Peripheral Nerve Regeneration In Rats Research Articles

Neuregulin 1 isoforms could be an effective therapeutic candidate to promote peripheral nerve regeneration.

Traumatic injuries of peripheral nerves represent common casualties and their social impact is considerably high. Although peripheral nerves retain a good regeneration potential, the clinical outcome after nerve lesion is far from being satisfactory and functional recovery is almost never complete, especially in the case of large nerve defects, that result in loss or diminished sensitivity and/or motor activity of the innervated target organs. Therefore, to improve the outcome after nerve damage, or in peripheral neuropathies, there is a need for further research in nerve repair and regeneration to identify factors that promote axonal regrowth, remyelination and target reinnervation. Among the different factors involved in these processes (Taveggia et al., 2010; Pereira et al., 2012), stands out neuregulin 1 (NRG1), a factor which plays a role both in the myelination occurring during development (Lemke, 2006) and in the response to peripheral nerve injury (Syed and Kim, 2010; Fricker and Bennett, 2011). NRG1 is a pleiotropic factor characterized by the existence of numerous isoforms arising from alternative splicing of exons that confer to the protein with deeply different characteristics (Falls, 2003; Mei and Xiong, 2008). NRG1 can be produced as a secreted or as a transmembrane protein ready to interact with its receptor, or as a transmembrane pro-protein that needs a proteolytic cleavage to release a soluble fragment or to protrude its receptor binding domain in the extracellular environment (Figure 1). According to its structure, NRG1 signals in a paracrine, autocrine or juxtacrine manner; moreover, juxtacrine interactions can signal both in a forward and reverse manner due to the production of a fragment containing the intracellular domain (ICD, Figure 1B) that can translocate into the nucleus and influence gene transcription (Bao et al., 2003; Bao et al., 2004; Chen et al., 2010). NRG1 interacts directly with two of the four members of the tyrosine kinase receptor family ErbB: ErbB4, that signals as homo or heterodimer, and ErbB3, that forms a heterodimer with ErbB2. Figure 1 Structure of soluble or transmembrane neuregulin 1 (NRG1) isoforms. In the peripheral nervous system, NRG1 soluble isoforms are mainly released by Schwann cells, while transmembrane isoforms are mainly expressed by the axon and both interact with the heterodimer receptor ErbB2-ErbB3, generally expressed by Schwann cells. NRG1 plays an important role both in the myelination occurring during development and in the different phases occurring after injury in the peripheral nerve: axon degeneration, axon regrowth, remyelination and target reinnervation (Taveggia et al., 2010; Fricker and Bennett, 2011; Pereira et al., 2012; Salzer, 2012; Gambarotta et al., 2013; Heermann and Schwab, 2013). These processes respond to different cues, as can be inferred from the analysis of transgenic mice models summarized in Figure 2. The difference between the myelination process occurring during development and the regeneration process occurring after nerve injury is underlined by the fact that soluble NRG1 isoforms play an important role after nerve injury, while their lack seems irrelevant during development. Figure 2 The role played by soluble and transmembrane neuregulin 1 (NRG1) isoforms in the myelination occurring during development and in the different phases occurring after nerve injury (axon degeneration, axon regeneration, remyelination and target reinnervation) ...

Nanofibrous nerve conduits for repair of 30-mm-long sciatic nerve defects.

It has been confirmed that nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nerve conduit can promote peripheral nerve regeneration in rats. However, its efficiency in repair of over 30-mm-long sciatic nerve defects needs to be assessed. In this study, we used a nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nerve conduit to bridge a 30-mm-long gap in the rat sciatic nerve. At 4 months after nerve conduit implantation, regenerated nerves were cally observed and histologically assessed. In the nanofibrous graft, the rat sciatic nerve trunk had been reconstructed by restoration of nerve continuity and formation of myelinated nerve fiber. There were Schwann cells and glial cells in the regenerated nerves. Masson's trichrome staining showed that there were no pathological changes in the size and structure of gastrocnemius muscle cells on the operated side of rats. These findings suggest that nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nerve conduit is suitable for repair of long-segment sciatic nerve defects.

The effects of gradients of nerve growth factor immobilized PCLA scaffolds on neurite outgrowth in vitro and peripheral nerve regeneration in rats

Introducing concentration gradients of nerve growth factor (NGF) into conduits for repairing of peripheral nerve injury is crucial for nerve regeneration and guidance. Herein, combining differential adsorption of NGF/silk fibroin (SF) coating, the gradient of NGF-immobilized membranes (G-Ms) and nanofibrous nerve conduits (G-nNCs) were successfully fabricated. The efficacy of NGF gradients was confirmed by a quantitative comparison of dorsal root ganglia (DRG) neurite outgrowth on the G-Ms or uniform NGF-immobilized membranes (U-Ms). Significantly, the neurite turning ratio was 0.48 ± 0.11 for G-M group, but it was close to zero for U-M group. The neurite length of DRGs in the middle of the G-Ms was significantly longer than that of U-M group, even though the average NGF concentration was approximated. Furthermore, 12 weeks after implantation in rats with a 14 mm gap of sciatic nerve injury, G-nNCs achieved satisfying outcomes of nerve regeneration associated with morphological and functional improvements, which was superior to that of the uniform NGF-immobilized nNCs (U-nNCs). Sciatic function index (SFI), compound muscle action potentials (CMAPs), total number of myelinated nerve fibers, thickness of myelin sheath were similar for the G-nNCs and autografts, with the G-nNCs having a higher density of axons than the autografts. Our results demonstrated the significant role of introducing NGF gradients into scaffolds in promoting nerve regeneration.

Homeopathic treatment for peripheral nerve regeneration: an experimental study in a rat sciatic nerve transection model

Effects of homeopathic treatment with Hypericum perforatum (Hypericum) on peripheral nerve regeneration was studied using a rat sciatic nerve transection model. Fifty-four male healthy White Wistar rats were divided into three experimental groups (n=18), randomly: Sham-operation (Sham), control: silicon tube (Sil) and treatment: silicon tube+Hypericum (Sil/Hypericum). In the Sham group after anesthesia left sciatic nerve was exposed through a gluteal muscle incision and after homeostasis muscle was sutured. In the Sil group the left sciatic nerve was exposed the same way and transected proximal to tibio-peroneal bifurcation leaving a 10-mm gap. Proximal and distal stumps were each inserted into a silicone tube. In the Sil/Hypericum group a silicone tube was implanted the same way and each animal received three oral drops of Hypericum 30c twice daily for 1 week. Each group was subdivided into three subgroups of six animals each studied 4, 8, 12 weeks after surgery. Data were analyzed statistically by factorial analysis of variance (ANOVA) and, the Bonferroni test for pair-wise comparisons. Functional study showed faster and better recovery of regenerated axons in Sil/Hypericum than in Sil group (P<0.05). Gastrocnemius muscle mass in Sil/Hypericum was significantly greater than in Sil group. Morphometric indices of regenerated fibers showed number and diameter of the myelinated fibers in Sil/Hypericum were significantly higher than in control group. Immunohistochemistry, showed the location of reactions to S-100 in Sil/Hypericum was clearly more positive than in Sil group. Hypericum improves functional recovery of peripheral nerve regeneration in rats.

Evaluation of Peripheral Nerve Regeneration Using a Novel Reinforced Nerve Conduit Across a Long Gap of the Transected Sciatic Nerve in Rats

Evaluation of Peripheral Nerve Regeneration Using a Novel Reinforced Nerve Conduit Across a Long Gap of the Transected Sciatic Nerve in Rats

Improved rate of peripheral nerve regeneration induced by extracorporeal shock wave treatment in the rat

De-focused low energy extracorporeal shock wave therapy (ESWT) has been widely used in various clinical and experimental models for the treatment of painful conditions such as epicondylitis and plantar fascitis and also bone and wound healing. There is evidence that ESWT improves the metabolic activity of various cell types, e.g. chondrocytes and endothelial cells but little is known about its effects on nervous tissue. The aim of this study was to investigate whether ESWT improves the regeneration of injured nerves in an experimental rat model.Sprague–Dawley rats received an 8mm long homotopic nerve autograft into the right sciatic nerve, fixed with epineurial sutures. Two experimental groups were set up: the group 1 animals received ESWT (300 impulses, 3Hz) immediately after nerve grafting whereas the group 2 (control) animals received only nerve autografts. Serial CatWalk automated gait analysis, electrophysiological studies and morphological investigations were carried out. The survival time was either 3weeks or 3months.At 6 to 8weeks of survival the ESWT group of animals exhibited a significantly improved functional recovery relative to the controls. Electrophysiological observations at 3weeks after surgery revealed marked values of amplitude (3.9±0.8mV, S.E.M.) and compound nerve action potential (CNAP, 5.9±1.4mV·ms, S.E.M.) in the ESWT group, whereas there were no detectable amplitudes in the control group. This finding was accompanied by significantly greater numbers of myelinated nerve fibres in the middle of the graft (4644±170 [S.E.M., ESWT] vs 877±68 [S.E.M., control]) and in the distal stump (1586±157 [S.E.M., ESWT] vs 308±29 [S.E.M., control]) of ESWT animals relative to the controls 3weeks after surgery. Three weeks after surgery the nerve grafts of control animals contained great numbers of phagocytes and unmyelinated nerve fibres, while the ESWT nerve grafts were filled with well-myelinated regenerating axons. There was no significant difference between the numbers of endoneural vessels in the ESWT and the control nerves. Three months after surgery, no significant differences were observed in the functional and electrophysiological data. Equally high numbers of myelinated axons distal to the graft could be found in both groups (7693±673 [S.E.M., ESWT] vs 6090±716 [S.E.M., control]).These results suggest that ESWT induces an improved rate of axonal regeneration, this phenomenon probably involving faster Wallerian degeneration, the improved removal of degenerated axons and a greater capacity of the injured axons to regenerate.

Experimetal research Dexamethasone and vitamin B12 synergistically promote peripheral nerve regeneration in rats by upregulating the expression of brain-derived neurotrophic factor

IntroductionDexamethasone and vitamin B12 are currently used in the clinic to treat peripheral nerve damage but their mechanisms of action remain incompletely understood. In this study we hypothesized that dexamethasone and vitamin B12 promote the production of endogenous neurotrophic factors, thereby enhancing peripheral nerve repair.Material and methodsNinety-six adult male Wistar rats were employed to establish a sciatic nerve injury model. They were then randomly divided into 4 groups to be subjected to different treatment: saline (group A), dexamethasone (group B), vitamin B12 (group C), and dexamethasone combined with vitamin B12 (group D). The walking behavior of rats was evaluated by footprint analysis, and the nerve regeneration was assessed by electrophysiological analysis and ultrastructural examination. The expression of brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor, NT-3 and IL-6 in the injured sciatic nerves was detected by immunohistochemical and RT-PCR analysis.ResultsDexamethasone and vitamin B12 promoted the regeneration of myelinated nerve fibers and the proliferation of Schwann cells. Furthermore, dexamethasone and vitamin B12 promoted the recovery of sciatic functional index and sensory nerve conduction velocity, and upregulated BDNF expression in the injured sciatic nerves.ConclusionsDexamethasone and vitamin B12 promote peripheral nerve repair in a rat model of sciatic nerve injury through the upregulation of BDNF expression. These findings provide new insight into the neurotrophic effects of dexamethasone and vitamin B12 and support the application of these agents in clinical treatment of peripheral nerve injury.

Glatiramer Acetate Immune System Augmentation for Peripheral Nerve Regeneration in Rat Crushed Sciatic Nerve Model

Glatiramer Acetate Immune System Augmentation for Peripheral Nerve Regeneration in Rat Crushed Sciatic Nerve Model

Glatiramer Acetate Immune System Augmentation for Peripheral Nerve Regeneration in Rat Crushed Sciatic Nerve Model

Protective antiself response to nervous system injury has been reported to be mediated by a T-cell subpopulation that can recognize self-antigens. Immune cells have been shown to play a role in the regulation of motor neuron survival after a peripheral nerve injury. The objective of the present study was to evaluate the effects of immune system augmentation with use of the antigen glatiramer acetate, which is known to affect T-cell immunity, on peripheral nerve regeneration. Wild-type and nude-type (T-cell-deficient) rats underwent crush injury of the sciatic nerve. Three and six weeks after the injury, the sciatic nerve was examined, both functionally (on the basis of footprint analysis and the tibialis anterior muscle response and weight) and histologically (on the basis of axon count). Significantly greater muscle responses were measured after three weeks in the group of wild-type rats that were treated with glatiramer acetate (control limb:injured limb ratio, 0.05 for the glatiramer acetate group [n = 9], compared with 0.51 for the saline solution group [n = 8]; p < 0.05). Higher axon counts were also found in this group (control limb:injured limb ratio, -0.07 for the glatiramer acetate group [n = 10], compared with 0.29 for the saline solution group [n = 8]; p < 0.05). The nude-type rats showed no response to the intervention after three weeks but showed a delayed response after six weeks. A second dose of glatiramer acetate, delivered forty-eight hours after the injury, did not result in an improved response as compared with the control groups. We found that a single treatment with glatiramer acetate resulted in accelerated functional and histological recovery after sciatic nerve crush injury. The role of T-cell immunity in the mechanism of glatiramer acetate was suggested by the partial and late response found in the T-cell-deficient rats.

Esteira com velocidade controlada para captação da marcha

Métodos histológicos e eletrofisiológicos de avaliação da regeneração dos nervos periféricos não provêem dados sobre o real estado funcional do membro interessado, mesmo em condições experimentais controladas. Alguns métodos de avaliação funcional têm sido propostos, mas a correlação entre seus resultados e aqueles dos métodos histológicos e eletrofisiológicos ainda não está perfeitamente estabelecida, o que demanda maiores investigações. Estas, por outro lado, necessitam do aprimoramento dos métodos de captação, armazenamento e processamento dos dados obtidos. Neste trabalho foi desenvolvido uma esteira para caminhada de animais com velocidade controlada para captação das pegadas de ratos submetidos a diferentes tipos de lesão dos nervos ciático, peroneiro e tibial, obtidas numa trilha de marcha captada por uma webcam acoplada a esteira e a um microcomputador capaz de armazenar as marchas filmadas para posteriormente serem digitalizadas para avaliação funcional. A esteira desenvolvida possibilita a captação e filmagem das marchas tendo sido testado em estudos experimentais em andamento sobre lesões do nervo ciático do rato, submetido a diferentes formas de tratamento. Também permite ao pesquisador a captação da marcha com velocidade contínua controlada e pré-estabelecida pelo pesquisador anulando algumas variáveis que possam prejudicar os resultados da pesquisa, além de permitir a visualização imediata da marcha.

An improved electrophysiological method to study peripheral nerve regeneration in rats

After restitution of motor function the grasping test alone is insufficient to figure out any further differences of axonal nerve regeneration of the median nerve in rats. To avoid this problem we developed a standardized electrophysiologic method for testing median nerve regeneration. Threshold, latency, compound muscle action potentials (CMAP) and velocity of neuromuscular transduction were recorded in 54 rats 20 weeks post-operatively. Animals of group 1 served as control group, no transection of the median nerve was carried out. Animals of groups 2 and 3 underwent either primary nerve coaptation or autologous nerve grafting after transection of the median nerve. To ensure validity of the method additional correlation between all parameters was investigated. Reliable electrophysiological results were observed in all animals. As expected, group 1 animals showed lowest threshold and latency and highest CMAP levels. Transection of the median nerve and additional nerve repair leads to significant increase of threshold and latency as well as reduction of CMAP. Furthermore, animals of group 3 showed higher levels for threshold and latency and reduced CMAP levels compared with animals of group 2. The grasping test alone could not demonstrate these slight differences 20 weeks post-operatively. Additionally, we observed strong correlations between threshold, latency and CMAP using the Spearman correlation ranking. We describe the usage of motor neurography as a reproducible and valid tool which should be mandatory for detailed analysis of regeneration in the rat median nerve model.

Compound nerve conduitpromoting peripheral nerve regeneration in rats

：Objective To explore therole of compound nerve conduit, made of nerve growth factors (NGF) encapsuled bybiodegradable core-shell nanofibers through coaxial electrospinning, in regeneration ofinjured sciatic nerves in rats. Methods The compound nerve conduits were developed fromthe core-shell structured biodegradable nanofibers with P(LLA-CL) as a shell and BSA/NGFor BSA as a core through coaxial electrospinning. Seventy-two Sprague-Dawley rats wererandomly divided into 4 even groups. The middle segments (10 mm) of the sciatic nerve wereexcised and the defects were repaired with sciatic nerve autograft (group A), withP(LLA-CL) conduit (group B), with PLLA-CL conduit and one injection of NGF (group C), andwith P(LLA-CL)/NGF controlled-release conduit (group D), respectively. Morphologic andfunctional evaluations of nerve regeneration were done by gross observation, sciaticfunction index, neural electrophysiological examination, resumption rates of tricepsweight, histological and ultrastructural observa-tion respectively in 1, 2, 3 months afterthe operation. Results Three months after the operation, although partial biodegradationand small cracks could be observed, conduits remained intact in outline. Based on thefunctional and histological observations, nerve regeneration, nerve fibers arrangement,myelination and nerve function reconstruction in the P(LLA-CL)/NGF controlled-releaseconduit (group D) were similar to those in nerve autograft (group A) and significantlysuperior to those in groups B and C (P<0.05). Conclusion As theP(LLA-CL)/NGF-controlled release conduit has favorable mechanical properties andbiocompatibility, it can effectively promote regeneration of the sciatic nerve in rats.

Peripheral nerve regeneration by transplantation of BMSC‐derived Schwann cells as chitosan gel sponge scaffolds

It is said that bone marrow stromal cells (BMSCs) are able to differentiate into different kinds of cells, including Schwann cells, under relevant conditions (Dezawa et al., Eur J Neurosci 2001;14:1771-1776). In the previous paper, we demonstrated that chitosan gel sponge is one of the effective scaffolds for regenerating axons of the rat sciatic nerve (Ishikawa et al., J Biomed Mater Res A 2007;83:33-40). In the present study, we examined whether BMSC-derived Schwann cells with chitosan gel sponges were one of the effective scaffolds for peripheral nerve regeneration in rats. BMSC-derived cells with Schwann cell characteristics were labeled by green fluorescent protein using a retrovirus. An 8-mm gap was made by removing a nerve segment from the rat peripheral nerve, and chitosan gel sponges containing BMSC-derived Schwann cells were grafted, sandwiching the proximal and distal stumps of the transected nerve. Rats were sacrificed at 7, 14, and 28 days, and 2 and 4 months after transplantation. Immunohistochemistry demonstrated that regenerating axons were found near transplanted Schwann cells 7 days after surgery and extended into the host distal nerve segment at 14 days after surgery. Electron microscopy showed that transplanted Schwann cells formed myelin sheaths on regenerating axons 1 month after transplantation. The mean diameter of myelinated fibers was increased from 2.58 mum at 2 months to 2.84 mum at 4 months postsurgery. This study indicates that chitosan gel sponges containing BMSC-derived Schwann cells have strong potentiality as a graft that can be used for peripheral nerve regeneration.

Lumbricus extract promotes the regeneration of injured peripheral nerve in rats

Background Earthworms regenerate amputated parts of their body if the nervous system is intact. Lumbricus is one traditional Chinese medicine (TCM), which has been used in China to promote nerve function for hundreds of years. Aim of the study To investigate the beneficial effect of lumbricus extract on peripheral nerve regeneration in rats. Materials and methods Nerve function was surgically impaired in Sprague–Dawley (SD) rats by clamping of the left sciatic nerve. The sham-operated group (surgery but no sciatic nerve clamping), control group, and treatment group were treated with 2 ml 0.9% NaCl, 0.9% NaCl, and lumbricus extract (1 g/ml), respectively. Treatments were administered once daily after the operation for 6 weeks. During this period, motor function was monitored by walking track analysis, conduction function of injured sciatic nerve was monitored by electrophysiology, and regeneration of myelinated nerve was assessed by immunohistochemistry. Results (1) For nerve function index value, treatment group is higher than control group. (2) For conduction velocity of injured sciatic nerve, treatment group is higher than control group at week 3 and 6. (3) For the number of regenerated myelinated nerve fibers, treatment group is higher than control group at week 2 and 6. Conclusions Lumbricus extract appears to enhance sciatic nerve regeneration and function recovery following injury, suggesting the clinical potential of lumbricus extract on the treatment of peripheral nerve injury in humans.

Influência da irradiação do laser na regeneração nervosa em diferentes locais de tratamento

OBJETIVO: Verificar a influência do laser de baixa intensidade de AsGaAl na lesão por esmagamento do nervo peroneiro de ratos através da avaliação funcional da marcha nos diferentes locais de irradiação. MÉTODOS: Foram utilizados 53 ratos, divididos em seis grupos: normal, lesado não tratado, lesado e tratado placebo, lesado e tratado na medula, lesado e tratado no nervo, lesado e tratado em ambos (nervo e medula). O esmagamento do nervo peroneiro foi realizado por meio de uma pinça e subsequente tratado com laser por 28 dias consecutivos. Na avaliação funcional foram analisadas as impressões das pegadas, registradas pela câmera de vídeo em uma passarela de acrílico, no pré-operatório e aos 14º, 21º e 28º dias de pós-operatório, e avaliadas na fórmula PFI por meio do software. RESULTADOS: Na avaliação funcional da marcha foram encontradas diferenças significantes somente no 14º dia de pós-operatório. CONCLUSÃO: A irradiação do laser AsGaAl de baixa intensidade foi capaz de acelerar e potencializar o processo de regeneração nervosa periférica de ratos no 14º dia de pós-operatório, de acordo com a avaliação funcional da marcha, tanto para o grupo tratado na medula quanto para o grupo tratado no nervo.

Functional effects of local thyroid hormone administration after sciatic nerve injury in rats

This study investigates potential functional effects of thyroid hormone (T3) on peripheral nerve regeneration in rats. Forty adult male Lewis rats were included in this study. After complete transection of the right sciatic nerve, the gap between the stumps was bridged with a silicone tube. In the first experimental group (group A, n = 12), T3 solution was used to fill the tube, whereas a sterile buffer solution was used in nontreated rats, (group B, n = 12). Additionally, sham operation with surgical incision and mobilization of the sciatic nerve without any other intervention was performed (group C, n = 10). In a few animals, alpha-segment of the nerve was excised and the stumps were reversed to exclude the possibility of regeneration (group D, n = 6). The process of peripheral nerve regeneration was assessed by functional indices at 3, 6, 9, 13, and 17 weeks postoperatively. Mid-stance angle, at the ankle, measured in degrees, was used as a kinematic index and the withdrawal reflex (measured in grams of applied force) was used to evaluate the return of sensory function. Kinematic indexes were not different between the groups A and B at all time points of the evaluation. Sensory function was significantly different in T3-treated animals compared with buffer-treated control group (x vs. y, P = 0.031) at 9 weeks. Thereafter, sensory function was comparable between groups. In conclusion, T3 seems to accelerate the return of sensory function after complete transection of the sciatic nerves in Lewis rats without a significant effect on motor nerve recovery.

Electrophysiologic and histopathologic evaluation of peripheral nerve regeneration at different nerve segments and with different repair techniques

We compared the electrophysiologic and histopathologic results of early primary nerve repair and grafting of transections made at different levels. Twenty-two male Sprague-Dawley rats were divided into three groups. In one group (distal group, n=8), the right sciatic nerve was transected near the proximal segment of, and in another (proximal group, n=7) at 15 mm proximal to, its branching. In the graft group (n=7), the nerve was resected from 5 mm to 15 mm proximal to its branching and the defect was repaired with the removed segment. All the nerves were repaired using the epiperineural technique. Electrophysiologic studies were performed before and after surgery. In the third month, bilateral biopsies were taken from the L4-5 dorsal root ganglion and from distal nerve segments for histopathologic examination and neuron and axon counts. At two months, the distal group exhibited significantly shorter latency (p=0.001) and higher amplitude (p=0.05) values. However, at three months, all the groups had similar values of latency, amplitude, and conduction velocity. At three months, the number of the dorsal root ganglion neurons was significantly greater in the distal group compared to the graft group (p<0.001), but this did not differ from the proximal group (p>0.05). Axon counts per square millimeter were similar (p>0.05), but axon diameter was greater in the distal group (p<0.05). In correlation analyses, increases in the number of L4-5 dorsal root ganglion neurons were significantly associated with increases in the percent changes in distal latency (p<0.05) and conduction velocity (p=0.018). Our findings suggest that distal injuries and primary repair of the sciatic nerve result in a faster and better recovery.

ATF3 Increases the Intrinsic Growth State of DRG Neurons to Enhance Peripheral Nerve Regeneration

Peripheral axons of dorsal root ganglion (DRG) neurons, but not their central axons in the dorsal columns, regenerate after injury. However, if the neurons are conditioned by a peripheral nerve injury into an actively growing state, the rate of peripheral axonal growth is accelerated and the injured central axons begin to regenerate. The growth-promoting effects of conditioning injuries have two components, increased axonal growth and a reduced response to inhibitory myelin cues. We have examined which transcription factors activated by peripheral axonal injury may mediate the conditioning effect by regulating expression of effectors that increase the intrinsic growth state of the neurons. Activating transcription factor 3 (ATF3) is a prime candidate because it is induced in all injured DRG neurons after peripheral, but not central, axonal damage. To investigate if ATF3 promotes regeneration, we generated transgenic mice that constitutively express this transcription factor in non-injured adult DRG neurons. The rate of peripheral nerve regeneration was enhanced in the transgenic mice to an extent comparable to that produced by a preconditioning nerve injury. The expression of some growth-associated genes, such as SPRR1A, but not others like GAP-43, was increased in the non-injured neurons. ATF3 increased DRG neurite elongation when cultured on permissive substrates but did not overcome the inhibitory effects of myelin or promote central axonal regeneration in the spinal cord in vivo. We conclude that ATF3 contributes to nerve regeneration by increasing the intrinsic growth state of injured neurons.

Neuroregeneration in Composite Tissue Allografts: Effect of Low-Dose FK506 and Mycophenolate Mofetil Immunotherapy

The immunosuppressant FK506 has been reported to increase the rate of peripheral nerve regeneration in nerve crush injury and nerve allograft models. The purpose of this study was to determine whether low doses of FK506 and mycophenolate mofetil had a neuroregenerative effect in revascularized peripheral nerve allografts in a rat hind limb transplantation model. Wistar Furth rat recipients received limbs from syngeneic Wistar Furth donors (group 1, n = 4) or from allogeneic August X Copenhagen Irish rat donors (group 2, n = 6). Wistar Furth recipients received limbs from August X Copenhagen Irish donors and were treated with FK506/mycophenolate mofetil for 5 months (group 3, n = 7). At the end of the follow-up period, histomorphometric analysis of sciatic and tibial nerves from transplanted and intact hind limbs was conducted. Sciatic and tibial nerves were examined at the level of coaptation and near the neuromuscular junction, respectively. Transplanted limbs in groups 1 and 3 completed the study without rejection, while the limbs in group 2 were rejected within a few days. Sciatic and tibial nerve analysis in groups 1 and 3 limbs showed myelinated axons of various diameters but in significantly fewer numbers than in nontransplanted contralateral nerves. The number and size of myelinated axons of transplanted nerves at corresponding levels were not significantly different between syngeneic and allogeneic (FK506/mycophenolate mofetil-treated) transplants. The authors conclude that long-term neuroregeneration of revascularized peripheral nerves using low-dose FK506/mycophenolate mofetil was similar to that of syngeneic transplants. The occurrence of acute rejection episodes with low-dose FK506/mycophenolate mofetil did not appear to benefit nor impair neuroregeneration.

Mice deficient for galanin receptor 2 have decreased neurite outgrowth from adult sensory neurons and impaired pain‐like behaviour

Expression of the neuropeptide galanin is markedly up-regulated within the adult dorsal root ganglia (DRG) following peripheral nerve injury. We have previously demonstrated that galanin knockout (Gal-KO) mice have a developmental loss of a subset of DRG neurons. Galanin also plays a trophic role in the adult animal, and the rate of peripheral nerve regeneration and neurite outgrowth is reduced in adult Gal-KO mice. Here we describe the characterization of mice with an absence of GalR2 gene transcription (GalR2-MUT) and demonstrate that they have a 15% decrease in the number of calcitonin gene-related peptide (CGRP) expressing neuronal profiles in the adult DRG, associated with marked deficits in neuropathic and inflammatory pain behaviours. Adult GalR2-MUT animals also have a one third reduction in neurite outgrowth from cultured DRG neurons that cannot be rescued by either galanin or a high-affinity GalR2/3 agonist. Galanin activates extracellular signal-regulated kinase (ERK) and Akt in adult wild-type (WT) mouse DRG. Intact adult DRG from GalR2-MUT animals have lower levels of pERK and higher levels of pAkt than are found in WT controls. These data suggest that a lack of GalR2 activation in Gal-KO and GalR2-MUT animals is responsible for the observed developmental deficits in the DRG, and the decrease in neurite outgrowth in the adult.