Extensive researches of mesolimbic ventral tegmental area(VTA) in drug addiction have been conducted. Recently, some evidence showed that VTA is involved in morphine analgesia. However, no data show whether the mesolimbic DA pathways involve the mechanism of electroacupuncture (EA) analgesia. In this study, the effect of bilateral 6 hydroxdopmine(with desipramine)lesions of VTA on analgesi a produced by EA with different frequencies (2 Hz and 100 Hz) was examined with tail flick tests in rats. These lesions depleted dopamine. The results showed th at EA with different frequencies produced the same degree of analgesia both in s ham lesioned and lesioned rats(P>0.05) though there was some decrease of tail flick latency(TFL) in the lesioned rats,while it appeared an increase o f TFL in lesioned rats after EA and possessed the significant difference from sh am lesioned rats( P<0.05). Further study should adopt different pain m odels to explore the effect of mesolimbic DA systems in EA analgesia.
The effect of low and high freqency electroacupuncture (EA) on the cocaine cravi ng was evaluated based on conditioned place preference (CPP) paradigm. Drug ind uced CPP in animals has been considered as a model of drug craving. In the prese nt experiments, rats were trained with an injection (i.p.) of different doses of cocaine under a "biased" CPP schedule and preference scores (PSs) were recorde d on the test session and used as the indicator of preference. 2 and 100 Hz of E A were given respectively before testing, with treatment of foot shock, needle i nsertion, restriction in the holder and no treatment being as the different kind s of control. The timecourse of the effect of EA on 5 mg/kg cocaine induced CPP was also observed. The results showed: ① The PSs after saline (0.27±0.08,n=12) and 0.5 mg/kg of cocaine (0 .26±0.10, n=12) conditioning had no difference from that of natural preference (0.38±0.12, n=12) (P>0.05), while the PSs of 1 ( 0.65±0.12, n=12), 5 (0.70± 0.09, n=12) and 10 mg/kg (0. 71± 0.09, n=12) of cocaine conditioning were significantly higher than tha t of natural preference (P<0.001), indicating that the 1 mg/kg and hig her doses of cocaine can induce significant place preference, which represents c ocaine craving. ② The PSs of 0.5 mg/kg of cocaine conditioning were similar wit h each other (P>0.05, compared with initial expression of CPP) when tes ting daily for at least 10 consecutive days, indicating that the cocaine craving is maintained for a long time once acquired. ③ 100 Hz EA significantly decreas ed the PSs of cocaine conditioning (P<0.05, compared with control grou p), while the treatment of 2 Hz of EA and all other kinds of control we used did n’t (P>0.05). ④ 100 Hz EA inhibited cocaine induced CPP when tested 10, 24 and 48 hours after stimulation. The results of the present study suggest that EA inhibits the cocaine craving in a frequency specific way and the effect of one treatment of EA maintains at least 48 hours.
High rate of relapse to drug using behavior after long period of abstinence cha racterizes the behavior of experienced users of heroin and other drugs of abuse, and the relapse remains the primary problem for treatment. In the present study we built a putative animal model that mimic human relapse i.e., the reinstatement o f morph ine induced conditioned place preference (CPP) in rats. In this study, we found electroacupuncture (EA) with low frequency (2 and 2/100 Hz) could inhibit drug priming or footshock induced CPP reinstatement in rats whe n it was given 18 hours before reinstatement, and these effects were found to be naloxone reversible, suggesting a mechanism involving the activation of opioid receptors by endogenous opioid ligands; while EA with high frequency (100 Hz) h ad no effect. Pr evious studies in our lab have amply shown that low frequency (2 Hz) stimulation could increase the release of enkephalin which acts on μ and δ opioid recepto rs up the spinal level, while high frequency (100 Hz) stimulation could increase the release of dynorphin which interacts with κ opioid receptor at spinal leve l. So we concluded the effect of EA with low frequency on relapse involving a me chanism of the activation of opioid receptors by endogenous opioid ligands above the spinal level. And we suggest that EA may be used as a putative measure for the prevention of relapse to drug use in humans.
