Standard toxicological assays using the zebrafish model system evaluate lethality and teratogenicity upon exposure during the first 2 days after fertilization. We tested the biological effects of several widely used drugs on zebrafish by acute treatment for 24 h starting at late embryonic stages, between 48 and 72 h post-fertilization. For 4 out of 6 compounds, we observed a higher sensitivity of late stage zebrafish embryos for general toxicity (lethality) compared to younger embryos. Morphological defects such as edema, body curvature, delayed growth, decreased heart rate and locomotion were observed for each of the compounds tested, often at sublethal concentrations. Gene expression studies on a set of four selected genes revealed a specific regulatory pattern for the different compounds tested. Our results allow us to compare various toxicological endpoints and may contribute to the design of a rational high throughput approach using the zebrafish model.
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