Misdirection of regenerating axons and functional recovery following sciatic nerve injury in rats

Therapeutic Electrical Stimulation for Surgeons: How it Works and How to Apply it

Electrical stimulation (ES) enhances peripheral nerve inherent regeneration capacity by promoting accelerated axonal outgrowth and selectivity toward appropriate motor and sensory targets. These effects lead to significantly improved functional outcomes and shorter recovery time. Electrical stimulation can be applied intra-operatively or immediately post-operatively. Active clinical trials are looking into additional areas of application, length of stimulation, and functional outcomes.

Physiology of Nerve Regeneration: Key Factors Affecting Clinical Outcomes

Functional recovery after peripheral nerve injuries is disappointing despite surgical advances in nerve repair. This review summarizes the relatively short window of opportunity for successful nerve regeneration due to the decline in the expression of growth-associated genes and in turn, the decline in regenerative capacity of the injured neurons and the support provided by the denervated Schwann cells, and the atrophy of denervated muscles. Brief, low-frequency electrical stimulation and post-injury exercise regimes ameliorate these deficits in animal models and patients, but the misdirection of regenerating nerve fibers compromises functional recovery and remains an important area of future research.

Air-stepping in the neonatal mouse: a powerful tool for analyzing early stages of rhythmic limb movement development

There is a lack of experimental methods in genetically tractable mouse models to analyze the developmental period at which newborns mature weight-bearing locomotion. To overcome this deficit, we introduce methods to study l-3,4-dihydroxyphenylalanine (l-DOPA)-induced air-stepping in mice at postnatal day (P)7 and P10. Air-stepping is a stereotypic rhythmic behavior that resembles mouse walking overground locomotion but without constraints imposed by weight bearing, postural adjustments, or sensory feedback. We propose that air-stepping represents the functional organization of early spinal circuits coordinating limb movements. After subcutaneous injection of l-DOPA (0.5 mg/g), we recorded air-stepping movements in all four limbs and electromyographic (EMG) activity from ankle flexor (tibialis anterior, TA) and extensor (lateral gastrocnemius, LG) muscles. Using DeepLabCut pose estimation, we analyzed rhythmicity and limb coordination. We demonstrate steady rhythmic stepping of similar duration from P7 to P10 but with some fine-tuning of interlimb coordination with age. Hindlimb joints undergo a greater range of flexion at older ages, indicating maturation of flexion-extension cycles as the animal starts to walk. EMG recordings of TA and LG show alternation but with more focused activation particularly in the LG from P7 to P10. We discuss similarities to neonatal rat l-DOPA-induced air-stepping and infant assisted walking. We conclude that limb coordination and muscle activations recorded with this method represent basic spinal cord circuitry for limb control in neonates and pave the way for future investigations on the development of rhythmic limb control in genetic or disease models with correctly or erroneously developing motor circuitry.NEW & NOTEWORTHY We present novel methods to study neonatal air-stepping in newborn mice. These methods allow analyses at the onset of limb coordination during the period in which altricial species like rats, mice, and humans "learn" to walk. The methods will be useful to test a large variety of mutations that serve as models of motor disease in newborns or that are used to probe for specific circuit mechanisms that generate coordinated limb motor output.

Target-selective vertebrate motor axon regeneration depends on interaction with glial cells at a peripheral nerve plexus

A critical step for functional recovery from peripheral nerve injury is for regenerating axons to connect with their pre-injury targets. Reestablishing pre-injury target specificity is particularly challenging for limb-innervating axons as they encounter a plexus, a network where peripheral nerves converge, axons from different nerves intermingle, and then re-sort into target-specific bundles. Here, we examine this process at a plexus located at the base of the zebrafish pectoral fin, equivalent to tetrapod forelimbs. Using live cell imaging and sparse axon labeling, we find that regenerating motor axons from 3 nerves coalesce into the plexus. There, they intermingle and sort into distinct branches, and then navigate to their original muscle domains with high fidelity that restores functionality. We demonstrate that this regeneration process includes selective retraction of mistargeted axons, suggesting active correction mechanisms. Moreover, we find that Schwann cells are enriched and associate with axons at the plexus, and that Schwann cell ablation during regeneration causes profound axonal mistargeting. Our data provide the first real-time account of regenerating vertebrate motor axons navigating a nerve plexus and reveal a previously unappreciated role for Schwann cells to promote axon sorting at a plexus during regeneration.

Treadmill training of rats after sciatic nerve graft does not alter accuracy of muscle reinnervation

Background and purpose

After peripheral nerve lesions, surgical reconstruction facilitates axonal regeneration and motor reinnervation. However, functional recovery is impaired by aberrant reinnervation.

Materials and methods

We tested whether training therapy by treadmill exercise (9 × 250 m/week) before (run-idle), after (idle-run), or both before and after (run-run) sciatic nerve graft improves the accuracy of reinnervation in rats. Female Lewis rats (LEW/SsNHsd) were either trained for 12 weeks (run) or not trained (kept under control conditions, idle). The right sciatic nerves were then excised and reconstructed with 5 mm of a congenic allograft. One week later, training started in the run-run and idle-run groups for another 12 weeks. No further training was conducted in the run-idle and idle-idle groups. Reinnervation was measured using the following parameters: counting of retrogradely labeled motoneurons, walking track analysis, and compound muscle action potential (CMAP) recordings.

Results

In intact rats, the common fibular (peroneal) and the soleus nerve received axons from 549 ± 83 motoneurons. In the run-idle group, 94% of these motoneurons had regenerated 13 weeks after the nerve graft. In the idle-run group, 81% of the normal number of motoneurons had regenerated into the denervated musculature and 87% in both run-run and idle-idle groups. Despite reinnervation, functional outcome was poor: walking tracks indicated no functional improvement of motion in any group. However, in the operated hindlimb of run-idle rats, the CMAP of the soleus muscle reached 11.9 mV (normal 16.3 mV), yet only 6.3-8.1 mV in the other groups.

Conclusion

Treadmill training neither altered the accuracy of reinnervation nor the functional recovery, and pre-operative training (run-idle) led to a higher motor unit activation after regeneration.

A glia cell dependent mechanism at a peripheral nerve plexus critical for target-selective axon regeneration

A critical step for functional recovery from peripheral nerve injury is for regenerating axons to connect with their pre-injury targets. Reestablishing pre-injury target specificity is particularly challenging for limb-innervating axons as they encounter a plexus, a network where peripheral nerves converge, axons from different nerves intermingle, and then re-sort into target-specific bundles. Here, we examine this process at a plexus located at the base of the zebrafish pectoral fin, equivalent to tetrapod forelimbs. Using live cell imaging and sparse axon labeling, we find that regenerating motor axons from three nerves coalesce into the plexus. There, they intermingle and sort into distinct branches, and then navigate to their original muscle domains with high fidelity that restores functionality. We demonstrate that this regeneration process includes selective retraction of mistargeted axons, suggesting active correction mechanisms. Moreover, we find that Schwann cells are enriched and associate with axons at the plexus, and that Schwann cell ablation during regeneration causes profound axonal mistargeting. Our data provide the first real time account of regenerating vertebrate motor axons navigating a nerve plexus and reveal a previously unappreciated role for Schwann cells to promote axon sorting at a plexus during regeneration.

Selective Repair of Motor Branches in the Femoral Nerve by Transferring the Motor Branches of Obturator Nerve: An Anatomical Feasibility Study

BACKGROUND

Anterior branch of the obturator nerve transfer has been proven as an effective method for femoral nerve injuries, but the patient still has difficulty in rising and squatting, up and downstairs. Here, we presented a novel neurotization procedure of selectively repairing 3 motor branches of the femoral nerve by transferring motor branches of the obturator nerve in the thigh level and assessing its anatomical feasibility.

METHODS

Eight adult cadavers (16 thighs) were dissected. The nerve overlap distance between the gracilis branch and the rectus femoris (RF) branch, the adductor longus (AL) branch and the vastus medialis (VM) branch, as well as the adductor magnus (AM) branch and the vastus intermedius (VI) branch were measured. Also, the axon counts of the donor and recipient nerve were evaluated by histological evaluation.

RESULTS

In all specimens, nerve overlap of at least 2.1 cm was observed in all 16 dissected thighs between the donor and recipient nerve branches, and the repair appeared to be without tension. There is no significant difference in the axon counts between gracilis branch (598 ± 83) and the RF branch (709 ± 151). The axon counts of the AL branch (601 ± 93) was about half of axon counts of the VM branch (1423 ± 189), and the axon counts of AM branch (761 ± 110) was also about half of the VI branch (1649 ± 281).

CONCLUSIONS

This novel technique of the combined nerve transfers below the inguinal ligament, specifically the gracilis branch to the RF branch, the AL branch to the VM branch, and the AM branch to the VI branch, is anatomically feasible. It provides a promising alternative in the repair of femoral nerve injuries and an anatomical basis for the clinical application of motor branches of the obturator nerve transfer to repair the motor portion of the injured femoral nerve.

Treatment With Nimodipine or FK506 After Facial Nerve Repair Neither Improves Accuracy of Reinnervation Nor Recovery of Mimetic Function in Rats

Purpose

Nimodipine and FK506 (Tacrolimus) are drugs that have been reported to accelerate peripheral nerve regeneration. We therefore tested these substances aiming to improve the final functional outcome of motoric reinnervation after facial nerve injury.

Methods

In 18 female rats, the transected facial nerve was repaired by an artificial nerve conduit. The rats were then treated with either placebo, nimodipine, or FK506, for 56 days. Facial motoneurons were pre-operatively double-labeled by Fluoro-Gold and again 56 days post-operation by Fast-Blue to measure the cytological accuracy of reinnervation. The whisking motion of the vibrissae was analyzed to assess the quality of functional recovery.

Results

On the non-operated side, 93–97% of those facial nerve motoneurons innervating the vibrissae were double-labeled. On the operated side, double-labeling only amounted to 38% (placebo), 40% (nimodipine), and 39% (FK506), indicating severe misdirection of reinnervation. Regardless of post-operative drug or placebo therapy, the whisking frequency reached 83–100% of the normal value (6.0 Hz), but whisking amplitude was reduced to 33–48% while whisking velocity reached 39–66% of the normal values. Compared to placebo, statistically neither nimodipine nor FK506 improved accuracy of reinnervation and function recovery.

Conclusion

Despite previous, positive data on the speed and quantity of axonal regeneration, nimodipine and FK506 do not improve the final functional outcome of motoric reinnervation in rats.

Comparison between normal and reverse orientation of graft in functional and histomorphological outcomes after autologous nerve grafting: An experimental study in the mouse model

BACKGROUND

Autologous nerve grafting has been considered the gold standard for the treatment of irreparable nerve gaps. However, the choice of effective proximodistal orientation of autografts (normal or reversed) is controversial. Therefore, we compared functional and histological outcomes between normal and reversed orientations of autografts in a mouse sciatic nerve model.

MATERIALS AND METHODS

Thirty C57BL/6J mice weighing 20-25 g were assigned to the donor, normally oriented autograft, and reverse-oriented autograft groups (n = 10 per group). A 10-mm section of the sciatic nerve was harvested from a donor mouse. Half the harvested nerve was grafted onto an irreparable gap in a recipient mouse using either a normal or reversed orientation. The sciatic functional index (SFI) was measured biweekly for up to 12 weeks postoperatively. Morphological analysis was performed using immunofluorescence staining for neurofilament (NF) and myelin protein zero (P0) in cross-sectional and whole-mount nerve preparations in 12 weeks postoperatively. Additionally, morphological analysis of the tibialis anterior muscle was performed using hematoxylin and eosin staining. NF or P0-expressing axons were counted and cross-sectional area (CSA) and minimum Feret's diameter of myofibers were measured.

RESULTS

The SFI recovered gradually up to 12 weeks after autografting, but there were no significant differences in the SFI between the normal and reversed orientations. The number of NF-expressing axons in center of graft was significantly higher in the normal orientation than in the reversed orientation (P < .05). However, there were no significant differences in the number and mean intensity of P0-expressing axons between the orientations. The CSA of myofibers was significantly larger in the normal orientation than in the reversed orientation (P < .05).

CONCLUSIONS

Normally oriented autografts promote axonal regrowth and prevent neurogenic muscular atrophy compared with reverse-oriented autografts. However, despite these positive histomorphometric effects, the proximodistal orientation of the autograft does not affect functional outcomes.

Efficacy of Silicone Conduit in the Rat Sciatic Nerve Repair Model: Journey of a Thousand Miles

Background

A lot of options have been tried for bridging the two ends of the injured nerves. Researchers have used decellularized nerve grafts, artificial materials and even nerve growth factors to augment functional recovery. These materials are either costly or inaccessible in developing world.

Objective

The study aimed to evaluate the efficacy of the silicone conduit in a rat sciatic nerve injury model.

Materials and Methods

24 healthy Sprague-Dawley (SD) rats (250-300 grams; 8-10 weeks) were used and right sciatic nerve was exposed; transected and re-anastomosed by two different methods in 16 rats. In control group, n = 8 (Group I) the sciatic nerve was untouched; Group II (reverse nerve anastomosis, n = 8): 1-centimeter of nerve was cut and re-anastomosed by using 10-0 monofilament suture; Group III (silicone conduit, n = 8) 1-centimeter nerve segment was cut, replaced by silicone conduit and supplemented by fibrin glue]. Evaluation of nerve recovery was done functionally (pain threshold and sciatic functional index) over 3 months and histologically and electron microscopically.

Results

Functional results showed a trend of clinical improvement in Group III and II but recovery was poor and never reached up to normal. Histopathological and electron microscopic results showed an incomplete axonal regeneration in Groups II and III. Psychological analyses showed that no outwards signs of stress were present and none of the rats showed paw biting and teeth chattering.

Conclusion

The silicone conduit graft may be an economical and effective alternative to presently available interposition grafts, however for short segments only.

Electrical stimulation to enhance peripheral nerve regeneration: Update in molecular investigations and clinical translation

Peripheral nerve injuries are common and frequently result in incomplete functional recovery even with optimal surgical treatment. Permanent motor and sensory deficits are associated with significant patient morbidity and socioeconomic burden. Despite substantial research efforts to enhance peripheral nerve regeneration, few effective and clinically feasible treatment options have been found. One promising strategy is the use of low frequency electrical stimulation delivered perioperatively to an injured nerve at the time of surgical repair. Possibly through its effect of increasing intraneuronal cyclic AMP, perioperative electrical stimulation accelerates axon outgrowth, remyelination of regenerating axons, and reinnervation of end organs, even with delayed surgical intervention. Building on decades of experimental evidence in animal models, several recent, prospective, randomized clinical trials have affirmed electrical stimulation as a clinically translatable technique to enhance functional recovery in patients with peripheral nerve injuries requiring surgical treatment. This paper provides an updated review of the cellular physiology of electrical stimulation and its effects on axon regeneration, Level I evidence from recent prospective randomized clinical trials of electrical stimulation, and ongoing and future directions of research into electrical stimulation as a clinically feasible adjunct to surgical intervention in the treatment of patients with peripheral nerve injuries.

Extradural Contralateral C7 Nerve Root Transfer in a Cervical Posterior Approach for Treating Spastic Limb Paralysis: A Cadaver Feasibility Study

STUDY DESIGN

Anatomic study in nine fresh-frozen cadavers.

OBJECTIVE

To confirm the anatomical feasibility of transferring the extradural ventral roots (VRs) and dorsal roots (DRs) of contralateral C7 nerves to those of the ipsilateral C7 nerves respectively through a cervical posterior approach.

SUMMARY OF BACKGROUND DATA

The contralateral C7 nerve root transfer technique makes breakthrough for treating spastic limb paralysis. However, its limitations include large surgical trauma and limited indications.

METHODS

Nine fresh-frozen cadavers (four females and five males) were placed prone, and the feasibility of exposing the bilateral extradural C7 nerve roots, separation of the extradural C7 VR and DR, and transfer of the VR and DR of the contralateral C7 to those of the ipsilateral C7 on the dural mater were assessed. The pertinent distances and the myelography results of each specimen were analyzed. The acetylcholinesterase (AChE) and antineurofilament 200 (NF200) double immunofluorescent staining were preformed to determine the nerve fiber properties.

RESULTS

A cervical posterior midline approach was made and the laminectomy was performed to expose the bilateral extradural C7 nerve roots. After the extradural C7 VR and DR are separated, the VR and DR of the contralateral C7 have sufficient lengths to be transferred to those of the ipsilateral C7 on the dural mater. The myelography results showed that the spinal cord is not compressed after the nerve anastomosis. The AChE and NF200 double immunofluorescent staining showed the distal ends of the contralateral C7 VRs were mostly motor nerve fibers, and the distal ends of the contralateral C7 DRs were mostly sensory nerve fibers.

CONCLUSION

Extradural contralateral C7 nerve root transfer in a cervical posterior approach for treating spastic limb paralysis is anatomically feasible.

LEVEL OF EVIDENCE

5.

Axonotmesis-evoked plantar vasodilatation as a novel assessment of C-fiber afferent function after sciatic nerve injury in rats

Quantitative assessment of the recovery of nerve function, especially sensory and autonomic nerve function, remains a challenge in the field of nerve regeneration research. We previously found that neural control of vasomotor activity could be potentially harnessed to evaluate nerve function. In the present study, five different models of left sciatic nerve injury in rats were established: nerve crush injury, nerve transection/suturing, nerve defect/autografting, nerve defect/conduit repair, and nerve defect/non-regeneration. Laser Doppler perfusion imaging was used to analyze blood perfusion of the hind feet. The toe pinch test and walking track analysis were used to assess sensory and motor functions of the rat hind limb, respectively. Transmission electron microscopy was used to observe the density of unmyelinated axons in the injured sciatic nerve. Our results showed that axonotmesis-evoked vasodilatation in the foot 6 months after nerve injury/repair recovered to normal levels in the nerve crush injury group and partially in the other three repair groups; whereas the nerve defect/non-regeneration group exhibited no recovery in vasodilatation. Furthermore, the recovery index of axonotmesis-evoked vasodilatation was positively correlated with toe pinch reflex scores and the density of unmyelinated nerve fibers in the regenerated nerve. As C-fiber afferents are predominantly responsible for dilatation of the superficial vasculature in the glabrous skin in rats, the present findings indicate that axonotmesis-evoked vasodilatation can be used as a novel way to assess C-afferent function recovery after peripheral nerve injury. This study was approved by the Ethics Committee for Laboratory Animals of Nantong University of China (approval No. 20130410-006) on April 10, 2013.

Zebrafish is a central model to dissect the peripheral neuropathy

The peripheral nervous system (PNS) is composed with all nerves extended from the brain and spinal cord, which are the central nervous system to other organs of the body. Dysfunctional peripheral motion resulting from the regressive neuronal axons in the defected PNS leads to several peripheral neuropathies including both inherited and non-inherited disorders. Because of poor understanding of cellular and molecular mechanisms involved in the peripheral neuropathy, there is currently non-targeted treatment of the disorder. Basic researches have paid attention to dissect roles of causative genes, identified from the inherited peripheral neuropathies, in PNS development. However, recent studies focusing on investigation of therapeutic targets have suggested that successful regeneration of the impaired peripheral nerves may be most effective treatment. The regeneration studies have been limited in the rodents system due to some of practical and physiological disadvantages until zebrafish model has emerged as an ideal system. Hence, this review aims to provide a comprehensive overview of the advantages of zebrafish as a model for the peripheral neuropathy researches and to suggest the disease genes-involved potential mechanisms targeting the PNS regeneration that may be demonstrated in zebrafish.

Regeneration of Transected Recurrent Laryngeal Nerve Using Hybrid-Transplantation of Skeletal Muscle-Derived Stem Cells and Bioabsorbable Scaffold

Hybrid transplantation of skeletal muscle-derived multipotent stem cells (Sk-MSCs) and bioabsorbable polyglyconate (PGA) felt was studied as a novel regeneration therapy for the transected recurrent laryngeal nerve (RLN). Sk-MSCs were isolated from green fluorescence protein transgenic mice and then expanded and transplanted with PGA felt for the hybrid transplantation (HY group) into the RLN transected mouse model. Transplantation of culture medium (M group) and PGA + medium (PGA group) were examined as controls. After eight weeks, trans-oral video laryngoscopy demonstrated 80% recovery of spontaneous vocal-fold movement during breathing in the HY group, whereas the M and PGA groups showed wholly no recoveries. The Sk-MSCs showed active engraftment confined to the damaged RLN portion, representing favorable prevention of cell diffusion on PGA, with an enhanced expression of nerve growth factor mRNAs. Axonal re-connection in the HY group was confirmed by histological serial sections. Immunohistochemical analysis revealed the differentiation of Sk-MSCs into Schwann cells and perineurial/endoneurial cells and axonal growth supportive of perineurium/endoneurium. The number of axons recovered was over 86%. These results showed that the stem cell and cytokine delivery system using hybrid transplantation of Sk-MSCs/PGA-felt is a potentially practical and useful approach for the recovery of transected RLN.

Tubulation repair mitigates misdirection of regenerating motor axons across a sciatic nerve gap in rats

The repair of peripheral nerve laceration injury to obtain optimal function recovery remains a big challenge in the clinic. Misdirection of regenerating axons to inappropriate target, as a result of forced mismatch of endoneurial sheaths in the case of end-to-end nerve anastomosis or nerve autografting, represents one major drawback that limits nerve function recovery. Here we tested whether tubulation repair of a nerve defect could be beneficial in terms of nerve regeneration accuracy and nerve function. We employed sequential retrograde neuronal tracing to assess the accuracy of motor axon regeneration into the tibial nerve after sciatic nerve laceration and entubulation in adult Sprague-Dawley rats. In a separate cohort of rats with the same sciatic nerve injury/repair protocols, we evaluated nerve function recovery behaviorally and electrophysiologically. The results showed that tubulation repair of the lacerated sciatic nerve using a 3-6-mm-long bioabsorbable guidance conduit significantly reduced the misdirection of motor axons into the tibial nerve as compared to nerve autografting. In addition, tubulation repair ameliorated chronic flexion contracture. This study suggests that tubulation repair of a nerve laceration injury by utilizing a bioresorbable nerve guidance conduit represents a potential substitute for end-to-end epineurial suturing and nerve autografting.

Combination therapy using evening primrose oil and electrical stimulation to improve nerve function following a crush injury of sciatic nerve in male rats

Peripheral nerve injuries with a poor prognosis are common. Evening primrose oil (EPO) has beneficial biological effects and immunomodulatory properties. Since electrical activity plays a major role in neural regeneration, the present study investigated the effects of electrical stimulation (ES), combined with evening primrose oil (EPO), on sciatic nerve function after a crush injury in rats. In anesthetized rats, the sciatic nerve was crushed using small haemostatic forceps followed by ES and/or EPO treatment for 4 weeks. Functional recovery of the sciatic nerve was assessed using the sciatic functional index. Histopathological changes of gastrocnemius muscle atrophy were investigated by light microscopy. Electrophysiological changes were assessed by the nerve conduction velocity of sciatic nerves. Immunohistochemistry was used to determine the remyelination of the sciatic nerve following the interventions. EPO + ES, EPO, and ES obviously improved sciatic nerve function assessed by the sciatic functional index and nerve conduction velocity of the sciatic nerve at 28 days after operation. Expression of the peripheral nerve remyelination marker, protein zero (P0), was increased in the treatment groups at 28 days after operation. Muscle atrophy severity was decreased significantly while the nerve conduction velocity was increased significantly in rats with sciatic nerve injury in the injury + EPO + ES group than in the EPO or ES group. Totally speaking, the combined use of EPO and ES may produce an improving effect on the function of sciatic nerves injured by a crush. The increased expression of P0 may have contributed to improving the functional effects of combination therapy with EPO and ES as well as the electrophysiological and histopathological features of the injured peripheral nerve.

Upslope treadmill exercise enhances motor axon regeneration but not functional recovery following peripheral nerve injury

Following peripheral nerve injury, moderate daily exercise conducted on a level treadmill results in enhanced axon regeneration and modest improvements in functional recovery. If the exercise is conducted on an upwardly inclined treadmill, even more motor axons regenerate successfully and reinnervate muscle targets. Whether this increased motor axon regeneration also results in greater improvement in functional recovery from sciatic nerve injury was studied. Axon regeneration and muscle reinnervation were studied in Lewis rats over an 11 wk postinjury period using stimulus evoked electromyographic (EMG) responses in the soleus muscle of awake animals. Motor axon regeneration and muscle reinnervation were enhanced in slope-trained rats. Direct muscle (M) responses reappeared faster in slope-trained animals than in other groups and ultimately were larger than untreated animals. The amplitude of monosynaptic H reflexes recorded from slope-trained rats remained significantly smaller than all other groups of animals for the duration of the study. The restoration of the amplitude and pattern of locomotor EMG activity in soleus and tibialis anterior and of hindblimb kinematics was studied during treadmill walking on different slopes. Slope-trained rats did not recover the ability to modulate the intensity of locomotor EMG activity with slope. Patterned EMG activity in flexor and extensor muscles was not noted in slope-trained rats. Neither hindblimb length nor limb orientation during level, upslope, or downslope walking was restored in slope-trained rats. Slope training enhanced motor axon regeneration but did not improve functional recovery following sciatic nerve transection and repair.

Assessment of Neuroprotective Effects of Local Administration of 17- Beta- Estradiol on Peripheral Nerve Regeneration in Ovariectomized Female Rats

OBJECTIVE

To assess the neuroprotective effects of local administration of 17- beta- estradiol on nerve regeneration.

METHODS

Sixty female Wistar rats were overiectomized and divided into four experimental groups (n = 15), randomly: In autograft group a segment of sciatic nerve was transected and re-implanted reversely. In sham-surgery group sciatic nerve was exposed and manipulated. In transected group left sciatic nerve was transected and stumps were fixed in adjacent muscle. In treatment group defect was bridged using a silicon conduit filled with 10 µL (0.1 mg/mL) 17- beta- estradiol. Each group was subdivided into four subgroups of five animals each and nerve fibers were studied in a 12-week period.

RESULTS

Behavioral, functional, biomechanical, electrophysiological and gastrocnemius muscle mass findings and morphometric indices confirmed faster recovery of regenerated axons in treatment group than in other groups (p<0.05). Immunohistochemical reactions to S-100 in treatment group were more positive than that in other groups.

CONCLUSION

Local administration of 17-beta-estradiol improved functional recovery and morphometric indices of sciatic nerve. It could have clinical implications for the surgical management of patients after facial nerve transection.

A regenerative microchannel device for recording multiple single-unit action potentials in awake, ambulatory animals

Despite significant advances in robotics, commercially advanced prosthetics provide only a small fraction of the functionality of the amputated limb that they are meant to replace. Peripheral nerve interfacing could provide a rich controlling link between the body and these advanced prosthetics in order to increase their overall utility. Here, we report on the development of a fully integrated regenerative microchannel interface with 30 microelectrodes and signal extraction capabilities enabling evaluation in an awake and ambulatory rat animal model. In vitro functional testing validated the capability of the microelectrodes to record neural signals similar in size and nature to those that occur in vivo. In vitro dorsal root ganglia cultures revealed striking cytocompatibility of the microchannel interface. Finally, in vivo, the microchannel interface was successfully used to record a multitude of single-unit action potentials through 63% of the integrated microelectrodes at the early time point of 3 weeks. This marks a significant advance in microchannel interfacing, demonstrating the capability of microchannels to be used for peripheral nerve interfacing.

Electrical Stimulation to Promote Peripheral Nerve Regeneration

Peripheral nerve injury afflicts individuals from all walks of life. Despite the peripheral nervous system’s intrinsic ability to regenerate, many patients experience incomplete functional recovery. Surgical repair aims to expedite this recovery process in the most thorough manner possible. However, full recovery is still rarely seen especially when nerve injury is compounded with polytrauma where surgical repair is delayed. Pharmaceutical strategies supplementary to nerve microsurgery have been investigated but surgery remains the only viable option. Brief low-frequency electrical stimulation of the proximal nerve stump after primary repair has been widely investigated. This article aims to review the currently known biological basis for the regenerative effects of acute brief low-frequency electrical stimulation on axonal regeneration and outline the recent clinical applications of the electrical stimulation protocol to demonstrate the significant translational potential of this modality for repairing peripheral nerve injuries. The review concludes with a discussion of emerging new advancements in this exciting area of research. The current literature indicates the imminent clinical applicability of acute brief low-frequency electrical stimulation after surgical repair to effectively promote axonal regeneration as the stimulation has yielded promising evidence to maximize functional recovery in diverse types of peripheral nerve injuries.

Strategies to promote peripheral nerve regeneration: electrical stimulation and/or exercise

Enhancing the regeneration of axons is often considered to be a therapeutic target for improving functional recovery after peripheral nerve injury. In this review, the evidence for the efficacy of electrical stimulation (ES), daily exercise and their combination in promoting nerve regeneration after peripheral nerve injuries in both animal models and in human patients is explored. The rationale, effectiveness and molecular basis of ES and exercise in accelerating axon outgrowth are reviewed. In comparing the effects of ES and exercise in enhancing axon regeneration, increased neural activity, neurotrophins and androgens are considered to be common requirements. Similarly, there are sex-specific requirements for exercise to enhance axon regeneration in the periphery and for sustaining synaptic inputs onto injured motoneurons. ES promotes nerve regeneration after delayed nerve repair in humans and rats. The effectiveness of exercise is less clear. Although ES, but not exercise, results in a significant misdirection of regenerating motor axons to reinnervate different muscle targets, the loss of neuromuscular specificity encountered has only a very small impact on resulting functional recovery. Both ES and exercise are promising experimental treatments for peripheral nerve injury that seem to be ready to be translated to clinical use.

Morphological Proof of nerve regeneration after long-term defects of rat sciatic nerves

Unsatisfactory efficacy of clinical cure for long-term delayed injuries and other disadvantages such as the low regeneration rate and speed of axotomized neurons and the questionable reinnervation ability of atrophic target organ lead to inaction to the long-term delayed injuries. Here we attempted to use autologous nerve to bridge a long-term delayed 10-mm defect in SD rats based on some previous positive messages of basic and clinical research. In this study, for experimental groups, the rat sciatic nerve had been transected leaving a 10-mm defect, which was maintained for 3 or 6 months before implantation with the autologous graft. The non-grafted animals served as negative control. Measuring with electrophysiological and histological techniques, we find: (1) A number of long-term axotomized neurons survived and sustained certain degree of axonal regenerative capacity; (2) A few denervated Schwann cells survived and retained their ability to provide trophic support and myelinate axons in at least 6 months; (3) the chronically denervated muscle can partially be reinnervated by regenerated axons. But the quantity and the quality of the regenerated nerve fibers and the reinnervated muscle fibers were all poor. Thus these observations provide new positive morphological proof of nerve regeneration after long-term defects and further studies will be needed to increase the survival rate and the regenerative speed of long-term chronic axotomized neurons, enhance the support provided by denervated distal stumps and protect the target muscle.

Improved regeneration after femoral nerve injury in mice lacking functional T- and B-lymphocytes

The immune system plays important functional roles in regeneration after injury to the mammalian central and peripheral nervous systems. After damage to the peripheral nerve several types of immune cells, invade the nerve within hours after the injury. To gain insights into the contribution of T- and B-lymphocytes to recovery from injury we used the mouse femoral nerve injury paradigm. RAG2-/- mice lacking mature T- and B-lymphocytes due to deletion of the recombination activating gene 2 were subjected to resection and surgical reconstruction of the femoral nerve, with the wild-type mice of the same inbred genetic background serving as controls. According to single frame motion analyses, RAG2-/- mice showed better motor recovery in comparison to control mice at four and eight weeks after injury. Retrograde tracing of regrown/sprouted axons of spinal motoneurons showed increased numbers of correctly projecting motoneurons in the lumbar spinal cord of RAG2-/- mice compared with controls. Whereas there was no difference in the motoneuron soma size between genotypes, RAG2-/- mice displayed fewer cholinergic and inhibitory synaptic terminals around somata of spinal motoneurons both prior to and after injury, compared with wild-type mice. Extent of myelination of regrown axons in the motor branch of the femoral nerve measured as g-ratio was more extensive in RAG2-/- than in control mice eight weeks after injury. We conclude that activated T- and B-lymphocytes restrict motor recovery after femoral nerve injury, associated with the increased survival of motoneurons and improved remyelination.

Use of natural neural scaffolds consisting of engineered vascular endothelial growth factor immobilized on ordered collagen fibers filled in a collagen tube for peripheral nerve regeneration in rats

The search for effective strategies for peripheral nerve regeneration has attracted much attention in recent years. In this study, ordered collagen fibers were used as intraluminal fibers after nerve injury in rats. Vascular endothelial growth factor (VEGF) plays an important role in nerve regeneration, but its very fast initial burst of activity within a short time has largely limited its clinical use. For the stable binding of VEGF to ordered collagen fibers, we fused a collagen-binding domain (CBD) to VEGF through recombinant DNA technology. Then, we filled the ordered collagen fibers-CBD-VEGF targeting delivery system in a collagen tube to construct natural neural scaffolds, which were then used to bridge transected nerve stumps in a rat sciatic nerve transection model. After transplantation, the natural neural scaffolds showed minimal foreign body reactions and good integration into the host tissue. Oriented collagen fibers in the collagen tube could guide regenerating axons in an oriented manner to the distal, degenerating nerve segment, maximizing the chance of target reinnervation. Functional and histological analyses indicated that the recovery of nerve function in the natural neural scaffolds-treated group was superior to the other grafted groups. The guiding of oriented axonal regeneration and effective delivery systems surmounting the otherwise rapid and short-lived diffusion of growth factors in body fluids are two important strategies in promoting peripheral nerve regeneration. The natural neural scaffolds described take advantage of these two aspects and may produce synergistic effects. These properties qualified the artificial nerve conduits as a putative candidate system for the fabrication of peripheral nerve reconstruction devices.

Linear ordered collagen scaffolds loaded with collagen-binding basic fibroblast growth factor facilitate recovery of sciatic nerve injury in rats

Natural biological functional scaffolds, consisting of biological materials filled with promoting elements, provide a promising strategy for the regeneration of peripheral nerve defects. Collagen conduits have been used widely due to their excellent biological properties. Linear ordered collagen scaffold (LOCS) fibers are good lumen fillers that can guide nerve regeneration in an ordered direction. In addition, basic fibroblast growth factor (bFGF) is important in the recovery of nerve injury. However, the traditional method for delivering bFGF to the lesion site has no long-term effect because of its short half-life and rapid diffusion. Therefore, we fused a specific collagen-binding domain (CBD) peptide to the N-terminal of native basic fibroblast growth factor (NAT-bFGF) to retain bFGF on the collagen scaffolds. In this study, a natural biological functional scaffold was constructed using collagen tubes filled with collagen-binding bFGF (CBD-bFGF)-loaded LOCS to promote regeneration in a 5-mm rat sciatic nerve transection model. Functional evaluation, histological investigation, and morphometric analysis indicated that the natural biological functional scaffold retained more bFGF at the injury site, guided axon growth, and promoted nerve regeneration as well as functional restoration.

The impact of motor axon misdirection and attrition on behavioral deficit following experimental nerve injuries

Peripheral nerve transection and neuroma-in-continuity injuries are associated with permanent functional deficits, often despite successful end-organ reinnervation. Axonal misdirection with non-specific reinnervation, frustrated regeneration and axonal attrition are believed to be among the anatomical substrates that underlie the poor functional recovery associated with these devastating injuries. Yet, functional deficits associated with axonal misdirection in experimental neuroma-in-continuity injuries have not yet been studied. We hypothesized that experimental neuroma-in-continuity injuries would result in motor axon misdirection and attrition with proportional persistent functional deficits. The femoral nerve misdirection model was exploited to assess major motor pathway misdirection and axonal attrition over a spectrum of experimental nerve injuries, with neuroma-in-continuity injuries simulated by the combination of compression and traction forces in 42 male rats. Sciatic nerve injuries were employed in an additional 42 rats, to evaluate the contribution of axonal misdirection to locomotor deficits by a ladder rung task up to 12 weeks. Retrograde motor neuron labeling techniques were utilized to determine the degree of axonal misdirection and attrition. Characteristic histological neuroma-in-continuity features were demonstrated in the neuroma-in-continuity groups and poor functional recovery was seen despite successful nerve regeneration and muscle reinnervation. Good positive and negative correlations were observed respectively between axonal misdirection (p<.0001, r(2)=.67), motor neuron counts (attrition) (p<.0001, r(2)=.69) and final functional deficits. We demonstrate prominent motor axon misdirection and attrition in neuroma-in-continuity and transection injuries of mixed motor nerves that contribute to the long-term functional deficits. Although widely accepted in theory, to our knowledge, this is the first experimental evidence to convincingly demonstrate these correlations with data inclusive of the neuroma-in-continuity spectrum. This work emphasizes the need to focus on strategies that promote both robust and accurate nerve regeneration to optimize functional recovery. It also demonstrates that clinically relevant neuroma-in-continuity injuries can now also be subjected to experimental investigation.

Effects of treadmill training on functional recovery following peripheral nerve injury in rats

Exercise, in the form of moderate daily treadmill training following nerve transection and repair leads to enhanced axon regeneration, but its effect on functional recovery is less well known. Female rats were exercised by walking continuously, at a slow speed (10 m/min), for 1 h/day on a level treadmill, beginning 3 days after unilateral transection and surgical repair of the sciatic nerve, and conducted 5 days/wk for 2 wk. In Trained rats, both direct muscle responses to tibial nerve stimulation and H reflexes in soleus reappeared earlier and increased in amplitude more rapidly over time than in Untrained rats. The efficacy of the restored H reflex was greater in Trained rats than in Untrained controls. The reinnervated tibialis anterior and soleus were coactivated during treadmill locomotion in Untrained rats. In Trained animals, the pattern of activation of soleus, but not tibialis anterior, was not significantly different from that found in Intact rats. The overall length of the hindlimb during level and up- and downslope locomotion was conserved after nerve injury in both groups. This conservation was achieved by changes in limb orientation. Limb length was conserved effectively in all rats during downslope walking but only in Trained rats during level and upslope walking. Moderate daily exercise applied immediately after sciatic nerve transection is sufficient to promote axon regeneration, to restore muscle reflexes, and to improve the ability of rats to cope with different biomechanical demands of slope walking.

Induction of rat facial nerve regeneration by functional collagen scaffolds

Nerve conduit provides a promising strategy for nerve regeneration, and the proper microenvironment in the lumen could improve the regeneration. Our previous work had demonstrated that linear ordered collagen scaffold (LOCS) could effectively guide the oriented growth of axons. Laminin is known as an important nerve growth promoting factor and can facilitate the growth cone formation. In addition, ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) can effectively improve the nerve regeneration after nerve injuries. However, in practice, diffusion caused by the body fluids is the major obstacle in their applications. To retain CNTF or BDNF on the scaffolds, we produced collagen binding CNTF (CBD-CNTF), collagen binding BDNF (CBD-BDNF) and laminin binding CNTF (LBD-CNTF), laminin binding BDNF (LBD-BDNF) respectively. In this work, we developed laminin modified LOCS fibers (L × LOCS) by chemical cross-linking LOCS fibers with laminin. Collagen binding or laminin binding neurotrophic factors were combined with LOCS or L × LOCS, and then filled them into the collagen nerve conduit. They were found to guide the ordered growth of axons, and improve the nerve functional recovery in the rat facial nerve transection model. The combination of CNTF and BDNF greatly enhanced the facial nerve regeneration and functional recovery.

Brief transvertebral electrical stimulation of the spinal cord improves the specificity of femoral nerve reinnervation

BACKGROUND

Functional outcomes are generally poor following peripheral nerve injury (PNI). The reason is multifactorial but includes the misdirection of regenerating axons to inappropriate end organs. It has been shown that brief electrical stimulation (Estim) of nerves has the potential to improve the accuracy and rate of peripheral axon regeneration.

OBJECTIVE

The present study explores a novel percutaneous transvertebral approach to Estim, which was tested in the mouse femoral nerve model.

METHODS

Inspired by the protocol of Gordon and colleagues (ie, 20 Hz, for 1 hour), we applied Estim to the cervicothoracic spinal cord (SC-Estim) to remotely activate lumbar motor neurons following transection and repair of the femoral nerve. Fluorescent dyes were applied to the distal nerve to label reinnervating cells. Sections of nerve were taken to quantify the numbers of reinnervating axons as well as to stain for a known femoral axon guidance molecule-polysialylated neural cell adhesion molecule (PSA-NCAM).

RESULTS

In comparison to sham treatment, SC-Estim led to significantly greater expression of PSA-NCAM as well as improved the specificity of motor reinnervation. Interestingly, although SC-Estim did not alter the number of early reinnervating (ie, pioneer) axons, there was a reduction in the number of retrogradely labeled neurons at 2 weeks postrepair. However, by 6 weeks postrepair, there was no difference in the number of neurons that had reinnervated the femoral nerve.

CONCLUSIONS

The present findings support the development of SC-Estim as a novel approach to enhance the specificity of reinnervation and potentially improve functional outcomes following PNI.

Reconstruction of sciatic nerve after traumatic injury in humans - factors influencing outcome as related to neurobiological knowledge from animal research

Background

The aim was to evaluate what can be learned from rat models when treating patients suffering from a sciatic nerve injury.

Methods

Two patients with traumatic sciatic nerve injury are presented with examination of motor and sensory function with a five-year follow-up. Reconstruction of the nerve injury was performed on the second and third day, respectively, after injury using sural nerve grafts taken from the injured leg. The patients were examined during follow-up by electromyography (EMG), MRI and functionalMRI (fMRI) to evaluate nerve reinnervation, cell death in dorsal root ganglia (DRG) and cortical activation; factors that were related to clinical history in the patients.

Results

One patient regained good motor function of the lower leg and foot, confirmed by EMG showing good activation in the leg muscles and some reinnervation in the foot muscles, as well as some sensory function of the sole of the foot. The other patient regained no motor (confirmed by EMG) or sensory function in the leg or foot. Factors most influential on outcome in two cases were type of injury, nerve gap length and particularly type of reconstruction. A difference in follow-up and rehabilitation likely also influence outcome. MRI did not show any differences in DRG size of injured side compared to the uninjured side. fMRI showed normal activation in the primary somatosensory cortex as a response to cutaneous stimulation of the normal foot. However, none of the two patients showed any activation in the primary somatosensory cortex following cutaneous stimulation of the injured foot.

Conclusions

In decision making of nerve repair and reconstruction data from animal experiments can be translated to clinical practice and to predict outcome in patients, although such data should be interpreted with caution and linked to clinical experience. Rat models may be useful to identify and study factors that influence outcome after peripheral nerve repair and reconstruction; procedures that should be done correctly and with a competent team. However, some factors, such as cognitive capacity and coping, known to influence outcome following nerve repair, are difficult to study in animal models. Future research has to find and develop new paths and techniques to study changes in the central nervous system after nerve injury and develop strategies to utilize brain plasticity during the rehabilitation.

Axonal regeneration and motor neuron survival after microsurgical nerve reconstruction

Rodent models are used extensively for studying nerve regeneration, but little is known about how sprouting and pruning influence peripheral nerve fiber counts and motor neuron pools. The purpose of this study was to identify fluctuations in nerve regeneration and neuronal survival over time. One hundred and forty-four Lewis rats were randomized to end-to-end repair or nerve grafting (1.5 cm graft) after sciatic nerve transection. Quantitative histomorphometry and retrograde labeling of motor neurons were performed at 1, 3, 6, 9, 12, and 24 months and supplemented by electron microscopy. Fiber counts and motor neuron counts increased between 1 and 3 months, followed by plateau. End-to-end repair resulted in persistently higher fiber counts compared to the grafting for all time points (P < 0.05). Percent neural tissue and myelin width increased with time while fibrin debris dissipated. In conclusion, these data detail the natural history of regeneration and demonstrate that overall fiber counts may remain stable despite pruning.

Spinal cord injury and physical activity: preservation of the body

SETTING

Spinal cord injury (SCI) causes devastating loss of function and can result in serious secondary complications. Although significant advances are being made to develop cellular and molecular therapies to promote regeneration, it is important to optimize physical interventions.

OBJECTIVES

The objective of this review was to examine the evidence for the effects of physical rehabilitation strategies on health and fitness, and maintenance of target systems below the level of injury (for example, muscle, bone, circulation).

RESULTS

Exercise appears to be a potent means of achieving these goals, using a variety of strategies.

CONCLUSION

Physical rehabilitation after SCI needs to move beyond the goal of maximizing independence to focus on maintenance of optimum health and fitness as well as maintenance of target system function below the level of injury. Issues requiring further investigation include identification of the optimum dosage of interventions to achieve specific goals, for example, prevention of muscle atrophy and osteoporosis, and development and validation of simple clinical measures to monitor the changes in body composition. Adoption of a classification system for physical interventions and standardized outcome measures would facilitate large-scale observational studies to identify the critical variables contributing to better outcomes.

Chondroitinase ABC reduces time to muscle reinnervation and improves functional recovery after sciatic nerve transection in rats

Application of chondroitinase ABC (ChABC) to injured peripheral nerves improves axon regeneration, but it is not known whether functional recovery is also improved. Recordings of EMG activity [soleus (Sol) M response and H reflexes] evoked by nerve stimulation and of Sol and tibialis anterior (TA) EMG activity and hindlimb and foot kinematics during slope walking were made to determine whether ChABC treatment of the sciatic nerve at the time of transection improves functional recovery. Recovery of evoked EMG responses began as multiple small responses with a wide range of latencies that eventually coalesced into one or two more distinctive and consistent responses (the putative M response and the putative H reflex) in both groups. Both the initial evoked responses and the time course of their maturation returned sooner in the ChABC group than in the untreated (UT) group. The reinnervated Sol and TA were coactivated during treadmill locomotion during downslope, level, and upslope walking throughout the study period in both UT and ChABC-treated rats. By 10 wk after nerve transection and repair, locomotor activity in Sol, but not TA, had returned to its pretransection pattern. There was an increased reliance on central control of Sol activation across slopes for both groups as interpreted from elevated prestance Sol EMG activity that was no longer modulated with slope. Limb length and orientation during locomotion were similar to those observed prior to nerve injury during upslope walking only in the ChABC-treated rats. Thus treatment of cut nerves with ChABC leads to improvements in functional recovery.

Effect of slope and sciatic nerve injury on ankle muscle recruitment and hindlimb kinematics during walking in the rat

Slope-related differences in hindlimb movements and activation of the soleus and tibialis anterior muscles were studied during treadmill locomotion in intact rats and in rats 4 and 10 weeks following transection and surgical repair of the sciatic nerve. In intact rats, the tibialis anterior and soleus muscles were activated reciprocally at all slopes, and the overall intensity of activity in tibialis anterior and the mid-step activity in soleus increased with increasing slope. Based on the results of principal components analysis, the pattern of activation of soleus, but not of tibialis anterior, changed significantly with slope. Slope-related differences in hindlimb kinematics were found in intact rats, and these correlated well with the demands of walking up or down slopes. Following recovery from sciatic nerve injury, the soleus and tibialis anterior were co-activated throughout much of the step cycle and there was no difference in intensity or pattern of activation with slope for either muscle. Unlike intact rats, these animals walked with their feet flat on the treadmill belt through most of the stance phase. Even so, during downslope walking limb length and limb orientation throughout the step cycle were not significantly changed from values found in intact rats. This conservation of hindlimb kinematics was not observed during level or upslope walking. These findings are interpreted as evidence that the recovering animals adopt a novel locomotor strategy that involves stiffening of the ankle joint by antagonist co-activation and compensation at more proximal joints. Their movements are most suitable to the requirements of downslope walking but the recovering rats lack the ability to adapt to the demands of level or upslope walking.

Potentials and limitations of peripheral nerve injury models in rodents with particular reference to the femoral nerve

Restoration of function after peripheral nerve repair in humans is unsatisfactory. Various causes of poor recovery have been proposed. Still, we do not understand which of these potential factors are indeed detrimental and do not know how to manipulate them experimentally in a clinically feasible way. Future success largely depends on methodological improvement in rodent models. An example of recent progress is the introduction of new functional and anatomical outcome measures in the facial nerve injury paradigm which led to novel insights into facial nerve regeneration and a new therapeutic concept. Less success can be ascribed to the use of the classical spinal nerve model, the sciatic nerve paradigm, not least because of its anatomical and functional complexity making assessment of recovery challenging. A simpler alternative to the sciatic nerve is the femoral nerve model. It offers, alongside with its known usefulness for studies on precision of motor reinnervation, the possibility of reliable functional assessments and a straightforward search of anatomical substrates of dysfunction. The structure-function approach in the femoral nerve paradigm has been useful for testing of novel therapeutic means and analyses of regeneration in mutant mice. The potential of the method has still not been really exploited and its more extensive use may contribute to better understanding of nerve regeneration.

Effect of axon misdirection on recovery of electromyographic activity and kinematics after peripheral nerve injury

In this study, patterns of activity in the soleus (Sol) and tibialis anterior (TA) muscles and hindlimb kinematics were evaluated during slope walking in rats after transection and surgical repair either of the entire sciatic nerve (Sci group) or of its two branches separately, the tibial and common fibular nerves (T/CF group). With the latter method, axons from the tibial and common fibular nerves could not reinnervate targets of the other nerve branch after injury, reducing the opportunity for misdirection. Activity in the TA shifted from the swing phase in intact rats to nearly the entire step cycle in both injured groups. Since these changes occur without misdirection of regenerating axons, they are interpreted as centrally generated. Sol activity was changed from reciprocal to that of TA in intact rats to coactivate with TA, but only in the Sci group rats. In the T/CF group rats, Sol activity was not altered from that observed in intact rats. Despite effects of injury that limited foot movements, hindlimb kinematics were conserved during downslope walking in both injury groups and during level walking in the T/CF group. During level walking in the Sci group and during upslope walking in both groups of injured rats, the ability to compensate for the effects of the nerve injury was less effective and resulted in longer limb lengths held at more acute angles throughout the step cycle. Changes in limb movements occur irrespective of axon misdirection and reflect compensatory changes in the outputs of the neural circuits that drive locomotion.

Non-surgical therapies for peripheral nerve injury

BACKGROUND

Non-surgical approaches have been developed to enhance nerve recovery, which are complementary to surgery and are an adjunct to the reinnervation process.

SOURCES OF DATA

A search of PubMed, Medline, CINAHL, DH data and Embase databases was performed using the keywords 'peripheral nerve injury' and 'treatment'.

AREAS OF CONTROVERSY

Most of the conservative therapies are focused to control neuropathic pain after nerve tissue damage. Only physical therapy modalities have been studied in humans and their effectiveness is not proved.

GROWING POINTS

Many modalities have been experimented with to promote nerve healing and restore function in animal models and in vitro studies. Despite this, none have been actually translated into clinical practice.

AREAS TIMELY FOR DEVELOPING RESEARCH

The hypotheses proved in animals and in vitro should be translated to human clinical practice.