Treadmill exercise and methylphenidate ameliorate symptoms of attention deficit/hyperactivity disorder through enhancing dopamine synthesis and brain-derived neurotrophic factor expression in spontaneous hypertensive rats

Abstract

Attention deficit/hyperactivity disorder (ADHD) is a developmental disorder of cognition. Behavioral symptoms of ADHD are inattention, hyperactivity, and impulsivity. We investigated the effects of treadmill exercise and methylphenidate (MPH) on activity and spatial learning memory in relation to dopamine synthesis and brain-derived neurotrophic factor (BDNF) expression using spontaneously hypertensive adult male rats. The rats in the MPH-treated group received 1 mg/kg MPH orally once a day for 28 days. The rats in the treadmill exercise group were made to run on a treadmill for 30 min once a day, five times a week, for 28 days. Activity was determined by an open-field test and spatial learning memory was evaluated by an 8-arm maze test. Immunohistochemistry and Western blotting were conducted to examine the levels of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, and BDNF. The rats in the ADHD group showed hyperactivity and spatial learning memory deficit. Reduction of TH in the striatum and substantia nigra and BDNF in the hippocampus was observed of the rats in the ADHD group. Treadmill exercise and MPH alleviated the ADHD-induced hyperactivity and spatial learning memory impairment. Expressions of TH and BDNF in the ADHD rats were also increased by both treadmill exercise and MPH. These findings provide a possibility that exercise may be used as an effective therapeutic intervention for ADHD patients as MPH treatment.