Suppression of the tail flick reflex by electroacupuncture delivered at the intra- and extrasegmental needling points

Electroacupuncture effects conveyed by A beta afferent nerve impulses from the different dermatomes, the Zusanli and the Hoku, was compared using the tail flick reflex in lightly anesthetized rats. The Zusanli stimulation decreased the EMG activity, but the threshold temperature did not change. These effects were not antagonized by naloxone (1 mg/kg). The Hoku stimulation also produced the suppression of the EMG activity without the increase of the threshold temperature. However, these effects were antagonized by naloxone (1 mg/kg). These results suggest that intrasegmental stimulation presynaptically inhibits the input of the noxious message in the spinal cord through the non-opiate system, while extrasegmental stimulation presynaptically inhibits this input through the opiate system.