Endocannabinoid mechanism for orofacial antinociception induced by electroacupuncture in acupoint St36 in rats.

INTRODUCTION: This study was conducted with the aim of evaluating whether electroacupuncture (EA) at acupoint St36 could produce antinociception through the activation of an endocannabinoid mechanism.

METHODS: Male Wistar rats were divided into experimental groups. Heat was applied to the faces of rats, and the latency to withdraw the face was measured. Furthermore, the influence of electrical stimulation (100HzP) of acupoint St36, at a 0.5mA intensity, was investigated in the facial withdrawal threshold.

RESULTS: The EA produced antinociception, which lasted for 180min. This effect was antagonized by the pre-injection of AM 251, a CB1 cannabinoid receptor antagonist, but not by AM 630, a CB2 cannabinoid receptor antagonist. Additionally, pretreatment with an endocannabinoid metabolizing enzyme inhibitor (MAFP) and an anandamide reuptake inhibitor (VDM11) prolonged and intensified the antinociceptive effect produced by EA.

CONCLUSION: This study demonstrated for the first time that the CB1 cannabinoid receptor participates in the antinociceptive effect induced by EA.