IntroductionThe nerve fiber or axon, is responsible for transmitting information between neuron cells. 1 In humans, axons are generally on the scale of 1 μm thick and some are more than 1 m long, 1 and in the peripheral nerve system (PNS), they are either unmyelinated or myelinated by Schwann cells.2 These cells are mainly wrapped around axons and form a multi-layered sheath preparing myelin structures for axons. 2,3 In case of injury, Schwann cells are activated and play a key role in nerve repair mechanism, not only concerning Wallerian degeneration and remyelination in the injured position, but also in promoting axonal growth. 4 Wallerian degeneration occurs when an axon is cut or injured, in which the axon degenerates distal to the injury site. [5][6][7] This is followed by secondary phenomena such as breakdown of the myelin sheet and activation of the Schwann and macrophages that clear up the debris. 8,9Nerve injuries are divided into 3 basic categories of neuropraxia, axonotmesis and neurotmesis based on the extent of injury, pathology and physiology according to Sir Herbert Seddon's scheme, 5,6 neuropraxia, the mildest nerve injury, is a temporary loss of sensory function. 10The injured site usually fully recovers within few weeks or months, and no Wallerian degeneration occurs in this type of injury. Axonotmesis is when axons are more seriously damaged and interrupted. 10 In this type of injury, the surrounding epineurium and perineurium layers remain almost intact, but there could be only partial recovery depending on the extent of injury to the axons. In addition, Wallerian degeneration may occur distal to Methods:In this research work, the effect of LLLT (780 nm) on the regeneration process and reconstruction of injured peripheral right side sciatic nerve was investigated. Twelve adult male Wistar rats underwent surgery in aseptic conditions under general anesthesia to induce a lesion to their right side sciatic nerve according to standard protocol. Before suturing the location, only the experimental group was treated by laser. The damaged nerve was directly irradiated with (2 J, 100 mW, 40 seconds). The irradiation procedure was terminated in 21 days with little improvement (4 J, 200 mW, 40 seconds) across the skin surface of experimental group. Rats were selected randomly from each group to be sacrificed on different periods and histopathological examination was carried out on the extracted nerves.Results: Significant acceleration of revascularization and angiogenesis of the injury site was observed in the experimental group. Furthermore, a reduction of hemorrhages and increase in blood supply was observed. Also, Wallerian degeneration decreased while higher axonal density compared to the control rats was observed. Moreover, the cross-section analysis of the injured area on the 14th and 21st days as post-surgery showed that the nerve sheath diameter in the lesion area of the experimental group was reduced. While the ratio between thicknesses increased in the control group. Conclusion:The results of...