Influence of naloxone on electro-acupuncture analgesia using an experimental dental pain test. Review of possible mechanisms of action.

The purpose of this study was to examine in man the analgesic effect of non-segmental electroacupuncture (EA) limited to a single point (Hoku hand point) and the influence of naloxone using an original modified electrical dental pain test. Results in the literature are still contradictory as to the degree and specificity of acupuncture analgesia and its opioid nature. Acupuncture techniques as well as experimental pain models are factors accounting for the discrepancies in the results. For this reason, we designed an experimental pain test characterized by a high degree of specificity, validity and reliability. We chose optimal conditions for eliciting specific acupuncture effect, i.e. non-segmental, low frequency and painful intensity range. A cross-over repeated measure experimental design was used. Five normal trained subjects participated in 65 sessions under four conditions (control, EA, EA+naloxone, EA+placebo). Changes in experimental dental pain thresholds served as indices of analgesia. The results indicated a 27% pain threshold increase after 30 minutes of EA stimulation (p less than .0001), with no differential effect between pain detection (mild pain sensation) and pain discomfort (strong pain sensation). This increase was partially blocked by the double blind injection of 0.8 mg naloxone IM (p less than .005). The experiment was designed in such a way as to prevent the occurrence of a stress analgesic effect. The endogenous opioid system was shown to be partially involved in acupuncture analgesia. Other mechanisms of action are discussed in view of the literature findings.