Repeated Oral Methylphenidate Administration Evokes Changes in Brain Plasticity Proteins in Juvenile Wistar Kyoto Rats: Evidence for Sex-Related Differences

Methylphenidate (MPH) is first-line pharmacotherapy for Attention Deficit Hyperactivity Disorder (ADHD). Misdiagnosis and misuse raise concerns about exposing children and adolescents to MPH. This study aimed to assess how clinically relevant oral doses of MPH influence the expression of brain proteins involved in synaptic plasticity and neuronal growth in both sexes. Thirty-seven Wistar-Kyoto (WKY) rats (18 males and 19 females) were divided into an MPH group (daily oral dose of 5 mg/kg MPH in a 5% sucrose solution) and a control group (equivalent volume of 5% sucrose solution). Daily gavage administration started on postnatal day (PND) 15 and lasted for 15 days, with sacrifice at PND 30. In five brain regions [prefrontal cortex (PFC), striatum, hippocampus, cerebellum, and diencephalon], GAP43, GAPDH and PSD-95 levels were measured by Western blot. Additionally, MAP2 and synaptophysin levels were assessed in the PFC, motor cortex, ventral and dorsal striatum, and hippocampus (including CA1, CA3, hilus, and dentate gyrus) using immunohistochemistry.In MPH-treated males, GAP43 and synaptophysin levels were reduced in the cerebellum and CA1 region, respectively, while PSD-95 and GAPDH levels increased in the striatum and diencephalon. MPH-treated females showed only a significant decrease in PSD-95 levels in the PFC. Regarding MAP2 levels, no significant changes were observed in any of the analyzed regions or sexes. In control animals, males exhibited higher MAP2 levels in the striatum compared to females. In conclusion, MPH in healthy rats can alter proteins associated with synaptic plasticity differently, highlighting the importance of sex as a variable.