Mechanisms of analgesic action of pulsed radiofrequency on adjuvant-induced pain in the rat: roles of descending adrenergic and serotonergic systems.

Pulsed radiofrequency (PRF) has been reported to be effective in the treatment of several types of pain. The mechanism of action, however, is not well known. In a recent study, the antinociceptive effects of acute thermal pain were shown to be mediated via descending pain inhibitory pathways. In this study we observed an analgesic effect of PRF treatment in an adjuvant induced inflammatory pain model in rats. In this model, sciatic nerves were treated with PRF at 37 degrees and 42 degrees , which inhibited hyperalgesia in the inflammatory groups when compared to RF and sham treatment. This effect was attenuated after intrathecal administration of the alpha2-adrenoceptor antagonist yohimbine, the selective 5-HT3 serotonin receptor antagonist MDL72222, and the non-selective serotonin receptor antagonist methysergide. All three drugs were found to significantly inhibit the analgesic effect of PRF. The results suggest that the analgesic action of PRF involves the enhancement of noradrenergic and serotonergic descending pain inhibitory pathways.