The Neurophysiological Basis of Ammonia Toxicity and Tolerance in Fishes

鱼类氨毒性和耐受性的神经生理学基础

• 批准号: RGPIN-2015-04248
• 负责人: Wilkie, Michael
• 金额: $ 2.4万
• 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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612853
• 关键词: Neurophysiological; Basis; Ammonia; Toxicity; Tolerance

The overarching aim of my research is to determine how fishes produce and excrete nitrogenous wastes such as ammonia, and how they cope with potentially toxic build-ups of this waste product. Ammonia normally arises from the breakdown of excess amino acids, but has neurotoxic effects at high concentrations. Fish are generally much more tolerant to ammonia than mammals, which need to detoxify ammonia to urea to survive. Yet little is known about the underlying mechanisms for these differences. Our recent work suggests that anoxia tolerant fishes, such as goldfish (Carassius auratus) and crucian carp (Carassius carassius), that have evolved neurophysiological mechanisms to withstand O2 starvation, are also ammonia tolerant. Indeed, the cascade of events that characterize anoxia/ischemia in the brain are similar to those that occur with ammonia toxicity. In mammals, excess ammonia causes overactivation of glutamate receptors in the brain, leading to excitotoxicity characterized by the generation of reactive oxygen species (ROS) and water accumulation by astrocyte cells, culminating in potentially fatal brain swelling. Our findings suggest, however, that fish readily tolerate ammonia-induced brain swelling. I propose to use an integrated approach to test the working hypothesis that the greater ammonia tolerance of fishes compared to mammals is related to a greater ability of the brain to resist the neurotoxic effects of ammonia. I also propose to test the related hypothesis that the physiological adaptations that contribute to the anoxia tolerance of the goldfish, also explains their greater ammonia tolerance. Over the next 5 years, the objectives of my research program will be to: (I) Characterize the underlying mechanism(s) of acute ammonia toxicity and tolerance in the central nervous system of ammonia-tolerant goldfish and ammonia-sensitive trout (Oncorhynchus mykiss); (II) Determine if high tolerance to ROS results in greater ammonia tolerance in goldfish compared to trout; (III) Identify the underlying mechanisms that lead to brain swelling in fishes in response to ammonia and other aquatic stressors; (IV) Determine how prolonged sub-lethal ammonia exposure and feeding affect ammonia tolerance in goldfish and trout. The integrative approach I will use in my research will include whole animal models, cultured brain slice models, molecular techniques, immunohistochemistry, and electrophysiology methods. An improved understanding of the neural mechanism(s) of ammonia toxicity and tolerance in fishes will improve our fundamental understanding how vertebrates cope with ammonia, and shed light on the selective pressures that led to the evolution of different mechanisms of ammonia detoxification and handling in the vertebrates. This work will also have practical implications by better explaining how fishes respond to and tolerate build-ups of ammonia in aquatic ecosystems.

我研究的首要目标是确定鱼类如何产生和排泄氨等含氮废物，以及它们如何应对这种废物的潜在有毒积累。氨通常由过量氨基酸的分解产生，但在高浓度下具有神经毒性作用。鱼类通常比哺乳动物对氨的耐受性要高得多，哺乳动物需要将氨解毒成尿素才能生存。然而，人们对这些差异的根本机制知之甚少。我们最近的研究表明，耐缺氧鱼类，例如金鱼（Carassius auratus）和鲫鱼（Carassius carassius），已经进化出神经生理机制来承受氧气饥饿，也具有氨耐受性。事实上，以大脑缺氧/缺血为特征的一系列事件与氨中毒发生的事件相似。在哺乳动物中，过量的氨会导致大脑中谷氨酸受体过度激活，从而导致兴奋性毒性，其特征是星形胶质细胞产生活性氧（ROS）和积水，最终导致可能致命的脑肿胀。然而，我们的研究结果表明，鱼类很容易耐受氨引起的脑肿胀。我建议使用综合方法来检验以下假设：与哺乳动物相比，鱼类对氨的耐受性更强，这与大脑抵抗氨的神经毒性作用的能力更强有关。我还建议检验相关的假设，即有助于金鱼耐缺氧的生理适应也解释了它们对氨的更大耐受性。在接下来的5年里，我的研究计划的目标将是：（I）描述耐氨金鱼和氨敏感鳟鱼（Oncorhynchus mykiss）中枢神经系统急性氨毒性和耐受性的潜在机制）； (II) 确定对 ROS 的高耐受性是否会导致金鱼比鳟鱼具有更高的氨耐受性； (III) 确定导致鱼类因氨和其他水生应激源而出现脑肿胀的根本机制； (IV) 确定长期亚致死氨暴露和喂养如何影响金鱼和鳟鱼的氨耐受性。我将在研究中使用的综合方法包括整体动物模型、培养脑切片模型、分子技术、免疫组织化学和电生理学方法。更好地了解鱼类氨毒性和耐受性的神经机制将提高我们对脊椎动物如何应对氨的基本理解，并揭示导致不同氨解毒和处理机制进化的选择性压力。脊椎动物。这项工作还将通过更好地解释鱼类如何响应和容忍水生生态系统中氨的积累而具有实际意义。