Motor dysfunction in Drosophila melanogaster as a biomarker for developmental neurotoxicity
Humans interact with numerous chemical compounds with direct health implications, with several able to induce developmental neurotoxicity (DNT), which bear developmental, behavioral, and cognitive consequences from a young age. Current guidelines for DNT testing are notably costly, time consuming, and unsuitable for testing large numbers of chemicals. Therefore, there is a need for adequate alternatives to conventional animal testing for neurotoxicity and DNT. Here we show that detailed kinematic analysis can provide a strong indicator for DNT, using known (chlorpyrifos, CPS) or putative ({beta}-N-methylamino-L-alanine, BMAA) neurotoxic compounds. We exposed Drosophila melanogaster to these compounds during development and evaluated for common general toxicity -- notably developmental survival and pupal positioning, together with the FlyWalker system, a detailed adult kinematics evaluation method. At concentrations that do not induce general toxicity, the solvent DMSO had a significant effect on kinematic parameters. Nonetheless, CPS not only induced developmental lethality but also significantly impaired coordination in comparison to DMSO, altering 16 motor parameters, validating the usefulness of our kinematic approach. Interestingly, BMAA, although not lethal during development, induced a dose-dependent motor decay, targeting most parameters in young adult animals, phenotypically resembling normally aged, non-exposed flies. This effect was subsequently attenuated during ageing, indicating an adaptive response. Furthermore, BMAA induced an abnormal terminal differentiation of leg motor neurons, without inducing degeneration, underpinning the observed altered mobility phenotype. Overall, our results support our kinematic approach as a novel, highly sensitive and reliable tool to assess potential DNT of chemical compounds.