Canadian Association of Neuroscience Review: Axonal Regeneration in the Peripheral and Central Nervous Systems – Current Issues and Advances

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

Enhancing structural plasticity of PC12 neurons during differentiation and neurite regeneration with a catalytically inactive mutant version of the zRICH protein

BACKGROUND

Studies of the molecular mechanisms of nerve regeneration have led to the discovery of several proteins that are induced during successful nerve regeneration. RICH proteins were identified as proteins induced during the regeneration of the optic nerve of teleost fish. These proteins are 2',3'-cyclic nucleotide, 3'-phosphodiesterases that can bind to cellular membranes through a carboxy-terminal membrane localization domain. They interact with the tubulin cytoskeleton and are able to enhance neuronal structural plasticity by promoting the formation of neurite branches.

RESULTS

PC12 stable transfectant cells expressing a fusion protein combining a red fluorescent protein with a catalytically inactive mutant version of zebrafish RICH protein were generated. These cells were used as a model to analyze effects of the protein on neuritogenesis. Differentiation experiments showed a 2.9 fold increase in formation of secondary neurites and a 2.4 fold increase in branching points. A 2.2 fold increase in formation of secondary neurites was observed in neurite regeneration assays.

CONCLUSIONS

The use of a fluorescent fusion protein facilitated detection of expression levels. Two computer-assisted morphometric analysis methods indicated that the catalytically inactive RICH protein induced the formation of branching points and secondary neurites both during differentiation and neurite regeneration. A procedure based on analysis of random field images provided comparable results to classic neurite tracing methods.

Canine bone marrow peri-adipocyte cells could therapeutically benefit acute spinal cord injury through migration and secretion of hepatocyte growth factor to inflammatory milieu

Spinal cord injury (SCI) is a common neurological disorder in dogs. A secondary injury that occurs in the acute phase causes expansion of inflammation, resulting in lesion extension and further loss of function. Mesenchymal stem cells (MSCs) have trophic effects and the ability to migrate toward injured tissues; therefore, MSC-based therapy is considered promising for the treatment of canine SCI. We recently reported that bone marrow peri-adipocyte cells (BM-PACs) can be obtained from canine bone marrow and have stem cell potential superior to that of conventional bone marrow MSCs (BMMSCs). However, their therapeutic potential for SCI have been still unknow. Here, we first evaluated the ability of BM-PACs to secrete hepatocyte growth factor (HGF) and their migration ability toward inflammatory milieu in vitro. BM-PACs can secrete HGF in response to pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α and IL-1β, and exhibit migration ability toward these cytokines. Next, BM-PACs were intravenously administered into nude mice with acute SCI to analyze the homing ability and therapeutic effects of HGF secreted by BM-PACs. BM-PACs homed to the injured spinal cord, where the HGF expression level increased 7 days after administration. Intravenous administration of BM-PACs induced functional recovery and pathological improvement, indicated by less demyelinating area, more preserved axons, and less glial scar formation compared with the mice only received vehicle. These findings suggest that the intravenous administration of BM-PACs can be a novel therapeutic intervention for acute canine SCI.

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.

Immediate Tendon Transfer with Nerve Repair in Low Combined Ulnar and Median Nerve Injury

Background:

Combined median-ulnar nerve injury at the level of distal forearm (below the musculotendinous junction) causes a detrimental effect on hand functions, which have a great impact on patients’ hands as well as a financial burden. Many previous authors advocated early or immediate tendon transfer in solitary median or ulnar nerve injuries.

Methods:

This study included 20 patients with combined distal ulnar-median nerve injury, who were divided into 2 groups. Group I (control) included 10 patients who underwent primary (group fascicular) repair of both nerves only. Group II (study) included 10 patients underwent primary (group fascicular) repair with immediate tendon transfer simultaneously: opponenplasty using extensor indicies and adductoplasty extensor carpi radialis brevis with appropriate splinting, postoperative rehabilitation, and biofeedback facilities.

Results:

Twenty patients (age: 18–38 years) were affected. The response of median and ulnar nerves showed invariable results in both groups, whilst the hand grip, hand pinch, and opposition showed marked improvements in group II. Moreover, inter-phalangeal and metacarpophalangeal joints of thumb showed no deformities in group II in comparison with high level of deformities in group I, owing to early regain of thumb movements.

Conclusions:

Immediate (during neurorrhaphy) tendon transfer may offer additional merits over nerve repair only for distal combined ulnar and median injury, as it offers scarless field, no adhesion, and no joint edema, leading to very early return to normal hand functions with a consequent decrease of thumb deformities, better hand grip, and key pinch.

Cut wires: The Electrophysiology of Regenerated Tissue

When nerves are damaged by trauma or disease, they are still capable of firing off electrical command signals that originate from the brain. Furthermore, those damaged nerves have an innate ability to partially regenerate, so they can heal from trauma and even reinnervate new muscle targets. For an amputee who has his/her damaged nerves surgically reconstructed, the electrical signals that are generated by the reinnervated muscle tissue can be sensed and interpreted with bioelectronics to control assistive devices or robotic prostheses. No two amputees will have identical physiologies because there are many surgical options for reconstructing residual limbs, which may in turn impact how well someone can interface with a robotic prosthesis later on. In this review, we aim to investigate what the literature has to say about different pathways for peripheral nerve regeneration and how each pathway can impact the neuromuscular tissue’s final electrophysiology. This information is important because it can guide us in planning the development of future bioelectronic devices, such as prosthetic limbs or neurostimulators. Future devices will primarily have to interface with tissue that has undergone some natural regeneration process, and so we have explored and reported here what is known about the bioelectrical features of neuromuscular tissue regeneration.

Electrophysiological, functional and histopathological assessments of high dose melatonin on regeneration after blunt sciatic nerve injury

The aim of this study was to determine the curative effects of high-dose (100 mg/kg) melatonin on peripheral nerve injury. Forty male Wistar albino rats were randomized into four groups as sham, vehicle, melatonin, and ischemia and their right sciatic nerves were exposed. The process was terminated in the sham group. In the other groups, nerve injury was induced by clip compression. The vehicle group was intraperitoneally administered ethanol 0.1 cc (melatonin solvent), while the melatonin group was intraperitoneally administered a single dose of melatonin (100 mg/kg). Following the surgery, sciatic nerve functional index (SFI) was measured using walking track analysis on days 7, 14, and 21, and latency, amplitude, and muscle action potentials (MAP) field values were measured using electroneuromyography (ENMG) on day 21. Histopathologically, edema, axonal degeneration, myelin damage, and inflammatory response were evaluated in all groups. SFI values were noted to be statistically significantly different among the vehicle, melatonin, and ischemia groups, and the melatonin group showed a faster recovery. In the ENMG evaluations, higher amplitude and field values in the melatonin group indicated that melatonin accelerated peripheral nerve recovery. Histopathologically, although fibers with loss of myelin were identified in the melatonin group, the myelin sheath was preserved in general and the axonal structure was noted to be normal. A single injection of high-dose melatonin was found to preserve myelin sheath, prevent axonal loss, and accelerate functional recovery during the nerve regeneration in peripheral nerve injury.

Neuroprotective Effects of Lacosamide in Experimental Peripheral Nerve Injury in Rats : A Prospective Randomized and Placebo-Controlled Trial

OBJECTIVE

To evaluate the neuroprotective effects of lacosamide after experimental peripheral nerve injury in rats.

METHODS

A total of 28 male wistar albino rats weighing 300-350 g were divided into four groups. In group I, the sciatic nerve exposed and the surgical wound was closed without injury; in group II, peripheral nerve injuries (PNI) was performed after dissection of the nerve; in group III, PNI was performed after dissection and lacosamide was administered, and in group IV, PNI was performed after dissection and physiological saline solution was administered. At 7 days after the injury all animals were sacrificed after walking track analysis. A 5 mL blood sample was drawn for biochemical analysis, and sciatic nerve tissues were removed for histopathological examination.

RESULTS

There is low tissue damage in lacosamide treated group and antioxidant anzymes and malondialdehyde levels were higher than non-treated and placebo treated group. However there was no improvement on clinical assessment.

CONCLUSION

The biochemical and histological analyses revealed that lacosamide has neuroprotective effect in PNI in rats. This neuroprotective capacity depends on its scavenger role for free oxygen radicals by increasing antioxidant enzyme activity.

Preprocessing of Medical Image Data for Three-Dimensional Bioprinted Customized-Neural-Scaffolds

IMPACT STATEMENT

Nerve damage, which can be devastating, triggers several biological cascades, which result in the insufficiencies of the human nervous system to provide complete nerve repair and regain of function. Since no therapeutic strategy exists to provide immediate attention and intervention to patients with newly acquired nerve damage, we propose a strategy in which accelerated medical image processing through graphical processing unit implementation and three-dimensional printing are combined to produce a time-efficient, patient-specific (custom-neural-scaffold) solution to nerve damage. This work aims to beneficially shorten the time required for medical decision-making so that improved patient outcomes are achieved.

Long-Term Denervated Rat Schwann Cells Retain Their Capacity to Proliferate and to Myelinate Axons in vitro

Functional recovery is poor after peripheral nerve injury and delayed surgical repair or when nerves must regenerate over long distances to reinnervate distant targets. A reduced capacity of Schwann cells (SCs) in chronically denervated distal nerve stumps to support and interact with regenerating axons may account for the poor outcome. In an in vitro system, we examined the capacity of adult, long-term denervated rat SCs to proliferate and to myelinate neurites in co-cultures with fetal dorsal root ganglion (DRG) neurons. Non-neuronal cells were counted immediately after their isolation from the distal sciatic nerve stumps that were subjected to acute denervation of 7 days or chronic denervation of either 7 weeks or 17 months. Thereafter, equal numbers of the non-neural cells were co-cultured with purified dissociated DRG neurons for 5 days. The co-cultures were then treated with ³H-Thymidine for 24 h to quantitate SC proliferation with S100 immunostaining and autoradiography. After a 24-day period of co-culture, Sudan Black staining was used to visualize and count myelin segments that were elaborated around DRG neurites by the SCs. Isolated non-neural cells from 7-week chronically denervated nerve stumps increased 2.5-fold in number compared to ~2 million in 7 day acutely denervated stumps. There were only <0.2 million cells in the 17-week chronically denervated stumps. Nonetheless, these chronically denervated SCs maintained their proliferative capacity although the capacity was reduced to 30% in the 17-month chronically denervated distal nerve stumps. Moreover, the chronically denervated SCs retained their capacity to myelinate DRG neurites: there was extensive myelination of the neurites by the acutely and chronically denervated SCs after 24 days co-culture. There were no significant differences in the extent of myelination. We conclude that the low numbers of surviving SCs in chronically denervated distal nerve stumps retain their ability to respond to axonal signals to divide and to elaborate myelin. However, their low numbers consequent to their poor survival and their reduced capacity to proliferate account, at least in part, for the poor functional recovery after delayed surgical repair of injured nerve and/or the repair of injured nerves far from their target organs.

Inflammaging impairs peripheral nerve maintenance and regeneration

The regenerative capacity of peripheral nerves declines during aging, contributing to the development of neuropathies, limiting organism function. Changes in Schwann cells prompt failures in instructing maintenance and regeneration of aging nerves; molecular mechanisms of which have yet to be delineated. Here, we identified an altered inflammatory environment leading to a defective Schwann cell response, as an underlying mechanism of impaired nerve regeneration during aging. Chronic inflammation was detected in intact uninjured old nerves, characterized by increased macrophage infiltration and raised levels of monocyte chemoattractant protein 1 (MCP1) and CC chemokine ligand 11 (CCL11). Schwann cells in the old nerves appeared partially dedifferentiated, accompanied by an activated repair program independent of injury. Upon sciatic nerve injury, an initial delayed immune response was followed by a persistent hyperinflammatory state accompanied by a diminished repair process. As a contributing factor to nerve aging, we showed that CCL11 interfered with Schwann cell differentiation in vitro and in vivo. Our results indicate that increased infiltration of macrophages and inflammatory signals diminish regenerative capacity of aging nerves by altering Schwann cell behavior. The study identifies CCL11 as a promising target for anti‐inflammatory therapies aiming to improve nerve regeneration in old age.

A neurophysiological approach to nerve transfer to restore upper limb function in cervical spinal cord injury

A successful nerve transfer surgery can provide a wealth of benefits to a patient with cervical spinal cord injury. The process of surgical decision making ideally uses all pertinent information to produce the best functional outcome. Reliance on clinical examination and imaging studies alone can miss valuable information on the state of spinal cord health. In this regard, neurophysiological evaluation has the potential to effectively gauge the neurological status of even select pools of anterior horn cells and their axons to small nerve branches in question to determine the potential efficacy of their use in a transfer. If available preoperatively, knowledge gained from such an evaluation could significantly alter the reconstructive surgical plan and avoid poor results. The authors describe their institution’s approach to the assessment of patients with cervical spinal cord injury who are being considered for nerve transfer surgery in both the acute and chronic setting and broadly review the neurophysiological techniques used.

The Glia Response after Peripheral Nerve Injury: A Comparison between Schwann Cells and Olfactory Ensheathing Cells and Their Uses for Neural Regenerative Therapies

The peripheral nervous system (PNS) exhibits a much larger capacity for regeneration than the central nervous system (CNS). One reason for this difference is the difference in glial cell types between the two systems. PNS glia respond rapidly to nerve injury by clearing debris from the injury site, supplying essential growth factors and providing structural support; all of which enhances neuronal regeneration. Thus, transplantation of glial cells from the PNS is a very promising therapy for injuries to both the PNS and the CNS. There are two key types of PNS glia: olfactory ensheathing cells (OECs), which populate the olfactory nerve, and Schwann cells (SCs), which are present in the rest of the PNS. These two glial types share many similar morphological and functional characteristics but also exhibit key differences. The olfactory nerve is constantly turning over throughout life, which means OECs are continuously stimulating neural regeneration, whilst SCs only promote regeneration after direct injury to the PNS. This review presents a comparison between these two PNS systems in respect to normal physiology, developmental anatomy, glial functions and their responses to injury. A thorough understanding of the mechanisms and differences between the two systems is crucial for the development of future therapies using transplantation of peripheral glia to treat neural injuries and/or disease.

The role of cAMP and its downstream targets in neurite growth in the adult nervous system

Injured neurons in the adult mammalian central nervous system (CNS) have a very limited capacity for axonal regeneration and neurite outgrowth. This inability to grow new axons or to regrow injured axons is due to the presence of molecules that inhibit axonal growth, and age related changes in the neuron's innate growth capabilities. Available levels of cAMP are thought to have an important role in linking both of these factors. Elevated levels of cAMP in the developing nervous system are important for the guidance and stability of growth cones. As the nervous system matures, cAMP levels decline and the growth promoting effects of cAMP diminish. It has frequently been demonstrated that increasing neuronal cAMP can enhance neurite growth and regeneration. Some methods used to increase cAMP include administration of cAMP agonists, conditioning lesions, or electrical stimulation. Furthermore, it has been proposed that multiple stages of cAMP induced growth exist, one directly caused by its downstream effector Protein Kinase A (PKA) and one caused by the eventual upregulation of gene transcription. Although the role cAMP in promoting axon growth is well accepted, the downstream pathways that mediate cAMP-mediated axonal growth are less clear. This is partly because various key studies that explored the link between PKA and axonal outgrowth relied on the PKA inhibitors KT5720 and H89. More recent studies have shown that both of these drugs are less specific than initially thought and can inhibit a number of other signalling molecules including the Exchange Protein Activated by cAMP (EPAC). Consequently, it has recently been shown that a number of intracellular signalling pathways previously attributed to PKA can now be attributed solely to activation of EPAC specific pathways, or the simultaneous co-activation of PKA and EPAC specific pathways. These new studies open the door to new potential treatments for repairing the injured spinal cord.

Emerging Putative Associations between Non-Coding RNAs and Protein-Coding Genes in Neuropathic Pain: Added Value from Reusing Microarray Data

Regeneration of injured nerves is likely occurring in the peripheral nervous system, but not in the central nervous system. Although protein-coding gene expression has been assessed during nerve regeneration, little is currently known about the role of non-coding RNAs (ncRNAs). This leaves open questions about the potential effects of ncRNAs at transcriptome level. Due to the limited availability of human neuropathic pain (NP) data, we have identified the most comprehensive time-course gene expression profile referred to sciatic nerve (SN) injury and studied in a rat model using two neuronal tissues, namely dorsal root ganglion (DRG) and SN. We have developed a methodology to identify differentially expressed bioentities starting from microarray probes and repurposing them to annotate ncRNAs, while analyzing the expression profiles of protein-coding genes. The approach is designed to reuse microarray data and perform first profiling and then meta-analysis through three main steps. First, we used contextual analysis to identify what we considered putative or potential protein-coding targets for selected ncRNAs. Relevance was therefore assigned to differential expression of neighbor protein-coding genes, with neighborhood defined by a fixed genomic distance from long or antisense ncRNA loci, and of parental genes associated with pseudogenes. Second, connectivity among putative targets was used to build networks, in turn useful to conduct inference at interactomic scale. Last, network paths were annotated to assess relevance to NP. We found significant differential expression in long-intergenic ncRNAs (32 lincRNAs in SN and 8 in DRG), antisense RNA (31 asRNA in SN and 12 in DRG), and pseudogenes (456 in SN and 56 in DRG). In particular, contextual analysis centered on pseudogenes revealed some targets with known association to neurodegeneration and/or neurogenesis processes. While modules of the olfactory receptors were clearly identified in protein-protein interaction networks, other connectivity paths were identified between proteins already investigated in studies on disorders, such as Parkinson, Down syndrome, Huntington disease, and Alzheimer. Our findings suggest the importance of reusing gene expression data by meta-analysis approaches.

Electrical Stimulation to Enhance Axon Regeneration After Peripheral Nerve Injuries in Animal Models and Humans

Injured peripheral nerves regenerate their lost axons but functional recovery in humans is frequently disappointing. This is so particularly when injuries require regeneration over long distances and/or over long time periods. Fat replacement of chronically denervated muscles, a commonly accepted explanation, does not account for poor functional recovery. Rather, the basis for the poor nerve regeneration is the transient expression of growth-associated genes that accounts for declining regenerative capacity of neurons and the regenerative support of Schwann cells over time. Brief low-frequency electrical stimulation accelerates motor and sensory axon outgrowth across injury sites that, even after delayed surgical repair of injured nerves in animal models and patients, enhances nerve regeneration and target reinnervation. The stimulation elevates neuronal cyclic adenosine monophosphate and, in turn, the expression of neurotrophic factors and other growth-associated genes, including cytoskeletal proteins. Electrical stimulation of denervated muscles immediately after nerve transection and surgical repair also accelerates muscle reinnervation but, at this time, how the daily requirement of long-duration electrical pulses can be delivered to muscles remains a practical issue prior to translation to patients. Finally, the technique of inserting autologous nerve grafts that bridge between a donor nerve and an adjacent recipient denervated nerve stump significantly improves nerve regeneration after delayed nerve repair, the donor nerves sustaining the capacity of the denervated Schwann cells to support nerve regeneration. These reviewed methods to promote nerve regeneration and, in turn, to enhance functional recovery after nerve injury and surgical repair are sufficiently promising for early translation to the clinic.

The neuroimmunology of degeneration and regeneration in the peripheral nervous system

Peripheral nerves regenerate following injury due to the effective activation of the intrinsic growth capacity of the neurons and the formation of a permissive pathway for outgrowth due to Wallerian degeneration (WD). WD and subsequent regeneration are significantly influenced by various immune cells and the cytokines they secrete. Although macrophages have long been known to play a vital role in the degenerative process, recent work has pointed to their importance in influencing the regenerative capacity of peripheral neurons. In this review, we focus on the various immune cells, cytokines, and chemokines that make regeneration possible in the peripheral nervous system, with specific attention placed on the role macrophages play in this process.

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.

An alternative to nerve repair using an antioxidant compound: a histological study in rats

The fascicular composition and organisation of the inferior alveolar nerve (IAN) were determined to confirm the microarchitecture of the IAN bundles into each of the mandibular teeth, including the composition of the mental nerve. The aim of this study was to evaluate peripheral nerve repair after the application of an antioxidant compound to the damaged nerve tissue to elevate the concentration and bioavailability of elements capable of favouring tissue repair. Twenty-five Wistar rats were divided into groups: The Control 1 (Ctl 1) (n = 5) animals had the ischiatic nerve exposed with no suture injury and were sacrificed at 30 days post-operatively. The Control 2 (Ctl 2) (n = 10) animals had the ischiatic nerve exposed, and the nerve was injured using suture in three distinct regions. In the experimental (Exp) animals (n = 10), an antioxidant organic compound was applied to the nerve injury site. The animals with nerve injury (Ctl2 and Exp group) were sacrificed at 15 and 30 days post-operatively. The histological analysis showed less degeneration in the Exp group at 15 and 30 days post-operatively. Nerve neoformation forming a connection between the distal and proximal suture sites was observed in the experimental group. This study presented an alternative to nerve repair using an antioxidant compound.

Nerve conduits for peripheral nerve surgery

Autologous nerve grafts are the current criterion standard for repair of peripheral nerve injuries when the transected nerve ends are not amenable to primary end-to-end tensionless neurorrhaphy. However, donor-site morbidities such as neuroma formation and permanent loss of function have led to tremendous interest in developing an alternative to this technique. Artificial nerve conduits have therefore emerged as an alternative to autologous nerve grafting for the repair of short peripheral nerve defects of less than 30 mm; however, they do not yet surpass autologous nerve grafts clinically. A thorough understanding of the complex biological reactions that take place during peripheral nerve regeneration will allow researchers to develop a nerve conduit with physical and biological properties similar to those of an autologous nerve graft that supports regeneration over long nerve gaps and in large-diameter nerves. In this article, the authors assess the currently available nerve conduits, summarize research in the field of developing these conduits, and establish areas within this field in which further research would prove most beneficial.

Effects of aging on genioglossus motor units in humans

The genioglossus is a major upper airway dilator muscle thought to be important in obstructive sleep apnea pathogenesis. Aging is a risk factor for obstructive sleep apnea although the mechanisms are unclear and the effects of aging on motor unit remodeled in the genioglossus remains unknown. To assess possible changes associated with aging we compared quantitative parameters related to motor unit potential morphology derived from EMG signals in a sample of older (n = 11; >55 years) versus younger (n = 29; <55 years) adults. All data were recorded during quiet breathing with the subjects awake. Diagnostic sleep studies (Apnea Hypopnea Index) confirmed the presence or absence of obstructive sleep apnea. Genioglossus EMG signals were analyzed offline by automated software (DQEMG), which estimated a MUP template from each extracted motor unit potential train (MUPT) for both the selective concentric needle and concentric needle macro (CNMACRO) recorded EMG signals. 2074 MUPTs from 40 subjects (mean±95% CI; older AHI 19.6±9.9 events/hr versus younger AHI 30.1±6.1 events/hr) were extracted. MUPs detected in older adults were 32% longer in duration (14.7±0.5 ms versus 11.1±0.2 ms; P  =  0.05), with similar amplitudes (395.2±25.1 µV versus 394.6±13.7 µV). Amplitudes of CNMACRO MUPs detected in older adults were larger by 22% (62.7±6.5 µV versus 51.3±3.0 µV; P<0.05), with areas 24% larger (160.6±18.6 µV.ms versus 130.0±7.4 µV.ms; P<0.05) than those detected in younger adults. These results confirm that remodeled motor units are present in the genioglossus muscle of individuals above 55 years, which may have implications for OSA pathogenesis and aging related upper airway collapsibility.

Aspects of ocular war injuries

Eye injuries are common in warfare with an incidence of approximately 10%. They carry a high morbidity, as they can determine an injured person’s future independence and employability. The majority are a combination of primary and secondary blast mechanisms, though tertiary and quaternary types are common. There is some evidence of quinary types from toxic elements from the explosion. Eye protection significantly reduces the incidence and severity of ballistic eye injury but does not eliminate it. Thermal ocular burns are relatively common in warfare. The treatment goal is to minimise limbal stem cell damage. Human amniotic membrane can be used to promote this. Retinal and optic nerve injury following closed eye trauma are currently untreatable, but neuroprotective and neuroregenerative agents are being developed to improve outcomes. Sensory substitution of the sense of touch for sight can help orientate blinded individual in their surroundings. Ophthalmology has a major impact on the lives of the war wounded.

History, Mechanisms and Clinical Value of Fibrillation Analyses in Muscle Denervation and Reinnervation by Single Fiber Electromyography and Dynamic Echomyography

This work reviews history, current clinical relevance and future of fibrillation, a functional marker of skeletal muscle denervated fibers. Fibrillations, i.e., spontaneous contraction, in denervated muscle were first described during the nineteenth century. It is known that alterations in membrane potential are responsible for the phenomenon and that they are related to changes in electrophysiological factors, cellular metabolism, cell turnover and gene expression. They are known to inhibit muscle atrophy to some degree and are used to diagnose neural injury and reinnervation that are occurring in patients. Electromyography (EMG) is useful in determining progress, prognosis and efficacy of therapeutic interventions and their eventual change. For patients with peripheral nerve injury, and thus without the option of volitional contractions, electrical muscle stimulation may be helpful in preserving the contractility and extensibility of denervated muscle tissue and in retarding/counteracting muscle atrophy. It is obvious from the paucity of recent literature that research in this area has declined over the years. This is likely a consequence of the decrease in funding available for research and the fact that the fibrillations do not appear to cause serious health issues. Nonetheless, further exploration of them as diagnostic tools in long-term denervation is merited, in particular if Single Fiber EMG (SFEMG) is combined with Dynamic Echomyography (DyEM), an Ultra Sound muscle approach we recently designed and developed to explore denervated and reinnervating muscles.

Controlled nerve ablation with direct current: parameters and mechanisms

Spastic hypertonus (muscle over-activity) often develops after spinal cord injury or stroke. Chemodenervating agents such as Botulinum toxin A (BtA) and phenol are often used to treat this condition. We have previously shown that the use of direct current (DC) to create controlled lesions of peripheral nerves may provide a means of reducing spastic hypertonus. Here, we explored a range of stimulation parameters that could be used clinically. Nerves were lesioned with DC in chronically implanted animals and the outcome was tracked over many months. In addition, we used DC to ablate nerves in animals with decerebrate rigidity (an animal model of spastic hypertonus) and we explored the possible mechanisms of DC nerve ablation. We found that nerve ablation with DC was effective in reducing hypertonus. Some stimulation paradigms were more likely to be clinically acceptable than others. Furthermore we showed that nerve regeneration occurs in the months following DC nerve ablation and we demonstrated that the ablation procedure is repeatable, much like BtA treatment. Regarding mechanism, our results did not support the hypothesis that DC caused nerve damage by overactivating sodium channels. Rather, the mechanism of damage seems to be related to changes in pH.

Obstetrical brachial plexus palsy: lessons in functional neuroanatomy

Obstetrical branchial plexus paralysis is a serious and possibly disabling disorder. While thoroughly described as a clinical entity, much concerning its pathogenesis is still unknown. Basic science studies alongside with studies on functional neuroanatomy of peripheral and central nervous system and their interactions lead to deeper understanding of its pathology. Research concentrates on the consequences of branchial plexus traction to peripheral nerves and muscles function and viability and rehabilitation options. Changes obstetrical branchial plexus paralysis causes to central nervous systems organisation have been, to some extent, investigated. It seems that central nervous system is not "blind" after obstetrical branchial plexus paralysis but instead proceeds to remodelling so to adapt to new needs. Research indicates that both this entity and organism's response are much more complicated than previously believed. Current treatment options include microsurgery and palliative surgery but their improvement is possible by focusing on central nervous system. Current report discusses these topics and tries to reach useful conclusions.

Targeting anti-inflammatory treatment can ameliorate injury-induced neuropathic pain

Tumor necrosis factor-α plays important roles in immune system development, immune response regulation, and T-cell-mediated tissue injury. The present study assessed the net value of anti-tumor necrosis factor-α treatment in terms of functional recovery and inhibition of hypersensitivity after peripheral nerve crush injury. We created a right sciatic nerve crush injury model using a Sugita aneurysm clip. Animals were separated into 3 groups: the first group received only a skin incision; the second group received nerve crush injury and intraperitoneal vehicle injection; and the third group received nerve crush injury and intraperitoneal etanercept (6 mg/kg). Etanercept treatment improved recovery of motor nerve conduction velocity, muscle weight loss, and sciatic functional index. Plantar thermal and von Frey mechanical withdrawal thresholds recovered faster in the etanercept group than in the control group. On day 7 after crush injury, the numbers of ED-1-positive cells in crushed nerves of the control and etanercept groups were increased compared to that in the sham-treated group. After 21 days, ED-1-positive cells had nearly disappeared from the etanercept group. Etanercept reduced expression of interleukin-6 and monocyte chemotactic and activating factor-1 at the crushed sciatic nerve. These findings demonstrate the utility of etanercept, in terms of both enhancing functional recovery and suppressing hypersensitivity after nerve crush. Etanercept does not impede the onset or progression of Wallerian degeneration, but optimizes the involvement of macrophages and the secretion of inflammatory mediators.

Spatiotemporal expression of SKIP after rat sciatic nerve crush

Ski-interacting protein (SKIP) is a highly conserved protein from yeast to Human. As an essential spliceosomal component and transcriptional co-regulator it plays an important role in preinitiation, splicing and polyadenylation. SKIP can also combine with Ski to overcome the G1 arrest and the growth-suppressive activities of pRb. Furthermore SKIP has the capacity to augment TGF-β dependent transcription. While the distribution and function of SKIP in peripheral nervous system lesion and regeneration remain unclear. Here, we investigated the spatiotemporal expression of SKIP in an acute sciatic nerve crush model in adult rats. Western Blot analysis revealed that SKIP was expressed in normal sciatic nerves. It gradually increased, reached a peak at 1 week after crush, and then returned to the normal level at 4 weeks. Besides, we observed that up-regulation of SKIP was approximately in parallel with Proliferating cell nuclear antigen (PCNA), and numerous Schwann cells (SCs) expressing SKIP were PCNA and Ki-67 positive. Collectively, we hypothesized peripheral nerve crush induced up-regulation of SKIP in the sciatic nerve, which was associated with SCs proliferation.

Fibrillation potential onset in peripheral nerve injury

INTRODUCTION

Fibrillation potentials are an accepted electrical marker of muscle denervation that occur in axonal nerve injury. Clinically, they are used to determine the type of, and prognosis for nerve injuries. The time of occurrence after nerve injury plays a critical role in clinical decision making. This study explores the evolution of the generally accepted guideline that fibrillation potentials occur 1 to 4 weeks after axonal nerve injury.

METHODS

Pubmed, Ovid, and EMBASE, and current textbooks were reviewed. References were recursively followed back to the initial description of fibrillation potentials.

RESULTS

The majority of our understanding regarding the timing of onset of fibrillation potentials appears to arise from animal experiments in the mid-20th century.

CONCLUSIONS

Despite frequent use in human clinical care, published evidence for the 1 to 4 week guideline comes almost entirely from animal studies. An appreciation of this background and resulting limitations aids clinical application of this guideline.

Receptor tyrosine kinases: molecular switches regulating CNS axon regeneration

The poor or lack of injured adult central nervous system (CNS) axon regeneration results in devastating consequences and poor functional recovery. The interplay between the intrinsic and extrinsic factors contributes to robust inhibition of axon regeneration of injured CNS neurons. The insufficient or lack of trophic support for injured neurons is considered as one of the major obstacles contributing to their failure to survive and regrow their axons after injury. In the CNS, many of the signalling pathways associated with neuronal survival and axon regeneration are regulated by several classes of receptor tyrosine kinases (RTK) that respond to a variety of ligands. This paper highlights and summarises the most relevant recent findings pertinent to different classes of the RTK family of molecules, with a particular focus on elucidating their role in CNS axon regeneration.

Extrinsic cellular and molecular mediators of peripheral axonal regeneration

The ability of injured peripheral nerves to regenerate and reinnervate their original targets is a characteristic feature of the peripheral nervous system (PNS). On the other hand, neurons of the central nervous system (CNS), including retinal ganglion cell (RGC) axons, are incapable of spontaneous regeneration. In the adult PNS, axonal regeneration after injury depends on well-orchestrated cellular and molecular processes that comprise a highly reproducible series of degenerative reactions distal to the site of injury. During this fine-tuned process, named Wallerian degeneration, a remodeling of the distal nerve fragment prepares a permissive microenvironment that permits successful axonal regrowth originating from the proximal nerve fragment. Therefore, a multitude of adjusted intrinsic and extrinsic factors are important for surviving neurons, Schwann cells, macrophages and fibroblasts as well as endothelial cells in order to achieve successful regeneration. The aim of this review is to summarize relevant extrinsic cellular and molecular determinants of successful axonal regeneration in rodents that contribute to the regenerative microenvironment of the PNS.

Fate of stem cell transplants in peripheral nerves

While damaged peripheral nerves demonstrate some potential to regenerate, complete functional recovery remains infrequent, owing to a functional loss of supportive Schwann cells distal to the injury. An emerging solution to improve upon this intrinsic regenerative capacity is to supplement injured nerves with stem cells derived from various tissues. While many of these strategies have proven successful in animal models, few studies have examined the behavior of transplanted stem cells in vivo, including whether they survive and differentiate. In previous work, we demonstrated that cells derived from neonatal rodent dermis (skin-derived precursor cells, or SKPs) could improve regenerative parameters when transplanted distal to both acute and chronic nerve injuries in Lewis rats. The aim of this work was to track the fate of these cells in various nerve injury paradigms and determine the response of these cells to a known glial growth factor. Here, we report that SKPs survive, respond to local cues, differentiate into myelinating Schwann cells, and avoid complete clearance by the host's immune defenses for a minimum of 10weeks. Moreover, the ultimate fate of SKPs in vivo depends on the nerve environment into which they are injected and can be modified by inclusion of heregulin-1β.

Wallerian degeneration: gaining perspective on inflammatory events after peripheral nerve injury

In this review, we first provide a brief historical perspective, discussing how peripheral nerve injury (PNI) may have caused World War I. We then consider the initiation, progression, and resolution of the cellular inflammatory response after PNI, before comparing the PNI inflammatory response with that induced by spinal cord injury (SCI).In contrast with central nervous system (CNS) axons, those in the periphery have the remarkable ability to regenerate after injury. Nevertheless, peripheral nervous system (PNS) axon regrowth is hampered by nerve gaps created by injury. In addition, the growth-supportive milieu of PNS axons is not sustained over time, precluding long-distance regeneration. Therefore, studying PNI could be instructive for both improving PNS regeneration and recovery after CNS injury. In addition to requiring a robust regenerative response from the injured neuron itself, successful axon regeneration is dependent on the coordinated efforts of non-neuronal cells which release extracellular matrix molecules, cytokines, and growth factors that support axon regrowth. The inflammatory response is initiated by axonal disintegration in the distal nerve stump: this causes blood-nerve barrier permeabilization and activates nearby Schwann cells and resident macrophages via receptors sensitive to tissue damage. Denervated Schwann cells respond to injury by shedding myelin, proliferating, phagocytosing debris, and releasing cytokines that recruit blood-borne monocytes/macrophages. Macrophages take over the bulk of phagocytosis within days of PNI, before exiting the nerve by the circulation once remyelination has occurred. The efficacy of the PNS inflammatory response (although transient) stands in stark contrast with that of the CNS, where the response of nearby cells is associated with inhibitory scar formation, quiescence, and degeneration/apoptosis. Rather than efficiently removing debris before resolving the inflammatory response as in other tissues, macrophages infiltrating the CNS exacerbate cell death and damage by releasing toxic pro-inflammatory mediators over an extended period of time. Future research will help determine how to manipulate PNS and CNS inflammatory responses in order to improve tissue repair and functional recovery.

Nerve Injury Triggers Changes in the Brain

It is well known that the adult brain is capable of profound plasticity. Much of our understanding of the mechanisms underlying injury-induced changes in the brain is based on animal models. The development of sophisticated noninvasive neuroimaging techniques over the past decade provides a unique opportunity to examine brain plasticity in humans. In this article, the authors examine the consequences of nerve injury and surgical repair on peripheral nerve degeneration and regeneration and review classic animal literature that laid the foundation of injury-induced plasticity research. They relate these concepts to recent findings of functional and structural changes in the human brain following peripheral nerve injury. They then present a working theoretical model that links behavioral outcomes of nerve injury with functional and structural brain plasticity and personality.

The role of neurotrophic factors in nerve regeneration

This review considers the 2 sources of neurotrophic factors in the peripheral nervous system (PNS), the neurons and the nonneuronal cells in the denervated distal nerve stumps, and their role in axon regeneration. Morphological assessment of regenerative success in response to administration of exogenous growth factors after nerve injury and repair has indicated a role of the endogenous neurotrophic factors from Schwann cells in the distal nerve stump. However, the increased number of axons may reflect more neurons regenerating their axons and/or increased numbers of axon sprouts from the same number of neurons. Using fluorescent dyes to count neurons that regenerated their axons across a suture site and into distal nerve stumps, brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) were found not to increase the number of neurons that regenerated their axons after immediate nerve repair. Nevertheless, the factors did reverse the deleterious effect of delayed nerve repair, indicating that the axons that regenerate into the distal nerve stump normally have access to sufficient levels of endogenous neurotrophic factors to sustain their regeneration, while neurons that do not have access to these factors require exogenous factors to sustain axon regeneration. Neurons upregulate neurotrophic factors after axotomy. The upregulation is normally slow, beginning after 7 days and occurring in association with a protracted period of axonal regeneration in which axons grow out from the proximal nerve stump across a suture site over a period of 1 month in rodents. This staggered axon regeneration across the suture site is accelerated by a 1-hour period of low-frequency electrical stimulation that simultaneously accelerates the expression of BDNF and its trkB receptor in the neurons. Elevation of the level of BDNF after 2 days to > 3 times that found in unstimulated neurons was accompanied by elevation of the level of cAMP and followed by accelerated upregulation of growth-associated genes, tubulin, actin, and GAP-43 and downregulation of neurofilament protein. Elevation of cAMP levels via rolipram inhibition of phosphodiesterase 4 mimicked the effect of the low-frequency electrical stimulation. In conclusion, the enhanced upregulation of neurotrophic factors in the electrically stimulated axotomized neurons accelerates axon outgrowth into the distal nerve stumps where endogenous sources of growth factors in the Schwann cells support the regeneration of the axons toward the denervated targets. The findings provide strong support for endogenous neurotrophic factors of axotomized neurons and of denervated Schwann cells playing a critical role in supporting axon regeneration in the PNS.

Pentoxifylline promotes recovery of erectile function in a rat model of postprostatectomy erectile dysfunction

BACKGROUND

Cavernous nerve (CN) injury during radical prostatectomy (RP) causes CN degeneration and secondary penile fibrosis and smooth muscle cell (SMC) apoptosis. Pentoxifylline (PTX) is a phosphodiesterase inhibitor that further inhibits multiple cytokine pathways involved in nerve degeneration, apoptosis, and fibrosis.

OBJECTIVES

To evaluate whether PTX enhances erectile function in a rat model of CN injury. DESIGN, SETTING AND INTERVENTIONS: Forty male Sprague-Dawley rats underwent CN crush injury and were randomized to oral gavage feeding of phosphate-buffered saline (vehicle) or PTX 25, PTX 50, or PTX 100 mg/kg per day. Ten animals underwent sham surgery and received vehicle treatment. Treatment continued for 28 d, followed by a wash-out period of 72 h. An additional eight rats underwent resection of the major pelvic ganglion (MPG) for tissue culture and examination of direct effects of PTX on neurite sprouting.

MEASUREMENTS

Intracavernous pressure recording on CN electrostimulation, immunohistologic examination of the penis and the CN distal to the injury site, and length of neurite sprouts in MPG culture.

RESULTS

Daily oral gavage feeding of PTX resulted in significant improvement of erectile function compared to vehicle treatment in all treated groups. After treatment with PTX 50 and PTX 100 mg/kg per day, the expression of neuronal nitric oxide synthase in the dorsal penile nerve was significantly higher than in vehicle-treated rats. Furthermore, PTX treatment prevented collagen deposition and SMC loss in the corpus cavernosum. In the CN, signs of Wallerian degeneration were ameliorated by PTX treatment. MPG culture in medium containing PTX resulted in a significant increase of neurite length.

CONCLUSIONS

PTX treatment following CN injury in rats improved erectile recovery, enhanced nerve regeneration, and preserved the corpus cavernosum microarchitecture. The clinical availability of this compound merits application in penile rehabilitation studies following RP in the near future.