Objective: To observe the effect of electroacupuncture (EA) on visceral pain and investigate the significance of the expression of c-fos and glial fibrillary acidic protein (GFAP) in medullary visceral zone (MVZ) in experimental visceral pain rats. Methods: Thirty-two male SD rats were randomized into control

visceral pain (VP)

EA+saline and EA+VP groups

with 8 rats in each group. Visceral pain model was established by intraperitoneal injection of 0.6% acetic acid ( 10 mL/kg ). EA ( 50 Hz

2- 5 V

intermittent waves) was applied to bilateral “Zusanli”(ST 36) for 30 min followed by establishment of VP. Saline ( 10 mL/kg ) was given (i.p.) to the rats after EA. Immuno-histochemical single or double staining methods (ABC) were used to show the immunoactivity of c-fos and GFAP in MVZ including nucleus of solitary tract (NTS) and dorsal motor nucleus of the vagus nerve (dmnx). The degree of visceral pain was evaluated by visceral pain index (VPI)

according to the Schmauss exponential method. Results: Pain reactions (writhing reactions: abdominal muscular contraction

hind-paw twitching

etc) happened in rats of model group and EA+VP group after injection of acetic acid

being more serious in the former group

and no such reactions were found in control and EA+saline groups. Fos-immunoreaction (IR)-positive neurons of VP

EA+saline and EA+VP groups found mainly in NTS and dmnx were significantly more than those of control group (P<0.05)

and in comparison with VP group

c-fos-IR-positive neurons of EA+saline and EA+VP groups were significantly fewer (P<0.05). The optical greyvalues of GFAP-IR-positive microglial cells found mainly in NTS and dmnx in VP

EA+saline and EA+VP groups were markedly higher than that of control group (P<0.05); while compared with VP group

the grey values of GFAP activity of EA+saline and EA+VP groups were significantly lower (P<0.05). Compared with VP group

VPI of EA+VP group was significantly lower (P<0.01) . Conclusion:EA has a marked antinociceptive effect in visceral pain model rats

which may be related to its effect in down-regulating c-fos and GFAP expression in MVZ.