Individual and combined effects of physical exercise and methylphenidate on orienting behavior and social interaction in spontaneously hypertensive rats.

This study determined the duration of exercise and amount of methylphenidate that is needed to affect attentional function and social behavior in spontaneously hypertensive rats (SHR), a commonly used animal model of Attention-Deficit/Hyperactivity Disorder (ADHD). Attention was assessed by measuring the orienting response to repeated presentations of a nonreinforced visual cue. Social behavior was examined by allowing rats to freely explore a large arena containing an unfamiliar conspecific rat. Consistent with their hyper-responsive phenotype, nonexercising SHRs exhibited a high level of orienting behavior and little habituation, as well as hyper-social behavior compared with normo-active rats. Exercise or methylphenidate decreased orienting behavior and social behavior in a dose-dependent fashion. In addition, we found an additive effect of combining doses of exercise and methylphenidate that alone were ineffective in altering behavior. These data indicate that physical exercise and methylphenidate can reduce hyper-responsiveness to irrelevant stimuli and reduce hyper-social behavior in SHR. Moreover, subthreshold doses of methylphenidate can be used in combination with moderate amounts of exercise to reduce distractibility, supporting the notion that exercise may be useful as an adjunctive or replacement therapy in ADHD.