Neuronal replacement strategies for spinal cord injury

Treatment of rats with spinal cord injury using human bone marrow-derived stromal cells prepared by negative selection

Background

Spinal cord injury (SCI) is a highly debilitating pathology without curative treatment. One of the most promising disease modifying strategies consists in the implantation of stem cells to reduce inflammation and promote neural regeneration. In the present study we tested a new human bone marrow-derived stromal cell preparation (bmSC) as a therapy of SCI.

Methods

Spinal cord contusion injury was induced in adult male rats at thoracic level T9/T10 using the Infinite Horizon impactor. One hour after lesion the animals were treated with a sub-occipital injection of human bmSC into the cisterna magna. No immune suppression was used. One dose of bmSC consisted, on average, of 2.3 million non-manipulated cells in 100 μL suspension, which was processed out of fresh human bone marrow from the iliac crest of healthy volunteers. Treatment efficacy was compared with intraperitoneal injections of methylprednisolone (MP) and saline. The recovery of motor functions was assessed during a surveillance period of nine weeks. Adverse events as well as general health, weight and urodynamic functions were monitored daily. After this time, the animals were perfused, and the spinal cord tissue was investigated histologically.

Results

Rats treated with bmSC did not reject the human implants and showed no sign of sickness behavior or neuropathic pain. Compared to MP treatment, animals displayed better recovery of their SCI-induced motor deficits. There were no significant differences in the recovery of bladder control between groups. Histological analysis at ten weeks after SCI revealed no differences in tissue sparing and astrogliosis, however, bmSC treatment was accompanied with reduced axonal degeneration in the dorsal ascending fiber tracts, lower Iba1-immunoreactivity (IR) close to the lesion site and reduced apoptosis in the ventral grey matter. Neuroinflammation, as evidenced by CD68-IR, was significantly reduced in the MP-treated group.

Conclusions

Human bmSC that were prepared by negative selection without expansion in culture have neuroprotective properties after SCI. Given the effect size on motor function, implantation in the acute phase was not sufficient to induce spinal cord repair. Due to their immune modulatory properties, allogeneic implants of bmSC can be used in combinatorial therapies of SCI.

Tree shrew neural stem cell transplantation promotes functional recovery of tree shrews with a hemi‑sectioned spinal cord injury by upregulating nerve growth factor expression

The aim of the present study was to determine the effect of implanted neural stem cells (NSCs) on the functional recovery of tree shrews (TSs) subjected to hemi-sectioned spinal cord injury (hSCI), and to investigate the possible mechanism involved. NSCs (passage 2), derived from the hippocampus of TSs (embryonic day 20), were labeled with Hoechst 33342 and transplanted intraspinally into the hSC of TSs at thoracic level 10 in the acute (immediately after injury) and chronic (day 9 post-injury) stages. The Basso-Beattie-Bresnahan (BBB) score was recorded from days 1 to 16 post-injury, and the survival, migration, differentiation and neurotrophic factor (NTF) expression in vivo were detected. In vitro and in vivo, the expanded NSCs were able to differentiate into neurons and astrocytes, and secreted a variety of NTFs, including ciliary NTF, transforming growth factor-β1, glial cell line-derived NTF, nerve growth factor (NGF), brain-derived NTF and insulin-like growth factor. Following transplantation, the BBB score in the TSs with chronic-stage transplantation exhibited a statistically significant increase, while there was no significant difference in the acute group, compared with the control group. This corresponded with the marked upregulation of NGF indicated by reverse transcription-quantitative polymerase chain reaction. In conclusion, the transplantation of NSCs into the hSC in the chronic phase, but not the acute stage, of hSCI in non-human primate TSs is effective and associated with upregulated NGF expression. These findings may provide novel strategies for the treatment of SCI in clinical patients.

Behavior of hippocampal stem/progenitor cells following grafting into the injured aged hippocampus

Multipotent neural stem/progenitor cells (NSCs) from the embryonic hippocampus are potentially useful as donor cells to repopulate the degenerated regions of the aged hippocampus after stroke, epilepsy, or Alzheimer's disease. However, the efficacy of the NSC grafting strategy for repairing the injured aged hippocampus is unknown. To address this issue, we expanded FGF-2-responsive NSCs from the hippocampus of embryonic day 14 green fluorescent protein-expressing transgenic mice as neurospheres in vitro and grafted them into the hippocampus of 24-month-old F344 rats 4 days after CA3 region injury. Engraftment, migration, and neuronal/glial differentiation of cells derived from NSCs were analyzed 1 month after grafting. Differentiation of neurospheres in culture dishes or after placement on organotypic hippocampal slice cultures demonstrated that these cells had the ability to generate considerable numbers of neurons, astrocytes, and oligodendrocytes. Following grafting into the injured aged hippocampus, cells derived from neurospheres survived and dispersed, but exhibited no directed migration into degenerated or intact hippocampal cell layers. Phenotypic analyses of graft-derived cells revealed neuronal differentiation in 3%-5% of cells, astrocytic differentiation in 28% of cells, and oligodendrocytic differentiation in 6%-10% cells. The results demonstrate for the first time that NSCs derived from the fetal hippocampus survive and give rise to all three CNS phenotypes following transplantation into the injured aged hippocampus. However, grafted NSCs do not exhibit directed migration into lesioned areas or widespread neuronal differentiation, suggesting that direct grafting of primitive NSCs is not adequate for repair of the injured aged brain without priming the microenvironment.

In vitro neural injury model for optimization of tissue-engineered constructs

Stem cell transplantation is a promising approach for the treatment of traumatic brain injury, although the therapeutic benefits are limited by a high degree of donor cell death. Tissue engineering is a strategy to improve donor cell survival by providing structural and adhesive support. However, optimization prior to clinical implementation requires expensive and time-consuming in vivo studies. Accordingly, we have developed a three-dimensional (3-D) in vitro model of the injured host-transplant interface that can be used as a test bed for high-throughput evaluation of tissue-engineered strategies. The neuronal-astrocytic cocultures in 3-D were subjected to mechanical loading (inducing cell death and specific astrogliotic alterations) or to treatment with transforming growth factor-beta1 (TGF-beta1), inducing astrogliosis without affecting viability. Neural stem cells (NSCs) were then delivered to the cocultures. A sharp increase in the number of TUNEL(+) donor cells was observed in the injured cocultures compared to that in the TGF-beta1-treated and control cocultures, suggesting that factors related to mechanical injury, but not strictly astrogliosis, were detrimental to donor cell survival. We then utilized the mechanically injured cocultures to evaluate a methylcellulose-laminin (MC-LN) scaffold designed to reduce apoptosis. When NSCs were co-delivered with MC alone or MC-LN to the injured cocultures, the number of caspase(+) donor cells significantly decreased compared to that with vehicle delivery (medium). Collectively, these results demonstrate the utility of an in vitro model as a pre-animal test bed and support further investigation of a tissue-engineering approach for chaperoned NSC delivery targeted to improve donor cell survival in neural transplantation.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Human fetal neural stem cells grafted into contusion-injured rat spinal cords improve behavior

Grafted human neural stem cells (hNSCs) may help to alleviate functional deficits resulting from spinal cord injury by bridging gaps, replacing lost neurons or oligodendrocytes, and providing neurotrophic factors. Previously, we showed that primed hNSCs differentiated into cholinergic neurons in an intact spinal cord. In this study, we tested the fate of hNSCs transplanted into a spinal cord T10 contusion injury model. When grafted into injured spinal cords of adult male rats on either the same day or 3 or 9 days after a moderate contusion injury, both primed and unprimed hNSCs survived for 3 months postengraftment only in animals that received grafts at 9 days postinjury. Histological analyses revealed that primed hNSCs tended to survive better and differentiated at higher rates into neurons and oligodendrocytes than did unprimed counterparts. Furthermore, only primed cells gave rise to cholinergic neurons. Animals receiving primed hNSC grafts on the ninth day postcontusion improved trunk stability, as determined by rearing activity measurements 3 months after grafting. This study indicates that human neural stem cell fate determination in vivo is influenced by the predifferentiation stage of stem cells prior to grafting. Furthermore, stem cell-mediated facilitation of functional improvement depends on the timing of transplantation after injury, the grafting sites, and the survival of newly differentiated neurons and oligodendrocytes.

Potential stem cell therapy and application in neurotrauma

Traumatic brain injury results from a sudden and external physical insult to the head, which is often accompanied by motor and cognitive impairment. Neurotrauma is characterized not only by focal abnormalities, but rather by multifocal, or even global structural and functional disturbances of the brain network. The impact initially causes necrotic cell death in the underlying tissue, followed by apoptotic cell death in the surrounding tissue due to multiple subsequent events, such as ischemia, excitotoxicity and altered gene expression. These pathological conditions are associated with high morbidity and mortality. Despite the high medical and economical relevance of neurotrauma there are currently no sufficient treatments. Supplementary therapeutic strategies have to be established. Many types of stem cells have the ability to engraft diffusely and become integral members of structures throughout the host CNS. Intrinsic factors appear to derive spontaneously from stem cells and seem to be capable of neuroprotective and/or neuroregenerative functions. Furthermore stem cells can be readily engineered to express specific genes. Such observations suggest that stem cells might participate in reconstructing the molecular and cellular milieu of traumatized brains. In this paper, the state of stem cell research is reviewed and its possible application in neurotrauma will be discussed.

Effect of growth factors on proliferation and phenotypic differentiation of human fetal neural stem cells

Human fetal neural stem cells (hNSCs) can be expanded in vitro by mitogens or growth factors, such as basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and/or leukemia inhibitory factor (LIF). Their effects on proliferation rate and differentiation pattern of hNSCs, however, have not been fully characterized. In this study, we cultured hNSCs in seven regimens, including bFGF, EGF, and LIF, either alone or in combinations. Cells were maintained as neurospheres in treatment media for various periods, up to six passages. A combination of bFGF, EGF, and LIF expanded hNSCs more efficiently than any other treatment as determined by counting total cell numbers using a trypan blue exclusion assay, a WST-1 cell viability assay, and a bromodeoxyuridine incorporation flow cytometric analysis. Differentiation patterns of hNSCs expanded under different conditions were also analyzed. We reported previously that hNSCs primed in vitro with a combination of bFGF, heparin, and laminin (FHL) induced neuronal differentiation toward a cholinergic phenotype. In this study, we show that the FHL priming increases neuronal differentiation while decreasing astroglial generation in all treatment groups as determined by immunostaining. However, cells proliferated under different growth factor conditions do vary in their phenotypic differentiation patterns. Particularly, significant generation of cholinergic cells was observed only in hNSCs expanded with EGF/bFGF or EGF/bFGF/LIF, but not with other treatment regimens, even when they are exposed to the same priming procedure. Our results indicate that hNSCs are highly plastic, with their proliferation and differentiation potential dependent on different growth factor treatments.

Dural closure, cord approximation, and clot removal: enhancement of tissue sparing in a novel laceration spinal cord injury model

OBJECT

Laceration-induced spinal cord injury (SCI) results in the invasion of a connective tissue scar, progressive damage to the spinal cord due to complex secondary injury mechanisms, and axonal dieback of descending motor pathways. The authors propose that preparation of the spinal cord for repair strategies should include hematoma removal and dural closure, resulting in apposition of the severed ends of the spinal cord. Such procedures may reduce the size of the postinjury spinal cord cyst as well as limit scar formation.

METHODS

Using a novel device, the Vibraknife, the authors created a dorsal hemisection of the spinal cord at C-6 in the adult rat. In Group 1 (eight rats), the dura mater was repaired with apposition of the two stumps of the spinal cord to reduce the lesion gap. In Group 2 (10 rats), the dura was not closed and the two cord stumps were not approximated. All rats were killed at 4 weeks postinjury, and the spinal cords from each group were removed and examined using histological, stereological, and immunohistochemical methods. In Group 1 rats a significant reduction of the total lesion volume and connective tissue scar was observed compared with those in Group 2 (Student t-test, p < 0.05). Approximation of the stumps did not promote the regeneration of corticospinal tract fibers or sensory axons through the lesion site.

CONCLUSIONS

Apposition of the severed ends of the spinal cord by dural closure reduces the lesion gap, cystic cavitation, and connective tissue scar formation. These outcomes may collectively reduce secondary tissue damage at the injury site and shorten the length of the lesion gap, which will facilitate transplantation-mediated axonal regeneration after laceration-induced SCI.

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.

Progenitor cells from the CA3 region of the embryonic day 19 rat hippocampus generate region-specific neuronal phenotypes in vitro

Progenitor cells that endure in different regions of the CNS after the initial neurogenesis can be expanded in culture and used as a source of donor tissue for grafting in neurodegenerative diseases. However, the proliferation and differentiation characteristics of residual neural progenitor cells from distinct regions of the CNS are mostly unknown. This study elucidated the characteristics of progenitor cells that endure in the CA3 region of the hippocampus after neurogenesis, by in vitro analyses of cells that are responsive to epidermal growth factor (EGF) or fibroblast growth factor-2 (FGF-2) in the embryonic day 19 (E19) rat hippocampus. Isolated cells from the E19 CA3 region formed neurospheres in the presence of either EGF or FGF-2, but the yield of neurospheres was greater with FGF-2 exposure, Differentiation cultures revealed a greater yield of neurons from FGF-2 neurospheres (60%) than from EGF neurospheres (35%). Exposure to brain-derived neurotrophic factor (BDNF) enhanced the yield of neurons from EGF neurospheres but had no consequence on FGF-2 neurospheres. A large number of neurons from EGF/FGF-2 neurospheres demonstrated clearly palpable morphological features of CA3 pyramidal neurons and lacked gamma-aminobutyric acid (GABA) expression. However, a fraction of neurons (17-20%) from EGF/FGF-2 neurospheres expressed GABA, and exposure to BDNF increased the number of GABAergic neurons (30%) from EGF neurospheres. Neurons from EGF/FGF-2 neurospheres also contained smaller populations of calbindin- and calretinin-positive interneuron-like cells. Thus, progenitor cells responsive to FGF-2 are prevalent in the CA3 region of the E19 rat hippocampus and give rise to a greater number of neurons than progenitor cells responsive to EGF. However, both FGF-2- and EGF-responsive progenitor cells from E19 CA3 region are capable of giving rise to CA3 field-specific phenotypic neurons. These results imply that progenitor cells that persist in the hippocampus after neurogenesis remain regionally restricted and hence retain their ability to give rise to region-specific phenotypic neurons even after isolation and expansion in vitro.

Brain activation sequences following electrical limb stimulation of normal and paraplegic subjects

In current clinical practice the degree of paraplegia or quadriplegia is objectively determined with transcranial magnetic stimulation (TMS) and somatosensory-evoked potentials (SSEP). We measured the MEG signal following electrical stimulation of upper and lower limbs in two normal and three clinically complete paraplegic subjects. From the MEG signal we computed distributed estimates of brain activity and identified foci just behind the central sulcus consistent in location with primary somatosensory (SI) for arm and foot and secondary somatosensory (SII) areas. Activation curves were computed from regions of interest defined around these areas. Activation of the SI foot area was observed in normal and paraplegic subjects when the upper limb was stimulated. Surprisingly, for each paraplegic subject, stimulation below the lesion was followed by cortical activations. These activations were weak, only loosely time-locked to the stimulus and were seen intermittently behind the central sulcus and nearby cortical areas. Statistical analysis of tomographic solutions and activation curves showed consistent responses following foot stimulation in one paraplegic (PS1) and intermittently in another paraplegic subject. We repeated the same experiment for PS1 in a different laboratory and the results from the analysis of foot stimulation from both laboratories revealed statistically significant focal cortical response only in the contralateral SI foot area.

Spinal cord regeneration: from gene to transplants

The past 20 years has seen the emergence of many exciting and promising experimental therapeutic strategies to promote regeneration of the injured spinal cord in laboratory animals. A greater understanding of the pathophysiologic mechanisms that contribute to the initial and secondary cord injury may facilitate the development of neuroprotective strategies that preserve axonal function and prevent apoptotic cell death, thus optimizing neurologic function. Neurotrophic factors have been used to augment the poor intrinsic regenerative capacity of central nervous system neurons, and the need for sophisticated delivery of such trophic agents has stimulated the application of gene therapy in this context. In addition to augmenting the neuronal capacity to regenerate axons, many researchers are developing strategies to overcome the inhibitory environment into which these axons must grow. Characterizing the inhibitory elements of the glial scar at the site of injury and of myelin in the distal tracts is therefore a focus of intense scientific interest. To this effect, a number of strategies have also been developed to bridge the injury site and facilitate axonal growth across the lesion with a variety of cellular substrates. These include fetal tissue transplants, stem cells, Schwann cells, and olfactory ensheathing cells. With the collaboration of basic scientists and clinicians, it is hoped that these experimental strategies coupled with a greater understanding of the neurobiology of spinal cord injury will be translatable to the clinical setting in the near future.

Feasibility and safety of neural tissue transplantation in patients with syringomyelia

Transplantation of fetal spinal cord (FSC) tissue has demonstrated significant potential in animal models for achieving partial anatomical and functional restoration following spinal cord injury (SCI). To determine whether this strategy can eventually be translated to humans with SCI, a pilot safety and feasibility study was initiated in patients with progressive posttraumatic syringomyelia (PPTS). A total of eight patients with PPTS have been enrolled to date, and this report presents findings for the first two patients through 18 months postoperative. The study design included detailed assessments of each subject at multiple pre- and postoperative time points. Outcome data were then compared with each subject's own baseline. The surgical protocol included detethering, cyst drainage, and implantation of 6-9-week postconception human FSC tissue. Immunosuppression with cyclosporine was initiated a few days prior to surgery and continued for 6 months postoperatively. Key outcome measures included: serial magnetic resonance imaging (MRI) exams, standardized measures of neurological impairment and functional disability, detailed pain assessment, and extensive neurophysiological testing. Through 18 months, the first two patients have been stable neurologically and the MRIs have shown evidence of solid tissue at the graft sites, without evidence of donor tissue overgrowth. Although it is still too soon to draw any firm conclusions, the findings from the initial two patients in this study suggest that intraspinal grafting of human FSC tissue is both feasible and safe.

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.

Neurobiology of human neurons (NT2N) grafted into mouse spinal cord: implications for improving therapy of spinal cord injury

Emerging data suggest that current strategies for the treatment of spinal cord injury might be improved or augmented by spinal cord grafts of neural cells, and it is possible that grafted neurons might have therapeutic potential. Thus, here we have summarized recent studies of the neurobiology of clonal human (NT2N) neurons grafted into spinal cord of immunodeficient athymic nude mice. Postmitotic human NT2N neurons derived in vitro from an embryonal carcinoma cell line (NT2) were transplanted into spinal cord of neonatal, adolescent and adult nude mice where they became integrated into the host gray and white matter, did not migrate from the graft site, and survived for > 15 months after implantation. The neuronal phenotype of the grafted NT2N cells was similar in gray and white matter regardless of host age at implantation, and some of the processes extended by the transplanted NT2N neurons became ensheathed by oligodendrocytes. However, there were consistent differences between NT2N processes traversing white versus gray matter. Most notably, NT2N processes with a trajectory in white matter extended over much longer distances (some for > 2 cm) than those confined to gray matter. Thus, NT2N neurons grafted into spinal cord of nude mice integrated into gray as well as white matter, where they exhibited and maintained the morphological and molecular phenotype of mature neurons for > 15 months after implantation. Also, the processes extended by grafted NT2N neurons differentially responded to cues restricted to gray versus white matter. Further insight into the neurobiology of grafted human NT2N neurons in the normal and injured spinal cord of experimental animals may lead to novel and more effective strategies for the treatment of spinal cord injury.

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.

Biological plasticity: the future of science in neurosurgery

THE FUTURE OF neurosurgery is intimately related to the future of neuroscientific research. Although the field of neuroscience is immense and not subject to brief review, it is clear that certain trends have become critical to future thinking regarding neurosurgery. An important theme that recurs in much of the current research and that will become more prominent in the future is the concept of plasticity. This refers not only to the changes in cortical representation that can occur after a variety of perturbations but also to a wide variety of neurologically relevant biological processes. In this review, we describe three areas of plasticity, i.e., the response of the brain to ischemia, cortical representational changes, and the potential for stem cell biological processes to allow us to manipulate plasticity. We posit that these trends will be crucial to the future of our specialty.

Effect of brain-derived neurotrophic factor, nerve growth factor, and neurotrophin-3 on functional recovery and regeneration after spinal cord injury in adult rats

This study examined whether continuous intramedullary infusion of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), or neurotrophin-3 (NT-3) had either an early neuroprotective effect or a delayed effect on regeneration after spinal cord injury (SCI) in adult rats. BDNF, NGF, NT-3 or vehicle was infused at a rate of 625 ng/h into the SCI site at T3 through an implanted cannula attached to an osmotic pump. This infusion was maintained for 14 days after a 35-g clip compression injury. At 4 weeks after injury, the axonal tracer fluorogold (FG) was introduced into the spinal cord caudal to the lesion and the animals sacrificed 3 days later following behavioral assessment. The inclined plane score was significantly higher in BDNF-treated animals (45 +/- 3 degrees) compared to control animals (36 -/+ 1 degrees) at 1 week after injury (p < 0.05), although the scores were not significantly different at later times. BDNF-treated animals also showed more FG-labeled cells in the red nucleus and sensorimotor cortex (1,638 +/- 350 and 124 +/- 83, respectively) compared to controls (1,228 +/- 217 and 36 +/- 15, respectively) and a lower percent cavitation at the injury site (21.4 +/- 10.4%) compared to control animals (32.3 +/- 11.7%). Invasion & proliferation of Schwann cells and formation of peripheral myelin were more prominent at the injury site in the BDNF-treated animals than in the other groups. These results indicate that continuous intramedullary infusion of BDNF provides neuroprotection and enhances some regenerative activity after SCI.

Neurons from stem cells: Implications for understanding nervous system development and repair

Neurodegenerative diseases cost the economies of the developed world billions of dollars per annum. Given ageing population profiles and the increasing extent of this problem, there has been a surge of interest in neural stem cells and in neural differentiation protocols that yield neural cells for therapeutic transplantation. Due to the oncogenic potential of stem cells a better characterisation of neural differentiation, including the identification of new neurotrophic factors, is required. Stem cell cultures undergoing synchronous in vitro neural differentiation provide a valuable resource for gene discovery. Novel tools such as microarrays promise to yield information regarding gene expression in stem cells. With the completion of the yeast, C. elegans, Drosophila, human, and mouse genome projects, the functional characterisation of genes using genetic and bioinformatic tools will aid in the identification of important regulators of neural differentiation.Key words: neural differentiation, neural precursor cell, brain repair, central nervous system repair, CNS.