The Synthesis of GABA in Epileptic Brain

这个项目是项目1(D.Coulter，PI)的“代谢对应物”，在这个项目中，我们提出证据，证明 谷氨酸-谷氨酰胺循环，通常是大脑合成GABA的主要来源，并不支持这一点 在癫痫脑中具有类似强度的关键作用。我们假设癫痫患者的大脑会招募 以维持GABA库为目的的替代前体。在这个项目(M.Yudkoff，PI)中，我们 通过使用稳定同位素(主要是15N和13C)来确定主要的GABA前体来仔细研究这一概念 并在匹罗卡品癫痫模型中测量GABA合成率。我们将利用质量 光谱分析，以量化同位素丰度。我们在以前的文章中已经有效地使用了这种方法 大脑氨基酸代谢的研究，我们现在寻求将这种方法学应用于 癫痫。我们的初步发现证实了谷氨酰胺成为一种相对不那么突出的 GABA前体在匹罗卡品模型中，特别是在海马体中。我们发现丙氨酸和亮氨酸 成为-NH2基团的两个重要供体，形成大脑脱羧基产生的谷氨酸 GABA。我们进一步假设，生酮饮食，我们之前已经证明增加 在非癫痫动物的大脑中合成GABA，在大鼠身上可能有类似的有益效果 癫痫用匹罗卡品治疗。事实上，这个项目的一个目标将是了解这种饮食的启动 在给予匹罗卡品之前，甚至可能引起或中止癫痫的发生。

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.