BACKGROUND: Visceral hypersensitivity is the main cause of irritable bowel syndrome, c-Fos is a marker of visceral hypersensitivity in the central nervous system. Electroacupuncture can relieve chronic visceral hypersensitivity in rats, but the mechanism is still unknown.OBJECTIVE: To identify c-Fos expression in the spinal cord and cerebral cortex of rats with chronic visceral hypersensitivity, and to test the effects of electroacupuncture on pain sensitivity in rats with chronic visceral hypersensitivity.DESIGN, TIME AND SETTING: A randomized controlled animal experiment was performed at the Animal Experimental Center, Shanghai University of Traditional Chinese Medicine, from January to April, 2007.MATERIALS: A total of 24 neonatal, male, Sprague Dawley rats, aged five days old, were equally and randomly assigned into a normal group, a model group, and an electroacupuncture group. Rabbit anti-rat c-Fos antibody and Evision secondary antibody kits (Sigma, USA), diaminobenzidine kit (Dako, Denmark), and an LD202H electroacupuncture apparatus (Huawei, Beijing, China) were used in this study.METHODS: Neonatal rats from the model and electroacupuncture groups were used to establish rat models of chronic visceral hypersensitivity by the saccule stimulation method. After model establishment, 0.25 mm diameter electric needles were inserted into Tianshu (ST 25) and Shangjuxu (ST37) at a depth of approximately 0.5 cm, with an square wave (altating current frequency at 100/20 Hz, amplitude ranged 0.2-0.6 ms, intensify at 1 mA) once for 20 minutes, once a day, for seven days. Rats in the normal and model groups were not treated.MAIN OUTCOME MEASURES: Following 7 days of treatment, c-Fos expression in the spinal cord and cerebral cortex was detected by immunohistochemistry. After the first electroacupuncture treatment, abdominal withdrawal reflex scores were investigated to evaluate the pain threshold for chronic visceral hypersensitivity in rats.RESULTS: Visceral hypersensitivity increased c-Fos staining (P < 0.05), and electroacupuncture significantly decreased the number of these cells to near normal levels (P > 0.05). Abdominal withdrawal reflex scores were significantly lower in the electroacupuncture and normal groups than in the model group (P<0.05) and were similar between the electroacupuncture and normal groups (P > 0.05).CONCLUSION: Electroacupuncture decreases c-Fos expression in the spinal cord and cerebral cortex and increases pain threshold in a chronic visceral hypersensitivity model in rats.