Electrical muscle stimulation elevates intramuscular BDNF and GDNF mRNA following peripheral nerve injury and repair in rats

Electrical Stimulation: How It Works and How to Apply It

Electrical stimulation is emerging as a perioperative strategy to improve peripheral nerve regeneration and enhance functional recovery. Despite decades of research, new insights into the complex multifaceted mechanisms of electrical stimulation continue to emerge, providing greater understanding of the neurophysiology of nerve regeneration. In this study, we summarize what is known about how electrical stimulation modulates the molecular cascades and cellular responses innate to nerve injury and repair, and the consequential effects on axonal growth and plasticity. Further, we discuss how electrical stimulation is delivered in preclinical and clinical studies and identify knowledge gaps that may provide opportunities for optimization.

Mapping the hotspots and future trends of electrical stimulation for peripheral nerve injury: A bibliometric analysis from 2002 to 2023

Peripheral nerve injuries often result in severe personal and social burden, and even with surgical treatment, patients continue to have poor clinical outcomes. Over the past two decades, electrical stimulation has been shown to promote axonal regeneration and alleviate refractory neuropathic pain. The aim of this study was to analyse this field using a bibliometric approach. Literature was searched through Web of Science Core Collection (WOSCC) for the years 2002-2023. Literature analysis included: (1) Describing publication trends in the field. (2) Exploring collaborative network relationships. (3) Finding research advances and research hotspots in the field. (4) Summarizing research trends in the field. With the number of studies in this field still increasing, a total of 693 publications were included in the analysis. This field of research is interdisciplinary in nature. Research hotspots include peripheral nerve regeneration, the treatment of neuropathic pain, materials for nerve injury repair, and the restoration of sensory function in patients with peripheral nerve injury. Correspondingly, the development of nerve conduits and systems for peripheral nerve electrical stimulation, clinical trials of peripheral nerve electrical stimulation, and tactile recovery and movement for amputees have shown significant promise as future research trends in this field.

Immediate effects of electroacupuncture in oculomotor nerve palsy following brainstem infarction: A case report

INTRODUCTION

Research has demonstrated that electroacupuncture (EA) stimulation of paralyzed muscles significantly improves nerve regeneration and functional recovery.

DESCRIPTION

An 81-year-old man with no history of diabetes mellitus or hypertension presented with a history of brainstem infarction. Initially, the patient had medial rectus palsy in the left eye and diplopia to the right in both eyes, which almost returned to normal after six sessions of EA.

METHODS

The CARE guidelines informed the case study report. The patient was diagnosed with oculomotor nerve palsy (ONP) and photographed to document ONP recovery after treatment. The selected acupuncture points and surgical methods are listed in the table.

DISCUSSION

Pharmacological treatment of oculomotor palsy is not ideal, and its long-term use has side effects. Although acupuncture is a promising treatment for ONP, existing treatments involve many acupuncture points and long cycles, resulting in poor patient compliance. We chose an innovative modality, electrical stimulation of paralyzed muscles, which may be an effective and safe complementary alternative therapy for ONP.

Application and underlying mechanism of acupuncture for the nerve repair after peripheral nerve injury: remodeling of nerve system

Peripheral nerve injury (PNI) is a structural event with harmful consequences worldwide. Due to the limited intrinsic regenerative capacity of the peripheral nerve in adults, neural restoration after PNI is difficult. Neurological remodeling has a crucial effect on the repair of the form and function during the regeneration of the peripheral nerve after the peripheral nerve is injured. Several studies have demonstrated that acupuncture is effective for PNI-induced neurologic deficits, and the potential mechanisms responsible for its effects involve the nervous system remodeling in the process of nerve repair. Moreover, acupuncture promotes neural regeneration and axon sprouting by activating related neurotrophins retrograde transport, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), N-cadherin, and MicroRNAs. Peripheral nerve injury enhances the perceptual response of the central nervous system to pain, causing central sensitization and accelerating neuronal cell apoptosis. Together with this, the remodeling of synaptic transmission function would worsen pain discomfort. Neuroimaging studies have shown remodeling changes in both gray and white matter after peripheral nerve injury. Acupuncture not only reverses the poor remodeling of the nervous system but also stimulates the release of neurotrophic substances such as nerve growth factors in the nervous system to ameliorate pain and promote the regeneration and repair of nerve fibers. In conclusion, the neurological remodeling at the peripheral and central levels in the process of acupuncture treatment accelerates nerve regeneration and repair. These findings provide novel insights enabling the clinical application of acupuncture in the treatment of PNI.

Effects of Electrical Stimulation of the Cell: Wound Healing, Cell Proliferation, Apoptosis, and Signal Transduction

Electrical stimulation of the cell can have a number of different effects depending on the type of cell being stimulated. In general, electrical stimulation can cause the cell to become more active, increase its metabolism, and change its gene expression. For example, if the electrical stimulation is of low intensity and short duration, it may simply cause the cell to depolarize. However, if the electrical stimulation is of high intensity or long duration, it may cause the cell to become hyperpolarized. The electrical stimulation of cells is a process by which an electrical current is applied to cells in order to change their function or behavior. This process can be used to treat various medical conditions and has been shown to be effective in a number of studies. In this perspective, the effects of electrical stimulation on the cell are summarized.

Basic mechanisms of peripheral nerve injury and treatment via electrical stimulation

Previous studies on the mechanisms of peripheral nerve injury (PNI) have mainly focused on the pathophysiological changes within a single injury site. However, recent studies have indicated that within the central nervous system, PNI can lead to changes in both injury sites and target organs at the cellular and molecular levels. Therefore, the basic mechanisms of PNI have not been comprehensively understood. Although electrical stimulation was found to promote axonal regeneration and functional rehabilitation after PNI, as well as to alleviate neuropathic pain, the specific mechanisms of successful PNI treatment are unclear. We summarize and discuss the basic mechanisms of PNI and of treatment via electrical stimulation. After PNI, activity in the central nervous system (spinal cord) is altered, which can limit regeneration of the damaged nerve. For example, cell apoptosis and synaptic stripping in the anterior horn of the spinal cord can reduce the speed of nerve regeneration. The pathological changes in the posterior horn of the spinal cord can modulate sensory abnormalities after PNI. This can be observed in cases of ectopic discharge of the dorsal root ganglion leading to increased pain signal transmission. The injured site of the peripheral nerve is also an important factor affecting post-PNI repair. After PNI, the proximal end of the injured site sends out axial buds to innervate both the skin and muscle at the injury site. A slow speed of axon regeneration leads to low nerve regeneration. Therefore, it can take a long time for the proximal nerve to reinnervate the skin and muscle at the injured site. From the perspective of target organs, long-term denervation can cause atrophy of the corresponding skeletal muscle, which leads to abnormal sensory perception and hyperalgesia, and finally, the loss of target organ function. The mechanisms underlying the use of electrical stimulation to treat PNI include the inhibition of synaptic stripping, addressing the excessive excitability of the dorsal root ganglion, alleviating neuropathic pain, improving neurological function, and accelerating nerve regeneration. Electrical stimulation of target organs can reduce the atrophy of denervated skeletal muscle and promote the recovery of sensory function. Findings from the included studies confirm that after PNI, a series of physiological and pathological changes occur in the spinal cord, injury site, and target organs, leading to dysfunction. Electrical stimulation may address the pathophysiological changes mentioned above, thus promoting nerve regeneration and ameliorating dysfunction.

Neuronal activity-dependent ATP enhances the pro-growth effect of repair Schwann cell extracellular vesicles by increasing their miRNA-21 loading

Functional recovery after peripheral nerve injuries is critically dependent on axonal regeneration. Several autonomous and non-cell autonomous processes regulate axonal regeneration, including the activation of a growth-associated transcriptional program in neurons and the reprogramming of differentiated Schwann cells (dSCs) into repair SCs (rSCs), triggering the secretion of neurotrophic factors and the activation of an inflammatory response. Repair Schwann cells also release pro-regenerative extracellular vesicles (EVs), but is still unknown whether EV secretion is regulated non-cell autonomously by the regenerating neuron. Interestingly, it has been described that nerve activity enhances axonal regeneration by increasing the secretion of neurotrophic factors by rSC, but whether this activity modulates pro-regenerative EV secretion by rSC has not yet been explored. Here, we demonstrate that neuronal activity enhances the release of rSC-derived EVs and their transfer to neurons. This effect is mediated by activation of P2Y receptors in SCs after activity-dependent ATP release from sensory neurons. Importantly, activation of P2Y in rSCs also increases the amount of miRNA-21 present in rSC-EVs. Taken together, our results demonstrate that neuron to glia communication by ATP-P2Y signaling regulates the content of SC-derived EVs and their transfer to axons, modulating axonal elongation in a non-cell autonomous manner.

Blockage of neuromuscular glutamate receptors impairs reinnervation following nerve crush in adult mice

Motor axons in peripheral nerves are capable of regeneration following injury. However, complete recovery of motor function is rare, particularly when reinnervation is delayed. We have previously found that glutamate receptors play a crucial role in the successful innervation of muscle during mouse development. In particular, blocking N-methyl-D-aspartate (NMDA) receptor activity delays the normal elimination of excess innervation of each neuromuscular junction. Here, we use behavioral, immunohistochemical, electrophysiological, and calcium imaging methods to test whether glutamate receptors play a similar role in the transition from polyneuronal to mono-innervation and in recovery of function following peripheral nerve injury in mature muscle.

Exosome-Mediated miR-21 Was Involved in the Promotion of Structural and Functional Recovery Effect Produced by Electroacupuncture in Sciatic Nerve Injury

PURPOSE

Our study is aimed at investigating the mechanism by which electroacupuncture (EA) promoted nerve regeneration by regulating the release of exosomes and exosome-mediated miRNA-21 (miR-21) transmission. Furthermore, the effects of Schwann cells- (SC-) derived exosomes on the overexpression of miR-21 for the treatment of PNI were investigated.

METHODS

A sciatic nerve injury model of rat was constructed, and the expression of miR-21 in serum exosomes and damaged local nerves was detected using RT-qPCR after EA treatment. The exosomes were identified under a transmission electron microscope and using western blotting analysis. Then, the exosome release inhibitor, GW4869, and the miR-21-5p-sponge used for the knockdown of miR-21 were used to clarify the effects of exosomal miR-21 on nerve regeneration promoted by EA. The nerve conduction velocity recovery rate, sciatic nerve function index, and wet weight ratio of gastrocnemius muscle were determined to evaluate sciatic nerve function recovery. SC proliferation and the level of neurotrophic factors were assessed using immunofluorescence staining, and the expression levels of SPRY2 and miR-21 were detected using RT-qPCR analysis. Subsequently, the transmission of exosomal miR-21 from SC to the axon was verified in vitro. Finally, the exosomes derived from the SC infected with the miR-21 overexpression lentivirus were collected and used to treat the rat SNI model to explore the therapeutic role of SC-derived exosomes overexpressing miR-21.

RESULTS

We found that EA inhibited the release of serum exosomal miR-21 in a PNI model of rats during the early stage of PNI, while it promoted its release during later stages. EA enhanced the accumulation of miR-21 in the injured nerve and effectively promoted the recovery of nerve function after PNI. The treatment effect of EA was attenuated when the release of circulating exosomes was inhibited or when miR-21 was downregulated in local injury tissue via the miR-21-5p-sponge. Normal exosomes secreted by SC exhibited the ability to promote the recovery of nerve function, while the overexpression of miR-21 enhanced the effects of the exosomes. In addition, exosomal miR-21 secreted by SC could promote neurite outgrowth in vitro.

CONCLUSION

Our results demonstrated the mechanism of EA on PNI from the perspective of exosome-mediated miR-21 transport and provided a theoretical basis for the use of exosomal miR-21 as a novel strategy for the treatment of PNI.

Effects of Varied Stimulation Parameters on Adipose-Derived Stem Cell Response to Low-Level Electrical Fields

Exogenous electrical fields have been explored in regenerative medicine to increase cellular expression of pro-regenerative growth factors. Adipose-derived stem cells (ASCs) are attractive for regenerative applications, specifically for neural repair. Little is known about the relationship between low-level electrical stimulation (ES) and ASC regenerative potentiation. In this work, patterns of ASC expression and secretion of growth factors (i.e., secretome) were explored across a range of ES parameters. ASCs were stimulated with low-level stimulation (20 mV/mm) at varied pulse frequencies, durations, and with alternating versus direct current. Frequency and duration had the most significant effects on growth factor expression. While a range of stimulation frequencies (1, 20, 1000 Hz) applied intermittently (1 h × 3 days) induced upregulation of general wound healing factors, neural-specific factors were only increased at 1 Hz. Moreover, the most optimal expression of neural growth factors was achieved when ASCs were exposed to 1 Hz pulses continuously for 24 h. In evaluation of secretome, apparent inconsistencies were observed across biological replications. Nonetheless, ASC secretome (from 1 Hz, 24 h ES) caused significant increase in neurite extension compared to non-stimulated control. Overall, ASCs are sensitive to ES parameters at low field strengths, notably pulse frequency and stimulation duration.

The Effect of a Portable Electrical Muscle Stimulation on Brain-Derived Neurotrophic Factor in Elderly People: Three Case Studies

Brain-derived neurotrophic factor (BDNF), which plays an important role in cognitive and nerve function, is released from skeletal muscle cells into the blood by muscle contractions and/or electrical muscle stimulation (EMS). However, the influence of EMS administered by a portable device on BDNF is unclear. The purpose of this case report was to quantify the influence of EMS administered by a portable device on BDNF and physical function. Three elderly people (age, 69.7 ± 1.5 years) were included in the present study. The participants used a portable EMS device to stimulate the bilateral quadriceps muscles for 8 weeks (23 min for 5 days/week). To determine the effects of EMS, the following parameters were assessed at baseline, 8 weeks, and 12 weeks (follow-up): knee extensor strength, muscle mass of the lower limb, Berg balance score, and blood BDNF level. All outcomes improved after the EMS intervention, but the improvements did not persist for 12 weeks. These findings suggest that portable EMS is potentially useful for improving the blood BDNF level and physical function.

GDNF to the rescue: GDNF delivery effects on motor neurons and nerves, and muscle re-innervation after peripheral nerve injuries

Peripheral nerve injuries commonly occur due to trauma, like a traffic accident. Peripheral nerves get severed, causing motor neuron death and potential muscle atrophy. The current golden standard to treat peripheral nerve lesions, especially lesions with large (≥ 3 cm) nerve gaps, is the use of a nerve autograft or reimplantation in cases where nerve root avulsions occur. If not tended early, degeneration of motor neurons and loss of axon regeneration can occur, leading to loss of function. Although surgical procedures exist, patients often do not fully recover, and quality of life deteriorates. Peripheral nerves have limited regeneration, and it is usually mediated by Schwann cells and neurotrophic factors, like glial cell line-derived neurotrophic factor, as seen in Wallerian degeneration. Glial cell line-derived neurotrophic factor is a neurotrophic factor known to promote motor neuron survival and neurite outgrowth. Glial cell line-derived neurotrophic factor is upregulated in different forms of nerve injuries like axotomy, sciatic nerve crush, and compression, thus creating great interest to explore this protein as a potential treatment for peripheral nerve injuries. Exogenous glial cell line-derived neurotrophic factor has shown positive effects in regeneration and functional recovery when applied in experimental models of peripheral nerve injuries. In this review, we discuss the mechanism of repair provided by Schwann cells and upregulation of glial cell line-derived neurotrophic factor, the latest findings on the effects of glial cell line-derived neurotrophic factor in different types of peripheral nerve injuries, delivery systems, and complementary treatments (electrical muscle stimulation and exercise). Understanding and overcoming the challenges of proper timing and glial cell line-derived neurotrophic factor delivery is paramount to creating novel treatments to tend to peripheral nerve injuries to improve patients’ quality of life.

Acute intermittent hypoxia enhances regeneration of surgically repaired peripheral nerves in a manner akin to electrical stimulation

The intrinsic repair response of injured peripheral neurons is enhanced by brief electrical stimulation (ES) at time of surgical repair, resulting in improved regeneration in rodents and humans. However, ES is invasive. Acute intermittent hypoxia (AIH) - breathing alternate cycles of regular air and air with ~50% normal oxygen levels (11% O₂), considered mild hypoxia, is an emerging, promising non-invasive therapy that promotes motor function in spinal cord injured rats and humans. AIH can increase neural activity and under moderately severe hypoxic conditions improves repair of peripherally crushed nerves in mice. Thus, we posited an AIH paradigm similar to that used clinically for spinal cord injury, will improve surgically repaired peripheral nerves akin to ES, including an impact on regeneration-associated gene (RAG) expression-a predictor of growth states. Alterations in early RAG expression were examined in adult male Lewis rats that underwent tibial nerve coaptation repair with either 2 days AIH or normoxia control treatment begun on day 2 post-repair, or 1 h ES treatment (20 Hz) at time of repair. Three days post-repair, AIH or ES treatments effected significant and parallel elevated RAG expression relative to normoxia control at the level of injured sensory and motor neuron cell bodies and proximal axon front. These parallel impacts on RAG expression were coupled with significant improvements in later indices of regeneration, namely enhanced myelination and increased numbers of newly myelinated fibers detected 20 mm distal to the tibial nerve repair site or sensory and motor neurons retrogradely labeled 28 mm distal to the repair site, both at 25 days post nerve repair; and improved return of toe spread function 5-10 weeks post-repair. Collectively, AIH mirrors many beneficial effects of ES on peripheral nerve repair outcomes. This highlights its potential for clinical translation as a non-invasive means to effect improved regeneration of injured peripheral nerves.

Effects of electrical stimulation on skin surface

ABSTRACT

Skin is the largest organ in the body, and directly contact with the external environment. Articles on the role of micro-current and skin have emerged in recent years. The function of micro-current is various, including introducing various drugs into the skin locally or throughout the body, stimulating skin wounds healing through various currents, suppressing pain caused by various diseases, and promoting blood circulation for postoperative muscle rehabilitation, etc. This article reviews these efforts. Compared with various physical and chemical medical therapies, micro-current stimulation provides a relatively safe, non-invasive therapy with few side effects, giving modern medicine a more suitable treatment option. At the same time, the cost of the electrical stimulation generating device is relatively low, which makes it have wider space to and more clinical application value. The current micro-current stimulation technology has become more and more mature, but there are still many problems in its research. The design of the experiment and the selection of the current parameters not standardized and rigorous. Now, clear regulations are needed to regulate this field. Micro-current skin therapy has become a robust, reliable, and well-structured system.

Stretchable, dynamic covalent polymers for soft, long-lived bioresorbable electronic stimulators designed to facilitate neuromuscular regeneration

Bioresorbable electronic stimulators are of rapidly growing interest as unusual therapeutic platforms, i.e., bioelectronic medicines, for treating disease states, accelerating wound healing processes and eliminating infections. Here, we present advanced materials that support operation in these systems over clinically relevant timeframes, ultimately bioresorbing harmlessly to benign products without residues, to eliminate the need for surgical extraction. Our findings overcome key challenges of bioresorbable electronic devices by realizing lifetimes that match clinical needs. The devices exploit a bioresorbable dynamic covalent polymer that facilitates tight bonding to itself and other surfaces, as a soft, elastic substrate and encapsulation coating for wireless electronic components. We describe the underlying features and chemical design considerations for this polymer, and the biocompatibility of its constituent materials. In devices with optimized, wireless designs, these polymers enable stable, long-lived operation as distal stimulators in a rat model of peripheral nerve injuries, thereby demonstrating the potential of programmable long-term electrical stimulation for maintaining muscle receptivity and enhancing functional recovery.

Molecular and neural adaptations to neuromuscular electrical stimulation; Implications for ageing muscle

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Muscle atrophy and functional declines observed with advancing age can be minimized via various NMES protocols.

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Animal models have shown that NMES induces motor axon regeneration and promotes axonal outgrowth and fibre reinnervation.

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The activation of BDNF-trkB contributes to promotion of nerve growth and survival and mediates neuroplasticity.

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NMES is able to regulate muscle protein homeostasis and elevate oxidative enzyme activity.

One of the most notable effects of ageing is an accelerated decline of skeletal muscle mass and function, resulting in various undesirable outcomes such as falls, frailty, and all-cause mortality. The loss of muscle mass directly leads to functional deficits and can be explained by the combined effects of individual fibre atrophy and fibre loss. The gradual degradation of fibre atrophy is attributed to impaired muscle protein homeostasis, while muscle fibre loss is a result of denervation and motor unit (MU) remodelling. Neuromuscular electrical stimulation (NMES), a substitute for voluntary contractions, has been applied to reduce muscle mass and functional declines. However, the measurement of the effectiveness of NMES in terms of its mechanism of action on the peripheral motor nervous system and neuromuscular junction, and multiple molecular adaptations at the single fibre level is not well described. NMES mediates neuroplasticity and upregulates a number of neurotropic factors, manifested by increased axonal sprouting and newly formed neuromuscular junctions. Repeated involuntary contractions increase the activity levels of oxidative enzymes, increase fibre capillarisation and can influence fibre type conversion. Additionally, following NMES muscle protein synthesis is increased as well as functional capacity. This review will detail the neural, molecular, metabolic and functional adaptations to NMES in human and animal studies.

Electroacupuncture Promoted Nerve Repair After Peripheral Nerve Injury by Regulating miR-1b and Its Target Brain-Derived Neurotrophic Factor

Growing evidence indicates that electroacupuncture (EA) has a definite effect on the treatment of peripheral nerve injury (PNI), but its mechanism is not completely clear. MicroRNAs (miRNAs) are involved in the regulation of a variety of biological processes, and EA may enhance PNI repair by regulating miRNAs. In this study, the rat sciatic nerve injury model was treated with EA for 4 weeks. Acupoints Huantiao (GB30) and Zusanli (ST36) were stimulated by EA 20 min once a day, 6 days a week for 4 weeks. We found that EA treatment downregulated the expression of miR-1b in the local injured nerve. In vitro experiments showed that overexpression of miR-1b inhibited the expression of brain-derived neurotrophic factor (BDNF) in rat Schwann cell (SC) line, while BDNF knockdown inhibited the proliferation, migration, and promoted apoptosis of SCs. Subsequently, the rat model of sciatic nerve injury was treated by EA treatment and injection of agomir-1b or antagomir-1b. The nerve conduction velocity ratio (NCV), sciatic functional index (SFI), and S100 immunofluorescence staining were examined and showed that compared with the model group, NCV, SFI, proliferation of SC, and expression of BDNF in the injured nerves of rats treated with EA or EA + anti-miR-1b were elevated, while EA + miR-1b was reduced, indicating that EA promoted sciatic nerve function recovery and SC proliferation through downregulating miR-1b. To summarize, EA may promote the proliferation, migration of SC, and nerve repair after PNI by regulating miR-1b, which targets BDNF.

Bioactive polymeric materials and electrical stimulation strategies for musculoskeletal tissue repair and regeneration

Electrical stimulation (ES) is predominantly used as a physical therapy modality to promote tissue healing and functional recovery. Research efforts in both laboratory and clinical settings have shown the beneficial effects of this technique for the repair and regeneration of damaged tissues, which include muscle, bone, skin, nerve, tendons, and ligaments. The collective findings of these studies suggest ES enhances cell proliferation, extracellular matrix (ECM) production, secretion of several cytokines, and vasculature development leading to better tissue regeneration in multiple tissues. However, there is still a gap in the clinical relevance for ES to better repair tissue interfaces, as ES applied clinically is ineffective on deeper tissue. The use of a conducting material can transmit the stimulation applied from skin electrodes to the desired tissue and lead to an increased function on the repair of that tissue. Ionically conductive (IC) polymeric scaffolds in conjunction with ES may provide solutions to utilize this approach effectively. Injectable IC formulations and their scaffolds may provide solutions for applying ES into difficult to reach tissue types to enable tissue repair and regeneration. A better understanding of ES-mediated cell differentiation and associated molecular mechanisms including the immune response will allow standardization of procedures applicable for the next generation of regenerative medicine. ES, along with the use of IC scaffolds is more than sufficient for use as a treatment option for single tissue healing and may fulfill a role in interfacing multiple tissue types during the repair process.

Brain Derived Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor-Transfected Bone Mesenchymal Stem Cells for the Repair of Periphery Nerve Injury

Peripheral nerve injury is a common clinical neurological disease. In our previous study, highly oriented poly (L-lactic acid) (PLLA)/soy protein isolate (SPI) nanofiber nerve conduits were constructed and exhibited a certain repair capacity for peripheral nerve injury. In order to further improve their nerve repairing efficiency, the bone mesenchymal stem cells (BMSCs) overexpressing brain derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) were introduced into the conduits as seed cells and then were used to repair the 10-mm sciatic nerve defects in rats. The nerve repair efficiency of the functional nerve conduits was evaluated by gait experiment, electrophysiological test, and a series of assays such as hemotoxylin-eosin (HE) staining, immunofluorescence staining, toluidine blue (TB) staining, transmission electron microscopy (TEM) observation of regenerated nerve and Masson's trichrome staining of gastrocnemius muscle. The results showed that the conduits containing BMSCs overexpressing BDNF and GDNF double-factors group had better nerve repairing efficiency than blank BMSCs and single BDNF or GDNF factor groups, and superior to autografts group in some aspects. These data demonstrated that BDNF and GDNF produced by BMSCs could synergistically promote peripheral nerve repair. This study shed a new light on the conduits and stem cells-based peripheral nerve repair.

Efficacy of Electrical Stimulation on Nerve Fiber Growth in Small Fiber Neuropathy

OBJECTIVES

To define whether electrical nerve stimulation (ENS) therapy would promote intraepidermal nerve growth and nerve regeneration in patients with small fiber neuropathy (SFN).

METHODS

This was a prospective study conducted on 8 subjects with previously diagnosed SFN. Nerve conduction testing, punch biopsies, and clinical examinations with a calculation of revised total neuropathy score were conducted on subjects before beginning ENS therapy and at 30 and 60 days after the start of ENS therapy.

RESULTS

Clinical examination findings and intraepidermal nerve fiber density measurements on day 30 and day 60 did not show statistically significant changes in the treated group compared with the untreated group.

CONCLUSIONS

Despite the success of previous animal studies, no meaningful nerve growth and regeneration in SFN was demonstrated with ENS therapy in this study. Studies of larger subject larger populations with longer duration of ENS treatment are warranted to confirm our findings.

Exercise training improves sleep quality: A randomized controlled trial

BACKGROUND

Exercise holds promise as a non-pharmacological intervention for the improvement of sleep quality. Therefore, this study investigates the effects of different training modalities on sleep quality parameters.

MATERIAL & METHODS

A total of 69 (52.7% women) middle-aged sedentary adults were randomized to (a) control group, (b) physical activity recommendation from the World Health Organization, (c) high-intensity interval training (HIIT) and (d) high-intensity interval training group adding whole-body electromyostimulation training (HIITEMS). Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) scale and accelerometers.

RESULTS

All intervention groups showed a lower PSQI global score (all P < .022). HIIT-EMS group improved all accelerometer parameters, with higher total sleep time and sleep efficiency, and lower wake after sleep onset (all P < .016). No differences were found between groups in any sleep quality parameter.

CONCLUSION

In conclusion, exercise training induced an improvement in subjective sleep quality in sedentary middleaged adults. Moreover, HIIT-EMS training showed an improvement in objective sleep quality parameters (total sleep time, sleep efficiency and wake after sleep onset) after 12 weeks of exercise intervention. The changes observed in the HIIT-EMS group were not statistically different to the other exercise modalities.

microRNA-192-5p is involved in nerve repair in rats with peripheral nerve injury by regulating XIAP

Objective: MicroRNAs (miRNAs) have been demonstrated to engage in the nerve injury, while the effect of microRNA-192-5p (miR-192-5p) on the nerve repair has not yet been well understood. This study is performed to investigate how miR-192-5p affects nerve repair in rats with peripheral nerve injury by regulating X-linked inhibitor of apoptosis protein (XIAP).Methods: The rat model of left sciatic nerve injury was established, and the expression of miR-192-5p was then detected. A series of experiments were conducted to investigate the role of miR-192-5p on nerve repair in rats with peripheral nerve injury. The expression of apoptosis-related proteins (Caspase-3, Bax and Bcl-2) and nerve repair factors (NGF, BDNF, and GAP-43) was measured. Bioinformatics analysis and dual-luciferase reporter gene assay confirmed the targeting relationship between miR-192-5p and XIAP.Results: MiR-192-5p inhibition promoted the recovery of sensory function and the recovery and regeneration in rats with sciatic nerve injury. MiR-192-5p inhibition promoted the recovery of muscle atrophy caused by nerve injury. MiR-192-5p inhibition inhibited neuronal apoptosis by affecting the expression of apoptosis-related proteins and promoted the recovery of nerve function by elevating the expression of nerve repair factors induced by peripheral nerve injury. Bioinformatics analysis and dual-luciferase reporter gene assay confirmed that XIAP was a target gene of miR-192-5p.Conclusion: This study demonstrates that miR-192-5p inhibition can up-regulate the expression of XIAP, decrease the apoptosis of nerve cells, and promote the repair and regeneration of peripheral nerve injury.

Electrical Muscle Stimulation Accelerates Functional Recovery After Nerve Injury

Electrical muscle stimulation has been demonstrated to facilitate nerve regeneration and functional recovery, but the underlying mechanism remains only partially understood. In this study, we investigated the positive effect of electrical muscle stimulation following nerve injury and its molecular mechanisms of autophagy regulation. The sciatic nerves of Sprague-Dawley rats were transected and immediately repaired. Gastrocnemius muscles were electrically stimulated using surface electrodes. Motor functional recovery was assessed by gait analysis, nerve conduction examination and histological appearance of the target muscle. Axon regeneration was investigated by morphometric analysis. Western blotting and immunofluorescence staining were used to detect the expression of molecular biological changes in distal nerve stump. Ultrastructural features of the nerve were evaluated by transmission electron microscope. We found that axon regeneration and motor functional recovery were improved by electrical muscle stimulation. The number of autophagosomes and the expression of autophagy marker LC3-Ⅱ in distal nerve stump were increased while the level of autophagy substrate protein P62 was decreased following electrical muscle stimulation. Blockage of the autophagy flux by chloroquine (CQ) diminished the positive effect of electrical muscle stimulation on nerve injury. These results illustrated that electrical muscle stimulation accelerates axon regeneration and functional recovery through promoting autophagy flux in distal nerve segments following nerve injury and immediate repair (IR) by a so far unknown mechanism.

Current Status of Therapeutic Approaches against Peripheral Nerve Injuries: A Detailed Story from Injury to Recovery

Peripheral nerve injury is a complex condition with a variety of signs and symptoms such as numbness, tingling, jabbing, throbbing, burning or sharp pain. Peripheral nerves are fragile in nature and can easily get damaged due to acute compression or trauma which may lead to the sensory and motor functions deficits and even lifelong disability. After lesion, the neuronal cell body becomes disconnected from the axon's distal portion to the injury site leading to the axonal degeneration and dismantlement of neuromuscular junctions of targeted muscles. In spite of extensive research on this aspect, complete functional recovery still remains a challenge to be resolved. This review highlights detailed pathophysiological events after an injury to a peripheral nerve and the associated factors that can either hinder or promote the regenerative machinery. In addition, it throws light on the available therapeutic strategies including supporting therapies, surgical and non-surgical interventions to ameliorate the axonal regeneration, neuronal survival, and reinnervation of peripheral targets. Despite the availability of various treatment options, we are still lacking the optimal treatments for a perfect and complete functional regain. The need for the present age is to discover or design such potent compounds that would be able to execute the complete functional retrieval. In this regard, plant-derived compounds are getting more attention and several recent reports validate their remedial effects. A plethora of plants and plant-derived phytochemicals have been suggested with curative effects against a number of diseases in general and neuronal injury in particular. They can be a ray of hope for the suffering individuals.

Comprehensive therapeutics targeting the corticospinal tract following spinal cord injury

Spinal cord injury (SCI), which is much in the public eye, is still a refractory disease compromising the well-being of both patients and society. In spite of there being many methods dealing with the lesion, there is still a deficiency in comprehensive strategies covering all facets of this damage. Further, we should also mention the structure called the corticospinal tract (CST) which plays a crucial role in the motor responses of organisms, and it will be the focal point of our attention. In this review, we discuss a variety of strategies targeting different dimensions following SCI and some treatments that are especially efficacious to the CST are emphasized. Over recent decades, researchers have developed many effective tactics involving five approaches: (1) tackle more extensive regions; (2) provide a regenerative microenvironment; (3) provide a glial microenvironment; (4) transplantation; and (5) other auxiliary methods, for instance, rehabilitation training and electrical stimulation. We review the basic knowledge on this disease and correlative treatments. In addition, some well-formulated perspectives and hypotheses have been delineated. We emphasize that such a multifaceted problem needs combinatorial approaches, and we analyze some discrepancies in past studies. Finally, for the future, we present numerous brand-new latent tactics which have great promise for curbing SCI.

Polyimide Electrode-Based Electrical Stimulation Impedes Early Stage Muscle Graft Regeneration

Given the increasing use of regenerative free muscle flaps for various reconstructive procedures and neuroprosthetic applications, there is great interest and value in their enhanced regeneration, revascularization, and reinnervation for improved functional recovery. Here, we implant polyimide-based mircroelectrodes on free flap grafts and perform electrical stimulation for 6 weeks in a murine model. Using electrophysiological and histological assessments, we compare outcomes of stimulated grafts with unstimulated control grafts. We find delayed reinnervation and abnormal electromyographic (EMG) signals, with significantly more polyphasia, lower compound muscle action potentials and higher fatigability in stimulated animals. These metrics are suggestive of myopathy in the free flap grafts stimulated with the electrode. Additionally, active inflammatory processes and partial necrosis are observed in grafts stimulated with the implanted electrode. The results suggest that under this treatment protocol, implanted epimysial electrodes and electrical stimulation to deinnervated, and devascularized flaps during the early recovery phase may be detrimental to regeneration. Future work should determine the optimal implantation and stimulation window for accelerating free muscle graft regeneration.

Review: Bioengineering approach for the repair and regeneration of peripheral nerve

Complex craniofacial surgeries of damaged tissues have several limitations, which present complications and challenges when trying to replicate facial function and structure. Traditional treatment techniques have shown suitable nerve function regeneration with various drawbacks. As technology continues to advance, new methods have been explored in order to regenerate damaged nerves in an effort to more efficiently and effectively regain original function and structure. This article will summarize recent bioengineering strategies involving biodegradable composite scaffolds, bioactive factors, and external stimuli alone or in combination to support peripheral nerve regeneration. Particular emphasis is made on the contributions of growth factors and electrical stimulation on the regenerative process.

Biomimetic sponges for regeneration of skeletal muscle following trauma

Skeletal muscle is inept in regenerating after traumatic injuries due to significant loss of basal lamina and the resident satellite cells. To improve regeneration of skeletal muscle, we have developed biomimetic sponges composed of collagen, gelatin, and laminin (LM)-111 that were crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC). Collagen and LM-111 are crucial components of the muscle extracellular matrix and were chosen to impart bioactivity whereas gelatin and EDC were used to provide mechanical strength to the scaffold. Morphological and mechanical evaluation of the sponges showed porous structure, water-retention capacity and a compressive modulus of 590-808 kPa. The biomimetic sponges supported the infiltration and viability of C₂ C₁₂ myoblasts over 5 days of culture. The myoblasts produced higher levels of myokines such as VEGF, IL-6, and IGF-1 and showed higher expression of myogenic markers such as MyoD and myogenin on the biomimetic sponges. Biomimetic sponges implanted in a mouse model of volumetric muscle loss (VML) supported satellite, endothelial, and inflammatory cell infiltration but resulted in limited myofiber regeneration at 2 weeks post-injury. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 92-103, 2019.

Myokines in Home-Based Functional Electrical Stimulation-Induced Recovery of Skeletal Muscle in Elderly and Permanent Denervation

Neuromuscular disorders, disuse, inadequate nutrition, metabolic diseases, cancer and aging produce muscle atrophy and this implies that there are different types of molecular triggers and signaling pathways for muscle wasting. Exercise and muscle contractions may counteract muscle atrophy by releasing a group of peptides, termed myokines, to protect the functionality and to enhance the exercise capacity of skeletal muscle. In this review, we are looking at the role of myokines in the recovery of permanent denervated and elderly skeletal muscle tissue. Since sub-clinical denervation events contribute to both atrophy and the decreased contractile speed of aged muscle, we saw a parallel to spinal cord injury and decided to look at both groups together. The muscle from lifelong active seniors has more muscle bulk and more slow fiber-type groupings than those of sedentary seniors, demonstrating that physical activity maintains slow motoneurons that reinnervate the transiently denervated muscle fibers. Furthermore, we summarized the evidence that muscle degeneration occur with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the peripheral nervous system. In these patients, suffering with an estreme case of muscle disuse, a complete loss of muscle fibers occurs within five to ten years after injury. Their recovered tetanic contractility, induced by home-based Functional Electrical Stimulation, can restore the muscle size and function in compliant Spinal Cord Injury patients, allowing them to perform electrical stimulation-supported stand-up training. Myokines are produced and released by muscle fibers under contraction and exert both local and systemic effects. Changes in patterns of myokine secretion, particularly of IGF-1 isoforms, occur in long-term Spinal Cord Injury persons and also in very aged people. Their modulation in Spinal Cord Injury and late aging are also key factors of home-based Functional Electrical Stimulation - mediated muscle recovery. Thus, Functional Electrical Stimulation should be prescribed in critical care units and nursing facilities, if persons are unable or reluctant to exercise. This will result in less frequent hospitalizations and a reduced burden on patients' families and public health services.

Fabrication of alignment polycaprolactone scaffolds by combining use of electrospinning and micromolding for regulating Schwann cells behavior

In the present study, a new approach for fabricating micropatterned polycaprolactone (PCL) scaffolds with ridge/groove structure on the surface was developed by combining use of electrospinning and micromolding method. A series of physicochemical properties, including morphology, wettability, component, crystal pattern and mechanical properties, of prepared PCL scaffolds were characterization, respectively. Stability of the micropatterned PCL scaffolds was measured using phosphate buffer solution immersion for a certain period. Then, the regulating effects of the micropatterned PCL scaffolds on attachment, orientation and normal biological function of Schwann cells were evaluated. And the protein adsorption behavior in various PCL scaffolds was also detected. The results showed that the micropatterned PCL scaffolds demonstrated a porous micro/nano complex structure with enhanced hydrophobicity and mechanical properties as a function of electrospun flow-rate of PCL solution. The micropatterned PCL scaffolds possessed good stability and could effectively regulate the attachment and orientation of Schwann cells at the early stage after cell culture. Importantly, the electrospun flow-rate of PCL solution was found to play an important role in scaffold properties, cell behavior and protein adsorption. The micropatterned scaffolds with a flow-rate of PCL solution at 0.12 mL h^-1 demonstrated the better regulation on Schwann cells attachment and alignment without negatively affect the normal biological function of the cells. To the best of our knowledge, this is the first report of combining use of electrospinning and micromolding method for preparing artificial nerve implants. The study is anticipated to have potential application in peripheral nerve and other tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3123-3134, 2018.

Laminin-111 functionalized polyethylene glycol hydrogels support myogenic activity in vitro

Skeletal muscle has a remarkable regenerative capability following mild physical or chemical insult. However, following a critical loss of muscle tissue, the regeneration process is impaired due to the inadequate myogenic activity of muscle resident stem cells (i.e., satellite cells). Laminin (LM) is a heterotrimeric structural protein in the satellite cell niche that is crucial for maintaining its function. In this study, we created hydrogels composed of poly (ethylene glycol) (PEG) and LM-111 to provide an elastic substrate for satellite cell proliferation at the site of injury. The PEG-LM111 conjugates were mixed with 5% and 10% (w/v) pure PEG-diacrylate (PEGDA) and photopolymerized to form 5% and 10% PEGLM gels. Pure 5% and 10% PEGDA gels were used as controls. The modulus of both hydrogels containing 10% (w/v) PEGDA was significantly higher than the hydrogels containing 5% (w/v) PEGDA. The 5% PEGLM hydrogels showed significantly higher swelling in aqueous medium suggesting a more porous structure. C₂C₁₂ myoblasts cultured on the softer 5% PEGLM hydrogels showed a flat and spread-out morphology when compared to the rounded, multicell clusters formed on the 5% PEGDA, 10% PEGDA, and 10% PEGLM hydrogels. The 5% PEGLM hydrogels also promoted a significant increase in both vascular endothelial growth factor and interleukin-6 (IL-6) production from the myoblasts. Additionally, the expression of MyoD was significantly higher while that of myogenin and α-actinin trended higher on the 5% PEGLM hydrogels compared to 5% PEGDA on day 5. Our data suggests that the introduction of LM-111 into compliant PEG hydrogels promoted myoblast adhesion, survival, pro-regenerative growth factor production, and myogenic activity.

Trace eyeblink conditioning is associated with changes in synaptophysin immunoreactivity in the cerebellar interpositus nucleus in guinea pigs

Synaptic plasticity plays a role during trace eyeblink conditioning (TEBC). Synaptophysin (Syn) is a major integral transmembrane protein, located particularly in the synaptic vesicles, and is considered a molecular marker of synapses. In addition, Syn immunoreactivity is an important indicator of synaptic plasticity. In the present study, we used immunohistochemical techniques to assess changes in Syn expression in the cerebellar interpositus nucleus (IN) of guinea pigs exposed to TEBC and pseudoconditioning. Additionally, we analyzed the relationship between Syn immunoreactivity and the percentage of trace-conditioned responses. Guinea pigs underwent trace conditioning or pseudoconditioning. Following two, six, or ten sessions, they were perfused and the cerebellum was removed for Syn immunohistochemical evaluation. After sessions 6 and 10, a significant increase in conditioned response (CR) percentage was observed in the trace-conditioned group, with the CR percentage reaching the learning criteria following session 10. Besides, for trace-conditioned animals, the Syn expression in IN was found significantly up-regulated after session 10 compared with pseudoconditioned ones. Our data suggest that the increase in Syn expression links to synaptic plasticity changes in the cerebellar IN and provides a histological substrate in the IN relating to TEBC training. The changing trend of Syn immunoreactivity in the IN is associated with CR percentage.

Glial cell-derived neurotrophic factor alleviates sepsis-induced neuromuscular dysfunction by decreasing the expression of γ- and α7-nicotinic acetylcholine receptors in an experimental rat model of neuromyopathy

Sepsis-induced neuromuscular dysfunction results from up-regulation of the expression of γ- and α7-nicotinic acetylcholine receptors (nAChR). Although glial cell derived neurotrophic factor (GDNF) has been implicated in repairing and supporting neurons, little is known about the effects of GDNF on demyelination of nerves in sepsis. In this study, we tested the hypothesis that GDNF could alleviate sepsis-induced neuromuscular dysfunction by decreasing the expression of γ- and α7-nAChR in an experimental rat model of neuromyopathy. Rats were randomly divided into a sham group and a sepsis group. Levels of inflammatory factors, muscle function, and nicotinic acetylcholine receptors were tested in rats after cecal ligation and puncture (CLP). At 24 h after CLP, GDNF was injected around the sciatic nerve of sepsis rats, cytokines were detected by enzyme-linked immunosorbent assay (ELISA), and immunofluorescence staining was used to detect the expression of nAChRs. GDNF and its downstream effector (Erk1/2 and GFR-α), neuregulin-1 (NRG-1) and γ- and α7-nAChR were measured using Western blot analysis. The expression of GDNF reached a minimum at 24 h after CLP. Compared with the sham group, the release of cytokines and the expression of γ- and α7-nAChR were significantly increased in the sepsis group. The administration of GDNF significantly alleviated sepsis-induced neuromuscular dysfunction, as well as reducing the expression of γ- and α7-nAChR. In addition, the expression of Erk1/2, GFR-α, NRG-1 were significantly increased after GDNF treatment. GDNF administration may improve patient outcomes by reducing the demyelination of nerves and the expression of γ- and α7-nAChR.

To Contrast and Reverse Skeletal Muscle Atrophy by Full-Body In-Bed Gym, a Mandatory Lifestyle for Older Olds and Borderline Mobility-Impaired Persons

Older olds, that is octogenarians, spend small amounts of time for daily physical activity, contributing to aggravate their independence limitations up to force them to bed and to more and more frequent hospitalizations. All progressive muscle contractile impairments, including advanced age-related muscle power decline, need permanent management. Inspired by the proven capability to recover skeletal muscle contractility and strength by home-based functional electrical stimulation and guided by common sense, we suggested to older olds a 15-30 min daily routine of 12 easy and safe physical exercises. Since persons can do many of them in bed (full-body in-bed gym), hospitalized elderly can continue this kind of light training that is an extension of the well-established cardiovascular-ventilation rehabilitation before and after admission. Monitoring arterial blood pressure before and after the daily routine demonstrates that peripheral resistance decreases in a few minutes by the functional hyperemia of the trained body muscles. Continued regularly, full-body in-bed gym helps to maintain the independence of frail older people and may reduce the risks of serious consequences of accidental falls.

A Novel Electroactive Agarose-Aniline Pentamer Platform as a Potential Candidate for Neural Tissue Engineering

Neuronal disorder is an important health challenge due to inadequate natural regeneration, which has been responded by tissue engineering, particularly with conductive materials. A bifunctional electroactive scaffold having agarose biodegradable and aniline pentamer (AP) conductive parts was designed that exhibits appropriate cell attachment/compatibility, as detected by PC12 cell seeding. The developed carboxyl-capped aniline-pentamer improved agarose cell adhesion potential, also the conductivity of scaffold was in the order 10-5 S/cm reported for cell membrane. Electrochemical impedance spectroscopy was applied to plot the Nyquist graph and subsequent construction of the equivalent circuit model based on the neural model, exhibiting an appropriate cell signaling and an acceptable consistency between the components of the scaffold model with neural cell model. The ionic conductivity was also measured; exhibiting an enhanced ionic conductivity, but lower activation energy upon a temperature rise. Swelling behavior of the sample was measured and compared with pristine agarose; so that aniline oligomer due to its hydrophobic nature decreased water uptake. Dexamethasone release from the developed electroactive scaffold was assessed through voltage-responsive method. Proper voltage-dependent drug release could be rationally expected because of controllable action and elimination of chemically responsive materials. Altogether, these characteristics recommended the agarose/AP biopolymer for neural tissue engineering.

An update on addressing important peripheral nerve problems: challenges and potential solutions

From time to time it is thoughtful and productive to review a medical field and reflect upon what are the major issues that need to be addressed and what is being done to do so. This review article is not meant to be all-inclusive but rather focuses on four evolving areas in the field of peripheral nerve disorders and treatments: (1) nerve surgery under ultrasound guidance using a new ultra-minimally invasive thread technique; (2) evolving magnetic resonance imaging (MRI) and ultrasound imaging techniques that are helping to both diagnose and treat a variety of peripheral nerve problems including entrapment neuropathies, traumatic nerve injuries, and masses arising from nerves; (3) promoting recovery after nerve injury using electrical stimulation; and (4) developing animal models to reproduce a severe nerve injury (neurotmetic grade in continuity) that requires a surgical intervention and repair. In each area we first describe the current challenges and then discuss new and emerging techniques and approaches. It is our hope that this article will bring added attention and resources to help better address peripheral nerve problems that remain a challenge for both patients and physicians.

Differential deregulation of NGF and BDNF neurotrophins in a transgenic rat model of Alzheimer's disease

Evidence from human neuropathological studies indicates that the levels of the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are compromised in Alzheimer's disease. However, the causes and temporal (pathology-dependent) evolution of these alterations are not completely understood. To elucidate these issues, we investigated the McGill-R-Thy1-APP transgenic rat, which exhibits progressive intracellular and extracellular amyloid-beta (Aβ) pathology and ensuing cognitive deficits. Neurochemical analyses revealed a differential dysregulation of NGF and BDNF transcripts and protein expression. While BDNF mRNA levels were significantly reduced at very early stages of amyloid pathology, before plaques appeared, there were no changes in NGF mRNA expression even at advanced stages. Paradoxically, the protein levels of the NGF precursor were increased. These changes in neurotrophin expression are identical to those seen during the progression of Alzheimer's disease. At advanced pathological stages, deficits in the protease cascade controlling the maturation and degradation of NGF were evident in McGill transgenic rats, in line with the paradoxical upregulation of proNGF, as seen in Alzheimer's disease, in the absence of changes in NGF mRNA. The compromise in NGF metabolism and BDNF levels was accompanied by downregulation of cortical cholinergic synapses; strengthening the evidence that neurotrophin dysregulation affects cholinergic synapses and synaptic plasticity. Our findings suggest a differential temporal deregulation of NGF and BDNF neurotrophins, whereby deficits in BDNF mRNA appear at early stages of intraneuronal Aβ pathology, before alterations in NGF metabolism and cholinergic synapse loss manifest.

The Non-Survival Effects of Glial Cell Line-Derived Neurotrophic Factor on Neural Cells

Glial cell line-derived neurotrophic factor (GDNF) was first characterized as a survival-promoting molecule for dopaminergic neurons (DANs). Afterwards, other cells were also discovered to respond to GDNF not only as a survival factor but also as a protein supporting other cellular functions, such as proliferation, differentiation, maturation, neurite outgrowth and other phenomena that have been less studied than survival and are now more extendedly described here in this review article. During development, GDNF favors the commitment of neural precursors towards dopaminergic, motor, enteric and adrenal neurons; in addition, it enhances the axonal growth of some of these neurons. GDNF also induces the acquisition of a dopaminergic phenotype by increasing the expression of Tyrosine Hydroxylase (TH), Nurr1 and other proteins that confer this identity and promote further dendritic and electrical maturation. In motor neurons (MNs), GDNF not only promotes proliferation and maturation but also participates in regenerating damaged axons and modulates the neuromuscular junction (NMJ) at both presynaptic and postsynaptic levels. Moreover, GDNF modulates the rate of neuroblastoma (NB) and glioblastoma cancer cell proliferation. Additionally, the presence or absence of GDNF has been correlated with conditions such as depression, pain, muscular soreness, etc. Although, the precise role of GDNF is unknown, it extends beyond a survival effect. The understanding of the complete range of properties of this trophic molecule will allow us to investigate its broad mechanisms of action to accelerate and/or improve therapies for the aforementioned pathological conditions.

Laminin-111 enriched fibrin hydrogels for skeletal muscle regeneration

Laminin (LM)-111 supplementation has improved muscle regeneration in several models of disease and injury. This study investigated a novel hydrogel composed of fibrinogen and LM-111. Increasing LM-111 concentration (50-450 μg/mL) in fibrin hydrogels resulted in highly fibrous scaffolds with progressively thinner interlaced fibers. Rheological testing showed that all hydrogels had viscoelastic behavior and the Young's modulus ranged from 2-6KPa. C₂C₁₂ myobalsts showed a significant increase in VEGF production and decrease in IL-6 production on LM-111 enriched fibrin hydrogels as compared to pure fibrin hydrogels on day 4. Western blotting results showed a significant increase in MyoD and desmin protein quantity but a significant decrease in myogenin protein quantity in myoblasts cultured on the LM-111 (450 μg/mL) enriched fibrin hydrogel. Combined application of electromechanical stimulation significantly enhanced the production of VEGF and IGF-1 from myoblast seeded fibrin-LM-111 hydrogels. Taken together, these observations offer an important first step toward optimizing a tissue engineered constructs for skeletal muscle regeneration.

Nanoengineered porous chitosan/CaTiO3 hybrid scaffolds for accelerating Schwann cells growth in peripheral nerve regeneration

To further improve the property of promoting peripheral nerve regeneration of chitosan materials, CaTiO₃ nanoparticles with various concentrations were synthesized in chitosan (CS) solution and formed to porous CS/CaTiO₃ hybrid scaffolds. The properties including morphology, wettability, porosity, crystallization intensity and surface charges were characterized, respectively. The influence of the porous CS/CaTiO₃ hybrid scaffolds on Schwann cells growth was evaluated. The results showed that the CaTiO₃ hybridized CS scaffolds possessed homogeneous nanoparticles distribution with concentration-dependent effect. The hybridization of CaTiO₃ nanoparticles could increase the hydrophobicity while reduce the porosity and surface charge density of the porous CS/CaTiO₃ hybrid scaffolds The crystal structure of the hybridized scaffolds was mainly the orthorhombic structure of the calcium titanate accompanied by the amorphous phase of chitosan. Culture of Schwann cells indicated that the CS/CaTiO₃ hybrid scaffolds with a suitable concentration of CaTiO₃ nanoparticles could obviously promote the attachment, proliferation and biological function maintenance of Schwann cells, thus showing potentially great significance towards application in peripheral nerve regeneration.

Nerve stepping stone has minimal impact in aiding regeneration across long acellular nerve allografts

INTRODUCTION

Acellular nerve allografts (ANAs) yield less consistent favorable outcomes compared with autografts for long gap reconstructions. We evaluated whether a hybrid ANA can improve 6-cm gap reconstruction.

METHODS

Rat sciatic nerve was transected and repaired with either 6-cm hybrid or control ANAs. Hybrid ANAs were generated using a 1-cm cellular isograft between 2.5-cm ANAs, whereas control ANAs had no isograft. Outcomes were assessed by graft gene and marker expression (n = 4; at 4 weeks) and motor recovery and nerve histology (n = 10; at 20 weeks).

RESULTS

Hybrid ANAs modified graft gene and marker expression and promoted modest axon regeneration across the 6-cm defect compared with control ANA (P < 0.05), but yielded no muscle recovery. Control ANAs had no appreciable axon regeneration across the 6-cm defect.

DISCUSSION

A hybrid ANA confers minimal motor recovery benefits for regeneration across long gaps. Clinically, the authors will continue to reconstruct long nerve gaps with autografts. Muscle Nerve 57: 260-267, 2018.

Effect of Training Exercise on Urinary Brain-derived Neurotrophic Factor Levels and Cognitive Performances in Overweight and Obese Subjects

Exercise-mediated, brain-derived neurotrophic factor induction benefits health and cognitive functions. The multifaceted interplay between physical activity, urinary brain-derived neurotrophic factor levels and cognitive functioning has been largely neglected in previous literature. In this pilot study, two bouts of training exercise (65% and 70% of heart rate reserve) influenced urinary brain-derived neurotrophic factor levels and cognitive performances in 12 overweight and obese participants. Percent heart rate reserve, expenditure energy, brain-derived neurotrophic factor urinary levels and cognitive performances were measured before and after the exercise. No significant variations in energy expenditure were observed, while differences of heart rate reserve between two groups were maintained. Both bouts of training exercise induced a similar reduction in urinary brain-derived neurotrophic factor levels. Only visuo-spatial working memory capacity at 65% of heart rate reserve showed a significant increase. These findings indicate a consistent effect of training exercise on urinary brain-derived neurotrophic factor levels and cognitive factors in overweight and obese participants.

Use it or Lose It: Tonic Activity of Slow Motoneurons Promotes Their Survival and Preferentially Increases Slow Fiber-Type Groupings in Muscles of Old Lifelong Recreational Sportsmen

Histochemistry, immuno-histochemistry, gel electrophoresis of single muscle fibers and electromyography of aging muscles and nerves suggest that: i) denervation contributes to muscle atrophy, ii) impaired mobility accelerates the process, and iii) lifelong running protects against loss of motor units. Recent corroborating results on the muscle effects of Functional Electrical Stimulation (FES) of aged muscles will be also mentioned, but we will in particular discuss how and why a lifelong increased physical activity sustains reinnervation of muscle fibers. By analyzing distribution and density of muscle fibers co-expressing fast and slow Myosin Heavy Chains (MHC) we are able to distinguish the transforming muscle fibers due to activity related plasticity, to those that adapt muscle fiber properties to denervation and reinnervation. In muscle biopsies from septuagenarians with a history of lifelong high-level recreational activity we recently observed in comparison to sedentary seniors: 1. decreased proportion of small-size angular myofibers (denervated muscle fibers); 2. considerable increase of fiber-type groupings of the slow type (reinnervated muscle fibers); 3. sparse presence of muscle fibers co-expressing fast and slow MHC. Immuno-histochemical characteristics fluctuate from those with scarce fiber-type modulation and groupings to almost complete transformed muscles, going through a process in which isolated fibers co-expressing fast and slow MHC fill the gaps among fiber groupings. Data suggest that lifelong high-level exercise allows the body to adapt to the consequences of the age-related denervation and that it preserves muscle structure and function by saving otherwise lost muscle fibers through recruitment to different slow motor units. This is an opposite behavior of that described in long term denervated or resting muscles. These effects of lifelong high level activity seems to act primarily on motor neurons, in particular on those always more active, i.e., on the slow motoneurons. The preferential reinnervation that follows along decades of increased activity maintains neuron and myofibers. All together the results open interesting perspectives for applications of FES and electroceuticals for rejuvenation of aged muscles to delay functional decline and loss of independence that are unavoidable burdens of advanced aging.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01679977.