Red laser light stimulation can have many physiological effects. The goal of this animal experimental study was to investigate how red laser stimulation influences the temperature of anesthetized rats at different acupuncture points and nonacupoints. For that reason 12 adult male Wistar Han rats (300–380 g) were investigated. Six anesthetized rats underwent red laser stimulation (wavelength 658 nm, output power 40 mW, diameter 500 µm, and duration 10 min) at the Baihui (GV20) acupoint, the Zusanli acupoint (ST36, bilateral), and a control point on the forelimb. The other six rats underwent the same procedure; however, the laser remained switched off. Significant decreases in temperature were found at the acupoints Baihui, Zusanli left, and Zusanli right. In addition there was no significant temperature effect at a control point. During placebo laser irradiation (deactivated laser) there were also significant temperature changes. The mechanism underlying the results is currently unknown, but brain stimulation (via laser or mechanical pressure) and mainly direct central mechanisms may be responsible for the local and peripheral temperature decrease.
Laser acupuncture is a trendsetting alternative method to the stimulation with metal needles. Many basic studies on this topic are available; however, there is still a lack of details concerning basic principles and mechanisms. It is also well-known that different kinds of lasers can produce different effects on skin temperature. For example, violet laser stimulation with a wavelength of 405 nm is able to produce significant increases in skin microcirculation and surface temperature [
The research team at the Medical University of Graz has performed several animal experimental studies assessing the effects of laser acupuncture on basic physiologic parameters [
The goal of the present study was to investigate how red laser stimulation influences the skin temperature of anesthetized rats at different acupuncture points in comparison to a control point and to placebo stimulation.
Twelve adult male Wistar Han rats (300–380 g) were purchased from Harlan Laboratories (AN Venray, Netherlands) and allowed to habituate to the new housing conditions for two weeks. The rats were housed in groups of 4 in standard Macrolon cages (Eurostandard Type IV) in an environmentally controlled colony room with a 12/12 h light-dark cycle. The lights were switched on at 8:00 AM. Food and water were available
The rats were anesthetized throughout the laser acupuncture session. For the induction of anesthesia, the animals were placed into a plexiglass chamber flooded with 4% isoflurane for 90–120 seconds. Subsequently, the rats were removed and placed prone while anesthesia was maintained through a nose cone with 2% isoflurane (see Figure
Anesthetic procedure and laser stimulation.
Red laser stimulation was performed in 6 rats at the acupuncture points Baihui (GV20) and Zusanli (ST36, bilateral) (see Figure
Schematic diagram of the stimulated acupoints.
The measurements of the skin temperature were performed using a Flir i7 (Flir Systems, Wilsonville, USA) infrared camera which operates at a wavelength range from 7.5 to 13
Temperature measurements using a Flir i7 infrared thermocamera.
All experiments took place during daytime (between 09:00 and 14:00; room temperature: ~21°C). Every rat completed the investigation. The rats were anesthetized throughout the laser acupuncture session with isoflurane (see Section
Experimental protocol.
Data were analyzed using SigmaPlot 12.0 software (Systat Software Inc., Chicago, USA). Testing was performed with one-way repeated measures ANOVA. Post hoc analysis was performed with Tukey’s test. The data are graphically presented as mean ± SE (standard error). The criterion for significance was
Typical examples of the results of thermal imaging are shown in Figures
Six thermal images from an anesthetized rat before (a), during ((b), (c), and (d)), and after ((e) and (f)) red light stimulation at the Baihui acupoint. Note the decrease of the temperature during and after red light irradiation.
Six thermal images from an anesthetized rat before (a), during ((b)–(d)), and after ((e) and (f)) red light stimulation at the left Zusanli acupoint. Note the decrease of the temperature during and after red light irradiation.
Six thermal images from an anesthetized rat before (a), during ((b)–(d)), and after ((e) and (f)) red light stimulation at the right Zusanli acupoint. Note the decrease of the temperature during and after red light irradiation.
Figure
Temperature values of all rats during the different phases (a–f, see Figure
Figure
Temperature values of all rats during the different phases (a–f, see Figure
The present study examined the effects of laser irradiation on two acupuncture points on skin temperature in laboratory rats.
Already in 1895, Pembrey [
In our present study in rats we also stimulated an acupuncture point located on the head (Baihui, GV20) and two points on the hind limbs (Zusanli, ST 36, bilateral). This stimulation scheme was found to decrease skin temperature in the local areas around the acupoints. At a control point no significant temperature effects could be found. During placebo stimulation (deactivated laser), some significant changes could be detected. The reason for these changes could be the mechanical stimulus applied via the laserneedle. At the moment the mechanisms underlying these interesting results are still unknown, but brain stimulation and central mechanisms may be involved in the local and peripheral temperature decrease observed in our experiments. As we could demonstrate in a previous study, red laser light with a wavelength of 658 nm is able to penetrate the human skull with a transmission factor of about 0.02 [
Surface temperature investigations and changes elicited by laser were also reported by Yen et al. in 1994 [
Our study has several limitations. Depending on the type of equipment used, the shaving of the rats might lead to changes in microcirculation and, in consequence, also temperature alterations. To avoid this possible influence in future investigations, fuzzy (nude) rats could be used for whole body skin temperature investigations because this type of rat is essentially hairless and does not require shaving in the regions of interest [
On the other hand, standardization of the evaluated parameters in rats has not yet been performed, so results from different studies and different rats cannot be compared. Because so many parameters play a role, the thermal effect should be investigated for each specific application separately [
The authors declare that there is no conflict of interests regarding the publication of this paper.
The scientific investigations were supported by the German Academy of Acupuncture, the Austrian Federal Ministries of Science, Research and Economy and of Health (Project title “Evidence-based high-tech acupuncture and integrative laser medicine for prevention and early intervention of chronic diseases”), and the Eurasia-Pacific Uninet (Technology Scholarship Award for Assistant Professor Xiaoyu Wang, Ph.D.). The authors would like to thank Ms. Ingrid Gaischek, M.S., Medical University of Graz, for her help in paper preparation.