Chronic alterations in the cellular composition of spinal cord white matter following contusion injury

Protecting the injured central nervous system: Do anesthesia or hypothermia ameliorate secondary injury?

Traumatic injury to the central nervous system (CNS) and stroke initiate a cascade of processes that expand the area of tissue loss. The current review considers recent studies demonstrating that the induction of an anesthetic state or cooling the affected tissue (hypothermia) soon after injury can have a therapeutic effect. We first provide an overview of the neurobiological processes that fuel tissue loss after traumatic brain injury (TBI), spinal cord injury (SCI) and stroke. We then examine the rehabilitative effectiveness of therapeutic anesthesia across a variety of drug categories through a systematic review of papers in the PubMed database. We also review the therapeutic benefits hypothermia, another treatment that quells neural activity. We conclude by considering factors related to the safety, efficacy and timing of treatment, as well as the mechanisms of action. Clinical implications are also discussed.

From Poison to Promise: The Evolution of Tetrodotoxin and Its Potential as a Therapeutic

Tetrodotoxin (TTX) is a potent neurotoxin that was first identified in pufferfish but has since been isolated from an array of taxa that host TTX-producing bacteria. However, determining its origin, ecosystem roles, and biomedical applications has challenged researchers for decades. Recognized as a poison and for its lethal effects on humans when ingested, TTX is primarily a powerful sodium channel inhibitor that targets voltage-gated sodium channels, including six of the nine mammalian isoforms. Although lethal doses for humans range from 1.5-2.0 mg TTX (blood level 9 ng/mL), when it is administered at levels far below LD₅₀, TTX exhibits therapeutic properties, especially to treat cancer-related pain, neuropathic pain, and visceral pain. Furthermore, TTX can potentially treat a variety of medical ailments, including heroin and cocaine withdrawal symptoms, spinal cord injuries, brain trauma, and some kinds of tumors. Here, we (i) describe the perplexing evolution and ecology of tetrodotoxin, (ii) review its mechanisms and modes of action, and (iii) offer an overview of the numerous ways it may be applied as a therapeutic. There is much to be explored in these three areas, and we offer ideas for future research that combine evolutionary biology with therapeutics. The TTX system holds great promise as a therapeutic and understanding the origin and chemical ecology of TTX as a poison will only improve its general benefit to humanity.

The Function of NG2/CSPG4-expressing Cells in the Rat Spinal Cord Injury: An Immunoelectron Microscopy Study

Emerging evidence supports an increased role for NG2/CSPG4-expressing cells in the process of neuroregeneration and synaptic plasticity, due to the increased production of multifunctional chondroitin sulfate proteoglycan (NG2/CSPG4). However, the response of NG2/CSPG4-expressing cells in spinal cord injury (SCI) remains to be elcudiated. Expression and distribution of NG2/CSPG4-expressing cells were studied by immunoelectron microscopy in the ventral horns (VH) of an intact and injured rat spinal cord. In the intact spinal cord, NG2/CSPG4 expression was detected on the cell membrane and in the cytoplasm of NG2 glia and was absent in neurons. Large amounts of NG2/CSPG4 were found on myelin membranes. The ability of intact astrocytes to produce NG2/CSPG4 was shown, although to a lesser extent than oligodendrocytes and NG2 glia. At 7 days after SCI at the Th8 level in the reactive glial zone of VH, the expression of NG2/CSPG4 sharply increased in NG2 glia at a distance of 3-5 mm and in reactive astrocytes were observed at all investigated distances caudally from the epicenter of injury. The obtained results indicate the presence of NG2/CSPG4-positive astrocytes in the intact spinal cord, and in the case of damage, an increase in the ability of reactive astrocytes to produce NG2/CSPG4. SCI leads to increased expression of NG2/CSPG4 by NG2 glia in the early stages after injury, which decreases with distance from the epicenter of the injury, as well as at later stages.

Numbers of Axons in Spared Neural Tissue Bridges But Not Their Widths or Areas Correlate With Functional Recovery in Spinal Cord-Injured Rats

The relationships between various parameters of tissue damage and subsequent functional recovery after spinal cord injury (SCI) are not well understood. Patients may regain micturition control and walking despite large postinjury medullar cavities. The objective of this study was to establish possible correlations between morphological findings and degree of functional recovery after spinal cord compression at vertebra Th8 in rats. Recovery of motor (Basso, Beattie, Bresnahan, foot-stepping angle, rump-height index, and ladder climbing), sensory (withdrawal latency), and bladder functions was analyzed at 1, 3, 6, 9, and 12 weeks post-SCI. Following perfusion fixation, spinal cord tissue encompassing the injury site was cut in longitudinal frontal sections. Lesion lengths, lesion volumes, and areas of perilesional neural tissue bridges were determined after staining with cresyl violet. The numbers of axons in these bridges were quantified after staining for class III β-tubulin. We found that it was not the area of the spared tissue bridges, which is routinely determined by magnetic resonance imaging (MRI), but the numbers of axons in them that correlated with functional recovery after SCI (Spearman's ρ > 0.8; p < 0.001). We conclude that prognostic statements based only on MRI measurements should be considered with caution.

KIF2A characterization after spinal cord injury

Axons in the central nervous system (CNS) typically fail to regenerate after injury. This failure is multi-factorial and caused in part by disruption of the axonal cytoskeleton. The cytoskeleton, in particular microtubules (MT), plays a critical role in axonal transport and axon growth during development. In this regard, members of the kinesin superfamily of proteins (KIFs) regulate the extension of primary axons toward their targets and control the growth of collateral branches. KIF2A negatively regulates axon growth through MT depolymerization. Using three different injury models to induce SCI in adult rats, we examined the temporal and cellular expression of KIF2A in the injured spinal cord. We observed a progressive increase of KIF2A expression with maximal levels at 10 days to 8 weeks post-injury as determined by Western blot analysis. KIF2A immunoreactivity was present in axons, spinal neurons and mature oligodendrocytes adjacent to the injury site. Results from the present study suggest that KIF2A at the injured axonal tips may contribute to neurite outgrowth inhibition after injury, and that its increased expression in inhibitory spinal neurons adjacent to the injury site might contribute to an intrinsic wiring-control mechanism associated with neuropathic pain. Further studies will determine whether KIF2A may be a potential target for the development of regeneration-promoting or pain-preventing therapies.

Label-free multiphoton microscopy reveals relevant tissue changes induced by alginate hydrogel implantation in rat spinal cord injury

The development of therapies promoting recovery after spinal cord injury is a challenge. Alginate hydrogels offer the possibility to develop biocompatible implants with mechanical properties tailored to the nervous tissue, which could provide a permissive environment for tissue repair. Here, the effects of non-functionalized soft calcium alginate hydrogel were investigated in a rat model of thoracic spinal cord hemisection and compared to lesioned untreated controls. Open field locomotion tests were employed to evaluate functional recovery. Tissue analysis was performed with label-free multiphoton microscopy using a multimodal approach that combines coherent anti-Stokes Raman scattering to visualize axonal structures, two-photon fluorescence to visualize inflammation, second harmonic generation to visualize collagenous scarring. Treated animals recovered hindlimb function significantly better than controls. Multiphoton microscopy revealed that the implant influenced the injury-induced tissue response, leading to decreased inflammation, reduced scarring with different morphology and increased presence of axons. Demyelination of contralateral white matter near the lesion was prevented. Reduced chronic inflammation and increased amount of axons in the lesion correlated with improved hindlimb functions, being thus relevant for locomotion recovery. In conclusion, non-functionalized hydrogel improved functional outcome after spinal cord injury in rats. Furthermore, label-free multiphoton microscopy qualified as suitable technique for regeneration studies.

The reactions and role of NG2 glia in spinal cord injury

Oligodendrocyte precursor cells (OPCs) react rapidly to brain and spinal cord injuries. This reaction is characterized by the retraction of cell processes, cell body swelling and increased expression of the NG2 chondroitin sulfate proteoglycan. Reactive OPCs rapidly divide and accumulate surrounding the injury site where they become major cellular components of the glial scar. The glial reaction to injury is an attempt to restore normal homeostasis and re-establish the glia limitans but the exact role of reactive OPCs in these processes is not well understood. Traumatic injury results in extensive oligodendrocyte cell death and the proliferating OPCs generate the large number of precursor cells necessary for remyelination. Reactive OPCs, however, also are a source of axon-growth inhibitory proteoglycans and may interact with invading inflammatory cells in complex ways. Here, I discuss these and other properties of OPCs after spinal cord injury. Understanding the regulation of these disparate properties may lead to new therapeutic approaches to devastating injuries of the spinal cord. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).

Lipoxin A4 inhibits microglial activation and reduces neuroinflammation and neuropathic pain after spinal cord hemisection

BACKGROUND

Spinal cord injury (SCI) is a severe neurological disorder with many disabling consequences, including persistent neuropathic pain, which develops in about 40 % of SCI patients and is induced and sustained by excessive and uncontrolled spinal neuroinflammation. Here, we have evaluated the effects of lipoxin A4 (LXA4), a member of a unique class of endogenous lipid mediators with both anti-inflammatory and analgesic properties, on spinal neuroinflammation and chronic pain in an experimental model of SCI.

METHODS

Spinal hemisection at T10 was carried out in adult male CD1 mice and Wistar rats. To test if LXA4 can reduce neuroinflammation and neuropathic pain, each animal received two intrathecal injections of LXA4 (300 pmol) or vehicle at 4 and 24 h after SCI. Sensitivity to mechanical stimulation of the hind paws was evaluated using von Frey monofilaments, and neuroinflammation was tested by measuring the mRNA and/or protein expression levels of glial markers and cytokines in the spinal cord samples after SCI. Also, microglia cultures prepared from murine cortical tissue were used to assess the direct effects of LXA4 on microglial activation and release of pro-inflammatory TNF-α.

RESULTS

LXA4 treatment caused significant reductions in the intensity of mechanical pain hypersensitivity and spinal expression levels of microglial markers and pro-inflammatory cytokines induced by SCI, when compared to rodents receiving control vehicle injections. Notably, the increased expressions of the microglial marker IBA-1 and of the pro-inflammatory cytokine TNF-α were the most affected by the LXA4 treatment. Furthermore, cortical microglial cultures expressed ALX/FPR2 receptors for LXA4 and displayed potentially anti-inflammatory responses upon challenge with LXA4.

CONCLUSIONS

Collectively, our results suggest that LXA4 can effectively modulate microglial activation and TNF-α release through ALX/FPR2 receptors, ultimately reducing neuropathic pain in rodents after spinal cord hemisection. The dual anti-inflammatory and analgesic properties of LXA4, allied to its endogenous nature and safety profile, may render this lipid mediator as new therapeutic approach for treating various neuroinflammatory disorders and chronic pain with only limited side effects.

Inhibition of Epidermal Growth Factor Receptor Improves Myelination and Attenuates Tissue Damage of Spinal Cord Injury

Preventing demyelination and promoting remyelination of denuded axons are promising therapeutic strategies for spinal cord injury (SCI). Epidermal growth factor receptor (EGFR) inhibition was reported to benefit the neural functional recovery and the axon regeneration after SCI. However, its role in de- and remyelination of axons in injured spinal cord is unclear. In the present study, we evaluated the effects of EGFR inhibitor, PD168393 (PD), on the myelination in mouse contusive SCI model. We found that expression of myelin basic protein (MBP) in the injured spinal cords of PD treated mice was remarkably elevated. The density of glial precursor cells and oligodendrocytes (OLs) was increased and the cell apoptosis in lesions was attenuated after PD168393 treatment. Moreover, PD168393 treatment reduced both the numbers of OX42 + microglial cells and glial fibrillary acidic protein + astrocytes in damaged area of spinal cords. We thus conclude that the therapeutic effects of EGFR inhibition after SCI involves facilitating remyelination of the injured spinal cord, increasing of oligodendrocyte precursor cells and OLs, as well as suppressing the activation of astrocytes and microglia/macrophages.

Proof-of Concept that an Acute Trophic Factors Intervention After Spinal Cord Injury Provides an Adequate Niche for Neuroprotection, Recruitment of Nestin-Expressing Progenitors and Regeneration

Trophic factor treatment has been shown to improve the recovery of brain and spinal cord injury (SCI). In this study, we examined the effects of TSC1 (a combination of insulin-like growth factor 1 and transferrin) 4 and 8 h after SCI at the thoracic segment level (T12) in nestin-GFP transgenic mice. TSC1 treatment for 4 and 8 h increased the number of nestin-expressing cells around the lesion site and prevented Wallerian degeneration. Treatment with TSC1 for 4 h significantly increased heat shock protein (HSP)-32 and HSP-70 expression 1 and 2 mm from lesion site (both, caudal and rostral). Conversely, the number of HSP-32 positive cells decreased after an 8-h TSC1 treatment, although it was still higher than in both, non-treated SCI and intact spinal cord animals. Furthermore, TSC1 increased NG2 expressing cell numbers and preserved most axons intact, facilitating remyelination and repair. These results support our hypothesis that TSC1 is an effective treatment for cell and tissue neuroprotection after SCI. An early intervention is crucial to prevent secondary damage of the injured SC and, in particular, to prevent Wallerian degeneration.

Chronic oligodendrogenesis and remyelination after spinal cord injury in mice and rats

Adult progenitor cells proliferate in the acutely injured spinal cord and their progeny differentiate into new oligodendrocytes (OLs) that remyelinate spared axons. Whether this endogenous repair continues beyond the first week postinjury (wpi), however, is unknown. Identifying the duration of this response is essential for guiding therapies targeting improved recovery from spinal cord injury (SCI) by enhancing OL survival and/or remyelination. Here, we used two PDGFRα-reporter mouse lines and rats injected with a GFP-retrovirus to assess progenitor fate through 80 d after injury. Surprisingly, new OLs were generated as late as 3 months after injury and their processes ensheathed axons near and distal to the lesion, colocalized with MBP, and abutted Caspr+ profiles, suggesting newly formed myelin. Semithin sections confirmed stereotypical thin OL remyelination and few bare axons at 10 wpi, indicating that demyelination is relatively rare. Astrocytes in chronic tissue expressed the pro-OL differentiation and survival factors CNTF and FGF-2. In addition, pSTAT3+ NG2 cells were present through at least 5 wpi, revealing active signaling of the Jak/STAT pathway in these cells. The progenitor cell fate genes Sox11, Hes5, Id2, Id4, BMP2, and BMP4 were dynamically regulated for at least 4 wpi. Collectively, these data verify that the chronically injured spinal cord is highly dynamic. Endogenous repair, including oligodendrogenesis and remyelination, continues for several months after SCI, potentially in response to growth factors and/or transcription factor changes. Identifying and understanding spontaneous repair processes such as these is important so that beneficial plasticity is not inadvertently interrupted and effort is not exerted to needlessly duplicate ongoing spontaneous repair.

The paradox of chronic neuroinflammation, systemic immune suppression, autoimmunity after traumatic chronic spinal cord injury

During the transition from acute to chronic stages of recovery after spinal cord injury (SCI), there is an evolving state of immunologic dysfunction that exacerbates the problems associated with the more clinically obvious neurologic deficits. Since injury directly affects cells embedded within the "immune privileged/specialized" milieu of the spinal cord, maladaptive or inefficient responses are likely to occur. Collectively, these responses qualify as part of the continuum of "SCI disease" and are important therapeutic targets to improve neural repair and neurological outcome. Generic immune suppressive therapies have been largely unsuccessful, mostly because inflammation and immunity exert both beneficial (plasticity enhancing) and detrimental (e.g. glia- and neurodegenerative; secondary damage) effects and these functions change over time. Moreover, "compartimentalized" investigations, limited to only intraspinal inflammation and associated cellular or molecular changes in the spinal cord, neglect the reality that the structure and function of the CNS are influenced by systemic immune challenges and that the immune system is 'hardwired' into the nervous system. Here, we consider this interplay during the progression from acute to chronic SCI. Specifically, we survey impaired/non-resolving intraspinal inflammation and the paradox of systemic inflammatory responses in the context of ongoing chronic immune suppression and autoimmunity. The concepts of systemic inflammatory response syndrome (SIRS), compensatory anti-inflammatory response syndrome (CARS) and "neurogenic" spinal cord injury-induced immune depression syndrome (SCI-IDS) are discussed as determinants of impaired "host-defense" and trauma-induced autoimmunity.

Efficient generation of astrocytes from human pluripotent stem cells in defined conditions

Astrocytes can be generated from various tissue sources including human pluripotent stem cells (PSC). In this manuscript, we describe a chemically defined xeno-free medium culture system for rapidly generating astrocytes from neural stem cells derived from PSC. We show that astrocyte development in vitro, mimics normal development in vivo, and also passes through a CD44(+) astrocyte precursor stage. Astrocytes generated by our method display similar gene expression patterns, morphological characteristics and functional properties to primary astrocytes, and they survive and integrate after xenotransplantation. Whole genome expression profiling of astrocyte differentiation was performed at several time points of differentiation, and the results indicate the importance of known regulators and identify potential novel regulators and stage-specific lineage markers.

Dorsal column sensory axons degenerate due to impaired microvascular perfusion after spinal cord injury in rats

The mechanisms contributing to axon loss after spinal cord injury (SCI) are largely unknown but may involve microvascular loss as we have previously suggested. Here, we used a mild contusive injury (120 kdyn IH impactor) at T9 in rats focusing on ascending primary sensory dorsal column axons, anterogradely traced from the sciatic nerves. The injury caused a rapid and progressive loss of dorsal column microvasculature and oligodendrocytes at the injury site and penumbra and an ~70% loss of the sensory axons by 24 h. To model the microvascular loss, focal ischemia of the T9 dorsal columns was achieved via phototoxic activation of intravenously injected rose bengal. This caused an ~53% loss of sensory axons and an ~80% loss of dorsal column oligodendrocytes by 24 h. Axon loss correlated with the extent and axial length of microvessel and oligodendrocyte loss along the dorsal column. To determine if oligodendrocyte loss contributes to axon loss, the glial toxin ethidium bromide (EB; 0.3 μg/μl) was microinjected into the T9 dorsal columns, and resulted in an ~88% loss of dorsal column oligodendrocytes and an ~56% loss of sensory axons after 72 h. EB also caused an ~75% loss of microvessels. Lower concentrations of EB resulted in less axon, oligodendrocyte and microvessel loss, which were highly correlated (R(2) = 0.81). These data suggest that focal spinal cord ischemia causes both oligodendrocyte and axon degeneration, which are perhaps linked. Importantly, they highlight the need of limiting the penumbral spread of ischemia and oligodendrocyte loss after SCI in order to protect axons.

Pilot study: elevated circulating levels of the proinflammatory cytokine macrophage migration inhibitory factor in patients with chronic spinal cord injury

OBJECTIVE

To test the hypothesis that the proinflammatory cytokine macrophage migration inhibitory factor (MIF) is elevated in the circulation of patients with chronic spinal cord injury (SCI) relative to uninjured subjects, and secondarily to identify additional immune mediators that are elevated in subjects with chronic SCI.

DESIGN

Prospective, observational pilot study.

SETTING

Outpatient clinic of a department of physical medicine and rehabilitation and research institute in an academic medical center.

PARTICIPANTS

Individuals with chronic (>1y from initial injury) SCI (n=22) and age- and sex-matched uninjured subjects (n=19).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Plasma levels of MIF, as determined by a commercially available multiplex suspension immunoassay. The relationship between MIF levels and clinical/demographic variables was also examined. As a secondary outcome, we evaluated other cytokines, chemokines, and growth factors.

RESULTS

Plasma MIF levels were significantly higher in subjects with chronic SCI than in control subjects (P<.001). Elevated MIF levels were not correlated significantly with any one clinical or demographic characteristic. Subjects with SCI also exhibited significantly higher plasma levels of monokine induced by interferon-gamma/chemokine C-X-C motif ligand 9 (P<.03), macrophage colony stimulating factor (P<.035), interleukin-3 (P<.044), and stem cell growth factor beta (SCGF-β) (P<.016). Among subjects with SCI, the levels of SCGF-β increased with the time from initial injury.

CONCLUSIONS

These data confirm the hypothesis that MIF is elevated in subjects with chronic SCI and identify additional novel immune mediators that are also elevated in these subjects. This study suggests the importance of examining the potential functional roles of MIF and other immune factors in subjects with chronic SCI.

Bench to bedside of neural stem cell in traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of major disability and death worldwide. Neural stem cells (NSCs) have recently been shown to contribute to the cellular remodelling that occurs following TBI and attention has been drawn to the area of neural stem cell as possible therapy for TBI. The NSCs may play an important role in the treatment of TBI by replacing the damaged cells and eventual remyelination. This paper summarized a critical assessment of recent data and developed a view comprising of six points to possible quality translation of NSCs in TBI.

Human umbilical cord blood-derived mesenchymal stem cell therapy promotes functional recovery of contused rat spinal cord through enhancement of endogenous cell proliferation and oligogenesis

Numerous studies have shown the benefits of mesenchymal stem cells (MSCs) on the repair of spinal cord injury (SCI) model and on behavioral improvement, but the underlying mechanisms remain unclear. In this study, to investigate possible mechanisms by which MSCs contribute to the alleviation of neurologic deficits, we examined the potential effect of human umbilical cord blood-derived MSCs (hUCB-MSCs) on the endogenous cell proliferation and oligogenesis after SCI. SCI was injured by contusion using a weight-drop impactor and hUCB-MSCs were transplanted into the boundary zone of the injured site. Animals received a daily injection of bromodeoxyuridine (BrdU) for 7 days after treatment to identity newly synthesized cells of ependymal and periependymal cells that immunohistochemically resembled stem/progenitor cells was evident. Behavior analysis revealed that locomotor functions of hUCB-MSCs group were restored significantly and the cavity volume was smaller in the MSCs-transplanted rats compared to the control group. In MSCs-transplanted group, TUNEL-positive cells were decreased and BrdU-positive cells were significantly increased rats compared with control group. In addition, more of BrdU-positive cells expressed neural stem/progenitor cell nestin and oligo-lineage cell such as NG2, CNPase, MBP and glial fibrillary acidic protein typical of astrocytes in the MSC-transplanted rats. Thus, endogenous cell proliferation and oligogenesis contribute to MSC-promoted functional recovery following SCI.

Delayed granulocyte colony-stimulating factor treatment promotes functional recovery in rats with severe contusive spinal cord injury

STUDY DESIGN

We used a severe contusive spinal cord injury (SCI) model and electrophysiologic, motor functional, immunohistochemical, and electron microscopic examinations to analyze the neuroprotective effects of delayed granulocyte colony-stimulating factor (G-CSF) treatment.

OBJECTIVE

To determine the neuroprotective effects of delayed G-CSF treatment using multimodality evaluations after severe contusive SCI in rats.

SUMMARY OF BACKGROUND DATA

Despite some reports that G-CSF treatment in the acute stage of different central nervous system injury models was neuroprotective, it has not been determined whether delayed G-CSF treatment can promote neural recovery in severe contusive SCI.

METHODS

Rats with severe contusive SCI were divided into 2 groups: G-CSF group rats were given serial subcutaneous injections of G-CSF, and control group rats (controls) were given only saline injections on postcontusion days 9 to 13. Using the Basso-Beattie-Bresnahan scale and cortical somatosensory evoked potentials, we recorded functional evaluations weekly. The spinal cords were harvested for protein and immunohistochemical analysis, and for electron microscopy examination.

RESULTS

The preserved spinal cord area was larger in G-CSF group rats than in control group rats. Both sensory and motor functions improved after G-CSF treatment. Detachment and disruption of the myelin sheets in the myelinated axons were significantly decreased, and axons sprouted and regenerated. There were fewer microglia and macrophages in the G-CSF group than in the control group. The levels of brain-derived neurotrophic factor were comparable between the 2 groups.

CONCLUSION

Delayed G-CSF treatment at the subacute stage of severe contusive SCI promoted spinal cord preservation and improved functional outcomes. The mechanism of G-CSF's protection may be related in part to attenuating the infiltration of microglia and macrophages.

Anti-inflammatory treatments during the chronic phase of spinal cord injury improve locomotor function in adult mice

Our previous data suggested that ongoing inflammation in the spinal cord 6 weeks following spinal cord injury was detrimental to locomotor function. Others have shown in the acute and sub-acute post-injury phase that microglial/macrophage activation and T regulatory cells are detrimental to recovery. Here, C57BL/6 mice with a moderately severe T9 contusion were injected intravenously daily with minocycline, which reduces microglial/macrophage activation, or with CD25 antibodies, which reduce T regulatory cell function, starting at 6 weeks after injury. Both anti-inflammatory drugs caused an improvement in hindlimb locomotor function over the 2-week treatment, as measured by the Basso Mouse Scale (BMS). The improvement was functionally important, with mice having problems with coordinated stepping (BMS ∼6) before treatment to walking essentially normally (BMS >7) at the end of the treatment. The effects diminished within 1 week after termination of the treatments, suggesting an ongoing and dynamic inflammatory process. The area of white matter or the inflammatory markers CD68 for activated microglia/macrophages and CD45 for leukocytes were not different between the groups. These data suggest that inflammation during the chronic phase following spinal cord injury reduces conduction through the epicenter, possibly by release of cytokines, and is amenable to treatment for improved neurological function.

The role of embryonic motoneuron transplants to restore the lost motor function of the injured spinal cord

Spinal cord injury or disease result in the loss of critical numbers of spinal motoneurons and consequentially, in severe functional impairment. The most successful way to replace missing motoneurons is the use of embryonic postmitotic motoneuron grafts. This method may also at least partially restore integrity of the injured spinal cord. It has been shown that grafted motoneurons survive, differentiate and integrate into the host cord and many of them are able to reinnervate the denervated muscles. If grafted motoneurons are provided with a conduit (e.g. reimplanted ventral root) the grafted cells are able to extend their axons along the entire length of the peripheral nerves and reach the hind or forelimb muscles and to restore limb locomotion patterns. Grafted motoneurons show excellent survival in motoneuron-depleted adult host cords, but the developing spinal cord appears to provide an unfavourable environment for these motoneurons as they do not survive in immature cords. The long term survival and maturation of the grafted neurons depend on the availability of a nerve conduit and one or more target muscles, independently of whether these are ectopic nerve-muscle implants or limb muscles in their original site. Thus, grafted and host motoneurons induce functional recovery in the denervated limb muscles when their axons can grow into an avulsed and reimplanted ventral root and then reach the limb muscles. Following segmental loss of motoneurons induced by partial spinal cord injury, motoneuron-enriched embryonic grafts can be placed into the gap-like hemisection cavity in the cervical spinal cord. Such transplants induce the regeneration of great numbers of host motoneurons possibly by the bridging effect of the grafts. In this case, the regenerating host motoneurons reinnervate their original target muscles while the small graft plays a minimal role in the reinnervation of muscles. These results suggest that reconstruction of the injured spinal cord using an embryonic motoneuron-enriched spinal cord graft is a feasible way to achieve improvement after severe functional motor deficits of the spinal cord.

Aquaporins in spinal cord injury: the janus face of aquaporin 4

Although malfunction of spinal cord water channels (aquaporins, AQP) likely contributes to severe disturbances in ion/water homeostasis after spinal cord injury (SCI), their roles are still poorly understood. Here we report and discuss the potential significance of changes in the AQP4 expression in human SCI that generates glial fibrillary acidic protein (GFAP)-labeled astrocytes devoid of AQP4, and GFAP-labeled astroglia that overexpress AQP4. We used a rat model of contusion SCI to study observed changes in human SCI. AQP4-negative astrocytes are likely generated during the process of SCI-induced replacement of lost astrocytes, but their origin and role in SCI remains to be investigated. We found that AQP4-overexpression is likely triggered by hypoxia. Our transcriptional profiling of injured rat cords suggests that elevated AQP4-mediated water influx accompanies increased uptake of chloride and potassium ions which represents a protective astrocytic reaction to hypoxia. However, unbalanced water intake also results in astrocytic swelling that can contribute to motor impairment, but likely only in milder injuries. In severe rat SCI, a low abundance of AQP4-overexpressing astrocytes was found during the motor recovery phase. Our results suggest that severe rat contusion SCI is a better model to analyze AQP4 functions after SCI. We found that AQP4 increases in the chronic post-injury phase are associated with the development of pain-like behavior in SCI rats, while possible mechanisms underlying pain development may involve astrocytic swelling-induced glutamate release. In contrast, the formation and size of fluid-filled cavities occurring later after SCI does not appear to be affected by the extent of increased AQP4 levels. Therefore, the effect of therapeutic interventions targeting AQP4 will depend not only on the time interval after SCI or animal models, but also on the balance between protective role of increased AQP4 in hypoxia and deleterious effects of ongoing astrocytic swelling.

Interaction of NG2(+) glial progenitors and microglia/macrophages from the injured spinal cord

Spinal cord contusion produces a central lesion surrounded by a peripheral rim of residual white matter. Despite stimulation of NG2(+) progenitor cell proliferation, the lesion remains devoid of normal glia chronically after spinal cord injury (SCI). To investigate potential cell-cell interactions of the predominant cells in the lesion at 3 days after injury, we used magnetic activated cell sorting to purify NG2(+) progenitors and OX42(+) microglia/macrophages from contused rat spinal cord. Purified NG2(+) cells from the injured cord grew into spherical masses when cultured in defined medium with FGF2 plus GGF2. The purified OX42(+) cells did not form spheroids and significantly reduced sphere growth by NG2(+) cells in co-cultures. Conditioned medium from these OX42(+) cells, unlike that from normal peritoneal macrophages or astrocytes also inhibited growth of NG2(+) cells, suggesting inhibition by secreted factors. Expression analysis of freshly purified OX42(+) cells for a panel of six genes for secreted factors showed expression of several that could contribute to inhibition of NG2(+) cells. Further, the pattern of expression of four of these, TNFalpha, TSP1, TIMP1, MMP9, in sequential coronal tissue segments from a 2 cm length of cord centered on the injury epicenter correlated with the expression of Iba1, a marker gene for OX42(+) cells, strongly suggesting a potential regional influence by activated microglia/macrophages on NG2(+) cells in vivo after SCI. Thus, the nonreplacement of lost glial cells in the central lesion zone may involve, at least in part, inhibitory factors produced by microglia/macrophages that are concentrated within the lesion.

Membrane trauma and Na+ leak from Nav1.6 channels

During brain trauma, white matter experiences shear and stretch forces that, without severing axons, nevertheless trigger their secondary degeneration. In central nervous system (CNS) trauma models, voltage-gated sodium channel (Nav) blockers are neuroprotective. This, plus the rapid tetrodotoxin-sensitive Ca2+ overload of stretch-traumatized axons, points to "leaky" Nav channels as a pivotal early lesion in brain trauma. Direct effects of mechanical trauma on neuronal Nav channels have not, however, been tested. Here, we monitor immediate responses of recombinant neuronal Nav channels to stretch, using patch-clamp and Na+-dye approaches. Trauma constituted either bleb-inducing aspiration of cell-attached oocyte patches or abrupt uniaxial stretch of cells on an extensible substrate. Nav1.6 channel transient current displayed irreversible hyperpolarizing shifts of steady-state inactivation [availability(V)] and of activation [g(V)] and, thus, of window current. Left shift increased progressively with trauma intensity. For moderately intense patch trauma, a approximately 20-mV hyperpolarizing shift was registered. Nav1.6 voltage sensors evidently see lower energy barriers posttrauma, probably because of the different bilayer mechanics of blebbed versus intact membrane. Na+ dye-loaded human embryonic kidney (HEK) cells stably transfected with alphaNav1.6 were subjected to traumatic brain injury-like stretch. Cytoplasmic Na+ levels abruptly increased and the trauma-induced influx had a significant tetrodotoxin-sensitive component. Nav1.6 channel responses to cell and membrane trauma are therefore consistent with the hypothesis that mechanically induced Nav channel leak is a primary lesion in traumatic brain injury. Nav1.6 is the CNS node of Ranvier Nav isoform. When, during head trauma, nodes experienced bleb-inducing membrane damage of varying intensities, nodal Nav1.6 channels should immediately "leak" over a broadly left-smeared window current range.

Effects of progesterone on oligodendrocyte progenitors, oligodendrocyte transcription factors, and myelin proteins following spinal cord injury

Progesterone is emerging as a myelinizing factor for central nervous system injury. Successful remyelination requires proliferation and differentiation of oligodendrocyte precursor cells (OPC) into myelinating oligodendrocytes, but this process is incomplete following injury. To study progesterone actions on remyelination, we administered progesterone (16 mg/kg/day) to rats with complete spinal cord injury. Rats were euthanized 3 or 21 days after steroid treatment. Short progesterone treatment (a) increased the number of OPC without effect on the injury-induced reduction of mature oligodendrocytes, (b) increased mRNA and protein expression for the myelin basic protein (MBP) without effects on proteolipid protein (PLP) or myelin oligodendrocyte glycoprotein (MOG), and (c) increased the mRNA for Olig2 and Nkx2.2 transcription factors involved in specification and differentiation of the oligodendrocyte lineage. Furthermore, long progesterone treatment (a) reduced OPC with a concomitant increase of oligodendrocytes; (b) promoted differentiation of cells that incorporated bromodeoxyuridine, early after injury, into mature oligodendrocytes; (c) increased mRNA and protein expression of PLP without effects on MBP or MOG; and (d) increased mRNA for the Olig1 transcription factor involved in myelin repair. These results suggest that early progesterone treatment enhanced the density of OPC and induced their differentiation into mature oligodendrocytes by increasing the expression of Olig2 and Nkx2.2. Twenty-one days after injury, progesterone favors remyelination by increasing Olig1 (involved in repair of demyelinated lesions), PLP expression, and enhancing oligodendrocytes maturation. Thus, progesterone effects on oligodendrogenesis and myelin proteins may constitute fundamental steps for repairing traumatic injury inflicted to the spinal cord.

Progesterone neuroprotection in traumatic CNS injury and motoneuron degeneration

Studies on the neuroprotective and promyelinating effects of progesterone in the nervous system are of great interest due to their potential clinical connotations. In peripheral neuropathies, progesterone and reduced derivatives promote remyelination, axonal regeneration and the recovery of function. In traumatic brain injury (TBI), progesterone has the ability to reduce edema and inflammatory cytokines, prevent neuronal loss and improve functional outcomes. Clinical trials have shown that short-and long-term progesterone treatment induces a significant improvement in the level of disability among patients with brain injury. In experimental spinal cord injury (SCI), molecular markers of functional motoneurons become impaired, including brain-derived neurotrophic factor (BDNF) mRNA, Na,K-ATPase mRNA, microtubule-associated protein 2 and choline acetyltransferase (ChAT). SCI also produces motoneuron chromatolysis. Progesterone treatment restores the expression of these molecules while chromatolysis subsided. SCI also causes oligodendrocyte loss and demyelination. In this case, a short progesterone treatment enhances proliferation and differentiation of oligodendrocyte progenitors into mature myelin-producing cells, whereas prolonged treatment increases a transcription factor (Olig1) needed to repair injury-induced demyelination. Progesterone neuroprotection has also been shown in motoneuron neurodegeneration. In Wobbler mice spinal cord, progesterone reverses the impaired expression of BDNF, ChAT and Na,K-ATPase, prevents vacuolar motoneuron degeneration and the development of mitochondrial abnormalities, while functionally increases muscle strength and the survival of Wobbler mice. Multiple mechanisms contribute to these progesterone effects, and the role played by classical nuclear receptors, extra nuclear receptors, membrane receptors, and the reduced metabolites of progesterone in neuroprotection and myelin formation remain an exciting field worth of exploration.

NG2 cell response in the CNP-EGFP mouse after contusive spinal cord injury

NG2(+) cells in the adult CNS are a heterogeneous population. The extent to which the subpopulation of NG2(+) cells that function as oligodendrocyte progenitor cells (OPCs) respond to spinal cord injury (SCI) and recapitulate their normal developmental progression remains unclear. We used the CNP-EGFP mouse, in which oligodendrocyte lineage cells express EGFP, to study NG2(+) cells in the normal and injured spinal cord. In white matter of uninjured mice, bipolar EGFP(+)NG2(+) cells and multipolar EGFP(neg)NG2(+) cells were identified. After SCI, EGFP(+)NG2(+) cell proliferation in residual white matter peaked at 3 days post injury (DPI) rostral to the epicenter, while EGFP(neg)NG2(+) cell proliferation peaked at 7 DPI at the epicenter. The expression of transcription factors, Olig2, Sox10, and Sox17, and the basic electrophysiological membrane parameters and potassium current phenotype of the EGFP(+)NG2(+) population after injury were consistent with those of proliferative OPCs during development. EGFP(neg)NG2(+) cells did not express transcription factors involved in oligodendrogenesis. EGFP(+)CC1(+) oligodendrocytes at 6 weeks included cells that incorporated BrdU during the peak of EGFP(+)NG2(+) cell proliferation. EGFP(neg)CC1(+) oligodendrocytes were never observed. Treatment with glial growth factor 2 and fibroblast growth factor 2 enhanced oligodendrogenesis and increased the number of EGFP(neg)NG2(+) cells. Therefore, based on EGFP and transcription factor expression, spatiotemporal proliferation patterns, and response to growth factors, two populations of NG2(+) cells can be identified that react to SCI. The EGFP(+)NG2(+) cells undergo cellular and physiological changes in response to SCI that are similar to those that occur in early postnatal NG2(+) cells during developmental oligodendrogenesis.

Interleukin-6 induces proliferation in adult spinal cord-derived neural progenitors via the JAK2/STAT3 pathway with EGF-induced MAPK phosphorylation

INTRODUCTION

In a previous study, we observed cell proliferation 3 days after spinal cord injury, and levels of interleukin-6 (IL-6) and epidermal growth factor (EGF) had significantly increased in the region of the injury.

OBJECTIVES

The purpose of the new study described here was to evaluate the roles of IL-6 and EGF after traumatic damage to the spinal cord having isolated neural progenitor cells (NPC) from adult mice.

METHODS AND RESULTS

Evidence provided by the trypan blue dye exclusion assay, 5-bromodeoxyuridine immunoreactivity and Western blot analysis indicated that IL-6 and EGF induced proliferation of these spinal cord-derived NPCs via phosphorylation of Janus-activated kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinases (MAPK), respectively. Combined treatment with IL-6 and EGF accelerated proliferation of cells synergistically and phosphorylation of STAT3 and extracellular signal-regulated kinase 1/2 (Erk1/2). Furthermore, AG490 and AG1478, JAK2 inhibitor and EGFR inhibitor, respectively, prevented the IL-6- and EGF-induced proliferation of the cells. Interestingly, IL-6-activated MAPKs but EGF did not influence JAK2/STAT3 activation; AG490 specifically inhibited IL-6-induced Erk1/2 phosphorylation without affecting IL-6-induced phosphorylation of Raf and MEK1/2. These results indicate that IL-6 is directly involved in Erk1/2 activation via JAK2 and that Erk1/2 provides a signal bridge between the IL-6-induced JAK2/STAT3 pathway and EGF-induced MAPK pathway.

CONCLUSIONS

Our study is the first demonstration of IL-6- and EGF-stimulated proliferation of spinal cord progenitor cells via JAK2/STAT3 and MAPK signalling pathways. These pathways play key roles in repopulation and regeneration of spinal cord tissue after injury. It may represent novel therapeutic targets for pharmacological intervention in central nervous system disease, including spinal cord injury.

Contuse lesion of the rat spinal cord of moderate intensity leads to a higher time-dependent secondary neurodegeneration than severe one. An open-window for experimental neuroprotective interventions

Secondary neurodegeneration takes place in the surrounding tissue of spinal cord trauma and modifies substantially the prognosis, considering the small diameter of its transversal axis. We analyzed neuronal and glial responses in rat spinal cord after different degree of contusion promoted by the NYU Impactor. Rats were submitted to vertebrae laminectomy and received moderate or severe contusions. Control animals were sham operated. After 7 and 30 days post surgery, stereological analysis of Nissl staining cellular profiles showed a time progression of the lesion volume after moderate injury, but not after severe injury. The number of neurons was not altered cranial to injury. However, same degree of diminution was seen in the caudal cord 30 days after both severe and moderate injuries. Microdensitometric image analysis demonstrated a microglial reaction in the white matter 30 days after a moderate contusion and showed a widespread astroglial reaction in the white and gray matters 7 days after both severities. Astroglial activation lasted close to lesion and in areas related to Wallerian degeneration. Data showed a more protracted secondary degeneration in rat spinal cord after mild contusion, which offered an opportunity for neuroprotective approaches. Temporal and regional glial responses corroborated to diverse glial cell function in lesioned spinal cord.

Mixed primary culture and clonal analysis provide evidence that NG2 proteoglycan-expressing cells after spinal cord injury are glial progenitors

NG2(+) cells in the adult rat spinal cord proliferate after spinal cord injury (SCI) and are postulated to differentiate into mature glia to replace some of those lost to injury. To further study these putative endogenous precursors, tissue at 3 days after SCI or from uninjured adults was dissociated, myelin partially removed and replicate cultures grown in serum-containing or serum-free medium with or without growth factors for up to 7 days in vitro (DIV). Cell yield after SCI was 5-6 times higher than from the normal adult. Most cells were OX42(+) microglia/macrophages but there were also more than twice the normal number of NG2(+) cells. Most of these coexpressed A2B5 or nestin, as would be expected for glial progenitors. Few cells initially expressed mature astrocyte (GFAP) or oligodendrocyte (CC1) markers, but more did at 7 DIV, suggesting differentiation of glial precursors in vitro. To test the hypothesis that NG2(+) cells after SCI express progenitor-like properties, we prepared free-floating sphere and single cell cultures from purified suspension of NG2(+) cells from injured spinal cord. We found that sphere cultures could be passaged in free-floating subcultures, and upon attachment the spheres clonally derived from an acutely purified single cell differentiated into oligodendrocytes and rarely astrocytes. Taken together, these data support the hypothesis that SCI stimulates proliferation of NG2(+) cells that are glial progenitor cells. Better understanding the intrinsic properties of the NG2(+) cells stimulated by SCI may permit future therapeutic manipulations to improve recovery after SCI.

Antiapoptotic therapies in the treatment of spinal cord injury

Mechanical trauma to the spinal cord triggers events resulting in the death of neurons and glia over several weeks following the initial injury. It has been suggested that the prevention of delayed apoptosis after spinal cord injury (SCI) is likely to have a beneficial effect by reducing the extent of neuronal and oligodendroglial death, which would translate into better functional outcomes. Drugs acting at different levels in the apoptotic cascade (i.e., caspase inhibitors and antiapoptotic Bcl-xL) have been shown to decrease apoptotic cell death, but benefits in functional outcomes result only when inflammation is also decreased. Furthermore, long-term antiapoptotic therapy can result in nonapoptotic death with necrotic features, which will further increase inflammation and worsen outcome. Even though neuroprotective therapies are one of the targets for the promotion of functional recovery after SCI, targeting only post-SCI apoptosis is unlikely to be as successful as more integrated interventions that also target inflammation.

Temporal-spatial dynamics in oligodendrocyte and glial progenitor cell numbers throughout ventrolateral white matter following contusion spinal cord injury

The aim of this study was to systematically determine the spatial distribution of oligodendrocytes (CC1(+)) and glial progenitor cells (NG2(+)) throughout the ventral lateral funiculi (VLF) of adult rat thoracic spinal cord white matter over the course of spontaneous hindlimb locomotor recovery following moderate contusion injury. We used the optical fractionator technique to establish an unbiased estimate of total CC1(+) and NG2(+) cell numbers throughout equivalent segments of VLF from normal and injured spinal cords at designated time points. The results demonstrated a greater than 60% loss of oligodendrocytes and a 50% increase in NG2(+) cells 2 days postinjury. Subsequently, there was a significant increase in oligodendrocytes 7 days postinjury that continued throughout the time course of our experiments (42 days) when the total numbers recovered to 80% of controls. Conversely, NG2(+) cell numbers progressively declined after 2 days postinjury but remained significantly higher than controls throughout the experiments. The pattern of acute loss and repopulation of oligodendrocytes in the VLF paralleled the initial recovery of hindlimb weight-bearing function. Whether such improvement is directly related to NG2(+) cell differentiation into functional oligodendrocytes is uncertain. However, of critical importance is that significant cellular dynamics occurred primarily distal to the injury, and these changes were mirrored by significant alterations in the expression of mature myelin proteins. This infers that site-specific genetic or cellular interventions designed to enhance locomotor recovery by fostering remyelination of spared and/or newly established relay circuits may need to target not only the injury site but also rostrocaudal regions.

Glial cell loss, proliferation and replacement in the contused murine spinal cord

Studies in the rat have shown that contusive spinal cord injury (SCI) results in devastating pathology, including significant loss of mature oligodendrocytes and astrocytes even in spared white matter. Subsequently, there is increased proliferation of endogenous NG2(+) cells, postulated to contribute to replacement of mature glia chronically, which is important for functional recovery. Studies of mechanisms that stimulate endogenous progenitor cells would be facilitated by using mouse models with naturally occurring and genetically engineered mutations. To determine whether the murine response is similar to that in the rat, we performed contusive SCI on adult female C57Bl/6 mice at the T8-9 level. Animals received bromodeoxyuridine injections in the first week following injury and were killed at 1, 3, 4, 7 or 28 days postinjury (DPI). The overall loss of macroglia and the temporal-spatial response of NG2(+) cells after SCI in the (C57Bl/6) mouse was very similar to that in the (Sprague-Dawley) rat. By 24 h after SCI nearly half of the macroglia in spared ventral white matter had been lost. Cell proliferation was increased at 1-7 DPI, peaking at 3-4 DPI. Dividing cells included NG2(+) cells and Cd11b(+) macrophages and microglia. Furthermore, cells dividing in the first week expressed markers of mature glia at 28 DPI. The similarities in endogenous progenitor cell response to SCI in the mouse and rat suggest that this is a fundamental injury response, and that transgenic mouse models may be used to further probe how this cellular response to SCI might be enhanced to improve recovery after SCI.

Toward accurate diagnosis of white matter pathology using diffusion tensor imaging

Diffusion tensor imaging (DTI) has been widely applied to investigate injuries in the central nervous system (CNS) white matter (WM). However, the underlying pathological correlates of diffusion changes have not been adequately determined. In this study the coregistration of histological sections to MR images and a pixel-based receiver operating characteristic (ROC) analysis were used to compare the axial (lambda( parallel)) and radial (lambda( perpendicular)) diffusivities derived from DTI and histological markers of axon (phosphorylated neurofilament, SMI-31) and myelin (Luxol fast blue (LFB)) integrity, respectively, in two different patterns of injury to mouse spinal cord (SC) WM. In contusion SC injury (SCI), a decrease in lambda( parallel) matched the pattern of axonal damage with high accuracy, but lambda( perpendicular) did not match the pattern of demyelination detected by LFB. In a mouse model of multiple sclerosis (MS), lambda( perpendicular) and lambda( parallel) did not match the patterns of demyelination or axonal damage, respectively. However, a region of interest (ROI) analysis suggested that lambda( perpendicular)-detected demyelination paralleled that observed with LFB, and lambda( parallel) decreased in both regions of axonal damage and normal-appearing WM (NAWM) as visualized by SMI-31. The results suggest that directional diffusivities may reveal abnormalities that are not obvious with SMI-31 and LFB staining, depending on the type of injury.

Immunomodulatory effect of the purine nucleoside inosine following spinal cord contusion injury in rat

STUDY DESIGN

In vivo study using a moderate spinal cord contusion injury (SCI) model in adult rat.

OBJECTIVE

To assess the immunomodulatory effects of the purine nucleoside inosine on macrophage/microglia activation at and near the lesion site and in white matter areas remote from the injury epicenter.

SETTING

Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, NY, USA.

METHODS

Animals (N=56) were injured using a moderate SCI at T9-T10 spinal level and were divided into three groups, depending on treatment paradigm. Rats received either intraperitoneal or subcutaneous injections of inosine (N=28) or vehicle (N=28). Spinal cord tissue was processed for ED-1 immunoreactivity and the volume fraction of ED-1(+) profiles was calculated using the Cavalieri method and unbiased stereology.

RESULTS

The volume fraction of ED-1(+) profiles within gray and lateral white matter regions at and around the lesion site was significantly reduced only following a twice daily-6 week treatment course, compared with vehicle controls, and white matter areas remote from the lesion were unaffected by all inosine treatment paradigms.

CONCLUSIONS

Continued subcutaneous delivery of inosine, beginning 15-min post-SCI and persisting throughout the survival period of 6 weeks exerted immunomodulatory effects at and around the lesion site.

Phenotypic changes in NG2+ cells after spinal cord injury

Following contusive spinal cord injury (SCI), 50% of oligodendrocytes in the residual white matter are lost within 24 h. NG2-expressing cell proliferation is maximal 3 days after SCI, and may be the source of mature oligodendrocytes and astrocytes that chronically replace those that were lost. We studied NG2(+) cells dissociated from the 3-day injured spinal cord for comparison with those from uninjured adult and early postnatal cords. After 24 h in serum-containing medium, we performed patch clamp analysis and immunocytochemistry for NG2 in combination with nestin (progenitors), and A2B5, O4, and O1 (oligodendrocyte lineage markers). We observed an NG2(+)/A2B5-/O4-/O1- population in both adult preparations. More than double the normal number of NG2(+) cells was isolated from the injured cord, but OX42(+) microglia/macrophages were the predominant cell type after injury. Most cells isolated at P7 were NG2-/A2B5(+), whereas those from the normal adult were NG2(+)/A2B5-. NG2(+) cells after SCI displayed altered voltage-gated potassium current profiles compared to normal adult and P7 animals. Additionally, less than 25% of adult cells (normal and injured) responded to GABA and glutamate, compared to 100% of P7 cells. Our results indicate that the adult NG2(+) cell pool is antigenically and physiologically different than the early postnatal pool, and that contusive injury induces changes in adult NG2(+) cells.

Erythropoietin-mediated preservation of the white matter in rat spinal cord injury

We investigated the effect of a single administration of recombinant human erythropoietin (rhEPO) on the preservation of the ventral white matter of rats at 4 weeks after contusive spinal cord injury (SCI), a time at which functional recovery is significantly improved in comparison to the controls [Gorio A, Necati Gokmen N, Erbayraktar S, Yilmaz O, Madaschi L, Cichetti C, Di Giulio AM, Enver Vardar E, Cerami A, Brines M (2002) Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma. Proc Natl Acad Sci U S A 99:9450-9455; Gorio A, Madaschi L, Di Stefano B, Carelli S, Di Giulio AM, De Biasi S, Coleman T, Cerami A, Brines M (2005) Methylprednisolone neutralizes the beneficial effects of erythropoietin in experimental spinal cord injury. Proc Natl Acad Sci U S A 102:16379-16384]. Specifically, we examined, by morphological and cytochemical methods combined with light, confocal and electron microscopy, i) myelin preservation, ii) activation of adult oligodendrocyte progenitors (OPCs) identified for the expression of NG2 transmembrane proteoglycan, iii) changes in the amount of the chondroitin sulfate proteoglycans neurocan, versican and phosphacan and of their glycosaminoglycan component labeled with Wisteria floribunda lectin, and iv) ventral horn density of the serotonergic plexus as a marker of descending motor control axons. Injured rats received either saline or a single dose of rhEPO within 30 min after SCI. The results showed that the significant improvement of functional outcome observed in rhEPO-treated rats was associated with a better preservation of myelin in the ventral white matter. Moreover, the significant increase of both the number of NG2-positive OPCs and the labeling for Nogo-A, a marker of differentiated oligodendrocytes, suggested that rhEPO treatment could result in the generation of new myelinating oligodendrocytes. Sparing of fiber tracts in the ventral white matter was confirmed by the increased density of the serotonergic plexus around motor neurons. As for chondroitin sulfate proteoglycans, only phosphacan, increased in saline-treated rats, returned to normal levels in rhEPO group, probably reflecting a better maintenance of glial-axolemmal relationships along nerve fibers. In conclusion, this investigation expands previous studies supporting the pleiotropic neuroprotective effect of rhEPO on secondary degenerative response and its therapeutic potential for the treatment of SCI and confirms that the preservation of the ventral white matter, which contains descending motor pathways, may be critical for limiting functional deficit.

Acute and chronic changes in aquaporin 4 expression after spinal cord injury

The effect of spinal cord injury (SCI) on the expression levels and distribution of water channel aquaporin 4 (AQP4) has not been studied. We have found AQP4 in gray and white matter astrocytes in both uninjured and injured rat spinal cords. AQP4 was detected in astrocytic processes that were tightly surrounding neurons and blood vessels, but more robustly in glia limitans externa and interna, which were forming an interface between spinal cord parenchyma and cerebrospinal fluid (CSF). Such spatial distribution of AQP4 suggests a critical role that astrocytes expressing AQP4 play in the transport of water from blood/CSF to spinal cord parenchyma and vice versa. SCI induced biphasic changes in astrocytic AQP4 levels, including its early down-regulation and subsequent persistent up-regulation. However, changes in AQP4 expression did not correlate well with the onset and magnitude of astrocytic activation, when measured as changes in GFAP expression levels. It appears that reactive astrocytes began expressing increased levels of AQP4 after migrating to the wound area (thoracic region) two weeks after SCI, and AQP4 remained significantly elevated for months after SCI. We also showed that increased levels of AQP4 spread away from the lesion site to cervical and lumbar segments, but only in chronically injured spinal cords. Although overall AQP4 expression levels increased in chronically-injured spinal cords, AQP4 immunolabeling in astrocytic processes forming glia limitans externa was decreased, which may indicate impaired water transport through glia limitans externa. Finally, we also showed that SCI-induced changes in AQP4 protein levels correlate, both temporally and spatially, with persistent increases in water content in acutely and chronically injured spinal cords. Although correlative, this finding suggests a possible link between AQP4 and impaired water transport/edema/syringomyelia in contused spinal cords.

Fate of endogenous stem/progenitor cells following spinal cord injury

The adult mammalian spinal cord contains neural stem and/or progenitor cells that slowly multiply throughout life and differentiate exclusively into glia. The contribution of adult progenitors to repair has been highlighted in recent studies, demonstrating extensive cell proliferation and gliogenesis following central nervous system (CNS) trauma. The present experiments aimed to determine the relative roles of endogenously dividing progenitor cells versus quiescent progenitor cells in posttraumatic gliogenesis. Using the mitotic indicator bromodeoxyuridine (BrdU) and a retroviral vector, we found that, in the adult female Fisher 344 rat, endogenously dividing neural progenitors are acutely vulnerable in response to T8 dorsal hemisection spinal cord injury. We then studied the population of cells that divide postinjury in the injury epicenter by delivering BrdU or retrovirus at 24 hours after spinal cord injury. Animals were euthanized at five timepoints postinjury, ranging from 6 hours to 9 weeks after BrdU delivery. At all timepoints, we observed extensive proliferation of ependymal and periependymal cells that immunohistochemically resembled stem/progenitor cells. BrdU+ incorporation was noted to be prominent in NG2-immunoreactive progenitors that matured into oligodendrocytes, and in a transient population of microglia. Using a green fluorescence protein (GFP) hematopoietic chimeric mouse, we determined that 90% of the dividing cells in this early proliferation event originate from the spinal cord, whereas only 10% originate from the bone marrow. Our results suggest that dividing, NG2-expressing progenitor cells are vulnerable to injury, but a separate, immature population of neural stem and/or progenitor cells is activated by injury and rapidly divides to replace this vulnerable population.

Regulation of microglial activities by glial cell line derived neurotrophic factor

Much attention has been paid to the ability of glial cell line-derived neurotrophic factor (GDNF) to protect neurons from neurotoxic insults in the central nervous system (CNS). However, little is known about GDNF action on CNS glia that also can express GDNF receptor systems. In this study, we examined the effects of GDNF on primary rat microglia that function as resident macrophages in the CNS and as the source of proinflammatory mediators upon activation. We found that treatment of primary rat microglia with GDNF had no effect on the secretion of the proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), but it increased the nitric oxide (NO) production to some extent. In addition, GDNF increased the enzymatic activity of superoxide dismutase (SOD), the gene expression of surface antigen intercellular adhesion molecule-1 (ICAM-1), the production of the integrin alpha5 subunit, and the phagocytotic capability in primary rat microglia. Furthermore, inhibition of mitogen-activated protein kinase (Erk-MAPK) in the mouse microglial cell line BV2 by U0126 indicated that the MAP kinase signaling pathway may be involved in the regulation of NO and integrin alpha5 production by GDNF. In vivo evidence also showed that amoeboid cells with integrin alpha5 or with ED1 immunoreactivity appeared in GDNF-treated spinal cord tissues at the lesion site 1 week post spinal cord injury (SCI). Furthermore, inhibition of Erk-MAPK in the mouse microglial cell line BV2 by U0126 indicated that the MAP kinase signaling pathway may be involved in the regulation of NO and integrin alpha5 production by GDNF. Taken together, our results indicate that GDNF has a positive regulatory effect on microglial activities, such as phagocytosis and the upregulation of adhesion molecules.

Effect of injury severity on lower urinary tract function after experimental spinal cord injury

Lower urinary tract dysfunction is a serious burden for patients following spinal cord injury. Patients are usually limited to treatment with urinary drainage catheters, which can lead to repeated urinary tract infections and lower quality of life. Most of the information previously obtained regarding lower urinary tract function after spinal cord injury has been in completely transected animals. After thoracic transection in the rat, plasticity of local lumbosacral spinal circuitry establishes a "reflex bladder," which results in partial recovery of micturition, albeit with reduced voiding efficiency. Since at least half of cord-injured patients exhibit neurologically incomplete injury, rat models of clinically relevant incomplete contusion injury have been developed. With respect to lower urinary tract function, recent anatomical and physiological studies have been performed after incomplete thoracic contusion injury. The results show greater recovery of lower urinary tract function that varies inversely with the severity of the initial trauma and is positively correlated with time after injury. Recovery, as measured by coordination of the bladder with the external urethral sphincter, occurs between 1 and 4 weeks after spinal cord injury. It is associated with normalization of: serotonin immunoreactivity and glutamate receptor subunit mRNA expression in the dorsolateral nucleus that innervates the external urethral sphincter muscle, the response to glutamatergic pharmacological probes administered at the lumbosacral spinal cord level, and c-Fos activation patterns in the lumbar spinal cord. Understanding the mechanisms involved in this recovery will provide a basis for enhancing lower urinary tract function in patients after incomplete spinal cord injury.

Increased growth factor expression and cell proliferation after contusive spinal cord injury

The damage caused by traumatic central nervous system (CNS) injury can be divided into two phases: primary and secondary. The initial injury destroys many of the local neurons and glia and triggers secondary mechanisms that result in further cell loss. Approximately 50% of the astrocytes and oligodendrocytes in the spared white matter of the epicenter die by 24 h after spinal cord injury (SCI), but their densities return to normal levels by 6 weeks. This repopulation is largely due to the proliferation of local progenitors that divide in response of CNS injury. Previous studies indicate that the secondary events that cause cell death after SCI also increase the local levels of several growth factors that stimulate the proliferation of these endogenous progenitors. We compared the spatial pattern of the post-injury up-regulation of the pro-mitotic growth factors with that of 5-bromodeoxyuridine (BrdU) incorporation to determine if each could play a role in proliferation. Three days after a standard contusive SCI or laminectomy, animals received intraperitoneal BrdU injections to label dividing cells and were perfused 2 h after the last injection. Immunohistochemistry for BrdU and basic fibroblast growth factor (FGF2) and in situ hybridization for ciliary neurotrophic factor (CNTF) and glial growth factor (GGF2) mRNA were used to compare the number of dividing cells with growth factor levels in sections 2 and 4 mm from the epicenter. All three growth factors are significantly up-regulated 3 days after SCI, when cell proliferation is maximal. The increase in GGF2 and FGF2 levels is highest in sections 2 mm rostral to the epicenter, mimicking BrdU incorporation. Addition of rhGGF2 to cultured cells isolated from the spinal cord 3 days after SCI increased the number of NG2+ glial progenitors. These data suggest that FGF2 and GGF2 may contribute to the spontaneous recovery observed after SCI by stimulating the proliferation of local progenitors that help repopulate the injured cord.

Real-time quantitative PCR analysis of temporal-spatial alterations in gene expression after spinal cord contusion

Rat spinal cord contusion injury models the histopathology associated with much clinical spinal cord injury (SCI). Studies on altered gene expression after SCI in these models may identify therapeutic targets for reducing secondary injury after the initial trauma and/or enhancing recovery processes. However, complex spatial and temporal alterations after injury could complicate interpretation of changes in gene expression. To test this hypothesis, we selected six genes and studied their temporal and spatial patterns of expression at 1 h, 1, 3 and 7 days after a standardized spinal cord contusion produced by a weight drop device (10 g x 25 mm at T8). Real-time RT-PCR using TaqMan probes was employed to quantify mRNA for proteolipid protein, glyceraldehyde-3-phosphate dehydrogenase, glial fibrillary acidic protein, nestin, and the GluR2 and NR1 subunits of glutamate receptors. We found widely different temporal and spatial patterns of altered gene expression after SCI, including instances of opposing up- and down-regulation at different locations in tissue immediately adjacent to the injury site. We conclude that greater use of the reliable and extremely sensitive technique of quantitative real-time PCR for regional tissue analysis is important for understanding the altered gene expression that occurs after CNS trauma.

Cell proliferation and replacement following contusive spinal cord injury

After spinal cord injury (SCI), about 50% of the oligodendrocytes and astrocytes in the residual white matter at the injury site are lost by 24 h. However, chronically after SCI, the density of oligodendrocytes is normal. Previous studies have shown that the adult rat spinal cord contains a pool of proliferating glial progenitors whose progeny could help restore cell density after injury. To study proliferation in response to injury, we performed SCI on adult female rats at the T8 level, using a standardized contusion model. Animals received bromodeoxyuridine (BrdU) injections during the first week after SCI, and were perfused within 2 h for acute studies, and at 6 weeks for chronic studies. The tissue was analyzed using immunohistochemical detection of BrdU and cell marker antigens. We demonstrate that cell proliferation in the residual white matter is increased at 1-7 days after SCI, peaking on day 3. Dividing cells include oligodendrocytes, astrocytes, microglia/macrophages, and a high proportion of NG2(+) glial precursors. By 6 weeks, some cells that had been labeled 2-4 days after SCI were still present. Double immunohistochemistry showed that while very few of these cells expressed NG2 or the microglia/macrophage marker OX42, about 50% expressed CC1 or glial fibrillary acidic protein (GFAP), markers of mature oligodendrocytes and astrocytes, respectively. The post-injury environment represented by residual white matter is thus permissive to the differentiation of glial precursors. Cells that are stimulated to divide during the first week after SCI develop chronically into mature phenotypes that replace macroglia lost after injury.