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Detecting Developmental Neurotoxicants Using Zebrafish Embryos
Citation:
COWDEN, J., D. L. HUNTER, B. K. PADNOS, K. F. JENSEN, R. C. MACPHAIL, AND S. J. PADILLA. Detecting Developmental Neurotoxicants Using Zebrafish Embryos. Presented at TestSmart DNT 2 Developmental Neurotoxicity Meeting, Reston, VA, November 12 - 14, 2008.
Impact/Purpose:
NA
Description:
As part of EPA’s program on the screening and prioritization of chemicals for developmental neurotoxicity, a rapid, cost-effective in vivo vertebrate screen is being developed using an alternative species approach. Zebrafish (Danio rerio), a small freshwater fish with external fertilization, develop rapidly (3-4 days) in an optically clear chorion allowing visual inspection throughout development. The screen consists of four general endpoints: death, teratology, nervous system structure and locomotor activity. To examine endpoint sensitivity and specificity of the screening approach, zebrafish embryos were exposed to either valproate or saccharin. Valproate is a potent teratogen and developmental neurotoxicant in mammals, whereas current evidence does not demonstrate neurotoxic outcomes following developmental saccharin exposure. Zebrafish embryos were exposed to a wide dose range (0.4 µM to 400 µM) from 6 hours post fertilization to 5 days post-fertilization (dpf). At 2 dpf embryos underwent whole mount anti-acetylated α-tubulin staining; at 6 dpf, animals were assessed for death, teratology, and locomotor activity. Valproate doses under 400 µM did not induce any lethality. Saccharin was not lethal at any dose tested. Valproate produced dose-dependent terata in developing zebrafish embryos, including nervous system terata such as microphthalmia and microencephaly. At a subteratogenic dose of 20 µM, developmental valproate exposure caused transient hyperactivity and reduced retino-tectal projection area. The highest dose of saccharin (400 µM) did not induce terata nor affect retino-tectal projection area. Locomotor activity changes were obtained following developmental saccharin exposure but were neither consistent, nor dose-related. These findings demonstrate that histological and behavioral assessments in zebrafish embryos may be of value in detecting developmental neurotoxicants. This is an abstract of a proposed presentation and does not necessarily reflect Agency policy.