Regeneration of mouse peripheral nerves in degenerating skeletal muscle: guidance by residual muscle fibre basement membrane

Fabrication of Artificial Nerve Conduits Used in a Long Nerve Gap: Current Reviews and Future Studies

There are many commercially available artificial nerve conduits, used mostly to repair short gaps in sensory nerves. The stages of nerve regeneration in a nerve conduit are fibrin matrix formation between the nerve stumps joined to the conduit, capillary extension and Schwann cell migration from both nerve stumps, and, finally, axon extension from the proximal nerve stump. Artificial nerves connecting transected nerve stumps with a long interstump gap should be biodegradable, soft and pliable; have the ability to maintain an intrachamber fibrin matrix structure that allows capillary invasion of the tubular lumen, inhibition of scar tissue invasion and leakage of intratubular neurochemical factors from the chamber; and be able to accommodate cells that produce neurochemical factors that promote nerve regeneration. Here, we describe current progress in the development of artificial nerve conduits and the future studies needed to create nerve conduits, the nerve regeneration of which is compatible with that of an autologous nerve graft transplanted over a long nerve gap.

Facial Nerve Repair by Muscle-Vein Conduit in Rats: Functional Recovery and Muscle Reinnervation

The facial nerve is the most frequently damaged nerve in head and neck traumata. Repair of interrupted nerves is generally reinforced by fine microsurgical techniques; nevertheless, regaining all functions is the exception rather than the rule. The so-called "postparalytic syndrome," which includes synkinesia and altered blink reflexes, follows nerve injury. The purpose of this study was to examine if nerve-gap repair using an autologous vein filled with skeletal muscle would improve axonal regeneration, reduce neuromuscular junction polyinnervation, and improve the recovery of whisking in rats with transected and sutured right buccal branches of the facial nerve. Vibrissal motor performance was studied with the use of a video motion analysis. Immunofluorescence was used to visualize and analyze target muscle reinnervation. The results taken together indicate a positive effect of muscle-vein-combined conduit (MVCC) on the improvement of the whisking function after reparation of the facial nerve in rats. The findings support the recent suggestion that a venal graft with implantation of a trophic source, such as autologous denervated skeletal muscle, may promote the monoinnervation degree and ameliorate coordinated function of the corresponding muscles.

Comparison of repair of peripheral nerve transection in predegenerated muscle with and without a vein graft

BACKGROUND

Despite substantial research into the topic and valiant surgical efforts, reconstruction of peripheral nerve injury remains a challenging surgery. This study was conducted to evaluate the effectiveness of axonal regeneration of a transected sciatic nerve through a vein conduit containing degenerated skeletal muscle compared with axonal regeneration in a transected sciatic nerve through degenerated skeletal muscle alone.

METHODS

In two of the three experimental rat groups, 10 mm of the left sciatic nerve was transected and removed. The proximal and distal ends of the transected sciatic nerve were then approximated and surrounded with either (a) a degenerated skeletal muscle graft; or (b) a graft containing both degenerated skeletal muscle and vein. In the group receiving the combined vein and skeletal muscle graft, the vein walls were subsequently sutured to the proximal and distal nerve stump epineurium. Sciatic functional index (SFI) was used for assessment of functional recovery. Tracing study and histological procedures were used to assess axonal regeneration.

RESULTS

At 60 days, the gait functional recovery as well as the mean number of myelinated axons in the middle and distal parts of the sciatic nerve significantly increased in the group with the vein graft compared to rats with only the muscular graft (P < 0.05). Mean diameter of myelinated nerve fiber of the distal sciatic nerve was also improved with the vein graft compared to the muscle graft alone (P < 0.05). The mean number of DiI-labeled motor neurons in the L4-L5 spinal segment increased in the vein with muscle group but was not significantly different between the two groups.

CONCLUSIONS

These findings demonstrated that a graft consisting of not only predegenerated muscle, but also predegenerated muscle with vein more effectively supported nerve regeneration, thus promoting functional recovery after sciatic nerve injury in rats.

Update on nerve repair by biological tubulization

Many surgical techniques are available for bridging peripheral nerve defects. Autologous nerve grafts are the current gold standard for most clinical conditions. In selected cases, alternative types of conduits can be used. Although most efforts are today directed towards the development of artificial synthetic nerve guides, the use of non-nervous autologous tissue-based conduits (biological tubulization) can still be considered a valuable alternative to nerve autografts. In this paper we will overview the advancements in biological tubulization of nerve defects, with either mono-component or multiple-component autotransplants, with a special focus on the use of a vein segment filled with skeletal muscle fibers, a technique that has been widely investigated in our laboratory and that has already been successfully introduced in the clinical practice.

[Regeneration of critical injuries of the peripheral nerve with growth factors]

INTRODUCTION

This project aims to study the regeneration of non-repairable lesions of peripheral nerve by muscle grafts enhanced with growth factors.

MATERIAL AND METHODS

The experiment was carried out in two phases. The first one compared direct suture of a critical defect in the sciatic nerve of ten rats, with the interposition of autologous muscle graft, denatured by heat, in another ten. The second phase compared ten rats with nerve repair using an acellular muscle graft, with injection of 2cc of IGF-1 (10mg/ml mecasermin, Injectable solution) into the acellular graft of another ten. A clinical and functional follow-up was carried out including, ambulation, footprint measurement, and "grasping test". . The animals were sacrificed at 90-100 days, and samples obtained for macro- and microscopic studies with toluidine blue, haematoxylin-eosin and Masson's trichrome staining.

RESULTS

The first experiment showed the characteristic findings of nerve tissue in muscle graft level sections. The second was an enhancement of the results: post-surgical clinical improvement, early ambulation, decrease in the rate of pressure ulcers in toes, recovery of the footprint, and increasing the percentage of nerve endings in distal sciatic regeneration (47-62%).

CONCLUSIONS

In this study the experimental and clinical possibilities of nerve defect repair by denatured muscle are demonstrated, confirming the suitability of the technique. Furthermore, it confirms our hypothesis with clinical and cellular determinations enriched by the addition of growth factors that promote nerve regeneration.

Emerging issues in peripheral nerve repair

It is today widely acknowledged that nerve repair is now more than a matter of perfect microsurgical reconstruction only and that, to further improve clinical outcome, the involvement of different scientific disciplines is required. This evolving reconstructive/regenerative approach is based on the interdisciplinary and integrated pillars of tissue engineering such as reconstructive microsurgery, transplantation and biomaterials. In this paper, some of the most promising innovations for the tissue engineering of nerves, emerging from basic science investigation, are critically overviewed with special focus on those approaches that appear today to be more suitable for clinical translation.

EXPERIMENTAL NERVE GRAFTING — TOWARDS FUTURE SOLUTIONS OF A CLINICAL PROBLEM

Restoration of function following complete nerve injuries with subsequent nerve repair is still not satisfactory and in many cases poor, especially when a gap has to be bridged by a graft. In such situations, there may be insufficient access to autologous graft material. Alternatives have to be developed and a close collaboration between basic scientists and clinicians is required. In the present article, current studies on experimental nerve grafts are discussed and some new alternatives to autologous nerve grafts are reviewed.

Peripheral nerve reconstruction with collagen tubes filled with denatured autologous muscle tissue in the rat model

Conventional nerve conduits lack cellular and extracellular guidance structures critical for bridging larger defects. In this study, an exogenous matrix for axonal regeneration was provided by pretreated muscle tissue. In 24 rats, 14-mm sciatic nerve segments were resected and surgically reconstructed using one of the following methods: autograft (AG); bovine type I collagen conduit; (MDM) collagen tube filled with modified denatured autologous muscle tissue. For 8 weeks, functional regeneration was evaluated by footprint and video gait analysis. Evaluation was complemented by electrophysiology, as well as qualitative and quantitative structural assessment of nerves and target muscles. Group AG was superior both structurally and functionally, showing higher axon counts, a more normal gait pattern, and less severe muscle atrophy. Fiber quality (fiber size and myelin thickness) was highest in group MDM, possibly related to the myelin-producing effect of muscular laminin. However, axon count was lowest in this group, and ultrastructural analysis of the denatured muscle tissue showed areas of incomplete denaturation that had acted as a mechanical barrier for regenerating axons. In light of these results, the often advocated use of muscular exogenous matrix for peripheral nerve reconstruction is reviewed in the literature, and its clinical application is critically discussed. In conclusion, combined muscle tubes may have a positive influence on nerve fiber maturation. However, muscle pretreatment is not without risks, and denaturation processes need to be further refined.

Neurite outgrowth at the biomimetic interface

Understanding the cues that guide axons and how we can optimize these cues to achieve directed neuronal growth is imperative for neural tissue engineering. Cells in the local environment influence neurons with a rich combination of cues. This study deconstructs the complex mixture of guidance cues by working at the biomimetic interface--isolating the topographical information presented by cells and determining its capacity to guide neurons. We generated replica materials presenting topographies of oriented astrocytes (ACs), endothelial cells (ECs), and Schwann cells (SCs) as well as computer-aided design materials inspired by the contours of these cells (bioinspired-CAD). These materials presented distinct topographies and anisotropies and in all cases were sufficient to guide neurons. Dorsal root ganglia (DRG) cells and neurites demonstrated the most directed response on bioinspired-CAD materials which presented anisotropic features with 90 degrees edges. DRG alignment was strongest on SC bioinspired-CAD materials followed by AC bioinspired-CAD materials, with more uniform orientation to EC bioinspired-CAD materials. Alignment on replicas was strongest on SC replica materials followed by AC and EC replicas. These results suggest that the topographies of anisotropic tissue structures are sufficient for neuronal guidance. This work is discussed in the context of feature dimensions, morphology, and guidepost hypotheses.

Optimization by Response Surface Methodology of Confluent and Aligned Cellular Monolayers for Nerve Guidance

Anisotropic tissue structures provide guidance for navigating neurons in vitro and in vivo. Here we optimized the generation of comparable anisotropic monolayers of astrocytes, endothelial cells, and Schwann cells as a first step toward determining which properties of anisotropic cells are sufficient for nerve guidance. The statistical experimental design method Design of Experiments and the experimental analysis method Response Surface Methodology were applied to improve efficiency and utility. Factors investigated included dimensions of microcontact printed protein patterns, cell density, and culture duration. Protein patterning spacing had the strongest influence. When cells initially aligned at borders and proliferated to fill in spaces, space between stripes was most effective when it was comparable to cell size. Maximizing the area of adhesive molecule coverage was also important for confluence of these types of cells. When cells adhered and aligned over the width of a stripe and broadened to fill spaces, space width about half the cell width was most effective. These findings suggest that if the mechanism of alignment, alignment at borders or over the width of the stripe, is predetermined and the cell size determined, the optimal size of the micropatterning for aligned monolayers of other cell types can be predicted. This study also demonstrates the effective use of DOE and RSM to probe cellular responses to various and multiple factors toward determination of optimal conditions for a desired cellular response.

Tissue-engineered peripheral nerve grafting by differentiated bone marrow stromal cells

Bone marrow stromal cells are multipotential stem cells that contribute to the differentiation of tissues such as bone, cartilage, fat and muscle. In the experiment, we found that bone marrow stromal cells can be induced to differentiate into cells expressing characteristic markers of Schwann cells, such as S-100 and glial fibrillary acidic protein, promoting peripheral nerve regeneration. Tissue-engineered bioartificial nerve grafting of rats by differentiated bone marrow stromal cells was applied for bridging a 10 mm-long sciatic nerve defect. Twenty-eight inbred strains of female F344 rats weighing 160 approximately 200 g were randomly divided into four nerve grafting groups, with seven rats in each group. Differentiated bone marrow stromal cell-laden group: poly(lactic-co-glycolic) acid tubes with an intrinsic framework were seeded with syngeneic bone marrow stromal cells which were induced for 5 days; Schwann cell-laden group: poly(lactic-co-glycolic) acid tubes with an intrinsic framework were seeded with syngeneic Schwann cells; acellular group: poly(lactic-co-glycolic) acid tubes were only filled with an intrinsic framework; autografts group. Three months later, a series of examinations was performed, including electrophysiological methods, walking track analysis, immunohistological staining of nerves, immunostaining of S-100 and neurofilament, and axon counts. The outcome indicated that bone marrow stromal cells are able to differentiate into Schwann-like cells and Schwann-like cells could promote nerve regeneration. Bone marrow stromal cells may be potentially optional seed cells for peripheral nerve tissue engineering because of abilities of promoting axonal regeneration.

The course of aberrant reinnervation following nerve repair with fresh or denatured muscle autografts

Denatured muscle grafts obtained by freeze thawing have been proposed to replace losses in the peripheral nerves. In the present report, we compare the performance of such grafts with fresh grafts in the rat median nerve. A long-term effect of muscle interposition on reinnervation was studied by behavioral assessment, muscle ATPase histochemistry, and retrograde labeling of motoneurons. There was no difference in grasping strength recovery between fresh and denatured 10-mm-long muscle grafts. Recovery was delayed and incomplete. Twelve months after surgery, only 50% of the normal grasping strength was attained. Grasping recovery was not observed in the 20-mm-long graft groups. Pathway reinnervation was non-specific with a huge amount of motor fiber misdirection. A decrease in the number of misdirected motor fibers occurred with time and activity recovery. Muscle reinnervation was not specific with disturbance of the mosaic pattern and type-grouping formation. Preference of type I axons for reinnervating deeper zones was observed. Type I aberrant reinnervation was demonstrated in the muscle periphery. The mosaic distribution of type I and II muscle fibers was not stable, and readjustments were observed with time, correlating with grasping improvement. During grasping strength recovery, there was a decrease in the number of type I fibers peripherally located and an increase of those deeply disposed. A time- and activity-related recovery was associated with readjustment in the pathways and muscle fiber rearrangement. We suggest that muscle activity generates specificity.

Nerve repair by means of tubulization: literature review and personal clinical experience comparing biological and synthetic conduits for sensory nerve repair

Nerve repair is usually accomplished by direct suture when the two stumps can be approximated without tension. In the presence of a nerve defect, the placement of an autologous nerve graft is the current gold standard for nerve restoration. However, over the last 20 years, an increasing number of research articles reported on the use of non-nervous tubes (tubulization) for repairing nerve defects. The clinical employment of tubes (both biological and synthetic) as an alternative to autogenous nerve grafts is mainly justified by the limited availability of donor tissue for nerve autografts and the related morbidity. In addition, tubulization was proposed as an alternative to direct nerve sutures in order to create optimal conditions for nerve regeneration over the short empty space intentionally left between two nerve stumps. This paper outlines recent important advances in this field. Different tubulization techniques proposed so far are described, focusing in particular on studies that reported on the employment of tubes with patients. Our personal clinical experience on tubulization repair of sensory nerve lesions (digital nerves), using both biological and synthetic tubes, is presented, and the clinical results are compared. In our case series, both types of tubes led to good clinical results. Finally, we speculate about the prospects in the clinical application of tubulization for peripheral nerve repair.

Use of Skeletal Muscle Tissue in Peripheral Nerve Repair: Review of the Literature

The management of peripheral nerve injury continues to be a major clinical challenge. The most widely used technique for bridging defects in peripheral nerves is the use of autologous nerve grafts. This technique, however, necessitates a donor nerve and corresponding deficit. Many alternative techniques have thus been developed. The use of skeletal muscle tissue as graft material for nerve repair is one example. The rationale regarding the use of the skeletal muscle tissue technique is the availability of a longitudinally oriented basal lamina and extracellular matrix components that direct and enhance regenerating nerve fibers. These factors provide superiority over other bridging methods as vein grafts or (non)degradable nerve conduits. The main disadvantages of this technique are the risk that nerve fibers can grow out of the muscle tissue during nerve regeneration, and that a donor site is necessary to harvest the muscle tissue. Despite publications on nerve conduits as an alternative for peripheral nerve repair, autologous nerve grafting is still the standard care for treatment of a nerve gap in the clinical situation; however, the use of the skeletal muscle tissue technique can be added to the surgeon's arsenal of peripheral nerve repair tools, especially for bridging short nerve defects or when traditional nerve autografts cannot be employed. This technique has been investigated both experimentally and clinically and, in this article, an overview of the literature on skeletal muscle grafts for bridging peripheral nerve defects is presented.

The use of a muscle graft to repair a segmentary nerve defect

The use of a devitalized skeletal muscle graft and conventional nerve graft to repair a 5mm long segmentary sciatic nerve lesion was studied in rats by means of functional, morphometric and spinal cord motor neuron cell response evaluation. Thirty-four rats were used and divided into four groups according to the procedure: (1) sham operation; (2) conventional nerve grafting; (3) muscle grafting; (4) unrepaired lesion. The sciatic functional index (SFI) was evaluated every fortnight up to the 105th postoperative day by measuring three parameters in the rats' footprint. The animals of Groups 2 and 3 presented initial complete functional loss, followed by slow but steady recovery, with final similar SFIs. The histologic and morphometric studies showed an increased small diameter/thin myelin sheath nerve fiber density distally to the lesion site for both types of graft. An increased population of motor neurons was observed in the anterior horn of the lumbar spinal cord segment with both types of grafts, but not in the control groups. The SFI, histologic and morphometric data did not differ significantly between the two types of graft, thus indicating a similar behavior. The authors conclude that a 5mm long skeletal muscle graft works as well as a conventional nerve graft.

Directed nerve outgrowth is enhanced by engineered glial substrates

In the present study, the influence of astrocyte alignment on the direction and length of regenerating neurites was examined in vitro. Astrocytes were experimentally manipulated by different approaches to create longitudinally aligned monolayers. When cultured on the aligned monolayers, dorsal root ganglion neurites grew parallel to the long axis of the aligned astrocytes and were significantly longer than controls. Engineered monolayers expressed linear arrays of fibronectin, laminin, neural cell adhesion molecule, and chondroitin sulfate proteoglycan that were organized parallel to one another, suggesting that a particular spatial arrangement of these molecules on the astrocyte surface may be necessary to direct nerve regeneration in vivo. In contrast, no bias in directional outgrowth was observed for neurites growing on unorganized monolayers. The results suggest that altering the organization of astrocytes and their scar-associated matrix at the lesion site may be used to influence the direction and the length of adjacent regenerating axons in the damaged brain and spinal cord.

Extracellular matrix of human amnion manufactured into tubes as conduits for peripheral nerve regeneration

The human amnion consists of the epithelial cell layer and underlying connective tissue. After removing the epithelial cells, the resulting acellular connective tissue matrix was manufactured into thin dry sheets called amnion matrix sheets. The sheets were further processed into tubes, amnion matrix tubes (AMTs), of varying diameters, with the walls of varying numbers of amnion matrix sheets with or without a gelatin coating. The AMTs were implanted into rat sciatic nerves. Regenerating nerves extended in bundles through tubes of 1-2 mm in diameter and further elongated into host distal nerves 1-3 weeks after implantation. Morphometrical analysis of the regenerated nerve cable at the middle of each amnion matrix tube 3 weeks after implantation was performed. The average numbers of myelinated axons were almost the same (ca. 80-112/10(4) microm(2)) in AMTs of 1-2 mm in diameter, as in the normal sciatic nerve (ca. 95/10(4) microm(2)). No myelinated fibers were found in AMTs composed of multiple thin tubes of 0.2 mm in diameter. The myelinated axons were thinner in implanted tubes than those in the normal sciatic nerve. The rate of occurrences of myelinated axons less than 4 microm in diameter was significantly higher in the AMTs, whereas axons in the normal sciatic nerve were diverse in distribution, with the highest population at 8-12 microm in diameter. Reinnervation to the gastrocnemius muscle was demonstrated electrophysiologically 9 months after implantation. It was concluded that the extracellular matrix sheet from the human amnion is an effective conduit material for peripheral nerve regeneration.

Muscle autografts in nerve gaps. Pattern of regeneration and myelination in various lengths of graft: an experimental study in guinea pigs

Denatured muscle autograft contains large inner basement membrane tubes, which are anatomically and chemically similar to peripheral nerve basement membrane tubes. These autografts can be used for bridging nerve gaps. In 30 Duncan-Hartley guinea pig sciatic nerves, experimentally induced gaps of 5 mm, 10 mm, and 15 mm were bridged with freeze-thawed gluteus maximus muscle autografts. The results were studied for up to 12 weeks. Functional and histological criteria, morphometry, and electron microscopy were used for the evaluation of regeneration and myelination. Functional recovery was seen by 12 weeks in 5-mm grafts. Morphometric study of 1-microm semithin sections was carried out, and the number of axons in each representative field was studied, as the percentage of myelinated and unmyelinated fibers; the thickness of myelin was also measured. The percentage of myelinated and unmyelinated fibers was estimated by transmission electron microscopy (TEM). Axonal repopulation in the distal segment was seen by the third week in the 5-mm graft, and myelination was more extensive in this group in comparison to the others. On morphometric analysis, the mean fiber diameter in the distal part of the graft was 3.81 microm in the 5-mm graft and 2.9 microm in the 15-mm graft at 12 weeks. The results of this experiment prove that the length of the graft is an important consideration for muscle autografts when they are used for mixed peripheral nerve repair.

Grafting of detergent-denatured skeletal muscles provides effective conduits for extension of regenerating axons in the rat sciatic nerve

The basal laminae of muscle fibers, when treated by denaturing methods including freeze thawing, have been used as conduits for regenerating nerves. In this study, we developed a new method for denaturing skeletal muscle fibers through treatment with a biological detergent, sodium dodecyl sulfate. Laminin and type IV collagen proteins of muscle fiber basal laminae were preserved after the detergent treatment. A segment of detergent-denatured muscle was grafted to a 1-cm defect of the rat sciatic nerve. One week after grafting, regenerating axons immunostained for neurofilaments were seen extending within laminin-positive muscle fiber basal lamina tubes. Four weeks after grafting, numerous myelinated axons at a much higher level than the control unoperated sciatic nerve, were found in the middle of the graft. They were smaller in diameter than those in the control nerve. Distal host nerves were well reinnervated 4 weeks after grafting. These findings suggest that the basal laminae of detergent-denatured muscle fibers provide effective conduits for regenerating axons.

Experimental study on nerve regeneration through the basement membrane tubes of the nerve, muscle, and artery

We evaluated neurotization after transplantation with lyophilized nerves, muscles, and arteries, and examined the possibility of practical application of long bridging grafts. Grafts of 10 mm and 25 mm of lyophilized nerves, muscles, and arteries harvested from Fisher rats were transplanted to the sciatic nerves of recipient Lewis rats. The histological changes undergone by short grafts were observed at weekly intervals. The sham-operated and isograft groups were used to compare the results of long grafts. In both the nerve and muscle-graft group, regenerated axons grew out through the residual basement membrane tube. But in the muscle graft group, phagocytosis of myofibril debris took longer than that of degenerated axons. No statistical differences were found between results of TSI, induced EMG, and quantitative analysis of myelinated axons in the nerve and muscle graft groups. No neurotization was noted in the long artery graft. In long grafts, laminin found on the basement membrane may not be sufficient to accelerate neurotization, and arteries should not be used for tubulization.

A 25-year perspective of peripheral nerve surgery: evolving neuroscientific concepts and clinical significance

In spite of an enormous amount of new experimental laboratory data based on evolving neuroscientific concepts during the last 25 years peripheral nerve injuries still belong to the most challenging and difficult surgical reconstructive problems. Our understanding of biological mechanisms regulating posttraumatic nerve regeneration has increased substantially with respect to the role of neurotrophic and neurite-outgrowth promoting substances, but new molecular biological knowledge has so far gained very limited clinical applications. Techniques for clinical approximation of severed nerve ends have reached an optimal technical refinement and new concepts are needed to further increase the results from nerve repair. For bridging gaps in nerve continuity little has changed during the last 25 years. However, evolving principles for immunosuppression may open new perspectives regarding the use of nerve allografts, and various types of tissue engineering combined by bioartificial conduits may also be important. Posttraumatic functional reorganizations occurring in brain cortex are key phenomena explaining much of the inferior functional outcome following nerve repair, and increased knowledge regarding factors involved in brain plasticity may help to further improve the results. Implantation of microchips in the nervous system may provide a new interface between biology and technology and developing gene technology may introduce new possibilities in the manipulation of nerve degeneration and regeneration.

Retinal axon regeneration in peripheral nerve, tectal, and muscle grafts in adult rats

This study examined whether prior regenerative growth through peripheral nerve (PN) bridging grafts influenced the specificity with which lesioned adult rat retinal ganglion cell (RGC) axons grew into co-grafts of developing target tissue (fetal superior colliculus). Growth into nontarget (muscle) tissue was also examined. Autologous PN was grafted onto the transected optic nerve. After 14 days, the distal ends of the PNs were placed next to, or inserted into, embryonic tectal tissue or into autologous muscle grafts placed in frontal cortex cavities. Host retinal projections were examined 3-8 months later using anterograde and retrograde tracing techniques. In rats in which there was good apposition between PN and tectal tissue, small numbers of RGC axons were observed growing into the tectal grafts (maximum distance of 180 microm). No evidence of specific innervation of appropriate target regions within tectal grafts was detected, even though such regions (identified by acetylcholinesterase histochemistry) were often located close to the PN grafts. In rats with PN/muscle co-grafts, the extent of retinal axon outgrowth was greater (up to 465 microm from the PN tip) and labelled profiles that resembled motor endplates were seen contacting muscle fibres. Previous studies have shown that spontaneously regenerating RGC axons consistently and selectively innervate appropriate target areas in fetal tectal tissue grafted directly into optic tract lesion cavities. Together, the data suggest that exposure to a PN environment may have reduced the extent of adult retinal axon growth into fetal tectal transplants and affected the way regenerating axons responded to specific developmental cues expressed by target cells in the co-grafted tissue.

An alternative preparation of the acellular muscle graft for reconstruction of the injured nerve--morphological and morphometric analysis

The application of cutaneous nerve grafts is accompanied by some disadvantages, including insufficient graft material for the reconstruction of a large mixed nerve. Recently, evacuated muscle autografts have been suggested as possible alternatives to cutaneous nerve grafts. In the present paper we have demonstrated a possible preparation of the evacuated muscle graft using an infiltration of Marcaine. The reinnervation of the distal stump of the rat median nerve was evaluated by morphological and morphometric analysis after application of the muscle acellular grafts prepared by three methods: an ordinary freeze-thawed muscle graft, a Marcaine evacuated muscle graft and a Marcaine treated graft with subsequent freezing and thawing. A comparison of the numbers and diameters of the myelinated axons in the distal nerve stumps revealed very similar conditions for axon regrowth and maturation in Marcaine evacuated and freeze-thawed muscle grafts. The best results with myelinated axon numbers and spectrum of their calibres were obtained when the Marcaine treated graft was repeatedly frozen and thawed. The pre-treatment of the muscle graft by Marcaine prevents it from shrinking and fragmenting, the main disadvantage during freeze-thawing of fresh muscle. The present results demonstrate that infiltration of striated muscles with a myotoxic compound, e.g. Marcaine, with subsequent freezing-thawing is the method of choice for the preparation of an acellular muscle graft used in peripheral nerve reconnection in the experimental model.

Gustatory otalgia and wet ear syndrome: a possible cross-innervation after ear surgery

HYPOTHESIS

The chorda tympani and Arnold's nerves have close approximation to each other and their cross-innervation is possible after ear surgery.

STUDY DESIGN

A retrospective study was performed with a temporal bone pathology case and two clinical cases as representatives of such a possibility. Patients had severe otalgia and wet ear during gustatory stimulation.

METHODS

A temporal bone pathology case was studied under a light microscope. Earache and/or wet ear were provoked during gustatory stimulation. Wet ear was tested with iodine-starch reaction after the subject tasted lemon juice.

RESULTS

The temporal bone specimen has clusters of regenerated fibers in the tympanic cavity in the area of the chorda tympani and Arnold's nerves, suggesting a possibility of mixing. There are regenerated fibers in the iter chordae anterius, showing successful bridging of the chorda tympani nerves across a long gap. Detachment of the skin over the operated mastoid bowl obscured signs in one clinical case. Another clinical case of gustatory wet ear showed objective evidence of cross-innervation with iodine-starch reaction.

CONCLUSION

The detachment procedure and iodine-starch reaction were the proofs that the signs were related to regenerated fibers. This is the first report of gustatory otalgia and wet ear after ear surgery.

Axonal regeneration through muscle autografts submitted to local anaesthetic pretreatment

Freeze-thawed muscle grafts (FTMG) have been used as an alternative to nerve grafts for the reconstruction of peripheral nerve defects, although their use has some disadvantages. For instance, FTMG may fragment easily after freeze-thawing, a fact impairing their use for surgery. In this study we describe a method to obtain muscle autografts based on the myotoxic properties of local anaesthetics. Fifteen adult rats had their left tibialis anterior muscles injected transcutaneously with 0.3 ml of 2% lidocaine hydrochloride. Twenty-four hours later the injected muscle was removed and a lidocaine muscle graft (LMG) was obtained by trimming the muscle to a rectangular block of approximately 1.0 cm in length. The left sciatic nerve was exposed in the mid-thigh region and a segment removed so that a final 1.0 cm-long gap was produced. The LMG was coaxially autografted to the epineurium between the proximal and distal nerve stumps. In another 15 rats, the sciatic nerve gap was repaired with FTMG obtained from the tibialis anterior muscle. Surgical procedures were similar in both groups. Axonal regeneration and muscle reinnervation were studied quantitatively and ultrastructurally 60 days after the insertion of LMG and FTMG. The results showed that axonal regeneration with the LMG was qualitatively similar to that observed with the FTMG, with no significant differences between groups. We conclude that LMG was a successful muscle graft and a suitable alternative to other denaturing methods, without the disadvantages of FTMG.

Enhancing nerve regeneration across a silicone tube conduit by using interposed short-segment nerve grafts

Isolated nerve segments may inherently contain all of the necessary factors required to support regeneration within a silicone tube conduit placed across a nerve gap. Thirty-six adult Lewis rats each weighing approximately 250 g were randomized into three groups. A sciatic nerve gap (13-15 mm in length) was bridged by an empty silicone tube (Group I), a silicone tube containing a short 2-mm interposed nerve segment (Group II), or a nerve autograft (Group III). At 16 weeks postoperatively, no regeneration was observed through the empty silicone tube. In contrast, regeneration across the silicone tube containing the isolated nerve segment was equivalent to that noted through nerve autografts as assessed by histological, electrophysiological, and functional criteria. Thus, an interposed nerve segment will extend the length of successful nerve regeneration through a silicone tube conduit.

Axonal regeneration through acellular muscle grafts

The management of peripheral nerve injury remains a major clinical problem. Progress in this field will almost certainly depend upon manipulating the pathophysiological processes which are triggered by traumatic injuries. One of the most important determinants of functional outcome after the reconstruction of a transected peripheral nerve is the length of the gap between proximal and distal nerve stumps. Long defects (> 2 cm) must be bridged by a suitable conduit in order to support axonal regrowth. This review examines the cellular and acellular elements which facilitate axonal regrowth and the use of acellular muscle grafts in the repair of injuries in the peripheral nervous system.

Peripheral nerve regeneration

Peripheral nerve regeneration comprises the formation of axonal sprouts, their outgrowth as regenerating axons and the reinnervation of original targets. This review focuses on the morphological features of axonal sprouts at the node of Ranvier and their subsequent outgrowth guided by Schwann cells or by Schwann cell basal laminae. Adhesion molecules such as N-CAM, L1 and N-cadherin are involved in the axon-to-axon and axon-to-Schwann cell attachment, and it is suggested that integrins such as alpha 1 beta 1 and alpha 6 beta 1 mediate the attachment between axons and Schwann cell basal laminae. The presence of synaptic vesicle-associated proteins such as synaptophysin, synaptotagmin and synapsin I in the growth cones of regenerating axons indicates the possibility that exocytotic fusion of vesicles with the surface axolemma supplies the membranous components for the extension of regenerating axons. Almost all the subtypes of protein kinase C have been localized in growth cones both in vivo and in vitro. Protein kinase C and GAP-43 are implicated to be involved in at least some part of the adhesion of growth cones to the substrate and their growth activity. The significance of tyrosine kinase in growth cones is emphasized. Tyrosine kinase plays an important role in intracellular signal transduction of the growth of regenerating axons mediated by both nerve trophic factors and adhesion molecules. Growth factors such as NGF, BDNF, CNTF and bFGF are also discussed mainly in terms of the influence of Schwann cells on regenerating axons.

Axonal regeneration

Axons damaged in a peripheral nerve are often able to regenerate from the site of injury along the degenerate distal segment of the nerve to reform functional synapses. Schwann cells play a central role in this process. However, in the adult mammalian central nervous system, from which Schwann cells are absent, axonal regeneration does not progress to allow functional recovery. This is due to inhibitors of axonal growth produced by both oligodendrocytes and astrocytes and also to the decreased ability of adult neurons to extend axons during regeneration compared to embryonic neurons during development. However once provided with a substrate conducive to axonal growth, such as a peripheral nerve graft, many central neurons are able to regenerate axons over long distances. Over the past year this response has been utilised in experimental models to produce a degree of behavioural recovery.

An immuno-electronmicroscopical study of the distribution of laminin within autografts of denatured muscle

We have used an immunogold post-embedding technique to examine, qualitatively and quantitatively, the distribution of laminin along sarcolemmal basal laminae of variously treated muscle autografts placed in transected rat sciatic nerves. We found that freeze-thawing or heating to 60 degrees C prior to grafting did not affect laminin labelling density along the sarcolemmal basal laminae, either at the time of preparation or 7 days after grafting. In sharp contrast, heating to 80 degrees C significantly reduced laminin labelling density. These findings are consistent with our earlier work showing that frozen-thawed or 60 degrees C muscle autografts both support axonal regeneration, whereas 80 degrees C grafts do not, and add further support to the view that laminin is a functionally important molecule in nerve regeneration. We have compared immunostaining using 10 nm gold particles with silver enhancement of 5 nm gold particles: although labelling density was higher in the silver-enhanced preparations, there was no increase in background labelling. Although empty sarcolemmal basal lamina tubes were frequently highly infolded, there was no evidence of preferential labelling of either 'peaks' or 'troughs' of the infolded basal laminae.

The role of conduits in nerve repair: a review

The restoration of effective and meaningful axonal function following peripheral nerve injury continues to be a considerable clinical challenge. The use of conduits to bridge the gap between severed ends is a contemporary experimental maneuver that isolates the microenvironment of regenerating axons. Entubulation has allowed analysis and manipulation of putative influences upon nerve regeneration. A review is provided of the research efforts that have explored the neurobiological and mechanical factors that guide nerve regeneration within conduits. Levels of specificity, from tissue specific growth to end-organ specific growth, are outlined within the framework of the theories of Neurotropism, Contact Guidance and Neurotrophism. Included are investigations utilizing different conduit materials and the few clinical applications of these conduits. A number of chamber manipulations, extra-cellular matrix substrates and growth factors and their molecular receptors have been implicated in enhanced regeneration specificity. This information has been extended to the conduit model. The interposition of healthy nerve segments into conduits is proposed as a means of extending the length of successful nerve regeneration.

Different muscle graft denaturing methods and their use for nerve repair

In an attempt to enhance recovery through denatured muscle grafts we have used different methods to denature muscle, either using dry heat in a microwave oven or by warming in sterile distilled water. Axonal regeneration was studied at intervals from day 5 to day 60 after insertion of the muscle grafts and compared to results found in frozen-thawed muscle grafts and in autologous nerve grafts used as controls. Axonal regeneration, Schwann cell behaviour and the degree of inflammation were quantified using immunohistochemical techniques and computerised image analysis. Autologous nerve grafts supported the highest rates and volumes of axonal regeneration until day 30 when the microwaved muscle grafts had the highest values for axonal immunostaining and at 60 days the highest level of Schwann cell immunoreactivity. We conclude that microwave heating is suitable as an alternative denaturing method for successful muscle grafts and has a potential clinical use.

An experimental study of three methods of lingual nerve defect repair

PURPOSE

This study compares three methods of lingual nerve defect repair.

MATERIALS AND METHODS

The recovery of the mechanosensitive and thermosensitive afferent fibers in the lingual branch of the trigeminal nerve in cats was studied using electrophysiological techniques 24 weeks after the removal of a segment of lingual nerve and repair of the defect by one of three methods. The nerve gap was closed by either stretching the nerve ends together and repairing under tension, insertion of a sural nerve graft, or use of a freeze-thawed muscle graft. The characteristics of the regenerated fibers were investigated and the data were compared with that from normal control animals.

RESULTS

After nerve repair, integrated whole-nerve activity evoked by thermal (cold) stimulation of the tongue was smaller than in the controls, but there were no differences between the repaired groups. However, recordings made from single axons in filaments dissected from the nerve revealed differences between the groups; the units were less sensitive after either method of grafting than after stretch repair.

CONCLUSIONS

It is concluded that repair of a short gap in the lingual nerve by stretch repair with an end-to-end anastomosis, even with some degree of tension, is followed by better recovery than by grafting. However, where a graft is necessary, a similar level of recovery will result from use of a frozen muscle graft or a sural nerve graft.

Extraocular muscles: basic and clinical aspects of structure and function

Although extraocular muscle is perhaps the least understood component of the oculomotor system, these muscles represent the most common site of surgical intervention in the treatment of strabismus and other ocular motility disorders. This review synthesizes information derived from both basic and clinical studies in order to develop a better understanding of how these muscles may respond to surgical or pharmacological interventions and in disease states. In addition, a detailed knowledge of the structural and functional properties of extraocular muscle, that would allow some degree of prediction of the adaptive responses of these muscles, is vital as a basis to guide the development of new treatments for eye movement disorders.

Vein conduits for repair of nerves with a prolonged gap or in unfavourable conditions: an analysis of three failed cases

Clinical failure of vein conduits for repair of four nerves in three cases is reported. Two digital nerves with gaps of 5.0 cm and 5.8 cm, respectively, and two median nerves with gaps of 4.0 cm and 5.0 cm were repaired with vein conduits. The digital nerves were repaired secondarily with insertion of nerve tissue slices. The median nerve lacerations were associated with compound soft tissue injuries and were repaired primarily by interfascicular vein conduits. There was no detectable recovery of sensibility in autonomous areas of these nerves and no sign of recovery of the innervated muscles during follow-up. Re-exploration revealed that the vein conduits used for repair of the median nerves were constricted by surrounding scar tissue and axon regeneration was precluded. The critical length for nerve regeneration in human beings and wound conditions unfavorable to nerve regeneration are discussed. This report suggests that vein conduits are not indicated in nerve gaps over 5.0 cm or in primary repair of nerves with compound injuries.

Nerve regeneration in different types of grafts: experimental study in rabbits

The nerve regeneration patterns of five different types of grafts were studied in 40 rabbits. Conventional nerve autografts, vascularized nerve autografts, fresh nerve allografts, frozen nerve allografts, and muscle autografts were sutured to a 1.5 cm gap in the sciatic nerve and compared with normal nerves and nerves with a 3 cm gap. Regeneration was evaluated by means of electromyography, light and electron microscopy. Quantitative data from morphometric analysis of axonal diameter and myelination were statistically analyzed. Results 5 months after grafting showed no significant differences between the conventional and vascularized nerve autografts. There were no significant differences between frozen nerve allografts and muscle autografts. The best regeneration was achieved with autografts.

Are Schwann cells essential for axonal regeneration into muscle autografts?

When axons regenerate through frozen-thawed (FT) muscle grafts, they are accompanied by co-migrating Schwann cells derived from the nerve stumps. Although acellular, FT muscle grafts contain an internal scaffold of basal laminae rich in components capable of supporting neurite outgrowth in vitro such as laminin and fibronectin: it is not known whether Schwann cells are essential for axonal regrowth within these grafts. In this paper we test the hypothesis that sarcolemmal basal laminae will support axonal regeneration in the absence of Schwann cells. Two groups of 12 adult Wistar rats were used. All rats received a 0.5 cm FT muscle graft, and 12 rats also received a subperineurial injection of the anti-mitotic agent mitomycin C (400 micrograms/ml in physiological saline) prior to grafting. Previous studies have shown that this dose effectively depresses cell proliferation within the endoneurium for 3-4 weeks [17, 18, 28]. Rats were killed (n = 3) 1, 2, 3 or 4 weeks later. The spatio-temporal sequence of axonal regeneration into the grafts was assessed histologically, by immunofluorescence using antibodies against GAP-43; S-100; RT97; laminin and macrophages (ED1), and by transmission electron microscopy. Outgrowth of almost all axons from the mitomycin C-treated proximal stumps was delayed for up to 3 weeks, after which time vigorous regeneration occurred into the persisting tubes of sarcolemmal basal lamina. All axons regenerating within the grafts (irrespective of mitomycin C-treatment) were accompanied by co-migrating Schwann cells. The results suggest that Schwann cells play an important role in axonal regeneration across FT muscle autografts and that sarcolemmal basal laminae alone are insufficient to support axonal regeneration.

Axonal regeneration through heat pretreated muscle autografts. An immunohistochemical and electron microscopic study

We have compared the regeneration of axons through frozen-thawed or heated muscle autografts in the sciatic nerve of adult rats. Our results have shown that axons regenerate through muscle grafts which had been either frozen-thawed or heated to 60 degrees C prior to transplantation. However, axons failed to regenerate through muscle grafts which had been pre-heated to 80 degrees C. We speculate that this difference may be related to the thermal lability of components of muscle basal lamina, such as laminin and fibronectin, which are known to play an important role in axonal outgrowth.

Repair of mixed peripheral nerves using muscle autografts: a preliminary communication

Twelve patients were reviewed following the reconstruction of mixed motor/sensory nerves using freeze-thawed skeletal muscle autografts. A total of 13 nerves were reconstructed-6 median and 7 ulnar. All the repairs were secondary procedures, with a mean time from injury to grafting of 17 months. Sensory and motor evaluation was carried out and the patients asked to complete a pain questionnaire. Five patients achieved an S3+ level of sensory recovery. Two underwent revision of their muscle grafts to nerve grafts. Motor recovery was universally poor.

Bridging nerve defects with combined skeletal muscle and vein conduits

The use of vein or muscle grafts to bridge nerve defects longer than 1-1.5 cm gives poor results. Veins collapse and in muscle grafts axons may regrow outside the graft. We used veins (to guide regeneration) filled with muscle (to avoid vein collapse). Nerve regeneration through 1 and 2 cm grafts made of vein plus muscle was compared with similarly long traditional nerve grafts, free fresh muscle grafts, and empty vein grafts. Regeneration was assessed clinically and histologically (qualitative and quantitative evaluation) in the graft and distal nerve stumps. Vein plus muscle grafts were superior to vein and fresh muscle grafts both functionally and histologically. Functional results were similar to those found in traditional nerve grafts, but axon number was superior in the veins filled with muscle. This suggests that vein filled with muscle might serve as a grafting conduit for the repair of peripheral nerve injuries and could give better results than traditional nerve grafting.

Neurotropism, frozen muscle grafts and other conduits

Axonal regeneration following nerve transection requires a number of cellular and biochemical phenomena in the axons as well as the nerve cell bodies. The nerve cells must survive the trauma. Since axonal severance means amputation of a large axoplasmic volume from the remaining parts of the nerve cell, the cell body must prepare for increased synthesis of axoplasm to replace the missing parts. A sprouting process must be initiated at the level of transection. Regenerating axonal processes are to regenerate towards peripheral targets, a process regulated by an interaction between genetic mechanisms in the nerve cell body and biochemical information at the molecular level along the pathway.

The role of Schwann cells in the regeneration of peripheral nerve axons through muscle basal lamina grafts

Evacuated muscle is a possible substitute for nerve autografts in the repair of damaged peripheral nerves. Previous experiments have shown that killed or evacuated muscle grafts are as effective as nerve autografts for bridging gaps of up to 4 cm between proximal and distal nerve stumps. Evacuated muscle grafts are made of extracellular matrix components, which are good substrates for axon growth in vitro. However, experiments in vivo have generally demonstrated that live Schwann cells are essential for successful axon regeneration. In the present experiments we have used immunohistochemical techniques with anti-S100 and anti-neurofilament antibodies to visualize axon growth and Schwann cell migration into muscle grafts over the first 10 days following grafting. We only saw axons growing into grafts accompanied by Schwann cells, and most though not all Schwann cells were associated with axons. Schwann cell migration from the proximal stump in association with axons was much faster and more extensive than from the distal stump. We examined muscle grafts over the first 20 days after grafting by electron microscopy. Regenerating axons were always associated with Schwann cells, which were mostly in the basal lamina-lined tubes left by the evacuated myofibrils. A comparison between evacuated muscle grafts and grafts in which the muscle had been killed but not evacuated revealed that 7 days after grafting there were more than twice as many regenerated axons in and distal to the evacuated grafts, but that by 20 days the numbers of axons were similar in the two groups.