[The action of medullary tail-flick related neurons in electroacupuncture analgesia]

Three types of cells, i.e., off-neurons, on-neurons and neutral neurons, could be recorded in the rostral ventromedial medulla (RVM) in light anesthetized rats. Just prior to the occurrence of tail flick elicited by noxious heat, the on-cells showed a burst of activity while the off-cells exhibited a cessation of discharge. No change of neutral cell activity related to tail flick was observed. Electroacupuncture at two "Ci Liao" points which resulted in inhibition of tail-flick reflex affected the spontaneous activity of off- and on-cells in a different way, i.e, the discharge of most off-cells was significantly increased (P < 0.001), while that of on-cells showed no obvious change (P > 0.05). Tail-flick related responses of the both cells were inhibited. These results provide the evidence that the off-cells may be the main efferent neurons in RVM involving in electroacupuncture analgesia.