13C and 15N MRS Study of glutamate control in epilepsy

谷氨酸兴奋毒性与癫痫发作有关。我们的目标是：（1）澄清 控制谷氨酸和谷氨酰胺的代谢通量和室间转运的机制， 完整的哺乳动物大脑和2）确定谷氨酸兴奋性毒性如何引起癫痫发作。 细胞外液中GLU的神经胶质摄取受损（GLUECF）可导致对神经胶质细胞的过度刺激。 GLU受体和神经元变性（GLU兴奋毒性）。神经递质的摄取率 GLU从细胞外液进入星形胶质细胞，随后代谢为GLN 通过a）通过同位素追踪选择性富集神经递质GLU的13 C，B）收集细胞外的 通过微透析分析GLU并通过气相色谱/质谱分析其13 C富集，以及c） 使用体内定位的13 C和15 N MRS观察星形胶质细胞中形成的[5- 13 C，5- 15 N] GLN。现在， 具体目标#1，GLN/GLU循环中的“缺失环节”，GLN从 将使用体内15 N、1H-15 N HMQC和13 C MRS确定星形胶质细胞与神经元的比例。 阐明最近发现的GLN转运蛋白在完整正常大脑中的作用，并确定是否 胶质细胞GLN流出率（假设#1）或神经元GLN摄取率（假设#2）限制了GLN/GLU循环 体内速率。具体目标#2将研究颞叶癫痫中GLU释放和摄取的动力学 采用慢性红藻氨酸诱导的癫痫（KA）大鼠模型。体内通量率将在 损伤和对侧海马，并与电生理和行为癫痫发作， 确定癫痫发作和传播是否是（假设#3）血糖异常的结果 释放，（假设#4）受损的GLU通过神经胶质转运蛋白的清除，或（假设#5） 这些过程。这些研究将有助于更好地了解 KA中GLN/GLU循环，并增加了替代颞叶癫痫手术治疗的可能性。

Glutamate excitotoxicity has been implicated in epileptic seizures. Our objectives are 1) to clarify the mechanisms that control the metabolic flux and intercompartmental transport of glutamate and glutamine in the intact mammalian brain and 2) determine how glutamate excitotoxicity may cause epileptic seizures. Impaired glial uptake of GLU in the extracellular fluid (GLUECF) can lead to excessive stimulation of the GLU receptors and to neuronal degeneration (GLU excitotoxicity). The rate of uptake of neurotransmitter GLU from the extracellular fluid into astrocytes and subsequent metabolism to GLN has been measured through a) selective 13C enrichment of neurotransmitter GLU by isotope chase, b) collection of extracellular GLU by microdialysis and analysis of its 13C enrichment by gas-chromatography/mass spectrometry and c) observation of [5-13C, 5-15N] GLN formed in astrocytes using localized in vivo 13C and 15N MRS. Now, Specific Aim #1, a 'missing-link' in the GLN/GLU cycle, the kinetics and mechanism of transport of GLN from astrocytes to neurons will be determined using in vivo 15N, 1H-15N HMQC and 13C MRS. The results will clarify the roles of recently identified GLN transporters in the intact normal brain and determine whether the rate of glial GLN efflux (hypothesis #1) or of neuronal GLN uptake (hypothesis #2) limits the GLN/GLU cycle rate in vivo. Specific Aim #2 Kinetics of GLU release and uptake in temporal lobe epilepsy will be studied using the chronic kainate-induced epileptic (KA) rats model. In vivo flux rates will be measured in the lesioned and contralateral hippocampus and correlated with electrophysiological and behavioral seizures, to determine whether the onset and propogation of seizures is the result of (hypothesis #3) abnormal GLU release, (hypothesis #4) impaired GLU clearance by glial transporters, or (hypothesis #5) a combination of these processes. Together these studies will contribute to a better understanding of the regulatory events of the GLN/GLU cycle in KA and increase potential to replace surgical management of temporal lobe epilepsy.