Paternal exposure to methylphenidate causes behavioral abnormalities in grandchildren

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that is widely observed from childhood to adulthood and is treated with methylphenidate (MPH) as a first-line treatment. However, recent findings indicate that the paternal environment preceding conception may influence offspring health, potentially affecting subsequent generations. Moreover, we previously reported that MPH administration to sires reduced anxiety-related behaviors and induced memory impairments in the F1 generation. Therefore, in the present study, we investigated the effects of MPH exposure to sires on development, behavior, and brain gene expression in the F2 generation to extend our previous findings and examine the range of transgenerational effects. Although MPH exposure did not affect the number of births or survival rates, the body weight of mice in the MPH group was significantly lower than those in the control group. Additionally, motor development showed transient delays in early development but normalized by the age of weaning. Behavioral analysis further revealed a pronounced reduction in anxiety-like behaviors in the MPH group, particularly in female mice, with no effect on learning or memory. Finally, transcriptome analysis of the female cortex predicted the activation of neuroplasticity-related pathways, including the S100 family and CREB signaling. Notably, MPH was not administered to male F1 mice whose fathers had been administered MPH. Therefore, the ova of females mated with F1 males were not exposed to MPH. Nevertheless, the confirmation of behavioral abnormalities in the F2 generation strongly suggests that these abnormalities may have been induced by epigenetic changes in germ cells.