Investigation of neural mechanisms of 670 and 830nm laser acupuncture in pain relief, using rat

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Background Chronic pain is common and costs $10 billion dollars per year in Australia. Drug therapies are widely used but serious side effects limit use. Patients actively seek non-drug treatments and laser acupuncture is one of the most commonly sought therapies for chronic pain, however, how it works is not well understood. Our previous work Researchers propose that laser acupuncture reduces pain by direct effects on nerves, altering how pain signals are transmitted to the brain. To investigate this we (CI A and CI B) previously undertook a study of infrared laser on nerve cell cultures. This followed on from a positive clinical study with the same laser wavelength in the treatment of neck pain, undertaken by CI B. We established that laser temporarily interrupts the nerve transport system, which is made up of a series of minute tubes, called microtubules. These act as a “monorail” system for transport of mitochondria, which provide energy for all nerve functions. We propose that temporary interruption of this system, called fast axonal transport, disrupts the conduction of pain signals along the nerve, resulting in pain relief. Important unanswered questions The mechanism by which 830nm laser acupuncture relieves pain clinically remains poorly understood. For its acceptance into mainstream clinical practice it is important to determine the effect of laser on the peripheral nerves and in particular the pain carrying fibres. We know from an earlier study that a single exposure causes significant but reversible changes in pain fibres including axonal microtubule disruption, decrease in mitochondrial membrane potential and block of fast axonal flow. These events would result in conduction failure. The question is whether the repeated irradiations, comparable to those delivered clinically result in the same changes. This would provide a scientific basis for understanding the clinical effectiveness of laser acupuncture. We also do not know if 670nm laser acupuncture would act in the same way. There is evidence that this may be more effective so that this remains another important unanswered question. Further, there is no evidence regarding which wavelength would be cost and time effective as it is desirable to deliver lower dose. We need to determine the most effective dose and wavelength so that clinical trials could be carried out as was done for the trials by CIB (Chow and Barnsley, 2006).