Objective To compare the effects of electroacupuncture(EA)preconditioning and post-conditioning on hippocampal neuronal nitric oxide synthase(nNOS)expression in rats with anxiety-like behavior

so as to explore the reasonable EA intervention time.Methods Forty-two SD rats were randomly divided into 6 groups:normal 1

normal 2

anxiety model 1

anxiety model 2

EA-pre-conditioning and EA-post-conditioning.The anxiety model was established by giving the rats with repeated foot shock stimulation(0.8mA

2-25s/time

10 times in 5min)combined with isolation-raising.Before or after modeling

EA stimulation was applied to"Baihui"(GV 20)and "Yintang"(GV 29)for 20 min

once a day for 7 days.Elevated plus maze(EPM)tests were performed to determine the percentages of time spent in the open arms and the percentages of entries into the open arms in 5min for evaluating the animals' anxiety-like behavioral activities.The reverse transcriptase polymerase chain reaction(RT-PCR)was used to detect hippocampal nNOS mRNA expression and the immunohistochemical staining adopted to detect the expression of nNOS protein in the hippocampal CA 1and CA 3areas

respectively.Results Compared with their own normal control group 1 and 2

both the percentage of time spent in the open arms and the percentage of entries into the open arms were significantly decreased in model group 1 and 2(P<0.05

P<0.01).After pre-and post-conditioning of EA

the decreased proportions of time spent and entries into the open arms were considerably increased(P<0.05)

suggesting an improvement of anxiety-like behavior activities after EA intervention.The expression levels of hippocampal nNOS mRNA and nNOS protein in the hippocampal CA 3region were significantly higher in the model group 1 and 2 than in their own normal control group 1 and 2(P<0.01)

but those of nNOS protein in the CA 1 area were markedly lower in the model group 1and 2than in their own normal control group 1 and 2(P<0.01).Following pre-and post-conditioning of EA

the increased expression levels of nNOS mRNA and protein of CA 3 area and the decreased level of nNOS protein of CA 1 area were all notably reversed(P<0.05

P<0.01).Conclusion Both pre-and post-conditioning of EA can improve anxiety-like behavior in anxiety rats

which may be associated with its effects in down-regulating hippocampal nNOS expression.