The Synthesis of GABA in Epileptic Brain

该项目是项目1（D。库尔特，PI），我们提出的证据表明， 谷氨酸-谷氨酰胺循环，通常是大脑GABA合成的主要来源， 在癫痫大脑中具有类似强度的关键作用。我们假设癫痫患者的大脑 替代前体，以维持GABA库。在这个项目中（M。Yudkoff，PI），我们 通过使用稳定同位素（主要是15 N和13 C）来识别主要的GABA前体， 并测量癫痫的匹鲁卡品模型中GABA合成的速率。我们将利用质量 光谱法来量化同位素丰度。我们在以前的项目中已经有效地利用了这种方法。 脑氨基酸代谢的研究，我们现在寻求应用的方法来研究 癫痫我们的初步研究结果证实了谷氨酰胺成为相对不那么突出的 GABA前体在毛果芸香碱模型，特别是在海马。我们发现丙氨酸和亮氨酸 成为-NH 2基团的两个重要供体，形成大脑脱羧产生的谷氨酸 GABA我们进一步假设，生酮饮食，我们以前已经证明，增加 脑GABA合成在非癫痫动物，可能有类似的有益效果， 匹鲁卡品治疗癫痫。事实上，这个项目的一个目标将是了解是否开始这种饮食 甚至可能延缓或中止癫痫发生。

This project is the "metabolic counterpart" to Project 1 (D. Coulter, PI), where we present evidence that the Glutamate-Glutamine Cycle, ordinarily the major source for brain GABA synthesis, does not subserve this crucial role with a similar intensity in epileptic brain. We hypothesize that in epilepsy the brain recruits alternate precursors for the purpose of maintaining pools of GABA. In this project (M. Yudkoff, PI), we scrutinize this concept by using stable isotopes (primarily 15N and 13C) to identify major GABA precursors and to measure rates of GABA synthesis in the pilocarpine model of epilepsy. We will utilize mass spectrometry to quantify isotopic abundance. We have made productive use of this approach in our prior investigations of brain amino acid metabolism, and we seek now to apply the methodology to the study of epilepsy. Our preliminary findings confirm the concept that glutamine becomes a relatively less prominent GABA precursor in the pilocarpine model, particularly in the hippocampus. We find that alanine and leucine become two important donors of -NH2 groups to form the glutamate that the brain decarboxylates to yield GABA. We further hypothesize that the ketogenic diet, which we have previously demonstrated to increase brain GABA synthesis in non-epileptic animals, might have a similarly salutary effect in rats rendered epileptic by pilocarpine treatment. Indeed, a goal of this project will be to learn whether initiation of this diet prior to administration of pilocarpine might even attentuate or abort epileptogenesis.