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Larval Behavioral Toxicity Screening: Light Intensity and the Order of Stimulus Presentation Affect the Outcome
Citation:
Jarema, K., D. Hunter, AND S. Padilla. Larval Behavioral Toxicity Screening: Light Intensity and the Order of Stimulus Presentation Affect the Outcome. Presented at Aquatic Models and 21st Century Toxicology Workshop, Raleigh, NC, May 05 - 06, 2014.
Impact/Purpose:
will be presented at the Collaborative Workshop on Aquatic Models and 21st Century Toxicology, May 5-6, 2014, Raleigh, NC
Description:
The U.S. Environmental Protection Agency is screening large numbers of chemicals using 6 day old zebrafish (Danio rerio). We use a behavioral testing paradigm that simultaneously tests individual zebrafish under both light and dark conditions in a 96-well plate using a video tracking system. By controlling the duration and level of intensity of light, we are able to manipulate the locomotor activity of the fish. Our ability to manipulate different variables allowed us to explore whether the light level affected our ability to detect effects of chemical exposure on locomotor activity. Using a testing paradigm that employed a wide range of light levels (0.01 lux to 51.3 lux), we assessed the activity of larvae dosed acutely with ethanol (a known disrupter of locomotor activity). We found that the highest ethanol concentration (2% ethanol; n=46) affected activity regardless of the level of the light stimulus. The other two ethanol concentrations ( 1% or 0.5%; n=46 and 47, respectively) showed the largest hyperactive effects during the periods with the lowest light levels. At higher light levels, a completely different pattern emerged with no difference in activity between the controls (n=44) and the 0.5% ethanol group, and little to no hypoactivity in the 1% group. Moreover, the order of stimulus presentation affected the outcome: in the 0.5 lux group that followed a 0.01 lux exposure period, there was no difference in activity among the 1%, 0.5% and control groups, but if that same light level (0.5 lux) was subsequent to a much brighter light presentation (51.3 lux), the 1% ethanol group exhibited hypoactivity. Therefore, in the zebrafish locomotor test, the level of light used and the order of presentation of the stimuli will affect the sensitivity of the assay and the direction of the effect. This abstract does not reflect official Agency policy.