Analysis of neurotransmitters in Daphnia magna affected by neuroactive pharmaceuticals using liquid chromatography-high resolution mass spectrometry.

Neurotransmission plays an essential role during the central nervous system (CNS) development. During the last years, several studies based on the changes produced in neurotransmitters of aquatic organisms caused by pharmaceuticals have been reported. Daphnia magna, the aquatic ecotoxicological model organism, shares several of the neurotransmitters targeted by antidepressant and other neuro-active drugs with vertebrates. Therefore, a method based on liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) has been applied for the first time to study the levels of 41 neurotransmitters in Daphnia magna under the effect of four different neuro-active pharmaceuticals (sertraline, venlafaxine, duloxetine and fluoxetine). In addition, the performance of LC-HRMS was studied in terms of linearity, sensitivity, intra- and inter-day precision, and overall robustness. The developed analytical method using LC-HRMS is a new tool for neurotoxicology research using the Daphnia magna model. As a result, general differences on the concentrations of those neurotransmitters exposed to the mentioned pharmaceuticals were observed.

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.