Cadmium (Cd) is a toxic metal known to accumulate in and have adverse effects on the olfactory systems of fish. The objective of this project was to investigate the effect of cadmium on zebrafish larvae, specifically the effects on the olfactory system at cellular and functional levels. Zebrafish larvae (72 hours post fertilization) were exposed to sublethal concentrations of cadmium (0.5, 1, 5, and 10 µM) for 96 h. Whole-body cadmium accumulation during this exposure period as quantified using GFAAS (graphite furnace atomic absorption spectroscopy) was found to increase with both exposure length and concentration. Using a transgenic strain of hsp70/eGFP (heat shock protein 70/enhanced green fluorescent protein reporter gene) zebrafish, dose-dependent induction of the heat shock response was observed in the olfactory epithelium. Expression of hsp70/eGFP in the olfactory epithelium was a highly sensitive biomarker for the effects of cadmium in the olfactory system with a lowest observed effects concentration (LOEC) of 0.5 µM Cd. Strong induction of the transgenic reporter gene correlated closely with cell death (LOEC of 5 µM Cd) and histological alterations (LOEC of 1 µM Cd) in the olfactory epithelium of zebrafish larvae following cadmium exposure. Additionally, loss of sensory cilia from the surface of the olfactory epithelium was observed in larvae exposed to 5 and 10 µM Cd. Furthermore, behaviour tests to assess olfactory function revealed sensory deficits, likely due in part to the cadmium-induced degeneration of the olfactory epithelium (p<0.05 for 1 µM; p<0.001 for 5 and 10 µM Cd). <p>To determine if cadmium was entering the cells of the olfactory epithelium by acting as a calcium (Ca) antagonist, zebrafish larvae were co-exposed to 1, 5, or 10 µM Cd with 1 or 5 mM Ca for 96 h. Whole-body cadmium accumulation as quantified using ICP-MS (inductively coupled plasma mass spectrometry) was decreased in larvae co-exposed to cadmium and calcium. Additionally, induction of the heat shock response was reduced in the presence of increasing calcium co-treatment. These ameliorating effects of calcium were further revealed in cell death and histological analyses of the olfactory epithelium. Also, larvae co-exposed to cadmium and calcium exhibited greater olfactory sensory function compared to larvae exposed to cadmium only. Significant increases in aversion response were observed in larvae exposed to 5 µM Cd with 1 and 5 mM Ca (p<0.05). These results indicate that cadmium gains entry to the olfactory epithelium via calcium uptake systems, wherein it causes damage to the olfactory system and can lead to sensory impairment.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-05302008-131554 |
| Date | 05 June 2008 |
| Creators | Matz, Carlyn Janel |
| Contributors | Rawlings, Norman C., Kulyk, William M., Krone, Patrick H., Hontel, Alice, Blakley, Barry R., Weber, Lynn P. |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-05302008-131554/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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