Advances in the study of endocannabinoid receptors in experimental acupuncture analgesia

The endocannabinoid system, an important biological network for maintaining and balancing various functions of the human body, is involved in many physiological functions such as pain, emotion, learning and memory, etc. Among which the endocannabinoid receptors ［including type I (CB1) and type II (CB2) receptors］ play an important role in the regulation of pain and have become an important target in the mechanism research of acupuncture analgesia. CB1 is mainly distributed in the central nervous system, including the spinal cord, cerebral cortex, amygdala, insular cortex, and basal ganglia, etc. CB2 is mainly distributed in peripheral immune tissues, such as spleen, bone, skin, etc. In the central and peripheral nervous systems, acupuncture can activate CB1 and CB2 receptors respectively, which is involved in the transmission of central nociceptive signals and related transmitters as well as the peri-pheral pro-nociceptive inflammatory response, thereby alleviating the nociceptive hypersensitivity in animal models. In this paper, we systematically summarize the roles of the above mechanisms in different types of animal models (inflammatory pain, neuropathological pain, visceral pain, etc.), so as to provide new ideas for the study of the underlying mechanisms of acupuncture analgesia.