Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Frontier Article Analysis of tail coiling activity of zebrafsh (Danio rerio) embryos allows for the diferentiation of neurotoxicants with diferent modes of action Florian Zindler ∗ , Franziska Beedgen, Diana Brandt, Madeleine Steiner, Daniel Stengel, Lisa Baumann, Thomas Braunbeck Aquatic Ecology and Toxicology Section, Centre for Organismal Studies, University of Heidelberg, Im Neuenheimer Feld 504, Heidelberg, D-69120, Germany ARTICLEINFO Keywords: Selective serotonin reuptake inhibitor Locomotor activity Spontaneous coiling movements Heavy metals Pesticides Acetylcholine esterase inhibitor ABSTRACT In (eco)toxicology, there is a critical need for efcient methods to evaluate the neurotoxic potential of en- vironmental chemicals. Recent studies proposed analysis of early coiling activity in zebrafsh embryos as a powerful tool for the identifcation of neurotoxic compounds. In order to demonstrate that the analysis of early tail movements of zebrafsh embryos allows for the discrimination of neurotoxicants acting via diferent me- chanisms, the present study investigated the efects of four diferent neurotoxicants on the embryogenesis (fsh embryo toxicity test) and early tail coiling movements of zebrafsh embryos. Cadmium predominantly increased the frequency of tail coiling at the late pharyngula stage. Dichlorvos delayed embryonic development and caused convulsive tail movements resulting in prolonged duration of tail coils. Embryos exposed to teratogenic con- centrations of fuoxetine and citalopram displayed absence of spontaneous tail movements at 24 h post-fertili- zation. In contrast, a non-teratogenic test concentration of citalopram decreased coiling frequency at multiple time points. Results demonstrated that the analysis of tail coiling movements of zebrafsh embryos has the potential to discriminate neurotoxic compounds with diferent primary modes of action. In addition, chemical- induced efects on coiling activity were shown to potentially overlap with efects on embryogenesis. Further studies are needed to clarify the interplay of unspecifc developmental toxicity of neurotoxic chemicals and efects resulting from specifc neurotoxic mechanisms. 1. Introduction Modern society notoriously faces pollution of the environment with industrial chemicals, heavy metals, pesticides, or pharmaceuticals (Calisto and Esteves, 2009; Grandjean and Landrigan, 2006, 2014). Chronic exposure to low concentrations of such contaminants has the potential to challenge neurological health in humans and wildlife (Grandjean and Landrigan, 2006, 2014). Regulatory attempts to ad- dress the multifaceted nature of neurotoxicity were found insufcient and it was concluded that there is a critical need for efcient, sensitive and afordable scientifc detection methods to identify the neurotoxic potential of a myriad of chemical compounds (Coecke et al., 2007; Fritsche et al., 2018; Lein et al., 2007). In addition to other promising in vitro and in vivo test methods, neurobehavioral experiments with em- bryonic zebrafsh (Danio rerio) provide relevant endpoints allowing the assessment of integrative efects at a whole-organism level including the developing nervous system (Fritsche et al., 2015). First locomotor activity of embryonic zebrafsh develops as spontaneously occurring one-sided tail coiling in the pharyngula stage at 17 h post-fertilization (hpf; Saint-Amant and Drapeau, 1998). This simple movement pattern derives from a single neural circuit located in the spinal cord (Saint- Amant and Drapeau, 2000) and can be modifed by exposure to a wide range of structurally diverse chemicals (Vliet et al., 2017). In the past, spontaneous coiling has increasingly been used to characterize efects of chemicals on the embryonic development and neuronal integrity of zebrafsh embryos upon chemical exposure (summarized in Richendrfer et al., 2014). More recently, coiling activity was examined for its suit- ability as an endpoint for the assessment of developmental neurotoxi- city (DNT). Selderslaghs and colleagues developed a new method to assess coiling activity in zebrafsh embryos (Selderslaghs et al., 2010) and verifed the specifcity and predictive power of their method by testing a set of neurotoxic and non-neurotoxic compounds (Selderslaghs et al., 2013). Velki et al. (2017) as well as Weichert et al. (2017) evaluated efects by selected compounds on coiling activity and com- pared sensitivity levels based on efective concentrations from coiling analyses and embryo toxicity tests and concluded that early coiling movements of zebrafsh can serve as a sensitive endpoint for the neu- rotoxic potential of chemicals. In contrast, Vliet et al. (2017) tested a https://doi.org/10.1016/j.ecoenv.2019.109754 Received 26 August 2019; Received in revised form 1 October 2019; Accepted 1 October 2019 ∗ Corresponding author. E-mail address: zindler@stud.uni-heidelberg.de (F. Zindler). Ecotoxicology and Environmental Safety 186 (2019) 109754 0147-6513/ © 2019 Elsevier Inc. All rights reserved. T