Figure 1.

Possible neurophysiologic mechanisms underlying acupuncture analgesia. Abbreviations: Arc, arcuate nucleus; PAG, periaqueductal grey; NRM, nucleus raphe magnus; LC, locus coeruleus; ATP, adenosine triphosphate; TRPV1, transient receptor potential vanilloid 1; 5-HT, 5-hydroxytryptamine (serotonin); NE, norepinephrine; SDH, spinal cord dorsal horn; HPA axis, hypothalamic-pituitary adrenal; COX-2, cyclooxygenase-2; PGE2, prostaglandin E2; MA, manual acupuncture; EA, electroacupuncture; RCTs, randomized controlled trials. The solid line indicates the pathway that has been shown in many studies, while the dotted line represents the pathway yet to be determined.