Mechanisms of nitrogen excretion, toxicity and tolerance in ancient and modern fishes

我的研究的首要目标是确定鱼类如何产生和排泄含氮废物（N-废物），如氨和尿素，以及它们如何科普这些产品的潜在毒性积累。 过量氨基酸的分解产生神经毒性氨，其必须被排出或转化为毒性较小的废物，如尿素。虽然氨靶向中枢神经系统（CNS），但其确切的毒性机制尚未解决。 由于哺乳动物的肝衰竭，血液和中枢神经系统氨可能达到有毒浓度。在鱼类中，内部氨在摄食后增加，并且当鳃的排泄物被改变的水化学（例如>水pH）或由自然（例如有机材料的分解）或人为来源（例如污水流出物，农业径流）引起的水氨升高所阻止时。我建议，以确定如何在鱼类的N-废物排泄系统的影响，喂养和生命阶段，并确定氨毒性和耐受性的潜在机制。七鳃鳗将成为研究排泄的模型。我以前的工作表明，喂养深刻刺激氨和尿素排泄在寄生七鳃鳗，因为他们吃的鲨鱼和鳟鱼的血液，使他们理想的了解更多的机制和进化的N-废物排泄策略在脊椎动物。金鱼和鳟鱼将用于确定当排泄受损或进食后，鱼类的中枢神经系统如何应对氨的积聚。我的目标，在未来5年将是：（一）确定氨和尿素运输系统是如何改变七鳃鳗的生命周期和喂养，（二）确定急性氨毒性和耐受性的机制，在中枢神经系统的金鱼和氨敏感鳟鱼，以及（三）确定如何喂养和长期亚致死氨暴露影响氨的耐受性和中枢神经系统的金鱼和鳟鱼。我将使用的综合方法将包括整个动物模型，培养的脑细胞，分子技术和电生理学。这项研究将回答有关脊椎动物排泄废物的机制和进化的基本问题，并可能确定鱼类耐氨性的新机制。

The overarching aim of my research is to determine how fishes produce and excrete nitrogenous wastes (N-wastes) such as ammonia and urea, and how they cope with potentially toxic build-ups of these products. The breakdown of excess amino acids generates neurotoxic ammonia that must either be excreted or converted to less toxic wastes such as urea. Although ammonia targets the central nervous system (CNS), its precise mechanism of toxicity is unresolved. Blood and CNS ammonia may reach toxic concentrations due to liver failure in mammals. In fishes, internal ammonia increases following feeding, and when excretion by the gill is prevented by altered water chemistry (e.g. > water pH) or elevated water ammonia arising from natural (e.g. decomposition of organic material) or anthropogenic sources (e.g. sewage effluent, agricultural run-off). I propose to determine how N-waste excretion systems in fishes are influenced by feeding and life-stage, and to identify the underlying mechanisms of ammonia toxicity and tolerance. Sea lampreys will be the model for studying excretion. My previous work demonstrated that feeding profoundly stimulated ammonia and urea excretion in parasitic lampreys as they fed on the blood of sharks and trout, making them ideal for learning more about the mechanisms and evolution of N-waste excretion strategies in vertebrates. Goldfish and trout will be used to determine how the CNS of fishes copes with build-ups of ammonia when excretion is impaired or after feeding. My objectives for the next 5 years will be to: (i) determine how ammonia and urea transport systems are altered during the lamprey life-cycle and by feeding, (ii) identify the mechanisms of acute ammonia toxicity and tolerance in the CNS of goldfish and more ammonia-sensitive trout, and (iii) ascertain how feeding and prolonged sub-lethal ammonia exposure affect the ammonia-tolerance and CNS of goldfish and trout. The integrative approach I will use will include whole animal models, cultured brain cells, molecular techniques, and electrophysiology. This research will answer fundamental questions on the mechanisms and evolution of waste excretion in vertebrates, and it may identify novel mechanisms of ammonia tolerance in fish.