Role of microglia in neurotrauma

Microglia are the primary mediators of the immune defense system of the CNS and are integral to the subsequent inflammatory response. The role of microglia in the injured CNS is under scrutiny, as research has begun to fully explore how postinjury inflammation contributes to secondary damage and recovery of function. Whether microglia are good or bad is under debate, with strong support for a dual role or differential activation of microglia. Microglia release a number of factors that modulate secondary injury and recovery after injury, including pro- and anti-inflammatory cytokines, chemokines, nitric oxide, prostaglandins, growth factors, and Superoxide species. Here we review experimental work on the complex and varied responses of microglia in terms of both detrimental and beneficial effects. Addressed in addition are the effects of microglial activation in two examples of CNS injury: spinal cord and traumatic brain injury. Microglial activation is integral to the response of CNS tissue to injury. In that light, future research is needed to focus on clarifying the signals and mechanisms by which microglia can be guided to promote optimal functional recovery.     

Arginase-1 is expressed exclusively by infiltrating myeloid cells in CNS injury and disease

Resident microglia and infiltrating myeloid cells play important roles in the onset, propagation, and resolution of inflammation in central nervous system (CNS) injury and disease. Identifying cell type-specific mechanisms will help to appropriately target interventions for tissue repair. Arginase-1 (Arg-1) is a well characterised modulator of tissue repair and its expression correlates with recovery after CNS injury. Here we assessed the cellular localisation of Arg-1 in two models of CNS damage. Using microglia specific antibodies, P2ry12 and Fc receptor-like S (FCRLS), we show the LysM-EGFP reporter mouse is an excellent model to distinguish infiltrating myeloid cells from resident microglia. We show that Arg-1 is expressed exclusively in infiltrating myeloid cells but not microglia in models of spinal cord injury (SCI) and experimental autoimmune encephalomyelitis (EAE). Our in vitro studies suggest that factors in the CNS environment prevent expression of Arg-1 in microglia in vivo. This work suggests different functional roles for these cells in CNS injury and repair and shows that such repair pathways can be switched on in infiltrating myeloid cells in pro-inflammatory environments.     

Glial Cells Shape Pathology and Repair After Spinal Cord Injury

Glial cell types were classified less than 100 years ago by del Rio-Hortega. For instance, he correctly surmised that microglia in pathologic central nervous system (CNS) were “voracious monsters” that helped clean the tissue. Although these historical predictions were remarkably accurate, innovative technologies have revealed novel molecular, cellular, and dynamic physiologic aspects of CNS glia. In this review, we integrate recent findings regarding the roles of glia and glial interactions in healthy and injured spinal cord. The three major glial cell types are considered in healthy CNS and after spinal cord injury (SCI). Astrocytes, which in the healthy CNS regulate neurotransmitter and neurovascular dynamics, respond to SCI by becoming reactive and forming a glial scar that limits pathology and plasticity. Microglia, which in the healthy CNS scan for infection/damage, respond to SCI by promoting axon growth and remyelination—but also with hyperactivation and cytotoxic effects. Oligodendrocytes and their precursors, which in healthy tissue speed axon conduction and support axonal function, respond to SCI by differentiating and producing myelin, but are susceptible to death. Thus, post-SCI responses of each glial cell can simultaneously stimulate and stifle repair. Interestingly, potential therapies could also target interactions between these cells. Astrocyte–microglia cross-talk creates a feed-forward loop, so shifting the response of either cell could amplify repair. Astrocytes, microglia, and oligodendrocytes/precursors also influence post-SCI cell survival, differentiation, and remyelination, as well as axon sparing. Therefore, optimizing post-SCI responses of glial cells—and interactions between these CNS cells—could benefit neuroprotection, axon plasticity, and functional recovery.     

Hepatocyte growth factor promotes endogenous repair and functional recovery after spinal cord injury

Many therapeutic interventions using neurotrophic factors or pharmacological agents have focused on secondary degeneration after spinal cord injury (SCI) to reduce damaged areas and promote axonal regeneration and functional recovery. Hepatocyte growth factor (HGF), which was identified as a potent mitogen for mature hepatocytes and a mediator of inflammatory responses to tissue injury, has recently been highlighted as a potent neurotrophic and angiogenic factor in the central nervous system (CNS). In the present study, we revealed that the extent of endogenous HGF up-regulation was less than that of c-Met, an HGF receptor, during the acute phase of SCI and administered exogenous HGF into injured spinal cord using a replication-incompetent herpes simplex virous-1 (HSV-1) vector to determine whether HGF exerts beneficial effects and promotes functional recovery after SCI. This treatment resulted in the significant promotion of neuron and oligodendrocyte survival, angiogenesis, axonal regrowth, and functional recovery after SCI. These results suggest that HGF gene delivery to the injured spinal cord exerts multiple beneficial effects and enhances endogenous repair after SCI. This is the first study to demonstrate the efficacy of HGF for SCI.     

The voltage-gated proton channel Hv1 plays a detrimental role in contusion spinal cord injury via extracellular acidosis-mediated neuroinflammation

Tissue acidosis is an important secondary injury process in the pathophysiology of traumatic spinal cord injury (SCI). To date, no studies have examined the role of proton extrusion as mechanism of pathological acidosis in SCI. In the present study, we hypothesized that the phagocyte-specific proton channel Hv1 mediates hydrogen proton extrusion after SCI, contributing to increased extracellular acidosis and poor long-term outcomes. Using a contusion model of SCI in adult female mice, we demonstrated that tissue pH levels are markedly lower during the first week after SCI. Acidosis was most evident at the injury site, but also extended into proximal regions of the cervical and lumbar cord. Tissue reactive oxygen species (ROS) levels and expression of Hv1 were significantly increased during the week of injury. Hv1 was exclusively expressed in microglia within the CNS, suggesting that microglia contribute to ROS production and proton extrusion during respiratory burst. Depletion of Hv1 significantly attenuated tissue acidosis, NADPH oxidase 2 (NOX2) expression, and ROS production at 3 d post-injury. Nanostring analysis revealed decreased gene expression of neuroinflammatory and cytokine signaling markers in Hv1 knockout (KO) mice. Furthermore, Hv1 deficiency reduced microglia proliferation, leukocyte infiltration, and phagocytic oxidative burst detected by flow cytometry. Importantly, Hv1 KO mice exhibited significantly improved locomotor function and reduced histopathology. Overall, these data suggest an important role for Hv1 in regulating tissue acidosis, NOX2-mediated ROS production, and functional outcome following SCI. Thus, the Hv1 proton channel represents a potential target that may lead to novel therapeutic strategies for SCI.     

IL‐4 drives microglia and macrophages toward a phenotype conducive for tissue repair and functional recovery after spinal cord injury

Macrophages and microglia play a key role in the maintenance of nervous system homeostasis. However, upon different challenges, they can adopt several phenotypes, which may lead to divergent effects on tissue repair. After spinal cord injury (SCI), microglia and macrophages show predominantly pro‐inflammatory activation and contribute to tissue damage. However, the factors that hamper their conversion to an anti‐inflammatory state after SCI, or to other protective phenotypes, are poorly understood. Here, we show that IL‐4 protein levels are undetectable in the spinal cord after contusion injury, which likely favors microglia and macrophages to remain in a pro‐inflammatory state. We also demonstrate that a single delayed intraspinal injection of IL‐4, 48 hours after SCI, induces increased expression of M2 marker in microglia and macrophages. We also show that delayed injection of IL‐4 leads to the appearance of resolution‐phase macrophages, and that IL‐4 enhances resolution of inflammation after SCI. Interestingly, we provide clear evidence that delayed administration of IL‐4 markedly improves functional outcomes and reduces tissue damage after contusion injury. It is possible that these improvements are mediated by the presence of macrophages with M2 markers and resolution‐phase macrophages. These data suggest that therapies aimed at increasing IL‐4 levels could be valuable for the treatment of acute SCI, for which there are currently no effective treatments. GLIA 2016;64:2079–2092     

Regulatory T cells promote functional recovery after spinal cord injury by alleviating microglia inflammation via STAT3 inhibition

Background

Immediately after spinal trauma, immune cells, and proinflammatory cytokines infiltrate the spinal cord and disrupt the focal microenvironment, which impedes axon regeneration and functional recovery. Previous studies have reported that regulatory T cells (Tregs) enter the central nervous system and exert immunosuppressive effects on microglia during multiple sclerosis and stroke. However, whether and how Tregs interact with microglia and modulate injured microenvironments after spinal cord injury (SCI) remains unknown.

Method

Regulatory T cells spatiotemporal characteristics were analyzed in a mouse contusion SCI model. Microglia activation status was evaluated by immunostaining and RNA sequencing. Cytokine production in injured spinal cord was examined using Luminex. The role of STAT3 in Treg–microglia crosstalk was investigated in a transwell system with isolated Tregs and primary microglia.

Results

Regulatory T cells infiltration of the spinal cord peaked on day 7 after SCI. Treg depletion promoted microglia switch to a proinflammatory phenotype. Inflammation-related genes, such as ApoD, as well as downstream cytokines IL-6 and TNF-α were upregulated in microglia in Treg-depleted mice. STAT3 inhibition was involved in Treg–microglia crosstalk, and STAT3 chemical blockade improved function recovery in Treg-depleted mice.

Conclusion

Our results suggest that Tregs promote functional recovery after SCI by alleviating microglia inflammatory reaction via STAT3.     

Critical role of connexin 43 in secondary expansion of traumatic spinal cord injury

Spinal cord injury (SCI) is often complicated by secondary injury as a result of the innate inflammatory response to tissue trauma and swelling. Previous studies have shown that excessive ATP release from peritraumatic regions contributes to the inflammatory response to SCI by activation of low-affinity P2X7 receptors. Because connexin hemichannels constitute an important route for astrocytic ATP release, we here evaluated the impact on post-traumatic ATP release of deletion of connexins (Cx30/Cx43) in astrocytes. In vivo bioluminescence imaging showed a significant reduction in ATP release after weight-drop injury in mice with deletion of Cx43 compared with Cx43-expressing littermates, both on a Cx30 knockout background. Moreover, astrogliosis and microglia activation were reduced in peritraumatic areas of those mice lacking Cx43; motor recovery was also significantly improved, and the traumatic lesion was smaller. Combined, these observations are consistent with a contribution by astrocytic hemichannels to post-traumatic ATP release that aggravates secondary injury and restrains functional recovery after experimental spinal cord injury. Connexins may thereby constitute a new therapeutic target in spinal cord injury.     

Central nervous system diseases related to pathological microglial phagocytosis

Microglia are important phagocytes of the central nervous system (CNS). They play an important role in protecting the CNS by clearing necrotic tissue and apoptotic cells in many CNS diseases. However, recent studies have found that microglia can phagocytose parts of neurons excessively, such as the neuronal cell body, synapse, or myelin sheaths, before or after the onset of CNS diseases, leading to aggravated injury and impaired tissue repair. Meanwhile, reduced phagocytosis of synapses and myelin results in abnormal circuit connections and inhibition of remyelination, respectively. Previous studies focused primarily on the positive effects of microglia phagocytosis, whereas only a few studies have focused on the negative effects. In this review, we use the term "pathological microglial phagocytosis" to refer to excessive or reduced phagocytosis by microglia that leads to structural or functional abnormalities in target cells and brain tissue. The classification of pathological microglial phagocytosis, the composition, and activation of related signaling pathways, as well as the process of pathological phagocytosis in various kinds of CNS diseases, are described in this review. We hypothesize that pathological microglial phagocytosis leads to aggravation of tissue damage and negative functional outcome. For example, excessive microglial phagocytosis of synapses can be observed in Alzheimer's disease and schizophrenia, leading to significant synapse loss and memory impairment. In Parkinson's disease, ischemic stroke, and traumatic brain injury, excessive microglial phagocytosis of neuronal cell bodies causes impaired gray matter recovery and sensory dysfunction. We therefore believe that more studies should focus on the mechanism of pathological microglial phagocytosis and activation to uncover potential targets of therapeutic intervention.     

Modulation of autophagy for neuroprotection and functional recovery in traumatic spinal cord injury

Spinal cord injury(SCI) is a serious central nervous system trauma that leads to loss of motor and sensory functions in the SCI patients. One of the cell death mechanisms is autophagy, which is ‘self-eating' of the damaged and misfolded proteins and nucleic acids, damaged mitochondria, and other impaired organelles for recycling of cellular building blocks. Autophagy is different from all other cell death mechanisms in one important aspect that it gives the cells an opportunity to survive or demise depending on the circumstances. Autophagy is a therapeutic target for alleviation of pathogenesis in traumatic SCI. However, functions of autophagy in traumatic SCI remain controversial. Spatial and temporal patterns of activation of autophagy after traumatic SCI have been reported to be contradictory. Formation of autophagosomes following therapeutic activation or inhibition of autophagy flux is ambiguous in traumatic SCI studies. Both beneficial and harmful outcomes due to enhancement autophagy have been reported in traumatic SCI studies in preclinical models. Only further studies will make it clear whether therapeutic activation or inhibition of autophagy is beneficial in overall outcomes in preclinical models of traumatic SCI. Therapeutic enhancement of autophagy flux may digest the damaged components of the central nervous system cells for recycling and thereby facilitating functional recovery. Many studies demonstrated activation of autophagy flux and inhibition of apoptosis for neuroprotective effects in traumatic SCI. Therapeutic induction of autophagy in traumatic SCI promotes axonal regeneration, supporting another beneficial role of autophagy in traumatic SCI. In contrast, some other studies demonstrated that disruption of autophagy flux in traumatic SCI strongly correlated with neuronal death at remote location and impaired functional recovery. This article describes our current understanding of roles of autophagy in acute and chronic traumatic SCI, crosstalk between autophagy and apoptosis, therapeutic activation or inhibition of autophagy for promoting functional recovery, and future of autophagy in traumatic SCI.     

小胶质细胞在中枢神经系统创伤后的双重作用及调控机制

小胶质细胞是中枢神经系统的固有免疫细胞,在脑或脊髓创伤后的神经炎症反应中起关键作用。神经系统损伤后小胶质细胞可提供神经保护因子,清除细胞碎片并调控神经修补过程。而另一方面,小胶质细胞会产生高水平的促炎及细胞毒性介质从而阻碍CNS修复,促使神经元失能及细胞死亡。小胶质细胞的双重特性可能与其损伤后的表型及功能反应有关。本综述探讨近年来有关脑和脊髓损伤后小胶质细胞活化表型的研究,以及小胶质细胞在神经元、血管、少突胶质细胞生长及再生中的可能发挥的作用。并简述已知的调控表型转换的分子机制,着重探讨可以影响小胶质细胞活化状态的治疗途径。了解小胶质细胞表型调控机制有助于我们增加神经系统损伤恢复的知识,并提供新的治疗策略。     

The mechanisms of microgliosis and pain following peripheral nerve injury

Microglia are the resident macrophages in the central nervous system (CNS). Any insult to the CNS homeostasis will induce a rapid change in microglia morphology, gene expression profile and functional behaviour. These responses of microglia have been collectively known as 'microgliosis'. Interestingly, damage to the nervous system outside the CNS, such as axotomy of a peripheral nerve, can lead to microgliosis in the spinal cord. There is a variation in the degree of microgliosis depending on the model of nerve injury employed for instance this response is more marked following traumatic nerve injury than in models of chemotherapy induced neuropathy. Following peripheral nerve injury nociceptive inputs from sensory neurons appear to be critical in triggering the development of spinal microgliosis. A number of signalling pathways including growth factors such as Neuregulin-1, matrix metalloproteases such as MMP-9 and multiple chemokines enable direct communication between injured primary afferents and microglia. In addition, we describe a group of mediators which although not demonstrably shown to be released from neurons are known to modulate microglial phenotype. There is a great functional diversity of the microglial response to peripheral nerve injury which includes: Cellular migration, proliferation, cytokine release, phagocytosis, antigen presentation and recruitment of T cells. It should also be noted that in certain contexts microglia may have a role in the resolution of neuro-inflammation. Although there is still no direct evidence demonstrating that spinal microglia have a role in neuropathic pain in humans, these patients present a pro-inflammatory cytokine profile and it is a reasonable hypothesis that these cells may contribute to this inflammatory response. Modulating microglial functions offers a novel therapeutic opportunity following nerve injury which ideally would involve reducing the pro-inflammatory nature of these cells whilst retaining their potential beneficial functions.     

Agmatine improves locomotor function and reduces tissue damage following spinal cord injury

Clinically effective drug treatments for spinal cord injury (SCI) remain unavailable. Agmatine, an NMDA receptor antagonist and inhibitor of nitric oxide synthase (NOS), is an endogenous neuromodulator found in the brain and spinal cord. Evidence is presented that agmatine significantly improves locomotor function and reduces tissue damage following traumatic SCI in rats. The results suggest the importance of future therapeutic strategies encompassing the use of single drugs with multiple targets for the treatment of acute SCI. The therapeutic targets of agmatine (NMDA receptor and NOS) have been shown to be critically linked to the pathophysiological sequelae of CNS injury and this, combined with the non-toxic profile, lends support to agmatine being considered as a potential candidate for future clinical applications.     

Intraspinal administration of an antibody against CD81 enhances functional recovery and tissue sparing after experimental spinal cord injury

We previously demonstrated that the tetraspanin protein CD81 is up-regulated by astrocytes and microglia after traumatic spinal cord injury in rats and that CD81 is involved in adhesion and proliferation of cultured astrocytes and microglia. Since these reactive glial cells contribute to secondary damage and glial scar formation, we studied the effect of local administration of an anti-CD81 antibody in experimental spinal cord injury. Adult rats were subjected to a moderate spinal cord contusion injury and treated for 2 weeks with different doses of the anti-CD81 antibody AMP1 (0.5-5 microg/h) or non-immune IgG (5.0 microg/h). A technique was developed to infuse the antibodies directly into the lesion site via an intraspinal cannula connected to a pump. Functional recovery was monitored during 8 postoperative weeks by means of the Basso, Beattie and Bresnahan (BBB) locomotor rating scale, the BBB subscore and Grid-walk test. At the end of the study, quantitative histology was performed to assess tissue sparing. Our data showed that by itself cannulation of the lesion site resulted in minimal functional and histological impairments. Application of 0.5 microg/h AMP1 resulted in a marked functional recovery (BBB 2 points; Grid-walk 30% less errors compared to control). This recovery was accompanied by an 18% increase in tissue sparing at the lesion epicentre. No gross histological changes in glial scarring were apparent. Our data demonstrate beneficial effects of an anti-CD81 antibody on functional recovery in spinal cord injured rats and suggest that this effect is mediated through a reduction in secondary tissue loss.     

Functional silica nanoparticle‐mediated neuronal membrane sealing following traumatic spinal cord injury

The mechanical damage to neurons and their processes induced by spinal cord injury (SCI) causes a progressive cascade of pathophysiological events beginning with the derangement of ionic equilibrium and collapse of membrane permeability. This leads to a cumulative deterioration of neurons, axons, and the tissue architecture of the cord. We have previously shown that the application of the hydrophilic polymer polyethylene glycol (PEG) following spinal cord or brain injury can rapidly restore membrane integrity, reduce oxidative stress, restore impaired axonal conductivity, and mediate functional recovery in rats, guinea pigs, and dogs. However there are limits to both the concentration and the molecular weight of the application that do not permit the broadest recovery across an injured animal population. In this study, PEG‐decorated silica nanoparticles (PSiNPs) sealed cells, as shown by the significantly reduced leakage of lactate dehydrogenase from damaged cells compared with uncoated particles or PEG alone. Further in vivo tests showed that PSiNPs also significantly reduced the formation of reactive oxygen species and the process of lipid peroxidation of the membrane. Fabrication of PSiNPs containing embedded dyes also revealed targeting of the particles to damaged, but not undamaged, spinal cord tissues. In an in vivo crush/contusion model of guinea pig SCI, every animal but one injected with PSiNPs recovered conduction through the cord lesion, whereas none of the control animals did. These findings suggest that the use of multifunctional nanoparticles may offer a novel treatment approach for spinal cord injury, traumatic brain injury, and possibly neurodegenerative disorders. © 2009 Wiley‐Liss, Inc.     

Bone marrow transplants provide tissue protection and directional guidance for axons after contusive spinal cord injury in rats

Contusive spinal cord injury (SCI) produces large fluid-, debris- and inflammatory cell-filled cystic cavities that lack structure to support significant axonal regeneration. The recent discovery of stem cells capable of generating central nervous system (CNS) tissues, coupled with success in neurotransplantation strategies, has renewed hope that repair and recovery from CNS trauma is possible. Based on results from several studies using bone marrow stromal cells (MSCs) to promote CNS repair, we transplanted MSCs into the rat SCI lesion cavity to further investigate their effects on functional recovery, lesion morphology, and axonal growth. We found that transplanted MSCs induced hindlimb airstepping--a spontaneous locomotor movement associated with activation of the stepping control circuitry--but did not alter the time course or extent of overground locomotor recovery. Using stereological techniques to describe spinal cord anatomy, we show that MSC transplants occupied the lesion cavity and were associated with preservation of host tissue and white matter (myelin), demonstrating that these cells exert neuroprotective effects. The tissue matrix formed by MSC grafts supported greater axonal growth than that found in specimens without grafts. Moreover, uniform random sampling of axon profiles revealed that the majority of neurites in MSC grafts were oriented with their long axis parallel to that of the spinal cord, suggesting longitudinally directed growth. Together, these studies support further investigation of marrow stromal cells as a potential SCI repair strategy.     

Expression and detrimental role of hematopoietic prostaglandin D synthase in spinal cord contusion injury

Prostaglandin D(2) (PGD(2) ) is a potent inflammatory mediator, which is implicated in both the initiation and resolution of inflammation in peripheral non-neural tissues. Its role in the central nervous system has not been fully elucidated. Spinal cord injury (SCI) is associated with an acute inflammatory response, which contributes to secondary tissue damage that worsens functional loss. We show here, with the use of hematopoietic prostaglandin D synthase (HPGDS) deficient mice and a HPGDS selective inhibitor (HQL-79), that PGD(2) plays a detrimental role after SCI. We also show that HPGDS is expressed in macrophages in the injured mouse spinal cord and contributes to the increase in PGD(2) in the contused spinal cord. HPGDS(-/-) mice also show reduced secondary tissue damage and reduced expression of the proinflammatory chemokine CXCL10 as well as an increase in IL-6 and TGFβ-1 expression in the injured spinal cord. This was accompanied by a reduction in the expression of the microglia/macrophage activation marker Mac-2 and an increase in the antioxidant metallothionein III. Importantly, HPGDS deficient mice exhibit significantly better locomotor recovery after spinal cord contusion injury than wild-type (Wt) mice. In addition, systemically administered HPGDS inhibitor (HQL-79) also enhanced locomotor recovery after SCI in Wt mice. These data suggest that PGD(2) generated via HPGDS has detrimental effects after SCI and that blocking the activity of this enzyme can be beneficial.     

Acute Inflammatory Response in Spinal Cord Following Impact Injury

Numerous factors are involved in the spread of secondary damage in spinal cord after traumatic injury, including ischemia, edema, increased excitatory amino acids, and oxidative damage to the tissue from reactive oxygen species. Neutrophils and macrophages can produce reactive oxygen species when activated and thus may contribute to the lipid peroxidation that is known to occur after spinal cord injury. This study examined the rostral–caudal distribution of neutrophils and macrophages/microglia at 4, 6, 24, and 48 h after contusion injury to the T10 spinal cord of rat (10 g weight, 50 mm drop). Neutrophils were located predominantly in necrotic regions, with a time course that peaked at 24 h as measured with assays of myeloperoxidase activity (MPO). The sharpest peak of MPO activity was localized between 4 mm rostral and caudal to the injury. Macrophages/microglia were visualized with antibodies against ED1 and OX-42. Numerous cells with a phagocytic morphology were present by 24 h, with a higher number by 48 h. These cells were predominantly located within the gray matter and dorsal funiculus white matter. The number of cells gradually declined through 6 mm rostral and caudal to the lesion. OX-42 staining also revealed reactive microglia with blunt processes, particularly at levels distant to the lesion. The number of macrophages/microglia was significantly correlated with the amount of tissue damage at each level. Treatments to decrease the inflammatory response are likely to be beneficial to recovery of function after traumatic spinal cord injury.     

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.