Single session of brief electrical stimulation immediately following crush injury enhances functional recovery of rat facial nerve

Electrophysiological and histopathological evaluation of the effectiveness of melatonin and glatiramer acetate for traumatic facial nerve injuries

AIM

This study aimed to evaluate the effect of systemic/local use of melatonin and glatiramer acetate on regeneration in traumatic nerve injury models.

MATERIALS AND METHODS

A total of 42 male Wistar albino rats were randomly divided into 6 groups: healthy control (Group 1), injured control (Group 2), local melatonin (Group 3), systemic melatonin (Group 4), local glatiramer acetate (Group 5), and systemic glatiramer acetate (Group 6). In all groups, electromyography recordings of the facial nerve were obtained after surgery and before sacrifice, and the damaged nerve region was histopathologically examined after sacrifice.

RESULTS

In the electrophysiological evaluation, the control group had the greatest decrease in amplitude and extension in latency time following surgery than the treatment groups. Furthermore, a significant decrease in the degenerative axon count, edematous areas, and fibrotic areas as well as a significant increase in axonal surface areas was observed in all the treatment groups compared with the damage control group.

CONCLUSIONS

Although both glatiramer acetate and melatonin are beneficial in regeneration in traumatic facial nerve injuries, it can be concluded that systemic use of melatonin can yield more positive results than glatiramer acetate and local use of both two drugs.

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Etiology and Management of 800 Patients With Facial Palsy at a Private Practice Setting Over a 5-Year Period

INTRODUCTION

Very few papers investigated the etiologic breakdown and demographic characteristics of patients with facial nerve (FN) palsy. Our paper aims to present the etiologic breakdown and demographic characteristics of patients with FN palsy, presenting at a private care center between 2014 and 2019, along with the treatment modalities that were offered to them.

METHODS

Charts of 800 patients with facial palsy (FP) were reviewed. Data included the etiology of their diagnosis, family history, recurrent FP, demographic information, and treatment provided before and after presentation.

RESULTS

Seventy-five percent of our study population were females. The average period between diagnosis with FP and presentation at our center was 10.8 years. The most commonly identified etiology was Bell's palsy, followed by acoustic neuroma. Eighty-one percent of the study subjects were prescribed steroids and/or antivirals. Facial neuromuscular retraining, electrical stimulation, chemodenervation, and surgical intervention were also part of some treatment plans for our population.

DISCUSSION

Recommendations for the treatment of idiopathic FP include steroids with adjuvant antiviral medications. Data remains uncertain whether the combination therapy of steroids and antivirals has better results compared to steroids alone. Electrical stimulation is still a controversial therapeutic tool for facial paralysis with a potential role in exacerbating synkinesis. The difference in referral patterns between tertiary and private care centers can explain the disparity in the ranking of the etiologies between our study and what has been published.

CONCLUSION

Management of FP is a complex process. The FN community must develop a common database to improve its understanding of the different presentations.

Advancements in autologous peripheral nerve transplantation care: a review of strategies and practices to facilitate recovery

Autologous peripheral nerve transplantation, a pioneering technique in nerve injury treatment, has demonstrated remarkable progress. We examine recent nursing strategies and methodologies tailored to various anatomical sites, highlighting their role in postoperative recovery enhancement. Encompassing brachial plexus, upper limb, and lower limb nerve transplantation care, this discussion underscores the importance of personalized rehabilitation plans, interdisciplinary collaboration, and innovative approaches like nerve electrical stimulation and nerve growth factor therapy. Moreover, the exploration extends to effective complication management and prevention strategies, encompassing infection control and pain management. Ultimately, the review concludes by emphasizing the advances achieved in autologous peripheral nerve transplantation care, showcasing the potential to optimize postoperative recovery through tailored and advanced practices.

The Role of Early Rehabilitation and Functional Electrical Stimulation in Rehabilitation for Cats with Partial Traumatic Brachial Plexus Injury: A Pilot Study on Domestic Cats in Portugal

This prospective observational cohort pilot study included 22 cats diagnosed with partial traumatic brachial plexus injury (PTBPI), aiming to explore responses to an early intensive neurorehabilitation protocol in a clinical setting. This protocol included functional electrical stimulation (FES), locomotor treadmill training and kinesiotherapy exercises, starting at the time with highest probability of nerve repair. The synergetic benefits of this multimodal approach were based on the potential structural and protective role of proteins and the release of neurotrophic factors. Furthermore, FES was parametrized according to the presence or absence of deep pain. Following treatment, 72.6% of the cats achieved ambulation: 9 cats within 15 days, 2 cats within 30 days and 5 cats within 60 days. During the four-year follow-up, there was evidence of improvement in both muscle mass and muscle weakness, in addition to the disappearance of neuropathic pain. Notably, after the 60 days of neurorehabilitation, 3 cats showed improved ambulation after arthrodesis of the carpus. Thus, early rehabilitation, with FES applied in the first weeks after injury and accurate parametrization according to the presence or absence of deep pain, may help in functional recovery and ambulation, reducing the probability of amputation.

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.

State of the Art and Current Challenges on Electroactive Biomaterials and Strategies for Neural Tissue Regeneration

The loss or failure of an organ/tissue stands as one of the healthcare system's most prevalent, devastating, and costly challenges. Strategies for neural tissue repair and regeneration have received significant attention due to their particularly strong impact on patients' well-being. Many research efforts are dedicated not only to control the disease symptoms but also to find solutions to repair the damaged tissues. Neural tissue engineering (TE) plays a key role in addressing this problem and significant efforts are being carried out to develop strategies for neural repair treatment. In the last years, active materials allowing to tune cell-materials interaction are being increasingly used, representing a recent paradigm in TE applications. Among the most important stimuli influencing cell behavior are the electrical and mechanical ones. In this way, materials with the ability to provide this kind of stimuli to the neural cells seem to be appropriate to support neural TE. In this scope, this review summarizes the different biomaterials types used for neural TE, highlighting the relevance of using active biomaterials and electrical stimulation. Furthermore, this review provides not only a compilation of the most relevant studies and results but also strategies for novel and more biomimetic approaches for neural TE.

Design of a high speed rat whiskers tracking and symmetry analysis system based on FPGA

This paper presents a high-speed rat whisker tracking and symmetry analysis system based on FPGA. The system utilizes high-speed image sensors recording rat face videos at 120 and 1000 fps. The Xilinx Ultra96 single computer board is chosen as the platform to implement the system's processing system (PS) and the programmable logic (PL) part. The PL part is responsible for high-speed image processing and whisker tracking, while the PS part analyzes the symmetry of rat face using the tracking results from the PL part. With a processing speed FoM of 118.5 fps/GHz on the Xilinx Ultra96 single computer board and 275.47 fps/GHz on a laptop with Intel Core i5-11500T@1.5GHz, the presented system achieves excellent performance. The proposed whisker detection method has a precision of 98.2% when a threshold with a 4-degree error is selected, with an average error angle of 0.98 degrees across more than 10,000 video frames. Moreover, the proposed system is capable of local video processing within millisecond delays. These results demonstrate the feasibility of developing a high-speed, accurate, and efficient whisker tracking and symmetry analysis system for rat behavior research.

Effects of Electrical Stimulation on Facial Paralysis Recovery after Facial Nerve Injury: A Review on Preclinical and Clinical Studies

Various methods have been used to improve function and manage facial nerve injury. Although electrical stimulation therapy is frequently used to treat facial paralysis, its effects have been found to vary and no clear standards have been developed. The current review describes the results of preclinical and clinical studies evaluating the effectiveness of electrical stimulation therapy in promoting the recovery of a peripheral facial nerve injury. Evidence is presented showing the efficacy of electrical stimulation in promoting nerve regeneration after peripheral nerve injuries in both animal models and human patients. The ability of electrical stimulation to promote the recovery of facial paralysis was found to depend on the type of injury (compression or transection), the species of animal tested, the type of disease, the frequency and method of electrical stimulation, and the duration of the follow-up. Electrical stimulation, however, can also have potential negative outcomes, such as reinforcing synkinesis, including mistargeted axonal regrowth via inappropriate routes; excessive collateral axonal branching at the lesion site; and multiple innervations at neuromuscular junctions. Because of the inconsistencies among studies and the low quality of evidence, electrical stimulation therapy is not currently regarded as a primary treatment of facial paralysis in patients. However, understanding the effects of electrical stimulation, as determined in preclinical and clinical studies, is important for the potential validity of future research on electrical stimulation.

Electrical Sympathetic Neuromodulation Protects Bone Marrow Niche and Drives Hematopoietic Regeneration during Chemotherapy

The sympathetic nervous system (SNS) of the bone marrow regulates the regeneration and mobilization of hematopoietic stem cells. Chemotherapy can damage bone marrow SNS, which impairs hematopoietic regeneration and aggravates hematologic toxicities. This leads to long-term bone marrow niche damage and increases mortality in patients undergoing chemotherapy. Electrical neuromodulation has been used to improve functional recovery after peripheral nerve injury. This study demonstrates that electrical sympathetic neuromodulation (ESN) of bone marrow can protect the bone marrow niche from chemotherapy-induced injury. Using carboplatin-treated rats, the SNS via the sciatic nerve innervating the femoral marrow with the effective protocol for bone marrow sympathetic activation is electrically stimulated. ESN can mediate several hematopoietic stem cells maintenance factors and promote hematopoietic regeneration after chemotherapy. It also activates adrenergic signals and reduces the release of pro-inflammatory cytokines, particularly interleukin-1 β, which contribute to chemotherapy-related nerve injury. Consequently, the severity of chemotherapy-related leukopenia, thrombocytopenia, and mortality can be reduced by ESN. As a result, in contrast to current drug-based treatment, such as granulocyte colony-stimulating factor, ESN can be a disruptive adjuvant treatment by protecting and modulating bone marrow function to reduce hematologic toxicity during chemotherapy.

Neuronal androgen receptor is required for activity dependent enhancement of peripheral nerve regeneration

Neuronal activity after nerve injury can enhance axon regeneration and the restoration of function. The mechanism for this enhancement relies in part on hormone receptors, and we previously demonstrated that systemic androgen receptor antagonism blocked the effect of exercise or electrical stimulation on enhancing axon regeneration after nerve injury in both sexes. Here, we tested the hypothesis that the site of this androgen receptor signaling is both neuronal and involves the classical, genomic signaling pathway. In vivo, dorsal root ganglion neurons successfully regenerate in response to activity-dependent neuronal activation, and conditional deletion of the DNA-binding domain of the androgen receptor in adults blocks this effect in males and females. Motoneurons in males and females also respond in this manner, but we also observed a sex difference. In vitro, cultured sensory dorsal root ganglion neurons respond to androgens via traditional androgen receptor signaling mechanisms leading to enhanced neurite growth and did not respond to a testosterone conjugate that is unable to cross the cell membrane. Given our previous observation of a requirement for activity-dependent androgen receptor signaling to promote regeneration in both sexes, we interpret our results to indicate that genomic neuronal androgen receptor signaling is required for activity-dependent axon regeneration in both sexes.

Experimental Injury Rodent Models for Oropharyngeal Dysphagia

Oropharyngeal dysphagia is a disorder that can make swallowing difficult and reduce the quality of life. Recently, the number of patients with swallowing difficulty has been increasing; however, no comprehensive treatment for such patients has been developed. Various experimental animal models that mimic oropharyngeal dysphagia have been developed to identify appropriate treatments. This review aims to summarize the experimentally induced oropharyngeal dysphagia rodent models that can be used to provide a pathological basis for dysphagia. The selected studies were classified into those reporting dysphagia rodent models showing lingual paralysis by hypoglossal nerve injury, facial muscle paralysis by facial nerve injury, laryngeal paralysis by laryngeal and vagus nerve injury, and tongue dysfunction by irradiation of the head and neck regions. The animals used in each injury model, the injury method that induced dysphagia, the screening method for dysphagia, and the results are summarized. The use of appropriate animal models of dysphagia may provide adequate answers to biological questions. This review can help in selecting a dysphagia animal system tailored for the purpose of providing a possible solution to overcome dysphagia.

Modern Management of Facial Nerve Disorders

Facial paralysis is a devastating condition, encompassing a spectrum of disorders, with resultant psychosocial, functional, and aesthetic sequelae. With this in mind, an individualized treatment approach based on the cause, pattern, and duration of palsy is necessary. Treatment options include pharmacologic agents, corneal protective interventions, physical therapy, and surgical procedures. The use of steroids and antivirals in the setting of idiopathic facial paralysis or virus-associated facial paralysis is well supported. Despite the diversity of surgical interventions described, there is a lack of consensus regarding optimal treatment. This article provides an overview of the current management of facial paralysis. Medical, surgical, and physical treatment options are discussed with a review of the relevant literature.

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

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

Facial nerve repair utilizing intraoperative repair strategies

OBJECTIVES

To determine whether functional and anatomical outcomes following suture neurorrhaphy are improved by the addition of electrical stimulation with or without the addition of polyethylene glycol (PEG).

METHODS

In a rat model of facial nerve injury, complete facial nerve transection and repair was performed via (a) suture neurorrhaphy alone, (b) neurorrhaphy with the addition of brief (30 minutes) intraoperative electrical stimulation, or (c) neurorrhaphy with the addition electrical stimulation and PEG. Functional recovery was assessed weekly for 16 weeks. At 16 weeks postoperatively, motoneuron survival, amount of regrowth, and specificity of regrowth were assessed by branch labeling and tissue analysis.

RESULTS

The addition of brief intraoperative electrical stimulation improved all functional outcomes compared to suturing alone. The addition of PEG to electrical stimulation impaired this benefit. Motoneuron survival, amount of regrowth, and specificity of regrowth were unaltered at 16 weeks postoperative in all treatment groups.

CONCLUSION

The addition of brief intraoperative electrical stimulation to neurorrhaphy in this rodent model shows promising neurological benefit in the surgical repair of facial nerve injury.

LEVEL OF EVIDENCE

Animal study.

Overexpression of Foxc1 regenerates crushed rat facial nerves by promoting Schwann cells migration via the Wnt/β-catenin signaling pathway

Facial paralysis can result in severe implications for patients. A good prognosis depends on the degree of nerve regeneration. Schwann cells (SCs) play an important role in facial nerve development and regeneration through migration. Forkhead box C1 (Foxc1), a member of the forkhead transcription factor family, is implicated in cell migration. However, the role of Foxc1 in the progression after facial nerve crush remains unknown. Our aim was to evaluate the effect of Foxc1 overexpression on SC migration and recovery of facial nerves after crush injury. The rat facial nerve crush injury model was established through the use of unilateral surgery. The results showed that the expression of Foxc1 was increased in the surgery group compared to that of the control group. SCs were isolated from the sciatic nerves and cultured. Foxc1, delivered by an adeno‐associated virus in vivo, or adenovirus in vitro, both induced overexpression of Foxc1, and increased the expression of CXCL12 and β‐catenin. After the transfection of Foxc1, the migration of SC was increased both in vitro and in vivo, was reduced by the inhibition of CXCL12 or β‐catenin. The facial nerve function and the nerve axon remyelination of the rats transfected with Foxc1 were significantly improved after nerve crush injury. Overall, the results demonstrated that overexpression of Foxc1 promoted SC migration by regulating CXCL12 via the Wnt/β‐catenin pathway, thus contributing to improved facial nerve function after crush injury.

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

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

A Mouse Model of Dysphagia After Facial Nerve Injury

OBJECTIVE

Dysphagia is common following facial nerve injury; however, research is sparse regarding swallowing-related outcomes and targeted treatments. Previous animal studies have used eye blink and vibrissae movement as measures of facial nerve impairment and recovery. The purpose of this study was to create a mouse model of facial nerve injury that results in dysphagia to enhance translational research outcomes.

STUDY DESIGN

Prospective animal study.

METHODS

Twenty C57BL/6J mice underwent surgical transection of the main trunk (MT) (n = 10) or marginal mandibular branch (MMB) (n = 10) of the left facial nerve. Videofluoroscopic swallow study (VFSS) assays for drinking and eating were performed at baseline and 14 days postsurgery to quantify several deglutition-related outcome measures.

RESULTS

VFSS analysis revealed that MT transection resulted in significantly slower lick and swallow rates during drinking (P ≤ .05) and significantly slower swallow rates and longer inter-swallow intervals during eating (P ≤ .05), congruent with oral and pharyngeal dysphagia. After MMB transection, these same VFSS metrics were not statistically significant (P > .05).

CONCLUSION

The main finding of this study was that transection of the facial nerve MT leads to oral and pharyngeal stage dysphagia in mice; MMB transection does not. These results from mice provide novel insight into specific VFSS metrics that may be used to characterize dysphagia in humans following facial nerve injury. We are currently using this surgical mouse model to explore promising treatment modalities such as electrical stimulation to hasten recovery and improve outcomes following various iatrogenic and idiopathic conditions affecting the facial nerve.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:17-24, 2021.

A rat study of the use of end-to-side peripheral nerve repair as a "babysitting" technique to reduce the deleterious effect of chronic denervation

OBJECTIVE

Functional recovery is disappointing after surgical repair of nerves that are injured far from their target organs and/or after delayed repair. In the former case, a nerve transfer that transects a distal nerve fascicle to innervate denervated targets is one strategy to promote nerve regeneration and functional recovery. An alternate strategy tested in this study is to perform an end-to-side neurorrhaphy to "babysit" (protect) the denervated distal nerve stump at the time of nerve repair and reduce the deleterious effect of chronic denervation on nerve regeneration.

METHODS

In the hindlimbs of Sprague-Dawley rats, the common peroneal (CP) nerve was transected unilaterally and the distal CP nerve stump inserted through a perineurial window into the intact tibial (TIB) nerve, i.e., CP-TIB end-to-side neurorrhaphy. In the first experiment, TIB nerve motoneurons that had regenerated and/or sprouted axons into the CP nerve within 3 months were stimulated to elicit contractions, and thereafter, identified with retrograde dyes for counting. In the second experiment, the intact TIB nerve was transected and cross-sutured to a 3-month chronically denervated distal CP nerve stump that had either been "protected" by ingrown TIB nerves after CP-TIB neurorrhaphy or remained chronically denervated. Thereafter, the number of retrogradely labeled TIB nerve motoneurons that had regenerated their nerves within 3 months were counted and reinnervated tibialis anterior (TA) muscles weighed.

RESULTS

A mean (± SE) of 231 ± 83 TIB nerve motoneurons grew into the end-to-side CP distal nerve stump with corresponding ankle flexion; 32% regenerated their axons and 24% sprouted axons from the intact TIB nerve, eliciting ankle flexor-extensor co-contraction. In the second experiment, after a 3-month period of TIB nerve regeneration, significantly more TIB motoneurons regenerated their axons into "protected" than "unprotected" CP distal nerve stumps within 3 months (mean 332 ± 43.6 vs 235 ± 39.3 motoneurons) with corresponding and significantly higher numbers of regenerated nerve fibers, resulting in significantly better recovery of reinnervated TA muscle weight.

CONCLUSIONS

These experiments in rats demonstrated that delayed nerve repair is more effective when the deleterious effects of chronic denervation of the distal nerve stump are reduced by protecting the nerve stump with ingrowing nerve fibers across an end-to-side insertion of the distal nerve stump into a neighboring intact nerve. Such an end-to-side neurorrhaphy may be invaluable as a means of preventing the atrophy of distal nerve stumps and target organs after chronic denervation, which allows for effective reinnervation of the protected distal nerve stumps and target organs over distance and time.

Advances in electrical and magnetic stimulation on nerve regeneration

Central and peripheral nerve injuries pose a great threat to people. Complications such as inflammation, muscle atrophy, traumatic neuromas and delayed reinnervation can bring huge challenges to clinical practices and barriers to complete nerve regrowth. Physical interventions such as electrical and magnetic stimulation show satisfactory results with varying parameters for acute and chronic nerve damages. The biological basis of electrical and magnetic stimulation mainly relies on protein synthesis, ion channel regulation and growth factor secretion. This review focuses on the various paradigms used in different models of electrical and magnetic stimulation and their regenerative potentials and underlying mechanisms in nerve injuries. The combination of physical stimulation and conductive biomaterial scaffolds displays an infinite potentiality in translational application in nerve regeneration.

Rat Facial Nerve Regeneration with Human Immature Dental Pulp Stem Cells

Facial paralysis can result in severe implications for the patients. However, stem cell biology has become an important field in regenerative medicine since the discovery and characterization of mesenchymal stem cells. Our aim was to evaluate the regeneration after facial nerve crush injury and application of human immature dental pulp stem cells (iDPSC). For this study 70 Wistar rats underwent a unilateral facial nerve crush injury and were divided into two groups: Group I (GI): Crushed; Group II (GII): Crushed and iDPSC, and distributed into study periods of 3, 7, 14, 21, and 42 postoperative days. Facial nerve regeneration was analyzed via functional recovery of whisker movement, histomorphometric analysis, and immunoblotting assay. The results show that GII had complete functional recovery at 14 days, while GI recovered after 42 days. Also, regarding the facial nerve trunk, GII presented histological improvement, evidencing better axonal and structural organization of the myelin sheath, and exhibited statistically higher values for the outer and inner perimeters and g-ratio. Nevertheless, GI exhibited statistically higher values for the thickness of myelin sheath. In the buccal branch, no differences were observed for all parameters between groups. At 42 days, both groups GI and GII were close to the levels observed for the control group. Concerning nerve growth factor expression, GII exhibited statistically greater values (p < 0.05) compared with the control group at 7 days. In summary, a single injection of human iDPSC promoted a positive effect on regeneration of the facial nerve trunk after 14 days and provided an alternative to support regeneration following peripheral nerve injury.

A Surgical Mouse Model for Advancing Laryngeal Nerve Regeneration Strategies

Iatrogenic recurrent laryngeal nerve (RLN) injury is a morbid complication of anterior neck surgical procedures. Existing treatments are predominantly symptomatic, ranging from behavioral therapy to a variety of surgical approaches. Though laryngeal reinnervation strategies often provide muscle tone to the paralyzed vocal fold (VF), which may improve outcomes, there is no clinical intervention that reliably restores true physiologic VF movement. Moreover, existing interventions neglect the full cascade of molecular events that affect the entire neuromuscular pathway after RLN injury, including the intrinsic laryngeal muscles, synaptic connections within the central nervous system, and laryngeal nerve anastomoses. Systematic investigations of this pathway are essential to develop better RLN regenerative strategies. Our aim was to develop a translational mouse model for this purpose, which will permit longitudinal investigations of the pathophysiology of iatrogenic RLN injury and potential therapeutic interventions. C57BL/6J mice were divided into four surgical transection groups (unilateral RLN, n = 10; bilateral RLN, n = 2; unilateral SLN, n = 10; bilateral SLN, n = 10) and a sham surgical group (n = 10). Miniaturized transoral laryngoscopy was used to assess VF mobility over time, and swallowing was assessed using serial videofluoroscopy. Histological assays were conducted 3 months post-surgery for anatomical investigation of the larynx and laryngeal nerves. Eight additional mice underwent unilateral RLN crush injury, half of which received intraoperative vagal nerve stimulation (iVNS). These 8 mice underwent weekly transoral laryngoscopy to investigate VF recovery patterns. Unilateral RLN injury resulted in chronic VF immobility but only acute dysphagia. Bilateral RLN injury caused intraoperative asphyxiation and death. VF mobility was unaffected by SLN transection (unilateral or bilateral), and dysphagia (transient) was evident only after bilateral SLN transection. The sham surgery group retained normal VF mobility and swallow function. Mice that underwent RLN crush injury and iVNS treatment demonstrated accelerated and improved VF recovery. We successfully developed a mouse model of iatrogenic RLN injury with impaired VF mobility and swallowing function that can serve as a clinically relevant platform to develop translational neuroregenerative strategies for RLN injury.

Stimulation and Repair of Peripheral Nerves Using Bioadhesive Graft-Antenna

An original wireless stimulator for peripheral nerves based on a metal loop (diameter ≈1 mm) that is powered by a transcranial magnetic stimulator (TMS) and does not require circuitry components is reported. The loop can be integrated in a chitosan scaffold that functions as a graft when applied onto transected nerves (graft-antenna). The graft-antenna is bonded to rat sciatic nerves by a laser without sutures; it does not migrate after implantation and is able to trigger steady compound muscle action potentials for 12 weeks (CMAP ≈1.3 mV). Eight weeks postoperatively, axon regeneration is facilitated in transected nerves that are repaired with the graft-antenna and stimulated by the TMS for 1 h per week. The graft-antenna is an innovative and minimally-invasive device that functions concurrently as a wireless stimulator and adhesive scaffold for nerve repair.

The Role of BDNF in Peripheral Nerve Regeneration: Activity-Dependent Treatments and Val66Met

Despite the ability of peripheral nerves to spontaneously regenerate after injury, recovery is generally very poor. The neurotrophins have emerged as an important modulator of axon regeneration, particularly brain derived neurotrophic factor (BDNF). BDNF regulation and signaling, as well as its role in activity-dependent treatments including electrical stimulation, exercise, and optogenetic stimulation are discussed here. The importance of a single nucleotide polymorphism in the BDNF gene, Val66Met, which is present in 30% of the human population and may hinder the efficacy of these treatments in enhancing regeneration after injury is considered. Preliminary data are presented on the effectiveness of one such activity-dependent treatment, electrical stimulation, in enhancing axon regeneration in mice expressing the met allele of the Val66Met polymorphism.

Hypoglossal-facial 'side'-to-side Neurorrhaphy Combined with Electrical Myostimulation for Facial Palsy in Rats

Introduction This study investigated the effect of combining hypoglossal-facial nerve “side”-to-side neurorrhaphy and electrical myostimulation in a rat model of facial palsy.

Methods Rats with facial nerve crush injury were subjected to control condition, monotherapy of either neurorrhaphy or electrical myostimulation, or bitherapy of the two treatments. After 1, 3, and 6 months, rats were performed the facial symmetry evaluation, electrophysiological examination and the retrograde labeling of motor neurons.

Results As early as 3 months after injury, face symmetry significantly improved in rats of the bitherapy group. At 3 or 6 months after injury, either the parameters of electrophysiological examination or the number of labeled motor neurons were significantly increased in the bitherapy group than in any other group.

Discussion The combination of neurorrhaphy and electrical myostimulation effectively promoted the functional recovery after facial nerve crush injury.

Medical Management of Acute Facial Paralysis

Acute facial paralysis (FP) describes acute onset of partial or complete weakness of the facial muscles innervated by the facial nerve. Acute FP occurs within a few hours to days. The differential diagnosis is broad; however, the most common cause is viral-associated Bell Palsy. A comprehensive history and physical examination are essential in arriving at a diagnosis. Medical treatment for acute FP depends on the specific diagnosis; however, corticosteroids and antiviral medications are the cornerstone of therapy. Lack of recovery after 4 months should prompt further diagnostic workup.

Electrostimulation of the lingual nerve by an intraoral device may lead to salivary gland regeneration: A case series study

Background

Salivary gland function is controlled by the salivary reflex, whose efferent arm is composed by the parasympathetic and the sympathetic divisions of the autonomic nervous system. Parenchymal injury is the main salivary gland involvement of Sjögren’s syndrome and head and neck radiotherapy, but neural damage has been reported as well. Recently an intraoral device for electrostimulation of the lingual nerve in vicinity to the lower third molar has been introduced. At this point this nerve carries efferent fibers for the innervation of the submandibular, sublingual and several minor salivary glands and afferent fibers of the salivary reflex. Therefore, excitation of these fibers potentially leads to increased secretion of all salivary glands. Thus, the study objective was to assess whether comprehensive neural activation by electrostimulation of the lingual nerve carries the potential to induce the regeneration of damaged salivary glands.

Material and Methods

The device was tested on three patients with no collectable resting and stimulated secretion of saliva during a double blind, sham controlled period of two months and nine open-label months.

Results

All three subjects developed the capacity to spit saliva, not only in direct response to the electrostimulation but also after free intervals without electrostimulation. In addition, their symptoms of dry mouth severity and frequency improved.

Conclusions

This recovery is probably due to the combined effect of increase in secretory functional gland mass and regain of nervous control of the secretory elements and blood vessels. Both are phenomena that would contribute to gland regeneration.

Key words:Xerostomia, dry mouth, saliva, electrostimulation, regeneration.

Electrical stimulation promotes regeneration and re-myelination of axons of injured facial nerve in rats

Objective To investigate the effects of electrical stimulation (ES) on the nerve regeneration and functional recovery of facial expression muscles in facial nerve defect rats. Methods Sixty rats were surgically introduced with a 1-cm defect on the right facial nerves and evenly divided into the Surgery group (Group A, the main trunk of the right facial nerve was surgically cut-off with a 1.0 cm at the foramina stylomastoideum) and the Surgery + ES group (Group B). Twenty normal rats were as normal control group (without receiving surgery or ES). For rats in group B, the orbicularis oris muscle of the right paralyzed face was stimulated with an electrical pulse of 3 V, 20 Hz and 0.3 mA for 1 h each day. The effects of ES on the facial muscle movement, compound muscle action potentials (CMAPs), histological structure, and the expression levels of S100B and NF200 proteins were comparatively studied. Results In group A, facial paralysis scores were slightly improved from day 1 to 28; the facial nerve trunks had swelled and malformed till day 14; and CMAPs could be induced in fewer animals and were abnormal, resulting in a slow recovery of the facial muscle movement. In group B, facial paralysis scores were improved from 4 to 2.6 during the 4 weeks; more rats showed a higher amplitude and shorter latency of CMAPs from day 14 to 28 after surgery; and increased axons and the expression of S100B and NF200 proteins and gradually decreased swelling in the injured facial nerve. Conclusion ES promotes outgrowth and myelination of axons and a partial functional recovery of facial muscles in injured facial nerve rats.

State-of-the-Art Techniques in Treating Peripheral Nerve Injury

BACKGROUND

Peripheral nerve injuries remain a major clinical concern, as they often lead to chronic disability and significant health care expenditures. Despite advancements in microsurgical techniques to enhance nerve repair, biological approaches are needed to augment nerve regeneration and improve functional outcomes after injury.

METHODS

Presented herein is a review of the current literature on state-of-the-art techniques to enhance functional recovery for patients with nerve injury. Four categories are considered: (1) electroceuticals, (2) nerve guidance conduits, (3) fat grafting, and (4) optogenetics. Significant study results are highlighted, focusing on histologic and functional outcome measures.

RESULTS

This review documents the current state of the literature. Advancements in neuronal stimulation, tissue engineering, and cell-based therapies demonstrate promise with regard to augmenting nerve regeneration and appropriate rehabilitation.

CONCLUSIONS

The future of treating peripheral nerve injury will include multimodality use of electroconductive conduits, fat grafting, neuronal stimulation, and optogenetics. Further clinical investigation is needed to confirm the efficacy of these technologies on peripheral nerve recovery in humans, and how best to implement this treatment for a diverse population of nerve-injured patients.

The effects of lipoic acid and methylprednisolone on nerve healing in rats with facial paralysis. Acta Otolaryngol 2018;138:537-541. [PMID: 29310488 DOI: 10.1080/00016489.2017.1420914]

OBJECTIVE

To investigate the effects of lipoic acid and methylprednisolone on nerve healing in rats with traumatic facial paralysis.

MATERIALS AND METHODS

The rats were randomly divided into four groups, with six rats in the control group and eight each in the remaining three groups. The buccal branch of the facial nerve in all groups except the control group was traumatized by a vascular clamp for 40 minutes. Group 1 was given lipoic acid (LA), Group 2 was given methylprednisolone (MP), and Group 3 was given lipoic acid and methylprednisolone (LA + MP) for one week. Nerve stimulus thresholds were measured before trauma, after trauma and at the end of the one week treatment period.

RESULTS

When the groups were compared with each other, post-treatment threshold levels of LA + MP were significantly lower than LA. Although post-treatment threshold levels of LA and MP were still higher than the control group, there was no significant difference between LA + MP and control values (p > .05).

CONCLUSION

Lipoic acid has a positive effect on nerve healing and can enhance the effect of methylprednisolone treatment. It is a good alternative in cases where methylprednisolone cannot be used.

Optogenetically enhanced axon regeneration: motor versus sensory neuron-specific stimulation

Brief neuronal activation in injured peripheral nerves is both necessary and sufficient to enhance motor axon regeneration, and this effect is specific to the activated motoneurons. It is less clear whether sensory neurons respond in a similar manner to neuronal activation following peripheral axotomy. Further, it is unknown to what extent enhancement of axon regeneration with increased neuronal activity relies on a reflexive interaction within the spinal circuitry. We used mouse genetics and optical tools to evaluate the precision and selectivity of system-specific neuronal activation to enhance axon regeneration in a mixed nerve. We evaluated sensory and motor axon regeneration in two different mouse models expressing the light-sensitive cation channel, channelrhodopsin (ChR2). We selectively activated either sensory or motor axons using light stimulation combined with transection and repair of the sciatic nerve. Regardless of genotype, the number of ChR2-positive neurons whose axons had regenerated successfully was greater following system-specific optical treatment, with no effect on the number of ChR2-negative neurons (whether motor or sensory neurons). We conclude that acute system-specific neuronal activation is sufficient to enhance both motor and sensory axon regeneration. This regeneration-enhancing effect is likely cell autonomous.

The influence of surface EMG-triggered multichannel electrical stimulation on sensomotoric recovery in patients with lumbar disc herniation: study protocol for a randomized controlled trial (RECO)

Background

Intervertebral disc degeneration is one of the most common reasons for chronic low back pain and sensomotoric deficits, often treated by lumbar sequestrectomy. Nevertheless, the prognostic factors relevant for time and quality of recovery, of the surgical procedure, relative to conservative treatment, remain controversial and require further investigation. Surface electrical stimulation (SES) may be an influential intervention, already showing positive impact on motor and sensory recovery in different patient groups. Since mechanisms of SES still remain unclear, further inquiry is needed.

Methods/Design

This is a prospective, monocentric, randomized, controlled clinical trial. A total of 80 adult patients suffering from a lumbar disc herniation (LDH; 40 treated surgically, 40 conservatively) are allocated in a ratio of 1:1. Patients in the treatment group will receive surface electromyography (EMG)-triggered electrical stimulation for eight weeks, whereas patients in the control group will not obtain any additional treatment. The primary outcome parameter is defined as the cold detection threshold (CDT), determined by quantitative sensory testing (QST), 24 months after intervention. Secondary outcome parameters include the inquiry of sensory nerve function by two-point discrimination and QST, the assessment of motor nerve function by manual muscle testing, and validated scales and scores. These include: the Oswestry Disability Index (ODI) and the Core Outcome Measures Index (COMI) assessing the domains pain, back-specific function, work disability, and patient satisfaction; the EQ-5D investigating the patient’s generic health status; the painDETECT questionnaire (PD-Q) to identify neuropathic pain components; and the Beck Depression Inventory (BDI) to assess severity of depression. Moreover, neurological status, pain medication usage, and blood samples (CRP, TNFα, IL-1β, IL-6) will be evaluated. Study data generation (study site) and data storage, processing, and statistical analysis are clearly separated.

Discussion

The results of the RECO study will detect the effect of EMG-triggered multichannel SES on the improvement of mechanical and thermal sensitivity and the effect on motor recovery and pain, associated with clinical and laboratory parameters. Furthermore, data comparing surgical and conservative treatment can be collected. This will hopefully allow treatment recommendations for patients with LDH accompanied by a sensomotoric deficit.

Trial registration

ISRCTN, ISRCTN12741173. Registered on 15 January 2017.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2310-z) contains supplementary material, which is available to authorized users.

Electrical stimulation and testosterone enhance recovery from recurrent laryngeal nerve crush

OBJECTIVE

This study investigated the effects of a combinatorial treatment, consisting of a brief period of nerve electrical stimulation (ES) and systemic supraphysiologic testosterone, on functional recovery following a crush of the recurrent laryngeal nerve (RLN).

STUDY DESIGN

Prospective, controlled animal study.

METHODS

After a crush of the left RLN, adult male Sprague-Dawley rats were divided into four treatment groups: 1) no treatment, 2) ES, 3) testosterone propionate (TP), and 4) ES + TP. Each group was subdivided into 1, 2, 3, or 4 weeks post-operative survival time points. Groups had an n of 4- 9. Recovery of vocal fold mobility (VFM) was assessed.

RESULTS

Brief ES of the proximal nerve alone or in combination with TP accelerated the initiation of functional recovery. TP administration by itself also produced increased VFM scores compared to controls, but there were no statistical differences between the ES-treated and TP-treated animals. Treatment with brief ES alone was sufficient to decrease the time required to recover complete VFM. Animals with complete VFM were seen in treatment groups as early as 1 week following injury; in the untreated group, this was not observed until at least 3 weeks post-injury, translating into a 66% decrease in time to complete recovery.

CONCLUSIONS

Brief ES, alone or in combination with TP, promise to be effective therapeutic interventions for promoting regeneration following RLN injury.

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.

Brief electrical stimulation after facial nerve transection and neurorrhaphy: a randomized prospective animal study

Background

Recent studies have examined the effects of brief electrical stimulation (BES) on nerve regeneration, with some suggesting that BES accelerates facial nerve recovery. However, the facial nerve outcome measurement in these studies has not been precise or accurate.

The objective of this study is to assess the effect of BES on accelerating facial nerve functional recovery from a transection injury in the rat model.

Methods

A prospective randomized animal study using a rat model was performed. Two groups of 9 rats underwent facial nerve surgery. Both group 1 and 2 underwent facial nerve transection and repair at the main trunk of the nerve, with group 2 additionally receiving BES on post-operative day 0 for 1 h using an implantable stimulation device. Primary outcome was measured using a laser curtain model, which measured amplitude of whisking at 2, 4, and 6 weeks post-operatively.

Results

At week 2, the average amplitude observed for group 1 was 4.4°. Showing a statistically significant improvement over group 1, the group 2 mean was 14.0° at 2 weeks post-operatively (p = 0.0004). At week 4, group 1 showed improvement having an average of 9.7°, while group 2 remained relatively unchanged with an average of 12.8°. Group 1 had an average amplitude of 13.63° at 6-weeks from surgery. Group 2 had a similar increase in amplitude with an average of 15.8°. There was no statistically significant difference between the two groups at 4 and 6 weeks after facial nerve surgery.

Conclusions

This is the first study to use an implantable stimulator for serial BES following neurorrhaphy in a validated animal model. Results suggest performing BES after facial nerve transection and neurorrhaphy at the main trunk of the facial nerve is associated with accelerated whisker movement in a rat model compared with a control group.

Electrical Stimulation to Promote Peripheral Nerve Regeneration

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

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

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

CD4 + T Cells and Neuroprotection: Relevance to Motoneuron Injury and Disease

We have established a physiologically relevant mechanism of CD4+ T cell-mediated neuroprotection involving axotomized wildtype (WT) mouse facial motoneurons (FMN) with significance in the treatment of amyotrophic lateral sclerosis (ALS), a fatal MN disease. Use of the transgenic mouse model of ALS involving expression of human mutant superoxide dismutase genes (SOD1(G93A); abbreviated here as mSOD1) has accelerated basic ALS research. Superimposition of facial nerve axotomy (FNA) on the mSOD1 mouse during pre-symptomatic stages indicates that they behave like immunodeficient mice in terms of increased FMN loss and decreased functional recovery, through a mechanism that, paradoxically, is not inherent within the MN itself, but, instead, involves a defect in peripheral immune: CNS glial cell interactions. Our goal is to utilize our WT mouse model of immune-mediated neuroprotection after FNA as a template to elucidate how a malfunctioning peripheral immune system contributes to motoneuron cell loss in the mSOD1 mouse. This review will discuss potential immune defects in ALS, as well as provide an up-to-date understanding of how the CD4+ effector T cells provide neuroprotection to motoneurons through regulation of the central microglial and astrocytic response to injury. We will discuss an IL-10 cascade within the facial nucleus that requires a functional CD4+ T cell trigger for activation. The review will discuss the role of T cells in ALS, and our recent reconstitution experiments utilizing our model of T cell-mediated neuroprotection in WT vs mSOD1 mice after FNA. Identification of defects in neural:immune interactions could provide targets for therapeutic intervention in ALS.

Brief electrical stimulation improves nerve regeneration after delayed repair in Sprague Dawley rats

Functional recovery after peripheral nerve injury and surgical repair declines with time and distance because the injured neurons without target contacts (chronic axotomy) progressively lose their regenerative capacity and chronically denervated Schwann cells (SCs) atrophy and fail to support axon regeneration. Findings that brief low frequency electrical stimulation (ES) accelerates axon outgrowth and muscle reinnervation after immediate nerve surgery in rats and human patients suggest that ES might improve regeneration after delayed nerve repair. To test this hypothesis, common peroneal (CP) neurons were chronically axotomized and/or tibial (TIB) SCs and ankle extensor muscles were chronically denervated by transection and ligation in rats. The CP and TIB nerves were cross-sutured after three months and subjected to either sham or one hour 20Hz ES. Using retrograde tracing, we found that ES significantly increased the numbers of both motor and sensory neurons that regenerated their axons after a three month period of chronic CP axotomy and/or chronic TIB SC denervation. Muscle and motor unit forces recorded to determine the numbers of neurons that reinnervated gastrocnemius muscle demonstrated that ES significantly increased the numbers of motoneurons that reinnervated chronically denervated muscles. We conclude that electrical stimulation of chronically axotomized motor and sensory neurons is effective in accelerating axon outgrowth into chronically denervated nerve stumps and improving target reinnervation after delayed nerve repair. Possible mechanisms for the efficacy of ES in promoting axon regeneration and target reinnervation after delayed nerve repair include the upregulation of neurotrophic factors.

The parameters of transcutaneous electrical nerve stimulation are critical to its regenerative effects when applied just after a sciatic crush lesion in mice

We investigated the effect of two frequencies of transcutaneous electrical nerve stimulation (TENS) applied immediately after lesion on peripheral nerve regeneration after a mouse sciatic crush injury. The animals were anesthetized and subjected to crushing of the right sciatic nerve and then separated into three groups: nontreated, Low-TENS (4 Hz), and High-TENS (100 Hz). The animals of Low- and High-TENS groups were stimulated for 2 h immediately after the surgical procedure, while the nontreated group was only positioned for the same period. After five weeks the animals were euthanized, and the nerves dissected bilaterally for histological and histomorphometric analysis. Histological assessment by light and electron microscopy showed that High-TENS and nontreated nerves had a similar profile, with extensive signs of degeneration. Conversely, Low-TENS led to increased regeneration, displaying histological aspects similar to control nerves. High-TENS also led to decreased density of fibers in the range of 6-12 μm diameter and decreased fiber diameter and myelin area in the range of 0-2 μm diameter. These findings suggest that High-TENS applied just after a peripheral nerve crush may be deleterious for regeneration, whereas Low-TENS may increase nerve regeneration capacity.

An in vitro model to study brain tissue recovery

Brain tissue slices can be maintained within metabolically stable conditions for long periods of time (hours). This experimental setting has been productive for investigating long-term neural function in vitro. Here, we utilize this experimental approach to describe the recovery of functional connectivity in slices from the mouse hippocampus. Hippocampal slices were cut up bisecting the CA1 region (parietal cut) and each severed half placed adjacent to the other. Stimulation and recording electrodes were placed on each side of the cut; with one electrode stimulating one hemi-slice (20 V, 0.033 Hz) and the other electrode recording the evoked response from the adjacent hemi-slice. As expected, no evoked response was observed shortly after the beginning of stimulation. However, 20-40 min after the initiation of stimulation a large depolarization signal was detected. Right after that, fiber volley potentials were observed in the adjacent hemi-slice. After 1h excitatory postsynaptic potentials (EPSP) were detected. Based on this observation, we hypothesize that recovery of functional connectivity is enhanced by constant delivery of electrical pulses at low frequency to the damaged neural tissue. The described in vitro slice system may become a very suitable experimental method to investigate strategies to enhance the recovery of neural connectivity after brain injury.

[Neuromuscular electric stimulation therapy in otorhinolaryngology]

BACKGROUND

Animal experiments have shown that after specific nerve traumatization, neuromuscular electrostimulation (NMES) can promote nerve regeneration and reduce synkinesia without negatively interfering with normal regeneration processes. NMES is used routinely in physical rehabilitation medicine.

METHODS

This systematic literature search in the Cochrane Central Register of Controlled Trials, the Cochrane Database of Systematic Reviews, the DAHTA database, the Health Technology Assessment Database and MEDLINE or PubMed considered studies on the use of NMES in otorhinolaryngology that have been published in German or English.

RESULTS

The search identified 180 studies. These were evaluated and relevant studies were included in the further evaluation.

DISCUSSION

In the fields of otorhinolaryngology and phoniatry/paediatric audiology, clinical studies investigating the effects of NMES on facial and laryngeal paresis, as well as dysphonia and dysphagia have been carried out. The evidence collected to date is encouraging; particularly for the treatment of certain forms of dysphagia and laryngeal paresis.

High-frequency electrical stimulation can be a complementary therapy to promote nerve regeneration in diabetic rats

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

Electrical stimulation accelerates nerve regeneration and functional recovery in delayed peripheral nerve injury in rats

The present study aims to investigate the potential of brief electrical stimulation (ES; 3 V, 20 Hz, 20 min) in improving functional recovery in delayed nerve injury repair (DNIR). The sciatic nerve of Sprague Dawley rats was transected, and the repair of nerve injury was delayed for different time durations (2, 4, 12 and 24 weeks). Brief depolarizing ES was applied to the proximal nerve stump when the transected nerve stumps were bridged with a hollow nerve conduit (5 mm in length) after delayed periods. We found that the diameter and number of regenerated axons, the thickness of myelin sheath, as well as the number of Fluoro-Gold retrograde-labeled motoneurons and sensory neurons were significantly increased by ES, suggesting that brief ES to proximal nerve stumps is capable of promoting nerve regeneration in DNIR with different delayed durations, with the longest duration of 24 weeks. In addition, the amplitude of compound muscle action potential (gastrocnemius muscle) and nerve conduction velocity were also enhanced, and gastrocnemius muscle atrophy was partially reversed by brief ES, indicating that brief ES to proximal nerve stump was able to improve functional recovery in DNIR. Furthermore, brief ES was capable of increasing brain-derived neurotrophic factor (BDNF) expression in the spinal cord in DNIR, suggesting that BDNF-mediated neurotrophin signaling might be one of the contributing factors to the beneficial effect of brief ES on DNIR. In conclusion, the present findings indicate the potential of using brief ES as a useful method to improve functional recovery for delayed repair of peripheral nerve lesions.