Regrowth of axons into the distal spinal cord through a Schwann-cell-seeded mini-channel implanted into hemisected adult rat spinal cord

A novel role of phospholipase A2in mediating spinal cord secondary injury

OBJECTIVE

To investigate whether phospholipase A2 (PLA2) plays a role in the pathogenesis of spinal cord injury (SCI).

METHODS

Biochemical, Western blot, histological, immunohistochemical, electron microscopic, electrophysiological, and behavior assessments were performed to investigate (1) SCI-induced PLA2 activity, expression, and cellular localization after a contusive SCI; and (2) the effects of exogenous PLA2 on spinal cord neuronal death in vitro and tissue damage, inflammation, and function in vivo.

RESULTS

After SCI, both PLA2 activity and cytosolic PLA2 expression increased significantly, with cytosolic PLA2 expression being localized mainly in neurons and oligodendrocytes. Both PLA2 and melittin, an activator of endogenous PLA2, induced spinal neuronal death in vitro, which was substantially reversed by mepacrine, a PLA2 inhibitor. When PLA2 or melittin was microinjected into the normal spinal cord, the former induced confined demyelination and latter diffuse tissue necrosis. Both injections induced inflammation, oxidation, and tissue damage, resulting in corresponding electrophysiological and behavioral impairments. Importantly, the PLA2-induced demyelination was significantly reversed by mepacrine.

INTERPRETATION

PLA2, increased significantly after SCI, may play a key role in mediating neuronal death and oligodendrocyte demyelination following SCI. Blocking PLA2 action may represent a novel repair strategy to reduce tissue damage and increase function after SCI.

Grafts of brain-derived neurotrophic factor and neurotrophin 3-transduced primate Schwann cells lead to functional recovery of the demyelinated mouse spinal cord

Experimental studies provided overwhelming proof that transplants of myelin-forming cells achieve efficient remyelination in the CNS. Among cellular candidates, Schwann cells can be used for autologous transplantation to ensure robust remyelination of lesions and to deliver therapeutic factors in the CNS. In the present study, macaque Schwann cells expressing green fluorescent protein (GFP) were infected with human immunodeficiency virus-derived vectors overexpressing brain-derived neurotrophic factor (BDNF) or Neurotrophin 3 (NT-3), two neurotrophins that also modulate glial cell biology. The ability of transgenic Schwann cells to secrete growth factors was assessed by ELISA and showed 35- and 62-fold increases in BDNF and NT-3, respectively, in transduced macaque Schwann cell supernatants. Conditioned media of BDNF- and NT-3-transduced Schwann cells reduced Schwann cell proliferation and favored their differentiation in vitro. Transgenic cells were grafted in demyelinated spinal cords of adult nude mice. Two behavioral assays showed that NT-3- and BDNF-transduced Schwann cells promoted faster and stronger functional recovery than GFP-transduced Schwann cells. Morphological analysis indicated that functional recovery correlated with enhanced proliferation and differentiation of resident oligodendrocyte progenitors and enhanced oligodendrocyte and Schwann cell differentiation. Moreover, NT-3-transduced Schwann cells provided neuroprotection and reduced astrogliosis. These results underline the potential therapeutic benefit of combining neuroprotection and activation of myelin-forming cells to restore altered functions in demyelinating diseases of the CNS.

Early profiles of axonal growth and astroglial response after spinal cord hemisection and implantation of Schwann cell-seeded guidance channels in adult rats

We previously demonstrated that transplantation of Schwann cell-seeded channels promoted the regrowth of injured axons in the adult spinal cord. It is not clear, however, whether injured axons recapitulate the developmental scenarios to accomplish regeneration. In the present study, we investigated the early events associated with axonal regrowth after spinal cord hemisection at the eighth thoracic level and implantation of a Schwann cell-seeded minichannel in adult rats. Animals were sacrificed at postoperative days (PO) 2, 4, 7, and 14. Anterograde tracing with fluoro-ruby showed that regenerating axons grew into the graft prior to PO2 and reached the distal end of the channel at PO7. These axons expressed both embryonic neural cell adhesion molecule (E-NCAM) and growth associated protein-43 (GAP-43). Although the expression of E-NCAM decreased by PO7, that of GAP-43 remained high throughout the first 2 weeks after implantation. A close relation of vimentin-positive astroglia to the growing axons in the host tissue suggested a contact-mediated role of these cells in axon guidance. Aggregation of glial fibrillary acidic protein (GFAP)-positive astrocytes together with the increased expression of chondroitin sulfate proteoglycans (CSPGs) starting at PO7 appeared to inhibit axonal growth at the host-graft interface. Thus, adult regenerating axons and astroglia do express developmentally related molecules that may facilitate axonal growth into a permissive graft at the early phase of injury and regeneration. These results suggest that molecules and astroglia essential to development are both important in influencing axonal regrowth in the adult spinal cord.

Olfactory mucosa autografts in human spinal cord injury: a pilot clinical study

BACKGROUND/OBJECTIVE

Olfactory mucosa is a readily accessible source of olfactory ensheathing and stem-like progenitor cells for neural repair. To determine the safety and feasibility of transplanting olfactory mucosa autografts into patients with traumatically injured spinal cords, a human pilot clinical study was conducted.

METHODS

Seven patients ranging from 18 to 32 years of age (American Spinal Injury Association [ASIA] class A) were treated at 6 months to 6.5 years after injury. Olfactory mucosa autografts were transplanted into lesions ranging from 1 to 6 cm that were present at C4-T6 neurological levels. Operations were performed from July 2001 through March 2003. Magnetic resonance imaging (MRI), electromyography (EMG), and ASIA neurological and otolaryngological evaluations were performed before and after surgery.

RESULTS

MRI studies revealed moderate to complete filling of the lesion sites. Two patients reported return of sensation in their bladders, and one of these patients regained voluntary contraction of anal sphincter. Two of the 7 ASIA A patients became ASIA C. Every patient had improvement in ASIA motor scores. The mean increase for the 3 subjects with tetraplegia in the upper extremities was 6.3 +/- 1.2 (SEM), and the mean increase for the 4 subjects with paraplegia in the lower extremities was 3.9 +/- 1.0. Among the patients who improved in their ASIA sensory neurological scores (all except one patient), the mean increase was 20.3 +/- 5.0 for light touch and 19.7 +/- 4.6 for pinprick. Most of the recovered sensation below the initial level of injury was impaired. Adverse events included sensory decrease in one patient that was most likely caused by difficulty in locating the lesion, and there were a few instances of transient pain that was relieved by medication. EMG revealed motor unit potential when the patient was asked to perform movement.

CONCLUSION

This study shows that olfactory mucosa autograft transplantation into the human injured spinal cord is feasible, relatively safe, and potentially beneficial. The procedure involves risks generally associated with any surgical procedure. Long-term patient monitoring is necessary to rule out any delayed side effects and assess any further improvements.

Characterization of non-neuronal elements within fibronectin mats implanted into the damaged adult rat spinal cord

Previous studies have shown that mats made from fibronectin (FN) integrate well into spinal cord lesion sites and support extensive axonal growth. Using immunohistochemistry, we have investigated the non-neuronal factors that contribute to these properties. Extensive vascularization was observed in FN mats by 1 week along with heavy macrophage infiltration by 3 days post-implantation. By 1 week post-implantation, laminin tubules had formed and were associated with axons and p75 immunoreactive Schwann cells. By 4 weeks post-implantation, most axons were associated with Schwann cell derived myelin. Few oligodendrocytes were present within the mat, even with an increase in the number of oligodendrocyte precursors around the implant site by 7 days post-implantation. Astrocyte proliferation also occurred in the intact tissue, with a prominent glial scar forming around the implant within 4 weeks. However, by 2 months post-implantation astrocytes were present in the FN implant site and were intermingled with the axons. Axonal ingrowth and integration of the FN mats is probably due to the ability of FN mats to support and organize infiltration of Schwann cells and deposition of laminin. At later time points, myelinated axons remain in the implant site, even after other elements (e.g. macrophages and laminin) have disappeared. Both of these properties are likely to be important in the design of biomaterial bridges for CNS regeneration.

Experimental study of neural repair of the transected spinal cord using peripheral nerve graft

It has been reported that transected spinal cord shows signs of axonal regeneration after peripheral nerve (PN) graft. We studied the membrane excitability and ion distribution in axons from transected rat spinal cord 3 weeks after PN graft using the spinal cord evoked potential, electron probe X-ray microanalysis, and the patch-clamp technique. Axonal structures were also observed using conventional electron microscopy. At the Th11 level, laminectomy was performed (=control) and the left thoracic segments of the spinal cord 2 mm in length were excised (=nongrafted group). PN sections from 8-week-old male Wistar rats were grafted into the spinal cord gap (=PN-grafted group). The spinal cord evoked potential in the PN-grafted group partly recovered in contrast to that in the nongrafted group, which showed no recovery. Higher Na, Cl, and Ca peaks and lower K peaks in the PN-grafted group were demonstrated compared with those in the nongrafted group. In the PN-grafted group, a higher current signal appeared in the axonal membrane of the spinal cord, suggesting a greater membrane activity compared with that in the nongrafted group. Unlike the nongrafted group, in which no myelinated axons were found, demyelinated axons that were myelinated by Schwann cells from the grafted peripheral nerve were observed in the PN-grafted group. These findings suggested that Schwann cells from the transplanted PN contributed to the repair of the transected spinal cord.

Lentiviral-mediated transfer of CNTF to schwann cells within reconstructed peripheral nerve grafts enhances adult retinal ganglion cell survival and axonal regeneration

We recently described a method for reconstituting peripheral nerve (PN) sheaths using adult Schwann cells (SCs). Reconstructed PN tissue grafted onto the cut optic nerve supports the regeneration of injured adult rat retinal ganglion cell (RGC) axons. To determine whether genetic manipulation of such grafts can further enhance regeneration, adult SCs were transduced with lentiviral vectors encoding either ciliary neurotrophic factor (LV-CNTF) or green fluorescent protein (LV-GFP). SCs expressed transgenes for at least 4 weeks after transplantation. There were high levels of CNTF mRNA and CNTF protein in PN grafts containing LV-CNTF-transduced SCs. Mean RGC survival was significantly increased with these grafts (11,863/retina) compared with LV-GFP controls (7064/retina). LV-CNTF-transduced SCs enhanced axonal regeneration to an even greater extent (3097 vs 393 RGCs/retina in LV-GFP controls). Many regenerated axons were myelinated. The use of genetically modified, reconstituted PN grafts to bridge tissue defects may provide new therapeutic strategies for the treatment of both CNS and PNS injuries.

Multiple-channel scaffolds to promote spinal cord axon regeneration

As molecular, cellular, and tissue-level treatments for spinal cord injury are discovered, it is likely that combinations of such treatments will be necessary to elicit functional recovery in animal models or patients. We describe multiple-channel, biodegradable scaffolds that serve as the basis for a model to investigate simultaneously the effects on axon regeneration of scaffold architecture, transplanted cells, and locally delivered molecular agents. Poly(lactic-co-glycolic acid) (PLGA) with copolymer ratio 85:15 was used for these initial experiments. Injection molding with rapid solvent evaporation resulted in scaffolds with a plurality of distinct channels running parallel along the length of the scaffolds. The feasibility of creating scaffolds with various channel sizes and geometries was demonstrated. Walls separating open channels were found to possess void fractions as high as 89%, with accessible void fractions as high as 90% through connections 220 microm or larger. Scaffolds degraded in vitro over a period of 30 weeks, over which time-sustained delivery of a surrogate drug was observed for 12 weeks. Primary neonatal Schwann cells were distributed in the channels of the scaffold and remained viable in tissue culture for at least 48 h. Schwann-cell containing scaffolds implanted into transected adult rat spinal cords contained regenerating axons at one month post-operation. Axon regeneration was demonstrated by three-dimensional reconstruction of serial histological sections.

Effects of glial transplantation on functional recovery following acute spinal cord injury

Numerous efforts have been made to maximize the efficacy of treatment for spinal cord injury (SCI). Recently, oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells have been reported to remyelinate focal areas of demyelinated spinal cord in adult rats. We conducted a study to investigate the therapeutic potential of transplantation of O-2A cells in a rat model of acute SCI. SCI was induced with an NYU Impactor at T9 of rats. O-2A cells labeled with bromodeoxyuridine (BrdU) were transplanted into sites of SCI at 1 week after the induction of SCI. At 6 weeks after cell transplantation, a behavioral test showed significant functional improvement in animals that had received O-2A-cell transplants as compared to animals given cell-culture medium alone. An electrophysiological study revealed that the transplants did not improve the amplitude or latency of somatosensory evoked potentials, but a recording of motor evoked potentials showed that the latency of these potentials in the O-2A-cell-transplant group was significantly shorter than that in the group treated with cell-culture medium. Following transplantation of BrdU-labeled O-2A cells, cells positive for BrdU were detected at and near sites of SCI. Cells labeled for both BrdU and 2',3' -cyclic nucleotide-3-phosphodiesterase were also detected, showing that the transplanted O-2A cells differentiated into oligodendrocytes. By contrast, cells labeled for BrdU and glial fibrillary acidic protein, or for neuronal nuclei antigen, were not detected. Furthermore, a tract-tracing study showed that numbers of retrogradely labeled neurons increased in areas of the brain stem after O-2A-cell transplantation. The study data showed that after being transplanted into an animal with SCI, O-2A cells migrated to the area adjacent to the site of injury and differentiated into oligodendrocytes. The behavioral test and the electrophysiological and morphological studies showed that transplantation of O-2A cells may play an important role in functional recovery and the regeneration of axons after SCI.

Osteonectin is a Schwann cell-secreted factor that promotes retinal ganglion cell survival and process outgrowth

We have investigated the factors made by Schwann cells (SCs) that stimulate survival and neurite outgrowth from postnatal rat retinal ganglion cells (RGCs). These effects are preserved under K252a blockade of the Trk family of neurotrophin receptors and are not fully mimicked by the action of a number of known trophic factors. To identify novel factors responsible for this regenerative activity, we have used a radiolabelling assay. Proteins made by SCs were labelled radioactively and then fed to purified RGCs. The proteins taken up by the RGCs were then isolated and further characterized. Using this assay we have identified a major 40 kDa factor taken up by RGCs, which was microsequenced and shown to be the matricellular protein osteonectin (ON). Using an in vitro assay of purified RGCs we show that ON promotes both survival and neurite outgrowth. We conclude that ON has a potential new role in promoting CNS repair.

Survival, integration, and axon growth support of glia transplanted into the chronically contused spinal cord

Due to an ever-growing population of individuals with chronic spinal cord injury, there is a need for experimental models to translate efficacious regenerative and reparative acute therapies to chronic injury application. The present study assessed the ability of fluid grafts of either Schwann cells (SCs) or olfactory ensheathing glia (OEG) to facilitate the growth of supraspinal and afferent axons and promote restitution of hind limb function after transplantation into a 2-month-old, moderate, thoracic (T8) contusion in the rat. The use of cultured glial cells, transduced with lentiviral vectors encoding enhanced green fluorescent protein (EGFP), permitted long-term tracking of the cells following spinal cord transplantation to examine their survival, migration, and axonal association. At 3 months following grafting of 2 million SCs or OEG in 6 microl of DMEM/F12 medium into the injury site, stereological quantification of the three-dimensional reconstructed spinal cords revealed that an average of 17.1 +/- 6.8% of the SCs and 2.3 +/- 1.4% of the OEG survived from the number transplanted. In the OEG grafted spinal cord, a limited number of glia were unable to prevent central cavitation and were found in patches around the cavity rim. The transplanted SCs, however, formed a substantive graft within the injury site capable of supporting the ingrowth of numerous, densely packed neurofilament-positive axons. The SC grafts were able to support growth of both ascending calcitonin gene-related peptide (CGRP)-positive and supraspinal serotonergic axons and, although no biotinylated dextran amine (BDA)-traced corticospinal axons were present within the center of the grafts, the SC transplants significantly increased corticospinal axon numbers immediately rostral to the injury-graft site compared with injury-only controls. Moreover, SC grafted animals demonstrated modest, though significant, improvements in open field locomotion and exhibited less foot position errors (base of support and foot rotation). Whereas these results demonstrate that SC grafts survive, support axon growth, and can improve functional outcome after chronic contusive spinal cord injury, further development of OEG grafting procedures in this model and putative combination strategies with SC grafts need to be further explored to produce substantial improvements in axon growth and function.

Freeze-dried agarose scaffolds with uniaxial channels stimulate and guide linear axonal growth following spinal cord injury

Although several approaches to stimulate axonal regeneration after spinal cord injury have succeeded in stimulating robust growth of axons into a lesion site, the growth is generally highly disorganized, losing the distinct arrangement of axonal tracts within the spinal cord. Previously described freeze-dried agarose scaffolds, composed of individual, uniaxial channels extending through their entire length, were prepared with and without recombinant Brain-Derived Neurotrophic Factor (BDNF) protein and tested in an adult rat model of spinal cord injury to determine whether regenerating axons could be guided across a site of injury in an organized fashion. After 1 month, both the cellular and axonal responses within and around scaffolds were evaluated. Scaffolds were found to be well integrated with host tissue, individual channels were penetrated by cells, and axons grew through scaffolds in a strikingly linear fashion. Furthermore, the regeneration was significantly augmented by the incorporation of BDNF protein into the walls and lumen of the scaffold. These findings clearly demonstrate that axonal regeneration can be organized and guided across a site of injury.

Directional Neurite Outgrowth Is Enhanced by Engineered Meningeal Cell-Coated Substrates

After injury to the CNS, the anatomical organization of the tissue is disrupted, posing a barrier to the regeneration of axons. Meningeal cells, a central participant in the CNS tissue response to injury, migrate into the core of the wound site in an unorganized fashion and deposit a disorganized extracellular matrix (ECM) that produces a nonpermissive environment. Previous work in our laboratory has shown that the presentation of nanometer-scale topographic cues to these cells influences their morphological, cytoskeletal, and secreted ECM alignment. In the present study, we provided similar environmental cues to meningeal cells and examined the ability of the composite construct to influence dorsal root ganglion regeneration in vitro. When grown on control surfaces of meningeal cells lacking underlying topographic cues, there was no bias in neurite outgrowth. In contrast, when grown on monolayers of meningeal cells with underlying nanometer-scale topography, neurite outgrowth length was greater and was directed parallel to the underlying surface topography even though there exists an intervening meningeal cell layer. The observed outgrowth was significantly longer than on laminin-coated surfaces, which are considered to be the optimal substrata for promoting outgrowth of dorsal root ganglion neurons in culture. These results suggest that the nanometer-level surface finish of an implanted biomaterial may be used to organize the encapsulation tissue that accompanies the implantation of materials into the CNS. It furthermore suggests a simple approach for improving bridging materials for repair of nerve tracts or for affecting cellular organization at a device-tissue interface.

Superparamagnetic iron oxide-labeled Schwann cells and olfactory ensheathing cells can be traced in vivo by magnetic resonance imaging and retain functional properties after transplantation into the CNS

Schwann cell (SC) and olfactory ensheathing cell (OEC) transplantation has been shown experimentally to promote CNS axonal regeneration and remyelination. To advance this technique into a clinical setting it is important to be able to follow the fates of transplanted cells by noninvasive imaging. Previous studies, using complex modification processes to enable uptake of contrast agents, have shown that cells labeled in vitro with paramagnetic contrast agents transplanted into rodent CNS can be visualized using magnetic resonance imaging (MRI). Here we show that SCs and OECs efficiently internalize dextran-coated superparamagnetic iron oxide (SPIO) from the culture medium by fluid phase pinocytosis. After transplantation into focal areas of demyelination in adult rat spinal cord both transplanted SPIO-labeled SCs and OECs produce a signal reduction using T(2)-weighted MRI in anesthetized rats that persists for up to 4 weeks. Although signal reduction was discernable after transplantation of unlabelled cells, this is nevertheless distinguishable from that produced by transplanted labeled cells. The region of signal reduction in SPIO-labeled cell recipients correlates closely with areas of remyelination. Because the retention of functional integrity by labeled cells is paramount, we also show that SPIO-labeled SCs and OECs are able to myelinate normally after transplantation into focal areas of demyelination. These studies demonstrate the feasibility of noninvasive imaging of transplanted SCs and OECs and represent a significant step toward the clinical application of promising experimental approaches.

Functional and electrophysiological changes after graded traumatic spinal cord injury in adult rat

A graded contusion spinal cord injury (SCI) was created in the adult rat spinal cord using the Infinite Horizons (IH) impactor to study the correlation between injury severity and anatomical, behavioral, and electrophysiological outcomes. Adult Fisher rats were equally divided into five groups and received contusion injuries at the ninth thoracic level (T9) with 100, 125, 150, 175, or 200 kdyn impact forces, respectively. Transcranial magnetic motor-evoked potentials (tcMMEPs) and BBB open-field locomotor analyses were performed weekly for 4 weeks postinjury. Our results demonstrated that hindlimb locomotor function decreased in accordance with an increase in injury severity. The locomotor deficits were proportional to the amount of damage to the ventral and lateral white matter (WM). Locomotor function was strongly correlated to the amount of spared WM, which contains the reticulospinal and propriospinal tracts. Normal tcMMEP latencies were recorded in control, all of 100-kdyn-injured and half of 125-kdyn-injured animals. Delayed latency responses were recorded in some of 125-kdyn-injured and all of 150-kdyn-injured animals. No tcMMEP responses were recorded in 175- and 200-kdyn-injured animals. Comparison of tcMMEP responses with areas of WM loss or demyelination identified the medial ventrolateral funiculus (VLF) as the location of the tcMMEP pathway. Immunohistochemical and electromicroscopic (EM) analyses showed the presence of demyelinated axons in WM tracts surrounding the lesion cavities at 28 days postinjury. These data support the notion that widespread WM damage in the ventral and lateral funiculi may be a major cause for locomotor deficits and lack of tcMMEP responses after SCI.

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

Here we review mechanisms and molecules that necessitate protection and oppose axonal growth in the injured spinal cord, representing not only a cast of villains but also a company of therapeutic targets, many of which have yet to be fully exploited. We next discuss recent progress in the fields of bridging, overcoming conduction block and rehabilitation after spinal cord injury (SCI), where several treatments in each category have entered the spotlight, and some are being tested clinically. Finally, studies that combine treatments targeting different aspects of SCI are reviewed. Although experiments applying some treatments in combination have been completed, auditions for each part in the much-sought combination therapy are ongoing, and performers must demonstrate robust anatomical regeneration and/or significant return of function in animal models before being considered for a lead role.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Delayed repair of corticospinal tract lesions as an assay for the effectiveness of transplantation of Schwann cells

We have previously shown that cultured adult olfactory ensheathing cells injected after 8 weeks into functionally complete unilateral lesions of the rat corticospinal tract induce restoration of paw reaching function to about 50% of normal, starting at around 10 days after transplantation. This provides an assay for determining the effectiveness of different methods of cell preparation or different cell types. We report that transplantation of cultured adult peripheral nerve Schwann cells also restores function, but the effect is delayed until around 30 days after transplantation and reaches only around 5-10% of normal. The presence of fibroblasts in the Schwann cell cultures neither improves, nor impairs the reparative effect, but fibroblasts alone (without Schwann cells) have no reparative effect. Without transplantation of exogenous Schwann cells, the ingrowth of endogenous Schwann cells which occurs spontaneously into these lesions does not restore function.

Neurogenesis and neuronal communication on micropatterned neurochips

Neural networks are formed by accurate connectivity of neurons and glial cells in the brain. These networks employ a three-dimensional bio-surface that both assigns precise coordinates to cells during development and facilitates their connectivity and functionality throughout life. Using specific topographic and chemical features, we have taken steps towards the development of poly(dimethylsiloxane; PDMS) neurochips that can be used to generate and study synthetic neural networks. These neurochips have micropatterned structures that permit adequate cell positioning and support cell survival. Within days of plating, cells differentiate into neurons displaying excitability and communication, as evidenced by intracellular calcium oscillations and action potentials. The structural and functional capacities of such simple neural networks open up new opportunities to study synaptic communication and plasticity.

Transplantation of Bone Marrow Stromal Cell-Derived Schwann Cells Promotes Axonal Regeneration and Functional Recovery after Complete Transection of Adult Rat Spinal Cord

The aim of this study was to evaluate whether transplantation of Schwann cells derived from bone marrow stromal cells (BMSC-SCs) promotes axonal regeneration and functional recovery in completely transected spinal cord in adult rats. Bone marrow stromal cells (BMSCs) were induced to differentiate into Schwann cells in vitro. A 4-mm segment of rat spinal cord was removed completely at the T7 level. An ultra-filtration membrane tube, filled with a mixture of Matrigel (MG) and BMSC-SCs (BMSC-SC group) or Matrigel alone (MG group), was grafted into the gap. In the BMSC-SC group, the number of neurofilament- and tyrosine hydroxylase-immunoreactive nerve fibers was significantly higher compared to the MG group, although 5-hydroxytryptamine- or calcitonin gene-related peptide-immunoreactive fibers were rarely detectable in both groups. In the BMSC-SC group, significant recovery of the hindlimb function was recognized, which was abolished by retransection of the graft 6 weeks after transplantation. These results demonstrate that transplantation of BMSC-SCs promotes axonal regeneration of lesioned spinal cord, resulting in recovery of hindlimb function in rats. Transplantation of BMSC-SCs is a potentially useful treatment for spinal cord injury.

Treatment of spinal cord injury with co-grafts of genetically modified Schwann cells and fetal spinal cord cell suspension in the rat

Fetal spinal cord cells, Schwann cells and neurotrophins all have the capacity to promote repair of injured spinal cord in animal models. To explore the possibility of using these approaches to treat clinical patients, we have examined whether a combination of these protocols produces functional and anatomical improvement. The spinal cords of adult rats (n=16) were injured with a modified New York University (NYU) device (10 gram.5cm). One week after injury, the injured cords were injected with Dulbecco-modified Eagles Medium (DMEM, control group), or fetal spinal cord cell suspension (FSCS) plus nerve growth factor (NGF) gene-modified Schwann cells (SC) and brain-derived neurotrophic factor (BDNF) gene-modified SC (treatment group). The rats were subjected to BBB (Basso, Beattie, Bresnahan, Exp. Neurol. 139:244, 1996) behavioral tests. Anterograde tracing of corticospinal tract was performed before sacrifice 3 months after the treatment. The results showed that the combination treatment elicited a robust growth of corticospinal axons within and beyond the injury site. A dramatic functional recovery in the treatment group was observed compared with the control group. We conclude that the combination of FSCS with genetically modified Schwann cells over-expressing NGF and BDNF was an effective protocol for the treatment of severe spinal cord injury.

Physical and biological performance of a novel block copolymer nerve guide

Although the ability to regenerate is evident in the nervous system, lesioned neurites are unable to cross gaps in neuronal pathways. In order to bridge gaps, guiding cues are essential to direct neurite regrowth. To overcome many of the shortcomings of polymer-based nerve guides, we developed a bioresorbable nerve guide composed of a novel trimethylene carbonate-caprolacton block copolymer (TMC-CL). Pore formation was controlled by using special solvent/precipitation media compositions in combination with the pore forming agent poly ethylene glycol (PEG). NMR spectroscopy, shear force-, compression-, and permeation assays were used for conduit characterization. The polymer conduit has a semipermeable wall with submicron pores to allow free metabolite/drug exchange. In order to investigate the principle of temporally controlled expression of therapeutic proteins in nerve guides, Neuro-2a cells were genetically engineered to express the reporter gene product green fluorescent protein (GFP) under the control of the Tet-On system. When these transduced cells were encapsulated in nerve guides, GFP expression could be induced for days by adding the antibiotic tetracycline derivative doxycycline to the nerve guide environment. Furthermore, encapsulated dorsal root ganglia (DRG) produced long neurites in vitro. In subsequent in vivo experiments, nerve guides filled with Schwann cells (SC) were implanted into lesioned spinal cords of adult rats. Regeneration of spinal cord axons into nerve guides was promoted by co-implanted Schwann cells. The data suggest that the novel TMC-CL nerve guides provide a promising tool for neuroregeneration.

Modification of the regenerative response of dorsal column axons by olfactory ensheathing cells or peripheral axotomy in adult rat

The regeneration of sciatic-dorsal column (DC) axons following DC crush injury and treatment with olfactory ensheathing cells (OECs) and/or sciatic axotomy ("conditioning lesion") was evaluated. Sciatic-DC axons were examined with a transganglionic tracer, cholera toxin conjugated to horseradish peroxidase, and evaluated at chronic time points, 2-26 weeks post-lesion. With DC injury alone (n = 7), sciatic-DC axons were localized to the caudal border of the lesion terminating in reactive end bulbs with no indication of growth into the lesion. In contrast, treatment with either a heterogeneous population of OECs (equal numbers of p75- and fibronectin-positive OECs) (n = 9) or an enriched population of OECs (75% p75-positive OECs) (n = 6) injected either directly into the lesion or 1-mm rostral and caudal to the injury, stimulated DC axon growth into the lesion. A similar regenerative response was observed with a conditioning lesion either concurrent to (n = 4) or 1 week before (n = 4) the DC injury. In either of the latter two paradigms, some DC axons grew across the injury, but no axons grew into the rostral intact spinal cord. Upon combining OEC treatment with the conditioning lesion (n = 21), the result was additive, increasing DC axon growth beyond the rostral border of the lesion in best cases. Additional factors that may limit DC regeneration were tested including formation of the glial scar (immunoreactivity to glial fibrillary acidic protein in astrocytes and to chondroitin sulfate proteoglycans), which remained similar between treated and untreated groups.

Transplantation of Schwann cells and olfactory ensheathing glia after spinal cord injury: does pretreatment with methylprednisolone and interleukin-10 enhance recovery?

Methylprednisolone (MP) and interleukin-10 (IL-10) are tissue protective acutely after spinal cord injury (SCI); their combination offers additive protection (Takami et al., 2002a). Our study examined if acute administration of MP (30 mg/kg i.v. at 5 min, and 2 and 4 h after injury) and IL-10 (30 mg/kg i.p. at 30 min after injury) increases the efficacy of Schwann cell (SC) or SC plus olfactory ensheathing glia (SC/OEG) grafts transplanted into rat thoracic cord 1 week after contusive injury. Efficacy was determined by histology, anterograde and retrograde tracing, immunohistochemistry for gliosis and specific nerve fibers, and several behavioral tests. Administration of MP/IL-10 or SC or SC/OEG transplantation significantly increased the total volume of a 9-mm segment of cord encompassing the injury site at 12 weeks. The combination of either SC or SC/OEG transplantation with MP/IL-10 most significantly reduced cavitation. The individual treatments all significantly increased the volume of normal-appearing tissue compared to injury-only controls; however, significant decreases in the volume of normal-appearing tissue were seen when MP/IL-10 and cell grafts were combined compared to MP/IL-10 alone. SC/OEG grafts were effective in promoting serotonergic fiber growth into the graft and led to more reticulospinal fibers caudal to the graft; combination with MP/IL-10 did not further increase fiber number. Only the combination of MP/IL-10 with SC/OEG transplants significantly improved gross locomotor performance (BBB scores) over injury-only controls. MP/IL-10 given prior to SC-only transplants, however, worsened behavioral outcome. Because beneficial effects of MP/IL-10 were not always additive when combined with cell transplantation, we need to understand (1) how tissue protective agents may transform the milieu of the injured spinal cord to the benefit or detriment of later transplanted cells and (2) whether neuroprotectants need to be re-administered at the time of cell grafting or less invasive transplantation techniques employed to reduce damage to tissue spared by an earlier protection strategy.

Basic Fibroblast Growth Factor Promotes Neuronal Survival but Not Behavioral Recovery in the Transected and Schwann Cell Implanted Rat Thoracic Spinal Cord

It was investigated whether the addition of basic fibroblast growth factor (FGF-2) enhances the efficacy of a Schwann cell (SC) bridge to repair the transected spinal cord by assessing tissue sparing and neuronal survival near the graft-cord interfaces, axonal regeneration and myelination in the graft, and behavioral recovery up to 12 weeks post-grafting. Experimental animals received a bridge of SCs within fibrin containing 1 microg of FGF-2; control animals received a SC implant without FGF-2. Sparing of tissue in a 2.5-mm-long segment near the graft-cord borders was 69% in the rostral and 52% in the caudal cord at 6 weeks post-grafting, not significantly different from the control group. With FGF-2, survival of NeuN-positive cells was increased in the rostral cord: 24.4%, 20.4%, and 17.2% of the number of positive cells in the uninjured cord compared to 13.5%, 9.1%, and 8.9% in controls at 3, 6, and 12 weeks post-grafting, respectively. Similarly, in the caudal cord, survival of NeuN-positive cells was increased with FGF-2: 19.3%, 16.8%, and 14.5% compared to 10.8%, 5.6%, and 6.1% in controls. The staining intensity of glial fibrillary acidic protein was significantly higher at the interfaces of both cord stumps at 3 weeks with SC/FGF-2 grafts; chondroitin sulfate proteoglycan (CS-56) staining was more intense in the rostral cord but only at 6 weeks. Blood vessels in the FGF-2 grafts were larger and less regular in shape than those in control grafts. Axonal growth into the bridge was not improved by the addition of FGF-2. Retrogradely traced neurons were not found rostral to the implant, indicating that axons had not grown a few mm into the caudal spinal tissue. Recovery of hind limb function was similar in both groups. Despite the neuroprotective effects of FGF-2, improved effects on axonal regeneration and functional recovery were not observed.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Synthetic hydrogel guidance channels facilitate regeneration of adult rat brainstem motor axons after complete spinal cord transection

Synthetic guidance channels or tubes have been shown to promote axonal regeneration within the spinal cord from brainstem motor nuclei with the inclusion of agents such as matrices, cells, or growth factors to the tube. We examined the biocompatibility and regenerative capacity of synthetic hydrogel tubular devices that were composed of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA). Two PHEMA-MMA channels, having a mean elastic modulus of either 177 or 311 kPa were implanted into T8-transected spinal cords of adult Sprague Dawley rats. The cord stumps were inserted into the channels and fibrin glue was applied to the cord-channel interface. An expanded polytetrafluoroethylene (ePTFE) membrane was used for duraplasty. Controls underwent cord transection alone. Gross and microscopic examination of the spinal cords showed continuity of tissue within the synthetic guidance channels between the cord stumps at 4 and 8 weeks. There was a trend towards an increased area and width of bridging neural tissue in the 311-kPa guidance channels compared to the 177-kPa channels. Neurofilament stained axons were visualized within the bridging tissue, and serotonergic axons were found to enter the 311-kPa channel. Retrograde axonal tracing revealed regeneration of axons from reticular, vestibular, and raphe brainstem motor nuclei. For both channels, there was minimal scarring at the channel-cord interface, and less scarring at the channel-dura interface compared to that observed next to the ePTFE. The present study is the first to show that axons from brainstem motor nuclei regenerated in unfilled synthetic hydrogel guidance channels after complete spinal cord transection.

Combined demyelination plus Schwann cell transplantation therapy increases spread of cells and axonal regeneration following contusion injury

Several cell populations have been shown to provide a permissive environment for axonal extension following transplantation to injury sites. The limited spread of transplanted cells from implantation sites in the mature CNS, and the superior substrate and trophic environment that they provide, likely contribute to the fact that few transplantation-based therapies have elicited axonal extension beyond the transplant. The aim of this study was to determine whether (1) regions of demyelination cranial and caudal to a spinal cord injury site would improve the spread of Schwann cells transplanted into the site of injury, and (2) whether this combination therapy was associated with improved anatomical regeneration. Three days following contusion injury, anti-galactocerebroside antibodies plus complement proteins were injected into the dorsal column cranial and caudal to the injury site, resulting in complete and well defined regions of demyelination that extended 8 mm either side of the injury site. One day later, naïve Schwann cells in suspension were injected into the contusion site. Transplanted Schwann cells homogeneously redistributed throughout the contusion site and the adjacent regions of demyelination cranial and caudal to the contusion site, providing a long-distance prospective path for repair that was free of myelin and contained transplanted cells. Animals that received demyelination plus transplantation therapy, but not untreated or single-treatment groups, exhibited robust axonal regeneration beyond the contusion site within the treated dorsal column. Axonal regeneration in these animals was not associated with an improvement in locomotor ability. These findings suggest that this combination therapy may overcome a central limitation of transplant strategies in which the permissive environment provided remains at the implantation site.

Fluid shear in viscous fibronectin gels allows aggregation of fibrous materials for CNS tissue engineering

Fibronectin (Fn) materials prepared from human plasma have been used in various forms as substrates for tissue engineering. Such purposes require that the soluble protein aggregates into insoluble fibrous structures which encourage the attachment and migration of cells. The method of aggregation due to mechanical shear was investigated by applying fluid shear forces directly to a viscous solution of Fn. Structural analysis revealed that mechanical shear resulted in the formation of an orientated fibrous protein material that was less soluble than its non-sheared counterpart. The suitability of this shear aggregated Fn material for CNS repair purposes was assessed in vitro where it supported the growth of fibroblasts, S100 immunoreactive Schwann cells and GFAP immunoreactive astrocytes. Implantation of the shear aggregated Fn material into a rat model of spinal cord injury provided a permissive environment for axonal growth. This was extended using an impermeable coating to improve orientation and straightness of axonal growth.

Animal models of spinal cord injury for evaluation of tissue engineering treatment strategies

Tissue engineering approaches to spinal cord injury (SCI) treatment are attractive because they allow for manipulation of native regeneration processes involved in restoration of the integrity and function of damaged tissue. A clinically relevant spinal cord regeneration animal model requires that the model mimics specific pathologic processes that occur in human SCI. This manuscript discusses issues related to preclinical testing of tissue engineering spinal cord regeneration strategies from a number of perspectives. This discussion includes diverse causes, pathology and functional consequences of human SCI, general and species related considerations, technical and animal care considerations, and data analysis methods.

Factors secreted by Schwann cells stimulate the regeneration of neonatal retinal ganglion cells

The adult mammalian central nervous system (CNS) does not repair after injury. However, we and others have shown in earlier work that the neonatal CNS is capable of repair and importantly of allowing regenerating axons to re-navigate through the same pathways as they did during development. This phase of neonatal repair is restricted by the fragility of neurons after injury and a lack of trophic factors that enable their survival. Our aim is to define better the factors that sustain neurons after injury and allow regeneration to occur. We describe some of our work using Schwann cells to promote the regeneration of neurons from young postnatal rodents. We have established rapid methods for purifying Schwann cells without the use of either anti-mitotic agents to suppress contaminating fibroblasts or mitotic stimulation to generate large numbers of Schwann cells. The rapidly purified Schwann cells have been used to generate conditioned medium that we have shown stimulates axon regeneration in cultured retinal ganglion cell neurons. We also show that the positive effects of Schwann cells are still present after pharmacological blockade of the neurotrophin receptors, suggesting that novel factors mediate these effects.

PKC mediates inhibitory effects of myelin and chondroitin sulfate proteoglycans on axonal regeneration

Successful axon regeneration in the mammalian central nervous system (CNS) is at least partially compromised due to the inhibitors associated with myelin and glial scar. However, the intracellular signaling mechanisms underlying these inhibitory activities are largely unknown. Here we provide biochemical and functional evidence that conventional isoforms of protein kinase C (PKC) are key components in the signaling pathways that mediate the inhibitory activities of myelin components and chondroitin sulfate proteoglycans (CSPGs), the major class of inhibitors in the glial scar. Both the myelin inhibitors and CSPGs induce PKC activation. Blocking PKC activity pharmacologically and genetically attenuates the ability of CNS myelin and CSPGs to activate Rho and inhibit neurite outgrowth. Intrathecal infusion of a PKC inhibitor, Gö6976, into the site of dorsal hemisection promotes regeneration of dorsal column axons across and beyond the lesion site in adult rats. Thus, perturbing PKC activity could represent a therapeutic approach to stimulating axon regeneration after brain and spinal cord injuries.

Neural tissue engineering: strategies for repair and regeneration

Nerve regeneration is a complex biological phenomenon. In the peripheral nervous system, nerves can regenerate on their own if injuries are small. Larger injuries must be surgically treated, typically with nerve grafts harvested from elsewhere in the body. Spinal cord injury is more complicated, as there are factors in the body that inhibit repair. Unfortunately, a solution to completely repair spinal cord injury has not been found. Thus, bioengineering strategies for the peripheral nervous system are focused on alternatives to the nerve graft, whereas efforts for spinal cord injury are focused on creating a permissive environment for regeneration. Fortunately, recent advances in neuroscience, cell culture, genetic techniques, and biomaterials provide optimism for new treatments for nerve injuries. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the current approaches that are being explored to aid peripheral nerve regeneration and spinal cord repair.

Olfactory ensheathing cells induce less host astrocyte response and chondroitin sulphate proteoglycan expression than Schwann cells following transplantation into adult CNS white matter

Both Schwann cells and olfactory ensheathing cells (OECs) create an environment favorable to axon regeneration when transplanted into the damaged CNS. However, transplanted cells can also exert an effect on the host tissue that will influence the extent to which regenerating axons can grow beyond the transplanted area and reenter the host environment. In this study equivalent numbers of Lac-Z-labeled Schwann cells and OECs have been separately transplanted into normal white matter of adult rat spinal cord and the host astrocyte response to each compared. Schwann cell transplantation resulted in a greater area of increased glial fibrillary acidic protein (GFAP) expression compared to that associated with OEC transplantation. This was accompanied by a greater increase in the expression of axon growth inhibitory chrondroitin sulfate proteoglycans (CSPGs) following Schwann cell transplantation compared to OEC transplantation. However, no differences were detected in the increased expression of the specific CSPG neurocan following transplantation of the two cell types. These results mirror differences in the interactions between astrocytes and either Schwann cells or OECs observed in tissue culture models and reveal one aspect of the complex biology of creating regeneration-promoting environments by cell transplantation where transplanted OECs have favorable properties compared to transplanted Schwann cells.

Microglia enhance dorsal root ganglion outgrowth in Schwann cell cultures

Transplantation of cellular populations to facilitate regrowth of damaged axons is a common experimental therapy for spinal cord injury. Schwann cells (SC) or microglia grafted into injury sites can promote axonal regrowth of central projections of dorsal root ganglion (DRG) sensory neurons. We sought to determine whether the addition of microglia or microglia-derived secretory products alters DRG axon regrowth upon cultures of SC. Rat DRG explants were grown on monolayers consisting of either SC, microglia, SC exposed to microglia-conditioned medium (MCM), or co-cultures with different relative concentrations of microglia. Image analysis revealed that, compared to SC alone, the extent of neurite outgrowth was significantly greater on SC-microglia co-cultures. Immunocytochemistry for extracellular matrix molecules showed that microglial cells stained positively for growth-promoting thrombospondin, whereas laminin and the inhibitory chondroitin sulfate proteoglycans (CSPGs) were localized primarily to SC. Notably, immunoreactivity for CSPGs appeared reduced in areas associated with DRG outgrowth in co-cultures and SC exposed to MCM. These results show that microglia or their secreted products can augment SC-mediated DRG regrowth in vitro, indicating that co-grafting SC with microglia provides a novel approach to augment sensory fiber regeneration after spinal cord injury.

Chondroitinase ABC enhances axonal regrowth through Schwann cell-seeded guidance channels after spinal cord injury

Grafting of Schwann cell-seeded channels into hemisected adult rat thoracic spinal cords has been tested as a strategy to bridge the injured cord. Despite success in guiding axonal growth into the graft, regeneration across the distal graft-host interface into the host spinal cord was limited. We hypothesized that chondroitin sulfate (CS) glycoforms deposited at the gliotic front of the interface constitute a molecular barrier to axonal growth into the host cord. Because CS glycoforms deposited by purified astrocytes in vitro were removable by digestion with chondroitinase ABC, we attempted to achieve likewise by infusion of the enzyme to the host side of the interface. By 1 month post-treatment, significant numbers of regenerating axons crossed an interface that was subdued in macrophage/microglia reaction and decreased in CS-immunopositivity. The axons extended as far into the caudal cord as 5 mm, in contrast to nil in vehicle-infused controls. Fascicular organizations of axon-Schwann cell units within the regenerated tissue cable were better-preserved in enzyme-treated cords than in vehicle-infused controls. We conclude that CS glycoforms deposited during gliosis at the distal graft-host interface could be cleared by the in vivo action of chondroitinase ABC to improve prospects of axonal regeneration into the host spinal cord.

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.

Effects of immunosuppression on regrowth of adult rat retinal ganglion cell axons into peripheral nerve allografts

Analysis of the effectiveness of allografts and immunosuppression in the repair of nerve defects in the adult peripheral nervous system (PNS) has a long experimental and clinical history. There is little information, however, on the use of allografts in peripheral nerve (PN) transplantation into the injured central nervous system (CNS). We assessed the ability of PN allografts (from Dark-Agouti rats) to support regeneration of adult rat retinal ganglion cell (RGC) axons in immunosuppressed host Lewis rats. PN allografts were sutured onto intraorbitally transected optic nerves. Three weeks after grafting, regenerating RGC axon numbers were determined using retrograde fluorescent labelling, and total axons within PN grafts were assessed using pan-neurofilament immunohistochemistry. In the absence of immunosuppression, PN allografts contained few axons and there were very few labelled RGC. These degenerate grafts contained many T cells and macrophages. Systemic (intraperitoneal) application of the immunosuppressants cyclosporin-A or FK506 reduced cellular infiltration into allografts and resulted in extensive axonal regrowth from surviving RGCs. The average number of RGCs regenerating axons into immunosuppressed allografts was not significantly different from that seen in PN autografts in rats sham-injected with saline. Many pan-neurofilament-positive axons, a proportion of which were myelinated, were seen in immunosuppressed allografts, particularly in proximal regions of the grafts toward the optic nerve-PN interface. This study demonstrates that PN allografts can support axonal regrowth in immunosuppressed adult hosts, and points to possible clinical use in CNS repair.

CNS regeneration: clinical possibility or basic science fantasy?

Following injury to the CNS, severed axons undergo a phase of abortive sprouting in the vicinity of the wound, but do not spontaneously re-grow or regenerate. From a long history of attempts to stimulate regeneraion, a major strategy that has been developed clinically is the implantation of tissue into denervated target regions. Unfortunately trials have so far not borne out the promise that this would prove a useful therapy for disorders such as Parkinson's disease. Many strategies have also been developed to stimulate the regeneration of axons across sites of injury, particularly in the spinal cord. Animal data have demonstrated that some of these approaches hold promise and that the spinal cord has a remarkable degree of intrinsic plasticity. Attempts are now being made to utilize experimental techniques in spinal patients.

Mats made from fibronectin support oriented growth of axons in the damaged spinal cord of the adult rat

A variety of biological as well as synthetic implants have been used to attempt to promote regeneration into the damaged spinal cord. We have implanted mats made from fibronectin (FN) into the damaged spinal cord to determine their effectiveness as a substrate for regeneration of axons. These mats contain oriented pores and can take up and release growth factors. Lesion cavities 1 mm in width and depth and 2 mm in length were created on one side of the spinal cord of adult rats. FN mats containing neurotrophins or saline were placed into the lesion. Mats were well integrated into surrounding tissue and showed robust well-oriented growth of calcitonin gene-related peptide, substance P, GABAergic, cholinergic, glutamatergic, and noradrenergic axons into FN mats. Transganglionic tracing using cholera toxin B indicated large-diameter primary afferents had grown into FN implants. Schwann cells had also infiltrated FN mats. Electron microscopy confirmed the presence of axons within implants sites, with most axons either ensheathed or myelinated by Schwann cells. Mats incubated in brain-derived neurotrophic factor and neurotrophin-3 showed significantly more neurofilament-positive and glutamatergic fibers compared to saline- and nerve growth factor-incubated mats, while mats incubated with nerve growth factor showed more calcitonin gene-related peptide-positive axons. In contrast, neurotrophin treatment had no effect on PGP 9.5-positive axons. In addition, in some animals with neurotrophin-3-incubated mats, cholera toxin B-labelled fibers had grown from the mat into adjoining intact areas of spinal cord. The results indicate that FN mats provide a substrate that is permissive for robust oriented axonal growth in the damaged spinal cord, and that this growth is supported by Schwann cells.

Human umbilical cord blood stem cells infusion in spinal cord injury: engraftment and beneficial influence on behavior

The use of human umbilical cord blood (hUCB)--a rich source of nonembryonic or adult stem cells--has recently been reported to ameliorate behavioral consequences of stroke. In this study, we tested whether human cord blood leukocytes also ameliorate behavioral impairments of spinal cord injury. Rats were divided into five groups: (1) laminectomy (without spinal cord injury) only; (2) laminectomy + cord blood infusion; (3) spinal cord injury + cord blood infused 1 day post injury; (4) spinal cord injury + cord blood infused 5 days post injury; and (5) spinal cord injury only. Spinal cord injury was induced by compressing the spinal cord for 1 min with an aneurysm clip calibrated to a closing pressure of 55 g. Open-field behavior was assessed 1, 2, and 3 weeks after intravenous injection of prelabeled human cord blood cells. Open-field test scores of spinal cord injured rats treated with human cord blood at 5 days were significantly improved as compared to scores of rats similarly injured but treated at day 1 as well as the otherwise untreated injured group. The results suggest that cord blood stem cells are beneficial in reversing the behavioral effects of spinal cord injury, even when infused 5 days after injury. Human cord blood-derived cells were observed in injured areas, but not in noninjured areas, of rat spinal cords, and were never seen in corresponding areas of spinal cord of noninjured animals. The results are consistent with the hypothesis that cord blood-derived stem cells migrate to and participate in the healing of neurological defects caused by traumatic assault.

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.

A new approach to CNS repair using chimeric peripheral nerve grafts

We have examined whether transplanted freeze-thawed peripheral nerve (PN) sheaths repopulated ex vivo with purified adult Schwann cells (SCs) support the regeneration of adult rat retinal ganglion cell (RGC) axons. Cultured adult SCs were derived from donor rats or from the host animals themselves. We also transplanted PN sheaths filled with neonatal SCs or donor adult olfactory ensheathing glia (OEG). 100,000 cells were injected into 1.5-cm lengths of freeze-thawed PN. After 2 days in culture, repopulated PN segments were grafted onto the transected optic nerve of adult Fischer rats. Three weeks later, 6% fluorogold (FG) was applied to distal PN. Retrogradely labeled RGCs were counted in retinal wholemounts and PN grafts were processed for immunohistochemistry. As expected, there was no RGC axon regeneration in cell-free grafts. Regrowth was also absent in neonatal SC- and adult OEG-filled grafts, which contained only small numbers of surviving donor cells. Many cells were, however, seen in adult SC repopulated PN grafts, intermingled with pan-neurofilament(+) and GAP-43(+) fibers. SCs were aligned along the grafts and were S-100(+), p75(+). Ultrastructurally, SCs were associated with myelinated and unmyelinated axons. Hundreds of FG-labeled RGCs were seen in retinas of rats with congeneic or allogeneic PN sheaths repopulated with either donor or autologous (host-derived) adult SCs. Intraocular CNTF injections significantly increased the number of regenerating RGCs in donor and autologous adult SC groups. The use of chimeric grafts to bridge CNS tissue defects could provide a clinical alternative to using multiple PN autografts, the harvesting of which would exacerbate peripheral dysfunction in already injured patients.

Reinnervation of the pretectum in adult rats by regenerated retinal ganglion cell axons: anatomical and functional studies

We have investigated the specificity of reinnervation and terminal arborization of injured retinal ganglion cell (RGC) axons in the brainstem with the object of studying in a simple situation the degree to which regenerating axons are able to replicate the characteristic patterns of terminal arborization and restore normal function. We have focussed here on the pathway that is responsible for the pupillary light reflex, which is mediated through the olivary pretectal nucleus (OPN). In adult rats, the left optic nerve was transected and a segment of peripheral nerve (PN) graft was used to bridge between the retina and different regions of the ipsilateral brainstem, including the superior colliculus. After 4-13 months, regenerated RGC axons were examined in coronal sections stained for cholera toxin B subunit. RGC axons were found extending into the ipsilateral brainstem for distances of up to 6 mm. Within the pretectum, axons innervated the OPN and the nucleus of the optic tract preferentially, and formed distinctive terminal arbors within each. Within the SC axons extended laterally into the visual layers and formed a different type of arborization. On testing the pupillary light reflex, it was found in best cases to show response amplitudes which were comparable to those recorded from control intact animals. However, unlike normals, the response amplitude tended to diminish with repeated stimulation and also appeared to deteriorate with age, although responses could still be detected in some cases as long as 15 months after grafting. These results indicate that regenerating axons can selectively reinnervate denervated nuclei, where they form typical terminal arborizations, and provide the substrates for restoring functional circuitry.

Activation and coordination of spinal motoneuron pools after spinal cord injury

Goal-directed movements of the limbs involve the coordinated activation of dozens of muscles. The neural signals activating these muscles are organized at spinal and supraspinal levels, the end result being trains of action potentials delivered to muscles by ensembles of spinal motoneurons (MNs). A new modelling approach has allowed us to visualize the activity of MNs controlling cat hindlimb locomotion. This reveals a rostrocaudal oscillation of MN activity distributed over about 30 mm of the lumbosacral spinal cord. The coordination and topographical distribution of MN pools thus revealed put an interesting perspective on the restoration of motor function with regeneration and neuroprosthetic techniques. Recent progress in the area of intraspinal microstimulation (ISMS) is reviewed, including the synthesis of locomotor movements with a small number of implanted microwires, eliciting movements after a spinal transection and facilitating weak voluntary movements with subliminal ISMS. We suggest that neuroprostheses may be useful in maximizing the benefits of neural regeneration in the future.

Identification of regenerative tissue cables using in vivo MRI after spinal cord hemisection and schwann cell bridging transplantation

The purpose of this study was to examine the feasibility of a non-invasive in vivo magnetic resonance imaging (MRI) procedure, performed at 1.5 T, to detect regenerative tissue cables in a rat spinal cord hemisection and Schwann cell (SC) bridging transplantation paradigm. Two months after implantation of a SC-seeded guidance channel (1.25 mm in diameter and 3.0 mm in length) into a T8 spinal cord hemisection-gap lesion, axial fast-spin echo (FSE) T2-weighted MR imaging (T2WI) was performed. Axial T2WI through the graft identified a circular area of low intensity surrounded by high-intensity signal within the guidance channel lumen. Correlative histological assessments of Toluidine blue-stained sections confirmed that the low-intensity signal represented a tissue cable, which, in most cases, contained a substantial number of myelinated axons oriented along the rostro-caudal axis of the spinal cord. The percentage of guidance channel cross-sectional area occupied by the tissue cable, expressed as the tissue cable index (TCI), was also determined from histological sections. Linear regression analysis of the TCI plotted relative to the number of myelinated axons revealed a strong positive correlation (r(2) = 0.85) between these two outcome measures. In addition, the sensitivity of MRI to detect regenerative tissue cables within guidance channels was 86%. These results demonstrate that (1). 1.5 T MR imaging performed 2 months after spinal cord hemisection and SC bridging transplantation is sensitive in detecting low-intensity regenerative tissue cables, and (2). the TCI strongly correlates with the extent of axonal regeneration into implanted SC-seeded guidance channels.

Peripheral nerve grafts and aFGF restore partial hindlimb function in adult paraplegic rats

The purpose of this study was to evaluate the degree of functional recovery in adult rats with completely transected spinal cord following experimental treatment regimens that include implantation of peripheral nerve segments and local application of acidic fibroblast growth factor (aFGF). Rats were randomly divided to five groups: (1) spinal cord transection, (2) spinal cord transection and aFGF treatment, (3) spinal cord transection and peripheral nerve grafts, (4) spinal cord transection, aFGF treatment, and peripheral nerve grafts, and (5) sham control (laminectomy only). The locomotor behavior of all rats was analyzed by the Basso, Beattie and Bresnahan (BBB) open field locomotor test over the six months survival time. Immunohistochemisty for neurofilament protein, and somatosensory (SSEP) and motor evoked potentials (MEP) were used to evaluate axon growth across the damage site following the different treatments. The results show four principal findings: (1) Only the combination of peripheral nerve grafts and aFGF treatment improved hindlimb locomotor function after spinal cord transection. (2) The SSEP and MEP demonstrated electrophysiological evidence of both sensory and motor information crossing the damaged site, but only in the combined nerve grafts and aFGF treatment rats. (3) Immunostaining demonstrated neurofilament positive axons extending through the graft area and into distal end of spinal cord, but only in the group with combined nerve grafts and aFGF treatment. (4) Retransection of group 4 rats eliminated the behavioral recovery, MEP, and SSEP responses, indicating that the improvement of hindlimb locomotor activity came from supraspinal control. These results demonstrate the ability of the repair strategy combining peripheral nerve grafts and aFGF treatment to facilitate the regeneration of spinal ascending and descending tracts and also recovery of motor behavior following spinal cord injury.

How do transplanted olfactory ensheathing cells restore function?

In this article, we review our work on regeneration of the corticospinal tract in rats following a lesion at upper cervical level. We outline the rationale for using olfactory ensheathing cells, and summarize the evidence for regeneration and functional recovery. The present interpretation on the mechanisms of functional recovery is partly hypothetical, and we emphasize where further experimental evidence is needed.

Schwann cell but not olfactory ensheathing glia transplants improve hindlimb locomotor performance in the moderately contused adult rat thoracic spinal cord

Cultured adult rat Schwann cells (SCs) or olfactory ensheathing glia (OEG), or both, were transplanted in the adult Fischer rat thoracic (T9) spinal cord 1 week after a moderate contusion (10 gm, 12.5 mm, NYU impactor). Rats received either a total of 2 x 10(6) cells suspended in culture medium or culture medium only (controls). At 12 weeks after injury, all grafted animals exhibited diminished cavitation. Although in medium-injected rats 33% of spinal tissue within a 5-mm-long segment of cord centered at the injury site was spared, significantly more tissue was spared in SC (51%), OEG (43%), and SC/OEG (44%) grafted animals. All three types of glial grafts were filled with axons, primarily of spinal origin. SC grafts contained more myelinated axons than SC/OEG and OEG grafts. Both types of SC-containing grafts expressed more intense staining for glial fibrillary acidic protein and chondroitin sulfate proteoglycan compared with OEG-only grafts. Retrograde tracing demonstrated that the number of propriospinal and brainstem axons reaching 5-6 mm beyond the grafted area was significantly higher with SC and SC/OEG grafts but not with OEG-only grafts compared with controls. Corticospinal fibers terminated closer to the lesion epicenter in all grafted animals than in controls. With SC-only grafts, a modest but statistically significant improvement in hindlimb locomotor performance was detected at 8-11 weeks after injury. Thus, in addition to this functional improvement, our results show that an SC graft is more effective in promoting axonal sparing/regeneration than an SC/OEG or OEG graft in the moderately contused adult rat thoracic spinal cord.