(+) anatoxin-a elicits differential survival, photolocomotor behavior, and gene expression in two alternative vertebrate models

Abstract

Anatoxin-a is a globally occurring, yet understudied, chiral cyanobacterial toxin which threatens public health and the environment. It has led to numerous dog and bird poisonings and although it has been studied in rodent models, comparatively little research has occurred in aquatic species. To advance a comparative toxicology understanding of this toxin in alternative vertebrate models, developing zebrafish and fathead minnow were exposed to environmentally relevant and elevated levels (13–4400 μg/L) of (+) anatoxin-a to examine potential mortality and sublethal effects, including photolocomotor behavior and gene expression. We observed significantly higher mortality (p < 0.05) in fathead minnows exposed to ≥ 1400 ug/L (65 – 83 % survival versus 97 % in controls). Using a ViewPoint Zebrabox, locomotor response profiles for zebrafish typically displayed hypoactivity after exposure to (+) anatoxin-a in both light and dark periods, while fathead minnows showed hyperactivity at the lowest treatment level, but only in light. Gene expression in zebrafish was significantly (p < 0.05) downregulated for mbp, which is associated with myelin sheath formation, and elavl3, which is involved in neurogenesis, along with cyp3a65 and gst, two genes related to phase I and II metabolism. However, no significant transcriptional changes were observed in the fathead minnow model. These differential responses between species highlight the need for more comparative studies to understand sensitivities and variations in organismal response. Furthermore, we identified higher mortality, refractory behavioral effects, and gene expression in (+) anatoxin-a exposed fish when compared to previously reported (±) anatoxin-a (racemic, 50:50 enantiomer mixture) studies, which is frequently used as a surrogate. Our findings highlight the importance of understanding species and enantiomer specific effects of natural toxins.