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

Abstract

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. 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. 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 (P<0.01，P<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 (P<0.01，P<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 (P<0.001). EA can suppress morphine-induced seeking behavior in rats, which may be related to its inhibitory effect on glutamatergic neurons in the VMPFC.