Deciphering the mode of action of pollutants impairing the fish larvae escape response with the vibrational startle response assay.

The escape response evoked by vibrational stimuli and its habituation, essential behaviors for fish larvae survival, can be altered by neurotoxic environmental pollutants commonly found in our aquatic ecosystems. In this study we have analyzed the suitability of the Vibrational Startle Response Assay (VSRA) to obtain mechanistic information about the mode of action (MoA) of the chemicals impairing the escape response and its habituation. As a proof of concept, the pathophysiological mechanisms behind the action of two common neurotoxic pesticides, chlorpyrifos-oxon (CPO) and imidacloprid, over their effects on arousal and habituation of the escape response were studied by using pharmacological antagonists of the nicotinic and muscarinic acetylcholine receptors, mecamylamine (MCA) and scopolamine, respectively. Furthermore, potential changes in the neurotransmitter profile were analyzed. Results revealed that whereas the effect of CPO on arousal was mainly mediated by the activation of nAChRs, its effect on habituation was mainly mediated by mAChRs. On the other hand, imidacloprid only affected larvae arousal which was found to be mediated by a cholinergic independent mechanism. No association between behavioral effects on arousal or habituation in affected larvae was found with their corresponding neurotransmitter profile. These results confirm the suitability of VSRA to provide mechanistic information about the potential MoA of neuroactive compounds.