5-HT content in medulla oblongata plus pons and DA level in brain stem obviously increased, while NA concentration in telencephalon markedly decreased in EAA. A previous injection of naloxone, a blocker of opiate receptor, could partially inhibit the EAA, abolish the effects of EA's increasing the 5-HT content in the medulla oblongata plus pons and the DA level in the brain stem, and decrease the NA level in the diencephalon after EA. These results indicate that EA may mediate the metabolism of the central monoamine neurotransmitters partially via opiate receptor to exert its analgesic effect.