Effect of extracellure concentration in post ischemic glutamate reuptake, depend on brain temperature and drug.

最近，我们报道了一种不依赖氧气的实时技术的应用，该技术用于监测体内缺血和缺氧时细胞外空间的谷氨酸水平，使用透析电极。这种透析电极技术不仅可以详细分析通过横断双侧颈动脉产生的严重急性缺血的体内动力学，还可以分析缺血再灌注模型的体内动力学。特别是，在缺血-再灌注期间，谷氨酸释放的机制被认为涉及三个连续的过程：1)神经递质，即谷氨酸，从突触囊泡释放（[Glu]_e的第一阶段），2)谷氨酸从神经元细胞代谢池中反向摄取（释放的第二阶段），以及3)在缺血后时期通过谷氨酸摄取载体系统的正常化重新摄取到细胞内空间（[Glu]_e的再摄取阶段）。我们发现，就上述三个[Glu]_e区室而言，缺血10分钟后，更多的细胞空间以及[Glu]_e再摄取到细胞内空间的减少，以及在缺血期间对温度敏感的缺血损伤机制实际上可能不会增加细胞外谷氨酸浓度（[Glu]_e）。而是损害谷氨酸再摄取系统，这一系统被认为与谷氨酸的反向摄取有关。我们推测，通过药理学或低温法增强Glu的再摄取，可能会缩短缺血后暴露于高[Glu]_e的时间，从而减少其对神经元细胞的有害兴奋毒性作用。预加载一种新型谷氨酸转运蛋白抑制剂（tPDC）可降低[Glu]e的第一和第二阶段升高。此外，用麦角生物碱衍生物尼麦角碱（32 mg /kg, i.p）治疗大鼠，对[Glu]_e升高的抑制作用最小，这种升高通常发生在缺血10分钟内，而在缺血后，当轻度亢进引起严重的短暂性全脑缺血时，Glu再摄取得到显著改善。此外，nicergoline （32 mg /kg, i.p）处理的大鼠在形态学上显示细胞死亡减少，死亡率明显降低。目前的研究表明，开发旨在抑制或预防缺血期间谷氨酸释放的反向摄取的治疗策略，即激活谷氨酸摄取机制，是减少脑缺血时发生的神经损伤的一种有希望的方法。少

Recently, we reported the application of an oxygen-independent real-time technique for monitoring glutamate levels in the extracellular space during in vivo ischemia and hypoxia, using a dialysis electrode. This dialysis electrode technique allows detailed analysis of the in vivo dynamics of not only severe acute ischemia produced by transecting the bilateral carotid arteries, but also those of an ischemia-reperfusion model. In particular, during the ischemia-reperfusion period, the mechanisms of glutamate release are assumed to involve three sequential processes : 1) neurotransmitter, i.e.glutamate, release from synaptic vesicles (1st phase of [Glu]_e), 2) reversed uptake of glutamate from the metabolic pool in neuronal cells (2nd phase of release), and 3) re-uptake into the intracellular space by normalization of the glutamate uptake carrier system during the postischemic period (re-uptake phase of [Glu]_e).We found that the in vivo dynamics of biphasic [Glu]_e output from the intrac … More ellular space, as well as reduced reuptake of [Glu]_e into the intracellular space following 10 minutes of ischemia in terms of the three above-mentioned [Glu]_e compartments, and that an ischemic injury mechanism which is sensitive to temperature may not actually increase the extracellular glutamate concentration ([Glu]_e) during the intraischemic period, but rather impairs the Glu re-uptake system, which has been suggested to be involved in the reversed uptake of glutamate. We speculated that enhancing Glu re-uptake, pharmacologically or hypothermically, may shorten exposure to high [Glu]_e in the postischemic period and thereby decrease its deleterious excitotoxic effect on neuronal cells.Preloading with a novel glutamate transporter inhibitor (tPDC) decreased both the 1st and 2nd phases of [Glu]e evation. Furthermore, rats treated with nicergoline (32 mg /kg, i.p.), an ergot alkaloid derivative, showed minimal mhibition of the [Glu]_e elevation which characteristically occurs during the 10-min intraischemic period, while Glu re-uptake was dramatically improved in the postischemic period, when severe transient global ischemia was caused by mild hyperthennia. Moreover, the nicergoline (32 mg /kg, i.p.) treated rats showed reduced cell death morphologically and clearly had a far lower mortality. The present study suggests that the development of therapeutic strategies aimed at inhibition or prevention of the reversed uptake of glutamate release during ischemia, i.e. activation of the glutamate uptake mechanism, is a promising approach to reduce neural damage occurring in response to brain ischemia. Less