Neurophysiological and Metabolic Adaptations to Increased Ammonia and Oxygen Starvation in Fishes.

鱼类对氨和缺氧增加的神经生理和代谢适应。

• 批准号: RGPIN-2020-06923
• 负责人: Wilkie, Michael
• 金额: $ 2.04万
• 依托单位: Wilfrid Laurier University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=718562
• 关键词: Neurophysiological; Metabolic; Adaptations; Increased; Ammonia

The overarching goal of my research is to determine how aquatic vertebrates cope with environmental stressors such as build-ups of internal ammonia and O2 starvation. Ammonia is a metabolic waste product that arises from the breakdown of excess amino acids, but at elevated concentrations it is neurotoxic. For this reason ammonia needs to be excreted or converted to less toxic nitrogenous waste (N-waste) products such as urea or uric acid, which are produced by terrestrial vertebrates. Due to its high water solubility, ammonia is the primary N-waste product of fishes because it can be excreted with relative ease across the gills to the water. However, fishes frequently have to cope with fluctuations in internal ammonia following feeding, exercise or exposure to high external ammonia. In mammals, an impaired ability to detoxify ammonia to urea (e.g. due to liver disease) leads to highly elevated ammonia in the body. This then results in “excitotoxicity” characterized by hyper-activation of the central nervous system (CNS), reactive oxygen species generation and increased brain water content leading to potentially fatal brain swelling. In contrast, we demonstrated that that brain swelling is readily tolerated by crucian carp and goldfish when exposed to ammonia and low environmental O2. This observation suggests that these fishes possess novel physiological mechanisms to protect the CNS from ammonia. Another notable finding of my NSERC Discovery work was that tolerance to elevated ammonia was linked to an ability to survive prolonged O2 starvation. Over the next 5 years, my students will test the hypothesis that this anoxia-ammonia cross-tolerance is due to the ability of these fishes to prevent excitotoxicity, high tolerance to oxidative stress, and resilience to brain swelling. My specific research objectives will be to: (I) Characterize the neurophysiological adaptations that protect the goldfish CNS from excitotoxic cell death during exposure to hypoxia or anoxia; (II) Contrast the mechanism(s) of ammonia toxicity and tolerance in the CNS of ammonia sensitive rainbow trout (Oncorhynchus mykiss) to those of the ammonia-tolerant goldfish; (III) Identify the link(s) between oxidative stress and the development of brain swelling in goldfish subjected to anoxia, hypoxia or ammonia exposure; (IV) Determine how elevated ammonia and feeding affect antioxidant capacity and neurophysiological processes in the Pacific hagfish and sea lamprey, two jawless fish species able to withstand ammonia and low O2. I will use an integrative research to address these objectives including whole animal models, isolated mitochondria, cultured brain slice models, molecular techniques, immunohistochemistry, and electrophysiology. This work will ultimately improve our understanding of the physiological adaptations used by fishes to cope with increased internal ammonia and O2 starvation, and identify the underlying mechanisms of anoxia-ammonia cross tolerance.

我的研究的总体目标是确定水生脊椎动物如何应对环境压力源，例如内部氨和O2饥饿。氨是由多余的氨基酸分解引起的代谢废物，但在浓度升高时，它是神经毒性的。因此，需要超越或转化为陆生脊椎动物产生的尿素或尿酸等毒性较小的氮废物（N废物）产品。由于其高水溶性，氨是鱼类的主要N废物产物，因为它在整个g上相对轻松而非常容易。但是，在进食，运动或暴露于高外部氨的情况下，鱼类经常必须应对内部氨的波动。在哺乳动物中，对尿素排毒的能力受损（例如由于肝病引起的）导致体内氨升高。然后，这导致了“兴奋性”，其特征是中枢神经系统过度激活（CNS），活性氧的产生并增加了脑水含量，从而导致潜在的致命脑肿胀。相比之下，我们证明了脑肿胀在暴露于氨和低环境O2时很容易被克鲁克鲤和金鱼耐受。该观察结果表明，这些鱼具有保护中枢神经系统免受氨的新生理机制。我的NSERC发现工作的另一个值得注意的发现是，对升高的氨的耐受性与长期O2饥饿的能力有关。在接下来的五年中，我的学生将检验以下假设：这种缺氧 - 氨交叉耐受性是由于这些鱼类防止兴奋性毒性，对氧化应激的高耐受性以及对脑肿胀的韧性的能力。我的具体研究目标是：（i）表征神经生理的适应性，可保护金鱼中枢神经系统在暴露于缺氧或缺氧期间免受兴奋性细胞死亡； （ii）将氨毒性和耐受性的机制与氨敏感的彩虹鳟鱼（Oncorhynchus mykiss）与耐氨耐氨的金鱼的机制进行了对比； （iii）确定氧化应激与受到缺氧，缺氧或氨气暴露的金鱼中脑肿胀的发展之间的联系； （iv）确定氨和喂养如何影响太平洋hag鱼和海七lamp虫的抗氧化能力和神经生理过程，两种无知的鱼类可以承受氨和低O2。我将使用一项综合研究来解决这些目标，包括整个动物模型，孤立的线粒体，培养的脑切片模型，分子技术，免疫组织化学和电生理学。这项工作最终将提高我们对鱼类用于应对内部氨和O2饥饿的物理适应性的理解，并确定缺氧 - ammonia跨耐受性的潜在机制。