Optic axons regenerate into sciatic nerve isografts only in the presence of Schwann cells

Optic axons regenerate into normal but not acellular peripheral nerve (PN) grafts. The first axons penetrate the PN graft before 5 days and grow inside the basal lamina tubes amongst the Schwann cells. By 30 days, 4% of the surviving retinal ganglion cells (RGC) regenerate axons for at least 10 mm into the PN graft. Laminin rich basal lamina tubes persist in the acellular PN transplants but only a few axons penetrate the most proximal parts of the tubes by 5 days and none grow farther into the graft by 30 days. RGC counts demonstrate that 34% of the normal RGC population survive 30 days after anastomosing a normal PN to the transected optic nerve. After anastomosing acellular PN grafts, 25% of RGCs survive compared with 10% after optic nerve section. These findings demonstrate that laminin does not promote regeneration of axons and that Schwann cells play the primary role of offering trophic support and even a substrate for growth. RGC survival is also enhanced by PN grafts even when Schwann cells are absent. This latter result suggests that RGC survival is promoted by a trophic substance released from axons and/or Schwann cells in the PN grafts which survives the thawing/freezing procedure (used to kill the Schwann cells) and is active in the grafts in the immediate post operative period.     

Schwann cell migration through freeze-killed peripheral nerve grafts without accompanying axons

Summary Freeze-dried tibial nerve grafts were anastomosed to either the proximal stump or the distal stump of severed tibial nerves in adult inbred Fischer rats. In the case of grafts attached to the proximal stump the tibial nerve was ligated three times, the most distal ligature from the spinal cord being 1 cm from the site of anastomosis. In both types of experiment Schwann cells were, therefore, free to enter the initially acellular grafts without accompanying axons. The grafts were examined 17 days to 12 weeks after operation. Immunofluorescence for S-100 protein was used to evaluate the distance migrated by the Schwann cells and electron microscopy was used to examine the morphology of the cells which invaded the grafts. Schwann cell migration was similar from the proximal and distal stumps. The migrating Schwann cells formed columns which resembled bands of Bungner. They were found mainly, but not exclusively, inside the pre-existing basal lamina tubes left behind by the killed nerve fibres. Some Schwann cells secreted a thin, patchy basal lamina even though they lacked axonal contact. Schwann cell columns became partially compartmentalized by fibroblast processes. Myelin and other debris were removed most rapidly in those parts of the grafts penetrated by large numbers of Schwann cells. The maximum distance the Schwann cells penetrated into the grafts was 8.5 mm and this was achieved by 6 to 8 weeks after operation. This is about half the maximum distance migrated by Schwann cells accompanying regenerating axons through similar grafts. The reasons why Schwann cells migrate shorter distances without axons and the significance of these results for the interpretation of axonal regeneration experiments using acellular grafts are discussed.Supported by a grant from the Medical Research Council     

Vascular endothelial growth factor stimulates Schwann cell invasion and neovascularization of acellular nerve grafts

The aim of this study was to investigate the effects of vascular endothelial growth factor (VEGF) on regeneration of the rat sciatic nerve in vivo. To that end we used 10-mm long cell-free nerve grafts to bridge a gap in the sciatic nerve. The grafts were pretreated with either VEGF (50, 100 or 250 ng/ml), nerve growth factor (NGF, 100 ng/ml) or laminin (100 ng/ml) before implantation. Outgrowth of axons, Schwann cells, blood vessels and macrophages were studied 10 days post-implantation by the use of immunocytochemistry and histochemistry. Grafts pretreated with VEGF stimulated the outgrowth of Schwann cells and blood vessels but not axons. In such grafts, the Schwann cells also exhibited a dramatic change in morphology and became filled with large lipid-containing vacuoles. These cells also showed an intense immunoreactivity for the VEGF receptor flk-1. Neither pretreatment with laminin nor NGF affected the outgrowth of Schwann cells. However, NGF treatment increased the number of axons in the graft but was not able to counteract injury-induced downregulation of substance P in the dorsal root ganglia. The results show that local application of VEGF promotes at least two events, invasion of Schwann cells and neovascularization, which are important during nerve regeneration. The findings suggest that the effects of the pretreatment by the growth factors is local and limited to the graft, whereas central events like neuropeptide synthesis is not affected.     

The role of Schwann cells and basal lamina tubes in the regeneration of axons through long lengths of freeze-killed nerve grafts

The ability of long acellular nerve grafts to support axonal regeneration was examined using inbred rats. Grafts (40 mm long) of tibial/plantar nerves were used either as live grafts or after freeze-drying to render the grafts acellular. The grafts were sutured to the proximal stump of severed tibial nerves in host animals which were then killed 1-12 weeks later. Axons rapidly regenerated through the living grafts but only extended 10-20 mm into the acellular grafts. This distance was achieved by 6 weeks and thereafter no significant further axonal extension occurred in the acellular grafts. A few naked axons lacking Schwann cell contact were identified in all acellular grafts, but became more numerous near the distal extent of axonal penetration into 6-12 week grafts. These axons contained large numbers of neurofilaments. When the distal 20 mm of 6 week acellular grafts (segments into which axons had not penetrated) were sutured to freshly severed tibial nerves, axons grew readily into the grafted tissue to a maximum distance of 9 mm. It is therefore likely that the limits to axonal regeneration through initially acellular grafts were set by factors intrinsic to the severed nerve. It is suggested that the limited migratory powers of Schwann cells may be one such factor. The concept that basal lamina tubes are not essential for axonal regeneration but may act as low resistance pathways for both axonal elongation and Schwann cell migration is discussed.     

GDNF‐treated acellular nerve graft promotes motoneuron axon regeneration after implantation into cervical root avulsed spinal cord

T‐H. Chu, L. Wang, A. Guo, V. W‐K. Chan, C. W‐M. Wong and W. Wu (2012) Neuropathology and Applied Neurobiology 38, 681–695 GDNF‐treated acellular nerve graft promotes motoneuron axon regeneration after implantation into cervical root avulsed spinal cord It is well known that glial cell line‐derived neurotrophic factor (GDNF) is a potent neurotrophic factor for motoneurons. We have previously shown that it greatly enhanced motoneuron survival and axon regeneration after implantation of peripheral nerve graft following spinal root avulsion. Aims: In the current study, we explore whether injection of GDNF promotes axon regeneration in decellularized nerve induced by repeated freeze‐thaw cycles. Methods: We injected saline or GDNF into the decellularized nerve after root avulsion in adult Sprague–Dawley rats and assessed motoneuron axon regeneration and Schwann cell migration by retrograde labelling and immunohistochemistry. Results: We found that no axons were present in saline‐treated acellular nerve whereas Schwann cells migrated into GDNF‐treated acellular nerve grafts. We also found that Schwann cells migrated into the nerve grafts as early as 4 days after implantation, coinciding with the first appearance of regenerating axons in the grafts. Application of GDNF outside the graft did not induce Schwann cell infiltration nor axon regeneration into the graft. Application of pleiotrophin, a trophic factor which promotes axon regeneration but not Schwann cell migration, did not promote axon infiltration into acellular nerve graft. Conclusions: We conclude that GDNF induced Schwann cell migration and axon regeneration into the acellular nerve graft. Our findings can be of potential clinical value to develop acellular nerve grafting for use in spinal root avulsion injuries.     

Treatment modality affects allograft-derived Schwann cell phenotype and myelinating capacity

We used peripheral nerve allografts, already employed clinically to reconstruct devastating peripheral nerve injuries, to study Schwann cell (SC) plasticity in adult mice. By modulating the allograft treatment modality we were able to study migratory, denervated, rejecting, and reinnervated phenotypes in transgenic mice whose SCs expressed GFP under regulatory elements of either the S100b (S100-GFP) or nestin (Nestin-GFP) promoters. Well-differentiated SCs strongly expressed S100-GFP, while Nestin-GFP expression was stimulated by denervation, and in some cases, axons were constitutively labeled with CFP to enable in vivo imaging. Serial imaging of these mice demonstrated that untreated allografts were rejected within 20 days. Cold preserved (CP) allografts required an initial phase of SC migration that preceded axonal regeneration thus delaying myelination and maturation of the SC phenotype. Mice immunosuppressed with FK506 demonstrated mild subacute rejection, but the most robust regeneration of myelinated and unmyelinated axons and motor endplate reinnervation. While characterized by fewer regenerating axons, mice treated with the co-stimulatory blockade (CSB) agents anti-CD40L mAb and CTLAIg-4 demonstrated virtually no graft rejection during the 28 day experiment, and had significant increases in myelination, connexin-32 expression, and Akt phosphorylation compared with any other group. These results indicate that even with SC rejection, nerve regeneration can occur to some degree, particularly with FK506 treatment. However, we found that co-stimulatory blockade facilitate optimal myelin formation and maturation of SCs as indicated by protein expression of myelin basic protein (MBP), connexin-32 and phospho-Akt.     

Comparison of different biogenic matrices seeded with cultured Schwann cells for bridging peripheral nerve defects

Tissue-engineering as laboratory based alternative to human autografts and allografts provides "custom made organs" cultured from patient's material. To overcome the limited donor nerve availability different biologic nerve grafts were engineered in a rat sciatic nerve model: cultured isogenic Schwann cells were implanted into acellular autologous matrices: veins, muscles, nerves, and epineurium tubes. Autologous nerve grafts, and the respective biogenic material without Schwann cells served as control. After 6 weeks regeneration was assessed clinically, histologically and morphometrically. The PCR analysis showed that the implanted Schwann cells remain within all the grafts. A good regeneration was noted in the muscle-Schwann cell-group, while regeneration quality in the other groups (with or without Schwann cells) was impaired. The muscle-Schwann cell graft showed a systematic and organized regeneration including a proper orientation of regenerated fibers. All venous and epineurium grafts had a more disorganized regeneration. Seemingly, the lack of endoneural tube like structures in vein grafts lead to impaired regeneration. And, apparently, the beneficial effects of implanted Schwann cells into a large luminal structure can only be demonstrated to a limited extent if endoneural like structures are lacking. A tube offers less area for Schwann cell adhesion and it is more likely to collapse. This underlines the role of the basal lamina, or at least an inner structure acting as scaffold in axonal regeneration. Although the conventional nerve graft remains the gold standard, the implantation of Schwann cells into an acellular muscle provides a biogenic graft with basal lamina tubes as pathway for regenerating axons and the positive effects of Schwann cells producing neurotrophic and neurotropic factors, and thus, supporting axonal regeneration.     

Hyperbaric oxygen treatment has different effects on nerve regeneration in acellular nerve and muscle grafts

Effects of hyperbaric oxygen treatment (HBO) on nerve regeneration in acellular nerve and muscle grafts were investigated in rats. Nerve and muscle grafts were made acellular by freeze-thawing and the obtained grafts were used to bridge a 10-mm gap in the sciatic nerve on the left and right sides, respectively. Rats were treated with HBO (100% oxygen for 90 minutes at 2.5 atmospheres absolute pressure ATA) twice a day for 7 days. Axonal outgrowth, Schwann cell migration and invasion of macrophages were examined 10 days after the graft procedure by staining neurofilaments, S-100 proteins and the macrophage antibodies ED1 and ED2, respectively. Axonal outgrowth and Schwann cell migration in acellular nerve grafts were superior to that found in the acellular muscle grafts. However, there was no difference between HBO-treated and nontreated rats in acellular nerve grafts. Such a difference was found in acellular muscle grafts concerning both axonal outgrowth and Schwann cell migration from the proximal nerve end. No differences in the content of macrophages or neovascularization (alkaline phosphatase staining) in either of the grafts and treatments were seen. It is concluded that there is a differential effect of HBO-treatment in acellular nerve and muscle grafts and that HBO-treatment has no effect on the regeneration process in acellular nerve grafts, in contrast to fresh cellular nerve grafts where a beneficial effect has previously been reported.     

Comparison of different biogenic matrices seeded with cultured Schwann cells for bridging peripheral nerve defects

Abstract

Tissue-engineering as laboratory based alternative to human autografts and allografts provides "custom made organs" cultured from patient's material. To overcome the limited donor nerve availability different biologic nerve grafts were engineered in a rat sciatic nerve model: cultured isogenic Schwann cells were implanted into acellular autologous matrices: veins, muscles, nerves, and epineurium tubes. Autologous nerve grafts, and the respective biogenic material without Schwann cells served as control. After 6 weeks regeneration was assessed clinically, histologically and morphometrically. The PCR analysis showed that the implanted Schwann cells remain within all the grafts. A good regeneration was noted in the muscle-Schwann cell-group, while regeneration quality in the other groups (with or without Schwann cells) was impaired. The muscle-Schwann cell graft showed a systematic and organized regeneration including a proper orientation of regenerated fibers. All venous and epineurium grafts had a more disorganized regeneration. Seemingly, the lack of endoneural tube like structures in vein grafts lead to impaired regeneration. And, apparently,the beneficial effects of implanted Schwann cells into a large luminal structure can only be demonstrated to a limited extent if endoneural like structures are lacking. A tube offers less area for Schwann cell adhesion and it is more likely to collapse. This underlines the role of the basal lamina, or at least an inner structure acting as scaffold in axonal regeneration. Although the conventional nerve graft remains the gold standard, the implantation of Schwann cells into an acellular muscle provides a biogenic graft with basal lamina tubes as pathway for regenerating axons and the positive effects of Schwann cells producing neurotrophic and neurotropic factors, and thus, supporting axonal regeneration.     

Morphological evidence for a transport of ribosomes from Schwann cells to regenerating axons

Recently, we showed that Schwann cells transfer ribosomes to injured axons. Here, we demonstrate that Schwann cells transfer ribosomes to regenerating axons in vivo. For this, we used lentiviral vector-mediated expression of ribosomal protein L4 and eGFP to label ribosomes in Schwann cells. Two approaches were followed. First, we transduced Schwann cells in vivo in the distal trunk of the sciatic nerve after a nerve crush. Seven days after the crush, 12% of regenerating axons contained fluorescent ribosomes. Second, we transduced Schwann cells in vitro that were subsequently injected into an acellular nerve graft that was inserted into the sciatic nerve. Fluorescent ribosomes were detected in regenerating axons up to 8 weeks after graft insertion. Together, these data indicate that regenerating axons receive ribosomes from Schwann cells and, furthermore, that Schwann cells may support local axonal protein synthesis by transferring protein synthetic machinery and mRNAs to these axons.     

Chondroitinase treatment increases the effective length of acellular nerve grafts

Acellular nerve allografts have been explored as an alternative to nerve autografting. It has long been recognized that there is a distinct limit to the effective length of conventional acellular nerve grafts, which must be overcome for many grafting applications. In rodent models nerve regeneration fails in acellular nerve grafts greater than 2 cm in length. In previous studies we found that nerve regeneration is markedly enhanced with acellular nerve grafts in which growth-inhibiting chondroitin sulfate proteoglycan was degraded by pretreatment with chondroitinase ABC (ChABC). Here, we tested if nerve regeneration can be achieved through 4-cm acellular nerve grafts pretreated with ChABC. Adult rats received bilateral sciatic nerve segmental resection and repair with a 4 cm, thermally acellularized, nerve graft treated with ChABC (ChABC graft) or vehicle-treated acellularized graft (Control graft). Nerve regeneration was examined 12 weeks after implantation. Our findings confirm that functional axonal regeneration fails in conventional long acellular grafts. In this condition we found very few axons in the distal host nerve, and there were marginal signs of sciatic nerve reinnervation in few (2/9) rats. This was accompanied by extensive structural disintegration of the distal graft and abundant retrograde axonal regeneration in the proximal nerve. In contrast, most (8/9) animals receiving nerve repair with ChABC grafts showed sciatic nerve reinnervation by direct nerve pinch testing. Histological examination revealed much better structural preservation and axonal growth throughout the ChABC grafts. Numerous axons were found in all but one (8/9) of the host distal nerves and many of these regenerated axons were myelinated. In addition, the amount of aberrant retrograde axonal growth (originating near the proximal suture line) was markedly reduced by repair with ChABC grafts. Based on these results we conclude that ChABC treatment substantially increases the effective length of acellular nerve grafts.     

Axonal outgrowth in muscle grafts made acellular by chemical extraction

Purpose: To compare nerve regeneration in autologous detergent extracted and freeze-thawed muscle grafts and to electrophoretically characterize the grafts. Methods: Autologous acellular muscie grafts were created either by freeze/thawing or by detergent extraction and then used to bridge a 10 mm gap in rat sciatic nerve. The autologous grafts were compared with respect to protein content, using electrophoresis preimplantation, and axonal outgrowth, Schwann cell and macrophage content, using immunocytochemistry (neurofilaments, S-100 protein, ED 1 macrophages) at 5-20 days postimplantation. Results: The extracted muscle grafts were elastic, but the amount of several proteins was reduced and laminin was still present at a position of basal laminae of the muscle fibers. The freeze/thawed grafts were brittle and lacked elasticity, but resulted in minor changes in major proteins. The axons regenerated through both types of grafts (initial delay 6 days and rate 0.7-0.8 mm/day), which shrunk in length by 25%. There were no apparent differences with respect to Schwann cells and macrophages. Conclusions: The results suggest that detergent extracted muscle tissue, in which some basal lamina proteins remain but cells are removed, could present a new favourable option for nerve grafting.     

Dynamic quantification of host Schwann cell migration into peripheral nerve allografts

Host Schwann cell (SC) migration into nerve allografts is the limiting factor in the duration of immunosuppression following peripheral nerve allotransplantation, and may be affected by different immunosuppressive regimens. Our objective was to compare SC migration patterns between clinical and experimental immunosuppression regimens both over time and at the harvest endpoint. Eighty mice that express GFP under the control of the Schwann cell specific S100 promoter were engrafted with allogeneic, nonfluorescent sciatic nerve grafts. Mice received immunosuppression with either tacrolimus (FK506), or experimental T-cell triple costimulation blockade (CSB), consisting of CTLA4-immunoglobulin fusion protein, anti-CD40 monoclonal antibody, and anti-inducible costimulator monoclonal antibody. Migration of GFP-expressing host SCs into wild-type allografts was assessed in vivo every 3 weeks until 15 weeks postoperatively, and explanted allografts were evaluated for immunohistochemical staining patterns to differentiate graft from host SCs. Immunosuppression with tacrolimus exhibited a plateau of SC migration, characterized by significant early migration (< 3 weeks) followed by a constant level of host SCs in the graft (15 weeks). At the endpoint, graft fluorescence was decreased relative to surrounding host nerve, and donor SCs persisted within the graft. CSB-treated mice displayed gradually increasing migration of host SCs into the graft, without the plateau noted in tacrolimus-treated mice, and also maintained a population of donor SCs at the 15-week endpoint. SC migration patterns are affected by immunosuppressant choice, particularly in the immediate postoperative period, and the use of a single treatment of CSB may allow for gradual population of nerve allografts with host SCs.     

Fresh and predegenerate nerve allografts and isografts in trembler mice

In order to investigate whether Schwann cell or myelin was the principal antigen responsible for nerve graft reiection, fresh nerve grafts and those in which myelin had been previously allowed to degenerate (predegenerate grafts) from both isogeneic BALB/c and allogeneic C57/B1 mice were inserted into trembler BALB/c mice. Schwann cells within nerve allografts from C57/B1 mice were rejected, whether or not the grafts contained myelin. Nerve isografts from normal BALB/c animals produced normally myelinated trembler axons within the grafted segments, and across these segments conduction velocity was restored towards the normal value. It is concluded that Schwann cells, not myelin, constitute the principlal antigen within nerve allografts and it is Schwann-cell rejection that limits the sucessful use of nerve allografts.     

Repair of extended peripheral nerve lesions in rhesus monkeys using acellular allogenic nerve grafts implanted with autologous mesenchymal stem cells

Despite intensive efforts in the field of peripheral nerve injury and regeneration, it remains difficult in humans to achieve full functional recovery following extended peripheral nerve lesions. Optimizing repair of peripheral nerve injuries has been hindered by the lack of viable and reliable biologic or artificial nerve conduits for bridging extended gaps. In this study, we utilized chemically extracted acellular allogenic nerve segments implanted with autologous non-hematopoietic mesenchymal stem cells (MSCs) to repair a 40 mm defect in the rhesus monkey ulnar nerve. We found that severely damaged ulnar nerves were structurally and functionally repaired within 6 months following placement of the MSC seeded allografts in all animals studied (6 of 6, 100%). Furthermore, recovery with the MSC seeded allografts was similar to that observed with Schwann cell seeded allografts and autologous nerve grafts. The findings presented here are the first demonstration of the successful use of autologous MSCs, expanded in culture and implanted in a biological conduit, to repair a peripheral nerve gap in primates. Given the difficulty in isolating and purifying sufficient quantities of Schwann cells for peripheral nerve regeneration, the use of MSCs to seed acellular allogenic nerve grafts may prove to be a novel and promising therapeutic approach for repairing severe peripheral nerve injuries in humans.     

The role of laminin, a component of Schwann cell basal lamina, in rat sciatic nerve regeneration within antiserum-treated nerve grafts

Regeneration of the sciatic nerve in transplanted nerve grafts in which laminin was inactivated was examined electron microscopically. Nerve grafts for transplantation were obtained from close cloned donor Wistar rats; 1-cm nerve segments of the sciatic nerve were frozen and thawed to kill the Schwann cells. Control recipient rats received grafts treated with normal rabbit serum to repair the artificially-made complete defect of the right sciatic nerve, and the experimental group of rats received grafts doubly treated with normal serum and rabbit anti-laminin antiserum. In the control grafts regenerating axons grew almost completely through the inside of the basal lamina scaffolds (92%) and adhered to the structure, while in the anti-laminin antiserum treated grafts the axons were present outside (52%) and inside (48%) the scaffolds simultaneously. In this case, the adhesion of axons to the scaffolds was obscure. Axons were associated with and without Schwann cells both inside and outside the basal lamina scaffolds. No unassociated Schwann cells were observed. The maximal number of axons in a 2 mm portion of the antiserum-treated grafts was approximately 250 axons per 100 × 100 μm square and 520 in the control at 15 days. At 30 days, almost the same number of axons was found at the distal (8 mm) portion of both groups. The growth in the former was delayed for 3 days. These results indicate that regenerating peripheral nerve axons may enter the basal lamina scaffolds and grow well because of the neurotrophic function of laminin present at the inner side of Schwann cell basal lamina.     

Tourniquet compression: a non-invasive method to enhance nerve regeneration in nerve grafts

One hindlimb of a rat was subjected to tourniquet compression (150, 200 and 300 mmHg; 2 h). After 6 days a 10 mm sciatic or tibial nerve graft from the compressed limb was sutured to bridge a 3-4 mm gap in the sciatic nerve of the non-compressed limb. The distances of regenerating sensory axons were measured 6 days post surgery (tibial grafts, 8 days). Compression at 200 and 300 mmHg led to significantly longer regeneration distances than those seen in controls. Incorporation of BrdU and expression of p75 receptor by non-neuronal cells (Schwann cells) in sciatic nerves 6 days after compression (150 and 300 mmHg; 2 h) was also increased as a sign of Schwann cell activation. Tourniquet compression may be used as a non-invasive method to enhance nerve regeneration in nerve grafts.     

Schwann cell basal lamina and nerve regeneration

Nerve segments approximately 7 mm long were excised from the predegenerated sciatic nerves of mice, and treated 5 times by repetitive freezing and thawing to kill the Schwann cells. Such treated nerve segments were grafted into the original places so as to be in contact with the proximal stumps. The animals were sacrificed 1, 2, 3, 5, 7 and 10 days after the grafting. The grafts were examined by electron microscopy in the middle part of the graft, i.e. 3-4 mm distal to the proximal end and/or near the proximal and distal ends of the graft. In other instances, the predegenerated nerve segments were minced with a razor blade after repetitive freezing and thawing. Such minced nerves were placed in contact with the proximal stumps of the same nerves. The animals were sacrificed 10 days after the grafting. Within 1-2 days after grafting, the dead Schwann cells had disintegrated into fragments. They were then gradually phagocytosed by macrophages. The basal laminae of Schwann cells, which were not attacked by macrophages, remained as empty tubes (basal lamina scaffolds). In the grafts we examined, no Schwann cells survived the freezing and thawing process. The regenerating axons always grew out through such basal lamina scaffolds, being in contact with the inner surface of the basal lamina (i.e. the side originally facing the Schwann cell plasma membrane). No axons were found outside of the scaffolds. One to two days after grafting, the regenerating axons were not associated with Schwann cells, but after 5-7 days they were accompanied by Schwann cells which were presumed to be migrating along axons from the proximal stumps. Ten days after grafting, proliferating Schwann cells observed in the middle part of the grafts had begun to sort out axons. In the grafts of minced nerves, the fragmented basal laminae of the Schwann cells re-arranged themselves into thicker strands or small aggregations of basal laminae. The regenerating axons, without exception, attached to one side of such modified basal laminae. Collagen fibrils were in contact with the other side, indicating that these modified basal laminae had the same polarity in terms of cell attachment as seen in the ordinary basal laminae of the scaffolds.(ABSTRACT TRUNCATED AT 400 WORDS)     

The influence of cultured Schwann cells on regeneration through acellular basal lamina grafts

Acellular basal lamina grafts have been shown to be less immunogenic in comparison to cellular grafts, but possess a limited potential for supporting axonal regeneration through them. The present study describes the effect of cultured Schwann cells on enhancing regeneration through acellular grafts. 2 cm long acellular grafts, and in vitro Schwann cell populated acellular grafts were used to repair a surgically created gap in the host peroneal nerve. The transplants were analyzed at 1, 2, 4 and 8 weeks to determine their ability to support axonal regeneration. Host axonal regeneration through Schwann cell cocultured acellular grafts occurred rapidly and was significantly better as compared to non-cultured acellular grafts. The results demonstrate a beneficial effect of Schwann cell culture pretreatment on regeneration through acellular grafts and an improved recovery of the target muscle. The procedure of first preparing acellular grafts with subsequent coculture with Schwann cells offers a novel approach for the repair of injured nervous tissue.     

Long term evaluation of experimental median nerve repair by frozen and fresh nerve autografts,allografts and allografts repopulated by autologous Schwann cells

The authors used different kinds of peripheral nerve grafts to reconstruct a terminal branch of the brachial plexus (the median nerve) gap of adult Sprague-Dawley rats, including fresh or frozen autografts and allografts from Norway rats. They also performed acellular allograft repopulation by autogenous Schwann cells, to improve the environment for nerve regeneration. Three, six, nine and twelve months after grafting, rats underwent histological assessment (muscle, nerve and spinal cord) and simple functional assessment by the grasping test. Initially, the functional recovery of frozen grafts was lower than fresh graft recovery, but twelve months after surgery it was similar for both types of graft.