Reinnervation and recovery of mouse soleus muscle after long-term denervation

The Role of Physical Exercise and Rehabilitative Implications in the Process of Nerve Repair in Peripheral Neuropathies: A Systematic Review

BACKGROUND

The various mechanisms involved in peripheral nerve regeneration, induced by exercise and electrical nerve stimulation, are still unclear.

OBJECTIVE

The aim of this review was to summarize the influence of physical exercise and/or electrical stimulation on peripheral nerve repair and regeneration and the variation of impact of intervention depending on timing, as well as kind and dosage of the intervention. A literature survey was conducted on PubMed, Scopus, and Web of Science, between February 2021 to July 2021, with an update in September 2022.

METHODOLOGY

The literature search identified 101,386 articles with the keywords: "peripheral nerve" OR "neuropathy" AND "sprouting" OR "neuroapraxia" OR "axonotmesis" OR "neurotmesis" OR "muscle denervation" OR "denervated muscle" AND "rehabilitation" OR "physical activity" OR "physical exercise" OR "activity" OR "electrical stimulation". A total of 60 publications were included. Eligible studies were focused on evaluating the process of nerve repair (biopsy, electromyographic parameters or biomarker outcomes) after electrical stimulation or physical exercise interventions on humans or animals with peripheral sensory or motor nerve injury.

SYNTHESIS

This study shows that the literature, especially regarding preclinical research, is mainly in agreement that an early physical program with active exercise and/or electrical stimulation promotes axonal regenerative responses and prevents maladaptive response. This was evaluated by means of changes in electrophysiological recordings of CMAPs for latency amplitude, and the sciatic functional index (SFI). Furthermore, this type of activity can cause an increase in weight and in muscle fiber diameter. Nevertheless, some detrimental effects of exercising and electrical stimulation too early after nerve repair were recorded.

CONCLUSION

In most preclinical studies, peripheral neuropathy function was associated with improvements after physical exercise and electrical stimulation. For humans, too little research has been conducted on this topic to reach a complete conclusion. This research supports the need for future studies to test the validity of a possible rehabilitation treatment in humans in cases of peripheral neuropathy to help nerve sprouting.

Use of aerobic treadmill exercises on nerve regeneration after sciatic nerve injury in spontaneously hypertensive rats

PURPOSE

Various postoperative protocols have been proposed to improve outcomes and accelerate nerve regeneration. Recently, the use of physical exercise in a post-surgical neurorraphy procedure has shown good results when started early. We experimentally investigated the hypothesis that post-operative exercise speeds up results and improves clinical and morphologic parameters.

METHODS

Isogenic rats were randomly divided into four groups: 1 SHAM; 2 SHAM submitted to the exercise protocol (EP); 3 Grafting of the sciatic nerve; and 4 Grafting of the sciatic nerve associated with the EP. The EP was based on aerobic activities with a treadmill, with a progressive increase in time and intensity during 6 weeks. The results were evaluated by the sciatic functional index (SFI), morphometric and morphologic analysis of nerve distal to the lesion, and the number of spinal cord motor neurons, positive to the marker Fluoro-Gold (FG), captured retrogradely through neurorraphy.

RESULTS

Functional analysis (SFI) did not show a statistical difference between the group grafted with (-50.94) and without exercise (-65.79) after 90 days. The motoneurons count (Spinal cord histology) also showed no diference between these groups (834.5 × 833 respectively). Although functionally there is no difference between these groups, morphometric study showed a greater density (53.62) and larger fibers (7.762) in GRAFT group. When comparing both operated groups with both SHAM groups, all values were much lower.

CONCLUSIONS

The experimental model that this aerobic treadmill exercises protocol did not modify nerve regeneration after sciatic nerve injury and repair with nerve graft.

Intramuscular Stem Cell Injection in Combination with Bioengineered Nerve Repair or Nerve Grafting Reduces Muscle Atrophy

BACKGROUND

Peripheral nerve injuries represent a clinical challenge, especially when they are accompanied by loss of neural tissue. In this study, the authors attempted to attain a better outcome after a peripheral nerve injury by both repairing the nerve lesion and treating the denervated muscle at the same time.

METHODS

Rat sciatic nerves were transected to create 10-mm gaps. Repair was performed in five groups (n = 5 rats for each), as follows: group 1, nerve repair using poly-3-hydroxybutyrate strips to connect the proximal and distal stumps, in combination with control growth medium injection in the gastrocnemius muscle; group 2, nerve repair with poly-3-hydroxybutyrate strip seeded with Schwann cell-like differentiated adipose stem cells (differentiated adipose stem cell strip) in combination with growth medium intramuscular injection; group 3, differentiated adipose stem cell strip in combination with intramuscular injection of differentiated adipose stem cells; group 4, repair using autograft (reverse sciatic nerve graft) in combination with intramuscular injection of growth medium; and group 5, autograft in combination with intramuscular injection of differentiated adipose stem cells. Six weeks after nerve injury, the effects of the stem cells on muscle atrophy were assessed.

RESULTS

Poly-3-hydroxybutyrate strips seeded with differentiated adipose stem cells showed a high number of βIII-tubulin-positive axons entering the distal stump and abundant endothelial cells. Group 1 animals exhibited more muscle atrophy than all the other groups, and group 5 animals had the greatest muscle weights and muscle fibers size.

CONCLUSION

Bioengineering nerve repair in combination with intramuscular stem cell injection is a promising technique to treat nerve lesions and associated muscle atrophy.

CLINICAL RELEVANCE STATEMENT

Nerve injuries and resulting muscle atrophy are a clinical challenge. To optimize functional recovery after a nerve lesion, the authors treated the nerve and muscle at the same time by using regenerative medicine with adipose stem cells and obtained encouraging results for future clinical applications.

Optimizing the timing of peripheral nerve transfers for functional re-animation in cervical spinal cord injury: a conceptual framework

Loss of upper extremity function following spinal cord injury (SCI) can have devastating consequences on quality of life. Peripheral nerve transfer surgery aims to restore motor control of upper extremities following cervical SCI and is poised to revolutionize surgical management in this population. The surgery involves dividing an expendable donor nerve above the level of the spinal lesion and coapting it to a recipient nerve arising from the lesional or infralesional segment of the injured cord. In order to maximize outcomes in this complex patient population, refinements in surgical technique need to be integrated with principles of spinal cord medicine and basic science. Deciding on the ideal timing of nerve transfer surgery is one aspect of care that is critical to maximizing recovery and has received very little attention to date in the literature. This complex topic is reviewed, with a focus on expectations for spontaneous recovery within upper motor neuron components of the injury, balanced against the need for expeditious reinnervation for lower motor neuron elements of the injury. The discussion also considers the case of a patient with C6 motor complete SCI where myotomes without electrodiagnostic evidence of denervation spontaneously improved by 6 months post-injury, thereby adjusting the surgical plan. The relevant concepts are integrated into a clinical algorithm with recommendations that consider maximal opportunity for spontaneous clinical improvement post-injury while avoiding excessive delays that may adversely affect patient outcomes.

Transcutaneous carbon dioxide application with hydrogel prevents muscle atrophy in a rat sciatic nerve crush model

The acceleration of nerve regeneration remains a clinical challenge. We previously demonstrated that transcutaneous CO₂ application using a novel hydrogel increases the oxygen concentration in local tissue via an "artificial Bohr effect" with the potential to prevent muscle atrophy. In this study, we investigated the effect of transcutaneous CO₂ administration on limb function after peripheral nerve injury in a rat sciatic nerve injury model. In total, 73 Sprague-Dawley rats were divided into a sham group, a control group (crush injury to sciatic nerve and no treatment) or a CO₂ group (crush injury with transcutaneous CO₂ application). CO₂ was administered percutaneously for 20 min five times per week. Scores for the sciatic function index and pinprick test were significantly higher in the CO₂ group than control group. The muscle wet weight ratios of the tibialis anterior and soleus muscles were higher in the CO₂ group than control group. Electrophysiological examination showed that the CO₂ group had higher compound motor action potential amplitudes and shorter distal motor latency than the control group. Histological examination of the soleus muscle sections at postoperative week 2 showed shorter fiber diameter in the control group than in the CO₂ group. The mRNA expression of Atrogin-1 and MuRF-1 was lower, mRNA expression of VEGF and myogenin and MyoD was higher in CO₂ group at postoperative week 2 compared to the control group.

CLINICAL SIGNIFICANCE

Transcutaneous CO₂ application has the therapeutic potential to accelerate the recovery of muscle atrophy in peripheral nerve injury. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1653-1658, 2018.

Motor Cortex Stimulation Regenerative Effects in Peripheral Nerve Injury: An Experimental Rat Model

BACKGROUND

Immediate microsurgical nerve suture remains the gold standard after peripheral nerve injuries. However, functional recovery is delayed, and it is satisfactory in only 2/3 of cases. Peripheral electrical nerve stimulation proximal to the lesion enhances nerve regeneration and muscle reinnervation. This study aims to evaluate the effects of the motor cortex electrical stimulation on peripheral nerve regeneration after injury.

METHODS

Eighty rats underwent right sciatic nerve section, followed by immediate microsurgical epineural sutures. Rats were divided into 4 groups: Group 1 (control, n = 20): no electrical stimulation; group 2 (n = 20): immediate stimulation of the sciatic nerve just proximal to the lesion; Group 3 (n = 20): motor cortex stimulation (MCS) for 15 minutes after nerve section and suture (MCSa); group 4 (n = 20): MCS performed over the course of two weeks after nerve suture (MCSc). Assessment included electrophysiology and motor functional score at day 0 (baseline value before nerve section), and at weeks 4, 8, and 12. Rats were euthanized for histological study at week 12.

RESULTS

Our results showed that MCS enhances functional recovery, nerve regeneration, and muscle reinnervation starting week 4 compared with the control group (P < 0.05). The MCS induces higher reinnervation rates even compared with peripheral stimulation, with better results in the MCSa group (P < 0.05), especially in terms of functional recovery.

CONCLUSIONS

MCS seems to have a beneficial effect after peripheral nerve injury and repair in terms of nerve regeneration and muscle reinnervation, especially when acute mode is used.

The Effects of Two Different Exercise Programs on the Ultrastructural Features of the Sciatic Nerve and Soleus Muscle After Sciatic Crush

Peripheral nerve injuries constitute a significant medical problem and the recovery is critically dependent on post-injury treatment. In this study, following sciatic nerve crush, we investigated the effects of a 4-week endurance training program (ET) and balance and coordination training program (BCT) on the ultrastructural features of the sciatic nerve and soleus muscle. The animals were randomly divided into Sham, non-trained (NT), ET, and BCT groups each of which included three animals. Ultra-thin cross and longitudinal sections (70-85 nm) were digitized and analyzed comparatively. The electron micrographic analysis of the sciatic nerve showed similar organelles features in the injury groups (myelin debris and swelling mitochondria). Nonetheless, the ET group presented better ultrastructural features as demonstrated by the greater predominance of rounded fibers and more defined organization in the myelinated axon bundles. In the soleus muscle's analyses, the injured groups demonstrated similar organelles' features (nucleus contained highly heterochromatic nuclei and smaller mitochondria). However, ET and BCT groups showed apparently enlarged myofibril cross-sectional areas and less collagen around muscle fibers, although, the ET group displayed reduced intermyofibrillar spaces and more closely aligned myofilaments when compared with the BCT group. Based on electron micrographic analysis, our findings suggest the presence of ultrastructural differences between the Sham, NT, and the trained groups. Therefore, exercise type seems to be responsible for producing some different positive features in the trained groups, while ET seems to have a more pronounced influence on the ultrastructural features of the sciatic nerve and the soleus muscle after a crush injury. Anat Rec, 300:1654-1661, 2017. © 2017 Wiley Periodicals, Inc.

Tumor prevention facilitates delayed transplant of stem cell-derived motoneurons

OBJECTIVE

Nerve injuries resulting in prolonged periods of denervation result in poor recovery of motor function. We have previously shown that embryonic stem cell-derived motoneurons transplanted at the time of transection into a peripheral nerve can functionally reinnervate muscle. For clinical relevance, we now focused on delaying transplantation to assess reinnervation after prolonged denervation.

METHODS

Embryonic stem cell-derived motoneurons were transplanted into the distal segments of transected tibial nerves in adult mice after prolonged denervation of 1-8 weeks. Twitch and tetanic forces were measured ex vivo 3 months posttransplantation. Tissue was harvested from the transplants for culture and immunohistochemical analysis.

RESULTS

In this delayed reinnervation model, teratocarcinomas developed in about one half of transplants. A residual multipotent cell population (~ 6% of cells) was found despite neural differentiation. Exposure to the alkylating drug mitomycin C eliminated this multipotent population in vitro while preserving motoneurons. Treating neural differentiated stem cells prior to delayed transplantation prevented tumor formation and resulted in twitch and tetanic forces similar to those in animals transplanted acutely after denervation.

INTERPRETATION

Despite a neural differentiation protocol, embryonic stem cell-derived motoneurons still carry a risk of tumorigenicity. Pretreating with an antimitotic agent leads to survival and functional muscle reinnervation if performed within 4 weeks of denervation in the mouse.

Side-To-Side Nerve Bridges Support Donor Axon Regeneration Into Chronically Denervated Nerves and Are Associated With Characteristic Changes in Schwann Cell Phenotype

BACKGROUND

Chronic denervation resulting from long nerve regeneration times and distances contributes greatly to suboptimal outcomes following nerve injuries. Recent studies showed that multiple nerve grafts inserted between an intact donor nerve and a denervated distal recipient nerve stump (termed "side-to-side nerve bridges") enhanced regeneration after delayed nerve repair.

OBJECTIVE

To examine the cellular aspects of axon growth across these bridges to explore the "protective" mechanism of donor axons on chronically denervated Schwann cells.

METHODS

In Sprague Dawley rats, 3 side-to-side nerve bridges were placed over a 10-mm distance between an intact donor tibial (TIB) nerve and a recipient denervated common peroneal (CP) distal nerve stump. Green fluorescent protein-expressing TIB axons grew across the bridges and were counted in cross section after 4 weeks. Immunofluorescent axons and Schwann cells were imaged over a 4-month period.

RESULTS

Denervated Schwann cells dedifferentiated to a proliferative, nonmyelinating phenotype within the bridges and the recipient denervated CP nerve stump. As donor TIB axons grew across the 3 side-to-side nerve bridges and into the denervated CP nerve, the Schwann cells redifferentiated to the myelinating phenotype. Bridge placement led to an increased mass of hind limb anterior compartment muscles after 4 months of denervation compared with muscles whose CP nerve was not "protected" by bridges.

CONCLUSION

This study describes patterns of donor axon regeneration and myelination in the denervated recipient nerve stump and supports a mechanism where these donor axons sustain a proregenerative state to prevent deterioration in the face of chronic denervation.

Design of barrier coatings on kink-resistant peripheral nerve conduits

Here, we report on the design of braided peripheral nerve conduits with barrier coatings. Braiding of extruded polymer fibers generates nerve conduits with excellent mechanical properties, high flexibility, and significant kink-resistance. However, braiding also results in variable levels of porosity in the conduit wall, which can lead to the infiltration of fibrous tissue into the interior of the conduit. This problem can be controlled by the application of secondary barrier coatings. Using a critical size defect in a rat sciatic nerve model, the importance of controlling the porosity of the nerve conduit walls was explored. Braided conduits without barrier coatings allowed cellular infiltration that limited nerve recovery. Several types of secondary barrier coatings were tested in animal studies, including (1) electrospinning a layer of polymer fibers onto the surface of the conduit and (2) coating the conduit with a cross-linked hyaluronic acid-based hydrogel. Sixteen weeks after implantation, hyaluronic acid-coated conduits had higher axonal density, displayed higher muscle weight, and better electrophysiological signal recovery than uncoated conduits or conduits having an electrospun layer of polymer fibers. This study indicates that braiding is a promising method of fabrication to improve the mechanical properties of peripheral nerve conduits and demonstrates the need to control the porosity of the conduit wall to optimize functional nerve recovery.

Anatomical study of the nerve regeneration after selective neurectomy in the rabbit: clinical application for esthetic calf reduction

The purposes of this study were therefore to characterize the degeneration and regeneration of nerves to the calf muscles after selective neurectomy, both macroscopically and microscopically, and to determine the incidence of such regeneration in a rabbit model. Seventy four New Zealand white rabbits were used. Selective neurectomy to the triceps surae muscles was performed, and the muscles were subsequently harvested and weighed 1-4 months postneurectomy. The gastrocnemius muscles were stained with Sihler's solution to enable the macroscopic observation of any nerve regeneration that may have occurred subsequent to neurectomy. The change in triceps surae muscle weight was measured along the time course of the experiment. After neurectomy, nerve degeneration was followed by regeneration in all cases. The weight of the triceps surae muscle decreased dramatically between completion of the neurectomy and 1 month postneurectomy, but increased thereafter. The nerve branches were weakly stained with Sihler's solution until 2 months postneurectomy, and then strongly stained after 3 months. The number of myelinated axons was decreased at 2 month after neurectomy compared to nonneurectomized controls, but then gradually increased thereafter. Although there are currently no reports on the incidence of recovery after calf reduction, it may be a very common occurrence in the clinical field based on our findings. The findings of this study provide fundamental anatomical and surgical information to aid planning and practice in calf-reduction surgery.

Sensory nerve cross-anastomosis and electrical muscle stimulation synergistically enhance functional recovery of chronically denervated muscle

BACKGROUND

Long-term muscle denervation leads to severe and irreversible atrophy coupled with loss of force and motor function. These factors contribute to poor functional recovery following delayed reinnervation. The authors' previous work demonstrated that temporarily suturing a sensory nerve to the distal motor stump (called sensory protection) significantly reduces muscle atrophy and improves function following reinnervation. The authors have also shown that 1 month of electrical stimulation of denervated muscle significantly improves function and reduces atrophy. In this study, the authors tested whether a combination of sensory protection and electrical stimulation would enhance functional recovery more than either treatment alone.

METHODS

Rat gastrocnemius muscles were denervated by cutting the tibial nerve. The peroneal nerve was then sutured to the distal tibial stump following 3 months of treatment (i.e., electrical stimulation, sensory protection, or both). Three months after peroneal repair, functional and histologic measurements were taken.

RESULTS

All treatment groups had significantly higher muscle weight (p<0.05) and twitch force (p<0.001) compared with the untreated group (denervated), but fiber type composition did not differ between groups. Importantly, muscle weight and force were significantly greater in the combined treatment group (p<0.05) compared with stimulation or sensory protection alone. The combined treatment also produced motor unit counts significantly greater than sensory protection alone (p<0.05).

CONCLUSIONS

The combination treatment synergistically reduces atrophy and improves reinnervation and functional measures following delayed nerve repair, suggesting that these approaches work through different mechanisms. The authors' research supports the clinical use of both modalities together following peripheral nerve injury.

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.

Phototherapy and nerve injury: focus on muscle response

Preservation of biochemical processes in muscles is a major challenge in patients with severe peripheral nerve injury. In this chapter, we address the effects of laser irradiation and biochemical transformation in muscle, using in vitro and in vivo experimental models. The authors attempt to explain the possible mechanism of laser phototherapy applied on skeletal muscle on the basis of literature review and new results. A detailed knowledge of the evolution of endplates acetylcholine receptors and creatine kinase activity following laser irradiation can help to understand the therapeutic effect of laser phototherapy on muscle. This study showed that the laser phototherapy increases biochemical activity in intact muscle and thus could have direct therapeutic applications on muscle, especially during progressive atrophy resulting from peripheral nerve injury.

Early sensory protection in reverse end-to-side neurorrhaphy to improve the functional recovery of chronically denervated muscle in rat: a pilot study

OBJECT

Early innervation by sensory nerves has been proposed to prevent atrophy of chronically denervated muscle, but conventional end-to-end (ETE) neurorrhaphy has been demonstrated to have adverse effects on muscle contractile function. The aim of the present study was to investigate the potential for modified sensory nerve protection in reverse end-to-side (ETS) neurorrhaphy as a way of improving the functional recovery of denervated muscle.

METHODS

Four groups of rats underwent surgical denervation of the tibial nerve projecting to the right hindlimbs (Group 1, unprotected controls; Group 2, positive control [immediate repair without delayed denervation]; Group 3, ETS protected; and Group 4, ETE protected). The proximal and distal stumps of the tibial nerve were ligated in all animals except for those in the immediate-repair group. Other animals underwent denervation without sural nerve protection, or with ETE or ETS neurorrhaphy. The ETE- and ETS-protected and unprotected groups underwent an additional surgery in which the trimmed proximal and distal tibial nerve stumps were sutured together. After 3 months of recovery, the tibial function index was determined, and electrophysiological, histological, and morphometric parameters were assessed.

RESULTS

Significant muscle atrophy was observed in the unprotected group, while a well-preserved ultrastructure was observed for the gastrocnemius muscle in the ETE- and ETS-protected groups. Enhanced recovery in the ETS-protected group was indicated by the tibial function index, motor nerve conduction velocity, muscle contractile force tests, and the histological results. In contrast, early sensory nerve protection in ETE neurorrhaphy impaired the recovery of the regenerated axons and diminished the contractile force of the denervated muscle.

CONCLUSIONS

Early sensory protection in reverse ETS neurorrhaphy is an effective method for improving the functional recovery of chronically denervated muscle following peripheral nerve injury in rats.

Function-triggering antibodies to the adhesion molecule L1 enhance recovery after injury of the adult mouse femoral nerve

L1 is among the few adhesion molecules that favors repair after trauma in the adult central nervous system of vertebrates by promoting neuritogenesis and neuronal survival, among other beneficial features. In the peripheral nervous system, L1 is up-regulated in Schwann cells and regrowing axons after nerve damage, but the functional consequences of this expression remain unclear. Our previous study of L1-deficient mice in a femoral nerve injury model showed an unexpected improved functional recovery, attenuated motoneuronal cell death, and enhanced Schwann cell proliferation, being attributed to the persistent synthesis of neurotrophic factors. On the other hand, transgenic mice over-expressing L1 in neurons led to improved remyelination, but not improved functional recovery. The present study was undertaken to investigate whether the monoclonal L1 antibody 557 that triggers beneficial L1 functions in vitro would trigger these also in femoral nerve repair. We analyzed femoral nerve regeneration in C57BL/6J mice that received this antibody in a hydrogel filled conduit connecting the cut and sutured nerve before its bifurcation, leading to short-term release of antibody by diffusion. Video-based quantitative analysis of motor functions showed improved recovery when compared to mice treated with conduits containing PBS in the hydrogel scaffold, as a vehicle control. This improved recovery was associated with attenuated motoneuron loss, remyelination and improved precision of preferential motor reinnervation. We suggest that function-triggering L1 antibodies applied to the lesion site at the time of injury over a limited time period will not only be beneficial in peripheral, but also central nervous system regeneration.

Functional recovery of denervated skeletal muscle with sensory or mixed nerve protection: a pilot study

Functional recovery is usually poor following peripheral nerve injury when reinnervation is delayed. Early innervation by sensory nerve has been indicated to prevent atrophy of the denervated muscle. It is hypothesized that early protection with sensory axons is adequate to improve functional recovery of skeletal muscle following prolonged denervation of mixed nerve injury. In this study, four groups of rats received surgical denervation of the tibial nerve. The proximal and distal stumps of the tibial nerve were ligated in all animals except for those in the immediate repair group. The experimental groups underwent denervation with nerve protection of peroneal nerve (mixed protection) or sural nerve (sensory protection). The experimental and unprotected groups had a stage II surgery in which the trimmed proximal and distal tibial nerve stumps were sutured together. After 3 months of recovery, electrophysiological, histological and morphometric parameters were assessed. It was detected that the significant muscle atrophy and a good preserved structure of the muscle were observed in the unprotected and protective experimental groups, respectively. Significantly fewer numbers of regenerated myelinated axons were observed in the sensory-protected group. Enhanced recovery in the mixed protection group was indicated by the results of the muscle contraction force tests, regenerated myelinated fiber, and the results of the histological analysis. Our results suggest that early axons protection by mixed nerve may complement sensory axons which are required for promoting functional recovery of the denervated muscle natively innervated by mixed nerve.

Dermatan 4-O-sulfotransferase1 ablation accelerates peripheral nerve regeneration

Chondroitin sulfate (CS) and dermatan sulfate (DS) proteoglycans are major components of the extracellular matrix implicated in neural development, plasticity and regeneration. While it is accepted that CS are major inhibitors of neural regeneration, the contributions of DS to regeneration have not been assessed. To enable a novel approach in studies on DS versus CS roles during development and regeneration, we generated a mouse deficient in the dermatan 4-O-sulfotransferase1 (Chst14(-/-)), a key enzyme in the synthesis of iduronic acid-containing modules found in DS but not CS. In wild-type mice, Chst14 is expressed at high levels in the skin and in the nervous system, and is enriched in astrocytes and Schwann cells. Ablation of Chst14, and the assumed failure to produce DS, resulted in smaller body mass, reduced fertility, kinked tail and increased skin fragility compared with wild-type (Chst14(+/+)) littermates, but brain weight and gross anatomy were unaffected. Neurons and Schwann cells from Chst14(-/-) mice formed longer processes in vitro, and Chst14(-/-) Schwann cells proliferated more than Chst14(+/+) Schwann cells. After femoral nerve transection/suture, functional recovery and axonal regrowth in Chst14(-/-) mice were initially accelerated but the final outcome 3months after injury was not better than that in Chst14(+/+) littermates. These results suggest that while Chst14 and its enzymatic products might be of limited importance for neural development, they may contribute to the regeneration-restricting environment in the adult mammalian nervous system.

Delayed repair of facial nerve trauma: an experimental study in guinea pigs

CONCLUSION

The curative effect in the group where facial-facial anastomosis (FFA) was delayed for 7 days was similar to that in the immediate FFA group and had a better repair within 60 days.

OBJECTIVE

Due to the uncertainty about optimal timing of delayed facial nerve repair, we designed an experimental study in guinea pigs to find out the cut-off duration for delayed nerve repair.

METHODS

In this study, 64 male guinea pigs were randomly divided into 8 groups: normal, immediate FFA, and delayed FFA for 7, 14, 21, 30, 60, and 90 days (n = 6). Two months after suture of the nerves, the passing rate of myelinated fibers growing from the proximal to the distal stumps was calculated.

RESULTS

The passing rates of myelinated fibers in the groups with immediate FFA and FFA delayed for 7 days were significantly higher than those in other delayed FFA groups and the difference was statistically significant (p < 0.05), whereas the passing rates of the groups where FFA was delayed for 60 and 90 days were apparently lower than those of the immediate FFA and other delayed FFA groups. Under the electron microscope, regenerated fibers of the groups with immediate FFA and FFA delayed for 7 days were very similar to the normal myelinated fibers.

Improved regeneration after spinal cord injury in mice lacking functional T- and B-lymphocytes

It is widely accepted that the immune system plays important functional roles in regeneration after injury to the spinal cord. Immune response towards injury involves a complex interplay of immune system cells, such as neutrophils, macrophages and microglia, T- and B-lymphocytes. We investigated the influence of the lymphocyte component of the immune system on the locomotor outcome of severe spinal cord injury in a genetic mouse model of immune suppression. Transgenic mice lacking mature T- and B-lymphocytes due to the recombination activating gene 2 gene deletion (RAG2-/- mice) were subjected to severe compression of the lower thoracic spinal cord, with the wild-type mice of the same inbred background serving as controls. According to both the Basso Mouse Scale score and single frame motion analysis, the RAG2-/- mice showed improved recovery in comparison to control mice at six weeks after injury. Better locomotor function was associated with enhanced catecholaminergic and cholinergic reinnervation of the spinal cord caudal to injury and increased axonal regrowth/sprouting at the site of injury. Myelination of axons in the ventral column measured as g-ratio was more extensive in RAG2-/- than in control mice 6weeks after injury. Additionally, the number of microglia/macrophages was decreased in the lumbar spinal cord of RAG2-/- mice after injury, whereas the number of astrocytes was increased compared with controls. We conclude that T- and B-lymphocytes restrict functional recovery from spinal cord injury by increasing numbers of microglia/macrophages as well as decreasing axonal sprouting and myelination.

Effect of Dipsaci Radix on Hind Limb Muscle Atrophy of Sciatic Nerve Transected Rats

It was reported that Dipsaci radix (DR) has a reinforcement effect on the bone-muscle dysfunction in the oriental medical classics and the experimental animal studies. The muscle atrophy was induced by unilateral transection of the sciatic nerve of the rats. Water-extract of DR was used as treatment once a day for 12 days. The muscle weights of the hind limb, atrophic changes, glycogen contents, compositions and cross-section areas of muscle fiber types in soleus and medial gastrocnemius were investigated. Muscle fiber type was classified to type-I and type-II with MHCf immunohistochemistry. Furthermore, Bax and Bcl-2 expressions were observed with immunohistochemiatry. DR treatment significantly increased muscle weights of soleus, medial gastrocnemius, lateral gastrocnemius, and posterior tibialis of the damaged hind limb. DR treatment reduced apoptotic muscle nuclei and hyaline-degenerated muscle fibers in soleus and medial gastrocnemius of the damaged hind limb. DR treatment also significantly increased glycogen contents in medial gastrocnemius of the damaged hind limb. DR treatment significantly attenuated the slow-to-fast shift in soleus of the damaged hind limb but not in medial gastrocnemius. DR treatment significantly increased cross-section areas of type-I and type-II fibers in soleus and medial gastrocnemius of the damaged hind limb. In soleus and medial gastrocnemius, DR treatment significantly reduced Bax positive muscle nuclei in the damaged hind limb. These results suggest that DR treatment has an anti-atrophic effect and an anti-apoptotic effect against myonuclear apoptosis induced by the peripheral nerve damage.

Force characteristics of the rat sternomastoid muscle reinnervated with end-to-end nerve repair

The goal of this study was to establish force data for the rat sternomastoid (SM) muscle after reinnervation with nerve end-to-end anastomosis (EEA), which could be used as a baseline for evaluating the efficacy of new reinnervation techniques. The SM muscle on one side was paralyzed by transecting its nerve and then EEA was performed at different time points: immediate EEA, 1-month and 3-month delay EEA. At the end of 3-month recovery period, the magnitude of functional recovery of the reinnervated SM muscle was evaluated by measuring muscle force and comparing with the force of the contralateral control muscle. Our results demonstrated that the immediately reinnervated SM produced approximately 60% of the maximal tetanic force of the control. The SM with delayed nerve repair yielded approximately 40% of the maximal force. Suboptimal recovery of muscle force after EEA demonstrates the importance of developing alternative surgical techniques to treat muscle paralysis.

Expression of nuclear-encoded genes involved in mitochondrial biogenesis and dynamics in experimentally denervated muscle

The abundance, morphology, and functional properties of mitochondria become altered in response to denervation. To gain insight into the regulation of this process, mitochondrial enzyme activities and gene expression involved in mitochondrial biogenesis and dynamics in mouse gastrocnemius muscle was investigated. Sciatic nerve transactions were performed on mice, and then gastrocnemius muscles were isolated at days 5 and 30 after surgery. Muscle weight was decreased significantly by 15% and 62% at days 5 and 30 after surgery, respectively. The activity of citrate synthase, a marker of oxidative enzyme, was reduced significantly by 31% and 53% at days 5 and 30, respectively. Enzyme histochemical analysis revealed that subsarcolemmal mitochondria were largely lost than intermyofibrillar mitochondria at day 5, and this trend was further progressed at day 30 after surgery. Expression levels of peroxisome proliferator-activated receptor, γ coactivator 1 (PGC-1)α, estrogen-related receptor α (ERRα), and mitofusin 2 were down-regulated throughout the experimental period, whereas those of PGC-1β, PRC, nuclear respiratory factor (NRF)-1, NRF-2, TFAM, and Lon protease were down-regulated at day 30 after surgery. These results suggest that PGC-1α, ERRα, and mitofusin 2 may be important factors in the process of denervation-induced mitochondrial adaptation. In addition, other PGC-1 family of transcriptional coactivators and DNA binding transcription factors may also contribute to mitochondrial adaptation after early response to denervation.

Side-to-Side Nerve Grafts Sustain Chronically Denervated Peripheral Nerve Pathways During Axon Regeneration and Result in Improved Functional Reinnervation

BACKGROUND:

Progressive atrophy of Schwann cells in denervated nerve stumps is a major reason for progressive failure of functional recovery after peripheral nerve injury and surgical repair.

OBJECTIVE:

To examine whether side-to-side nerve bridges between an intact donor nerve and a recipient denervated distal nerve stump promote nerve growth and in turn, protect distal nerve stumps to improve axon regeneration after delayed surgical repair.

METHODS:

In Sprague-Dawley rats, 1 or 3 side-to-side common peroneal (CP) nerve bridges were used to bridge between the donor intact tibial (TIB) nerve and a recipient denervated CP distal nerve stump in the contralateral hind limb. No bridges were placed in control animals. After 4 months, either a fluorescent retrograde dye was applied to back-label TIB motoneurons with axons that had grown into the CP nerve stump or the proximal and distal CP nerve stumps were resutured in experimental and control animals to encourage CP nerve regeneration for 5 months. Retrograde dyes were again applied to count CP motoneurons that regenerated their axons through protected and unprotected nerve stumps.

RESULTS:

Significantly more donor TIB motoneurons regenerated axons into the recipient denervated CP nerve stump through 3 side-to-side CP nerve bridges compared with 1 bridge. This TIB nerve protection significantly increased the number of CP motoneurons regenerating axons through the denervated CP nerve stumps, the number of regenerated axons, and the weight of the reinnervated muscles.

CONCLUSION:

Multiple side-to-side nerve bridges protect chronically denervated nerve stumps to improve axon regeneration and target reinnervation after delayed nerve repair.

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.

Adhesion molecule L1 overexpressed under the control of the neuronal Thy-1 promoter improves myelination after peripheral nerve injury in adult mice

L1 is an adhesion molecule favorably influencing the functional and anatomical recoveries after central nervous system (CNS) injuries. Its roles in peripheral nervous system (PNS) regeneration are less well understood. Studies using knockout mice have surprisingly revealed that L1 has a negative impact on functional nerve regeneration by inhibiting Schwann cell proliferation. To further elucidate the roles of L1 in PNS regeneration, here we used a novel transgenic mouse overexpressing L1 in neurons, but not in PNS or CNS glial cells, under the control of a neuron-specific Thy-1 promoter. Without nerve injury, the transgene expression, as compared to wild-type mice, had no effect on femoral nerve function, numbers of quadriceps motoneurons and myelinated axons in the femoral nerve but resulted in slightly reduced myelination in the sensory saphenous nerve and increased neurofilament density in myelinated axons of the quadriceps motor nerve branch. After femoral nerve injury, L1 overexpression had no impact on the time course and degree of functional recovery. Unaffected were also numbers of regenerated quadriceps motoneurons, precision of muscle reinnervation, axon numbers and internodal lengths in the regenerated nerves. Despite the lack of functional effects, myelination in the motor and sensory femoral nerve branches was significantly improved and loss of perisomatic inhibitory terminals on motoneurons was attenuated in the transgenic mice. Our results indicate that L1 is a regulator of myelination in the injured PNS and warrant studies aiming to improve function in demyelinating PNS and CNS disorders using exogenous L1.

Passive and active exercise improve regeneration and muscle reinnervation after peripheral nerve injury in the rat

INTRODUCTION

Lesions of peripheral nerves cause loss of motor and sensory function and also lead to hyperreflexia and hyperalgesia. Activity-dependent therapies promote axonal regeneration and functional recovery and may improve sensory-motor coordination and restoration of adequate circuitry at the spinal level.

METHODS

We compared the effects of passive (bicycle) and active (treadmill) exercise on nerve regeneration and modulation of the spinal H reflex after transection and repair of the rat sciatic nerve. Animals were evaluated during 2 months using electrophysiological, functional, and histological methods.

RESULTS

Moderate exercise for 1 hour/day, either active treadmill walking or passive cycling, improved muscle reinnervation, increased the number of regenerated axons in the distal nerve, and reduced the increased excitability of spinal reflexes after nerve lesion.

DISCUSSION

Maintenance of denervated muscle activity and afferent input, by active or passive exercise, may increase trophic factor release to act on regenerating axons and to modulate central neuronal plasticity.

Orderly recruitment of motor units under optical control in vivo

A drawback of electrical stimulation for muscle control is that large, fatigable motor units are preferentially recruited before smaller motor units by the lowest-intensity electrical cuff stimulation. This phenomenon limits therapeutic applications because it is precisely the opposite of the normal physiological (orderly) recruitment pattern; therefore, a mechanism to achieve orderly recruitment has been a long-sought goal in physiology, medicine and engineering. Here we demonstrate a technology for reliable orderly recruitment in vivo. We find that under optical control with microbial opsins, recruitment of motor units proceeds in the physiological recruitment sequence, as indicated by multiple independent measures of motor unit recruitment including conduction latency, contraction and relaxation times, stimulation threshold and fatigue. As a result, we observed enhanced performance and reduced fatigue in vivo. These findings point to an unanticipated new modality of neural control with broad implications for nervous system and neuromuscular physiology, disease research and therapeutic innovation.

Motor axonal sprouting and neuromuscular junction loss in an animal model of Charcot-Marie-Tooth disease

Muscle weakness in Charcot-Marie-Tooth Type 1A disease (CMT1A) caused by mutations in peripheral myelin protein 22 (PMP22) has been attributed to an axonopathy that results in denervation and muscle atrophy. The underlying pathophysiological mechanisms involved are not understood. We investigated motor performance, neuromuscular junctions (NMJs), physiological parameters, and muscle morphometry of PMP22 transgenic mice. Neuromuscular junctions were progressively lost in hindlimb muscles of PMP22 transgenic mice, but their motor performance did not completely deteriorate during the observation period. There was considerable variability, including in laterality, in deficits among the animals. Cross-sectional areas and mean fiber size measurements indicated variable myofiber atrophy in hindlimb muscles. There was substantial concomitant axonal sprouting, and loss of neuromuscular junctions was inversely correlated with the accumulated length of axonal branches. Synaptic transmission studied in isolated nerve/muscle preparations indicated variable partial muscle denervation. Acetylcholine sensitivity was higher in the mutant muscles, and maximum tetanic force evoked by direct or indirect stimulation, specific force, and wet weights were markedly reduced in some mutant muscles. In summary, there is partial muscle denervation, and axons may retain some regenerative capacity but fail to reinnervate muscles in PMP22 transgenic mice.

Sensory protection of rat muscle spindles following peripheral nerve injury and reinnervation

BACKGROUND

Skeletal muscle structure and function are dependent on intact innervation. Prolonged muscle denervation results in irreversible muscle fiber atrophy, connective tissue hyperplasia, and deterioration of muscle spindles, specialized sensory receptors necessary for proper skeletal muscle function. The protective effect of temporary sensory innervation on denervated muscle, before motor nerve repair, has been shown in the rat. Sensory-protected muscles exhibit less fiber atrophy and connective tissue hyperplasia and maintain greater functional capacity than denervated muscles. The purpose of this study was to determine whether temporary sensory innervation also protects muscle spindles from degeneration.

METHODS

Rat tibial nerve was transected and repaired with either the saphenous or the original transected nerve. Negative controls remained denervated. After 3 to 6 months, the electrophysiologic response of the nerve to stretch in the rat gastrocnemius muscle was measured (n = 3 per group). After the animals were euthanized, the gastrocnemius muscle was removed, sectioned, stained, and examined for spindle number (n = 3 per group) and morphology (one rat per group). Immunohistochemical assessment of muscle spindle innervation was examined in four additional animals.

RESULTS

Significant deterioration of muscle spindles was seen in denervated muscle, whereas in muscle reinnervated with the tibial or the saphenous nerve, spindle number and morphology were improved. Histologic and functional evidence of spindle reinnervation by the sensory nerve was obtained.

CONCLUSION

These findings add to the known means by which motor or sensory nerves exert protective effects on denervated muscle, and further promote the use of sensory protection for improving the outcome after peripheral nerve injury.

Polysialic acid glycomimetic promotes functional recovery and plasticity after spinal cord injury in mice

Regeneration after injury of the central nervous system is poor due to the abundance of molecules inhibiting axonal growth. Here we pursued to promote regeneration after thoracic spinal cord injury in young adult C57BL/6J mice using peptides which functionally mimic polysialic acid (PSA) and human natural killer cell-1 (HNK-1) glycan, carbohydrate epitopes known to promote neurite outgrowth in vitro. Subdural infusions were performed with an osmotic pump, over 2 weeks. When applied immediately after injury, the PSA mimetic and the combination of PSA and HNK-1 mimetics, but not the HNK-1 mimetic alone, improved functional recovery as assessed by locomotor rating and video-based motion analysis over a 6-week observation period. Better outcome in PSA mimetic-treated mice was associated with higher, as compared with control mice, numbers of cholinergic and glutamatergic terminals and monaminergic axons in the lumbar spinal cord, and better axonal myelination proximal to the injury site. In contrast to immediate post-traumatic application, the PSA mimetic treatment was ineffective when initiated 3 weeks after spinal cord injury. Our data suggest that PSA mimetic peptides can be efficient therapeutic tools improving, by augmenting plasticity, functional recovery when applied during the acute phase of spinal cord injury.

A spatio-temporal analysis of motoneuron survival, axonal regeneration and neurotrophic factor expression after lumbar ventral root avulsion and implantation

Reimplantation of avulsed rat lumbar spinal ventral roots results in poor recovery of function of the denervated hind limb muscles. In contrast, reimplantation of cervical or sacral ventral roots is a successful repair strategy that results in a significant degree of regeneration. A possible explanation for this difference could be that following lumbar root avulsion, axons have to travel longer distances towards their target muscles, resulting in prolonged denervation of the distal nerve and a diminished capacity to support regeneration. Here we present a detailed spatio-temporal analysis of motoneuron survival, axonal regeneration and neurotrophic factor expression following unilateral avulsion and implantation of lumbar ventral roots L3, L4, and L5. Reimplantation prolongs the survival of motoneurons up to one month post-lesion. The first regenerating motor axons entered the reimplanted ventral roots during the first week and large numbers of fibers gradually enter the lumbar plexus between 2 and 4 weeks, indicating that axons enter the reimplanted roots and plexus over an extended period of time. However, motor axon counts show that relatively few axons reach the distal sciatic nerve in the 16 week post-lesion period. The observed initial increase and subsequent decline in expression of glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor correlate with the apparent spatio-temporal decline in the regenerative capacity of motor axons, indicating that the distal nerve is losing its capacity to support regenerating motor axons following prolonged denervation. These findings have important implications for future strategies to promote long-distance regeneration through distal, chronically denervated peripheral nerves.

Chitosan/polyglycolic acid nerve grafts for axon regeneration from prolonged axotomized neurons to chronically denervated segments

Peripheral nerve regeneration for long-term delayed injuries is usually unsatisfied. Here we attempted to use a chitosan/polyglycolic acid (PGA) artificial nerve graft to bridge a long-term delayed 10-mm defect in SD rats based on the previous studies on the graft used for immediate repair of 30-mm-long dog sciatic nerve defects and for clinical treatment of a 35-mm-long median nerve defect at elbow of a human patient. 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 chitosan/PGA artificial nerve graft. The animals non-grafted or grafted with autograft served as negative or positive control group. In experiment groups, nerve regeneration with functional recovery was achieved as measured by electrophysiological and histological techniques, although differences in the quantity and the quality of the regenerated nerve were observed between the 3- and 6-month delayed subgroups. The results showed that: (1) a few denervated Schwann cells survived and sustained their ability to myelinate axons at least 6 months, and (2) the atrophic denervated muscle could be reinnervated by regenerated axons through new muscle-nerve connections. These observations provide the possibility of guiding regenerated axons from survived axotomized neurons to distal nerve stump by the chitosan/PGA artificial nerve graft.

Ablation of adhesion molecule L1 in mice favours Schwann cell proliferation and functional recovery after peripheral nerve injury

The adhesion molecule L1 is one of the few adhesion molecules known to be beneficial for repair processes in the adult central nervous system of vertebrates by promoting axonal growth and neuronal survival. In the peripheral nervous system, L1 is up-regulated by myelination-competent Schwann cells and regenerating axons after nerve damage but its functional role has remained unknown. Here we tested the hypothesis that L1 is, as in the central nervous system, beneficial for nerve regeneration in the peripheral nervous system by performing combined functional and histological analyses of adult L1-deficient mice (L1y/-) and wild-type (L1y/+) littermates. Contrary to our hypothesis, quantitative video-based motion analysis revealed better locomotor recovery in L1y/- than in L1y/+ mice at 4-12 weeks after transection and surgical repair of the femoral nerve. Motoneuron regeneration in L1y/- mice was also enhanced as indicated by attenuated post-traumatic loss of motoneurons, enhanced precision of motor reinnervation, larger cell bodies of regenerated motoneurons and diminished loss of inhibitory synaptic input to motoneurons. In search of mechanisms underlying the observed effects, we analysed peripheral nerves at short time-periods (3-14 days) after transection and found that Schwann cell proliferation is strongly augmented in L1y/- versus L1y/+ mice. L1-deficient Schwann cells showed increased proliferation than wild-type Schwann cells, both in vivo and in vitro. These findings suggest a novel role for L1 in nerve regeneration. We propose that L1 negatively regulates Schwann cell proliferation after nerve damage, which in turn restricts functional recovery by limiting the trophic support for regenerating motoneurons.

Electrical stimulation combined with exercise increase axonal regeneration after peripheral nerve injury

Although injured peripheral axons are able to regenerate, functional recovery is usually poor after nerve transection. In this study we aim to elucidate the role of neuronal activity, induced by nerve electrical stimulation and by exercise, in promoting axonal regeneration and modulating plasticity in the spinal cord after nerve injury. Four groups of adult rats were subjected to sciatic nerve transection and suture repair. Two groups received electrical stimulation (3 V, 0.1 ms at 20 Hz) for 1 h, immediately after injury (ESa) or during 4 weeks (1 h daily; ESc). A third group (ES+TR) received 1 h electrical stimulation and was submitted to treadmill running during 4 weeks (5 m/min, 2 h daily). A fourth group performed only exercise (TR), whereas an untreated group served as control (C). Nerve conduction, H reflex and algesimetry tests were performed at 1, 3, 5, 7 and 9 weeks after surgery, to assess muscle reinnervation and changes in excitability of spinal cord circuitry. Histological analysis was made at the end of the follow-up. Groups that received acute ES and/or were forced to exercise in the treadmill showed higher levels of muscle reinnervation and increased numbers of regenerated myelinated axons when compared to control animals or animals that received chronic ES. Combining ESa with treadmill training significantly improved muscle reinnervation during the initial phase. The facilitation of the monosynaptic H reflex in the injured limb was reduced in all treated groups, suggesting that the maintenance of activity helps to prevent the development of hyperreflexia.

Electrical stimulation of paralyzed vibrissal muscles reduces endplate reinnervation and does not promote motor recovery after facial nerve repair in rats

The outcome of peripheral nerve injuries requiring surgical repair is poor. Recent work has suggested that electrical stimulation (ES) of denervated muscles could be beneficial. Here we tested whether ES has a positive influence on functional recovery after injury and surgical repair of the facial nerve. Outcomes at 2 months were compared to animals receiving sham stimulation (SS). Starting on the first day after end-to-end suture (facial-facial anastomosis), electrical stimulation (square 0.1 ms pulses at 5 Hz at an ex tempore established threshold amplitude of between 3.0 and 5.0V) was delivered to the vibrissal muscles for 5 min a day, 3 times a week. Restoration of vibrissal motor performance following ES or SS was evaluated using the video-based motion analysis and correlated with the degree of collateral axonal branching at the lesion site, the number of motor endplates in the target musculature and the quality of their reinnervation, i.e. the degree of mono- versus poly-innervation. Neither protocol reduced collateral branching. ES did not improve functional outcome, but rather reduced the number of innervated motor endplates to approximately one-fifth of normal values and failed to reduce the proportion of poly-innervated motor endplates. We conclude that ES is not beneficial for recovery of whisker function after facial nerve repair in rats.

Slow myosin heavy chain expression in the absence of muscle activity

Innervation has been generally accepted to be a major factor involved in both triggering and maintaining the expression of slow myosin heavy chain (MHC-1) in skeletal muscle. However, previous findings from our laboratory have suggested that, in the mouse, this is not always the case (30). Based on these results, we hypothesized that neurotomy would not markedly reduced the expression of MHC-1 protein in the mouse soleus muscles. In addition, other cellular, biochemical, and functional parameters were also studied in these denervated soleus muscles to complete our study. Our results show that denervation reduced neither the relative amount of MHC-1 protein, nor the percentage of muscle fibers expressing MHC-1 protein (P > 0.05). The fact that MHC-1 protein did not respond to muscle inactivity was confirmed in three different mouse strains (129/SV, C57BL/6, and CD1). In contrast, all of the other histological, biochemical, and functional muscle parameters were markedly altered by denervation. Cross-sectional area (CSA) of muscle fibers, maximal tetanic isometric force, maximal velocity of shortening, maximal power, and citrate synthase activity were all reduced in denervated muscles compared with innervated muscles (P < 0.05). Contraction and one-half relaxation times of the twitch were also increased by denervation (P < 0.05). Addition of tenotomy to denervation had no further effect on the relative expression of MHC-1 protein (P > 0.05), despite a greater reduction in CSA and citrate synthase activity (P < 0.05). In conclusion, a deficit in neural input leads to marked atrophy and reduction in performance in mouse soleus muscles. However, the maintenance of the relative expression of slow MHC protein is independent of neuromuscular activity in mice.