Data are means ± SEM. Numbers in brackets represent the number of animal/group. DSP: daily sperm production. CTR: distilled water; MPH 2.5: methylphenidate 2.5 mg/kg; MPH 5.0:methylphenidate 5.0 mg/kg. * p > 0.05 compared to CTR (ANOVA complemented with Bonferroni).