Behavioural and physiological impacts of varying doses of methotrexate on Drosophila melanogaster.

This study investigates the in vivo effects of different doses of the common immunosuppressive drug methotrexate (MTX) on the behaviour, morphology, and development of Drosophila melanogaster. Drosophila first instar larvae were exposed to different doses of MTX (10, 20, 30, 40, 50, 60, and 100 µg/mL) in the diet until the flies emerged. To study the behavioural parameters, larval crawling assay, larval temperature sensitivity, pupation height, and negative geotaxis assays were performed. Fecundity rate, gut damage, and morphological changes were also studied in all dose groups. It was observed that exposure to MTX resulted in a dose-dependent significant decrease in temperature sensitivity, larval crawling speed, and trailing path as compared to the control. Furthermore, the results in comparison to the control indicated that higher doses of MTX exerted a cytotoxic effect on third instar larvae, resulting in gut damage. There was a significant reduction in the pupation height in MTX-treated groups, indicating that larval locomotion was affected. Adult flies that emerged following MTX treatment displayed minor phenotypic anomalies, impaired geotaxis behaviour, and poor reproductive performance as evident from reduced fecundity. Thus, it is concluded that MTX has a dose-dependent effect on various physiological and behavioural parameters of Drosophila, especially neuromuscular activity as apparent from the larval crawling assay, reduced pupation height, and negative geotaxis. The findings of this study provide insights into the effects that MTX has on the health and behaviour of the model organism D. melanogaster, which can further be explored using other animal models.