NT-3, but not BDNF, prevents atrophy and death of axotomized spinal cord projection neurons

Regenerative replacement of neural cells for treatment of spinal cord injury

Introduction: Traumatic Spinal Cord Injury (SCI) results from primary physical injury to the spinal cord, which initiates a secondary cascade of neural cell death. Current therapeutic approaches can attenuate the consequences of the primary and secondary events, but do not address the degenerative aspects of SCI. Transplantation of neural stem/progenitor cells (NPCs) for the replacement of the lost/damaged neural cells is suggested here as a regenerative approach that is complementary to current therapeutics.Areas Covered: This review addresses how neurons, oligodendrocytes, and astrocytes are impacted by traumatic SCI, and how current research in regenerative-NPC therapeutics aims to restore their functionality. Methods used to enhance graft survival, as well as bias progenitor cells towards neuronal, oligodendrogenic, and astroglia lineages are discussed.Expert Opinion: Despite an NPC's ability to differentiate into neurons, oligodendrocytes, and astrocytes in the transplant environment, their potential therapeutic efficacy requires further optimization prior to translation into the clinic. Considering the temporospatial identity of NPCs could promote neural repair in region specific injuries throughout the spinal cord. Moreover, understanding which cells are targeted by NPC-derived myelinating cells can help restore physiologically-relevant myelin patterns. Finally, the duality of astrocytes is discussed, outlining their context-dependent importance in the treatment of SCI.

Interplay of BDNF and GDNF in the Mature Spinal Somatosensory System and Its Potential Therapeutic Relevance

The growth factors BDNF and GDNF are gaining more and more attention as modulators of synaptic transmission in the mature central nervous system (CNS). The two molecules undergo a regulated secretion in neurons and may be anterogradely transported to terminals where they can positively or negatively modulate fast synaptic transmission. There is today a wide consensus on the role of BDNF as a pro-nociceptive modulator, as the neurotrophin has an important part in the initiation and maintenance of inflammatory, chronic, and/or neuropathic pain at the peripheral and central level. At the spinal level, BDNF intervenes in the regulation of chloride equilibrium potential, decreases the excitatory synaptic drive to inhibitory neurons, with complex changes in GABAergic/glycinergic synaptic transmission, and increases excitatory transmission in the superficial dorsal horn. Differently from BDNF, the role of GDNF still remains to be unraveled in full. This review resumes the current literature on the interplay between BDNF and GDNF in the regulation of nociceptive neurotransmission in the superficial dorsal horn of the spinal cord. We will first discuss the circuitries involved in such a regulation, as well as the reciprocal interactions between the two factors in nociceptive pathways. The development of small molecules specifically targeting BDNF, GDNF and/or downstream effectors is opening new perspectives for investigating these neurotrophic factors as modulators of nociceptive transmission and chronic pain. Therefore, we will finally consider the molecules of (potential) pharmacological relevance for tackling normal and pathological pain.

Therapeutic repair for spinal cord injury: combinatory approaches to address a multifaceted problem

The recent years saw the advent of promising preclinical strategies that combat the devastating effects of a spinal cord injury (SCI) that are progressing towards clinical trials. However, individually, these treatments produce only modest levels of recovery in animal models of SCI that could hamper their implementation into therapeutic strategies in spinal cord injured humans. Combinational strategies have demonstrated greater beneficial outcomes than their individual components alone by addressing multiple aspects of SCI pathology. Clinical trial designs in the future will eventually also need to align with this notion. The scenario will become increasingly complex as this happens and conversations between basic researchers and clinicians are required to ensure accurate study designs and functional readouts.

Descending motor circuitry required for NT-3 mediated locomotor recovery after spinal cord injury in mice

Locomotor function, mediated by lumbar neural circuitry, is modulated by descending spinal pathways. Spinal cord injury (SCI) interrupts descending projections and denervates lumbar motor neurons (MNs). We previously reported that retrogradely transported neurotrophin-3 (NT-3) to lumbar MNs attenuated SCI-induced lumbar MN dendritic atrophy and enabled functional recovery after a rostral thoracic contusion. Here we functionally dissected the role of descending neural pathways in response to NT-3-mediated recovery after a T9 contusive SCI in mice. We find that residual projections to lumbar MNs are required to produce leg movements after SCI. Next, we show that the spared descending propriospinal pathway, rather than other pathways (including the corticospinal, rubrospinal, serotonergic, and dopaminergic pathways), accounts for NT-3-enhanced recovery. Lastly, we show that NT-3 induced propriospino-MN circuit reorganization after the T9 contusion via promotion of dendritic regrowth rather than prevention of dendritic atrophy.

Stroke Recovery in Rats after 24-Hour-Delayed Intramuscular Neurotrophin-3 Infusion

Objective

Neurotrophin‐3 (NT3) plays a key role in the development and function of locomotor circuits including descending serotonergic and corticospinal tract axons and afferents from muscle and skin. We have previously shown that gene therapy delivery of human NT3 into affected forelimb muscles improves sensorimotor recovery after stroke in adult and elderly rats. Here, to move toward the clinic, we tested the hypothesis that intramuscular infusion of NT3 protein could improve sensorimotor recovery after stroke.

Methods

Rats received unilateral ischemic stroke in sensorimotor cortex. To simulate a clinically feasible time to treatment, 24 hours later rats were randomized to receive NT3 or vehicle by infusion into affected triceps brachii for 4 weeks using implanted catheters and minipumps.

Results

Radiolabeled NT3 crossed from the bloodstream into the brain and spinal cord in rodents with or without strokes. NT3 increased the accuracy of forelimb placement during walking on a horizontal ladder and increased use of the affected arm for lateral support during rearing. NT3 also reversed sensory impairment of the affected wrist. Functional magnetic resonance imaging during stimulation of the affected wrist showed spontaneous recovery of peri‐infarct blood oxygenation level–dependent signal that NT3 did not further enhance. Rather, NT3 induced neuroplasticity of the spared corticospinal and serotonergic pathways.

Interpretation

Our results show that delayed, peripheral infusion of NT3 can improve sensorimotor function after ischemic stroke. Phase I and II clinical trials of NT3 (for constipation and neuropathy) have shown that peripheral high doses are safe and well tolerated, which paves the way for NT3 as a therapy for stroke. ANN NEUROL 2019;85:32–46.

Silver nanoparticles conjugated with Neurotrophin 3 upregulate myelin gene transcription pathway

Mathematical modeling is the art of converting problems from the biological area into handy mathematical formulations whose theoretical and numerical analysis provides understandings about the directions and solutions to the particular problem. Recently, the combination therapy treatments have been revealed exceptionally fruitful by using mathematical modeling technique. The human nervous system is composed of axons, covered by the myelin sheath. Axons carry signals and promote myelin development. The abnormalities in myelination formation due to mutations in myelin gene result in memory disorders and impaired cognitive activities. The ERBb gene family is responsible for causing abnormalities in myelin gene. Using this knowledge, the pathway of mutated myelin gene was retrieved and its model was developed. Modeling and simulation analysis was performed to determine the level of expression of several genes. The Neurotrophin 3 ligand-coated with silver nanoparticle was induced in the model to normalize the transcription of myelin gene. It was observed that the myelin gene expression level increases from 0 after two days of NT3 induction and reaches to the maximum level on the 10th day of drug induction along with an increase in ERBb expression. This research work can be used in the future as a part of drug discovery and formulation.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Intramuscular Neurotrophin-3 normalizes low threshold spinal reflexes, reduces spasms and improves mobility after bilateral corticospinal tract injury in rats

Brain and spinal injury reduce mobility and often impair sensorimotor processing in the spinal cord leading to spasticity. Here, we establish that complete transection of corticospinal pathways in the pyramids impairs locomotion and leads to increased spasms and excessive mono- and polysynaptic low threshold spinal reflexes in rats. Treatment of affected forelimb muscles with an adeno-associated viral vector (AAV) encoding human Neurotrophin-3 at a clinically-feasible time-point after injury reduced spasticity. Neurotrophin-3 normalized the short latency Hoffmann reflex to a treated hand muscle as well as low threshold polysynaptic spinal reflexes involving afferents from other treated muscles. Neurotrophin-3 also enhanced locomotor recovery. Furthermore, the balance of inhibitory and excitatory boutons in the spinal cord and the level of an ion co-transporter in motor neuron membranes required for normal reflexes were normalized. Our findings pave the way for Neurotrophin-3 as a therapy that treats the underlying causes of spasticity and not only its symptoms.

DOI:http://dx.doi.org/10.7554/eLife.18146.001

Injuries to the brain and spinal cord cause disability in millions of people worldwide. Physical rehabilitation can restore some muscle control and improve mobility in affected individuals. However, no current treatments provide long-term relief from the unwanted muscle contractions and spasms that affect as many as 78% of people with a spinal cord injury. These spasms can seriously hamper a person’s ability to carry out day-to-day tasks and get around independently. A few treatments can help in the short term but have side effects; indeed while Botox injections are used to paralyse the muscle, these also reduce the chances of useful improvements. As such, better therapies for muscle spasms are needed; especially ones that reduce spasms in the arms.

Rats with injuries to the spinal cord between their middle to lower back typically develop spasms in their legs or tail, and rat models have helped scientists begin to understand why these involuntary movements occur. Now, Kathe et al. report that cutting one specific pathway that connects the brain to the spinal cord in anesthetised rats leads to the development of spasms in the forelimbs as well. Several months after the surgery, the rats had spontaneous muscle contractions in their forelimbs and walked abnormally. Further experiments showed that some other neural pathways in the rats became incorrectly wired and hyperactive and that this resulted in the abnormal movements.

Next, Kathe et al. asked whether using gene therapy to deliver a protein that is required for neural circuits to form between muscles and the spinal cord (called neurotrophin-3) would stop the involuntary movements in the forelimbs. Delivering the gene therapy directly into the forelimb muscles of the disabled rats a day after their injury increased the levels of neurotrophin-3 in these muscles. Rats that received this treatment had fewer spasms and walked better than those that did not. Further experiments confirmed that this was because the rats’ previously hyperactive and abnormally wired neural circuits became more normal after the treatment.

Together these results suggest that neurotrophin-3 might be a useful treatment for muscle spasms in people with spinal injury. There have already been preliminary studies in people showing that treatment with neurotrophin-3 is safe and well tolerated. Future studies are needed to confirm that it could be useful in humans.

DOI:http://dx.doi.org/10.7554/eLife.18146.002

Cell Transplantation and Neuroengineering Approach for Spinal Cord Injury Treatment: A Summary of Current Laboratory Findings and Review of Literature

Spinal cord injury (SCI) can cause severe traumatic injury to the central nervous system (CNS). Current therapeutic effects achieved for SCI in clinical medicine show that there is still a long way to go to reach the desired goal of full or significant functional recovery. In basic medical research, however, cell transplantation, gene therapy, application of cytokines, and biomaterial scaffolds have been widely used and investigated as treatments for SCI. All of these strategies when used separately would help rebuild, to some extent, the neural circuits in the lesion area of the spinal cord. In light of this, it is generally accepted that a combined treatment may be a more effective strategy. This review focuses primarily on our recent series of work on transplantation of Schwann cells and adult stem cells, and transplantation of stem cell-derived neural network scaffolds with functional synapses. Arising from this, an artificial neural network (an exogenous neuronal relay) has been designed and fabricated by us—a biomaterial scaffold implanted with Schwann cells modified by the neurotrophin-3 (NT-3) gene and adult stem cells modified with the TrkC (receptor of NT-3) gene. More importantly, experimental evidence suggests that the novel artificial network can integrate with the host tissue and serve as an exogenous neuronal relay for signal transfer and functional improvement of SCI.

Expression of neurotrophic factors in injured spinal cord after transplantation of human-umbilical cord blood stem cells in rats

We induced percutaneous spinal cord injuries (SCI) using a balloon catheter in 45 rats and transplanted human umbilical cord blood derived mesenchymal stem cells (hUCB-MSCs) at the injury site. Locomotor function was significantly improved in hUCB-MSCs transplanted groups. Quantitative ELISA of extract from entire injured spinal cord showed increased expression of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and neurotrophin-3 (NT-3). Our results show that treatment of SCI with hUCB-MSCs can improve locomotor functions, and suggest that increased levels of BDNF, NGF and NT-3 in the injured spinal cord were the main therapeutic effect.

Neurotrophine-3 may contribute to neuronal differentiation of mesenchymal stem cells through the activation of the bone morphogenetic protein pathway

We investigated whether neurotrophin-3 (NT-3) can promote differentiation of mouse bone mesenchymal stem cells (MSCs) into neurons via the bone morphogenetic protein pathway. MSCs were prepared from rat bone marrow and either transfected with pIRES2-EGFP or pIRES2-EGFP-NT-3 or treated with bone morphogenetic protein 4. The pIRES2-EGFP-NT-3-transfected MSCs further underwent noggin treatment or siRNA-mediated knockout of the TrkC gene or were left untreated. Immunofluorescence staining, real-time PCR and Western blot analyses were performed to evaluate the transcription and expression of neural-specific genes and BMP-Smad signaling. MSCs were efficiently transduced by the NT-3 gene via pIRES2-EGFP vectors. pIRES2- EGFP-NT-3 could initiate the transcription and expression of neural-specific genes, including nestin, NSE and MAP-2, and stimulate BMP-Smad signaling. The transcription and expression of neural-specific genes and BMP-Smad signaling were significantly suppressed by siRNA-mediated knockdown of the TrkC gene of MSCs. These findings suggest that the BMP signaling pathway may be a key regulatory point in NT-3-transfected neuronal differentiation of MSCs. The BMP and neurotrophin pathways contribute to a tightly regulated signaling network that directs the precise connections between neuronal differentiation of MSCs and their targets.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

Strategies for neurotrophin-3 and chondroitinase ABC release from freeze-cast chitosan-alginate nerve-guidance scaffolds

Freeze casting, or controlled unidirectional solidification, can be used to fabricate chitosan-alginate (C-A) scaffolds with highly aligned porosity that are suitable for use as nerve-guidance channels. To augment the guidance of growth across a spinal cord injury lesion, these scaffolds are now evaluated in vitro to assess their ability to release neurotrophin-3 (NT-3) and chondroitinase ABC (chABC) in a controlled manner. Protein-loaded microcapsules were incorporated into C-A scaffolds prior to freeze casting without affecting the original scaffold architecture. In vitro protein release was not significantly different when comparing protein loaded directly into the scaffolds with release from scaffolds containing incorporated microcapsules. NT-3 was released from the C-A scaffolds for 8 weeks in vitro, while chABC was released for up to 7 weeks. Low total percentages of protein released from the scaffolds over this time period were attributed to limitation of diffusion by the interpenetrating polymer network matrix of the scaffold walls. NT-3 and chABC released from the scaffolds retained bioactivity, as determined by a neurite outgrowth assay, and the promotion of neurite growth across an inhibitory barrier of chondroitin sulphate proteoglycans. This demonstrates the potential of these multifunctional scaffolds for enhancing axonal regeneration through growth-inhibiting glial scars via the sustained release of chABC and NT-3. Copyright © 2014 John Wiley & Sons, Ltd.

Neuroprotective effects of NGF, BDNF, NT-3 and GDNF on axotomized extraocular motoneurons in neonatal rats

Neurotrophic factors delivered from target muscles are essential for motoneuronal survival, mainly during development and early postnatal maturation. It has been shown that the disconnection between motoneurons and their innervated muscle by means of axotomy produces a vast neuronal death in neonatal animals. In the present work, we have evaluated the effects of different neurotrophic factors on motoneuronal survival after neonatal axotomy, using as a model the motoneurons innervating the extraocular eye muscles. With this purpose, neonatal rats were monocularly enucleated at the day of birth (postnatal day 0) and different neurotrophic treatments (NGF, BDNF, NT-3, GDNF and the mixture of BDNF+GDNF) were applied intraorbitally by means of a Gelfoam implant (a single dose of 5 μg of each factor). We first demonstrated that extraocular eye muscles of neonatal rats expressed these neurotrophic factors and therefore constituted a natural source of retrograde delivery for their innervating motoneurons. By histological and immunocytochemical methods we determined that all treatments significantly rescued extraocular motoneurons from axotomy-induced cell death. For the dose used, NGF and GDNF were the most potent survival factors for these motoneurons, followed by BDNF and lastly by NT-3. The simultaneous administration of BDNF and GDNF did not increase the survival-promoting effects above those obtained by GDNF alone. Interestingly, the rescue effects of all neurotrophic treatments persisted even 30 days after lesion. The administration of these neurotrophic factors, with the exception of NT-3, also prevented the loss of the cholinergic phenotype observed by 10 days after axotomy. At the dosage applied, NGF and GDNF were revealed again as the most effective neuroprotective agents against the axotomy-induced decrease in ChAT. Two remarkable findings highlighted in the present work that contrasted with other motoneuronal types after neonatal axotomy: first, the extremely high efficacy of NGF as a neuroprotective agent and, second, the long-lasting effects of neurotrophic administration on cell survival and ChAT expression in extraocular motoneurons.

The therapeutic profile of rolipram, PDE target and mechanism of action as a neuroprotectant following spinal cord injury

The extent of damage following spinal cord injury (SCI) can be reduced by various neuroprotective regimens that include maintaining levels of cyclic adenosine monophosphate (cyclic AMP), via administration of the phosphodiesterase 4 (PDE4) inhibitor Rolipram. The current study sought to determine the optimal neuroprotective dose, route and therapeutic window for Rolipram following contusive SCI in rat as well as its prominent PDE target and putative mechanism of protection. Rolipram or vehicle control (10% ethanol) was given subcutaneously (s.c.) daily for 2 wk post-injury (PI) after which the preservation of oligodendrocytes, neurons and central myelinated axons was stereologically assessed. Doses of 0.1 mg/kg to 1.0 mg/kg (given at 1 h PI) increased neuronal survival; 0.5 mg to 1.0 mg/kg protected oligodendrocytes and 1.0 mg/kg produced optimal preservation of central myelinated axons. Ethanol also demonstrated significant neuronal and oligo-protection; though the preservation provided was significantly less than Rolipram. Subsequent use of this optimal Rolipram dose, 1.0 mg/kg, via different routes (i.v., s.c. or oral, 1 h PI), demonstrated that i.v. administration produced the most significant and consistent cyto- and axo- protection, although all routes were effective. Examination of the therapeutic window for i.v. Rolipram (1.0 mg/kg), when initiated between 1 and 48 h after SCI, revealed maximal neuroprotection at 2 h post-SCI, although the protective efficacy of Rolipram could still be observed when administration was delayed for up to 48 h PI. Importantly, use of the optimal Rolipram regimen significantly improved locomotor function after SCI as measured by the BBB score. Lastly we show SCI-induced changes in PDE4A, B and D expression and phosphorylation as well as cytokine expression and immune cell infiltration. We demonstrate that Rolipram abrogates SCI-induced PDE4B1 and PDE4A5 production, PDE4A5 phosphorylation, MCP-1 expression and immune cell infiltration, while preventing post-injury reductions in IL-10. This work supports the use of Rolipram as an acute neuroprotectant following SCI and defines an optimal administration protocol and target for its therapeutic application.

BDNF: the career of a multifaceted neurotrophin in spinal cord injury

Brain-derived neurotrophic factor (BDNF) has been identified as a potent promoter of neurite growth, a finding that has led to an ongoing exploration of this neurotrophin as a potential treatment for spinal cord injury. BDNF's many effects in the nervous system make it an excellent candidate for neuroprotective strategies as well as for promoting axonal regeneration, plasticity and re-myelination. In addition, neuronal activity and physical exercise can modulate the expression of BDNF, suggesting that non-invasive means to increase BDNF levels might exist. Nonetheless, depending on the location, amount and duration of BDNF delivery, this potent neurotrophin can also have adverse effects, such as modulation of nociceptive pathways or contribution to spasticity. Taken together, the benefits and possible risks require careful assessment when considering this multifaceted neurotrophin as a treatment option for spinal cord injury.

Combination therapies

Spinal cord injury (SCI) has multiple consequences, ranging from molecular imbalances to glial scar formation to functional impairments. It is logical to think that a combination of single treatments implemented in the right order and at the right time will be required to repair the spinal cord. However, the single treatments that compose the combination therapy will need to be chosen with caution as many have multiple outcomes that may or may not be synergistic. Single treatments may also elicit unwanted side-effects and/or effects that would decrease the repair potential of other components and/or the entire combination therapy. In this chapter a number of single treatments are discussed with respect to their multiplicity of action. These include strategies to boost growth and survival (such as neurotrophins and cyclic AMP) and strategies to reduce inhibitory factors (such as antimyelin-associated growth inhibitors and digestion of glial scar-associated inhibitors). We also present an overview of combination therapies that have successfully or unsuccessfully been tested in the laboratory using animal models. To effectively design a combination therapy a number of considerations need to be made such as the nature and timing of the treatments and the method for delivery. This chapter discusses these issues as well as considerations related to chronic SCI and the logistics of bringing combination therapies to the clinic.

Implantation of adult bone marrow-derived mesenchymal stem cells transfected with the neurotrophin-3 gene and pretreated with retinoic acid in completely transected spinal cord

Implantation of marrow-derived mesenchymal stem cells (MSCs) is the most promising therapeutic strategy for the treatment of spinal cord injury (SCI), especially because of their potential for clinical application, such as the avoidance of immunologic rejection, their strong secretory properties, and their plasticity for developing into neural cells. However, the recovery from SCI after MSC implantation is minimal due to their limited capacity for the reduction of cystic cavitation, for the axonal regeneration and their uncertain neural plasticity in the spinal cord. We previously pretreated MSCs with all-trans retinoic acid (RA) in vitro. Then we genetically modified them to overexpress neurotrophin-3 (NT-3) via a recombinant adenoviral vector (Adv). This combined treatment not only permitted more neuronal differentiation of MSCs, but stimulated more NT-3 secretion prior to grafting, according to our previous and present results. When these cells were implanted into the transected spinal cord of rats, the animals had some improvement (both functionally and structurally), including the recovery of hindlimb locomotor function, shown by the highest Basso, Beattie, and Bresnahan (BBB) scores, as well as dramatically reduced cavity volume, clear axonal regeneration and more neuronal survival. In contrast, simple MSC implantation is not a very effective therapy for spinal transection. However, the neuronal differentiation of MSCs after treatment with a combination of Adv-mediated NT-3 gene transfer and RA was only mildly improved in vivo.

Muscle injection of AAV-NT3 promotes anatomical reorganization of CST axons and improves behavioral outcome following SCI

Here we propose the use of adeno-associated virus (AAV) vectors as a non-invasive vehicle for the nervous system to deliver genes to spinal motoneurons, based on their retrograde transport from muscle. Long-term protein expression in lower cervical motoneurons was achieved after injections of AAV into the triceps, independently of serotypes 1, 2, or 5. Muscle injections of AAV5-neurotrophin 3 (NT3) resulted in a significant increase in the levels of NT3 in the cervical enlargement, compared to those obtained after injections of AAV5-GFP. Following a dorsal lesion at C4/C5, animals injected with AAV5-NT3 made fewer errors (footslips) in the horizontal ladder test compared to those injected with AAV5-GFP. In parallel, the number and length of corticospinal tract (CST) fibers circumventing the injury site were significantly increased in rats injected with AAV5-NT3. Compared to controls, we observed less astrogliosis and less CST axonal retraction and/or enhanced sprouting in animals injected with AAV5-NT3. In sum, we demonstrate here that the delivery of nt3 via retrograde transport of AAV from triceps to cervical motoneurons leads to reduced functional loss and anatomical reorganization of the CST following injury, without introducing additional injury to the spinal cord.

Cutaneous C-polymodal fibers lacking TRPV1 are sensitized to heat following inflammation, but fail to drive heat hyperalgesia in the absence of TPV1 containing C-heat fibers

BACKGROUND

Previous studies have shown that the TRPV1 ion channel plays a critical role in the development of heat hyperalgesia after inflammation, as inflamed TRPV1-/- mice develop mechanical allodynia but fail to develop thermal hyperalgesia. In order to further investigate the role of TRPV1, we have used an ex vivo skin/nerve/DRG preparation to examine the effects of CFA-induced-inflammation on the response properties of TRPV1-positive and TRPV1-negative cutaneous nociceptors.

RESULTS

In wildtype mice we found that polymodal C-fibers (CPMs) lacking TRPV1 were sensitized to heat within a day after CFA injection. This sensitization included both a drop in average heat threshold and an increase in firing rate to a heat ramp applied to the skin. No changes were observed in the mechanical response properties of these cells. Conversely, TRPV1-positive mechanically insensitive, heat sensitive fibers (CHs) were not sensitized following inflammation. However, results suggested that some of these fibers may have gained mechanical sensitivity and that some previous silent fibers gained heat sensitivity. In mice lacking TRPV1, inflammation only decreased heat threshold of CPMs but did not sensitize their responses to the heat ramp. No CH-fibers could be identified in naïve nor inflamed TRPV1-/- mice.

CONCLUSIONS

Results obtained here suggest that increased heat sensitivity in TRPV1-negative CPM fibers alone following inflammation is insufficient for the induction of heat hyperalgesia. On the other hand, TRPV1-positive CH fibers appear to play an essential role in this process that may include both afferent and efferent functions.

Manipulating the glial scar: chondroitinase ABC as a therapy for spinal cord injury

Chondroitin sulphate proteoglycans (CSPGs) are potent inhibitors of growth in the adult CNS. Use of the enzyme chondroitinase ABC (ChABC) as a strategy to reduce CSPG inhibition in experimental models of spinal cord injury has led to observations of a remarkable capacity for repair. Here we review the evidence that treatment with ChABC, either as an individual therapy or in combination with other strategies, can have multiple beneficial effects on promoting repair following spinal cord injury. These include promoting regeneration of injured axons, plasticity of uninjured pathways and neuroprotection of injured projection neurons. More importantly, ChABC therapy has been demonstrated to promote significant recovery of function to spinal injured animals. Thus, there is robust pre-clinical evidence demonstrating beneficial effects of ChABC treatment following spinal cord injury. Furthermore, these effects have been replicated in a number of different injury models, with independent confirmation by different laboratories, providing an important validation of ChABC as a promising therapeutic strategy. We discuss putative mechanisms underlying ChABC-mediated repair as well as potential issues and considerations in translating ChABC treatment into a clinical therapy for spinal cord injury.

MRI and X-ray scanning images of the brain of 3-, 6- and 9-month-old rats with bilateral neonatal ventral hippocampus lesions

Rats with bilateral neonatal ventral hippocampus lesions (NVHL) are commonly used for modeling developmental aspects of the pathophysiology of schizophrenia. Given that functional changes become significant only after puberty, NVHL as well as sham-operated rats were analyzed at the ages of 21, 42 and 63days (i.e. as pups, adolescents and adults), using MRI to examine the damage caused by surgery over time. Morphometric evaluations were considered and lesions were classified as small, medium and large. The volume of lesions increased regularly with age, to a greater extent than increases in overall brain size. This was relatively linear, corresponding to a gradually shrinking forebrain, and these observations held true for each class of lesions considered. Following the observation that the lesion procedure elicited calcifications in the brain, the same rats were subjected to 3D X-ray scanning the day after each MRI session, allowing precise measurements of skull size to be carried out. The NVHL rats had smaller skulls; however, the dimensions of the calcifications did not grow more than the skull size over time. The mechanisms underlying the progressive anatomical changes following surgery are discussed, and we propose this in vivo follow-up method to investigate therapeutic strategies aimed at countering or limiting the post-lesion consequences of a neonatal brain damage.

Role of Neurotrophin 3 in spinal neuroplasticity in rats subjected to cord transection

That neuroplasticity occurs in mammalian spinal cord is well known, though the underlying mechanism still awaits elucidation. This study evaluated the role of endogenous Neurotrophin-3 (NT-3) in the spinal neuroplasticity. Following cord transection at the junction between T9 and T10, the hindlimb locomotor functions of rats showed gradual but significant improvement from 7 to 28 days post-operation. Corresponding to this was a significant increase in the level of NT-3 in the cord segments caudal to injury site. Significantly, after NT-3-antibody administration, the spinal transected rats displayed poor hindlimb locomotor functions and a decrease in the number of neurons in spinal laminae VIII-IX. Whether NT-3-antibody was administered, corticospinal tract regeneration and somatosensory evoked potentials could not be detected. Our findings suggested that endogenous NT-3 could play an important role in spinal plasticity in adult spinal cords subjected to transection, possibly through a regulation of neuronal activity in the local circuitry.

Pain and learning in a spinal system: contradictory outcomes from common origins

The long-standing belief that the spinal cord serves merely as a conduit for information traveling to and from the brain is changing. Over the past decade, research has shown that the spinal cord is sensitive to response-outcome contingencies, demonstrating that spinal circuits have the capacity to modify behavior in response to differential environmental cues. If spinally transected rats are administered shock contingent on leg extension (controllable shock), they will maintain a flexion response that minimizes shock exposure. If, however, this contingency is broken, and shock is administered irrespective of limb position (uncontrollable shock), subjects cannot acquire the same flexion response. Interestingly, each of these treatments has a lasting effect on behavior; controllable shock enables future learning, while uncontrollable shock produces a long-lasting learning deficit. Here we suggest that the mechanisms underlying learning and the deficit may have evolved from machinery responsible for the spinal processing of noxious information. Experiments have shown that learning and the deficit require receptors and signaling cascades shown to be involved in central sensitization, including activation of NMDA and neurokinin receptors, as well as CaMKII. Further supporting this link between pain and learning, research has also shown that uncontrollable stimulation results in allodynia. Moreover, systemic inflammation and neonatal hindpaw injury each facilitate pain responding and undermine the ability of the spinal cord to support learning. These results suggest that the plasticity associated with learning and pain must be placed in a balance in order for adaptive outcomes to be observed.

The yellow fluorescent protein (YFP-H) mouse reveals neuroprotection as a novel mechanism underlying chondroitinase ABC-mediated repair after spinal cord injury

Chondroitinase ABC (ChABC) represents a promising therapeutic strategy for the treatment of spinal cord injury due to its potent effects on restoring function to spinal-injured adult mammals. However, there is limited mechanistic insight as to the underlying effects of ChABC treatment, where the effects are mediated, and which signaling pathways are involved in ChABC-mediated repair. Here we use a transgenic (YFP-H) mouse to demonstrate that cortical layer V projection neurons undergo severe atrophy 4 weeks after thoracic dorsal column injury and that ChABC is neuroprotective for these neurons after ICV infusion. ChABC also prevented cell atrophy after localized delivery to the spinal cord, suggesting a possible retrograde neuroprotective effect mediated at the injury site. Furthermore, neuroprotection of corticospinal cell somata coincided with increased axonal sprouting in the spinal cord. In addition, Western blot analysis of a number of kinases important in survival and growth signaling revealed a significant increase in phosphorylated ERK1 at the spinal injury site after in vivo ChABC treatment, indicating that activated ERK may play a role in downstream repair processes after ChABC treatment. Total forms of PKC and AKT were also elevated, indicating that modification of the glial scar by ChABC promotes long-lasting signaling changes at the lesion site. Thus, using the YFP-H mouse as a novel tool to study degenerative changes and repair after spinal cord injury we demonstrate, for the first time, that ChABC treatment regulates multiple signaling cascades at the injury site and exerts protective effects on axotomized corticospinal projection neurons.

Peripherally-derived BDNF promotes regeneration of ascending sensory neurons after spinal cord injury

Background

The blood brain barrier (BBB) and truncated trkB receptor on astrocytes prevent the penetration of brain derived neurotrophic factor (BDNF) applied into the peripheral (PNS) and central nervous system (CNS) thus restrict its application in the treatment of nervous diseases. As BDNF is anterogradely transported by axons, we propose that peripherally derived and/or applied BDNF may act on the regeneration of central axons of ascending sensory neurons.

Methodology/Principal Findings

The present study aimed to test the hypothesis by using conditioning lesion of the sciatic nerve as a model to increase the expression of endogenous BDNF in sensory neurons and by injecting exogenous BDNF into the peripheral nerve or tissues. Here we showed that most of regenerating sensory neurons expressed BDNF and p-CREB but not p75NTR. Conditioning-lesion induced regeneration of ascending sensory neuron and the increase in the number of p-Erk positive and GAP-43 positive neurons was blocked by the injection of the BDNF antiserum in the periphery. Enhanced neurite outgrowth of dorsal root ganglia (DRG) neurons in vitro by conditioning lesion was also inhibited by the neutralization with the BDNF antiserum. The delivery of exogenous BDNF into the sciatic nerve or the footpad significantly increased the number of regenerating DRG neurons and regenerating sensory axons in the injured spinal cord. In a contusion injury model, an injection of BDNF into the footpad promoted recovery of motor functions.

Conclusions/Significance

Our data suggest that endogenous BDNF in DRG and spinal cord is required for the enhanced regeneration of ascending sensory neurons after conditioning lesion of sciatic nerve and peripherally applied BDNF may have therapeutic effects on the spinal cord injury.

Distinct types of microglial activation in white and grey matter of rat lumbosacral cord after mid-thoracic spinal transection

The inflammatory response has been characterized in the lumbosacral segments (L4-S1) of rats after spinal transection at T8. Immune cells were identified immunohistochemically using antibodies to complement type 3 receptor, CD11b (OX-42), the macrophage lysosomal antigen, CD68 (ED1), major histocompatibility complex class II (MHC II), and CD163 (ED2), a marker of perivascular cells. One week after cord transection, OX-42+ microglial density had nearly doubled. In the white matter, microglia became enlarged, often with retracted processes. In contrast, microglia in the grey matter remained ramified although nearly half of those lying medially contained clusters of ED1+ granules. After 8 weeks, ED1+ (+/-MHC II) macrophages were prominent in regions of Wallerian degeneration extending from dorsolateral to ventral funiculi. Microglial density remained raised in grey matter, particularly in the ventral horns of L4/5. Ramified microglia expressing MHC II+ (+/-ED1) extended from deep in the dorsal columns and around the central canal to the ventral columns. More ED2+ (+/-MHC II) perivascular and meningeal cells were recruited and expressed ED1. Thus, distinct from their conversion into macrophages in the white matter, the activation of ramified microglia after degeneration in the grey matter involves expression of ED1 without morphologic transformation.

Transient growth factor delivery sustains regenerated axons after spinal cord injury

Growth factors influence the topography of axonal projections during nervous system development and facilitate axonal sprouting and regeneration after injury in the adult. However, in the absence of target reinnervation and reestablishment of synaptic activity, we hypothesized that continuing delivery of neurotrophins would be required to sustain regenerating axons for prolonged times points after neurotrophin-induced axon growth after spinal cord injury (SCI) in the adult. Using tetracycline-inducible expression of brain-derived neurotrophic factor by genetically modified fibroblasts, we were able to extensively and significantly turn growth factor expression "on" or "off" in vitro and in vivo within sites of SCI. Notably, we find that transient growth factor delivery is sufficient to sustain regenerated axons for prolonged time periods within spinal cord lesion sites. Immunohistochemical analysis demonstrated an absence of neuronal targets or synapses within transient growth factor expressing grafts but the persistent presence of Schwann cells. Thus, the adult CNS appears capable of sustaining axons that have extended after transient growth factor delivery, an effect potentially attributable to the persistence of Schwann cells in lesion/graft sites.

Locomotor exercise alters expression of pro-brain-derived neurotrophic factor, brain-derived neurotrophic factor and its receptor TrkB in the spinal cord of adult rats

Previous evidence indicates that locomotor exercise is a powerful means of increasing brain-derived neurotrophic factor (BDNF) and its signal transduction receptor TrkB mRNA levels, immunolabeling intensity and number of BDNF- and TrkB-immunopositive cells in the spinal cord of adult rats but the contribution of specific cell types to changes resulting from long-term activity is unknown. As changes in BDNF protein distribution due to systemic stimuli may reflect either its in-situ synthesis or its translocation from other sources, we investigated where BDNF and TrkB mRNA are expressed in the spinal lumbar segments. We report on the cell types defined by size, BDNF mRNA levels and number of cells with TrkB transcripts in sedentary and exercised animals following 28 days of treadmill walking. In the majority of cells, exercise increased perikaryonal levels of BDNF mRNA but did not affect TrkB transcript levels. Bidirectional changes in a number of TrkB mRNA-expressing cells occurred in small groups of ventral horn neurons. An increase in BDNF transcripts was translated into changes in pro-BDNF and BDNF levels. A 7-day walking regimen increased BDNF protein levels similarly to 28-day treadmill walking. Our observations indicate that long- and short-term locomotor activity of moderate intensity produce stimuli sufficient to recruit a majority of spinal cells to increased BDNF synthesis, suggesting that continuous tuning of pro-BDNF and BDNF levels permits spinal networks to undergo trophic modulation not requiring changes in TrkB mRNA supply.

Endogenous TrkB ligands suppress functional mechanosensory plasticity in the deafferented spinal cord

Dorsal root injury (DRI) disrupts the flow of sensory information to the spinal cord. Although primary afferents do not regenerate to their original targets, spontaneous recovery can, by unknown mechanisms, occur after DRI. Here, we show that brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), but not nerve growth factor or neurotrophin-4, are upregulated in the spinal gray matter after DRI. Because endogenous BDNF and NT-3 have well established roles in synaptic and axonal plasticity, we hypothesized that they contributed to spontaneous recovery after DRI. We first developed a model of DRI-induced mechanosensory dysfunction: rat C7/8 DRI produced a deficit in low-threshold cutaneous mechanosensation that spontaneously improved within 10 d but did not recover completely. To determine the effects of endogenous BDNF and NT-3, we administered TrkB-Fc or TrkC-Fc fusion proteins throughout the recovery period. To our surprise, TrkB-Fc stimulated complete recovery of mechanosensation by 6 d after DRI. It also stimulated mechanosensory axon sprouting but prevented deafferentation-induced serotonergic sprouting. TrkC-Fc had no effect on low-threshold mechanosensory behavior or axonal plasticity. There was no mechanosensory improvement with single-bolus TrkB-Fc infusions at 10 d after DRI (despite significantly reducing rhizotomy-induced cold pain), indicating that neuromodulatory effects of BDNF did not underlie mechanosensory recovery. Continuous infusion of the pan-neurotrophin antagonist K252a also stimulated behavioral and anatomical plasticity, indicating that these effects of TrkB-Fc treatment occurred independent of signaling by other neurotrophins. These results illustrate a novel, plasticity-suppressing effect of endogenous TrkB ligands on mechanosensation and mechanosensory primary afferent axons after spinal deafferentation.

Spinal cord transection enhances afferent-evoked inhibition in lamina II neurons and abolishes BDNF-induced facilitation of their sensory input

We previously reported that the pronociceptive neurotrophin brain-derived neurotrophic factor (BDNF) induces facilitation of C-fiber evoked EPSCs and NMDA currents in lamina II neurons of rats up to P40. Here, patch-clamp recording was used to study BDNF-induced modification of synaptic and NMDA-evoked responses in transverse spinal slices from lumbar (L2-L5) spinal cord of rats from P3 to P21 following complete spinal cord transection at P2. After transection injury at either T13/L1 or L6/S1, BDNF failed to facilitate synaptic AMPA-kainate currents or agonist-induced NMDA currents. The evoked synaptic currents were smaller in amplitude, often consisting of a biphasic (excitatory-inhibitory) response. The EPSC decayed more rapidly in neurons from transected cords than in those from uninjured cords. In transected cords most neurons responded to the GABA(A) receptor antagonist bicuculline with a significant increase in duration of the excitatory synaptic response. This could subsequently be blocked by D-APV, suggesting an NMDA-receptor mediated component. These findings suggest that following spinal cord transection, BDNF spinal actions are no longer predominantly pronociceptive. It is possible that a diminished availability of full-length TrkB and an enhanced expression of truncated TrkB receptors in the injured cord could play an important role in reducing the effect of BDNF following injury. These data are compared to those obtained after contusion, and it is concluded that the physiological changes after spinal injury differ according to nature of the injury.

Temporal changes in the expression of some neurotrophins in spinal cord transected adult rats

Functional recovery of neurons in the spinal cord after physical injury is essentially abortive in clinical cases. As neurotrophins had been reported to be responsible, at least partially, for the lesion-induced recovery of spinal cord, it is not surprising that they have become the focus of numerous studies. Studies on endogenous neurotrophins, especially the three more important ones, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in injured spinal cord might provide some important clues in clinical treatment. Here we investigate the immunohistological expression of the above three factors at lower thoracic levels of the spinal cord as well as changes in the motor functions of the adult rat hindlimbs after cord transection. The injured rats were allowed to survive 3, 7, 14 and 21 days post operation (dpo). Flaccid paralysis was seen at 3 dpo following cord transection, however, hindlimb function showed partial recovery from 7 dpo to 21 dpo. The numbers of NGF, BDNF and NT-3 immunopositive neurons and their optical densities all increased in the lesion-induced cord. The immuno-expression of NGF and BDNF peaked at 7 dpo, while that of NT-3 peaked at 7 dpo and remained so at least up to 14 dpo. These results suggested that neurotrophins might play essential roles in functional recovery of after spinal cord injury, but the time points for the expression of the three factors differed somewhat.

Recombinant adenovirus vector-mediated functional expression of neurotropin-3 receptor (TrkC) in neural stem cells

We have constructed a recombinant adenovirus expression vector carrying the human neurotrophin-3 (NT-3) receptor TrkC (tyrosine protein kinase C) gene (rAd-TrkC; 2478 bp) and confirmed the expression of the encoded TrkC in green fluorescent protein (GFP)-murine neural stem cells (NSCs) by reverse transcription polymerase chain reaction (RT-PCR), Western blot analysis, and immunocytochemistry. The activity of the expressed rAd-TrkC was verified in vitro by evaluating dose-related responses of NSCs to NT-3, a TrkC specific ligand. TrkC-GFP-NSCs had a significantly higher percentage of neuronal differentiation when treated with NT-3 relative to the rAd-LacZ control cells (55.2% vs. 29.8%; P<0.05, chi(2) test). Thus, our rAd-TrkC vector can transfect NSCs and produce functional TrkC receptors to promote neuronal differentiation of NSCs.

Cotransplant of neural stem cells and NT-3 gene modified Schwann cells promote the recovery of transected spinal cord injury

STUDY DESIGN

An animal model of transected spinal cord injury (SCI) was used to test the hypothesis that cografted neural stem cells (NSCs) and NT-3-SCs promote morphologic and functional recoveries of injured spinal cord.

OBJECTIVE

To explore whether cotransplant of NSCs and NT-3-SCs could promote the injured spinal cord repair.

SETTING

Zhongshan Medical College, Sun Yat-sen University, PR China.

METHODS

Female Sprague-Dawley (SD) rats weighing on 200-220 g were used to prepare SCI models. The spinal cord was transected between T(9) and T(10), then NSCs, SCs+NSCs, LacZ-SCs+NSCs, or NT-3-SCs+NSCs were grafted into the transected site.

RESULTS

(1) Part of NSCs could differentiate to neuron-like cells in the transected site and the percentage of differentiation was NT-3-SCs+NSCs group>SCs+NSCs group>NSCs group. (2) In the grafted groups, there were 5-HT, CGRP, and SP positive nerve fibres within the transected site. Some fluorogold (FG)-labeled cells were found in the spinal cord rostral to the transected site, the red nuclei and the inner pyramidal layer of sensorimotor cortex. (3) The cells grafted could enhance the injured neurons survival in inner pyramidal layer of sensorimotor cortex, red nuclei of midbrain, and Clark's nuclei of spinal cord's L1 segment, could decrease the latency and increase the amplitude of cortical somatosensory evoked potential (CSEP) and cortical motor evoked potential (CMEP), and could promote partly structural and functional recovery of the SCI rats.

CONCLUSION

These results demonstrate that cografted NT-3-SCs and NSCs is a potential therapy for SCI.

SPONSORSHIP

This research was supported by Chinese National Key Project for Basic Research (G1999054009), Chinese National Natural Science Foundation (30270700) and Social Developmental Foundation of Guangdong Province (2003C33808) to YS Zeng; Natural Science Foundation of Guangdong Province (04300468) and Medical Science Research Grant of Guangdong Province (A2004081) to JS Guo.

Transplantation of embryonic stem cell-derived neural stem cells for spinal cord injury in adult mice

AIMS

To investigate the efficacy of embryonic stem cell-derived neural stem cells (NSCs) for spinal cord injury (SCI) in mice and whether a combination treatment with thyroid hormone provides a more effective ES cell-based therapy.

METHODS

Nestin-positive NSCs were induced from undifferentiated mouse ES cells by a step-by-step culture and used as grafts. Thirty-six mice were subjected to an SCI at Th10 and divided into three groups of 12. Graft cells were transplanted into the injury site 10 days after injury. Group 1 mice were left under observation without receiving graft cells, while mice in Group 2 received 2 x 104 graft cells, and those in Group 3 received 2 x 104 graft cells and were treated with a continuous intraperitoneal injection of thyroxin using osmotic mini-pumps. Behavioral improvement was assessed by a scoring system throughout the experimental period until post-transplantation day (PD) 28.

RESULTS

Mice in Groups 2 and 3 demonstrated an improved behavioral function, as compared to those in Group 1 after PD 14. There was no significant difference in behavioral recovery between Groups 2 and 3.

CONCLUSIONS

Transplantation of ES-NSCs into the injury site was effective for SCI, while thyroxine did not deliver additional effectiveness.

Ultrastructural evidence for a pre- and postsynaptic localization of full-length trkB receptors in substantia gelatinosa (lamina II) of rat and mouse spinal cord

Brain-derived neurotrophic factor (BDNF) exerts its trophic effects by acting on the high-affinity specific receptor trkB. BDNF also modulates synaptic transmission in several areas of the CNS, including the spinal cord dorsal horn, where it acts as a pain modulator by yet incompletely understood mechanisms. Spinal neurons are the main source of trkB in lamina II (substantia gelatinosa). Expression of this receptor in dorsal root ganglion (DRG) cells has been a matter of debate, whereas a subpopulation of DRG neurons bears trkA receptors and contains BDNF. By the use of two different trkB antibodies we observed that 7.7% and 10.8% of DRG neurons co-expressed BDNF + trkB but not trkA, respectively, in rat and mouse. Ultrastructurally, full-length trkB (fl-trkB) receptors were present at somato-dendritic membranes of lamina II neurons (rat: 66.8%; mouse: 73.8%) and at axon terminals (rat: 33.2%; mouse: 26.2%). In both species, about 90% of these terminals were identified as primary afferent fibres (PAFs) considering their morphology and/or neuropeptide content. All fl-trkB-immunopositive C boutons in type Ib glomeruli were immunoreactive for BDNF and, at individual glomeruli and axo-dendritic synapses, fl-trkB receptors were located in a mutually exclusive fashion at pre- or postsynaptic membranes. Thus, only a small fraction of fl-trkB-immunoreactive dendrites were postsynaptic to BDNF-immunopositive PAFs. This is the first ultrastructural description of fl-trkB localization at synapses between first- and second-order sensory neurons in lamina II, and suggests that BDNF may be released by fl-trkB-immunopositive PAFs to modulate nociceptive input in this lamina of dorsal horn.

Developmental toxicity evaluation of nerve growth factor for injection in Wistar rats

Nerve growth factor (NGF) for injection is now used as an agent to cure peripheral nerve injury. To assess its potential embryo-lethal and teratogenic toxicity, five groups of pregnant Wistar rats received 0, 40, 200 and 1000U/kg NGF by muscle injection from gestational days (GD) 6 to 17. Maternal body weight was monitored at regular intervals throughout gestation. We selected 7mg/kg body weight cyclophosphamide (CPA) given to positive control group testing the Wistar rats of this study whether sensitive to teratogens or not. The dams were euthanized on GD 20, the day just before expected parturition. All fetuses were removed by cesarean section and examined for external, visceral and skeletal malformations under a dissecting microscope. There were no treatment-related maternal deaths. Our statistical findings were a reduction in maternal body weight and the occurrence of fetal body length shorten in 1000U/(kgday) dose group, which suggesting mild embryotoxicity of NGF. There were no major changes observed in other doses groups such as viable fetuses rate, resorption and dead fetuses rate, external, skeletal, visceral abnormality, fetal weight and length, tail length, indicating no evident maternal toxicity, embryotoxicity and teratogenicity resulted from NGF. Thus, it seems a favorable preclinical safety evaluation profile for NGF.

BDNF-Induced Facilitation of Afferent-Evoked Responses in Lamina II Neurons Is Reduced After Neonatal Spinal Cord Contusion Injury

We previously reported that brain-derived neurotrophic factor (BDNF), a pronociceptive neurotransmitter, induces synaptic facilitation of excitatory postsynaptic current (EPSC) in lamina II neurons of neonatal rats up to P14 in a N-methyl-d-aspartate (NMDA) receptor-dependent manner. Here we used the patch-clamp technique to study synaptic and NMDA-evoked responses in transverse spinal slices in the lumbar enlargement as well as the ability of BDNF to modify these responses from 1 day to 6 wk after neonatal contusion. In older uninjured animals (>P14), BDNF continued to evoke synaptic facilitation although superfusion of NMDA (in TTX) induced inward current of significantly smaller amplitude than that observed in younger rats. After contusion injury, BDNF was unable to facilitate dorsal root-evoked EPSCs in lamina II neurons despite the finding that NMDA-evoked currents were only slightly smaller than those observed in age-matched uninjured animals. These findings suggest that although BDNF-induced facilitation of the AMPA/kainate receptor-mediated response to dorsal root stimulation is maintained in the mature dorsal horn from intact rats, BDNF may no longer elicit these pronociceptive actions after neonatal contusion injury. The lack of change in NMDA-evoked currents in contused cords suggests that diminished NMDA receptor function is not the major cause of the decline in BDNF action after contusion. It seems more likely that diminished trkB expression and enhanced expression of truncated trkB receptors in the contused cord play a significant role in determining the reduced effect of BDNF under these conditions.

Regulation of neuropilin 1 by spinal cord injury in adult rats

Using RT-PCR, in situ hybridization, Western blotting, and immunofluorescence, we have analyzed the expression of neuropilin 1 (Np1) in two models of spinal cord injury (spinal cord hemisection and dorsal column crush) and following dorsal root rhizotomy in adult rats. Our results show that Np1 RNA and protein are up-regulated in the spinal cord after all these lesions but remain unaltered in the adjacent dorsal root ganglia. In control animals, Np1 levels in the spinal cord are low and appear to be localized mainly in blood vessels, motoneurons, and in the superficial layers of the dorsal horn. After DCC and rhizotomy, Np1 is expressed de novo around the injury and in the deafferentated dorsal horn, respectively, mainly by OX42-positive microglial cells. Both lesions affect the sensory projections, and interestingly a consistent increase of Np1 signal is additionally seen in the dorsal horn where these projections terminate. Unexpectedly, this increase is bilateral after unilateral rhizotomy.

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

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

Axonal responses to cellularly delivered NT-4/5 after spinal cord injury

Neurotrophic factors delivered to the injured spinal cord have been shown to enhance axonal growth, prevent neuronal degeneration and partially improve sensorimotor function. The present study examined the effects of NT-4/5 on growth of spinal and supraspinal axons, glia, and functional outcome after spinal cord injury. Adult Fischer 344 rats received spinal cord dorsal hemisections or complete transections at the midthoracic level. Fibroblasts modified to secrete NT-4/5 or green fluorescent protein as controls were immediately grafted to the lesion site. Axonal growth responses were determined between 3 and 6 months postinjury by retrograde and anterograde tracing and immunohistochemistry. Motor axons, coerulospinal, reticulospinal, and propriospinal axons responded to NT-4/5 delivery after thoracic spinal cord injury with significantly increased axonal penetration into NT-4/5 secreting grafts compared to GFP-expressing control grafts. Axonal growth beyond NT-4/5-producing grafts and functional recovery were not observed. Numerous Schwann cells, but not oligodendrocytes, were present within NT-4/5-secreting grafts and remyelinated axons inside the graft. Thus, NT-4/5 and BDNF appear to be interchangeable to elicit substantial axonal growth in the injured spinal cord.

Adeno-associated viral vector-mediated gene transfer of brain-derived neurotrophic factor reverses atrophy of rubrospinal neurons following both acute and chronic spinal cord injury

Rubrospinal neurons (RSNs) undergo marked atrophy after cervical axotomy. This progressive atrophy may impair the regenerative capacity of RSNs in response to repair strategies that are targeted to promote rubrospinal tract regeneration. Here, we investigated whether we could achieve long-term rescue of RSNs from lesion-induced atrophy by adeno-associated viral (AAV) vector-mediated gene transfer of brain-derived neurotrophic factor (BDNF). We show for the first time that AAV vectors can be used for the persistent transduction of highly atrophic neurons in the red nucleus (RN) for up to 18 months after injury. Furthermore, BDNF gene transfer into the RN following spinal axotomy resulted in counteraction of atrophy in both the acute and chronic stage after injury. These novel findings demonstrate that a gene therapeutic approach can be used to reverse atrophy of lesioned CNS neurons for an extended period of time.

Delayed grafting of BDNF and NT-3 producing fibroblasts into the injured spinal cord stimulates sprouting, partially rescues axotomized red nucleus neurons from loss and atrophy, and provides limited regeneration

Ex vivo gene therapy, utilizing modified fibroblasts that deliver BDNF or NT-3 to the acutely injured spinal cord, has been shown to elicit regeneration and recovery of function in the adult rat. Delayed grafting into the injured spinal cord is of great clinical interest as a model for treatment of chronic injury but may pose additional obstacles that are not present after acute injury, such as the need to remove an established scar, increased retrograde cell loss and/or atrophy, and diminished capacity for regeneration by neurons which may be doubly injured. The purpose of the present study was to determine if delayed grafting of neurotrophin secreting fibroblasts would have anatomical effects similar to those seen in acute grafting models. We grafted a mixture of BDNF and NT-3 producing fibroblasts or control fibroblasts into a complete unilateral cervical hemisection after a 6-week delay. Fourteen weeks after delayed grafting we found that both the neurotrophin secreting fibroblasts and control fibroblasts survived, but that only the neurotrophin secreting grafts provided a permissive environment for host axon growth, as indicated by immunostaining for RT-97, a marker for axonal neurofilaments, GAP-43, a marker for elongating axons, CGRP, a marker for dorsal root axons, and 5-HT, a marker for raphe spinal axons, within the graft. Anterograde tracing of the uninjured vestibulospinal tract showed growth into neurotrophin producing transplants but not into control grafts, while anterograde tracing of the axotomized rubrospinal tract showed a small number of regenerating axons within the genetically modified grafts, but none in control grafts. The neurotrophin expressing grafts, but not the control grafts, significantly reduced retrograde degeneration and atrophy in the injured red nucleus. Grafts of BDNF + NT-3 expressing fibroblasts delayed 6 weeks after injury therefore elicit growth from intact segmental and descending spinal tracts, stimulate modest regenerative growth by rubrospinal axons, and partially rescue axotomized supraspinal neurons and protect them from atrophy. The regeneration of rubrospinal axons into delayed transplants was much less than has been observed when similar transplants were placed acutely into a lateral funiculus or, after a 4-week delay, into a hemisection lesion. This suggests that the regenerative capacity of chronically injured red nucleus neurons was markedly diminished. The increased GAP43 reactivity in the corticospinal tracts ipsilaterally and contralaterally to the combination grafts suggests that these axons remain responsive to the neurotrophins, that the neurotrophins may stimulate both regenerative and sprouting responses, and that the grafted cells continue to secrete the neurotrophins.

BDNF sensitizes the response of lamina II neurons to high threshold primary afferent inputs

Brain-derived neurotrophic factor (BDNF) is up-regulated and released in the dorsal horn following peripheral inflammation and has therefore been implicated in spinal mechanisms of sensitization. Despite these observations, the mechanisms associated with such a role for BDNF are not yet fully determined. Here, we investigate the effect of BDNF on dorsal root-evoked synaptic transmission in lamina II neurons. In a transverse spinal cord slice preparation from neonatal rats (P1-15), the whole cell patch-clamp technique was used to record from these neurons. Brief application of BDNF (50-200 ng/mL) facilitated the evoked synaptic currents; they remained enhanced even after BDNF was washed out. A significant minority of cells was minimally affected by BDNF and consistent with this, not all neurons in lamina II were immunoreactive for the tyrosine kinase (trk) B receptor. No facilitation was elicited when N-methyl-d-aspartate (NMDA) receptors were blocked with D-APV, when the postsynaptic NMDA receptors were selectively blocked with intracellular MK-801, or when postsynaptic neurons were loaded with BAPTA. Additionally, inhibiting phospholipase C (PLC) or protein kinase C (PKC) prior to BDNF application completely blocked facilitation. However, once synaptic current underwent BDNF-induced facilitation, the PKC inhibitors failed to reverse the effect, suggesting that PKC is needed for initiation, but not maintenance of BDNF-induced facilitation. These results demonstrate that BDNF functions at the spinal level to enhance synaptic efficacy in an NMDA receptor-dependent manner and requires the action of the PLC/PKC pathway. This action of BDNF may contribute to central sensitization and exaggerated pain states.

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

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