The ability of human Schwann cell grafts to promote regeneration in the transected nude rat spinal cord

Peripheral nerve regeneration through guidance tubes

Biological nerve grafts have been extensively utilized in the past to repair peripheral nerve injuries. More recently, the use of synthetic guidance tubes in repairing these injuries has gained in popularity. This review focuses on artificial conduits, nerve regeneration through them, and an account of various synthetic materials that comprise these tubes in experimental animal and clinical trials. It also lists and describes several biomaterial considerations one should regard when designing, developing, and manufacturing potential guidance channel candidates. In the future, it it likely that the most successful synthetic nerve conduit will be one that has been fabricated with some of these strategies in mind.

Stem cell transplantation and other novel techniques for promoting recovery from spinal cord injury

A number of potential approaches aim to optimize functional recovery after spinal cord injury. They include minimizing the progression of secondary injury, manipulating the neuroinhibitory environment of the spinal cord, replacing lost tissue with transplanted cells or peripheral nerve grafts, remyelinating denuded axons, and maximizing the intrinsic regenerative potential of endogenous progenitor cells. We review the application of stem cell transplantation to the spinal cord, emphasizing the use of embryonic stem cells for remyelinating damaged axons. We speculate that harnessing the potential of endogenously born stem cells already present in the spinal cord represents an important therapeutic target. We also discuss the potential application of peripheral nervous system reconstruction to recovery from spinal cord injury. The principles of peripheral nerve regeneration and concepts of nerve grafting are reviewed. Particular attention is given to peripheral nerve allotransplantation for repairing extensively injured tissue when autologous donor nerve material is scarce. The potential role of nerve transfers for reconstructing the injured spinal cord, particularly the cauda equina and lumbosacral plexus, are also described.

Premotor nitric oxide synthase immunoreactive pathway connecting lumbar segments with the ventral motor nucleus of the cervical enlargement in the dog

In this study we investigate the occurrence and origin of punctate nitric oxide synthase immunoreactivity in the neuropil of the ventral motor nucleus in C7-Th1 segments of the dog spine, which are supposed to be the terminal field of an ascending premotor propriospinal nitric oxide synthase-immunoreactive pathway. As the first step, nitric oxide synthase immunohistochemistry was used to distinguish nitric oxide synthase-immunoreactive staining of the ventral motor nucleus. Dense, punctate nitric oxide synthase immunoreactivity was found on control sections in the neuropil of the ventral motor nucleus. After hemisection at Th10-11, axotomy-induced retrograde changes consisting in a strong upregulation of nitric oxide synthase-containing neurons were found mostly unilaterally in lamina VIII, the medial part of lamina VII and in the pericentral region in all segments of the lumbosacral enlargement. Concurrently, a strong depletion of the punctate nitric oxide synthase immunopositivity in the neuropil of the ventral motor nucleus ipsilaterally with the hemisection was detected, thus revealing that an uncrossed ascending premotor propriospinal pathway containing a fairly high number of nitric oxide synthase-immunoreactive fibers terminates in the ventral motor nucleus. Application of the retrograde fluorescent tracer Fluorogold injected into the ventral motor nucleus and analysis of alternate sections processed for nitric oxide synthase immunocytochemistry revealed the presence of Fluorogold-labeled and nitric oxide synthase-immunoreactive axons in the ventrolateral funiculus and in the lateral and medial portions of the ventral column throughout the thoracic and upper lumbar segments. A noticeable number of Fluorogold-labeled and nitric oxide synthase-immunoreactive somata detected on consecutive sections were found in the lumbosacral enlargement, mainly in laminae VIII-IX, the medial part of lamina VII and in the pericentral region (lamina X), ipsilaterally with the injection of Fluorogold into the ventral motor nucleus. In summary, the present study provides evidence for a hitherto unknown ascending premotor propriospinal nitric oxide synthase-immunoreactive pathway connecting the lumbosacral enlargement with the motoneurons of the ventral motor nucleus in the dog.

Alginate Enhances Elongation of Early Regenerating Axons in Spinal Cord of Young Rats

Freeze-dried alginate sponge cross-linked with covalent bonds has been demonstrated to enhance nerve regeneration in peripheral nerves and spinal cords. The present study examined, at early stages after surgery, the outgrowth of regenerating axons and reactions of astrocytes at the stump of transected spinal cord in young rats. Two segments (Th7-8) were resected, and alginate was implanted in the lesion. As controls, collagen gel was implanted in place of alginate or the lesion was left without implantation. Two and 4 weeks after surgery, nerve outgrowth and astrocyte reactions were examined. Many regenerating axons, some of which were accompanied by astrocytic processes, were found to extend from the stump into the alginate-implanted lesion. In the all nonimplanted animals, large cystic cavities were formed at both interfaces with no definite axonal outgrowth into the lesion. In collagen-implanted animals, cavity formation was found in some rats, and regenerating axons once formed at the stumps did not extend further into the lesion. Astrocytic processes extending into alginate-implanted lesion had no basal laminae, whereas those found in control experiments were covered by basal laminae. These findings suggest that alginate contributed to reducing the barrier composed of connective tissues and reactive astrocytic processes, and served as a scaffold for the outgrowth of regenerating axons and elongation of astrocytic processes.

Motor Recovery and Anatomical Evidence of Axonal Regrowth in Spinal Cord-Repaired Adult Rats

Behavioral assessments of hindlimb motor recovery and anatomical assessments of extended axons of long spinal tracts were conducted in adult rats following complete spinal cord transection. Rats were randomly divided into 3 groups: 1) sham control group (laminectomy only; n = 12); 2) transection-only group, spinal cord transection at T8 (n = 20); and 3) experimental treatment group, spinal cord transection at T8, with peripheral nerve grafts (PNG) and application of acidic fibroblast growth factor (aFGF) (n = 14). The locomotor behavior and stepping of all rats were analyzed over a 6-month survival time using the Basso, Beattie, Bresnahan (BBB) open field locomotor test and the contact placing test. Immunohistochemistry for serotonin (5-HT), anterograde tracing with biotinylated dextran amine (BDA), and retrograde tracing with fluoro-gold were used to evaluate the presence of axons below the damage site following treatment. When compared with the transection-only group, the nerve graft with the aFGF group showed 1) significant improvement in hindlimb locomotion and stepping, 2) the presence of 5-HT-labeled axons below the lesion site at lumbar cord level (these were interpreted as regenerated axons from the raphe nuclei), 3) the presence of anterograde BDA labeling of corticospinal tract axons at the graft site and below, and 4) fluoro-gold retrograde labeling of neuron populations in motor cortex and in red nucleus, reticulospinal nuclei, raphe nuclei, and vestibular nuclei. We conclude that peripheral nerve grafts and aFGF treatments facilitate the regrowth of the spinal axons and improve hindlimb function in a T-8 spinal cord-transected rat model.

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.

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.

Growth factor enhancement of peripheral nerve regeneration through a novel synthetic hydrogel tube

OBJECT

The authors' long-term goal is repair of peripheral nerve injuries by using synthetic nerve guidance devices that improve both regeneration and functional outcome relative to an autograft. They report the in vitro processing and in vivo application of synthetic hydrogel tubes that are filled with collagen gel impregnated with growth factors.

METHODS

Poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous 12-mm-long tubes with an inner diameter of 1.3 mm and an outer diameter of 1.8 mm were used to repair surgically created 10-mm gaps in the rat sciatic nerve. The inner lumen of the tubes was filled with collagen matrix alone or matrix supplemented with either neurotropin-3 at 1 microg/ml, brain-derived neurotrophic factor at 1 microg/ml, or acidic fibroblast growth factor (FGF-1) at 1 or 10 microg/ml. Nerve regeneration through the growth factor-enhanced tubes was assessed at 8 weeks after repair by histomorphometric analysis at the midgraft level and in the nerve distal to the tube repair. The tubes were biostable and biocompatible, and supported nerve regeneration in more than 90% of cases. Nerve regeneration was improved in tubes in which growth factors were added, compared with empty tubes and those containing collagen gel alone (negative controls). Tubes filled with 10 microg/ml of FGF-1 dispersed in collagen demonstrated regeneration comparable to autografts (positive controls) and showed significantly better regeneration than the other groups.

CONCLUSIONS

The PHEMA-MMA tubes augmented with FGF-1 in their lumens appear to be a promising alternative to autografts for repair of nerve injuries. Studies are in progress to assess the long-term biocompatibility of these implants and to enhance regeneration further.

Adeno-associated viral vector-mediated neurotrophin gene transfer in the injured adult rat spinal cord improves hind-limb function

To foster axonal growth from a Schwann cell bridge into the caudal spinal cord, spinal cells caudal to the implant were transduced with adeno-associated viral (AAV) vectors encoding for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (AAV-NT-3). Control rats received AAV vectors encoding for green fluorescent protein or saline. AAV-BDNF- and AAV-NT-3-transduced 293 human kidney cells produced and secreted BDNF or NT-3, respectively, in vitro. The secreted neurotrophins were biologically active; they both promoted outgrowth of sensory neurites in vitro. In vivo, transgene expression was observed predominantly in neurons for at least 16 weeks after injection. Compared with controls, a modest though significant improvement in hind-limb function was found in rats that received AAV-BDNF and AAV-NT-3. Retrograde tracing demonstrated that twice as many neurons with processes extending toward the Schwann cell graft were present in the second lumbar cord segment of AAV-BDNF- and AAV-NT-3-injected animals compared with controls. We found no evidence, however, for growth of regenerated axons from the Schwann cell implant into the caudal cord. Our results suggest that AAV vector-mediated overexpression of BDNF and NT-3 in the cord caudal to a Schwann cell bridge modified the local lumbar axonal circuitry, which was beneficial for locomotor function.

Addition of fibronectin to alginate matrix improves peripheral nerve regeneration in tissue-engineered conduits

Schwann cell (SC) transplantation has been proposed to encourage peripheral nerve regeneration, but an optimal SC-carrying matrix would be needed. The aim of this study was to characterize how the addition of fibronectin to alginate would affect the outcome of nerve regeneration promoted by Schwann cells embedded in this matrix. Genetically labeled rat SCs were obtained by lacZ gene transduction. SCs were suspended in alginate hydrogel matrix with/without addition of liquid fibronectin, and their viability and growth in the different types of matrices were assessed in vitro by AlamarBlue assay. In vivo assessment of SC transplantation in the matrix was carried out with poly-3-hydroxybutyrate (PHB) conduits to bridge a sciatic nerve gap. The grafted conduits were harvested at 2, 3, and 6 weeks and assessed for the presence of labeled SCs in relation to regrowing axons. The amount and rate of axonal regeneration were assessed by quantitative immunohistochemistry. Addition of fibronectin to alginate hydrogel improved SC viability and growth profile in vitro. X-Gal staining confirmed that SCs transplanted in PHB conduits were viable throughout the time course, and that the labeled SCs were clearly associated with regenerating axons. The regeneration rate was enhanced when liquid fibronectin was added to the alginate matrix. Furthermore, the presence of SCs also enhanced regeneration and there was an additive effect when both SCs and fibronectin were combined with alginate. In conclusion, the addition of fibronectin to alginate hydrogel matrix contributed to improve nerve regeneration, supporting SC viability and augmenting their effect on axonal growth when transplanted in a bioengineered nerve conduit.

Promotion of axonal regeneration in the injured CNS

Molecules that are found in the extracellular environment at a CNS lesion site, or that are associated with myelin, inhibit axon growth. In addition, neuronal changes--such as an age-dependent reduction in concentrations of cyclic AMP--render the neuron less able to respond to axotomy by a rapid, forward, actin-dependent movement. An alternative mechanism, based on the protrusive forces generated by microtubule elongation or the anterograde transport of cytoskeletal elements, may underlie a slower form of axon elongation that happens during regeneration in the mature CNS. Therapeutic approaches that restore the extracellular CNS environment or the neuron's characteristics back to a more embryonic state increase axon regeneration and improve functional recovery after injury. These advances in the understanding of regeneration in the CNS have major implications for neurorehabilitation and for the use of axonal regeneration as a therapeutic approach to disorders of the CNS such as spinal-cord injury.

Rat Schwann cells in bioresorbable nerve guides to promote and accelerate axonal regeneration

A micro-structured, biodegradable, semipermeable hollow nerve guide implant was developed to bridge nerve lesions. Quantitative comparison of cell migration and axonal growth using time lapse video recording in vitro revealed that axons grow eight times faster than neuritotrophic Schwann cells migrate. To accelerate regeneration, purified Schwann cells are best injected into nerve guides before implantation. Nerve guides made from resorbable poly-lactide-co-glycolide support Schwann cell attachment, cell survival, and axonal outgrowth in vitro. The therapeutic concept aims at the development of an 'intelligent neuroprosthesis' that first mediates regeneration and then disappears.

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.

Ensheathing cells and methylprednisolone promote axonal regeneration and functional recovery in the lesioned adult rat spinal cord

Axons fail to regenerate after spinal cord injury (SCI) in adult mammals, leading to permanent loss of function. After SCI, ensheathing cells (ECs) promote recovery in animal models, whereas methylprednisolone (MP) promotes neurological recovery in humans. In this study, the effectiveness of combining ECs and MP after SCI was investigated for the first time. After lesioning the corticospinal tract in adult rats, ECs were transplanted into the lesion, and MP was administered for 24 hr. At 6 weeks after injury, functional recovery was assessed by measuring successful performance of directed forepaw reaching (DFR), expressed as percentages. Axonal regeneration was analyzed by counting the number of corticospinal axons, anterogradely labeled with biotin dextran tetramethylrhodamine, caudal to the lesion. Lesioned control rats, receiving either no treatment or vehicle, had abortive axonal regrowth (1 mm) and poor DFR success (38 and 42%, respectively). Compared with controls, MP-treated rats had significantly more axons 7 mm caudal to the lesion, and DFR performance was significantly improved (57%). Rats that received ECs in combination with MP had significantly more axons than all other lesioned rats up to 13 mm. Successful DFR performance was significantly higher in rats with EC transplants, both without (72%) and with (78%) MP, compared with other lesioned rats. These data confirm previous reports that ECs promote axonal regeneration and functional recovery after spinal cord lesions. In addition, this research provides evidence that, when used in combination, MP and ECs improve axonal regrowth up to 13 mm caudal to the lesion at 6 weeks after injury.

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.

Cationic liposome-mediated GDNF gene transfer after spinal cord injury

Glial cell line-derived neurotrophic factor (GDNF) has been shown to protect cranial and spinal motoneurons, which suggests potential uses of GDNF in the treatment of spinal cord injury (SCI) and motor neuron disease. We examined neuroprotective effect of cationic liposome-mediated GDNF gene transfer in vivo on axonal regeneration and locomotor function recovery after SCI in adult rats. The mixture of DC-Chol liposomes and recombinant plasmid pEGFP-GDNF cDNA was injected after SCI. RT-PCR confirmed the increased expression of GDNF mRNA in the injected areas at 7 days after injection. The expression of EGFP-GDNF was observed in the cells around the injection locus by fluorescence microscope at least 4 weeks after injection. Four weeks after GDNF gene transfer, regeneration of the corticospinal tracts was assessed using anterograde tract tracing. There are more HRP labeling of corticospinal tract axons across the lesion in GDNF group compared with control group. In GDNF group, the maximum distance these labeled axons extended varied in different animals and ranged from 5 mm to approximately 9 mm from the lesion. In control group, no HRP labeled axons extended caudal to the lesion. The locomotion function of hindlimbs of rats was evaluated using inclined plane test and BBB locomotor scores. The locomotion functional scores in GDNF group were higher than that in control group within 1-4 weeks after SCI (p < 0.05). These data demonstrate that in vivo transfer of GDNF cDNA can promote axonal regeneration and enhance locomotion functional recovery, suggesting that cationic liposome-mediated delivery of GDNF cDNA may be a practical gene transfer method for traumatic SCI treatment.

Cryopreserved cells isolated from the adult canine olfactory bulb are capable of extensive remyelination following transplantation into the adult rat CNS

Naturally occurring spinal cord injury in dogs provides a potentially powerful intermediate model for testing the efficacy of therapeutic strategies developed in experimental rodent models before phase 1 trials in human patients. A particularly promising strategy involves transplantation of olfactory ensheathing cells (OECs) that both promote axon regeneration and generate new myelin sheaths. As a first step in developing OEC transplantation in the canine intermediate model we describe the isolation, purification, and characterization of OECs from adult dog olfactory bulb. We also show that the canine OEC behaves in a manner similar to its rodent counterpart following transplantation into demyelinating lesions in rat spinal cord and that these properties are retained following cryopreservation.

Brain-derived neurotrophic factor applied to the motor cortex promotes sprouting of corticospinal fibers but not regeneration into a peripheral nerve transplant

Previous experiments from our laboratory have shown that application of brain-derived neurotrophic factor (BDNF) to the red nucleus or the motor cortex stimulates an increase in the expression of regeneration-associated genes in rubrospinal and corticospinal neurons. Furthermore, we have previously shown that BDNF application stimulates regeneration of rubrospinal axons into a peripheral graft after a thoracic injury. The current study investigates whether application of BDNF to the motor cortex will facilitate regeneration of corticospinal neurons into a peripheral nerve graft placed into the thoracic spinal cord. In adult Sprague Dawley rats, the dorsal columns and the corticospinal tract between T9 and T10 were ablated by suction, and a 5-mm-long segment of predegenerated tibial nerve was autograft implanted into the lesion. With an osmotic pump, BDNF was infused directly into the parenchyma of the motor cortex for 14 days. Growth of the corticospinal tract into the nerve graft was then evaluated by transport of an anterograde tracer. Anterogradely labeled corticospinal fibers were not observed in the peripheral nerve graft in animals treated with saline or BDNF. Serotinergic and noradrenergic fibers, as well as peripheral sensory afferents, were observed to penetrate the graft, indicating the viability of the peripheral nerve graft as a permissive growth substrate for these specific fiber types. Although treatment of the corticospinal fibers with BDNF failed to produce regeneration into the graft, there was a distinct increase in the number of axonal sprouts rostral to the injury site. This indicates that treatment of corticospinal neurons with neurotrophins, e.g., BDNF, can be used to enhance sprouting of corticospinal axons within the spinal cord. Whether such sprouting leads to functional recovery after spinal cord injury is currently under investigation.

Viral vector-mediated gene expression in olfactory ensheathing glia implants in the lesioned rat spinal cord

Implantation of olfactory ensheathing glia (OEG) is a promising strategy to augment long-distance regeneration in the injured spinal cord. In this study, implantation of OEG following unilateral hemisection of the dorsal cervical spinal cord was combined with ex vivo gene transfer techniques. We report, to our knowledge for the first time, that purified cultures of primary OEG are capable of expressing a foreign gene following adenoviral (AdV) and lentiviral (LV) vector-mediated gene transfer. OEG implants subjected to AdV vector-mediated gene transfer expressed high levels of transgenic protein in both intact and lesioned spinal cord at 7 days after implantation. However, the levels of transgene expression gradually declined between 7 and 30 days after implantation in lesioned spinal cord. Infection with LV vectors resulted in stable transduction of primary OEG cultures and transgene expression persisted for at least 4 months after implantation. Genetic engineering of OEG opens the possibility of expressing additional neurotrophic genes and create optimal 'bridging' substrates to support spinal axon regeneration. Furthermore, stable transduction of OEG allows us to reliably study the behaviour of implanted cells and to obtain better understanding of their regeneration supporting properties.

Axonal regeneration into Schwann cell grafts within resorbable poly(alpha-hydroxyacid) guidance channels in the adult rat spinal cord

Axonal growth and myelination in a SC graft contained in a resorbable tubular scaffold made of poly(D,L-lactic acid) (PLA50) or high molecular weight poly(L-lactic acid) mixed with 10% poly(L-lactic acid) oligomers (PLA(100/10)) were studied for up to 4 months after implantation in the completely transected adult rat thoracic spinal cord. The PLA50 tubes collapsed soon after implantation and, consequently, compressed the graft inside, leading to only occasional thin cables with SCs and a low number of myelinated axons: 17 +/- 6 at 1 and 158 +/- 11 at 2 months post-grafting. The cable contained 32 +/- 23 blood vessels at 2 weeks, 55 +/- 33 at 1 month and 46 +/- 30 at 2 months after implantation. PLA(100/10) tubes, on the other hand, were found to break up into large pieces, which compressed and sometimes protruded into the tissue cable inside. At all time points studied, however, cables contained SCs and were well vascularized with 414 +/- 47 blood vessels at 2 weeks, 437 +/- 139 at 1, 609 +/- 134 at 2 and 396 +/- 95 at 4 months post-grafting. The number of myelinated axons was 712 +/- 509 at 1 month, 1819 +/- 837 at 2 months and 609 +/- 132 at 4 months post implantation. These results demonstrated that fiber growth and myelination into a SC graft contained in a resorbable PLA(100/10) tube increases over the first 2 months post-implantation but decreases thereafter. Changes in geometry of both types of polymer tubes were detrimental to axonal regeneration. Future research should explore the use of polymers that better retain the appropriate mechanical, geometrical and permeability properties over time.

Poly(D,L-lactide) foams modified by poly(ethylene oxide)-block-poly(D,L-lactide) copolymers and a-FGF: in vitro and in vivo evaluation for spinal cord regeneration

The first goal of this study was to examine the influence that poly(ethylene oxide)-block-poly(D,L-lactide) (PELA) copolymer can have on the wettability, the in vitro controlled delivery capability, and the degradation of poly(D,L-lactide) (PDLLA) foams. These foams were prepared by freeze-drying and contain micropores (10 microm) in addition of macropores (100 microm) organized longitudinally. Weight loss, water absorption, changes in molecular weight, polymolecularity (Mw/Mn) and glass transition temperature (Tg) of PDLLA foams mixed with various amounts of PELA were followed with time. It was found that 10wt% of PELA increased the wettability and the degradation rate of the polymer foams. The release of sulforhodamine (SR) was compared for PDLLA and PDLLA-PELA foams in relation with the foam porosity. An initial burst release was observed only in the case of the 90:10 PDLLA/PELA foam. The ability of the foam of this composition to be integrated and to promote tissue repair and axonal regeneration in the transected rat spinal cord was investigated. After implantation of ca. 20 polymer rods assembled with fibrin-glue, the polymer construct was able to bridge the cord stumps by forming a permissive support for cellular migration, angiogenesis and axonal regrowth.

Horseradish peroxidase retrograde labeling of primary sensory neurons: a comparison of four intraspinal application methods

The purpose of this study was to optimize the methods of retrograde labeling of sensory neurons in demonstrating the continuity of post-ganglionic primary sensory axons. This was accomplished by comparing four different methods of horseradish peroxidase (HRP) application into the lower thoracic spinal cord of adult rats (level T11). HRP application with a piece of Gelfoam via a dorsal myelotomy (group 1, n = 8), stereotactic injections with a 0.72-mm tip diameter needle (group 2, n = 8), with a 0.24-mm tip needle (group 3, n = 8), and with a 0.08-mm tip glass micropipette (group 4, n = 5). Histological examination of the application site showed that the extent of spinal cord injury was directly proportional to the diameter of the needle tip. The mean number of dorsal root ganglia (DRG) sensory neurons retrogradely stained by HRP differed among the four experimental groups: 77 +/- 45 (SEM) per DRG in group 1, 106 +/- 24 in group 2, 652 +/- 90 in group 3, and 238 +/- 60 in group 4. A significant difference was found between group 3 and the other ones (P < 0.05). Intraspinal injection of HRP with a fine needle (0.24-mm tip diameter) using a stereotactic approach can achieve effective and reliable retrograde labeling of primary sensory neurons. This reproducible method may be useful in studies dealing with regeneration of post-ganglionic primary sensory axons.

Creating porous tubes by centrifugal forces for soft tissue application

Chemically crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) tubes were synthesized by applying centrifugal forces to propagating polymer chains in solution. Initiated monomer solutions, with a composition typical for PHEMA sponges, were placed into a cylindrical mold that was rotated about its long axis. As polymerization proceeded, phase separated PHEMA formed a sediment at the periphery under centrifugal action. The solvent remained in the center of the mold while the PHEMA phase gelled, resulting in a tube. By controlling the rotational speed and the formulation chemistry (i.e., monomer, initiator and crosslinking agent concentrations), the tube dimensions and wall morphology were manipulated. Tube manufacture was limited by a critical casting concentration [M]c, above which only rods formed. All tubes had an outer diameter of 2.4 mm, reflecting the internal diameter of the mold and a wall thickness of approximately 40-400 microm. Wall morphologies varied from interconnecting polymer and water phases to a closed cell, gel-like, structure. Concentric tubes were successfully prepared by using formulations that enhanced phase separation over gelation/network formation. This was achieved by using formulations with lower concentrations of monomer and crosslinking agent and higher concentrations of initiator. This technique offers a new approach to the synthesis of polymeric tubes for use in soft tissue applications, such as nerve guidance channels.

Transplants of cells genetically modified to express neurotrophin-3 rescue axotomized Clarke's nucleus neurons after spinal cord hemisection in adult rats

To test the idea that genetically engineered cells can rescue axotomized neurons, we transplanted fibroblasts and immortalized neural stem cells (NSCs) modified to express neurotrophic factors into the injured spinal cord. The neurotrophin-3 (NT-3) or nerve growth factor (NGF) transgene was introduced into these cells using recombinant retroviral vectors containing an internal ribosome entry site (IRES) sequence and the beta-galactosidase or alkaline phosphatase reporter gene. Bioassay confirmed biological activity of the secreted neurotrophic factors. Clarke's nucleus (CN) axons, which project to the rostral spinal cord and cerebellum, were cut unilaterally in adult rats by T8 hemisection. Rats received transplants of fibroblasts or NSCs genetically modified to express NT-3 or NGF and a reporter gene, only a reporter gene, or no transplant. Two months postoperatively, grafted cells survived at the hemisection site. Grafted fibroblasts and NSCs expressed a reporter gene and immunoreactivity for the NGF or NT-3 transgene. Rats receiving no transplant or a transplant expressing only a reporter gene showed a 30% loss of CN neurons in the L1 segment on the lesioned side. NGF-expressing transplants produced partial rescue compared with hemisection alone. There was no significant neuron loss in rats receiving grafts of either fibroblasts or NSCs engineered to express NT-3. We postulate that NT-3 mediates survival of CN neurons through interaction with trkC receptors, which are expressed on CN neurons. These results support the idea that NT-3 contributes to long-term survival of axotomized CN neurons and show that genetically modified cells rescue axotomized neurons as efficiently as fetal CNS transplants.

Degeneration and sprouting of identified descending supraspinal axons after contusive spinal cord injury in the rat

Contusive spinal cord injury (SCI) results in the formation of a chronic lesion cavity surrounded by a rim of spared fibers. Tissue bridges containing axons extend from the spared rim into the cavity dividing it into chambers. Whether descending axons can grow into these trabeculae or whether fibers within the trabeculae are spared fibers remains unclear. The purposes of the present study were (1) to describe the initial axonal response to contusion injury in an identified axonal population, (2) to determine whether and when sprouts grow in the face of the expanding contusion cavity, and (3) in the long term, to see whether any of these sprouts might contribute to the axonal bundles that have been seen within the chronic contusion lesion cavity. The design of the experiment also allowed us to further characterize the development of the lesion cavity after injury. The corticospinal tract (CST) underwent extensive dieback after contusive SCI, with retraction bulbs present from 1 day to 8 months postinjury. CST sprouting occurred between 3 weeks and 3 months, with penetration of CST axons into the lesion matrix occurring over an even longer time course. Collateralization and penetration of reticulospinal fibers were observed at 3 months and were more extensive at later time points. This suggests that these two descending systems show a delayed regenerative response and do extend axons into the lesion cavity and that the endogenous repair can continue for a very long time after SCI.

A novel method for simultaneous anterograde and retrograde labeling of spinal cord motor tracts in the same animal

Examination of repaired spinal cord tracts has usually required separate groups of animals for anterograde and retrograde tracing owing to the incompatibility of techniques such as tissue fixation. However, anterograde and retrograde labeling of different animals subjected to the same repair may not allow accurate examination of that repair strategy because widely variable results can occur in animals subjected to the same strategy. We have developed a reliable method of labeling spinal cord motor tracts bidirectionally in the same animal using DiI, a lipophilic dye, to anterogradely label the corticospinal tract and Fluoro-Gold (FG) to retrogradely label cortical and brainstem neurons of several spinal cord motor tracts in normal and injured adult rats. Other tracer combinations (lipophilic dyes or fluorescent dextrans) were also investigated but were less effective. We also developed methods to minimize autofluorescence with the DiI/FG technique, and found that the DiI/FG technique is compatible with decalcification and immunohistochemistry for several markers relevant for studies of spinal cord regeneration. Thus, the use of anterograde DiI and retrograde FG is a novel technique for bidirectional labeling of the motor tracts of the adult spinal cord with fluorescent tracers and should be useful for demonstrating neurite regeneration in studies of spinal cord repair.(J Histochem Cytochem 49:1111-1122, 2001)

Neurotrophic factors, cellular bridges and gene therapy for spinal cord injury

Injury to the adult mammalian spinal cord results in extensive axonal degeneration, variable amounts of neuronal loss, and often severe functional deficits. Restoration of controlled function depends on regeneration of these axons through an injury site and the formation of functional synaptic connections. One strategy that has emerged for promoting axonal regeneration after spinal cord injury is the implantation of autologous Schwann cells into sites of spinal cord injury to support and guide axonal growth. Further, more recent experiments have shown that neurotrophic factors can also promote axonal growth, and, when combined with Schwann cell grafts, can further amplify axonal extension after injury. Continued preclinical development of these approaches to neural repair may ultimately generate strategies that could be tested in human injury.

Could enhanced reflex function contribute to improving locomotion after spinal cord repair?

Although numerous treatments have been found to improve locomotion in spinal cord injured mammals, the underlying mechanisms are very poorly understood. Some of the main possibilities are: (1) regeneration of axons across the injury site and the re-establishment of descending pathways needed to voluntarily initiate and maintain stepping in the hind legs, (2) enhanced effectiveness of undamaged neurons in preparations with incomplete transections of the cord, (3) non-specific facilitation of reflexes and intrinsic spinal networks by transmitters released from regenerated axons and/or by substances introduced by the treatment, and (4) enhanced trunk movements close to the injury site strengthening the mechanical coupling of the trunk to the hind legs via spinal reflexes. In addition, any procedure that even slightly improves stepping may be further enhanced by use-dependent modification of reflex pathways and interneuronal networks in the lumbar cord. The emphasis of this review is on the contribution of spinal reflexes to the patterning of motor activity for walking, and how enhancing reflex function may contribute to the improvement of locomotion by treatments aimed at restoring locomotion after complete transection of the spinal cord.

Bridging areas of injury in the spinal cord

There is a devastating loss of function when substantial numbers of axons are interrupted by injury to the spinal cord. This loss may be eventually reversed by providing bridging prostheses that will enable axons to regrow across the injury site and enter the spinal cord beyond. This review addresses the bridging strategies that are being developed in a number of spinal cord lesion models: complete and partial transection and cavities arising from contusion. Bridges containing peripheral nerve, Schwann cells, olfactory ensheathing glia, fetal tissue, stem cells/neuronal precursor cells, and macrophages are being evaluated as is the administration of neurotrophic factors, administered by infusion or secreted by genetically engineered cells. Biomaterials may be an important factor in developing successful strategies. Due to the complexity of the sequelae following spinal cord injury, no one strategy will be effective. The compelling question today is: What combinations of the strategies discussed, or new ones, along with an initial neuroprotective treatment, will substantially improve outcome after spinal cord injury?

Towards micro electrode implants: in vitro guidance of rat spinal cord neurites through polyimide sieves by Schwann cells

Our goal is to develop biohybrid neural microprobe implants with sieve electrodes for external stimulation of co-implanted neurons whose axons penetrate through the holes of electrodes and innervate host targets such as denervated muscle fibers. For evaluation of implants, potential scar formation was imitated in fibroblast-spinal cord co-cultures. In vitro neurite extension through flexible 10-microm thick polyimide sieves was inhibited by co-cultured fibroblasts. In contrast, the neurite penetration of sieves could be greatly stimulated by oriented exposure to Schwann cells. To our knowledge this is the first direct proof that Schwann cells display a guidance effect on spinal cord neurons in vitro. The results pave the way for novel biohybrid neuro-implants and provide means to circumvent the obstacle of inhibitory scar formation.

Functional recovery and regeneration of descending tracts in rats after spinal cord transection in infancy

STUDY DESIGN

The functional recovery of rats that underwent spinal cord transection in infancy was evaluated by multimodal examination (functional tests, electrophysiologic evaluation, tract-tracing) to determine the basis for the recovery.

OBJECTIVES

To determine whether the hind limb function in rats that underwent spinal cord transection in infancy is regained completely, which descending tracts regenerate after the transection, and whether the functional recovery is correlated with axonal reconnection.

SUMMARY OF BACKGROUND DATA

It is widely accepted that a newborn rat recovers its hind limb function after spinal cord transection even without any specific treatments. This functional recovery might be attributed to possible regeneration of some descending pathways, although there is a counterargument that well-trained spinal cord reflexes may bring about functional compensation.

METHODS

The thoracic spinal cord of infant rats was completely transected at Th10 when they were 2 weeks of age. Multimodal functional tests and electrophysiologic studies were performed 5 weeks later. Some recovered rats (i.e., those able to walk after the transection) underwent spinal cord retransection, with subsequent reevaluation of locomotion and muscle-evoked potentials. At 6 weeks after the initial transection, tract-tracing studies were performed in some animals.

RESULTS

A motor performance score detected the functional differences between the control and the recovered rats. Muscle-evoked potentials of hind limbs after electrical stimulation to the brain were recorded in some of the recovered rats, but never in the unrecovered rats. Moreover, the muscle-evoked potentials of the recovered rats disappeared after spinal cord retransection that resulted in loss of voluntary movement. Morphologic studies in two rats provided evidence that reconnection of rubrospinal, vestibulospinal, and reticulospinal tracts had occurred, whereas corticospinal regeneration was not detected.

CONCLUSIONS

It can be concluded that the hind limb function of rats that underwent spinal cord transection in infancy was partially regained; that axonal regeneration of the rubrospinal, vestibulospinal, or reticulospinal tracts was demonstrated, whereas the reconnection of the corticospinal tract was not observed; and that the axonal regeneration of these tracts is involved in the functional recovery.

Under one roof: the Miami Project to Cure Paralysis model for spinal cord injury research

Concentrating a wide range of spinal cord injury (SCI) research laboratories in a single location to accelerate progress and draw attention to the promise of SCI research has made The Miami Project to Cure Paralysis one of the most publicly recognized and often controversial research groups in the neurosciences. A "Center of Excellence" at the University of Miami School of Medicine, the Miami Project also serves as a model for SCI research programs being developed nationally and internationally. Founded in 1985, the Miami Project set out on an unprecedented path-to develop a research center dedicated to improving treatments for SCI by bridging basic and clinical science. In doing so, neurosurgeon Barth Green, M.D., enlisted not only a multidisciplinary team of scientists but also a devoted following of financial donors and volunteer research subjects, and support from the University of Miami and Florida legislature. Highly visible spokespersons, including cofounder ex-Miami Dolphin Nick Buoniconti and his son Marc, brought the issue of SCI paralysis and the promise of research before the public, the media, and sports communities. As progress in the neurosciences has raced ahead, public attention to medical research, and SCI research in particular, has grown exponentially. This review will assess the Miami Project as a model for disease-based research that unites academic, philanthropic, and patient communities in a common cause.

Alginate, a bioresorbable material derived from brown seaweed, enhances elongation of amputated axons of spinal cord in infant rats

Freeze-dried alginate sponge crosslinked with covalent bonds was developed in our laboratory and has been demonstrated to enhance peripheral nerve regeneration. In this study, we examined spinal cord repair using alginate sponge in infant rats. On postnatal day 8-12, the spinal cord was transversely resected at Th7-Th8 to produce a 2-mm gap. The gap was filled with alginate sponge in the alginate group. For the control group, the gap was left empty. In the alginate group, the recovery of evoked electromyogram and sensory-evoked potentials 6 weeks after surgery indicated that elongation of axons could establish electrophysiologically functional projections through the gap. A histological study revealed that myelinated and unmyelinated axons, surrounded by a perineurial-like structure, had elongated across the gap. An immunohistochemical examination revealed that elongation of astrocytic processes and/or migration of astrocytes into the alginate sponge was induced, whereas astrocyte gliosis was reduced at the interface between the implanted alginate and the host spinal cord, compared with the control group. However, a horseradish peroxidase tracing study revealed ascending and descending fibers had also elongated into the gap and reentered the other stump of the transected spinal cord beyond the gap. These results suggest that alginate might provide a permissive microenvironment for elongation of spinal cord axons.

Inhibitory proteoglycan immunoreactivity is higher at the caudal than the rostral Schwann cell graft-transected spinal cord interface

To begin to evaluate the influence that proteoglycans may have on the success of Schwann cell (SC) transplants to induce axonal regrowth across a complete transection lesion and beyond, we determined the pattern of expression of inhibitory chondroitin sulfate proteoglycans (CSPGs) 3 weeks after transplantation into completely transected adult rat thoracic spinal cord. Using immunohistochemistry, we observed that: (1) CSPGs recognized by CS-56 antibody are present on astrocytes, fibroblasts, and SCs in the distal graft, and at lesion and cystic cavity borders; (2) CS-56 immunoreactivity (IR) is greater at the caudal SC graft-host cord interface than the rostral interface; (3) phosphacan-IR, also greater at the caudal interface, is associated with astrocytes, fibroblasts, as yet unidentified cells, and extracellular matrix; (4) neurocan-IR is present on astrocytes and as yet unidentified cells in grey and white matter; and (5) NG2-IR is associated with matrix near SC grafts, unidentified cells mainly in white matter, and lesion borders and cysts. Neither oligodendrocytes nor activated macrophages/microglia were immunostained. In sum, the CSPGs studied are increased at 3 weeks, especially at the caudal SC graft-cord interface, possibly contributing to an inhibitory molecular barrier that precludes regrowing descending axons from entering the caudal host cord.

Sciatic nerve regeneration through alginate with tubulation or nontubulation repair in cat

A novel material for nerve regeneration, alginate, was employed in both tubulation and nontubulation repair of a long peripheral nerve defect injury. Twelve cats underwent severing of the right sciatic nerve to generate a 50-mm gap, which was treated by tubulation repair (n = 6) or nontubulation repair (n = 6). In the tubulation group, a nerve conduit consisting of polyglycolic acid mesh tube filled with alginate sponge was implanted into the gap and the tube was sutured to both nerve stumps. In the nontubulation group, the nerve defect was repaired by a simple interpolation of two pieces of alginate sponge without any suture. The animals in both groups exhibited similar recovery of locomotor function. Three months postoperatively, successful axonal elongation and reinnervation in both the afferent and efferent systems were detected by electrophysiological examinations. Intracellular electrical activity was also recorded, which is directly indicative of continuity of the regenerated nerve and restoration of the spinal reflex circuit. Eight months after operation, many regenerated myelinated axons with fascicular organization by perineurial cells were observed within the gap, peroneal and tibial branches were found in both groups, while no alginate residue was found within the regenerated nerves. In morphometric analysis of the axon density and diameter, there were no significant differences between the two groups. These results suggest that alginate is a potent material for promoting peripheral nerve regeneration. It can also be concluded that the nontubulation method is a possible repair approach for peripheral nerve defect injury.

Inhibition of p38 mitogen-activated protein kinase provides neuroprotection in cerebral focal ischemia

Mitogen-activated protein kinases (MAPKs) are involved in many cellular processes. The stress-activated MAPK, p38, has been linked to inflammatory cytokine production and cell death following cellular stress. Here, we demonstrate focal ischemic stroke-induced p38 enzyme activation (i.e., phosphorylation) in the brain. The second generation p38 MAPK inhibitor SB 239063 was identified to exhibit increased kinase selectivity and improved cellular and in vivo activity profiles, and thus was selected for evaluation in two rat models of permanent focal ischemic stroke. SB 239063 was administered orally pre- and post-stroke and intravenously post-stroke. Plasma concentration levels were achieved in excess of those that effectively inhibit p38 activity. In both moderate and severe stroke, SB 239063 reduced infarct size by 28-41%, and neurological deficits by 25-35%. In addition, neuroprotective plasma concentrations of SB 239063 that reduced p38 activity following stroke also reduced the stroke-induced expression of IL-1beta and TNFalpha (i.e., cytokines known to contribute to stroke-induced brain injury). SB 239063 also provided direct protection of cultured brain tissue to in vitro ischemia. This robust SB 239063-induced neuroprotection emphasizes a significant opportunity for targeting MAPK pathways in ischemic stroke injury, and also suggests that p38 inhibition be evaluated for protective effects in other experimental models of nervous system injury and neurodegeneration.

Neural transplantation in spinal cord injury

Although medical advancements have significantly increased the survival of spinal cord injury patients, restoration of function has not yet been achieved. Neural transplantation has been studied over the past decade in animal models as a repair strategy for spinal cord injury. Although spinal cord neural transplantation has yet to reach the point of clinical application and much work remains to be done, reconstructive strategies offer the greatest hope for the treatment of spinal cord injury in the future. This article presents the scientific basis of neural transplantation as a repair strategy and reviews the current status of neural transplantation in spinal cord injury.

Spinal cord repair: strategies to promote axon regeneration

Neurons in the central nervous system have a remarkable capacity to regenerate their transected axons when provided with an appropriate growth environment. Advances in our understanding of axon regeneration have allowed the development of different experimental strategies to stimulate axon regeneration in animal models of spinal cord injury. Growth inhibitory proteins block axon regeneration in the CNS, and many of these proteins have been identified. Various methods that are now used to stimulate regeneration in the injured spinal cord are directed at overcoming the growth inhibitory environment of the CNS. Three general approaches tested in vivo stimulate regeneration in the spinal cord. First, antibodies that bind inhibitory proteins in myelin allow axon regeneration in the CNS. Second, methods that modulate neuronal intracellular signaling allow axons to grow directly on the inhibitory substrate of the CNS. Third, transplantation of cells to the lesioned spinal cord promotes repair. In this paper we review current advances in each of these research domains.

Columns of Schwann cells extruded into the CNS induce in-growth of astrocytes to form organized new glial pathways

Our previous work showed that stereotaxic microextrusion of columns of purified peripheral nerve-derived Schwann cells into the thalamus of syngeneic adult rats induces host axons to grow into the column and form a new fiber tract. Here we describe the time course of cellular events that lead to the formation of this new tract. At 2 h postoperation, numerous OX42-positive microglia accumulated at the graft-host interface, after which donor columns became progressively and heavily infiltrated by microglia/macrophages that took on an elongated morphology in parallel with the highly orientated processes of the donor Schwann cells. The penetration of host astrocytic processes into the Schwann cell columns was substantially slower in onset, being first detected at 4 days postoperation. This event was contemporaneous with the in-growth of host thalamic axons. Between 7 and 14 days postoperation, GFAP-positive astrocytes became fully incorporated into the transplants, where they too adopted an elongated form, orientated in parallel with the longitudinal axis of the graft. Thus, the columns became a mosaic of elongated and highly orientated donor Schwann cells intimately mingled with host microglia, astrocytes, and numerous, largely unbranched 200-kDa neurofilament-positive axons from the adjacent thalamus. Electron microscopy demonstrated that the processes of donor Schwann cells and host astrocytes within the column formed tightly packed bundles that were surrounded by a partial or complete basal lamina. Control columns, formed by extruding freeze-thaw-killed Schwann cells or purified peripheral nerve fibroblasts induced a reactive injury response by the adjacent host microglia and astrocytes, but neither host astrocytes nor neurofilament-positive axons were incorporated into the columns. A better understanding of the mechanisms that regulate the interactions between donor and host glia should facilitate improved integration of such grafts and enhance their potential for inducing tissue repair.

Therapeutic potential of anti-inflammatory drugs in focal stroke

The importance of cytokines, especially TNF-alpha and IL-1beta, are emphasised in the propagation and maintenance of the brain inflammatory response to injury. Much data supports the case that ischaemia and trauma elicit an inflammatory response in the injured brain. This inflammatory response consists of mediators (cytokines, chemokines and adhesion molecules) followed by cells (neutrophils early after the onset of brain injury and then a later monocyte infiltration). De novo upregulation of pro-inflammatory cytokines, chemokines and endothelial-leukocyte adhesion molecules occurs soon after focal ischaemia and trauma, as well as at the time when the tissue injury is evolving. The significance of this brain inflammatory response and its contribution to brain injury is now becoming more understood. In this review, we discuss the role of TNF-alpha and IL-1beta in traumatic and ischaemic brain injury and associated inflammation and the co-operative actions of chemokines and adhesion molecules in this process. We also address novel approaches to target cytokines and reduce the brain inflammatory response and thus brain injury, in stroke and neurotrauma. The mitogen-activated protein kinase (MAPK), p38, has been linked to inflammatory cytokine production and cell death following cellular stress. Stroke-induced p38 enzyme activation in the brain has been demonstrated and treatment with a second generation p38 MAPK inhibitor, SB-239063, provides a significant reduction in infarct size, neurological deficits and inflammatory cytokine expression produced by focal stroke. SB-239063 can also provide direct protection of cultured brain tissue to in vitro ischaemia. This robust SB-239063-induced neuroprotection emphasises a significant opportunity for targeting MAPK pathways in ischaemic stroke injury and also suggests that p38 inhibition should be evaluated for protective effects in other experimental models of nervous system injury and neurodegeneration.

[Horseradish peroxidase retrograde labeling of primary sensory axons in rats: a comparison between three different intraspinal injections methods]

STUDY AIM

In order to improve the results of intraspinal retrograde labeling of post-ganglionic primary sensory axons by horseradish peroxidase (HRP), the authors compared three different intraspinal injection methods of this tracer into the inferior thoracic spinal cord in the rat.

MATERIAL AND METHOD

'Open field' method (group 1, N = 8); stereotactic injection, needle tip diameter = 0.72 mm (group 2, N = 8); stereotactic injection, needle tip diameter = 0.24 mm (group 3, N = 8). Histological features of the spinal injection site showed that tissue damages due to injection was more extensive and deeper than expected. HRP transported in retrograde fashion from injection site to sensory body cells located in dorsal root ganglia (DRG) was revealed by the Mesulam histochemical technique.

RESULTS

The mean number of labeled neurons per DRG was 652 in group 3, 116 in group 2, and 77 in group 1. Differences were statistically significant, especially between groups 1 and 3 (P = 4.10(-16)) and groups 2 and 3 (P = 2.10(-17)).

CONCLUSION

Retrograde labeling of primary sensory axons by HRP (or another axonal tracer) with fine needle stereotactic intraspinal injection may represent an alternative to anterograde labeling. This reliable and reproducible method may be useful in studies dealing with regeneration of post-ganglionic primary sensory axons.

Cellular transplantation and spinal cord injury

Spinal cord injury is often characterized by immediate and irreversible loss of sensory and motor functions below the level of injury. Cellular transplantation in various experimental models of spinal cord injury has been used as a strategy for reducing deficits and improving functional recovery. The general strategy has been aimed at promoting regeneration of intrinsic injured axons with the development of alternative pathways that facilitate a partial functional connection. Other objectives of cellular transplantation studies have included replacement of lost cellular elements, alleviation of chronic pain, and modulation of the inflammatory response after injury. This review focuses on the cell types that have been used in spinal cord transplantation studies in the context of evolving biological perspectives, technological advances, and new therapeutic strategies and serves as a point of reference for future studies.

Attempted endogenous tissue repair following experimental spinal cord injury in the rat: involvement of cell adhesion molecules L1 and NCAM?

It is widely accepted that the devastating consequences of spinal cord injury are due to the failure of lesioned CNS axons to regenerate. The current study of the spontaneous tissue repair processes following dorsal hemisection of the adult rat spinal cord demonstrates a phase of rapid and substantial nerve fibre in-growth into the lesion that was derived largely from both rostral and caudal spinal tissues. The response was characterized by increasing numbers of axons traversing the clearly defined interface between the lesion and the adjacent intact spinal cord, beginning by 5 days post operation (p.o.). Having penetrated the lesion, axons became associated with a framework of NGFr-positive non-neuronal cells (Schwann cells and leptomeningeal cells). Surprisingly few of these axons were derived from CGRP- or SP-immunoreactive dorsal root ganglion neurons. At the longest survival time (56 days p.o.), there was a marked shift in the overall orientation of fibres from a largely rostro-caudal to a dorso-ventral axis. Attempts to identify which recognition molecules may be important for these re-organizational processes during attempted tissue repair demonstrated the widespread and intense expression of the cell adhesion molecules (CAM) L1 and N-CAM. Double immunofluorescence suggested that both Schwann cells and leptomeningeal cells contributed to the pattern of CAM expression associated with the cellular framework within the lesion.

Advances and strategies for spinal cord regeneration

Although a cure for spinal cord injuries does not currently exist, advances have been made in the field of spinal cord regeneration. This article discusses the pathophysiology of spinal cord injury, animal models, and strategies for restoration and regeneration of the spinal cord.