Failure of the glutamate uptake-ascorbic acid exchange drives seizure susceptibility and severity

癫痫发作与阿尔茨海默病的共存显著改变了预后，并加速了认知功能的丧失 克莱恩。即使是轻微的癫痫发作，可能没有被照顾者发现，也会增加阿尔茨海默病的发病率- SIS并可独立导致神经退行性变和认知功能障碍。亚临床(非坏血酸) 维生素C(抗坏血酸)缺乏在美国很普遍，尤其是在老年人和退伍军人中。 吸烟和与氧化应激相关的疾病，如动脉粥样硬化和糖尿病的常见疾病。 兴奋性信号转导过程中神经元保护的一个关键机制是谷氨酸上调--这一机制尚未得到充分研究 星形胶质细胞中的抗坏血酸释放交换。当谷氨酸通过GLT被摄取到突触周围星形胶质细胞- 1、抗坏血酸被释放到细胞外液中，提供对氧化损伤的急性保护。如果GLT- 1转运蛋白功能受到氧化损伤的影响，或者如果没有足够的抗坏血酸可供释放， 然后，这种保护作用就会减弱，而长期接触谷氨酸的神经毒性效应就会被放大。 最近的数据支持抗坏血酸治疗在减轻癫痫发作影响方面的作用，但以前的研究结果表明 搜索受到合成抗坏血酸的啮齿动物模型的严重限制，因此不能- 变得有缺陷。小鼠脑内抗坏血酸水平的降低与人类的缺乏有关，可通过Ge-Ge-Ge 抗坏血酸在肝脏中合成能力的磁性修饰(Gulo-/-)结合差异抗坏血酸 补充。这些小鼠也可以与阿尔茨海默病的APP/PSEN1小鼠模型杂交 建立饮食不足与一种疾病相结合的模型，在这种疾病中，癫痫发作是常见的。 具体目的1)证明抗坏血酸在支持培养的星形胶质细胞清除谷氨酸方面的作用。 使用从小鼠和人类培养的星形胶质细胞，我们将研究条件如何改变氧化- 培养液(如抗坏血酸和β-淀粉样蛋白)的动态平衡决定了谷氨酸甘油三酯-1的性质。 配偶吸收。我们还将测试在这些情况下改变的谷氨酸清除如何影响神经元的活性。 用共培养技术检测原代培养神经元的存活和树突分枝 在接触谷氨酸之后。这些实验将直接支持Gluta的重要性- 配偶-抗坏血酸交换机制在支持神经元健康和保护谷氨酸毒性中的作用。 特定目标2)确定低脑部抗坏血酸状况与对Spintane敏感性的关系 OU和药物引起的癫痫。我们将记录神经元的超兴奋性并测量癫痫发作 基线条件下和癫痫诱导后的脑电事件 海藻酸。这类研究以前没有在低抗坏血酸条件下进行过，因为缺乏 广泛获得适当的模型。我们将使用植入式遥测(无线)系统，允许 长期测量动物在家中笼子中的脑电。这是对更多行业的重大进步- 国家“系留”脑电系统。我们还将确定反复暴露于谷氨酸能的程度 激动剂，即使没有明确的行为(癫痫)相关性，也会对认知能力和 APP/PSEN1小鼠β-淀粉样蛋白的产生以探讨阿尔茨海默病患者癫痫发作的功能结局 疾病模型除野生型和古罗-/-鼠外。 具体目标3)确定上调GLT-1在多大程度上促进谷氨酸清除和去谷氨酸 减少红藻氨酸处理的有害影响。GLT-1，因此谷氨酸清除，代表一种 有针对性的策略，以减少过度兴奋或癫痫发作后神经损伤的程度。我们会 研究一种已知可上调GLT-1表达的化合物头孢曲松，并评估其抑制GLT-1表达的能力。 增加癫痫的敏感性和严重程度。我们的长期目标是证明保护谷氨酸摄取和 避免抗坏血酸缺乏可以最大限度地减少特定人群癫痫发作的影响，并提供一种廉价的预 针对认知衰退的宣泄策略。

Co-occurrence of seizures with Alzheimer's disease dramatically alters prognosis, and speeds cognitive de- cline. Even mild seizures that may go undetected by caregivers can increase Alzheimer's disease pathogene- sis and also independently lead to neurodegeneration and cognitive dysfunction. Subclinical (non-scorbutic) vitamin C (ascorbate) deficiency is widespread in the USA, particularly among the elderly, and veteran popula- tions where smoking and oxidative stress-related diseases such as atherosclerosis and diabetes are common. A critical, but understudied, mechanism of neuronal protection during excitatory signaling is the glutamate up- take-ascorbate release exchange in astrocytes. As glutamate is taken up into perisynaptic astrocytes via GLT- 1, ascorbate is released into the extracellular fluid providing acute protection against oxidative damage. If GLT- 1 transporter function is compromised by oxidative damage, or if insufficient ascorbate is available for release, then this protection is diminished and the neurotoxic effects of prolonged glutamate exposure are magnified. Recent data support the role of ascorbate treatments in mitigating the effects of seizures, but previous re- search has been critically limited by the use of rodent models that synthesize ascorbate and thus cannot be- come deficient. Decreased brain ascorbate, at levels relevant to human deficiency, is achieved in mice by ge- netic modification of the ability to synthesize ascorbate in liver (Gulo-/-) combined with differential ascorbate supplementation. These mice can also be crossed with the APP/PSEN1 mouse model of Alzheimer's disease to model dietary insufficiency in combination with a disease in which co-occurrence of seizures is common. Specific Aim 1) Demonstrate the role of ascorbate in supporting glutamate clearance by cultured astrocytes. Using cultured astrocytes from both mice and humans we will investigate how conditions that alter the oxida- tive balance of the culture media (e.g. ascorbate and β-amyloid) determine the properties of GLT-1 in gluta- mate uptake. We will also test how altered glutamate clearance under these situations impacts neuronal sur- vival using co-culture techniques and measuring survival and dendritic branching of primary cultured neurons following exposure to glutamate. These experiments will provide direct support for the importance of the gluta- mate-ascorbate exchange mechanism in supporting neuronal health and protecting against glutamate toxicity. Specific Aim 2) Determine relationship between low brain ascorbate conditions and susceptibility to spontane- ous and pharmacologically-induced seizures. We will record neuronal hyper excitability and measure seizure events through electroencephalography (EEG) under baseline conditions and following seizure induction using kainic acid. Such studies have not previously been conducted in low ascorbate conditions owing to lack of widespread access to appropriate models. We will use an implantable telemetry (wireless) system that allows long-term measuring of EEG in animals within their home cages. This is a significant advance on more tradi- tional `tethered' EEG systems. We will also determine the extent to which repeated exposures to glutamatergic agonists, even without a clear behavioral (seizure) correlate, can negatively impact both cognitive ability, and β-amyloid production in the APP/PSEN1 mice to explore the functional outcome of seizures in an Alzheimer's disease model in addition to wild-type and Gulo-/- mice. Specific Aim 3) Establish the extent to which upregulation of GLT-1 improves glutamate clearance and de- creases detrimental effects of kainic acid treatments. GLT-1, and therefore glutamate clearance, represents a targetable strategy to reduce the extent of neural damage following hyperexcitability, or seizure events. We will investigate a compound, ceftriaxone, known to up-regulate GLT-1 expression, and assess its ability to de- crease seizure susceptibility and severity. Our long-term goal is to show that protecting glutamate uptake and avoiding ascorbate deficiency can minimize effects of seizure in specific populations, and provide a cheap pre- ventative strategy against cognitive decline.