Objective: To observe the effect of electroacupuncture (EA) on changes of expression of L-Arg transporter 2 (CAT-2) mRNA and nitric oxide synthase (iNOS) mRNA and protein and contents of NO and cGMP of L4-L6 segments of spinal cord in rats with spared nerve injury (SNI), so as to reveal its mechanism underlying reducing neuropathic pain.

Methods: A total of 120 male SD rats were randomly divided into sham operation, model, EA and NOS inhibitor (N omega-Nitro-L-arginine methyl ester hydrochloride, L-NAME) groups, with 30 rats in each group. The neuropathic pain model was established by ligating and cutting the tibial nerve and the common peroneal nerve. EA (2 Hz, 1-3 mA) was applied to "Weizhong" (BL40) and "Huantiao" (GB30)on the damaged hindlimb for 30 min, once daily from day 11 to 17 after SNI. Rats of the L-NAME group received i.p. of L-NAME (60 mg·kg-1·d-1) for 7 consecutive days. The mechanical pain threshold (PT) was determined before and 10 and 16 d after SNI, respectively. The expression le-vels of CAT-2 mRNA and iNOS mRNA, and iNOS protein in the L4-L6 segments of the spinal cord were detected by using reverse transcription - polymerase chain reaction (RT-PCR) and Western blot, respectively, and the contents of NO and cGMP of L4-L6 assayed using nitrate/nitrite reductase method and radioimmunoassay, respectively.

Results: After modeling, the PT was significantly decreased on day 10 and 16 after SNI in comparison with the sham operation group and their own baseline data of pre-operation in each group (P<0.01), and remarkably increased in the EA and L-NAME groups relevant to the model group on day 16 (P<0.01, P<0.05). Compared with the sham operation group, the expression levels of CAT-2 mRNA and iNOS mRNA and protein, as well as the contents of NO2－/NO3－and cGMP were signi-ficantly up-regulated in the model group (P<0.05, P<0.01). Following EA intervention, the levels of CAT-2 mRNA and iNOS mRNA and iNOS protein, and NO2－/NO3－and cGMP contents were all reversed in both EA and L-NAME groups (P<0.05, P<0.01). The effect of EA was significantly superior to that of L-NAME in raising the PT on day 16 after SNI (P<0.05), but obviously inferior to that of L-NAME in down-regulating the expression of CAT-2 mRNA and iNOS mRNA and protein (P<0.05). No significant differences were found between the EA and L-NAME groups in down-regulating NO2－/NO3－ andcGMP contents (P>0.05).

Conclusions: EA intervention can effectively relieve neuropathic pain in SNI rats, which may be closely related to its function in suppressing L-Arg/NO/cGMP pathway in the lumbar spinal cord.