Experimental spinal cord injury: quantitation of axonal damage by automated image analysis

Automated quantification of axonal and myelin changes in contusion, dislocation, and distraction spinal cord injuries: Insights into targeted remyelination and axonal regeneration

Quantifying axons and myelin is essential for understanding spinal cord injury (SCI) mechanisms and developing targeted therapies. This study proposes and validates an automated method to measure axons and myelin, applied to compare contusion, dislocation, and distraction SCIs in a rat model. Spinal cords were processed and stained for neurofilament, tubulin, and myelin basic protein, with histology images segmented into dorsal, lateral, and ventral white matter regions. Custom MATLAB scripts identified axons and myelin through brightness-based object detection and shape analysis, followed by an iterative dilation process to differentiate myelinated from unmyelinated axons. Validation showed a high correlation with manual counts of total and myelinated axons, with no significant differences between methods. Application of this method revealed distinct injury-specific changes: dislocation caused the greatest axonal loss, while distraction led to the lowest myelin-to-axon-area ratio, indicating preserved axons but severe demyelination. All injuries resulted in increased axon diameter and a decreased myelin-sheath-thickness-to-axon-diameter ratio, suggesting disrupted myelination. These results indicate that remyelination therapies may be most effective for distraction injuries, where preserved axons make remyelination crucial, while axonal regeneration therapies are likely better suited for dislocation injuries with extensive axonal loss. Contusion injuries, involving both axonal and myelin damage, may benefit from a combination of neuroprotective and remyelination strategies. These findings highlight the importance of tailoring treatments to the distinct pathophysiological features of each SCI type to optimize recovery outcomes.

NMDA receptor blockage with 2-amino-5-phosphonovaleric acid improves oxidative stress after spinal cord trauma in rats

STUDY DESIGN

2-amino-5-phosphonovaleric acid (APV) is an N-methyl-D-aspartate (NMDA) receptor blocker and has neuroprotective properties. This study is aimed at evaluating the effect of APV treatment on oxidative status after spinal cord injury (SCI).

METHODS

The experiment was carried out on the following five groups: Group 1: sham operated, non-traumatized; Group 2: with injured spinal cord, no treatment; Group 3: with SCI, injected with 100 microg kg(-1) APV; Group 4: with SCI, injected with 200 microg kg(-1) APV; and Group 5: with SCI, injected with 400 microg kg(-1) APV. SCI was inflicted by epidural compression with a cerebral vascular clip after T9-11 laminectomy. The experiments were completed after 12 h of trauma. Spinal cords were excised for evaluation of superoxide dismutase (SOD), catalase, reduced glutathione (GSH) and malonyldialdehyde (MDA) levels.

RESULTS

After SCI, SOD and GSH levels decreased and the MDA level increased significantly. APV treatment decreased the MDA level and increased SOD, catalase and GSH levels. The maximum decrease in MDA was detected in the group treated with 100 microg kg(-1) APV compared with the other groups. The GSH level was significantly increased in the group treated with 200 microg kg(-1) APV. The SOD level was significantly increased in the group treated with 200 microg kg(-1) APV.

CONCLUSION

The results of this study have shown that APV treatment creates a dose-dependent antioxidant effect in rats with SCI and may be used for the treatment of SCIs.

Glial and axonal regeneration following spinal cord injury

Spinal cord injury (SCI) has been regarded clinically as an irreversible damage caused by tissue contusion due to a blunt external force. Past research had focused on the analysis of the pathogenesis of secondary injury that extends from the injury epicenter to the periphery, as well as tissue damage and neural cell death associated with secondary injury. Recent studies, however, have proven that neural stem (progenitor) cells are also present in the brain and spinal cord of adult mammals including humans. Analyses using spinal cord injury models have also demonstrated active dynamics of cells expressing several stem cell markers, and methods aiming at functional reconstruction by promoting the potential self-regeneration capacity of the spinal cord are being explored. Furthermore, reconstruction of the neural circuit requires not only replenishment or regeneration of neural cells but also regeneration of axons. Analysis of the tissue microenvironment after spinal cord injury and research aiming to remove axonal regeneration inhibitors have also made progress. SCI is one of the simplest central nervous injuries, but its pathogenesis is associated with diverse factors, and further studies are required to elucidate these complex interactions in order to achieve spinal cord regeneration and functional reconstruction.

Erythropoietin improves oxidative stress following spinal cord trauma in rats

Spinal cord injury (SCI) is a very destructive process for both patients and society. Lipid peroxidation is the main cause of the further secondary damage which starts after mechanical destruction of tissues. Recent studies have shown that erythropoietin (EPO) has neuroprotective properties. In this study, we aimed to see the effect of EPO treatment after spinal cord injury on the oxidant and anti-oxidant enzyme systems and the relationship with the N-methyl-D-Aspartate (NMDA) blockage. Spinal cord injury was produced by epidural compression with a cerebral vascular clip that has a closing force of 40 g for 30s after a limited multilevel laminectomy (T9-11). Experiment was done in 5 groups: Group 1: Sham-operated untraumatised, Group 2: SCI untreated, Group 3: 150 i.u./kg EPO injected i.p. at the end of the first hour following the trauma. Group 4: NMDA receptor antagonist ketamine (100mg/kg) i.p. Group 5: EPO+ketamine i.p. The experiments were finished after 12h of the trauma. The spinal cords were excised for biochemical examinations. Anti-oxidant enzymes; catalase and reduced glutathione (GSH) levels increased and lipid peroxidation product, malonyldialdehyde (MDA) level decreased in EPO treated group when compared to the other groups. TNF-alpha levels decreased in EPO treated group. Application of ketamine before EPO treatment decreased effects of EPO. In conclusion, our results suggest that 150 i.u./kg i.p. EPO, a therapeutic dose in anaemic patients, applied after 1h of spinal cord injury significantly attenuated the oxidative damage of spinal cord injuries in rats. This activity is abolished via ketamine pretreatment.

Retrograde axonal degeneration "dieback" in the corticospinal tract after transection injury of the rat spinal cord: a confocal microscopy study

Axonal dieback is a process in which axons in spinal tracts retract away from the initial site of injury. The purpose of this project is to study the dynamics of dieback in corticospinal tract (CST) axons after various time intervals post-injury, to find the optimal spatial-temporal window for regenerative treatment. Rats received transection injuries at the T8 spinal level and were sacrificed at different time periods (1, 2, 4, 8, and 16 weeks). Three weeks prior to sacrifice, DiI crystals were implanted in the sensorimotor cortex and produced excellent CST labeling, and clear delineation of the terminal bulbs of transected axons. With DiI and confocal microscopy, we visualized axons along the entire length of the CST, and quantified the temporal and spatial features of dieback in axons of the CST based on the location of the terminal bulbs. We found that the majority of axons stopped dieing back 4 weeks after injury by which time they were approximately 2.5 mm from the site of injury. However, at 8 and 16 weeks after injury, some terminal bulbs were more than 10 and 19 mm, respectively, from the site of injury.

Quantitation of spinal cord demyelination, remyelination, atrophy, and axonal loss in a model of progressive neurologic injury

Spinal cord pathology, such as demyelination and axonal loss, is a common feature in multiple models of central nervous system (CNS) injury and disease. Development of methods to quantify spinal cord pathology objectively would aid studies designed to establish mechanisms of damage, correlate pathology with neurologic function, and assess therapeutic interventions. In this study, we describe sensitive methods to objectively quantify spinal cord demyelination, remyelination, atrophy, and axonal loss following the initiation of a progressive inflammatory demyelinating disease with Theiler's murine encephalomyelitis virus (TMEV). Spinal cord demyelination, remyelination, and atrophy were quantified from representative 1-microm-thick cross sections embedded in Araldite plastic using interactive image analysis. In addition, this study demonstrates novel, automated methodology to quantify axonal loss from areas of normal-appearing white matter, as a measure of secondary axonal injury following demyelination. These morphologic methods, which are applicable to various models of CNS injury, provide an innovative way to assess the benefits of therapeutic agents, to determine mechanisms of spinal cord damage, or to establish a correlation with sensitive measures of neurologic function. J. Neurosci Res 58:492-504.

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.

Spinal cord injury produced by consistent mechanical displacement of the cord in rats: behavioral and histologic analysis

We examined the ability of an electromechanical device to produce consistent and incomplete thoracic (T9) spinal cord injuries in rats by brief displacement (Dspl) of the exposed dural surface. Open field walking, inclined plane, grid walking, and footprint analysis, and a determination of the percentage of tissue spared at the lesion center were used to assess chronic outcome (6 weeks postinjury). Laminectomy control animals showed no evidence of a functional deficit or histologic lesion. Complete spinal cord transections in normal rats and in a group of animals previously injured (1.1 mm Dspl) and allowed to recover resulted in complete loss of hindlimb function, demonstrating an important functional role for the remaining spared fibers at the lesion site. Consistent spinal cord displacements (0.80 mm, 0.95 mm, and 1.10 mm) resulted in behavioral groups with low outcome variability over a narrow range of incomplete recovery of neurologic function. Significant behavioral (open field walking, inclined plane, and grid walking) and histologic differences were found between the control and Dspl groups and between the 0.80 mm and 1.10 mm Dspl groups. Significant correlations were observed among the injury parameters, behavioral, and histologic scores. Open field walking and inclined plane performance were sensitive indicators of both the early and late phases of neurologic recovery. Grid walking was most useful in animals with small chronic residual deficits. The footprint analysis resulted in less significant correlations and differences between the behavioral groups than the other outcome measures. This may result from a relatively narrow range of sensitivity (open field walking scores between 3.3 and 4.0) and increased variability within the groups.

Selective cortical neuronal damage after middle cerebral artery occlusion in rats

We studied histopathologic changes in cerebral cortex of 20 rats after middle cerebral artery occlusion by using the Fink-Heimer suppressive silver impregnation method and conventional stains. At 6 hours after occlusion, Fink-Heimer-stained sections revealed abundant coarsely granular, intensely argyrophilic neurons in the ischemic cortex. These distinctive argyrophilic neurons could be clearly differentiated from neurons that suffered postmortem changes; argyrophilic neurons were present in all layers of the lateral parietal cortex but in only the superficial cortical layers II and III in the parasagittal area of the frontoparietal cortex and the temporo-occipital area. At 24 hours after occlusion as the ischemic region progressed to pannecrosis, argyrophilic neurons were still evident in peri-infarct regions, with more prominent neuritic silver deposits but no changes in number or spatial distribution. Over 2-7 days, the argyrophilic neurons gradually disappeared while many fine silver-impregnated degenerating terminals appeared in the peri-infarct regions. At 3-6 weeks after occlusion, no more argyrophilic neurons were seen in the cortex although degenerating axons were still present in the deep white matter. Our results indicate selective neuronal damage in the superficial cortical layers and massive axonal degeneration in the cerebrum surrounding infarcts. The neuronal damage does not appear to progress beyond 6 hours after middle cerebral artery occlusion. The Fink-Heimer method has many advantages over existing conventional stains for documenting selective neuronal damage in focal cerebral ischemia.

Corticofugal axonal degeneration in rats after middle cerebral artery occlusion

We used the Fink-Heimer method to study degenerating corticofugal axons after unilateral middle cerebral artery occlusion in 14 adult male Long-Evans hooded rats. Axonal degeneration in the pyramidal tracts was prominent at 1-3 weeks, manifesting in well-defined silver-impregnated axonal bundles coursing from the internal capsule to the pyramids and crossing completely to the contralateral spinal cord. In half of eight rats examined at 1-3 weeks, the cortical infarct included the forelimb region of the sensorimotor cortex, and degenerating corticospinal axons could be traced to the lower cervical segments; in rats with involvement of the hindlimb cortical area as well, axonal degeneration extended to the lumbosacral segments. Terminal degeneration products were present in the forebrain, midbrain, and brainstem within 2 days after arterial occlusion; the number of degenerating terminals peaked at 7 days and decreased gradually thereafter up to 6 weeks. Dense terminal degeneration was observed in the trigeminal nuclear complex of all seven rats studied at 2 and 7 days. In these seven rats, five had small cortical infarcts, and silver-impregnated terminals were observed in the lateral reticular formation; in two rats with large cortical lesions, terminal degeneration was prominent in the medial reticular formation as well. We conclude that infarcts produced by middle cerebral artery occlusion cause axonal degeneration in the brainstem and spinal cord. The Fink-Heimer method may be useful for evaluating the rat middle cerebral artery occlusion model.

Evolution of tissue damage in compressive spinal cord injury in rats

The evolution of tissue damage in compressive spinal cord injuries in rats was studied using an immunohistochemical technique and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The rupture of small vessels accompanied by intense tissue permeation of serum components in and around the hemorrhagic foci appeared to be immediate consequences of the mechanical insult. The loss of cell membrane integrity in neural elements became evident within 1 hour after injury as shown by the diffuse albumin-immunoreactivity of the cytoplasm. At the site of mechanical insult, approximately 30% of the neurofilament proteins were degraded within 1 hour, and 70% of them were lost within 4 hours after injury. A large number of cells positive for glial fibrillary acidic protein were found to demarcate the injured tissue within 1 hour after injury. The progression of tissue damage largely subsided within 48 hours. One week after injury, severe degeneration of the ascending tracts in the posterior funiculus was shown clearly by axon staining and less convincingly by myelin staining. Secondary degeneration of the corticospinal tract in distal segments remained inconspicuous for up to 3 months.

Suppression of neurofilament degradation by protease inhibitors in experimental spinal cord injury

Intraperitoneal administration of the neutral protease inhibitors leupeptin and E-64c substantially suppressed the degradation of neurofilament proteins (NFP) at the site of mechanical insult and secondary axonal degeneration, and facilitated the recovery of motor functions in acute spinal cord injury in rats. The drug effects were assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis of NFP fractions from the injured tissue and by morphometry of degenerating axons revealed by the Fink-Heimer method in distal spinal cord segments with the aid of an automated image analyzer. The role of calcium-activated neutral proteases in acute central nervous tissue damage and potential use of protease inhibitors as therapeutic modalities are discussed.

Morphometric assessment of drug effects in experimental spinal cord injury

The effect of large doses of methylprednisolone sodium succinate (MPSS) and two protease inhibitors, leupeptin and bestatin, on experimental acute spinal cord injury was evaluated by morphometric analysis of degenerating axons with the aid of an automated image analyzer. Spinal cord injury was produced by epidural compression with a surgical clip on the T-11 segment in rats. The extent of axonal damage was assessed in Rexed's lamina VIII in the L-6 segment by measuring the amount of silver grains, representing degenerating axons and their terminals, using the Fink-Heimer method. The severity of axonal damage was expressed as the degeneration index: that is, the amount of silver grains in experimental animals/the amount of silver grains in cord-transected animals. When examined on the 7th postoperative day, axonal degeneration in MPSS-treated rats was significantly decreased, with an average degeneration index difference of 6 (p less than 0.05). Increased preservation of axons was seen in the leupeptin-treated rats sacrificed 7, 10, and 14 days after trauma. The difference in the degeneration index between the leupeptin-treated and untreated groups was 16 on Day 7 (p less than 0.001), 12 on Day 10 (p less than 0.001), and 13 on Day 14 (p less than 0.01). Bestatin had no beneficial effect. The implications for the use of calcium-activated neutral protease inhibitors in acute spinal cord injury are discussed.