前疗法至关重要 为这样的国家和设计新的。

A major hypothesis of CNS injury is that the increased extracellular excitatory amino acid (EAA) levels which occur after such injuries cause increased intra-neuronal calcium levels due to excessive activation of glutamate receptors, leading to neuronal damage and death. This scheme is supported by several lines of evidence such as, that treatment with glutamate receptor blockers or inhibition of the increased EAA levels in vivo are protective. In sharp contrast to the considerable body of work on the effects of the increased EAA levels, the cellular sources and mechanisms of the increased EAR have been little-studied. Both increased release and decreased uptake would contribute to increased EAAs. Surprisingly, in recent microdialysis studies, much of the increased EAA levels seen in animal models of ischemia has been found to be Ca2+ insensitive, suggesting that exocytotic release from nerve terminals is not a major contributor to the increased EAA levels, and that other mechanisms and sources must be considered. Extracellular K+ increases markedly in ischemia, and two Ca2+-independent release mechanisms for EAAs have been identified in in vitro which are stimulated by raised K+. These are reversal of the glutamate transporter seen in synaptosomes and cultured neurons and astrocytes, and swelling- induced release of EAAs seen in astrocytes. We will study primary astrocyte cultures and synaptosomes derived from the hippocampus and cultured cerebellar granule cells for our in vitro studies, as there are no hippocampal neuronal cultures that provide sufficient quantities of cells for transport studies. By confirming the transporter forms seen in the different in vitro preparations we will see if they have different reversal characteristics. Another major contributor to the increased EAA levels would be inhibition of uptake and astrocytes have very active and astrocyte-specific EAA uptake systems. We will study inhibition of EAA uptake by increased medium K+ in astrocytes in vitro. Using the data obtained on the different systems in vitro, we will determine their contributions to the increased levels of EAAs in vivo by microdialysis experiments in the rat hippocampus with reversible global ischemia. In addition we will produce localized depletion of astrocytes with gliotoxins and neurons by kainic acid, and determine the influence of these procedures on the ischemia-induced release of EAAs. Understanding the different sources and mechanisms of EAA release or impaired uptake and their respective contributions to the elevated EAA levels in ischemia and other pathological states is vital to interpretation of current therapies for such states and devising new ones.