Roles of levo-tetrahydropalmatine in modulating methamphetamine reward behavior

Levo-tetrahydropalmatine (l-THP), as an alkaloid purified from the traditional Chinese herbal medicine Corydalis and Stephania, has been widely used to produce many traditional Chinese herbal preparations. The effect of l-THP on methamphetamine-induced reward learning still remains unclear although it has been proved to be effective on treating allodynia and drug addiction. This experiment has been designed to examine the effect of l-THP on the acquisition, expression, extinction, and reinstatement of methamphetamine-induced conditioned place preference (CPP) in mice. The results show that methamphetamine (METH) could induce CPP in mice at doses of 0.5 mg/kg, 1.0 mg/kg and 2.0 mg/kg respectively, but l-THP alone could not do so. Meanwhile, l-THP could not induce conditioned place aversion at doses of 1.25 mg/kg to 20.0 mg/kg in mice, but it could attenuate the acquisition and expression of METH-induced CPP and facilitate the extinction of METH-induced CPP in mice. Besides, l-THP could inhibit the reinstatement of METH-induced CPP at the dose of 10.0 mg/kg whether it was given in the extinction training phase or 30 min before the reinstatement. These results suggest that l-THP can globally suppress the rewarding properties of METH on all phases of the CPP task and it may have potential effects on the treatment of METH abuse.