Effects of the κ-opioid receptor on the inhibition of 100 Hz electroacupuncture on cocaine-induced conditioned place preference.

The administration of 100 Hz electroacupuncture has been demonstrated to suppress cocaine-induced conditioned place preference (CPP) in rats, and there is evidence that the κ-opioid receptor may have a role in cocaine addiction. The present study sought to explore the mechanisms underlying the inhibitory effects of 100 Hz electroacupuncture on cocaine-induced CPP in rats. A rat model of cocaine-induced CPP was used in the present study to investigate the following: i) Naloxone treatment (5 and 10 mg/kg) following 100 Hz electroacupuncture-mediated inhibition on cocaine-induced CPP, revealing that a high dose (10 mg/kg) of naloxone blocked the inhibitory effects of 100 Hz electroacupuncture on cocaine-induced CPP; ii) nor-binaltorphimine (nor-BNI) on 100 Hz electroacupuncture-mediated inhibition on cocaine-induced CPP, which indicated that administration of 10 µg/5 µl and 0.3 µg/1 µl nor-BNI intracerebroventricularly and via the nucleus accumbens, respectively, reversed the inhibitory effects of 100 Hz electroacupuncture on cocaine-induced CPP, and that injection of nor-BNI in different brain areas of rats blocks the inhibitory effects of electroacupuncture on cocaine-induced CPP; and iv) 100 Hz electroacupuncture on the mRNA expression levels of the κ-opioid receptor in the rat nucleus accumbens and amygdala, which established that mRNA expression levels of κ-opioid receptor in the nucleus accumbens were increased with 100 Hz electroacupuncture plus cocaine-induced CPP. Overall, the results of the present study indicated that 100 Hz electroacupuncture was able to suppress cocaine-induced CPP via the κ-opioid receptor in the nucleus accumbens.