Neurochemical Basis of Acupuncture Analgesia

A review on acupuncture and its neurochemical basis may not seem to be within the general scope of this series. However, the phenomenon has attracted the interest of scientists from several disciplines, including phar­ macologists, and the use of drugs as probes has been instrumental in estab­ lishing the neurochemical basis of acupuncture. We have found it necessary to limit our review to studies of acupuncture for the relief of pain since research in other areas is still in its infancy. Since much of the work in this field has been published in periodicals not easily accessible to the general scientific community for linguistic or other reasons, we have chosen to provide a fairly extensive documentation. Although acupuncture has a very long history as a means for relieving pain (1, 2), its scientific study began very recently. Early studies revealed that the analgesic effect was blocked by procaine infiltration of acupuncture points and that it was not possible to induce analgesia in paraplegic or hemiplegic patients, pointing to the importance of afferent transmission (3-6). Involvement of chemical mediators in the central nervous system (CNS) was suggested from experiments where the cerebrospinal fluid (CSF) of donor rabbits given acupuncture was infused into the cerebral ventricles of recipient rabbits, increasing their pain thresholds (7). An important series of findings came in the 1970s when several investiga­ tors presented carefully controlled experimental studies using different ap­ proaches. Andersson et al verified the effect of acupuncture on thresholds to pain, experimentally induced by tooth pulp stimulation in healthy volun-