Objective To investigate the effect of opiate receptor antagonist naloxone on the electroencephalographic (EEG) power spectrum in morphine-addicted rats.Methods 20 male adult Wistar rats were alternately injected with morphine (Mf, 10 mg/kg,sc.;Mf withdrawal (Mf-Wd) group, n=10) or saline (Sal, 1 ml/kg, sc.;Sal-Wd group, n=10) for 8 days to establish Mf physical dependent model.Withdrawal scores were evaluated by naloxone-precipitated withdrawl signs (5 mg/kg,ip.).Another 20 rats were divided into Sal-CPP group and Mf-CPP group with 10 rats in each group.Rats in the sal-CPP group were injected with saline once a day for 8 days while rats in the Mf-CPP group were injected with saline and morphine alternatively once a day for 8 days.The EEG signals were recorded from their dorsal hippocampi before and after naloxone injection under anesthesia;and the EEG power data (1 ～ 100 Hz) were analyzed.Results (1) Compared with Sal-Wd group (22.69± 3.59), the Mf-Wd group showed a higher withdrawal scores after naloxone injection(84.90± 13.40, P＜0.01).(2) The CPP scores of Mf-CPP rats (80.69± 14.96) were significantly higher than the baseline (45.29± 15.79) and the Sal-CPP rats (41.84± 12.47;all P＜0.01).(3)After naloxone injection,the EEG powers of δ band and γ band of Mf-CPP rats decreased temporarily c ompared with their baseline (δ band: (81.80±30.91) mV2 · Hz vs (112.49±39.43) mV2 · Hz;γ band:(25.35±11.20)mV2 · Hzvs (28.71±13.06)mV2 · Hz;allP＜0.05).Conclusion Opiate receptor antagonist naloxone can decrease the hippocampal EEG powers of δ band and γband in Mf-addicted rats.