Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8883671 | Aquatic Toxicology | 2018 | 8 Pages |
Abstract
Studies have shown that olfactory-mediated behaviors that are critical to survival can be disrupted by exposure to certain metals. Polluted waterways often contain elevated levels of metals, yet only a subset have been characterized for their potential to cause olfactory toxicity. A larval zebrafish behavioral assay was developed to characterize concentration-response curves for zinc (Zn), hexavalent chromium (Cr), and arsenate (As) olfaction inhibition. Cadmium (Cd), an established olfactory toxicant, was used as a positive control. As expected, following a 24-hour exposure to Cd, we observed a reduced response to taurocholic acid (TCA), a substrate for ciliated olfactory sensory neurons (OSNs), thus validating the behavioral assay. Zn exposure similarly decreased the olfactory response toward TCA, (IC50: 36â¯Î¼g/L and 76â¯Î¼g/L, for Cd and Zn, respectively). The response towards a secondary odorant L-cysteine (Cys), a substrate for ciliated and microvillous OSNs, was significantly altered by both Cd and Zn exposure, although the response to Cys was not completely removed in Zn treated larvae, suggesting preferential toxicity towards ciliated OSNs. No significant changes in olfactory responses were observed following Cr and As exposures. Exposures to binary mixtures of Cd and Zn indicated that Zn had a protective effect against Cd toxicity at low Zn concentrations. QuantiGene (QDP) RNA analysis revealed Cd to be a potent inducer of metallothionein 2 (mt2) mRNA in zebrafish larvae, and Zn to be a weak mt2 inducer, suggesting a protective role of mt2 in Cd and Zn olfactory injury. By contrast, QDP analysis of eight other genes important in mitigating the effects of oxidative stress suggested an antioxidant response to Cd, but not Zn, As, and Cr suggesting that oxidative stress was not a primary mechanism of Zn-induced olfactory dysfunction. In summary, our study indicates that Zn inhibits zebrafish olfaction at environmental concentrations and may potentially mitigate Cd induced olfactory dysfunction when present in mixtures. The zebrafish behavioral trough assay incorporating the odorants L-cysteine and TCA is an effective assay to assess the effects of metals on olfactory function.
Keywords
SOD1NAD(P)H dehydrogenase, quinone 1Prdx1Trpc2HPRT1GSTPGCLCNQO1SOD2OMPhsp70SRPGAPDHMORDPFNrf2TCAArsenicTaurocholic acidolfactory epitheliumdays post fertilizationolfactionAntioxidant gene expressionOSNolfactory sensory neuronOlfactory sensory neuronsZincMetalsglutamate-cysteine ligase, catalytic subunitMetallothioneinHypoxanthine phosphoribosyltransferase 1Peroxiredoxin 1olfactory bulbCadmiumChromiumGlutathione S-transferase Piglyceraldehyde-3-phosphate dehydrogenaseZebrafisholfactory receptor
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Authors
Kevin Heffern, Keith Tierney, Evan P. Gallagher,