Objective: To observe the effect of electroacupuncture (EA) on pain thresh old and experimental arthritis induced cutaneous c fos expression and the influ ence of intraventricular injection of orphanin (OFQ) on EA analgesia and arthrit is induced c fos expression in rheumatoid arthritis (RA) SD rats. Met hods: 44 SD rats were randomly divided into A RA model + lateral ventri cular injection (LVI) of normal saline 20 μL + EA, n=8, B (model +L VI of OFQ+EA,n=8), C (normal control, n=8), D (RA model , n=10) and E (model+EA, n=10) groups. RA rat model was esta blished by injection of Freund’s complete adjuvant into the ankle joint space. A cupoints of "Taixi" (KI 3) and "Zusanli" (ST 36) on the right hindlimb were puncture d and stimulated electrically with WQ 10C Electronic Acupoint Detection and The rapeutic Apparatus by setting the parameters of frequency 2/100 Hz, 2～4 V, wave width 0.2～0.6 ms and stimulating duration 20 min. Expression of c fos pr otein in the rat plantar region was detected with immunohistochemical method. OFQ 20 μL, 50 μg/mL was injected into the lateral ventricle of the rat brain. Results: ① In RA rats, the pain threshold in A, B, D and E groups was lowered significantly, while after EA treatment, the pain threshold values, particularly on the 3rd, 4t h and 5th day, were increased significantly (P<0.01). There were no si gnificant differences between model+ OFQ+EA and RA model groups in the pain thre shold (P>0 .05), suggesting an antagonizing effect of OFQ on EA analgesia. ② In comparison with normal control group, the positive neurons of c fos expression in A (82.5 4±24.64) and B (174.87±38.23), D (168.42±34.75) and E (99.65±25.36) grou ps w ere increased considerably in comparison with group C (0.00±0.00), showing a st riking increase of c fos expression. The c fos positive neuron numbers in A a nd D groups were significant lower than that of B and D groups (P< 0.01), display ing that EA can significantly suppress RA induced c fos expression while this effect of EA is anta
