Increased oxidative-related mechanisms in the spinal cord injury in old rats

Moving CNS axon growth and regeneration research into human model systems

Axon regeneration is limited in the adult mammalian central nervous system (CNS) due to both intrinsic and extrinsic factors. Rodent studies have shown that developmental age can drive differences in intrinsic axon growth ability, such that embryonic rodent CNS neurons extend long axons while postnatal and adult CNS neurons do not. In recent decades, scientists have identified several intrinsic developmental regulators in rodents that modulate growth. However, whether this developmentally programmed decline in CNS axon growth is conserved in humans is not yet known. Until recently, there have been limited human neuronal model systems, and even fewer age-specific human models. Human in vitro models range from pluripotent stem cell-derived neurons to directly reprogrammed (transdifferentiated) neurons derived from human somatic cells. In this review, we discuss the advantages and disadvantages of each system, and how studying axon growth in human neurons can provide species-specific knowledge in the field of CNS axon regeneration with the goal of bridging basic science studies to clinical trials. Additionally, with the increased availability and quality of 'omics datasets of human cortical tissue across development and lifespan, scientists can mine these datasets for developmentally regulated pathways and genes. As there has been little research performed in human neurons to study modulators of axon growth, here we provide a summary of approaches to begin to shift the field of CNS axon growth and regeneration into human model systems to uncover novel drivers of axon growth.

Spinal cord injury leads to more neurodegeneration in the hippocampus of aged male rats compared to young rats

Although the disruptive effects of spinal cord injury (SCI) on the hippocampus have been confirmed in some animal studies, no study has investigated its retrograde manifestations in the hippocampus of aged subjects. Herein, we compared the aged rats with young ones 3 weeks after the induction of SCI (Groups: Sham.Young, SCI.Young, Sham.Aged, SCI.Aged). The locomotion, hippocampal apoptosis, hippocampal rhythms (Delta, Theta, Beta, Gamma) max frequency (Max.rf) and power, hippocampal neurogenesis, and hippocampal receptors (NMDA, GABA A, Muscarinic1/M1), which are important in the generation of rhythms and neurogenesis, were compared in aged rats in contrast to young rats. At the end of the third week, the number of apoptotic (Tunel⁺) cells in the hippocampus (CA1, DG) of SCI animals was significantly higher compared to the sham animals, and also, it was significantly higher in the SCI.Aged group compared to SCI.Young group. Moreover, the rate of neurogenesis (DCX⁺, BrdU⁺ cells) and expression of M1 and NMDA receptors were significantly lower in the SCI.Aged group compared to SCI.Young group. The power and Max.fr of all rhythms were significantly lower in SCI groups compared to sham groups. Despite the decrease in the power of rhythms in the SCI.Aged group compared to SCI.Young group, there was no significant difference between them, and in terms of Max.fr index, only the Max.fr of theta and beta rhythms were significantly lower in the SCI.Aged group compared to SCI.Young group. This study showed that SCI could cause more neurodegeneration in the hippocampus of aged animals compared to young animals.

Improving translatability of spinal cord injury research by including age as a demographic variable

Pre-clinical and clinical spinal cord injury (SCI) studies differ in study design, particularly in the demographic characteristics of the chosen population. In clinical study design, criteria such as such as motor scores, neurological level, and severity of injury are often key determinants for participant inclusion. Further, demographic variables in clinical trials often include individuals from a wide age range and typically include both sexes, albeit historically most cases of SCI occur in males. In contrast, pre-clinical SCI models predominately utilize young adult rodents and typically use only females. While it is often not feasible to power SCI clinical trials to test multi-variable designs such as contrasting different ages, recent pre-clinical findings in SCI animal models have emphasized the importance of considering age as a biological variable prior to human experiments. Emerging pre-clinical data have identified case examples of treatments that diverge in efficacy across different demographic variables and have elucidated several age-dependent effects in SCI. The extent to which these differing or diverging treatment responses manifest clinically can not only complicate statistical findings and trial interpretations but also may be predictive of worse outcomes in select clinical populations. This review highlights recent literature including age as a biological variable in pre-clinical studies and articulates the results with respect to implications for clinical trials. Based on emerging unpredictable treatment outcomes in older rodents, we argue for the importance of including age as a biological variable in pre-clinical animal models prior to clinical testing. We believe that careful analyses of how age interacts with SCI treatments and pathophysiology will help guide clinical trial design and may improve both the safety and outcomes of such important efforts.

Reprogramming neurons for regeneration: The fountain of youth

Neurons in the central nervous system (CNS) are terminally differentiated cells that gradually lose their ability to support regeneration during maturation due to changes in transcriptomic and chromatin landscape. Similar transcriptomic changes also occur during development when stem cells differentiate into different types of somatic cells. Importantly, differentiated cells can be reprogrammed back to induced pluripotent stems cells (iPSCs) via global epigenetic remodeling by combined overexpression of pluripotent reprogramming factors, including Oct4, Sox2, Klf4, c-Myc, Nanog, and/or Lin28. Moreover, recent findings showed that many proneural transcription factors were able to convert non-neural somatic cells into neurons bypassing the pluripotent stage via direct reprogramming. Interestingly, many of these factors have recently been identified as key regulators of CNS neural regeneration. Recent studies indicated that these factors could rejuvenate mature CNS neurons back to a younger state through cellular state reprogramming, thus favoring regeneration. Here we will review some recent findings regarding the roles of genetic cellular state reprogramming in regulation of neural regeneration and explore the potential underlying molecular mechanisms. Moreover, by using newly emerging techniques, such as multiomics sequencing with big data analysis and Crispr-based gene editing, we will discuss future research directions focusing on better revealing cellular state reprogramming-induced remodeling of chromatin landscape and potential translational application.

Modeling chronic cervical spinal cord injury in aged rats for cell therapy studies

With an expanding elderly population, an increasing number of older adults will experience spinal cord injury (SCI) and might be candidates for cell-based therapies, yet there is a paucity of research in this age group. The objective of the present study was to analyze how aged rats tolerate behavioral testing, surgical procedures, post-operative complications, intra-spinal cell transplantation and immunosuppression, and to examine the effectiveness of human iPSC-derived Neural Progenitor Cells (IMR90-hiPSC-NPCs) in a model of SCI. We performed behavioral tests in rats before and after inducing cervical hemi-contusions at C4 level with a fourth-generation Ohio State University Injury Device. Four weeks later, we injected IMR90-hiPSC-NPCs in animals that were immunosuppressed by daily cyclosporine injection. Four weeks after injection we analyzed locomotor behavior and mortality, and histologically assessed the survival of transplanted human NPCs. As rats aged, their success at completing behavioral tests decreased. In addition, we observed high mortality rates during behavioral training (41.2%), after cervical injury (63.2%) and after cell injection (50%). Histological analysis revealed that injected cells survived and remained at and around the grafted site and did not cause tumors. No locomotor improvement was observed in animals four weeks after IMR90-hiPSC-NPC transplantation. Our results show that elderly rats are highly vulnerable to interventions, and thus large groups of animals must be initially established to study the potential efficacy of cell-based therapies in age-related chronic myelopathies.

Designing neuroreparative strategies using aged regenerating animal models

In our ever-aging world population, the risk of age-related neuropathies has been increasing, representing both a social and economic burden to society. Since the ability to regenerate in the adult mammalian central nervous system is very limited, brain trauma and neurodegeneration are often permanent. As a consequence, novel scientific challenges have emerged and many research efforts currently focus on triggering repair in the damaged or diseased brain. Nevertheless, stimulating neuroregeneration remains ambitious. Even though important discoveries have been made over the past decades, they did not translate into a therapy yet. Actually, this is not surprising; while these disorders mainly manifest in aged individuals, most of the research is being performed in young animal models. Aging of neurons and their environment, however, greatly affects the central nervous system and its capacity to repair. This review provides a detailed overview of the impact of aging on central nervous system functioning and regeneration potential, both in non-regenerating and spontaneously regenerating animal models. Additionally, we highlight the need for aging animal models with regenerative capacities in the search for neuroreparative strategies.

An In Vivo Compression Model of Spinal Cord Injury

Animal spinal cord injury (SCI) models have proven highly useful for investigating the mechanisms involved in the injury process and evaluating the effectiveness of experimental therapeutic interventions. Over the last years, substantial improvements have been made in producing consistent and reproducible animal SCI models. Different SCI models have been developed to address the mechanism of injury, being divided into contusion, compression, distraction, dislocation, transection, or chemical models. The method described here is a mouse compression model of SCI that, in many respects, faithfully reproduces SCI in man.

Enhanced Functional Recovery from Spinal Cord Injury in Aged Mice after Stem Cell Transplantation through HGF Induction

The number of elderly patients with spinal cord injury (SCI) is increasing worldwide, representing a serious burden for both the affected patients and the community. Previous studies have demonstrated that neural stem cell (NSC) transplantation is an effective treatment for SCI in young animals. Here we show that NSC transplantation is as effective in aged mice as it is in young mice, even though aged mice exhibit more severe neurological deficits after SCI. NSCs grafted into aged mice exhibited better survival than those grafted into young mice. Furthermore, we show that the neurotrophic factor HGF plays a key role in the enhanced functional recovery after NSC transplantation observed in aged mice with SCI. The unexpected results of the present study suggest that NSC transplantation is a potential therapeutic modality for SCI, even in elderly patients.

The age factor in axonal repair after spinal cord injury: A focus on neuron-intrinsic mechanisms

Age is an important consideration for recovery and repair after spinal cord injury. Spinal cord injury is increasingly affecting the middle-aged and aging populations. Despite rapid progress in research to promote axonal regeneration and repair, our understanding of how age can modulate this repair is rather limited. In this review, we discuss the literature supporting the notion of an age-dependent decline in axonal growth after central nervous system (CNS) injury. While both neuron-intrinsic and extrinsic factors are involved in the control of axon growth after injury, here we focus on possible intrinsic mechanisms for this age-dependent decline.

Age increases reactive oxygen species production in macrophages and potentiates oxidative damage after spinal cord injury

Age potentiates neurodegeneration and impairs recovery from spinal cord injury (SCI). Previously, we observed that age alters the balance of destructive (M1) and protective (M2) macrophages; however, the age-related pathophysiology in SCI is poorly understood. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) contributes to reactive oxygen species (ROS)-mediated damage and macrophage activation in neurotrauma. Further, NOX and ROS increase with central nervous system age. Here, we found significantly higher ROS generation in 14 versus 4-month-old (MO) mice after contusion SCI. Notably, NOX2 increased in 14 MO ROS-producing macrophages suggesting that macrophages and NOX contribute to SCI oxidative stress. Indicators of lipid peroxidation, a downstream cytotoxic effect of ROS accumulation, were significantly higher in 14 versus 4 MO SCI mice. We also detected a higher percentage of ROS-producing M2 (Arginase-1-positive) macrophages in 14 versus 4 MO mice, a previously unreported SCI phenotype, and increased M1 (CD16/32-positive) macrophages with age. Thus, NOX and ROS are age-related mediators of SCI pathophysiology and normally protective M2 macrophages may potentiate secondary injury through ROS generation in the aged injured spinal cord.

Perturbed cholesterol homeostasis in aging spinal cord

The spinal cord is vital for the processing of sensorimotor information and for its propagation to and from both the brain and the periphery. Spinal cord function is affected by aging, however, the mechanisms involved are not well-understood. To characterize molecular mechanisms of spinal cord aging, microarray analyses of gene expression were performed on cervical spinal cords of aging rats. Of the metabolic and signaling pathways affected, cholesterol-associated pathways were the most comprehensively altered, including significant downregulation of cholesterol synthesis-related genes and upregulation of cholesterol transport and metabolism genes. Paradoxically, a significant increase in total cholesterol content was observed-likely associated with cholesterol ester accumulation. To investigate potential mechanisms for the perturbed cholesterol homeostasis, we quantified the expression of myelin and neuroinflammation-associated genes and proteins. Although there was minimal change in myelin-related expression, there was an increase in phagocytic microglial and astrogliosis markers, particularly in the white matter. Together, these results suggest that perturbed cholesterol homeostasis, possibly as a result of increased inflammatory activation in spinal cord white matter, may contribute to impaired spinal cord function with aging.

Comparison of catalase immunoreactivity in the hippocampus between young, adult and aged mice and rats

Catalase (CAT) is an important antioxidant enzyme and is crucial in modulating synaptic plasticity in the brain. In this study, CAT expression as well as neuronal distribution was compared in the hippocampus among young, adult and aged mice and rats. Male ICR mice and Sprague Dawley rats were used at postnatal month (PM) 1, PM 6 and PM 24 as the young, adult and aged groups, respectively (n=14/group). CAT expression was examined by immunohistochemistry and western blot analysis. In addition, neuronal distribution was examined by NeuN immunohistochemistry. In the present study, the mean number of NeuN-immunoreactive neurons was marginally decreased in mouse and rat hippocampi during aging, although this change was not identified to be significantly different. However, CAT immunoreactivity was significantly increased in pyramidal and granule neurons in the adult mouse and rat hippocampi and was significantly decreased in the aged mouse and rat hippocampi compared with that in the young animals. CAT protein levels in the hippocampus were also lowest in the aged mouse and rat hippocampus. These results indicate that CAT expression is significantly decreased in the hippocampi of aged animals and decreased CAT expression may be closely associated with aging.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Promotes Neuronal Regeneration after Spinal Cord Injury

Spinal cord injury (SCI) stimulates activation of astrocytes and infiltration of immune cells at the lesion site; however, the mechanism that promotes the birth of new neurons is still under debate. Neuronal regeneration is restricted after spinal cord injury, but can be stimulated by experimental intervention. Previously we demonstrated that treatment co-ultramicronized palmitoylethanolamide and luteolin, namely co-ultraPEALut, reduced inflammation. The present study was designed to explore the neuroregenerative properties of co-ultraPEALut in an estabished murine model of SCI. A vascular clip was applied to the spinal cord dura at T5-T8 to provoke injury. Mice were treated with co-ultraPEALut (1 mg/kg, intraperitoneally) daily for 72 h after SCI. Co-ultraPEALut increased the numbers of both bromodeoxyuridine-positive nuclei and doublecortin-immunoreactive cells in the spinal cord of injured mice. To correlate neuronal development with synaptic plasticity a Golgi method was employed to analyze dendritic spine density. Co-ultraPEALut administration stimulated expression of the neurotrophic factors brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, nerve growth factor, and neurotrophin-3. These findings show a prominent effect of co-ultraPEALut administration in the management of survival and differentiation of new neurons and spine maturation, and may represent a therapeutic treatment for spinal cord and other traumatic diseases.

Characterization of recovery, repair, and inflammatory processes following contusion spinal cord injury in old female rats: is age a limitation?

Background

Although the incidence of spinal cord injury (SCI) is steadily rising in the elderly human population, few studies have investigated the effect of age in rodent models. Here, we investigated the effect of age in female rats on spontaneous recovery and repair after SCI. Young (3 months) and aged (18 months) female rats received a moderate contusion SCI at T9. Behavioral recovery was assessed, and immunohistocemical and stereological analyses performed.

Results

Aged rats demonstrated greater locomotor deficits compared to young, beginning at 7 days post-injury (dpi) and lasting through at least 28 dpi. Unbiased stereological analyses revealed a selective increase in percent lesion area and early (2 dpi) apoptotic cell death caudal to the injury epicenter in aged versus young rats. One potential mechanism for these differences in lesion pathogenesis is the inflammatory response; we therefore assessed humoral and cellular innate immune responses. No differences in either acute or chronic serum complement activity, or acute neutrophil infiltration, were observed between age groups. However, the number of microglia/macrophages present at the injury epicenter was increased by 50% in aged animals versus young.

Conclusions

These data suggest that age affects recovery of locomotor function, lesion pathology, and microglia/macrophage response following SCI.

Neuroprotective effect of the proanthocyanidin-rich fraction in experimental model of spinal cord injury

OBJECTIVES

In this study, we evaluated the effect of the proanthocyanidins-rich fraction (PRF) obtained from Croton celtidifolius bark in an experimental animal model of spinal cord injury and cell death induced by glutamate.

METHODS

Experiments were conducted using adult male Wistar rats (10 weeks old and weighing 270-300g). Experimental groups were randomly allocated into the following groups: spinal cord injury (SCI) + vehicle group: rats were subjected to SCI plus intraperitoneal administration of vehicle (saline 10 ml/kg); SCI + PRF: rats were subjected to SCI plus intraperitoneal administration of PRF (10 mg/kg) at 1 and 6 h after injury and sham operated.

KEY FINDINGS

The treatment with the proanthocyanidin-rich fraction significantly improved not only motor recovery and grip force but also H2 O2 or glutamate-induced cell death and reactive oxygen species generation induced by glutamate in dorsal root ganglion cells. In this study we demonstrate that the neuroprotective effect triggered by the proanthocyanidins-rich fraction appears to be mediated in part by the inhibition of N-methyl-D-aspartate-type glutamate receptors.

CONCLUSIONS

Taken together, our results demonstrate that PRF treatment ameliorates spinal cord injury and glutamatergic excitotoxicity and could have a potential therapeutic use.

A new co-ultramicronized composite including palmitoylethanolamide and luteolin to prevent neuroinflammation in spinal cord injury

Background

It has recently been demonstrated that palmitoylethanolamide (PEA), an endogenous lipid amide belonging to the N-acylethanolamine family, exerts neuroprotection in central nervous system (CNS) pathologies. In recent studies, we have demonstrated that treatment with PEA significantly reduced inflammatory secondary events associated with spinal cord injury (SCI). Since oxidative stress is considered to play an important role in neuroinflammatory disorders, in the present work we studied a new composite, a formulation including PEA and the antioxidant compound luteolin (Lut), subjected to an ultramicronization process, co-ultraPEALut. We investigated the effect of co-ultraPEALut (in the respective fixed doses of 10:1 in mass) in both an ex vivo organotypic spinal cord culture model and an in vivo model of SCI.

Methods

For the organotypic cultures, spinal cords were prepared from mice at postnatal day 6 and were cut into transverse slices of 400 μm thickness to generate the lumbar organotypic slice cultures. After 7 days of culturing, the slices were mechanically injured onto the center of the slice and the co-ultraPEALut was applied at different concentrations (0.00009, 0.0009 and 0.009 g/l) 1 hour before damage. For in vivo studies, SCI was induced in mice through spinal cord compression by the application of vascular clips (force of 24 g) to the dura via a four-level T5 to T8 laminectomy, and co-ultraPEALut (1 mg/kg ip) was administered at 1 and 6 hours after SCI. At 24 hours after SCI, mice were sacrificed and the spinal cords were collected for further evaluation. Additional animals were treated similarly and sacrificed 10 days after SCI.

Results

Pretreatment with co-ultraPEALut significantly reduced cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression in a concentration-dependent manner, restored neuronal nitric oxide synthase (nNOS) expression at all three tested concentrations, and protected cells by cell death (MTT assay) in spinal cord organotypic cultures. Moreover, we demonstrated in vivo that co-ultraPEALut 1 mg/kg reduced the severity of trauma induced by compression and improved the motor activity evaluated at 10 days post-injury.

Conclusion

The present study demonstrates that the protective effect of PEA on SCI-associated neuroinflammation could be improved by co-ultramicronization with Lut possibly due to its antioxidant properties.

The role of mTOR signaling pathway in spinal cord injury

The mammalian target of rapamycin (mTOR) signaling pathway plays an important role in multiple cellular functions, such as cell metabolism, proliferation and survival. Many previous studies have shown that mTOR regulates both neuroprotective and neuroregenerative functions in trauma and various diseases in the central nervous system (CNS). Recently, we reported that inhibition of mTOR using rapamycin reduces neural tissue damage and locomotor impairment after spinal cord injury (SCI) in mice. Our results demonstrated that the administration of rapamycin at four hours after injury significantly increases the activity of autophagy and reduces neuronal loss and cell death in the injured spinal cord. Furthermore, rapamycin-treated mice show significantly better locomotor function in the hindlimbs following SCI than vehicle-treated mice. These findings indicate that the inhibition of mTOR signaling using rapamycin during the acute phase of SCI produces neuroprotective effects and reduces secondary damage at lesion sites. However, the role of mTOR signaling in injured spinal cords has not yet been fully elucidated. Various functions are regulated by mTOR signaling in the CNS, and multiple pathophysiological processes occur following SCI. Here, we discuss several unresolved issues and review the evidence from related articles regarding the role and mechanisms of the mTOR signaling pathway in neuroprotection and neuroregeneration after SCI.

Chemokines in CNS injury and repair

Recruitment of inflammatory cells is known to drive the secondary damage cascades that are common to injuries of the central nervous system (CNS). Cell activation and infiltration to the injury site is orchestrated by changes in the expression of chemokines, the chemoattractive cytokines. Reducing the numbers of recruited inflammatory cells by the blocking of the action of chemokines has turned out be a promising approach to diminish neuroinflammation and to improve tissue preservation and neovascularization. In addition, several chemokines have been shown to be essential for stem/progenitor cell attraction, their survival, differentiation and cytokine production. Thus, chemokines might indirectly participate in remyelination, neovascularization and neuroprotection, which are important prerequisites for CNS repair after trauma. Moreover, CXCL12 promotes neurite outgrowth in the presence of growth inhibitory CNS myelin and enhances axonal sprouting after spinal cord injury (SCI). Here, we review current knowledge about the exciting functions of chemokines in CNS trauma, including SCI, traumatic brain injury and stroke. We identify common principles of chemokine action and discuss the potentials and challenges of therapeutic interventions with chemokines.

Age-related differences in cellular and molecular profiles of inflammatory responses after spinal cord injury

Previous experimental and clinical studies have suggested that the behavioral and pathological outcomes of spinal cord injury (SCI) are affected by the individual's age at the time of injury. However, the underlying mechanism responsible for these differences remains elusive because it is difficult to match injuries of similar severities between young and adult animals due to differences in the sizes of their respective spinal cords. In this study, the spinal cord size-matched young (4-week-old) and adult (10-week-old) mice were compared to evaluate their locomotor functions and inflammatory cellular/molecular responses after standardized contusion SCI. During the acute phase of SCI, young mice showed better functional recovery and lower pro-inflammatory cytokines/chemokines compared to adult mice. Flow-cytometric analysis revealed that the time courses of leukocyte infiltration were comparable between both groups, while the number of infiltrating neutrophils significantly decreased from 6 h after SCI in young mice. By combining flow-cytometric isolation and gene expression analysis of each inflammatory cell fraction, we found that microglial cells immediately initiate the production of several cytokines in response to SCI, which serve as major sources of IL-6, TNFa, and CXCL1 in injured spinal cord. Interestingly, the secretion of pro-inflammatory cytokines/chemokines but not anti-inflammatory cytokines by microglia was significantly lower in young mice compared to that in adult mice at 3 h after SCI, which will be attributed to the attenuation of the subsequent neutrophil infiltration. These results highlight age-related differences in pro-inflammatory properties of microglial cells that contribute to the amplification of detrimental inflammatory responses after SCI.

Differential effect of aging on axon sprouting and regenerative growth in spinal cord injury

The demographics of acute spinal cord injury (SCI) are changing with an increased incidence in older age. However, the influence of aging on the regenerative growth potential of central nervous system (CNS) axons following SCI is not known. We investigated axonal sprouting along with the efficiency of the infusion of the stromal cell-derived growth factor-1 (SDF-1/CXCL12) and regenerative growth along with the anti-scarring treatment (AST) in young (2-3 months) and geriatric (22-28 months) female rats following SCI. AST included local injection of iron chelator (2,2'-dipyridine-5,5'-dicarboxylic acid) and 8-bromo-cyclic adenosine monophosphate solution into the lesion core. Axon outgrowth was investigated by immunohistological methods at 5 weeks after a partial dorsal hemisection at thoracic level T8. We found that aging significantly reduces spontaneous axon sprouting of corticospinal (CST), serotonergic (5-HT) raphespinal and catecholaminergic (TH) coerulospinal tracts in distinct regions of the spinal cord rostral to the lesion. However, impairment of axon sprouting could be markedly attenuated in geriatric animals by local infusion of SDF-1. Unexpectedly and in contrast to rostral sprouting, aging does not diminish the regenerative growth capacity of 5-HT-, TH- and calcitonin gene-related peptide (CGRP)-immunoreactive axons at 5 weeks after SCI. Moreover, 5-HT and TH axons maintain the ability to react upon AST with significantly enhanced regeneration in aged animals. These data are the first to demonstrate, that old age compromises axonal plasticity, but not regenerative growth, after SCI in a fiber tract-specific manner. Furthermore, AST and SDF-1 infusions remain efficient, which implicates that therapy in elderly patients is still feasible.

Effects of advanced age on the morphometry and degenerative state of the cervical spine in a rat model

Aging causes changes in the geometry of the human cervical spine that may influence the tissue response to applied loads. Rat models are often used to study spinal cord injuries (SCI) and have the potential to enhance our understanding of the effect of age on SCI. The goal of this study was to characterize the morphometry and degenerative state of the cervical spine in Fisher 344 rats, and to determine the influence of age on these variables. Fifteen rats were split into three age groups: young adult (3 months of age), aged (12-18 months) and geriatric (30 months). Following tissue harvest we used a μCT scanner to image the cervical and upper thoracic spine from each specimen. Analysis software was used to measure variables including canal pinch diameter (the most rostral point on the dorsal aspect of a vertebral body to the most caudal aspect of the lamina on the immediately rostral vertebra), vertebral canal depth, width, and area, vertebral body height, depth, width, and area, and intervertebral disc thickness. Orthopaedic surgeons used midsagittal images to rate the degenerative state of the intervertebral discs. For all measures except disc thickness there was a significant increase (mean (SD) = 15.0 (9.7)%) for the aged compared to young specimens (P < 0.05). There were significant differences between the aged and geriatric specimens for only vertebral body depth (P = 0.016) and area (P = 0.020). Intervertebral disc degeneration was significantly greater on the ventral aspect of the spinal column (P < 0.001), with a trend toward increased degeneration in the geriatric specimens (P = 0.069). The results suggest that age-related morphometric differences may need to be accounted for in experimental aging models of SCI in rats.

Comparison of immunoreactivities in 4-HNE and superoxide dismutases in the cervical and the lumbar spinal cord between adult and aged dogs

Aging shows slowly progressive changes and is associated with many functional and morphological changes in the central nervous system. The accumulation of reactive oxygen species causes age-related deterioration in neuronal function and contributes to the increase of disease susceptibility during normal aging. In the present study, we compared the neuronal distribution and immunoreactivities of 4-hydroxy-2E-nonenal (4-HNE, end product of lipid peroxidation), and superoxide dismutase 1 (SOD1) and SOD2 in the cervical and lumbar spinal cord between adult (2-3 years) and aged (10-12 years) dogs. No significant change in neuronal morphology was observed after cresyl violet staining. The number of NeuN (a marker for neurons)-immunoreactive neurons was not significantly changed in the aged group compare to the adult group. In addition, we could not find Fluoro-Jade B (a marker for degenerating neurons) positive cells in both the adult and aged dogs. However, numbers of 4-HNE-, SOD1- and SOD2-immunoreactive cells were significantly increased in both the cervical and lumbar spinal cord of the aged dog: The increase rates of these cells in the aged spinal cord were higher in the lumbar level than the cervical level. In brief, 4-HNE, SOD1 and SOD2 levels are much increased in the aged spinal cord compared to the adult spinal cord.

Treatment with green tea extract attenuates secondary inflammatory response in an experimental model of spinal cord trauma

In this study, we evaluated the effect of green tea extract (that was administered 25 mg/kg intraperitoneal at 1 and 6 h after injury) in experimental animal model of spinal cord injury. The spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5–T8 laminectomy. Spinal cord injury in mice resulted in severe trauma characterised by oedema, neutrophilic infiltration and apoptosis. Also, immunohistochemical examination demonstrated a marked increase in immune reactivity for nitrotyrosine. All parameters of inflammation were attenuated by green tea extract. The degree of spinal cord inflammation, nitrotyrosine, poli (ADP-ribosio) synthetase (PARS) and neutrophilic infiltration was markedly reduced. Green tea extract significantly ameliorated the recovery of limb function. Values shown are mean ± SE mean of ten mice for each group. *p < 0.01 versus sham, °p < 0.01 versus spinal cord injury. Taken together, our results clearly demonstrate that green tea extract treatment ameliorates spinal cord injury oxidative stress.

Myelin pathogenesis and functional deficits following SCI are age-associated

Most spinal cord injuries (SCI) occur in young adults. In the past few decades however, the average age at time of SCI and the percentage of injuries in persons over the age of 60 have increased. Studies have shown that there is an age-associated delay in the rate of remyelination following toxin-induced demyelination of the spinal cord, suggesting that there may be an age-associated difference in regenerative efficiency. Here we examine for the first time locomotor recovery, bladder recovery, and myelin pathology in young (3 months), aged (12 months), and geriatric (24 months) female rats following contusion SCI. Our assessments indicate that aged and geriatric rats have a delayed rate of locomotor recovery following contusion SCI as compared to young rats. Additionally, aged and geriatric rats have significantly slower bladder recovery as compared to young rats. Examination of myelin pathology reveals that aged and geriatric rats have significantly greater area of pathology and amount of demyelination, as well as significantly less remyelination as compared to young rats following contusion SCI. These data are the first to indicate that there is an age-associated decline in the rate and extent of both locomotor and bladder recovery following contusion SCI, and that age adversely affects the degree of general pathology, demyelination, and remyelination that accompanies contusion SCI.

Strapping the spinal cord: an innovative experimental model of CNS injury in rats

Experimental models of spinal cord (SC) lesion are essential for understanding a few of the primary and secondary mechanisms of injury and functional recovery of the central nervous system (CNS). We have developed an experimental model of SC injury in adult rats (n=32), that involves the use of a device (SC-STRAPPER) that straps the SC and promotes gradual and controlled SC injury similar to clinical compressive SC injuries. SC strapping is a less-invasive procedure in comparison to other SC injury models, and it performs compression with smaller infection risk and undetectable paravertebral or vertebral lesions. The survival of the rats was 100%, minimizing the suffering of the animals. We have analyzed the histopathological changes that occur during experimental SC compression, as well as the immunohistochemical labeling for glial fibrillary acidic protein (GFAP). Animals survived for 21 days being thereafter anesthetized and perfused with aldehydes. SC lesions were associated with motor deficits and local increase in GFAP immunolabeling proportionate to the severity of the compression. This experimental model represents a potential contribution for neuroscientific research, providing a low-cost and rather simple system of controllable and reproducible SC experimental damage.

Voluntary running attenuates age-related deficits following SCI

Over the past few decades, the average age at time of spinal cord injury (SCI) has increased. Here we examined locomotor recovery and myelin pathology in both young and aged adult rats following contusion SCI. Our assessment indicates that the rate of locomotor recovery following SCI is significantly delayed in aged rats as compared to young rats, and is associated with a greater degree of pathology and demyelination. Additionally, we examined the effect of voluntary exercise, pre- and post-injury, on locomotor recovery and myelin pathology following contusion SCI. Our data indicate that exercise improves the locomotor recovery of injured aged rats such that it is comparable to the recovery rate of injured young rats, and is associated with a decreased area of pathology and amount of demyelination. Interestingly, the rate of locomotor recovery and myelin pathology in the aged exercised rats was similar to that of the young sedentary rats after injury, indicating that exercise attenuates the delayed recovery of function and associated histopathology in aged rats. These data indicate that there is an age-related delay in locomotor recovery following SCI, and an age-related increase in histopathology following SCI. Importantly, our data indicate that exercise attenuates these age-related deficits following SCI.

Combination of dexamethasone and etanercept reduces secondary damage in experimental spinal cord trauma

The aim of our study was to evaluate the therapeutic efficacy of combination therapy with etanercept and dexamethasone (DEX) in vivo in experimental murine model of spinal cord trauma, which was induced by the application of vascular clips (force of 24 g) to the dura via a four-level T5-T8 laminectomy. Spinal cord injury in mice resulted in severe trauma characterized by edema, neutrophil infiltration, and cytokine production followed by recruitment of other inflammatory cells, production of inflammation mediators, tissue damage, apoptosis and disease. Treatment of the mice with etanercept (1.25 mg/kg) and DEX (0.025 mg/kg) when administered as a combination therapy but not as a single treatment significantly reduced the degree of (1) spinal cord inflammation and tissue injury (histological score), (2) infiltration of neutrophils (MPO evaluation), (3) inducible nitric oxide synthase, nitrotyrosine, and cytokines expression (tumor necrosis factor-alpha and interleukin-1 beta), (4) and apoptosis (Terminal deoxynucleotidyltransferase-mediated UTP end labeling staining, Fas-ligand expression and Bax and Bcl-2 expression). In a separate set of experiments we have also clearly demonstrated that the combination therapy significantly ameliorated the recovery of limb function (evaluated by motor recovery score). Taken together, our results clearly demonstrate for the first time that strategies targeting multiple proinflammatory pathways may be more effective than a single effector molecule for the treatment of spinal cord trauma.