Objective: To explore the effect of oxytocin (OT) of periaqueducta l grey (PAG) of the midbrain on acupuncture analgesia and its relation with endo genous opiates.Methods: Potassium iron iontophoresis method was used to induce pain

tail flicking was considered as the pain index and the pai n threshold changes were detected before and after microinjection of oxytocin(OT

2 ng/0.5 μL for each side)

anti oxytocin serum (AOTS

1 ng/0.5 μL)

naloxo ne (Nx

5 ng/0.5 μL )

anti β endorphin serum(AEPS)

anti metenkephalin seru m (AMEKS) and anti dynorphin A 1～13 serum(ADYNS) into PAG of rats. Results: After bilateral microinjection of OT

the analgesic effect of electroacupuncture (EA) increased significantly in com parison with that of microinjection of same dose of normal saline and presented a dose effect relation (P<0.01). Following microinjection of AOTS

the analgesic effect of EA decreased considerably in comparison with that of normal rabbit se rum (NRS

P<0.01). After microinjection of Nx

the analgesic effec t of EA also d eclined significantly compared with that of normal saline group (P <0.01). After microinjection of Nx and then OT

the effect of EA increased obviously compared with that of Nx+EA group(P<0.01). After microinjection of AEPS or and the n OT

the effect of EA also increased significantly in comparison with that of A EPS+EA and AMEKS+EA group (P<0.01). Following microinjection of AD YNS

the analg esic effect of EA had no significant changes in comparison with NRS group. After microinjection of ADYNS and then OT

the effect of EA increased significantly i n comparison with that of ADYNS+EA group while had no apparent changes in compar ison with that of OT+EA group (P>0.05). The results showed that OT in PAG plays an important role in the EA analgesia

and its effect is independ ent of endogen ous opiate peptides.Conclusion: In the central nervous system

m ultiple analge sic systems may exist simultaneously and OT participates in EA induced analgesic process.