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Keitel-Gröner F, Bamber S, Bechmann RK, Lyng E, Gomiero A, Tronci V, Gharbi N, Engen F, Taban IC, Baussant T. Effects of chronic exposure to the water-soluble fraction of crude oil and in situ burn residue of oil on egg-bearing Northern shrimp (Pandalus borealis). Ecotoxicol Environ Saf 2021; 228:113013. [PMID: 34839140 DOI: 10.1016/j.ecoenv.2021.113013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 11/15/2021] [Accepted: 11/17/2021] [Indexed: 06/13/2023]
Abstract
Oil spill clean-up measures using in situ burning can potentially result in seafloor contamination affecting benthic organisms. To mimic realistic exposure and measure effects, ovigerous Northern shrimp were continuously exposed for two weeks to the water-soluble fraction of oil coated on gravel followed by two weeks in clean seawater. North Sea crude oil (NSC) and field generated in situ burn residue (ISBR) of NSC were used (Low: 3 g/kg gravel, Medium: 6 g/kg gravel and High: 12 g/kg gravel). The concentrations of polyaromatic hydrocarbons (PAHs) in the water resulting from NSC were higher compared to ISBR. No mortality was observed in any treatment and overall moderate sublethal effects were found, mostly after exposure to NSC. Feeding was temporarily reduced at higher concentrations of NSC. PAH levels in hepatopancreas tissue were significantly elevated following exposure and still significantly higher at the end of the experiment in NSCHigh and ISBRHigh compared to control. Mild inflammatory response reactions and tissue ultrastructural alterations in gill tissue were observed in both treatments. Signs of necrosis occurred in ISBRHigh. No change in shrimp locomotory activity was noted from NSC exposure. However, ISBR exposure increased activity temporarily. Larvae exposed as pleopod-attached embryos showed significant delay in development from stage I to stage II after exposure to NSCHigh. Based on this study, oil-contaminated seafloor resulting from in situ burning clean-up actions does not appear to cause serious effects on bottom-living shrimp.
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Affiliation(s)
| | - Shaw Bamber
- NORCE Norwegian Research Centre, Mekjarvik 12, 4072 Randaberg, Norway
| | - Renée K Bechmann
- NORCE Norwegian Research Centre, Mekjarvik 12, 4072 Randaberg, Norway
| | - Emily Lyng
- NORCE Norwegian Research Centre, Mekjarvik 12, 4072 Randaberg, Norway
| | - Alessio Gomiero
- NORCE Norwegian Research Centre, Mekjarvik 12, 4072 Randaberg, Norway
| | - Valentina Tronci
- NORCE Norwegian Research Centre, Nygårdsgaten 112, 5008 Bergen, Norway
| | - Naouel Gharbi
- NORCE Norwegian Research Centre, Nygårdsgaten 112, 5008 Bergen, Norway
| | - Frode Engen
- NOFO Norwegian Clean Seas Association for Operating Companies, Vassbotnen 1, 4313 Sandnes, Norway
| | - Ingrid C Taban
- NOFO Norwegian Clean Seas Association for Operating Companies, Vassbotnen 1, 4313 Sandnes, Norway
| | - Thierry Baussant
- NORCE Norwegian Research Centre, Mekjarvik 12, 4072 Randaberg, Norway.
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2
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Gharbi N, Røise D, Førre JE, Edson AJ, Hushagen HA, Tronci V, Frøyset AK, Fladmark KE. Reintroduction of DJ-1 in Müller Cells Inhibits Retinal Degeneration in the DJ-1 Deficient Retina. Antioxidants (Basel) 2021; 10:1862. [PMID: 34942966 PMCID: PMC8698414 DOI: 10.3390/antiox10121862] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2021] [Revised: 11/14/2021] [Accepted: 11/16/2021] [Indexed: 12/19/2022] Open
Abstract
The eye is continuously under oxidative stress due to high metabolic activity and reactive oxygen species generated by daily light exposure. The redox-sensitive protein DJ-1 has proven to be essential in order to protect retina and retinal pigment epithelium (RPE) from oxidative-stress-induced degeneration. Here, we analyzed the specific role of Müller cell DJ-1 in the adult zebrafish retina by re-establishing Müller-cell-specific DJ-1 expression in a DJ-1 knockout retina. Loss of DJ-1 resulted in an age-dependent retinal degeneration, including loss of cells in the ganglion cell layer, retinal thinning, photoreceptor disorganization and RPE cell dysfunction. The degenerative phenotype induced by the absence of DJ-1 was inhibited by solely expressing DJ-1 in Müller cells. The protective effect was dependent upon the cysteine-106 residue of DJ-1, which has been shown to be an oxidative sensor of DJ-1. In a label-free proteomics analysis of isolated retinas, we identified proteins differentially expressed after DJ-1 knockout, but with restored levels after Müller cell DJ-1 re-insertion. Our data show that Müller cell DJ-1 has a major role in protecting the retina from age-dependent oxidative stress.
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Affiliation(s)
- Naouel Gharbi
- Integrative Fish Biology Group (IFB), NORCE Norwegian Research Center AS, N-5020 Bergen, Norway; (N.G.); (V.T.)
| | - Dagne Røise
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
| | - Jorunn-Elise Førre
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
| | - Amanda J. Edson
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
| | - Helena A. Hushagen
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
| | - Valentina Tronci
- Integrative Fish Biology Group (IFB), NORCE Norwegian Research Center AS, N-5020 Bergen, Norway; (N.G.); (V.T.)
| | - Ann-Kristin Frøyset
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
| | - Kari E. Fladmark
- Department of Biological Science, University of Bergen, N-5020 Bergen, Norway; (D.R.); (J.-E.F.); (A.J.E.); (H.A.H.); (A.-K.F.)
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3
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Aranguren-Abadía L, Donald CE, Eilertsen M, Gharbi N, Tronci V, Sørhus E, Mayer P, Nilsen TO, Meier S, Goksøyr A, Karlsen OA. Expression and localization of the aryl hydrocarbon receptors and cytochrome P450 1A during early development of Atlantic cod (Gadus morhua). Aquat Toxicol 2020; 226:105558. [PMID: 32673888 DOI: 10.1016/j.aquatox.2020.105558] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 06/25/2020] [Accepted: 07/01/2020] [Indexed: 06/11/2023]
Abstract
The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor that mediates the toxicity of dioxins and dioxin-like compounds (DLCs) in vertebrates. Two clades of the Ahr family exist in teleosts (Ahr1 and Ahr2), and it has been demonstrated that Ahr2 is the main protein involved in mediating the toxicity of dioxins and DLCs in most teleost species. Recently, we characterized the Atlantic cod (Gadus morhua) Ahr1a and Ahr2a receptors. To further explore a possible subfunction partitioning of Ahr1a and Ahr2a in Atlantic cod we have mapped the expression and localization of ahr1a and ahr2a in early developmental stages. Atlantic cod embryos were continuously exposed in a passive-dosing exposure system to the Ahr agonist, benzo[a]pyrene (B[a]P), from five days post fertilization (dpf) until three days post hatching (dph). Expression of ahr1a, ahr2a, and the Ahr-target genes, cyp1a and ahrrb, was assessed in embryos (8 dpf and 10 dpf) and larvae (3 dph) with quantitative real-time PCR analyses (qPCR), while in situ hybridization was used to assess the localization of expression of ahr1a, ahr2a and cyp1a. Quantitative measurements showed an increased cyp1a expression in B[a]P-exposed samples at all sampling points, and for ahr2a at 10 dpf, confirming the activation of the Ahr-signalling pathway. Furthermore, B[a]P strongly induced ahr2a and cyp1a expression in the cardiovascular system and skin, respectively, of embryos and larvae. Induced expression of both ahr2a and cyp1a was also revealed in the liver of B[a]P-exposed larvae. Our results suggest that Ahr2a is the major subtype involved in mediating responses to B[a]P in early developmental stages of Atlantic cod, which involves transcriptional regulation of biotransformation genes, such as cyp1a. The focused expression of ahr1a in the eye of embryos and larvae, and the presence of ahr2a transcripts in the jaws and fin nodes, further indicate evolved specialized roles of the two Ahrs in ontogenesis.
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Affiliation(s)
| | | | - Mariann Eilertsen
- Department of Biological Sciences, University of Bergen, Bergen, Norway
| | - Naouel Gharbi
- NORCE Norwegian Research Centre AS, Uni Research Environment, Bergen, Norway
| | - Valentina Tronci
- NORCE Norwegian Research Centre AS, Uni Research Environment, Bergen, Norway
| | - Elin Sørhus
- Institute of Marine Research, Bergen, Norway
| | - Philipp Mayer
- Department of Environmental Engineering, Technical University of Denmark, Lyngby, Denmark
| | - Tom Ole Nilsen
- Department of Biological Sciences, University of Bergen, Bergen, Norway
| | | | - Anders Goksøyr
- Department of Biological Sciences, University of Bergen, Bergen, Norway; Institute of Marine Research, Bergen, Norway
| | - Odd André Karlsen
- Department of Biological Sciences, University of Bergen, Bergen, Norway.
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4
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Tang P, Nilsen TO, Gharbi N, Osberg C, Handeland S, Ebbesson L, Käkelä R, Tronci V, Pedrosa C, Balseiro P, Stefansson S. How Does Temperature Affect Primary Barrier Functions in Atlantic Salmon (
Salmo Salar
L.) Post‐Smolts? FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.544.23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Patrik Tang
- Department of Biological SciencesUniversity of BergenBergenNorway
| | | | | | - Camilla Osberg
- Department of BiomedicineUniversity of BergenBergenNorway
| | | | | | - Reijo Käkelä
- Helsinki Institute for Life Science (HiLIFE) and Molecular and Integrative Biosciences Research ProgrammeHelsinki UniversityHelsinkiFinland
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Balseiro P, Moe Ø, Gamlem I, Shimizu M, Sveier H, Nilsen TO, Kaneko N, Ebbesson L, Pedrosa C, Tronci V, Nylund A, Handeland SO. Comparison between Atlantic salmon Salmo salar post-smolts reared in open sea cages and in the Preline raceway semi-closed containment aquaculture system. J Fish Biol 2018; 93:567-579. [PMID: 29952001 DOI: 10.1111/jfb.13659] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 05/06/2018] [Indexed: 06/08/2023]
Abstract
The use of closed containment (CCS) or semi-closed containment systems (S-CCS) for Atlantic salmon Salmo salar aquaculture is under evaluation in Norway. One such system is the Preline S-CCS, a floating raceway system that pumps water from 35 m depth creating a constant current through the system. Exposing fish to moderate water currents is considered aerobic exercise and it is often perceived as positive for fish welfare, growth, food utilization, muscle development and cardiac health. The present study compared fish reared in the Preline S-CCS and in a reference open pen. Samples were taken in fresh water before being transferred to the seawater systems and after 1, 2 and 4 months in seawater and analysed for growth, mortality, muscle development and plasma insulin-like growth factor I (IGF-I) levels. Moreover, gene transcription were determined in the skeletal muscle [igf-I, insulin-like growth factor 1 receptor a (igf1ra) and insulin-like growth factor 1 binding protein 1a (igf1bp1a)] and cardiac transcription factors [myocyte-specific enhancer factor 2C (mef2c), gata4 and vascular endothelial growth factor (vegf)]. While the results suggest that post-smolts in Preline S-CCS were smaller than reference fish, fish from Preline S-CCS have less accumulated mortality at the end of the experiment and showed 2.44 times more small muscle fibres than the reference group fish after 4 months in seawater. These results confirmed what was previously observed in the second generation of Preline. Similar levels of big muscle fibres between Preline S-CCS and reference suggest a similar hypertrophy of muscle fibres even with lower IGF-I expression in the Preline S-CCS. Cardiac gene transcription suggests cardiac hypertrophy was observed after 4 months in seawater in the Preline S-CCS group. Altogether, Preline S-CCS is a promising technology able to produce more robust S. salar with a faster growth and lower mortality in the subsequent standard open cage system growth period.
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Affiliation(s)
- Pablo Balseiro
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | - Øyvind Moe
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | - Ingrid Gamlem
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | - Munetaka Shimizu
- Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
| | | | - Tom O Nilsen
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | - Nobuto Kaneko
- Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
| | - Lars Ebbesson
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | - Cindy Pedrosa
- Uni Research Environment, Uni Research AS, Bergen, Norway
| | | | - Are Nylund
- Department of Biology, University of Bergen, Bergen, Norway
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6
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Vindas MA, Gorissen M, Höglund E, Flik G, Tronci V, Damsgård B, Thörnqvist PO, Nilsen TO, Winberg S, Øverli Ø, Ebbesson LOE. How do individuals cope with stress? Behavioural, physiological and neuronal differences between proactive and reactive coping styles in fish. ACTA ACUST UNITED AC 2017; 220:1524-1532. [PMID: 28167808 DOI: 10.1242/jeb.153213] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 02/01/2017] [Indexed: 12/19/2022]
Abstract
Despite the use of fish models to study human mental disorders and dysfunctions, knowledge of regional telencephalic responses in non-mammalian vertebrates expressing alternative stress coping styles is poor. As perception of salient stimuli associated with stress coping in mammals is mainly under forebrain limbic control, we tested region-specific forebrain neural (i.e. mRNA abundance and monoamine neurochemistry) and endocrine responses under basal and acute stress conditions for previously characterised proactive and reactive Atlantic salmon. Reactive fish showed a higher degree of the neurogenesis marker proliferating cell nuclear antigen (pcna) and dopamine activity under basal conditions in the proposed hippocampus homologue (Dl) and higher post-stress plasma cortisol levels. Proactive fish displayed higher post-stress serotonergic signalling (i.e. higher serotonergic activity and expression of the 5-HT1A receptor) in the proposed amygdala homologue (Dm), increased expression of the neuroplasticity marker brain-derived neurotropic factor (bdnf) in both Dl and the lateral septum homologue (Vv), as well as increased expression of the corticotropin releasing factor 1 (crf1 ) receptor in the Dl, in line with active coping neuro-profiles reported in the mammalian literature. We present novel evidence of proposed functional equivalences in the fish forebrain with mammalian limbic structures.
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Affiliation(s)
- Marco A Vindas
- Uni Environment, Uni Research AS, Bergen NO-5020, Norway .,Department of Biosciences, University of Oslo, Oslo NO-0316, Norway
| | - Marnix Gorissen
- Radboud University, Institute for Water and Wetland Research, Department of Animal Ecology & Physiology, Nijmegen 6525 AJ, The Netherlands
| | - Erik Höglund
- National Institute of Aquatic Resources, Technical University of Denmark, Hirtshals DK-9850, Denmark
| | - Gert Flik
- Radboud University, Institute for Water and Wetland Research, Department of Animal Ecology & Physiology, Nijmegen 6525 AJ, The Netherlands
| | | | - Børge Damsgård
- The University Centre of Svalbard, Longyearbyen NO-9171, Norway.,Nofima, Tromsø NO-9291, Norway
| | - Per-Ove Thörnqvist
- Department of Neuroscience, Uppsala University, Uppsala SE-75124, Sweden
| | - Tom O Nilsen
- Uni Environment, Uni Research AS, Bergen NO-5020, Norway
| | - Svante Winberg
- Department of Neuroscience, Uppsala University, Uppsala SE-75124, Sweden
| | - Øyvind Øverli
- Department of Food Safety and Infection Biology, Norwegian University of Life Sciences, Oslo NO-0033, Norway
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7
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Macirella R, Guardia A, Pellegrino D, Bernabò I, Tronci V, Ebbesson LOE, Sesti S, Tripepi S, Brunelli E. Effects of Two Sublethal Concentrations of Mercury Chloride on the Morphology and Metallothionein Activity in the Liver of Zebrafish (Danio rerio). Int J Mol Sci 2016; 17:361. [PMID: 26978352 PMCID: PMC4813222 DOI: 10.3390/ijms17030361] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 03/02/2016] [Accepted: 03/04/2016] [Indexed: 02/03/2023] Open
Abstract
Mercury (Hg) is a highly hazardous pollutant widely used in industrial, pharmaceutical and agricultural fields. Mercury is found in the environment in several forms, elemental, inorganic (iHg) and organic, all of which are toxic. Considering that the liver is the organ primarily involved in the regulation of metabolic pathways, homeostasis and detoxification we investigated the morphological and ultrastructural effects in Danio rerio liver after 96 h exposure to two low HgCl2 concentrations (7.7 and 38.5 μg/L). We showed that a short-term exposure to very low concentrations of iHg severely affects liver morphology and ultrastructure. The main effects recorded in this work were: cytoplasm vacuolization, decrease in both lipid droplets and glycogen granules, increase in number of mitochondria, increase of rough endoplasmic reticulum and pyknotic nuclei. Pathological alterations observed were dose dependent. Trough immunohistochemistry, in situ hybridization and real-time PCR analysis, the induction of metallothionein (MT) under stressor conditions was also evaluated. Some of observed alterations could be considered as a general response of tissue to heavy metals, whereas others (such as increased number of mitochondria and increase of RER) may be considered as an adaptive response to mercury.
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Affiliation(s)
- Rachele Macirella
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | - Antonello Guardia
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | - Daniela Pellegrino
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | - Ilaria Bernabò
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | | | - Lars O E Ebbesson
- Uni Research Environment, Uni Research, Bergen 5006, Norway.
- Department of Biology, University of Bergen, Bergen High Technology Center, Bergen 5020, Norway.
| | - Settimio Sesti
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | - Sandro Tripepi
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
| | - Elvira Brunelli
- Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, Rende (Cosenza) 87036, Italy.
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Grassie C, Braithwaite VA, Nilsson J, Nilsen TO, Teien HC, Handeland SO, Stefansson SO, Tronci V, Gorissen M, Flik G, Ebbesson LOE. Aluminum exposure impacts brain plasticity and behavior in Atlantic salmon (Salmo salar). J Exp Biol 2013; 216:3148-55. [DOI: 10.1242/jeb.083550] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Summary
Aluminum (Al) toxicity occurs frequently in natural aquatic ecosystems as a result of acid deposition and natural weathering processes. Detrimental effects of Al toxicity on aquatic organisms are well known and can have consequences for survival. Fish exposed to Al in low pH waters will experience physiological and neuroendocrine changes that disrupt homeostasis and alter behavior. To investigate the effects of Al exposure to both brain and behavior, Atlantic salmon (Salmo salar) kept in water treated with Al (pH 5.7, 0.37±0.04 µmol 1-1 of Al) for 2 weeks were compared to fish kept in a control condition (pH 6.7, <0.04 µmol 1-1 of Al). Fish exposed to Al and acidic conditions had increased Al accumulation in the gills and decreased gill Na+, K+-ATPase activity, which impaired osmoreguatory capacity and caused physiological stress, indicated by elevated plasma cortisol and glucose levels. Here we show for the first time that exposure to Al in acidic conditions also impaired learning performance in a maze task. Al toxicity reduced the expression of NeuroD1 transcript levels in the forebrain of exposed fish. As in mammals, these data show that exposure to chronic stress, such as acidified Al, can reduce neural plasticity during behavioral challenges in salmon, and may impair coping ability to new environments.
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9
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Ebbesson LOE, Nilsen TO, Helvik JV, Tronci V, Stefansson SO. Corticotropin-releasing factor neurogenesis during midlife development in salmon: genetic, environmental and thyroid hormone regulation. J Neuroendocrinol 2011; 23:733-41. [PMID: 21592238 DOI: 10.1111/j.1365-2826.2011.02164.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Salmon parr-smolt transformation (smoltification) is a mid-life transitional stage between life in freshwater and seawater that entails a wide range of neural, endocrine and physiological modifications. In salmon, the neuroendocrine corticotropin-releasing factor (CRF) system regulates pituitary adrenocorticotrophic hormone and thyrotrophin release. Four experimental groups of Atlantic salmon, Salmo salar, were used to investigated CRF neurogenesis and its regulation during smoltification. We compared: (i) developmental stages (parr and early-smolt) in anadromous controls; (ii) a developmentally arrested model: anadromous reared under continuous light (LL) with anadromous controls; (iii) a natural hypoendocrine/incomplete smolt development salmon model (landlocked) with anadromous controls; and (iv) landlocked treated with thyroxine to anadromous control smolt levels. CRF neurogenesis between groups was studied with bromodeoxyuradine (BrdU) incorporation followed by double-labelling CRF and BrdU immunhistochemistry. The rate of CRF neurogenesis in the preoptic area (POA) increased from parr to early-smolts in anadromous salmon. By contrast, neurogenesis was inhibited in the LL group and reduced in the landlocked salmon. The administration of thyroxine in landlocked salmon to match anadromous levels increased the rate of CRF neurogenesis to anadromous levels. In conclusion, newly-formed CRF cells in the POA during smoltification are associated with increased retinal innervation to the POA and endocrine responsiveness to increased photoperiod. Both genetic and environmental factors influence the degree of salmon brain development. Thyroid hormones increase CRF neurogenesis during this critical period of development in salmon. We hypothesise that a positive-feedback of thyroid hormones on CRF neurogenesis may be an important event in reaching the developmental climax during critical periods.
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