Expression of pro-inflammatory cytokine and chemokine mRNA upon experimental spinal cord injury in mouse: an in situ hybridization study

Altered chemokine expression in the spinal cord and brain contributes to differential interleukin-1beta-induced neutrophil recruitment

The pattern of neutrophil recruitment that accompanies inflammation in the CNS depends on the site of injury and the stage of development. The adult brain parenchyma is refractory to neutrophil recruitment and associated damage as compared to the spinal cord or juvenile brain. Using quantitative Taqman RT-PCR and enzyme-liked immunosorbent assay (ELISA), we compared mRNA and protein expression of the rat neutrophil chemoattractant chemokines (CINC) in spinal cord and brain of adult and juvenile rats to identify possible association with the observed differences in neutrophil recruitment. Interleukin-1beta (IL-1beta) injection resulted in up-regulated chemokine expression in both brain and spinal cord. CINC-3 mRNA was elevated above CINC-1 and CINC-2alpha, with expression levels for each higher in spinal cord than in brain. By ELISA, IL-1beta induced greater CINC-1 and CINC-2alpha expression compared to CINC-3, with higher protein levels in spinal cord than in brain. In the juvenile brain, significantly higher levels of CINC-2alpha protein were observed in response to IL-1beta injection than in the adult brain following an equivalent challenge. Correspondingly, neutrophil recruitment was observed in the juvenile brain and adult spinal cord, but not in the adult brain. No expression of CINC-2beta mRNA was detected. Thus differential chemokine induction may contribute to variations in neutrophil recruitment in during development and between the different CNS compartments.

Induction of manganese superoxide dismutase in acute spinal cord injury

Free radical-mediated mechanisms of cellular damage have been implicated in the early stages of spinal cord injury (SCI). Manganese superoxide dismutase (MnSOD) is a potent scavenger of superoxide radicals and likely serves an important cytoprotective role in preventing cellular damage after SCI. We have evaluated the expression of MnSOD to address its role during the early events of SCI using a well-established rat contusion model. Northern analysis showed a rapid induction of MnSOD mRNA between 2 and 6 h post injury. Observed time-dependent increases in MnSOD message was maximal 6 h post injury over that of MnSOD mRNA levels induced by laminectomy alone. Immunoblot and immunohistochemical analysis demonstrated increased expression of MnSOD protein 24 h after SCI with localization primarily within neurons. Interestingly, laminectomy alone also caused an induction of MnSOD gene and protein expression. To evaluate one potential mechanism of MnSOD induction, we microinjected the naive spinal cord with IL-1beta, which caused a similar fold induction of MnSOD mRNA levels by 6 h as observed with SCI, thus implicating it as a potential inducer of MnSOD during SCI. In summary, these results demonstrate that this potent cytoprotective antioxidant enzyme is rapidly and significantly induced as a consequence of SCI.

The neuropathological and behavioral consequences of intraspinal microglial/macrophage activation

Activated microglia and macrophages (CNS macrophages) have been implicated in the secondary or "bystander" pathology (e.g. axon injury, demyelination) that accompanies traumatic or autoimmune injury to the brain and spinal cord. These cells also can provide neurotrophic support and promote axonal regeneration. Studying the divergent functional potential of CNS macrophages in trauma models is especially difficult due to the various degradative mechanisms that are initiated prior to or concomitant with microglial/macrophage activation (e.g. hemorrhage, edema, excitotoxicity, lipid peroxidation). To study the potential impact of activated CNS macrophages on the spinal cord parenchyma, we have characterized an in vivo model of non-traumatic spinal cord neuroinflammation. Specifically, focal activation of CNS macrophages was achieved using stereotaxic microinjections of zymosan. Although microinjection does not cause direct mechanical trauma, localized activation of macrophages with zymosan acts as an "inflammatory scalpel" causing tissue injury at and nearby the injection site. The present data reveal that activation of CNS macrophages in vivo can result in permanent axonal injury and demyelination. Moreover, the pathology can be graded and localized to specific white matter tracts to produce quantifiable behavioral deficits. Further development of this model will help to clarify the biological potential of microglia and macrophages and the molecular signals that control their function within the spinal cord.

Monocyte recruitment and myelin removal are delayed following spinal cord injury in mice with CCR2 chemokine receptor deletion

The inflammatory response initiated after spinal cord injury (SCI) is characterized by the accumulation of macrophages at the impact site. Monocyte chemoattractant protein-1 (MCP-1) is a strong candidate for mediating chemotaxis of monocytes to the injured nervous system. To help in defining the role of MCP-1 in inflammation after SCI, we evaluated the time course of macrophage accumulation for 2 weeks following a midthoracic spinal cord contusion injury in mice lacking CCR2, a principal receptor for MCP-1. Mice with a deletion of CCR2 resulted in significantly reduced Mac-1 immunoreactivity restricted to the lesion epicenter at 7 days postinjury. The regions devoid of Mac-1 immunoreactivity corresponded to areas of reduced myelin degradation at this time. By 14 days postinjury, however, there were no differences in Mac-1 staining between CCR2 (+/+) and CCR2 (-/-) mice. Analyses of mRNA levels by RNase protection assay (RPA) revealed increases in MCP-1 as well as MCP-3 and MIP-2 mRNA at 1 day postinjury compared with 7 day postinjury. There were no differences in chemokine expression between CCR2-deficient mice and wild-type littermate controls. The CCR2-deficient mice also exhibited reduced expression of mRNA for chemokine receptors CCR1 and CCR5. Together, these results indicate that chemokines acting through CCR2 contribute to the early recruitment of monocytes to the lesion epicenter following SCI.

Targeting the host inflammatory response in traumatic spinal cord injury

Both acute and chronic inflammatory processes have been shown to influence outcome in experimental models of spinal cord injury. Although early inflammatory responses may participate in secondary injury processes, more delayed inflammatory events may be reparative. Therapeutic strategies that target these events are currently based on experimental findings that have clarified the cellular and molecular processes involved in the inflammatory response to injury. An increasing body of literature supports the hypothesis that acute inflammatory events are attenuated by therapeutic hypothermia and other anti-inflammatory strategies, whereas immune neuroprotection and axonal regeneration can be achieved by transfer of activated T cells or by treatment with therapeutic vaccines. These data are summarized in the present review.

Interleukin-4, interleukin-10, and interleukin-1-receptor antagonist but not transforming growth factor-beta induce ramification and reduce adhesion molecule expression of rat microglial cells

The activity of microglial cells is strictly controlled in order to maintain central nervous system (CNS) immune privilege. We hypothesized that several immunomodulatory factors present in the CNS parenchyma, i.e., the Th2-derived cytokines interleukin (IL)-4 and IL-10, interleukin-1-receptor-antagonist (IL-1-ra), or transforming growth factor (TGF)-beta can modulate microglial morphology and functions. Microglial cells were incubated with IL-4, IL-10, IL-1-ra, TGF-beta, or with astrocyte conditioned media (ACM) and were analyzed for morphological changes, expression of intercellular adhesion molecule (ICAM)-1, and secretion of IL-1beta or tumor necrosis factor (TNF)-alpha. Whereas untreated controls showed an amoeboid morphology both Th2-derived cytokines, IL-1-ra, and ACM induced a morphological transformation to the ramified phenotype. In contrast, TGF-beta-treated microglial cells showed an amoeboid morphology. Even combined with the neutralizing antibodies against IL-4, IL-10, or TGF-beta ACM induced microglial ramification. Furthermore, ACM did not contain relevant amounts of IL-4 and IL-10, as measured by enzyme-linked immunosorbent assay (ELISA). Flow cytometry showed that lipopolysaccharide (LPS)-induced ICAM-1-expression on microglial cells was strongly suppressed by ACM, significantly modulated by IL-4, IL-10, or IL-1-ra, but not influenced by TGF-beta. The LPS-induced secretion of IL-1beta and TNF-alpha was only reduced after application of ACM, whereas IL-4 or IL-10 did not inhibit IL-1beta- or TNF-alpha secretion. TGF-beta enhanced IL-1beta- but not TNF-alpha secretion. In summary, we demonstrate that IL-4, IL-10, and IL-1-ra induce microglial ramification and reduce ICAM-1-expression, whereas the secretion of proinflammatory cytokines is not prevented. TGF-beta has no modulating effects. Importantly, unidentified astrocytic factors that are not identical with IL-4, IL-10, or TGF-beta possess strong immunomodulatory properties.

DNA microarray analysis of the contused spinal cord: effect of NMDA receptor inhibition

Spinal cord injury (SCI)-induced neurodegeneration leads to irreversible and devastating motor and sensory dysfunction. Post-traumatic outcomes are determined by events occurring during the first 24 hours after SCI. An increase in extracellular glutamate concentration to neurotoxic levels is one of the earliest events after SCI. We used Affymetrix DNA oligonucleotide microarrays (with 1,322 DNA probes) analysis to measure gene expression in order to test the hypothesis that SCI-induced N-methyl-D-aspartate (NMDA) receptor activation triggers significant postinjury transcriptional changes. Here we report that SCI, 1 hour after trauma, induced change in mRNA levels of 165 genes and expression sequence tags (ESTs). SCI affected mRNA levels of those genes that regulate predominantly transcription factors, inflammation, cell survival, and membrane excitability. We also report that NMDA receptor inhibition (with -(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate [MK-801]) reversed the effect of SCI on about 50% of the SCI-affected mRNAs. Especially interesting is the finding that NMDA receptor activation participates in the up-regulation of inflammatory factors. Therefore, SCI-induced NMDA receptor activation is one of the dominant, early signals after trauma that leads to changes in mRNA levels of a number of genes relevant to recovery processes. The majority of MK-801 effects on the SCI-induced mRNA changes reported here are novel. Additionally, we found that the MK-801 treatment also changed the mRNA levels of 168 genes and ESTs that had not been affected by SCI alone, and that some of their gene products could have harmful effects on SCI outcome.

Cytokine activity contributes to induction of inflammatory cytokine mRNAs in spinal cord following contusion

Injury of the spinal cord leads to an inflammatory tissue response, probably mediated in part by cytokines. Because a common therapy for acute spinal cord injury is the use of an antiinflammatory synthetic glucocorticoid (methylprednisolone), we sought to determine mechanisms contributing to inflammation shortly after acute injury. Cytokine mRNAs [interleukin (IL)-1alpha, IL-1beta, tumor necrosis factor (TNF)-alpha, and IL-6] were increased during the first 2 hr following weight-drop compression injury by RNase protection assay, prior to the reported appearance of circulating lymphocytes. This immediate pattern of cytokine mRNA induction could be replicated in cultured, explanted spinal cord slices but not in whole blood of injured animals, which is consistent with a tissue source of cytokine mRNAs. Western blotting detected IL-1beta-like immunoreactivity released into culture medium following explantation and pro-IL-1beta-like immunoreactivity in freshly dissected spinal cord tissue. Pharmacologically blocking IL-1 and TNF-alpha receptors significantly reduced expression of IL-1alpha, IL-1beta, and TNF-alpha mRNAs. Finally, mice lacking both IL-1 and TNF-alpha receptors exhibited diminished induction of TNF-alpha, IL-6, and IL-1ra mRNAs following injury. Therefore, we conclude that contusion injury induces an immediate release of cytokines, which then contributes to the induction of cytokine mRNAs.

Heme oxygenase-1 expression after spinal cord injury: the induction in activated neutrophils

Tissue damage and neurological dysfunction after spinal cord injury may result, in part, from delayed or secondary mechanisms that appear to involve several endogenous factors. Among them, neutrophils are known to play important roles in the pathomechanisms of the secondary injury, that is, neutrophils are activated by an interaction with the endothelial cells, migrate into the damaged tissue and release several kinds of proteases or oxygen radicals. In the present study, we examined heme oxygenase-1 expression in the damaged spinal cord. The administration of an inhibitor of heme oxygenase-1 in vivo produced a delayed recovery of motor function after spinal cord injury, suggesting that heme oxygenase-1 may play roles as an endogenous anti-inflammatory enzyme and protective gene in the damaged and inflammatory tissue. We found that many neutrophils expressing heme oxygenase-1 mRNA and protein were recruited into the damaged spinal cord with extensive hemorrhages during early stage of spinal cord injury. In an in vitro study, neutrophils incubated with proinflammatory cytokines, such as interleukin-1, 6 or interferon-gamma, expressed heme oxygenase-1 mRNA and protein. Based on these findings we conclude that the activated neutrophils can express heme oxygenase-1 in the injured spinal cord tissue, perhaps expecting modulatory and neuroprotective actions in the inflammatory response to spinal cord injury.

Non-surgical management of spinal cord injury

Spinal cord injury remains a devastating neurological condition with limited therapeutic opportunities. Since decompressive surgery and high-dose methylprednisolone have limited utility for most patients, spinal cord injury clearly represents a major medical challenge. Experimental evidence has suggested that secondary cellular injury processes may be a realistic target for therapeutic intervention with the goal of inhibiting the progression of detrimental changes that normally follows traumatic injury to the cord. Preventing or reducing this delayed cellular injury may alone improve neurological recovery or facilitate future regenerative approaches to the injured cord. This review summarises recent advances in the development of pharmacological agents targeting the acute phase of spinal cord injury as well as potential strategies to facilitate regeneration of the spinal cord.

Expression of functional chemokine receptors by rat cerebellar neurons

In this study, we examined chemokine receptor expression and function in rat cerebellar neurons. Calcium imaging experiments demonstrated that a wide variety of chemokines elicited [Ca(2+)](i) transients in acutely isolated and cultured cerebellar Purkinje and granule neurons. In many cases, these chemokine responses were pertussis toxin (PTX) insensitive. In addition, chemokines activated the Ca(2+) and cAMP-dependent transcription factor CREB and the extracellular response kinases ERK1/ERK2. Chemokines increased the survival of Purkinje neurons deprived of their trophic support. Thus, the presence of chemokine receptors and the signaling pathways they activate suggest that chemokines play a role in the control of cerebellar neuron survival and development and may mediate communication between the CNS and the immune system.

Spinal cord injury induces expression of RGS7 in microglia/macrophages in rats

RGS proteins regulate G protein-mediated signalling pathways through direct interaction with the Galpha subunits and facilitation of GTP hydrolysis. An RGS subfamily consisting of RGS 6, 7, 9, and 11 also interacts with the G protein beta subunit Gbeta5 via a characteristic Ggamma-like domain. Thus far, these complexes were found only in neurons, with RGS7 being the most widely distributed in the brain. Here we confirm the expression of RGS7 in spinal neurons and show as a novel finding that following an experimental spinal cord injury in rats, expression of RGS7 is induced in a subpopulation of other cells. Immunofluorescent confocal microscopy using a series of cell specific antibodies identified these RGS7 positive cells as activated microglia and/or invading peripheral macrophages. To rule out interference from the adjacent neurons and confirm the presence of RGS7-Gbeta5 complex in inflammatory cells, we performed immunocytochemistry, RT-PCR, Western blot, and immunoprecipitation using microglial (BV2) and peripheral macrophage (RAW) cell lines. Expression of RGS7 mRNA and protein are nearly undetectable in non-stimulated BV2 and RAW cells, but remarkably increased after stimulation with LPS or TNF-alpha In addition, RGS7-positive cells were also found in the perinodular rim in the rat spleen. Our findings show that RGS7-Gbeta5 complex is expressed in immunocompetent cells such as resident microglia and peripheral macrophages following spinal cord injury. This expression might contribute to the post-traumatic inflammatory responses in the central nervous system.

Recruiting the immune response to promote axon regeneration in the injured spinal cord

Myelin contains molecules that can inhibit the growth and regeneration of axons. Neutralizing the activity of these inhibitors can enhance axon regeneration in the adult mammalian central nervous system (CNS). The complexity of the CNS-immune system interactions after CNS trauma is now beginning to be better understood. Recent studies indicate that both cell-mediated and antibody-mediated immune responses can help in promoting axon regeneration after CNS injury. It is hoped that such advances will lead to the development of safe and effective vaccine and cytokine treatments for spinal cord injuries.

Development and characterization of a novel, graded model of clip compressive spinal cord injury in the mouse: Part 1. Clip design, behavioral outcomes, and histopathology

In order to take advantage of various genetically manipulated mice available to study the pathophysiology of spinal cord injury (SCI), we adapted an extradural clip compression injury model to the mouse (FEJOTA mouse clip). The dimensions of the modified aneurysm clip blades were customized for application to the mouse spinal cord. Three clips with different springs were made to produce differing magnitudes of closing force (3, 8, and 24 g). The clips were calibrated regularly to ensure that the closing force remained constant. The surgical procedure involved a laminectomy at T3 and T4, followed by extradural application of the clip at this level for 1 min to produce SCI. Three injury severities (3, 8, and 24 g), sham (passage of dissector extradurally at T3-4), and transection control groups were examined (n = 12/group). Quantitative behavioural assessments using the Basso, Beattie, and Bresnahan (BBB; H > 46; df = 4; p < 0.001; Kruskal-Wallis one-way ANOVA) and inclined plane (IP; F = 123; df = 4; p < 0.0001; two-way repeated measures ANOVA) tests showed a significant graded increase in neurological deficits with increasing severity of injury. By day 14, the motor recovery of the mice plateaued. Qualitative examination of the injury site morphology indicated that microcystic cavitation, degenerating axons, and robust astrogliosis were characteristic of the murine response to clip compressive SCI. Morphometric analyses of H&E/Luxol Fast Blue stained sections at every 50 microm from the injury epicenter indicated that with greater injury severity there was a progressive decrease in residual tissue (F = 220, df = 3; p < 0.0001; two-way ANOVA). In addition, statistically significant differences were found in the amount of residual tissue at the injury epicenter between all of the injury severities (p < 0.05, SNK test). This novel, graded compressive model of SCI will facilitate future studies of the pathological mechanisms of SCI using transgenic and knockout murine systems.

PAF antagonist treatment reduces pro-inflammatory cytokine mRNA after spinal cord injury

Platelet-activating factor (PAF) is a pro-inflammatory molecule which contributes to secondary damage after spinal cord injury (SCI). To test if PAF contributes to cytokine induction following SCI, female Long-Evans rats were pretreated with the PAF antagonist WEB 2170 prior to receiving a contusion injury at spinal cord level T10 using the NYU impactor. RNase protection assay (RPA) analysis revealed that IL-1alpha mRNA peaked at I h post-injury while IL-1beta and IL-6 mRNA levels were higher and peaked at 6 h.TNF-alpha mRNA was almost undetectable. All mRNA levels approached baseline by 24 h. Treatment with WEB 2170 (1 mg/kg, i.p.) 15 min prior to injury significantly decreased mRNA levels for all three cytokines at 6 h post-injury, but not at I h post-injury. These results demonstrate a role for PAF in proinflammatory cytokine induction after SCI.

Gene expression profiling of acute spinal cord injury reveals spreading inflammatory signals and neuron loss

We have completed the first large-scale gene expression study of acute spinal cord injury (SCI) in rat. Oligonucleotide microarrays containing 1,200 gene-specific probes were used to quantify mRNA levels, relative to uninjured controls, in spinal cords injured using a standard contusion model. Our results revealed a marked loss of neuron-specific mRNAs at the injury site. The surviving cells showed a characteristic inflammatory response that started at the injury site and spread to the distal cord. Changes in several mRNA levels were associated with putative regenerative responses in the spinal cord. Notably, phosphodiesterase 4, nestin, glia-derived neurite promoting factor, and GAP-43 mRNAs increased significantly. Other mRNAs clustered temporally and spatially with these regeneration-associated genes. Thus we have described global patterns of gene expression following acute SCI, and we have identified targets for future study and possible therapeutic intervention.

GeneChip analysis after acute spinal cord injury in rat

Spinal cord injury (SCI) leads to induction and/or suppression of several genes, the interplay of which governs the neuronal death and subsequent loss of motor function. Using GeneChip, the present study analyzed changes in the mRNA abundance at 3 and 24 h after SCI in adult rats. SCI was induced at T9 level by the New York University impactor by dropping a 10-g weight from a height of 25 mm. Several transcription factors, immediate early genes, heat-shock proteins, pro-inflammatory genes were up-regulated by 3 h, and persisted at 24 h, after SCI. On the other hand, some neurotransmitter receptors and transporters, ion channels, kinases and structural proteins were down-regulated by 3 h, and persisted at 24 h, after SCI. Several genes that play a role in growth/differentiation, survival and neuroprotection were up-regulated at 24 h after SCI. Using real-time quantitative PCR, the changes observed by GeneChip were confirmed for seven up-regulated (interleukin-6, heat-shock protein-70, heme oxygenase-1, suppressor of cytokine signaling 2, suppressor of cytokine signaling 3, interferon regulatory factor-1, neuropeptide Y), two down-regulated (vesicular GABA transporter and cholecystokinin precursor) and two unchanged (Cu/Zn-superoxide dismutase and phosphatidyl inositol-3-kinase) genes. The present study shows that inflammation, neurotransmitter dysfunction, increased transcription, ionic imbalance and cytoskeletal damage starts as early as 3 h after SCI. In addition to these effects, 24 h after SCI the repair and regeneration process begins in an attempt to stabilize the injured spinal cord.

Apoptotic death of neurons exhibiting peripherin aggregates is mediated by the proinflammatory cytokine tumor necrosis factor-alpha

Peripherin, a neuronal intermediate filament protein associated with axonal spheroids in amyotrophic lateral sclerosis (ALS), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. To further clarify the selectivity and mechanism of peripherin-induced neuronal death, we analyzed the effects of peripherin overexpression in primary neuronal cultures. Peripherin overexpression led to the formation of cytoplasmic protein aggregates and caused the death not only of motor neurons, but also of dorsal root ganglion (DRG) neurons that were cultured from dissociated spinal cords of peripherin transgenic embryos. Apoptosis of DRG neurons containing peripherin aggregates was dependent on the proinflammatory central nervous system environment of spinal cultures, rich in activated microglia, and required TNF-alpha. This synergistic proapoptotic effect may contribute to neuronal selectivity in ALS.

Repetitive intrathecal injections of poliovirus replicons result in gene expression in neurons of the central nervous system without pathogenesis

Poliovirus-based vectors (replicons) can be used for gene delivery to motor neurons of the CNS. In the current study, a replicon encoding green fluorescent protein (GFP) was encapsidated into authentic poliovirions, using established procedures. Intrathecal delivery of encapsidated replicons encoding GFP to the CNS of mice transgenic for the human poliovirus receptor did not result in any functional deficits as judged by behavioral testing. Histological analysis of the CNS of mice given a single intrathecal injection of poliovirus replicons encoding GFP revealed no obvious pathogenesis in neurons (or other cell types) within the CNS. The expression of GFP was confined to motor neurons throughout the neuroaxis; a time course of expression of GFP revealed that expression was detectable 24 hr postinoculation and returned to background levels by 120 hr postinoculation. A procedure was devised to allow repetitive inoculation of replicons within the same animal. Behavioral testing of animals that had received 6 to 13 independent inoculations of replicons revealed no functional deficits. Histological analysis of the CNS from animals that had received 6 to 13 sequential inoculations of replicons revealed no obvious abnormalities in neurons or other cell types in the CNS; expression of GFP was demonstrated in neurons 24 to 72 hr after the final inoculation of the replicon. Furthermore, there was no obvious inflammatory response in the CNS after the multiple inoculations. These studies establish the safety and efficacy of replicons for gene delivery to the CNS and are discussed with respect to use of replicons as new therapeutic strategies for spinal cord injuries and/or neurological diseases.

Tumor necrosis factor receptor deletion reduces nuclear factor-kappaB activation, cellular inhibitor of apoptosis protein 2 expression, and functional recovery after traumatic spinal cord injury

Tumor necrosis factor-alpha (TNF-alpha) expression has been documented extensively in animal models of traumatic spinal cord injury (SCI). However, the pathophysiological significance of TNF-alpha expression in the injured cord remains to be delineated. The TNF receptor (TNFR)-nuclear factor-kappaB (NF-kappaB) signal transduction pathway is important for maintaining cell viability. NF-kappaB exerts anti-apoptotic effects via an endogenous caspase inhibitory system mediated by cellular inhibitor of apoptosis protein 2 (c-IAP2). NF-kappaB transactivates c-IAP2 to inhibit caspase-3 activation. Progressive cell death, including morphological and biochemical features suggestive of apoptosis, has been noted after SCI. We explored the effects of TNFR1 or TNFR2 deletion on the apoptotic events downstream of NF-kappaB in relation to SCI pathology and functional recovery. Nuclear proteins from the injured cords of the TNFR1(-/-) mice had a reduced NF-kappaB binding activity compared with the wild-type controls. This decrease in NF-kappaB activation was accompanied by a reduction in c-IAP2 expression and an increase in the active form of caspase-3 protein. After SCI the TNFR1(-/-) mice had greater numbers of apoptotic cells, a larger lesion size, and worse functional recovery than wild-type mice. TNFR2-deficient mice had a similar, although not as pronounced, consequence as the TNFR1(-/-) mice. These findings support the argument that the TNFR-NF-kappaB pathway is beneficial for limiting apoptotic cell death after SCI and that a defective TNFR-NF-kappaB pathway results in a poorer neurological outcome. A worse functional outcome in TNFR(-/-) mice suggests that an endogenous apoptosis inhibitory mechanism mediated by TNFR activation, NF-kappaB, and c-IAP2 may be of pathophysiological importance.

A neutrophil elastase inhibitor (ONO-5046) reduces neurologic damage after spinal cord injury in rats

In view of a cytoprotective effect of elastase inhibitor on chemokine-mediated tissue injury, we examined the neuroprotective effect of ONO-5046, a specific inhibitor of neutrophil elastase, in rats with spinal cord injury. Standardized spinal cord compression markedly increased cytokine-induced neutrophil chemo-attractant (CINC)-1 mRNA and protein. Their increases correlated with neurologic severity of injured rats. Immunohistochemically, CINC-1 protein was detected sequentially in vascular endothelial cells at 4 h, in perivascular neutrophils at 8 h, and in neutrophils infiltrating into cord substance at 12 h. Pretreatment with ONO-5046 (50 mg/kg) markedly ameliorated motor disturbance in injured rats, and reduced CINC-1 protein and mRNA expression. ONO-5046 also significantly reduced the increase of neutrophil accumulation or infiltration estimated by myeloperoxidase activity, and the extent of vascular permeability by Evans blue extravasation in the injured cord segment in comparison to control animals receiving vehicle. These results suggest that CINC-1 contributed to inflammation in rat spinal cord injury and ONO-5046 attenuated neurologic damage partly by blocking CINC-1 production of the chemoattractant, preventing neutrophil activation and vascular endothelial cell injury.

IL-1 receptor antagonist prevents apoptosis and caspase-3 activation after spinal cord injury

One of the consequences of cytokine-orchestrated inflammation after CNS trauma is apoptosis. Our hypothesis is that cell death in the spinal cord after injury results in part from increased synthesis and release of IL-1beta. Using a ribonuclease protection assay, we demonstrated that there is increased transient expression of IL-1beta mRNA and, by using IL-1beta protein ELISA assay, that there are increased IL-1beta protein levels in the contused rat spinal cord, initially localized to the impact region of the spinal cord (segment T8). Using an ELISA cell death assay, we showed that there is apoptosis in the spinal cord 72 h after injury, a finding that was confirmed by measuring caspase-3 activity, which also significantly increased at the site of injury 72 h after trauma. Treatment of the contused spinal cord at the site of injury with the IL-1 receptor antagonist (rmIL-lra, 750 ng/mL) for 72 h using an osmotic minipump completely abolished the increases in contusion-induced apoptosis and caspase-3 activity.

Support of axonal regrowth by endogenous mechanisms following spinal cord injury in adult rats

Because of its non-invasive nature and ease of regulation, a closely monitored cryogenic method of tissue injury was used to create a degree of spinal cord injury within which there would be an extended regrowth of axons. The parameters of cooling used in the present study resulted in an injury length of 1 cm through which 3 mm of measured axonal regrowth and 8 mm of observed regrowth occurred over a 56-day period in the ascending fibers of the dorsal column of the mature rat. This was associated with the development of a cellular matrix consisting of macrophages, macroglia and Schwann cells which gradually expands within the injured area initially dominated by macrophages. It is the authors' impression that the presence of a substantial microglial component within the macrophage population may be a significant factor in the success of the axonal regrowth. Under this influence and that of the invading axons, the astrocyte, which provides the immediate cell support to the growing axon, can be maintained in a functional state that is supportive and not obstructive to the axon, presumably through the recruitment of astrocyte precursors from an indigenous stem cell population. These tissue changes indicate that adult mammalian spinal cord tissue does have the capacity to develop on its own a matrix capable of supporting the regrowth of axons.

MIP-1alpha, MCP-1, GM-CSF, and TNF-alpha control the immune cell response that mediates rapid phagocytosis of myelin from the adult mouse spinal cord

The slow immune response in the adult mammalian CNS results in slow myelin phagocytosis along degenerating white matter after injury. This has important consequences for axon regeneration because of the presence of axon growth inhibitors in myelin. In addition, abnormal immune cell responses in the CNS lead to demyelinating disease. Lysophosphatidylcholine (LPC) can induce an inflammatory response in the CNS, producing rapid demyelination without much damage to adjacent cells. In this study, we searched for the molecular switches that turn on this immune cell response. Using reverse transcription PCR analysis, we show that mRNA expression of macrophage inflammatory protein-1alpha (MIP-1alpha), macrophage chemotactic protein-1 (MCP-1), granulocyte macrophage-colony stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF-alpha) in the spinal cord is rapidly and transiently upregulated after intraspinal injection of LPC. Neutralizing these signaling molecules with function-blocking antibodies suppresses recruitment of T-cells, neutrophils, and monocytes into the spinal cord, as well as significantly reduces the number of phagocytic macrophages and the demyelination induced by LPC. These findings will have important implications for CNS regeneration and demyelinating disease.

Bone marrow chimeric rats reveal the unique distribution of resident and recruited macrophages in the contused rat spinal cord

Brain and spinal cord inflammation that develops after traumatic injury is believed to differentially influence the structural and/or physiological integrity of surviving neurons and glia. It is possible that the functional dichotomy of CNS inflammation results from the activity of a heterogeneous macrophage population elicited by trauma. Indeed, unique functions have been attributed to macrophages derived from resident microglia versus those originating from infiltrating monocytes. Thus, whether progressive tissue injury or repair is favored could be explained by the disproportionate contributions of one macrophage subset relative to the other. Descriptive neuroanatomical studies are a reasonable first approach to revealing a relationship between microglia, recruited blood monocytes/macrophages, and regions of tissue degeneration and/or repair. Unfortunately, it is not possible to differentiate between CNS macrophage subsets using conventional immunohistochemical approaches. In the present study, we have used radiation bone marrow chimeric rats to definitively characterize the macrophage reaction elicited by experimental spinal contusion injury. In chimeric animals, antibodies raised against unique cell surface molecules expressed on bone marrow-derived cells (BMCs) were used to distinguish infiltrating BMCs from resident microglial-derived macrophages. Our findings indicate that the onset and plateau of macrophage activation (previously shown to be 3 and 7 days postinjury, respectively) is dominated initially by microglial-derived macrophages and then is supplanted by hematogenous cells. While resident macrophages are ubiquitously distributed throughout the injury site, leukocyte-derived monocytes exclusively infiltrate the gray matter and to a lesser extent subpial white matter. Generally, monocyte foci in white matter remain associated with the lumen or abluminal surface of blood vessels, i.e. few cells actually infiltrate the parenchyma. If functional differences exist between CNS macrophage subsets, differences in the time-dependent accumulation and distribution of these cell types could differentially influence the survival of surrounding neurons and glia.

Astrocytic factors protect neuronal integrity and reduce microglial activation in an in vitro model of N-methyl-D-aspartate-induced excitotoxic injury in organotypic hippocampal slice cultures

Acute CNS lesions lead to neuronal injury and a parallel glial activation that is accompanied by the release of neurotoxic substances. The extent of the original neuronal damage can therefore be potentiated in a process called secondary damage. As astrocytes are known to secrete immunomodulatory and neuroprotective substances, we investigated whether astrocytic factors can attenuate the amount of neuronal injury as well as the degree of microglial activation in a model of excitotoxic neurodegeneration. Treatment of organotypic hippocampal slice cultures with N-methyl-D-aspartate (NMDA) resulted in a reproducible loss of viable granule cells, partial destruction of the regular hippocampal cytoarchitecture and a concomitant accumulation of amoeboid microglial cells at sites of neuronal damage. Astrocyte-conditioned media reduced the amount of NMDA-induced neuronal injury by 45.3%, diminished the degree of microglial activation and resulted in an improved preservation of the hippocampal cytoarchitecture. Transforming growth factor (TGF)-beta failed to act as a neuroprotectant and even enhanced the amount of neuronal injury by 52.5%. Direct effects of astrocytic factors on isolated microglial cells consisted of increased microglial ramification and down-regulated expression of intercellular adhesion molecule-1, whereas incubation with TGF-beta had no such effects. In summary, our findings show that hitherto unidentified astrocyte-derived factors that are probably not identical with TGF-beta can substantially enhance neuronal survival, either by eliciting direct neuroprotective effects or by modulating the microglial response to neuronal injury.

Differences in Neurotrophic Factor Gene Expression Profiles between Neonate and Adult Rat Spinal Cord after Injury

The capacity of the central nervous system for axonal growth decreases as the age of the animal at the time of injury increases. Changes in the expression of neurotrophic factors within embryonic and early postnatal spinal cord suggest that a lack of trophic support contributes to this restrictive growth environment. We examined neurotrophic factor gene profiles by ribonuclease protection assay in normal neonate and normal adult spinal cord and in neonate and adult spinal cord after injury. Our results show that in the normal developing spinal cord between postnatal days 3 (P3) and P10, compared to the normal adult spinal cord, there are higher levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and glial-derived neurotrophic factor (GDNF) mRNA expression and a lower level of ciliary neurotrophic factor (CNTF) mRNA expression. Between P10 and P17, there is a significant decrease in the expression of NGF, BDNF, NT-3, and GDNF mRNA and a contrasting steady and significant increase in the level of CNTF mRNA expression. These findings show that there is a critical shift in neurotrophic factor expression in normal developing spinal cord between P10 and P17. In neonate spinal cord after injury, there is a significantly higher level of BDNF mRNA expression and a significantly lower level of CNTF mRNA expression compared to those observed in the adult spinal cord after injury. These findings suggest that high levels of BDNF mRNA expression and low levels of CNTF mRNA expression play important roles in axonal regrowth in early postnatal spinal cord after injury.

Cellular localization of tumor necrosis factor-alpha following acute spinal cord injury in adult rats

Posttraumatic inflammatory reaction may contribute to secondary injury after traumatic spinal cord injury (SCI). Expression of tumor necrosis factor-alpha (TNF-alpha), a key inflammatory mediator, has been demonstrated in the injured cord. However, the specific cell types that are responsible for TNF-alpha expression after SCI remain to be identified. In the present study, cellular sources of TNF-alpha were examined in rats that received a spinal cord impact injury at the 9th thoracic (T9) level. Here we demonstrate that, within hours after SCI, increased TNF-alpha immunoreactivity was localized in neurons, glial cells (including astrocytes, oligodendrocytes, and microglia), and endothelial cells in areas of the spinal cord adjacent to the lesion site. Myelin breakdown was noted in oligodendrocytes that are immunopositive for TNF-alpha. In sham-operated controls, a low level of TNF-alpha immunoreactivity was detected. In antigen-absorption experiments, no TNF-alpha immunoreactivity was detected, indicating the specificity of TNF-alpha immunocytochemistry in the present study. Results suggest that various cell types, including neurons, glial cells, and vascular endothelial cells, contribute to TNF-alpha production in the injured cord.

Methylprednisolone reduces spinal cord injury in rats without affecting tumor necrosis factor-alpha production

Methylprednisolone (MPS) is the only therapeutic agent currently available for traumatic spinal cord injury (SCI). However, little is known about its therapeutic mechanisms. We have demonstrated that tumor necrosis factor-alpha (TNF-alpha) plays a critical role in posttraumatic SCI in rats. Since MPS has been shown to inhibit TNF-alpha production in vitro, it is possible that MPS can reduce SCI by inhibiting TNF-alpha production. To examine this possibility, we investigated the effect of MPS on TNF-alpha production in injured segments of rat spinal cord. Leukocytopenia and high-dose intravenous administration of MPS markedly reduced the motor disturbances observed following spinal cord trauma. Both treatments also reduced the intramedullary hemorrhages observed histologically 24 hr posttrauma. Leukocytopenia significantly reduced tissue levels of both TNF-alpha mRNA and TNF-alpha, 1 and 4 hr posttrauma, respectively, and it also inhibited the accumulation of leukocytes in the injured segments 3 hr posttrauma, while MPS had no effects. Lipid peroxidation and vascular permeability at the site of spinal cord lesion were both significantly increased over time after the induction of SCI, peaking 3 hr posttrauma. These events were significantly reduced in animals with leukocytopenia and in those given anti-P-selectin monoclonal antibody compared to sham-operated animals. Administration of MPS significantly inhibited both the increase in lipid peroxidation and the vascular permeability. These findings suggested that MPS reduces the severity of SCI, not by inhibiting the production of TNF-alpha at the site of spinal cord trauma, but by inhibiting activated leukocyte induced lipid peroxidation of the endothelial cell membrane. This suggests that MPS may attenuate spinal cord ischemia by inhibiting the increase in endothelial permeability at the site of spinal cord injury.

Intrathecally administered endotoxin or cytokines produce allodynia, hyperalgesia and changes in spinal cord neuronal responses to nociceptive stimuli in the rat

Inflammatory processes occurring within the central nervous system (CNS) can produce 'illness induced behaviours' which include fever, sleep and the development of allodynia and hyperalgesia. Here we demonstrate the effects of the pro-inflammatory mediators, bacterial endotoxin, and rat recombinant interleukin 1 beta (rrIL-1 beta) or tumour necrosis factor-alpha (rrTNF alpha) on the integration of somatosensory information at the single neuronal level, via recordings from wide-dynamic range neurones in the dorsal horn of the spinal cord in anaesthetized rats. Intrathecal administration of E. coli lipopolysaccharide (LPS, 10 and 100 microg, i.t.) enhanced the activity of dorsal horn neurones, including facilitation of neuronal post-discharge. Intrathecal administration of IL-1 beta (5-5000 pg) or TNF-alpha (5-5000 pg) enhanced dorsal horn neuronal responses, including the acute responses to C-fibre stimulation, wind-up and post-discharge, however, the effects of IL-1 beta were more robust than those of TNF alpha. Intrathecal administration of IL-1 beta (1-1000 pg) also leads to the development of mechanical allodynia and hyperalgesia. On the other hand intrathecal application of TNF alpha did not produce changes in sensitivity to mechanical stimuli. Changes in the activity of spinal wide-dynamic range neurones induced by local inflammation may provide a pathomechanism for the clinical pathology of central pain syndrome, which can accompany CNS disease or acute CNS injury.

Dexamethasone reduces the expression of p75 neurotrophin receptor and apoptosis in contused spinal cord

Apoptosis is an important cause of secondary cell death in spinal cord injury (SCI). SCI induces the expression of the low affinity neurotrophin receptor p75 (p75NTR), that in the absence of the high affinity component, TrkA, can promote cell death by apoptosis. We therefore hypothesized that a reduction of p75NTR expression in SCI may increase tissue sparing and therefore improve recovery of function. As a tool to test our hypothesis we used the synthetic glucocorticoid dexamethasone (DEX) to down-regulate p75NTR expression. A standardized thoracic spinal cord contusion injury was produced in female rats. Laminectomized and SCI rats received various doses of DEX immediately after injury and the treatment was continued daily for 7 days. DEX, given at high doses (20 mg/kg, s.c.) but not at low doses (1 or 8 mg/kg) prevented the increase in p75NTR mRNA and protein in SCI rats, without affecting the expression of TrkA. High doses of DEX also reduced cellular apoptosis both in white and gray matters. This effect correlated with the ability of DEX to accelerate behavioral recovery of function measured by a combined behavioral score. These data suggest that reduction of p75NTR in SCI may be a therapeutic strategy to limit cell and tissue damage and therefore to improve recovery of function in SCI patients.

Improved recovery after spinal cord injury in neuronal nitric oxide synthase-deficient mice but not in TNF-alpha-deficient mice

Wild-type mice and mice lacking nitric oxide synthase (NOS) of neuronal type or TNF-alpha were subjected to an extradural compression of the thoracic spinal cord. The functional outcome of the hind limbs was assessed by using a motor function score (MFS). The injury resulted in paraplegia of the hind limbs in wild-type mice at day 1 after injury. Gradual recovery was observed during the following 14 days. Injured NOS -/- animals had an improved hind limb motor function during the entire observation period compared to wild-type controls. The difference was statistically significant on day 10 (p < 0.022) and day 14 (p < 0.048) after injury. At the site of injury, there was a trend of gray matter preservation in NOS -/- mice, as measured by MAP2 staining (p < 0.077). Injured mice lacking TNF-alpha had the lowest motor score among all the groups on day 1. During the following period, they had motor scores similar to those of wild-type controls and there was no significant difference at any time point. TNF-alpha -/- animals showed a trend of decreased white matter preservation compared to wild-type animals (p < 0.097). Our study shows that after spinal cord injury, mice lacking NOS have a better functional ability of their hind limbs than controls with the same degree of injury. This would indicate that the functional outcome is influenced in a negative way in wild mice by the presence of NO. The degree of secondary damage to the spinal cord might be attenuated in NOS-deficient mice.

Preventive effects of lecithinized superoxide dismutase and methylprednisolone on spinal cord injury in rats: transcriptional regulation of inflammatory and neurotrophic genes

The effects of lecithinized superoxide dismutase (PC-SOD) and/or methylpredisolone (MP) in preventing secondary pathological changes after spinal cord injury (SCI) were investigated in rats with reference to recovery of hindlimb motor function and expression of mRNA of pro-inflammatory and neurotrophic genes. Hindlimb motor function was assessed as the BBB open field locomotor scores. The BBB scores of three groups treated with either PC-SOD (40,000 units/kg), MP (30 mg/kg), or a combination of PC-SOD and MP (PC-SOD+MP) increased with time until 3 days after SCI, and were significantly higher than that of the control group (p < 0.05). Thereafter, the score of the PC-SOD group increased, whereas that of the MP group showed a temporary decrease from day 3 to 5 and then it gradually recovered. The scores in all groups reached a plateau about 18 days after SCI. The PC-SOD+MP group did not show a synergism but a tendency similar to that of the MP group. PC-SOD and MP had down-regulatory effects on mRNA expression of pro-inflammatory substances such as interleukin-1beta (IL-1beta), intercellular adhesion molecule-1 (ICAM-1), and inducible-nitric oxide synthetase (i-NOS) after spinal cord compression at 3, 6, and 24 h, respectively, as judged by a semiquantitative reverse transcription-polymerase chain reaction and on the lipid peroxide (LPO) level 1 h after injury as determined by thiobarbituric acid-reactive substances. The suppression of pro-inflammatory genes expression, especially IL-1beta were greater in the MP group than in the PC-SOD group, while suppression of LPO level was similar in these two groups. PC-SOD+MP treatment augmented the suppression of all three pro-inflammatory genes expression and the decrease of the LPO level. The level of neurotrophin-3 (NT-3) mRNA increased from 6 h after SCI and reached a maximum after 48 h. NT-3 mRNA level was enhanced by PC-SOD treatment, but not by MP treatment. Thus, the effect of MP in suppressing these pro-inflammatory genes expression was more than that of PC-SOD. The difference in motor function in the early and later stage may be partially due to differences in expression of IL-1beta and NT-3 after either treatment, through an IL-1beta-dependent or NT-3-mediated repair response.

Behavioural, histological and immunocytochemical consequences following 192 IgG-saporin immunolesions of the basal forebrain cholinergic system

Use of the selective immunotoxin; 192 IgG-saporin, is helping to elucidate the role of the cholinergic system in cognition by overcoming the problems of interpretation associated with the use of non-specific lesioning agents. In separate studies, we have compared the long- and short-term effects of single site and combined saporin lesions of the nucleus basalis magnocellularis and medial septal area, on spatial learning and memory in radial arm and water maze tasks. At 11 months, only rats with combined lesions showed deficits in both radial and water maze tasks, although terminal cholinergic deafferentation was substantial and extensive tissue loss was seen at the injection sites in both single and combined lesions. However, the extensive tissue loss with long-term lesions suggested that behavioural deficits were not solely attributable to cholinergic deafferentation. In contrast, when rats with combined lesions were tested 5 months after lesioning, no deficits were apparent, although there was almost complete loss of choline acetyltransferase- and nerve growth factor receptor-immunoreactivity in the basal forebrain with no tissue damage at the injection sites. This study supports existing literature that selective loss of cholinergic neurons in the basal forebrain does not produce behavioural impairments in standard tasks of learning and memory, but deficits are apparent when damage is non-selective as occurs late after lesioning, confounding interpretation of behavioural data. It further highlights potential problems with this immunotoxin in long-term studies.

Rapid upregulation of caspase-3 in rat spinal cord after injury: mRNA, protein, and cellular localization correlates with apoptotic cell death

Although the precise mechanisms explaining loss of, and failure to regain, function after spinal cord injury are unknown, there is increasing interest in the role of "secondary cell death." One prevalent theme in cell loss in other regions of the CNS involves apoptosis executed by the intracellular caspase proteases. A recent study demonstrated that spinal cord injury rapidly increased the activation of caspase-3. Our previous studies demonstrated peak apoptosis in three of four cellular compartments 3 days after controlled contusion in the rat. We have extended these analyses to include enzyme and substrate studies of caspase subfamilies both in rostral and in caudal adjacent segments compared to the lesion site. Although presumed activation of programmed proenzyme is considered the mechanism for enhanced caspases, our novel analyses were designed to detect upregulation of gene expression. We surveyed traumatically injured spinal cord for caspase family messages with a modified differential mRNA display approach and found that the caspase-3 (CASP3) message was present and upregulated severalfold after injury. Our results clearly demonstrate that cell death in the spinal cord occurs after posttranslational activation of caspases that follow, at least for caspase-3, initial upregulation of CASP3 mRNA levels.

Sustained induction of heme oxygenase-1 in the traumatized spinal cord

Oxidative stress contributes to secondary injury after spinal cord trauma. Among the consequences of oxidative stress is the induction of heme oxygenase-1 (HO-1), an inducible isozyme that metabolizes heme to iron, biliverdin, and carbon monoxide. Here we examine the induction of HO-1 in the hemisected spinal cord, a model that results in reproducible degeneration in the ipsilateral white matter. HO-1 was induced in microglia and macrophages from 24 h to at least 42 days after injury. Within the first week after injury, HO-1 was induced in both the gray and the white matter. Thereafter, HO-1 expression was limited to degenerating fiber tracts. HSP70, a heat shock protein induced mainly by the presence of denatured proteins, was consistently colocalized with HO-1 in the microglia and macrophages. This study to demonstrates long-term induction of HO-1 and HSP70 in microglia and macrophages after traumatic injury and an association between induction of HO-1 and Wallerian degeneration. White matter degeneration is characterized by phagocytosis of cellular debris and remodeling of surviving tissue. This results in the metabolism, synthesis, and turnover of heme and heme proteins. Thus, sustained induction of HO-1 and HSP70 in microglia and macrophages suggests that tissue degeneration is an ongoing process, lasting 6 weeks and perhaps even longer.

Neuronal, astroglial and microglial cytokine expression after an excitotoxic lesion in the immature rat brain

Cytokines are important intercellular messengers involved in neuron-glia interactions and in the microglial-astroglial crosstalk, modulating the glial response to brain injury and the lesion outcome. In this study, excitotoxic lesions were induced by the injection of N-methyl-D-aspartate in postnatal day 9 rats, and the cytokines interleukin-1 beta (IL-1beta), interleukin-6 (IL-6), tumour necrosis factor alpha (TNFalpha) and transforming growth factor beta 1 (TGF-beta1) analysed by ELISA and/or immunohistochemistry. Moreover, cytokine-expressing glial cells were identified by means of double labelling with glial fibrillary acidic protein or tomato lectin binding. Our results show that both neurons and glia were capable of cytokine expression following different patterns in the excitotoxically damaged area vs. the nondegenerating surrounding grey matter (SGM). Excitotoxically damaged neurons showed upregulation of IL-6 and downregulation of TNFalpha and TGF-beta1 before they degenerated. Moreover, in the SGM, an increased expression of neuronal IL-6, TNFalpha and TGF-beta1 was observed. A subpopulation of microglial cells, located in the SGM and showing IL-1beta and TNFalpha expression, were the earliest glial cells producing cytokines, at 2-10 h postinjection. Later on, cytokine-positive glial cells were found within the excitotoxically damaged area and the adjacent white matter: some reactive astrocytes expressed TNFalpha and IL-6, and microglia/macrophages showed mild IL-1beta and TGF-beta1. Finally, the expression of all cytokines was observed in the glial scar. As discussed, this pattern of cytokine production suggests their implication in the evolution of excitotoxic neuronal damage and the associated glial response.

Induction of VEGF and VEGF receptors in the spinal cord after mechanical spinal injury and prostaglandin administration

Vascular endothelial growth factor (VEGF) is an angiogenetic factor that promotes endothelial cell proliferation during development and after injury to various types of tissue, including the central nervous system (CNS). Using immunohistochemical and in situ hybridization methods we have here demonstrated that VEGF and its receptors Flk-1, Flt-1 and Neuropilin-1 mRNAs and proteins are induced after incisions in the rat spinal cord. The inducible enzyme for prostaglandin synthesis cyclooxygenase-2 (COX-2) is known to be upregulated after spinal injury, cerebral ischemia and to stimulate angiogenesis. To test the hypothesis that prostaglandins may be involved in the VEGF response after lesion we investigated whether intraspinal microinjections of prostaglandin F2alpha (PGF2alpha) alters VEGF expression in the spinal cord. Such treatment was followed by a strong upregulation of VEGF mRNA and protein in the injection area. Finally, by use of an in vitro model with cell cultures of meningeal fibroblast and astrocyte origin, resembling the lesion area cellular content after spinal cord injury but devoid of inflammatory cells, we showed that VEGF is expressed in this in vitro model cell system after treatment with PGF2alpha and prostaglandin E2 (PGE2). These data suggest that cells within a lesion area in the spinal cord are capable of expressing VEGF and its receptors in response to mechanical injury and that prostaglandins may induce VEGF expression in such cells, even in the absence of inflammatory cells.

Central nervous system-initiated inflammation and neurotrophism in trauma: IL-1 beta is required for the production of ciliary neurotrophic factor

Injury to the CNS results in the production and accumulation of inflammatory cytokines within this tissue. The origin and role of inflammation within the CNS remains controversial. In this paper we demonstrate that an acute trauma to the mouse brain results in the rapid elevation of IL-1beta. This increase is detectable by 15 min after injury and significantly precedes the influx of leukocytes that occurs hours after. To confirm that IL-1beta up-regulation is initiated by cells within the CNS, in situ hybridization for cytokine transcript was combined with cell type immunohistochemistry. The results reveal parenchymal microglia to be the sole source of IL-1beta at 3 h postinjury. A role for CNS-initiated inflammation was addressed by examining the expression of the neurotrophic factor, ciliary neurotrophic factor (CNTF). Analysis of their temporal relationship suggests the up-regulation of CNTF by IL-1beta, which was confirmed through three lines of evidence. First, the application of IL-1 receptor antagonist into the lesion site attenuated the up-regulation of CNTF. Second, the examination of corticectomized animals genetically deficient for IL-1beta found no CNTF up-regulation. Third, the lack of CNTF elevation in IL-1beta null mice was rescued through exogenous application of IL-1beta into the lesion site. These findings provide the first evidence of the requirement for IL-1beta in the production of CNTF following CNS trauma, and suggest that inflammation can have a beneficial impact on the regenerative capacity of the CNS.

Vascular Events After Spinal Cord Injury: Contribution to Secondary Pathogenesis

Traumatic spinal cord injury results in the disruption of neural and vascular structures (primary injury) and is characterized by an evolution of secondary pathogenic events that collectively define the extent of functional recovery. This article reviews the vascular responses to spinal cord injury, focusing on both early and delayed events, including intraparenchymal hemorrhage, inflammation, disruption of the blood-spinal cord barrier, and angiogenesis. These vascular-related events not only influence the evolution of secondary tissue damage but also define an environment that fosters neural plasticity in the chronically injured spinal cord.

Reactions of oligodendrocytes to spinal cord injury: cell survival and myelin repair

The aim of this study was to elucidate whether oligodendrocytes die in fiber tracts that are spared by a spinal cord injury but are in close vicinity of inflammatory cells. Adult rat spinal cords were studied histologically 1 day to 2 weeks after a contusion lesion that left the ventral white matter largely intact. Massive oligodendrocyte death occurred in the lesion center, along with the death of neurons, microglia, and astrocytes. Oligodendrocytes, specifically positive for proteolipid protein (PLP) mRNA, were counted in the ventral white matter where axons at the rostral and caudal edges of the lesion were histologically intact. Although these regions contained many macrophages and neutrophils hypothesized to contribute to secondary tissue loss, there was no significant loss of oligodendrocytes. In the ventral funiculus, 3 and 6 mm rostral and caudal to the lesion, oligodendrocyte numbers were also unchanged, in spite of the presence of many activated microglial cells. From day 7 on, oligodendrocytes in close vicinity to the lesion increased their expression of PLP mRNA. We conclude that, at least within the first 2 weeks after a spinal cord contusion lesion, there is no major devastating influence of inflammatory cells or their mediators on oligodendrocytes. When death occurs, it may be due to mechanical trauma, ischemia, or excitotoxicity within the lesion or it may occur as a result of axonal degeneration.

Vasoactive intestinal peptide and pituitary adenylyl cyclase-activating polypeptide inhibit tumor necrosis factor-alpha production in injured spinal cord and in activated microglia via a cAMP-dependent pathway

Tumor necrosis factor-alpha (TNF-alpha) production accompanies CNS insults of all kinds. Because the neuropeptide vasoactive intestinal peptide (VIP) and the structurally related peptide pituitary adenylyl cyclase-activating polypeptide (PACAP) have potent anti-inflammatory effects in the periphery, we investigated whether these effects extend to the CNS. TNF-alpha mRNA was induced within 2 hr after rat spinal cord transection, and its upregulation was suppressed by a synthetic VIP receptor agonist. Cultured rat microglia were used to examine the mechanisms underlying this inhibition because microglia are the likely source of TNF-alpha in injured CNS. In culture, increases in TNF-alpha mRNA resulting from lipopolysaccharide (LPS) stimulation were reduced significantly by 10(-7) m VIP and completely eliminated by PACAP at the same concentration. TNF-alpha protein levels were reduced 90% by VIP or PACAP at 10(-7) m. An antagonist of VPAC(1) receptors blocked the action of VIP and PACAP, and a PAC(1) antagonist blocked the action of PACAP. A direct demonstration of VIP binding on microglia and the existence of mRNAs for VPAC(1) and PAC(1) (but not VPAC(2)) receptors argue for a receptor-mediated effect. The action of VIP is cAMP-mediated because (1) activation of cAMP by forskolin mimics the action; (2) PKA inhibition by H89 reverses the neuropeptide-induced inhibition; and (3) the lipophilic neuropeptide mimic, stearyl-norleucine(17) VIP (SNV), which does not use a cAMP-mediated pathway, fails to duplicate the inhibition. We conclude that VIP and PACAP inhibit the production of TNF-alpha from activated microglia by a cAMP-dependent pathway.

Spinal cord injury in ICAM-1-deficient mice: assessment of functional and histopathological outcome

Adhesion molecule-mediated adhesion and extravasation of leukocytes may constitute a mechanism of secondary tissue damage following spinal cord injury (SCI). The objective of the present study was to determine to what extent genetic deficiency in the adhesion molecule ICAM-1 influences functional and histopathological measures of outcome following SCI. ICAM-1-/- (n = 11) and wild-type (n = 9) mice were subjected to a compression-type SCI. Assessment of hind-limb motor function was done on days 1, 2, 4, 7, 10, and 14 after injury, using a motor function scoring system. Injury resulted in a drastically impaired hind limb motor function at day one after injury followed by a partial recovery during the observation period. No significant functional differences were found between the experimental groups at any time-point. Fourteen days after injury the animals were sacrificed and the spinal cords were processed for histopathological and immunohistochemical evaluation. Luxol-stained, MAP2-, GFAP- and iba-1-immunostained cross-sectional areas were quantitated using a computerized image analysis system to investigate white matter damage, neuronal loss, astrocytic response and microglial activation respectively. None of these parameters differed significantly between the groups. Separate experiments revealed that the early (24 h postinjury) infiltration of polymorphonuclear leukocytes was significantly reduced in white matter but not in the grey matter of ICAM-1-/- mice, compared to injured controls. In summary, these results do not support the concept that ICAM-1 alone mediates secondary tissue damage following traumatic SCI in the mouse.

Role of leukocytes in spinal cord injury in rats

Spinal cord injury (SCI) is a serious condition that produces life-long disabilities. Only limited therapeutic measures are currently available for its treatment. This review describes the role of leukocytes in pathologic mechanisms of trauma-induced SCI in rats, which contributes to new understanding of the pathologic process involved in SCI and could lead to the development of new therapeutic strategies by which leukocyte activation can be regulated. SCI induced by trauma is a consequence of an initial physical insult that is followed by a progressive injury process which involves various pathochemical events that lead to tissue destruction. Therapeutic intervention in SCI should therefore be directed at reducing or alleviating this secondary process. Although the mechanisms are not fully understood, progressive vascular events, especially activated neutrophil-induced endothelial cell damage, have been shown to be implicated. We have found that some therapeutic agents, which inhibit leukocyte activation directly or indirectly, alleviate the motor disturbances observed in a rat model of SCI. Methylprednisolone (MPS) and GM1 ganglioside, which are the only two pharmacological agents currently clinically available for treatment of acute SCI, do not inhibit neutrophil activation in this rat model. Taken together, these observations raise a possibility that pharmacological agents that inhibit leukocyte activation used in conjunction with MPS or GM1 may have a synergistic effect in the clinical treatment of traumatic SCI in humans.

Nerve growth factor in glia and inflammatory cells of the injured rat spinal cord

Nerve growth factor (NGF) is crucial for the development of sympathetic and small-diameter sensory neurons and for maintenance of their mature phenotype. Its role in generating neuronal pathophysiology is less well understood. After spinal cord injury, central processes of primary afferent fibers sprout into the dorsal horn, contributing to the development of autonomic dysfunctions and pain. NGF may promote these states as it stimulates sprouting of small-diameter afferent fibers and its concentration in the spinal cord increases after cord injury. The cells responsible for this increase must be identified to develop a strategy to prevent the afferent sprouting. Using immunocytochemistry, we identified cells containing NGF in spinal cord sections from intact rats and from rats 1 and 2 weeks after high thoracic cord transection. In intact rats, this neurotrophin was present in a few ramified microglia and in putative Schwann cells in the dorsal root. Within and close to the lesion of cord-injured rats, NGF was in many activated, ramified microglia, in a subset of astrocytes, and in small, round cells that were neither glia nor macrophages. NGF-immunoreactive putative Schwann cells were prevalent throughout the thoracolumbar cord in the dorsal roots and the dorsal root entry zones. Oligodendrocytes were never immunoreactive for this protein. Therapeutic strategies targeting spinal cord cells that produce NGF may prevent primary afferent sprouting and resulting clinical disorders after cord injury.

Effects of spinal cord X-irradiation on the recovery of paraplegic rats

Axonal regrowth is limited in the adult CNS, especially in the spinal cord, one of the major sites of traumatic lesions. Pathophysiological changes occurring after spinal cord injury include complex acute, subacute, and late processes. In this study, we assessed whether X-irradiation interferes with the acute/subacute phases, thereby improving the functional recovery of paraplegic animals. Two days after acute compression of adult rat spinal cords, various doses (0, 2, 5, 10, 20 Gy) of X-rays were administered as one single dose to the compression site. The animals were functionally evaluated over the course of 1 month after injury, using the Tarlov scale and the Rivlin and Tator scale. We also designed a "physiological" scale, including an assessment of urinary function and infection, appropriate for the evaluation of spinal-cord-lesioned animals. Behavioral analysis suggested that the high doses, 20 Gy and, to a lesser extent, 5 and 10 Gy, were toxic, as shown by morbidity rate and "physiological" score. The 2-Gy group showed better motor performances than the lesioned nonirradiated (LNI) animals and the 5- and 20-Gy groups. Motor performance in the 5-, 10-, and 20-Gy groups was poorer than that seen in the LNI group. Gliosis was reduced in the 2-Gy group compared to LNI animals, and there was high levels of gliosis in the highly (>/=5 Gy) irradiated animals. There was a 23% less lesion-induced syringomyelia in the 2-Gy group than in the other groups (LNI and 5-20 Gy). Thus, low doses of X-rays may interfere with the formation of syringomyelia and glial scar, thereby facilitating the recovery of paraplegic animals. These findings suggest that low-dose irradiation of the lesion site, in association with other therapies, is a potentially promising treatment for improving recovery after spinal cord injury.