The Nicotine-Evoked Locomotor Response: A Behavioral Paradigm for Toxicity Screening in Zebrafish (Danio rerio) Embryos and Eleutheroembryos Exposed to Methylmercury

Abstract

This study is an adaptation of the nicotine-evoked locomotor response (NLR) assay, which was originally utilized for phenotype-based neurotoxicity screening in zebrafish embryos. Zebrafish embryos do not exhibit spontaneous swimming until roughly 4 days post-fertilization (dpf), however, a robust swimming response can be induced as early as 36 hours post-fertilization (hpf) by means of acute nicotine exposure (30–240μM). Here, the NLR was tested as a tool for early detection of locomotor phenotypes in 36, 48 and 72 hpf mutant zebrafish embryos of the non-touch-responsive maco strain; this assay successfully discriminated mutant embryos from their non-mutant siblings. Then, methylmercury (MeHg) was used as a proof-of-concept neurotoxicant to test the effectiveness of the NLR assay as a screening tool in toxicology. The locomotor effects of MeHg were evaluated in 6 dpf wild type eleutheroembryos exposed to waterborne MeHg (0, 0.01, 0.03 and 0.1μM). Afterwards, the NLR assay was tested in 48 hpf embryos subjected to the same MeHg exposure regimes. Embryos exposed to 0.01 and 0.03μM of MeHg exhibited significant increases in locomotion in both scenarios. These findings suggest that similar locomotor phenotypes observed in free swimming fish can be detected as early as 48 hpf, when locomotion is induced with nicotine.

Mercury-induced epigenetic transgenerational inheritance of abnormal neurobehavior is correlated with sperm epimutations in zebrafish

“…Refer to the studies of Mora-Zamorano et al . [ 29 , 30 ] for a diagram and further description of the behavioral observation chamber. The fish were acclimated for 5 minutes and then the spontaneous locomotion ( i .…”

Zebrafish Larvae as a Behavioral Model in Neuropharmacology

“…The light-dark locomotion test in zebrafish larvae is also used to study the developmental neurotoxicity of metals, metallic ions, and metallic nanoparticles, such as methylmercury, copper, and silver [91,94,95,114]. Methylmercury is a known neurotoxicant and it decreases locomotion in zebrafish larvae [114].…”

“…The light-dark locomotion test in zebrafish larvae is also used to study the developmental neurotoxicity of metals, metallic ions, and metallic nanoparticles, such as methylmercury, copper, and silver [91,94,95,114]. Methylmercury is a known neurotoxicant and it decreases locomotion in zebrafish larvae [114]. Although the mechanism of action is unknown, this effect is similar to that observed in rodents, where it also decreases the locomotor activity [115] and exploratory activity [116].…”

Developmental Methylmercury Exposure Affects Swimming Behavior and Foraging Efficiency of Yellow Perch (Perca flavescens) Larvae

“…The direct waterborne MeHg exposure of zebrafish embryos, per procedures analogous to those in the present yellow perch study, also caused hyperactivity. 32 These differences in behavioral outcomes may be attributable to not only the inherent distinctions between species but also exposure duration and critical windows of exposures during development. These observations underline the current difficulties of estimating the effects of environmental contaminants on nonmodel organisms on the basis of data collected from model organisms; thus, an effort must be made to match experimental conditions when analyzing behavioral end points in different species of organisms.…”

“… 35 , 36 This direct exposure method using newly fertilized embryos is intended to mimic the maternal transfer of MeHg to the offspring and is a common exposure procedure for chemical toxicity assays in zebrafish embryos. 32 , 37 The yellow perch embryos remained in the exposure solutions incubated at 10 °C for 20 h, after which all dishes were rinsed three times with fresh 10 °C E2 medium to stop any further MeHg exposure. Once the eggs were thoroughly rinsed, they were kept in fresh E2 medium and returned to the incubator; the E2 medium was exchanged daily.…”