title: Ambient CO2, fish behaviour and altered GABAergic neurotransmission: exploring the mechanism of CO2-altered behaviour by taking a hypercapnia dweller down to low CO2 levels.
abstract: Recent studies suggest that projected rises of aquatic CO2 levels cause acid-base regulatory responses in fishes that lead to altered GABAergic neurotransmission and disrupted behaviour, threatening fitness and population survival. It is thought that changes in Cl(-) and HCO3 (-) gradients across neural membranes interfere with the function of GABA-gated anion channels (GABAA receptors). So far, such alterations have been revealed experimentally by exposing species living in low-CO2 environments, like many oceanic habitats, to high levels of CO2 (hypercapnia). To examine the generality of this phenomenon, we set out to study the opposite situation, hypothesizing that fishes living in typically hypercapnic environments also display behavioural alterations if exposed to low CO2 levels. This would indicate that ion regulation in the fish brain is fine-tuned to the prevailing CO2 conditions. We quantified pH regulatory variables and behavioural responses of Pangasianodon hypophthalmus, a fish native to the hypercapnic Mekong River, acclimated to high-CO2 (3.1 kPa) or low-CO2 (0.04 kPa) water. We found that brain and blood pH was actively regulated and that the low-CO2 fish displayed significantly higher activity levels, which were reduced after treatment with gabazine, a GABAA receptor blocker. This indicates an involvement of the GABAA receptor and altered Cl(-) and HCO3 (-) ion gradients. Indeed, Goldman calculations suggest that low levels of environmental CO2 may cause significant changes in neural ion gradients in P. hypophthalmus. Taken together, the results suggest that brain ion regulation in fishes is fine-tuned to the prevailing ambient CO2 conditions and is prone to disruption if these conditions change.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 regan@zoology.ubc.ca.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Regan
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Andy J
authors.initials: AJ
authors.lastname: Turko
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California at Irvine, Irvine, CA 92697-2525, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Heras
authors.affiliation: Department of Bioscience, Aarhus University, 8000 Aarhus-C, Denmark.
authors.forename: Mads Kuhlmann
authors.initials: MK
authors.lastname: Andersen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo NO-0316, Norway.
authors.forename: Sjannie
authors.initials: S
authors.lastname: Lefevre
authors.affiliation: Department of Bioscience, Aarhus University, 8000 Aarhus-C, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
authors.affiliation: Department of Bioscience, Aarhus University, 8000 Aarhus-C, Denmark.
authors.forename: Mark
authors.initials: M
authors.lastname: Bayley
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Brauner
authors.affiliation: College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam.
authors.forename: Do Thi Thanh
authors.initials: do TT
authors.lastname: Huong
authors.affiliation: College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam.
authors.forename: Nguyen Thanh
authors.initials: NT
authors.lastname: Phuong
authors.affiliation: Department of Biosciences, University of Oslo, Oslo NO-0316, Norway.
authors.forename: Göran E
authors.initials: GE
authors.lastname: Nilsson
mesh_terms: D000064:Acclimatization; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001923:Brain Chemistry; D002245:Carbon Dioxide / Q000494:pharmacology*; D002397:Catfishes / Q000502:physiology*; D005618:Fresh Water / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D011963:Receptors, GABA-A / Q000378:metabolism; D045483:Rivers; D009435:Synaptic Transmission; D014744:Vietnam
chemical_list: D011963:Receptors, GABA-A; D002245:Carbon Dioxide
keywords: Acid–base regulation; Carbon dioxide; Climate change; Gabazine; Pangasianodon hypophthalmus