Comparative behavioral toxicology with two common larval fish models: Exploring relationships among modes of action and locomotor responses

Abstract

Behavioral responses inform toxicology studies by rapidly and sensitively detecting molecular initiation events that propagate to physiological changes in individuals. These behavioral responses can be unique to chemical specific mechanisms and modes of action (MOA) and thus present diagnostic utility. In an initial effort to explore the use of larval fish behavioral response patterns in screening environmental contaminants for toxicity and to identify behavioral responses associated with common chemical specific MOAs, we employed the two most common fish models, the zebrafish and the fathead minnow, to define toxicant induced swimming activity alterations during interchanging photoperiods. Though the fathead minnow (Pimephales promelas) is a common model for aquatic toxicology research and regulatory toxicology practice, this model has received little attention in behavioral studies compared to the zebrafish, a common biomedical model. We specifically compared behavioral responses among 7 different chemicals (1-heptanol, phenol, R-(-)-carvone, citalopram, diazinon, pentylenetetrazole (PTZ), and xylazine) that were selected and classified based on anticipated MOA (nonpolar narcosis, polar narcosis, electrophile, specific mechanism) according to traditional approaches to examine whether these comparative responses differ among chemicals with various structure-based predicted toxicity. Following standardized experimental guidelines, zebrafish embryos and fathead minnow larvae were exposed for 96 h to each compound then were observed using digital behavioral analysis. Behavioral observations included photomotor responses, distance traveled, and stimulatory, refractory and cruising locomotor activity. Though fathead minnow larvae displayed greater behavioral sensitivity to 1-heptanol, phenol and citalopram, zebrafish were more sensitive to diazinon and R-(-)-carvone. Both fish models were equally sensitive to xylazine and PTZ. Further, the pharmaceuticals citalopram and xylazine significantly affected behavior at therapeutic hazard values, and each of the seven chemicals elicited unique behavioral response profiles. Larval fish behaviors appear useful as early tier diagnostics to identify mechanisms and pathways associated with diverse biological activities for chemicals lacking mechanistic data.

Emerging investigator series: use of behavioural endpoints in the regulation of chemicals

“…(1) provides a connection from molecular and physiological processes to population level processes; (2) is a sensitive 'early warning signal' of chemical contamination since behavioural responses can occur at lower levels of contamination than more traditional endpoints; (3) improves the ecological relevance of environmental risk assessments due to the well-established theoretical framework and suite of tness-related endpoints underpinning behavioural studies; and (4) provides a high throughput identication of potential underlying chemical mode of actions. [8][9][10][11][12][13][14] In addition, it can be argued that from a resource and animal welfare perspective, behavioural endpoints of sufficient reliability (i.e. inherent quality and repeatability) and relevance (i.e.…”

Towards Sustainable Environmental Quality: Priority Research Questions for the Australasian Region of Oceania

“…The AOP approach has been proposed as a tool to help assess the safety of chemicals that, when coupled with robust computational toxicology, will reduce reliance on biological testing (Burden et al 2015). In fact, molecular docking (McRobb et al 2014) and quantum mechanics approaches are advancing the science beyond traditional log K ow based QSAR approaches (Kostal 2018). Also as noted above, one such attempt is the United States Environmental Protection Agency's (USEPA) ToxCast program, which employs computational and high-throughput screening (HTS) tools for prioritizing environmental contaminants (Dix et al 2006;Cote et al 2016).…”

“…Guidelines derived for individual stressors may not be sufficiently protective when ecosystems are exposed to multiple stressors. However, metabolic transformation of contaminants and other basic scientific limitations remain when extrapolating in vitro to in vivo effects and even comparing responses among the 2 most common fish models (Corrales et al 2016;Steele et al 2018). Salinization is particularly relevant to regions in Australasia, yet influences of salinity gradients on contaminants with diverse modes of action are poorly understood among species (Canedo-Arguelles et al 2018).…”

“…Also as noted above, one such attempt is the United States Environmental Protection Agency's (USEPA) ToxCast program, which employs computational and high-throughput screening (HTS) tools for prioritizing environmental contaminants (Dix et al 2006;Cote et al 2016). In fact, molecular docking (McRobb et al 2014) and quantum mechanics approaches are advancing the science beyond traditional log K ow based QSAR approaches (Kostal 2018).…”

“…Unprecedented opportunities are emerging with use of high-throughput in vitro, transgenic fish lines, and in situ toxicogenomic platforms when coupled with targeted and nontargeted chemical analyses (Bradley et al 2017) in the field Bradley et al 2017;Perkins et al 2017). However, metabolic transformation of contaminants and other basic scientific limitations remain when extrapolating in vitro to in vivo effects and even comparing responses among the 2 most common fish models (Corrales et al 2016;Steele et al 2018). Advancing AOP efforts for mixtures and predictive modeling of these complex lowlevel constituents will be important.…”