Warm needle acupuncture at Pungsi (GB31) has an enhanced analgesic effect on formalin-induced pain in rats

Warm needle acupuncture (WNA) therapy combines the effects of acupuncture and heat produced by moxibustion. This therapy has been widely used in Korean traditional medicine to treat a number of health problems. We evaluated the analgesic effect of WNA treatment on formalin-induced pain behavior and c-Fos expression in the spinal cord of rats. Acupuncture and heat stimulation by moxibustion were performed at the Pungsi (GB31) acupoint. Needle insertion without heat stimulation (ACU) and heat stimulation without needle insertion (SWNA) were used as negative controls. WNA therapy was executed by burning 1.5 g of cylinder-shaped moxa on top of the needle that was inserted at the acupoint. We measured temperatures of two different locations on the needle using an automatic temperature-acquisition system. Needle temperatures were overwhelmingly dependent on the distance from moxa while burning and showed a maximum of 44.9 °C at the location 7 mm apart from the ground after ignition. WNA treatment was more effective than ACU or SWNA in alleviating pain during the late phase in the rat formalin test. WNA, ACU, and SWNA significantly reduced c-Fos expression in the superficial dorsal horn by 23.5, 28.3 and 19.4%, respectively.