Lasers in Surgery and Medicine 42:673–682 (2010) Effects of 660 and 780 nm Low-Level Laser Therapy on Neuromuscular Recovery After Crush Injury in Rat Sciatic Nerve Davilene Gigo-Benato, PhD, 1 * Thiago Luiz Russo, PhD, 2 Erika Harumi Tanaka, 1 Lı ´via Assis, MS, 1 Tania Fa ´ tima Salvini, PhD, 2 and Nivaldo Antonio Parizotto, PhD 1 1 Thermophototherapy Unit, Physical Therapy Department, Federal University of Sa˜o Carlos (UFSCar), Sa˜o Carlos, SP13565-905, Brazil 2 Skeletal Muscle Plasticity Unit, Physical Therapy Department, Federal University of Sa˜o Carlos (UFSCar), Sa˜o Carlos, SP 13565-905, Brazil Background and Objective: Post-traumatic nerve repair is still a challenge for rehabilitation. It is particularly important to develop clinical protocols to enhance nerve regeneration. The present study investigated the effects of 660 and 780 nm low-level laser therapy (LLLT) using different energy densities (10, 60, and 120 J/cm 2 ) on neuromuscular and functional recovery as well as on matrix metalloproteinase (MMP) activity after crush injury in rat sciatic nerve. Materials and Methods: Rats received transcutaneous LLLT irradiation at the lesion site for 10 consecutive days post-injury and were sacrificed 28 days after injury. Both the sciatic nerve and tibialis anterior muscles were analyzed. Nerve analyses consisted of histology (light microscopy) and measurements of myelin, axon, and nerve fiber cross-sectional area (CSA). S-100 labeling was used to identify myelin sheath and Schwann cells. Muscle fiber CSA and zymography were carried out to assess the degree of muscle atrophy and MMP activity, respectively. Stat- istical significance was set at 5% (P0.05). Results: Six hundred sixty nanometer LLLT either using 10 or 60 J/cm 2 restored muscle fiber, myelin and nerve fiber CSA compared to the normal group (N). Furthermore, it increased MMP-2 activity in nerve and decreased MMP-2 activity in muscle and MMP-9 activity in nerve. In contrast, 780 nm LLLT using 10 J/cm 2 decreased MMP-9 activity in nerve compared to the crush group (CR) and N; it also restored normal levels of myelin and nerve fiber CSA. Both 60 and 120 J/cm 2 decreased MMP-2 activity in muscle compared to CR and N. 780 nm did not prevent muscle fiber atrophy. Functional recovery in the irradiated groups did not differ from the non- irradiated CR. Conclusion: Data suggest that 660 nm LLLT with low (10 J/cm 2 ) or moderate (60 J/cm 2 ) energy densities is able to accelerate neuromuscular recovery after nerve crush injury in rats. Lasers Surg. Med. 42:673 – 682, 2010. ß 2010 Wiley-Liss, Inc. Key words: peripheral nerve repair; laser therapy; denervated muscle; rehabilitation; functional analysis INTRODUCTION Peripheral nerve injury is a common clinical event which is generally related to incapacity [1]. According to a U.S. study, 50,000 subjects suffer traumatic injury to peripheral nerves every year [2,3] representing a significant public health problem. In Brazil, a recent study classified 456 cases of nerve injury and showed that axonotmesis represents the most common nerve injury (45%) followed by neurotmesis (41%) and neuropraxia (14%), respectively [4]. The mechanisms involving nerve regeneration are well- described. When nerve fiber continuity is interrupted, the distal stump undergoes Wallerian degeneration [5]. The proximal axon stump can then regenerate along the nerve tract distal to the lesion and reach the peripheral target (muscle fibers and sensory receptors) [5]. Another tissue strongly affected by peripheral nerve injuries is skeletal muscle. Innervation is critical for muscle functionality and structural integrity [6,7]. Thus, denervation leads to a profound loss of muscle mass and inability to generate force [8,9]. The regeneration process depends on numerous changes in the extracellular matrix (ECM) [10] occurring concom- itantly in both injured nerve and denervated muscles [11 – 13]. These changes require the action of proteolytic zinc- containing enzymes called matrix metalloproteinases (MMPs), which play a critical role in the ECM reorganiza- tion. MMPs are secreted by Schwann cells, intramuscular axons, muscle satellite cells, and fibroblasts into the skeletal muscle at the neuromuscular junction (NMJ) and around muscle fibers [11,14–16]. Contract grant sponsor: Fundac ¸a ˜o de Amparo a ` Pesquisa do Estado de Sa ˜ o Paulo (FAPESP); Contract grant numbers: 2006/ 52931-4, 08/03499-8. *Correspondence to: Davilene Gigo-Benato, PhD, Physical Therapy Department, Federal University of Sa ˜ o Carlos (UFSCar), Rodovia Washington Luı ´s km 235, C.P. 676—CEP 13565-905, Sa ˜o Carlos, SP, Brazil. E-mail: benatodavilene@yahoo.com.br Accepted 5 September 2010 Published online 15 October 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/lsm.20978 ß 2010 Wiley-Liss, Inc.