Localization of central structures involved in descending inhibitory effect of acupuncture on viscero-somatic reflex discharges.

The pain reaction provoked by visceral traction has been one of the main problems to be solved in acupuncture anesthesia. By means of recording the viscero-somatic reflex activity in the animals, we have found that this reflex activity can be inhibited by acupuncture, and that the inhibitory effect originates from the supraspinal structures. The central structures involved in the inhibitory effect of acupuncture have been identified in a series of transection and lesion experiments. In decerebrated animals the inhibitory effect during acupuncture was preserved, but the after-inhibition of acupuncture disappeared; transection at the lower medulla as well as the cervical cord abolished near completely the whole inhibitory effect of acupuncture; a median lesion in the medulla including the nucleus raphe maguns resulted in a significant decrease of the inhibitory effect during acupuncture and a complete disappearance of the after-inhibition of acupuncture. The available evidence indicates that the median region of the medulla is involved in the elaboration of the inhibitory effect of acupuncture on the viscero-somatic reflex. A suggestion is thus offered that these supraspinal structures may be the essential link of the centre which is activated by acupuncture and involved in the descending inhibitory influence on the pain reaction of visceral stimulation.