Effects of tetrahydroprotoberberines on dopamine release and 3,4-dihydroxyphenylacetic acid level in corpus striatum measured by in vivo voltammetry

The extracellular (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in rat striatum were measured by in vivo voltammetry to elucidate the effects of 3 tetrahydroprotoberberines on DA neurotransmission. l-tetrahydropalmatine (l-THP, 2 mg.kg-1) or l-stepholidine (l-SPD, 0.5 mg.kg-1) iv increased the striatal DA release by 225% and 233%, respectively; and l-SPD increased the DOPAC level by 70%. Moreover, the enantiomer d-THP (2 mg.kg-1) increased the DA release by 97%, and a large dose of d-THP (20 mg.kg-1) dramatically increased the extracellular DA by 1456% while it slightly elevated the DOPAC level by 123%. These results support the previous ideas that l-SPD and l-THP can block DA receptors and d-THP can deplete neuronal DA.