Exposure to methylphenidate during peri-adolescence affects endocrine functioning and sexual behavior in female Long-Evans rats

The present study was designed to test the effects of methylphenidate (MPH) exposure on the maturation of endocrine functioning and sexual behavior. Female rat pups received either MPH (2.0 mg/kg, i.p.) or saline twice daily between postnatal days 20-35. This period of exposure represents the time just prior to puberty as well as puberty onset. Approximately five weeks after the last injection of MPH or saline, female subjects were hormone-primed and tested during their first sexual experience. Subjects were given the choice to interact with a sexually active male or a sexually receptive female rat (i.e., the partner-preference test). The partner-preference paradigm allows us to assess multiple aspects of female sexual behavior. MPH exposure during peri-adolescence delayed puberty and, when mated for the first time, affected sexual behavior (e.g., increased time spent with the male stimulus and decreased the likelihood of leaving after mounts) during the test of partner preference. When monitoring estrous cyclicity, female subjects treated with MPH during peri-adolescence frequently experienced irregular estrous cycles. The results of the present study suggest that chronic exposure to a therapeutic dose of MPH around the onset of puberty alters long-term endocrine functioning, but with hormone priming, increases sensitivity to sexual stimuli.