Dimethyl sulfoxide perturbs sleep-related behavioral organization in multiple species and confounds interpretation of sleep phenotypes.

INTRODUCTION: Dimethyl sulfoxide (DMSO) is a very commonly used solvent in biological research and generally considered an inert experimental vehicle. However, DMSO can alter physiological functions, raising concerns regarding its effects on behavioral phenotypes. Such concerns may be particularly important in sleep research because sleep-related behaviors are highly sensitive to physiological perturbations. METHODS: In this study, we systematically examined the effects of DMSO on sleep-related behaviors in Drosophila melanogaster and Hydra vulgaris. RESULTS: In Drosophila, DMSO dose-dependently altered nighttime sleep, increased locomotor activity, prolonged sleep latency, reduced average sleep-bout length, and increased sleep-bout number. In Hydra, 2% DMSO increased total sleep-like behavior together with an increased number of sleep bouts while reducing waking locomotor activity and sleep latency. Although the direction of total sleep changes differed between these species, both organisms exhibited disrupted sleep-related behavioral organization following DMSO exposure. Furthermore, high concentrations of DMSO induced severe physiological impairment, including a shortened lifespan in Drosophila and morphological deterioration and death in Hydra. DISCUSSION: These findings demonstrate that DMSO is not merely a passive solvent in sleep research, but a biologically active perturbant, which is capable of confounding sleep-related behavioral phenotypes in both Drosophila and Hydra. Our study highlights the importance of carefully evaluating solvent effects in behavioral and pharmacological studies of sleep.