Altered c-Fos expression demonstrates neuronal stress in mummichog, Fundulus heteroclitus, exposed to Pfiesteria shumwayae and Chaetoceros concavicornis
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To better understand sublethal effects of harmful algal blooms (HABs) on fish, mummichog, Fundulus heteroclitus (L.), were exposed in the laboratory to varying, environmentally relevant densities of Pfiesteria shumwayae (Glasgow et Burkholder, CCMP 2089, dinoflagellate) and Chaetoceros concavicornis (Mangin, CCMP 169, diatom). Two experiments were conducted during the spring of 2003 and 2004 to quantitatively examine the effects of acute (2 h) P. shumwayae and C. concavicornis algal exposure on mummichog brain activity using c-Fos expression as a marker of altered neuronal activity. Brains from HAB-exposed fish were removed, sectioned, and stained using immunocytochemistry prior to quantifying neuronal c-Fos expression. Fish exposed to P. shumwayae and C. concavicornis showed increased c-Fos expression compared to unexposed control fish. A significant dose-response relationship was observed, with increased labeling in brains of fish exposed to higher cell densities for both HAB species tested (P ≤ 0.01). Increased labeling was found in the telencephalon, optic lobes, midbrain, and portions of the medulla. The greatest increases in expression were observed in the telencephalon of P. shumwayae-exposed fish, and in the telencephalon and optic lobes of C. concavicornis-exposed fish (P ≤ 0.01). These increases in c-Fos expression are consistent with other physical and chemical stress exposures observed in fish. Neuronal stress, evidenced by c-Fos expression, demonstrates a sublethal effect of exposure and changes in brain activity in fish exposed to HAB species.
KeywordsOptic Lobe Optic Tectum Exposed Fish Fundulus Heteroclitus Sublethal Exposure
Portions of this study were supported by the U.S. Environmental Protection Agency, Science to Achieve Results (STAR) program (#R82-8224), the Maryland Department of Health and Mental Hygiene, and the Centers for Disease Control and Prevention. The authors thank N. Snyder, A. Miller, and C. Squyars, for their assistance with the brain processing and data collection. We also thank R. Andersen, Bigelow Marine Laboratory, for providing the C. concavicornis cultures. Reported experiments complied with regulations set by the Institutional Animal Care and Use Committee of the University of Maryland (Protocol R-00-36B) and VIMS (IACUC protocol 0129, IBC protocols 9906 & 0206).
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