The biomechanical and functional relationships of the proximal radioulnar joint, distal radioulnar joint, and interosseous ligament

This biomechanical study assessed integrated function of the proximal radioulnar joint (PRUJ), interosseous ligament (IOL), and distal radioulnar joint (DRUJ). Tekscan™ pressure sensors were inserted into the DRUJ and PRUJ of 15 cadaveric specimens. MicroStrain(®) sensors were mounted onto the IOL on nine of these specimens. A customized biomechanical jig was used to apply axial loads and take measurements through pronosupination. The PRUJ, IOL, and DRUJ were shown to function as an integrated osseoligamentous system distributing applied load. The PRUJ has transmitted pressure profiles similar to those of the DRUJ. Different IOL components support loading at different stages of pronosupination. The IOL is lax during pronation. Mid-IOL tension peaks in the midrange of forearm rotation; distal-IOL tension peaks in supination. Axial loading consistently increases IOL strain in a non-linear fashion. There are clinical implications of this work: disease or surgical modification of any of these structures may compromise normal biomechanics and function.

Differentiated adipose-derived stem cells act synergistically with RGD-modified surfaces to improve neurite outgrowth in a co-culture model

Peripheral nerve damage is a problem encountered after trauma and during surgery and the development of synthetic polymer conduits may offer a promising alternative to autografts. In order to improve the performance of the polymer to be used for nerve conduits, poly-ε-caprolactone (PCL) films were chemically functionalized with RGD moieties, using a chemical reaction previously developed. In vitro cultures of dissociated dorsal root ganglion (DRG) neurons provide a valid model to study different factors affecting axonal growth. In this work, DRG neurons were cultured on RGD-functionalized PCL films. Adult adipose-derived stem cells differentiated to Schwann cells (dASCs) were initially cultured on the functionalized PCL films, resulting in improved attachment and proliferation. dASCs were also co-cultured with DRG neurons on treated and untreated PCL to assess stimulation by dASCs on neurite outgrowth. Neuron response was generally poor on untreated PCL films, but long neurites were observed in the presence of dASCs or RGD moieties. A combination of the two factors enhanced even further neurite outgrowth, acting synergistically. Finally, in order to better understand the extracellular matrix (ECM)-cell interaction, a β1 integrin blocking experiment was carried out. Neurite outgrowth was not affected by the specific antibody blocking, showing that β1 integrin function can be compensated by other molecules present on the cell membrane. Copyright © 2013 John Wiley & Sons, Ltd.

Differentiation of adipose-derived stem cells into Schwann cell phenotype induces expression of P2X receptors that control cell death

Schwann cells (SCs) are fundamental for development, myelination and regeneration in the peripheral nervous system. Slow growth rate and difficulties in harvesting limit SC applications in regenerative medicine. Several molecules, including receptors for neurosteroids and neurotransmitters, have been suggested to be implicated in regulating physiology and regenerative potential of SCs. Adipose-derived stem cells (ASCs) can be differentiated into SC-like phenotype (dASC) sharing morphological and functional properties with SC, thus representing a valid SC alternative. We have previously shown that dASC express γ-aminobutyric-acid receptors, which modulate their proliferation and neurotrophic potential, although little is known about the role of other neurotransmitters in ASC. In this study, we investigated the expression of purinergic receptors in dASC. Using reverse transriptase (RT)-PCR, western blot analyses and immunocytochemistry, we have demonstrated that ASCs express P2X3, P2X4 and P2X7 purinoceptors. Differentiation of ASCs towards glial phenotype was accompanied by upregulation of P2X4 and P2X7 receptors. Using Ca(2+)-imaging techniques, we have shown that stimulation of purinoceptors with adenosine 5'-triphosphate (ATP) triggers intracellular Ca(2+) signals, indicating functional activity of these receptors. Whole-cell voltage clamp recordings showed that ATP and BzATP induced ion currents that can be fully inhibited with specific P2X7 antagonists. Finally, using cytotoxicity assays we have shown that the increase of intracellular Ca(2+) leads to dASC death, an effect that can be prevented using a specific P2X7 antagonist. Altogether, these results show, for the first time, the presence of functional P2X7 receptors in dASC and their link with critical physiological processes such as cell death and survival. The presence of these novel pharmacological targets in dASC might open new opportunities for the management of cell survival and neurotrophic potential in tissue engineering approaches using dASC for nerve repair.

Micro-structural geometry of thin films intended for the inner lumen of nerve conduits affects nerve repair

Damage to peripheral nerves can cause significant motor or sensory injuries. In serious cases, a nerve is sacrificed from another part of the body to repair a damaged nerve (autograft). The development of biodegradable polymer conduits may offer an alternative to autografts. This study investigated the surface topography and mechanical properties of smooth, pitted and grooved structures of ultra-thin poly (ε-caprolactone)/poly lactic acid blended, solvent-cast films. We have investigated the effect of the groove shape on cell morphology and alignment. Photolithography and dry/wet etching was used to develop patterned silicon substrates with grooves with accurate geometries (V shaped, sloped walls and square shaped). Using a neural cell line (NG108-15), in vitro experiments confirmed good cell attachment and proliferation on all the polymer scaffolds. Imaging techniques demonstrated that there was different cellular responses and morphology according to the shape of the groove. Studies showed that the geometry, particularly the angle of the slope and the space between grooves, affected cellular responses. In addition, biomechanical studies showed that the patterned films had excellent mechanical properties and were stronger than the natural nerve. The conduit tubes were made by rolling the films around a mandrel and using a thermal welding technique to join the edges. The promising biomechanical and in vitro results demonstrate that nerve cell responses are affected by the shape of longitudinal grooves, and particularly by the angle of the slope of the groove walls.

Glial differentiation of human adipose-derived stem cells: implications for cell-based transplantation therapy

Increasing evidence has shown that adipose-derived stem cells (ASCs) could transdifferentiate into Schwann cell (SC)-like cells to enhance nerve regeneration, suggesting potential new cell-based transplantation therapy for peripheral nerve injuries and neurodegenerative disorders. For the implementation of these results to the clinical setting, it is of great importance to establish the differentiation of human ASCs (hASCs) into a SC phenotype. In this study, we studied hASCs obtained from subcutaneous fat tissue of healthy donors. By a mixture of glial growth factors we differentiated them into Schwann cell-like cells (dhASCs). We then assessed their ability to act as Schwann cells in vitro and in vivo and also compared them with primary human Schwann cells (hSCs). Enzyme-linked immunosorbent assay showed that dhASCs secreted brain-derived neurotrophic factor (BDNF)/nerve growth factor (NGF) at a comparable level, and glial cell-derived neurotrophic factor (GDNF) at a level even higher than hSCs, whereas undifferentiated hASCs (uhASCs) secreted low levels of these neurotrophic factors. In co-culture with NG108-15 neuronal cells we found that both dhASCs and hSCs significantly increased the percentage of cells with neurites, the neurite length, and the number of neurites per neuron, whereas uhASCs increased only the percentage of cells with neurites. Finally, we transplanted green fluorescent protein (GFP)-labeled hASCs into the crushed tibial nerve of athymic nude rats. The transplanted hASCs showed a close association with PGP9.5-positive axons and myelin basic protein (MBP)-positive myelin at 8weeks after transplantation. Quantitative analysis revealed that dhASCs transplantation resulted in significantly improved survival and myelin formation rates (a 7-fold and a 10-fold increase, respectively) as compared with uhASCs transplantation. These findings suggest that hASCs took part in supporting and myelinating regenerating axons, and thus have achieved full glial differentiation in vivo. In conclusion, hASCs can differentiate into SC-like cells that possess a potent capacity to secrete neurotrophic factors as well as to form myelin in vivo. These findings make hASCs an interesting prospect for cell-based transplantation therapy for various peripheral nerve disorders.

Subluxation-related ulnar neuropathy (SUN) syndrome related to distal radioulnar joint instability

Ulnar neuropathy coexistent with distal radioulnar joint (DRUJ) instability has previously been observed in our practice. The aim of this study was to define this phenomenon and investigate the hypothesis that the cause of this intermittent, positional ulnar neuropathy is related to kinking of the ulnar nerve about the DRUJ. Ulna neuropathy was present in 10/51 (19.6%) of a historical cohort of patients who presented with DRUJ instability. Nine subsequent patients with DRUJ instability and coexistent ulnar neuropathy underwent 3-T magnetic resonance imaging to better understand the mechanism of the observed syndrome. Both 3D qualitative and quantitative analyses were used to assess the presence of nerve 'kinking', displacing the nerve from its normal course and causing nerve compression/distraction in the distal forearm and Guyon's canal. Results of the quantitative analysis were statistically significant (p < 0.05). The clinical features of the condition have been delineated and termed subluxation-related ulnar neuropathy or SUN syndrome. The imaging study was a level II diagnostic study.

Nerve repair with adipose-derived stem cells protects dorsal root ganglia neurons from apoptosis

Novel approaches are required in the clinical management of peripheral nerve injuries because current surgical techniques result in deficient sensory recovery. Microsurgery alone fails to address extensive cell death in the dorsal root ganglia (DRG), in addition to poor axonal regeneration. Incorporation of cultured cells into nerve conduits may offer a novel approach in which to combine nerve repair and enhance axonal regeneration with neuroprotective therapies. We examined apoptotic mediator expression in rat DRG neurons following repair of a 10-mm sciatic nerve gap using a novel synthetic conduit made of poly ε-caprolactone (PCL) and primed with adipose-derived stem cells (ADSC) differentiated towards a Schwann cell phenotype or with primary adult Schwann cells. Differentiated ADSC expressed a range of neurotrophic factors including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), and neurotrophin-4 (NT4). Incorporation of either differentiated ADSC or Schwann cells significantly increased anti-apoptotic Bcl-2 mRNA expression (P<0.001) in the DRG, while significantly decreasing pro-apoptotic Bax (P<0.001) and caspase-3 mRNA (P<0.01) expression. Cleaved caspase-3 protein was observed in the DRG following nerve injury which was attenuated when nerve repair was performed using conduits seeded with cells. Cell incorporation into conduit repair of peripheral nerves demonstrates experimental promise as a novel intervention to prevent DRG neuronal loss.

Long-term in vivo regeneration of peripheral nerves through bioengineered nerve grafts

Although autologous nerve graft is still the first choice strategy in nerve reconstruction, it has the severe disadvantage of the sacrifice of a functional nerve. Cell transplantation in a bioartificial conduit is an alternative strategy to improve nerve regeneration. Nerve fibrin conduits were seeded with various cell types: primary Schwann cells (SC), SC-like differentiated bone marrow-derived mesenchymal stem cells (dMSC), SC-like differentiated adipose-derived stem cells (dASC). Two further control groups were fibrin conduits without cells and autografts. Conduits were used to bridge a 1 cm rat sciatic nerve gap in a long term experiment (16 weeks). Functional and morphological properties of regenerated nerves were investigated. A reduction in muscle atrophy was observed in the autograft and in all cell-seeded groups, when compared with the empty fibrin conduits. SC showed significant improvement in axon myelination and average fiber diameter of the regenerated nerves. dASC were the most effective cell population in terms of improvement of axonal and fiber diameter, evoked potentials at the level of the gastrocnemius muscle and regeneration of motoneurons, similar to the autografts. Given these results and other advantages of adipose derived stem cells such as ease of harvest and relative abundance, dASC could be a clinically translatable route towards new methods to enhance peripheral nerve repair.

In vitro and in vivo testing of novel ultrathin PCL and PCL/PLA blend films as peripheral nerve conduit

In an attempt to obviate the drawbacks of nerve autograft, ultrathin microporous biodegradable PCL and PCL/PLA films were tested for their compatibility with motor neuron-like NG108-15 cells and primary Schwann cells. Data obtained from MTS colorimetric and DNA fluorimetric assays showed that both cell lines readily attached and proliferated on these materials. Images taken using scanning electron microscope and fluorescence microscope confirmed these observations. Enhanced cell-surface interaction was achieved by pretreating the films in NaOH solution. Importantly, NG108-15 cells could be induced into differentiated phenotype with long, un-branched neurites growing across the surface of the materials. The bipolar spindle-shaped phenotype of Schwann cells was also retained on these scaffolds. Positive immunochemical staining using antibodies against neurofilament for NG108-15 cells and S100 for Schwann cells indicated the expression of these marker proteins. In a small-scaled pilot testing, the performance of PCL conduits in bridging up a 10 mm gap in rat sciatic nerve model was assessed. Immunohistochemical staining showed that regenerated nerve tissue and penetrated Schwann cells have the potential to span the whole length of the conduit in 2 weeks.

Regeneration potential and survival of transplanted undifferentiated adipose tissue-derived stem cells in peripheral nerve conduits

Adipose tissue-derived stem cells (ADSCs) have shown potential for the treatment of nerve injuries. Most previous efforts have aimed at stimulating regeneration by using neural-differentiation protocols, but the potential of undifferentiated ADSCs to enhance axonal growth as well as their ability to transdifferentiate in situ have been poorly investigated. In this study, using a rat sciatic nerve model we show that ADSCs, transplanted in an artificial nerve conduit, stimulate axonal outgrowth from the proximal nerve stump and evoke greater Schwann cell (SC) proliferation/intrusion in the distal stump. To track the fate of the transplanted cells, we used green fluorescent protein (GFP)-labelling and polymerase chain reaction (PCR) for the detection of the sex determining region Y (SRY) gene in the donor male cells. Both methods indicated a lack of significant quantities of viable cells 14 days after transplantation. These results suggest that any regenerative effect of transplanted ADSCs is more likely to be mediated by an initial boost of released growth factors and/or by an indirect effect on endogenous SCs activity. Future studies need to address long-term cell survival in tissue-engineered nerve conduits to improve the neuroregenerative potential of ADSCs.

Laryngeal transplantation in minipigs: vascular, myologic and functional outcomes

There is no effective way of replacing all the functions of the larynx in those requiring laryngectomy. Regenerative medicine offers promise, but cannot presently deliver implants with functioning neuromuscular units. A single well-documented laryngeal transplant in man was a qualified success, but more information is required before clinical trials may be proposed. We studied the early response of the larynx to laryngeal transplantation between 17 pairs of NIH minipigs full matched at the MHC2 locus. Following iterative technical improvements, pigs had good swallowing and a patent airway at 1 week. No significant changes in mucosal blood flux were observed compared with pre-operative measurements. Changes in muscle morphology and fibre phenotype were observed in transplant muscles retrieved after 7 days: the levels of fast and slow myosin heavy chain (MyHC) protein were reduced and embryonic MyHC was up regulated consistent with denervation induced atrophy. At 1 week laryngeal transplantation can result in good swallowing, and is not associated with clinical evidence of ischemia-reperfusion injury in MHC-matched pigs.

Adipose-derived stem cells enhance peripheral nerve regeneration

Traumatic injuries resulting in peripheral nerve lesions often require a graft to bridge the gap. Although autologous nerve auto-graft is still the first-choice strategy in reconstructions, it has the severe disadvantage of the sacrifice of a functional nerve. Cell transplantation in a bioartificial conduit is an alternative strategy to create a favourable environment for nerve regeneration. We decided to test new fibrin nerve conduits seeded with various cell types (primary Schwann cells and adult stem cells differentiated to a Schwann cell-like phenotype) for repair of sciatic nerve injury. Two weeks after implantation, the conduits were removed and examined by immunohistochemistry for axonal regeneration (evaluated by PGP 9.5 expression) and Schwann cell presence (detected by S100 expression). The results show a significant increase in axonal regeneration in the group of fibrin seeded with Schwann cells compared with the empty fibrin conduit. Differentiated adipose-derived stem cells also enhanced regeneration distance in a similar manner to differentiated bone marrow mesenchymal stem cells. These observations suggest that adipose-derived stem cells may provide an effective cell population, without the limitations of the donor-site morbidity associated with isolation of Schwann cells, and could be a clinically translatable route towards new methods to enhance peripheral nerve repair.

Schwann cell strip for peripheral nerve repair

Many strategies have been investigated to provide an ideal substitute to treat a nerve gap injury. Initially, silicone conduits were used and more recently conduits fabricated from natural materials such as poly-3-hydroxybutyrate (PHB) showed good results but still have their limitations. Surgically, a new concept optimising harvested autologous nerve graft has been introduced as the single fascicle method. It has been shown that a single fascicle repair of nerve grafting is successful. We investigated a new approach using a PHB strip seeded with Schwann cells to mimic a small nerve fascicle. Schwann cells were attached to the PHB strip using diluted fibrin glue and used to bridge a 10-mm sciatic nerve gap in rats. Comparison was made with a group using conventional PHB conduit tubes filled with Schwann cells and fibrin glue. After 2 weeks, the nerve samples were harvested and investigated for axonal and Schwann cell markers. PGP9.5 immunohistochemistry showed a superior nerve regeneration distance in the PHB strip group versus the PHB tube group (> 10 mm, crossed versus 3.17+/- 0.32 mm respectively, P<0.05) as well as superior Schwann cell intrusion (S100 staining) from proximal (> 10 mm, crossed versus 3.40+/- 0.36 mm, P<0.01) and distal (> 10 mm, crossed versus 2.91+/- 0.31 mm, P<0.001) ends. These findings suggest a significant advantage of a strip in rapidly connecting a nerve gap lesion and imply that single fascicle nerve grafting is advantageous for nerve repair in rats.

[Fibrin matrix enhances adherence of peripheral nerve regenerative cells]

Optimal seeding of a nerve conduit with cells is a core problem in tissue engineering of constructing an artificial nerve substitute to gap lesions in the peripheral nerve system. An ideal nerve gap substitute would have to present an equally distributed number of cells that can activate the regrowing axons. This work shows a new in vitro technique of two-step seeding of cells inside a conduit and on layered mats that allows a valuable targeting of the cells and a proven survival in the environment of poly-3-hydroxybutyrate (PHB) conduits. The technique uses two components of diluted fibrin glue Tisseel. Initially, the chosen area on the mat was coated with thrombin followed from the seeding of a fibrinogen-cell compound. Using Sprague Dawley rat cells, we could demonstrate with immunohistochemistry (S100, DAPI) techniques that undifferentiated (uMSC) and Schwann cells (SC) mimicking differentiated mesenchymal stem cells (dMSC) as well as SC can be suspended and targeted significantly better in dissolvable diluted fibrin glue than in growth medium. Analysis showed significantly better values for adherence (p < 0.001) and drop off (p < 0.05) from seeded cells. Using this two-step application allows the seeding of the cells to be more precise and simplifies the handling of cell transplantation.

Fibrin matrix for suspension of regenerative cells in an artificial nerve conduit

Peripheral nerve injury presents with specific problems of neuronal reconstructions, and from a clinical viewpoint a tissue engineering approach would facilitate the process of repair and regeneration. We have previously used artificial nerve conduits made from bioresorbable poly-3-hydroxybutyrate (PHB) in order to refine the ways in which peripheral nerves are repaired and reconnected to the target muscles and skin. The addition of Schwann cells (SC) or differentiated mesenchymal stem cells (dMSC) to the conduits enhances regeneration. In this study, we have used a matrix based on fibrin (Tisseel) to fill optimally the nerve-conduits with cells. In vitro analysis showed that both SC and MSC adhered significantly better to PHB in the presence of fibrin and cells continued to maintain their differentiated state. Cells were more optimally distributed throughout the conduit when seeded in fibrin than by delivery in growth medium alone. Transplantation of the nerve conduits in vivo showed that cells in combination with fibrin matrix significantly increased nerve regeneration distance (using PGP9.5 and S100 distal and proximal immunohistochemistry) when compared with empty PHB conduits. This study shows the beneficial combinatory effect of an optimised matrix, cells and conduit material as a step towards bridging nerve gaps which should ultimately lead to improved functional recovery following nerve injury.

The role of neuropeptides in psoriasis

The pathogenesis of psoriasis is incompletely understood but cutaneous neurogenic inflammation is probably involved. This involvement is suggested by a number of clinical and histological observations. Reports about the distribution of cutaneous nerves and the quantification of nerve growth factor and neuropeptides, including calcitonin gene-related peptide and vasoactive intestinal peptide, in lesional and nonlesional psoriatic skin suggest that sensory neuropeptides contribute to the development of psoriasis. This review summarizes what is known about the role of neurogenic markers in psoriasis.

Analysis of the dose-response of N-acetylcysteine in the prevention of sensory neuronal loss after peripheral nerve injury

BACKGROUND

N-Acetylcysteine (NAC) is a safe pharmaceutical agent known to protect cells from oxidative damage. Following peripheral nerve transection, NAC has been found to eliminate sensory neuronal loss. This study examines the dose-response relationship of NAC in preventing neuronal death.

METHODS AND FINDINGS

The rat sciatic nerve transection model was used, and stereological quantification of sensory neuron survival carried out at two weeks post-axotomy. NAC was administered systemically as an intraperitoneal injection to five groups of rats at a range of doses (1-300 mg/kg/day). Significant neuronal loss was observed in the 1 mg/kg/day dosage group (18.5% loss, p = 0.067 vs. sham treatment). A degree of neuroprotection occurred with 10 mg/kg/day (9.1% loss, p < 0.005 vs. control), whilst there was no significant loss with either 150 or 300 mg/kg/day.

CONCLUSIONS

The prevention of sensory neuronal loss with NAC is dose dependent and effective over a wide therapeutic range. This analysis confirms the efficacy of systemic administration and provides a dose framework with which NAC has clinical potential to improve outcome after peripheral nerve trauma.

The reinnervation pattern of wounds and scars may explain their sensory symptoms

Anaesthesia, pruritus and pain are common in cutaneous scars. The reinnervation pattern of healing wounds and scars might help to explain these symptoms, as sensory neurotransmitters are known to be mediators of inflammation and healing. We quantified the regeneration patterns of blood vessels and nerves in excisional skin wounds as they matured into scars. Mice underwent 1cm(2) full thickness skin excisions. Wounds were harvested between five and 84 days. Sections underwent immunohistochemical staining for protein gene product 9.5 (PGP9.5) a pan-neuronal marker, and the sensory neuropeptides calcitonin gene related peptide (CGRP) and substance P (SP). The endothelial marker von Willebrand factor (VWF) was used to allow co-localisation and quantification of blood vessels. Nerve fibre density was quantified at multiple sites within wounds. There was no difference in the reinnervation/revascularisation pattern between peripheral and central sites. The density of PGP9.5, CGRP, SP and VWF peaked between 14 and 42 days, and levels of PGP9.5, CGRP and VWF all decreased to approximately those found in unwounded skin by 84 days (mature scar). SP levels, however, remained elevated at approximately twice the density found in unwounded skin. Increased densities of SP and CGRP in healing wounds could explain the unpleasant sensory symptoms of healing wounds.

End-to-side nerve coaptation: a qualitative and quantitative assessment in the primate

There are several reasons why end-to-side nerve coaptation has not been widely adopted clinically. Among these are the putative damage inflicted on the donor nerve and the variable quality of the regeneration in the recipient nerve. So far experiments on end-to-side nerve repair have been short term and mostly carried out on rats. This long-term study of end-to-side nerve repair of ulnar to median and median to ulnar nerve was performed using adult nonhuman primates. Eleven nerve repairs were studied at different time points. Eighteen, 22, 33 and 57 months after surgery a qualitative and quantitative analysis of the donor nerve and regenerating nerve revealed variable levels of percentage axonal regeneration compared with matched controls (1.4%-136%). Morphological evidence of donor nerve damage was identified distal to the coaptation site in four of the 11 cases, and in these cases the best axonal regeneration in the corresponding recipient nerves was observed. This donor nerve damage could neither be demonstrated in terms of a decrease in axon counts distal to the coaptation nor as donor target organ denervation. Recipient target organ regeneration like the axonal regeneration varied, with evidence of motor regeneration in eight out of 11 cases and sensory regeneration, as measured by percentage innervation density compared with matched controls, varied from 12.5% to 49%. Results from the present study demonstrate that the end-to-side coaptation technique in the nonhuman primate does not give predictable results. In general the motor recovery appeared better than the sensory and in those cases where donor nerve damage was observed there was better motor and sensory regeneration overall than in the remaining cases.

Neuronal survival, regeneration and musclemorphology after posterior C7 nerve transfer:An experimental study

C7 nerve transfer has been widely used in treating brachial plexus avulsion injuries. Little is known regarding the survival and regeneration of C7 motor and sensory neurons including their morphological changes after this procedure and also the possible change of muscle fibre phenotype. In this experimental study, the posterior division of C7 nerve was transferred to the musculocutaneous nerve ipsilaterally, and using fluorescent tracing techniques, the C7 spinal cord segment and dorsal root ganglion were found to contain 630.9 +/- 86.7 motor neurons and 3916.0 +/- 517.3 sensory neurons, respectively. Six months following transfer, 90% of the motor neurons and 78% of the sensory neurons survived and approximately 40% of them had regenerated and all displayed normal soma size. After posterior C7 transfer and reinnervation, the target muscles showed a percentage pattern of distribution and mean fibre diameters similar to those seen in normal biceps muscle. The present study suggests that the posterior C7 nerve transfer provides sufficient number of neurons and satisfactory results for regeneration to obtain an acceptable functional recovery.

Nerve fibre and sensory end organ density in the epidermis and papillary dermis of the human hand

Quantification of sensory recovery after peripheral nerve surgery is difficult and no accurate techniques are available at present. Quantification of reinnervated skin has been used experimentally, and in some clinical studies, but the lack of knowledge about the normal sensory distribution has been a problem. The purpose of this study was, therefore, to map the density of sensory end organs, nerve fibres and free nerve endings in the glabrous skin of the human hand. Skin biopsies were taken from patients undergoing acute and elective hand surgery. Nerve fibres were stained in the epidermis and papillary dermis and quantified in five sites on the palm of the hand, using protein gene product 9.5 immunoreactivity-a panneuronal marker. The finger tip skin was found to have more than twice the nerve fibre density in the papillary dermis than the skin of the palm, and the number of Meissner corpuscles in the finger tip was also higher than in the palm. We found a reduction in innervation density with increasing age in the dermis, however, that was not the case for the epidermis. The innervation of the epidermis showed high interindividual variability and unlike the papillary dermis did not display any pattern of distribution in the hand.

Quantification of N-CAM and N-cadherin expression in axotomized and crushed rat sciatic nerve

Adhesion molecules are important in supporting axonal regeneration. Qualitative studies have described increased expression of neural cell adhesion molecule (NCAM) and N-cadherin in models of nerve injury allowing active regeneration. In this study we have used quantitative immunohistochemistry to compare expression of NCAM and N-cadherin after nerve injury either with active regeneration (crush) into the distal stump or without (axotomy and capping). Quantification was performed 15 days after axotomy in proximal and distal stumps. Quantification after crush either proximal, distal or within the crushed area was performed at 2, 7, 15 and 30 days after injury. Axotomy induced increases in expression in proximal stumps between two and three times those in uninjured nerves for both molecules. In distal stumps, N-cadherin levels increased seven-fold, yet NCAM levels did not exceed control values. After crush, NCAM immunoreactivity increased in the crushed area and distal stump in contrast to axotomy and NCAM-positive axons co-localized with PGP9.5. N-cadherin levels in the distal stump increased above control levels, but the magnitude of the increase seen after crush was different to those seen after axotomy. In conclusion, increased expression of adhesion molecules, particularly NCAM, in the distal stump of injured nerves is dependent upon the presence of regenerating axons.

Sensory neuroprotection, mitochondrial preservation, and therapeutic potential of N-acetyl-cysteine after nerve injury

Neuronal death is a major factor in many neuropathologies, particularly traumatic, and yet no neuroprotective therapies are currently available clinically, although antioxidants and mitochondrial protection appear to be fruitful avenues of research. The simplest system involving neuronal death is that of the dorsal root ganglion after peripheral nerve trauma, where the loss of approximately 40% of primary sensory neurons is a major factor in the overwhelmingly poor clinical outcome of the several million nerve injuries that occur each year worldwide. N-acetyl-cysteine (NAC) is a glutathione substrate which is neuroprotective in a variety of in vitro models of neuronal death, and which may enhance mitochondrial protection. Using TdT uptake nick-end labelling (TUNEL), optical disection, and morphological studies, the effect of systemic NAC treatment upon L4 and 5 primary sensory neuronal death after sciatic nerve transection was investigated. NAC (150 mg/kg/day) almost totally eliminated the extensive neuronal loss found in controls both 2 weeks (no treatment 21% loss, NAC 3%, P=0.03) and 2 months after axotomy (no treatment 35% loss, NAC 3%, P=0.002). Glial cell death was reduced (mean number TUNEL positive cells 2 months after axotomy: no treatment 51/ganglion pair, NAC 16/ganglion pair), and mitochondrial architecture was preserved. The effects were less profound when a lower dose was examined (30 mg/kg/day), although significant neuroprotection still occurred. This provides evidence of the importance of mitochondrial dysregulation in axotomy-induced neuronal death in the peripheral nervous system, and suggests that NAC merits investigation in CNS trauma. NAC is already in widespread clinical use for applications outside the nervous system; it therefore has immediate clinical potential in the prevention of primary sensory neuronal death, and has therapeutic potential in other neuropathological systems.

A composite poly-hydroxybutyrate-glial growth factor conduit for long nerve gap repairs

There is considerable evidence that peripheral nerves have the potential to regenerate in an appropriate microenvironment. We have developed a novel artificial nerve guide composed of poly 3-hydroxybutyrate (PHB) filled with glial growth factor (GGF) suspended in alginate hydrogel. Gaps of 2-4 cm in rabbit common peroneal nerve were bridged using a PHB conduit containing either GGF in alginate hydrogel (GGF) or alginate alone (Alginate), or with an empty PHB conduit (Empty). Tissues were harvested 21, 42 and 63 days post-operatively. Schwann cell and axonal regeneration were assessed using quantitative immunohistochemistry. At 21 days, addition of GGF increased significantly the distance of axonal and Schwann cells regeneration in comparison with that observed in Alginate and Empty conduits for both gap lengths. The axons bridged the 2-cm GGF conduits gap by 63 days, with a comparable rate of regeneration seen in 4-cm conduits. Schwann cells and axonal regeneration quantity was similar for both gap lengths in each group. However, at all time points the quantity of axonal and Schwann cells regeneration in GGF grafts was significantly greater than in both Alginate and Empty conduits, the latter showing better regeneration than Alginate conduits. The results indicate an inhibitory effect of alginate on regeneration, which is partially reversed by the addition of GGF to the conduits. In conclusion, GGF stimulates a progressive and sustainable regeneration increase in long nerve gap conduits.

Exogenous leukaemia inhibitory factor enhances nerve regeneration after late secondary repair using a bioartificial nerve conduit

The clinical outcome of peripheral nerve injuries remains disappointing, even in the ideal situation of a primary repair performed with optimal microsurgical techniques. Primary repair is appropriate for only about 85% of injuries, and outcome is worse following secondary nerve repair, partly owing to the reduced regenerative potential of chronically axotomised neurons. Leukaemia inhibitory factor (LIF) is a gp-130 neurocytokine that is thought to act as an 'injury factor', triggering the early-injury phenotype within neurons and potentially boosting their regenerative potential after secondary nerve repair. At 2-4 months after sciatic nerve axotomy in the rat, 1 cm gaps were repaired using either nerve isografts or poly-3-hydroxybutyrate conduits containing a calcium alginate and fibronectin hydrogel. Regeneration was determined by quantitative immunohistochemistry 6 weeks after repair, and the effect of incorporating recombinant LIF (100 ng/ml) into the conduits was assessed. LIF increased the regeneration distance in repairs performed after both 2 months (69%, P=0.019) and 4 months (123%, P=0.021), and was statistically comparable to nerve graft. The total area of axonal immunostaining increased by 21% (P>0.05) and 63% (P>0.05), respectively. Percentage immunostaining area was not increased in the 2 months group, but increased by 93% in the repairs performed 4 months after axotomy. Exogenous LIF, therefore, has a potential role in promoting peripheral nerve regeneration after secondary repair, and can be effectively delivered within poly-3-hydroxybutyrate bioartificial conduits used for nerve repair.

Increased innervation of the vulval vestibule in patients with vulvodynia

BACKGROUND

Vulval vestibulitis is a condition characterized by the sudden onset of a painful burning sensation, hyperalgesia, mechanical allodynia, and occasionally pruritus, localized to the region of the vulval vestibulus. It is considered the commonest subset of vulvodynia. Pain precipitated in the absence of nociceptor stimuli might be triggered by previous peripheral nerve injury, or by the release of neuronal mediators, which set off inappropriate impulses in nonmyelinated pain fibres sensitizing the dorsal horn neurones. The pathophysiology of vulval vestibulitis is still unclear.

OBJECTIVES

The objective of this study was to evaluate the nerve fibre density and pattern, in specimens of vulval vestibulus, in normal subjects and in patients with vestibulitis, and provide objective diagnostic criteria for this condition. Methods Twelve patients with a history of the vestibulitis type of vulvodynia, and eight normal subjects underwent biopsy of the posterior wall of the vulval vestibule. Quantitative immunohistochemistry was performed, using antisera to the general neuronal marker protein gene product (PGP) 9.5, and to the neuropeptide calcitonin gene-related peptide (CGRP), on 15- microm sections.

RESULTS

There was a statistically significant increase of density and number of PGP 9.5 immunoreactive in the papillary dermis of patients with vulvodynia of the vestibulitis type, compared with those of controls. However, the distribution pattern of the innervation showed no significant change. There were no significant differences in CGRP staining between patients and controls.

CONCLUSIONS

It is concluded that the increase of PGP 9.5 immunoreactive nerve fibres, in patients with vulvodynia, may be either secondary to nerve sprouting, or may represent neural hyperplasia. Increased innervation may be applied as an objective diagnostic finding in vulval vestibulitis syndrome.

Poly-3-hydroxybutyrate (PHB): a resorbable conduit for long-gap repair in peripheral nerves

The repair of peripheral nerve injuries with an autologous nerve graft is still the treatment of choice, although it is widely recognised that the method is associated with donor-site morbidity and a suboptimal functional outcome. An alternative approach is to use a nerve conduit to provide a guidance channel for the regenerating nerve. This study investigates the potential of poly-3-hydroxybutyrate (PHB) nerve conduits to bridge long nerve gaps (up to 4 cm) in a rabbit common-peroneal-nerve injury model. Regeneration was assessed up to 63 days postoperatively, and compared with that achieved using nerve autografts. By 42 days, regenerating axons had bridged nerve gaps of all lengths in groups with nerve autografts and in those with PHB conduits. The regeneration distance increased with time but did not vary with gap length (P </= 0.009, 14 versus 21 days, PHB tube 2 cm, 3 cm and 4 cm, Mann-Whitney U -test). At 42 days, the area of immunostained regenerating fibres in the PHB group was greater than that in the nerve autograft group (P < 0.001, PHB versus autograft, 21 and 42 days, three-way analysis of variance (ANOVA)). These results suggest that PHB conduits support peripheral nerve regeneration up to 63 days, and that they are suitable for long-gap nerve injury repair.

Increased sodium channel SNS/PN3 immunoreactivity in a causalgic finger

The sodium channels SNS/PN3 and NaN/SNS2 are regulated by the neurotrophic factors-nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF), and may play an important role in the development of pain after nerve injury or inflammation. These key molecules have been studied in an amputated causalgic finger and control tissues by immunohistochemistry. There was a marked increase in the number and intensity of SNS/PN3-immunoreactive nerve terminals in the affected finger, while GDNF-immunoreactivity was not observed, in contrast to controls. No differences were observed for NGF, trk A, NT-3 or NaN/SNS2-immunoreactivity. While further studies are required, these findings suggest that accumulation of SNS/PN3 and/or loss of GDNF may contribute to pain in causalgia, and that selective blockers of SNS/PN3 and/or rhGDNF may provide effective novel treatments.

A novel use of alginate hydrogel as Schwann cell matrix

The use of bioresorbable conduits supplemented with Schwann cells (SCs) is a promising tissue engineering technique to replace nerve grafting. Alginate hydrogel (AH), as a SC tissue engineering matrix, has many advantages over previously used matrices but has not been evaluated for this purpose. In this study, the viability and proliferation of SCs together with SC function in AH was evaluated in vitro. AlamarBlue cell assay was used to monitor the viability of SCs in AH and compared to SC viability in collagen gel, fibrin glue, hyaluronic acid, Matrigel, and standard culture plate over 5 days in culture. The results showed that the viability and growth of SCs in different matrices over the culture period did not significantly differ to culture plate culture. SC function when suspended in AH was monitored using chick embryo dorsal root ganglia (CDRG) growth assay. Growth of CDRG in AH with or without SCs was compared to CDRG growth without AH matrix. After 3 days in culture, the mean length of neurite sprouting was measured. The results showed that there was neurite growth in AH but was reduced to 43% of control. The neurite growth in AH was, however, enhanced by 170% when SCs were suspended in the gel. In conclusion, AH supported SC viability and function in vitro and may be useful in peripheral nerve tissue engineering in reconstructive procedures.

Retroviral labeling of Schwann cells: in vitro characterization and in vivo transplantation to improve peripheral nerve regeneration

Transplantation of Schwann cells (SCs) is a promising treatment modality to improve neuronal regeneration. Identification of the transplanted cells is an important step when studying the development of this method. Genetic labeling is the most stable and reliable method of cell identification, but it is still unclear whether it has deleterious effect on SC characteristics. Our aim was to achieve a stable population of SCs transduced with the lacZ gene at a high frequency using a retroviral vector in vitro, and to follow the labeled SC in vitro to assess their viability and phenotypic marker expression. Furthermore, we transplanted lacZ-labeled SCs in a conduit to repair peripheral nerve to investigate their effect on nerve regeneration in vivo. Rat and human SCs were cultured and transduced with an MFG lacZ nls marker gene, achieving a transduction rate of 80% and 70%, respectively. Rat SCs were kept in culture for 27 weeks and examined every 4 weeks for expression of lacZ, viability, and phenotypic marker expression of GFAP, p75, MHC I and II. Throughout this period, transduced rat SCs remained viable and continued to proliferate. The proportion of cells expressing lacZ dropped only by 10% and the expression of phenotypic markers remained stable. Transduced human SCs were followed up for 4 weeks in culture. They proliferated and continued to express the lacZ gene and phenotypic marker expression of GFAP and p75 was preserved. Primary culture of transduced rat SCs were transplanted, syngeneically, in a conduit to bridge a 10 mm gap in sciatic nerve and the grafts were examined after 3 weeks for the presence and participation of labeled SCs and for axonal regeneration distance. Transplanted transduced rat SCs were clearly identified, taking part in the regeneration process and enhancing the axonal regeneration rate by 100% (at the optimal concentration) compared to conduits without SCs. Thus, retroviral introduction of lacZ gene has no deleterious effect on SCs in vitro and these SCs take part and enhance nerve regeneration in vivo.

Long-term effect of vital labelling on mixed Schwann cell cultures

Schwann cell transplantation following neuronal injury could encourage regeneration of spinal cord as well as improving peripheral nerve gap repair. In order to gain a better understanding of the role of transplanted Schwann cells in vivo, it is essential to be able to follow their behaviour after transplantation. Our aim was to evaluate the suitability of two vital fluorescent labels on the proliferation rate and phenotypic stability of Schwann cells, in either pure culture or mixed co-culture. Primary cultures of Schwann cells were obtained from Dark Agouti and Lewis neonatal rats and labelled with H33342 and PKH26, respectively. In mixed cultures, a 50: 50 mixture of Dark Agouti and Lewis Schwann cells was present. Labelled cultured cells were examined at 1, 2 and 4 weeks for viability and phenotypic marker expression of S100, GFAP, p75, MHC I, MHC II and compared with corresponding unlabelled cells. The results showed that although there was no deleterious interaction in the mixed cultures, the viability was reduced by the labelling after 2 weeks. Labelled cells could be distinguished up to 4 weeks, but there was leakage of H33342 label after 2 weeks. Labelled Schwann cells showed reduced expression of phenotypic markers, especially p75 when labelled with H33342. In conclusion, H33342 and PKH26 can be used as fluorescent markers of Schwann cells for short-term studies, for a maximum of 2 weeks, but different markers may be needed for longer experiments.

Differential effects of NT-3 on reinnervation of the fast extensor digitorum longus (EDL) and the slow soleus muscle of rat

Previous studies of gastrocnemius muscle reinnervation showed specific normalization of the proportion and diameter of fast type 2b muscle fibres following NT-3 delivery to the proximal stump of the cut sciatic nerve. Here, we investigate if normalization was related to greater improvement of muscle reinnervation of fast (extensor digitorum longus; EDL) than slow (soleus) motor units. NT-3-impregnated (NT-3 group) or plain fibronectin (FN group) mats were inserted into a sciatic nerve gap. Neuromuscular junctions (NMJs) labelled with TRITC-alpha-bungarotoxin were colabelled with calcitonin gene-related peptide (CGRP) or 4E2 antisera and imaged using confocal microscopy. CGRP and 4E2 were used as markers for newly reinnervated and structurally mature NMJs, respectively. At 40 days postsurgery, denervated NMJs in EDL and soleus muscles of both groups presented a 50% decrease of surface area due to decreased width. At day 80 in EDL, more NMJs were reinnervated by CGRP-immunoreactive terminals in the NT-3 (7.1%) than in the FN group (4.2%); there was no difference between groups for soleus. At 120 days, 4E2-immunoreactive NMJs were more numerous in EDL of the NT-3 (40.0%) than in the FN group (7.3%), unlike in soleus (NT-3, 1. 6%; FN, 1.8%), and presented a partial size recovery. These results indicate that NT-3 preferentially improves reinnervation of fast muscles over slow muscle, although the mechanism of this improvement is still unclear.

Do nerve growth factor-related mechanisms contribute to loss of cutaneous nociception in leprosy?

While sensory loss in leprosy skin is the consequence of invasion by M. leprae of Schwann cells related to unmyelinated fibres, early loss of cutaneous pain sensation, even in the presence of nerve fibres and inflammation, is a hallmark of leprosy, and requires explanation. In normal skin, nerve growth factor (NGF) is produced by basal keratinocytes, and acts via its high affinity receptor (trk A) on nociceptor nerve fibres to increase their sensitivity, particularly in inflammation. We have therefore studied NGF- and trk A-like immunoreactivity in affected skin and mirror-site clinically-unaffected skin from patients with leprosy, and compared these with non-leprosy, control skin, following quantitative sensory testing at each site. Sensory tests were within normal limits in clinically-unaffected leprosy skin, but markedly abnormal in affected skin. Sub-epidermal PGP 9.5- and trk A- positive nerve fibres were reduced only in affected leprosy skin, with fewer fibres contacting keratinocytes. However, NGF-immunoreactivity in basal keratinocytes, and intra-epidermal PGP 9.5-positive nerve fibres, were reduced in both sites compared to non-leprosy controls, as were nerve fibres positive for the sensory neurone specific sodium channel SNS/PN3, which is regulated by NGF, and may mediate inflammation-induced hypersensitivity. Keratinocyte trk A expression (which mediates an autocrine role for NGF) was increased in clinically affected and unaffected skin, suggesting a compensatory mechanism secondary to reduced NGF secretion at both sites. We conclude that decreased NGF- and SNS/PN3-immunoreactivity, and loss of intra-epidermal innervation, may be found without sensory loss on quantitative testing in clinically-unaffected skin in leprosy; this appears to be a sub-clinical change, and may explain the lack of cutaneous pain with inflammation. Sensory loss occurred with reduced sub-epidermal nerve fibres in affected skin, but these still showed trk A-staining, suggesting NGF treatment may restore pain sensation.

Nerve growth factor enhances peripheral nerve regeneration in non-human primates

Fibronectin mat implants impregnated with NGF have been successfully used in rat nerve regeneration model. The aim of this study was to assess their action in a primate model. Mats were implanted into a 5 mm gap in a peripheral nerve in Macaca fascicularis monkeys, either alone (Fn) or in the presence of nerve growth factor (Fn + NGF). Four months postoperatively, the regenerated nerve was analysed by light microscopy, and target skin reinnervation was assessed by quantification of cutaneous nerve terminals immunostained with protein gene product (PGP) antibodies. The diameter of the regenerated nerve was similar in Fn + NGF grafts and nerve autografts, but significantly larger for plain Fn grafts with evidence of more connective tissue surrounding the axons. Myelinated fibres counts showed similarities in normal control nerve, nerve autograft and Fn + NGF graft groups. However, in nerve grafted with plain Fn mats the regenerating fibres were lower in number and showed a wider variability in diameter and myelination, resulting in a significantly smaller G-ratio (axonal diameter/myelinated fibre diameter). The amount of cutaneous reinnervation was lowest in Fn graft group, while comparable amounts of skin reinnervation were observed in the Fn + NGF and autograft groups. These results suggest that Fn-mats are a suitable conduit to promote peripheral nerve regeneration also in primate, and supplying NGF locally at the lesion site can further enhance nerve regrowth.

Primary sensory neuron survival following targeted administration of nerve growth factor to an injured nerve

Nerve injuries induce neurochemical changes within primary sensory neurons, including expression of neuropeptides, and a loss of a substantial proportion of the neurons may possibly be caused by a lack of neurotrophic support. In the present study the role of nerve growth factor (NGF) in preventing these changes was investigated in monkeys by giving NGF peripherally through a fibronectin (Fn) conduit. A sensory nerve (superficial radial) was transected and a gap of 5 mm was bridged with either autologous sural nerve graft (SNG), Fn, or Fn impregnated with NGF (Fn-NGF). After four months the dorsal root ganglia, that received the cutaneous afferents of the nerve, were removed and analysed by quantitative immunohistochemistry using antibodies to calcitonin gene related polypeptide (CGRP) and substance P. The percentage of immunostained cells was taken as an indication of neuronal survival. The results showed that SNG and Fn-NGF reduced the loss of CGRP positive sensory neurons compared with Fn alone. For substance P-positive neurons the differences were small with only a tendency towards reduction of neuronal death after NGF had been given, suggesting that NGF might act preferentially on a subpopulation of CGRP immunoreactive sensory neurons that do not coexist with substance P.

A resorbable nerve conduit as an alternative to nerve autograft in nerve gap repair

Poly-3-hydroxybutyrate (PHB) occurs within bacterial cytoplasm as granules and is available as bioabsorbable sheets. Previously, the advantage of PHB in primary repair has been investigated while in this study the same material has been used to bridge an irreducible gap. The aim was to assess the level of regeneration in PHB conduits compared to nerve autografts. The rat sciatic nerve was exposed, a 10 mm nerve segment was resected and bridged with either an autologous nerve graft or a PHB conduit. The grafted segments were harvested up to 30 days. Immunohistochemical staining was performed and computerised quantification of penetration distance and volume of axonal regeneration was estimated by protein gene product (PGP) immunostaining and calcitonin gene-related peptide (CGRP) positive fibres. Penetration and proliferation density of Schwann cells into the conduit was measured by quantifying S-100 staining. The inflammatory response was quantified with ED-1 staining for macrophages. Antibodies to vWf provided an assessment of angiogenesis and capillary infiltration. Percentage immunostaining for PGP in autograft and PHB groups showed a progressive increase up to 30 days with a significant linear trend with time and an increase in the volume of axonal regeneration. A similar pattern of progressive increase with time was observed with CGRP immunostaining for both groups and with S-100 in the PHB group. Good angiogenesis was present at the nerve ends and through the walls of the conduit. The results demonstrate good nerve regeneration in PHB conduits in comparison with nerve grafts.

Cellular changes in denervated tissue during wound healing in a rat model

There is increasing evidence that innervation, possibly mediated via neuropeptides, promotes wound healing. This study presents data on the early cellular events during healing in denervated tissue. Free oblique groin flaps were raised on 25 adult Sprague-Dawley rats. Excisional wounds were placed within the flap and in two control sites, the contralateral inguinal region and the thorax. The absence of innervation in the free flap wounds was confirmed 10 days after surgery by indirect immunofluorescence with a pan-neuronal marker. The cellular infiltrate of the wounds was analysed immunohistochemically with a panel of antibodies to rat macrophages and monocytes (ED1), rat B lymphocytes (CD45R) and T lymphocytes (CD2). The immunostained cellular infiltrate was quantified at 2, 4, 7 and 10 days postoperatively. Our results show that denervated wounds have a significantly lower macrophage and T-lymphocyte count at day 4 of wound healing (P < 0.05). Inflammatory cells, particularly macrophages, are known to play an important part in wound healing and their reduced chemotaxis in denervated tissue may be related to the observed delay in wound closure.

A new resorbable wrap-around implant as an alternative nerve repair technique

Poly-3-hydroxybutyrate (PHB), a bacterial storage product, is available as bioabsorbable sheets and has been used in this study for primary nerve repair. The aim was to assess axonal regeneration following such repair and determine the inflammatory response to PHB. In 20 adult cats, the transected superficial radial nerve was wrapped in PHB sheets, while primary epineural repair was carried out in the contralateral limb. At 6 and 12 months, the repair sites were assessed immunohistochemically for macrophage infiltration and myelinated axons were counted in the distal nerve. Mean macrophage counts across the whole width of the nerve in both groups at 6 and 12 months showed no statistically significant difference. Nor was there any significant difference between the two groups at both time-points in axon counts, axon diameter, myelin thickness and g-ratio. There was a statistically significant increase in fibre diameters at 12 months, indicating that fibres were undergoing continuous maturation.

Peripheral nerve regeneration and neurotrophic factors

The role of neurotrophic factors in the maintenance and survival of peripheral neuronal cells has been the subject of numerous studies. Administration of exogenous neurotrophic factors after nerve injury has been shown to mimic the effect of target organ-derived trophic factors on neuronal cells. After axotomy and during peripheral nerve regeneration, the neurotrophins NGF, NT-3 and BDNF show a well defined and selective beneficial effect on the survival and phenotypic expression of primary sensory neurons in dorsal root ganglia and of motoneurons in spinal cord. Other neurotrophic factors such as CNTF, GDNF and LIF also exert a variety of actions on neuronal cells, which appear to overlap and complement those of the neurotrophins. In addition, there is an indirect contribution of GGF to nerve regeneration. GGF is produced by neurons and stimulates proliferation of Schwann cells, underlining the close interaction between neuronal and glial cells during peripheral nerve regeneration. Different possibilities have been investigated for the delivery of growth factors to the injured neurons, in search of a suitable system for clinical applications. The studies reviewed in this article show the therapeutic potential of neurotrophic factors for the treatment of peripheral nerve injury and for neuropathies.

A morphological study of Schwann cells and axonal regeneration in chronically transected human peripheral nerves

Relatively little is known about the effects of chronic transection on human peripheral nerves. In this study intraoperative biopsies were obtained from proximal and distal nerve stumps and intervening neuromas resected before peripheral nerve reconstruction. Biopsies were collected from ten patients following differing types of nerve injury, with delays to repair ranging from 8 to 53 months. Nerves were examined by light and electron microscopy. In general, reinnervation was poor, although even following the most severe injuries, all of the distal stumps contained some regrowing axons, which were always associated with Schwann cells. Denervated Schwann cells, arranged in typical bands of Büngner were consistently present in each distal stump. Our findings confirm that the morphology of chronically denervated human peripheral nerves is essentially similar to that described in experimental models.