title: Reversible brain swelling in crucian carp (Carassius carassius) and goldfish (Carassius auratus) in response to high external ammonia and anoxia.
abstract: Increased internal ammonia (hyperammonemia) and ischemic/anoxic insults are known to result in a cascade of deleterious events that can culminate in potentially fatal brain swelling in mammals. It is less clear, however, if the brains of fishes respond to ammonia in a similar manner. The present study demonstrated that the crucian carp (Carassius carassius) was not only able to endure high environmental ammonia exposure (HEA; 2 to 22 mmol L(-1)) but that they experienced 30% increases in brain water content at the highest ammonia concentrations. This swelling was accompanied by 4-fold increases in plasma total ammonia (TAmm) concentration, but both plasma TAmm and brain water content were restored to pre-exposure levels following depuration in ammonia-free water. The closely related, ammonia-tolerant goldfish (Carassius auratus) responded similarly to HEA (up to 3.6 mmol L(-1)), which was accompanied by 4-fold increases in brain glutamine. Subsequent administration of the glutamine synthetase inhibitor, methionine sulfoximine (MSO), reduced brain glutamine accumulation by 80% during HEA. However, MSO failed to prevent ammonia-induced increases in brain water content suggesting that glutamine may not be directly involved in initiating ammonia-induced brain swelling in fishes. Although the mechanisms of brain swelling are likely different, exposure to anoxia for 96 h caused similar, but lesser (10%) increases in brain water content in crucian carp. We conclude that brain swelling in some fishes may be a common response to increased internal ammonia or lower oxygen but further research is needed to deduce the underlying mechanisms behind such responses.
authors.affiliation: Department of Biology and Institute for Water Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada; Department of Biosciences, University of Oslo, Oslo, Norway. Electronic address: mwilkie@wlu.ca.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Wilkie
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway; Department of Biological Sciences, University of Alaska Anchorage, Anchorage, USA.
authors.forename: Jonathan A W
authors.initials: JA
authors.lastname: Stecyk
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Christine S
authors.initials: CS
authors.lastname: Couturier
authors.affiliation: Department of Biology and Institute for Water Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada.
authors.forename: Sanya
authors.initials: S
authors.lastname: Sidhu
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Guro K
authors.initials: GK
authors.lastname: Sandvik
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Göran E
authors.initials: GE
authors.lastname: Nilsson
mesh_terms: D000641:Ammonia / Q000008:administration & dosage*; D000818:Animals; D001834:Body Water; D001929:Brain Edema / Q000209:etiology*; D002347:Carps; D000431:Ethanol / Q000378:metabolism; D006054:Goldfish; D000860:Hypoxia
chemical_list: D000431:Ethanol; D000641:Ammonia
keywords: Ammonia toxicity; Astrocyte; Brain; Encephalopathy; Ethanol; Glutamine; Glutamine synthetase; Hyperammonemia; Methionine sulfoximine; Neurotoxicity