Daphnia magna: a viable, alternative model for Parkinson’s research

Abstract

Objective: Despite a high level of toxicity, Paraquat is a widely used herbicide. Respiratory failure is the most severe consequence of acute poisoning, but a mechanistic link was also established to Parkinson’s disease (PD). Consequently, paraquat has become a reference neurotoxin used to induce Parkinson’s in experimental models, particularly mice. However, given the increasing restriction on the use of mammals in basic research, alternative models for PD research are needed. In line with this, we explored the possibility to use the invertebrate crustacean Daphnia magna. In this work we assessed paraquat’s acute toxicity to D. magna. Methods: Paraquat acute toxicity was evaluated in D. magna neonates using the OECD Protocol No.202, with slight modifications. Neonates with less than 24h were exposed to increasing concentrations of paraquat. After 24 and 48h of exposure, immobilization was evaluated and the EC50 (concentration responsible for 50% immobilization) was calculated. Since one of PD characteristics is movement disorders, daphnids’ movement after 24 and 48h was evaluated, and the heartbeat was also monitored. Results: Overall, the results disclosed large variations in mortality with EC50 values varying widely depending on the age of neonates, from 6.95 ± 1.32 mg.L-1 for 2h-old organisms and 10.22 ± 0.13 mg.L-1 for 20h-old organisms. The heartbeat was dependent on the paraquat concentrations, with higher heartbeat rates at higher concentrations. An opposite trend was observed in the Daphnia movement, with paraquat exposure being responsible for a reduction of movements at higher concentrations. Conclusions: Daphnia magna showed sensitivity to increasing concentrations of Paraquat, as demonstrated by variations of heart frequency and perturbations of movement. However, results showed age-dependent variability. As such, even though the OECD protocol recommends that acute tests should be performed with neonates with less than 24h, our results highlight the need to narrow the age range to ensure reproducibility.