Diffuse noxious inhibitory controls in anti-nociception produced by acupuncture and moxibustion on trigeminal caudalis neurons in rats

Numerous studies have demonstrated that acupuncture and moxibustion induce analgesic effects. This study examined whether diffuse noxious inhibitory controls (DNIC) participated in acupuncture and moxibustion induced-analgesia. Single unit extracellular recordings from neurons in the trigeminal nucleus caudalis of urethane-anesthetized Wistar rats were obtained with a glass micropipette. A total of 52 single units, including 36 wide dynamic range (WDR), 5 nociceptive specific (NS) and 11 low-threshold mechanoreceptive (LTM) units were examined. During noxious test stimulation (cutaneous pinch or electrical stimulation), acupuncture, moxibustion or pinch stimulation was applied as the conditioning stimulus to the remote area of the receptive fields. When the conditioning stimulation induced rapid suppression of noxious receptive field stimulation response, examination revealed that various areas of the entire body were affected and suppression increased in an intensity-dependent manner. These features resemble DNIC phenomena. The suppression was observed on both WDR and NS neurons but not on LTM neurons. Eight of 16 WDR neurons examined were inhibited by acupuncture, five of 14 by moxibustion, and seventeen of 21 by pinching stimulation. Of the NS neurons, one of 2 units examined was suppressed by acupuncture, one of 2 by moxibustion, and two of 3 by pinch stimulation. pinch stimulation induced the most profound suppression followed by manual acupuncture. Moxibustion induced moderate suppression with a long induction time. These results suggest that DNIC may be involved in the analgesic mechanism of acupuncture and moxibustion.