Tail Coiling Assay in Zebrafish (Danio rerio) Embryos: Stage of Development, Promising Positive Control Candidates, and Selection of an Appropriate Organic Solvent for Screening of Developmental Neurotoxicity (DNT)

It is relatively recent that tail coiling assay in zebrafish (Danio rerio) embryos has been proposed as an alternative method to screen for developmental neurotoxicity (DNT) induced by chemicals. Despite the considerable use of the method, there is no consensus related to the most suitable age of embryos and other experimental parameters. Non-exposed embryos were videotaped for tail-coiling activity from 18 to 54 h post-fertilization (hpf) and after exposure to positive control candidates (caffeine, fluoxetine, and tricaine (MS-222)) and organic solvents (acetone, dimethyl-sulfoxide (DMSO), and ethanol) from 26.0 to 28.5 hpf. Results demonstrated that embryos from 22 to 29 hpf presented a constant coiling activity, with no significant differences between the activity measurements. We also found that stimulant properties of caffeine and the anesthetic effects of MS-222 induced hyperactivity and hypoactivity, respectively. Finally, even using DMSO at 1%, it seems to be safer as a solvent for neurotoxicity evaluation by tail coiling assay. The period from 26.0 to 28.5 hpf was appropriate for a fast protocol of tail coiling assay. Caffeine and MS-222 were demonstrated to be promising positive control candidates, whereas DMSO was considered the most appropriate solvent choice for tail coiling assay.