Methodological evaluation to analyze functional recovery after sciatic nerve injury

The Impact of Sciatic Nerve Injury on Extracellular Matrix of Lower Limb Muscle and Thoracolumbar Fascia: An Observational Study

Peripheral nerve injury (PNI) is a complex clinical challenge resulting in functional disability. Neurological recovery does not always ensure functional recovery, as extracellular matrix (ECM) alterations affect muscle function. This study evaluates hyaluronan (HA) and collagen concentration in the gastrocnemius muscle and thoracolumbar fascia (TLF) in unilateral lower limb PNI rats to explore systemic ECM alterations following PNI and their impacts on functional recovery. Eighteen 8-week-old male Sprague-Dawley rats were divided into experimental (n = 12 left sciatic nerve injury) and control (n = 6) groups. After six weeks, motor function was evaluated. Muscle and TLF samples were analysed for HA and collagen distribution and concentrations. SFI and gait analysis confirmed a functional deficit in PNI rats 6 weeks after surgery. HA concentration in both sides of the muscles decreased by approximately one-third; both sides showed significantly higher collagen concentration than healthy rats (12.74 ± 4.83 µg/g), with the left (32.92 ± 11.34 µg/g) significantly higher than the right (20.15 ± 7.03 µg/g). PNI rats also showed significantly lower HA (left: 66.95 ± 20.08 µg/g; right: 112.66 ± 30.53 µg/g) and higher collagen (left: 115.89 ± 28.18 µg/g; right: 90.43 ± 20.83 µg/g) concentrations in both TLF samples compared to healthy rats (HA: 167.18 ± 31.13 µg/g; collagen: 47.51 ± 7.82 µg/g), with the left TLF more affected. Unilateral lower limb PNI induced HA reduction and collagen accumulation in both the lower limb muscles and the TLF, potentially exacerbating motor function impairment and increasing the risk of low back dysfunctions.

Development and preclinical evaluation of bioactive nerve conduits for peripheral nerve regeneration: A comparative study

In severe peripheral nerve injuries, nerve conduits (NCs) are good alternatives to autografts/allografts; however, the results the available devices guarantee for are still not fully satisfactory. Herein, differently bioactivated NCs based on the new polymer oxidized polyvinyl alcohol (OxPVA) are compared in a rat model of sciatic nerve neurotmesis (gap: 5 mm; end point: 6 weeks). Thirty Sprague Dawley rats are randomized to 6 groups: Reverse Autograft (RA); Reaxon®; OxPVA; OxPVA + EAK (self-assembling peptide, mechanical incorporation); OxPVA + EAK-YIGSR (mechanical incorporation); OxPVA + Nerve Growth Factor (NGF) (adsorption). Preliminarily, all OxPVA-based devices are comparable with Reaxon® in Sciatic Functional Index score and gait analysis; moreover, all conduits sustain nerve regeneration (S100, β-tubulin) without showing substantial inflammation (CD3, F4/80) evidences. Following morphometric analyses, OxPVA confirms its potential in PNI repair (comparable with Reaxon®) whereas OxPVA + EAK-YIGSR stands out for its myelinated axons total number and density, revealing promising in injury recovery and for future application in clinical practice.

Effects of Low-Level Laser Therapy and Purified Natural Latex (Hevea brasiliensis) Protein on Injured Sciatic Nerve in Rodents: Morpho-Functional Analysis

The present study analyzed the effects of low-level laser therapy (LLLT) and the purified natural latex protein (Hevea brasiliensis, F1 protein) on the morpho-function of sciatic nerve crush injuries in rats. One-hundred and eight male Wistar rats were randomly allocated to six groups (n = 18): 1. Control; 2. Exposed (nerve exposed); 3. Injury (injured nerve without treatment); 4. LLLT (injured nerve irradiated with LLLT (15 J/cm2, 780 nm)); 5. F1 (injured nerve treated with F1 protein (0.1%)); and 6. LLLT + F1 (injured nerve treated with LLLT and F1). On the 1st, 7th, 14th, and 56th days after injury, a functional sensory analysis of mechanical allodynia and mechanical hyperalgesia and a motor analysis of grip strength and gait were performed. After 3, 15, and 57 days, the animals were euthanized for morphometric/ultrastructural analyses. The treatments applied revealed improvements in morphometric/ultrastructural parameters compared to the injured group. Sensory analyses suggested that the improvements observed were associated with time progression and not influenced by the treatments. Motor analyses revealed significant improvements in grip strength from the 7th day in the LLLT group and in gait from the 56th day in all treated groups. We concluded that even though the morphological analyses showed improvements with the treatments, they did not influence sensory recovery, and LLLT improved motor recovery.

Neuroregeneration of injured peripheral nerve by fraction B of catfish epidermal secretions through the reversal of the apoptotic pathway and DNA damage

Introduction: Crush injuries occur from acute traumatic nerve compression resulting in different degrees of neural damage leading to permanent functional deficits. Recently, we have shown that administration of Fraction B (FB) derived from catfish epidermal secretions accelerates healing of damaged nerve in a sciatic nerve crush injury, as it ameliorates the neurobehavioral deficits and enhances axonal regeneration, as well as protects spinal neurons and increases astrocytic activity and decreasing GAP-43 expression. The present study aimed to investigate the role of FB treatment on the apoptotic pathway in the neuroregeneration of the sciatic nerve crush injury. Methods: Male Wistar rats were randomly assigned into five groups: (I) SHAM, (II) CRUSH, (III) CRUSH + (1.5 mg/kg) FB, (IV) CRUSH + (3 mg/kg) FB, and (V) CRUSH + (4.5 mg/kg) FB. Rats underwent sciatic nerve crush surgery, followed by treatment with FB administered intraperitoneally (IP) daily for two weeks and then sacrificed at the end of the fourth week. Results: FB improved the recovery of neurobehavioral functions with a concomitant increase in axonal regeneration and neuroprotective effects on spinal cord neurons following crush injury. Further, FB enhanced Schwann cells (SCs) proliferation with a significant increase in myelin basic protein expression. FB-treated animals demonstrated higher numbers of neurons in the spinal cord, possibly through ameliorating oxidative DNA damage and alleviating the mitochondrial-dependent apoptotic pathway by inhibiting the release of cytochrome c and the activation of caspase-3 in the spinal cord neurons. Conclusion: FB alleviates the neurodegenerative changes in the lumbar spinal cord neurons and recovers the decrease in the neuronal count through its anti-apoptotic and DNA antioxidative properties.

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

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Analysis of Epineurial Lidocaine Injection for Nerve Transfers in a Rat Sciatic Nerve Model

PURPOSE

Nerve transfers for peripheral nerve injuries can result in variable outcomes. We investigated the neuroprotective effect of epineurial lidocaine injection in the donor nerve prior to transection, with the hypothesis that proximal axon loss would be decreased with consequent increased neuroregeneration and functional recovery.

METHODS

A rat sciatic nerve model was used with 4 intervention groups: (1) lidocaine; (2) lidocaine/calcium gluconate (CG); (3) CG; or (4) saline (control). Behavioral testing and qualitative and quantitative histological evaluation was performed at 8 and 12 weeks. Histological assays included transmission electron microscopy, retrograde fluorogold labeling, and whole mount immunostaining.

RESULTS

Functional assessments through the sciatic functional index and Basso, Beattie, and Bresnahan scale showed a statistically significant increase in recovery at 8 and 12 weeks with lidocaine treatment. Significantly higher axonal counts were obtained in the lidocaine-treated groups. Fragmentation and increased myelin damage was present in the CG and saline groups. Retrograde fluorogold labeling showed a statistically significant increase in the number of L4-6 dorsal root ganglion neurons in the lidocaine-treated groups. Whole mount immunostaining identified extension of the axonal growth cone past the nerve coaptation site in lidocaine-treated groups, but not in CG and saline groups.

CONCLUSIONS

Our results suggest that epineurial lidocaine injection prior to donor nerve transection for nerve transfer has a neuroprotective effect, resulting in increased proximal axon counts and improved functional recovery.

CLINICAL RELEVANCE

These findings may have direct clinical application because epineurial lidocaine can be used in surgery as a simple and inexpensive intervention for promoting improved clinical outcomes after nerve transfer.

Epineural adipose-derived stem cell injection in a sciatic rodent model

BACKGROUND

The aim was to evaluate the regenerative effect of epineural injection of rat ASCs (rASCs) in three different settings of acute and chronic compression in a rat sciatic nerve model.

METHODS

Acute compression (60 s) with a vessel clamp over a distance of 1 mm (group 1) or 10 mm (group 2), as well as chronic compression with a permanent remaining, nonabsorbable polymeric clip over a distance of 1 mm (group 3) was performed. Depending on the group, either 5 × 106 rASCs or the same volume (25 μl) of culture medium (CM) was injected with a 30G needle in the epineurium at the time of compression. Outcome measures were functional gait evaluations, imaging analysis, histomorphometric analyses, and muscle weight.

RESULTS

The rats in group 2 had a better function than those with group 1 at one and especially at 2 weeks. After 4 weeks however, almost all rats were close to a normal function. There was a similar Muscle Weight Ratio (MWR) after 2 weeks in all groups, whereas after 4 weeks, the MWR in group 3 was lower compared with group 1 and 2. Histomorphometric analysis showed a better myelination in group 1 & 2 compared to group 3 after 4 weeks. ASCs have a beneficial effect on myelin thickness (G-Ratio).

CONCLUSIONS

We successfully evaluated the regenerative effect of epineural injection of rASCs in three different settings of acute and chronic compression. However, there were no significant differences in outcomes between the ASC-treated groups and control groups.

Partially oxidized polyvinyl alcohol conduitfor peripheral nerve regeneration

Surgical reconstruction of peripheral nerves injuries with wide substance-loss is still a challenge. Many studies focused on the development of artificial nerve conduits made of synthetic or biological materials but the ideal device has not yet been identified. Here, we manufactured a conduit for peripheral nerve regeneration using a novel biodegradable hydrogel we patented that is oxidized polyvinyl alcohol (OxPVA). Thus, its characteristics were compared with neat polyvinyl alcohol (PVA) and silk-fibroin (SF) conduits, through in vitro and in vivo analysis. Unlike SF, OxPVA and neat PVA scaffolds did not support SH-SY5Y adhesion and proliferation in vitro. After implantation in rat model of sciatic nerve transection, the three conduits sustained the regeneration of the injured nerve filling a gap of 5 mm in 12 weeks. Implanted animals showed a good gait recovery. Morphometric data related to the central portion of the explanted conduit interestingly highlighted a significantly better outcome for OxPVA scaffolds compared to PVA conduits in terms of axon density, also with respect to the autograft group. This study suggests the potential of our novel biomaterial for the development of conduits for clinical use in case of peripheral nerve lesions with substance loss.

Evaluation of a Nerve Fusion Technique With Polyethylene Glycol in a Delayed Setting After Nerve Injury

PURPOSE

Polyethylene glycol (PEG) has been hypothesized to restore axonal continuity using an in vivo rat sciatic nerve injury model when nerve repair occurs within minutes after nerve injury. We hypothesized that PEG could restore axonal continuity when nerve repair was delayed.

METHODS

The left sciatic nerves of female Sprague-Dawley rats were transected and repaired in an end-to-end fashion using standard microsurgical techniques at 3 time points (1, 8, and 24 hours) after injury. Polyethylene glycol was delivered to the neurorrhaphy in the experimental group. Post-repair compound action potentials were immediately recorded after repair. Animals underwent behavioral assessments at 3 days and 1 week after surgery using the sciatic functional index test. The animals were sacrificed at 1 week to obtain axon counts.

RESULTS

The PEG-treated nerves had improved compound action potential conduction and animals treated with PEG had improved sciatic function index. Compound action potential conduction was restored in PEG-fused rats when nerves were repaired at 1, 8, and 24 hours. In the control groups, no compound action potential conduction was restored when nerves were repaired. Sciatic functional index was superior in PEG-fused rats at 3 and 7 days after surgery compared with control groups at all 3 time points of nerve repair. Distal motor and sensory axon counts were higher in the PEG-treated rats.

CONCLUSIONS

Polyethylene glycol fusion is a new adjunct for nerve repair that allows rapid restoration of axonal continuity. It effective when delayed nerve repair is performed.

CLINICAL RELEVANCE

Nerve repair with application of PEG is a potential therapy that may have efficacy in a clinical setting. It is an experimental therapy that needs more investigation as well as clinical trials.

Nrf2 and NF-κB modulation by Plumbagin attenuates functional, behavioural and biochemical deficits in rat model of neuropathic pain

BACKGROUND

Plumbagin is known to exhibit a broad range of biological activities including anti-cancer, antimicrobial and has been widely used traditionally. Nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) inhibitory and Nuclear factor (erythroid derived-2) like-2 (Nrf2) modulatory activities of Plumbagin have been reported already. In nerve injury model of neuropathy in rats, the role of NF-κB upregulation and declined antioxidant defence has been well recognized. So, we evaluated neuroprotective potential of Plumbagin in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in male Sprague-Dawley rats.

METHODS

Animals were tested for functional, behavioural and biochemical changes. Various markers associated with oxidative stress and inflammatory changes were assessed in the sciatic nerve and dorsal root ganglion (DRG) of the animals exposed to CCI mediated nerve injury.

RESULTS

CCI induced nerve injury led to long-lasting mechanical hyperalgesia, loss of hind limb function and abnormal pain sensation. Plumbagin treatment (10 and 20mg/kg, po) significantly and dose-dependently reversed mechanical hyperalgesia and other functional deficits. There was a marked increase in NF-κB and reduced Nrf2 levels in sciatic nerve and DRG following nerve injury. Plumbagin strengthened the antioxidant defence by improving Nrf2 levels and checked the neuroinflammation by decreasing NF-κB levels in sciatic nerve and DRG.

CONCLUSIONS

Together, these results suggested that Plumbagin alleviated CCI-induced neuropathic pain via antioxidant and anti-inflammatory mechanisms. Hence, the study suggests that Plumbagin may be useful for the management of trauma-induced neuropathic pain.

Analysis of the variation in low-level laser energy density on the crushed sciatic nerves of rats: a morphological, quantitative, and morphometric study

The objective of this study was to evaluate three energy densities of low-level laser therapy (LLLT, GaAlAs, 780 nm, 40 mW, 0.04 cm²) for the treatment of lesions to peripheral nerves using the sciatic nerve of rats injured via crushing model (15 kgf, 5.2 MPa). Thirty Wistar rats (♂, 200-250 g) were divided into five groups (n = 6): C-control, not injured, and irradiated; L0-injured nerve without irradiation; L4-injured nerve irradiated with LLLT 4 J/cm² (0.16 J); L10-injured nerve irradiated with LLLT 10 J/cm² (0.4 J); and L50-injured nerve irradiated with LLLT 50 J/cm² (2 J). The animals were sacrificed 2 weeks after the injury via perfusion with glutaraldehyde (2.5%, 0.1 M sodium cacodylate buffer). The nerve tissue was embedded in historesin, cut (3 μm), mounted on slides, and stained (Sudan black and neutral red). The morphological and quantitative analysis (myelin and blood capillary densities) and morphometric parameters (maximum and minimum diameters of nerve fibers, axon diameter, G-ratio, myelin sheath thickness) were assessed using the ImageJ software. ANOVA (parametric) or Kruskal-Wallis (nonparametric) tests were used for the statistical analysis. Groups L0, L4, L10, and L50 exhibited diminished values of all the quantitative and morphometric parameters in comparison to the control group. The morphological, quantitative, and morphometric data revealed improvement after injury in groups L4, L10, and L50 (irradiated groups) compared to the injured-only group (L0); the best results, in general, were observed for the L10 group after 15 days of nerve injury.

Brain injury in combination with tacrolimus promotes the regeneration of injured peripheral nerves

Both brain injury and tacrolimus have been reported to promote the regeneration of injured peripheral nerves. In this study, before transection of rat sciatic nerve, moderate brain contusion was (or was not) induced. After sciatic nerve injury, tacrolimus, an immunosuppressant, was (or was not) intraperitoneally administered. At 4, 8 and 12 weeks after surgery, Masson's trichrome, hematoxylin-eosin, and toluidine blue staining results revealed that brain injury or tacrolimus alone or their combination alleviated gastrocnemius muscle atrophy and sciatic nerve fiber impairment on the experimental side, simultaneously improved sciatic nerve function, and increased gastrocnemius muscle wet weight on the experimental side. At 8 and 12 weeks after surgery, brain injury induction and/or tacrolimus treatment increased action potential amplitude in the sciatic nerve trunk. Horseradish peroxidase retrograde tracing revealed that the number of horseradish peroxidase-positive neurons in the anterior horn of the spinal cord was greatly increased. Brain injury in combination with tacrolimus exhibited better effects on repair of injured peripheral nerves than brain injury or tacrolimus alone. This result suggests that brain injury in combination with tacrolimus promotes repair of peripheral nerve injury.

Effect of Frankincense Extract on Nerve Recovery in the Rat Sciatic Nerve Damage Model

This study investigated the effect of frankincense extract on peripheral nerve regeneration in a crush injury rat model. Forty-eight Sprague-Dawley rats were randomly divided into four groups: control and frankincense extract low-, medium-, and high-dose groups. At days 7, 14, 21, and 28 following the surgery, nerve regeneration and functional recovery were evaluated using the sciatic functional index (SFI), expression of GAP-43, and the proliferation of Schwann cells (SCs) in vivo and in vitro. At day 7, the SFI in the frankincense extract high-dose group was significantly improved compared with the control group. After day 14, SFI was significantly improved in the medium- and high-dose groups. There was no significant difference in GAP-43 expression among the groups at day 7. However, after day 14, expression of GAP-43 in the high-dose group was higher than that in the control group. Histological evaluation showed that the injured nerve of frankincense extract high-dose group recovered better than the other groups 28 days after surgery. Further, S100 immunohistochemical staining, MTT colorimetry, and flow cytometry assays all showed that frankincense extract could promote the proliferation of SCs. In conclusion, frankincense extract is able to promote sciatic nerve regeneration and improve the function of a crushed sciatic nerve. This study provides a new direction for the repair of peripheral nerve injury.

Netrin-1 overexpression in bone marrow mesenchymal stem cells promotes functional recovery in a rat model of peripheral nerve injury

Transplantation of bone marrow mesenchymal stem cells (BMSCs) has been developed as a new method of treating diseases of the peripheral nervous system. While netrin-1 is a critical molecule for axonal path finding and nerve growth, it may also affect vascular network formation. Here, we investigated the effect of transplanting BMSCs that produce netrin-1 in a rat model of sciatic nerve crush injury. We introduced a sciatic nerve crush injury, and then injected 1×10(6) BMSCs infected by a recombinant adenovirus expressing netrin-1 Ad5-Netrin-1-EGFP or culture medium into the injured part in the next day. At day 7, 14 and 28 after injection, we measured motor nerve conduction and detected mRNA expressions of netrin-1 receptors UNC5B and Deleted in Colorectal Cancer (DCC), and neurotrophic factors brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) by real-time PCR. We also detected protein expressions of BDNF and NGF by Western blotting assays and examined BMSCs that incorporated into myelin and vascellum. The results showed that BMSCs infected by Ad5-Netrin-1-EGFP significantly improved the function of the sciatic nerve, and led to increased expression of BDNF and NGF (P<0.05). Moreover, 28 days after injury, more Schwann cells were found in BMSCs infected by Ad5-Netrin-1-EGFP compared to control BMSCs. In conclusion, transplantation of BMSCs that produce netrin-1 improved the function of the sciatic nerve after injury. This method may be a new treatment of nerve injury.

Seawater immersion aggravates sciatic nerve injury in rats

The aim of the present study was investigate the impact of seawater immersion on peripheral nerve injury and the underlying mechanisms. A total of 234 specific pathogen-free Sprague-Dawley male rats were randomly divided into a sham group, injury control group and seawater immersion + injury group. The Sciatic Functional Index (SFI) was used to assess nerve function for 6 weeks after injury. Compound muscle action potentials were measured and hematoxylin and eosin (H&E) staining of nerve specimens was carried out at week 6. Levels of reactive oxygen species (ROS) and malondialdehyde (MDA) in nerve tissues were measured by enzyme-linked immunosorbent assay (ELISA), and the expression levels of inducible nitric oxide synthase (iNOS) mRNA and protein were measured by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry, respectively. The SFI value in the seawater immersion + injury group after 6 weeks was lower than that in the injury control group (P<0.05). The compound muscle action potential in the seawater immersion + injury group had a prolonged latency, and the amplitude and nerve conduction velocity were decreased compared with those in the other groups (P<0.05). H&E staining demonstrated that nerve fiber regeneration was worse in the seawater immersion + injury group. The ROS and MDA levels in the seawater immersion + injury group were higher than those in the other groups (P<0.05). The expression levels of iNOS mRNA and protein gradually increased in the injury and seawater immersion + injury groups and peaked at 48 h after surgery. Immersion in seawater further aggravated sciatic nerve injury and led to worse neuronal recovery. The mechanism may be associated with oxidative stress.

Craniocerebral injury promotes the repair of peripheral nerve injury

The increase in neurotrophic factors after craniocerebral injury has been shown to promote fracture healing. Moreover, neurotrophic factors play a key role in the regeneration and repair of peripheral nerve. However, whether craniocerebral injury alters the repair of peripheral nerve injuries remains poorly understood. Rat injury models were established by transecting the left sciatic nerve and using a free-fall device to induce craniocerebral injury. Compared with sciatic nerve injury alone after 6–12 weeks, rats with combined sciatic and craniocerebral injuries showed decreased sciatic functional index, increased recovery of gastrocnemius muscle wet weight, recovery of sciatic nerve ganglia and corresponding spinal cord segment neuron morphologies, and increased numbers of horseradish peroxidase-labeled cells. These results indicate that craniocerebral injury promotes the repair of peripheral nerve injury.

Green tea pain modulating effect in sciatic nerve chronic constriction injury rat model

We investigated the effect of green tea (GT) in unilateral chronic constriction injury (CCI) to the rat scaitic nerve. Five groups (n = 6 rats/group) sham group: rats which underwent operation but with no ligation to the scaitic nerve, and received tap water for two weeks before and for five weeks after the surgery. Four experimental groups underwent CCI to the right sciatic nerve, divided randomly as follows: group E were given tap water throughout the study. Group B received GT before and after CCI. Group C was given GT following CCI. Group D received GT for two weeks prior to CCI. Groups which consumed GT showed significant improvement in the toe spread (P < 0.001) and foot positioning (P < 0.001) tests compared to the experimental control group. In addition, these groups showed a significant decrease in the behavioral mechanical hyperalgesia (P < 0.0001) and allodynia (P < 0.0002). Consumption of GT improves both reflexes and sensation which are often affected in the course of peripheral neuropathy.

A standardized method to create peripheral nerve injury in dogs using an automatic non-serrated forceps

This study describes a method that not only generates an automatic and standardized crush injury in the skull base, but also provides investigators with the option to choose from a range of varying pressure levels. We designed an automatic, non-serrated forceps that exerts a varying force of 0 to 100 g and lasts for a defined period of 0 to 60 seconds. This device was then used to generate a crush injury to the right oculomotor nerve of dogs with a force of 10 g for 15 seconds, resulting in a deficit in the pupil-light reflex and ptosis. Further testing of our model with Toluidine-blue staining demonstrated that, at 2 weeks post-surgery disordered oculomotor nerve fibers, axonal loss, and a thinner than normal myelin sheath were visible. Electrophysiological examination showed occasional spontaneous potentials. Together, these data verified that the model for oculomotor nerve injury was successful, and that the forceps we designed can be used to establish standard mechanical injury models of peripheral nerves.

Hydrophilic polymers enhance early functional outcomes after nerve autografting

BACKGROUND

Approximately 12% of operations for traumatic neuropathy are for patients with segmental nerve loss, and less than 50% of these injuries obtain meaningful functional recovery. Polyethylene glycol (PEG) therapy has been shown to improve functional outcomes after nerve severance, and we hypothesized this therapy could also benefit nerve autografting.

METHODS

We used a segmental rat sciatic nerve injury model in which we repaired a 0.5-cm defect with an autograft using microsurgery. We treated experimental animals with solutions containing methylene blue (MB) and PEG; control animals did not receive PEG. We recorded compound action potentials (CAPs) before nerve transection, after solution therapy, and at 72 h postoperatively. The animals underwent behavioral testing at 24 and 72 h postoperatively. After we euthanized the animals, we fixed the nerves, sectioned and immunostained them to allow for quantitative morphometric analysis.

RESULTS

The introduction of hydrophilic polymers greatly improved morphological and functional recovery of rat sciatic axons at 1-3 d after nerve autografting. Polyethylene glycol therapy restored CAPs in all animals, and CAPs were still present 72 h postoperatively. No CAPS were detectable in control animals. Foot Fault asymmetry scores and sciatic functional index scores were significantly improved for PEG therapy group at all time points (P < 0.05 and P < 0.001; P < 0.001 and P < 0.01). Sensory and motor axon counts were increased distally in nerves treated with PEG compared with control (P = 0.019 and P = 0.003).

CONCLUSIONS

Polyethylene glycol therapy improves early physiologic function, behavioral outcomes, and distal axonal density after nerve autografting.

High voltage pulsed current stimulation of the sciatic nerve in rats: analysis by the SFI

Objective

To analyze the efficiency of high voltage pulsed current (HVPC) with early application in three different sites, in the regeneration of the sciatic nerve in rats submitted to crush injury, the sciatic functional index (SFI) was used to assess the functional recovery.

Methods

After crushing of the nerve, 57 animals were submitted to cathodal HVPC at frequency of 50Hz and voltage of 100V, 20 minutes per day, 5 days per week. The rats were divided into five groups: control group; ganglion group; ganglion + muscle group; muscle group; and sham group. The SFI was determined weekly for seven weeks, from the preoperative period to the 6^th postoperative week.

Results

Compared with the control group, the results showed a significantly better performance of group 2 for the first 3 weeks; group 3 showed significantly better performance in the third week; and group 4 showed a significantly negative performance during the 4^th and 6^th weeks.

Conclusion

Early application of HVPC had a positive effect in the treatment of the spinal cord region and the sciatic nerve root ganglion with a dispersive electrode on the contralateral lumbar region or on the gastrocnemius. However, HVPC had a negative effect in the treatment with an active electrode on the gastrocnemius and a dispersive electrode on the contralateral thigh. Level of evidence II, Prospective comparative study.

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

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

A novel motion analysis approach reveals late recovery in C57BL/6 mice and deficits in NCAM-deficient mice after sciatic nerve crush

Assessment of motor abilities after sciatic nerve injury in rodents, in particular mice, relies exclusively on walking track (footprint) analysis despite known limitations of this method. Using principles employed recently for video-based motion analyses after femoral nerve and spinal cord injuries, we have designed and report here a novel approach for functional assessments after sciatic nerve lesions in mice. Functional deficits are estimated by angle and distance measurements on single video frames recorded during beam-walking and inclined ladder climbing. Analyses of adult C57BL/6J mice after crush of the sciatic, tibial, or peroneal nerve allowed the identification of six numerical parameters, detecting impairments of the plantar flexion of the foot and the toe spread. Some of these parameters, as well as footprint functional indices, revealed severe impairment after crush injury of the sciatic or tibial, but not the peroneal nerve, and complete recovery within 3 weeks after lesion. Other novel estimates, however, showed that complete recovery is reached as late as 2-3 months after sciatic nerve crush. These measures detected both tibial and peroneal dysfunction. In contrast to the complete restoration of function in wild-type mice (100%), our new parameters, in contrast to the sciatic functional index, showed incomplete recovery (85%) 90 days after sciatic nerve crush in mice deficient in the neural cell adhesion molecule (NCAM). We conclude that the novel video-based approach is more precise, sensitive, and versatile than established tests, allowing objective numerical assessment of different motor functions in a sciatic nerve injury paradigm in mice.

Plasticity of nodose ganglion neurons after capsaicin- and vagotomy-induced nerve damage in adult rats

Previous reports show that vagal afferent innervation of the stomach eventually regenerates from surviving nodose ganglion (NG) neurons after subdiaphragmatic vagotomy. Systemic capsaicin treatment destroys gastric vagal afferent neurons expressing vanilloid receptor 1 (VR1). However, it is not known whether gastric innervation lost after neuronal destruction can be restored. Here, we report that capsaicin-induced damage of NG neurons innervating the stomach in adult rats is followed by restoration of vagal afferent projections. Specifically, we compared measures of neuronal plasticity in NG and vagi after subdiaphragmatic vagotomy or capsaicin treatment. The numbers of VR1-immunoreactive neurons projecting to the stomach were significantly reduced 10 days after either capsaicin treatment or vagotomy. However, the VR1-immunoreactive afferent innervation of the stomach was restored to levels exceeding those of vagotomized rats by 37 days after capsaicin, whereas neither total afferent innervation nor VR1-immunoreactive innervation reached control levels, even by 67 days after vagotomy. Capsaicin treatment significantly increased NG neuronal nitric oxide synthase (nNOS) immunoreactivity at 10 days after capsaicin, and this increase was sustained for the duration of the study, indicating higher nNOS demand in restoration of vagal projections. Vagotomy was associated with a much smaller increase in the number of nNOS-immunoreactive NG neurons, detectable only at 10 days after surgery. The number of nNOS-immunopositive gastric-projecting neurons was dramatically reduced 10 days after either capsaicin treatment or vagotomy but returned to the control level in both groups at 67 days. We found a significantly higher number of growth cones in capsaicin-treated animals compared with controls. Capsaicin significantly increased the number of nNOS-immunopositive and nNOS-immunonegative growth cones in NG at all time points. Vagotomy did not increase the number of nNOS(-) growth cones in NG. We conclude that capsaicin treatment may result in more significant restorative capacities than vagotomy, mainly because of sprouting of capsaicin-insensitive nerve fibers.

Muscle mitochondrial uncoupling dismantles neuromuscular junction and triggers distal degeneration of motor neurons

Background

Amyotrophic lateral sclerosis (ALS), the most frequent adult onset motor neuron disease, is associated with hypermetabolism linked to defects in muscle mitochondrial energy metabolism such as ATP depletion and increased oxygen consumption. It remains unknown whether muscle abnormalities in energy metabolism are causally involved in the destruction of neuromuscular junction (NMJ) and subsequent motor neuron degeneration during ALS.

Methodology/Principal Findings

We studied transgenic mice with muscular overexpression of uncoupling protein 1 (UCP1), a potent mitochondrial uncoupler, as a model of muscle restricted hypermetabolism. These animals displayed age-dependent deterioration of the NMJ that correlated with progressive signs of denervation and a mild late-onset motor neuron pathology. NMJ regeneration and functional recovery were profoundly delayed following injury of the sciatic nerve and muscle mitochondrial uncoupling exacerbated the pathology of an ALS animal model.

Conclusions/Significance

These findings provide the proof of principle that a muscle restricted mitochondrial defect is sufficient to generate motor neuron degeneration and suggest that therapeutic strategies targeted at muscle metabolism might prove useful for motor neuron diseases.

Activity cage as a method to analyze functional recovery after sciatic nerve injury in mice

The aim of this paper is to show the activity cage as a viable method for tracking functional nerve recovery. The activity cage measures spontaneous coordinate activity, meaning movement in either the horizontal or vertical plane, of experimental animals within a specified amount of time. This uses a minimum of researcher time conducting functional testing to determine functional recovery of the nerve. Using microsurgical forceps, a crush injury was inflicted unilaterally, on the left side, upon the 4-month-old C3H mice creating a very high degree of pressure for 6 s upon the exposed sciatic nerve. The locomotion function of the mice was evaluated using the activity cage preoperatively, 1, 7, 14, 21, and 28 days after the surgical procedure. We found that using the activity cage functional recovery occurred by 14 days after nerve crush injury. It was also shown that, coinciding with functional recovery, immunohistochemistry changes for GD1a and nNOS appeared at the level of L4, where the sciatic nerve joins the spinal column. GD1a and nNOS have both been linked to regenerative processes in mammalian nervous systems.

In peripheral nerve regeneration environment enriched with activity stimulating factors improves functional recovery

Enriched environment stimulates brain plasticity processes after brain lesion. Less is known about the influence of enriched environment with activity stimulating factors as determinants of functional outcome after peripheral nerve repair. BDNF (brain-derived neurotrophic factor) plays a role in activity-dependent neuronal plasticity and changes in motor cortex in rats learning complex motor skills. Our study aimed to elucidate if enriched environment influences functional results after peripheral nerve repair. The results in this rat sciatic nerve transection and repair model showed that environment enriched with activity stimulating factors can improve functional results.

Reinnervation of the tibialis anterior following sciatic nerve crush injury: a confocal microscopic study in transgenic mice

Transgenic mice whose axons and Schwann cells express fluorescent chromophores enable new imaging techniques and augment concepts in developmental neurobiology. The utility of these tools in the study of traumatic nerve injury depends on employing nerve models that are amenable to microsurgical manipulation and gauging functional recovery. Motor recovery from sciatic nerve crush injury is studied here by evaluating motor endplates of the tibialis anterior muscle, which is innervated by the deep peroneal branch of the sciatic nerve. Following sciatic nerve crush, the deep surface of the tibialis anterior muscle is examined using whole mount confocal microscopy, and reinnervation is characterized by imaging fluorescent axons or Schwann cells (SCs). One week following sciatic crush injury, 100% of motor endplates are denervated with partial reinnervation at 2 weeks, hyperinnervation at 3 and 4 weeks, and restoration of a 1:1 axon to motor endplate relationship 6 weeks after injury. Walking track analysis reveals progressive recovery of sciatic nerve function by 6 weeks. SCs reveal reduced S100 expression within 2 weeks of denervation, correlating with regression to a more immature phenotype. Reinnervation of SCs restores S100 expression and a fully differentiated phenotype. Following denervation, there is altered morphology of circumscribed terminal Schwann cells demonstrating extensive process formation between adjacent motor endplates. The thin, uniformly innervated tibialis anterior muscle is well suited for studying motor reinnervation following sciatic nerve injury. Confocal microscopy may be performed coincident with other techniques of assessing nerve regeneration and functional recovery.

A new approach to assess function after sciatic nerve lesion in the mouse—Adaptation of the sciatic static index

Among the numerous ways of assessing regeneration after peripheral nerve lesions, the analysis of gait is one of the most important, because it shows the recovery of function, which is the ultimate goal of the repair machinery. The sciatic function index was introduced as a method to assess reinnervation after an experimental sciatic nerve lesion, and was adapted to the mouse model. The sciatic static index (SSI), is more simple and practical to perform, and is not so influenced by gait's velocity, but this method has not yet been adapted to the mouse model of sciatic lesion. We used 63 male Swiss mice (Mus musculus) to develop a formula to the sciatic static index in mice (SSIm). The animals were divided on three groups (control, transection and crush). They were evaluated at the preoperative and 7th, 14th, 21st, 28th, 35th and 42nd days postoperative by the ink track method (SFI), and by the acquisition of photographs of the plantar aspects of the injured and uninjured hind paws. The parameters evaluated were the 1-5 toe spread (TS), the 2-4 toe spread (ITS) and the distance between the tip of the third toe and the most posterior aspect of the paw (PL), on both methods. After verifying the temporal pattern of function, correlation and reproducibility of the measurements, we performed a multiple regression analysis using SFI values as dependent variable, and the TS, ITS and PL measured with the photo method as independent variables, and found the formula of the SSI for mice (SSIm). The three groups (control, transection and crush) had a characteristic pattern of dysfunction. The parameters measured in the ink and photo method had variable but significant correlations between them (P<0.000), but photo method of measurement showed a better reproducibility. The correlation between SFI and SSIm showed a high correlation coefficient (r=0.892, P<0.000), and demonstrates that SSIm can be used as an alternative method to assess the functional status relative of sciatic nerve activity in mice.

Índice funcional do ciático nas lesões por esmagamento do nervo ciático de ratos. Avaliação da reprodutibilidade do método entre examinadores

Foi avaliada a reprodutibilidade inter-pessoal do método de avaliação do Índice Funcional do Ciático (IFC), medido por um programa de computação desenvolvido para este fim. Foram empregados 20 ratos Wistar, cujo nervo ciático direito era abordado sob anestesia geral e esmagado num segmento de 5 mm proximal à sua trifurcação com um dispositivo especial, com carga fixa de 5 Kg por 10 minutos. Impressões das pegadas dos animais foram obtidas na fase pré-operatória e, depois, semanalmente, da 1ª à 8ª semana, em uma pista de marcha. As impressões eram digitalizadas, armazenadas e avaliadas, pela medida de parâmetros predeterminados, por quatro examinadores, seguindo sempre a mesma seqüência de marcação dos parâmetros. Os resultados foram submetidos a análise estatística, que mostrou haver um alto índice de correlação entre examinadores na avaliação pré-operatória e nas 3a, 4a, 5a, 7a e 8a semanas (igual ou maior que 0,82), com queda casual na 6a semana, mas manteve significante como as demais (pF<0,01). Na 1a e 2a semanas, o índice de correlação foi próximo de zero, mostrando a pouca reprodutibilidade do método nesse período, em que a variabilidade entre os animais não diferiu da variabilidade entre os examinadores (p=0,24 e 0,32, respectivamente), devido à pouca definição das impressões das pegadas.

Choosing the correct functional assay: A comprehensive assessment of functional tests in the rat

While there are several ways to quantify peripheral nerve regeneration; the true measure of successful outcome is functional recovery. Functional tests are relatively easily conducted in human subjects; however it is more difficult in a laboratory animal. The laboratory rat is an excellent animal model of peripheral nerve injury and has been used extensively in the field of peripheral nerve research. Due to the intense interest in the rat as an experimental model, functional assays have been reported. In an effort to provide a resource to which investigators can refer when considering the most appropriate functional assay for a given experiment, the authors have compiled and tabulated the available functional tests applicable to various models of rat nerve injury.

Contralateral cytokine gene induction after peripheral nerve lesions: dependence on the mode of injury and NMDA receptor signaling

There is increasing evidence that unilateral nerve injury evokes contralateral responses, but the underlying mechanisms are largely unknown. In the present investigation, we analyzed cytokine and chemokine gene induction in contralateral, non-lesioned nerves after sciatic nerve crush and chronic constriction injury (CCI) by quantitative reverse transcriptase polymerase chain reaction in mice. After sciatic nerve crush, contralateral changes in cytokine gene expression were restricted to interleukin (IL)-1beta, which showed a monophasic peak at the first postoperative day. Following CCI, contralateral transcripts for IL-1beta, IL-10 and monocyte chemoattractant protein-1 (MCP-1) were significantly increased already at day 1 and upregulation persisted over the next 4 weeks. In contrast, tumor necrosis factor alpha (TNF-alpha) levels remained unchanged. Contralateral gene induction was restricted to the homonymous opposite sciatic nerve, but spared the femoral nerve. NMDA receptor blockade completely abolished contralateral cytokine expression after CCI on the mRNA level. In contralateral dorsal root ganglia, only IL-10 mRNA levels were modified after nerve injury. Sham operation significantly increased the cytokine and chemokine gene expression at the ipsilateral side, but could not mediate contralateral effects. Our study confirms that nerve injury evokes contralateral responses and identifies NMDA-mediated signaling as one underlying mechanism.