Experimental acute traumatic injury of the adult rat spinal cord by a subdural inflatable balloon: methodology, behavioral analysis, and histopathology

Relationship between Preoperative Neuroradiological Findings and Intraoperative Bulbocavernosus Reflex Amplitude in Patients with Intradural Extramedullary Tumors

The current study aimed to evaluate the relationship between preoperative neuroradiological findings and intraoperative bulbocavernosus reflex (BCR) amplitude in patients with intradural extramedullary tumors. A total of 24 patients with lesions below the 12th thoracic vertebra were included in the analysis. Objective and subjective urinary symptoms were investigated using data obtained from medical records and the core lower urethral symptom score (CLSS) questionnaire. The lesion compression rate was evaluated with MRI. In the epiconus-to-conus medullaris (Epi-CM) group, BCR amplitude changes were found to be correlated with the compression rate (p <0.05). The preoperative CLSS of the group with a BCR amplitude of <50% was worse than that of the group with ≥50% (p <0.01). The group did not experience symptom improvement 6 months postoperatively based on the CLSS. The preoperative CLSS of the group with compression rate of ≥80% on imaging was worse than that of the group with <80% (p <0.05). In the group with preoperative compression rate of ≥80%, CLSS at 1 month and 6 months postoperatively was improved as compared to preoperative CLSS (p <0.01, p <0.05). Hence, BCR amplitude changes are associated with the degree of lesion compression on preoperative images and pre- and postoperative urinary symptoms. Patients with intradural extramedullary Epi-CM lesions with strong compression are likely to present with low BCR amplitude and worsened postoperative symptoms. It is considered that the risk of postoperative urinary symptoms increases even with careful surgical manipulation under these conditions.

Time-dependent microglia and macrophages response after traumatic spinal cord injury in rat: a systematic review

OBJECTIVE

To acquire evidence-based knowledge in temporal and spatial patterns of microglia/macrophages changes to facilitate finding proper intervention time for functional restoration after traumatic spinal cord injury (TSCI).

SETTING

Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Tehran, Iran.

METHODS

We searched PubMed and EMBASE via Ovid SP with no temporal and linguistic restrictions. Besides, hand-search was performed in the bibliographies of relevant studies. The experimental non-interventional and non-transgenic animal studies confined to the rat species which assess the pathological change of microglia /macrophages at the specified time were included.

RESULTS

We found 15,315 non-duplicate studies. Screening through title and abstract narrowed down to 607 relevant articles, 31 of them were selected based on the inclusion criteria. The reactivity of the microglia/macrophages initiates in early hours PI in contusion, compression and transection models. Cells activity reached a maximum within 48 h to 28 days in compression, 7 days in contusion and between 4 and 60 days in transection models. Inflammatory response occurred at the epicenter, in or near the lesion site in both gray and white matter in all three injury models with a maximum extension of one centimeter caudal and rostral to the epicenter in the gray matter in contusion and transection models.

CONCLUSION

This study was designed to study spatial-temporal changes in the activation of microglia/macrophages overtime after TSCI. We were able to demonstrate time-dependent cell morphological changes after TSCI. The peak times of cell reactivity and the areas where the cells responded to the injury were determined.

Rodent, large animal and non-human primate models of spinal cord injury

In this narrative review we aimed to assess the usefulness of the different animal models in identifying injury mechanisms and developing therapies for humans suffering from spinal cord injury (SCI). Results obtained from rodent studies are useful but, due to the anatomical, molecular and functional differences, confirmation of these findings in large animals or non-human primates may lead to basic discoveries that cannot be made in rodent models and that are more useful for developing treatment strategies in humans. SCI in dogs can be considered as intermediate between rodent models and human clinical trials, but the primate models could help to develop appropriate methods that might be more relevant to humans. Ideally, an animal model should meet the requirements of availability and repeatability as well as reproduce the anatomical features and the clinical pathological changing process of SCI. An animal model that completely simulates SCI in humans does not exist. The different experimental models of SCI have advantages and disadvantages for investigating the different aspects of lesion development, recovery mechanisms and potential therapeutic interventions. The potential advantages of non-human primate models include genetic similarities, similar caliber/length of the spinal cord as well as biological and physiological responses to injury which are more similar to humans. Among the potential disadvantages, high operating costs, infrastructural requirements and ethical concerns should be considered. The translation from experimental repair strategies to clinical applications needs to be investigated in future carefully designed studies.

Technique of spinal cord compression induced by inflation of epidural balloon catheter in rabbits (Oryctologus cuniculus): efficient and easy to use model

The most common cause of spinal cord injury are high impact trauma, which often result in some motor impairment, sensory or autonomic a greater or lesser extent in the distal areas the level of trauma. In terms of survival and complications due to sequelae, veterinary patients have a poor prognosis unfavorable. Therefore justified the study of experimental models of spinal cord injury production that could provide more support to research potential treatments for spinal cord injuries in medicine and veterinary medicine. Preclinical studies of acute spinal cord injury require an experimental animal model easily reproducible. The most common experimental animal model is the rat, and several techniques for producing a spinal cord injury. The objective of this study was to describe and evaluate the effectiveness of acute spinal cord injury production technique through inflation of Fogarty(r) catheter using rabbits as an experimental model because it is a species that has fewer conclusive publications and contemplating. The main requirements of a model as low cost, handling convenience, reproducibility and uniformity. The technique was adequate for performing preclinical studies in neuro-traumatology area, effectively leading to degeneration and necrosis of the nervous tissue fostering the emergence of acute paraplegia.

The relative contribution of edema and hemorrhage to raised intrathecal pressure after traumatic spinal cord injury

Raised intrathecal pressure (ITP) after traumatic spinal cord injury (SCI) is a critically important aspect of injury development that may result in significantly greater tissue damage and worsened functional outcome. Raised ITP is caused by the accumulation of blood and/or water (edema), and while their occurrence after traumatic SCI has been well established, the relative contribution of both processes to the development of ITP after SCI has not yet been determined. Accordingly, the current study investigates the temporal profile of raised ITP after traumatic SCI in relation to both hemorrhage and edema development. A closed balloon compression injury was induced at T10 in New Zealand White rabbits. Animals were thereafter assessed for spinal water content (edema), ITP, lesion and hemorrhage volume, and albumin immunoreactivity from 5 h to 1 week post-SCI. Early increases in ITP at 5 h post-injury were associated with significant increases in blood volume. ITP, however, was maximal at 3 days post-SCI, at which time there was an associated significant increase in edema that persisted for 1 week. We conclude that raised ITP after traumatic SCI is initially driven by volumetric increases in hemorrhage, while edema becomes the primary driver of ITP at 3 days post-injury.

tPA promotes ADAMTS-4-induced CSPG degradation, thereby enhancing neuroplasticity following spinal cord injury

Although tissue plasminogen activator (tPA) is known to promote neuronal remodeling in the CNS, no mechanism of how this plastic function takes place has been reported so far. We provide here in vitro and in vivo demonstrations that this serine protease neutralizes inhibitory chondroitin sulfate proteoglycans (CSPGs) by promoting their degradation via the direct activation of endogenous type 4 disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-4). Accordingly, in a model of compression-induced spinal cord injury (SCI) in rats, we found that administration of either tPA or its downstream effector ADAMTS-4 restores the tPA-dependent activity lost after the SCI and thereby, reduces content of CSPGs in the spinal cord, a cascade of events leading to an improved axonal regeneration/sprouting and eventually long term functional recovery. This is the first study to reveal a tPA-ADAMTS-4 axis and its function in the CNS. It also raises the prospect of exploiting such cooperation as a therapeutic tool for enhancing recovery after acute CNS injuries.

NK1 receptor blockade is ineffective in improving outcome following a balloon compression model of spinal cord injury

The neuropeptide substance P (SP) is a well-known mediator of neurogenic inflammation following a variety of CNS disorders. Indeed, inhibition of SP through antagonism of its receptor, the tachykinin NK1 receptor, has been shown to be beneficial following both traumatic brain injury and stroke. Such studies demonstrated that administration of an NK1 receptor antagonist reduced blood-brain-barrier permeability, edema development and improved functional outcome. Furthermore, our recent studies have demonstrated a potential role for SP in mediating neurogenic inflammation following traumatic spinal cord injury (SCI). Accordingly, the present study investigates whether inhibition of SP may similarly play a neuroprotective role following traumatic SCI. A closed balloon compression injury was induced at T10 in New Zealand White rabbits. At 30 minutes post-injury an NK1 receptor antagonist was administered intravenously. Animals were thereafter assessed for blood spinal cord barrier (BSCB) permeability, spinal water content (edema), intrathecal pressure (ITP), and histological and functional outcome from 5 hours to 2 weeks post-SCI. Administration of an NK1 receptor antagonist was not effective in reducing BSCB permeability, edema, ITP, or functional deficits following SCI. We conclude that SP mediated neurogenic inflammation does not seem to play a major role in BSCB disruption, edema development and consequential tissue damage seen in acute traumatic SCI. Rather it is likely that the severe primary insult and subsequent hemorrhage may be the key contributing factors to ongoing SCI injury.

Targeting endothelin receptors A and B attenuates the inflammatory response and improves locomotor function following spinal cord injury in mice

After spinal cord injury (SCI), the disruption of blood-spinal cord barrier by activation of the endothelin (ET) system is a critical event leading to leukocyte infiltration, inflammatory response and oxidative stress, contributing to neurological disability. In the present study, we showed that blockade of ET receptor A (ETAR) and/or ET receptor B (ETBR) prevented early inflammatory responses directly via the inhibition of neutrophil and monocyte diapedesis and inflammatory mediator production following traumatic SCI in mice. Long-term neurological improvement, based on a series of tests of locomotor performance, occurred only in the spinal cord‑injured mice following blockade of ETAR and ETBR. We also examined the post‑traumatic changes of the micro-environment within the injured spinal cord of mice following blockade of ET receptors. Oxidative stress reflects an imbalance between malondialdehyde and superoxide dismutase in spinal cord‑injured mice treated with vehicle, whereas blockade of ETAR and ETBR reversed the oxidation state imbalance. In addition, hemeoxygenase-1, a protective protease involved in early SCI, was increased in spinal cord‑injured mice following the blockade of ETAR and ETBR, or only ETBR. Matrix metalloproteinase-9, a tissue-destructive protease involved in early damage, was decreased in the injured spinal cord of mice following blockade of ETAR, ETBR or a combination thereof. The findings of the present study therefore suggested an association between ETAR and ETBR in regulating early pathogenesis of SCI and determining the outcomes of long‑term neurological recovery.

Long-term characterization of axon regeneration and matrix changes using multiple channel bridges for spinal cord regeneration

Spinal cord injury (SCI) results in loss of sensory and motor function below the level of injury and has limited available therapies. The host response to SCI is typified by limited endogenous repair, and biomaterial bridges offer the potential to alter the microenvironment to promote regeneration. Porous multiple channel bridges implanted into the injury provide stability to limit secondary damage and support cell infiltration that limits cavity formation. At the same time, the channels provide a path that physically directs axon growth across the injury. Using a rat spinal cord hemisection injury model, we investigated the dynamics of axon growth, myelination, and scar formation within and around the bridge in vivo for 6 months, at which time the bridge has fully degraded. Axons grew into and through the channels, and the density increased overtime, resulting in the greatest axon density at 6 months postimplantation, despite complete degradation of the bridge by that time point. Furthermore, the persistence of these axons contrasts with reports of axonal dieback in other models and is consistent with axon stability resulting from some degree of connectivity. Immunostaining of axons revealed both motor and sensory origins of the axons found in the channels of the bridge. Extensive myelination was observed throughout the bridge at 6 months, with centrally located and peripheral channels seemingly myelinated by oligodendrocytes and Schwann cells, respectively. Chondroitin sulfate proteoglycan deposition was restricted to the edges of the bridge, was greatest at 1 week, and significantly decreased by 6 weeks. The dynamics of collagen I and IV, laminin, and fibronectin deposition varied with time. These studies demonstrate that the bridge structure can support substantial long-term axon growth and myelination with limited scar formation.

Substance P as a mediator of neurogenic inflammation after balloon compression induced spinal cord injury

Although clinical spinal cord injury (SCI) occurs within a closed environment, most experimental models of SCI create an open injury. Such an open environment precludes the measurement of intrathecal pressure (ITP), whose increase after SCI has been linked to the development of greater tissue damage and functional deficits. Raised ITP may be potentiated by edema, which we have recently shown to be associated with substance P (SP) induced neurogenic inflammation in both traumatic brain injury and stroke. The present study investigates whether SP plays a similar role as a mediator of neurogenic inflammation after SCI. A closed balloon compression injury was induced at T10 in New Zealand white rabbits. Animals were thereafter assessed for blood spinal cord barrier (BSCB) permeability, edema, ITP, histological outcome, and functional outcome from 5 h to 2 weeks post-SCI. The balloon compression model produced significant increases in BSCB permeability, edema, and ITP along with significant functional deficits that persisted for 2 weeks. Histological assessment demonstrated decreased SP immunoreactivity in the injured spinal cord while NK1 receptor immunoreactivity initially increased before returning to sham levels. In addition, aquaporin 4 immunoreactivity increased early post-SCI, implicating this water channel in the development of edema after SCI. The changes described in the present study support a role for SP as a mediator of neurogenic inflammation after SCI.

Meta-analysis of pre-clinical studies of early decompression in acute spinal cord injury: a battle of time and pressure

Background

The use of early decompression in the management of acute spinal cord injury (SCI) remains contentious despite many pre-clinical studies demonstrating benefits and a small number of supportive clinical studies. Although the pre-clinical literature favours the concept of early decompression, translation is hindered by uncertainties regarding overall treatment efficacy and timing of decompression.

Methods

We performed meta-analysis to examine the pre-clinical literature on acute decompression of the injured spinal cord. Three databases were utilised; PubMed, ISI Web of Science and Embase. Our inclusion criteria consisted of (i) the reporting of efficacy of decompression at various time intervals (ii) number of animals and (iii) the mean outcome and variance in each group. Random effects meta-analysis was used and the impact of study design characteristics assessed with meta-regression.

Results

Overall, decompression improved behavioural outcome by 35.1% (95%CI 27.4-42.8; I²=94%, p<0.001). Measures to minimise bias were not routinely reported with blinding associated with a smaller but still significant benefit. Publication bias likely also contributed to an overestimation of efficacy. Meta-regression demonstrated a number of factors affecting outcome, notably compressive pressure and duration (adjusted r²=0.204, p<0.002), with increased pressure and longer durations of compression associated with smaller treatment effects. Plotting the compressive pressure against the duration of compression resulting in paraplegia in individual studies revealed a power law relationship; high compressive forces quickly resulted in paraplegia, while low compressive forces accompanying canal narrowing resulted in paresis over many hours.

Conclusion

These data suggest early decompression improves neurobehavioural deficits in animal models of SCI. Although much of the literature had limited internal validity, benefit was maintained across high quality studies. The close relationship of compressive pressure to the rate of development of severe neurological injury suggests that pressure local to the site of injury might be a useful parameter determining the urgency of decompression.

Dual differentiation-exogenous mesenchymal stem cell therapy for traumatic spinal cord injury repair in a murine hemisection model

Mesenchymal stem cell (MSC) transplantation has shown tremendous promise as a therapy for repair of various tissues of the musculoskeletal, vascular, and central nervous systems. Based on this success, recent research in this field has focused on complex tissue damage, such as that which occurs from traumatic spinal cord injury (TSCI). As the critical event for successful exogenous, MSC therapy is their migration to the injury site, which allows for their anti-inflammatory and morphogenic effects on fracture healing, neuronal regeneration, and functional recover. Thus, there is a need for a cost-effective in vivo model that can faithfully recapitulate the salient features of the injury, therapy, and recovery. To address this, we review the recent advances in exogenous MSC therapy for TSCI and traumatic vertebral fracture repair and the existing challenges regarding their translational applications. We also describe a novel murine model designed to take advantage of multidisciplinary collaborations between musculoskeletal and neuroscience researchers, which is needed to establish an efficacious MSC therapy for TSCI.

Improved rat spinal cord injury model using spinal cord compression by percutaneous method

Here, percutaneous spinal cord injury (SCI) methods using a balloon catheter in adult rats are described. A balloon catheter was inserted into the epidural space through the lumbosacral junction and then inflated between T9-T10 for 10min under fluoroscopic guidance. Animals were divided into three groups with respect to inflation volume: 20 µL (n = 18), 50 µL (n = 18) and control (Fogarty catheter inserted but not inflated; n = 10). Neurological assessments were then made based on BBB score, magnetic resonance imaging and histopathology. Both inflation volumes produced complete paralysis. Gradual recovery of motor function occurred when 20 µL was used, but not after 50 µL was applied. In the 50 µL group, all gray and white matter was lost from the center of the lesion. In addition, supramaximal damage was noted, which likely prevented spontaneous recovery. This percutaneous spinal cord compression injury model is simple, rapid with high reproducibility and the potential to serve as a useful tool for investigation of pathophysiology and possible protective treatments of SCI in vivo.

Grafted human embryonic progenitors expressing neurogenin-2 stimulate axonal sprouting and improve motor recovery after severe spinal cord injury

Background

Spinal cord injury (SCI) is a widely spread pathology with currently no effective treatment for any symptom. Regenerative medicine through cell transplantation is a very attractive strategy and may be used in different non-exclusive ways to promote functional recovery. We investigated functional and structural outcomes after grafting human embryonic neural progenitors (hENPs) in spinal cord-lesioned rats.

Methods and Principal Findings

With the objective of translation to clinics we have chosen a paradigm of delayed grafting, i.e., one week after lesion, in a severe model of spinal cord compression in adult rats. hENPs were either naïve or engineered to express Neurogenin 2 (Ngn2). Moreover, we have compared integrating and non-integrating lentiviral vectors, since the latter present reduced risks of insertional mutagenesis. We show that transplantation of hENPs transduced to express Ngn2 fully restore weight support and improve functional motor recovery after severe spinal cord compression at thoracic level. This was correlated with partial restoration of serotonin innervations at lumbar level, and translocation of 5HT1A receptors to the plasma membrane of motoneurons. Since hENPs were not detectable 4 weeks after grafting, transitory expression of Ngn2 appears sufficient to achieve motor recovery and to permit axonal regeneration. Importantly, we also demonstrate that transplantation of naïve hENPs is detrimental to functional recovery.

Conclusions and Significance

Transplantation and short-term survival of Ngn2-expressing hENPs restore weight support after SCI and partially restore serotonin fibers density and 5HT1A receptor pattern caudal to the lesion. Moreover, grafting of naïve-hENPs was found to worsen the outcome versus injured only animals, thus pointing to the possible detrimental effect of stem cell-based therapy per se in SCI. This is of major importance given the increasing number of clinical trials involving cell grafting developed for SCI patients.

Post-mortem assessment of rat spinal cord injury and white matter sparing using inversion recovery-supported proton density magnetic resonance imaging

STUDY DESIGN

This was an experimental study.

OBJECTIVES

White matter sparing influences locomotor recovery after traumatic spinal cord injury (SCI). The objective of the present post-mortem magnetic resonance imaging (MRI) investigation was to assess the potential of a simple inversion recovery (IR) sequence in combination with high-resolution proton density (PD) images to selectively depict spared white matter after experimental SCI in the rat.

SETTING

This study was conducted at University of Liège and Centre Hospitalier Universitaire, Liège, Belgium and Hasselt University, Diepenbeek, Belgium.

METHODS

Post-mortem 9.4 tesla (T) MRI was obtained from five excised rat spines 2 months after compressive SCI. The locomotor recovery had been followed weekly using the standardized Basso-Beattie-Bresnahan scale. IR MRI was used to depict normal white matter as very hypo-intense. Preserved white matter, cord atrophy and lesion volume were assessed, and histology was used to confirm MRI data.

RESULTS

MRI showed lesion severity and white matter sparing in accordance with the degree of locomotor recovery. IR MRI enhanced detection of spared and injured white matter by selectively altering the signal of spared white matter. Even subtle white matter changes could be detected, increasing diagnostic accuracy as compared to PD alone. MRI accuracy was confirmed by histology.

CONCLUSION

High-resolution IR-supported PD MRI provides useful micro-anatomical information about white matter damage and sparing in the post-mortem assessment of chronic rat SCI.

Early functional outcomes and histological analysis after spinal cord compression injury in rats

Object

Neuroprotective and repair strategies in spinal cord injuries (SCIs) have been so far largely unsuccessful. One of the prerequisites is the use of appropriate preclinical models to decipher pathophysiological mechanisms; another is the identification of optimal time windows for therapeutic interventions. The authors undertook this study to characterize early motor, sensory, autonomic, and histological outcomes after balloon compression of the spinal cord at the T8–9 level in adult rats.

Methods

A total of 91 rats were used in this study. Spinal cord balloon compression was performed at T8–9 in adult rats by inflation of a 2 Fr Fogarty catheter into the epidural space. The authors first characterized early motor, sensory, and autonomic outcomes of 2 volumes of compression (10 and 15 μl) using behavioral tests and then examined histological outcomes in the spinal cord using Luxol fast blue staining. To further substantiate the characterization of the epidural balloon-compression model, they used a noncompetitive N-methyl-d-aspartate antagonist, GK11, and demonstrated the involvement of excitotoxicity in this model.

Results

Proportional and reproducible functional impairment resulted from compression caused by balloon inflation with either 10 or 15 μl of water and corresponded to the extent of the lesion. Indeed, during the early phase following SCI (1 week postinjury), recovery of locomotor function and bladder control correlated with the volume of inflation, whereas outcomes with respect to sensory function and reflexes were independent of compression severity. Treatment with GK11 significantly improved motor function in all groups of rats 1 week after injury and bladder voiding in the 10-μl injured rats compared to the 15-μl injured rats.

Conclusions

The results of this study demonstrate that spinal balloon-compression injury in the rat is a well-characterized, reproducible, and predictable model to analyze early events following SCI.

A remotely controlled model of spinal cord compression injury in mice: toward real-time analysis

OBJECT

To date, there has been no efficient therapeutic approach to spinal cord injuries (SCIs). This may be attributable, at least in part, to difficulties in forming predictive and accurate experimental animal models. The authors' previous studies have identified 2 relevant conditions of such a model. The first condition is the ability to compare data derived from rat models of SCI by developing mouse models of SCI that permit access to a large range of transgenic models. The second condition is that the exploration of the consequences of each mechanism of spinal trauma requires modeling the different etiologic aspects of the injury.

METHODS

To fulfill these 2 conditions a new model of mouse spinal cord compression injury was devised using a thread-driven olive-shaped compressive device. The authors characterized early motor, sensory, and histological outcomes using 3 olive diameters and different compression durations.

RESULTS

A gradual and reproducible functional severity that correlated with lesion extension was demonstrated in 76 mice. To further substantiate the characterization of this model, a noncompetitive N-methyl-d-aspartate antagonist was administered in 30 mice, which demonstrated the involvement of excitotoxicity in this model.

CONCLUSIONS

The study demonstrated that spinal olive-compression injury in the mouse is a reproducible, well-characterized, and predictable model for analyzing early events after SCI. The nonmagnetic and remotely controlled design of this model will allow completion of the lesion while the animal is in the MR imaging apparatus, thus permitting further real-time MR imaging studies that will provide insights into the characterization of early events in the spatial and temporal evolution of SCI. Moreover, this model lays the foundation for future in vivo studies of functional and histological outcomes following SCI in genetically engineered animals.

Minimum information about animal experiments: supplier is also important

It has now been established that functional recovery after spinal cord injury (SCI) depends on several parameters, including animal strain. Here we demonstrate that rats from the same strain (Wistar) but from two independent commercial suppliers present different motor, sensory, and autonomic outcomes after a standard model of SCI, the so-called compression model. Recovery is correlated with the extension of the lesion, and we show that the vertebral canal diameter varies between the two suppliers. To substantiate this point, we carried out another set of experiments, with the so-called contusion model, which requires bone ablation and thus whose extension is not related to vertebral canal diameter. We show that there is no difference between the two suppliers. The purpose of our communication is to alert researchers on how crucial it is to control experimental parameters as closely as possible and to establish a standard for animal experiment in order to avoid unexpected biases.

Rapid, postmortem 9.4 T MRI of spinal cord injury: correlation with histology and survival times

High field magnetic resonance imaging (MRI) has been increasingly used to assess experimental spinal cord injury (SCI). In the present investigation, after partial spinal cord injury and excision of the whole spine, pathological changes of the spinal cord were studied in spinal cord-spine blocks, from the acute to the chronic state (24 h to 5 months). Using proton density (PD) weighted imaging parameters at a magnetic field strength of 9.4 tesla (T), acquisition times ranging from <1 to 10 h per specimen were used. High in-plane pixel resolution (68 and 38 microm, respectively) was obtained, as well as high signal-to-noise ratio (SNR), which is important for optimal contrast settings. The quality of the resulting MR images was demonstrated by comparison with histology. The cord and the lesion were shown in their anatomical surroundings, detecting cord swelling in the acute phase (24 h to 1 week) and cord atrophy at the chronic stage. Haemorrhage was detected as hypo-intense signal. Oedema, necrosis and scarring were hyper-intense but could not be distinguished. Histology confirmed that the anatomical delimitation of the lesion extent by MRI was precise, both with high and moderate resolution. The present investigation thus demonstrates the precision of spinal cord MRI at different survival delays after compressive partial SCI and establishes efficient imaging parameters for postmortem PD MRI.

Development of an improved canine model of percutaneous spinal cord compression injury by balloon catheter

We developed a minimally invasive canine model of spinal cord injury (SCI). A balloon catheter was inserted into the epidural space via the lumbosacral space, and inflated between L2 and L3 for 30 or 60 min under fluoroscopic guidance. Motor function after SCI was assessed using modified Tarlov scale. All seven dogs showed complete paraplegia after the procedure, neurological problems were evident and the modified Tarlov scores remained at zero after the SCI procedure; no improvement in clinical signs was observed. The dogs underwent 3T MR imaging at 3 days and 1 year after SCI. Histopathologic examinations were conducted at 2 weeks, 12 weeks and 1 year after SCI. In the present study, we described an animal model of minimally invasive spinal cord injury using a balloon catheter without laminectomy under fluoroscopic guidance. And, this percutaneous spinal cord compression injury model has many potential applications. The described percutaneous spinal cord compression injury model offers a new means of administering SCI and has many potential applications.

Establishment of a canine spinal cord injury model induced by epidural balloon compression

A model that provides reproducible, submaximal yet sufficient spinal cord injury is needed to allow experiments leading to development of therapeutic techniques and prediction of clinical outcome to be conducted. This study describes an experimental model for spinal cord injury that uses three different volumes of balloon inflation and durations of compression to create a controlled gradation outcome in adult dogs. Twenty-seven mongrel dogs were used for this study. A 3-french embolectomy catheter was inserted into the epidural space through a left hemilaminectomy hole at the L₄ vertebral arch. Balloons were then inflated with 50, 100, or 150 µl of a contrast agent at the L1 level for 6, 12, or 24 h and spinal canal occlusion (SCO) measured using computed tomography. Olby score was used to evaluate the extent of spinal cord injury and a histopathologic examination was conducted 1 week after surgery. The SCO of the 50, 100, and 150 µl inflations was 22-46%, 51-70%, and 75-89%, respectively (p < 0.05). Olby scores were diminished significantly by a combination of the level of SCO and duration of inflation in all groups. Olby scores in the groups of 150 µl-12 h, 150 µl-24 h, and 100 µl-24 h were 0.5, 0, and 1.7, respectively. Based on these results, a SCO > 50% for 24 h, and > 75% for 12 h induces paraplegia up to a week after spinal cord injury.

Schwann cell and olfactory ensheathing cell implantation for repair of the contused spinal cord

A contusion injury to the spinal cord results in impaired neurological functions due to neuronal death, and axonal damage and demyelination. In time, a fluid-filled cyst forms at the site of the initial impact. There are no effective endogenous repair mechanisms and, consequently, injury-induced functional deficits are permanent. One aspect of spinal cord repair is that severed descending and ascending axons need to regenerate beyond the site of injury towards the denervated spinal regions where they can become part of axonal circuits involved in motor and sensory function. Implantation of cells into the injured cord has been studied extensively as a means to promote axonal regeneration in the injured spinal cord. Depending on the overall damage, different cell types may be appropriate in different types of injury. To accomplish axonal regeneration in the contused spinal cord, the strengths and limitations of two glial cell types in particular will be discussed; Schwann cells and olfactory ensheathing cells. It is known that with these implants, axonal regeneration is frustrated by the presence of a glial scar surrounding the contused area. I will review current approaches aimed at overcoming this axonal growth inhibitory scar. Future studies need to focus on identifying interventions that, in combination with cellular implants, will elicit substantial axonal growth beyond the contusion injury, which may then be the basis for biologically significant functional recovery.

Delayed GM‐CSF treatment stimulates axonal regeneration and functional recovery in paraplegic rats via an increased BDNF expression by endogenous macrophages

Macrophages (monocytes/microglia) could play a critical role in central nervous system repair. We have previously found a synchronism between the regression of spontaneous axonal regeneration and the deactivation of macrophages 3-4 wk after a compression-injury of rat spinal cord. To explore whether reactivation of endogenous macrophages might be beneficial for spinal cord repair, we have studied the effects of granulocyte-macrophage colony stimulating factor (GM-CSF) in the same paraplegia model and in cell cultures. There was a significant, though transient, improvement of locomotor recovery after a single delayed intraperitoneal injection of 2 microg GM-CSF, which also increased significantly the expression of Cr3 and brain-derived neurotrophic factor (BDNF) by macrophages at the lesion site. At longer survival delays, axonal regeneration was significantly enhanced in GM-CSF-treated rats. In vitro, BV2 microglial cells expressed higher levels of BDNF in the presence of GM-CSF and neurons cocultured with microglial cells activated by GM-CSF generated more neurites, an effect blocked by a BDNF antibody. These experiments suggest that GM-CSF could be an interesting treatment option for spinal cord injury and that its beneficial effects might be mediated by BDNF.

Clinical canine spinal cord injury provides an opportunity to examine the issues in translating laboratory techniques into practical therapy

STUDY DESIGN

Review.

OBJECTIVES

To highlight the value of investigating the effects of putative therapeutic interventions in clinical spinal cord injury (SCI) in domestic dogs.

SETTING

England, UK.

METHODS

Many experimental interventions in laboratory rodents have been shown to ameliorate the functional deficits caused by SCI; the challenge now is to determine whether they can be translated into useful clinical techniques. Important differences between clinical SCI in human patients and that in laboratory rodents are in the size of the spinal cord and heterogeneity of injury severity. A further key issue is whether the statistical difference in outcome in the laboratory will translate into a useful difference in clinical outcome. Here, we stress the value of investigating the effects of putative therapies in clinical SCI in domestic dogs. The causes of injury, ability to categorise the severity and methods available to measure outcome are very similar between canine and human patients. Furthermore, postmortem tissue more rapidly becomes available from dogs because of their short lifespan than from human patients.

RESULTS

The role that investigation of canine SCI might play is illustrated by our preliminary trials on intraspinal transplantation of olfactory glial cells for severe SCI.

CONCLUSIONS

This canine translational model provides a means of 'filtering' putative treatments before human application.

Animal Models for Studying Potential Training Strategies in Persons with Spinal Cord Injury

In the late 1980s, it was clearly demonstrated that adult spinal cats can be re-trained to walk after a complete spinal cord transection, using treadmill training. This has led to profound changes in the rehabilitation of persons with spinal cord injury. The use of animal models to study training-induced locomotor plasticity after spinal cord injury has expanded since this original demonstration. The goal of the present review is to summarize findings obtained with these animal models that may be of relevance to the re-training of humans with spinal cord injury. From the complete spinal cord transection models, adaptive capacity, retention of training, task-specificity, role of cutaneous inputs, effect of training with robotic devices, and spinal cord stimulation will be discussed. From the partial spinal lesion models, the effect of ventral or dorsal lesions of the cord will be presented. Finally, the effects of drugs on training will be compared between the complete and partial spinal lesions models.

New canine spinal cord injury model free from laminectomy

The present report details the successful development of a model for spinal cord injury (SCI). This model is simple, reproducible, and requires no laminectomy. Development of the model was carried out using fourteen dogs. A balloon catheter was inserted into the extradural space via the intervertebral foramen of each dog, then the balloon was inflated at the L1 level by injection of saline. Six dogs underwent compression with a balloon volume of 1.5 ml, three dogs with a volume of 1.0 ml, and the remaining five dogs were used as uninjured controls. We applied the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale to the dogs. Compression of the spinal cord for 10 min at 1.5 ml produced severe paraplegia (BBB remained zero or one for 6 months following surgery), while compression for the same time interval at 1.0 ml produced moderate paraplegia. Electrophysiological tests showed no hindlimb movement upon stimulation cranial to the site of injury in the 1.5-ml group. The volume of abnormal-intensity lesions in the 1.0-ml group calculated using MR imaging showed no marked changes in either high- or low-intensity lesions after 3 months, whereas in the 1.5-ml group, the low-intensity lesions alone showed a marked increase. Pathological examination of the damaged spinal cord showed the formation of cavities surrounded by scar tissue containing high levels of collagen. These findings closely resembled those of clinical cases. It was concluded that 10 min of balloon compression with a volume of 1.5 ml caused irreversible paraplegia in dogs.

From Animal Models to Humans

There are currently no fully restorative therapies for human spinal cord injury (SCI). Here,we briefly review the different types of human SCI pathology as well as the most commonly used rodent and nonhuman primate models of SCI that are used to simulate these pathologies and to test potential therapies. We then discuss various high profile (sometimes controversial) experimental strategies that have reported CNS axon regeneration and functional recovery of limb movement using these animal models of SCI. We particularly focus upon strategies that have been tested both in rodents and in nonhuman primates, and highlight those which are currently transitioning to clinical tests or trials in humans. Finally we discuss ways in which animal studies might be improved and what the future may hold for physical therapists involved in rehabilitation of humans with SCI.

Rodent models for treatment of spinal cord injury: research trends and progress toward useful repair

PURPOSE OF REVIEW

In this review, we have documented some current research trends in rodent models of spinal cord injury. We have also catalogued the treatments used in studies published between October 2002 and November 2003, with special attention given to studies in which treatments were delayed for at least 4 days after injury.

RECENT FINDINGS

Most spinal cord injury studies are performed with one of three general injury models: transection, compression, or contusion. Although most treatments are begun immediately after injury, a growing number of studies have used delayed interventions. Mice and the genetic tools they offer are gaining in popularity. Some researchers are setting their sights beyond locomotion, to issues more pressing for people with spinal cord injury (especially bladder function and pain).

SUMMARY

Delayed treatment protocols may extend the window of opportunity for treatment of spinal cord injury, whereas continued progress in the prevention of secondary cell death will reduce the severity of new cases. The use of mice will hopefully accelerate progress towards useful regeneration in humans. Researchers must improve cross-study comparability to allow balanced decisions about potentially useful treatments.

Repetitive transcranial magnetic stimulation improves open field locomotor recovery after low but not high thoracic spinal cord compression-injury in adult rats

Electromagnetic fields are able to promote axonal regeneration in vitro and in vivo. Repetitive transcranial magnetic stimulation (rTMS) is used routinely in neuropsychiatric conditions and as an atraumatic method to activate descending motor pathways. After spinal cord injury, these pathways are disconnected from the spinal locomotor generator, resulting in most of the functional deficit. We have applied daily 10 Hz rTMS for 8 weeks immediately after an incomplete high (T4-5; n = 5) or low (T10-11; n = 6) thoracic closed spinal cord compression-injury in adult rats, using 6 high- and 6 low-lesioned non-stimulated animals as controls. Functional recovery of hindlimbs was assessed using the BBB locomotor rating scale. In the control group, the BBB score was significantly better from the 7th week post-injury in animals lesioned at T4-5 compared to those lesioned at T10-11. rTMS significantly improved locomotor recovery in T10-11-injured rats, but not in rats with a high thoracic injury. In rTMS-treated rats, there was significant positive correlation between final BBB score and grey matter density of serotonergic fibres in the spinal segment just caudal to the lesion. We propose that low thoracic lesions produce a greater functional deficit because they interfere with the locomotor centre and that rTMS is beneficial in such lesions because it activates this central pattern generator, presumably via descending serotonin pathways. The benefits of rTMS shown here suggest strongly that this non-invasive intervention strategy merits consideration for clinical trials in human paraplegics with low spinal cord lesions.

The effect of treadmill training on motor recovery after a partial spinal cord compression-injury in the adult rat

Locomotor training on a treadmill is a therapeutic strategy used for several years in human paraplegics in whom it was shown to improve functional recovery mainly after incomplete spinal cord lesions. The precise mechanisms underlying its effects are not known. Experimental studies in adult animals were chiefly performed after complete spinal transections. The objective of this experiment was to assess the effects of early treadmill training on recovery of spontaneous walking capacity after a partial spinal cord lesion in adult rats. Following a compression-injury by a subdurally inflated microballoon, seven rats were trained daily on a treadmill with a body weight support system, whereas six other animals were used as controls and only handled. Spontaneous walking ability in an open field was compared weekly between both groups by two blinded observers, using the Basso, Beattie and Bresnahan (BBB) locomotor rating scale. Mean BBB score during 12 weeks was globally significantly greater in the treadmill-trained animals than in the control group, the benefit of training appearing as early as the 2nd week. At week 7, locomotor recovery reached a plateau in both animal groups, but remained superior in trained rats. Daily treadmill training started early after a partial spinal cord lesion in adult rats, which accelerates recovery of locomotion and produces a long-term benefit. These findings in an animal model mimicking the closed spinal cord injury occurring in most human paraplegics are useful for future studies of optimal locomotor training programs, their neurobiologic mechanisms, and their combination with other treatment strategies.

Increased expression of neurotrophins and their receptors in the mechanically compressed spinal cord of the spinal hyperostotic mouse (twy/twy)

The purpose of the present study was to identify any compensatory changes at the site of chronic compression of the spinal cord and neighboring segments. For this purpose, serial immunohistochemical and immunoblot analyses were performed for the expression levels of endogenous brain-derived neurotrophic factor (BDNF), neurotrophin (NT)-3, and their receptors, trkB and trkC in 24 tip-toe walking Yoshimura mice (twy/twy) aged 12-24 weeks. The twy mouse exhibits spontaneous calcified deposits posteriorly at the C1-C2 level, compressing the spinal cord. Immunoreactivities for BDNF, NT-3, trkB and trkC were preferentially localized in the gray matter, particularly in the anterior horn cells. In 24-week-old twy mice with severe compression, expression levels of these neurotrophins at the site of maximal compression were significantly lower than at the less- or non-compressed sites. In contrast, the expression levels of BDNF, NT-3, trkB and trkC were significantly higher at the rostral and caudal sites immediately adjacent to the maximal compression site. No such changes were noted in 12-week-old twy mice or in control Institute of Cancer Research mice. Our results suggest that overexpression of BDNF, NT-3, trkB and trkC in motoneuron areas neighboring the site of mechanical compression may represent compensatory changes in response to the compromised neuronal function at the level of compression, and that these proteins possibly contribute to neuronal survival and plasticity.

Endothelin receptor expression in the normal and injured spinal cord: potential involvement in injury-induced ischemia and gliosis

The endothelins (ETs) are a family of peptides that exert their biological effects via two distinct receptors, the endothelin A receptor (ET(A)R) and the endothelin B receptor (ET(B)R). To more clearly define the potential actions of ETs following spinal cord injury, we used immunohistochemistry and confocal microscopy to examine the protein expression of ET(A)R and ET(B)R in the normal and injured rat spinal cord. In the normal spinal cord, ET(A)R immunoreactivity (IR) is expressed by vascular smooth muscle cells and a subpopulation of primary afferent nerve fibers. ET(B)R-IR is expressed primarily by radial glia, a small population of gray and white matter astrocytes, ependymal cells, vascular endothelial cells, and to a lesser extent in smooth muscle cells. Fourteen days following compression injury to the spinal cord, there was a significant upregulation in both the immunoexpression and number of astrocytes expressing the ET(B)R in both gray and white matter and a near disappearance of ET(B)R-IR in ependymal cells and ET(A)R-IR in primary afferent fibers. Conversely, the vascular expression of ET(A)R and ET(B)R did not appear to change. As spinal cord injury has been shown to induce an immediate increase in plasma ET levels and a sustained increase in tissue ET levels, ETs would be expected to induce an initial marked vasoconstriction via activation of vascular ET(A)R/ET(B)R and then days later a glial hypertrophy via activation of the ET(B)R expressed by astrocytes. Strategies aimed at blocking vascular ET(A)R/ET(B)R and astrocyte ET(B)Rs following spinal cord injury may reduce the resulting ischemia and astrogliosis and in doing so increase neuronal survival, regeneration, and function.

Progressive changes in neurofilament proteins and growth-associated protein-43 immunoreactivities at the site of cervical spinal cord compression in spinal hyperostotic mice

STUDY DESIGN

Immunohistochemical examination of the expression and localization of neurofilament (NF) proteins and growth-associated protein (GAP)-43 in spinal hyperostotic (twy/twy) mice with progressive compression of the cervical spinal cord.

OBJECTIVE

To determine the biologic functions of NF proteins and GAP-43 in the mouse cervical spinal cord during chronic mechanical compression.

SUMMARY OF BACKGROUND DATA

The pathologic and repair process in the chronically compressed spinal cord are understood poorly. The present authors hypothesized that there existed an increased expression of NF proteins and GAP-43 in twy/twy mice during the lengthy period of spinal cord compression, which resembles compressive myelopathy.

METHODS

The cervical spinal cords of 54 twy mice (aged 8 weeks [n = 18], 14 weeks [n = 18], and 20 weeks [n = 18]) and 18 control animals were examined histologically. Using appropriate antibodies, sections were also stained immunohistochemically for NF proteins and GAP-43.

RESULTS

Separation of the myelin sheath from the axon and axonal swelling with deformation were detected in the anterior and lateral funiculi of the spinalcords of 20-week-old twy/twy mice. No such changes were noted in 8-week-old twy mice. In twy/twy mice aged 8 and 14 weeks with mild-to-moderate compression, weak immunoreactivities (mainly in the white matter) for NF proteins and GAP-43 were noted; however, in 20-week-old twy/twy mice, these axons stained strongly positive and immunoreactive swollen axons were present. The relative area of GAP-43 immunoreactive axons gradually increased between 8 and 20 weeks in each column, particularly in the anterior and lateral funiculi in the contralateral side of compression.

CONCLUSIONS

The results showed that the expression of NF proteins and GAP-43 in the white matter increased proportionally with the magnitude of spinal cord compression, and indicated the possible involvement of GAP-43 in both axonal degeneration and repair processes in the chronically compressed spinal cord.

Spinal cord reconstruction using NeuroGel implants and functional recovery after chronic injury

There is currently a lack of effective ways to achieve functional tissue repair of the chronically injured spinal cord. We investigated the potential of using NeuroGel, a biocompatible polymer hydrogel, to induce a reconstruction of the rat spinal cord after chronic compression-produced injury. NeuroGel was inserted 3 months after a severe injury into the post-traumatic lesion cavity. Rats were placed in an enriched environment and the functional deficits were measured using the BBB rating scale. A significant improvement in the mean BBB scores was observed. Rats without enriched environment and severely injured rats with an enriched environment alone showed no improvement; however, 7 months after reconstructive surgery using NeuroGel, a reparative neural tissue had formed within the polymer gel that included myelinated axons and dendro-dendritic contacts. NeuroGel implantation into a chronic spinal cord injury therefore resulted in tissue reconstruction and functional improvement, suggesting that such an approach may have therapeutic value in the repair of focal lesions in humans.

A simple and reproducible model of spinal cord injury induced by epidural balloon inflation in the rat

This paper describes a modification of a balloon-compression technique to produce spinal cord injury in adult rats. A 2-French Fogarty catheter is inserted into the dorsal epidural space through a small hole made in T10 vertebral arch, advanced cranially to T8-9 spinal level, and inflated for 5 min. Spinal cord damage is graded by increasing the volume of saline used to inflate the balloon. Quantitative neurological and histopathological outcomes are presented with three different volumes (10, 15, and 20 microl of saline) to characterize the gradation of injury. Volume of 15 microl produced complete paraplegia followed by gradual recovery, finally reaching approximately the middle of the scale used to quantitate the locomotor performance. With these animals, after 4 weeks, the center of the lesion shows complete loss of grey matter and partial sparing of the white matter. We conclude that 15 microl volume produced submaximal injury that will be useful for studying the pathophysiology and effects of protective therapies with this compression-injury model.

Gacyclidine: a new neuroprotective agent acting at the N-methyl-D-aspartate receptor

Gacyclidine is a new phencyclidine derivative with neuroprotective properties. Tritiated gacyclidine and its enantiomers bind to NMDA receptors with binding parameters similar to those of other non-competitive NMDA receptor antagonists. The (-)enantiomer, (-)GK11, exhibits an affinity (2.5 nM) similar to that of dizocilpine (MK-801), while the (+)enantiomer, (+)GK11, has a 10 times lower affinity. When its interaction with NMDA receptors is prevented, gacyclidine binds also to "non-NMDA" binding sites which are mainly located in the molecular layer of the cerebellum on the dendritic tree of Purkinje cells. These binding sites do not appear to be related to any known neurotransmitters. In primary cortical cultures, gacyclidine and its enantiomers, at 0.1 to 5.0 microM, prevent glutamate-induced neuronal death. In rats, in vivo neurotoxicity of gacyclidine is far low than that of MK-801. No necrotic neurons were detected in animals sacrificed at 18 or 96 h after treatment with gacyclidine (1, 5, 10 or 20 mg/kg i.v.). At the highest (20 mg/kg) but not the lower doses (1-100 mg/kg) electron microscopy revealed the presence of few cytoplasmic or intramitochondrial vacuoles. In soman-treated monkeys gacyclidine enhanced neuroprotective activity of "three drugs cocktail" (atropine + diazepam + pralidoxime). Moreover, in rats, gacyclidine exerts a dose- and time-dependent neuroprotection in three models of spinal cord lesion. Beneficial effects of gacyclidine include reduction of lesion size and improvement of functional parameters after injury. In traumatic brain injury models gacyclidine improves also behavioral parameters and neuronal survival. Optimal protection is obtained when gacyclidine is administered at 0 to 30 min after injury. It is, therefore, concluded that gacyclidine exhibits neuroprotective effects similar to those of other NMDA receptor antagonists, with the advantage of being substantially less neurotoxic maybe due to its interaction with "non-NMDA" binding sites.

Matrix metalloproteinases: potential therapeutic target in spinal cord injury

Mediators of extracellular matrix proteins degradation, the matrix metalloproteinases (MMPs), involved in inflammation as well as facilitation of process outgrowth of oligodendrocytes are interesting targets for neural repair. Recent data reported their activation after seizures, cerebral ischemia and spinal cord injury. The present study was designed to localize at cellular level the gelatinase activity by in situ zymography in a rat spinal cord contusion model. The kinetic of gelatinase activation was monitored by in situ zymography on 20 microm cryostat sections. The fluorescein-quenched DQ gelatin digestion yielded cleaved fluorescent peptides enabling the detection of gelatinase activity at cellular level. Twenty four hours and 48 h after injury, a strong gelatinase activity was detected at the lesion site in and around vascular structures and infiltrated cells. A preincubation with either MMP-2 or MMP-9 antibodies significantly decreases the gelatinase activity pattern, suggesting the involvement of at least both MMPs. Our results are consistent with a role for MMPs in the blood spinal barrier disruption, the leukocytes infiltration, the disruption of the extracellular matrix and the clearance of debris.

Distribution of gacyclidine enantiomers after experimental spinal cord injury in rats: possible involvement of an active transport system

The pharmacokinetics of gacyclidine enantiomers, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist, were studied in plasma and spinal cord extracellular fluid (ECF) after experimental spinal cord injury in rats. Spinal cord trauma was produced by introducing an inflatable balloon in the dorsal subdural space. Upon implantation of microdialysis probes in spinal cord (T9) and intravenous (iv) bolus administration of (+/-)-gacyclidine (2.5 mg/kg), concentrations in plasma and ECF were monitored over 5 h and analyzed by a stereospecific gas chromatography-mass spectrometry (GC-MS) assay. In plasma, concentrations of (+)-gacyclidine were approximately 25% higher than those of (-)-gacyclidine over the duration of the experiment and decayed in parallel (t(1/2 alpha) approximately 7 min; t(1/2 beta) approximately 90 min) with no significant difference between the two enantiomers. Clearance (CL) and volume of distribution (Vd) of (-)-gacyclidine were approximately 20% higher than those of its optical antipode (CL: 285 versus 236 mL. kg(-1). min(-1); Vd(beta): 39.3 versus 31.2 l/kg). Protein binding (approximately 91%) was not stereoselective. In spinal cord ECF, both enantiomers were quantifiable within 10 min after drug administration, and their concentration remained stable over the duration of the experiment in spite of changing blood concentrations. Repeated iv bolus injections of gacyclidine did not modify these profiles. Areas under the curves (AUCs) of concentration in ECF versus time were similar for both enantiomers and not correlated with AUCs in plasma. Penetration of (-)-gacyclidine was, however, significantly higher (approximately 30%) than that of (+)-gacyclidine. In summary, the disposition of gacyclidine enantiomers is stereoselective. Both enantiomers exhibit a high affinity for spinal cord tissue, and the drug exchange between plasma and spinal cord ECF involves an active transport system. These findings contribute to the explanation of the discrepancy between drug concentrations in plasma and spinal cord ECF.

Gacyclidine: a new neuroprotective agent acting at the N-methyl-D-aspartate receptor

Gacyclidine is a new phencyclidine derivative with neuroprotective properties. Tritiated gacyclidine and its enantiomers bind to NMDA receptors with binding parameters similar to those of other non-competitive NMDA receptor antagonists. The (-)enantiomer, (-)GK11, exhibits an affinity (2.5 nM) similar to that of dizocilpine (MK-801), while the (+)enantiomer, (+)GK11, has a 10 times lower affinity. When its interaction with NMDA receptors is prevented, gacyclidine binds also to "non-NMDA" binding sites which are mainly located in the molecular layer of the cerebellum on the dendritic tree of Purkinje cells. These binding sites do not appear to be related to any known neurotransmitters. In primary cortical cultures, gacyclidine and its enantiomers, at 0.1 to 5.0 microM, prevent glutamate-induced neuronal death. In rats, in vivo neurotoxicity of gacyclidine is far low than that of MK-801. No necrotic neurons were detected in animals sacrificed at 18 or 96 h after treatment with gacyclidine (1, 5, 10 or 20 mg/kg i.v.). At the highest (20 mg/kg) but not the lower doses (1-100 mg/kg) electron microscopy revealed the presence of few cytoplasmic or intramitochondrial vacuoles. In soman-treated monkeys gacyclidine enhanced neuroprotective activity of "three drugs cocktail" (atropine + diazepam + pralidoxime). Moreover, in rats, gacyclidine exerts a dose- and time-dependent neuroprotection in three models of spinal cord lesion. Beneficial effects of gacyclidine include reduction of lesion size and improvement of functional parameters after injury. In traumatic brain injury models gacyclidine improves also behavioral parameters and neuronal survival. Optimal protection is obtained when gacyclidine is administered at 0 to 30 min after injury. It is, therefore, concluded that gacyclidine exhibits neuroprotective effects similar to those of other NMDA receptor antagonists, with the advantage of being substantially less neurotoxic maybe due to its interaction with "non-NMDA" binding sites.

Efficacy of a new neuroprotective agent, gacyclidine, in a model of rat spinal cord injury

Prevention of the immediate excitotoxic phase occurring in response to spinal cord injury (SCI) is a major issue to reduce the neuronal damage responsible for any ensuing motor deficits. The present study evaluated the neuroprotective efficacy of three noncompetitive NMDA receptor antagonists: Gacyclidine (GK-11), a new compound, Dizocilpine (MK-801), and Cerestat (CNS-1102) in a rat spinal cord contusion model. To mimic human SCI, a standardized model of rat spinal cord closed contusion in which animals spontaneously and progressively recover from the induced paraplegia was employed. Such model, characterized by a slow recovery of hindlimb locomotor function enables easy quantification of the neuroprotection at both the behavioral and cellular level. The animals were treated intravenously with the respective drugs 10 min after the spinal contusion. The dose range study suggested that 1 mg/kg of Gacyclidine was the most effective dose to promote functional recovery in reducing by half the time needed to reach full locomotor recovery. Racemate and enantiomers of Gacyclidine showed similar neuroprotective effects, but treatment with the enantiomers were not as efficacious in promoting full functional recovery. Similarly, a prolonged treatment with the racemate was not as efficious as a single dose, suggesting that a prolonged blockade of the amino-excitatory neurotransmission may be deleterious. Finally, Dizocilpine and Cerestat treatments induced only a partial and delayed neuroprotective effect compared to Gacyclidine. Neuroprotection characterized by a reduction of the cystic cavity and of the astrogliosis was observed with all treatments. As Gacyclidine is already in clinical trials, the present findings suggest the premise that it is a promising agent for limiting the initial neuronal damage induced by CNS trauma leading to better functional recovery.

Distribution of gacyclidine enantiomers in spinal cord extracellular fluid

PURPOSE

Determination of the pharmacokinetics of gacyclidine enantiomers, a non-competitive NMDA antagonist, in plasma and spinal cord extracellular fluid (ECF) of rats.

METHODS

Implantation of microdialysis probes in spinal cord (T9). Serial collection of plasma samples and ECF dialysates over 5 hours after IV bolus administration of (+/-)-gacyclidine (2.5 mg/kg). Plasma protein binding determined in vivo by equilibrium dialysis. Chiral GC/ MS assay.

RESULTS

Plasma concentrations of (+)-gacyclidine were approximately 25% higher than those of (-)-gacyclidine over the duration of the experiment in all animals. Plasma concentrations decayed in parallel in a biphasic manner (t1/2alpha approximately 9 min; t1/2beta approximately 90 min) with no significant difference between enantiomers. Clearance and volume of distribution of (-)-gacyclidine were approximately 20% higher than those of its optical antipode (CL: 248 vs 197 ml.kg(-1)x min(-1); Vdbeta: 31.6 vs 23.5 1/kg). Protein binding (approximately 90%) was not stereoselective. Both gacyclidine enantiomers were quantifiable in spinal cord ECF 10 min after drug administration and remained stable over the duration of the experiment in spite of changing blood concentrations. Penetration of (-)-gacyclidine was significantly higher (approximately 40%) than that of (+)-gacyclidine in all animals. Yet, exposure of spinal cord ECF was similar for both enantiomers, and not correlated with plasma AUCs.

CONCLUSIONS

The disposition of gacyclidine enantiomers is stereoselective. Both enantiomers exhibit a high affinity for spinal cord tissue and their distribution may involve a stereoselective and active transport system. This hypothesis could also explain the discrepancy between drug concentrations in plasma and spinal cord ECE

Effects of spinal cord X-irradiation on the recovery of paraplegic rats

Axonal regrowth is limited in the adult CNS, especially in the spinal cord, one of the major sites of traumatic lesions. Pathophysiological changes occurring after spinal cord injury include complex acute, subacute, and late processes. In this study, we assessed whether X-irradiation interferes with the acute/subacute phases, thereby improving the functional recovery of paraplegic animals. Two days after acute compression of adult rat spinal cords, various doses (0, 2, 5, 10, 20 Gy) of X-rays were administered as one single dose to the compression site. The animals were functionally evaluated over the course of 1 month after injury, using the Tarlov scale and the Rivlin and Tator scale. We also designed a "physiological" scale, including an assessment of urinary function and infection, appropriate for the evaluation of spinal-cord-lesioned animals. Behavioral analysis suggested that the high doses, 20 Gy and, to a lesser extent, 5 and 10 Gy, were toxic, as shown by morbidity rate and "physiological" score. The 2-Gy group showed better motor performances than the lesioned nonirradiated (LNI) animals and the 5- and 20-Gy groups. Motor performance in the 5-, 10-, and 20-Gy groups was poorer than that seen in the LNI group. Gliosis was reduced in the 2-Gy group compared to LNI animals, and there was high levels of gliosis in the highly (>/=5 Gy) irradiated animals. There was a 23% less lesion-induced syringomyelia in the 2-Gy group than in the other groups (LNI and 5-20 Gy). Thus, low doses of X-rays may interfere with the formation of syringomyelia and glial scar, thereby facilitating the recovery of paraplegic animals. These findings suggest that low-dose irradiation of the lesion site, in association with other therapies, is a potentially promising treatment for improving recovery after spinal cord injury.

A mouse model of graded contusive spinal cord injury

A mouse model of spinal cord injury (SCI) could further increase our basic understanding of the mechanisms involved in injury and recovery by taking advantage of naturally-occurring and genetically engineered mutations available in mice. We have, therefore, investigated whether methods used to produce and evaluate graded experimental contusive SCI in the rat could be modified to produce a mouse model of traumatic SCI. C57BL6 mice were anesthetized with 2,2,2-tribromoethanol and a restricted laminectomy performed at the T8 vertebral level. The spinal column was stabilized and a weight drop technique used to produce contusive injury. Experimental groups were distinguished by the amount of weight or the height from which the weight was dropped onto an impounder resting on the dura (1 g x 2.5 cm, 2 g x 2.5 cm, 3 g x 2.5 cm, and 3 g x 5.0 cm). Functional deficits over time were examined up to 28 days after SCI by testing hindlimb reflex responses and coordinated motor function. Chronic lesion histopathology was evaluated by light microscopy and analyzed with morphometric techniques. All groups demonstrated profound functional deficits after injury followed by gradual recovery. Recovery correlated with the weight dropped and percent of white matter spared that was 41.3+/-6.0% (mean +/- SEM) in the 2 g x 2.5 cm group and 24.3+/-5.0% in the 3 g x 2.5 cm group. A replicate experiment confirmed reproducibility of the injury. This new mouse model of contusive SCI could pave the way for in vivo studies of the effect of genetic modifications produced by specific mutations on injury and recovery processes after spinal cord trauma.

Effects of macrophage transplantation in the injured adult rat spinal cord: a combined immunocytochemical and biochemical study

Early and robust invasion by macrophages may be one of the reasons why axonal regeneration is more effective in the PNS than in the CNS. Therefore, we have grafted autologous peritoneal macrophages labeled with fluorescent latex microspheres into spinal cord compression lesions. At various survival times, we have studied their effect on the expression of neuronal (neurofilaments [NF], calcitonin gene-related peptide [CGRP], 5-hydroxytryptamine [5-HT]) and nonneuronal markers (myelin-associated glycoprotein [MAG], glial fibrillary acidic protein [GFAP], laminin) by using semiquantitative Western blot and immunohistochemical techniques. After 1 month, we observed a significant decrease of the expression of MAG as well as an important invasion of the lesion site by neurites, chiefly peptidergic axons of presumed dorsal root origin, in macrophage-grafted animals compared with controls. In addition, angiogenesis and Schwann cell infiltration were more pronounced after macrophage grafts, providing an increase in laminin, a favorable substrate for axonal regrowth. By using reverse transcription-polymerase chain reaction (RT-PCR), mRNAs for tumor necrosis factor-alpha (TNF-alpha) were detected in the transplanted cells, whereas results were negative for nerve growth factor (NGF), neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), or acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF). Thus, macrophage grafts may represent an interesting strategy to promote axonal regeneration in the CNS. Our study suggests that they may exert their beneficial effects by degrading myelin products, which inhibit axonal regrowth, and by promoting a permissive extracellular matrix containing notably laminin. No evidence for a direct synthesis of neurotrophic factors by the transplanted macrophages was found in this study, but resident glial cells could secrete such factors as a result of stimulation by macrophage-released cytokines.

Corticospinal tract regrowth

The natural ability of the adult central nervous system of higher vertebrates to recover from injury is highly limited. This limitation is most likely due to an inhospitable environment and/or intrinsic incapacities of the neurons to re-extend their neurites after injury or axotomy. The rat corticospinal tract is the largest tract leading from brain to spinal cord and is often used as a model in developmental and regeneration studies. The extensive know-how of factors involved in the development of the corticospinal tract did provide the foundation for many studies on corticospinal tract regrowth after injury in the adult spinal cord. The results of these experiments, as discussed in this review, have led to important contributions to the further understanding of central nervous system regeneration.

Clip compression injury in the spinal cord: a correlative study of neurological and morphological alterations

Rats subjected to experimental spinal cord compression of different degrees induced by aneurysm clips were neurologically tested 3 and 5 weeks postinjury. The development of spinal cord tissue destruction over time was similar to what has been described for other experimental spinal cord injuries with characteristics such as early edema, axonal swelling, and later necrosis. Three weeks after injury a reactive gliosis was found at the injury epicenter and regenerating axons could be identified in the otherwise necrotic cavity. The extent of degeneration was highly correlated with the closing force of the aneurysm clip. The results of a number of neurological tests were correlated to the degree of clip-induced compression, to lesion volume, and to the remaining area of white matter at the epicenter. The neurological tests with the highest correlation to morphological descriptors were beam walk (r(s) = 0.89-0.95) and motor performance score (r(s) = 0.88-0.92). We conclude that the motor performance score, previously validated for photochemically induced ischemic spinal cord injuries, is equally suitable for clip compression injuries as a fast and reliable neurological test paradigm.

Three-dimensional topographic analysis of spinal accessory motoneurons under chronic mechanical compression: an experimental study in the mouse

We investigated the effect of chronic mechanical compression of the cervical spinal cord on the number of spinal accessory motoneurons in 25 tiptoe-walking Yoshimura mice. The animals had calcified deposits in the atlantoaxial membrane at the C1-C2 vertebral level, compressing the spinal cord posterolaterally. Motoneurons of the spinal accessory nerve between C1 and C5 segments were labelled using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injected into the sternocleidomastoid muscles. The counted cells were processed into a three-dimensional computer display to analyse the cytoarchitectonic changes caused by external cord compression. The number of WGA-HRP-labelled spinal accessory motoneurons was significantly reduced on the affected side. The number of motoneurons in compromised C2 and C3 cord segments correlated linearly with the extent of mechanical compression, but no such relationship was present on the contralateral side. There was an increase in the number of WGA-HRP-labelled spinal accessory motoneurons in the medial cell pools of the anterior grey horn at a level most rostral to the compression, and in the ventrolateral cell pools at levels immediately rostral to the compression. Our findings suggest that the spinal accessory motoneurons translocate rostral to the area of external compression in order to avoid mechanical injury.