MODELING COMPARTMENTATION IN THE BRAIN

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 在体内13 C NMR光谱已成为一种独特的工具，研究区室化的脑代谢。例如，在输注13 C标记的底物（例如[1- 13 C]葡萄糖或[2- 13 C]乙酸盐）期间测量13 C标记掺入脑氨基酸中，随后用代谢模型分析13 C NMR时间过程，已经允许脑中TCA循环速率和谷氨酸-谷氨酰胺循环速率的非侵入性测量。 由于不同细胞类型（如神经元和星形胶质细胞）之间的代谢区室化，代谢建模在大脑中特别具有挑战性。这种区室化在30多年前已经使用14 C标记的底物证明，并导致了现在广泛接受的谷氨酸-谷氨酰胺循环的概念，其中突触前神经元释放的谷氨酸被星形胶质细胞吸收，转化为谷氨酰胺，并送回神经元重新合成谷氨酸。 在过去的十年里，在建立区室化代谢模型方面取得了很大进展。然而，这些复杂的模型需要足够的实验数据来确保拟合过程的稳定性，例如，包括13 C标记不仅掺入谷氨酸和谷氨酰胺的C4位置，而且掺入C3和C2位置的时间过程。这些额外的数据有助于稳定拟合过程并降低拟合参数的不确定性。虽然解决检测对应于个别同位素异构体的多重峰现在是可行的，在体内，代谢建模已被传统上进行使用的时间过程中的总13 C标记在每个碳位置，忽略了额外的信息，从多重标记的分子。这些单独的同位素异构体，在13 C光谱中检测到不同的多重峰，提供了有价值的信息，可用于提高代谢建模研究的鲁棒性。这已经在心脏中得到证实，但尚未用于大脑研究。这项合作的目标是通过开发一个可以使用这些信息的模型，充分利用来自多标记同位素异构体的信息。我们预计，这项工作将导致新的代谢建模方法，使最佳利用的高度具体的信息，可以获得与13 C NMR和最近已成为也在体内，最终增加的鲁棒性和精度的代谢建模研究在大脑中。这是重要的，因为脑代谢通量的13 C NMR测量将提供一种直接和非侵入性地测量各种神经和精神疾病中人脑中的葡萄糖代谢和谷氨酸神经传递的手段。 初步数据：研究设计-1。开发和实施一个两室模型，包括来自单个和多个标记的同位素异构体的13 C时间过程的信息。2.使用在不同的3.使用蒙特-卡罗模拟评估新模型的可靠性，并将其与现有模型进行比较，该模型适合每个碳位置的总13 C标记。 方法-新模型将基于最新的脑代谢研究的二室模型和UT西南开发的方法，包括来自个体同位素异构体的信息。 这将包括在9.4特斯拉下可在体内检测到的以下同位素异构体的信息：（谷氨酸GluC 4S、GluC 4D 43、GluC 3S、GluC 3D、GluC 3 T、GluC 2S、GluC 2D 23、GluC 2D 21、GluC 2DD）、谷氨酰胺（GlnC 4S、GlnC 4D 43、GlnC 3S、GlnC 3D、GlnC 3 T、GlnC 2S、GlnC 2D 23、GlnC 2D 21、GlnC 2DD）。在第二步中，还可以包括来自天冬氨酸和GABA同位素异构体的信息。在[1，6 - 13 C2]葡萄糖输注期间，将在大鼠脑中获得体内光谱，并将使用程序LCModel进行定量，以获得多重标记的同位素异构体的时间进程。将使用在体内时间进程结束时获得的脑提取物的13 C NMR对所得13 C时间进程进行缩放，以反映实际13 C浓度。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In vivo 13C NMR spectroscopy has emerged as a unique tool to study compartmentalized brain metabolism. For example, measurements of 13C label incorporation into brain amino acids during infusion of a 13C labeled-substrate (e.g. [1-13C]glucose or [2-13C]acetate and subsequent analysis of 13C NMR time courses with a metabolic model has permitted non-invasive measurements of the TCA cycle rate and the rate of glutamate-glutamine cycle in the brain. Metabolic modeling is particularly challenging in the brain due to compartmentation of metabolism between different cell types such as neurons and astrocytes. This compartmentation has been demonstrated over 30 years ago using 14C labeled substrates and has led to the now widely accepted concept of glutamate-glutamine cycle, whereby glutamate released by presynaptic neurons is taken up by astrocytes, converted to glutamine, and sent back to neurons to resynthesize glutamate. Much progress has been done in the past ten years to develop metabolic models of compartmentalized metabolism. However, these complex models require sufficient experimental data to ensure the stability of the fitting procedure, e.g. including time courses of 13C label incorporation not only into the C4 position of glutamate and glutamine, but also the C3 and C2 positions. This additional data helps stabilize the fitting procedure and reduce uncertainty on fitted parameters. Although resolved detection of multiplets corresponding to individual isotopomers is now feasible in vivo, metabolic modeling has been traditionally performed using time courses of total 13C label at each carbon position, ignoring the additional information from multiply labeled molecules. These individual isotopomers, detected as distinct multiplets in 13C spectra, provide valuable information that could be used to improve the robustness of metabolic modeling studies. This has been demonstrated in the heart, but has not been exploited for brain studies. The goal of this collaboration is to take full advantage of the information from multiply labeled isotopomers by developing a model that can use this information. We expect that this work will lead to new metabolic modeling approaches that make optimal use of the highly specific information that can be obtained with 13C NMR and has recently become available also in vivo, ultimately increasing the robustness and precision of metabolic modeling studies in the brain. This is significant because 13C NMR measurements of brain metabolic fluxes would provide a means to directly and non-invasively measure glucose metabolism and glutamate neurotransmission in the human brain in a variety of neurological and psychiatric disorders. Preliminary data: Research Design- 1. Develop and implement a two-compartment model that includes information from 13C time courses of individual singly and multiply-labeled isotopomers. 2. Validate the new models using in vivo data obtained in the rat brain during infusion of [1,6- 13C2]glucose under different 3. Assess the reliability of the new models using Monte-Carlo simulations and compare it with the exiting model that fits total 13C label at each carbon position. Methods - The new model will be based on the most current two-compartment model for brain metabolic studies and on methods developed at UTSouthwestern to include information from individual isotopomers. This will include information from the following isotopomers that can be detected in vivo at 9.4 Tesla: (Glutamate GluC4S, GluC4D43, GluC3S, GluC3D, GluC3T, GluC2S, GluC2D23, GluC2D21, GluC2DD), Glutamine (GlnC4S, GlnC4D43, GlnC3S, GlnC3D, GlnC3T, GlnC2S, GlnC2D23, GlnC2D21, GlnC2DD). In a second step, information from aspartate and GABA isotopomers could also be included. In vivo spectra will be obtained in the rat brain during infusion of[1,6-13C2]glucose and will be quantified using the program LCModel in order to obtain time courses for multiply-labeled isotopomers.The resulting 13C time courses will be scaled to reflect actual 13C concentration using 13C NMR of brain extracts obtained at the end of the in vivo time course.