Altered norepinephrine metabolism following experimental spinal cord injury. 1. Relationship to hemorrhagic necrosis and post-wounding neurological deficits

mTOR pathway: A potential therapeutic target for spinal cord injury

Spinal cord injury (SCI) is the most common disabling spinal injury, and the complex pathological process can eventually lead to severe neurological dysfunction. Many studies have reported that the mammalian target of rapamycin (mTOR) signaling pathway plays an important role in synaptogenesis, neuron growth, differentiation, and survival after central nervous system injury. It is also involved in various traumatic and central nervous system diseases, including traumatic brain injury, neonatal hypoxic-ischemic brain injury, Alzheimer's disease, Parkinson's disease, and cerebral apoplexy. mTOR has also been reported to play an important regulatory role in various pathophysiological processes following SCI. Activation of mTOR signals after SCI can regulate physiological and pathological processes, such as proliferation and differentiation of neural stem cells, regeneration of nerve axons, neuroinflammation, and glial scar formation, through various pathways. Inhibition of mTOR activity has been confirmed to promote repair in SCI. At present, many studies have reported that Chinese herbal medicine can inhibit the SCI-activated mTOR pathway to improve the microenvironment and promote nerve repair after SCI. Due to the role of the mTOR pathway in SCI, it may be a potential therapeutic target for SCI. This review is focused on the pathophysiological process of SCI, characteristics of the mTOR pathway, role of the mTOR pathway in SCI, role of inhibition of mTOR on SCI, and role and significance of inhibition of mTOR by related Chinese herbal medicine inhibitors in SCI. In addition, the review discusses the deficiencies and solutions to mTOR and SCI research shortcomings. This study hopes to provide reference for mTOR and SCI research and a theoretical basis for SCI biotherapy.

Cardio-centric hemodynamic management improves spinal cord oxygenation and mitigates hemorrhage in acute spinal cord injury

Chronic high-thoracic and cervical spinal cord injury (SCI) results in a complex phenotype of cardiovascular consequences, including impaired left ventricular (LV) contractility. Here, we aim to determine whether such dysfunction manifests immediately post-injury, and if so, whether correcting impaired contractility can improve spinal cord oxygenation (SCO₂), blood flow (SCBF) and metabolism. Using a porcine model of T2 SCI, we assess LV end-systolic elastance (contractility) via invasive pressure-volume catheterization, monitor intraparenchymal SCO₂ and SCBF with fiberoptic oxygen sensors and laser-Doppler flowmetry, respectively, and quantify spinal cord metabolites with microdialysis. We demonstrate that high-thoracic SCI acutely impairs cardiac contractility and substantially reduces SCO₂ and SCBF within the first hours post-injury. Utilizing the same model, we next show that augmenting LV contractility with the β-agonist dobutamine increases SCO₂ and SCBF more effectively than vasopressor therapy, whilst also mitigating increased anaerobic metabolism and hemorrhage in the injured cord. Finally, in pigs with T2 SCI survived for 12 weeks post-injury, we confirm that acute hemodynamic management with dobutamine appears to preserve cardiac function and improve hemodynamic outcomes in the chronic setting. Our data support that cardio-centric hemodynamic management represents an advantageous alternative to the current clinical standard of vasopressor therapy for acute traumatic SCI.

Multiple parameters for evaluating posterior longitudinal ligaments in thoracolumbar burst fractures

BACKGROUND

The posterior longitudinal ligament plays a key role in spinal stability. The purpose of this study was to determine the injuries of the posterior longitudinal ligament (PLL) in thoracolumbar burst fractures.

PATIENTS AND METHODS

Patients suffering a thoracolumbar burst fracture from January 2011 to December 2015 were divided into an intact group and a disrupted group according to the status of the PLL. Mid-sagittal canal diameter, width and height of bone fragments, inversion angle and horizontal rotation angle of bone fragments and local kyphosis angle were measured. Anterior, middle and posterior vertebrae compression ratio, mid-sagittal diameter compression ratio, ratio of height of bone fragments occupying the posterior wall of the injured vertebral body and ratio of the width of bone fragment occupying the transverse canal diameter were calculated.

RESULTS

A total of 95 patients were included in the study including 52 patients in the intact group and 43 patients in the disrupted group. There were significant differences on anterior and posterior vertebrae compression ratio, mid-sagittal diameter compression ratio, inversion angle and horizontal rotation angle of bone fragment (P  0.05) between the two groups. Injury of the PLL showed a positive correlation with the mid-sagittal diameter compression ratio and inversion angle of bone fragment (P  0.05).

CONCLUSION

The mid-sagittal diameter compression ratio and inversion angle of bone fragment can be used to assess the status of the PLL in thoracolumbar burst fractures. When the mid-sagittal diameter compression ratio was 52% and the inversion angle of the bone fragment was 33° the PLL was likely to be disrupted.

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.

Dorsal column sensory axons degenerate due to impaired microvascular perfusion after spinal cord injury in rats

The mechanisms contributing to axon loss after spinal cord injury (SCI) are largely unknown but may involve microvascular loss as we have previously suggested. Here, we used a mild contusive injury (120 kdyn IH impactor) at T9 in rats focusing on ascending primary sensory dorsal column axons, anterogradely traced from the sciatic nerves. The injury caused a rapid and progressive loss of dorsal column microvasculature and oligodendrocytes at the injury site and penumbra and an ~70% loss of the sensory axons by 24 h. To model the microvascular loss, focal ischemia of the T9 dorsal columns was achieved via phototoxic activation of intravenously injected rose bengal. This caused an ~53% loss of sensory axons and an ~80% loss of dorsal column oligodendrocytes by 24 h. Axon loss correlated with the extent and axial length of microvessel and oligodendrocyte loss along the dorsal column. To determine if oligodendrocyte loss contributes to axon loss, the glial toxin ethidium bromide (EB; 0.3 μg/μl) was microinjected into the T9 dorsal columns, and resulted in an ~88% loss of dorsal column oligodendrocytes and an ~56% loss of sensory axons after 72 h. EB also caused an ~75% loss of microvessels. Lower concentrations of EB resulted in less axon, oligodendrocyte and microvessel loss, which were highly correlated (R(2) = 0.81). These data suggest that focal spinal cord ischemia causes both oligodendrocyte and axon degeneration, which are perhaps linked. Importantly, they highlight the need of limiting the penumbral spread of ischemia and oligodendrocyte loss after SCI in order to protect axons.

Metoprolol treatment decreases tissue myeloperoxidase activity after spinal cord injury in rats

Neutrophil infiltration has been reported to play an important role in spinal cord injury (SCI). In addition to their cardioprotective effects, beta-blockers have been found to have neuroprotective effects on the central nervous system, but their effect on SCI has not yet been studied. In the current study, we investigated the effect of metoprolol on myeloperoxidase (MPO) activity, a marker of neutrophil activation, in the spinal cord after experimental SCI in rats. Rats were divided into six groups: controls received only laminectomy and spinal cord samples were taken immediately; the sham operated group received laminectomy, and spinal cord samples were taken 4h after laminectomy; the trauma only group underwent a 50g/cm contusion injury but received no medication; and three other groups underwent trauma as for the trauma group, and received 30mg/kg methylprednisolone, 1mg/kg metoprolol, or 1mL saline, respectively. All the medications were given intraperitoneally as single doses, immediately after trauma. Spinal cord samples were taken 4h after trauma and studied for MPO activity. The results showed that tissue MPO activity increased after injury. Both metoprolol and methylprednisolone treatments decreased MPO activity, indicating a reduction in neutrophil infiltration in damaged tissue. The effect of metoprolol on MPO activity was found to be similar to methylprednisolone. In view of these data, we conclude that metoprolol may be effective in protecting rat spinal cord from secondary injury.

Tissue expression of 165-aa vascular permeability factor after spinal cord injury is not influenced by dexamethasone administration in rats

Using immunohistochemistry, RT-PCR, and Western Blot techniques, we studied the tissue expression of the 165-aa Vascular permeability factor (VPF) after spinal cord injury (SCI) in adult Wistar rats. The results were compared according to that the animals received or non-dexamethasone, at the dose of 1mg/kg and day after trauma. Furthermore, the different functional recovery between treated and non-treated animals was recorded. Although the administration of dexamethasone showed a beneficial effect on the functional recovery of the animals, the tissue expression of VPF after SCI is not influenced by dexamethasone administration. Therefore, the neuroprotective effect of the dexamethasone after experimental SCI is not mediated through an interference on the biological effects of the 165-aa vascular permeability factor.

Caffeine impairs short-term neurological outcome after concussive head injury in rats

OBJECTIVE

Adenosine is an endogenous neuroprotective agent that is released during ischemia, hypoxia, epilepsy, and ischemic brain injury. Caffeine is a receptor antagonist for adenosine that might interfere with the neuroprotective effect of adenosine in ischemic-hypoxic conditions. An investigation was undertaken to study the effect of caffeine on neurological function, edema formation, and blood-brain barrier permeability after experimental head injury in rats.

METHODS

Adult female Wistar rats classified into different groups received caffeine intraperitoneally at doses of 0, 50, 100, and 150 mg/kg body weight. Thirty minutes after the caffeine treatment, the animals were subjected to concussive head injury (CHI) administered by a controlled cortical impact device. Neurological severity score was recorded in each rat at 2 hours after CHI. Specific gravity, water content (as an indicator of edema), and blood-brain barrier impairment were analyzed in the cortical tissue surrounding the injury site. The levels of myeloperoxidase and malondialdehyde in the cortical region were measured as indicators of neutrophil infiltration and lipid peroxidation, respectively.

RESULTS

A significant increase in righting latency and neurological deficiency after CHI was observed in caffeine-treated rats as compared with untreated animals. Although no deaths occurred in the rats exposed to CHI after pretreatment with saline, pretreatment with caffeine caused significant mortality of animals after trauma in a dose-dependent manner. Caffeine also exacerbated neutrophil infiltration, edema, and disruption of blood-brain barrier in the traumatic cortex. Light microscopy of brain revealed more severe hemorrhage and neuronal degeneration in the injured hemisphere of caffeine-treated rats as compared with rats in the injury-alone group. A significant increase in malondialdehyde in the brain of injured rats treated with caffeine before CHI clearly indicated the role of oxidative stress.

CONCLUSION

Caffeine adversely affects outcome after CHI, possibly as a result of blockade of adenosine receptors. The findings also point toward the involvement of free radical-mediated neuronal damage in caffeine-induced exacerbation of neurotrauma.

Spinal cord contusion models

Most human spinal cord injuries involve contusions of the spinal cord. Many investigators have long used weight-drop contusion animal models to study the pathophysiology and genetic responses of spinal cord injury. All spinal cord injury therapies tested to date in clinical trial were validated in such models. In recent years, the trend has been towards use of rats for spinal cord injury studies. The MASCIS Impactor is a well-standardized rat spinal cord contusion model that produces very consistent graded spinal cord damage that linearly predicts 24-h lesion volumes, 6-week white matter sparing, and locomotor recovery in rats. All aspects of the model, including anesthesia for male and female rats, age rather than body weight criteria, and arterial blood gases were empirically selected to enhance the consistency of injury.

Effects of dexamethasone on apoptosis-related cell death after spinal cord injury

OBJECT

The purpose of this study was to analyze the expression of F7-26 (Apostain) in injured spinal cord tissue, and the modifying effects of dexamethasone administration.

METHODS

A total of 56 adult female Wistar rats were subjected to traumatic spinal cord injury (SCI) to induce complete paraplegia. These rats were divided into two groups according to whether they received dexamethasone (doses of 1 mg/kg daily) post-SCI. Injured spinal cord tissue was studied by means of conventional histological techniques, and Apostain expression was determined by immunohistochemical analysis at 1, 4, 8, 24, and 72 hours, and at 1 and 2 weeks after SCI in all the animals. Apostain-positive cells, mainly neurons and glial cells, were detected 1 hour after injury, peaking at 8 hours, after which the number decreased. One week after injury, apoptosis was limited to a few glial cells, mainly oligodendrocytes, and 2 weeks after injury there was no evidence of Apostain-positive cells. In the group of paraplegic rats receiving post-SCI intraperitoneal dexamethasone, there was a significant decrease in the number of Apostain-positive cells.

CONCLUSIONS

Analysis of the results indicated that apoptosis plays a role in the early period after SCI and that administration of dexamethasone decreases apoptosis-related cell death in the injured spinal cord tissue.

Experimental study of the protection of ischemic preconditioning to spinal cord ischemia

BACKGROUND

Since the advent of ischemic preconditioning in myocardium, more and more attention has been paid to ischemic preconditioning in the central nervous system (CNS). This study was designed to evaluate the protective effect of ischemic preconditioning on spinal cord ischemia.

METHODS

Interventional neuroradiological techniques were used to induce spinal cord ischemia in a rabbit model. Hydrogen electrode technique was used to determine the regional blood flow of the spinal cord. Catecholamines and their metabolites were measured by high performance liquid chromatography (HPLA). Spinal cord evoked potentials were recorded to show spinal cord neurofunction.

RESULTS

After 5 minutes ischemic preconditioning with 20 minutes reperfusion, the regional spinal cord blood flow (rSCBF) was increased, as may be seen by the slight increase of catecholamine, especially NE. This is in positive proportion to the cAMP and indicates the enhancement of the metabolic activities of the spinal cord. After 30 minutes of irreversible ischemia, the great increase in catecholamine caused vascular spasm, endotheliocyte fissure, multiple hemorrhagic suffusion, and necrosis, which would injure the spinal cord as a result. The slight increase of the rSCBF and the maintenance of the rSCBF after irreversible ischemia may enhance the protection of ischemic preconditioning to the spinal cord neurofunction, which was proved by spinal cord evoked potentials (SCEPs).

CONCLUSIONS

Our study showed that 5 minutes of ischemic preconditioning can increase the rSCBF, enhance the tolerance of the spinal cord to irreversible ischemia, and protect the neurofunction of the spinal cord. The biological mechanism of the protective effect of ischemic preconditioning to spinal cord ischemia should be further studied.

An evidence-based review of decompressive surgery in acute spinal cord injury: rationale, indications, and timing based on experimental and clinical studies

OBJECT

The authors conducted an evidence-based review of the literature to evaluate critically the rationale and indications for and the timing of decompressive surgery for the treatment of acute, nonpenetrating spinal cord injury (SCI).

METHODS

The experimental and clinical literature concerning the role of, and the biological rationale for, surgical decompression for acute SCI was reviewed. Clinical studies of nonoperative management of SCI were also examined for comparative purposes. Evidence from clinical trials was categorized as Class I (well-conducted randomized prospective trials), Class II (well-designed comparative clinical studies), or Class II (retrospective studies). Examination of studies in which animal models of SCI were used consistently demonstrated a beneficial effect of early decompressive surgery, although it is difficult to apply these data directly to the clinical setting. The clinical studies provided suggestive (Class III and limited Class II) evidence that decompressive procedures improve neurological recovery after SCI. However, no clear consensus can be inferred from the literature as to the optimum timing for decompressive surgery. Many authors have advocated delayed treatment to avoid medical complications, although good evidence from recent Class II trials indicates that early decompressive surgery can be performed safely without causing added morbidity or mortality.

CONCLUSIONS

There is biological evidence from experimental studies in animals that early decompressive surgery may improve neurological recovery after SCI, although the relevant interventional timing in humans remains unclear. To date, the role of surgical decompression in patients with SCI is only supported by Class III and limited Class II evidence. Accordingly, decompressive surgery for SCI can only be considered a practice option. Furthermore, analysis of the literature does not allow definite conclusions to be drawn regarding appropriate timing of intervention. Hence, there is a need to conduct well-designed experimental and clinical studies of the timing and neurological results of decompressive surgery for the treatment of acute SCI.

Involvement of nicotinergic mechanisms in thyrotropin-releasing hormone-induced neurologic recovery after concussive head injury in the mouse

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in the thyrotropin-releasing hormone (TRH)-induced improvement of consciousness after concussive head injury in the mouse. Intravenous administration of TRH dose dependently shortened the duration of unconsciousness after concussion in the mouse (ED50 = 3.2 mg/kg). The improvement of recovery evoked by TRH (3 mg/kg i.v.) after concussion was not affected by i.p. pretreatment with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, alpha-methyl-para-tyrosine, p-chlorophenylalanine, scopolamine or methylscopolamine. However, mecamylamine or hexamethonium i.p. pretreatment completely inhibited the TRH-induced improvement of outcome in traumatic brain injury. The results imply that TRH-induced improvement of recovery after concussion is not associated with increased activity of monoaminergic neurons in the brain. These results suggest that the inhibitory effect of TRH upon unconsciousness after concussion in mice is mainly produced by activation of central cholinergic systems via nicotinic receptors whereas muscarinic receptors seem to be not implicated.

Role of norepinephrine and excitatory amino acids in edema of the spinal cord after experimental compression injury in rats

The role of norepinephrine and excitatory amino acids in edema of the spinal cord after an acute experimental compression injury was studied in rats. Control rats received the compression injury only. Intraspinal norepinephrine was depleted in one rat group by injection of 6-hydroxydopamine (6-OHDA) into the subarachnoid space to selectively destroy catecholamine neurons and in a third group MK-801 was administered intravenously to block receptors for N-methyl-d-aspartate (NMDA), an excitatory amino acid. Recovery from motor paralysis and suppression of edema of the spinal cord were then compared in the three groups. Significant recovery from motor paralysis was found 12 h after injury in the 6-OHDA-treated rats, compared with the controls, and 24 h after injury in the MK-801-treated rats. Edema of the spinal cord was significantly suppressed for up to 24 h after injury in the 6-OHDA-treated rats. The MK-801-treated rats showed no significant suppression of the edema until 24 h after the spinal cord injury. It was concluded that norepinephrine is primarily involved in the formation of vasogenic edemas, which develop in the early stages after an injury, whereas excitatory amino acids affect the formation of cytotoxic edemas, which develop at a relatively later stage.

Endogenous neuropeptides in patients with acute traumatic head injury. II: Changes in the levels of cerebrospinal fluid substance P, serotonin and lipid peroxidation products in patients with head trauma

The cerebrospinal fluid (CSF) levels of substance P (SP), serotonin (5-HT) and lipid peroxidation (LPx) products were measured in patients with traumatic head injury and then compared to the levels obtained from control subjects. CSF samples were collected from 45 patients (31 male, 14 female, aged 19.2 +/- 17.79) within 24 h of the head trauma and the control CSF samples were obtained from 25 healthy subjects (23 male, 2 female, aged 51.44 +/- 17.6 years) having minor surgical operations under spinal anaesthesia. CSF SP and 5-HT levels in patients with head trauma were significantly lower than the levels in controls (P < 0.005, P < 0.001, respectively). On the other hand, the CSF Lpx products were significantly increased in patients with head trauma (P < 0.001). No significant correlation was found between the CSF changes and the admission Glasgow Coma Scale scores of the patients. This study constitutes the second part of our work on endogenous neuropeptides in patients with traumatic head injury and it emphasizes the role of SP, 5-HT and lipid peroxidation as additional endogenous factors in traumatic head injuries.

Spinal shock

The term "spinal shock" applies to all phenomena surrounding physiologic or anatomic transection of the spinal cord that results in temporary loss or depression of all or most spinal reflex activity below the level of the injury. Hypotension due to loss of sympathetic tone is a possible complication, depending on the level of the lesion. The mechanism of injury that causes spinal shock is usually traumatic in origin and occurs immediately, but spinal shock has been described with mechanisms of injury that progress over several hours. Spinal cord reflex arcs immediately above the level of injury may also be severely depressed on the basis of the Schiff-Sherrington phenomenon. The end of the spinal shock phase of spinal cord injury is signaled by the return of elicitable abnormal cutaneospinal or muscle spindle reflex arcs. Autonomic reflex arcs involving relay to secondary ganglionic neurons outside the spinal cord may be variably affected during spinal shock, and their return after spinal shock abates is variable. The returning spinal cord reflex arcs below the level of injury are irrevocably altered and are the substrate on which rehabilitation efforts are based.

Role of N-methyl-D-aspartate receptor in acute spinal cord injury

To clarify the role of N-methyl-D-aspartate (NMDA) receptors in acute spinal cord injury, changes in the intraspinal microcirculation after acute spinal cord injury in rabbits were examined. Systemic administration of MK-801, an NMDA receptor antagonist, at a dose of 5 mg/kg, significantly improved motor recovery after injury and significantly reduced edema formation at the injured site without altering spinal cord blood flow or vascular permeability at the injured site. These findings indicate that excitatory amino acids contribute to secondary spinal cord damage, especially edema formation, mediated by NMDA receptors in the early stage after injury.

Three-dimensional analysis of the vascular system in the rat spinal cord with scanning electron microscopy of vascular corrosion casts. Part 2: Acute spinal cord injury

The purpose of this study was to investigate the vascular mechanisms involved in the pathophysiology of acute spinal cord injury. Vascular corrosion casts of traumatized rat spinal cords at C7-T1 were inspected by scanning electron microscopy. Nineteen rats were subjected to a 51g acute clip compression at C8-T1 and then underwent transcardial perfusion with polyester resin at 15 minutes, 4 hours, or 24 hours after injury. The injured spinal cord appeared almost avascular at the compression site, although the large vessels on the surface of the spinal cord were all intact. The sulcal arteries at the injury site frequently showed constriction, and the impressions of endothelial nuclei were more slender and less distinct in the constricted arterial casts. Extravasation of the injected resin at the injury site was observed most frequently in the 15-minute group. Poorly filled distal branches of the sulcal arteries were seen at the injury site in every group. Indeed, it was concluded that the disruption and occlusion of the sulcal arteries and their branches accounted for a considerable amount of the posttraumatic ischemia of the cord. Occlusion of the sulcal arteries in the anterior median sulcus at the injury site was more frequently observed in the 24-hour group than in earlier groups. This observation suggests that there was a progressive circulatory disturbance of the damaged sulcal arteries at the injury site. The 4- and 24-hour groups showed avascular areas extending longitudinally from the injury site in the posterior columns, probably the result of hemorrhage and venous obstruction.

Lipid peroxidation in experimental spinal cord injury: time-level relationship

Damage which occurs following spinal traumas is often irreversible. During recent years free oxygen radicals formed due to the pathological changes following neural tissue ischemia have been identified as being responsible for the ethio-pathogenesis of such damage. In our experimental study, model lesions are formed in spinal cords of rats by standard trauma. Malondialdehyde (MDA), a lipid peroxidation product, was measured in the spinal tissues distal to the trauma in order to examine indirectly the time-quantity relationship of free oxygen radicals in the area. For this study 60 rats in six groups, including one control group, were used to determine the formation of MDA. Under a surgical microscope, the spines of all rats were exposed by C5-Th6 laminectomy, and pressure was applied to the spinal cords of animals, except the members of the control group, at the level of C7 by a Yaşargil aneurysm clip. MDA was measured in spinal cord tissues in order to determine free oxygen radicals at the first and fifteenth minutes and at the first, second, and fourth hours. The statistical evaluation of the findings revealed a significant increase in MDA, starting from the 15th minute after the compression, reaching a maximum at 1 hour, and then decreasing. This observation may provide an important guide for studies on prevention of neural destruction.

Implications of focal spinal cord lesions following trauma: evaluation with magnetic resonance imaging

In a series of 15 patients who underwent early and follow up magnetic resonance imaging following spinal cord injury, those with focal spinal cord abnormalities such as cord contusion or haematoma had worse neurological outcomes, and most developed spinal cord cysts, showing as well-defined areas of CSF intensity within the cord on T1 weighted images. Patients with cord oedema initially, had better outcomes, with the development of residual areas of myelomalacia. These observations suggest that patients with focal initial spinal cord abnormalities may have an increased risk of developing posttraumatic spinal cord cysts, which may be associated with the development of delayed neurological deterioration.

Silicone rubber microangiography of acute spinal cord injury in the rat

The purpose of this study was to investigate the acute changes in the large vessels and microvasculature of the spinal cord after acute clip compression injury in the rat. Nineteen female Wistar rats underwent acute compression of the spinal cord at C8-T1 at 53 g for 1 min. Silicone rubber was injected into the ascending aorta at 15 minutes, 1, 4, or 24 hours after injury. An additional nine rats served as normal controls. The perfused spinal cords were cleared by the alcohol-methylsalicylate technique. The results showed that, in the normal rat, the centrifugal arterial system from the sulcal arteries provided the major blood supply to the gray matter and the lateral and ventral white matter extending all the way to the pial surface. In the normal rat, there were large veins in the posterior columns coursing longitudinally in the parasagittal plane at the base of the posterior columns. The injured spinal cords displayed marked ischemia and hemorrhage at the injury site. The hemorrhage predominated in the gray matter and posterior white columns and extended rostrally and caudally for 2 to 7 mm in each direction from the injury site. Remote hemorrhages originated from damage to the large parasagittal veins in the posterior columns. Extravasations of silicone rubber were frequently seen at the earlier posttraumatic times and often originated from the sulcal arteries or their branches at the injury site. Occluded sulcal arteries were identified at the injury site at 4 and 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Review of the secondary injury theory of acute spinal cord trauma with emphasis on vascular mechanisms

In patients with spinal cord injury, the primary or mechanical trauma seldom causes total transection, even though the functional loss may be complete. In addition, biochemical and pathological changes in the cord may worsen after injury. To explain these phenomena, the concept of the secondary injury has evolved for which numerous pathophysiological mechanisms have been postulated. This paper reviews the concept of secondary injury with special emphasis on vascular mechanisms. Evidence is presented to support the theory of secondary injury and the hypothesis that a key mechanism is posttraumatic ischemia with resultant infarction of the spinal cord. Evidence for the role of vascular mechanisms has been obtained from a variety of models of acute spinal cord injury in several species. Many different angiographic methods have been used for assessing microcirculation of the cord and for measuring spinal cord blood flow after trauma. With these techniques, the major systemic and local vascular effects of acute spinal cord injury have been identified and implicated in the etiology of secondary injury. The systemic effects of acute spinal cord injury include hypotension and reduced cardiac output. The local effects include loss of autoregulation in the injured segment of the spinal cord and a marked reduction of the microcirculation in both gray and white matter, especially in hemorrhagic regions and in adjacent zones. The microcirculatory loss extends for a considerable distance proximal and distal to the site of injury. Many studies have shown a dose-dependent reduction of spinal cord blood flow varying with the severity of injury, and a reduction of spinal cord blood flow which worsens with time after injury. The functional deficits due to acute spinal cord injury have been measured electrophysiologically with techniques such as motor and somatosensory evoked potentials and have been found proportional to the degree of posttraumatic ischemia. The histological effects include early hemorrhagic necrosis leading to major infarction at the injury site. These posttraumatic vascular effects can be treated. Systemic normotension can be restored with volume expansion or vasopressors, and spinal cord blood flow can be improved with dopamine, steroids, nimodipine, or volume expansion. The combination of nimodipine and volume expansion improves posttraumatic spinal cord blood flow and spinal cord function measured by evoked potentials. These results provide strong evidence that posttraumatic ischemia is an important secondary mechanism of injury, and that it can be counteracted.

Delayed changes of vascular permeability in the cat's spinal cord following continuous electrical stimulation

Liquefactive necrosis coexistent with alteration of vascular permeability was studied following electrical stimulation of the spinal cord. Evans blue albumen complex (EBA) (2.5%) was perfused one hour before electrical stimulation for 30 min with 10 mA current of 0.3 msec duration at a frequency of 20 Hz. Perfusion with saline and formalin was carried out at 0, 1, 3, 6 and 12 h after stimulation had been completed. Results were independent of the time lapse after completion of the stimulation. Liquefactive necrosis, swelling and moniliform degeneration and myelinoclasia of the myelin sheath were noted only in the external layer of the white matter. EBA leakage occurred, but there was no further expansion with time.

Central nervous system bioaminergic responses to mechanical trauma. An experimental study

Changes in biogenic amines in the brain and spinal cord following penetrating injury were studied in male Wistar rats using high-performance liquid chromatography with electrochemical detection. Rapid increase in hemispheric concentration of these substances was noted beginning shortly after trauma. This trend continued until they were about three to four times control levels by about 24 to 48 hours postinjury. In the spinal cord, however, there was an initial sharp reduction in regional concentrations 2 hours postinjury followed by a slow rise thereafter. By 48 hours postinjury, levels of norepinephrine, dopamine, and serotonin of the cords of injured animals were still less than those of nontraumatized controls. This variation in the central nervous system bioaminergic response with the level of injury raises questions as to its precise role in neurological damage following mechanical insult.

Evaluation of traumatic spinal cord edema using evoked potentials recorded from the spinal epidural space. An experimental study in the rat

Spinal cord evoked potentials (SCEP) elicited by simultaneous distal tibial and sural nerve stimulation were continuously recorded from the epidural space at the T9 and T12 levels of urethane anaesthetized rats before and after a unilateral incision (about 3 mm deep and 5 mm long) in the right dorsal horn of the T10-11 segments. The changes in SCEP were correlated with the increase in spinal cord water content measured 5 h after injury. In addition, the influence of serotonin (5-HT) in mediating such changes was explored using a pharmacological approach. The changes in SCEP immediately after injury correlated well with development of spinal cord edema measured 5 h after injury. Thus, the maximal negative peak (MNP) amplitude of SCEP decreased by an average of 64.0% immediately after injury and the water content of the spinal cord was increased from 71.6% (controls) to 77.6% 5 h after injury. Pretreatment with p-CPA (a serotonin synthesis inhibitor) prevented the initial decrease of the MNP amplitude and also the increase of water content (72.5%). On the other hand, pretreatment with cyproheptadine (a 5-HT2 receptor antagonist) enhanced both the initial decrease of the MNP amplitude as well as the increase of water content (81.3%). The results show a good correlation between changes of SCEP immediately after injury and the magnitude of spinal cord edema (r = 0.9) measured 5 h after injury. The findings reveal a major role of serotonin in mediating early changes of SCEP and later development of spinal cord edema and demonstrate a prognostic value of early SCEP recordings in predicting the final outcome of traumatic spinal cord injuries.

[Surgically stabilizing "complex therapy" of unstable injury of the lower cervical spine]

Numerous assessments of the stability of screws within the cervical vertebral bodies after strong mechanical loading showed that spondylodesis can be considered as a stable fixation whether it is performed as a ventral, dorsal of combined procedure. Luxation fractures of the cervical spine, however, often do not only show lesions of the osteo-ligamentary structures, but are also accompanied by lesions of the spinal marrow. In addition to surgical measures, the self-destructing fermentative processes occurring in the mechanically injured spinal marrow have to be and can be eliminated or at least reduced by chemotherapy. The immediate simultaneous chemotherapeutic and surgical treatment is presented as "complex therapy" and recommended because of its good results.

Early accumulation of serotonin in rat spinal cord subjected to traumatic injury. Relation to edema and blood flow changes

Changes in the concentration of serotonin (5-hydroxytryptamine) in the early period after a focal traumatic injury to rat spinal cord were determined and related to the formation of edema and alterations in blood flow. A unilateral, 5-mm-long and 3-mm-deep traumatic injury located 2 mm from the midline was created in the T10-11 segment of the cord. Five hours after the injury the serotonin concentration in the traumatized segment had increased more than 100% compared with controls. There was also a progressive increase in water content of the traumatized segment measured 1-5 h after the injury. On the other hand, the spinal cord blood flow showed a progressive decrease to about 35% of its initial value at 5 h. Pretreatment with p-chlorophenylalanine, a serotonin synthesis inhibitor, impeded the elevation in water content measured 5 h after the trauma. The spinal cord blood flow remained close to normal values and the increase in serotonin was absent. Our results show that trauma to the rat spinal cord will induce changes in the serotonin concentration of the tissue and that the associated formation of edema and blood flow alterations can be alleviated in serotonin depleted rats. Obviously, serotonin plays a significant role in the pathophysiology of traumatic injury of rat spinal cord.

Acute aggregation of serotonin-immunoreactive platelets in the injured spinal cord of rat and change of serotonin content in the neural fibers

Serotonin (5-HT) immunoreactivity was investigated at the injury site of the rat spinal cord by light and electron microscopic immunohistochemistry. The animals were perfused with fixative immediately, 1-5 min, 7-60 min, and 1-48 h after a 3-sec extradural compression of the thoracic cord with a Sugita aneurysm clip. Five minutes after injury, abundant hemostatic plugs containing platelets with high 5-HT immunoreactivity appeared at the traumatized cord segment, whereas 5-HT-containing varicose fibers became less immunoreactive. The 5-HT-immunoreactive platelets initially were localized to the periphery of the hemostatic plugs. By 30 min after injury, the platelets had decreased 5-HT, but neural fibers and terminals began to show increased 5-HT immunoreactivity, which increased and lasted as long as 48 h. These results indicate that platelets contributed to the initial 5-HT concentration increase at the injury site but that later 5-HT accumulation occurred in the neural elements.

Effect of regional spinal cord blood flow and central control in recovery from spinal cord injury

Forty-two cats were subjected to decerebration, thoracic and lumbar laminectomies, and isolation of the sciatic nerves. Spinal evoked potentials in response to bilateral sciatic nerve stimulation were recorded at L-3, and the spinal cord blood flow (SCBF) was measured by the hydrogen clearance technique. Thoracic cordotomy did not alter the lumbar SCBF or the central conduction time as determined by spinal evoked potentials. Thoracic cordotomy significantly lowered the lumbar spinal cord injury threshold. Continuous sciatic nerve stimulation increased the lumbar SCBF in normal and traumatized animals; however, it did not affect the spinal cord injury threshold as measured by recovery of the spinal evoked potentials. It appears that rostral spinal cord integrity is far more significant in recovery from spinal cord injury than the maintenance of regional SCBF.

The effect of nimodipine and dextran on axonal function and blood flow following experimental spinal cord injury

There is evidence that posttraumatic ischemia is important in the pathogenesis of acute spinal cord injury (SCI). In the present study spinal cord blood flow (SCBF), measured by the hydrogen clearance technique, and motor and somatosensory evoked potentials (MEP and SSEP) were recorded to evaluate whether the administration of nimodipine and dextran 40, alone or in combination, could increase posttraumatic SCBF and improve axonal function in the cord after acute SCI. Thirty rats received a 53-gm clip compression injury on the cord at T-1 and were then randomly and blindly allocated to one of six treatment groups (five rats in each). Each group was given an intravenous infusion of one of the following over 1 hour, commencing 1 hour after SCI: placebo and saline; placebo and dextran 40; nimodipine 0.02 mg/kg and saline; nimodipine 0.02 mg/kg and dextran 40; nimodipine 0.05 mg/kg and saline; and nimodipine 0.05 mg/kg and dextran 40. The preinjury physiological parameters, including the SCBF at T-1 (mean +/- standard error of the mean: 56.84 +/- 4.51 ml/100 gm/min), were not significantly different (p greater than 0.05) among the treatment groups. Following SCI, there was a significant decrease in the SCBF at T-1 (24.55 +/- 2.99 ml/100 gm/min; p less than 0.0001) as well as significant changes in the MEP recorded from the spinal cord (MEP-C) (p less than 0.0001), the MEP recorded from the sciatic nerve (MEP-N) (p less than 0.0001), and the SSEP (p less than 0.002). Only the combination of nimodipine 0.02 mg/kg and dextran 40 increased the SCBF at T-1 (43.69 +/- 6.09 ml/100 gm/min; p less than 0.003) and improved the MEP-C (p less than 0.0001), MEP-N (p less than 0.04), and SSEP (p less than 0.002) following SCI. With this combination, the changes in SCBF were significantly related to improvement in axonal function in the motor tracts (p less than 0.0001) and somatosensory tracts (p less than 0.0001) of the cord. This study provides quantitative evidence that an increase in posttraumatic SCBF can significantly improve the function of injured spinal cord axons, and strongly implicates posttraumatic ischemia in the pathogenesis of acute SCI.

Effect of transection on the blood-spinal cord barrier of the rat after isolation from descending sources

The disruption of descending pathways and subsequent release of vasoactive neurotransmitters may contribute to the abnormal vascular permeability observed after spinal cord injury. Therefore, the relationship between disruption of long descending fiber tracts in the rat spinal cord and the development of blood-spinal cord barrier breakdown to the protein horseradish peroxidase (HRP) was evaluated. This was accomplished by first transecting the cord in order to deplete transmitter stores in the distal (caudal) segments. One month after this isolation procedure, a second transection was made several segments distal to the first transection. The axial distribution of barrier permeability to HRP was evaluated at both the light and electron microscopic levels in this 'isolated cord' preparation. Camera lucida drawings, delineating the distribution of tracer leakage in the spinal cord, were used to quantify the extent of protein extravasation. Vascular leakage of the tracer was identified as early as 1 h postinjury but was restricted to segments adjacent to the second transection. By 1 day after injury, protein extravasation was more marked, as compared to the earlier time points, and axial spread of barrier breakdown occurred along more distal vascular sites. Abnormal permeability to HRP was confirmed at the ultrastructural level where the protein was present within vesicles in the endothelium and the surrounding smooth muscle layer and basal lamina. The tracer was also identified in the cytoplasmic compartment of neurons and glia and within the adjacent extracellular space.

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.

Monoaminergic responses to spinal trauma. Participation of serotonin in posttraumatic progression of neural damage

The monoamines norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and their major metabolites were measured in the spinal cord of rabbits following laminectomy or impact injury to the thoracic cord. Samples were taken 30 minutes, 60 minutes, 4 hours, and 6 weeks after injury. Utilization ratios (metabolite/transmitter) were calculated from the data. Turnover rates for NE and DA were also calculated at 30 minutes using the alpha-methylparatyrosine method. Trauma resulted in rapid and sustained elevations in 5-HT concentration at and around the injury site. The catecholamines were depleted slightly at the injury site. Levels of 5-hydroxyindole-3-acetic acid were elevated at 30 minutes but fell to baseline by 4 hours, resulting in a decrease in the 5-HT utilization ratio. The utilization and turnover of NE was increased at the injury site, while DA function was not affected. The large short-term increase in 5-HT levels may have been due to extravasation of platelet 5-HT stores into spinal tissue, rather than due to changes in neuronal 5-HT metabolism. At 6 weeks after injury, each monoamine and metabolite appeared to accumulate in spinal cord tissue proximal to the insult. Distal to the injury, depleted amine stores displayed augmented utilization. The data are discussed in terms of a serotonergic hypothesis of the progression of neural damage after trauma, with the interaction of 5-HT with raphe-spinal nerve terminals as a principal event.

Role of monoamines in experimental spinal cord injury in rats. Relationship between Na+-K+-ATPase and lipid peroxidation

A spinal cord injury was produced in Wistar rats by extradural compression of the cord with a Sugita aneurysm clip for 5 seconds. During a 2-week observation period following the injury, the tissue norepinephrine (NE), dopamine (DA), and serotonin (5-HT) concentrations decreased uniformly at and below the injured site. The chemical denervation of NE or 5-HT neurons produced by the intraspinal injection of 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT) 2 weeks before the injury did not cause a marked difference in the extent of hemorrhagic necrosis of the spinal cord after trauma as compared to control animals without pretreatment. In the rats pretreated with 6-OHDA, NE was decreased to less than 30% of control (non-pretreated) values, and, beginning at 5 days after injury, motor performance (assessed quantitatively with the inclined-plane method) was significantly improved compared to results in the non-pretreated control rats. The rats pretreated with 5,7-DHT showed no change from control animals. Spinal cord samples from non-pretreated control animals obtained at the injury site 30 minutes after the compression injury showed a marked decrease in the activity of synaptosomal Na+-K+-ATPase (adenosine triphosphatase) of about 50%, and an increase in both thiobarbituric acid reaction substance (about 170%) and cyclic guanine monophosphate (about 150%). The NE-denervated rats showed no significant changes in these three parameters. The results indicated that NE released after crush injury may impair the neuronal cell membrane around the lesion site by induction of lipid peroxidation. The possible mechanisms by which released NE may alter membrane function are discussed.