Balance and coordination training after sciatic nerve injury

BALANCE AND COORDINATION TRAINING AFTER SCIATIC NERVE INJURY LEANDRO VIC ¸ OSA BONETTI, PT, MSc,1,2 ARTHIESE KORB, PT, MSc,1,2 SANDRO ANTUNES DA SILVA,2 JOCEMAR ILHA, PT, MSc,1,2 SIMONE MARCUZZO, PT, PhD,1,2 MATILDE ACHAVAL, MD, PhD,1,2 and MARIA CRISTINA FACCIONI-HEUSER, PhD1,2 1 Programa de Po´s-Graduaçaõ em Neurocieˆncias, Instituto de Cieˆncias Ba´sicas da Sau´de, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil 2 Laborato´rio de Histofisiologia Comparada, Departamento de Cieˆncias Morfolo´gicas, Instituto de Cieˆncias Ba´sicas da Sau´de, Universidade Federal do Rio Grande do Sul, Sarmento Leite 500, CEP 90050-170, Porto Alegre, Rio Grande do Sul, Brazil Accepted 7 December 2010 ABSTRACT: Introduction: Numerous therapeutic interventions have been tested to enhance functional recovery after peripheral nerve injuries. Methods: After sciatic nerve crush in rats we tested balance and coordination and motor control training in sensorimotor tests and analyzed nerve and muscle histology. Results: The balance and coordination training group and the sham group had better results than the sedentary and motor control groups in sensorimotor tests. The sham and balance and coordination groups had a significantly larger muscle area than the other groups, and the balance and coordination group showed significantly better values than the sedentary and motor control groups for average myelin sheath thickness and g-ratio of the distal portion of the nerve. Conclusions: The findings indicate that balance and coordination training improves sciatic nerve regeneration, suggesting that it is possible to revert and/ or prevent soleus muscle atrophy and improve performance on sensorimotor tests. Muscle Nerve 44: 55–62, 2011

Peripheral

nerve problems are common and encompass a wide spectrum of traumatic injuries, diseases, tumors, and iatrogenic lesions. The incidence of traumatic injuries worldwide is estimated to be >500,000 new patients annually. Injury to peripheral nerves results in partial or total loss of motor, sensory, and autonomic functions in the involved segments of the body.1 Peripheral nerve injuries reduce muscle recruitment and sensation and can disrupt coordination through the changes that occur in the peripheral and central nervous systems.2,3 In addition, deficits in sensorimotor control are experienced immediately after nerve injury.4 Numerous therapeutic interventions intended to enhance functional recovery after peripheral nerve injuries have been tested. Several forms of exercise training have shown beneficial effects in various parameters related to muscle and nerve function in animal models of nerve injury.5–8 For example, in rats, swimming and prolonged wheel running decreased denervated muscle atrophy.9 Abbreviations: ANOVA, analysis of variance; BC, balance and coordination; CNS, central nervous system; HLRWT, horizontal ladder rung walking test; ICBS, Instituto de Cieˆncias Ba´sicas da Sau´de; MC, motor control; NBT, narrow beam test; PB, phosphate buffer; SE, sedentary; SH, sham Key words: balance, coordination, crush, nerve, regeneration Correspondence to: M. C. FACCIONI-HEUSER; e-mail: [email protected] C 2011 Wiley Periodicals, Inc. V

Published online 12 April 2011 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.21996

Balance and Coordination Training

Furthermore, the animals with sciatic nerve crush in which the hindlimb remained unloaded during the post-lesion regenerative period had worse nerve regeneration when compared with animals that supported their weight, showing that hindlimb weight bearing facilitates recovery of neural function and muscle weight.10 Moreover, a previous study in our laboratory showed that endurance training improves sciatic nerve regeneration after traumatic nerve injury, although resistance training and the combination of two strategies delayed functional recovery and did not alter sciatic nerve fiber regeneration.8 Although these studies showed that motor and sensory stimuli are important factors during peripheral nerve regeneration, there have been no studies in animal models that explored balance and coordination training (proprioceptive training) in the treatment of peripheral nerve lesions. For this reason, this study was designed to analyze the effects of balance and coordination training on sensorimotor recovery and to carry out a morphometric analysis of sciatic nerve and soleus muscle fibers after nerve injury induced by sciatic nerve crushing.

METHODS Experimental Design and Surgical Procedures. The experiment was performed on 23 male Wistar rats, 3 months of age and weighing 280–330 g (initial age and weight), obtained from a local breeding colony (ICBS, Universidade Federal do Rio Grande do Sul, Brazil). The animals were housed in standard plexiglass boxes, under a 12:12-h light/dark cycle, in a temperature-controlled environment (20 6 1 C) with food and water ad libitum. All procedures were approved by the ethics committee at the Federal University of Rio Grande do Sul, and all animals were handled in accordance with Brazilian laws. The rats were randomly divided into four groups: (1) sham-operated, without sciatic crush and unexercised, sham (SH, n ¼ 5); (2) sciatic crush and unexercised, sedentary (SE, n ¼ 6); (3) sciatic crush and motor control training (MC, n ¼ MUSCLE & NERVE

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6); and (4) sciatic crush and balance and coordination training (BC, n ¼ 6). Before the surgical procedures, animals were adapted for 5 days in each training program protocol. For the surgical procedures, animals were anesthetized using ketamine and xylazine (90 and 15 mg/kg, intraperitoneally, respectively; Vetbrands, Brazil), and the sciatic nerve was exposed through a skin incision extending from the greater trochanter to the mid-thigh, followed by splitting of the overlying gluteal muscle. Nerve crush injury was performed with a 1-mm hemostatic forceps for 30 seconds (as previously described by Bridge et al.11), 10 mm above the bifurcation into the tibial and common fibular nerves. The muscle and skin were then closed with 4-0 nylon sutures (Somerville, Brazil), and the animals were put in their cages to rest. Forty-eight hours after the surgery, the animals from the MC and BC groups began specific training for 4 weeks, whereas SH and SE animals were put in the same location as the MC and BC animals for a few minutes in order to equalize as much as possible the handling of all groups, but they did not perform any kind of motor activity. Training Protocols. The balance and coordination training program was adapted from acrobatic training.12–14 Animals were required to traverse five different elevated obstacles per day, such as suspension bridges, rope bridges, parallel bars, etc. (each 100 cm long), ending in a dark box. These obstacles require motor learning, balance, and coordination from the animals, and each rat from this group crossed these obstacles 25 times, walking 2500 cm each day of training. The difficulty of the tracks was increased as the training progressed, eventually including more unstable and more challenging obstacles than in the first training week. The motor control training program14 was performed on a flat, obstacle-free runway 100 cm long and 8.5 cm wide, ending in a dark box. Each rat from this group crossed the runway 25 times, walking 2500 cm per day of training. The training programs comprised five sessions per week for 4 weeks. Sensorimotor Studies. At the end of the training period, the horizontal ladder rung walking test (HLRWT) and the narrow beam test (NBT) were used to examine hindlimb sensorimotor function. On the last training day, the animals were adapted to the test apparatus, and the sensorimotor tests were performed 1 day after the end of the training programs. For each test, the animals were filmed three times from a lateral view. The HLRWT apparatus was 100 cm long and 5 cm wide, with horizontal parallel metal rungs (3 mm in diameter) that could be inserted to create a floor with a minimum 56


distance of 1 cm between rungs, elevated 30 cm above the floor, and with a small dark box at the end. In this test, animals were required to walk along a horizontal ladder with an irregular pattern (the distance between the rungs varied from 1 to 5 cm), which was changed from the adaptation phase to the testing phase to prevent the animal from learning the pattern. The number of hindlimb step slips was counted by two blinded observers. The NBT consisted of walking along a 100-cm-long, 3cm-wide flat surface beam (for the adaptation) and a 100-cm-long, 2.6-cm-wide surface beam (for the test) elevated 30 cm above the floor, to reach a small dark box at the end. The number of hindlimb step slips was counted by two blinded observers. Histological and Morphometric Studies. Two days after the sensorimotor tests the animals were anesthetized with sodium thiopental (50 mg/kg, intraperitoneally; Crista´lia, Brazil), injected with 1000 IU heparin (Crista´lia, Brazil) and transcardially perfused with 300 ml of saline solution, followed by 0.5% glutaraldehyde (Sigma Chemical Co., St. Louis, Missouri) and 4% paraformaldehyde (Reagen, Brazil) in a 0.1 M phosphate buffer (PB, pH 7.4) at room temperature. Two short segments (2 mm) of the right sciatic nerve were rapidly excised, one from 5 mm before and one after the crush injury site, proximal and distal portions, respectively.8 The right soleus muscles were carefully dissected free from surrounding tissue, and small samples (2 1 mm) of the central part of each soleus muscle were selected.15 The specimens were postfixed by immersion in the same fixative solution at 4 C until processed. The samples were then washed in 0.1 M PB and postfixed in 1% OsO4 (Sigma Co.) in 0.1 M PB for 30 min. They were again washed in 0.1 M PB, dehydrated in a graded series of acetone, embedded in resin (Durcupan; ACM-Fluka, Switzerland), and polymerized at 60 C. Semithin cross-sections (1 lm) were obtained using an ultramicrotome (MT 6000-XL; RMC, Tucson, Arizona) and stained with 1% toluidine blue (Merck, Germany) in 1% sodium tetraborate (Ecibra, Brazil).8,15 Images of the proximal and distal portions of the right sciatic nerve and the right hindlimb soleus muscle were captured and digitized (nerve portions initially 1000 and muscle 200, and both were further amplified 200% for analysis) using a microscope (Eclipse E-600; Nikon, Japan) coupled to a high-performance CCD camera (Pro-Series) and processed with Image-Pro Plus software, version 6.0 (Media Cybernetics, Bethesda, Maryland).8,15 For morphometric evaluation of the nerve, both proximal and distal portions of the right MUSCLE & NERVE

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FIGURE 1. Comparison of sensorimotor tests. Data are expressed as mean and SEM. (A) HLRWT: aP < 0.05 compared with the SH 0 0 group; bP < 0.05 compared with the SE group. (B) NBT: a P < 0.05 compared with the SH group; b P < 0.05 compared with the SE 0 group; c P < 0.05 compared with the MC group. HLWRT, horizontal ladder rung walking test; NBT, narrow beam test; SH, sham; SE, sedentary; MC, motor control trained; BC, balance and coordination trained. Open bar: non-affected hindlimb slips; filled bar: affected hindlimb slips.

sciatic nerves were separately analyzed, and a set of eight images was chosen using random sampling of one slice of each portion. Morphometric measurements of the sciatic nerve included: (1) average myelinated fiber area (lm2); (2) average myelin sheath thickness (lm); (3) average myelinated fiber diameter (lm); (4) average axon diameter (lm) of the myelinated fiber; and (5) g-ratio (the quotient axon diameter/fiber diameter, a measure of the degree of myelination). These morphological parameters were chosen to assess the differentiation of regenerating sciatic nerves.8 For morphometric evaluation of the soleus muscle, a set of five images was chosen using random sampling of one slice and later digitized. Twenty different muscle fibers from each image were selected (100 fibers from each animal were analyzed). Morphometric measurements of the soleus muscle included the average muscle fiber area (lm2).15 The average myelin sheath thickness was estimated using the measurement tools of Image-Pro Plus software. The measurements of areas (muscle fiber and nerve fiber areas) were estimated with a point-counting technique,8,15 using grids with point density of 1 point per 59.17 lm2 and 1.75 lm2 (for muscle and nerve, respectively) and the ˆ ¼ Rpa/p, where A ˆ is area, following equation: A Rp the sum of points, and a/p the area/point value. To estimate the axon and neural fiber diameters, the area of each individual fiber was converted to the diameter of a circle with an equivalent area. Statistical Analysis. Sensorimotor tests and morphometric measurements of the sciatic nerve were analyzed using repeated-measures analysis of variance (ANOVA), and the soleus muscles were analyzed using one-way ANOVA. All analyses were followed by post hoc Duncan tests. Data are expressed as mean 6 standard error of the mean Balance and Coordination Training

(SEM). The significance level was P < 0.05. Statistical analyses were performed using statistical software. RESULTS Sensorimotor Tests. In the HLRWT (Fig. 1A), the number of affected hindlimb slips was significantly greater than the number of non-affected hindlimb slips in the SE group, a difference that was not observed in the other groups. The SE group showed more affected hindlimb slips (1.8 6 0.3) than the SH and BC groups (0.5 6 0.4 and 0.6 6 0.3, respectively; P < 0.05). Apart from that, there were no significant differences in affected hindlimb slips between the SH, MC, and BC groups, and there were no significant differences in the number of non-affected hindlimb slips across the groups. In the NBT (Fig. 1B), the number of affected hindlimb slips did not differ from the number of non-affected hindlimb slips in the SH and BC groups. The BC group showed fewer affected hindlimb slips (0.7 6 0.4) than the SE and MC groups (2.3 6 0.4 and 2.5 6 0.4, respectively; P < 0.05); however, there were no significant differences in the affected hindlimb slips between the SH and BC groups and in non-affected hindlimb slips between all the groups. Histological Studies. Histological analysis of regenerating nerves (Fig. 2) showed major differences between the SH and experimental groups (SE, MC, and BC). These differences were found in the distal portion of regenerating sciatic nerve. In the SH group, the nerve showed small and large myelinated fibers and scant space between fibers. However, the experimental groups showed a predominance of small-diameter, thin myelin sheath fibers, increased endoneurial connective tissue between the nerve fibers, and degeneration debris in this portion of the nerve. Nevertheless, we note MUSCLE & NERVE

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FIGURE 2. Digitized images of transverse semithin sections (1 lm) obtained from right sciatic nerves. (A, B) Proximal and distal portions, respectively, from normal nerves of the SH group. (C, D) Proximal and distal portions, respectively, from regenerating nerves of the SE group. (E, F) Proximal and distal portions, respectively, from regenerating nerves of the MC group. (G, H) Proximal and distal portions, respectively, from regenerating nerves of the BC group. Mf, myelinated nerve fiber; Sc, Schwann cell; *, endoneurial connective tissue; Dd, degeneration debris; BV, blood vessel; SH, sham; SE, sedentary; MC, motor control trained; BC, balance and coordination trained; P, proximal portion; D, distal portion. Sections were stained with toluidine blue. Scale bar ¼ 20 lm.

that in the BC group, the myelin sheath appeared to be thicker than in the SE and MC groups. Histological analysis of muscle fibers (Fig. 3) revealed differences between the groups. The structure of the muscle fibers in the BC group and in the SH group was similar, presenting mostly large polygonal-shaped muscle fibers, with minimal 58


connective tissue space between them. The muscle fibers in the SE and MC groups were shorter and rounded with much more connective tissue between them. Morphometric Studies. In nerve morphometry, significant differences were seen in terms of mean MUSCLE & NERVE

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FIGURE 3. Digitized images of transverse semithin sections (1 lm) obtained from the central part of the right soleus muscle. (A) Central part of soleus muscle of the SH group. (B) Central part of soleus muscle of the SE group. (C) Central part of soleus muscle of the MC group. (D) Central part of the soleus muscle of the BC group. SH, sham; SE, sedentary; MC, motor control trained; BC, balance and coordination trained. Sections were stained with toluidine blue. Scale bar ¼ 50 lm.

area of nerve fibers (Fig. 4A) between the proximal and distal portion in the SE, MC, and BC groups, although no such differences were seen in the SH group. The mean area of the nerve fibers in the distal portion of the SH group (37.25 6 2.15 lm2; P < 0.05) was significantly larger than in the SE (10.18 6 1.76 lm2; P < 0.05), MC (10.89 6 1.92 lm2; P < 0.05), and BC (12.76 6 2.15 lm2; P < 0.05) groups. When the mean thickness of the myelin sheath in the proximal and distal portions of the injured sciatic nerve was compared (Fig. 4B), all groups had statistically different values. In the analysis of the mean thickness of the myelin sheath in the distal portion of this nerve, the SH group (1.22 6 0.02 lm; P < 0.05) had significantly higher values than the SE (0.43 6 0.02 lm; P < 0.05), MC (0.49 6 0.02 lm; P < 0.05), and BC (0.59 6 0.02 lm; P < 0.05) groups, but the BC group had significantly higher values than the SE and MC groups. In the analysis of the mean diameter of the myelinated fibers (Fig. 4C), when the mean values of the proximal and distal portions of the sciatic nerve were compared, the SE, MC, and BC groups showed significantly different values, whereas no such difference was seen in the SH group. In the analysis of the mean diameter of the fibers in the distal portion, the mean value was significantly greater in the SH group (7.10 6 0.24 lm; P < 0.05) than in the SE (3.59 6 0.20 lm; P < 0.05), Balance and Coordination Training

MC (3.71 6 0.22 lm; P < 0.05), and BC (3.97 6 0.24 lm; P < 0.05) groups. When the mean axon diameter was analyzed (Fig. 4D), all groups had significant differences between the mean values of the proximal and distal portions of the injured sciatic nerve. In the analysis of the distal portion of the nerve, the SH group (4.39 6 0.19 lm; P < 0.05) had a greater mean diameter than the SE (2.71 6 0.15 lm; P < 0.05), MC (2.71 6 0.17 lm; P < 0.05), and BC (2.78 6 0.19 lm; P < 0.05) groups. In the comparison of g-ratios (Fig. 4E), only the BC group did not show a significant difference between the mean values of the proximal and distal portions of the affected sciatic nerve. In the analysis of the distal portion, the SH group (0.64 6 0.01; P < 0.05) had significantly lower values than the SE (0.75 6 0.009; P < 0.05), MC (0.73 6 0.009; P < 0.05), and BC (0.69 6 0.01; P < 0.05) groups, but the BC group had significantly lower values than the SE and MC groups. The mean values of the g-ratio in the SH and BC groups indicate a greater degree of maturation of the myelinated fibers in these groups. In the analysis of muscle fiber morphometric data, the average fiber area (Fig. 5) was significantly greater in the SH and BC groups (1305.20 6 77.80 and 1225.50 6 71.02 lm2, respectively; P < 0.05) than in the SE and MC groups (998.88 6 71.02 and 1000.49 6 71.02 lm2, respectively; P < 0.05). However, there was no significant difference in the mean area of the muscle fibers between the SH and BC groups, and between the SE and MC groups. DISCUSSION

Crush injuries are appropriate for the investigation of cellular and molecular mechanisms of peripheral nerve regeneration and assessment of the role of different factors in the regeneration process.16 Rodents have become the most frequently utilized animal models for the study of peripheral nerve regeneration.1,17 Rats appear to use coordinated forelimb movements to guide forward locomotion during the task, whereas the hindlimbs appear to be primarily involved in maintaining balance and whole-body postural stability.18 After a crush lesion, sensory loss affects hindlimb kinematics.19 Strategies developed to improve peripheral nerve regeneration require quantitative approaches intended to evaluate functional outcome, whereas regeneration can be assessed by numerous methods.17 Although axons in peripheral nerves are known to regenerate better than those in the central nervous system (CNS), methods of accelerating regeneration are needed due to the slow overall rate of growth.20 The approaches intended to MUSCLE & NERVE

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FIGURE 4. Morphometric parameters of sciatic nerve. (A) Average myelinated fiber area in the proximal and distal portions. (B) Average myelin sheath thickness in the proximal and distal portions. (C) Myelinated fiber diameter in the proximal and distal portions. (D) Axon diameter in the proximal and distal portions. (E) The g-ratio in the proximal and distal portions. Data are expressed as mean and SEM. aP < 0.05 compared with the proximal nerve portion of the SH group; bP < 0.05 compared with the proximal nerve portion of 0 the SE group; cP < 0.05 compared with the proximal nerve portion of the MC group; a P < 0.05 compared with the distal nerve portion 0 b0 of the SH group; P < 0.05 compared with the distal nerve portion of the SE group; and c P < 0.05 compared with the distal nerve portion of the MC group. SH, sham; SE, sedentary; MC, motor control; BC, balance and coordination. Filled bar: proximal nerve; open bar: distal nerve.

accelerate regeneration after nerve injury that have been studied, such as treadmill training, resistance training, and swimming,5,8,9,20 may underestimate the role of balance and coordination deficits in this condition. In this study we have investigated whether balance and coordination exercise training could produce different effects in sensorimotor tests and morphological changes in nerve regeneration and in affected hindlimb soleus muscle after a crush lesion of the sciatic nerve. Our results show that the animals in the balance and coordination group and in the sham 60


group had fewer hindlimb slips than the animals in the sedentary and motor control groups in both sensorimotor tests. These tests were performed 1 day after completion of the training protocols, as the HLRWT requires minimal training21 and in the NBT the rats reached maximal task performance within a single test session, reducing the need for extensive training and increasing the reliability of the data.22 These findings show that balance and coordination exercise training improved the performance of animals with nerve injury in motor ability tasks, and also showed that the deficit MUSCLE & NERVE

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FIGURE 5. Morphometric parameters of the central part of the right soleus muscle. Graphs show the average area of muscle fibers from different groups. Data are expressed as mean and SEM. aP < 0.05 compared with the SH group. SH, sham; SE, sedentary; MC, motor control trained; BC, balance and coordination trained.

in these motor abilities remained 4 weeks after injury in both the non-trained injured group and in the motor control group. Therefore, the balance and coordination deficits seen in animals with peripheral nerve injury require specific training, like that used in this study, in order to improve. Exercises that demand balance and coordination from the rats require that they learn various forelimb and hindlimb skills, as well as good coordination of the whole body to perform the activities. The morphometric parameters of nerve fibers were significantly different between the proximal and distal portions of the sciatic nerve in the sedentary, motor control, and balance and coordination groups. When these parameters were compared between the groups, the proximal portion of the nerve was similar across all groups. According to another study,3 when there is a crush lesion, the axon undergoes alterations both in the distal and proximal portions of the lesion, but such lesions occur mainly in the distal portion; thus, the morphometric parameters distal to the nerve lesion are more important for analysis of the influence of exercise in nerve regeneration. In this portion of the nerve, the sham group had significantly different values from the other experimental groups, among which no significant differences were seen in most of the parameters analyzed (average myelinated fiber area, myelinated fiber diameter, and axon diameter). However, concerning average myelin sheath thickness and g-ratio, the balance and coordination group showed significantly better values than the sedentary and motor control groups. The greater myelin sheath thickness and smaller g-ratio values in the balance and coordination–trained animals showed a greater degree of myelinated fiber maturation compared with the sedentary and motor control groups. Exercise training in reaching bottles of water support the Balance and Coordination Training

suggestion that the speed of axonal growth is increased by this particular training protocol5; voluntary physical activity can prime adult sensory neurons for enhanced axonal regeneration after subsequent axotomy. Neurons from these exercised animals showed overall more robust neurite extension when compared with neurons from sedentary animals,7 and treadmill training improved sciatic nerve regeneration after experimental crush injury.8,20,23 All these findings indicate that different types of exercise can positively influence peripheral nerve regeneration. The mean area of muscle fibers was larger for balance and coordination–trained animals than for sedentary and motor control animals. The values in the balance and coordination group were similar to those of the sham-operated group, thus showing that 4-week physical training of this type avoided muscle atrophy after nerve crush. Denervation resulted in a reduction of soleus muscle fiber size and, consequently, produced severe muscle atrophy,24 emphasizing the importance of using exercises that may revert/avoid this muscle atrophy. The forced use of denervated hindlimb muscle, by contralateral immobilization25 or by overuse induced by maximal stretching to the top of a plexiglass box to reach a water bottle,26 also led to an increase in mean fiber diameter and the return of sensory function after sciatic nerve crush. Histological analysis showed that the structure of the muscle fibers in the balance and coordination group and in the sham group were similar, presenting mostly large, polygonal-shaped muscle fibers, with little connective tissue space between them. This differed from the fibers in the sedentary and motor control groups, which were shorter and rounded with greater connective tissue space between them. In conclusion, our data show that balance and coordination training improves sciatic nerve regeneration after experimental traumatic injury. Trained animals showed a greater degree of myelinated fiber maturation, so as to make it possible to revert/prevent soleus muscle atrophy and improve sensorimotor performance. On the other hand, simple walking training (motor control group) does not alter sciatic nerve fiber regeneration, as these animals showed the same results as the sedentary group in all analyzed parameters. Balance and coordination exercises are widely used in the rehabilitation process of various pathologies, but our results show that this type of exercise can also be used as a therapeutic exercise to optimize the process of rehabilitation of patients with peripheral neuropathy. Our findings may influence future studies aimed at relating more effective nerve regeneration in response to specific physical MUSCLE & NERVE

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activities, with different types, lengths, and intensity from those proposed herein, and may also influence strategies used by health professionals when treating peripheral neuropathies. REFERENCES 1. Rodrı´guez FJ, Valero-Cabre´ A, Navarro X. Regeneration and functional recovery following peripheral nerve injury. Drug Discov Today 2004;1:177–185. 2. Hansson T, Brismar T. Loss of sensory discrimination after median nerve injury and activation in the primary somatosensory cortex on functional magnetic resonance imaging. J Neurosurg 2003;99: 100–105. 3. Johnson EO, Zoubos AB, Soucacos PN. Regeneration and repair of peripheral nerves. Injury Int J Care Injured 2005;36S(suppl): S24–S29. 4. Duff SV. Impact of peripheral nerve injury on sensorimotor control. J Hand Ther 2005;18:277–291. 5. van Meeteren NLU, Brakkee JH, Hamers FPT, Helders PJM, Gispen WH. Exercise training improve functional recovery and motor nerve conduction velocity after sciatic nerve crush lesion in the rat. Arch Phys Med Rehabil 1997;78:70–77. 6. Meek MF, Koning MAJ, Nicolai JA, Gransbergen A. Rehabilitation strategy using enhanced housing environment during neural regeneration. J Neurosci Methods 2004;136:179–185. 7. Molteni R, Zheng J, Go´mez-Pinilla F, Twiss JL. Voluntary exercise increases axonal regeneration from sensory neurons. Proc Natl Acad Sci 2004;101:8473–8478. 8. Ilha J, Araujo RT, Malysz T, Hermel EES, Rigon P, Xavier LL, et al. Endurance and resistance exercise training programs elicit specific effects on sciatic nerve regeneration after experimental traumatic lesion in rats. Neurorehabil Neural Repair 2008;22:355–366. 9. Irintchev A, Carmody J, Wernig A. Effects on recovery of soleus and extensor digitorum longus muscle of prolonged wheel running during a period of repeated nerve damage. Neuroscience 1991;44: 515–519. 10. Matsuura T, Ikata T, Takata T, Kashiwaguchi S, Nima M, Sogabi T, et al. Effect of weight bearing on recovery from nerve injury in skeletal muscle. J Appl Physiol 2001;91:2334–2341. 11. Bridge PM, Ball DJ, Mackinnon SE, Nakao Y, Brandt K, Hunter DA, et al. Nerve crush injuries: a model for axonotmesis. Exp Neurol 1994;127:284–290. 12. Black JE, Issacs KR, Anderson BJ, Alcantara AA, Geenough WT. Learning causes synaptogenesis, whereas motor activity causes angio-

62


13. 14. 15.

16. 17.

18. 19. 20. 21.

22. 23. 24. 25. 26.

genesis, in cerebellar cortex of adult rats. Proc Natl Acad Sci 1990; 87:5568–5572. Anderson BJ, Alcantara AA, Geenough WT. Changes in synaptic organization of the rat cerebellar cortex. Neurobiol Learn Mem 1996; 66:221–229. Kleim JA, Lussnig E, Schwarz ER, Comery TA, Greenough WT. Synaptogenesis and FOS expression in the motor cortex of the adult rat after motor skill learning. J Neurol Sci 1996;16:4529–4535. Marcuzzo S, Dutra MF, Stigger F, Do Nascimento PS, Ilha J, KalilGaspar PI, et al. Beneficial effects of treadmill training in a cerebral palsy-like rodent model: walking pattern and soleus quantitative histology. Brain Res 2008;1222:129–140. Udina E, Ceballos D, Gold BG, Navarro X. FK506 enhances reinnervation by regeneration and by collateral sprouting of peripheral nerve fibers. Exp Neurol 2003;183:220–231. Baptista AF, Gomes JRS, Oliveira JT, Santos SMG, Vannier-Santos MA, Martinez AMB. A new approach to assess function after sciatic nerve lesion in the mouse—adaptation of the sciatic static index. J Neurosci Methods 2007;161:259–264. Chu CJ, Jones TA. Experience-dependent structural plasticity in cortex heterotopic to focal sensorimotor cortical damage. Exp Neurol 2000;166:403–414. Varej~o ASP, Meek MF, Ferreira AJA, Patrıćio JAB, Cabrita AMS. Functional evaluation of peripheral nerve regeneration in the rat: walking track analysis. J Neurosci Methods 2001;108:1–9. Sabatier MJ, Redmon N, Schwartz G, English AW. Treadmill training promotes axon regeneration in injured peripheral nerves. Exp Neurol 2008;211:489–493. Metz GA, Whishaw IQ. Cortical and subcortical lesions impair skilled walking in the ladder rung walking test: a new task to evaluate foreand hindlimb stepping, placing, and co-ordination. J Neurosci Methods 2002;115:169–179. Allbutt HN, Henderson JM. Use of the narrow beam test in the rat, 6-hydroxidopamine model of Parkinson’s disease. J Neurosci Methods 2007;159:195–202. Seo TB, Han IS, Yoon JH, Hong KE, Yoon SJ, Namgung U. Involvement of CDC2 in axonal regeneration enhanced by exercise training in rats. Med Sci Sports 2006;38:1267–1276. Sakakima H, Yoshida Y. Effects of short duration static stretching on the denervated and reinnervated soleus muscle morphology in the rat. Arch Phys Med Rehabil 2003;84:1339–1342. Eisen AA, Carpenter S, Karpati G, Bellavance A. The effect of muscle hyper- and hypoactivity upon fiber diameters of intact and regenerating nerves. J Neurol Sci 1973;20:457–469. van Meeteren NLU, Brakkee JH, Helders PJM, Gispen WH. The effect of exercise training on functional recovery after sciatic nerve crush in the rat. J Peripher Nerv Syst 1998;3:277–282.

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