Objective: To determine if chronic morphine treatm ent affects the rat’s learni ng-memory ability and the induction of long-term potentiation (LTP) of hippoca mpal CA3 region

and to examine if electroacupuncture (EA) can improve learning -memo ry and LTP in morphine-dependent rats. Methods: 64 SD rats wer e randomized into co ntrol

morphine-abstinence model

EA-one-session and EA-multi-session grou ps. Mo rphine-abstinence model was established by i.p. of hydrochloride morphine. EA ( 2 Hz

1～3 mA

30 min) was applied to bilateral “Zusanli”(ST 36) and “Sany injiao”( SP 6)

once and multiple times. The rats’ passive and active avoidance reaction s in a compartment equipped with a grid floor through which an electric shock (40 V) was delivered were used as the indexes of learning-memory. The population spi ke (PS) was recorded from pyramidal cells of CA3 in vivo

following stimulation of lateral perforant path in control and morphine-abstinence rats. For the ind uc tion of LTP

4 trains (50 shocks/train

500 Hz) high-frequency tetanic stimula tio ns were applied to lateral perforant path. Results: Results i ndicated that the attack times of morphine withdrawal syndrome of EA-one-session group at 24 h and EA-multi-session group at 24 h

48 h and 72 h times were significantly fewer than t hose of morphine-abstinence model group (P<0.05). Passive expe riments displayed that the latency values of platform leaving of EA-one-session and EA-multi- sessi on groups were significantly shorter than that of model group (P<0.05). Results of active avoidance experiments indicated that the avoidance-reaction correct r at es of EA-multi-session group on the 1st

2nd

3rd days were significantly higher than those of model group

showing an improvement of learning-memory after acupunc tu re. In model group

the amplitude of tetanic stimulation induced PS potential w as attenuated significantly in comparison with that of control group

and those of EA-one-session and EA-multi-session groups were higher than that of mode l gro up

suggesting that EA could reverse morphine induced harmful influence on LTP a nd better synaptic transmission of hippocampal neurons. Local application of naloxone to CA3 area

the effect of EA on LTP was inhibited significantly

sugge sting an involvement of opium system in the therapeutic effect of EA. C onclusion:EA can improve morphine- induced lesion of learning-memory and modulate the sy naptic plasticity of neurons in perforant path- CA3 in morphine-dependent rats

a nd the effect of EA may be mediated by the endogenous opium system.