Objective:To study the effect of oxytocin(OT)in nucleus raphe magnus (NRM) on electroacupuncture (EA) analgesia and its correlation with the endogenous 5-HT. Methods: In the first part of the study

24 Wistar rats were randomly divided into normal saline group (n=8)

OT group (n=6)

normal saline (NS)+EA group (n=6) and OT+EA group (n=6) for observing the effect of injection of OT (4 ng) into NRM on EA analgesia. In the second part of the study

18 Wistar rats were randomized into NS+EA

Cyproheptadin (C

an antagonist of 5-HT receptors) +NS+EA and C+OT+EA groups for analyzing the effect of injection of C (10 μg) into NRM on EA analgesia. The potassium iontophoresis induced tail-flick was used to measure the pain threshold. Results: Following administration of OT into NRM

EA and OT+EA

and during EA and after cease of EA

the percentages of the increased pain threshold were considerably higher than those of NS group. There were significant differences between OT and NS groups and between NS+EA and OT+EA groups (P< 0.01)

showing that microinjection of OT in NRM can induce an enhancement of EA analgesia. Following administration of C in NRM

the percentages of the increased pain threshold of C+NS+EA and C+OT+EA groups were strikingly lower than those of NS+EA group

displaying that after administration of antagonist of 5-HT receptors

the effect of EA analgesia is weakened pronouncedly.Conclusion: OT in NRM is involved in EA analgesia

that is probably accomplished partially by endogenous 5-HT.