a Occurrence of the endpoint “craniofacial deformation” in zebrafish (Danio rerio) embryos exposed for 120 h to valproic acid and selected analogues. Data are given as % of affected embryos (n = 20–40). Whereas embryos exposed to 2-n-propylheptanoic acid, valproic acid, 2-ethylhexanoic acid, 4-ene valproic acid, 2-methylpentanoic acid, 2,2-dimethylvaleric acid, hexanoic acid, 4-pentenoic acid and 2-methylhexanoic acid showed an increase in the number of individuals with craniofacial deformation, embryos exposed to 2-ethylbutyric acid did not show an effect. b (a) Normal development of craniofacial structures in 120 h old zebrafish (Danio rerio) embryos. (b) Endpoint “craniofacial deformation” in zebrafish embryos after treatment with 400 µM valproic acid: lower jaws are massively reduced in extension. Area of interest outlined in red
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