Tolerance to electroacupuncture and its cross tolerance to morphine

Electroacupuncture (EA) applied to both legs of the rat for 30 min (1session) raised the average tail flick latency to 89% above the control level. Repeated electroacupuncture for 6 sessions, with 30 min between successive sessions, resulted in a gradual decline in the hypoalgesic effect. The time-course of the development and disappearance of acupuncture tolerance was studied. A bidirectional cross-tolerance between electroacupuncture and morphine points to the similarity between the underlying mechanisms of electroacupuncture hypoalgesia and morphine analgesia.