Serres Sébastien, Raffard Gérard, Franconi Jean-Michel, Merle Michel
Unité de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS-Université Victor Segalen, Bordeaux, France.
J Cereb Blood Flow Metab. 2008 Apr;28(4):712-24. doi: 10.1038/sj.jcbfm.9600568. Epub 2007 Oct 17.
Carbon metabolism in the rat brain was studied in animals anesthetized with a light dose of pentobarbital and in awake animals under morphine, which were infused with either [1-13C]glucose+acetate or glucose+[2-13C]acetate for various periods of time. Brain amino-acid enrichments in tissue extracts were determined by nuclear magnetic resonance (NMR) spectroscopy and their time evolution was analyzed by automatic fitting. Acetyl-coenzyme A C2 enrichment and ratio between pyruvate carboxylase and pyruvate dehydrogenase activity (PC/PDH) were determined from glutamate and glutamine labeling. The following results were obtained: (i) amino-acid enrichment patterns implied metabolic compartmentation and occurrence of the glutamate-glutamine cycle; (ii) kinetics of aspartate, GABA, and glutamate labeling from [1-13C]glucose and of glutamine labeling from [2-13C]acetate indicated a twofold higher metabolic activity in awake than in anesthetized rat brain; (iii) evaluation of the contributions of the astrocytic and neuronal metabolisms to glutamine synthesis in both groups of rats indicated a coupling between neuronal tricarboxylic acid (TCA) cycle, glutamate-glutamine cycle and glial TCA cycle; and (iv) analyzing the extrapolations back to time zero and the steady-state values of PC/PDH indicated a close coupling between PC activity and both astrocytic and neuronal TCA cycles. All these results suggest a cooperative-like behavior of astrocytic and neuronal metabolisms to fulfill the anabolic and energy needs linked to brain activation.
在使用小剂量戊巴比妥麻醉的动物以及处于吗啡作用下的清醒动物中，研究了大鼠脑中的碳代谢情况，这些动物被输注了[1-¹³C]葡萄糖+乙酸盐或葡萄糖+[2-¹³C]乙酸盐，持续不同时间段。通过核磁共振（NMR）光谱法测定组织提取物中脑氨基酸的富集情况，并通过自动拟合分析其随时间的变化。根据谷氨酸和谷氨酰胺的标记情况确定乙酰辅酶A C2富集以及丙酮酸羧化酶与丙酮酸脱氢酶活性之比（PC/PDH）。得到以下结果：（i）氨基酸富集模式暗示了代谢区室化以及谷氨酸-谷氨酰胺循环的存在；（ii）[1-¹³C]葡萄糖生成天冬氨酸、γ-氨基丁酸和谷氨酸的标记动力学以及[2-¹³C]乙酸盐生成谷氨酰胺的标记动力学表明，清醒大鼠脑的代谢活性比麻醉大鼠脑高两倍；（iii）对两组大鼠中星形胶质细胞和神经元代谢对谷氨酰胺合成的贡献评估表明，神经元三羧酸（TCA）循环、谷氨酸-谷氨酰胺循环和胶质细胞TCA循环之间存在耦合；（iv）分析PC/PDH外推至时间零点的值和稳态值表明，PC活性与星形胶质细胞和神经元TCA循环均紧密耦合。所有这些结果表明，星形胶质细胞和神经元代谢存在类似协同的行为，以满足与脑激活相关的合成代谢和能量需求。
