Analgesic effects by electroacupuncture were decreased in inducible nitric oxide synthase knockout mice

Abstract Background: This study was designed to investigate the involvement of inducible nitric oxide synthase (iNOS) in electroacupuncture (EA)-induced analgesia. Methods: Two and 100 Hz EA stimulation were applied at acupoint ST 36 (Zusanli) in iNOS knockout mice (n = 28). Needles were inserted 5 mm in depth in ST36. After insertion, the needles were fixed in situ with adhesive tape. EA was applied after the basal threshold determination. The EA parameters were set as follows: constant square wave current output (pulse width: 0.6 ms at 2 Hz and 0.2 ms at 100 Hz) and 2 mA intensities. EA was performed for 30 minutes and tail-flick latencies (TFLs) were evaluated every 15 minutes for 1 hour. Results: In 2 Hz EA stimulation, the tail-flick response (TFR) of wild-type mice for durations of 0, 15, 30, 45 and 60 minutes were 2.70 ± 0.26, 4.19 ± 0.37, 4.17 ± 0.34, 3.57 ± 0.27 and 3.39 ± 0.32 seconds of TFLs. Meanwhile, iNOS −/− mice showed 4.10 ± 0.33, 4.77 ± 0.24, 5.26 ± 0.30, 4.48 ± 0.33 and 5.00 ± 0.41 seco...