Local changes in vascular architecture following partial spinal cord lesion in the rat

Therapeutic efficacy of adrenergic agents on systemic and spinal hemodynamics in an acute cervical spinal cord injury rodent model

BACKGROUND

Cervical spinal cord injury usually results in cardiorespiratory dysfunctions due to interruptions of the bulbospinal pathways innervating the cervical phrenic motoneurons and thoracic sympathetic preganglionic neurons.

PURPOSE

The present study aimed to evaluate the therapeutic effects of adrenergic agents on systemic and spinal hemodynamics during acute cervical spinal cord injury.

STUDY DESIGN

In vivo animal study.

METHODS

The cardiorespiratory function and spinal cord blood flow and oxygenation level were monitored in response to cervical spinal cord contusion and intravenous infusion of three types of adrenergic agents (phenylephrine, dobutamine, and norepinephrine).

RESULTS

Cervical spinal cord contusion resulted in immediate reduction of respiratory airflow, arterial blood pressure, and spinal cord blood flow. The arterial blood pressure and spinal cord blood flow remained lower than the pre-injury value in contused animals infused with saline at 60 min post-injury. Infusion of phenylephrine (500, 1000, and 2000 μg/kg) and norepinephrine (125, 250, and 500 μg/kg) significantly increased the arterial blood pressure, while only norepinephrine augmented the spinal cord blood flow. Conversely, dobutamine (1000 and 2000 μg/kg) reduced both arterial blood pressure and spinal cord blood flow. Notably, administration of adrenergic agents tended to increase spinal cord hemorrhage in contused animals.

CONCLUSIONS

Infusion of norepinephrine can effectively maintain the blood pressure and improve spinal cord blood flow during acute spinal cord injury.

CLINICAL SIGNIFICANCE

Norepinephrine may be a superior medicine for hemodynamic management; however, the potential hemorrhage should be considered when utilizing the vasopressor to regulate systemic and spinal hemodynamics at the acute injured stage.

Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging

Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo.

Acute Hyperoxia Improves Spinal Cord Oxygenation and Circulatory Function Following Cervical Spinal Cord Injury in Rats

Spinal cord injury is associated with spinal vascular disruptions that result in spinal ischemia and tissue hypoxia. This study evaluated the therapeutic efficacy of normobaric hyperoxia on spinal cord oxygenation and circulatory function at the acute stage of cervical spinal cord injury. Adult male Sprague Dawley rats underwent dorsal cervical laminectomy or cervical spinal cord contusion. At 1-2 days after spinal surgery, spinal cord oxygenation was monitored in anesthetized and spontaneously breathing rats through optical recording of oxygen sensor foils placed on the cervical spinal cord and pulse oximetry. The arterial blood pressure, heart rate, blood gases, and peripheral oxyhemoglobin saturation were also measured under hyperoxic (50% O2) and normoxic (21% O2) conditions. The results showed that contused animals had significantly lower spinal cord oxygenation levels than uninjured animals during normoxia. Peripheral oxyhemoglobin saturation, arterial oxygen partial pressure, and mean arterial blood pressure are significantly reduced following cervical spinal cord contusion. Notably, spinal oxygenation of contused rats could be improved to a level comparable to uninjured animals under hyperoxia. Furthermore, acute hyperoxia elevated blood pressure, arterial oxygen partial pressure, and peripheral oxyhemoglobin saturation. These results suggest that normobaric hyperoxia can significantly improve spinal cord oxygenation and circulatory function in the acute phase after cervical spinal cord injury. We propose that adjuvant normobaric hyperoxia combined with other hemodynamic optimization strategies may prevent secondary damage after spinal cord injury and improve functional recovery.

Protection of the Vascular System by Polyethylene Glycol Reduces Secondary Injury Following Spinal Cord Injury in Rats

BACKGROUND

Polyethylene glycol (PEG) is a hydrophilic polymer, which has been known to have a neuroprotective effect by sealing the ruptured cell membrane, but PEG effects on the vascular systems and its underlying mechanisms remain unclear. Here, we showed the neuroprotective effect of PEG by preventing damage to the vascular system.

METHODS

A spinal contusion was made at the T11 segment in male Sprague-Dawley rats. PEG was injected into the subdural space immediately after SCI. Vascular permeability was assessed for 24 h after SCI using intraperitoneally injected Evans blue dye. Junctional complexes were stained with CD31 and ZO-1. Infarct size was analyzed using triphenyltetrazolium chloride, and blood vessels were counted in the epicenter. Behavioral tests for motor and sensory function were performed for 6 weeks. And then the tissue-sparing area was assessed.

RESULTS

Immediately applied PEG significantly reduced the vascular permeability at 6, 12, and 24 h after SCI when it compared to saline, and infarct size was also reduced at 0, 6, and 24 h after SCI. In addition, a great number of blood vessels were observed in PEG group at 6 and 24 h after SCI compared to those of the saline group. The PEG group also showed a significant improvement in motor function. And tissue-sparing areas in the PEG were greater than those of the saline group.

CONCLUSION

The present results provide preclinical evidence for the neuroprotective effects of PEG as a promising therapeutic agent for reducing secondary injury following SCI through vascular protection.

Development and repair of blood vessels in the zebrafish spinal cord

The vascular system is inefficiently repaired after spinal cord injury (SCI) in mammals, resulting in secondary tissue damage and immune deregulation that contribute to the limited functional recovery. Unlike mammals, zebrafish can repair the spinal cord (SC) and restore motility, but the vascular response to injury has not been investigated. Here, we describe the zebrafish SC blood vasculature, starting in development with the initial vessel ingression in a body size-dependent manner, the acquisition of perivascular support and the establishment of ventral to dorsal blood circulation. The vascular organization grows in complexity and displays multiple barrier specializations in adulthood. After injury, vessels rapidly regrow into the lesion, preceding the glial bridge and axons. Vascular repair involves an early burst of angiogenesis that creates dysmorphic and leaky vessels. Dysfunctional vessels are later removed, as pericytes are recruited and the blood-SC barrier is re-established. This study demonstrates that zebrafish can successfully re-vascularize the spinal tissue, reinforcing the value of this organism as a regenerative model for SCI.

Ultrafast Doppler imaging and ultrasound localization microscopy reveal the complexity of vascular rearrangement in chronic spinal lesion

Acute spinal cord injury (SCI) leads to severe damage to the microvascular network. The process of spontaneous repair is accompanied by formation of new blood vessels; their functionality, however, presumably very important for functional recovery, has never been clearly established, as most studies so far used fixed tissues. Here, combining ultrafast Doppler imaging and ultrasound localization microscopy (ULM) on the same animals, we proceeded at a detailed analysis of structural and functional vascular alterations associated with the establishment of chronic SCI, both at macroscopic and microscopic scales. Using a standardized animal model of SCI, our results demonstrate striking hemodynamic alterations in several subparts of the spinal cord: a reduced blood velocity in the lesion site, and an asymmetrical hypoperfusion caudal but not rostral to the lesion. In addition, the worsening of many evaluated parameters at later time points suggests that the neoformed vascular network is not yet fully operational, and reveals ULM as an efficient in vivo readout for spinal cord vascular alterations. Finally, we show statistical correlations between the diverse biomarkers of vascular dysfunction and SCI severity. The imaging modality developed here will allow evaluating recovery of vascular function over time in pre-clinical models of SCI. Also, used on SCI patients in combination with other quantitative markers of neural tissue damage, it may help classifying lesion severity and predict possible treatment outcomes in patients.

Perspectives in the Cell-Based Therapies of Various Aspects of the Spinal Cord Injury-Associated Pathologies: Lessons from the Animal Models

Traumatic injury of the spinal cord (SCI) is a devastating neurological condition often leading to severe dysfunctions, therefore an improvement in clinical treatment for SCI patients is urgently needed. The potential benefits of transplantation of various cell types into the injured spinal cord have been intensively investigated in preclinical SCI models and clinical trials. Despite the many challenges that are still ahead, cell transplantation alone or in combination with other factors, such as artificial matrices, seems to be the most promising perspective. Here, we reviewed recent advances in cell-based experimental strategies supporting or restoring the function of the injured spinal cord with a particular focus on the regenerative mechanisms that could define their clinical translation.

Future Perspectives in Spinal Cord Repair: Brain as Saviour? TSCI with Concurrent TBI: Pathophysiological Interaction and Impact on MSC Treatment

Traumatic spinal cord injury (TSCI), commonly caused by high energy trauma in young active patients, is frequently accompanied by traumatic brain injury (TBI). Although combined trauma results in inferior clinical outcomes and a higher mortality rate, the understanding of the pathophysiological interaction of co-occurring TSCI and TBI remains limited. This review provides a detailed overview of the local and systemic alterations due to TSCI and TBI, which severely affect the autonomic and sensory nervous system, immune response, the blood-brain and spinal cord barrier, local perfusion, endocrine homeostasis, posttraumatic metabolism, and circadian rhythm. Because currently developed mesenchymal stem cell (MSC)-based therapeutic strategies for TSCI provide only mild benefit, this review raises awareness of the impact of TSCI-TBI interaction on TSCI pathophysiology and MSC treatment. Therefore, we propose that unravelling the underlying pathophysiology of TSCI with concomitant TBI will reveal promising pharmacological targets and therapeutic strategies for regenerative therapies, further improving MSC therapy.

Histological and functional outcomes in a rat model of hemisected spinal cord with sustained VEGF/NT-3 release from tissue-engineered grafts

Microvascular disturbance, excessive inflammation and gliosis are key pathophysiologic changes in relation to functional status following the traumatic spinal cord injury (SCI). Continuous release of vascular endothelial growth factor (VEGF) to the lesion site was proved be able to promote the vascular remodelling, whereas the effects on reduction of inflammation and gliosis remain unclear. Currently, aiming at exploring the synergistic roles of VEGF and neurotrophin-3 (NT-3) on angiogenesis, anti-inflammation and neural repair, we developed a technique to co-deliver VEGF₁₆₅ and NT-3 locally with a homotopic graft of tissue-engineered acellular spinal cord scaffold (ASCS) in a hemisected (3 mm in length) SCI model. As the potential in secretion of growth factors (GFs), bone mesenchymal stem cells (BMSCs) were introduced with the aim to enhance the VEGF/NT-3 release. Our data demonstrate that sustained VEGF/NT-3 release from ASCS significantly increases the local levels of VEGF/NT-3 and angiogenesis, regardless of whether it is in combination with BMSCs transplantation that exhibits positive effects on anti-inflammation, axonal outgrowth and locomotor recovery. This study verifies that co-delivery of VEGF/NT-3 reduces inflammation and gliosis in the hemisected spinal cord, promotes axonal outgrowth and results in better locomotor recovery, while the BMSCs transplantation facilitates these functions limitedly.

Therapeutic Effect of Platelet-Rich Plasma in Rat Spinal Cord Injuries

Platelet-rich plasma (PRP) is prepared by centrifuging fresh blood in an anticoagulant state, and harvesting the platelet-rich portion or condensing platelets. Studies have consistently demonstrated that PRP concentrates are an abundant source of growth factors, such as platelet-derived growth factor (PDGF), transforming growth factor β (TGF-β), insulin-like growth factor 1 (IGF-1), and epithelial growth factor (EGF). The complex mechanisms underlying spinal cord injury (SCI) diminish intrinsic repair and neuronal regeneration. Several studies have suggested that growth factor-promoted axonal regeneration can occur for an extended period after injury. More importantly, the delivery of exogenous growth factors contained in PRP, such as EGF, IGF-1, and TGF-β, has neurotrophic effects on central nervous system (CNS) injuries and neurodegenerative diseases. However, only a few studies have investigated the effects of PRP on CNS injuries or neurodegenerative diseases. According to our review of relevant literature, no study has investigated the effect of intrathecal (i.t.) PRP injection into the injured spinal cord and activation of intrinsic mechanisms. In the present study, we directly injected i.t. PRP into rat spinal cords and examined the effects of PRP on normal and injured spinal cords. In rats with normal spinal cords, PRP induced microglia and astrocyte activation and PDGF-B and ICAM-1 expression. In rats with SCIs, i.t. PRP enhanced the locomotor recovery and spared white matter, promoted angiogenesis and neuronal regeneration, and modulated blood vessel size. Furthermore, a sustained treatment (a bolus of PRP followed by a 1/3 dose of initial PRP concentration) exerted more favorable therapeutic effects than a single dose of PRP. Our findings suggest by i.t. PRP stimulate angiogenesis, enhancing neuronal regeneration after SCI in rats. Although PRP induces minor inflammation in normal and injured spinal cords, it has many advantages. It is an autologous, biocompatible, nontoxic material that does not result in a major immune response. In addition, based on its safety and ease of preparation, we hypothesize that PRP is a promising therapeutic agent for SCI.

Targeting the vasculature to improve neural progenitor transplant survival

Neural progenitor transplantation is a promising therapeutic option for several neurological diseases and injuries. In nearly all human clinical trials and animal models that have tested this strategy, the low survival rate of progenitors after engraftment remains a significant challenge to overcome. Developing methods to improve the survival rate will reduce the number of cells required for transplant and will likely enhance functional improvements produced by the procedure. Here we briefly review the close relationship between the blood vasculature and neural progenitors in both the embryo and adult nervous system. We also discuss previous studies that have explored the role of the vasculature and hypoxic pre-conditioning in neural transplants. From these studies, we suggest that hypoxic pre-conditioning of a progenitor pool containing both neural and endothelial cells will improve engrafted transplanted neuronal survival rates.

Rewiring of regenerated axons by combining treadmill training with semaphorin3A inhibition

BACKGROUND

Rats exhibit extremely limited motor function recovery after total transection of the spinal cord (SCT). We previously reported that SM-216289, a semaphorin3A inhibitor, enhanced axon regeneration and motor function recovery in SCT adult rats. However, these effects were limited because most regenerated axons likely do not connect to the right targets. Thus, rebuilding the appropriate connections for regenerated axons may enhance recovery. In this study, we combined semaphorin3A inhibitor treatment with extensive treadmill training to determine whether combined treatment would further enhance the "rewiring" of regenerated axons. In this study, which aimed for clinical applicability, we administered a newly developed, potent semaphorin3A inhibitor, SM-345431 (Vinaxanthone), using a novel drug delivery system that enables continuous drug delivery over the period of the experiment.

RESULTS

Treatment with SM-345431 using this delivery system enhanced axon regeneration and produced significant, but limited, hindlimb motor function recovery. Although extensive treadmill training combined with SM-345431 administration did not further improve axon regeneration, hindlimb motor performance was restored, as evidenced by the significant improvement in the execution of plantar steps on a treadmill. In contrast, control SCT rats could not execute plantar steps at any point during the experimental period. Further analyses suggested that this strategy reinforced the wiring of central pattern generators in lumbar spinal circuits, which, in turn, led to enhanced motor function recovery (especially in extensor muscles).

CONCLUSIONS

This study highlights the importance of combining treatments that promote axon regeneration with specific and appropriate rehabilitations that promote rewiring for the treatment of spinal cord injury.

Segmental spinal root avulsion in the adult rat: a model to study avulsion injury pain

Road traffic accidents are the most common cause of avulsion injury, in which spinal roots are torn from the spinal cord. Patients suffer from a loss of sensorimotor function, intractable spontaneous pain, and border-zone hypersensitivity. The neuropathic pains are particularly difficult to treat because the lack of a well-established animal model of avulsion injury prevents identifying the underlying mechanisms and hinders the development of efficacious drugs. This article describes a hindlimb model of avulsion injury in adult rats where the L5 dorsal and ventral spinal root are unilaterally avulsed (spinal root avulsion [SRA]), leaving the adjacent L4 spinal root intact. SRA produced a significant ipsilateral hypersensitivity to mechanical and thermal stimulation by 5 days compared with sham-operated or naïve rats. This hypersensitivity is maintained for up to 60 days. No autotomy was observed and locomotor deficits were minimal. The hypersensitivity to peripheral stimuli could be temporarily ameliorated by administration of amitriptyline and carbamazepine, drugs that are currently prescribed to avulsion patients. Histological assessment of the L4 ganglion cells revealed no significant alterations in calcitonin gene-related peptide (CGRP), IB4, transient receptor potential cation channel subfamily V member 1 (TrpV1), or N52 staining across groups. Immunohistochemistry of the spinal cord revealed a localized glial response, phagocyte infiltration, and neuronal loss within the ipsilateral avulsed segment. A comparable response from glia and phagocytes was also found in the intact L4 spinal cord, supporting the role for central mechanisms within the L4-5 spinal cord in contributing to the generation of the pain-related behavior. The SRA model provides a platform to investigate possible new pharmacological treatments for avulsion injuries.

Noninvasive Bioluminescence Imaging of Olfactory Ensheathing Glia and Schwann Cells following Transplantation into the Lesioned Rat Spinal Cord

In this study, we assess the feasibility of bioluminescence imaging to monitor the survival of Schwann cells (SCs) and olfactory ensheathing glia cells (OECs) after implantation in the lesioned spinal cord of adult rats. To this end, purified SCs and OECs were genetically modified with lentiviral vectors encoding luciferase-2 and GFP and implanted in the lesioned dorsal column. The bioluminescent signal was monitored for over 3 months, and at 7 and 98 days postsurgery, the signal was compared to standard histological analysis of GFP expression in the spinal cords. The temporal profile of the bioluminescent signal showed three distinct phases for both cell types. (I) A relatively stable signal in the first week. (II) A progressive decline in signal strength in the second and third week. (III) After the third week, the average bioluminescent signal stabilized for both cell types. Interestingly, in the first week, the peak of the bioluminescent signal after luciferin injection was delayed when compared to later time points. Similar to in vitro, our data indicated a linear relationship between the in vivo bioluminescent signal and the GFP signal of the SCs and OECs in the spinal cords when the results of both the 7 and 98 day time points are combined. This is the first report of the use of in vivo bioluminescence to monitor cell survival in the lesioned rat spinal cord. Bioluminescence could be a potentially powerful, non-invasive strategy to examine the efficacy of treatments that aim to improve the survival of proregenerative cells transplanted in the injured rat spinal cord.

Molecular and cellular mechanisms underlying the role of blood vessels in spinal cord injury and repair

Spinal cord injury causes immediate damage of nervous tissue accompanied by the loss of motor and sensory function. The limited self-repair ability of damaged nervous tissue underlies the need for reparative interventions to restore function after spinal cord injury. Blood vessels play a crucial role in spinal cord injury and repair. Injury-induced loss of local blood vessels and a compromised blood-brain barrier contribute to inflammation and ischemia and thus to the overall damage to the nervous tissue of the spinal cord. Lack of vasculature and leaking blood vessels impede endogenous tissue repair and limit prospective repair approaches. A reduction of blood vessel loss and the restoration of blood vessels so that they no longer leak might support recovery from spinal cord injury. The promotion of new blood vessel formation (i.e., angio- and vasculogenesis) might aid repair but also incorporates the danger of exacerbating tissue loss and thus functional impairment. The delicate interplay between cells and molecules that govern blood vessel repair and formation determines the extent of damage and the success of reparative interventions. This review deals with the cellular and molecular mechanisms underlying the role of blood vessels in spinal cord injury and repair.

The challenges of long-distance axon regeneration in the injured CNS

Injury to the central nervous system (CNS) that results in long-tract axonal damage typically leads to permanent functional deficits in areas innervated at, and below, the level of the lesion. The initial ischemia, inflammation, and neurodegeneration are followed by a progressive generation of scar tissue, dieback of transected axons, and demyelination, creating an area inhibitory to regrowth and recovery. Two ways to combat this inhibition is to therapeutically target the extrinsic and intrinsic properties of the axon-scar environment. Scar tissue within and surrounding the lesion site can be broken down using an enzyme known as chondroitinase. Negative regulators of adult neuronal growth, such as Nogo, can be neutralized with antibodies. Both therapies greatly improve functional recovery in animal models. Alternatively, modifying the intrinsic growth properties of CNS neurons through gene therapy or pharmacotherapy has also shown promising axonal regeneration after injury. Despite these promising therapies, the main challenge of long-distance axon regeneration still remains; achieving a level of functional and organized connectivity below the level of the lesion that mimics the intact CNS.

Adipose tissue and bone marrow-derived stem cells react similarly in an ischaemia-like microenvironment

Mesenchymal stem cells (MSCs) from adipose tissue and bone marrow are promising cell sources for autologous cell therapy of nerve injuries, as demonstrated by their intrinsic neurotrophic potential. However, extensive death of transplanted cells limits their full benefits. This study investigated the effects of ischaemia (metabolically induced by sodium azide and 2-deoxyglucose) and serum-derived mitogens on the viability and functional profile of MSCs in vitro. MSCs were more susceptible to combined, rather than individual, blockade of glycolysis and oxidative phosphorylation. Apoptosis and autophagy were involved in ischaemia-induced cell death. Chemical ischaemia alone and serum withdrawal alone induced a similar amount of cell death, with significantly different intracellular ATP maintenance. Combined ischaemia and serum deprivation had additive effects on cell death. Expression of the extracellular matrix (ECM) molecules laminin and fibronectin was attenuated under ischaemia and independent of serum level; however, BDNF and NGF levels remained relatively constant. Strong upregulation of VEGF and to a lesser extent angiopoietin-1 was observed under ischaemia but not in serum withdrawal conditions. Importantly, this study demonstrated similar reactions of MSCs derived from adipose and bone marrow tissue, in ischaemia-like and mitogen-deprived microenvironments in terms of viability, cellular energetics, cell death mechanisms and expression levels of various growth-promoting molecules. Also, the results suggest that ischaemia has a larger impact on the ability of MSCs to survive transplantation than withdrawal of mitogens.

Bone marrow mesenchymal stem cells in a three-dimensional gelatin sponge scaffold attenuate inflammation, promote angiogenesis, and reduce cavity formation in experimental spinal cord injury

Three-dimensional (3D) gelatin sponge (GS) scaffolds were constructed by ensheathing GS with a thin film of poly-(lactide-co-glycolide) (PLGA). Rat bone marrow-derived mesenchymal stem cells (MSCs) were isolated, cultured, and then seeded to the scaffolds. Distribution of cells and cell growth, survival, and proliferation within the scaffolds were then determined. Immunofluorescence and Western blot analysis were employed to detect the deposition of fibronectin to the scaffolds on day 3 and day 7 of culture. Scaffolds with or without MSCs were then transplanted into the transected rat spinal cord. One or 8 weeks following transplantation, cavity areas, activated macrophages/microglia, expression of TNF-α and IL-1β, and neovascularization within the grafts were examined and quantified. Deposition of fibronectin (FN) and expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) as potential inducing factors for angiogenesis were also examined. Results showed that 3D GS scaffolds allowed MSCs to adhere, survive, and proliferate and also FN to deposit. In vivo transplantation experiments demonstrated that these scaffolds were biocompatible, and MSCs seeded to the scaffolds played an important role in attenuating inflammation, promoting angiogenesis, and reducing cavity formation. Therefore, the GS scaffolds with MSCs may serve as promising supporting transplants for repairing spinal cord injury.

Spinal cord - MR of rodent models

Different MR techniques, such as relaxation times, diffusion, perfusion, and spectroscopy have been employed to study rodent spinal cord. In this chapter, a description of these methods is given, along with examples of normal metrics that can be derived from the MR acquisitions, as well as examples of applications to pathology.

Neutralizing endogenous VEGF following traumatic spinal cord injury modulates microvascular plasticity but not tissue sparing or functional recovery

Acute loss of spinal cord vascularity followed by an endogenous adaptive angiogenic response with concomitant microvascular dysfunction is a hallmark of traumatic spinal cord injury (SCI). Recently, the potent vasoactive factor vascular endothelial growth factor (VEGF) has received much attention as a putative therapeutic for the treatment of various neurodegenerative disorders, including SCI. Exogenous VEGF exerts both protective and destabilizing effects on microvascular elements and tissue following SCI but the role of endogenous VEGF is unclear. In the present study, we systemically applied a potent and well characterized soluble VEGF antagonist to adult C57Bl/6 mice post-SCI to elucidate the relative contribution of VEGF on the acute evolving microvascular response and its impact on functional recovery. While the VEGF Trap did not alter vascular density in the injury epicenter or penumbra, an overall increase in the number of Griffonia simplicifolia isolectin-B4 bound microvessels was observed, suggesting a VEGF-dependency to more subtle aspects of endothelial plasticity post-SCI. Neutralizing endogenous VEGF neither attenuated nor exacerbated chronic histopathology or functional recovery. These results support the idea that overall, endogenous VEGF is not neuroprotective or detrimental following traumatic SCI. Furthermore, they suggest that angiogenesis in traumatically injured spinal tissue is regulated by multiple effectors and is not limited by endogenous VEGF activation of affected spinal microvessels.

Quantitative analysis by in vivo imaging of the dynamics of vascular and axonal networks in injured mouse spinal cord

Understanding the endogenous repair capacity of spinal cord is pivotal to develop strategies to improve it. Here we design a paradigm of spinal cord lesion in the dorsal column using a 2-photon microscopy technique to dynamically and chronically monitor simultaneous changes of vascular and axonal networks in living mice up to 4 months postinjury. High-resolution images showed that early explorative sprouting of surviving injured axons resulted in extensive regrowth until and past the lesion site within 2 months. Blood vessel density was transiently up-regulated and most neurovascular interactions occurred within 2 weeks. Time-lapse analysis showed that neovessels exerted a potent growth stimulating action, but no guidance effect on neighboring sprouts, possibly because of their geometry and plasticity. Nevertheless, if reconnection depends on axon sprout density, stimulation of angiogenesis would probably be beneficial to repair. More generally, this imaging approach is showing promise to aid in monitoring brain diseases and the efficacy of potential treatments.

Engineering angiogenesis following spinal cord injury: a coculture of neural progenitor and endothelial cells in a degradable polymer implant leads to an increase in vessel density and formation of the blood-spinal cord barrier

Angiogenesis precedes recovery following spinal cord injury and its extent correlates with neural regeneration, suggesting that angiogenesis may play a role in repair. An important precondition for studying the role of angiogenesis is the ability to induce it in a controlled manner. Previously, we showed that a coculture of endothelial cells (ECs) and neural progenitor cells (NPCs) promoted the formation of stable tubes in vitro and stable, functional vascular networks in vivo in a subcutaneous model. We sought to test whether a similar coculture would lead to the formation of stable functional vessels in the spinal cord following injury. We created microvascular networks in a biodegradable two-component implant system and tested the ability of the coculture or controls (lesion control, implant alone, implant + ECs or implant + NPCs) to promote angiogenesis in a rat hemisection model of spinal cord injury. The coculture implant led to a fourfold increase in functional vessels compared with the lesion control, implant alone or implant + NPCs groups and a twofold increase in functional vessels over the implant + ECs group. Furthermore, half of the vessels in the coculture implant exhibited positive staining for the endothelial barrier antigen, a marker for the formation of the blood-spinal cord barrier. No other groups have shown positive staining for the blood-spinal cord barrier in the injury epicenter. This work provides a novel method to induce angiogenesis following spinal cord injury and a foundation for studying its role in repair.

Acute changes of nidogen immunoreactivity in the basal lamina of the spinal cord vessels following dorsal hemisection without correlative changes of nidogen gene expression

Previous studies have revealed that the immunoreactivities of basal lamina components in the central nervous system (CNS) vasculature change after lesions. The purpose of the present study was to determine the acute response of nidogen immunoreactivity (Nd-ir) in blood vessels of the spinal cord following a dorsal hemisection. Nd-ir immunoreactivity in the vascular basal lamina was dramatically increased within 24 h of injury, and returned to basal level after 1 week. This temporal profile of the Nd-ir change was almost the same as that of laminin. However, reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis revealed that there was no significant increase in nidogen expression after the injury. These findings indicate that changes of antibody accessibility or epitope structure, but not a change in the expression of nidogen, may be responsible for the temporal change of Nd-ir in blood vessels following the spinal cord lesion.

Spinal cord injury-induced expression of the antiangiogenic endostatin/collagen XVIII in areas of vascular remodelling

OBJECT

Spinal cord injury (SCI) induces the disruption of neural and vascular structures. In contrast to the emerging knowledge of mechanisms regulating the onset of the postinjury angiogenic response, little is known about counterregulatory signals.

METHODS

Using immunohistochemical methods, the authors investigated the expression of the endogenous angiogenic inhibitor endostatin/collagen XVIII during the tissue remodeling response to SCI.

RESULTS

After SCI, endostatin/collagen XVIII+ cells accumulated at the lesion site, in pannecrotic regions (especially in areas of cavity formation), at the lesion margin/areas of ongoing secondary damage, and in perivascular Virchow-Robin spaces. In remote areas (> 0.75 cm from the epicenter) a more modest accumulation of endostatin/collagen XVIII+ cells was observed, especially in areas of pronounced Wallerian degeneration. The numbers of endostatin/collagen XVIII+ cells reached their maximum on Day 7 after SCI. The cell numbers remained elevated in both, the lesion and remote regions, compared with control spinal cords for 4 weeks afterwards. In addition to being predominantly confined to ED1+-activated microglia/macrophages within the pannecrotic lesion core, endostatin/collagen XVIII expression was frequently detected by the endothelium/vessel walls. Numbers of lesional endostatin/collagen XVIII+ endothelium/vessel walls were found to increase early by Day 1 postinjury, reaching their maximum on Day 3 and declining subsequently to enhanced (above control) levels 30 days after SCI.

CONCLUSIONS

The authors detected that in comparison to the early expression of neoangiogenic factors, there was a postponed lesional expression of the antiangiogenic endostatin/collagen XVIII. Furthermore, the expression of endostatin/collagen XVIII was localized to areas of neovascular pruning and retraction (cavity formation). The expression of endostatin/collagen XVIII by macrophages in a "late" activated phagocytic mode suggests that this factor plays a role in counteracting the preceding "early" neoangiogenic response after SCI.

Neuroprotective Effect of Bone Marrow–Derived Mononuclear Cells Promoting Functional Recovery from Spinal Cord Injury

Neural cell transplantation, a new therapeutic strategy for replacing injured neural components and obtaining functional recovery, has shown beneficial effects in animal models. Use of this strategy in human patients, however, requires that a number of serious issues be addressed, including ethics, immunorejection, and the therapeutic time window within which the procedure will be effective. Bone marrow-derived mononuclear cells (BM-MNC) are attractive for transplantation because they can be used as an autograft, can be easily collected within a short time period, and do not have to be cultured. In a rat model of spinal cord injury (SCI), we transplanted BM-MNC at 1 h after SCI at Th 8-9 by injecting them into the cerebrospinal fluid (CSF), and investigated the effect of this on neurologic function. In the acute stage of injury, we found a neuroprotective antiapoptotic effect, with an elevated concentration of hepatocyte growth factor in CSF. At 1 week after transplantation, the Basso-Beattie-Bresnahan locomotor score had increased significantly over its base-line value. In the chronic stage of injury, we observed suppressed cavity formation and functional improvement. We conclude that transplantation of BM-MNC after SCI has a remarkable neuroprotective effect in the acute stage of injury, suppressing cavity formation, and contributing to functional recovery. Our results suggest that transplantation of BM-MNC via the CSF is a potentially effective means of enhancing functional recovery after SCI in humans.

Developmental and injury-induced expression of alpha1beta1 and alpha6beta1 integrins in the rat spinal cord

Loss and damage to blood vessels are thought to contribute to secondary tissue loss after spinal cord injury. Integrins might be therapeutic targets to protect the vasculature and/or promote angiogenesis, as their activation can promote tubule formation and survival of endothelial cells in vitro. Here, we show that immunostaining with an antibody against the alpha1beta1 integrin heterodimer is present only in blood vessels from postnatal day 1 (P1) through adulthood in Sprague-Dawley rats. After a spinal cord contusion at T9 in adults, the area of alpha1beta1 integrin positive blood vessels increases within 11 mm from the injury site at 3 days post-injury and remains prominent within the injured core only at 7 days. Staining for the alpha6beta1 integrin heterodimer increases in blood vessels between P10 and adulthood and is present in preganglionic neurons of the intermediolateral cell column (IML) at all ages. The alpha6beta1 integrin is also expressed by motor neurons postnatally, and oligodendrocyte precursors (OPCs), as previously reported. After the contusion, the area of alpha6beta1-stained blood vessels is increased at 3 days and most prominently, 1 mm from the injury site, followed by a significant reduction at 7 days, when alpha6beta1 integrin staining is most prominent around the injured core. Staining is also present in a subset of microglia and/or macrophages. These results raise the possibility that alpha1beta1 and alpha6beta1 integrins in blood vessels might be targeted to reduce blood vessel loss and promote angiogenesis, which may promote tissue sparing after spinal cord injury.

EphA4 regulates central nervous system vascular formation

Molecules involved in axon guidance have recently also been shown to play a role in blood vessel guidance. To examine whether axon guidance molecules, such as the EphA4 receptor tyrosine kinase, might also play a role in development of the central nervous system (CNS) vasculature and repair following CNS injury, we examined wild-type and EphA4 null mutant (-/-) mice. EphA4-/- mice exhibited an abnormal CNS vascular structure in both the cerebral cortex and the spinal cord, with disorganized branching and a 30% smaller diameter. During development, EphA4 was expressed on endothelial cells. This pattern of expression was not maintained in the adult. After spinal cord injury in wild-type mice, expression of EphA4 was markedly up-regulated on activated astrocytes, many of which were tightly associated with blood vessels. In EphA4-/- spinal cord following injury, astrocytes were not as tightly associated with blood vessels as the wild-type astrocytes. In uninjured EphA4-/- mice, the blood-brain barrier (BBB) appeared normal, but it showed prolonged leakage following spinal cord injury. These results support a role for EphA4 in CNS vascular formation and guidance during development and an additional role in BBB repair.

Dural repair reduces connective tissue scar invasion and cystic cavity formation after acute spinal cord laceration injury in adult rats

This study examined whether duraplasty after acute cervical laceration spinal cord injury (SCI) in a rat model could (1) improve cerebrospinal fluid (CSF) circulation adjacent to the injury; (2) minimize connective tissue scarring; and (3) reduce post-traumatic inflammation and cystic cavitation. Following a transverse dural/arachnoid incision and C5-6 dorsal spinal hemisection, a 5-mm2 cadaveric dura mater allograft was placed over the lesion and fixed with fibrin glue (n=12). Control animals received an identical dural/arachnoid incision and cervical dorsal hemisection without dural repair (n=12). At 1, 5, and 10 weeks post-injury, plain film myelograms were obtained to characterize CSF circulation, and stereological methods were used to compare the extent of tissue sparing between the two groups. Immunohistochemical studies were performed to assess the degree of inflammation (ED-1), connective tissue scarring (laminin and type IV collagen), and reactive astrogliosis (GFAP). Our results indicate that dural allograft can improve CSF flow adjacent to the site of injury, which may be due to reduced meningeal fibrosis/scarring at the lesion site. Stereological analysis demonstrated that duraplasty resulted in a significant reduction in lesion volume at each time-point (p<0.01) associated with a nearly complete attenuation of post-traumatic cystic cavitation (p<0.001). Immunofluorescence studies demonstrated that duraplasty reduced the infiltration of ED-1-positive macrophages/microglia into and surrounding the lesion site, which may be responsible for the marked reduction in secondary injury following duraplasty. We conclude that duraplasty following acute spinal cord laceration may (1) improve CSF flow by limiting meningeal fibrosis; (2) reduce connective tissue scar formation; and (3) attenuate macrophage accumulation and progressive secondary injury.

Inhibition of vascular endothelial growth factor receptor 2 activity in experimental brain contusions aggravates injury outcome and leads to early increased neuronal and glial degeneration

Angiogenesis following traumatic brain injuries (TBIs) may be of importance for post-traumatic reparative processes and the development of secondary injuries. We have previously shown expression of vascular endothelial growth factor (VEGF), a major regulator of endothelial cell proliferation, angiogenesis and vascular permeability, and VEGF receptors (VEGFR1 and 2) after TBI in rat. In the present work we tried to further elucidate the role of VEGF after TBI by performing specific VEGFR2 activity inhibition. In rats subjected to VEGFR2 blockage we report an increased haemorrhagic area (P < 0.05), early increase in serum levels of neural injury marker neuron-specific enolase (P < 0.05) and glial injury marker S100beta (P < 0.05), and increased numbers of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labelling- (TUNEL-) and FluoroJade B- (P < 0.05) positive cells, all increases preceding the known VEGF/VEGFR vascular response in brain trauma. An increase in lesion area, as measured by decreased microtubuli-associated protein 2 expression (P < 0.05) and increased glial fibrillary acidic protein reactivity (P < 0.05), could also be demonstrated. In addition, vascular density, as measured by von Willebrandt factor-positive cells, was decreased (P < 0.05). No differences in post-traumatic inflammatory response, as measured by stainings for macrophages, granulocytes and intracellular adhesion molecules, were shown between the groups. Taken together, our findings point towards VEGF/VEGFR2 up-regulation after TBI as being an important endogenous cytoprotective mechanism in TBI. The possible importance of VEGF on the vascular, neuronal and glial compartments of the neurovascular unit after TBI is discussed.

Neuroprotective action of hypothalamic peptide PRP-1 at various time survivals following spinal cord hemisection

The purpose of the present study was to evaluate the neuroprotective action of proline-rich peptide-1 (PRP-1) produced by hypothalamic nuclei cells (nuclei paraventricularis and supraopticus) following lateral hemisection of spinal cord (SC). The dynamics of rehabilitative shifts were investigated at various periods of postoperative survival (1-2, 3, and 4 weeks), both with administration of PRP-1 and without it (control). We registered evoked spike flow activity in both interneurons and motoneurons of the same segment of transected and symmetric intact sides of SC and below it on the stimulation of mixed (n. ischiadicus), flexor (n. gastrocnemius) and extensor (n. peroneus communis) nerves. In the control group (administration of 0.9% saline as placebo), no significant decrease of post-stimulus activity of neurons was observed on the transected side by the 2nd week. This activity strongly decreased by week 3 postaxotomy, with some increase on the intact side, possibly of compensatory origin. No shifts occurred by the 4th week. Regardless of the period of administration, PRP-1 increased neuronal activity on the transected side, with the same activation levels on both SC sides. These data were confirmed by histochemical investigation. PRP-1 administration, both daily and every other day, for a period of 2-3 weeks led to prevention of scar formation and promotion of the re-growth of white matter nerve fibers in the damaged area. It also resulted in prevention of neuroglial elements degeneration and reduction in gliosis expression in the lesion supporting neuronal survival. Thus, PRP-1 achieved protection against "tissue stress", which was also confirmed by the registration of activity on the level of transection and restoration of the motor activity on the injured side. The obtained data propose the possibility of PRP-1 application in clinical practice for prevention of neurodegeneration of traumatic origin.

VEGF and VEGF receptor expression after experimental brain contusion in rat

Angiogenesis following traumatic brain injury (TBI) may be of importance not only for post-traumatic reparative processes but also for the development of secondary injuries. Vascular endothelial growth factor (VEGF) is a major regulator of endothelial cell proliferation, angiogenesis, and vascular permeability, though its possible involvement in secondary injuries after TBI is largely unknown. This study was undertaken to analyze the expression of VEGF and the VEGF receptors in experimental brain contusion in rat. Twenty-three adult female Sprague-Dawley rats were subjected to a focal cerebral contusion injury by use of a weight-drop model. Four additional rats underwent craniotomy only. The animals were sacrificed 6 h, or 1, 2, 4, 6, 8, or 16 days post-injury. Expression of VEGF and the VEGF receptors VEGFR1 (Flt-1) and VEGFR2 (Flk-1) were studied by in situ hybridization and immunohistochemistry. VEGF messenger (m)RNA and protein expression were detected in astrocytes, neutrophils, and macrophages in or adjacent to the injury from 1 day after injury, with a peak expression after 4-6 days. Flt-1 and Flk-1 mRNA and protein were detected in vessels adjacent to the lesion from 1 day after injury throughout day 6 after injury. It was also noted that Flt-1/Flk-1 and VEGF-positive vessels often were negative for SMI-71, a marker for vessels in areas with blood-brain barrier (BBB). In conclusion, we have demonstrated that TBI leads to an upregulation of VEGF, Flt-1, and Flk-1 mRNA and protein in and around the lesion. The data provide a foundation for future pharmacological intervention studies focusing on posttraumatic angiogenesis and possible injury repair effects of the VEGF system in TBI.

Spinal cord injury induction of lesional expression of profibrotic and angiogenic connective tissue growth factor confined to reactive astrocytes, invading fibroblasts and endothelial cells

OBJECT

The glial scar composed of astrogliosis and extracellular matrix deposition represents a major impediment to axonal regeneration. The authors investigated the role of a novel profibrotic and angiogenic peptide connective tissue growth factor (CTGF [Hcs24/IGFBP-r2P]) in glial scar formation following spinal cord injury (SCI) in rats.

METHODS

The effects of SCI on CTGF expression during glial scar maturation 1 day to 1 month post-SCI were investigated using fluorescein-activated cell sorter (FACS) immunohistochemical analysis; these findings were compared with those obtained in sham-operated (control) spinal cords. The CTGF-positive cells accumulated at the spinal cord lesion site (p < 0.0001) corresponding to areas of glial scar formation. In the perilesional rim, CTGF expression was confined to invading vimentin-positive, glial fibrillary acidic protein (GFAP)-negative fibroblastoid cells, endothelial and smooth-muscle cells of laminin-positive vessels, and GFAP-positive reactive astrocytes. The CTGF-positive astrocytes coexpressed the activation-associated intermediate filaments nestin, vimentin (> 80%), and mesenchymal scar component fibronectin (50%).

CONCLUSIONS

The restricted accumulation of CTGF-reactive astrocytes and CTGF-positive fibroblastoid cells lining the laminin-positive basal neolamina suggests participation of these cells in scar formation. In addition, perilesional upregulation of endothelial and smooth-muscle CTGF expression points to a role in blood-brain barrier function modulating edema-induced secondary damage.

Endogenous recovery of injured spinal cord: longitudinal in vivo magnetic resonance imaging

Pathological changes were followed longitudinally with in vivo magnetic resonance imaging (MRI) and behavioral studies in experimental spinal cord injury (SCI). MRI-observed pathology was correlated with histology. On MRI, the cavitated regions of the injured cord were gradually filled with viable tissue between two and 8 weeks postinjury, and a concomitant improvement was observed in the neurobehavioral scores. By weeks 3-6, on MRI, the gray matter (GM) returned in the segments caudal, but not rostral, to the injury site. The corresponding histological sections revealed motor neurons as well as other nuclei in the gray matter immediately caudal to the epicenter, but not at the site of injury, suggesting neuronal recovery in perilesioned areas. The neuronal and neurological recovery appeared to occur about the same time as neovasculature that was reported on the contrast-enhanced MRI, suggesting a role for angiogenesis in recovery from SCI. The role of angiogenesis in neuronal recovery is further supported by the immunohistochemical observation of greater bromodeoxyuridine uptake by blood vessels near the lesion site compared with uninjured cords.

Freeze-dried poly(d,l-lactic acid) macroporous guidance scaffolds impregnated with brain-derived neurotrophic factor in the transected adult rat thoracic spinal cord

The effects of poly(D,L-lactic acid) macroporous guidance scaffolds (foams) with or without brain-derived neurotrophic factor (BDNF) on tissue sparing, neuronal survival, axonal regeneration, and behavioral improvements of the hindlimbs following implantation in the transected adult rat thoracic spinal cord were studied. The foams were embedded in fibrin glue containing acidic-fibroblast growth factor. One group of animals received fibrin glue with acidic-fibroblast growth factor only. The foams were prepared by a thermally induced polymer-solvent phase separation process and contained longitudinally oriented macropores connected to each other by a network of micropores. Both foams and fibrin only resulted in a similar gliotic and inflammatory response in the cord-implant interfaces. With BDNF foam, up to 20% more NeuN-positive cells in the spinal nervous tissue close to the rostral but not caudal spinal cord-implant interface survived than with control foam or fibrin only at 4 and 8 weeks after implantation. Semithin plastic sections and electron microcopy revealed that cells and axons more rapidly invaded BDNF foam than control foam. Also, BDNF foam contained almost twice as many blood vessels than control foam at 8 weeks after implantation. Tissue sparing was similar in all three implantation paradigms; approximately 42% of tissue was spared in the rostral cord and approximately 37% in the caudal cord at 8 weeks post grafting. The number of myelinated and unmyelinated axons was low and not different between the two types of foams. Many more axons were found in the fibrin only graft. Serotonergic axons were not found in any of the implants and none of the axons regenerated into the caudal spinal cord. The behavioral improvements in the hindlimbs were similar in all groups. These findings indicated that foam is well tolerated within the injured spinal cord and that the addition of BDNF promotes cell survival and angiogenesis. However, the overall axonal regeneration response is low. Future research should explore the use of poly(D,L-lactic acid) foams, with or without axonal growth-promoting factors, seeded with Schwann cells to enhance the axonal regeneration and myelination response.

Prevention of gliotic scar formation by NeuroGel? allows partial endogenous repair of transected cat spinal cord

Spinal cords of adult cats were transected and subsequently reconnected with the biocompatible porous poly (N-[2-hydroxypropyl] methacrylamide) hydrogel, NeuroGel. Tissue repair was examined at various time points from 6-21 months post reconstructive surgery. We examined two typical phenomena, astrogliosis and scar formation, in spines reconstructed with the gel and compared them to those from transected non-reconstructed spines. Confocal examination with double immunostaining for glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) showed that the interface formed between the hydrogel and the spine stumps did prevent scar formation and only a moderate gliosis was observed. The gel implant provided an adequate environment for growth of myelinated fibers and we saw angiogenesis within the gel. Electron microscopy showed that regenerating axons were myelinated by Schwann cells rather than oligodendrocytes. Moreover, the presence of the gel implant lead to a considerable reduction in damage to distal caudal portions of the spine as assessed by the presence of more intact myelinated fibers and a reduction of myelin degradation. Neurologic assessments of hindlimb movement at various times confirmed that spinal cord reconstruction was not only structural but also functional. We conclude that NeuroGel lead to functional recovery by providing a favorable substrate for regeneration of transected spinal cord, reducing glial scar formation and allowing angiogenesis.

VEGF165 therapy exacerbates secondary damage following spinal cord injury

Vascular endothelial growth factor (VEGF) demonstrates potent and well-characterized effects on endothelial cytoprotection and angiogenesis. In an attempt to preserve spinal microvasculature and prolong the endogenous neovascular response observed transiently following experimental spinal cord injury (SCI), exogenous recombinant human VEGF (rhVEGF165) was injected into the injured rat spinal cord. Adult female Fischer 344 rats were subjected to moderate SCI (12.5 g-cm) using the NYU impactor. At 72 h after injury, animals were randomly assigned to three experimental groups receiving no microinjection or injection of saline or saline containing 2 microg of rhVEGF165. Acutely, VEGF injection resulted in significant microvascular permeability and infiltration of leukocytes into spinal cord parenchyma. 6 weeks postinjection, no significant differences were observed in most measures of microvascular architecture following VEGF treatment, but analysis of histopathology in spinal cord tissue revealed profound exacerbation of lesion volume. These results support the idea that intraparenchymal application of the proangiogenic factor VEGF may exacerbate SCI, likely through its effect on vessel permeability.

Spinal cord injury induces lesional expression of the proinflammatory and antiangiogenic cytokine EMAP II

Inflammatory cellular responses to spinal cord injury are promoted by proinflammatory messengers. We have analyzed expression of endothelial monocyte activating polypeptide II (EMAP II), a proinflammatory, antiangiogenic cytokine in rats after spinal cord injury (SCI) in comparison to normal rat spinal cords. Immunohistochemical analysis demonstrated a highly significant (p < 0.0001) accumulation of EMAP II(+) microglia/macrophages at the lesion site compared to remote areas and uninjured controls. After peaking at day 3, EMAP II(+) microglia/macrophage cell numbers declined gradually until day 28 after SCI-but still remained elevated. Further, EMAP II(+) cells formed clusters in perivascular Virchow-Robin spaces reaching a maximum at day 3. Prolonged accumulation of EMAP II(+), ED1(+) microglia/macrophages suggest a role of EMAP II in the pathophysiology of secondary injury following SCI.

Ephrin-B2 and EphB2 regulation of astrocyte-meningeal fibroblast interactions in response to spinal cord lesions in adult rats

The present study provides the first evidence that signaling occurs between B-ephrins and EphB receptors in the adult CNS in response to injury. Specifically, our combined histological and biochemical data indicate that two members of the B-class of ephrins and Eph receptors, ephrin-B2 and EphB2, are expressed by astrocytes and meningeal fibroblasts, respectively, in the adult spinal cord. In response to thoracic spinal cord transection lesions, ephrin-B2 and EphB2 protein levels exhibit an initial decrease (1 d after lesion), followed by a significant increase by day 14. Immunohistochemical data indicate that ephrin-B2 is expressed by reactive CNS astrocytes, and EphB2 is present on fibroblasts invading the lesion site from the adjacent meninges. During the first 3 d after injury, there is intermingling of ephrin-B2-expressing reactive astrocytes at the lesion surface with EphB2-containing fibroblasts that is concurrent with bidirectional activation (phosphorylation) of ephrin-B2 and EphB2. By 7 d, both cell types are establishing restricted cellular domains containing dense networks of cells and interweaving processes. This astroglial-meningeal fibroblast scar is fully developed by day 14 when there is strict segregation of ephrin-B2-expressing astrocytes from EphB2-positive meningeal fibroblasts. These morphological changes are concomitant with a simultaneous decrease in ephrin-B2 and EphB2 activation. These observations provide strong evidence that cell contact-mediated bidirectional signaling between ephrin-B2 on reactive astrocytes and EphB2 on meningeal fibroblasts is an early event in the cellular cascades that result in the development of the glial scar and the exclusion of meningeal fibroblasts from the injured spinal cord.

Neuropilin and class 3 semaphorins in nervous system regeneration

Injury to the mature mammalian central nervous system (CNS) is often accompanied by permanent loss of function of the damaged neural circuits. The failure of injured CNS axons to regenerate is thought to be caused, in part, by neurite outgrowth inhibitory factors expressed in and around the lesion. These include several myelin associated inhibitors, proteoglycans, and tenascin-R. Recent studies have documented the presence of class 3 semaphorins in fibroblast-like meningeal cells present in the core of the neural scar formed following CNS injury. Class 3 semaphorins display neurite growth-inhibitory effects on growing axons during embryonic development. The induction of the expression of class 3 semaphorins in the neural scar and the persistent expression of their receptors, the neuropilins and plexins, by injured CNS neurons suggest that they contribute to the regenerative failure of CNS neurons. Neuropilins are also expressed in the neural scar in a subpopulation of meningeal fibroblast and in neurons in the vicinity of the scar. Semaphorin/neuropilin signaling might therefore also be important for cell migration, angiogenis and neuronal cell death in or around neural scars. In contrast to neurons in the CNS, neuropilin/plexin positive neurons in the PNS do display long distance regeneration following injury. Injured PNS neurons do not encounter a semaphorin positive neural scar. Furthermore, Semaphorin 3A is downregulated in the regenerating spinal motor neurons themselves. This was accompanied by a transient upregulation of Semaphorin 3A in the target muscle. These observations suggest that the injury induced regulation of Semaphorin 3A in the PNS contributes to successful regeneration and target reinnervation. Future studies in genetically modified mice should provide more insight into the mechanisms by which neuropilins and semaphorins influence nervous system regeneration and degeneration.

Lesional expression of a proinflammatory and antiangiogenic cytokine EMAP II confined to endothelium and microglia/macrophages during secondary damage following experimental traumatic brain injury

We analyzed expression of Endothelial Monocyte-Activating Polypeptide II (EMAP II), a proinflammatory, antiangiogenic cytokine in rat brains after stab wound injury and observed a highly significant (p<0.0001) lesional accumulation confined to microglia/macrophages. Maximum numbers were seen at day 5 declining until 21 days after injury. Further, EMAP II(+) microglia/macrophages formed clusters in perivascular Virchow-Robin spaces. Prolonged accumulation of EMAP II(+), ED1(+) microglia/macrophages and increased lesional numbers of EMAP II(+) endothelial/smooth muscle cells during the acute postinjury period might indicate that EMAP II enrich the proinflammatory and antiangiogenic repertoire of effector molecules expressed by activated microglia/macrophages during secondary damage.

Promotion of regeneration of corticospinal tract axons in rats with recombinant vascular endothelial growth factor alone and combined with adenovirus coding for this factor

OBJECT

After spinal cord transection in adult rats, the axons of the corticospinal tract (CST) degenerate retrogradely and do not regenerate. This phenomenon is thought to be related to either secondary ischemia or deficiency of growth factors. To overcome the deficiency of both blood flow and growth factors, the authors added exogenous vascular endothelial growth factor (VEGF165) to the transected spinal cord either as recombinant protein alone or combined with an adenovirus coding for VEGF165. Because most growth factors are rapidly inactivated in the extracellular environment, the authors used an adenovirus coding for VEGF165 to maintain its activity for several days.

METHODS

In adult rats, the dorsal two thirds of the spinal cord were transected at the T-8 level. In experimental rats, either human recombinant VEGF165 or a combination of this factor and a replication-defective adenovirus coding for VEGF165 (Ad.CMV.VEGF165) was applied at the lesion site. Both recombinant VEGF165 alone and combined with Ad.CMV.VEGF165 were mixed with Matrigel, which is a reconstituted membrane basement protein extract. Control rats received Matrigel alone or Matrigel plus an adenoviral vector containing the LACZ gene (Ad.CMV.LACZ). Thirty days after spinal cord injury, the number of newly formed blood vessels was assessed in the injured area. In addition, the sensorimotor cortex was injected with anterogradely transported horseradish peroxidase (HRP) to label the CST axons in the spinal cord and to evaluate the extent of retrograde axonal degeneration and regeneration. Gene transfer was assessed using semiquantitative reverse transcription-polymerase chain reaction analysis, enzyme-linked immunosorbent assay for human VEGF and beta-galactosidase expression in injured rats treated with Matrigel plus Ad.CMV.LACZ, Matrigel plus Ad.CMV.VEGF165, and untreated injured rats. A strong gene transfer in the spinal cord tissue of adenovirus-treated rats was found from Day 3 to Day 10 postinjury, confirming infection. In the injured spinal cord area, a significant increase of blood vessels (300% over control, p < 0.005) occurred both in rats treated with recombinant VEGF165 alone and in those treated with the combination of recombinant VEGF165 and Ad.CMV.VEGF165. Also, in both of these groups of animals the retrograde degeneration of CST axons was significantly reduced compared with rats treated with Matrigel alone or Matrigel plus Ad.CMV.LACZ. Furthermore, in rats treated with recombinant VEGF165 alone or combined with Ad.CMV.VEGF165, a few HRP-labeled CST axons, which were not detectable in control rats, were seen distal to the spinal cord injury, indicating some regeneration across the injured area.

CONCLUSIONS

These results indicate that locally applied VEGF exerts angiogenic as well as neurotrophic effects in the injured spinal cord of rats.

Experimental models of partial lesion of rat spinal cord to investigate neurodegeneration, glial activation, and behavior impairments

The article demonstrates two experimental models of spinal cord partial injury in rats: a contuse model promoted by the NYU impactor system and a partial hemitransection model achieved by a stereotaxic-positioned adjustable wire knife. By means of a defined impact weight (10 g) and a digital optical potentiometer linked to a computer, the impactor transferred and registered a moderate or a severe contusion to the rat spinal cord at a low thoracic level after dropping the weight from distances of 25 mm and 50 mm, respectively, to the dorsal surface of the exposed dura spinal cord. Impact curve was calculated and the parameters of the trauma, like impact velocity, cord compression distance and cord compression rates were obtained in order to demonstrate trauma severity. To promote partial hemitransection, rats were positioned in a spinal cord unit of a stereotaxic apparatus and lesion was made with the adjustable wire knife spatially oriented. By means of a computerized infrared motion sensor-home cage activity monitor and a noncomputerized evaluation of motor behavior using the inclined plane and the motor score of Tarlov tests, behavior was analyzed in an acute period postlesion. Rats were sacrificed and spinal cords were processed for routine staining to show neurons and for GFAP and OX42 immunohistochemistry to demonstrate glial cells. The tissue labelings were quantified using computer assisted stereology by means of an optical disector and microdensitometric image analysis by means of quantification of gray values of discriminated profiles. While partial hemitransection model favored a more accurate control of the lesion location, the contuse model allowed us to perform different degrees of lesion severity. A close correlation between behavioral impairment and severity of trauma was seen in the rats submitted to spinal cord contusion. The stereologic lesion index showed a correlation between severity of trauma and tissue damage by 7 days and demonstrated a time-dependent secondary degeneration after moderate but not after severe spinal cord contusion from 7 to 30 days after injury. Long-lasting activations of astrocytes and microglia seen by persisted increases in the specific mean gray values of immunoreactivities were also found in all levels of the white and gray matters of the partial hemitransected spinal cord until 3 months postinjury which can be related to wound/repair events and paracrine trophic support to spinal cord remaining neurons. The results showed that controlled partial lesions may provide an important toll to study trophism and plasticity in the spinal cord.

Temporal progression of angiogenesis and basal lamina deposition after contusive spinal cord injury in the adult rat

After spinal cord injury (SCI), the absence of an adequate blood supply to injured tissues has been hypothesized to contribute to the lack of regeneration. In this study, blood vessel changes were examined in 28 adult female Fischer 344 rats at 1, 3, 7, 14, 28, and 60 days after a 12.5 g x cm NYU impactor injury at the T9 vertebral level. Laminin, collagen IV, endothelial barrier antigen (SMI71), and rat endothelial cell antigen (RECA-1) immunoreactivities were used to quantify blood vessel per area densities and diameters in ventral gray matter (VGM), ventral white matter (VWM), and dorsal columns (DC) at levels ranging 15 mm rostral and caudal to the epicenter. This study demonstrates an angiogenic response, defined as SMI71/RECA-1-immunopositive endothelial cells that colocalize with a robust deposition of basal lamina and basal lamina streamers, 7 days after injury within epicenter VGM. This angiogenesis diminishes concurrent with cystic cavity formation. GAP43- and neurofilament- (68 kDa and 210 kDa) immunopositive fiber outgrowth was associated with these new blood vessels by day 14. Between 28 and 60 days after injury, increases in SMI71-immunopositive blood vessel densities were observed in the remaining VWM and DC with a corresponding increase in vessel diameters up to 15 mm rostral and caudal to the epicenter. This second angiogenesis within VWM and DC, unlike the acute response observed in VGM, did not correspond to any previously described changes in locomotor behaviors in this model. We propose that therapies targeting angiogenic processes be directed at the interval between 3 and 7 days after SCI.

New vascular tissue rapidly replaces neural parenchyma and vessels destroyed by a contusion injury to the rat spinal cord

Blood vessels identified by laminin staining were studied in uninjured spinal cord and at 2, 4, 7, and 14 days following a moderate contusion (weight drop) injury. At 2 days after injury most blood vessels had been destroyed in the lesion epicenter; neurons and astrocytes were also absent, and few ED1+ cells were seen infiltrating the lesion center. By 4 days, laminin associated with vessel staining was increased and ED1+ cells appeared to be more numerous in the lesion. By 7 days after injury, the new vessels formed a continuous cordon oriented longitudinally through the lesion center. ED1+ cells were abundant at this time point and were found in the same area as the newly formed vessels. Astrocyte migration from the margins of the lesion into the new cordon was apparent. By 14 days, a decrease in the number of vessels in the lesion center was observed; in contrast, astrocytes were more prominent in those areas. In addition to providing a blood supply to the lesion site, protecting the demise of the newly formed vascular bridge might provide an early scaffold to hasten axonal regeneration across the injury site.