Electroacupuncture analgesia is enhanced in transgenic nociceptin/orphanin FQ knock-out mice

Abstract

Objective: The modulatory effects of nociceptin/orphanin FQ (OFQ) on acupuncture (EA, a modern version of acupuncture)-induced analgesia are still controversial. Transgenic OFQ knock-out mice provide us a useful tool to investigate the role of endogenous OFQ in EA analgesia. The present study aims to investigate the role of OFQ in the EA-induced analgesia with OFQ knock-out mice.

Methods: Acupoints were selected as "Zusanli" (ST36) and "Sanyinjiao" (SP6), EA parameters were as follows: constant current output, rectangular (square) wave pulses, increased intensities of 0.5, 0.7, 0.9 mA with stepwise fashion, 10 min for each intensity, frequency of 100 Hz (with 0.2 ms as pulse width) or 2 Hz (with 0.6 ms as pulse width). Tail flick latency (TFL) evoked by radiant heat was used to evaluate the change of pain threshold before, during and after EA application. The knock-out mice were divided randomly into 3 groups: needling control, EA at 100 Hz and 2 Hz. Wild-type mice of littermates of were used as Control.

Results: It was found that OFQ knock -out mice had a longer basal thermal threshold; EA had enhanced analgesic effect in the knock-out mice than in wild-type Control mice.

Conclusion: Endogenous OFQ might be algesic in basal condition and antagonize EA analgesia.