A reproducible spinal cord injury model in the cat

Morphometry of cervical spinal cord in cat using design-based stereology

The spinal cord harbours nerve fibres that facilitate reflex actions and that transmit impulses to and from the brain. The cervical spinal cord is an area of particular interest in medicine and veterinary due to frequent pathologic alterations in this region. This study describes the morphometric features of the cervical spinal cord in cat using design-unbiased stereological methods. The cervical spinal cords of four male cats were dissected and samples were taken according to systematic uniform random sampling. Each sample was embedded in agar and cut into 60-µm thick sections and stained with cresyl violet 0.1% for stereological estimations. The total cervical spinal cord volume obtained by the Cavalieri estimator was 2,321.21 ± 285.5 mm³ . The relative volume of grey matter and white matter was 23.8 ± 1.3% and 76.1 ± 1.3%. The dorsal horn and ventral horn volume were 12.3 ± 1.2% and 11.4 ± 0.7% of the whole cervical spinal cord. The volume of central canal was estimated to 3.8 ± 1 mm³ . The total number of neurons was accounted 3,405,366.2 ± 267,469.4 using the optical disector/fractionator method. The number of motoneurons and interneurons was estimated to be 1,120,433.2 ± 174,796.7 and 2,284,932.9 ± 127,261.5, respectively. The average volume of the motoneurons and interneurons was estimated to 1980 µm³ and 680 µm³ , respectively, using the spatial rotator method. This knowledge of cat spinal cord findings may serve as a foundation as a translational model in spinal cord experimental research and provide basic findings for diagnosis and treatment of spinal cord disorders.

Traumatic rib head subluxation through the intervertebral foramen causing spinal cord contusive injury in a cat

Case summary

A 4-year-old cat involved in a road traffic accident presented with paraparesis, which was worse on the right-hand side. Neurolocalisation was to the T3–L3 spinal cord segments. Survey radiographs showed rib fractures but no definitive diagnosis for the paraparesis. CT revealed fracture of the dorsal rim and a T9 rib subluxation through the intervertebral foramen at T8–T9. This caused a contusive spinal injury. Treatment consisted of rest and analgesia. The cat recovered well, with the owner reporting no abnormalities 5 months following the injury.

Relevance and novel information

Road traffic accidents are a common cause of injury in the cat population, with a significant number having thoracic injuries. These include rib injures such as fractures. This is the first reported case of a traumatic rib subluxation causing a contusive injury in the spinal cord of any species. Previously reported rib subluxations have been seen in humans with spinal deformities. Conservative management in this case was sufficient.

Recovery of locomotion in cats after severe contusion of the low thoracic spinal cord

Large bilateral contusions of the T10 thoracic spinal cord were performed in 16 adult cats using a calibrated impactor. EMG and video recordings allowed weekly assessments of key locomotor parameters during treadmill training for 5 wk. Thirty-five days postcontusion, several hindlimb locomotor parameters were very similar to the prelesion ones despite some long-term deficits such as paw drag and disrupted fore-hindlimb coupling. Nine out of ten tested cats could step over obstacles placed on the treadmill. Acute electrophysiological experiments showed viable connectivity between segments rostral and caudal to the contusion. At the fifth postcontusion week, a complete spinalization was performed at T13 in 10 cats and all expressed remarkable bilateral hindlimb locomotion within 24-72 h. From our histological evaluation, we concluded that only a small percentage (~10%) of spinal cord pathways was necessary to initiate and maintain a voluntary quadrupedal locomotor pattern on a treadmill and even to negotiate obstacles. Our findings suggest that hindlimb stepping largely resulted from the activity of spinal locomotor circuits, which gradually recovered autonomy week after week. Our histological and electrophysiological evidence indicated that the persistence of specific deficits or else the maintenance of specific functions was related to the integrity of specific supraspinal and propriospinal pathways. The conclusion is that the recovery of locomotion after large spinal contusions depends on a homeostatic recalibration of a tripartite control system involving interactions between spinal circuits (central pattern generator), supraspinal influences, and sensory feedback activated through locomotor training.NEW & NOTEWORTHY The recovery of quadrupedal treadmill locomotion after a large bilateral contusion at the low thoracic T10 spinal level and the ability to negotiate obstacles were studied for 5 wk in 16 cats. Ten cats were further completely spinalized at T13 and were found to walk with the hindlimbs within 24-72 h. We conclude that the extent of locomotor recovery after large spinal contusions hinges both on remnant supraspinal pathways and on a spinal pattern generator.

Novel aspects of spinal cord evoked potentials (SCEPs) in the evaluation of dorso-ventral and lateral mechanical impacts on the spinal cord

OBJECTIVES

The aim of the current study was to mimic mechanical impacts on the spinal cord by manifesting the effects of dorsoventral (DVMP) and lateral (LMP) mechanical pressure on neural activity to address points to be considered during surgery for different purposes, including spinal cord decompression.

APPROACHES

Spinal cords of anesthetized rats were compressed at T13. Different characteristics of axons, including vulnerability, excitability, and conduction velocity (CV), in response to promptness, severity, and duration of pressure were assessed by spinal cord evoked potentials (SCEPs). Real-time SCEPs recorded at L4-5 revealed N1, N2, and N3 peaks that were used to represent the activity of injured sensory afferents, interneurons, and MN fibers. The averaged SCEP recordings were fitted by trust-region algorithm to find the equivalent Gaussian and polynomial equations.

MAIN RESULTS

The pyramidal and extrapyramidal pathways possessed CVs of 3-11 and 16-80 m s(-1), respectively. DVMP decreased the excitability of myelinated neural fibers in antidromic and orthodromic pathways. The excitability of fibers in extrapyramidal and pyramidal pathways of lateral corticospinal (LCS) and anterior corticospinal (ACS) tracts decreased following LMP. A significant drop in the amplitude of N3 and its conduction velocity (CV) revealed higher susceptibility of less-myelinated fibers to both DVMP and LMP. The best parametric fitting model for triplet healthy spinal cord CAP was a six-term Gaussian equation (G6) that fell into a five-term equation (G5) at the complete compression stage.

SIGNIFICANCE

The spinal cord is more susceptible to dorsoventral than lateral mechanical pressures, and this should be considered in spinal cord operations. SCEPs have shown promising capabilities for evaluating the severity of SCI and thus can be applied for diagnostic or prognostic intraoperative monitoring (IOM).

Effect of spinal cord compression on local vascular blood flow and perfusion capacity

Spinal cord injury (SCI) can induce prolonged spinal cord compression that may result in a reduction of local tissue perfusion, progressive ischemia, and potentially irreversible tissue necrosis. Due to the combination of risk factors and the varied presentation of symptoms, the appropriate method and time course for clinical intervention following SCI are not always evident. In this study, a three-dimensional finite element fluid-structure interaction model of the cervical spinal cord was developed to examine how traditionally sub-clinical compressive mechanical loads impact spinal arterial blood flow. The spinal cord and surrounding dura mater were modeled as linear elastic, isotropic, and incompressible solids, while blood was modeled as a single-phased, incompressible Newtonian fluid. Simulation results indicate that anterior, posterior, and anteroposterior compressions of the cervical spinal cord have significantly different ischemic potentials, with prediction that the posterior component of loading elevates patient risk due to the concomitant reduction of blood flow in the arterial branches. Conversely, anterior loading compromises flow through the anterior spinal artery but minimally impacts branch flow rates. The findings of this study provide novel insight into how sub-clinical spinal cord compression could give rise to certain disease states, and suggest a need to monitor spinal artery perfusion following even mild compressive loading.

Development of a large-animal model to measure dynamic cerebrospinal fluid pressure during spinal cord injury

Object

Spinal cord injury (SCI) often results in considerable permanent neurological impairment, and unfortunately, the successful translation of effective treatments from laboratory models to human patients is lacking. This may be partially attributed to differences in anatomy, physiology, and scale between humans and rodent models. One potentially important difference between the rodent and human spinal cord is the presence of a significant CSF volume within the intrathecal space around the human cord. While the CSF may “cushion” the spinal cord, pressure waves within the CSF at the time of injury may contribute to the extent and severity of the primary injury. The objective of this study was to develop a model of contusion SCI in a miniature pig and establish the feasibility of measuring spinal CSF pressure during injury.

Methods

A custom weight-drop device was used to apply thoracic contusion SCI to 17 Yucatan miniature pigs. Impact load and velocity were measured. Using fiber optic pressure transducers implanted in the thecal sac, CSF pressures resulting from 2 injury severities (caused by 50-g and 100-g weights released from a 50-cm height) were measured.

Results

The median peak impact loads were 54 N and 132 N for the 50-g and 100-g injuries, respectively. At a nominal 100 mm from the injury epicenter, the authors observed a small negative pressure peak (median −4.6 mm Hg [cranial] and −5.8 mm Hg [caudal] for 50 g; −27.6 mm Hg [cranial] and −27.2 mm Hg [caudal] for 100 g) followed by a larger positive pressure peak (median 110.5 mm Hg [cranial] and 77.1 mm Hg [caudal] for 50 g; 88.4 mm Hg [cranial] and 67.2 mm Hg [caudal] for 100 g) relative to the preinjury pressure. There were no significant differences in peak pressure between the 2 injury severities or the caudal and cranial transducer locations.

Conclusions

A new model of contusion SCI was developed to measure spinal CSF pressures during the SCI event. The results suggest that the Yucatan miniature pig is an appropriate model for studying CSF, spinal cord, and dura interactions during injury. With further development and characterization it may be an appropriate in vivo largeanimal model of SCI to answer questions regarding pathological changes, therapeutic safety, or treatment efficacy, particularly where humanlike dimensions and physiology are important.

Padronização da lesão de medula espinal em ratos Wistar

OBJETIVO: Padronizar um modelo experimental de lesão de medula espinal em ratos Wistar, utilizaram-se um equipamento computadorizado para impacto por queda de peso e os parâmetros determinados pelo Multicenter Animal Spinal Cord Injury Study - MASCIS. MÉTODOS: Avaliaram-se 30 ratos, com idade variando entre 20 e 25 semanas de vida. O peso variou de 200 a 300 g, para as fêmeas, e de 232 a 430 g para os machos. Realizaram-se impactos com pesos de 10 g de 12,5; 25 e 50 mm de altura, controlando-se a velocidade de impacto e o coeficiente de compressão. O impacto ocorreu sobre a superfície da medula espinal na altura da décima vértebra torácica, após laminectomia. Monitoraram-se os sinais vitais e realizaram-se gasometrias previamente e posteriormente à lesão da medula. O volume de lesão foi avaliado pela análise quantitativa dos íons de sódio e potássio. RESULTADOS: Verificaram-se correlações estatisticamente significantes entre o volume de lesão e os parâmetros mecânicos. O volume de lesão provocado por queda de 50 mm de altura foi superior aos de 12,5 e 25 mm, que não diferiram entre si. CONCLUSÃO: O modelo demonstrou-se eficaz e capaz de gerar lesões medulares padronizadas em ratos Wistar.

Spinal cord injury: plasticity, regeneration and the challenge of translational drug development

Over the past three decades, multiple mechanisms limiting central nervous system regeneration have been identified. Here, we address plasticity arising from spared systems as a particularly important and often unrecognized mechanism that potentially contributes to functional recovery in studies of 'regeneration' after spinal cord injury. We then discuss complexities involved in translating findings from animal models to human clinical trials in spinal cord injury; current strategies might be too limited in scope to yield detectable benefits in the complex and variable arena of human injury. Our animal models are imperfect, and the very variability that we attempt to control in the course of conducting rigorous research might, ironically, limit our ability to identify the most promising therapies in the human arena. Therapeutic candidates are most likely to have a detectable effect in human trials if they elicit benefits in severe contusion and larger animal models and pass the test of independent replication.

A vertebral dislocation model of spinal cord injury in rats

A new model of spinal cord injury (SCI) has been developed in the rat, which produces axonal and vascular injury within the spinal cord through lateral displacement of the vertebral column. An electromechanical feedback-controlled device produces the injury by displacing the vertebral column to the left hand side. The speed and lateral displacement is controllable by the user, and the resulting injury ranges from no histologically evident injury, to total disruption of the vertebral column with associated widespread axonal and vascular damage. Histological and immunohistological techniques were employed to correlate mechanical parameters with the extent of pathological injury of spinal cord. Axonal injury was most severe in the left lateral white matter, and vascular injury was concentrated in the gray matter.

Behavioral Testing After Spinal Cord Injury: Congruities, Complexities, and Controversies

Selection and implementation of behavioral tests in spinal cord injury research is an important process, and yet few papers have focused on these issues. The critical component of any behavioral experiment is the ability to produce reliable, reproducible, and worthwhile data. Unfortunately, the difference between worthwhile and worthless data is often subtle. This paper describes factors that must be considered in order to select the most sensitive behavioral tests to match the hypothesis of the experiment and apply any test in a standardized, consistent manner. Classifications of behavioral tests, their strengths and limitations, as well as methods to overcome these limitations are discussed. Recent work in translating behavioral tests from rats to mice is also provided. The purpose of this article is to provide a framework by which behavioral testing can be standardized within and across spinal cord injury labs.

Análise comparativa da avaliação funcional realizada na lesão medular em animais

A avaliação comportamental após, a contusão da medula espinhal, enfocou por um tempo a locomoção em campo aberto usando uma escala de classificação desenvolvida por Tarlov et al.(18). Tarlov(17) realizou estudos experimentais em cães, produzindo compressão medular com atribuição de zero a cinco para graduação dos movimentos do animal. Contudo, esta escala tem sido modificada por pesquisadores e suas alterações feitas por vários grupos tornaram as comparações das medidas do resultado locomotor difíceis. Um aspecto crítico da pesquisa utilizando lesão medular em animais é a padronização da avaliação da recuperação locomotora. A escala desenvolvida por Tator(19) é simples e de fácil utilização, porém pode não analisar todos os aspectos necessários . Basso, Beattie e Bresnahan(2,3) apresentaram uma escala de classificação com índice de recuperação locomotora em ratos que sofreram lesão medular produzida em laboratório. Os dados indicam que a escala BBB é uma medida válida para a recuperação locomotora capaz de distinguir os resultados comportamentais em função de ferimentos diferentes e para prever alterações anatômicas no centro da lesão. O propósito deste estudo foi analisar e comparar escalas de classificação locomotora sem ambigüidade, eficientes e expandida para se padronizar as medidas resultantes nos laboratórios.

Exposure to pulsed magnetic fields enhances motor recovery in cats after spinal cord injury

STUDY DESIGN

Animal model study of eight healthy commercial cats was conducted.

OBJECTIVE

To determine whether pulsed electromagnetic field (PMF) stimulation results in improvement of function after contusive spinal cord injury in cats.

SUMMARY OF BACKGROUND DATA

PMF stimulation has been shown to enhance nerve growth, regeneration, and functional recovery of peripheral nerves. Little research has been performed examining the effects of PMF stimulation on the central nervous system and no studies of PMF effects on in vivo spinal cord injury (SCI) models have been reported.

MATERIALS AND METHODS

PMF stimulation was noninvasively applied for up to 12 weeks to the midthoracic spine of cats with acute contusive spinal cord injury. The injury was produced using a weight-drop apparatus. Motor functions were evaluated with the modified Tarlov assessment scale. Morphologic analyses of the injury sites and somatosensory-evoked potential measurements were conducted to compare results between PMF-stimulated and control groups.

RESULTS

There was a significant difference in locomotor recovery between the PMF-stimulated and control groups. Although not statistically significant, PMF-stimulated spinal cords demonstrated greater sparing of peripheral white matter and smaller lesion volumes compared to controls. Somatosensory-evoked potential measurements indicated that the PMF-stimulated group had better recovery of preinjury waveforms than the control group; however, this observation also was not statistically significant because of the small sample size.

CONCLUSIONS

This preliminary study indicates that pulsed magnetic fields may have beneficial effects on motor function recovery and lesion volume size after acute spinal cord injury.

Continuous intrathecal infusion of SB203580, a selective inhibitor of p38 mitogen-activated protein kinase, reduces the damage of hind-limb function after thoracic spinal cord injury in rat

P38 mitogen-activated protein kinase (MAPK) is one of the key enzymes in apoptosis induction pathways. We tested continuous intrathecal infusion of SB203580, a selective inhibitor of p38-MAPK, after spinal cord compression injury by a 20 g weight for 40 min at the 11th vertebra level-thoracic spinal cord. SB203580 (1 microg/day) was infused for 1 week after the compression. Hind-limb function was evaluated by measuring the frequency of 'standing' posture; raising fore limbs and sustaining body weight with hind-limbs. One-week after the compression, frequency of standing spinal cord injured rat was decreased to about half of that in sham operated animals which underwent laminectomy without compression. The frequency of standing in rats infused SB203580 recovered 2-3 weeks after the spinal cord injury, on the other hand, vehicle animals infused with saline did not recover. Myelin staining by Luxol fast blue showed severe myelin degradation in vehicle animals in lateral and dorsal funiculi. Apoptotic cells, detected by TUNEL staining, appeared in lateral funiculi of spinal cord injured rats. The application of SB203580 decreased the number of apoptotic cells. The SB203580-treated animals showed no significant degeneration of myelin structure. These results suggest that inhibition of p38-MAPK is one candidate for therapeutic agents against neurological deficits after spinal cord injury.

Animal and cellular models of chronic pain

Chronic pain, especially neuropathic pain and cancer pain, is often not adequately treated by currently available analgesics. Animal models provide pivotal systems for preclinical study of pain. This article reviews some of the most widely used or promising new models for chronic pain. Partial spinal ligation, chronic constriction injury, and L5/L6 spinal nerve ligation represent three of the best characterized rodent models of peripheral neuropathy. Recently, several mouse and rat bone cancer pain models have been reported. Primary or permanent cultures of sensory neurons have been established to study the molecular mechanism of pain, especially for neurotransmitter release and signal transduction. The emerging gene microarray, genomics and proteomics methods may be applied to throughly characterize these cells. Each model is uniquely created with distinct mechanisms, it is therefore essential to report and interpret results in the context of a specific model.

Delayed neuronal damage related to microglia proliferation after mild spinal cord compression injury

In order to investigate the mechanism of delayed progressive or secondary neuronal damage after the spinal cord injury, we developed a mild-compression injury model in the rat thoracic spinal cord. Our compression device consists of a soft silicone point of contact to the dura, in order to prevent violent injury that may cause axonal tears or hemorrhages in the spinal cord. Since rats often assume a 'standing' posture, i.e. raising head with lifting their fore-limbs, damage to the thoracic spinal cord was evaluated by measuring the frequency of 'standing', which effectively indicates hind limb function. Twenty-four hours after compression by a 20 g weight for 10 or 20 min, the standing frequency of the injured rat was almost the same as that of sham animals that underwent laminectomy without compression. However, the standing frequency decreased with time; the frequency of standing at 72 h was approximately 30-50% that of sham animals. In the compressed spinal cord tissue, microglial cells, detected by lectin staining, proliferated with time. An enormous amount of microglia was observed at 48 and 72 h after compression, although only a small amount of cells were positive to lectin staining at 24 h after the compression. These results suggest that our mild-compression spinal cord injury model showed late-onset or delayed neuronal damage that may be related to pathological microglia proliferation.

Animal models used in spinal cord regeneration research

STUDY DESIGN

A literature review was conducted.

OBJECTIVES

To review animal models and injury paradigms used in the neurobiologic study of spinal cord regeneration, and to assist the spinal clinician in interpreting the many encouraging reports of potential therapies emerging from basic science laboratories.

SUMMARY OF BACKGROUND DATA

An enormous amount of interest in spinal cord regeneration research has been generated within the past 20 years with the hope that experimental therapies will become available for individuals with spinal cord injuries. The use of various animal models in the laboratory setting has been critical to the development of such experimental therapies.

METHODS

A literature review was conducted.

RESULTS

Experimental interventions in animal models of spinal cord injury were evaluated both anatomically and functionally. Anatomic assessments use various histologic techniques and frequently include the use of anterograde and retrograde axonal tracers. Functional assessments can be performed neurophysiologically or by the observation of motor and sensory performance on a number of different tests. Sharp spinal cord injury paradigms in which the cord is completely or partially transected are useful for assessing axonal regeneration anatomically. In contrast, blunt injury models in which the cord is compressed or contused more accurately mimic the typical human injury and provide a good setting for the study of secondary pathophysiologic processes immediately after injury.

CONCLUSIONS

Animal models will continue to play a critical role in the development of experimental therapies for spinal cord injuries. Both sharp and blunt spinal cord injury paradigms have unique characteristics that make them useful in addressing slightly different neurobiologic problems.

Behavioral and histological outcomes following graded spinal cord contusion injury in the C57Bl/6 mouse

A computer-controlled electromagnetic spinal cord injury device (ESCID) has been adapted to develop a mouse model of spinal cord contusion injury. In the present study, we have extended this model in C57Bl/6 mice with behavioral and histopathological outcome assessment. Three groups of mice received a laminectomy at the T(9) vertebral level followed by a contusion injury from a predetermined starting load of 1500 dynes. Contusion was produced by rapid displacement of the spinal cord to a peak distance of 0.3, 0.5, or 0.8 mm, with the entire injury and retraction procedure completed over a 23-ms epoch. Control groups received laminectomy alone or complete transection. Functional recovery was examined for 9 weeks after injury using the BBB locomotor rating scale, grid walking, and footprint analysis. Distinct patterns of locomotor recovery were evident across the five groups. Measurements of spared white matter at the epicenter, lesion length, and cross-sectional area of fibronectin-immunopositive scar tissue were also significantly different between injury groups. The severity of injury corresponded with the biomechanical measures recorded at the time of impact as well as with behavioral and histological parameters. The results demonstrate that graded contusion injuries can be produced reliably in mice using the ESCID. The data provide a thorough and quantitative analysis of the effects of contusion injury on long-term behavioral and histological outcome measures in this strain and species.

Traumatic spinal cord injury produced by controlled contusion in mouse

Previous work from this laboratory has described a rat spinal cord injury (SCI) model in which the mid-thoracic spinal cord is subjected to a single rapid and calibrated displacement at the site of a dorsal laminectomy. Injury is initiated at the tip of a vertical shaft driven by an electromagnetic shaker. Transducers arranged in series with the shaft record the patterns of displacement and force during the impact sequence. In the present study, this device and the relevant surgical procedures were adapted to produce a spinal contusion injury model in laboratory mice. The signal generator for the injury device has also been converted to a computer-controlled interface to permit extension of the model to other laboratories. Mice were subjected to SCI across a range of severities by varying the amplitude of displacement and the magnitude of measured preload force on the dural surface. A moderate injury produced by displacement of 0.5 mm over 25 msec resulted in initial paralysis and recovery of locomotion with chronic deficits in hindlimb function. The magnitude of the peak force, impulse, power, and energy generated at impact were correlated with behavioral outcome at 1 day postinjury, while peak displacement and impulse were the best predictors of behavioral outcome at 28 days postinjury. The shape of the force recording proved to be a highly sensitive measure of subtle variations in the spinal compartment that were otherwise difficult to detect in this small species. The results demonstrate that the electromagnetic spinal cord injury device (ESCID) can be used to produce a well-controlled contusion injury in mice. The unique features of controlled displacement and monitoring of the biomechanical parameters at the time of impact provide advantages of this model for reducing outcome variability. Use of this model in mice with naturally occurring and genetically engineered mutations will facilitate understanding of the molecular mechanisms of pathophysiology following traumatic spinal cord injury.

Canal geometry changes associated with axial compressive cervical spine fracture

STUDY DESIGN

A laboratory study using isolated ligamentous human cadaveric cervical spines to investigate canal occlusion during (transient) and after (steady-state) axial compressive fracture.

OBJECTIVES

To determine whether differences exist between transient and postinjury canal occlusion under axial compressive loading, and to examine the effect of loading rate on canal occlusion.

SUMMARY OF BACKGROUND DATA

Prior studies have shown no correlation between neurologic deficit and canal occlusion measurements made on radiographs and computed tomography scans. The authors hypothesized that postinjury radiographic assessment does not provide an appreciation for the transient occlusion that occurs during the traumatic fracture event, which may significantly affect the neurologic outcome.

METHODS

Twelve human cervical spines were instrumented with a specially designed canal occlusion transducer, which dynamically monitored canal occlusion during axial compressive impact. Six specimens were subjected to a fast-loading rate (time to peak load, approximately 20 msec), and the other six were subjected to a slow-loading rate (time to peak load, approximately 250 msec). After impact, two different postinjury canal occlusion measurements were performed.

RESULTS

Each of the six specimens subjected to the fast-loading rate incurred burst fractures, whereas the slow-loading rate produced six wedge-compression fractures. For the fast-rate group, the postinjury occlusion-measurements were significantly smaller than the transient occlusion. In contrast, transient occlusion was not found to be significantly different from postinjury occlusion in the slow-rate group. All of the comparisons between loading rate groups showed significant differences, with the fast-rate fractures producing larger amounts of canal occlusion in every category.

CONCLUSIONS

The findings indicate that even if canal occlusion could be measured immediately after axial compressive trauma, the measurement would underestimate the maximal amount of transient canal occlusion. Therefore, postinjury measurement of canal occlusion may indicate a smaller degree of neurologic deficit than what might be expected if the transient occlusion could be measured.

Beneficial effects of the melanocortin alpha-melanocyte-stimulating hormone on clinical and neurophysiological recovery after experimental spinal cord injury

OBJECTIVE

Melanocortins, peptides related to melanocyte-stimulating hormone (MSH) and corticotropin (ACTH), exhibit neurotrophic and neuroprotective activity in several established models of peripheral and central nervous system damage. The beneficial effects of melanocortins on functional recovery after experimental brain damage and central demyelinating diseases have prompted us to investigate alpha MSH treatment in a weight drop model of traumatic spinal cord injury in rats.

METHODS

In two independent randomized blinded experiments, treatment with either alpha MSH (75 micrograms/kg of body weight administered subcutaneously every 48 h for 3 weeks after trauma) or single high-dose (30 mg/kg, 30 min after injury) methylprednisolone was compared with saline treatment in rats subjected to a moderately severe 20-gcm weight drop injury. Spinal cord function was monitored using behavioral, electrophysiological, and histological parameters.

RESULTS

In both experiments, alpha MSH significantly improved recovery, as illustrated by Tarlov scores, thoracolumbar height, and amplitude of rubrospinal motor evoked potentials. The magnitude of the alpha MSH effect on motor performance was comparable with the one observed after treatment with methylprednisolone.

CONCLUSION

The reproducible neurological and electrophysiological improvement in spinal cord function of animals treated with alpha MSH suggests a new lead in the treatment of traumatic spinal cord injury.

New assessment techniques for evaluation of posttraumatic spinal cord function in the rat

To evaluate new pharmacologic agents with potentially beneficial effects on posttraumatic spinal cord function, we used a modified weight drop (WD) technique to induce spinal cord injuries. These contusive spinal cord injuries in the rat closely mimic the human clinicopathologic situation. Especially for drug screening purposes, the moderate and mild injuries are of interest, as both the beneficial and potentially harmful effects of experimental treatment can be detected. In this study, we describe two new functional tests that were particularly designed to detect small differences in spinal cord function after moderate and mild injuries. First, for examination of locomotion, a computer analysis of the thoracolumbar height (TLH) was designed. Second, for investigation of the conduction properties of the injured rat spinal cord, we measured rubrospinal motor evoked potentials (MEP). The efficacy of the new assessment techniques to monitor spinal cord function was compared to Tarlov scores and to morphometric analysis of preserved white matter at the injury site. The results of this study indicated that for behavioral analysis, TLH measurements as compared with Tarlov rating appeared to be more sensitive for exact and objective discrimination between small differences in motor function. Amplitudes of the rubrospinal MEP, but not latencies or the number of peaks, proved to be most sensitive to determine subtle differences in posttraumatic spinal cord function. A significant linear correlation was found between TLH and amplitude of the rubrospinal MEP. We conclude that for objective assessment of the spinal cord after moderate and mild contusive injury, TLH and rubrospinal MEP amplitudes are very valuable measures to demonstrate small functional differences.

Characterization of an experimental spinal cord injury model using waveform and morphometric analysis

STUDY DESIGN

A weight-drop device based on a displacement transducer and feedback detection circuitry was designed to produce consistent experimental spinal cord injuries in a rat model. The device was characterized and evaluated based on biomechanical parameters, quantitative histology, and neurologic behavior.

OBJECTIVE

To develop, characterize, and evaluate a spinal cord injury device for use in animal models.

SUMMARY OF BACKGROUND DATA

The biomechanical parameters of spinal cord injury, including compression, velocity, force, energy, impulse-momentum, and power, can be derived from the displacement waveform. It has been shown that the magnitude and variability of certain of these injury parameters are correlated with lesion size and neurologic deficit.

METHODS

Two groups of six male Sprague-Dawley rats were injured using the device and their injury displacement waveforms digitally recorded on a personal computer equipped with a data acquisition board. Group 1 animals were sacrificed immediately after injury, whereas Group 2 animals were sacrificed 14 days after injury. Quantitative morphometric and numerical analyses were performed on histologic specimens and injury waveforms, respectively. Biomechanical injury parameters were compared with histologic and behavioral measures of injury.

RESULTS

All kinetic injury parameters were reproducible to within standard deviations of less than +/- 22%, whereas spinal cord displacement variability was +/- 29%. Motor scores for animals on day 14 animals were 4.3 +/- 0.4, whereas lesion sizes were much more variable, exhibiting percent volumes of 5.5 +/- 2.5 immediately after injury, and 11.9 +/- 7.1 on day 14.

CONCLUSION

This device should benefit studies of experimental spinal cord injury in animals by reducing interanimal variations in injury severity, especially in the acute phase of injury.

Quantitative MRI of spinal cord injury in a rat model

Sequential in vivo MRI studies of experimental spinal cord injuries (SCI) were performed using a three-dimensional implementation of the FATE (Fast low-Angle spin echo sequence with short TE) sequence. MRI-observed pathology was quantified using a multispectral segmentation algorithm. Neurological analysis was performed on the same animals concurrently, in addition to end-point histology, for comparison with quantitative MRI results. These studies suggest that it is possible to use MRI to detect the onset of secondary injury in the spinal cord. The data also indicate that early detection of MRI-visible pathology may provide the necessary markers for predicting the long-term level of neurologic deficit.

An electromechanical spinal injury technique with dynamic sensitivity

Over the past decade, our laboratory has attempted to create a simple, accurate device that could be used to produce reliable and quantifiable spinal cord injuries in the rodent. We report here on our latest of several modifications of a spinal cord impactor that has allowed us to meet these design criteria. The impactor uses the dynamic capacity of an electromagnetic driver (Ling shaker) and a unique pattern generator to briefly compress the dorsal surface of the spinal cord at velocities that may mimic compression injuries seen in the human. Calibrated, independent transducer systems provide open-loop output of the precise movement (displacement) of the impactor probe and the force necessary to achieve a given displacement. Touch sensitivity is accomplished by vibrating the probe slightly as it approaches the dural surface. This also allows a known biomechanical starting point. This combination of improvements in sensitivity and ability to measure all components of the dynamic compression has allowed us to determine detailed biomechanical descriptors of these impact injuries with low coefficients of variation. Furthermore, such descriptors correlate highly with histopathologic and behavioral outcome measures in animal populations with a variety of injury severities.

Morphometric analysis of a model of spinal cord injury in guinea pigs, with behavioral evidence of delayed secondary pathology

A model of spinal cord trauma in guinea pigs is described, based on the concept of compression to a set thickness, as an alternative to compression or contusion with a set force or displacement. The model is technically simple and reliable and circumvents some of the biomechanical problems of contusion techniques. It was designed initially to produce moderate injuries, allowing significant recovery of function. A pair of forceps was modified to form an instrument to compress the spinal cord laterally, over a 5-mm length, to a thickness of 1.2 mm. Such compression injuries of the lower thoracic cord were produced in 12 anesthetized, adult guinea pigs, and the outcome monitored, using successive behavioral tests and morphometry of the lesion at 2-3 months. Chronic histopathology was examined quantitatively with line-sampling of axons in 1-micron plastic sections through the lesion center, stained with toluidine blue. The type and distribution of damage to axons was similar to that seen following weight-drop contusion trauma in cats. Spinal cord function was examined by means of hindlimb reflex testing and motor behavior, vestibulospinal reflex testing, and mapping the receptive field of the cutaneus trunci muscle (CTM) reflex. These injuries characteristically resulted in a delayed onset of functional deficits at 1-2 days after injury, followed by partial recovery over the course of several weeks. Overall, functional outcome correlated significantly with the number of surviving axons in the lesion. The phenomenon of "secondary" pathology was striking at the behavioral level, whereas evidence of delayed injury has been indirect in most animal models. The onset of this secondary process occurred with a longer delay than has been assumed or implied by most suggested mechanisms of secondary pathology. The time course of secondary loss and recovery may be related to that of the inflammatory response at the injury site, particularly the phagocytic activity of macrophages.

Allodynia-like effects in rat after ischaemic spinal cord injury photochemically induced by laser irradiation

We report behaviours suggesting the presence of allodynia elicited by non-noxious brushing and mechanical pressure following photochemically induced ischaemic spinal cord injury in the rat. Female rats were intravenously injected with Erythrosin B and the T10 vertebra was irradiated with a laser beam for 1, 5 or 10 min. These procedures initiated an intravascular photochemical reaction, resulting in ischaemic spinal cord injury. After irradiation a clear allodynia was observed in most rats. The animals vocalized intensely to light touch during gentle handling and were clearly agitated to light brushing of the flanks. The vocalization threshold in response to the mechanical pressure measured with von Frey hairs was markedly decreased during this period. In some animals the existence of spontaneous pain was suggested by spontaneous vocalization. The duration of the allodynia varied among animals from several hours to several days. The severity and duration of allodynia seemed not to be related to the duration of irradiation. In sham-operated rats a slight, transient allodynia was also noted around the wound within a few hours after surgery, which was effectively relieved by systemic morphine (2 mg/kg, i.p.). Morphine (2 mg/kg, i.p.) also partially relieved the allodynia in spinally injured rats 4 h after irradiation. However, morphine, even at a higher dose (5 mg/kg, i.p.), failed to alleviate the allodynia in spinally injured rats 24-48 h after the injury. Systemic injection of the GABAB agonist baclofen (0.01-0.1 mg/kg, i.p.), but not the GABAA agonist muscimol (1 mg/kg, i.p.), effectively relieved allodynia during this period. Pretreatment with guanethidine 24 h and just prior to the irradiation (20 mg/kg, s.c.) did not prevent the occurrence of allodynia in spinal cord injured rats. The present observation is the first to show that ischaemic spinal cord injury could result in cutaneous mechanical allodynia. This phenomenon is resistant to morphine and may not involve the sympathetic system. Histological examination of allodynic animals 3 days after spinal cord injury revealed considerable morphological damage in the dorsal spinal cord of a rat irradiated for 5 min. The related dorsal roots were also slightly affected in this animal, while the dorsal root ganglia were normal. However, in rats irradiated for 1 min, despite the existence of strong allodynia, no damage could be found at this time in the spinal cord, dorsal roots or dorsal root ganglia. It is suggested that functional deficits in the GABAB system in the spinal cord may be related to this allodynia-like phenomenon.(ABSTRACT TRUNCATED AT 400 WORDS)

Perspectives in anatomy and pathology of paraplegia in experimental animals

Three models of inducing spinal trauma in experimental animals--weight-dropping model, severance-by-knife model, and laceration-type-lesions model--are reviewed critically. Contributions by these models in understanding paraplegia in anatomical and pathological terms are brought out. Important distinctions between subthreshold traumas vs. threshold and suprathreshold traumas, transient and permanent paraplegic syndrome, and regeneration of served axonal fibers vs. prevention of development of permanent paraplegia, are stressed while evaluating each model of spinal trauma. Conceptual contributions by these three models and their bearing on the potential clinical applications are discussed.

Mechanical factors in experimental spinal cord injury

Reliable animal models of spinal cord injury are essential for studying pathological mechanisms and for laboratory testing of experimental treatments. The normal unpredictability of neurological outcome following experimental injury results partly from variations in the mechanics of both apparatus and tissue. Weight drop contusion models have been used extensively, and often effectively within a given study, but direct comparison between studies is usually made impossible by differences in the experimental parameters. The most important differences include the weight-height combination, the mass of the interface between weight and cord, and the support given to the cord from below. There are also important dimensional and physiological variables intrinsic to the biological material, which are usually ignored. A morphometric study of contusion injuries of the cat thoracic cord indicates that the major determinant of axon disruption is the extrusion of tissue from the impact site, due to viscoelastic distortion of the parenchyma within the meningeal tube. Direct compression and shear do not appear to play an important role in this kind of injury, where a brief compression of the cord occurs at an initial velocity of about 1.5 m/sec. The pathology produced by slower compression rates may vary, but the pattern of central necrosis, expected to be produced by extrusion, is common to most types of experimental lesion and to a large proportion of human injuries.

Spinal cord extracellular microenvironment. Can the changes resulting from trauma be graded?

It is now clear that alternatives are available to the standard method of producing spinal injury with the Allen drop technique. We have shown that small groups of animals with predictably consistent mechanical injury descriptors can now be produced for studies of this type. These groups can easily be selected to have minimal or maximal injury results, depending upon this series of mechanical descriptors. In addition, important physiological variables seem to show acute recovery patterns consistent with recovery of function in chronic animals. Since marginal injuries are likely to be more responsive to pharmacological or surgical intervention, a sensible approach would be to design studies in which animals are close to, but not at, some degree of injury from which they will spontaneously recover. Shifts of the acute physiological, chronic behavioral, or histopathological recovery curves would then indicate the potential therapeutic index of different interventions. Only in this way can significant advances be made in the selection of protocols for human trials.

Functional analysis of an electromechanical spinal cord injury device

Feedback control in our injury device allowed the impactor to be sensitive to the biomechanical characteristics of the spinal cord and produce mechanically predictable injuries. We tested the hypotheses that (i) extracellular calcium [( Ca2+]e) in the rat spinal cord recovers with a time course dependent on the magnitude of injury intensity, (ii) [Ca2+]e is initially depressed at the injury epicenter to the same degree independent of injury severity, and (iii) acute (less than 3.0 h) recovery of [Ca2+]e to normal values occurs in that group of animals that shows only transient neurologic deficits in the postinjury period. Three levels of injury (light, intermediate, and heavy) were produced by controlling spinal displacement during the injury process. After injury, [Ca2+]e at the injury site decreased to values less than 0.1 mM and then recovered during the next 3 h. Incomplete recoveries occurred in the intermediate- and heavy-injury groups (0.72 +/- 0.01 and 0.58 +/- 0.01 mM, respectively). [Ca2+]e activity in the lightly injured group recovered to normal values by 3 h. Specific injury protocols therefore resulted in reproducible responses in the cellular microenvironment. Behavioral recovery could be predicted from mechanical impact parameters. Animals in the light-injury group had transient neurologic deficits in some behavioral tests (open-field walking) with no alteration in others (inclined-plane analysis). Neurologic tests that required coordination between fore and hind limbs (grid walking) did not reveal significant deficiencies until 14 days postinjury. Those animals in the intermediate and heavy groups showed initial and continuing neurological effects in all behavioral measures. It is therefore probable that acute mechanical descriptors and hypocalcia transients are predictive of the ongoing and subsequent pathology of spinal cord injury.

Correlation between parameters of spinal cord impact and resultant injury

It is difficult and expensive to produce and maintain animals with experimental spinal cord injuries. In order to reduce the expenditure of time, money, and animals, a method of predicting the final neurologic deficit from the mechanical parameters of the initial injury is needed. An attempt was made to ascertain the mechanical parameter(s) of a spinal cord injuring impact which best predict(s) the extent of the subsequent injury. Twelve rats were laminectomized and the spinal cords contused with an impactor which recorded force and cord surface displacement. Spinal cord lesion volume was measured after killing at 21 days. The records of displacement and force were used to generate velocity, momentum, power, and energy. The maximum values of the six descriptors of the impact were checked for linear statistical correlation with lesion volume. The nonparametric correlations of the impact descriptors with gait scores from other work were also examined. All descriptors correlated at the 1% level many times; force and displacement correlated at the 1% level most of the time. The displacement of one cord surface with respect to the other was judged to be the most useful parameter because it correlated very nearly as well as force with the subsequent measures of trauma and better than the others (but perhaps not significantly better), and because it is technically easier to measure and control.

A behavioral and anatomical analysis of spinal cord injury produced by a feedback-controlled impaction device

In order to provide a reproducible experimental spinal cord injury with immediate feedback on the mechanical properties of the impact, we have developed an electro-mechanically driven, feedback-controlled impaction device. The device is sensitive to the characteristics of the injured tissue and allows continuous manipulation of impact force or tissue displacement. The current study describes the anatomical and behavioral outcomes of a range of impacts and examines the ability of the device to produce a consistent traumatic injury. Rats were subjected to spinal cord trauma at the midthoracic level. Group II received a wide range of impacts that were preset at a desired force level and group III received impacts preset for a constant displacement of the spinal cord surface. Group I served as laminectomy controls. Behavioral testing included assessments of general and fine locomotor skills (open field and grid walking) and postural adjustment to displacement (inclined plane). Lesion volumes and percentage area of the cord occupied by the lesion were assessed postmortem. For group II, significant correlations between the physical descriptors of the impact and the behavioral measures were observed early during the postoperative period for open field and inclined plane performance and later in the recovery period for grid walking. Lesion measures correlated significantly with impact descriptors and with behavioral measures as well. Group III showed consistent behavioral deficits which partially recovered in the postoperative interval. The behavioral results correlated well with the lesion measures for this group also. The results indicate that it is possible to produce an intermediate lesion in the rat which results in consistent recovery with a residual deficit 3 weeks postoperatively, using a device that allows for immediate assessment of the physical descriptors of impact trauma.

Morphometric analysis of experimental spinal cord injury in the cat: the relation of injury intensity to survival of myelinated axons

The pattern of axonal destruction and demyelination that occurs in experimental contusion injury of cat thoracic spinal cord was studied by line sampling of axons in 1 micron thick plastic sections with the light microscope. Injuries were produced by a weight-drop apparatus, with the vertebral body (T9) below the impact stabilized by supports under the transverse processes. The effects of two combinations of weight and height were examined: 10 or 13 g dropped 20 cm onto an impact area of 5 mm diameter. Animals were kept for 3-5 months after injury, then fixed by perfusion for histological analysis. The number of surviving myelinated axons was found to vary both with the weight used and with the size of the spinal cord. A measure of impact intensity was derived from the calculated momentum of the weight at impact divided by the cross sectional area of the cord (interpolated from dimensions measured rostral and caudal of the lesion following fixation). At impact intensities greater than 0.02 kg-m/s/cm2 there was practically no survival of axons at the center of the injury site, combined with almost complete breakdown of the pial margin. Between 0.08 and 0.2 kg-m/s/cm2 the number of surviving axons varied between 100,000 and 2,000, approximating a negative exponential function (r = -0.88). The number of axons surviving in the outer 100 microns of the cord varied practically linearly (r = -0.82) between near normal and less than 1% of normal over the same range of injury intensity. The number of surviving axons decreased with depth from the pia, also approximating a negative exponential function, with a 10-fold decrease in density over approximately 500 microns. The average slope of this relation with depth remained similar over the range of injury intensity examined, though the slope appeared inversely related to variation in axonal survival for different individuals at a given intensity. It is argued that the loss of axons is probably determined primarily by mechanical stretch at the time of impact. Its centrifugal pattern may be explained by longitudinal displacement of the central contents of the cord, reflecting the viscoelastic "boundary layer" properties of parenchymal flow within the meningeal tube. This is illustrated with reference to the behavior of a gelatin model under compression. The preferential loss of large caliber axons and the characteristic shift to abnormally thin myelin sheaths (resulting from post-traumatic demyelination) both varied in extent independently of injury intensity and overall axonal survival.(ABSTRACT TRUNCATED AT 400 WORDS)

Photochemically induced spinal cord injury in the rat

We have developed in the rat a minimally invasive model of reproducible spinal cord injury initiated photochemically. With the exposed spinal column intact, 560 nm irradiation of the translucent dorsal surface induces excitation of the systemically injected dye, rose Bengal, in the spinal cord microvasculature. The resultant photochemical reaction leads to vascular stasis. Histopathological changes at 7 days include hemorrhagic necrosis of the central gray matter, edematous pale-staining white matter tracts and vascular congestion. At the level of cord irradiation (T8) the entire cord thickness is necrosed except for the periphery of the anterior funiculus. Voluntary motor function is consistently lost in the subacute phase of injury.

Failure of nimodipine to reverse acute experimental spinal cord injury

The calcium-channel blocking agent, nimodipine, was administered to cats for 5 days after acute experimental SCI. Six weeks after injury, no significant differences in neurologic recovery or white matter tissue preservation at the injury site were found between treated and control animals.

Therapeutic trial of hypercarbia and hypocarbia in acute experimental spinal cord injury

Hypocarbia, normocarbia, or hypercarbia was maintained for an 8-hour period beginning 30 minutes after acute threshold spinal cord injuries in cats. No statistically significant differences in neurological recovery or histologically assessed tissue preservation were found among the three groups of animals 6 weeks after injury. No animal recovered the ability to walk. It is concluded that maintenance of hypercarbia or hypocarbia during the early postinjury period is no more therapeutic than maintenance of normocarbia. Mortality rates and tissue preservation data suggest, however, that postinjury hypocarbia may be less damaging than hypercarbia.

Failure of tetracaine to reverse spinal cord injury in the cat

Beginning 30 minutes after acute spinal cord injury, cats were treated by the administration of continuous spinal anesthesia for 8 hours. This was achieved by the intermittent injection of hyperbaric tetracaine into the subarachnoid space at the site of injury via an indwelling catheter. There were no significant differences in functional recovery or histologically assessed tissue preservation between treated cats and concurrently managed control animals. The indwelling subarachnoid catheter used for drug administration was found to have no significant effect on the spinal cord injury.

The vestibulospinal free fall response: a test of descending function in spinal-injured cats

A major problem in spinal cord injury research is quantification of motor function in animals. Most investigators in the field currently use neurologic scoring systems, relying on subjective observations of complex behaviours and assigning scores based on arbitrary criteria. These scoring scales are prone to observer bias and are nonspecific. We describe here a simple, reproducible, noninvasive, and objective test of a limited aspect of spinal motor function in cats, based on a well-known involuntary response of animals to sudden free fall. Free fall responses, or FFRs, have been studied in many species, including man, and are thought to be carried in ventral and lateral column pathways, i.e., vestibulospinal, reticulospinal, and rubrospinal tracts. We recorded the FFRs from hind and forelimb muscles of 100 cats before and after thoracic spinal cord injury. Hindlimb FFRs were shown to have three quantifiable components: a fast synchronous activation (E1) followed by a short silent period during which spinal segmental reflexes are inhibited (I1) and a late desynchronized excitatory burst (E2). Thoracic spinal injury produced hindlimb FFR losses ranging from greatly reduced amplitude to complete absence of response. Residual FFRs correlated with the extent of ventral column preservation and locomotory ability. Individual FFR components can be preserved. For example, some injured cats exhibited only 11 responses. Our work suggests that FFRs are a reliable and sensitive test of motor recovery in spinal cord injury.