[Effect of electroacupuncture on morphine-conditioned place preference and activation of glutamatergic neurons in the ventromedial prefrontal cortex in rats].

Objective: To observe the effect of electroacupuncture (EA) at "Zusanli"(ST36) and "Sanyinjiao"(SP6) on conditioned place preference (CPP) and activation of glutamatergic neurons in the ventromedial prefrontal cortex (VMPFC) of morphine-addiction rats, so as to explore its mechanisms underlying detoxification.

Methods: Thirty male SD rats were randomly and equally divided into control, model and EA groups. The rats with acquisition of morphine-induced CPP received intraperitoneal injection of morphine (10 mg/kg) in the morphine-paired chamber, once daily for 3 consecutive days, and those of the control group received intraperitoneal injection of the same dose of normal saline in saline-paired chamber. Thirty minutes before CPP acquisition training, EA (2 Hz/100 Hz, 0.5 to 1.0 mA) was applied to ST36 and SP6 for 20 min every day. The double-labeled neurons of Fos/vesicular glutamate transporter 2 (VGLUT2) in the VMPFC were detected by using fluorescent immunohistochemistry. The discharges of the VMPFC neurons were recorded by using a multi-channel microarray electrophysiological system, followed by performing a z-score standardized processing. The ratio of firing rate frequency of rats in the morphine-paired chamber/saline-paired chamber was calculated, and further statistical analysis was conducted on the data based on the standardized z-scores. The neuronal firing characteristic of glutamatergic neuron is low frequency and wide wave.

Results: Compared with the control group, the score of morphine-induced CPP and numbers of Fos, VGLUT2-positive and Fos-VGLUT2 double-labeled positive cells were significantly increased in the model group (<0.01，<0.05). After EA and in comparison with the model group, the morphine CPP score and numbers of Fos, VGLUT2-positive and Fos-VGLUT2 double-labeled cells were significantly reduced in the EA group (<0.01，<0.05). The ratio of firing rate of the VMPFC neurons in the preference chamber and the percentage of inhibitory neurons as well as the z-score were considerably lower in the EA group than in the model group (<0.001).

Conclusion: EA can suppress morphine-induced seeking behavior in rats, which may be related to its inhibitory effect on glutamatergic neurons in the VMPFC.