Microdialysis monitoring of methylphenidate in blood and brain correlated with changes in dopamine and rat activity.

Methylphenidate (MPD), also called Ritalin, changes the extracellular levels of dopamine (DA) in the brain. This study coupled multiple-site microdialysis sampling with appropriate analytical methods to simultaneously profile the MPD concentration in blood and brain, while monitoring changes in the extracellular level of DA in the striatum of awake and freely moving rats. The animals' activity was also recorded. The maximum concentration of MPD in the blood and brain occurred during the first 20 min of sampling. The maximum DA concentration was reached in the first 20 min and gradually returned to the basal level after 3 h. The activity peak correlated well with the MPD and DA peaks and remained elevated for about 2.5 h. The ability to obtain and correlate data in this manner has the potential to reduce the number of animals required for a given study and to minimize interanimal variation.