Metabolism and Excitability in Rodent Hippocampus

描述（由申请人提供）：兴奋性和抑制性突触传递都依赖于谷氨酸的供应。谷氨酸是由葡萄糖从头合成的，也通过神经元和星形胶质细胞之间的谷氨酸-谷氨酰胺循环循环。用于突触传递的GABA也依赖于神经元-胶质循环，因为GABA是由谷氨酸合成的，谷氨酸可以通过摄取或通过谷氨酰胺进入中间神经元。本研究的主要目的是验证一个广泛的假设，即细胞兴奋性与谷氨酸-谷氨酰胺-氨基丁酸循环状态密切相关，特别是在持续的神经元活动期间，由于合成氨基丁酸需要额外的能量依赖步骤，氨基丁酸能传递比兴奋传递对循环中断更敏感。在特异性目标1中，我们将在几个不同的水平上中断循环，包括阻断谷氨酰胺、谷氨酸和GABA合成酶以及阻断谷氨酰胺摄取。这些代谢抑制剂对突触抑制的影响将从生理学上进行检验。

DESCRIPTION (provided by applicant): Both excitatory and inhibitory synaptic transmission rely on the supply of glutamate. Glutamate is synthesized de novo from glucose and also recycled through the glutamate-glutamine cycle between neurons and astrocytes. GABA used for synaptic transmission is also dependent on neuronal-glial cycling as GABA is synthesized from glutamate which can enter interneurons either via uptake or through glutamine. The main goal of this proposal is to test the broad hypothesis that cellular excitability is intimately tied to the status of glutamate-glutamine-GABA cycling and specifically that GABAergic transmission is more sensitive than excitatory transmission to disruption in cycling during periods of sustained neuronal activity because of the added energy-dependent steps needed for the synthesis of GABA. In Specific Aim 1 we will interrupt cycling a several different levels including blockade of the synthetic enzymes of glutamine, glutamate and GABA as well as by blocking glutamine uptake. The effect of these metabolic inhibitors on synaptic inhibition will be examined physiologically. In Specific Aim 2, we will use mass spectometry to measure the changes in the levels of glutamate, glutamine and GABA induced by alterations in neurotransmitter cycling in both the tissue and in the bathing medium to address the time-dependent changes in transmitter levels. In Specific Aim 3 will use 13C isomer spectroscopy to assess the effect of those compounds that cross the blood brain barrier (the GS inhibitor methionine sulfoximine and the glutamine transporter MeAIB) on glutamate-glutamine-GABA cycling in control animals. These experiments should provide important data on the regulation of normal synaptic transmission as well as an understanding of the pathology of a number of neurological disorders where changes in neural energetics have been seen including epilepsy, ALS and Huntington's disease.