Tetrahydropalmatine (THP) has two enantiomers with different effects on the brain dopaminergic system. Using [~3H]spiperone for DA receptor binding assay, it was found that l-THP had an affinity to DA receptors (K_1=0.2μM). Neither d-THP nor reserpine showed such an effect even at concentrations higher than 100 or 1000μM. Based on the fact that the presynaptic DA receptors take part in feed-back regulation on tyrosiue hydroxylase activity, DOPA accumulation could be observed in rat striatum after injection of benserazide. A small dose of l-THP (2.5, 5, 10 mg/kg, ip.) caused an elevation of DOPA level by 49—282% versus the control value, and could reverse the decrease of DOPA level induced by apomorphine, a DA receptor agonist. On the contrary, d-THP displayed a biphasic effect on DOPA level, slight decrement (26—37%) at 10 and 25mg/kg, naught at 50mg/kg, and a 91% increment at 100 mk/kg, which was less than that of l-THP at 5mg/kg. Moreover, measured by pulse voltammetry, DOPAC level in the striatum Tetrahydropalmatine (THP) has two enantiomers with different effects on the brain dopaminergic system. Using [~ 3H] spiperone for DA receptor binding assay, it was found that THP had an affinity to DA receptors (K_1 = 0.2 μM) -THP nor reserpine showed such an effect even at concentrations higher than 100 or 1000 μM. Based on the fact that the presynaptic DA receptors take part in feed-back regulation on tyrosiue hydroxylase activity, DOPA accumulation could be observed in rat striatum after injection of benserazide . A small dose of l-THP (2.5, 5, 10 mg / kg, ip.) Caused an elevation of DOPA level by 49-282% versus the control value, and could reverse the decrease of DOPA level induced by apomorphine, a DA receptor agonist. On the contrary, d-THP displayed a biphasic effect on DOPA level, slight decrement (26-37%) at 10 and 25 mg / kg, naught at 50 mg / kg, and a 91% increment at 100 mk / kg , which was less than that of l-THP at 5 mg / kg. Moreover, measured by pulse voltammetry, DOPAC l evel in the striatum