Abstract:Aim: Exogenously administered orphanin FQ (OFQ) has been reported to antagonize morphine analgesia and electroacupuncture (EA) analgesia (EAA) in the brain but potentiate morphine analgesia and EAA in the spinal cord of rats. Here we report the effectiveness of EAA in OFQ knockout mice. Methods: Two pairs of metallic acupuncture needles were inserted into specific acupoints ST 36 and SP 6, the needles were connected to one of the output channels of an electric pulse generator named HANS. EA parameters were as follows: constant current output, rectangular (square) pulses, intensities increased with stepwise fashion at 1.0 1.2 1.4 mA, 10 min for each step, frequencies were 100 Hz (0.2 ms pulse) or 2 Hz (0.6 ms pulse). The pain threshold was measured by radiant heat-induced tail flick latency (TFL). Three TFL values taken before EA stimulation were averaged as basal TFL. Wild type and knockout animals were divided randomly into 3 groups: needle control, 100 Hz EA and 2 Hz EA. The peak value obtained among the 6 time points (3 tests during and 3 tests after EA stimulation) was taken to represent the EA effect. The net change of this peak value relative to its own basal TFL (T peak T basal ) was calculated, and analyzed by Analysis of Variance (ANOVA) among groups. Results: The basal threshold in knockout mice was significantly longer than that in the wild type animals. The analgesic effect induced by EA at 100 Hz, but not 2 Hz, was significantly stronger in OFQ knockout mice. Conclusion: Endogenous OFQ seems to increase the sensitivity of nociception and plays an antagonistic role in 100 Hz electroacupuncture-induced analgesia.
