Evoked Muscle Action Potentials Research Articles

Effects of Electrical Stimulation on Peripheral Nerve Regeneration in a Silicone Rubber Conduit in Taxol-Treated Rats

Taxol, a type of antimitotic agent, could modulate local inflammatory conditions in peripheral nerves, which may impair their regeneration and recovery when injured. This study provided in vivo trials of silicone rubber chambers to bridge a long 10 mm sciatic nerve defect in taxol-treated rats. It was aimed to determine the effects of electrical stimulation at various frequencies on regeneration of the sciatic nerves in the bridging conduits. Taxol-treated rats were divided into four groups (n = 10/group): sham control (no current delivered from the stimulator); and electrical stimulation (3 times/week for 3 weeks at 2, 20, and 200 Hz with 1 mA current intensity). Neuronal electrophysiology, animal behavior, neuronal connectivity, macrophage infiltration, calcitonin gene-related peptide (CGRP) expression levels, and morphological observations were evaluated. At the end of 4 weeks, animals in the low- (2 Hz) and medium-frequency (20 Hz) groups had dramatic higher rates of successful regeneration (90% and 80%) across the wide gap as compared to the groups of sham and high-frequency (200 Hz) (60% and 50%). In addition, the 2 Hz group had significantly larger amplitudes and evoked muscle action potentials compared to the sham and the 200 Hz group, respectively (P < 0.05). Heat, cold plate licking latencies, motor coordination, and neuronal connectivity were unaffected by the electrical stimulation. Macrophage density, CGRP expression level, and axon number were all significantly increased in the 20 Hz group compared to the sham group (P < 0.05). This study suggested that low- (2 Hz) to medium-frequency (20 Hz) electrical stimulation could ameliorate local inflammatory conditions to augment recovery of regenerating nerves by accelerating their regrowth and improving electrophysiological function in taxol-treated peripheral nerve injury repaired with the silicone rubber conduit.

Effect of direct current electrical stimulation on the recovery of facial nerve crush injury

This study aimed to evaluate the effect of noninvasive electrical stimulation (ES) using transcutaneous direct current on facial nerve crush injury by assessing in vitro cellular responses including proliferation and differentiation using PC12 cells as well as by performing in vivo functional and morphological assessments. Compared to the non-treated cells, the cells subjected to ES treatment showed clear in vitro neurite outgrowth and enhanced expression of differentiation genes. In this animal model, functional assessment of recovery was performed using vibrissa movement orientation and electrically stimulated muscle action potential. Moreover, histological observation was performed using a transmission electron microscope. A higher score of recovered vibrissa movement and more significant reduction of the threshold of electrically evoked muscle action potential were observed in the ES group than in the control group. Furthermore, histomorphometric evaluation showed that the experimental group had statistically significantly higher axon counts than did the control group. Regenerative nerve fibers were prominent in the distal segments of the ES group.

Use new poly (ε-caprolactone/collagen/NBG) nerve conduits along with NGF for promoting peripheral (sciatic) nerve regeneration in a rat

Regeneration of peripheral nerve defects remained a remarkable clinical challenge. Engineered nerve conduits represent a promising strategy to improve functional recovery in peripheral nerve injury repair. However, nerve conduits require additional factors such as neurotrophic factors to create a more conducive microenvironment for nerve regeneration. Neurotrophic factors have well-demonstrated abilities to improve neurite outgrowth, making them great candidates for repairing of defected nerves. To this end, we examined the beneficial effects of repairing the transected rat sciatic nerve by loading of nerve growth factor (NGF) in nerve conduits. The PCL/Collagen/NBG conduits were interposed into the 10 mm right sciatic nerve defects. Twenty-four rats were randomly allocated into four groups: 1- nerve autograft group, 2- a nongrafted group with gap 10-mm, 3- conduit group and 4- the conduits loaded with NGF. Motor and sensory functional recovery, the evoked muscle action potential, and motor distal latency showed significant improvement in rats treated with NGF. The histology and immunohistochemistry studies revealed less fibrosis and a high level of expression of CD31 and NF-200 protein at the crush site in the Conduit + NGF group. In conclusion, the PCL/Collagen/NBG conduit loaded with NGF, which exhibited nanometer-scale features, neurotrophic activity, favorable mechanical properties and biocompatibility could improve sciatic nerve regeneration in rats.

Novel synaptobrevin-1 mutation causes fatal congenital myasthenic syndrome.

ObjectiveTo identify the molecular basis and elucidate the pathogenesis of a fatal congenital myasthenic syndrome.MethodsWe performed clinical electrophysiology studies, exome and Sanger sequencing, and analyzed functional consequences of the identified mutation.ResultsClinical electrophysiology studies of the patient revealed several‐fold potentiation of the evoked muscle action potential by high frequency nerve stimulation pointing to a presynaptic defect. Exome sequencing identified a homozygous c.340delA frameshift mutation in synaptobrevin 1 (SYB1), one of the three SNARE proteins essential for synaptic vesicle exocytosis. Analysis of both human spinal cord gray matter and normal human muscle revealed expression of the SYB1A and SYB1D isoforms, predicting expression of one or both isoforms in the motor nerve terminal. The identified mutation elongates the intravesicular C‐terminus of the A isoform from 5 to 71, and of the D isoform from 4 to 31 residues. Transfection of either mutant isoform into bovine chromaffin cells markedly reduces depolarization‐evoked exocytosis, and transfection of either mutant isoform into HEK cells significantly decreases expression of either mutant compared to wild type.InterpretationThe mutation is pathogenic because elongation of the intravesicular C‐terminus of the A and D isoforms increases the energy required to move their C‐terminus into the synaptic vesicle membrane, a key step for fusion of the synaptic vesicle with the presynaptic membrane, and because it is predicted to reduce expression of either isoform in the nerve terminal.

Effect of local anesthesia on facial nerve blood flow and muscle action potential

Background & objectiveThe effect of direct application of local lidocaine with epinephrine on the facial nerve (FN) has not been reported. The aim of this study is to assess the effects of 2% lidocaine with 1:100,000 epinephrine at clinically relevant concentrations in a rat FN model with respect to facial nerve blood flow (FNBF) and subsequent electrophysiological changes. Materials and methodsTo assess the influence of drugs on FNBF and electrically evoked muscle action potential (EMAP), small pieces of gelfoam were soaked in PBS 100μl (n=5, control group), 50μl (n=5, treatment group A) and 100μl (n=5, group B) of 2% lidocaine with 1:100,000 epinephrine, and 50μl (n=5, group C) and 100μl (n=5, group D) of 2% lidocaine. After 5min of stable recordings, we applied a 2% lidocaine with or without 1:100,000 epinephrine impregnated gelfoam over the main trunk of the facial nerve of rats for 30min. After removing the applied gelfoam, FNBF and threshold of EMAP were measured separately in each group. ResultsCompared to the control group, the treatment groups showed a significant reduction in FNBF in a dose-dependent manner. The maximal reductions in FNBF were observed in all treatment groups for a period after 10min of the application. Synergistic reduction in FNBF was greater in groups A and B than in the lidocaine applied groups (C and D). The maximal increase in the EMAP threshold was observed immediately after the respective drug application in all groups. The greatest increase in the EMAP threshold was observed in group B. The increased EMAP threshold returned to the baseline value within 120min in groups A and C. ConclusionFrom these results, it can be considered that the topical application of lidocaine with epinephrine caused reduction in FNBF and elevation of EMAP threshold. These acute reductions in FNBF and elevations in the EMAP threshold were restored in a time-dependent manner.

Current-modulated electrical stimulation as a treatment for peripheral nerve regeneration in diabetic rats

To study if electrical stimulation (ES) can be a useful tool to improve functional recovery after neuronal injury in the peripheral nervous system. We studied the effects of 2 Hz of percutaneous ES at different intensities of 1, 10 and 20 mA on peripheral nerve regeneration in rats with diabetes induced by streptozotocin. Non-stimulated diabetic rats were used as the sham-controls. A10-mm gap was made in the rat sciatic nerve by suturing the stumps into silicone rubber tubes and stimulation was carried out every other day for 3 weeks starting 1 week after surgery. After 4 weeks of recovery, the diabetic rats showed that ES of 1 mA or above could increase the cutaneous blood flow in their ipsilateral hindpaw to the injury. ES of 10 mA could improve the amplitude and the area of evoked muscle action potentials with faster target muscle reinnervation. ES of 10 mA could also ameliorate the calcitonin gene-related peptide expression in lamina I-II regions in the dorsal horn ipsilateral to the injury and the number of macrophages in the diabetic distal sciatic nerve. The impaired growth and maturation of regenerating axons in diabetic rat could be improved by ES of 10 mA or above. All these results lead to the conclusion that ES of 10 mA or above might be necessary to improve regeneration after a dissect lesion of the sciatic nerve in the diabetic rat.

High-Frequency Electrical Stimulation Can Be a Complementary Therapy to Promote Nerve Regeneration in Diabetic Rats

The purpose of this study was to evaluate whether 1 mA of percutaneous electrical stimulation (ES) at 0, 2, 20, or 200 Hz augments regeneration between the proximal and distal nerve stumps in streptozotocin diabetic rats. A10-mm gap was made in the diabetic rat sciatic nerve by suturing the stumps into silicone rubber tubes. Normal animals were used as the controls. Starting 1 week after transection, ES was applied between the cathode placed at the distal stump and the anode at the proximal stump every other day for 3 weeks. At 4 weeks after surgery, the normal controls and the groups receiving ES at 20, and 200 Hz had a higher success percentage of regeneration compared to the ES groups at 0 and 2 Hz. In addition, quantitative histology of the successfully regenerated nerves revealed that the groups receiving ES at a higher frequency, especially at 200 Hz, had a more mature structure with more myelinated fibers compared to those in the lower-frequency ES groups. Similarly, electrophysiology in the ES group at 200 Hz showed significantly shorter latency, larger amplitude, larger area of evoked muscle action potentials and faster conduction velocity compared to other groups. Immunohistochemical staining showed that ES at a higher frequency could significantly promote calcitonin gene-related peptide expression in lamina I-II regions in the dorsal horn and recruit a higher number of macrophages in the diabetic distal sciatic nerve. The macrophages were found that they could stimulate the secretion of nerve growth factor, platelet-derived growth factor, and transforming growth factor-β in dissected sciatic nerve segments. The ES at a higher frequency could also increase cutaneous blood flow in the ipsilateral hindpaw to the injury. These results indicated that a high-frequency ES could be necessary to heal severed diabetic peripheral nerve with a long gap to be repaired.

Ferulic Acid Enhances Peripheral Nerve Regeneration across Long Gaps

This study investigated the effect of ferulic acid (FA) on peripheral nerve injury. In the in vitro test, the effect of FA on viability of Schwann cells was studied. In the in vivo test, right sciatic nerves of the rats were transected, and a 15 mm nerve defect was created. A nerve conduit made of silicone rubber tube filled with FA (5 and 25 μg/mL), or saline (control), was implanted into the nerve defect. Results show that the number of proliferating Schwann cells increased significantly in the FA-treated group at 25 μg/mL compared to that in the control group. After 8 weeks, the FA-treated group at 25 μg/mL had a higher rate of successful regeneration across the wide gap, a significantly calcitonin gene-related peptide (CGRP) staining of the lamina I-II regions in the dorsal horn ipsilateral to the injury, a significantly diminished number of macrophages recruited, and a significantly shortening of the latency and an acceleration of the nerve conductive velocity (NCV) of the evoked muscle action potentials (MAPs) compared with the controls. In summary, the FA may be useful in the development of future strategies for the treatment of peripheral nerve injury.

Effect of Arecoline on Regeneration of Injured Peripheral Nerves

The present study provides in vitro and in vivo evaluation of arecoline on peripheral nerve regeneration. In the in vitro study, we found that arecoline at 50 μg/ml could significantly promote the survival and outgrowth of cultured Schwann cells as compared to the controls treated with culture medium only. In the in vivo study, we evaluated peripheral nerve regeneration across a 10-mm gap in the sciatic nerve of the rat, using a silicone rubber nerve chamber filled with the arecoline solution. In the control group, the chambers were filled with normal saline only. At the end of the fourth week, morphometric data revealed that the arecoline-treated group at 5 μg/ml significantly increased the number and the density of myelinated axons as compared to the controls. Immunohistochemical staining in the arecoline-treated animals at 5 μg/ml also showed their neural cells in the L4 and L5 dorsal root ganglia ipsilateral to the injury were strongly retrograde-labeled with fluorogold and lamina I-II regions in the dorsal horn ipsilateral to the injury were significantly calcitonin gene-related peptide-immunolabeled compared with the controls. In addition, we found that the number of macrophages recruited in the distal sciatic nerve was increased as the concentration of arecoline was increased. Electrophysiological measurements showed the arecoline-treated groups at 5 and 50 μg/ml had a relatively larger nerve conductive velocity of the evoked muscle action potentials compared to the controls. These results indicate that arecoline could stimulate local inflammatory conditions, improving the recovery of a severe peripheral nerve injury.

Electroacupuncture and Acupuncture Promote the Rat's Transected Median Nerve Regeneration.

Background. Acupuncture and electroacupuncture treatments of damaged nerves may aid nerve regeneration related to hindlimb function, but the effects on the forelimb-related median nerve were not known. Methods. A gap was made in the median nerve of each rat by suturing the stumps into silicone rubber tubes. The influences of acupuncture and electroacupuncture treatments on transected median nerve regeneration were evaluated from morphological, electrophysiological, and functional angles. Results. Morphologically, the group receiving acupuncture and electroacupuncture treatments had larger total nerve area and blood vessel number compared with the controls. Electrophysiologically, the group receiving electroacupuncture had significantly larger amplitude and larger area of the evoked muscle action potentials compared with the controls. Functionally, the acupuncture and electroacupuncture treatments enhanced the injured paw's ability to regain its grasping power and resulted in a faster efficiency to a new bilateral balance. Conclusion. Our findings provide multiapproach evidence of the efficacy of acupuncture and electroacupuncture treatments to the regeneration of median nerve. Indeed, acupuncture and electroacupuncture appear to have positive effects on the regeneration processes. This platform is beneficial to further study the clinical application of acupuncture and electroacupuncture alternative treatments on nerve-injured patients.

Growth-Promoting Effects of Quercetin on Peripheral Nerves in Rats

The present study evaluated in vitro and in vivo the effects of quercetin (QC), a major ingredient in various flavonoids, on peripheral nerve regeneration. In the in vitro study, we found that QC at concentrations of 0.1, 1, and 10 µg/mL could significantly promote the survival and outgrowth of cultured Schwann cells as compared with the controls treated with culture medium only. In the in vivo study, we evaluated peripheral nerve regeneration across a 15-mm gap in the sciatic nerve of the rat, using a silicone rubber nerve chamber filled with the QC solution. In the control group, the chambers were filled with normal saline only. At the end of 8 weeks, morphometric data revealed that all 3 QC groups significantly increased the count and density of myelinated axons as compared with the controls. Electrophysiological measurements showed that the QC-treated group at 1 µg/mL had a significantly larger area of evoked muscle action potential (MAP) compared with the controls. In addition, the amplitude of the MAP in the QC-treated groups at 0.1 and 1 µg/mL was significantly larger than that in the controls. All of these results indicate that QC treatment has nerve growth-promoting effects which may lead to a promising herbal medicine for the recovery of regenerating peripheral nerves.

Time Course of Neuromuscular Changes during Running in Well-Trained Subjects

Prolonged exercise reduces the capacity of the neuromuscular system to produce force, which is known as fatigue. The purpose of this study was to examine the time course of neural and contractile processes during a 20-km running bout. Eight experienced runners (mean T SD: age = 31 T 6 yr, VO2max = 60.1 T 2.2 mL x kg(-1) x min(-1)) completed an all-out self-paced 20-km treadmill run. Isometric knee extensor torque and EMG responses of the vastus lateralis (VL) in response to percutaneous electrical stimulation and voluntary contraction were measured before and after 5, 10, 15, and 20 km of exercise. Participant's RPE, measured using the Borg 6-20 scale, increased steadily throughout the run to a value of 18 T 1 at exercise termination. Maximal voluntary contraction (MVC) of the knee extensors only decreased during the final 5 km of running, with a 15% +/- 12% (P = 0.02) decrease at 20 km. Vastus lateralis EMG during an MVC was reduced after 15 km (-18% +/- 21%, P = or <0.01) and 20 km (-20% +/- 22%, P = 0.03). A significant correlation (r = 0.71, P = 0.048) was observed between the final reduction in MVC and the maximal EMG. Voluntary activation, estimated by the twitch interpolation technique, decreased by 13% +/- 6% at 20 km (P = or < 0.01), and this was significantly correlated (r = 0.70, P = 0.049) with MVC loss. There were no significant changes in the amplitude of the electrically evoked muscle action potential (M-wave) or potentiated twitch during or after the 20-km run. A reduction in knee extensor MVC only occurs during the final 5 km of a 20-km self-paced run. Impaired voluntary activation and neural drive but not contractile processes are responsible for this decreased strength.

Use of Electrical Stimulation at Different Current Levels to Promote Recovery After Peripheral Nerve Injury in Rats

Electrical stimulation of damaged peripheral nerve may aid regeneration. A 10-mm gap was made in rat sciatic nerve by suturing the stumps into silicone rubber tubes. A control group received no stimulation. To determine whether 2 Hz of percutaneous electrical stimulation at 1 mA, 2 mA, or 4 mA augments regeneration between the proximal and distal nerve stumps. The groups receiving electrical treatment had larger mean values of axon number, endoneurial area, total nerve area, blood vessel number, and blood vessel area compared with the controls. In addition, the group receiving electrical stimulation, especially at 1 mA had significantly shorter latency, larger amplitude, larger area of the evoked muscle action potentials and faster conduction velocity compared with the controls. However, electrical stimulation at 4 mA provoked adverse responses to the function recovery of regenerated nerves in the kinematic gait analysis. Indeed, the electrical stimulation appears to have a detrimental effect on the regeneration process. It could promote the growth of regenerating nerves; however, excessive direct current could be repulsive to regrowing fibers. This reveals the importance for physical therapists using safe stimulus protocols for rehabilitation purposes.

Hyperthermia impairs short-term memory and peripheral motor drive transmission.

The aims of this study were to determine (i) the effect of passive hyperthermia on motor drive and cognitive function, and (ii) whether head cooling can limit the hyperthermia-induced alterations. Sixteen subjects were randomly exposed for 2 h to three different conditions: control (Con, 20°C), hot (Hot, 50°C) and hot head cool (HHC – where cold packs were applied to the head under Hot conditions). Three cognitive tests measuring attention and two measuring memory were performed. Neuromuscular testing included electrically evoked muscle action potentials (M-waves) and reflex waves (H-reflex) at rest and during brief (4–5 s) and sustained (120 s) maximal voluntary contractions (MVC) of the plantar flexors. All the tests were performed in the environmental room. During brief MVC, torque was significantly lower in both Hot and HHC as compared to Con (P < 0.05). The decrease in muscle activation was significant in Hot (P < 0.05) but not in HBC (P= 0.07). This was accompanied by peripheral failures in the transmission of the neural drive at both spinal (significant decrements in H-reflexes and V-waves, P < 0.05) and neuromuscular junction (significant decrements in M-waves, P < 0.05) levels. During sustained MVC, muscle activation was further depressed (P < 0.05) without any concomitant failures in M-waves, suggesting neural activation adjustments occurring probably at the supraspinal level. Cerebral perturbations were confirmed by significant decrements in both memory tests in Hot as compared with Con (P < 0.05) but not in simple tests (attention tests) that were not affected by hyperthermia. The decrement in memory capacity suggested the existence of frontal lobe activity impairments. Thus, HHC preserved memory capacity but not the visual memory.

79 Examination of potential sources of smooth muscle for use as a transplantable, innervated sphincter.

Aim: To examine the electrical and mechanical properties of different smooth muscle tissues for their suitability to assist the malfunctioning urethral sphincter in the treatment of stress urinary incontinence.Methods: Changes in contractile state and membrane potential, in response to nerve stimulation, were measured from guinea‐pig mesenteric veins, detrusor smooth muscle and rat dartos.Results: Intracellular recordings made from mesenteric veins (diameter 100–250 ??m) displayed stable resting membrane potentials (RMPs) of –65.2 ± 2.7 mV (10 cells, five animals). Stimulation with long trains at low frequencies (80s, 0.5–2 Hz), evoked slow sustained membrane depolarizations and constrictions which reached a peak within 50s. Stimulation at 2Hz evoked a membrane depolarization of 16.3 ± 4mV and a 17 ± 7% reduction in vessel diameter. Upon cessation of stimulation, the membrane potential and blood vessel diameter rapidly returned to baseline levels. Detrusor smooth muscle cells had RMPs of –40 ± 4 mV (n = 3). Stimulation at frequencies of 1 to 5 Hz evoked muscle action potentials and contractions. Contractions evoked by long trains of nerve stimulation were not sustained for the duration of stimulus. For example, a stimulus train of 80 s at 1 Hz, evoked a contraction of 20 ± 9 mN which reduced to 3 ± 1 mN (n = 3). Hyoscine reduced the secondary phase of the contraction from 3 ± 0.4 mN to 0.7 ± 0.4 mN (P &lt; 0.01, n = 3). Rat dartos smooth muscle had a RMP of –64 ± 1 mV (n = 38). Long trains of low frequency nerve stimulation (1 Hz for 80s), evoked a slow membrane depolarization of 15 ± 4 mV and sustained contraction of 12 ± 2 mN. Increasing the frequency of stimulation caused a graded increase in the amplitude of both the membrane depolarization and contraction. Following the cessation of stimulus, the membrane potential and force generated by the smooth muscle immediately returned to baseline. All responses were blocked by the α‐adrenoceptor antagonists phentolamine (1 μM) and prazosin (0.1 μM).Conclusion: Smooth muscles of the mesenteric vein and dartos display contractile properties which make them suitable for use as transplantable sphincters. In addition, dartos smooth muscle possesses similar pharmacological properties to the proximal urethral sphincter.

Effects of a laminin peptide (YIGSR) immobilized on crab‐tendon chitosan tubes on nerve regeneration

Thiolated and nonthiolated hydroxyapatite-coated crab-tendon chitosan (t-chitosan/HAp-SH and t-chitosan/HAp, respectively) tubes, both alone and conjugated with CDPGYIGSR (YIGSR) peptide, were compared, in order to determine their biocompatibility and efficacy as nerve conduits. YIGSR peptide was adsorbed on the t-chitosan/HAp (HAp) tubes, and covalently bound on the t-chitosan/HAp-SH (HAp-SH) tubes (Y/HAp and Y/HAp-SH tubes, respectively). HAp, HAp-SH, Y/HAp, or Y/HAp-SH tubes measuring 15 mm were bridge grafted into the sciatic nerve of SD rats. Grafting of 15-mm-long Type I atelocollagen tubes and isografting of sciatic nerves were also carried out (N = 6 in each group). After 12 weeks, evoked muscle action potentials were recorded to calculate the terminal latency quotient. Histological observation and analysis of myelinated axons were also carried out. Nerve-tissue regeneration did not occur directly on the tubes' surfaces in the YIGSR peptide-unconjugated groups. Transplantation of YIGSR-conjugated tubes, however, gave rise to regenerated nerve tissue attached to thin layers of epineurium-like structure formed on the inner-tube surface. Histological and electrophysiological analyses suggested that although thiolation retards nerve-tissue regeneration, adsorbed YIGSR, and, to a lesser extent, peptide that had been covalently bound onto the tube surfaces, enhance nerve regeneration, promoting sprouting from the proximal nerve stump and bridging of regenerated axons throughout the tube.

Reliability of burst superimposed technique to assess central activation failure during fatiguing contraction

Recording a superimposed electrically-induced contraction at the limit of endurance during voluntary contraction is used as an indicator of failure of muscle activation by the central nervous system and discards the existence of peripheral muscle fatigue. We questioned on the reliability of this method by using other means to explore peripheral muscle failure. Fifteen normal subjects sustained handgrip at 60% of maximal voluntary contraction (MVC) until exhaustion. During sustained contraction, the power spectrum analysis of the flexor digitorum surface electromyogram allowed us to calculate the leftward shift of median frequency (MF). A superimposed 60 Hz 3 s pulse train (burst superimposition) was delivered to the muscle when force levelled off close to the preset value. Immediately after the fatigue trial had ended, the subject was asked to perform a 5 s 60% MVC and we measured the peak contractile response to a 60 Hz 3 s burst stimulation. Recordings of the compound evoked muscle action potential (M-wave) allowed us to explore an impairment of neuromuscular propagation. A superimposed contraction was measured in 7 subjects in their two forearms, whereas it was absent in the 8 others. Despite these discrepancies, all subjects were able to reproduce a 3 s 60% MVC immediately after the fatigue trial ended and there was no post-fatigue decrease of contraction elicited by the 60 Hz 3 s burst stimulation, as well as no M-wave decrease in amplitude and conduction time. Thus, there was no indication of peripheral muscle fatigue. MF decrease was present in all individuals throughout the fatiguing contraction and it was not correlated with the magnitude of superimposed force. These observations indicate that an absence of superimposed electrically-induced muscle contraction does not allow us to conclude the existence of a sole peripheral muscle fatigue in these circumstances.

Microsurgical repair of nerve lesions with nerve grafts: the effect of nerve growth factor 7S

This study investigated the effect of local administration of nerve growth factor 7S (NGF-7S) on the axonal regrowth of mixed peripheral nerves through nerve grafts. Sixty male Wistar rats were randomized into two groups (n=30). A defect 12 mm long in the right sciatic nerve was created and repaired with a nerve autograft. NGF-7S (group A) or normal saline (group B-control) was locally administered daily during the first 3 weeks. For this purpose a subcutaneously implanted reservoir connected to a silicone tube was used. Electrophysiological and histological-morphometric studies were carried out 4, 6, 8, 10 and 12 weeks postoperatively (subgroups a, b, c, d, and e, respectively, n=6 each). Data analysis showed that: (a) the evoked muscle action potential and (b) the orientation, number, myelin thickness, and diameter of myelinated fibers were better in the NGF-7S than in the control group. These findings present strong evidence of the beneficial effect of NGF-7S on peripheral nerve regeneration through nerve grafts.

Evaluation of cross-linking procedures of collagen tubes used in peripheral nerve repair

Three different cross-linking methods were compared to prepare collagen tubes, namely irradiation by ultraviolet (UV), heating and immersing in glutaraldehyde (GA). Bridge grafting of 15 mm was carried out with these tubes, as well as with non-cross-linked collagen tubes for comparison, in a defect of rat sciatic nerves ( N=21 in each group). As a control, isografting was carried out ( N=6). The specimens were taken from the grafted site in each experimental group for histological observation after, respectively 1, 2, 4, 6 and 8 weeks ( N=3 each). Evoked muscle action potentials were recorded on the calf muscle in the experimental and control groups after 12 weeks, and the grafted material and tibial nerve were harvested for histological analysis ( N=6). The inner space of UV-irradiated tubes was preserved with almost no cell infiltration and nerve regeneration matching for isograft was obtained. Rapid degradation of the heat-treated tubes occurred and many macrophages were mobilized to remove the collagen debris. The non-treated tube swelled and the regenerated nerve tissue in the tube was constricted with time. The GA-immersed tubes showed less cellular activity and poor regenerated nerve tissue compared with the other cross-linking methods. Therefore, UV irradiation to collagen tubes is recommended as a cross-linking method for nerve conduit.

Autogenous venous graft with one-stage prepared Schwann cells as a conduit for repair of long segmental nerve defects.

The use of autogenous venous graft with intraluminal injection of Schwann cells to enhance nerve regeneration of long segmental nerve defects was evaluated in a rabbit tibial nerve-repair model. Schwann cells were isolated from the excised rabbit tibial nerve by using the polylysine differential adhesion method. The cultured cells were identified by immunocytochemical labeling for S-100 protein. Tibial nerve defects in 4-cm segments were created in 24 animals, which were then divided into three groups. In Group 1, the tibial nerve defect was repaired with interposition vein graft alone; in Group 2, the nerve defect was repaired with a vein graft with intraluminal injection of Schwann-cell suspension; in Group 3, the nerve defect was repaired by autogenous nerve graft alone. At 2 months postoperatively, electrophysiologic evaluation showed that an evoked muscle action potential was recorded for the animals in Group 2, with vein grafting plus Schwann cells, and for those in Group 3, with autogenous nerve grafting, but not for those in Group 1, where vein grafting alone was used. The average motor nerve conduction velocity in the group with vein grafting and Schwann cells was 3.4 +/- 1.5 m/sec, which was slower than the nerve grafting group (7.8 +/- 1.8 m/sec). Histologic analysis confirmed there was formation of new nerve fascicles with myelination in the vein graft filled with Schwann cells. No nerve regrowth was found in the vein grafts without Schwann cells. These results suggested that isolated Schwann cells are able to survive in a vein graft, and that the vein graft with intraluminal seeded Schwann cells could be an alternative for repairing injured nerves with long gaps.