Electroacupuncture(EA)has been demonstrated effective for pain relief.However

repeated application may decline analgesic effect of EA

which is termed EA tolerance

that reduces the clinical efficacy of EA.Therefore

it has attracted attention from researchers in recent years and the progresses include:(1)acute and chronic EA tolerance animal models have been established;(2)cross-tolerance between EA and morphine;(3)Anti-opioid substances

including cholecystokinin

orphanin FQ and angiotensin Ⅱ

have been reported to contribute to EA tolerance;(4)glutamate receptors and transporters

5-hydroxytryptamine and norepinephrine have been revealed involvement in EA tolerance;(5)cyclic adenosine monophosphate

cyclic guanosine monophosphate and Ca

(2+)

have been reported to be the second messengers cellularly in EA tolerance.The current EA tolerance effect lacks in-depth researches.Therefore

studies on its molecular mechanisms and signaling pathway are necessarily required.