Effects of l-tetrahydropalmatine on conditioned place preference and expression of dopamine in the striatum of morphine dependent rats

Abstract

Objective To observe effects of conditioned place preference(CPP) of morphine dependent rats, variation of dopamine neurotransmitter and its receptor 2 of the striatum in rats suffered from l-tetrahydropalmatine(l-THP). Methods The CPP model was established by morphine injection in rats with a increasing dose for 10 days, with the initial dose of 10 mg·kg-1 and the final dose of 100 mg·kg-1, 10 mg·kg-1 was increased each day, thus 100 mg·kg-1 was injected by day 10. Treatments with administration of l-THP(3.76, 1.88 and 0.94 mg/kg) were performed respectively for 6 days, and the effects of CPP for psychological dependence in these rats were observed. Striatum samples were taken out and their variable contents of dopamine neurotransmitter and its receptor 2 in striatum were detected by high performance liquid chromatography and immunohistochemisty, respectively. Results Compared with the NS treatment group, the time of animals treated with l-THP(3.76 and 1.88 mg/kg) staying in drug-paired compartment were reduced(354±58, 373±79) (P<0.01); the raised of variation contents of dopamine neurotransmitter were reduced in striatum from those rats(5.49±1.95, 6.11±1.05), while the expression level of dopamine receptor 2 was increased(0.08±0.02, 0.07±0.03)(P<0.01 or P<0.05). Conclusion Reversing dopamine neurotransmitter and its receptor 2 in striatum of morphine dependent rats may be one of the possible mechanisms that l-THP effectively inhibit the effects of morphine CPP. Key words: l-tetrahydropalmatine; Morphine; Psychological dependence; Dopamine system