Striatal dopamine turnover during treadmill running in the rat: relation to the speed of running

To evaluate the physiological action of striatal dopamine (DA) in exercise, rats were trained to run on a straight treadmill. Extracellular DA and its metabolites, dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were measured by in vivo microdialysis, and striatal tissue tyrosine hydroxylase (TH) activity and monoamine oxidase (MAO) activity were measured using high performance liquid chromatography (HPLC) and spectrophotometer. DA turnover was increased by running, and the increase in DOPAC and HVA was closely related to the speed of running, while the increase in DA had no relationship to the speed. The threshold for the increase in DA, DOPAC, and HVA was between 300 and 660 cm/min. Striatal tissue TH activity was elevated up to 135% of basal values after the rats were trained for 7 days to run at 1800 cm/min. Just after running for 20 min, there was a further increase to 180%. These values became 150% and 90% of basal values at 2 h and 6 h, showing a similar time course as DA detected by microdialysis. MAO-B activity increased up to 160% of basal values after 7 days training but decreased to 130% and 110% just after and 2 h after running, then increased to 145% 6 h after running. MAO-A showed a similar variation as MAO-B. These data suggest that both the synthesis and metabolism of DA have a close relationship with physical exercise and might contribute to adjusting extracellular DA levels within an adequate range in response to exercise intensity.