Proteoglycans and other repulsive molecules in glial boundaries during development and regeneration of the nervous system

Inflammatory Mediators of Axon Regeneration in the Central and Peripheral Nervous Systems

Although most pathways in the mature central nervous system cannot regenerate when injured, research beginning in the late 20th century has led to discoveries that may help reverse this situation. Here, we highlight research in recent years from our laboratory identifying oncomodulin (Ocm), stromal cell-derived factor (SDF)-1, and chemokine CCL5 as growth factors expressed by cells of the innate immune system that promote axon regeneration in the injured optic nerve and elsewhere in the central and peripheral nervous systems. We also review the role of ArmC10, a newly discovered Ocm receptor, in mediating many of these effects, and the synergy between inflammation-derived growth factors and complementary strategies to promote regeneration, including deleting genes encoding cell-intrinsic suppressors of axon growth, manipulating transcription factors that suppress or promote the expression of growth-related genes, and manipulating cell-extrinsic suppressors of axon growth. In some cases, combinatorial strategies have led to unprecedented levels of nerve regeneration. The identification of some similar mechanisms in human neurons offers hope that key discoveries made in animal models may eventually lead to treatments to improve outcomes after neurological damage in patients.

Pericytes for Therapeutic Approaches to Ischemic Stroke

Pericytes are perivascular multipotent cells located on capillaries. Although pericytes are discovered in the nineteenth century, recent studies have found that pericytes play an important role in maintaining the blood—brain barrier (BBB) and regulating the neurovascular system. In the neurovascular unit, pericytes perform their functions by coordinating the crosstalk between endothelial, glial, and neuronal cells. Dysfunction of pericytes can lead to a variety of diseases, including stroke and other neurological disorders. Recent studies have suggested that pericytes can serve as a therapeutic target in ischemic stroke. In this review, we first summarize the biology and functions of pericytes in the central nervous system. Then, we focus on the role of dysfunctional pericytes in the pathogenesis of ischemic stroke. Finally, we discuss new therapies for ischemic stroke based on targeting pericytes.

Role of Chondroitin Sulfation Following Spinal Cord Injury

Traumatic spinal cord injury produces long-term neurological damage, and presents a significant public health problem with nearly 18,000 new cases per year in the U.S. The injury results in both acute and chronic changes in the spinal cord, ultimately resulting in the production of a glial scar, consisting of multiple cells including fibroblasts, macrophages, microglia, and reactive astrocytes. Within the scar, there is an accumulation of extracellular matrix (ECM) molecules—primarily tenascins and chondroitin sulfate proteoglycans (CSPGs)—which are considered to be inhibitory to axonal regeneration. In this review article, we discuss the role of CSPGs in the injury response, especially how sulfated glycosaminoglycan (GAG) chains act to inhibit plasticity and regeneration. This includes how sulfation of GAG chains influences their biological activity and interactions with potential receptors. Comprehending the role of CSPGs in the inhibitory properties of the glial scar provides critical knowledge in the much-needed production of new therapies.

Roles of Pericytes in Stroke Pathogenesis

Stroke is a cerebrovascular disorder that affects many people worldwide. In addition to the well-established functions of astrocytes and microglia in stroke pathogenesis, pericytes also play an important role in stroke progression and recovery. As perivascular multi-potent cells and an important component of the blood–brain barrier (BBB), pericytes have been shown to exert a large variety of functions, including serving as stem/progenitor cells and maintaining BBB integrity. Here in this review, we summarize the roles of pericytes in stroke pathogenesis, with a focus on their effects in cerebral blood flow, BBB integrity, angiogenesis, immune responses, scar formation and fibrosis.

New approach for the treatment of neuropathic pain: Fibroblast growth factor 1 gene-transfected adipose-derived mesenchymal stem cells

BACKGROUND

Neuropathic pain triggered by peripheral nerve lesion is extremely difficult to manage with current approaches, hence the importance of exploring therapeutic alternatives.

METHODS

We have analysed adipose-derived mesenchymal stem cells (AD-MSCs) and fibroblast growth factor 1 gene-transfected adipose-derived mesenchymal stem cells (AD-MSCs ^FGF1 ) on chronic constriction injury (CCI). The mechanical and thermal hypersensitivity were assessed using the von Frey filament, radiant heat and acetone drop tests. Histopathological and apoptotic changes and the level of FGF1, GFAP and TNFα proteins were assessed in the lumbar portion (L4-L6). Moreover, AD-MSCs ^FGF1 were labelled with ^99m Tc -HMPAO and isolated organ counting were performed upon AD-MSCs ^FGF1 administration.

RESULTS

Administration of AD-MSCs ^FGF1 attenuated the CCI-induced mechanical and thermal hypersensitivity. Spinal structural alterations and apoptosis were decreased in the AD-MSCs ^FGF1 group. The injection of either phosphate-buffered saline or normal NIH3T3 fibroblasts could not attenuate the behavioural symptoms of neuropathic pain. Increased genetically engineered cells were counted in the injured sciatic nerve and the elevated levels of FGF1 were detected in the spinal tissue. Stem cell therapy lead to decrement the level of the CCI-induced TNF-α and GFAP expression.

CONCLUSION

The intravenous administration of AD-MSCs ^FGF1 could be considered as a potential remedy for the management of neuropathic pain.

SIGNIFICANCE

AD-MSCs ^FGF1 attenuated the CCI-induced mechanical and thermal hypersensitivity. Spinal structural alterations and apoptosis were significantly decreased in the AD-MSCs ^FGF1 group. Elevated levels of FGF1 were detected in the spinal tissue.

Does CNS Myelin Inhibit Axon Regeneration?

Membrane proteins on oligodendrocytes and CNS myelin (NI35/250) have been shown to block axon out-growth in culture, and this is thought to be one of the major reasons for severely limited regeneration of severed axons in the CNS of higher vertebrates. In a recent study, adult dorsal root ganglion (DRG) neurons, which are sensitive to these inhibitory proteins, regenerated successfully after transplantation into two white matter tracts of the rat brain without any intervention to suppress the inhibitory activity of CNS myelin. The results and implications of these two studies are considered.

Recent advances in managing a spinal cord injury secondary to trauma

Traumatic spinal cord injuries (SCIs) affect 1.3 million North Americans, producing devastating physical, social, and vocational impairment. Pathophysiologically, the initial mechanical trauma is followed by a significant secondary injury which includes local ischemia, pro-apoptotic signaling, release of cytotoxic factors, and inflammatory cell infiltration. Expedient delivery of medical and surgical care during this critical period can improve long-term functional outcomes, engendering the concept of "Time is Spine". We emphasize the importance of expeditious care while outlining the initial clinical and radiographic assessment of patients. Key evidence-based early interventions (surgical decompression, blood pressure augmentation, and methylprednisolone) are also reviewed, including findings of the landmark Surgical Timing in Acute Spinal Cord Injury Study (STASCIS). We then describe other neuroprotective approaches on the edge of translation such as the sodium-channel blocker riluzole, the anti-inflammatory minocycline, and therapeutic hypothermia. We also review promising neuroregenerative therapies that are likely to influence management practices over the next decade including chondroitinase, Rho-ROCK pathway inhibition, and bioengineered strategies. The importance of emerging neural stem cell therapies to remyelinate denuded axons and regenerate neural circuits is also discussed. Finally, we outline future directions for research and patient care.

Concise Review: Bridging the Gap: Novel Neuroregenerative and Neuroprotective Strategies in Spinal Cord Injury

Spinal cord injuries (SCIs) result in devastating lifelong disability for patients and their families. The initial mechanical trauma is followed by a damaging secondary injury cascade involving proapoptotic signaling, ischemia, and inflammatory cell infiltration. Ongoing cellular necrosis releases ATP, DNA, glutamate, and free radicals to create a cytotoxic postinjury milieu. Long-term regeneration of lost or injured networks is further impeded by cystic cavitation and the formation of an inhibitory glial-chondroitin sulfate proteoglycan scar. In this article, we discuss important neuroprotective interventions currently applied in clinical practice, including surgical decompression, blood pressure augmentation, and i.v. methylprednisolone. We then explore exciting translational therapies on the horizon, such as riluzole, minocycline, fibroblast growth factor, magnesium, and hypothermia. Finally, we summarize the key neuroregenerative strategies of the next decade, including glial scar degradation, Rho-ROCK inhibition, cell-based therapies, and novel bioengineered adjuncts. Throughout, we emphasize the need for combinatorial approaches to this multifactorial problem and discuss relevant studies at the forefront of translation. We conclude by providing our perspectives on the future direction of SCI research.

SIGNIFICANCE

Spinal cord injuries (SCIs) result in devastating, lifelong disability for patients and their families. This article discusses important neuroprotective interventions currently applied in clinical practice, including surgical decompression, blood pressure augmentation, and i.v. methylprednisolone. Translational therapies on the horizon are discussed, such as riluzole, minocycline, fibroblast growth factor, magnesium, and hypothermia. The key neuroregenerative strategies of the next decade are summarized, including glial scar degradation, Rho-ROCK inhibition, cell-based therapies, and novel bioengineered adjuncts. The need for combinatorial approaches to this multifactorial problem is emphasized, relevant studies at the forefront of translation are discussed, and perspectives on the future direction of SCI research are presented.

Scar-modulating treatments for central nervous system injury

Traumatic injury to the adult mammalian central nervous system (CNS) leads to complex cellular responses. Among them, the scar tissue formed is generally recognized as a major obstacle to CNS repair, both by the production of inhibitory molecules and by the physical impedance of axon regrowth. Therefore, scar-modulating treatments have become a leading therapeutic intervention for CNS injury. To date, a variety of biological and pharmaceutical treatments, targeting scar modulation, have been tested in animal models of CNS injury, and a few are likely to enter clinical trials. In this review, we summarize current knowledge of the scar-modulating treatments according to their specific aims: (1) inhibition of glial and fibrotic scar formation, and (2) blockade of the production of scar-associated inhibitory molecules. The removal of existing scar tissue is also discussed as a treatment of choice. It is believed that only a combinatorial strategy is likely to help eliminate the detrimental effects of scar tissue on CNS repair.

Nerve regeneration restores supraspinal control of bladder function after complete spinal cord injury

A life-threatening disability after complete spinal cord injury is urinary dysfunction, which is attributable to lack of regeneration of supraspinal pathways that control the bladder. Although numerous strategies have been proposed that can promote the regrowth of severed axons in the adult CNS, at present, the approaches by which this can be accomplished after complete cord transection are quite limited. In the present study, we modified a classic peripheral nerve grafting technique with the use of chondroitinase to facilitate the regeneration of axons across and beyond an extensive thoracic spinal cord transection lesion in adult rats. The novel combination treatment allows for remarkably lengthy regeneration of certain subtypes of brainstem and propriospinal axons across the injury site and is followed by markedly improved urinary function. Our studies provide evidence that an enhanced nerve grafting strategy represents a potential regenerative treatment after severe spinal cord injury.

Scaffolds to promote spinal cord regeneration

Substantial research effort in the spinal cord injury (SCI) field is directed towards reduction of secondary injury changes and enhancement of tissue sparing. However, pathway repair after complete transections, large lesions, or after chronic injury may require the implantation of some form of oriented bridging structure to restore tissue continuity across a trauma zone. These matrices or scaffolds should be biocompatible and create an environment that facilitates tissue growth and vascularization, and allow axons to regenerate through and beyond the implant in order to reconnect with "normal" tissue distal to the injury. The myelination of regrown axons is another important requirement. In this chapter, we describe recent advances in biomaterial technology designed to provide a terrain for regenerating axons to grow across the site of injury and/or create an environment for endogenous repair. Many different types of scaffold are under investigation; they can be biodegradable or nondegradable, natural or synthetic. Scaffolds can be designed to incorporate immobilized signaling molecules and/or used as devices for controlled release of therapeutic agents, including growth factors. These bridging structures can also be infiltrated with specific cell types deemed suitable for spinal cord repair.

Motor recovery and synaptic preservation after ventral root avulsion and repair with a fibrin sealant derived from snake venom

BACKGROUND

Ventral root avulsion is an experimental model of proximal axonal injury at the central/peripheral nervous system interface that results in paralysis and poor clinical outcome after restorative surgery. Root reimplantation may decrease neuronal degeneration in such cases. We describe the use of a snake venom-derived fibrin sealant during surgical reconnection of avulsed roots at the spinal cord surface. The present work investigates the effects of this fibrin sealant on functional recovery, neuronal survival, synaptic plasticity, and glial reaction in the spinal motoneuron microenvironment after ventral root reimplantation.

METHODOLOGY/PRINCIPAL FINDINGS

Female Lewis rats (7 weeks old) were subjected to VRA and root replantation. The animals were divided into two groups: 1) avulsion only and 2) replanted roots with fibrin sealant derived from snake venom. Post-surgical motor performance was evaluated using the CatWalk system twice a week for 12 weeks. The rats were sacrificed 12 weeks after surgery, and their lumbar intumescences were processed for motoneuron counting and immunohistochemistry (GFAP, Iba-1 and synaptophysin antisera). Array based qRT-PCR was used to evaluate gene regulation of several neurotrophic factors and receptors as well as inflammatory related molecules. The results indicated that the root reimplantation with fibrin sealant enhanced motor recovery, preserved the synaptic covering of the motoneurons and improved neuronal survival. The replanted group did not show significant changes in microglial response compared to VRA-only. However, the astroglial reaction was significantly reduced in this group.

CONCLUSIONS/SIGNIFICANCE

In conclusion, the present data suggest that the repair of avulsed roots with snake venom fibrin glue at the exact point of detachment results in neuroprotection and preservation of the synaptic network at the microenvironment of the lesioned motoneurons. Also such procedure reduced the astroglial reaction and increased mRNA levels to neurotrophins and anti-inflammatory cytokines that may in turn, contribute to improving recovery of motor function.

Microglial inhibitory factor (MIF/TKP) mitigates secondary damage following spinal cord injury

Spinal cord injury (SCI) induces an immune response during which microglia, the resident immunocompetent cells of the central nervous system, become activated and migrate to the site of damage. Depending on their state of activation, microglia secrete neurotoxic or neurotrophic factors that influence the surrounding environment and have a detrimental or restorative effect following SCI, including causing or protecting bystander damage to nearby undamaged tissue. Subsequent infiltration of macrophages contributes to the SCI outcome. We show here that suppressing microglia/macrophage activation using the tripeptide macrophage/microglia inhibitory factor (MIF/TKP) reduced secondary injury around the lesion epicenter in the murine dorsal hemisection model of SCI; it decreased the hypertrophic change of astrocytes and caused an increase in the number of axons present within the lesion epicenter. Moreover, timely inhibition of microglial/macrophage activation prevented demyelination and axonal dieback by modulating oligodendrocyte survival and oligodendrocyte precursor maturation. Microglia/macrophages located within or proximal to the lesion produced neurotoxic factors, such as tumor necrosis factor alpha (TNF-α). These results suggest that microglia/macrophages within the epicenter at early time points post injury are neurotoxic, contributing to demyelination and axonal degeneration and that MIF/TKP could be used in combination with other therapies to promote functional recovery.

The role of well-defined patterned substrata on the regeneration of DRG neuron pathfinding and integrin expression dynamics using chondroitin sulfate proteoglycans

Injured neurons intrinsically adapt to and partially overcome inhibitory proteoglycan expression in the central nervous system by upregulating integrin expression. It remains unclear however, to what extent varying proteoglycan concentrations influence the strength of this response, how rapidly neurons adapt to proteoglycans, and how pathfinding dynamics are altered over time as integrin expression is modulated in response to proteoglycan signals. To investigate these quandaries, we created well-defined substrata in which postnatal DRG neuron pathfinding dynamics and growth cone integrin expression were interrogated as a function of proteoglycan substrata density. DRGs responded by upregulating integrin expression in a proteoglycan dose dependent fashion and exhibited robust outgrowth over all proteoglycan densities at initial time frames. However, after prolonged proteoglycan exposure, neurons exhibited decreasing velocities associated with increasing proteoglycan densities, while neurons growing on low proteoglycan levels exhibited robust outgrowth at all time points. Additionally, DRG outgrowth over proteoglycan density step boundaries, and a brief β1 integrin functional block proved that regeneration was integrin dependent and that DRGs exhibit delayed slowing and loss in persistence after even transient encounters with dense proteoglycan boundaries. These findings demonstrate the complexity of proteoglycan regulation on integrin expression and regenerative pathfinding.

Role of the lesion scar in the response to damage and repair of the central nervous system

Traumatic damage to the central nervous system (CNS) destroys the blood–brain barrier (BBB) and provokes the invasion of hematogenous cells into the neural tissue. Invading leukocytes, macrophages and lymphocytes secrete various cytokines that induce an inflammatory reaction in the injured CNS and result in local neural degeneration, formation of a cystic cavity and activation of glial cells around the lesion site. As a consequence of these processes, two types of scarring tissue are formed in the lesion site. One is a glial scar that consists in reactive astrocytes, reactive microglia and glial precursor cells. The other is a fibrotic scar formed by fibroblasts, which have invaded the lesion site from adjacent meningeal and perivascular cells. At the interface, the reactive astrocytes and the fibroblasts interact to form an organized tissue, the glia limitans. The astrocytic reaction has a protective role by reconstituting the BBB, preventing neuronal degeneration and limiting the spread of damage. While much attention has been paid to the inhibitory effects of the astrocytic component of the scars on axon regeneration, this review will cover a number of recent studies in which manipulations of the fibroblastic component of the scar by reagents, such as blockers of collagen synthesis have been found to be beneficial for axon regeneration. To what extent these changes in the fibroblasts act via subsequent downstream actions on the astrocytes remains for future investigation.

Modifying neurorepair and neuroregenerative factors with tPA and edaravone after transient middle cerebral artery occlusion in rat brain

Changes in expression of neurorepair and neuroregenerative factors were examined after transient cerebral ischemia in relation to the effects of tissue plasminogen activator (tPA) and the free radical scavenger edaravone. Physiological saline or edaravone was injected twice during 90 min of transient middle cerebral artery occlusion (tMCAO) in rats, followed by the same saline or tPA at reperfusion. Sizes of the infarct and protein factors relating to neurorepair and neuroregeneration were examined at 4d after tMCAO. The protein factors examined were: a chondroitin sulfate proteoglycan neurocan, semaphorin type 3A (Sema3A), a myelin-associated glycoprotein receptor (Nogo receptor, Nogo-R), a synaptic regenerative factor (growth associated protein-43, GAP43), and a chemotropic factor netrin receptor (deleted in colorectal cancer, DCC). Two groups treated by edaravone only or edaravone plus tPA showed a reduction in infarct volume compared to the two groups treated by vehicle only or vehicle plus tPA. Immunohistochemistry and western blot analyses indicated that protein expression of neurocan, Sema3A, Nogo-R, GAP43, and DCC was decreased with tPA, but recovered with edaravone. Additive edaravone prevented the reductions of these five proteins induced by tPA. The present study demonstrates for the first time that exogenous tPA reduced protein factors involved in inhibiting and promoting axonal growth, but that edaravone ameliorated such damage in brain repair after acute ischemia.

Comparison of canine umbilical cord blood-derived mesenchymal stem cell transplantation times: involvement of astrogliosis, inflammation, intracellular actin cytoskeleton pathways, and neurotrophin-3

Canine mesenchymal stem cells (cMSCs) derived from umbilical cord blood represent a potentially useful source of stem cells for therapy. The aim of this study was to compare the effects of different transplantation times of cMSCs after spinal cord injury (SCI). A total of 21 dogs were subjected to SCI by balloon-induced compression of the first lumbar vertebrae for 12 h. Of the 21 dogs, 12 were divided into four groups of three according to the time of stem cell (1 × 10(6)) transplantation at the injury site: control no treatment, 12 h, 1 week, and 2 weeks. The remaining 9 animals were negative harvest (HA) time controls for each treatment group (n = 3). Olby and Tarlov scores were used to evaluate functional recovery of the hindlimbs. Markers for neuronal regeneration (Tuj-1, nestin, MAP2, and NF-M), astrogliosis (GALC, GFAP, and pSTAT3), signal molecules for actin cytoskeleton (RhoA, Cdc42, and Rac1), inflammation (COX-2), and neurotrophins (NT-3) were evaluated by Western blot analysis. Scores of the 1-week transplantation group showed significant improvement compared to controls. Hematoxylin and eosin (H&E) staining revealed less fibrosis at the injury site in the 1-week transplantation group compared to other groups and immunohistochemistry showed increased expression of neuronal markers. Furthermore, in both 1-week and 2-week transplantation groups, Tuj-1, nestin, MAP2, NF-M, NT-3, and GFAP increased, but pSTAT3, GALC, and COX2 decreased. RhoA decreased and Rac1 and Cdc42 increased in the 1-week transplantation group. In conclusion, transplantation of cMSCs 1 week after SCI was more effective in improving clinical signs and neuronal regeneration and reducing fibrosis formation compared to the other transplantation times evaluated. Subsequently, these data may contribute to the optimization of timing for MSC transplantation used as a therapeutic modality.

Sustained delivery of activated Rho GTPases and BDNF promotes axon growth in CSPG-rich regions following spinal cord injury

BACKGROUND

Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) within astroglial scar tissue at the lesion.

METHODOLOGY/PRINCIPAL FINDINGS

We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site.

CONCLUSION

Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPG-mediated regenerative failure after SCI.

Endogenous signals initiating inflammation in the injured nervous system

Glial cells are known to respond to a variety of neural injuries and play an important role in tissue damage and repair in the injured nervous system. This glial response, which is initially characterized by the expression of proinflammatory cytokines and chemokines and the attraction of microglial cells toward sites of injury, literally occurs within seconds to minutes of the injury. This suggests that signals that are endogenous to the nervous system are responsible for initiating neuroinflammation. In this review, we summarize the most recent advances made in the identification of these endogenous signals and describe the receptors and signaling pathways by which these ligands stimulate the production of cytokines and chemokines. Among these endogenous damage signals are ligands for toll-like receptors, including several heat shock proteins and extracellular matrix components, as well as self-derived RNA and DNA and associated proteins. Growing evidence also suggests that nucleotides released upon injury and acting through P2 receptors, such as ATP and UTP or their analogues, could serve as endogenous signals for the rapid response of glial cells.

Regeneration of nigrostriatal dopaminergic axons after transplantation of olfactory ensheathing cells and fibroblasts prevents fibrotic scar formation at the lesion site

The fibrotic scar formed after central nervous system injury has been considered an obstacle to axonal regeneration. The present study was designed to examine whether cell transplantation into a damaged central nervous system can reduce fibrotic scar formation and promote axonal regeneration. Nigrostriatal dopaminergic axons were unilaterally transected in rats and cultures of olfactory-ensheathing cells (OECs), and olfactory nerve fibroblasts were transplanted into the lesion site. In the absence of transplants, few tyrosine hydroxylase-immunoreactive axons extended across the lesion 2 weeks after the transection. Reactive astrocytes increased around the lesion, and a fibrotic scar containing type IV collagen deposits developed in the lesion center. The immunoreactivity of chondroitin sulfate side chains and core protein of NG2 proteoglycan increased in and around the lesion. One and 2 weeks after transection and simultaneous transplantation, dopaminergic axons regenerated across the transplanted tissues, which consisted of p75-immunoreactive OECs and fibronectin-immunoreactive fibroblasts. Reactive astrocytes and chondroitin sulfate immunoreactivity increased around the transplants, whereas the deposition of type IV collagen and fibrotic scar formation were completely prevented at the lesion site. Transplantation of meningeal fibroblasts similarly prevented the formation of the fibrotic scar, although its effect on regeneration was less potent than transplantation of OECs and olfactory nerve fibroblasts. The present results suggest that elimination of the inhibitory fibrotic scar is important for neural regeneration.

Down-regulation of neurocan expression in reactive astrocytes promotes axonal regeneration and facilitates the neurorestorative effects of bone marrow stromal cells in the ischemic rat brain

The glial scar, a primarily astrocytic structure bordering the infarct tissue inhibits axonal regeneration after stroke. Neurocan, an axonal extension inhibitory molecule, is up-regulated in the scar region after stroke. Bone marrow stromal cells (BMSCs) reduce the thickness of glial scar wall and facilitate axonal remodeling in the ischemic boundary zone. To further clarify the role of BMSCs in axonal regeneration and its underlying mechanism, the current study focused on the effect of BMSCs on neurocan expression in the ischemic brain. Thirty-one adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 x 10(6) rat BMSCs (n = 16) or phosphate-buffered saline (n = 15) into the tail vein 24 h later. Animals were sacrificed at 8 days after stroke. Immunostaining analysis showed that reactive astrocytes were the primary source of neurocan, and BMSC-treated animals had significantly lower neurocan and higher growth associated protein 43 expression in the penumbral region compared with control rats, which was confirmed by Western blot analysis of the brain tissue. To further investigate the effects of BMSCs on astrocyte neurocan expression, single reactive astrocytes were collected from the ischemic boundary zone using laser capture microdissection. Neurocan gene expression was significantly down-regulated in rats receiving BMSC transplantation (n = 4/group). Primary cultured astrocytes showed similar alterations; BMSC coculture during reoxygenation abolished the up-regulation of neurocan gene in astrocytes undergoing oxygen-glucose deprivation (n = 3/group). Our data suggest that BMSCs promote axonal regeneration by reducing neurocan expression in peri-infarct astrocytes.

The influence of sub-micron inhibitory clusters on growth cone substratum attachments and CD44 expression

Proteoglycan expression patterns in the central nervous system guide neuronal pathfinding during development, but also disrupt regeneration after injuries. To deepen our understanding of the molecular level effects of proteoglycan spatial arrangements on neuronal pathfinding, we designed micropatterning stamps for the precise placement of near single molecule chondroitin sulfate proteoglycan (CSPG) clusters into regularly spaced arrays. Actin ultrastructural analysis in dorsal root ganglion neurons grown on laminin-coated substrata patterned with aggrecan cluster arrays revealed filopodial and lamellapodial edge contact avoidance of individual clusters, while growth cone lamellapodia and central domains were able to span multiple clusters over a range of cluster densities. Total internal reflection fluorescence microscopy interrogation of growth cone substratum morphology further revealed persistence of integrin mediated substratum adhesion and local out-of-plane membrane bending over clusters on the height scale of aggrecan glycosaminoglycan side chains. Direct imaging of cell adhesion molecule CD44 expression in growth cones revealed an aggrecan dose dependent upregulation in CD44 molecules. Evidence of CD44 clustering coinciding with underlying aggrecan molecules implies CSPG-CD44 interactions. The results reveal the limited local repulsive effect of CSPGs on neuronal structures and provide evidence that CD44 upregulation in neurons is affected by local CSPG expression.

Structural reorganization of the dentate gyrus following entorhinal denervation: species differences between rat and mouse

Deafferentation of the dentate gyrus by unilateral entorhinal cortex lesion or unilateral perforant pathway transection is a classical model to study the response of the central nervous system (CNS) to denervation. This model has been extensively characterized in the rat to clarify mechanisms underlying denervation-induced gliosis, transneuronal degeneration of denervated neurons, and collateral sprouting of surviving axons. As a result, candidate molecules have been identified which could regulate these changes, but a causal link between these molecules and the postlesional changes has not yet been demonstrated. To this end, mutant mice are currently studied by many groups. A tacit assumption is that data from the rat can be generalized to the mouse, and fundamental species differences in hippocampal architecture and the fiber systems involved in sprouting are often ignored. In this review, we will (1) provide an overview of some of the basics and technical aspects of the entorhinal denervation model, (2) identify anatomical species differences between rats and mice and will point out their relevance for the axonal reorganization process, (3) describe glial and local inflammatory changes, (4) consider transneuronal changes of denervated dentate neurons and the potential role of reactive glia in this context, and (5) summarize the differences in the reorganization of the dentate gyrus between the two species. Finally, we will discuss the use of the entorhinal denervation model in mutant mice.

Brevican and phosphacan expression and localization following transient middle cerebral artery occlusion in the rat

The ECM (extracellular matrix) is a complex molecular framework that provides physical support to cells and tissues, while also providing signals for cell growth, migration, differentiation and survival. The ECM of the CNS (central nervous system) is unusual in that it is rich in CSPGs (chondroitin sulfate proteoglycans), hyaluronan and tenascins. The CSPGs are widely expressed throughout the developing and adult CNS and have a role in guiding or limiting neurite outgrowth and cell migration. Alterations in the synthesis or breakdown of the ECM may contribute to disease processes. Here, we examine changes in the brain-specific CSPGs, brevican and phosphacan, following transient middle cerebral artery occlusion, a model of stroke in the rat. We have investigated their expression at various time points as well as their spatial relationship with ADAMTS-4 (adisintegrin and metalloprotease with thrombospondin motifs 4). The co-localization of ADAMTS or its activity may indicate a functional role for this matrix–protease pair in degeneration/regeneration processes that occur in stroke.

Regeneration of nigrostriatal dopaminergic axons by degradation of chondroitin sulfate is accompanied by elimination of the fibrotic scar and glia limitans in the lesion site

Chondroitin sulfate increases around a lesion site after central nervous system injury and is believed to be an impediment to axonal regeneration, because administration of chondroitinase ABC, a chondroitin sulfate-degrading enzyme, promotes axonal regeneration of central neurons. To examine the physiological role of chondroitin sulfate up-regulation after injury, the nigrostriatal dopaminergic axons were unilaterally transected in mice, and chondroitinase ABC was then injected into the lesion site. In mice transected only, tyrosine hydroxylase-immunoreactive axons did not extend across the lesion at 1 or 2 weeks after the transection. Immunoreactivities of chondroitin sulfate side chains and core protein of NG2 proteoglycan increased in and around the lesion site, and a fibrotic scar containing type IV collagen deposits developed in the lesion center. In contrast, in mice transected and treated with chondroitinase ABC, numerous tyrosine hydroxylase-immunoreactive axons were regenerated across the lesion at 1 and 2 weeks after the transection. In these animals, chondroitin sulfate immunoreactivity remarkably decreased, and immunoreactivity of 2B6 antibody, which recognizes the stub of degraded chondroitin sulfate side chains, was enhanced. Furthermore, the formation of a fibrotic scar and a glia limitans that surrounds the former was completely prevented, although type IV collagen immunoreactivity remained in newly formed blood capillaries around the lesion site. We discuss the question of whether the chondroitin sulfate is acting as a direct inhibitor of axonal regeneration or whether the observed changes are due to a prevention of the fibrotic scar formation and a rearrangement of astrocytic membranes.

Lesion-Induced Axonal Sprouting in the Central Nervous System

Injury or neuronal death often come about as a result of brain disorders. Inasmuch as the damaged nerve cells are interconnected via projections to other regions of the brain, such lesions lead to axonal loss in distal target areas. The central nervous system responds to deafferentation by means of plastic remodeling processes, in particular by inducing outgrowth of new axon collaterals from surviving neurons (collateral sprouting). These sprouting processes result in a partial reinnervation, new circuitry, and functional changes within the deafferented brain regions. Lesioning of the entorhinal cortex is an established model system for studying the phenomenon of axonal sprouting. Using this model system, it could be shown that the sprouting process respects the pre-existing lamination pattern of the deafferented fascia dentata, i. e., it is layer-specific. A variety of different molecules are involved in regulating this reorganization process (extracellular matrix molecules, cell adhesion molecules, transcription factors, neurotrophic factors, growth-associated proteins). It is proposed here that molecules of the extracellular matrix define the boundaries of the laminae following entorhinal lesioning and in so doing limit the sprouting process to the deafferented zone. To illustrate the role of axonal sprouting in disease processes, special attention is given to its significance for neurodegenerative disorders, particularly Alzheimer's disease (AD), and temporal lobe epilepsy. Finally, we discuss both the beneficial as well as disadvantageous functional implications of axonal sprouting for the injured organism in question.

Mechanisms of Disease: what factors limit the success of peripheral nerve regeneration in humans?

Functional recovery after repair of peripheral nerve injury in humans is often suboptimal. Over the past quarter of a century, there have been significant advances in human nerve repair, but most of the developments have been in the optimization of surgical techniques. Despite extensive research, there are no current therapies directed at the molecular mechanisms of nerve regeneration. Multiple interventions have been shown to improve nerve regeneration in small animal models, but have not yet translated into clinical therapies for human nerve injuries. In many rodent models, regeneration occurs over relatively short distances, so the duration of denervation is short. By contrast, in humans, nerves often have to regrow over long distances, and the distal portion of the nerve progressively loses its ability to support regeneration during this process. This can be largely attributed to atrophy of Schwann cells and loss of a Schwann cell basal lamina tube, which results in an extracellular environment that is inhibitory to nerve regeneration. To develop successful molecular therapies for nerve regeneration, we need to generate animal models that can be used to address the following issues: improving the intrinsic ability of neurons to regenerate to increase the speed of axonal outgrowth; preventing loss of basal lamina and chronic denervation changes in the denervated Schwann cells; and overcoming inhibitory cues in the extracellular matrix.

Possible involvement of increase in spinal fibronectin following peripheral nerve injury in upregulation of microglial P2X4, a key molecule for mechanical allodynia

We have recently demonstrated that the P2X4 receptor, an ATP-gated cation channel, in spinal microglia is a key molecule that mediates the mechanical allodynia induced by peripheral nerve injury. Although microglial P2X4 receptor expression is increased after peripheral nerve injury, the molecular mechanism(s) underlying its upregulation remains largely unknown. Fibronectin is a member of the extracellular matrix molecules and is actively produced in response to injury and diseases in the CNS. Here, we describe the influence of fibronectin on P2X4 receptor expression in microglia and the upregulation of fibronectin after peripheral nerve injury. Microglia that were cultured on fibronectin-coated dishes showed a marked increase in P2X4 receptor expression, both at the mRNA and protein levels, as compared to those cultured on control dishes. Fibronectin also enhanced the microglial Ca2+ responses mediated by P2X4 receptors. Moreover, Western blot examination of the spinal cord from a rat with spinal nerve injury indicated that fibronectin was upregulated on the ipsilateral side. Interestingly, intrathecal injection of ATP-stimulated microglia to the rat lumber spinal cord revealed that microglia cultured on fibronectin-coated dishes was more effective in the induction of allodynia than microglia cultured on control dishes. Taken together, our results suggest that spinal fibronectin is elevated after the peripheral nerve injury and it may be involved in the upregulation of the P2X4 receptor in microglia, which leads to the induction of neuropathic pain.

NG2 glial cells provide a favorable substrate for growing axons

NG2 cells (polydendrocytes) comprise an abundant glial population that is widely and uniformly distributed throughout the developing and mature CNS and are identified by the expression of the NG2 proteoglycan at the cell surface. Although recent electrophysiological studies suggest that they are capable of receiving signals from axon terminals, other studies, based on the finding that the NG2 molecule itself induces growth cone collapse, have led to a widely held speculation that NG2 cells themselves also repel and inhibit growing axons. In this study, we have examined the effects of rat NG2 cells on growing hippocampal and neocortical axons in vitro and in vivo. NG2 cells did not repel growing axons but promoted their growth in vitro, and axonal growth cones formed extensive contacts with NG2 cells both in vitro and in the developing corpus callosum. Punctate immunoreactivity for fibronectin and laminin was found to be colocalized with NG2 on the surface of NG2 cells. Altering the level of cell surface NG2 expression had no effect on the growth-promoting effects of NG2 cells on growing axons. Thus, our study indicates that NG2 cells are not inhibitory to growing axons but provide an adhesive substrate for axonal growth cones and promote their growth even in the presence of elevated levels of the NG2 proteoglycan. These findings suggest a novel role for NG2 cells in facilitating axonal growth during development and regeneration.

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

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

Inhibition of collagen synthesis overrides the age-related failure of regeneration of nigrostriatal dopaminergic axons

To investigate the mechanism of the age-related failure of regeneration of transected axons, nigrostriatal dopaminergic axons were unilaterally transected in the lateral hypothalamus in adult mice and in immature mice aged postnatal days 7, 14, and 21. Ten days after the transection, tyrosine hydroxylase-immunoreactive axons had regenerated from caudally to rostrally across the lesion site in mice transected at postnatal day 7, whereas they stopped and did not extend across the lesion site in mice transected at postnatal day 14 or older. Reactive astrocytes bearing chondroitin sulfate proteoglycans were observed around the lesion in mice transected at all ages. However, a fibrotic scar containing type IV collagen-immunoreactive deposits, which was consistently formed at the lesion site in mice transected at postnatal day 14 or older, was not formed in mice lesioned at postnatal day 7. When 2,2'-dipyridyl, an inhibitor of collagen synthesis, was injected into the lesion site at the time of transection in both postnatal day 14 and adult mice, the deposition of type IV collagen and the formation of a fibrotic scar were completely prevented, and large numbers of tyrosine hydroxylase-immunoreactive axons extended across the lesion and reinnervated the striatum. These results imply that the fibrotic scar formed in the lesion site is a crucial impediment to the regeneration of ascending dopaminergic axons in adult mice and suggest that type IV collagen is required for the development of the fibrotic response to adult brain injury.

Chondroitinase ABCI improves locomotion and bladder function following contusion injury of the rat spinal cord

Chondroitin sulfate proteoglycans are synthesized and deposited in the spinal cord following injury. These proteoglycans may restrict regeneration and plasticity and contribute to the limited recovery seen after an injury. Chondroitinase, a bacterial enzyme that catalyzes the hydrolysis of the chondroitin chains on proteoglycans, has been shown to improve motor and sensory function following partial transection lesions of the spinal cord. To assess the effects of chondroitinase in a clinically relevant model of spinal cord injury, 128 female Long-Evans rats received either a severe, moderate, or mild contusion injury at the vertebral level T9/T10 with a forceps model and were treated for 2 weeks with chondroitinase ABCI at 0.06 Units per dose, penicillinase, or vehicle control via an intrathecal catheter placed near the injury. Motor behavior was measured by open-field testing of locomotion and bladder function monitored by measuring daily residual urine volumes. Animals treated with chondroitinase showed significant improvements in open-field locomotor activity as measured by the Basso, Beattie and Bresnahan scoring system after both severe and moderate SCI (p<0.05 and 0.01, respectively). No significant locomotor differences were observed in the mild injury group. In the moderate injury group, residual urine volumes were reduced with chondroitinase treatment by 2 weeks after injury (p<0.05) and in the severe injury group, by 6 weeks after injury (NS). These results demonstrate that chondroitinase is effective at promoting both somatic and autonomic motor recovery following a clinically relevant contusion spinal cord injury and is a candidate as a therapeutic for human spinal cord injury.

Expression of neurocan after transient middle cerebral artery occlusion in adult rat brain

Neurocan is one of the major chondroitin sulfate proteoglycans in the nervous tissues. The expression and proteolytic cleavage of neurocan are developmentally regulated in the normal rat brain, and the full-length neurocan is detected in juvenile brains but not in normal adult brains. Recently, some studies showed that the full-length neurocan was detectable even in the adult brain when it was exposed to mechanical incision or epileptic stimulation. In the present study, we demonstrated by Western blot analysis that the full-length neurocan transiently appeared in the peri-ischemic region of transient middle cerebral artery occlusion (tMCAO) in adult rat with a peak level at 4 days after tMCAO. Immunohistochemical analysis showed that a clear positive signal of neurocan was observed 4 days after tMCAO in the peri-ischemic region of cerebral cortex and caudate, where cells strongly positive in GFAP expression were also distributed. These results indicate that accumulation of the full-length neurocan produced by reactive astrocytes may be one of the processes for tissue repair and reconstruction of neural networks after focal brain ischemia as well.

Modulation of Rho GTPase activity alleviates chondroitin sulfate proteoglycan-dependent inhibition of neurite extension

The central nervous system (CNS) fails to regenerate after injury. A glial scar forms at the injury site, contributing to regenerative failure partly resulting from the chondroitin sulfate proteoglycans (CSPGs) in the glial scar. The family of Rho GTPases, which includes Cdc42, Rac1, and RhoA, is involved in growth cone dynamics. Although the response of neural cells to the inactivation of Rho when contacting myelin-related substrates, or CSPG, has been investigated, Rac1's and Cdc42's abilities to modulate CSPG-dependent inhibition have yet to be explored. In this study, a stripe assay was utilized to examine the effects of modulating all three Rho GTPases on neurite extension across inhibitory CSPG lanes. Alternating laminin (LN) and CSPG lanes were created and NG108-15 cells and E9 chick dorsal root ganglia (DRGs) were cultured on the lanes. By using the protein delivery agent Chariot, the neuronal response to exposure of constitutively active (CA) and dominant negative (DN) mutants of the Rho GTPases, along with the bacterial toxin C3, was determined by quantifying the percentage ratio of neurites crossing the CSPG lanes. CA-Cdc42, CA-Rac1, and C3 transferase significantly increased the number of neurites crossing into the CSPG lanes compared with the negative controls for both the NG108-15 cells and the E9 chick DRGs. We also show that these mutant proteins require the delivery vehicle, Chariot, to enter the neurons and affect neurite extension. Therefore, activation of Cdc42 and Rac, as well as inhibition of Rho, helps overcome the CSPG-dependent inhibition of neurite extension.

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

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

Comparison of commissural sprouting in the mouse and rat fascia dentata after entorhinal cortex lesion

Reactive axonal sprouting occurs in the fascia dentata after entorhinal cortex lesion. This sprouting process has been described extensively in the rat, and plasticity-associated molecules have been identified that might be involved in its regulation. To demonstrate causal relationships between these candidate molecules and the axonal reorganization process, it is reasonable to analyze knockout and transgenic animals after entorhinal cortex lesion, and because gene knockouts are primarily generated in mice, it is necessary to characterize the sprouting response after entorhinal cortex lesion in this species. In the present study, Phaseolus vulgaris-leucoagglutinin (PHAL) tracing was used to analyze the commissural projection to the inner molecular layer in mice with longstanding entorhinal lesions. Because the commissural projection to the fascia dentata is neurochemically heterogeneous, PHAL tracing was combined with immunocytochemistry for calretinin, a marker for commissural/associational mossy cell axons. Using both techniques singly as well as in combination (double-immunofluorescence) at the light or electron microscopic level, it could be shown that in response to entorhinal lesion mossy cell axons leave the main commissural fiber plexus, invade the denervated middle molecular layer, and form asymmetric synapses within the denervated zone. Thus, the commissural sprouting response in mice has a considerable translaminar component. This is in contrast to the layer-specific commissural sprouting observed in rats, in which the overwhelming majority of mossy cell axons remain within their home territory. These data demonstrate an important species difference in the commissural/associational sprouting response between rats and mice that needs to be taken into account in future studies.

Neurite elongation on chondroitin sulfate proteoglycans is characterized by axonal fasciculation

In the developing or regenerating nervous system, migrating growth cones are exposed to regulatory molecules that positively and/or negatively affect guidance. Chondroitin sulfate proteoglycans (CSPGs) are complex macromolecules that are typically negative regulators of growth cone migration in vivo and in vitro. However, in certain cases, neurites sometimes traverse regions expressing relatively high levels of CSPGs, seemingly a paradox. In our continuing efforts to characterize CSPG inhibition in vitro, we manipulated the ratio of CSPGs to growth-promoting laminin-1 to produce a substratum that supports outgrowth of a subpopulation of dorsal root ganglia (DRG) neurites, while still being inhibitory to other populations of DRG neurons [Exp. Neurol. 109 (1990), 111; J. Neurobiol. 51 (2002), 285]. This model comprises a useful tool in the analysis of mechanisms of growth cone guidance and is particularly useful to analyze how CSPGs can be inhibitory under some conditions, and growth permissive under others. We grew embryonic (E9-10) chicken DRG neurons on nervous system-isolated, substratum-bound CSPGs at a concentration that supports an intermittent pattern of outgrowth, alternating with regions adsorbed with growth-promoting laminin-1 alone, and analyzed outgrowth behaviors qualitatively and quantitatively. A novel finding of the study was that DRG neurites that elongated onto CSPGs were predominantly fasciculated, but immediately returned to a defasciculated state upon contact with laminin-1. Further, cursory inspection suggests that outgrowth onto CSPGs may be initially accomplished by pioneer axons, along which subsequent axons migrate. The outgrowth patterns characterized in vitro may accurately reflect outgrowth in vivo in locations where inhibitory CSPGs and growth-promoting molecules are coexpressed, e.g., in the developing retina where fasciculated outgrowth may be instrumental in the guidance of retinal ganglion cells from the periphery to the optic fissure.

Effect of Neuregen nutrient medium on survival of cortical neurons after aspiration lesion in rats

OBJECT

During brain surgery, it would be beneficial to irrigate the surgical cavity with a solution that promotes neuronal growth and survival. The authors find that incubation of cultured neurons with normal saline, also known as buffered salts, which are often used in brain surgery in humans, does not support neuron survival. Neuregen is an optimized serum-free culture medium that promotes regeneration of adult rat and human central nervous system neurons in vitro. It includes balanced salts, glucose, amino acids, vitamins, essential fatty acids, hormones, antioxidants, and other ingredients. The authors hypothesize that brain lesions irrigated and soaked in Neuregen nutrients will have better neuron survival rates in deafferented regions than lesions irrigated with saline.

METHODS

Lesioning of the rat fimbria-fornix area was achieved by aspiration through the cortex; animals were killed 4 weeks later. Brain sections were stained with cresyl violet for neuron counts in the medial septum and cortex. Treatment of the lesion cavity with Neuregen resulted in a 55% increase in neuron density in the septum compared with saline treatment (p = 0.02). Cortical lesions treated with Neuregen showed a 27% increase in neuron density compared with saline-treated lesions (p = 0.015); the neuron density in Neuregen-treated rat brains was equivalent to that seen with sham treatment. Efficacy of Neuregen with basic fibroblast growth factor (bFGF) was significantly better than with Dulbecco modified Eagle medium bFGF, but not better than Neuregen alone. Neuregen produced a coincidental fourfold reduction in glial fibrillary acidic protein immunoreactivity at 4 weeks compared with saline (p = 0.002), to levels equivalent to those found in sham lesions.

CONCLUSIONS

These results indicate that a highly optimized nutrient medium promotes neuron survival after brain surgery.

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

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

Transient expression of juvenile-type neurocan by reactive astrocytes in adult rat brains injured by kainate-induced seizures as well as surgical incision

Neurocan is one of the major chondroitin sulfate proteoglycans expressed in nervous tissues. The expression of neurocan is developmentally regulated, and full-length neurocan is detected in juvenile brains but not in adult brains. In the present study, we demonstrated by western blot analysis that full-length neurocan transiently appeared in adult rat hippocampus when it was lesioned by kainate-induced seizures. Immunohistochemical studies showed that neurocan was detected mainly around the CA1 region although the seizure resulted in neuronal cell degeneration in both the CA1 and CA3 regions of the hippocampus. Double-labeling for neurocan mRNA and glial fibrillary acidic protein demonstrated that many reactive astrocytes expressed neurocan mRNA. The re-expression of full-length neurocan was also observed in the surgically injured adult rat brain. In contrast, the expression of other nervous tissue chondroitin sulfate proteoglycans, such as phosphacan and neuroglycan C, was not intensified but rather was either reduced in the kainate-lesioned hippocampus or in the surgically injured cerebral cortex. These observations indicate that induction of neurocan expression by reactive astrocytes is a common phenomenon in the repair process of adult brain injury, and therefore, it can be postulated that juvenile-type neurocan plays some roles in brain repair.

Axonal regeneration and functional recovery after complete spinal cord transection in rats by delayed treatment with transplants and neurotrophins

Little axonal regeneration occurs after spinal cord injury in adult mammals. Regrowth of mature CNS axons can be induced, however, by altering the intrinsic capacity of the neurons for growth or by providing a permissive environment at the injury site. Fetal spinal cord transplants and neurotrophins were used to influence axonal regeneration in the adult rat after complete spinal cord transection at a midthoracic level. Transplants were placed into the lesion cavity either immediately after transection (acute injury) or after a 2-4 week delay (delayed or chronic transplants), and either vehicle or neurotrophic factors were administered exogenously via an implanted minipump. Host axons grew into the transplant in all groups. Surprisingly, regeneration from supraspinal pathways and recovery of motor function were dramatically increased when transplants and neurotrophins were delayed until 2-4 weeks after transection rather than applied acutely. Axonal growth back into the spinal cord below the lesion and transplants was seen only in the presence of neurotrophic factors. Furthermore, the restoration of anatomical connections across the injury site was associated with recovery of function with animals exhibiting plantar foot placement and weight-supported stepping. These findings suggest that the opportunity for intervention after spinal cord injury may be greater than originally envisioned and that CNS neurons with long-standing injuries can reinitiate growth, leading to improvement in motor function.

Characterization of rat meningeal cultures on materials of differing surface chemistry

To better understand the interactions of cells derived from meningeal tissues with the surfaces of devices used for the treatment of central nervous system disorders, the behavior of primary postnatal day 1 rat meningeal cultures was evaluated on biomaterials of differing surface chemistry. Meningeal cultures in serum containing media were analyzed for attachment, spread cell area, proliferation, the production of extracellular matrix (ECM), and neuronal outgrowth. In general, both cell attachment as well as cell spread area decreased with increasing substrate hydrophobicity, whereas cell division as indicated by BrdU incorporation and time to confluence, was lower on the most hydrophobic materials. We suggest that such differences immediately after cell seeding were most likely mediated by differences in surface adsorption of proteins. In longer-term experiments, most of the materials were colonized by meningeal cultures irrespective of surface chemistry, and all cultures were equally inhibitory to neuronal outgrowth suggesting that over time, cells can modify the substrate perhaps by secretion of extracellular matrix molecule proteins. Our data suggests that cell type-specific differences in response to different biomaterials may play an important role in determining the ultimate nature and composition of the CNS at the host-biomaterial interface.

Adult neuronal regeneration induced by transgenic integrin expression

In a variety of adult CNS injury models, embryonic neurons exhibit superior regenerative performance when compared with adult neurons. It is unknown how young neurons extend axons in the injured adult brain, in which adult neurons fail to regenerate. This study shows that cultured adult neurons do not adapt to conditions that are characteristic of the injured adult CNS: low levels of growth-promoting molecules and the presence of inhibitory proteoglycans. In contrast, young neurons readily adapt to these same conditions, and adaptation is accompanied by an increase in the expression of receptors for growth-promoting molecules (receptors of the integrin family). Surprisingly, the regenerative performance of adult neurons can be restored to that of young neurons by gene transfer-mediated expression of a single alpha-integrin.