Sympathetic nervous system implicated in acupuncture analgesia

By Joanna Lyford, Senior medwireNews Reporter

Acupuncture appears to activate the sympathetic nervous system (SNS) in people experiencing pain, a randomized study indicates.

The research offers clues to the mechanisms involved in acupuncture analgesia, although the precise interplay of local versus systemic effects remains unclear.

Barbara Shay (University of Manitoba, Winnipeg, Canada) recruited 36 healthy adults who completed an exercise protocol designed to elicit delayed-onset muscle pain in the nondominant forearm.

The participants returned 48 hours later and were randomly assigned to one of three groups: no treatment; a single 15-minute session of acupuncture with penetrating needles; or a session of non-penetrating sham acupuncture.

Three measures of SNS activation - skin conductance, skin temperature, and perfusion- were monitored bilaterally before, during, and after treatment, report Shay et al in Acupuncture in Medicine.

In the group that received acupuncture, skin conductance increased significantly within 5 minutes of starting acupuncture and returned to baseline levels by 10 minutes after the end of acupuncture.

By contrast, skin conductance in the sham-acupuncture and no-treatment groups was unchanged.

Similarly, both ipsilateral and contralateral distal skin temperature decreased for participants in the acupuncture group 5 minutes after starting treatment and throughout the recovery phase, whereas temperature did not change in the other two groups.

Interestingly, all groups showed a general trend toward lower proximal skin temperature, both ipsilaterally and contralaterally, after the intervention.

Finally, ipsilateral skin perfusion increased by a "dramatic" 35% within 5 minutes of needle insertion in the acupuncture group and remained at this level until 10 minutes after the end of treatment.

This measure was unchanged in the other two groups, although modest increases in contralateral skin perfusion were noted in both the no-treatment and sham-treatment groups.

Taken together, these findings indicate that the SNS is activated in response to acupuncture, and that the increase is mediated systemically rather than locally, Shay and co-authors write.

Additionally, the unilateral increase in perfusion near the needle site appears to be due to local circulatory modulation.

"Further study into the response of the SNS to acupuncture is required to enhance understanding of acupuncture analgesia," the team concludes.

"To date, it is difficult to determine whether the effect of acupuncture on the SNS is central or segmental in origin. Thus, further study should include the placement of sensors at non-segmental locations."

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