2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline reduces glial loss and acute white matter pathology after experimental spinal cord contusion

Stem Cell Therapy and Thiamine Deficiency-Induced Brain Damage

Wernicke's encephalopathy (WE) is a major central nervous system disorder resulting from thiamine deficiency (TD) in which a number of brain regions can develop serious damage including the thalamus and inferior colliculus. Despite decades of research into the pathophysiology of TD and potential therapeutic interventions, little progress has been made regarding effective treatment following the development of brain lesions and its associated cognitive issues. Recent developments in our understanding of stem cells suggest they are capable of repairing damage and improving function in different maladys. This article puts forward the case for the potential use of stem cell treatment as a therapeutic strategy in WE by first examining the effects of TD on brain functional integrity and its consequences. The second half of the paper will address the future benefits of treating TD with these cells by focusing on their nature and their potential to effectively treat neurodegenerative diseases that share some overlapping pathophysiological features with TD. At the same time, some of the obstacles these cells will have to overcome in order to become a viable therapeutic strategy for treating this potentially life-threatening illness in humans will be highlighted.

Macrophage migration inhibitory factor as a therapeutic target after traumatic spinal cord injury: a systematic review

PURPOSE

Macrophages play an important role in mediating damage after Spinal cord injury (SCI) by secreting macrophage migration inhibitory factor (MMIF) as a secondary injury mediator. We aimed to systematically review the role of MMIF as a therapeutic target after traumatic SCI.

METHODS

Our systematic review has been performed according to the PRISMA 2009 Checklist. A systematic search in the scientific databases was carried out for studies published before 20 February 2019 from major databases. Two researchers independently screened titles. The risk of bias of eligible articles was assessed, and data were extracted. Finally, we systematically analyzed and interpreted related data.

RESULTS

785 papers were selected for the title and abstract screening. 12 papers were included for data extraction. Eight animal studies were of high quality and the remaining two were of medium quality. One of the two human studies was of poor quality and the other was of fair quality. MMIF as a pro-inflammatory mediator can cause increased susceptibility to glutamate-related neurotoxicity, increased nitrite production, increased ERK activation, and increased COX2/PGE2 signaling pathway activation and subsequent stimulation of CCL5-related chemotaxis. Two human studies and six animal studies demonstrated that MMIF level increases after SCI. MMIF inhibition might be a potential therapeutic target in SCI by multiple different mechanisms (6/12 studies).

CONCLUSION

Most animal studies demonstrate significant neurologic improvement after administration of MMIF inhibitors, but these inhibitors have not been studied in humans yet. Further clinical trials are need to further understand MMIF inhibitor utility in acute or chronic SCI.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with the consistently applied reference standard and blinding.

Sodium-Calcium Exchangers of the SLC8 Family in Oligodendrocytes: Functional Properties in Health and Disease

The solute carrier 8 (SLC8) family of sodium-calcium exchangers (NCXs) functions as an essential regulatory system that couples opposite fluxes of sodium and calcium ions across plasmalemmal membranes. NCXs, thereby, play key roles in maintaining an ion homeostasis that preserves cellular integrity. Hence, alterations in NCX expression and regulation have been found to lead to ionic imbalances that are often associated with intracellular calcium overload and cell death. On the other hand, intracellular calcium has been identified as a key driver for a multitude of downstream signaling events that are crucial for proper functioning of biological systems, thus highlighting the need for a tightly controlled balance. In the CNS, NCXs have been primarily characterized in the context of synaptic transmission and ischemic brain damage. However, a much broader picture is emerging. NCXs are expressed by virtually all cells of the CNS including oligodendrocytes (OLGs), the cells that generate the myelin sheath. With a growing appreciation of dynamic calcium signals in OLGs, NCXs are becoming increasingly recognized for their crucial roles in shaping OLG function under both physiological and pathophysiological conditions. In order to provide a current update, this review focuses on the importance of NCXs in cells of the OLG lineage. More specifically, it provides a brief introduction into plasmalemmal NCXs and their modes of activity, and it discusses the roles of OLG expressed NCXs in regulating CNS myelination and in contributing to CNS pathologies associated with detrimental effects on OLG lineage cells.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.

Clinical translation of stem cell based interventions for spinal cord injury - Are we there yet?

Recent advances in basic science in research related to spinal cord injury (SCI) and regeneration have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Stem cell and other cellular interventions have gained lot of attention due to their immense potential of regeneration. These interventions have been tested for their efficacy in case of SCI both at the pre-clinical and clinical level. In this review we critically discuss the published literature on the cellular interventions for SCI and their clinical applications with respect to the strength of evidence established by these studies. The need to curb unethical practice of offering unproven stem cell "therapies" for SCI at a global level is also discussed.

Defining recovery neurobiology of injured spinal cord by synthetic matrix-assisted hMSC implantation

Mesenchymal stromal stem cells (MSCs) isolated from adult tissues offer tangible potential for regenerative medicine, given their feasibility for autologous transplantation. MSC research shows encouraging results in experimental stroke, amyotrophic lateral sclerosis, and neurotrauma models. However, further translational progress has been hampered by poor MSC graft survival, jeopardizing cellular and molecular bases for neural repair in vivo. We have devised an adult human bone marrow MSC (hMSC) delivery formula by investigating molecular events involving hMSCs incorporated in a uniquely designed poly(lactic-co-glycolic) acid scaffold, a clinically safe polymer, following inflammatory exposures in a dorsal root ganglion organotypic coculture system. Also, in rat T9-T10 hemisection spinal cord injury (SCI), we demonstrated that the tailored scaffolding maintained hMSC stemness, engraftment, and led to robust motosensory improvement, neuropathic pain and tissue damage mitigation, and myelin preservation. The scaffolded nontransdifferentiated hMSCs exerted multimodal effects of neurotrophism, angiogenesis, neurogenesis, antiautoimmunity, and antiinflammation. Hindlimb locomotion was restored by reestablished integrity of submidbrain circuits of serotonergic reticulospinal innervation at lumbar levels, the propriospinal projection network, neuromuscular junction, and central pattern generator, providing a platform for investigating molecular events underlying the repair impact of nondifferentiated hMSCs. Our approach enabled investigation of recovery neurobiology components for injured adult mammalian spinal cord that are different from those involved in normal neural function. The uncovered neural circuits and their molecular and cellular targets offer a biological underpinning for development of clinical rehabilitation therapies to treat disabilities and complications of SCI.

A Model of Glial Scarring Analogous to the Environment of a Traumatically Injured Spinal Cord Using Kainate

OBJECTIVE

To develop an in vitro model analogous to the environment of traumatic spinal cord injury (SCI), the authors evaluated change of astrogliosis following treatments with kainate and/or scratch, and degree of neurite outgrowth after treatment with a kainate inhibitor.

METHODS

Astrocytes were obtained from the rat spinal cord. Then, 99% of the cells were confirmed to be GFAP-positive astrocytes. For chemical injury, the cells were treated with kainate at different concentrations (10, 50 or 100 µM). For mechanical injury, two kinds of uniform scratches were made using a plastic pipette tip by removing strips of cells. For combined injury (S/K), scratch and kainate were provided. Cord neurons from rat embryos were plated onto culture plates immediately after the three kinds of injuries and some cultures were treated with a kainate inhibitor.

RESULTS

Astro-gliosis (glial fibrillary acidic protein [GFAP], vimentin, chondroitin sulfate proteoglycan [CSPG], rho-associated protein kinase [ROCK], and ephrin type-A receptor 4 [EphA4]) was most prominent after treatment with 50 µM kainate and extensive scratch injury in terms of single arm (p<0.001) and in the S/K-induced injury model in view of single or combination (p<0.001). Neurite outgrowth in the seeded spinal cord (β-III tubulin) was the least in the S/K-induced injury model (p<0.001) and this inhibition was reversed by the kainate inhibitor (p<0.001).

CONCLUSION

The current in vitro model combining scratch and kainate induced glial scarring and inhibitory molecules and restricted neurite outgrowth very strongly than either the mechanically or chemically-induced injury model; hence, it may be a useful tool for research on SCI.

Glutamate-Induced White Matter Injury: Excitotoxicity without Synapses

White matter of the brain and spinal cord is irreversibly damaged by ischemia and trauma. Recent evidence indicates that despite the absence of synaptic elements, excitotoxic mechanisms play an important role in the pathogenesis of white matter damage. Glial cells, including astrocytes and oligodendrocytes, possess non-NMDA glutamate receptors and are injured by excessive exposure to AMPA/kainate agonists. In addition, the myelin sheath itself appears to respond directly to glutamate stimulation via AMPA receptors, which may also lead to injury of this key constituent of myelinated axons. During white matter anoxia/ischemia or trauma, endogenous glutamate is released mainly from axoplasmic pools in a nonvesicular fashion through Na+-dependent glutamate transporters, stimulated to operate in the glutamate efflux mode by collapse of transmembrane ion gradients and depolarization. It appears that parallel mechanisms are triggered by injurious stimuli, involving reverse Na+-Ca2+ exchange and voltage-gated Ca2+ channels producing Ca2+ overload of the axon cylinder, whereas glutamate release with AMPA receptor overactivation causes Ca2+-dependent damage to the ensheathing myelin and sup-porting glia. The emerging complexity of white matter injury mechanisms requires a thorough understanding of the interrelated steps to optimize therapeutic design.

Glutamate and ATP at the Interface Between Signaling and Metabolism in Astroglia: Examples from Pathology

Glutamate is the main excitatory transmitter in the brain, while ATP represents the most important energy currency in any living cell. Yet, these chemicals play an important role in both processes, enabling them with dual-acting functions in metabolic and intercellular signaling pathways. Glutamate can fuel ATP production, while ATP can act as a transmitter in intercellular signaling. We discuss the interface between glutamate and ATP in signaling and metabolism of astrocytes. Not only do glutamate and ATP cross each other's paths in physiology of the brain, but they also do so in its pathology. We present the fabric of this process in (patho)physiology through the discussion of synthesis and metabolism of ATP and glutamate in astrocytes as well as by providing a general description of astroglial receptors for these molecules along with the downstream signaling pathways that may be activated. It is astroglial receptors for these dual-acting molecules that could hold a key for medical intervention in pathological conditions. We focus on two examples disclosing the role of activation of astroglial ATP and glutamate receptors in pathology of two kinds of brain tissue, gray matter and white matter, respectively. Interventions at the interface of metabolism and signaling show promise for translational medicine.

Assessment of the Neuroprotective Effects of Lavandula angustifolia Extract on the Contusive Model of Spinal Cord Injury in Wistar Rats

Introduction: Spinal cord injury (SCI) involves a primary trauma and secondary cellular processes that can lead to severe damage to the nervous system, resulting in long-term spinal deficits. At the cellular level, SCI causes astrogliosis, of which glial fibrillary acidic protein (GFAP) is a major index.

Objective: The aim of this study was to investigate the neuroprotective effects of Lavandula angustifolia (Lav) on the repair of spinal cord injuries in Wistar rats.

Materials and Methods: Forty-five female rats were randomly divided into six groups of seven rats each: the intact, sham, control (SCI), Lav 100, Lav 200, and Lav 400 groups. Every week after SCI onset, all animals were evaluated for behavior outcomes by the Basso, Beattie, and Bresnahan (BBB) score. H&E staining was performed to examine the lesions post-injury. GFAP expression was assessed for astrogliosis. Somatosensory evoked potential (SEP) testing was performed to detect the recovery of neural conduction.

Results: BBB scores were significantly increased and delayed responses on sensory tests were significantly decreased in the Lav 200 and Lav 400 groups compared to the control group. The greatest decrease of GFAP was evident in the Lav 200 and Lav 400 groups. EMG results showed significant improvement in the hindlimbs in the Lav 200 and Lav 400 groups compared to the control group. Cavity areas significantly decreased and the number of ventral motor neurons significantly increased in the Lav 200 and Lav 400 groups.

Conclusion: Lav at doses of 200 and 400 mg/kg can promote structural and functional recovery after SCI. The neuroprotective effects of L. angustifolia can lead to improvement in the contusive model of SCI in Wistar rats.

PPAR agonists as therapeutics for CNS trauma and neurological diseases

Traumatic injury or disease of the spinal cord and brain elicits multiple cellular and biochemical reactions that together cause or are associated with neuropathology. Specifically, injury or disease elicits acute infiltration and activation of immune cells, death of neurons and glia, mitochondrial dysfunction, and the secretion of substrates that inhibit axon regeneration. In some diseases, inflammation is chronic or non-resolving. Ligands that target PPARs (peroxisome proliferator-activated receptors), a group of ligand-activated transcription factors, are promising therapeutics for neurologic disease and CNS injury because their activation affects many, if not all, of these interrelated pathologic mechanisms. PPAR activation can simultaneously weaken or reprogram the immune response, stimulate metabolic and mitochondrial function, promote axon growth and induce progenitor cells to differentiate into myelinating oligodendrocytes. PPAR activation has beneficial effects in many pre-clinical models of neurodegenerative diseases and CNS injury; however, the mechanisms through which PPARs exert these effects have yet to be fully elucidated. In this review we discuss current literature supporting the role of PPAR activation as a therapeutic target for treating traumatic injury and degenerative diseases of the CNS.

The impact of oxidative stress in thiamine deficiency: a multifactorial targeting issue

Thiamine (vitamin B1) deficiency, the underlying cause of Wernicke-Korsakoff syndrome, is associated with the development of focal neuronal loss in vulnerable areas of the brain. Although the actual mechanism(s) that lead to the selective histological lesions characteristic of this disorder remain unresolved, oxidative stress has been shown to play a major role in its pathophysiology. In this review, the multifactorial influence of oxidative stress on a variety of processes known to take part in the development of structural lesions in TD including excitotoxicity, neuroinflammation, blood-brain barrier integrity, mitochondrial integrity, apoptosis, nucleic acid function, and neural stem cells will be discussed, and therapeutic strategies undertaken for treating neurodegeneration examined which may have an impact on the future treatment of this important vitamin deficiency.

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

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

Reduction in expression of the astrocyte glutamate transporter, GLT1, worsens functional and histological outcomes following traumatic spinal cord injury

The astrocyte glutamate transporter, GLT1, is responsible for the vast majority of glutamate uptake in the adult central nervous system (CNS), thereby regulating extracellular glutamate homeostasis and preventing excitotoxicity. Glutamate dysregulation plays a central role in outcome following traumatic spinal cord injury (SCI). To determine the role of GLT1 in secondary cell loss following SCI, mice heterozygous for the GLT1 astrocyte glutamate transporter (GLT1+/-) and wild-type mice received thoracic crush SCI. Compared with wild-type controls, GLT1+/- mice had an attenuated recovery in hindlimb motor function, increased lesion size, and decreased tissue sparing. GLT1+/- mice showed a decrease in intraspinal GLT1 protein and functional glutamate uptake compared with wild-type mice, accompanied by increased apoptosis and neuronal loss following crush injury. These results suggest that astrocyte GLT1 plays a role in limiting secondary cell death following SCI, and also show that compromise of key astrocyte functions has significant effects on outcome following traumatic CNS injury. These findings also suggest that increasing intraspinal GLT1 expression may represent a therapeutically relevant target for SCI treatment.

Acute administration of AMPA/Kainate blocker combined with delayed transplantation of neural precursors improves lower urinary tract function in spinal injured rats

To evaluate bladder function recovery after spinal cord injury (SCI) in response to a combination treatment of an acutely administered AMPA/kainate receptor antagonist and delayed transplantation of neuronal precursors. Female rats received a contusion injury at T8/9. The AMPA/kainate receptor antagonist NBQX was directly administered into the lesion site immediately after injury. Nine days post-injury, NRP/GRP were delivered into the lesion site. Controls received NRP/GRP grafts only or no treatment (OP-Controls). Animals underwent bladder function testing during the course of the experiment and at the endpoint. Motor function was evaluated as well. After sacrifice, histological analysis of lesion site and lumbosacral spinal cord regions was performed. Rats receiving the combined treatment (NBQX&NRP/GRP) had voided volumes/micturition resembling that of normal animals and showed greater improvement of urodynamic parameters, compared to NRP/GRP alone or OP-Controls. Similarly, NBQX&NRP/GRP induced more spouting, regeneration or sparing of descending projections to the lumbosacral cord. The density of primary afferent projections at the lumbosacral spinal cord in rats with combined treatments was similar to that of NRP/GRP alone with decreased sprouting of primary afferents in lumbosacral cord, compared to OP-Control. Immunohistochemical evaluation revealed that the combined treatment reduced the size of the lesion to a greater extent than NRP/GRP alone or OP-Controls. NRP/GRP with and without NBQX produced a significant recovery of hindlimb compared to OP-Controls. In conclusion, transplants of NRP/GRP combined with NBQX promote recovery of micturition function following spinal cord injury, likely through increased neuroprotection.

Spatial and temporal changes in promoter activity of the astrocyte glutamate transporter GLT1 following traumatic spinal cord injury

After traumatic spinal cord injury (SCI), there is an opportunity for preserving function by attenuating secondary cell loss. Astrocytes play crucial roles in the adult CNS and are responsible for the vast majority of glutamate buffering, potentially preventing excitotoxic loss of neurons and oligodendrocytes. We examined spatial and temporal changes in gene expression of the major astrocyte glutamate transporter GLT1 following moderate thoracic contusion SCI using transgenic BAC-GLT1-eGFP promoter reporter mice. In dorsal column white matter, total intensity of GLT1-eGFP expression per region was significantly reduced following SCI at both lesion epicenter and at rostral and caudal areas where no tissue loss occurred. This regional decrease in GLT1 expression was due to significant loss of GLT1-eGFP(+) cells, partially accounted for by apoptosis of eGFP(+) /GFAP(+) astrocytes in both white and gray matter. There were also decreased numbers of GLT1-eGFP-expressing cells in multiple gray matter regions following injury; nevertheless, there was sustained or even increased regional GLT1-eGFP expression in gray matter as a result of up-regulation in astrocytes that continued to express GLT1-eGFP. Although there were increased numbers of GFAP(+) cells both at the lesion site and in surrounding intact spinal cord following SCI, the majority of proliferating Ki67(+) /GFAP(+) astrocytes did not express GLT1-eGFP. These findings demonstrate that spatial and temporal alterations in GLT1 expression observed after SCI result from both astrocyte death and gene expression changes in surviving astrocytes. Results also suggest that following SCI a significant portion of astrocytes lacks GLT1 expression, possibly compromising the important role of astrocytes in glutamate homeostasis.

Facile Synthesis of Imidazoisoindolones and Quinoxalinediones from 2,3-diamino-1,4-naphthoquinone

In aqueous acetic acid, 2,3-diamino-1,4-naphthoquinone reacted with phthalic anhydride and 4,5,6,7-tetrabromophthalic anhydride to give naphtho[2’,3’:4,5]imidazo[2,1- a]isoindole-6,11,13-triones. In the same solvent, the reaction of diaminonaphthoquinone with 2,2-dihydroxy-1 H-indene-1,3(2 H)-dione gave 11 H-benzo[ g]indeno [1,2- b]quinoxaline-6,11,13-trione. Under the same conditions, diaminonaphthoquinone reacted with succinic anhydride and with maleic anhydride, the corresponding 4-(3-amino-1,4-dioxo-1,4-dihydronaphthalene-2-ylamino)-4-oxobutanoic acid and 3,5,10-trioxo-3,4,5,10-tetrahydrobenzo[ g]-quinoxaline-2(1 H)-ylidene-acetic acid derivatives were obtained. The reaction of 2,3-diamino-1,4-naphthoquinone with ( E)-1,2-dibenzoylethylene and 1,4-diphenylbut-2-yne-1,4-dione in aqueous acetic acid afforded dihydrobenzo[ g]quinoxaline-5,10-diones.

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

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

Dysmyelinated axons in shiverer mice are highly vulnerable to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor-mediated toxicity

Glutamate excitotoxicity plays a role in white matter injury in many neurological diseases. Oligodendrocytes in particular are highly vulnerable to excitotoxicity, mediated through activation of AMPA/kainate receptors. Myelin may also be injured independently via NMDA (N-methyl-D-aspartic acid) receptors located on peripheral oligodendroglial processes. Central axons are susceptible to glutamate receptor activation in vivo, but it is unclear whether this is mediated directly by activation of receptors expressed on axons, or indirectly through glutamate toxicity of myelin or neighboring glial cells. We examined axonal vulnerability in mice deficient in myelin basic protein (shiverer), also expressing yellow fluorescent protein (YFP) in a subset of axons. YFP fluorescence, EM, and mouse behavior were assessed 24 h after microstereotactical injections of S-AMPA or NMDA into lumbar dorsal columns. S-AMPA injection led to impaired rotarod performance and widespread axonal degeneration and was more pronounced in shiverer mice than controls. In contrast, NMDA injection did not cause axonal injury or behavioral changes in either group. These results indicate that spinal cord axons in vivo are vulnerable to toxicity mediated by AMPA but not NMDA receptors. The presence of compact myelin is not required for excitotoxic axon damage, and its absence may increase vulnerability. Further understanding of AMPA receptor-mediated axonal toxicity may provide new targets for neuroprotective therapy in WM diseases.

Ischemic injury to white matter: an age-dependent process

The risk for ischemic stroke increases drastically with age, although reasons for this remain unexplored. White matter (WM) and gray matter constitute equal proportions of the brain, and WM is injured in most strokes. Axonal injury and dysfunction are responsible for much of the disability associated with clinical deficits observed after stroke. The authors recently reported that central nervous system WM is inherently more vulnerable to ischemic injury in older mice, and the mechanisms of WM injury change as a function of age. Ischemic WM injury in older mice is predominantly mediated by a Ca2+-independent excitotoxicity involving overactivation of AMPA/kainate receptors. Glutamate release, due to reverse glutamate transport, occurs earlier and is more robust in older mice that show up-regulation of GLT1, the main glutamate transporter. Blockade of NMDA receptors does not improve WM function after ischemia in the young but aggravates ischemic injury in older mice. The main goals of this research update are to summarize the evidence for equivalent brain insults inducing more damage with aging, and to highlight the importance of age in any successful stroke therapy.

Glutamate receptors on myelinated spinal cord axons: II. AMPA and GluR5 receptors

OBJECTIVE

Glutamate receptors, which play a major role in the physiology and pathology of central nervous system gray matter, are also involved in the pathophysiology of white matter. However, the cellular and molecular mechanisms responsible for excitotoxic damage to white matter elements are not fully understood. We explored the roles of AMPA and GluR5 kainate receptors in axonal Ca(2+) deregulation.

METHODS

Dorsal column axons were loaded with a Ca(2+) indicator and imaged in vitro using confocal microscopy.

RESULTS

Both AMPA and a GluR5 kainate receptor agonist increased intraaxonal Ca(2+) in myelinated rat dorsal column fibers. These responses were inhibited by selective antagonists of these receptors. The GluR5-mediated Ca(2+) increase was mediated by both canonical (ie, ionotropic) and noncanonical (metabotropic) signaling, dependent on a pertussis toxin-sensitive G protein/phospholipase C-dependent pathway, promoting Ca(2+) release from inositol triphosphate-dependent stores. In addition, the GluR5 response was reduced by intraaxonal NO scavengers. In contrast, GluR4 AMPA receptors operated via Ca(2+)-induced Ca(2+) release, dependent on ryanodine receptors, and unaffected by NO scavengers. Neither pathway depended on L-type Ca(2+) channels, in contrast with GluR6 kainate receptor action.1 Immunohistochemistry confirmed the presence of GluR4 and GluR5 clustered at the surface of myelinated axons; GluR5 coimmunoprecipitated with nNOS and often colocalized with neuronal nitric oxide synthase clusters on the internodal axon.

INTERPRETATION

Central myelinated axons express functional AMPA and GluR5 kainate receptors, and can directly respond to glutamate receptor agonists. These glutamate receptor-dependent signaling pathways promote an increase in intraaxonal Ca(2+) levels potentially contributing to axonal degeneration.

Astrocytes are a major target in thiamine deficiency and Wernicke's encephalopathy

Thiamine deficiency (TD) is the underlying cause, and an established model, of Wernicke's encephalopathy (WE). Although the neurologic dysfunction and brain damage that results from TD has been well-described, the precise mechanisms that lead to the selective histological lesions characteristic of this disorder remain a mystery. Over the course of many years, various processes have been proposed that could lead to focal neuronal cell death in this disorder. But despite a concerted effort to relate these processes to a clear sequelae of events culminating in development of the focal neuropathology, little success has resulted. In recent years, however, a role for astrocytes in the pathophysiology of TD has been emerging. Here, alterations in glutamate uptake, and levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in TD and WE, are discussed in terms of an excitotoxic event, along with the GABA transporter subtype GAT-3, and changes in other astrocytic proteins including GFAP and glutamine synthetase. Lactic acidosis, changes in the water channel protein AQP-4 and brain edema are also a focus of attention in relation to astrocyte dysfunction, while involvement of oxidative stress and inflammatory processes, along with white matter injury in terms of excitotoxicity are other key issues considered. In summary, a new appraisal of the extent of involvement of astrocytes in TD and WE is presented, with the evidence suggesting these cells represent a major target for damage during the disease process.

Impaired axonal transport and neurofilament compaction occur in separate populations of injured axons following diffuse brain injury in the immature rat

Diffuse brain injury is a leading cause of mortality in infants and children under 4 years of age and results in cognitive deficits in survivors. The anatomic basis for these behavioral deficits may be traumatic axonal injury (TAI), which manifests as impaired axonal transport (IAT) and neurofilament compaction (NFC), and may occur as a result of glutamate receptor activation. The extent of IAT and NFC was evaluated at 6, 24 and 72 h following non-contusive brain trauma in the 17 day-old rat to examine the causal relationship between these two pathologic entities; in addition, the effect of antagonists to the ionotropic glutamate receptors on TAI was evaluated. At 6 h post-injury, NFC was observed primarily in the cingulum, and appeared as swollen axons and terminal bulbs. By 24 h, swollen axons were additionally present in the corpus callosum and lateral white matter tracts, and appeared to increase in diameter. At 72 h, the extent of axonal swellings exhibiting compacted neurofilaments appeared to decrease, and was accompanied by punctate immunoreactivity within axon tracts suggestive of axonal degeneration. Although NFC was present in the same anatomical locations where axonal accumulation of amyloid precursor protein (APP) has been observed, double-label immunohistochemistry revealed no evidence of colocalization of compacted neurofilament and APP. Pre-injury treatment with either the NMDA receptor antagonist, ifenprodil, or the AMPA receptor antagonist, NBQX, had no significant effect on the extent of TAI, suggesting that excitotoxicity may not be a primary mechanism underlying TAI. Importantly, these data are indicative of the heterogeneity of mechanisms underlying TAI in the traumatically-injured immature brain.

Impact of sex and hormones on new cells in the developing rat hippocampus: a novel source of sex dimorphism?

The hippocampus is a key brain region regulating complex cognitive and emotional responses, and is implicated in the etiology of depressive and anxiety disorders, many of which exhibit some degree of sex difference. The male rat hippocampus is consistently reported to be slightly but significantly larger than the female. The majority of studies on the development of volumetric sex differences have focused on the effects of estradiol (E2), with relatively few focusing on androgens. We examined the impact of both E2 and androgens on newly born cells in the developing rat hippocampus, and report that neonatal males have significantly more 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU)+ cells than females. Both testosterone (T) and dihydrotestosterone treatment of females significantly increased the number of BrdU+ cells, an effect blocked by the androgen receptor antagonist, flutamide. However, only T significantly increased the number of neuronal nuclear antigen+ neurons in the female rat hippocampus. Interestingly, E2 treatment also increased BrdU+ cells in females, but had no effect on neuron number. Instead, E2 and T significantly increased the number of newly born glial fibrillary acidic protein or glutamine synthetase+ glial cells in females, indicating that androgens and E2 may act independently to achieve distinct endpoints. Quantification of pyknotic cells at two different developmental time points indicates no sex difference in the number of cells dying, suggesting, but not proving, that gonadal steroids are promoting cell genesis.

FK1706, a novel non-immunosuppressant neurophilin ligand, ameliorates motor dysfunction following spinal cord injury through its neuroregenerative action

Injured spinal cord axons fail to regenerate in part due to a lack of trophic support. While various methods for replacing neurotrophins have been pursued, clinical uses of these methods face significant barriers. FK1706, a non-immunosuppressant neurophilin ligand, potentiates nerve growth factor signaling, suggesting therapeutic potential for functional deficits following spinal cord injury. Here, we demonstrate that FK1706 significantly improves behavioral outcomes in animal models of spinal cord hemisection and contusion injuries in rats. Furthermore, we show that FK1706 is effective even if administration is delayed until 1 week after injury, suggesting that FK1706 has a reasonable therapeutic time-window. Morphological analysis of injured axons in the dorsal corticospinal tract showed an increase in the radius and perimeter of stained axons, which were reduced by FK1706 treatment, suggesting that axonal swelling and retraction balls observed in injured spinal cord were improved by the neurotrophic effect of FK1706. Taken together, FK1706 improves both behavioral motor function and the underlying morphological changes, suggesting that FK1706 may have therapeutic potential in meeting the significant unmet needs in spinal cord injury.

Microdialysis in central nervous system disorders and their treatment

Central nervous system (CNS) insults elevate endogenous toxins and alter levels of indicators of metabolic disorder. These contribute to neurotrauma, neurodegenerative diseases and chronic pain and are possible targets for pharmaceutical treatment. Microdialysis samples substances in the extracellular space for chemical analysis. It has demonstrated that toxic levels of glutamate are released and that toxic levels of the reactive species O(2)(-), H(2)O(2), HO. NO and HOONO are generated upon CNS injury. Agent administration by microdialysis can also help elucidate mechanisms of damage and protection, and to identify targets for clinical application. Microdialysis sampling indicates that circuits descending from the brain to the spinal cord transmit and modulate pain signals by releasing neurotransmitter amines and amino acids. Efforts are under way to develop microdialysis into a technique for intensive care monitoring and predicting outcomes of brain insults. Finally, microdialysis sampling has demonstrated in vivo elevation of glial cell line-derived neurotrophic factor following grafting of primed fetal human neural stem cells into brain-injured rats, the first in vivo demonstration of the release of a neurotrophic factor by grafted stem cells. This increased release correlated with significantly improved spatial learning and memory.

Glutamate-induced losses of oligodendrocytes and neurons and activation of caspase-3 in the rat spinal cord

The toxicity of released glutamate contributes substantially to secondary cell death following spinal cord injury (SCI). In this work, the extent and time courses of glutamate-induced losses of neurons and oligodendrocytes are established. Glutamate was administered into the spinal cords of anesthetized rats at approximately the concentration and duration of its release following SCI. Cells in normal tissue, in tissue exposed to artificial cerebrospinal fluid and in tissue exposed to glutamate were counted on a confocal system in control animals and from 6 h to 28 days after treatment to assess cell losses. Oligodendrocytes were identified by staining with antibody CC-1 and neurons by immunostaining for Neuronal Nuclei (NeuN) or Neurofilament H. The density of oligodendrocytes declined precipitously in the first 6 h after exposure to glutamate, and then relatively little from 24 h to 28 days post-exposure. Similarly, neuron densities first declined rapidly, but at a decreasing rate, from 0 h to 72 h post-glutamate exposure and did not change significantly from 72 h to 28 days thereafter. The nuclei of many cells strongly and specifically stained for activated caspase-3, an indicator of apoptosis, in response to exposure to glutamate. Caspase-3 was localized to the nucleus and may participate in apoptotic cell death. However, persistence of caspase-3 staining for at least a week after exposure to glutamate during little to no loss of oligodendrocytes and neurons demonstrates that elevation of caspase-3 does not necessarily lead to rapid cell death. Beyond about 48 h after exposure to glutamate, locomotor function began to recover while cell numbers stabilized or declined slowly, demonstrating that functional recovery in the experiments presented involves processes other than replacement of oligodendrocytes and/or neurons.

Excitotoxic mechanisms of ischemic injury in myelinated white matter

Axonal injury and dysfunction in white matter (WM) are caused by many neurologic diseases including ischemia. We characterized ischemic injury and the role of glutamate-mediated excitotoxicity in a purely myelinated WM tract, the mouse optic nerve (MON). For the first time, excitotoxic WM injury was directly correlated with glutamate release. Oxygen and glucose deprivation (OGD) caused duration-dependent loss of axon function in optic nerves from young adult mice. Protection of axon function required blockade of both alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate receptors, or removal of extracellular Ca(2+). Blockade of N-methyl-D-aspartate receptors did not preserve axon function. Curiously, even extended periods of direct exposure to glutamate or kainate or AMPA failed to induce axon dysfunction. Brief periods of OGD, however, caused glutamate receptor agonist exposure to become toxic, suggesting that ionic disruption enabled excitotoxic injury. Glutamate release, directly measured using quantitative high-performance liquid chromatography, occurred late during a 60-mins period of OGD and was due to reversal of the glutamate transporter. Brief periods of OGD (i.e., 15 mins) did not cause glutamate release and produced minimal injury. These results suggested that toxic glutamate accumulation during OGD followed the initial ionic changes mediating early loss of excitability. The onset of glutamate release was an important threshold event for irreversible ischemic injury. Regional differences appear to exist in the specific glutamate receptors that mediate WM ischemic injury. Therapy for ischemic WM injury must be designed accordingly.

Temporal characterization of mitochondrial bioenergetics after spinal cord injury

Mitochondrial dysfunction following spinal cord injury (SCI) may be critical for the development of secondary pathophysiology and neuronal cell death. Previous studies have demonstrated a loss of mitochondrial bioenergetics at 24 h following SCI. To begin to understand the evolution and study the contribution of mitochondrial dysfunction in pathophysiology of SCI, we investigated mitochondrial bioenergetics in the mid-thoracic region at 6, 12, and 24 h following contusion SCI. It is widely accepted that increased free radical generation plays a critical role in neuronal damage after SCI. Hence, to ascertain the role of free radicals in SCI-induced mitochondrial dysfunction, markers for oxidative damage, including nitrotyrosine (3-NT), lipid peroxidation byproduct (4-hydroxynonenal [HNE]), and protein oxidation (protein carbonyls) were quantified in the same samples of isolated mitochondria during the 24-h time course. The results demonstrate that a significant decline in mitochondrial function begins to occur 12 h post-injury and persists for a least 24 h following SCI. Furthermore, there was a progressive increase in mitochondrial oxidative damage that preceded the loss of mitochondrial bioenergetics, suggesting that free radical damage may be a major mitochondrial secondary injury process. Based on the present results, the temporal profile of mitochondrial dysfunction indicates that interventions targeting mitochondrial oxidative damage and dysfunction may serve as a beneficial pharmacological treatment for acute SCI.

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

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

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

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

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

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

Stability of complex spike timing-dependent plasticity in cerebellar learning

Dynamics of spike-timing dependent synaptic plasticity are analyzed for excitatory and inhibitory synapses onto cerebellar Purkinje cells. The purpose of this study is to place theoretical constraints on candidate synaptic learning rules that determine the changes in synaptic efficacy due to pairing complex spikes with presynaptic spikes in parallel fibers and inhibitory interneurons. Constraints are derived for the timing between complex spikes and presynaptic spikes, constraints that result from the stability of the learning dynamics of the learning rule. Potential instabilities in the parallel fiber synaptic learning rule are found to be stabilized by synaptic plasticity at inhibitory synapses if the inhibitory learning rules are stable, and conditions for stability of inhibitory plasticity are given. Combining excitatory with inhibitory plasticity provides a mechanism for minimizing the overall synaptic input. Stable learning rules are shown to be able to sculpt simple-spike patterns by regulating the excitability of neurons in the inferior olive that give rise to climbing fibers.

Kainate induces rapid redistribution of the actin cytoskeleton in ameboid microglia

Microglia are key mediators of the immune response in the central nervous system (CNS). They are closely related to macrophages and undergo dramatic morphological and functional changes after CNS trauma or excitotoxic lesions. Microglia can be directly stimulated by excitatory neurotransmitters and are known to express many neurotransmitter receptors. The role of these receptors, however, is not clear. This study describes the microglial response to the glutamate receptor agonist kainate (KA) and shows via immunochemistry that the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptor subunit GluR1 is present on cultured microglia. In the presence of 100 microM or 1 mM KA, cultured microglia underwent dramatic morphological and cytoskeletal changes as observed by time-lapse photography and quantitative confocal analysis of phalloidin labeling. KA-stimulated microglia showed condensation of cytoplasmic actin filaments, rapid de- and repolymerization, and cytoplasmic redistribution of condensed actin bundles. Rearrangement of actin filaments-thought to be involved in locomotion and phagocytosis and to indicate an increased level of activation (for reviews see Greenberg [ 1995] Trends Cell Biol. 5:93-99; Imai and Kohsaka [ 2002] Glia 40:164-174)-was significantly increased in treated vs. control cultures. Morphological plasticity and membrane ruffling were also seen. These findings suggest direct microglial excitation via glutamate receptor pathways. Thus, neurotransmitter release after brain or spinal cord injury might directly modulate the inflammatory response.

Complex interplay between glutamate receptors and intracellular Ca2+ stores during ischaemia in rat spinal cord white matter

Electrophysiological recordings of propagated compound action potentials (CAPs) and axonal Ca(2+) measurements using confocal microscopy were used to study the interplay between AMPA receptors and intracellullar Ca(2+) stores in rat spinal dorsal columns subjected to in vitro combined oxygen and glucose deprivation (OGD). Removal of Ca(2+) or Na(+) from the perfusate was protective after 30 but not 60 min of OGD. TTX was ineffective with either exposure, consistent with its modest effect on ischaemic depolarization. In contrast, AMPA antagonists were very protective, even after 60 min of OGD where 0Ca(2+) + EGTA perfusate was ineffective. Similarly, blocking ryanodine receptor-mediated Ca(2+) mobilization from internal stores (0Ca(2+) + nimodipine or 0Ca(2+) + ryanodine), or inositol 1,4,5-trisphosphate (IP(3))-dependent Ca(2+) release (block of group 1 metabotropic glutamate receptors with 1-aminoindan-1,5-dicarboxylic acid, inhibition of phospholipase C with U73122 or IP(3) receptor block with 2APB; each in 0Ca(2+)) were each very protective, with the combination resulting in virtually complete functional recovery after 1 h OGD (97 +/- 32% CAP recovery versus 4 +/- 6% in artificial cerebrospinal fluid). AMPA induced a rise in Ca(2+) concentration in normoxic axons, which was greatly reduced by blocking ryanodine receptors. Our data therefore suggest a novel and surprisingly complex interplay between AMPA receptors and Ca(2+) mobilization from intracellular Ca(2+) stores. We propose that AMPA receptors may not only allow Ca(2+) influx from the extracellular space, but may also significantly influence Ca(2+) release from intra-axonal Ca(2+) stores. In dorsal column axons, AMPA receptor-dependent mechanisms appear to exert a greater influence than voltage-gated Na(+) channels on functional outcome following OGD.

Lentiviral transduction of murine oligodendrocytes in vivo

Lentiviral vectors are used widely to direct efficient gene transfer in vivo. We examined cell-specific expression in adult murine white matter after stereotaxic microinjection of four lentiviral constructs. We synthesized vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped lentiviruses with combinations of two promoters, cytomegalovirus (CMV) or myelin basic protein (MBP), and two reporter sequences, cytosolic enhanced green fluorescent protein (eGFP) or a plasma membrane-targeted eGFP (human lymphocyte-specific protein tyrosine kinase [Lck]-eGFP). For all constructs, intracerebral injections to lateral corpus callosum resulted in widespread GFP expression in forebrain white matter glial cells. Intense cellular GFP fluorescence was observed within 3 days after injection and lasted for at least 28 days. The CMV promoter directed GFP expression in multiple glial cell types, whereas the MBP promoter targeted GFP specifically to oligodendrocytes. Expression of the membrane-targeted Lck-eGFP construct distinctly labeled individual myelinating processes of oligodendrocytes. Lentiviral constructs expressing eGFP or Lck-eGFP under the MBP promoter provide excellent visualization of oligodendrocyte morphology in intact white matter, and may prove valuable for delivering additional genes of interest to oligodendrocytes in vivo.

Ontogeny of AMPA and NMDA receptor gene expression in the developing sheep white matter and cerebral cortex

This study examined the hypothesis that the high prevalence of white matter injury in premature infants is associated with increased expression of calcium-permeable forms of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of glutamate receptors in pre-myelinating white matter. We characterized expression of subunits of the AMPA, and for reference, the N-methyl-d-aspartate (NMDA), glutamate receptors at 0.5, 0.65, 0.85, and term gestation in the ovine fetal white matter and cerebral cortex. There was a low expression of the critical calcium-impermeable AMPA receptor GluR2 subunit in subcortical white matter both absolutely and relative to other AMPA subunits throughout gestation. In contrast, GluR2 subunit mRNA expression fell in the cerebral cortex with increasing gestation whereas protein expression increased. These findings suggest a vulnerability of subcortical white matter to AMPA receptor-mediated calcium toxicity throughout the second half of gestation. Thus, the hypothesis that AMPA receptor-mediated glutamate toxicity contributes to brain damage in premature infants needs to be revised.

α-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid-mediated excitotoxic axonal damage is attenuated in the absence of myelin proteolipid protein

In vivo and in vitro studies have shown that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated excitotoxicity causes cytoskeletal damage to axons. AMPA/kainate receptors are present on oligodendrocytes and myelin, but currently there is no evidence to suggest that axon cylinders contain AMPA receptors. Proteolipid protein (PLP) and DM20 are integral membrane proteins expressed by CNS oligodendrocytes and located in compact myelin. Humans and mice lacking normal PLP/DM20 develop axonal swellings and degeneration, suggesting that local interactions between axons and the oligodendrocyte/myelin unit are important for the normal functioning of axons and that PLP/DM20 is involved in this process. To determine whether perturbed glial-axonal interaction affects AMPA-receptor-mediated axonal damage, AMPA (1.5 nmol) was injected into the caudate nucleus of anesthetized Plp knockout and wild-type male mice (n = 13). Twenty-four hours later, axonal damage was detected by using neurofilament 200 (NF 200) immunohistochemistry and neuronal damage detected via histology. AMPA-induced axonal damage, assessed with NF 200 immunohistochemistry, was significantly reduced in Plp knockout mice compared with wild-type mice (P = 0.015). There was no significant difference in the levels of neuronal perikaryal damage between the Plp knockout and wild-type mice. In addition, there was no significant difference in the levels of glutamate receptor subunits GluR1-4 or KA2 in Plp knockout compared with wild-type littermates. The present study suggests that PLP-mediated interactions among oligodendrocytes, myelin, and axons may be involved in AMPA-mediated axonal damage.

Systematic analysis of axonal damage and inflammatory response in different white matter tracts of acutely injured rat spinal cord

The mechanisms of white matter (WM) damage during secondary degeneration are a fundamental issue in the pathophysiology of central nervous system (CNS) diseases. Our main goal was to describe the pattern of an acute inflammatory response and secondary damage to axons in different WM tracts of acutely injured rat spinal cord. Adult rats were deeply anesthetized and injected with 20 nmol of NMDA into the spinal cord ventral horn on T7. Animals were perfused after survival times of 1 day, 3 days and 7 days. Ten micrometer sections were submitted to immunocytochemical analysis for activated macrophages/microglia, neutrophils and damaged axons. There were inflammatory response and progressive tissue destruction of ventral WM (VWM) with formation of microcysts in both VWM and lateral WM (LWM). In the VWM, the number of beta-amyloid precursor protein (beta-APP) end-bulbs increased from 1 day with a peak at 3 days, decreasing by 7 days following the injection. APP end-bulbs were present in the dorsal WM (DWM) at 3 days survival time but were not in the LWM. Electron microscopic analysis revealed different degrees of myelin disruption and axonal pathology in the vacuolated WM up to 14 mm along the rostrocaudal axis. Quantitative analysis revealed a significant loss of medium and large axons (P < 0.05), but not of small axons (P > 0.05). Our results suggest that bystander axonal damage and myelin vacuolation are important secondary component of the pathology of WM tracts following rat SCI. Further studies are needed to understand the mechanisms of these pathological events.

An adult rat spinal cord contusion model of sensory axon degeneration: the estrus cycle or a preconditioning lesion do not affect outcome

A therapeutic strategy for acute spinal cord injury would be to reduce the progressive degeneration and disconnection of axons from their targets. Here, we describe a model to evaluate degeneration of the ascending sensory projections to the nuclei in the medulla following graded spinal cord contusions in adult female Sprague-Dawley rats. Cholera toxin B (CTB) labeling from the sciatic nerve of naive rats revealed effective labeling of the terminal fibers in the gracile nucleus at 3 days post-injection and a subpopulation of rapidly transporting fibers after 1 day. Seven days after contusions using the Infinite Horizon impactor the area of CTB-labeled terminal fibers had a negative correlation with increasing impact force. Moderate spinal contusions of around 150 kilodyne (kdyn or 0.15 x 10(-3) newton) caused a reduction to 40% in the fiber area which will enable the identification of protective as well as detrimental drugs and post-injury mechanisms. A preconditioning injury of the sciatic nerve reportedly can enhance growth of sensory axons but did not affect the terminal fiber area in the gracile nucleus. Estrogen and progesterone are protective in various systems and could therefore influence experimental outcomes when using females. However, the phase of the estrus cycle at the time of contusion or during the post-injury time did not affect the outcome of the contusion, indicating that female rats may be used without consideration of the estrus cycle. This model can readily be used to evaluate pharmacological agents for protection of sensory axons and pathophysiological mechanisms of their degeneration.

Injectable intrathecal delivery system for localized administration of EGF and FGF-2 to the injured rat spinal cord

The administration of growth factors (GFs) for treatment of experimental spinal cord injury (SCI) has shown limited benefits. One reason may be the mode of delivery to the injury site. We have developed a minimally invasive and safe drug delivery system (DDS) consisting of a highly concentrated collagen solution that can be injected intrathecally at the site of injury providing localized delivery of GFs. Using the injectable DDS, epidermal growth factor (EGF) and basic fibroblast growth factor (FGF-2) were co-delivered in the subarachnoid space of Sprague-Dawley rats. The in vivo distribution of EGF and FGF-2 in both injured and uninjured animals was monitored by immunohistochemistry. Although significant differences in the distribution of EGF and FGF-2 in the spinal cord were evident, localized delivery of the GFs resulted in significantly less cavitation at the lesion epicenter and for at least 720 mum caudal to it compared to control animals without the DDS. There was also significantly more white matter sparing at the lesion epicenter in animals receiving the GFs compared to control animals. Moreover, at 14 days post-injection, delivery of the GFs resulted in significantly greater ependymal cell proliferation in the central canal immediately rostral and caudal to the lesion edge compared to controls. These results demonstrate that the injectable DDS provides a new paradigm for localized delivery of bioactive therapeutic agents to the injured spinal cord.

Nicotine Attenuates Morphological Deficits in a Contusion Model of Spinal Cord Injury

Protection against the progression of secondary injury appears to be an effective therapeutic strategy in spinal cord injury (SCI). Evidence indicates that nicotine can induce potent neuroprotective effects against injury to spinal cord neurons. Therefore, the present study was focused on the effects of nicotine on the behavioral and morphological recovery associated with SCI. Adult male Long-Evans rats were subjected to a moderate contusion model of SCI and received subcutaneous injections of nicotine for 14 days at the dose of 0.35 or 7 mg/kg/day. The rats were examined using the BBB locomotor rating scale for 6 weeks. At the end of the BBB recording, spinal cords were examined for the volumetric tissue sparing of gray and white matters. All SCI rats demonstrated a loss of hindlimb function followed by a recovery phase that peaked at 2-3 weeks after the trauma. Compared to untreated SCI rats, chronic nicotine administration appeared to improve the recovery of the locomotor functions. Indeed, nicotine-treated animals scored consistently higher on the BBB scale indicating that the treatment altered animal behavior. However, when taking under consideration correction factors for multiple comparisons, these data did not reach significance at overall experimental levels of significance 0.05. Nevertheless, nicotine administration was effective in sparing tissue at injury epicenter and a lower dose of nicotine also resulted in significant sparing of white matter of the injured spinal cord. These results suggest that agonists of neuronal nicotinic receptors can be attractive candidates for SCI therapy.

Glutamate-mediated glial injury: Mechanisms and clinical importance

Primary and/or secondary glial cell death can cause and/or aggravate human diseases of the central nervous system (CNS). Like neurons, glial cells are vulnerable to glutamate insults. Astrocytes, microglia, and oligodendrocytes express a wide variety of glutamate receptors and transporters that mediate many of the deleterious effects of glutamate. Astrocytes are responsible for most glutamate uptake in synaptic and nonsynaptic areas and consequently, are the major regulators of glutamate homeostasis. Microglia in turn may secrete cytokines, which can impair glutamate uptake and reduce the expression of glutamate transporters. Finally, oligodendrocytes, the myelinating cells of the CNS, are very sensitive to excessive glutamate signaling, which can lead to the apoptosis or necrosis of these cells. This review aims at summarizing the mechanisms leading to glial cell death as a consequence of alterations in glutamate signaling, and their clinical relevance. A thorough understanding of these events will undoubtedly lead to better therapeutic strategies to treat CNS diseases affecting glia and in particular, those that involve damage to white matter tracts.

Reversal or reduction of glutamate and GABA transport in CNS pathology and therapy

A dysfunction of amino acid neurotransmitter transporters occurs in a number of central nervous system disorders, including stroke, epilepsy, cerebral palsy and amyotrophic lateral sclerosis. This dysfunction can comprise a reversal of transport direction, leading to the release of neurotransmitter into the extracellular space, or an alteration in transporter expression level. This review analyses the role of glutamate and GABA transporters in the pathogenesis and therapy of a number of acute and chronic neurological disorders.

Glutamate receptor subunit expression after spinal cord injury in young rats

To investigate the possibility that glutamate receptor levels in the spinal cord are altered following injury to young rats, we used a previously characterized model of spinal cord contusion that produces a reliable injury in rats at postnatal day 14-15. Quantitative Western blot analysis was used to measure relative amounts of protein for several glutamate receptor subunits acutely (24 h) and chronically (28 days) after spinal cord injury (SCI). Acutely after injury significant decreases were observed in the GluR1, GluR2, and GluR4 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionate (AMPA) receptor, and the NR2A and NR2B subunits, but not the NR1 subunit, of the N-methyl-d-aspartate (NMDA) receptor. However, 28 days after injury only one subunit (GluR4) was shown to be altered. These widespread changes that occur acutely in receptor subunit expression may be an attempt to protect cells from glutamate-induced death. The injured spinal cord in these young animals, however, appears to have the capacity to regulate receptor subunit levels to normal within a month of injury.