Threshold changes of the jaw-opening reflex by the impulses of afferent nerve fibers for conveying electroacupuncture analgesia in rats.

The effects of the conditioning electrical stimuli applied directly to the nerves (45 Hz, 0.1 ms, 15 min) innervating the meridian points of Yin-Hsiang (infraorbital nerve), Ho-Ku (radial nerve) and Zu-Sanli (common peroneal nerve) on the pulp-evoked jaw-opening reflex were investigated in the Wistar albino rats. The threshold change of the digastric electromyogram activity in the reflex was monitored during and after the conditioning stimulation. There was a gradual change in the threshold and the effect remained for several minutes after the cessation of the conditioning stimulation. In case of stimulating each ipsilateral nerve, the effective degree was 210 to 260% of the control. On the other hand, when each contralateral nerve was stimulated, the degree was 170 to 200% of the control. The reflex was also evoked by the low intensity of the direct infraorbital nerve stimulation. The threshold value of this reflex was not altered by the conditioning stimulation of each nerve.