Objective Recently numerous of epidemiological data have proven that physical activity or regular exercise beneficially affects brain function and increases neuronal development, but the mechanisms of exercise has not been clear.Rho GTPases act as the central regulators of cytoskeleton and function as binary molecular switches.In this family, RhoA, Rac 1 and Cdc42 have been characterized most extensively.Recently, the role of Rho GTPases in neuronal development has been studied.Therefore, the aim of this study was to investigate the effects of 8 weeks treadmill exercise on the Rho GTPases in the rat special brain regions.Methods 3 months male Wistar rats were randomly assigned to either a sedentary or a treadmill exercise group.Exercised rats were familiarized to treadmill exercise for 5 days, then ran 30 min/day at 10m/min on a 5% slope for the first 2 weeks.The running speed and duration of the exercise were gradually increased, up to 60 min/day at 22 m/min on a 10% slope for 6 weeks.All rats were killed 48 h after the last exercise session.The levels of synaptophysin in the cortex and hippocampus were separately detected with the ICH and IF method, which has been widely used to assess synapse density.Furthermore, the protein levels of RhoA, Racl and Cdc42 were measured using Western blotting and the mRNA levels were measured using real time PCR.Data were analyzed using one-way analysis of variance (ANOVA).The level of statistical significance was set at P<0.05.Results (1) The increase of synapse density appeared in both cortex (P<0.05) and hippocampus (P<0.05) in exercised groups compared with sedentary groups.(2) Exercise decreased the protein levels of RhoA in both cortex (P<0.01) and hippocampus (P<0.01), at the same time increased the mRNA levels in both cortex (P<0.001) and hippocampus (P<0.001).(3) Exercise increased the protein levels of Racl in both cortex (P<0.01) and hippocampus (P<0.01).Exercise increased the mRNA level of Racl in cortex (P<0.01) but decreased the mRNA level in hippocampus (P<0.01).(4) Exercise increased the protein level of Cdc42 in cortex (P<0.01), but decreased the protein level in hippocampus (P<0.01).While exercise decreased the mRNA level of Cdc42 in cortex (P<0.05), increased the mRNA level in hippocampus (P<0.001).Conclusion 8 weeks treadmill exercise results in an increased level of synapse density in the cortex and hippocampus.And the expressions and transductions of RhoA, Rac 1 and Cdc42 can be mediated by exercise, which may be an important molecular mechanism of exercise-induced neuronal development.The results also suggest that there exists a different biochemical pattern for the effects of exercise on the neuronal developmem in special brain regions.Furthermore investigations on this mechanism are needed.