Molecular evidence of repair and plasticity following spinal cord injury

Applying univariate vs. multivariate statistics to investigate therapeutic efficacy in (pre)clinical trials: A Monte Carlo simulation study on the example of a controlled preclinical neurotrauma trial

BACKGROUND

Small sample sizes combined with multiple correlated endpoints pose a major challenge in the statistical analysis of preclinical neurotrauma studies. The standard approach of applying univariate tests on individual response variables has the advantage of simplicity of interpretation, but it fails to account for the covariance/correlation in the data. In contrast, multivariate statistical techniques might more adequately capture the multi-dimensional pathophysiological pattern of neurotrauma and therefore provide increased sensitivity to detect treatment effects.

RESULTS

We systematically evaluated the performance of univariate ANOVA, Welch's ANOVA and linear mixed effects models versus the multivariate techniques, ANOVA on principal component scores and MANOVA tests by manipulating factors such as sample and effect size, normality and homogeneity of variance in computer simulations. Linear mixed effects models demonstrated the highest power when variance between groups was equal or variance ratio was 1:2. In contrast, Welch's ANOVA outperformed the remaining methods with extreme variance heterogeneity. However, power only reached acceptable levels of 80% in the case of large simulated effect sizes and at least 20 measurements per group or moderate effects with at least 40 replicates per group. In addition, we evaluated the capacity of the ordination techniques, principal component analysis (PCA), redundancy analysis (RDA), linear discriminant analysis (LDA), and partial least squares discriminant analysis (PLS-DA) to capture patterns of treatment effects without formal hypothesis testing. While LDA suffered from a high false positive rate due to multicollinearity, PCA, RDA, and PLS-DA were robust and PLS-DA outperformed PCA and RDA in capturing a true treatment effect pattern.

CONCLUSIONS

Multivariate tests do not provide an appreciable increase in power compared to univariate techniques to detect group differences in preclinical studies. However, PLS-DA seems to be a useful ordination technique to explore treatment effect patterns without formal hypothesis testing.

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

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

miR-155-5p Promotes Dorsal Root Ganglion Neuron Axonal Growth in an Inhibitory Microenvironment via the cAMP/PKA Pathway

Sensory dysfunction post spinal cord injury causes patients great distress. Sciatic nerve conditioning injury (SNCI) has been shown to restore sensory function after spinal cord dorsal column injury (SDCL); however, the underlying mechanism of this recovery remains unclear. We performed a microarray assay to determine the associated miRNAs that might regulate the process of SNCI promoting SDCL repair. In total, 13 miRNAs were identified according to our inclusion criteria, and RT-qPCR was used to verify the microarray results. Among the 13 miRNAs, the miR-155-5p levels were decreased at 9 h, 3 d, 7 d, 14 d, 28 d, 2 m and 3 m timepoints in the SDCL group, while the SNCI group had a smaller decrease. Thus, miR-155-5p was chosen for further study after a literature review and an analysis with the TargetScan online tool. Specifically, miR-155-5p targets PKI-α, and the expression pattern of PKI-α was opposite that of miR-155-5p in both the SDCL and SNCI groups. Interestingly, miR-155-5p could promote dorsal root ganglion (DRG) neuron axon growth via the cAMP/PKA pathway and in a TNF-α, IL-1β or MAG inhibitory microenvironment in vitro. Furthermore, miR-155-5p could regulate the cAMP/PKA pathway and promote sensory conduction function recovery post dorsal column injury as detected by NF-200 immunohistochemistry, somatosensory-evoked potentials, BBB scale and tape removal test. Collectively, our results demonstrated that miR-155-5p participates in the molecular mechanism by which SNCI promotes the repair of SDCL and that upregulated miR-155-5p can repair SDCL by enhancing DRG neuron axon growth via the cAMP/PKA pathway. These findings suggest a novel treatment target for spinal cord injury.

Role of APOE and IL18RAP gene polymorphisms in cervical spondylotic myelopathy in Indian population

Cervical spondylotic myelopathy (CSM) is a progressive degenerative spine disease. It is not clear why certain patients develop symptomatic myelopathy whereas others do not, even in the presence of radiographic features of cervical stenosis. Genetic predisposition has been suggested, supported by familial occurrence of CSM. In this study we explored the demographic and radiographic features of CSM in Indian population and studied the association between polymorphisms in interleukin18RAP and apo-lipoprotein genes in CSM. A total of 100 CSM patients and 100 healthy control subjects were included in this study. Genotyping of APOE (rs7412 and rs429358) and IL18RAP (rs1420106 and rs917997) gene polymorphisms was performed by Taqman allelic discrimination assay. Comparison of allelic frequencies, ε2 versus ε3 (OR = 4.4, 95%CI = 1.23-15.73, P = 0.002) and ε2 versus ε4 (OR = 6.67, 95%CI = 1.58-28.04, P = 0.009) showed a statistically significant association for the risk of CSM. There was no significant association between different genotypes with sex, T2 signal intensity change and Nurick grade. Only patients having multiple level cervical prolapsed intervertebral disc (PIVD) on MRI, had a higher proportion of the ε2 allele as compared to controls (p = <0.0001). No significant association was found between IL18RAP gene polymorphisms (rs1420106 and rs917997) with the risk of CSM. ε2 allele was associated with the risk of CSM in Indian population. There was no significant association between the two single nucleotide polymorphisms (SNPs) of IL18RAP gene with risk of CSM.

Folic Acid Modulates Matrix Metalloproteinase-9 Expression Following Spinal Cord Injury

Background

Treatment of spinal cord injury (SCI) induced neuropathic pain (NP) proves to be extremely clinically challenging as the mechanism behind SCINP is poorly understood. Matrix metalloproteinase (MMP) is largely responsible for the early disruption of the blood spinal cord barrier. This system initiates macrophage infiltration and degradation of myelin, which plays a pivotal role in how NP occurs. In a recent study, we demonstrated that folic acid (FA) treatment to cSCI rats reduced NP and improved functional recovery by repressing MMP-2 expression. We hypothesize that MMP-2 expression is suppressed because FA actively methylates the DNA sequence that encodes for the MMP-2 protein. However, modulation of MMP-2 expression for alleviation of NP is only pertinent to the mid- to late-phase of injury. Therefore, we need to explore alternate therapeutic methods to target the early- to mid-phase of injury to wholly alleviate NP.

Purpose

Furthering our previous findings on inhibiting MMP-2 expression by FA in mid- and late- phase following cSCI in rats, we hypothesized that FA will methylate and suppress MMP-9 expression during the early- phase, day 1, 3, 7 post cSCI and mid- phase (day 18 post cSCI), in comparison with MMP-2 expression during mid- and the late-phase of cSCI.

Methods

Adult male Sprague Dawley rats (250–270g) underwent cSCI, using a NYU impactor, with 12.5 gm/cm injury. The spinal cord-injured animals were treated intraperitoneally (i.p.) with a standardized dose of FA (80 μg/kg body weight) on day 1, 2, 3, prior to cSCI, followed by daily injection up to 14 or 17 days post-cSCI in different experiments. Animals were euthanized on day 1, 3, 7 post cSCI (early- phase), day 18 post cSCI (mid- phase), and day 42 post cSCI (late-phase) and the epicenter region of injured spinal cord were harvested for MMP-9 and MMP-2 expression analysis by Western blots technique.

Results

i) During early-phase on day 1, 3, and 7, the quantitation displayed no statistical significance in MMP-9 expression, between water- and FA- injected rats. ii) On day 18 post-cSCI, FA significantly modulates the expression of MMP-9 (p = 0.043) iii) Comparing results with MMP-2 expression and inhibition, FA significantly modulates the expression of MMP-2 on day 18 post cSCI (FA- and water-injected rats (p = 0.003). iv) In addition, FA significantly modulates the expression of MMP-2 on day 42 post-cSCI comparing FA- and water- injected rat groups (p = 0.034).

Conclusion

We report that FA administration results in alleviating cSCI-induced NP by inhibiting MMP-9 in the proposed mid- phase of cSCI. However, FA administration resulted in MMP-2 decline during both mid- through late- phase following cSCI. Our study elucidates a new phase of cSCI, the mid-phase. We conclude that further investigation on discovering and quantifying the nature of the mid- phase of SCI injury is needed.

Apolipoprotein E Deficiency Exacerbates Spinal Cord Injury in Mice: Inflammatory Response and Oxidative Stress Mediated by NF-κB Signaling Pathway

Spinal cord injury (SCI) is a severe neurological trauma that involves complex pathological processes. Inflammatory response and oxidative stress are prevalent during the second injury and can influence the functional recovery of SCI. Specially, Apolipoprotein E (APOE) induces neuronal repair and nerve regeneration, and the deficiency of Apoe impairs spinal cord-blood-barrier and reduces functional recovery after SCI. However, the mechanism by which Apoe mediates signaling pathways of inflammatory response and oxidative stress in SCI remains largely elusive. This study was designed to investigate the signaling pathways that regulate Apoe deficiency-dependent inflammatory response and oxidative stress in the acute stage of SCI. In the present study, Apoe^−/− mice retarded functional recovery and had a larger lesion size when compared to wild-type mice after SCI. Moreover, deficiency of Apoe induced an exaggerated inflammatory response by increasing expression of interleukin-6 (IL-6) and interleukin-1β (IL-1β), and increased oxidative stress by reducing expression of Nrf2 and HO-1. Furthermore, lack of Apoe promoted neuronal apoptosis and decreased neuronal numbers in the anterior horn of the spinal cord after SCI. Mechanistically, we found that the absence of Apoe increased inflammation and oxidative stress through activation of NF-κB after SCI. In contrast, an inhibitor of nuclear factor-κB (NF-κB; Pyrrolidine dithiocarbamate) alleviates these changes. Collectively, these results indicate that a critical role for activation of NF-κB in regulating Apoe-deficiency dependent inflammation and oxidative stress is detrimental to recovery after SCI.

Folic Acid Modulates Matrix Metalloproteinase-2 Expression, Alleviates Neuropathic Pain, and Improves Functional Recovery in Spinal Cord-Injured Rats

BACKGROUND

The molecular underpinnings of spinal cord injury (SCI) associated with neuropathic pain (NP) are unknown. Recent studies have demonstrated that matrix metalloproteinases (MMPs) such as MMP2 play a critical role in inducing NP following SCI. Promoter methylation of MMPs is known to suppress their transcription and reduce NP. In this context, it has been shown in rodents that folic acid (FA), an FDA approved dietary supplement and key methyl donor in the central nervous system (CNS), increases axonal regeneration and repair of injured CNS in part via methylation.

PURPOSE

Based on above observations, in this study, we test whether FA could decrease MMP2 expression and thereby decrease SCI-induced NP.

METHODS

Sprague-Dawley male rats weighing 250-270 g received contusion spinal cord injuries (cSCIs) with a custom spinal cord impactor device that drops a 10 g weight from a height of 12.5 mm. The injured rats received either i.p. injections of FA (80 µg/kg) or water (control) 3 days prior and 17 days post-cSCI (mid phase) or for 3 days pre-cSCI and 14 days post-cSCI ending on the 42nd day of cSCI (late phase). The functional neurological deficits due to cSCI were then assessed by Basso, Beattie, and Bresnahan (BBB) scores either on post-impaction days 0 through 18 post-cSCI (mid phase) or on days 0, 2, 7, 14, 21, 28, 35, and 42 (late phase). Baseline measurements were taken the day before starting treatments. Thermal hyperalgesia (TH) testing for pain was performed on 4 days pre-cSCI (baseline data) and on days 18, 21, 28, 35, and 42 post-cSCI. Following TH testing, animals were euthanized and spinal cords harvested for MMP-2 expression analysis.

RESULT

The FA-treated groups showed higher BBB scores during mid phase (day 18) and in late phase (day 42) of injury compared to controls, suggesting enhanced functional recovery. There is a transient decline in TH in animals from the FA-treated group compared to controls when tested on days 18, 21, 28, and 35, indicative of a decrease in NP. However, when tested 25 days after stopping FA administration on day 42 of cSCI, no significant difference in TH was observed between FA-treated and control animals. Western blot analysis of the injured spinal cord from FA-treated animals showed significant decline in MMP2 expression compared to spinal cord samples from water-treated controls.

CONCLUSION

Together, these data suggest that FA could alleviate NP and improve functional recovery post-SCI, possibly by reducing the expression of MMP2. Further studies will open up a novel and easy natural therapy, ideal for clinical translation with minimal side effects, for managing SCI-induced NP. Such studies might also throw light on a possible epigenetic mechanism in FA-induced recovery after SCI.

Role of Matrix Metalloproteinases 2 in Spinal Cord Injury-Induced Neuropathic Pain

Neuropathic pain (NP) affects approximately 4 million people in the United States with spinal cord injury (SCI) being a common cause. Matrix metalloproteinases (MMPs) play an integral role in mediating inflammatory responses, cellular signaling, cell migration, extracellular matrix degradation and tissue remodeling and repair. As such, they are major components in the pathogenesis of secondary injury within the central nervous system. Other gene regulatory pathways, specifically MAPK/extracellular signaling-regulated kinase (ERK) and Wnt/β-catenin, are also believed to participate in secondary injury likely intersect. The study aims to examine the MMP-2 signaling pathway associated with ERK and Wnt/β-catenin activity during contusion SCI (cSCI)-induced NP in a rat model. This is an experimental study investigating the implication of MMP-2 in SCI-induced NP and its association with the cellular and molecular changes in the interactions between extracellular signaling kinase and β-catenin. Adult Sprague-Dawley rats received cSCI injury by NYU impactor by dropping 10 g weight from a height of 12.5 mm. Locomotor functional recovery of injured rats was measured on post cSCI day 1, and weekly thereafter for 6 weeks using Basso, Beattie and Bresnahan scores. Thermal hyperalgesia (TH) testing was performed on days 21, 28, 35 and 42 post cSCI. The expression and/or activity of MMP-2, β-catenin and ERK were studied following harvest of spinal cord tissues between 3 and 6 weeks post cSCI. All experiments were funded by the department of Neurological Surgery at the University of Wisconsin, School of Medicine and Public Health having no conflict of interest. MMP-2 and β-catenin expression were elevated and gradually increased from days 21 to 42 compared to sham-operated rats and injured rats that did not exhibit TH. The expression of phosphorylated ERK (phospho-ERK) increased on day 21 but returned to baseline levels on day 42 whereas total ERK levels remained relatively unchanged and constant. Chronic NP is associated with changes in the expression of MMP-2, β-catenin and ERK. Our data suggest that the transient upregulation of phospho-ERK is involved in the initial upregulation of both β-catenin and MMP-2 following cSCI-induced NP states.

Spinal cord injury induced neuropathic pain: Molecular targets and therapeutic approaches

Neuropathic pain, especially that resulting from spinal cord injury, is a tremendous clinical challenge. A myriad of biological changes have been implicated in producing these pain states including cellular interactions, extracellular proteins, ion channel expression, and epigenetic influences. Physiological consequences of these changes are varied and include functional deficits and pain responses. Developing therapies that effectively address the cause of these symptoms require a deeper knowledge of alterations in the molecular pathways. Matrix metalloproteinases and tissue inhibitors of metalloproteinases are two promising therapeutic targets. Matrix metalloproteinases interact with and influence many of the studied pain pathways. Gene expression of ion channels and inflammatory mediators clearly contributes to neuropathic pain. Localized and time dependent targeting of these proteins could alleviate and even prevent neuropathic pain from developing. Current therapeutic options for neuropathic pain are limited primarily to analgesics targeting the opioid pathway. Therapies directed at molecular targets are highly desirable and in early stages of development. These include transplantation of exogenously engineered cell populations and targeted gene manipulation. This review describes specific molecular targets amenable to therapeutic intervention using currently available delivery systems.

Pathogenesis of spinal cord injury induced edema and neuropathic pain: expression of multiple isoforms of wnk1

Background

Neuropathic pain (NP) is a common occurrence following spinal cord injury (SCI). Identification of specific molecular pathways that are involved in pain syndromes has become a major priority in current SCI research. We have investigated the role of a cation-dependent chloride transporter, Cl-regulatory protein Na⁺-K⁺-Cl^- 1 (NKCC1), phosphorylation profile of NKCC1 and its specific involvement in neuropathic pain following contusion SCI (cSCI) using a rat model. Administration of the NKCC1 inhibitor bumetanide (BU) increases the mean hindpaw withdrawal latency time (WLT), thermal hyperalgesia (TH) following cSCI. These results demonstrate implication of NKCC1 co-transporter and BUin SCI-induced neuropathic pain. The with-no-lysine (K)–1 (WNK1) kinase has been shown to be an important regulator of NKCC1 phosphorylation in many systems, including nocioception. Mutations in a neuronal-specific exon of WNK1 (HSN2) was identified in patients that have hereditary sensory neuropathy type II (HSANII) also implicates WNK1 in nocioception, such that these patients have loss of perception to pain, touch and heat. In our ongoing research we proposed two studies utilizing our contusion SCI (cSCI) NP model of rat.

Purpose

Study 1 aimed at NKCC1 expression and activity is up-regulated following cSCI in the early edema and chronic neuropathic pain phases. Study 2 aimed at identifying the expression profile of alternatively spliced WNK1 isoforms in animals exhibiting thermal hyperalgesia (TH) following cSCI.

Methods

Adult male Sprague Dawley rats (275–300 g) following laminectomy received cSCI at T9 with the NYU impactor-device II by dropping 10 g weight from the height of 12.5 mm. Control rats obtained laminectomy but no impaction. Following injury, functional recovery was assessed by BBB locomotor scores on day 1, 7, 14, 21, 35, and 42 and development of thermal hyperalgesia on day 21, 28, 35, and 42 day of injury by monitoring hind paw withdraw latency time (WLT) in seconds compared with the baseline data before injury.

Results

Increased NKCC1 may explain observed increase in magnetic resonance imaging (MRI) T2, exhibiting NKCC1 localization in neurons. This data supports NKCC1’s role in the pathogenesis of acute and chronic phases of injury, namely spinal cord edema and chronic phase neuropathic pain. NKCC1 dependent chloride influx requires the phosphorylation at specific residues. Probing for the HSN2 exon of WNK1 reveals two key findings: i) the HSN2 exon is found in alternatively spliced neuronal isoforms found at 250 kDa and 230 kDa; ii) the 250 kDa isoform is found only in tissue that is injured.

Conclusions

This data implicates the NKCC1/WNK1/WNK1HSN2 involvement in post-injury response that contributes to the development of neuropathic pain. Targeting this system may have therapeutic benefit.

Metabolomics uncovers dietary omega-3 fatty acid-derived metabolites implicated in anti-nociceptive responses after experimental spinal cord injury

Chronic neuropathic pain is a frequent comorbidity following spinal cord injury (SCI) and often fails to respond to conventional pain management strategies. Preventive administration of docosahexaenoic acid (DHA) or the consumption of a diet rich in omega-3 polyunsaturated fatty acids (O3PUFAs) confers potent prophylaxis against SCI and improves functional recovery. The present study examines whether this novel dietary strategy provides significant antinociceptive benefits in rats experiencing SCI-induced pain. Rats were fed control chow or chow enriched with O3PUFAs for 8weeks before being subjected to sham or cord contusion surgeries, continuing the same diets after surgery for another 8 more weeks. The paw sensitivity to noxious heat was quantified for at least 8weeks post-SCI using the Hargreaves test. We found that SCI rats consuming the preventive O3PUFA-enriched diet exhibited a significant reduction in thermal hyperalgesia compared to those consuming the normal diet. Functional neurometabolomic profiling revealed a distinctive deregulation in the metabolism of endocannabinoids (eCB) and related N-acyl ethanolamines (NAEs) at 8weeks post-SCI. We found that O3PUFAs consumption led to a robust accumulation of novel NAE precursors, including the glycerophospho-containing docosahexaenoyl ethanolamine (DHEA), docosapentaenoyl ethanolamine (DPEA), and eicosapentaenoyl ethanolamine (EPEA). The tissue levels of these metabolites were significantly correlated with the antihyperalgesic phenotype. In addition, rats consuming the O3PUFA-rich diet showed reduced sprouting of nociceptive fibers containing CGRP and dorsal horn neuron p38 mitogen-activated protein kinase (MAPK) expression, well-established biomarkers of pain. The spinal cord levels of inositols were positively correlated with thermal hyperalgesia, supporting their role as biomarkers of chronic neuropathic pain. Notably, the O3PUFA-rich dietary intervention reduced the levels of these metabolites. Collectively, these results demonstrate the prophylactic value of dietary O3PUFA against SCI-mediated chronic pain.

A hydrogen sulfide-releasing cyclooxygenase inhibitor markedly accelerates recovery from experimental spinal cord injury

Spinal cord trauma causes loss of motor function that is in part due to the ensuing inflammatory response. Hydrogen sulfide (H2S) is a potent, endogenous anti-inflammatory and neuroprotective substance that has been explored for use in the design of novel nonsteroidal anti-inflammatory drugs. In the current study, we evaluated the potential beneficial effects of ATB-346 [2-(6-methoxynapthalen- 2-yl)-propionic acid 4-thiocarbamoyl-phenyl ester], an H2S-releasing derivative of naproxen, in a murine model of spinal cord injury (SCI). SCI was induced in mice by spinal cord compression, produced through the application of vascular clips to the dura via a T5 to T8 laminectomy. ATB-346, naproxen (both at 30 μmol/kg), or vehicle was orally administered to the mice 1 and 6 h after SCI and once daily thereafter for 10 d. Motor function [Basso Mouse Scale (BMS) of locomotion] improved gradually in the mice treated with naproxen. However, those treated with ATB-346 exhibited a significantly more rapid and sustained recovery of motor function, achieving greater than double the increase in locomotion score of the naproxen group by the 10th day of treatment. ATB-346 also significantly reduced the severity of inflammation (proinflammatory cytokines, apoptosis of neural tissue, and nitrosative stress) that characterized the secondary effects of SCI. Again, the effects of ATB-346 were superior to those of naproxen for several parameters. These results showed marked beneficial effects of an H2S-releasing derivative of naproxen in an animal model of SCI, significantly enhancing recovery of motor function, possibly by reducing the secondary inflammation and tissue injury that characterizes this model. The combination of inhibition of cyclooxygenase and delivery of H2S may offer a promising alternative to existing therapies for traumatic injury.

Dietary omega-3 polyunsaturated fatty acids improve the neurolipidome and restore the DHA status while promoting functional recovery after experimental spinal cord injury

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) confer multiple health benefits and decrease the risk of neurological disorders. Studies are needed, however, to identify promising cellular targets and to assess their prophylactic value against neurodegeneration. The present study (1) examined the efficacy of a preventive diet enriched with ω-3 PUFAs to reduce dysfunction in a well-established spinal cord injury (SCI) animal model and (2) used a novel metabolomics data analysis to identify potential neurolipidomic targets. Rats were fed with either control chow or chow enriched with ω-3 PUFAs (750 mg/kg/day) for 8 weeks before being subjected to a sham or a contusion SCI operation. We report new evidence showing that rats subjected to SCI after being pre-treated with a diet enriched with ω-3 PUFAs exhibit significantly better functional outcomes. Pre-treated animals exhibited lower sensory deficits, autonomic bladder recovery, and early improvements in locomotion that persisted for at least 8 weeks after trauma. We found that SCI triggers a robust alteration in the cord PUFA neurolipidome, which was characterized by a marked docosahexaenoic acid (DHA) deficiency. This DHA deficiency was associated with dysfunction and corrected with the ω-3 PUFA-enriched diet. Multivariate data analyses revealed that the spinal cord of animals consuming the ω-3 PUFA-enriched diet had a fundamentally distinct neurolipidome, particularly increasing the levels of essential and long chain ω-3 fatty acids and lysolipids at the expense of ω-6 fatty acids and its metabolites. Altogether, dietary ω-3 PUFAs prophylaxis confers resiliency to SCI mediated, at least in part, by generating a neuroprotective and restorative neurolipidome.

Apolipoprotein E Mimetic Promotes Functional and Histological Recovery in Lysolecithin-Induced Spinal Cord Demyelination in Mice

Objective

Considering demyelination is the pathological hallmark of multiple sclerosis (MS), reducing demyelination and/or promoting remyelination is a practical therapeutic strategy to improve functional recovery for MS. An apolipoprotein E (apoE)-mimetic peptide COG112 has previously demonstrated therapeutic efficacy on functional and histological recovery in a mouse experimental autoimmune encephalomyelitis (EAE) model of human MS. In the current study, we further investigated whether COG112 promotes remyelination and improves functional recovery in lysolecithin induced focal demyelination in the white matter of spinal cord in mice.

Methods

A focal demyelination model was created by stereotaxically injecting lysolecithin into the bilateral ventrolateral funiculus (VLF) of T8 and T9 mouse spinal cords. Immediately after lysolecithin injection mice were treated with COG112, prefix peptide control or vehicle control for 21 days. The locomotor function of the mice was measured by the beam walking test and Basso Mouse Scale (BMS) assessment. The nerve transmission of the VLF of mice was assessed in vivo by transcranial magnetic motor evoked potentials (tcMMEPs). The histological changes were also examined by by eriochrome cyanine staining, immunohistochemistry staining and electron microscopy (EM) method.

Results

The area of demyelination in the spinal cord was significantly reduced in the COG112 group. EM examination showed that treatment with COG112 increased the thickness of myelin sheaths and the numbers of surviving axons in the lesion epicenter. Locomotor function was improved in COG112 treated animals when measured by the beam walking test and BMS assessment compared to controls. TcMMEPs also demonstrated the COG112-mediated enhancement of amplitude of evoked responses.

Conclusion

The apoE-mimetic COG112 demonstrates a favorable combination of activities in suppressing inflammatory response, mitigating demyelination and in promoting remyelination and associated functional recovery in animal model of CNS demyelination. These data support that apoE-mimetic strategy may represent a promising therapy for MS and other demyelination disorders.

Metabolite profiles correlate closely with neurobehavioral function in experimental spinal cord injury in rats

Traumatic spinal cord injury (SCI) results in direct physical damage and the generation of local factors contributing to secondary pathogenesis. Untargeted metabolomic profiling was used to uncover metabolic changes and to identify relationships between metabolites and neurobehavioral functions in the spinal cord after injury in rats. In the early metabolic phase, neuronal signaling, stress, and inflammation-associated metabolites were strongly altered. A dynamic inflammatory response consisting of elevated levels of prostaglandin E2 and palmitoyl ethanolamide as well as pro- and anti-inflammatory polyunsaturated fatty acids was observed. N-acetyl-aspartyl-glutamate (NAAG) and N-acetyl-aspartate (NAA) were significantly decreased possibly reflecting neuronal cell death. A second metabolic phase was also seen, consistent with membrane remodeling and antioxidant defense response. These metabolomic changes were consistent with the pathology and progression of SCI. Several metabolites, including NAA, NAAG, and the ω-3 fatty acids docosapentaenoate and docosahexaenoate correlated greatly with the established Basso, Beattie and Bresnahan locomotive score (BBB score). Our findings suggest the possibility of a biochemical basis for BBB score and illustrate that metabolites may correlate with neurobehavior. In particular the NAA level in the spinal cord might provide a meaningful biomarker that could help to determine the degree of injury severity and prognosticate neurologic recovery.

Spinal cord trauma and the molecular point of no return

A mechanical trauma to the spinal cord can be followed by the development of irreversible and progressive neurodegeneration, as opposed to a temporary or partially reversible neurological damage. An increasing body of experimental and clinical evidence from humans and animal models indicates that spinal cord injury may set in motion the development of disabling and at times fatal neuromuscular disorders, whose occurrence is not normally associated with any major environmental event. This outcome appears to be dependent on the co-occurrence of a particular form of mechanical stress and of a genetically-determined vulnerability. This increased vulnerability to spinal cord injury may depend on a change of the nature and of the timing of activation of a number of neuroprotective and neurodestructive molecular signals in the injured cord. Among the main determinants, we could mention an altered homeostasis of lipids and neurofilaments, an earlier inflammatory response and the failure of the damaged tissue to rein in oxidative damage and apoptotic cell death. These changes could force injured tissue beyond a point of no return and precipitate an irreversible neurodegenerative process. A better knowledge of the molecular signals activated in a state of increased vulnerability to trauma can inform future treatment strategies and the prediction of the neurological outcome after spinal cord injury.

Molecular target discovery for neural repair in the functional genomics era

A comprehensive understanding of the molecular pathways activated by traumatic neural injury is of major importance for the development of treatments for spinal cord injury (SCI). High-throughput gene expression profiling is a powerful approach to reveal genome-wide changes in gene expression during a specific biological process. Microarray analysis of injured nerves or neurons would ideally generate new hypotheses concerning the progression or deregulation of injury- and repair-related biological processes, such as neural scar formation and axon regeneration. These hypotheses should subsequently be tested experimentally and would eventually provide the molecular substrates for the development of novel therapeutics. Over the last decade, this approach has elucidated numerous extrinsic (mostly neural scar-associated) as well as neuron-intrinsic genes that are regulated following an injury. To date, the main challenge is to translate the observed injury-induced gene expression changes into a mechanistic framework to understand their functional implications. To achieve this, research on neural repair will have to adopt the conceptual advances and analytical tools provided by the functional genomics and systems biology revolution. Based on progress made in bioinformatics, high-throughput and high-content functional cellular screening, and in vivo gene transfer technology, we propose a multistep "roadmap" that provides an integrated strategy for molecular target discovery for repair of the injured spinal cord.

Syndromics: a bioinformatics approach for neurotrauma research

Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational "syndrome" produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call "syndromics", which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings.

Cannabinoid subtype-2 receptors modulate the antihyperalgesic effect of WIN 55,212-2 in rats with neuropathic spinal cord injury pain

BACKGROUND CONTEXT

There is increasing evidence for a role of the cannabinoid (CB) system in the development of neuropathic pain (NP) after spinal cord injury (SCI). The nonspecific CB₁ and CB₂ receptor agonists, WIN 55, 212-2 (WIN), have previously been shown to alleviate both mechanical and thermal hyperalgesia (TH) after peripheral nerve injury.

PURPOSE

The present study was designed to identify the CB receptors involved in the antihyperalgesic effect of WIN by using selective antagonists for CB₁ and CB₂ receptors.

STUDY DESIGN

This is an in vivo and behavioral study using a moderate T9 contusion SCI. After injury, TH of the hind paws was measured on postinjury days 21 through 42.

METHODS

Sprague-Dawley rats underwent a contusion SCI using the Multicenter Animal Spinal Cord Injury Study (MASCIS) weight-drop impactor, which induced a moderate T9 SCI. Only animals showing consistent plantar stepping and consistent forelimb and hind limb coordination (Basso, Beattie, and Bresnahan score=15) were tested for TH. Animals exhibiting decreased withdrawal latency time, indicating TH, on or before Day 42, were selected for pharmacological intervention. Animals not exhibiting TH did not receive pharmacological intervention and were sacrificed. Rats underwent hind paw testing before any drug administration (after injury), 45 minutes after selective CB antagonist (AM 251 or AM 630) administration (postantagonist) and again 45 minutes after WIN administration (post-WIN). There were a total of seven treatment groups: saline vehicle control; Dimethyl sulfoxide (DMSO) vehicle control; low-dose WIN (0.2 mg/kg); and high-dose WIN (2.0 mg/kg); AM 251 (3 mg/kg) and AM 630 (1 mg/kg) were given subcutaneously in a total volume of 0.5 mL. Followed by intraperitoneal injection of WIN after each antagonist, sham-operated rats repeated pharmacological intervention used with treatment Groups 5 and 6.

RESULTS

Thermal hyperalgesia was significantly ameliorated in a dose-dependent manner with systemically administered WIN. Cannabinoid receptor Type 1 antagonist AM 251 pretreatment did not affect the antihyperalgesic effect of WIN. By contrast, pretreatment with the CB₂ receptor antagonist AM 630 significantly attenuated the effect of WIN.

CONCLUSION

Taken together, these results suggest a role of the CB₂ receptor in modulating SCI-induced TH. Selective activation of the CB₂ receptor could potentially lead to analgesic effects on NP while avoiding psychotropic side effects in patients with SCI.

Effect of apolipoprotein E genotype on the outcome after anterior cervical decompression and fusion in patients with cervical spondylotic myelopathy

Object

The authors examined a possible association between apolipoprotein E (APOE) gene polymorphism and the outcome after anterior microsurgical decompression in patients with cervical spondylotic myelopathy (CSM).

Methods

The authors conducted a prospective study of 60 consecutive patients (40 men, 20 women) with CSM who underwent anterior microsurgical decompression. The patients ranged in age from 26 to 86 years (mean 61.5 ± 14.6 years). Neurological deficits were classified according to the modified Japanese Orthopaedic Association Scale. Mean follow-up was 18.8 ± 4.6 months and APOE genotyping was carried out by isolation of DNA from venous blood samples. The APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and polyacrylamide gel electrophoresis of digested fragments. Categorical variables were analyzed with the chi-square test, continuous data with the Mann-Whitney U-test, and for multiple groups with the Kruskal-Wallis H-test. A backward stepwise binary logistic regression analysis was performed to determine the effect of APOE in a multivariate model.

Results

Of the 60 patients with CSM, 35 (58.3%) improved and 25 (41.7%) did not improve or suffered deterioration (no-improvement group). In the improvement group 5 patients (8.3%) possessed the ε4 allele compared with 16 patients (26.7%) in the no-improvement group (p = 0.002, OR 3.3, 95% CI 1.7–6.1). In a multivariate model, the occurrence of the ε4 allele was a significant independent predictor for no improvement after anterior decompression and fusion (p = 0.004, OR 8.6, 95% CI 5.1–20.6).

Conclusions

The results of this study show that APOE gene polymorphism influences the short-term outcome of CSM patients after surgical decompressive and stabilizing therapy in the way that the presence of the APOE ε4 allele is an independent predictor for a no improvement. The presence of APOE may explain in part the different responses to operative therapies in patients with cervical myelopathy.

The role of cation-dependent chloride transporters in neuropathic pain following spinal cord injury

BACKGROUND

Altered Cl- homeostasis and GABAergic function are associated with nociceptive input hypersensitivity. This study investigated the role of two major intracellular Cl- regulatory proteins, Na+-K+-Cl- cotransporter 1 (NKCC1) and K+-Cl- cotransporter 2 (KCC2), in neuropathic pain following spinal cord injury (SCI).

RESULTS

Sprague-Dawley rats underwent a contusive SCI at T9 using the MASCIS impactor. The rats developed hyperalgesia between days 21 and 42 post-SCI. Thermal hyperalgesia (TH) was determined by a decrease in hindpaw thermal withdrawal latency time (WLT) between days 21 and 42 post-SCI. Rats with TH were then treated with either vehicle (saline containing 0.25% NaOH) or NKCC1 inhibitor bumetanide (BU, 30 mg/kg, i.p.) in vehicle. TH was then re-measured at 1 h post-injection. Administration of BU significantly increased the mean WLT in rats (p < 0.05). The group administered with the vehicle alone showed no anti-hyperalgesic effects. Moreover, an increase in NKCC1 protein expression occurred in the lesion epicenter of the spinal cord during day 2-14 post-SCI and peaked on day 14 post-SCI (p < 0.05). Concurrently, a down-regulation of KCC2 protein was detected during day 2-14 post-SCI. The rats with TH exhibited a sustained loss of KCC2 protein during post-SCI days 21-42. No significant changes of these proteins were detected in the rostral region of the spinal cord.

CONCLUSION

Taken together, expression of NKCC1 and KCC2 proteins was differentially altered following SCI. The anti-hyperalgesic effect of NKCC1 inhibition suggests that normal or elevated NKCC1 function and loss of KCC2 function play a role in the development and maintenance of SCI-induced neuropathic pain.

Apolipoprotein E gene polymorphism and the risk of cervical myelopathy in patients with chronic spinal cord compression

STUDY DESIGN

Prospective evaluation of apolipoprotein E (APOE) genotypes in 106 consecutive patients with stenosis of the cervical spinal canal.

OBJECTIVE

To determine the association between cervical spondylotic myelopathy (CSM) in patients with chronic spinal cord compression and the APOE genotype.

SUMMARY OF BACKGROUND DATA

The APOE allele epsilon 4 is a risk factor for the occurrence, progression, and poor outcome in several neurologic diseases. Information of the association between APOE genotype and CSM in the literature are lacking so far.

METHODS

One hundred six consecutive patients with chronic cervical spinal cord compression due to stenosis of the spinal canal were evaluated prospectively. APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and sodiumdodecylsulfate poyacrylamide gel electrophoresis (SDS PAGE) of digested fragments. Clinical and radiologic variables evaluated were age, occurrence of CSM, duration of symptoms, number of affected segments, and diameter of spinal canal of most affected segment. Univariate association between variables was tested. A backward stepwise method was used to construct multivariate logistic regression models in relation to the occurrence of CSM as dependent variable.

RESULTS

The following distribution of APOE genotypes was found: epsilon 2 epsilon 2 3 patients (2.8%), epsilon 2 epsilon 3 9 patients (8.5%), epsilon 2 epsilon 4 1 patient (0.9), epsilon 3 epsilon 3 67 patients (63.2%), epsilon 3 epsilon 4 24 patients (22.6%), epsilon 4 epsilon 4 2 patients (1.9%). Univariate analysis showed that patients with chronic spinal cord compression and homo- or heterozygous allele epsilon 4 are more likely to develop CSM than patients without allele epsilon 4 (65.0% vs. 35.0%, P < 0008; OR 3.5; 95% CI 1.3-9.8). This effect remained significant in a binary logistic regression model adjusted to other known risk factors for CSM. Inclusion of the variable homo- or heterozygous epsilon 4 allele led to an increased goodness of fit of the model compared with the model without epsilon 4. CONCLUSION.: This study supports the hypothesis that the APOE epsilon 4 allele increases the risk of CSM in patients with chronic cervical spinal cord compression; however, a larger prospective population-based study is needed to answer this question definitively.

Changes in PDGF expression in spared dorsal root ganglia and associated spinal dorsal horns in cats subjected to partial dorsal root ganglionectomy

Changes in the platelet derived growth factor (PDGF) in the spared dorsal root ganglia (DRG) and associated spinal dorsal horns were evaluated in cats subjected to unilateral removal of L1-L5 and L7-S2 DRG, sparing the L6 DRG. The number of PDGF immunopositive neurons and protein expression decreased significantly in the spared DRG and associated dorsal horns of the L3 and L6 cord segments at 3 days post-operation (dpo). It bottomed to the lowest level at 7 dpo in the DRG, then returned to the control level at 14 dpo; while in the L6 dorsal horn, it rapidly increased at 7 dpo and exceeded the control level at 14 dpo. This showed a significant upregulation in the spared DRG and associated spinal dorsal horns, especially in the L6 cord segment following a transient decrease. Meanwhile, a significant upregulation of PDGF mRNA was also seen in L6 DRG and L3 and L6 dorsal horns at 3 dpo. The upregulation of the endogenous PDGF in the said structures indicated a potential role of this factor in spinal cord plasticity after partial dorsal root ganglia removal in cats.

Antihyperalgesic effects of vanilloid-1 and bradykinin-1 receptor antagonists following spinal cord injury in rats

Object

The authors previously discovered that genes for the bradykinin-1 (B1) receptor and the transient receptor potential vanilloid subtype 1 (TRPV1) were overexpressed in animals exhibiting thermal hyperalgesia (TH) following spinal cord injury (SCI). They now report the effect of TRPV1 (AMG9810) and B1 (Lys-[Des-Arg9, Leu8]-bradykinin) antagonists on TH in animals following SCI.

Methods

The rats were subjected to contusion SCI and then divided into groups in which TH did or did not develop. The animals from both groups were given either AMG9810, Lys-(Des-Arg9, Leu8)-bradykinin, or the drug-specific vehicle (control groups). Animals were tested for TH preinjury and at regular intervals after SCI by using the hindlimb withdrawal latency test.

Conclusions

The administration of AMG9810 likely improves TH as a result of a generalized analgesic effect, whereas the effect of Lys-(Des-Arg9, Leu8)-bradykinin appears more specific to the reversal of TH. This information has potential usefulness in the development of treatment strategies for post-SCI neuropathic pain.

Changes in spinal cord injury-induced gene expression in rat are strain-dependent

BACKGROUND AND CONTEXT

The functional recovery of animals subject to experimental spinal cord injury (SCI) is dependent on the injury model as well as the species and strain of animal used. Previous studies have shown differences in rates and degree of recovery between rats of different strains.

PURPOSE

We sought to explore the hypothesis that differences in gene expression are associated with differences in functional recovery.

STUDY DESIGN/SETTING

Laboratory study involving cohorts of three different strains of rat.

METHODS

We used the Impactor device to produce identical spinal cord contusion injuries in groups of Long Evans, Sprague-Dawley, and Lewis rats (10 each). The functional recovery of animals was assessed using the Basso, Beattie, and Bresnahan rating scale. Six weeks after injury, rats were killed and the spinal cords were harvested for deoxyribonucleic acid microarray analysis. Changes in gene expression compared with intraspecies controls (3 each) were assessed at the region of injury and at a rostral segment of the spinal cord. Selected genes were also studied with real-time polymerase chain reaction.

RESULTS

We found that different strains tended to exhibit different patterns of functional recovery. There were differences between the strains in terms of gene expression.

CONCLUSIONS

These results emphasize the importance of testing novel therapies for SCI in a variety of animal species before introduction into human trials. Further research into the influence of several gene products on functional recovery is needed.

Introduction of the MASH1 gene into mouse embryonic stem cells leads to differentiation of motoneuron precursors lacking Nogo receptor expression that can be applicable for transplantation to spinal cord injury

ES cells transfected with the MASH1 gene yielded purified spinal motoneuron precursors expressing HB9 and Islet1. The cells lacked the expression of Nogo receptor that was of great advantage for axon growth after transplantation to an injured spinal cord. After transplantation, mice with the complete transection of spinal cord exhibited excellent improvement of the motor functions. Electrophysiological assessment confirmed the quantitative recovery of motor-evoked potential in the transplanted spinal cord. In the grafted spinal cord, gliosis was inhibited and Nogo receptor expression was scarcely detected. The transplanted cells labeled with GFP showed extensive outgrowth of axons positive for neurofilament middle chain, connected to each other and expressed Synaptophysin, Lim1/2 and Islet1. Thus, the in vivo differentiation into mature spinal motoneurons and the reconstitution of neuronal pathways were suggested. The grafted cell population was purified for neurons and was free from teratoma development. These therapeutic strategies may contribute to a potent treatment for spinal cord injury in future.

Microarray analysis of gene expression patterns in adult spinal motoneurons after different types of axonal injuries

Three experimental models of axonal injuries in adult rat spinal motoneurons were established to investigate changes of gene expression in response to such injuries. We took advantage of cDNA microarray analysis to determine the differential expression of genes in injured motoneurons following distal axotomy or root avulsion in the absence or presence of BDNF. The major finding was that, in response to proximal axonal injury (avulsion), expression of genes that are known to facilitate neuronal survival and axonal regeneration (e.g., IGFRII, PI3K, IGFBP-6, GSTs, GalR2) were down-regulated; but following treatment with BDNF they were up-regulated. In addition, the expression of genes known to be involved in apoptosis and DNA damage (e.g., ANX5, TS, ALR) were down-regulated in BDNF-treated animals with avulsion. Furthermore, many functional families of genes previously shown to play roles in the pathophysiology of axonal injury, including SNAP-25A, SV2B, Ras-related ras3a/4b, ERK1/2, 14-3-3 proteins, proteasome proteins, oncogenes, GAP-43, and NMDAR1, were altered after either distal axotomy or avulsion injury. Some of the changes in gene expression, including Lim-2, FRAG1, GlaR2, GSTs, ALR, TS, ANX3/5, and nhe1/2, are first reported here in injured motoneurons. The differential expression of genes identified by the expression arrays was confirmed by gene-specific RT-PCR for eight genes (GAP-43, IGFR II, Lim-2, MIF, NDAP1, TS, PCC3, and FRAG1) and by in situ hybridization for Lim-2. These results suggest that abnormal regulation of particular biochemical pathways may induce motoneuron death after ventral root avulsion in adult animals. This study presents an approach for selecting specific genes and their products that may be involved in motoneuron degeneration following axonal injuries.

Intraspinal application of endothelin results in focal ischemic injury of spinal gray matter and restricts the differentiation of engrafted neural stem cells

Previous data have shown that pluripotent stem cells engrafted into the contused spinal cord differentiate only along an astrocytic lineage. The unknown restrictive cues appear to be quite rigid as even neuronal-restricted precursors fail to differentiate to the mature potential they exhibit in vitro after similar grafting into the contused spinal cord. It has been hypothesized that this potent lineage restriction is, in part, the result of the significant loss of both gray and white matter observed following spinal contusion, which elicits a massive acute inflammatory response and is manifested chronically by dramatic cystic cavitation. To evaluate the gray matter component, we developed a clinically relevant model of focal gray matter ischemic injury using the potent vasoconstrictor endothelin (ET-1) and characterized the differentiation of pluripotent stem cells transplanted into this atraumatic vascular SCI. Results demonstrate that low dose ET-1 microinjection into cervical spinal gray matter results in an inflammatory response that is temporally comparable to that observed following traumatic SCI, as well as chronic gray matter loss, but without significant cystic cavitation or white matter degeneration. However, despite the preservation of host spinal parenchyma, no elaboration of neuronal phenotypes was observed from engrafted stem or precursor cells. These results suggest that a common pathologic component responsible for this lineage restriction exists between contusive SCI and ET-1 mediated focal ischemic SCI.

Genetic approaches to autonomic dysreflexia

Autonomic dysreflexia is a potentially life-threatening condition in which episodic hypertension occurs after injuries above the mid-thoracic segments of the spinal cord. Despite the seriousness of this condition, little is known of the molecular mechanisms that lead to its development. The completed sequencing of the mouse genome, its dense genetic map, and the large repository of engineered and spontaneous mouse mutants, make the mouse an ideal model organism in which to study the molecular mechanisms underlying autonomic dysreflexia. We subjected two wild-type strains of mice, 129Sv and C57BL/6, and one spontaneous mouse mutant, Wallerian degeneration slow (Wld s), to spinal cord transection and clip-compression injury. We found that the incidence of autonomic dysreflexia is greatly reduced, compared to spinal cord-transected wild-type mice, in Wld s mice after both injury paradigms and in 129Sv and C57BL/6 that have undergone the clip-compression injury. We also found that the amplitude of the dysreflexic response was greater in cord-compressed 129Sv than in C57BL/6 mice. These results implicate axonal degeneration as an important source of signals that trigger the development of autonomic dysreflexia and are discussed in the context of mouse genetics, interstrain differences and possible molecular mechanisms underlying autonomic dysreflexia after spinal cord injury.

Real-time quantitative PCR analysis of temporal-spatial alterations in gene expression after spinal cord contusion

Rat spinal cord contusion injury models the histopathology associated with much clinical spinal cord injury (SCI). Studies on altered gene expression after SCI in these models may identify therapeutic targets for reducing secondary injury after the initial trauma and/or enhancing recovery processes. However, complex spatial and temporal alterations after injury could complicate interpretation of changes in gene expression. To test this hypothesis, we selected six genes and studied their temporal and spatial patterns of expression at 1 h, 1, 3 and 7 days after a standardized spinal cord contusion produced by a weight drop device (10 g x 25 mm at T8). Real-time RT-PCR using TaqMan probes was employed to quantify mRNA for proteolipid protein, glyceraldehyde-3-phosphate dehydrogenase, glial fibrillary acidic protein, nestin, and the GluR2 and NR1 subunits of glutamate receptors. We found widely different temporal and spatial patterns of altered gene expression after SCI, including instances of opposing up- and down-regulation at different locations in tissue immediately adjacent to the injury site. We conclude that greater use of the reliable and extremely sensitive technique of quantitative real-time PCR for regional tissue analysis is important for understanding the altered gene expression that occurs after CNS trauma.

Gene expression profiling of experimental traumatic spinal cord injury as a function of distance from impact site and injury severity

Changes in gene expression contribute to pathophysiological alterations following spinal cord injury (SCI). We examined gene expression over time (4 h, 24 h, 7 days) at the impact site, as well as rostral and caudal regions, following mild, moderate, or severe contusion SCI in rats. High-density oligonucleotide microarrays were used that included approximately 27,000 genes/ESTs (Affymetrix RG-U34; A, B and C arrays), together with multiple analyses (MAS 5.0, dChip). Alterations after mild injury were relatively rapid (4 and 24 h), whereas they were delayed and prolonged after severe injury (24 h and 7 days). The number and magnitude of gene expression changes were greatest at the injury site after moderate injury and increased in rostral and caudal regions as a function of injury severity. Sham surgery resulted in expression changes that were similar to mild injury, suggesting the importance of using time-linked surgical controls as well as naive animals for these kinds of studies. Expression of many genes and ESTs was altered; these were classified functionally based on ontology. Overall representation of these functional classes varied with distance from the site of injury and injury severity, as did the individual genes that contributed to each functional class. Different clustering approaches were used to identify changes in neuronal-specific genes and several transcription factors that have not previously been associated with SCI. This study represents the most comprehensive evaluation of gene expression changes after SCI to date. The results underscore the power of microarray approaches to reveal global genomic responses as well as changes in particular gene clusters and/or families that may be important in the secondary injury cascade.

Issues about the fMRI of the human spinal cord

Noninvasive functional studies on human spinal cord by means of magnetic resonance imaging (MRI) are gaining attention because of the promising applications in the study of healthy and injured central nervous system. The findings obtained are generally consistent with the anatomic knowledge based on invasive methods, but the origin and specificity of functional contrast is still debated. In this paper, a review of current knowledge and major issues about functional MRI (fMRI) in the human spinal cord is presented, with emphasis on the main methodological and technical problems and on forthcoming applications as clinical tool.