Effects of sub-chronic methylphenidate on risk-taking and sociability in zebrafish (Danio rerio).

Attention deficit hyperactive disorder (ADHD) is the most common psychiatric disorder in children affecting around 11% of children 4-17 years of age (CDC 2019). Children with ADHD are widely treated with stimulant medications such as methylphenidate (Ritalin®). However, there has been little research on the developmental effects of methylphenidate on risk-taking and sociability. We investigated in zebrafish the potential developmental neurobehavioral toxicity of methylphenidate on these behavioral functions. We chose zebrafish because they provide a model with extensive genetic tools for future mechanistic studies. We studied whether sub-chronic methylphenidate exposure during juvenile development causes neurobehavioral impairments in zebrafish. Methylphenidate diminished responses to environmental stimuli after both acute and sub-chronic dosing. In adult zebrafish, acute methylphenidate impaired avoidance of an approaching visual stimulus modeling a predator and decreased locomotor response to the social visual stimulus of conspecifics. Adult zebrafish dosed acutely with methylphenidate demonstrated behaviors of less retreat from threatening visual stimuli and less approach to conspecifics compared with controls. In a sub-chronic dosing paradigm during development, methylphenidate caused less robust exploration of a novel tank. In the predator avoidance paradigm, sub-chronic dosing that began at an older age (28 dpf) decreased activity levels more than sub-chronic dosing that began at earlier ages (14 dpf and 21 dpf). In the social shoaling task, sub-chronic methylphenidate attenuated reaction to the social stimulus. Acute and developmental methylphenidate exposure decreased response to environmental cues. Additional research is needed to determine critical mechanisms for these effects and to see how these results may be translatable to neurobehavioral toxicity of prescribing Ritalin® to children and adolescents.