Effects of the antidepressant mirtazapine on the swimming behaviour and gene expression rate of Danio rerio embryos - Is the sedating effect seen in humans also evident for fish?

In the last decade, mirtazapine has become an important antidepressant in clinical use and has also been found at many different environmental sampling sites. Several homologies between the zebrafish Danio rerio and humans, combined with a number of advantages for behavioural and gene expression research using zebrafish embryos, make their use for the analysis of mirtazapine appropriate. The sedative effect of mirtazapine in humans was also found for a specific concentration range in zebrafish embryos (1333.4 μg/L - 2666.9 μg/L). Specifically, 116 hpf old zebrafish embryos showed a reduced swimming distance when exposed to 1334.4 μg/L mirtazapine. Furthermore, changes at the gene regulatory level could be measured (1333.4 μg/L), in particular in the superordinate regulatory systems. For selected transporters of all regulatory systems, an up regulation of the genes by a factor of more than five times could be measured at the highest mirtazapine exposure concentration that was tested. Finally, studies on the protein levels demonstrated an increase in acetylcholinesterase activity for several exposure concentrations (83.3 μg/L and 666.7 μg/L). The physiological changes in zebrafish embryos caused by mirtazapine demonstrate the relevance of these types of studies in aquatic non-target organisms. Such neuroactive substances could pose a potential risk for aquatic organisms below the previously considered concentration threshold for morphological effects.