Objective To observe the effect of electroacupuncture(EA) on hippocampal nitric oxide(NO)-cyclic guanosine 3

5-monophosphate(cGMP) signaling pathway in depression rats in order to explore the underlying mechanism of EA in improving depression.Methods Thirty male SD rats were equally randomized into control

model and EA groups.Depression model was established by using chronic unpredictable mild stress stimulation(forced ice-water swimming

electric shock

tailclamping

etc.) combined with lonely raising for 21 days.EA(2 Hz

0.6 mA

20 min) was applied to"Baihui"(GV 20) and"Yintang"(EX-HN 3)

once daily for 21 days.The expression of neuronal nitric oxide synthase(nNOS) and the content of cGMP in the hippocampus were determined by immuno-histochemistry and radioimmunoassay separately.Results Many nNOS immuno -reaction(IR)-positive granular cells were observed in the hippocampus in control group

fewer found in EA group and fewest in model group.Image analysis showed that the grey value of model group was significantly higher than that of control group (P<0.01)

and that of EA group was obviously lower than that of model group(P<0.01)

suggesting upregulation of nNOS expression after EA.Compared with control group the content of cGMP in hippocampus in model group showed a decreasing trend

but without significant difference between two groups(P>0.05).In comparison with model group

hippocampal cGMP content of EA group increased considerably(P<0.01)

being comparable to that of control group(P>0.05).Conclusion Electroacupuncture of"Baihui"(GV 20) and"Yintang"(EX-HN 3) can upregulate the expression of nNOS and the content of cGMP in the hippocampus in depression rats

maintaining a normal activity of the NO/cGMP signaling pathway

which may contribute to its effect in relieving depression.