Neuropathic pain (NP) is caused by damage to the nervous system due to reactive oxygen spices (ROS) increase, antioxidants reduction, ATP production imbalance, and induction of apoptosis. In this investigation, we applied low-level laser 660 nm (photobiomodulation therapy) as a new strategy to modulate pain. In order to study the effects of photobiomodulation therapy (660 nm) on NP, chronic constriction injury (CCI) model was selected. Low-level laser of 660 nm was used for 2 weeks. Thermal and mechanical hyperalgesia were measured before and after surgery on days 7 and 14, respectively. Paw withdrawal thresholds were also evaluated. Expression of p2x3, Bax, and bcl2 protein was measured by western blotting. The amount of glutathione (GSH) was measured in the spinal cord by continuous spectrophotometric rate determination method. The results are presented as mean ± SD. Statistical analysis of data was carried out using SPSS 21. CCI decreased the pain threshold, 2-week photobiomodulation therapy significantly increased mechanical and thermal threshold, decreased P2X3 expression (p < 0.001), and increased bcl2 expression (p < 0.01), but it was not effective on the Bax expression. We speculated that although photobiomodulation therapy increased ROS generation, it increased antioxidants such as GSH. Increase in bcl2 is another mitochondrial protection mechanism for cell survival and that pain relief and decrease in P2X3 expression confirm it.

Background: Different types of pain such as neuropathic pain (NP) are still challengeable conditions in medical disciplines. Neuropathy leads to medical, social and economic problems for the patient, thus various therapies are being used to treat or reduce it. There are numerous studies mainly focused on the role of reactive oxygen species (ROS) and oxidative stress for NP. Recently, Low level Laser Therapy (LLLT) has been used in certain areas of medicine and neuro-rehabilitation. Chronic constriction injury (CCI) is a well-known model for neuropathic pain studies. Objectives: The present research was designed to find the effects of 660 wave length LLLT on injured sciatic nerve. Materials and Methods: Twenty Wistar adult male rats (230-320 g) were used in this study. The animals were randomly divided into three groups (n = 10). To induce neuropathic pain for sciatic nerve, CCI technique was used. Low Level Laser of 660nm was used for consecutive two weeks. Thermal and mechanical hyperalgesia were performed before and after the operation on days 7 and 14 respectively. Paw withdrawal thresholds were also evaluated. Results: Our results showed that CCI decreased the pain threshold; whereas, LLLT of 660nm wave length for two weeks increased the mechanical and thermal thresholds significantly. Comparison of the mechanical and thermal thresholds showed significant therapeutic effects of LLLT in trial groups than control. Conclusions: Although our results showed the therapeutic effects of LLLT on NP and might be used for clinical application in neuropathic cases; more future clinical studies are needed.