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() c-FOS expression as a biomarker of neuronal stress in fish associated with harmful algae exposure.
Salierno, James1, Shields, Jeffrey2, Snyder, Natalie3, Murphy, Anne4, Kane, Andrew1, 1 University of Maryland College Park, College Park, Maryland, USA2 Virginia Institute of Marine Sciences, Gloucester Point, Virginia, USA3 University of Maryland School of Medicine, Baltimore, Maryland, USA4 Georgia State University, Atlanta, Georgia, USA
ABSTRACT- Behavioral changes in organisms can result from alterations at the biochemical and physiological levels of organization. The goal of this work was to develop and test the utility of c-Fos expression using immunocytochemistry as a biomarker of stress exposure in killifish, Fundulus heteroclitus. c-fos, an immediate early gene, and its protein product c-Fos, are induced in neurons as a result of neuronal stimulation. This study examined alterations in the brains of killifish exposed to different harmful algal bloom (HAB) stressors including brevetoxin, domoic acid, Chaetocerous concavicornis, and Pfiesteria shumwayae. Brains of exposed fish were removed, sectioned and stained, and neurons expressing Fos were quantified. HAB-exposed fish brains showed increased neuronal Fos labeling compared to control fish brains. A dose response relationship was observed in the C. concavicornis and P. shumwayae exposed fish, with increased labeling in fish exposed to higher cell counts. Areas of the brain with increased labeling included the telencephalon, optic lobes, midbrain, and portions of the medulla. Alterations in swimming and respiratory behaviors were observed during HAB neurotoxin and P. shumwayae exposures, which may be associated with the increased regional neuronal activity. In addition, gill damage resulting from C. concavicornis exposures were documented, which included hyperplasia, hypertrophy, and fusion of secondary gill lamellae. Alterations in c-Fos labeling as a biomarker of exposure may link quantifiable changes in fish swimming behavior and gill physiology associated with HAB exposure to changes in brain activity. General alterations in brain activity, as well as knowledge of specific, stress-activated regions within the brain, can provide valuable insights into the neural control of fish behavior as well as sublethal effects of chemical and physical HAB stressors. This research was supported in part by an EcoHAB grant (#R828224-010) from the USEPA Science to Achieve Results (STAR) Program.
Key words: harmful algae, c-Fos, Fundulus heteroclitus, Fish brain