Laser Acupuncture and Analgesia: Preliminary Evidence for a Transient and Opioid-Mediated Effect

摘要

Acupuncture is frequently used to treat pain. Although human pain quantification is difficult and often subjective, in rodent models the tail-flick test provides a well-established and objective assessment of analgesia. This test measures the time taken before a rat withdraws its tail from a heat source. Needle and electroacupuncture at the acupuncture point Spleen-6, located at the tibia's posterior margin above the medial malleolus, has been found to increase tail-flick time in rats. The aim of the current study was to determine if laser acupuncture had a similar effect. A 550 μm diameter optic fiber was used to irradiate Spleen-6 for 2 minutes (690 nm, 130 mW) in female Sprague-Dawley rats. In addition, control experiments were performed in which rats were subjected to sham treatment (restraint but no irradiation) or irradiation of an non-acupuncture point (the tail's dorsal surface, 1cm from the base) using the same laser parameters. The baseline tail-flick time was measured and 15 minutes later the laser acupuncture or the control protocols were performed and tail-flick time re-measured 10 minutes after treatment. Additional experiments were done in which the opioid-blocker naloxone (20 mg/kg, intraperitoneal injection) was administered one hour before laser acupuncture. Tail-flick time increased after laser acupuncture (P = 0.0002), but returned to baseline values one hour later. In contrast, no increase was found after either sham treatment or tail irradiation. Pretreatment with naloxone attenuated the increase in tail-flick time. In summary, laser acupuncture exerts a transient analgesic effect which may act via an opioid-mediated mechanism.