Descending Systems Contributing to Locomotor Recovery After Mild or Moderate Spinal Cord Injury in Rats: Experimental Evidence and a Review of Literature

Restorative Neurology and Neuroscience. 2002  |  Pubmed ID: 12515895

Locomotor recovery after spinal cord contusion injury (SCI) may be mediated by descending axons spared at the lesion epicenter. Greater axonal sparing is associated with more extensive recovery. Therefore, we identified the source and relative proportion of spared axons associated with extensive or limited locomotor recovery after SCI.

Control of Synaptic Strength by Glial TNFalpha

Science (New York, N.Y.). Mar, 2002  |  Pubmed ID: 11910117

Activity-dependent modulation of synaptic efficacy in the brain contributes to neural circuit development and experience-dependent plasticity. Although glia are affected by activity and ensheathe synapses, their influence on synaptic strength has largely been ignored. Here, we show that a protein produced by glia, tumor necrosis factor alpha (TNFalpha), enhances synaptic efficacy by increasing surface expression of AMPA receptors. Preventing the actions of endogenous TNFalpha has the opposite effects. Thus, the continual presence of TNFalpha is required for preservation of synaptic strength at excitatory synapses. Through its effects on AMPA receptor trafficking, TNFalpha may play roles in synaptic plasticity and modulating responses to neural injury.

ProNGF Induces P75-mediated Death of Oligodendrocytes Following Spinal Cord Injury

Neuron. Oct, 2002  |  Pubmed ID: 12408842

The neurotrophin receptor p75 is induced by various injuries to the nervous system, but its role after injury has remained unclear. Here, we report that p75 is required for the death of oligodendrocytes following spinal cord injury, and its action is mediated mainly by proNGF. Oligodendrocytes undergoing apoptosis expressed p75, and the absence of p75 resulted in a decrease in the number of apoptotic oligodendrocytes and increased survival of oligodendrocytes. ProNGF is likely responsible for activating p75 in vivo, since the proNGF from the injured spinal cord induced apoptosis among p75(+/+), but not among p75(-/-), oligodendrocytes in culture, and its action was blocked by proNGF-specific antibody. Together, these data suggest that the role of proNGF is to eliminate damaged cells by activating the apoptotic machinery of p75 after injury.

Kainate-induced Excitotoxicity is Dependent Upon Extracellular Potassium Concentrations That Regulate the Activity of AMPA/KA Type Glutamate Receptors

Journal of Neurochemistry. Nov, 2002  |  Pubmed ID: 12421366

In addition to well-known N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity, recent studies suggest that non-NMDA type ionotropic glutamate receptors are also important mediators of excitotoxic neuronal death, and that their functional expression can be regulated by the cellular environment. In this study, we used cerebellar granule cells (CGCs) in culture to investigate kainate (KA)-induced excitotoxicity. Although previous reports indicated that KA induces apoptosis of CGCs in culture, no KA-induced excitotoxic cell death was observed in CGCs treated with KA when cells were maintained in high potassium media (24 mm K+). In contrast, when mature CGCs were shifted into low potassium media (3 mm K+), KA produced significant excitotoxicity. In electrophysiological studies, the KA-induced inward current density was significantly elevated in CGCs shifted into low K+ media compared with those maintained in high K+ media. Non-desensitizing aspects of KA currents observed in this study suggest that these responses were mediated by AMPA rather than KA receptors. In immunofluorescence studies, the surface expression of GluR1 subunits increased when mature CGCs were shifted into a low K+ environment. This study suggests that KA-induced excitotoxicity in mature CGCs is dependent upon the extracellular potassium concentration, which modulates functional expression and excitability of AMPA/KA receptors.

Cell Death in Models of Spinal Cord Injury

Progress in Brain Research. 2002  |  Pubmed ID: 12440358

Current treatments for acute spinal cord injury are based on animal models of human spinal cord injury (SCI). These models have shown that the initial traumatic injury to cord tissue is followed by a long period of secondary injury that includes a number of cellular and biochemical cascades. These secondary injury processes are potential targets for therapies. Continued refinement of rat and mouse models of SCI, along with more detailed analyses of the biology of the lesion in these models, points to both necrotic and apoptotic mechanisms of cell death after SCI. In this chapter, we review recent evidence for long-term apoptotic death of oligodendrocytes in long tracts undergoing Wallerian degeneration following SCI. This process appears to be related closely to activation of microglial cells. It is has been thought that microglial cells might be the source of cytotoxic cytokines, such as tumor necrosis factor-alpha (TNF-alpha), that kill oligodendrocytes. However, more recent evidence in vivo suggests that TNF-alpha by itself may not induce necrosis or apoptosis in oligodendrocytes. We review data that suggests other possible pathways for apoptosis, such as the neurotrophin receptor p75 which is expressed in both neurons and oligodendrocytes after SCI in rats and mice. In addition, it appears that microglial activation and TNF-alpha may be important in acute SCI. Ninety minutes after a moderate contusion lesion, microglia are activated and surround dying neurons. In an 'atraumatic' model of SCI, we have now shown that TNF-alpha appears to greatly potentiate cell death mediated by glutamate receptors. These studies emphasize that multiple mechanisms and interactions contribute to secondary injury after SCI. Continued study of both contusion models and other new approaches to studying these mechanisms will be needed to maximize strategies for acute and chronic therapies, and for neural repair.

Descending Spinal Projections from the Rostral Gigantocellular Reticular Nuclei Complex

The Journal of Comparative Neurology. Jan, 2003  |  Pubmed ID: 12454986

Electrophysiological and physiological studies have suggested that the ventral medullary gigantocellular reticular nuclei (composed of the gigantocellular ventralis and pars alpha nuclei as well as the adjacent lateral paragigantocellular nucleus; abbreviated Gi-LPGi complex) provide descending control of pelvic floor organs (Mackel [1979] J. Physiol. (Lond.) 294:105-122; Hubscher and Johnson [1996] J. Neurophysiol. 76:2474-2482; Hubscher and Johnson [1999] J. Neurophysiol. 82:1381-1389; Johnson and Hubscher [1998] Neuroreport 9:341-345). Specifically, this complex of paramedian reticular nuclei has been implicated in the inhibition of sexual reflexes. In the present study, an anterograde fluorescent tracer was used to investigate direct descending projections from the Gi-LPGi complex to retrogradely labeled pudendal motoneurons (MN) in the male rat. Our results demonstrated that, although a high density of arborizations from Gi-LPGi fibers appears to be in close apposition to pudendal MNs, this relationship also applies to other MNs throughout the entire spinal cord. The Gi-LPGi also projects to spinal autonomic regions, i.e., both the intermediolateral cell column and the sacral parasympathetic nucleus, as well as to regions of the intermediate gray, which contain interneurons involved in the organization of pelvic floor reflexes. Lastly, throughout the length of the spinal cord, numerous neurons located primarily in laminae VII-X, were retrogradely labeled with Fluoro-Ruby after injections into the Gi-LPGi. The diffuse descending projections and arborizations of this pathway throughout the spinal cord suggest that this brainstem area is involved in the direct, descending control of a variety of spinal activities. These results are in contrast with our observations of the discrete projections of the caudal nucleus raphe obscurus, which target the autonomic and somatic MNs involved specifically in sexual and eliminative functions (Hermann et al. [1998] J. Comp. Neurol. 397:458-474).

Acute Transplantation of Glial-restricted Precursor Cells into Spinal Cord Contusion Injuries: Survival, Differentiation, and Effects on Lesion Environment and Axonal Regeneration

Experimental Neurology. Dec, 2004  |  Pubmed ID: 15530870

Transplantation of stem cells and immature cells has been reported to ameliorate tissue damage, induce axonal regeneration, and improve locomotion following spinal cord injury. However, unless these cells are pushed down a neuronal lineage, the majority of cells become glia, suggesting that the alterations observed may be potentially glially mediated. Transplantation of glial-restricted precursor (GRP) cells--a precursor cell population restricted to oligodendrocyte and astrocyte lineages--offers a novel way to examine the effects of glial cells on injury processes and repair. This study examines the survival and differentiation of GRP cells, and their ability to modulate the development of the lesion when transplanted immediately after a moderate contusion injury of the rat spinal cord. GRP cells isolated from a transgenic rat that ubiquitously expresses heat-stable human placental alkaline phosphatase (PLAP) were used to unambiguously detect transplanted GRP cells. Following transplantation, some GRP cells differentiated into oligodendrocytes and astrocytes, retaining their differentiation potential after injury. Transplanted GRP cells altered the lesion environment, reducing astrocytic scarring and the expression of inhibitory proteoglycans. Transplanted GRP cells did not induce long-distance regeneration from corticospinal tract (CST) and raphe-spinal axons when compared to control animals. However, GRP cell transplants did alter the morphology of CST axons toward that of growth cones, and CST fibers were found within GRP cell transplants, suggesting that GRP cells may be able to support axonal growth in vivo after injury.

Inflammation and Apoptosis: Linked Therapeutic Targets in Spinal Cord Injury

Trends in Molecular Medicine. Dec, 2004  |  Pubmed ID: 15567326

The secondary cascade of cell death that follows central nervous system (CNS) injury or ischemia has long been considered a target for neuroprotective agents aimed at sparing tissue and function. Recently, several laboratories have shown remarkable protection and recovery of function in rodent models of spinal cord injury using treatments that target components of the CNS inflammatory response. The use of minocycline, an antibiotic that reduces microglial activation, antibody blockade of the CD95 (FAS) ligand and the blockade of glycosphingolipid-induced iNOS (inducible nitric oxide synthase) have recently been shown to reduce neuronal and glial apoptosis with concomitant improvement in neurological function, and appear to enhance the efficacy of cell transplantation strategies.

A Simple Post Hoc Transformation That Improves the Metric Properties of the BBB Scale for Rats with Moderate to Severe Spinal Cord Injury

Journal of Neurotrauma. Nov, 2004  |  Pubmed ID: 15684652

The Basso, Beattie, Bresnahan (BBB) open field locomotor scale is a popular measure of functional recovery following spinal cord injury (SCI). To examine the metric properties of the scale, we performed detailed analyses of BBB scores from 643 rats with moderate and severe SCI (12.5, 25, or 50 mm MASCIS) from two different laboratories. The analyses revealed that the BBB scale is ordinal in the most frequently used portion of the scale. Higher scores (14 and greater) were not frequently assigned in the dataset as animals with mild injuries were not sampled, making the ordinal nature of the upper end of the scale difficult to assess. The rare scores assigned in this range disproportionately increased variance. Under these conditions collapsing scores above 14 into one category increased effect size. Analysis of the lower region of the scale revealed that some scores (2 and 3) were rarely assigned, implying a discontinuity in the scale. The discontinuous nature of the lower portion of the scale presents a problem for both parametric and nonparametric statistical analyses. Pooling scores 2/3/4 eliminated the gap, enhancing the metric properties of the scale. Under the injury conditions evaluated, the transformation helped assure that the data were continuous and ordered. Further, interval durations were comparable across the entire range of the transformed scale, allowing application of parametric statistical techniques. The transformation should be applied in a post hoc fashion to reduce variability and increase power in cases where few scores fall in upper portion of the scale.

TNFalpha-induced AMPA-receptor Trafficking in CNS Neurons; Relevance to Excitotoxicity?

Neuron Glia Biology. Aug, 2004  |  Pubmed ID: 16520832

Injury and disease in the CNS increases the amount of tumor necrosis factor alpha (TNFalpha) that neurons are exposed to. This cytokine is central to the inflammatory response that occurs after injury and during prolonged CNS disease, and contributes to the process of neuronal cell death. Previous studies have addressed how long-term apoptotic-signaling pathways that are initiated by TNFalpha might influence these processes, but the effects of inflammation on neurons and synaptic function in the timescale of minutes after exposure are largely unexplored. Our published studies examining the effect of TNFalpha on trafficking of AMPA-type glutamate receptors (AMPARs) in hippocampal neurons demonstrate that glial-derived TNFalpha causes a rapid (<15 minute) increase in the number of neuronal, surface-localized, synaptic AMPARs leading to an increase in synaptic strength. This indicates that TNFalpha-signal transduction acts to facilitate increased surface localization of AMPARs from internal postsynaptic stores. Importantly, an excess of surface localized AMPARs might predispose the neuron to glutamate-mediated excitotoxicity and excessive intracellular calcium concentrations, leading to cell death. This suggests a new mechanism for excitotoxic TNFalpha-induced neuronal death that is initiated minutes after neurons are exposed to the products of the inflammatory response.Here we review the importance of AMPAR trafficking in normal neuronal function and how abnormalities that are mediated by glial-derived cytokines such as TNFalpha can be central in causing neuronal disorders. We have further investigated the effects of TNFalpha on different neuronal cell types and present new data from cortical and hippocampal neurons in culture. Finally, we have expanded our investigation of the temporal profile of the action of this cytokine relevant to neuronal damage. We conclude that TNFalpha-mediated effects on AMPAR trafficking are common in diverse neuronal cell types and very rapid in their onset. The abnormal AMPAR trafficking elicited by TNFalpha might present a novel target to aid the development of new neuroprotective drugs.

Serotonergic Fiber Sprouting to External Anal Sphincter Motoneurons After Spinal Cord Contusion

Experimental Neurology. May, 2005  |  Pubmed ID: 15817262

The present study analyzed the anatomical plasticity of serotonergic immunoreactive projections to external anal sphincter (EAS) motoneurons, and the behavioral plasticity of EAS reflexes, penile erection, and locomotion in rats with spinal contusion injury (SCI) or complete spinal cord transection (TX). Electromyographic activity of the EAS, penile erection latency, and BBB locomotor score exhibited parallel recovery over the 6-week recovery period after contusion SCI. This pattern of recovery was not observed in TX animals. While locomotor scores demonstrated a small increase after TX, erectile and anorectal function remained at abnormal levels established immediately after injury. Serotonergic immunofluorescent (5-HT-IF) staining at the lesion site identified a small number of fibers spared after SCI that may provide a substrate for functional recovery. Pixel density measurements of 5-HT-IF in the vicinity of retrogradely labeled EAS and unlabeled pudendal motoneurons necessary for penile erection provide indirect evidence of serotonergic sprouting that parallels the observed functional recovery in animals with SCI. No 5-HT-IF was detected caudal to the injury site in TX animals. These studies indicate: (1) lumbosacral eliminative and reproductive reflexes provide a valid means of studying the mechanisms of post-SCI plasticity; (2) the similar recovery curves suggest similar return of descending control, perhaps through sprouting of descending serotonergic fibers; (3) the observed deficits after TX likely represent the permanent removal of descending inhibition and reflect reorganization of segmental circuitry.

Telemetric Monitoring of Corpus Spongiosum Penis Pressure in Conscious Rats for Assessment of Micturition and Sexual Function Following Spinal Cord Contusion Injury

Journal of Neurotrauma. Apr, 2005  |  Pubmed ID: 15853461

Disruption of bladder function and sexual reflexes are major complications following spinal cord injury (SCI). We examined the use of telemetric monitoring of corpus spongiosum penis (CSP) pressures for assessment of micturition and erectile events following SCI in rats. Pressure catheters were implanted in the bulb of the CSP of seven male Long-Evans hooded rats, subjected to a standardized weight drop SCI (10 g x 12.5 mm) at T10. CSP pressures were analyzed for spontaneously occurring micturition and erectile events, and during ex copula reflex erection tests until 25 days after SCI. Urine volume was determined until 21 days after SCI. Results show initial loss of bladder function after SCI with gradual return of reflex micturition. When compared to baseline (BL), micturition pressure characteristics after SCI included prolonged duration, increased area under the curve (AUC), increased mean pressures, increased number of pressure peaks, and increased peak frequency. At 21 days after SCI, the urine volume per micturition was significantly increased. The number of full erectile events decreased significantly following SCI. Pressure wave analyses demonstrated increased AUC, increased maximum pressures, increased suprasystolic peak duration, increased AUC of the suprasystolic peaks, and increased maximum pressures of the suprasystolic peaks during recovery. The number of partial erectile events decreased significantly following SCI. Ex copula reflex erection testing demonstrated significantly decreased latency. The study demonstrates that telemetric monitoring of CSP pressures in conscious rats is a valuable and reliable method for assessing recovery of autonomic function following SCI.

A Sublethal Dose of TNFalpha Potentiates Kainate-induced Excitotoxicity in Optic Nerve Oligodendrocytes

Neurochemical Research. Jun-Jul, 2005  |  Pubmed ID: 16187221

Glutamate receptor-induced cell death, known as excitotoxicity in both neurons and oligodendrocytes, has been implicated as a common pathway of cell death in numerous central nervous system (CNS) diseases and trauma. Research in both neuronal and oligodendrocyte excitotoxicity has examined glutamate's receptor-mediated effects on CNS cells, and explored strategies to protect cells exposed to the elevated glutamate levels that occur in CNS trauma and disease. Proinflammatory cytokines are also elevated in the injured CNS, and have also been implicated in CNS cell death. Recently, several laboratories have examined cytokines' effects on neuronal and glial excitotoxicity. Here, we review literature concerning the dynamic susceptibility of both neurons and oligodendrocytes to excitotoxicity, and present new data from our laboratory showing that the susceptibility of oligodendrocytes to excitotoxicity is acutely potentiated by the proinflammatory cytokine TNFalpha.

Alterations in Eliminative and Sexual Reflexes After Spinal Cord Injury: Defecatory Function and Development of Spasticity in Pelvic Floor Musculature

Progress in Brain Research. 2006  |  Pubmed ID: 16198713

Spinal cord injury often results in loss of normal eliminative and sexual functions. This chapter is focused on defecatory function, although aspects of micturition and erectile function will be covered as well due to the overlap in anatomical organization and response to injury. These systems have both autonomic and somatic components, and are organized in the thoracolumbar (sympathetic), lumbosacral (somatic), and sacral (parasympathetic) spinal cord. Loss of supraspinal descending control and plasticity-mediated alterations at the level of the spinal cord, result in loss of voluntary control and in abnormal functioning of these systems including the development of dyssynergies and spasticity. There are several useful models of spinal cord injury in rodents that exhibit many of the autonomic dysfunctions observed after spinal cord injury in humans. Numerous studies involving these animal models have demonstrated development of abnormalities in bladder, external anal sphincter, and erectile function, such as detrusor-sphincter-dyssynergia and external anal sphincter hyperreflexia. Here we review many of these studies and show some of the anatomical alterations that develop within the spinal cord during the development of these hyperreflexias. Furthermore, we show that spasticity develops in other pelvic floor musculature as well, such as the bulbospongiosus muscle, which results in increased duration and magnitude of pressures developed during erectile events and increased duration of micturition. Advances and continued improvement in the use of current animal models of spinal cord injury should encourage and increase the laboratory work devoted to this relatively neglected area of experimental spinal cord injury.

Behavioral and Histological Characterization of Unilateral Cervical Spinal Cord Contusion Injury in Rats

Journal of Neurotrauma. Jan, 2006  |  Pubmed ID: 16430371

Most experimental studies of spinal cord injury (SCI) in rats damage the thoracic cord, with the consequent functional loss being due to interruption of long tracts connecting the caudal spinal cord to the rostral nervous system. Less work has been done evaluating injury to the cervical cord, even though it is the most common level of human SCI. In addition to the long tracts, the cervical spinal cord contains the sensory and motor neurons responsible for upper extremity function. The purpose of this study was to further develop a rat model of cervical spinal cord contusion injury using a modified NYU/MASCIS weight drop device. Mild (6.25 mm) and moderate (12.5 mm) C5 unilateral injuries were produced. Behavioral recovery was examined using a grooming test, a paw preference test, a walkway test (The Catwalk), and a horizontal ladder test. Histological outcome measures included sparing at the lesion epicenter, sparing throughout the extent of the lesion, quantification of myelin loss rostral and caudal to the lesion, and motor neuron counts. Compared to controls, animals receiving SCI exhibited injury severity-specific deficits in forelimb, locomotor, and hindlimb function persisting for 6-weeks post-SCI. Histological analysis revealed ipsilateral containment of the injury, and differentiation between groups on all measures except motor neuron counts. This model has many advantages: (1) minimal animal care requirements post-SCI, (2) within subject controls, (3) functional loss involves primarily the ipsilateral forelimb, and (4) it is a behavioral and histological model for both gray and white matter damage caused by contusive SCI.

Kainate Induces Rapid Redistribution of the Actin Cytoskeleton in Ameboid Microglia

Journal of Neuroscience Research. Jul, 2006  |  Pubmed ID: 16625662

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.

Novel Technique for Monitoring Micturition and Sexual Function in Male Rats Using Telemetry

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology. Mar, 2007  |  Pubmed ID: 17095649

We developed a novel technique to simultaneously monitor micturitions and erections in rats by using pressure monitoring within the corpus spongiosum of the penis (CSP). We present data validating this technique and report pressure waveform characteristics of micturition and erectile events during four different behavioral contexts in 10 awake, freely-moving male rats. Telemetric pressure transducers were implanted in the bulb of the CSP. CSP pressure was monitored while the animals were simultaneously recorded on video for determination of presence and volume (n = 7) of micturitions and while the animals underwent behavioral tests for determination of erections. Observed micturitions and CSP pressure waveforms characteristic of micturitions occurred simultaneously (r = 0.98) at a frequency of 32 +/- 4 micturitions per 24 h and with a volume of 0.95 +/- 0.12 ml/urination. Micturition duration recorded by CSP pressure and volume determined by urine weight were highly correlated (r = 0.82). We found that 100% of visually confirmed erectile events occurred simultaneously with CSP pressure waveforms characteristic of erections during ex copula reflex erection tests. During noncontact erection and mating tests more erections were identified by telemetry than by observation alone. Erections during mating tests had a different appearance than those seen in other contexts; they were shorter in duration (P < 0.05) and typically were characterized by a single suprasystolic CSP pressure peak, highlighting the context-specificity of erections. Quality of recordings remained stable in three of four rats we followed for 8 wk. We demonstrate that telemetric recording of CSP pressure provides a quantitative and qualitative assessment of penile erections and micturition in freely behaving rats.

Developmental Stage of Oligodendrocytes Determines Their Response to Activated Microglia in Vitro

Journal of Neuroinflammation. 2007  |  Pubmed ID: 18039385

Oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes are both lost in central nervous system injury and disease. Activated microglia may play a role in OPC and oligodendrocyte loss or replacement, but it is not clear how the responses of OPCs and oligodendrocytes to activated microglia differ.

Longitudinal Comparison of Two Severities of Unilateral Cervical Spinal Cord Injury Using Magnetic Resonance Imaging in Rats

Journal of Neurotrauma. Jan, 2008  |  Pubmed ID: 18355154

Magnetic resonance imaging (MRI) should be a powerful tool for characterization of spinal cord pathology in animal models. We evaluated the utility of medium-field MRI for the longitudinal assessment of progression of spinal cord injury (SCI) in a rat model. Thirteen adult rats were subjected to a 6.25 or 25 g-cm unilateral cervical SCI, and underwent MRI and behavioral tests during a 3-week study period. MRI was also performed post-mortem. Quantification of cord swelling, hypointense and hyperintense signal, and lesion length were the most valuable parameters to determine and were highly correlated to behavioral and histopathological measures. Immediately after injury, MRI showed loss of gray matter-white matter differentiation, presence of scattered hyperintense signal and local hypointense signal, and cord swelling in both groups. At 7 days after injury, the spinal cord in the 25 g-cm group was significantly larger than that of the 6.25 g-cm group (p = 0.02). Contrast enhancement of the lesion was seen at 24 h in the 6.25 g-cm group, and at 24 h and 7 days in the 25 g-cm group. The volume of hypointense signal, representing hemorrhage, throughout the lesion region was significantly larger in the 25 g-cm compared to the 6.25 g-cm group at both 14 and 21 days after SCI (p,

Cell Death After Spinal Cord Injury is Exacerbated by Rapid TNF Alpha-induced Trafficking of GluR2-lacking AMPARs to the Plasma Membrane

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Oct, 2008  |  Pubmed ID: 18971481

Glutamate, the major excitatory neurotransmitter in the CNS, is implicated in both normal neurotransmission and excitotoxicity. Numerous in vitro findings indicate that the ionotropic glutamate receptor, AMPAR, can rapidly traffic from intracellular stores to the plasma membrane, altering neuronal excitability. These receptor trafficking events are thought to be involved in CNS plasticity as well as learning and memory. AMPAR trafficking has recently been shown to be regulated by glial release of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) in vitro. This has potential relevance to several CNS disorders, because many pathological states have a neuroinflammatory component involving TNFalpha. However, TNFalpha-induced trafficking of AMPARs has only been explored in primary or slice cultures and has not been demonstrated in preclinical models of CNS damage. Here, we use confocal and image analysis techniques to demonstrate that spinal cord injury (SCI) induces trafficking of AMPARs to the neuronal membrane. We then show that this effect is mimicked by nanoinjections of TNFalpha, which produces specific trafficking of GluR2-lacking receptors which enhance excitotoxicity. To determine if TNFalpha-induced trafficking affects neuronal cell death, we sequestered TNFalpha after SCI using a soluble TNFalpha receptor, and significantly reduced both AMPAR trafficking and neuronal excitotoxicity in the injury penumbra. The data provide the first evidence linking rapid TNFalpha-induced AMPAR trafficking to early excitotoxic secondary injury after CNS trauma in vivo, and demonstrate a novel way in which pathological states hijack mechanisms involved in normal synaptic plasticity to produce cell death.

Small Molecule Activation of Adaptive Gene Expression: Tilorone or Its Analogs Are Novel Potent Activators of Hypoxia Inducible Factor-1 That Provide Prophylaxis Against Stroke and Spinal Cord Injury

Annals of the New York Academy of Sciences. Dec, 2008  |  Pubmed ID: 19076458

A major challenge for neurological therapeutics is the development of small molecule drugs that can activate a panoply of downstream pathways without toxicity. Over the past decade our group has shown that a family of enzymes that regulate posttranscriptional and transcriptional adaptive responses to hypoxia are viable targets for neuronal protection and repair. The family is a group of iron, oxygen, and 2-oxoglutarate-dependent dioxygenases, known as the HIF prolyl 4-hydroxylases (HIF PHDs). We have previously shown that pluripotent protection offered by iron chelators is mediated, in part, via the ability of these agents to inhibit the HIF PHDs. Our group and others have implicated the transcriptional activator HIF-1 in some of the salutary effects of iron chelation-induced PHD inhibition. While some iron chelators are currently employed in humans for conditions such as hemochromatosis, the diverse utilization of iron in physiological processes in the brain makes the development of HIF activators that do not bind iron a high priority. Here we report the development of a high throughput screen to develop novel HIF activators and/or PHD inhibitors for therapeutic use in the central nervous system (CNS). We show that tilorone, a low-molecular weight, antiviral, immunomodulatory agent is the most effective activator of the HIF pathway in a neuronal line. We also show that tilorone enhances HIF protein levels and increases the expression of downstream target genes independent of iron chelation and HIF PHD inhibition in vitro. We further demonstrate that tilorone can activate an HIF-regulated reporter gene in the CNS. These studies confirm that tilorone can penetrate the blood-brain barrier to activate HIF in the CNS. As expected from these findings, we show that tilorone provides effective prophylaxis against permanent ischemic stroke and traumatic spinal cord injury in male rodents. Altogether these findings identify tilorone as a novel and potent modulator of HIF-mediated gene expression in neurons with neuroprotective properties.

Hypertonic Saline Attenuates Cord Swelling and Edema in Experimental Spinal Cord Injury: a Study Utilizing Magnetic Resonance Imaging

Critical Care Medicine. Jul, 2009  |  Pubmed ID: 19487936

To use magnetic resonance imaging (MRI) to characterize secondary injury immediately after spinal cord injury (SCI), and to show the effect of hypertonic saline on MRI indices of swelling, edema, and hemorrhage within the cord.

Extensive Spontaneous Plasticity of Corticospinal Projections After Primate Spinal Cord Injury

Nature Neuroscience. Dec, 2010  |  Pubmed ID: 21076427

Although axonal regeneration after CNS injury is limited, partial injury is frequently accompanied by extensive functional recovery. To investigate mechanisms underlying spontaneous recovery after incomplete spinal cord injury, we administered C7 spinal cord hemisections to adult rhesus monkeys and analyzed behavioral, electrophysiological and anatomical adaptations. We found marked spontaneous plasticity of corticospinal projections, with reconstitution of fully 60% of pre-lesion axon density arising from sprouting of spinal cord midline-crossing axons. This extensive anatomical recovery was associated with improvement in coordinated muscle recruitment, hand function and locomotion. These findings identify what may be the most extensive natural recovery of mammalian axonal projections after nervous system injury observed to date, highlighting an important role for primate models in translational disease research.

Effects of Axon Degeneration on Oligodendrocyte Lineage Cells: Dorsal Rhizotomy Evokes a Repair Response While Axon Degeneration Rostral to Spinal Contusion Induces Both Repair and Apoptosis

Glia. Aug, 2010  |  Pubmed ID: 20607865

Wallerian degeneration in the dorsal columns (DC) after spinal cord injury (SCI) is associated with microglial activation and prolonged oligodendrocyte (OL) apoptosis that may contribute to demyelination and dysfunction after SCI. But, there is an increase in OL lineage cells after SCI that may represent a reparative response, and there is evidence for remyelination after SCI. To assess the role of axonal degeneration per se in OL apoptosis and proliferation, we cut the L2-S2 dorsal roots producing massive axonal degeneration and microglial activation in the DC, and found no evidence of OL loss or apoptosis. Rather, the numbers of OL-lineage cells positive for NG2 and APC (CC1) increased, and BrdU studies suggested new OL formation. We then tested contusion SCI (cSCI) that results in comparable degeneration in the DC rostral to the injury, microglial activation, and apoptosis of DC OLs by eight days. NG2+ cell proliferation and oligodendrogenesis was seen as after rhizotomy. The net result of this combination of proliferation and apoptosis was a reduction in DC OLs, confirming earlier studies. Using an antibody to oxidized nucleic acids, we found rapid and prolonged RNA oxidation in OLs rostral to cSCI, but no evidence of oxidative stress in DC OLs after rhizotomy. These results suggest that signals associated with axonal degeneration are sufficient to induce OL proliferation, and that secondary injury processes associated with the central SCI, including oxidative stress, rather than axonal degeneration per se, are responsible for OL apoptosis.

AMPA-receptor Trafficking and Injury-induced Cell Death

The European Journal of Neuroscience. Jul, 2010  |  Pubmed ID: 20646045

AMPA receptors (AMPARs) are critical for synaptic plasticity, and are subject to alterations based on subunit composition and receptor trafficking to and from the plasma membrane. One of the most potent regulators of AMPAR trafficking is the pro-inflammatory cytokine tumor necrosis factor (TNF)α, which is involved in physiological regulation of synaptic strength (Beattie et al., (2002) Science, 295, 2282-2285; Stellwagen and Malenka, (2006) Nature, 440, 1054-1059) and is also present at high concentrations after CNS injury. Here, we review evidence that TNF can rapidly alter the surface expression of AMPARs so that the proportion of Ca(++) -permeable receptors is increased and that this increase, in combination with increased levels of extracellular glutamate after injury, plays an important role in enhancing excitotoxic cell death after CNS injury. Thus, the pathophysiological hijacking of a critical regulator of synaptic plasticity and homeostasis by the secondary injury cascade may represent a new therapeutic target for neuroprotection.

Glial Restricted Precursor Cell Transplant with Cyclic Adenosine Monophosphate Improved Some Autonomic Functions but Resulted in a Reduced Graft Size After Spinal Cord Contusion Injury in Rats

Experimental Neurology. Jan, 2011  |  Pubmed ID: 21040723

Transplantation of glial restricted precursor (GRP) cells has been shown to reduce glial scarring after spinal cord injury (SCI) and, in combination with neuronal restricted precursor (NRP) cells or enhanced expression of neurotrophins, to improve recovery of function after SCI. We hypothesized that combining GRP transplants with rolipram and cAMP would improve functional recovery, similar to that seen after combining Schwann cell transplants with increasing cAMP. A short term study, (1) uninjured control, (2) SCI+vehicle, and (3) SCI+cAMP, showed that spinal cord [cAMP] was increased 14days after SCI. We used 51 male rats subjected to a thoracic SCI for a 12-week survival study: (1) SCI+vehicle, (2) SCI+GRP, (3) SCI+cAMP, (4) SCI+GRP+cAMP, and (5) uninjured endpoint age-matched control (AM). Rolipram was administered for 2weeks after SCI. At 9days after SCI, GRP transplantation and injection of dibutyryl-cAMP into the spinal cord were performed. GRP cells survived, differentiated, and formed extensive transplants that were well integrated with host tissue. Presence of GRP cells increased the amount of tissue in the lesion; however, cAMP reduced the graft size. White matter sparing at the lesion epicenter was not affected. Serotonergic input to the lumbosacral spinal cord was not affected by treatment, but the amount of serotonin immediately caudal to the lesion was reduced in the cAMP groups. Using telemetric monitoring of corpus spongiosum penis pressure we show that the cAMP groups regained the same number of micturitions per 24hours when compared to the AM group, however, the frequency of peak pressures was increased in these groups compared to the AM group. In contrast, the GRP groups had similar frequency of peak pressures compared to baseline and the AM group. Animals that received GRP cells regained the same number of erectile events per 24hours compared to baseline and the AM group. Since cAMP reduced the GRP transplant graft, and some modest positive effects were seen that could be attributable to both GRP or cAMP, future research is required to determine how cAMP affects survival, proliferation, and/or function of progenitor cells and how this is related to function. cAMP may not always be a desirable addition to a progenitor cell transplantation strategy after SCI.

Severity of Locomotor and Cardiovascular Derangements After Experimental High-Thoracic Spinal Cord Injury is Anesthesia Dependent in Rats

Journal of Neurotrauma. Aug, 2011  |  Pubmed ID: 21545262

Abstract Anesthetics affect outcomes from central nervous system (CNS) injuries differently. This is the first study to show how two commonly used anesthetics affect continuously recorded hemodynamic parameters and locomotor recovery during a 2-week period after two levels of contusion spinal cord injury (SCI) in rats. We hypothesized that the level of cardiovascular depression and recovery of locomotor function would be dependent upon the anesthetic used during SCI. Thirty-two adult female rats were subjected to a sham, 25-mm or 50-mm SCI at T3-4 under pentobarbital or isoflurane anesthesia. Mean arterial pressure (MAP) and heart rate (HR) were telemetrically recorded before, during, and after SCI. Locomotor function recovered best in the 25-mm-injured isoflurane-anesthetized animals. There was no significant difference in locomotor recovery between the 25-mm-injured pentobarbital-anesthetized animals and the 50-mm-injured isoflurane-anesthetized animals. White matter sparing and extent of intermediolateral cell column loss appeared larger in animals anesthetized with pentobarbital, but this was not significant. There were no differential effects of anesthetics on HR and MAP before SCI, but recovery from anesthesia was significantly slower in pentobarbital-anesthetized animals. At the time of SCI, MAP was acutely elevated in the pentobarbital-anesthetized animals, whereas MAP decreased in the isoflurane-anesthetized animals. Hypotension occurred in the pentobarbital-anesthetized groups and in the 50-mm-injured isoflurane-anesthetized group. In pentobarbital-anesthetized animals, SCI resulted in acute elevation of HR, although HR remained low. Return of HR to baseline was much slower in the pentobarbital-anesthetized animals. Severe SCI at T3 produced significant chronic tachycardia that was injury severity dependent. Although some laboratories monitor blood pressure, HR, and other physiological variables during surgery for SCI, inherently few have monitored cardiovascular function during recovery. This study shows that anesthetics affect hemodynamic parameters differently, which in turn can affect functional outcome measures. This supports the need for a careful evaluation of cardiovascular and other physiological measures in experimental models of SCI. Choice of anesthetic should be an important consideration in experimental designs and data analyses.

Tight Squeeze, Slow Burn: Inflammation and the Aetiology of Cervical Myelopathy

Brain : a Journal of Neurology. May, 2011  |  Pubmed ID: 21596766

Spinal Cord Injury: Taking a Detour to Recovery (Commentary on Schnell Et Al.)

The European Journal of Neuroscience. Oct, 2011  |  Pubmed ID: 21999581

Prenatal Repair of Myelomeningocele with Aligned Nanofibrous Scaffolds-a Pilot Study in Sheep

Journal of Pediatric Surgery. Dec, 2011  |  Pubmed ID: 22152865

Spinal cord damage in myelomeningocele (MMC) results from abnormal cord development and subsequent local trauma. Prenatal surgery prevents additional neural injury. However, existing damage is not reversed. Biodegradable nanofibrous scaffolds (NSs) promote regeneration of neural tissues. They mimic the microtopography of the extracellular matrix and guide tissue formation and organization. The purpose of this pilot study was to evaluate the practicality and safety of using biodegradable NS as a regenerative device in prenatal MMC repair.

A Grading System to Evaluate Objectively the Strength of Pre-clinical Data of Acute Neuroprotective Therapies for Clinical Translation in Spinal Cord Injury

Journal of Neurotrauma. Aug, 2011  |  Pubmed ID: 20507235

The past three decades have seen an explosion of research interest in spinal cord injury (SCI) and the development of hundreds of potential therapies that have demonstrated some promise in pre-clinical experimental animal models. A growing number of these treatments are seeking to be translated into human clinical trials. Conducting such a clinical trial, however, is extremely costly, not only for the time and money required to execute it, but also for the limited resources that will then no longer be available to evaluate other promising therapies. The decision about what therapies have sufficient pre-clinical evidence of efficacy to justify testing in humans is therefore of utmost importance. Here, we have developed a scoring system for objectively grading the body of pre-clinical literature on neuroprotective treatments for acute SCI. The components of the system include an evaluation of a number of factors that are thought to be important in considering the "robustness" of a therapy's efficacy, including the animal species and injury models that have been used to test it, the time window of efficacy, the types of functional improvements effected by it, and whether efficacy has been independently replicated. The selection of these factors was based on the results of a questionnaire that was performed within the SCI research community. A modified Delphi consensus-building exercise was then conducted with experts in pre-clinical SCI research to refine the criteria and decide upon how to score them. Finally, the grading system was applied to a series of potential neuroprotective treatments for acute SCI. This represents a systematic approach to developing an objective method of evaluating the extent to which the pre-clinical literature supports the translation of a particular experimental treatment into human trials.

Methods for Functional Assessment After C7 Spinal Cord Hemisection in the Rhesus Monkey

Neurorehabilitation and Neural Repair. Feb, 2012  |  Pubmed ID: 22331214

BACKGROUND: Reliable outcome measures are essential for preclinical modeling of spinal cord injury (SCI) in primates. MEASURES: need to be sensitive to both increases and decreases in function in order to demonstrate potential positive or negative effects of therapeutics. OBJECTIVES: To develop behavioral tests and analyses to assess recovery of function after SCI in the nonhuman primate. METHODS: In all, 24 male rhesus macaques were subjected to complete C7 lateral hemisection. The authors scored recovery of function in an open field and during hand tasks in a restraining chair. In addition, EMG analyses were performed in the open field, during hand tasks, and while animals walked on a treadmill. Both control and treated monkeys that received candidate therapeutics were included in this report to determine whether the behavioral assays were capable of detecting changes in function over a wide range of outcomes. RESULTS: The behavioral assays are shown to be sensitive to detecting a wide range of motor functional outcomes after cervical hemisection in the nonhuman primate. Population curves on recovery of function were similar across the different tasks; in general, the population recovers to about 50% of baseline performance on measures of forelimb function. CONCLUSIONS: The behavioral outcome measures that the authors developed in this preclinical nonhuman primate model of SCI can detect a broad range of motor recovery. A set of behavioral assays is an essential component of a model that will be used to test efficacies of translational candidate therapies for SCI.