White matter injury in spinal cord ischemia: protection by AMPA/kainate glutamate receptor antagonism

New insights into the roles of oligodendrocytes regulation in ischemic stroke recovery

Oligodendrocytes (OLs), the myelin-forming cells of the central nervous system, are integral to axonal integrity and function. Hypoxia-ischemia episodes can cause severe damage to these vulnerable cells through excitotoxicity, oxidative stress, inflammation, and mitochondrial dysfunction, leading to axonal dystrophy, neuronal dysfunction, and neurological impairments. OLs damage can result in demyelination and myelination disorders, severely impacting axonal function, structure, metabolism, and survival. Adult-onset stroke, periventricular leukomalacia, and post-stroke cognitive impairment primarily target OLs, making them a critical therapeutic target. Therapeutic strategies targeting OLs, myelin, and their receptors should be given more emphasis to attenuate ischemia injury and establish functional recovery after stroke. This review summarizes recent advances on the function of OLs in ischemic injury, as well as the present and emerging principles that serve as the foundation for protective strategies against OL deaths.

Biochemical, pathological and ultrastructural investigation of whether lamotrigine has neuroprotective efficacy against spinal cord ischemia reperfusion injury

INTRODUCTION

Lamotrigine, an anticonvulsant drug with inhibition properties of multi-ion channels, has been shown to be able to attenuates secondary neuronal damage by influencing different pathways. The aim of this study was to look into whether lamotrigine treatment could protect the spinal cord from experimental spinal cord ischemia-reperfusion injury.

MATERIALS AND METHODS

Thirty-two rats, eight rats per group, were randomly assigned to the sham group in which only laparotomy was performed, and to the ischemia, methylprednisolone and lamotrigine groups, where the infrarenal aorta was clamped for thirty minutes to induce spinal cord ischemia-reperfusion injury. Tissue samples belonging to spinal cords were harvested from sacrificed animals twenty-four hours after reperfusion. Tumor necrosis factor-alpha levels, interleukin-1 beta levels, nitric oxide levels, superoxide dismutase activity, catalase activity, glutathione peroxidase activity, malondialdehyde levels and caspase-3 activity were studied. Light and electron microscopic evaluations were also performed to reveal the pathological alterations. Basso, Beattie, and Bresnahan locomotor scale and the inclined-plane test was used to evaluate neurofunctional status at the beginning of the study and just before the animals were sacrificed.

RESULTS

Lamotrigine treatment provided significant improvement in the neurofunctional status by preventing the increase in cytokine expression, increased lipid peroxidation and oxidative stress, depletion of antioxidant enzymes activity and increased apoptosis, all of which contributing to spinal cord damage through different paths after ischemia reperfusion injury. Furthermore, lamotrigine treatment has shown improved results concerning the histopathological and ultrastructural scores and the functional tests.

CONCLUSION

These results proposed that lamotrigine may be a useful therapeutic agent to prevent the neuronal damage developing after spinal cord ischemia-reperfusion injury.

Subchronic exposure to concentrated ambient PM2.5 perturbs gut and lung microbiota as well as metabolic profiles in mice

Exposure to ambient fine particular matter (PM2.5) are linked to an increased risk of metabolic disorders, leading to enhanced rate of many diseases, such as inflammatory bowel disease (IBD), cardiovascular diseases, and pulmonary diseases; nevertheless, the underlying mechanisms remain poorly understood. In this study, BALB/c mice were exposed to filtered air (FA) or concentrated ambient PM2.5 (CPM) for 2 months using a versatile aerosol concentration enrichment system(VACES). We found subchronic CPM exposure caused significant lung and intestinal damage, as well as systemic inflammatory reactions. In addition, serum and BALFs (bronchoalveolar lavage fluids) metabolites involved in many metabolic pathways in the CPM exposed mice were markedly disrupted upon PM2.5 exposure. Five metabolites (glutamate, glutamine, formate, pyruvate and lactate) with excellent discriminatory power (AUC = 1, p < 0.001) were identified to predict PM2.5 exposure related toxicities. Furthermore, subchronic exposure to CPM not only significantly decreased the richness and composition of the gut microbiota, but also the lung microbiota. Strong associations were found between several gut and lung bacterial flora changes and systemic metabolic abnormalities. Our study showed exposure to ambient PM2.5 not only caused dysbiosis in the gut and lung, but also significant systemic and local metabolic alterations. Alterations in gut and lung microbiota were strongly correlated with metabolic abnormalities. Our study suggests potential roles of gut and lung microbiota in PM2.5 caused metabolic disorders.

Glutaminase C overexpression in the brain induces learning deficits, synaptic dysfunctions, and neuroinflammation in mice

Glutaminolysis, a metabolic process that converts glutamine to glutamate, is particularly important for the central nervous system since glutamate is the major transmitter of excitatory synapses. Glutaminase is the mitochondrial enzyme that catalyzes the first step of glutaminolysis. Two genes encode at least four isoforms of glutaminase in humans. Gls1 gene encodes isoforms kidney-type glutaminase (KGA) and glutaminase C (GAC) through alternative splicing, whereas Gls2 gene encodes liver-type glutaminase isoforms. KGA and GAC have been associated with several neurological diseases. However, it remains unclear whether changes in their expressions can directly cause brain abnormalities. Using a transgenic approach, we generated mice that overexpressed GAC in the brain. The resulting transgenic mice had severe impairments in spatial and fear learning compared with littermate controls. The learning deficits were consistent with diminished hippocampal long-term potentiation in the hippocampal slices of the GAC transgenic mice. Furthermore, we found increases in astrocyte and microglia markers, inflammatory factors, and a decrease in synapse marker synaptophysin, suggesting neuroinflammation and synaptic changes in the GAC transgenic mouse brains. In conclusion, these findings provide the first evidence that GAC overexpression in the brain has deleterious effects on learning and synaptic integrity in vivo.

Arterial Blood Supply to the Spinal Cord in Animal Models of Spinal Cord Injury. A Review

Animal models are used to examine the results of experimental spinal cord injury. Alterations in spinal cord blood supply caused by complex spinal cord injuries contribute significantly to the diversity and severity of the spinal cord damage, particularly ischemic changes. However, the literature has not completely clarified our knowledge of anatomy of the complex three-dimensional arterial system of the spinal cord in experimental animals, which can impede the translation of experimental results to human clinical applications. As the literary sources dealing with the spinal cord arterial blood supply in experimental animals are limited and scattered, the authors performed a review of the anatomy of the arterial blood supply to the spinal cord in several experimental animals, including pigs, dogs, cats, rabbits, guinea pigs, rats, and mice and created a coherent format discussing the interspecies differences. This provides researchers with a valuable tool for the selection of the most suitable animal model for their experiments in the study of spinal cord ischemia and provides clinicians with a basis for the appropriate translation of research work to their clinical applications. Anat Rec, 300:2091-2106, 2017. © 2017 Wiley Periodicals, Inc.

Enhancing excitatory activity of somatosensory cortex alleviates neuropathic pain through regulating homeostatic plasticity

Central sensitization and network hyperexcitability of the nociceptive system is a basic mechanism of neuropathic pain. We hypothesize that development of cortical hyperexcitability underlying neuropathic pain may involve homeostatic plasticity in response to lesion-induced somatosensory deprivation and activity loss, and can be controlled by enhancing cortical activity. In a mouse model of neuropathic pain, in vivo two-photon imaging and patch clamp recording showed initial loss and subsequent recovery and enhancement of spontaneous firings of somatosensory cortical pyramidal neurons. Unilateral optogenetic stimulation of cortical pyramidal neurons both prevented and reduced pain-like behavior as detected by bilateral mechanical hypersensitivity of hindlimbs, but corpus callosotomy eliminated the analgesic effect that was ipsilateral, but not contralateral, to optogenetic stimulation, suggesting involvement of inter-hemispheric excitatory drive in this effect. Enhancing activity by focally blocking cortical GABAergic inhibition had a similar relieving effect on the pain-like behavior. Patch clamp recordings from layer V pyramidal neurons showed that optogenetic stimulation normalized cortical hyperexcitability through changing neuronal membrane properties and reducing frequency of excitatory postsynaptic events. We conclude that development of neuropathic pain involves abnormal homeostatic activity regulation of somatosensory cortex, and that enhancing cortical excitatory activity may be a novel strategy for preventing and controlling neuropathic pain.

Daidzein ameliorates spinal cord ischemia/reperfusion injury-induced neurological function deficits in Sprague-Dawley rats through PI3K/Akt signaling pathway

Daidzein (DZ) has a broad spectrum of biological activities, including antioxidant, anti-inflammatory and anticancer as well as cardio- and hepatoprotective properties. The present study was designed to elucidate the in-depth mechanism underlying the neuroprotective efficacy of DZ against spinal cord ischemic/reperfusion injury (SCII) in a rat model by comparison with the standard neuroprotective agent methylprednisolone (MP). A total of 48 rats were divided into four groups of twelve rats in each (n=12). In sham-operated group (Control) group, rats received only saline (Fogarty catheter was inserted without balloon inflation), whereas rats in the SCII induction group (SCII) were subjected to SCII insult by insertion of a Fogarty balloon catheter, which was inflated in the descending thoracic aorta to cause an occlusion. A proportion of rats was treated with DZ (20 mg/kg; DZ+SCII group) or MP (50 mg/kg; MP+SCII group) for seven days prior to and after SCII. The locomotor function (neurological activity) and antioxidant levels (superoxide dismutase and catalase) levels were significantly improved upon treatment with DZ and MP in comparison with those in the SCII group. A concomitant decline in edema, inflammatory markers (myeloperoxidase, tumor necrosis factor-α and nuclear factor κB p65), the apoptotic marker caspase-3 and the number of cells with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling was also observed in the DZ and MP groups. The protein levels of phosphoinositide-3 kinase (PI3K), the phosphorylated Akt/Akt ratio and B-cell lymphoma 2 (Bcl-2) were substantially downregulated, while Bcl-2-associated X protein levels were upregulated SCII insult group, which was inhibited by treatment with DZ. To conclude, pre-treatment with DZ significantly improved the neurological function by upregulating PI3K/Akt signaling and thereby considerably attenuating the inflammatory response and apoptosis, thus maintaining the neuronal count in an SCII-induced rat model.

Serial deletion reveals structural basis and stability for the core enzyme activity of human glutaminase 1 isoforms: relevance to excitotoxic neurodegeneration

Background

Glutaminase 1 is a phosphate-activated metabolic enzyme that catalyzes the first step of glutaminolysis, which converts glutamine into glutamate. Glutamate is the major neurotransmitter of excitatory synapses, executing important physiological functions in the central nervous system. There are two isoforms of glutaminase 1, KGA and GAC, both of which are generated through alternative splicing from the same gene. KGA and GAC both transcribe 1–14 exons in the N-terminal, but each has its unique C-terminal in the coding sequence. We have previously identified that KGA and GAC are differentially regulated during inflammatory stimulation and HIV infection. Furthermore, glutaminase 1 has been linked to brain diseases such as amyotrophic lateral sclerosis, Alzheimer’s disease, and hepatic encephalopathy. Core enzyme structure of KGA and GAC has been published recently. However, how other coding sequences affect their functional enzyme activity remains unclear.

Methods

We cloned and performed serial deletions of human full-length KGA and GAC from the N-terminal and the C-terminal at an interval of approximately 100 amino acids (AAs). Prokaryotic expressions of the mutant glutaminase 1 protein and a glutaminase enzyme activity assay were used to determine if KGA and GAC have similar efficiency and efficacy to convert glutamine into glutamate.

Results

When 110 AAs or 218 AAs were deleted from the N-terminal or when the unique portions of KGA and GAC that are beyond the 550 AA were deleted from the C-terminal, KGA and GAC retained enzyme activity comparable to the full length proteins. In contrast, deletion of 310 AAs or more from N-terminal or deletion of 450 AAs or more from C-terminal resulted in complete loss of enzyme activity for KGA/GAC. Consistently, when both N- and C-terminal of the KGA and GAC were removed, creating a truncated protein that expressed the central 219 AA - 550 AA, the protein retained enzyme activity. Furthermore, expression of the core 219 AA - 550 AA coding sequence in cells increased extracellular glutamate concentrations to levels comparable to those of full-length KGA and GAC expressions, suggesting that the core enzyme activity of the protein lies within the central 219 AA - 550 AA. Full-length KGA and GAC retained enzyme activities when kept at 4 °C. In contrast, 219 AA - 550 AA truncated protein lost glutaminase activities more readily compared with full-length KGA and GAC, suggesting that the N-terminal and C-terminal coding regions are required for the stability KGA and GAC.

Conclusions

Glutaminase isoforms KGA and GAC have similar efficacy to catalyze the conversion of glutamine to glutamate. The core enzyme activity of glutaminase 1 protein is within the central 219 AA - 550 AA. The N-terminal and C-terminal coding regions of KGA and GAC help maintain the long-term activities of the enzymes.

A study of methylprednisolone neuroprotection against acute injury to the rat spinal cord in vitro

Methylprednisolone sodium succinate (MPSS) has been proposed as a first-line treatment for acute spinal cord injury (SCI). Its clinical use remains, however, controversial because of the modest benefits and numerous side-effects. We investigated if MPSS could protect spinal neurons and glia using an in vitro model of the rat spinal cord that enables recording reflexes, fictive locomotion and morphological analysis of damage. With this model, a differential lesion affecting mainly either neurons or glia can be produced via kainate-evoked excitotoxicity or application of a pathological medium (lacking O2 and glucose), respectively. MPSS (6-10 μM) applied for 24 h after 1-h pathological medium protected astrocytes and oligodendrocytes especially in the ventrolateral white matter. This effect was accompanied by the return of slow, alternating oscillations (elicited by NMDA and 5-hydroxytryptamine (5-HT)) reminiscent of a sluggish fictive locomotor pattern. MPSS was, however, unable to reverse even a moderate neuronal loss and the concomitant suppression of fictive locomotion evoked by kainate (0.1 mM; 1 h). These results suggest that MPSS could, at least in part, contrast damage to spinal glia induced by a dysmetabolic state (associated to oxygen and glucose deprivation) and facilitate reactivation of spinal networks. Conversely, when even a minority of neurons was damaged by excitotoxicity, MPSS did not protect them nor did it restore network function in the current experimental model.

Assessment of white matter loss using bond-selective photoacoustic imaging in a rat model of contusive spinal cord injury

White matter (WM) loss is a critical event after spinal cord injury (SCI). Conventionally, such loss has been measured with histological and histochemical approaches, although the procedures are complex and may cause artifact. Recently, coherent Raman microscopy has been proven to be an emerging technology to study de- and remyelination of the injured spinal cord; however, limited penetration depth and small imaging field prevent it from comprehensive assessments of large areas of damaged tissues. Here, we report the use of bond-selective photoacoustic (PA) imaging with 1730-nm excitation, where the first overtone vibration of CH2 bond is located, to assess WM loss after a contusive SCI in adult rats. By employing the first overtone vibration of CH2 bond as the contrast, the mapping of the WM in an intact spinal cord was achieved in a label-free three-dimensional manner, and the physiological change of the spinal cord before and after injury was observed. Moreover, the recovery of the spinal cord from contusive injury with the treatment of a neuroprotective nanomedicine ferulic-acid-conjugated glycol chitosan (FA-GC) was also observed. Our study suggests that bond-selective PA imaging is a valuable tool to assess the progression of WM pathology after SCI as well as neuroprotective therapeutics in a label-free manner.

Changes in gap junction expression and function following ischemic injury of spinal cord white matter

Gap junctions are widely present in spinal cord white matter; however, their role in modulating the dynamics of axonal dysfunction remains largely unexplored. We hypothesized that inhibition of gap junctions reduces the loss of axonal function during oxygen and glucose deprivation (OGD). The functional role of gap junctions was assessed by electrophysiological recordings of compound action potentials (CAPs) in Wistar rat spinal cord slices with the sucrose gap technique. The in vitro slices were subjected to 30-min OGD. Gap junction connexin (Cx) mRNA expression was determined by qPCR and normalized to β-actin. A 30-min OGD resulted in reduction of CAPs to 14.8 ± 4.6% of their pre-OGD amplitude (n = 5). In the presence of gap junction blockers carbenoxolone (Cbx; 100 μM) and 1-octanol (Oct; 300 μM), the CAP reduction in OGD was to only 35.7 ± 5.7% of pre-OGD amplitude in Cbx (n = 9) and to 37.4 ± 8.9% of pre-OGD amplitude in Oct (n = 10). Both drugs also noticeably prolonged the half-decline time of CAP amplitudes in OGD from 6.0 min in no-drug conditions to 9.6 min in the presence of Cbx and to 7.7 min in the presence of Oct, suggesting that blocking gap junctions reduces conduction loss during OGD. With application of Cbx and Oct in the setting of OGD, expression of Cx30 and Cx43 mRNA was downregulated. Our data provide new insights into the role of gap junctions in white matter ischemia and reveal the necessity of a cautious approach in determining detrimental or beneficial effects of gap junction blockade in white matter ischemia.

Paraplegia prevention by oral pretreatment with memantine in a rabbit model

OBJECTIVE

To evaluate the role of memantine (N-methyl-d-aspartate receptor antagonist) pretreatment for the prevention of spinal cord ischemia after infrarenal aortic clamping in a rabbit model.

METHODS

Thirty New Zealand White rabbits were divided into 5 different groups of 6 rabbits. Groups 60-7 and 60-5 received oral memantine 60 mg once a day for 7 and 5 days, respectively, and groups 30-5 and 30-3 received oral memantine 30 mg once a day for 5 and 3 days, respectively, all before surgery. Group C (control) received normal feeds without memantine. A paraplegic model was created by clamping both the aorta and the inferior vena cava infrarenally and just proximal to their bifurcations for 45 minutes. The modified Tarlov score, motor evoked potential (MEP), serum memantine concentration, and histopathology of the spinal cord were evaluated.

RESULTS

The mean modified Tarlov scores were 4.2±1.3, 4.3±1.0, 4.2±1.3, 4.3±1.2, and 0.8±1.6 in groups 60-7, 60-5, 30-5, 30-3, and C, respectively at 6, 24, 48, and 72 hours (P<.009 for individual groups vs control). Percentage amplitude loss of MEP by the end of surgery was 29.5%±46.3%, 11.9%±28.0%, 30.0%±46.8%, 16.7%±40.8%, and 81.8%±40.3% for the 5 groups, respectively (P=.049). After declamping, MEP reappeared in 83%, 100%, 83%, 83%, and 33% of cases in the 5 groups, respectively (P=.073). The serum memantine level was similar in the 4 memantine groups. Spinal cords were normal in most of the rabbits in groups 60-7, 60-5, 30-5, and 30-3, but severely ischemic in most of the rabbits in group C (P=.041).

CONCLUSIONS

Oral memantine pretreatment is protective against spinal cord ischemia, and can be an additional strategy for the prevention of paraplegia during thoracoabdominal aortic surgeries.

Oligodendrocyte pathophysiology and treatment strategies in cerebral ischemia

Oligodendrocytes (OLs), the myelin-forming cells of the central nervous system, form a functional unit with axons and play a crucial role in axonal integrity. An episode of hypoxia-ischemia causes rapid and severe damage to these particularly vulnerable cells via multiple pathways such as overactivation of glutamate and ATP receptors, oxidative stress, and disruption of mitochondrial function. The cardinal effect of OL pathology is demyelination and dysmyelination, and this has profound effects on axonal function, transport, structure, metabolism, and survival. The OL is a primary target of ischemia in adult-onset stroke and especially in periventricular leukomalacia and should be considered as a primary therapeutic target in these conditions. More emphasis is needed on therapeutic strategies that target OLs, myelin, and their receptors, as these have the potential to significantly attenuate white matter injury and to establish functional recovery of white matter after stroke. In this review, we will summarize recent progress on the role of OLs in white matter ischemic injury and the current and emerging principles that form the basis for protective strategies against OL death.

IL-1β and TNF-α induce neurotoxicity through glutamate production: a potential role for neuronal glutaminase

Glutaminase 1 is the main enzyme responsible for glutamate production in mammalian cells. The roles of macrophage and microglia glutaminases in brain injury, infection, and inflammation are well documented. However, little is known about the regulation of neuronal glutaminase, despite neurons being a predominant cell type of glutaminase expression. Using primary rat and human neuronal cultures, we confirmed that interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), two pro-inflammatory cytokines that are typically elevated in neurodegenerative disease states, induced neuronal death and apoptosis in vitro. Furthermore, both intracellular and extracellular glutamate levels were significantly elevated following IL-1β and/or TNF-α treatment. Pre-treatment with N-Methyl-D-aspartate (NMDA) receptor antagonist MK-801 blocked cytokine-induced glutamate production and alleviated the neurotoxicity, indicating that IL-1β and/or TNF-α induce neurotoxicity through glutamate. To determine the potential source of excess glutamate production in the culture during inflammation, we investigated the neuronal glutaminase and found that treatment with IL-1β or TNF-α significantly upregulated the kidney-type glutaminase (KGA), a glutaminase 1 isoform, in primary human neurons. The up-regulation of neuronal glutaminase was also demonstrated in situ in a murine model of HIV-1 encephalitis. In addition, IL-1β or TNF-α treatment increased the levels of KGA in cytosol and TNF-α specifically increased KGA levels in the extracellular fluid, away from its main residence in mitochondria. Together, these findings support neuronal glutaminase as a potential component of neurotoxicity during inflammation and that modulation of glutaminase may provide therapeutic avenues for neurodegenerative diseases.

Topiramate treatment is neuroprotective and reduces oligodendrocyte loss after cervical spinal cord injury

Excess glutamate release and associated neurotoxicity contributes to cell death after spinal cord injury (SCI). Indeed, delayed administration of glutamate receptor antagonists after SCI in rodents improves tissue sparing and functional recovery. Despite their therapeutic potential, most glutamate receptor antagonists have detrimental side effects and have largely failed clinical trials. Topiramate is an AMPA-specific, glutamate receptor antagonists that is FDA-approved to treat CNS disorders. In the current study we tested whether topiramate treatment is neuroprotective after cervical contusion injury in rats. We report that topiramate, delivered 15-minutes after SCI, increases tissue sparing and preserves oligodendrocytes and neurons when compared to vehicle treatment. In addition, topiramate is more effective than the AMPA-receptor antagonist, NBQX. To the best of our knowledge, this is the first report documenting a neuroprotective effect of topiramate treatment after spinal cord injury.

Effects of minocycline on hind-limb motor function and gray and white matter injury after spinal cord ischemia in rats

STUDY DESIGN

A prospective, randomized laboratory investigation.

OBJECTIVE

To investigate whether administration of minocycline attenuates hind-limb motor dysfunction and gray and white matter injury after spinal cord ischemia.

SUMMARY OF BACKGROUND DATA

Minocycline, a semisynthetic tetracycline antibiotic, has been shown to have neuroprotective effects in models of focal and global cerebral ischemia. However, there have been no data available regarding the effects of minocycline in a model of spinal cord ischemia.

METHODS

Thirty-six rats were randomly allocated to one of three groups; control (C) group (n = 11), minocycline (M) group (n = 13), or sham group (n = 12). Minocycline or saline was intraperitoneally administered for 3 days beginning at 12 hours before 10 minutes of spinal cord ischemia or sham operation. Spinal cord ischemia was induced with intraaortic balloon catheter and blood withdrawal. Seventy-two hours after reperfusion, hind-limb motor functions were assessed using Basso, Beattie, Bresnahan (BBB) Scale (0 = paraplegia, 21 = normal). For histologic assessments, the gray and white matter injury was evaluated using the number of normal neurons and the extents of vacuolations in the white matter, respectively. Activated microglia was also evaluated using Iba-1 immunohistochemistry.

RESULTS

BBB scores and the numbers of normal neurons in the M group were significantly higher than those in the C group. The percentage areas of vacuolations in the white matter and the number of Iba-1 positive cells were significantly lower in the M group compared with those in the C group.

CONCLUSION

The results indicated that minocycline administration improved hind-limb motor function and attenuated gray and white matter injury and microglial activation after spinal cord ischemia in rats.

Reduction of spinal cord ischemia/reperfusion injury with simvastatin in rats

BACKGROUND

Surgery of the thoracic or thoracoabdominal aorta may cause spinal cord ischemia and subsequent paraplegia. However, conventional strategies for preventing paraplegia due to spinal cord ischemia provide insufficient protection and cause additional side effects. We hypothesized that simvastatin, a drug recently shown to be neuroprotective against brain ischemia/reperfusion, would be neuroprotective in a rat spinal cord ischemia/reperfusion model.

METHODS

Rats were randomly assigned to simvastatin, vehicle, or sham-surgery (sham) groups (n = 6 per group). Simvastatin (10 mg/kg) or vehicle was administered subcutaneously once daily for 7 days before aortic balloon occlusion, and once at 24 hours after reperfusion. Spinal cord ischemia was induced by balloon inflation of a 2F Fogarty catheter in the thoracic aorta, and the proximal mean arterial blood pressure was maintained at 40 mm Hg for 12 minutes. The sham group received the same operation without inflation of the balloon. Ischemic injury was assessed by hindlimb motor function using the Motor Deficit Index score at 6 to 48 hours after ischemic reperfusion, and histological assessment of the spinal cord was performed 48 hours after reperfusion.

RESULTS

The Motor Deficit Index scores at 24 and 48 hours after reperfusion were significantly improved in the simvastatin group compared with the vehicle group (P = 0.021 and P = 0.023, respectively). Furthermore, there were significantly more normal motor neurons in the simvastatin group than in the vehicle group (P = 0.037). The percentage area of white matter vacuolation was significantly smaller in the simvastatin group than in the vehicle group (P = 0.030).

CONCLUSIONS

Simvastatin treatment can attenuate hindlimb motor dysfunction and histopathological changes in spinal cord ischemia/reperfusion injury in rats.

Delayed administration of dapsone protects from tissue damage and improves recovery after spinal cord injury

After spinal cord injury (SCI), a complex cascade of pathophysiological processes increases the primary damage. The inflammatory response plays a key role in this pathology. Recent evidence suggests that myeloperoxidase (MPO), an enzyme produced and released by neutrophils, is of special importance in spreading tissue damage. Dapsone (4,4'-diaminodiphenylsulfone) is an irreversible inhibitor of MPO. Recently, we demonstrated, in a model of brain ischemia/reperfusion, that dapsone has antioxidant, antiinflammatory, and antiapoptotic effects. The effects of dapsone on MPO activity, lipid peroxidation (LP) processes, motor function recovery, and the amount of spared tissue were evaluated in a rat model of SCI. MPO activity had increased 24.5-fold 24 hr after SCI vs. the sham group, and it had diminished by 38% and 19% in the groups treated with dapsone at 3 and 5 hr after SCI, respectively. SCI increased LP by 45%, and this increase was blocked by dapsone. In rats treated with dapsone, a significant motor function recovery (Basso-Beattie-Bresnahan score, BBB) was observed beginning during the first week of evaluation and continuing until the end of the study. Spontaneous recovery 8 weeks after SCI was 9.2 ± 1.12, whereas, in the dapsone-treated groups, it reached 13.6 ± 1.04 and 12.9 ± 1.17. Spared tissue increased by 42% and 33% in the dapsone-treated groups (3 and 5 hr after SCI, respectively) vs. SCI without treatment. Dapsone significantly prevented mortality. The results show that inhibition of MPO by dapsone significantly protected the spinal cord from tissue damage and enhanced motor recovery after SCI.

Glucocorticoid protection of oligodendrocytes against excitotoxin involving hypoxia-inducible factor-1alpha in a cell-type-specific manner

Glucocorticoids are commonly used in treating diseases with white matter lesions, including demyelinating diseases and spinal cord injury (SCI). However, glucocorticoids are ineffective in gray matter injuries, such as head injury and stroke. The differential glucocorticoid effects in white and gray matter injuries are unclear. We report here a novel mechanism of methylprednisolone (MP), a synthetic glucocorticoid widely used for treating multiple sclerosis and SCI, in protecting oligodendrocytes (OLGs) against AMPA-induced excitotoxicity, which has been implicated in the white matter injuries and diseases. The cytoprotective action of MP in OLGs is causally related to its upregulation of a neuroprotective cytokine erythropoietin (Epo). MP transactivation of Epo expression involves dual transcription factors: glucocorticoid receptor (GR) and hypoxia-inducible factor-1alpha (HIF-1alpha). Coimmunoprecipitation, chromatin immunoprecipitation analysis, yeast two-hybrid analysis, and structure modeling of three-dimensional protein-protein interactions confirm that MP induces interaction between GR DNA binding domain and HIF-1alpha PAS domain, with subsequent recruitment of HIF-1beta to transactivate Epo expression in OLGs. In contrast, MP activates GR but does not induce GR-HIF-1alpha interaction, HIF-1alpha binding to Epo enhancer/promoter, or Epo expression in cultured cortical neurons. The OLG-specific GR-HIF-1alpha transactivation of Epo provides novel insights into the development of more effective therapies for diseases affecting the white matter.

The AMPA receptor as a therapeutic target: current perspectives and emerging possibilities

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is a subtype of the ionotropic glutamate receptors that plays a prominent role in neurotransmission and is widespread throughout the CNS. Because of this, its malfunction can result in a multitude of nervous system diseases. This review looks at compounds that are able to modulate AMPAR function by binding to one of several sites on the receptor that either downregulate its function (competitive, noncompetitive and uncompetitive antagonists) or upregulate its function (positive modulators). It will also give an account of the various diseases that have implicated AMPAR dysfunction and how specific types of AMPAR modulator may be beneficial in their treatment. The AMPAR remains an unexploited but important therapeutic target.

Suppressive effects of intrathecal granulocyte colony-stimulating factor on excessive release of excitatory amino acids in the spinal cerebrospinal fluid of rats with cord ischemia: role of glutamate transporters

Recently, the hematopoietic factor, granulocyte colony-stimulating factor (G-CSF), has been shown to exhibit neuroprotective effects in CNS injuries. Our previous study demonstrated that intrathecal (i.t.) G-CSF significantly improved neurological defects in spinal cord ischemic rats. Considerable evidence indicates that the release of excessive amounts of excitatory amino acids (EAAs) plays a critical role in neuron injury induced by ischemic insult. In the present study, we used a spinal cord ischemia-microdialysis model to examine whether i.t. G-CSF exerted antiexcitotoxicity effects in a rat model of spinal cord ischemia. I.t. catheters and a microdialysis probe were implanted in male Wistar rats. The results revealed that spinal cord ischemia-induced neurological defects were accompanied by a significant increase in the concentration of EAAs (aspartate and glutamate) in the spinal dialysates from 30 min to 2 days after reperfusion. I.t administration of G-CSF immediately after the performance of surgery designed to induce ischemia led to a significant reduction in ischemia-induced increases in the levels of spinal EAAs. Moreover, i.t. G-CSF also brought about a significant reduction in the elevation of spinal EAA concentrations induced by exogenous i.t. administration of glutamate (10 microl of 500 mM). I.t. G-CSF attenuated spinal cord ischemia-induced downregulation of expression of three glutamate transporters (GTs), glial transporter Glu-Asp transporter (GLAST), Glu transporter-1 (GLT-1), and excitatory amino acid carrier 1 (EAAC1) protein 48 h after spinal cord ischemic surgery. Immunohistofluorescent staining showed that i.t. G-CSF significantly upregulated expression of the three GTs in the gray matter of the lumbar spinal cord from 3 to 24 h after injection. We propose that i.t. G-CSF possesses an ability to reduce the extent of spinal cord ischemia-induced excitotoxicity by inducing the expression of glutamate transporters.

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.

Hyperbaric oxygen preconditioning attenuates early apoptosis after spinal cord ischemia in rats

This study tested the hypothesis that spinal cord ischemic tolerance induced by hyperbaric oxygen preconditioning (HBO-PC) is mediated by inhibition of early apoptosis. Male Sprague-Dawley rats were preconditioned with consecutive 4 cycles of 1-h HBO exposures (2.5 atmospheres absolute [ATA], 100% O(2)) at a 12-h interval. At 24 h after the last HBO pretreatment, rats underwent 9 min of spinal cord ischemia induced by occlusion of the descending thoracic aorta in combination with systemic hypotension (40 mmHg). Spinal cord ischemia produced marked neuronal death and neurological dysfunction in animals. HBO-PC enhanced activities of Mn-superoxide dismutase (Mn-SOD) and catalase, as well as the expression of Bcl-2 in the mitochondria in the normal spinal cord at 24 h after the last pretreatment (before spinal cord ischemia), and retained higher levels throughout the early reperfusion in the ischemic spinal cord. In parallel, superoxide and hydrogen peroxide levels in mitochondria were decreased, cytochrome c release into the cytosol was reduced at 1 h after reperfusion, and activation of caspase-3 and -9 was subsequently attenuated. HBO-PC improved neurobehavioral scores and reduced neuronal apoptosis in the anterior, intermediate, and dorsal gray matter of lumbar segment at 24 h after spinal cord ischemia. HBO-PC increased nitric oxide (NO) production. L-nitroarginine-methyl-ester (L-NAME; 10 mg/kg), a nonselective NO synthase (NOS) inhibitor, applied before each HBO-PC protocol abolished these beneficial effects of HBO-PC. We conclude that HBO-PC reduced spinal cord ischemia-reperfusion injury by increasing Mn-SOD, catalase, and Bcl-2, and by suppressing mitochondrial apoptosis pathway. NO may be involved in this neuroprotection.

Glutamate receptors on myelinated spinal cord axons: I. GluR6 kainate receptors

OBJECTIVE

The deleterious effects of glutamate excitotoxicity are well described for central nervous system gray matter. Although overactivation of glutamate receptors also contributes to axonal injury, the mechanisms are poorly understood. Our goal was to elucidate the mechanisms of kainate receptor-dependent axonal Ca(2+) deregulation.

METHODS

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

RESULTS

Activation of glutamate receptor 6 (GluR6) kainate receptors promoted a substantial increase in axonal [Ca(2+)]. This Ca(2+) accumulation was due not only to influx from the extracellular space, but a significant component originated from ryanodine-dependent intracellular stores, which, in turn, depended on activation of L-type Ca(2+) channels: ryanodine, nimodipine, or nifedipine blocked the agonist-induced Ca(2+) increase. Also, GluR6 stimulation induced intraaxonal production of nitric oxide (NO), which greatly enhanced the Ca(2+) response: quenching of NO with intraaxonal (but not extracellular) scavengers, or inhibition of neuronal NO synthase with intraaxonal Nomega-nitro-L-arginine methyl ester, blocked the Ca(2+) increase. Loading axons with a peptide that mimics the C-terminal PDZ binding sequence of GluR6, thus interfering with the coupling of GluR6 to downstream effectors, greatly reduced the agonist-induced axonal Ca(2+) increase. Immunohistochemistry showed GluR6/7 clusters on the axolemma colocalized with neuronal NO synthase and Ca(v)1.2.

INTERPRETATION

Myelinated spinal axons express functional GluR6-containing kainate receptors, forming part of novel signaling complexes reminiscent of postsynaptic membranes of glutamatergic synapses. The ability of such axonal "nanocomplexes" to release toxic amounts of Ca(2+) may represent a key mechanism of axonal degeneration in disorders such as multiple sclerosis where abnormal accumulation of glutamate and NO are known to occur.

Extracts of Liriopsis tuber protect AMPA induced brain damage and improve memory with the activation of insulin receptor and ERK I/II

The brain insulin receptor and ERK I/II are known to play an important role in memory formation and neuroprotection. A series of experiments was designed to explore if Liriopsis tuber (LT) extracts could exhibit neuroprotection and memory enhancing actions. LT was extracted with 70% methanol and subsequently fractionated into chloroform (fraction C), chloroform/methanol-(3:1) (fraction CM), methanol-soluble (fraction M) and methanol-insoluble, water-soluble fractions (fraction A). The LT fractions (T, C, M, A) significantly inhibited the cortical depolarization induced by AMPA in cortical slices of rats. In addition, these fractions were also effective in promoting memory in the passive avoidance test in mice. To gain insight into the mechanism of memory enhancing effects by Liriopsis tuber extracts, the activities of hippocampal insulin receptors and ERK I/II were tested in rats. Extract of LT (T) dramatically stimulated tyrosine phosphorylation of the insulin receptor, while fraction C of LT also significantly stimulated the same. In addition, ERK I/II were stimulated and cholinesterase activities were inhibited by fractions T, C, M and A in the rat hippocampus. These results suggest that Liriopsis tuber extracts may exert neuroprotection and memory enhancing effects via activation of the insulin receptor and ERK I/II as well as inhibiting cholinesterase.

Effects of delta-opioid agonist SNC80 on white matter injury following spinal cord ischemia in normothermic and mildly hypothermic rats

PURPOSE

Although the delta-opioid agonist SNC80 has been shown to attenuate hind-limb motor function and gray matter injury in normothermic rats subjected to spinal cord ischemia (SCI), its effects on white matter injury remain undetermined. In the present study, we investigated whether SNC80 could attenuate white matter injury in normothermic and mildly hypothermic rats.

METHODS

Forty rats were randomly allocated to one of following five groups: vehicle or SNC80 with 10 min of SCI at 38 degrees C (V-38-10m or SNC-38-10m, respectively), vehicle or SNC80 with 22 min of SCI at 35 degrees C (V-35-22m or SNC-35-22m, respectively), or sham. SNC80 or vehicle was intrathecally administered 15 min before SCI. Forty-eight hours after reperfusion, the white matter injury was evaluated by the extent of vacuolation.

RESULTS

The percent area of vacuolation in the ventral white matter was significantly lower in the SNC-38-10m and SNC-35-22m groups compared with that in the V-38-10m and V-35-22m groups, respectively (P < 0.05).

CONCLUSION

The results indicate that intrathecal treatment with the delta-opioid agonist SNC80 can attenuate the ventral white matter injury following SCI in rats under normothermic and mildly hypothermic conditions.

Diffuse axonal damage, myelin impairment, astrocytosis and inflammatory response following microinjections of NMDA into the rat striatum

White matter damage and inflammatory response are important secondary outcomes after acute neural disorders. Nevertheless, a few studies addressed the temporal outcomes of these pathological events using non-traumatic models of acute brain injury. In the present study, we describe acute inflammatory response and white matter neuropathology between 1 and 7 days after acute excitotoxic striatal damage. Twenty micrometer sections were stained by hematoxylin and eosin technique for gross histopathological analysis and immunolabed for neutrophils (anti-mbs-1), activated macrophages/microglia (anti-ed1), astrocytes (anti-gfap), damaged axons (anti-betaapp) and myelin basic protein (MBP). Recruitment peak of neutrophils and macrophages occurred at 1 and 7 days post-nmda injection, respectively. Diffuse damaged axons (beta-app + end-bulbs) were apparent at 7 days, concomitant with progressive myelin impairment and astrocytosis. Further studies using electron microscopy and blockers of inflammatory response and glutamatergic receptors should be performed to confirm and address the mechanisms of white matter damage following an excitotoxic lesion.

Differential patterns of inflammatory response, axonal damage and myelin impairment following excitotoxic or ischemic damage to the trigeminal spinal nucleus of adult rats

Inflammatory response, axonal damage and demyelination are important components of the pathophysiology of acute neurodegenerative diseases. We have investigated the outcome of these pathological events following an excitotoxic or an ischemic damage to the spinal nucleus of adult rats at 1 and 7 days postinjury. Microinjections of 80 nmol of NMDA or 40 pmol of endothelin-1 into the rat spinal nucleus induced differential histopathological events. NMDA injection induced intense tissue loss in the gray matter (GM) without significant tissue loss in the white matter (WM). There was a mild inflammatory response, with recruitment of a few neutrophils and macrophages. Axonal damage was present in the GM following NMDA injection, with negligible axonal damage in the WM. Myelin impairment was apparent at 7 days. Microinjections of endothelin-1 into the same region induced lesser tissue loss than NMDA injections, concomitant with an intense inflammatory response characterized by recruitment of macrophages, but not of neutrophils. There were more axonal damage and early myelin impairment after endothelin-1 injection. These results were confirmed by quantitative analysis. Microcysts were present in the WM of the trigeminothalamic tract at 7 days following injection of endothelin-1. These results show that an ischemic damage to the spinal nucleus affects both GM and WM with more bystander inflammation, axonal damage and myelin impairment, while excitotoxic damage induces effects more restricted to the GM. These pathological events may occur following acute damage to the human brain stem and can be an important contributing factor to the underlying functional deficits.

AMPA-mediated excitotoxicity in oligodendrocytes: role for Na(+)-K(+)-Cl(-) co-transport and reversal of Na(+)/Ca(2+) exchanger

We investigated the role of Na(+)-K(+)-Cl(-) co-transporter isoform 1 (NKCC1) and reversal of Na(+)/Ca(2+) exchanger (NCX(rev)) in glutamate-mediated excitotoxicity in oligodendrocytes obtained from rat spinal cords (postnatal day 6-8). An immunocytochemical characterization showed that these cultures express NKCC1 and Na(+)/Ca(2+) exchanger isoforms 1, 2, and 3 (NCX1, NCX2, NCX3). Exposing the cultures to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) plus cyclothiazide (CTZ) led to a transient rise in intracellular (), which was followed by a sustained overload, NKCC1 phosphorylation, and a NKCC1-mediated Na(+) influx. In the presence of a specific AMPA receptor inhibitor 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX), the AMPA/CTZ failed to elicit any changes in . The AMPA/CTZ-induced sustained rise led to mitochondrial Ca(2+) accumulation, release of cytochrome c from mitochondria, and cell death. The AMPA/CTZ-elicited increase, mitochondrial damage, and cell death were significantly reduced by inhibiting NKCC1 or NCX(rev). These data suggest that in cultured oligodendrocytes, activation of AMPA receptors leads to NKCC1 phosphorylation that enhances NKCC1-mediated Na(+) influx. The latter triggers NCX(rev) and NCX(rev)-mediated overload and compromises mitochondrial function and cellular viability.

White matter axon vulnerability to AMPA/kainate receptor-mediated ischemic injury is developmentally regulated

Periventricular white matter injury (PWMI) is the leading cause of neurodevelopmental morbidity in survivors of premature birth. Cerebral ischemia is considered a major etiologic factor in the generation of PWMI. In adult white matter (WM), ischemic axonal damage is mediated by AMPA/kainate receptors. Mechanisms of ischemic axonal injury during development are not well defined. We used a murine brain slice model to characterize mechanisms of ischemic axonal injury in developing WM. Acute coronal brain slices were prepared from thy1-yellow fluorescent protein (YFP) mice at postnatal day 3 (P3), P7, P10, and P21. Ischemia was simulated by oxygen-glucose deprivation (OGD). YFP-positive axon morphology in the corpus callosum was preserved for at least 15 h under normoxic conditions. OGD resulted in delayed degeneration of YFP-positive axons, characterized by axonal beading, fragmentation, and loss of YFP. AMPA and cyclothiazide damaged WM axons at P7, P10, and P21 but not at P3. The AMPA/kainate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) decreased OGD-induced axonal degeneration and oligodendrocyte loss at P10 and P21. At P3 and P7, NBQX protected oligodendrocytes but did not prevent axonal degeneration after OGD. The NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate] provided no protection at any age. These results indicate that developing WM axons are susceptible to ischemic injury. However, mechanisms of axonal degeneration are developmentally regulated. At P3 and P7, corresponding developmentally to the window of peak vulnerability to PWMI in humans, ischemic axonal injury is not mediated by AMPA/kainate receptors. Strategies to protect WM during this period may be substantially different from those used at later developmental stages.

Controlled low-pressure perfusion at the beginning of reperfusion attenuates neurologic injury after spinal cord ischemia

OBJECTIVE

Paraplegia caused by spinal cord ischemia remains a serious complication after surgical repair of thoracoabdominal aortic aneurysms. This study tests the hypothesis that controlled low-pressure perfusion at the beginning of reperfusion can attenuate neurologic injury of the spinal cord after transient ischemia.

METHODS

Spinal cord ischemia was accomplished in rabbits by occlusion of the infrarenal aorta with a balloon catheter for 25 minutes. In the normal reperfusion group, reperfusion was completely restored immediately after ischemia, whereas perfusion pressure was controlled between 45 and 55 mm Hg during the first 10 minutes followed by complete reperfusion in the low-pressure reperfusion group. Functional evaluation with the Tarlov score during a 14-day observation period, histopathologic assessment of the lumbar spinal cord, and measurements of malondialdehyde levels and amyloid precursor protein immunoreactivity were performed.

RESULTS

Neurologic impairment was remarkably attenuated in the low-pressure reperfusion group (compared with the Tarlov scores of the normal reperfusion group, P < .05 at day 2; P < .01 at days 1, 7, and 14). Compared with the normal reperfusion group, malondialdehyde levels were significantly lower in the low-pressure reperfusion group (P < .05), and the large motor neurons of the low-pressure reperfusion group were preserved to a much greater extent (P < .05). White matter injury of the low-pressure reperfusion group was also markedly attenuated as evidenced by reduction of vacuolation area of the white matter (P < .05) and decrease of the amyloid precursor protein immunoreactivity (P < .05).

CONCLUSION

Reperfusion initiated with low-pressure perfusion exerts neuroprotective effects on the spinal cord against ischemia/reperfusion injury.

Neuronal damage in rat brain and spinal cord after cardiac arrest and massive hemorrhagic shock*

OBJECTIVE

Severe global ischemia often results in severe damage to the central nervous system of survivors. Hind-limb paralysis is a common deficit caused by global ischemia. Until recently, most studies of global ischemia of the central nervous system have examined either the brain or spinal cord, but not both. Spinal cord damage specifically after global ischemia has not been studied in detail. Because the exact nature of the neuronal damage to the spinal cord and the differences in neuronal damage between the brain and spinal cord after global ischemia are poorly understood, we developed a new global ischemia model in the rat and specifically studied spinal cord damage after global ischemia. Further, we compared the different forms of neuronal damage between the brain and spinal cord after global ischemia.

DESIGN

Randomized, controlled study using three different global ischemia models in the rat.

SETTING

University research laboratory.

SUBJECTS

Male, adult Sprague-Dawley rats (300 g).

INTERVENTIONS

Animals were divided into three experimental groups, group A (n = 6, survived for 7 days), 12 mins of hemorrhagic shock; group B (n = 6, survived for 7 days), 5 mins of cardiac arrest; or group C (n = 6, each for 6 hrs, 12 hrs, 1 day, 3 days, and 7 days), 7 mins of hemorrhagic shock and 5 mins of cardiac arrest. Motor deficit of the hind limbs was studied 6 hrs to 7 days after resuscitation. Also, nonoperated animals (n = 6) were used as the control. Histologic analysis (hematoxylin and eosin, Fluoro-Jade B, terminal deoxynucleotidyl transferase- mediated dUTP end-labeling [TUNEL], Klüver-Barrera) and ultrastructural analysis using electron microscopy were performed on samples from the CA1 region of the hippocampus and lumbar spinal cord. Demyelination of the white matter of the lumbar spinal cord was analyzed semiquantitatively using Scion Image software.

MAIN RESULTS

No paraplegic animals were observed in either group A or B. All group C animals showed severe hind-limb paralysis. Severe neuronal damage was found in the CA1 region of the hippocampus in all groups, and the state of delayed neuronal cell death was similar among the three groups. Neuronal damage in the lumbar spinal cord was detected only in group C animals, mainly in the dorsal horn and intermediate gray matter. Demyelination was prominent in the ventral and ventrolateral white matter in group C. A significant difference was observed between control and group C rats with Scion Image software. Ultrastructural analysis revealed extensive necrotic cell death in the intermediate gray matter in the lumbar spinal cord in group C rats.

CONCLUSION

The combination in the global ischemia model (i.e., hemorrhagic shock followed by cardiac arrest) caused severe neuronal damage in the central nervous system. Thereby, hind-limb paralysis after global ischemia might result from spinal cord damage. These results suggest that therapeutic strategies for preventing spinal cord injury are necessary when treating patients with severe global ischemia.

Hypoxic injury of isolated axons is independent of ionotropic glutamate receptors

Axonal injury in white matter is an important consequence of many acute neurological diseases including ischemia. A role for glutamate-mediated excitotoxicity is suggested by observations from in vitro and in situ models that AMPA/kainate blockers can reduce axonal injury. We assessed axonal vulnerability in primary murine neuronal cultures, with axons isolated from their cell bodies using a compartmented chamber design. Transient removal of oxygen and glucose in the axon compartment resulted in irreversible loss of axon length and neurofilament labeling. This injury was not prevented by addition of ionotropic glutamate receptor blockers and could not be reproduced by glutamate receptor agonists. However, hypoxic injury was prevented by blockade of voltage-gated sodium channels, inhibition of calpain and removal of extracellular calcium. These results suggest that isolated, unmyelinated axons are vulnerable to hypoxic injury which is mediated by influx of sodium and calcium but is independent of glutamate receptor activation.

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.

The effect of glutamate receptor blockers on glutamate release following spinal cord injury. Lack of evidence for an ongoing feedback cascade of damage --> glutamate release --> damage --> glutamate release --> etc

It is widely hypothesized that excitotoxicity of released glutamate following a CNS insult is propagated by the cyclic cascade: glutamate release --> damage --> glutamate release --> further damage --> etc. We tested this hypothesis by determining the effects of attempting to interrupt the loop by administering glutamate receptor antagonists and Na(+)-channel blockers on glutamate release following spinal cord injury (SCI). The effects of administering the NMDA receptor blockers MK-801 and memantine, the AMPA/kainate receptor blockers NBQX and GYKI 52466, the AMPA receptor desensitization blocker cyclothiazide and the sodium channel blockers riluzole, mexiletine and QX-314 on post-SCI were determined. Agents were administered into the site of injury by direct injection, by microdialysis or systemically. None of these agents had an appreciable effect on glutamate release following SCI. Thus, it is unlikely that the above cascade produces significant secondary glutamate release and ongoing damage following SCI, although such cascades may worsen other CNS insults. We attribute our results to overwhelming effects of much greater release by direct mechanical damage and reversal of transport following SCI.

AMPA/kainate receptors mediate axonal morphological disruption in hypoxic white matter

We used acute brain slices to investigate the hypothesis that oxygen-glucose deprivation (OGD) induced loss of axon function and neurofilament labeling are correlated to axonal morphological disruption in the corpus callosum of adult brain. Coronal brain slices including corpus callosum were prepared from adult mice. White matter immunohistochemical properties and conduction along axons remained stable over 12 h after preparation. White matter injury was assessed by recording compound action potentials (CAPs) across corpus callosum, combined with immunofluorescence for axonal neurofilaments and by bright field microscopy of myelin profiles in semi-thin sections. OGD for 30 min resulted in irreversible loss of the CAPs, formation of axon heads and bulbs, and swelling of myelin profiles in slices examined 1h after OGD. In slices followed for 9 h after OGD, there was complete loss of neurofilament labeling and myelin profiles. Because overactivation of AMPA/kainate receptors mediates axon structural and functional disruption in hypoxic corpus callosum slices, we tested whether blockade of AMPA/kainate receptors reduced OGD-induced axonal morphological disruption. NBQX (30 microM), an AMPA/kainate receptor antagonist, prevented OGD-induced formation of axon heads and bulbs, swelling of myelin profiles, loss of neurofilament staining and preserved axonal morphology. These results expand our previous findings that the AMPA/kainate receptor activation contributes to axonal morphological disruption, as well as loss of electrical function.

An Evaluation of White Matter Injury After Spinal Cord Ischemia in Rats: A Comparison with Gray Matter Injury

We quantitatively assessed both gray and white matter injury after spinal cord ischemia in rats, and the relationship between the magnitude of gray and white matter injury was determined. Twenty-five male rats were anesthetized with isoflurane, and spinal cord ischemia (SCI) was induced by balloon intraaortic occlusion combined with hypotension. The animals were randomly allocated to one of the following three groups: animals with SCI for 12 min (SCI-12; n = 8), 15 min (SCI-15; n = 9), or those with sham operation (n = 8). Twenty-four hours after reperfusion, hindlimb motor function was assessed using the Basso-Beattie-Bresnahan scale scoring. Gray matter damage was assessed on the basis of the number of normal neurons in the ventral horn. White matter damage was assessed on the basis of the extent of vacuolation and amyloid precursor protein immunoreactivity in the ventral and ventrolateral white matter. There were significantly less normal neurons in the SCI-15 group compared with those in the SCI-12 and sham groups (P < 0.05). There was a significant positive correlation between the Basso-Beattie-Bresnahan scores and the number of normal neurons. The percentages of vacuolation areas in the SCI-15 group were significantly larger compared with those in the SCI-12 and sham groups (30% +/- 10% versus 9% +/- 7%, 0% +/- 0%, P < 0.05). Immunohistochemical analysis revealed increased amyloid precursor protein immunoreactivity in the swollen axons, especially in the SCI-15 group. There was a significant negative correlation between the number of normal neurons and percentages of vacuolation areas. These results indicate that both gray and white matter were injured after SCI in rats and the degree of white mater injury was correlated with the severity of gray matter injury after a relatively short recovery period.