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. Tailflick 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.
Anecdotal evidence suggests that laser revascularization has long-term benefits on tissue perfusion, perhaps by stimulating angiogenesis. To test this hypothesis, we made 6 transmural channels in rat hearts randomized to either; (1) laser: channels made using a 500 micrometers diameter optic fiber coupled to a holmium:YAG laser, (2) needle: channels made using a 500 micrometers diameter needle, or (3) control: no channels made. Two months later, the rats underwent 90 minutes of coronary artery occlusion followed by 41/2 hours of reperfusion. Prior to the end of the experiment, the artery was reoccluded and the heart perfused with blue dye to detect collateral perfusion within the risk region. Microscopic analysis revealed more dye-containing vessels in needle-treated hearts than in laser or control groups (12 +/- 6*, 3 +/- 1, 2 +/- 1 vessels per field of view, * p < 0.05). Needle channels also appeared to limit necrosis: infarct size was 41 +/- 6* (needle), 61 +/- 6 (laser), 70 +/- 5 (control) % of the risk region in the three groups (*p < 0.05 versus control). Thus, needle- treatment may be capable of reducing infarct size by supplying blood via a collateral circulation apparently stimulated by the channels making process.
We sought to compare the properties of cylindrical and ball tip fibers (in conjunction with a holmium:YAG laser) by examining both their beam characteristics and the characteristics of the channels formed when the fibers passed through myocardial tissue. We found that the cylindrical fiber tip was able to produce a wider, more uniform channel with less surrounding thermal damage than the ball tip fiber. We attribute these findings to the shorter focal length, smaller beam spot size, and greater beam divergence produced by the ball tip fiber.
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