title: Expression of genes involved in brain GABAergic neurotransmission in three-spined stickleback exposed to near-future CO2.
abstract: Change in the activity of the main inhibitory receptor, GABAA, has been suggested to be a general mechanism behind the behavioural alterations reported in ocean acidification studies on fish. It has been proposed that regulatory acid-base mechanisms in response to high CO2alter the neuronal Cl-and HCO3-gradients that are important for GABAAreceptor function. Here, we report a comprehensive analysis of gene expression of GABAAreceptor subunits and of genes involved in GABAergic transmission in the brain of fish exposed to near-future CO2. Altogether, 56 mRNA transcripts were quantified in brains of three-spined stickleback (Gasterosteus aculeatus) kept in control pCO2(333 ± 30 μatm CO2) or at high pCO2levels (991 ± 57 μatm) for 43 days. The gene expression analysis included GABAAreceptor subunits (α1-6, β1-3, γ1-3, δ, π and ρ1-3), enzymes and transporters involved in GABA metabolism (GAD1-2, GABAT and GAT1-3), GABAAreceptor-associated proteins (GABARAP and GABARAPL), ion cotransporters (KCC1-4, NKCC1, ClC21-3, AE3 and NDAE) and carbonic anhydrase (CAII). Exposure to high CO2had only minor effects on the expression of genes involved in GABAergic neurotransmission. There were significant increases in the mRNA levels of α family subunits of the GABAAreceptor, with a more pronounced expression of α12, α3, α4 and α6b. No changes were detected in the expression of other GABAAsubunits or in genes related to receptor turnover, GABA metabolism or ion transport. Although the minor changes seen for mRNA levels might reflect compensatory mechanisms in the high-CO2conditions, these were apparently insufficient to restore normal neural function, because the behavioural changes persisted within the time frame studied.
authors.affiliation: Section for Physiology and Cell Biology , Department of Biosciences , University of Oslo , Norway.
authors.forename: Floriana
authors.initials: F
authors.lastname: Lai
authors.affiliation: Section for Physiology and Cell Biology , Department of Biosciences , University of Oslo , Norway.
authors.forename: Cathrine E
authors.initials: CE
authors.lastname: Fagernes
authors.affiliation: Department of Biology , Norwegian University of Science and Technology , Trondheim , Norway.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Jutfelt
authors.affiliation: Section for Physiology and Cell Biology , Department of Biosciences , University of Oslo , Norway.
authors.forename: Göran E
authors.initials: GE
authors.lastname: Nilsson
keywords: GABAA receptor; GABAergic system; ion cotranporters; ocean acidification; quantitative polymerase chain reaction; three-spined stickleback