Neuronal Fatigue in Aging Hippocampus during Sustained Metabolic Demand

描述（由申请人提供）：衰老可能与对代谢挑战的反应能力下降有关，例如，在认知任务中疲劳或对底物剥夺的易感性增加，如相对低血糖或缺氧。我们假设衰老过程中内在中枢神经系统生物能量学（即神经元-胶质相互作用，有氧和无氧代谢途径，底物有效性等）调节的细胞和分子变化会损害对持续能量需求的适应性反应。我们建议在缺乏系统因素（如脉管系统不良或系统底物供应）的情况下，研究老年动物离体脑组织的长期代谢需求和疲劳，以确定神经元代谢和神经元-神经胶质相互作用的内在变化。老年动物的体外脑切片保留了该年龄的体内代谢特征，以及导致局部组织尺度代谢调节的内在回路和其他因素。初步实验表明，与年轻动物的组织相比，衰老海马中的神经元功能和线粒体氧化还原状态更容易受到代谢应激的影响，例如葡萄糖水平降低和突触刺激时间延长，这表明老年个体可能在较长时间内支持氧化代谢速率增加的能力下降。我们将通过使用直接组织乳酸、葡萄糖和Po2测量、NAD(P)H荧光和海马神经元反应，研究氧气利用、线粒体氧化还原状态和神经元活动之间的能量关系，来评估长时间代谢应激期间的神经元疲劳和神经元-胶质相互作用。这些技术将在长时间的突触刺激（代谢需求增加）和底物递送有限的情况下使用。这些结果将有助于了解局部组织反应和生物能量学如何影响衰老过程中的代谢。对神经疲劳机制的理解可能会提示新的治疗目标，这可能会提高持续认知任务的表现。

DESCRIPTION (provided by applicant): Aging can be associated with a decreased ability to respond to metabolic challenges resulting, for example, in fatigue on cognitive tasks or increased susceptibility to substrate deprivation, such as relative hypoglycemia or hypoxia. We hypothesize that cellular and molecular changes in the regulation of intrinsic CNS bioenergetics (i.e., neuronal-glial interactions, aerobic and anaerobic metabolic pathways, substrate availability, etc.) during aging can impair adaptive responses to sustained energy demand. We propose to study prolonged metabolic demand and fatigue in isolated brain tissue from aged animals, in the absence of systemic factors such as poor vasculature or systemic substrate supply, to identify intrinsic changes in neuronal metabolism and neuronal-glial interactions. In vitro brain slices obtained from aged animals retain the in vivo metabolic characteristics of that age, as well as the intrinsic circuits and other factors leading to regulation of metabolism on a local tissue scale. Preliminary experiments indicate that neuronal function and mitochondrial redox state in aging hippocampus are more vulnerable to metabolic stress, such as lowered glucose levels and prolonged synaptic stimulation, compared to tissue from younger animals, suggesting that aged individuals may have reduced ability to support an increased rate of oxidative metabolism for an extended period of time. We will evaluate neuronal fatigue and neuronal-glial interactions during prolonged metabolic stress by studying the energetic relationships between oxygen utilization, mitochondrial redox state, and neuronal activity, using direct tissue lactate, glucose and Po2 measurements, NAD(P)H fluorescence, and neuronal responses in hippocampus. These techniques will be used during prolonged synaptic stimulation (increased metabolic demand) and conditions of limited substrate delivery. These results will facilitate understanding how local tissue responses and bioenergetics affect metabolism in aging. The understanding of the mechanisms underlying neuronal fatigue may indicate novel targets for treatment which may enhance performance on sustained cognitive tasks. PUBLIC HEALTH RELEVANCE: This proposal seeks to understand how metabolism in the brain changes with aging, assessing both mechanisms underlying fatigue to persistent responses and possible treatment directions. The goal is to assess components of oxidative and glycolytic metabolism, particularly during sustained metabolic demand, over minutes, which are intrinsic to neurons and glia. The in vitro slice preparation proposed here allows assessment of local metabolic interactions directly in brain tissue, without direct involvement of the vascular system and systemic provision of substrates.