Rufus R. Noble An undetermined etiology and a lack of response to conventional treatments define Neuropathy. The lack of effectiveness and the numerous adverse effects of the medications used to treat Neuropathy call for developing new strategies for treating the pain. Laser therapy has proven to be effective in reducing pain sensitivity, which improves the level of living. However, its application and effectiveness parameters in chronic pain must be further studied. We studied Photobiomodulation Therapy’s pain-relieving and enhancing effects in the rat model of compressive mononeuropathy caused by chronic Sciatic Nerve (CCI) constriction. Laser (MLS-MiS) applications began seven days following surgery and were repeated ten times over three weeks. The results showed decreased mechanical hypersensitivity and spontaneous pain from the first treatment with lasers until the study’s conclusion. The ex-in vivo analysis revealed the protective effect of the laser on the myelin sheath’s recovery within the sciatic nerve. It also showed an inhibition of iNOS expression and increased EAAT-2 levels within the spinal cord. This research confirms laser therapy as an option for future treatment strategies in those suffering from neuropathic pain due to trauma.
Introduction
Neuropathy is caused by damage (due to disease or injury) of the central nervous system (including nerves), the spinal cord, and other regions of the central nervous system 1, 2, and 3. Patients suffering from neuropathy experience spontaneous pain, allodynia (pain response to standard stimulus), or hyperalgesia (aggravated pain caused by harmful stimuli) that affect their lives 4,6. Several experimental models have been created to understand Neuropathy. The chronic constriction Injury (CCI) model devised by Bennett and Xie 7 is a popular mononeuropathy model that reproduces the majority of symptoms seen in patients seven, eight, nine, and 10 in rats.
The most popular method to treat pain is the treatment of pain medications. However, they have been proven effective only in 30% of patients suffering from Neuropathy, whichmaking research into novel and efficient methods a continuous problem 11-12, 13.
The development of research and clinical application of lasers in medical practice dates back to the late 60s, 14 years since laser radiation was recognized as one of the top non-pharmacological treatments. Laser therapy has grown in popularity because it is a non-invasive method with a limited number of contraindications and few side effects and is cost-effectiveness, which is why it is widely accepted by patients 15.16. The literature regarding the action mechanisms involved in laser therapy is vast, but with some controversial findings that are hard to evaluate and interpret due to the many different research conditions (in particular, the kind of laser source and the parameters for treatment, which include the wavelength, power as well as fluence, exposure time and more) …) that are used in research. However, through the years, laser therapy has demonstrated its effectiveness in treating several pathological conditions17,18,19,20,21,22,23,24. The potential to treat lasers in numerous pathological states is contingent on radiation’s effects on vital biological processes.
Many studies published in the literature have revealed that laser radiation efficiently enhances the efficiency of cell energy metabolism by causing ATP production. 2526 and 27. Additional insights into the mechanisms behind the improved energy metabolism were revealed through a proteomic analysis that was conducted on myoblasts exposed to near-infrared (NIR) radiofrequency (808 as well as 905 nm), which showed an increase in ATP binding proteins and Protein Phosphatase 1 (PP1) was detected 28. In the same study, it was found that the laser radiation caused an increase in NLRP10, an anti-inflammatory protein inhibiting the creation of the interleukin-1b protein 28. The analgesic effect may also be due to the other mechanisms acting in the design of anti-nociceptive chemicals (endorphins) as well as peripheral nerve conduction, and the transmission of stimuli that cause nociceptive such as the fast analgesic effect that is caused by laser radiation in the animal models of chronic painfulness 18.29.30.31.
Preliminary studies showed that the anti-hypersensitivity effect and its persistence depended on treatment protocols and parameters (irradiation mode, treatment frequency, source wavelength, power, and pulse frequency)31.
The present study aimed to investigate the effectiveness of a high-power, dual-wavelength NIR laser source (Multiwavelength Locked System laser, MLS-MiS) in producing a persistent anti-hypersensitivity effect in CCI-induced Neuropathy caused by compressive damage in the rat. The mechanisms of action for laser therapy were also evaluated using ex-in vivo examinations of the central and peripheral nervous systems, which were designed to reveal how the sciatic nerve is regenerated and the decrease in the inflammation processes in the spinal cord.
Results
The effects of treatment with lasers on hypersensitivity induced by CCI
Behavioral measurements were performed to evaluate the anti-hypersensitivity effect of repeated laser treatments on CCI-induced peripheral mononeuropathy in the rat. The treatment was initiated one week following surgery. It included ten sessions each day until the three 4th week (Fig. 1). The assessment of hypersensitivity (Paw pressure test) was conducted immediately before and 30 minutes after each laser session. Figure 2 illustrates the mean values measured for the three categories of animals (sham CCI, CCI, and CCI + laser) before any of the laser treatments.
