Abstract
The photomotor response (PMR) of zebrafish embryos, a light pulse-triggered undirected movement, is known to be altered by neuroactive chemicals. Here, we developed an approach for data analysis of the distribution of PMR movement activities along the time axis; differences between treatment and respective controls are expressed by an aggregated value integrating the time-resolved density of the movement parameter as a measure for a chemically elicited PMR effect. Logistic concentration-PMR effect relationships were modeled for neuroactive test compounds with different modes of action (acetylcholinesterase inhibition, activation and inhibition of voltage-gated sodium channels); 50% effect concentrations (EC50) were in the low to medium µM range (EC50 < 10 µM for flucythrinate, esfenvalerate, azinphos-methyl, propoxur; EC50 > 10 µM for tricaine). Modulation of movement activities in different phases of the PMR (i.e., “fingerprint”) by neuroactive test compounds varied across concentrations showing that mode of action-specific PMR fingerprints are also concentration-dependent. Above 10% lethal concentrations causing 10% lethality (LC10; 48h) 3,4-dichloroaniline caused movement inhibition. This substance presumably is not neuroactive, its effect on the PMR therefore was considered as a secondary toxic effect. Quantitative morphological examinations of chemically exposed embryos showed that malformations occurred only above PMR effect concentrations, indicating that changes in the PMR were not due to such indirect effects. The PMR assay will provide useful measures in ecotoxicological risk assessment of neuroactive chemicals with zebrafish embryos and could potentially be used to infer acute fish toxicity levels from PMR effect concentrations of neurotoxic compounds.
Highlights
Acute fish toxicity (AFT) tests are the most frequently used vertebrate tests in regulatory ecotoxicology (Scholz et al, 2013)
3 Results and discussion Behavioral assays with zebrafish embryos have been suggested as an approach for identifying chemicals with neuroactive mode of action (MoA) (Kokel et al, 2010; Klüver et al, 2015) and to improve the prediction of AFT (Klüver et al, 2015)
This study focused on the analysis of the photomotor response (PMR) to address two main questions: (1) How can the time course of the PMR response be considered appropriately in the characterization and quantification of chemical effects? (2) Are PMR effect concentrations similar to AFT concentrations of neuroactive compounds, and could they be used to predict AFT?
Summary
Acute fish toxicity (AFT) tests are the most frequently used vertebrate tests in regulatory ecotoxicology (Scholz et al, 2013). When using the OA-density approach for analysis of the movement activity parameter (Selderslaghs et al, 2010) for a PMR measurement, differences between treatment and control do not become visible because the changes in movement along the time axis are not considered (Fig. 1c).
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