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

Traumatic Spinal Cord Injury: An Overview of Pathophysiology, Models and Acute Injury Mechanisms

Traumatic spinal cord injury (SCI) is a life changing neurological condition with substantial socioeconomic implications for patients and their care-givers. Recent advances in medical management of SCI has significantly improved diagnosis, stabilization, survival rate and well-being of SCI patients. However, there has been small progress on treatment options for improving the neurological outcomes of SCI patients. This incremental success mainly reflects the complexity of SCI pathophysiology and the diverse biochemical and physiological changes that occur in the injured spinal cord. Therefore, in the past few decades, considerable efforts have been made by SCI researchers to elucidate the pathophysiology of SCI and unravel the underlying cellular and molecular mechanisms of tissue degeneration and repair in the injured spinal cord. To this end, a number of preclinical animal and injury models have been developed to more closely recapitulate the primary and secondary injury processes of SCI. In this review, we will provide a comprehensive overview of the recent advances in our understanding of the pathophysiology of SCI. We will also discuss the neurological outcomes of human SCI and the available experimental model systems that have been employed to identify SCI mechanisms and develop therapeutic strategies for this condition.

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

Excitotoxicity and neurological disorders: involvement of membrane phospholipids

Excitatory amino acids and their receptors play an important role in membrane phospholipid metabolism. Persistent stimulation of excitatory amino acid receptors by glutamate may be involved in neurodegenerative diseases and brain and spinal cord trauma. The molecular mechanism of neurodegeneration induced by excitatory amino acids is, however, not known. Excitotoxin-induced calcium entry causes the stimulation of phospholipases and lipases. These enzymes act on neural membrane phospholipids and their stimulation results in accumulation of free fatty acids, diacylglycerols, eicosanoids, and lipid peroxides in neurodegenerative diseases and brain and spinal cord trauma. Other enzymes, such as protein kinase C and calcium-dependent proteases, may also contribute to the neuronal injury. Excitotoxin-induced alterations in membrane phospholipid metabolism in neurodegenerative diseases and neural trauma can be studied in animal and cell culture models. These models can be used to study the molecular mechanisms of the neurodegenerative processes and to screen the efficacy of therapeutic drugs.

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.

Excitatory amino acid receptors, neural membrane phospholipid metabolism and neurological disorders

Excitatory amino acids and their receptors play an important role in membrane phospholipid metabolism. Persistent stimulation of excitatory amino acid receptors by glutamate may be involved in neurodegenerative diseases and brain and spinal cord trauma. The molecular mechanism of neurodegeneration induced by excitatory amino acids is, however, not known. Excitotoxin induced calcium entry causes the stimulation of phospholipases and lipases. These enzymes act on neural membrane phospholipids and their stimulation results in accumulation of free fatty acids, diacylglycerols, eicosanoids and lipid peroxides in neurodegenerative diseases and brain and spinal cord trauma. Other enzymes such as protein kinase C and calcium-dependent proteases may also contribute to the neuronal injury. Excitotoxin-induced alteration in membrane phospholipid metabolism in neurodegenerative diseases and neural trauma can be studied in animal and cell culture models. The models can be used to study the molecular mechanisms of the neurodegenerative processes and to screen the efficacy of therapeutic drugs for neurodegenerative disease and brain and spinal cord trauma.

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.

Effects of p-chlorophenylalanine on microvascular permeability changes in spinal cord trauma. An experimental study in the rat using 131I-sodium and lanthanum tracers

The possibility that serotonin can take part in the initiation of the increased microvascular permeability occurring in a spinal cord trauma was investigated in a rat model with 131I-sodium and lanthanum as tracers. We influenced the serotonin content in the tissue pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA), before the production of the injury and compared the results with injured, untreated controls. A small incision was made in the dorsal horn of the lower thoracic cord. It caused a progressive extravasation of 131I-sodium in the damaged segment, measured after 1, 2 and 5 h. Rostral and caudal segments also showed a significant but lower accumulation of 131I-sodium. Lanthanum added to the fixative was used as an ionic tracer detectable by electron microscopy. The endothelial cells of microvessels removed from the perifocal region after 5 h showed a marked increase in the number of lanthanum-filled vesicles. Many endothelial cells had a diffuse penetration of the tracer into the cytoplasm and the basement membrane. However, the tight junctions usually remained closed to lanthanum. Pretreatment with p-CPA markedly reduced the extravasation of 131I-sodium measured at 5 h in the traumatized cord. At the cellular level, the endothelial vesicles filled with lanthanum approached the condition of uninjured animals. The diffuse infiltration of lanthanum into endothelial cells and its spread into the basement membrane of the vascular wall were usually absent. Our results indicate that serotonin plays a role in the initiation of the increased microvascular permeability which occurs in spinal cord injuries.

Edema formation and cellular alterations following spinal cord injury in the rat and their modification with p-chlorophenylalanine

The possibility that serotonin can modify the early pathological sequences occurring in spinal cord trauma was investigated in a rat model. To that end we took advantage of the possibility of influencing serotonin pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA) before the production of the injury and compared the results with injured, untreated controls. A unilateral incision was made into the dorsal horn of the lower thoracic cord (about 2.5 mm deep, 4.5 mm long) and the rats were allowed to survive up to 5 h after the trauma. The injured region from untreated animals showed macroscopically at that time a pronounced swelling and the water content had increased by 3.5% as compared to intact controls. The segments rostral and caudal to the lesion also exhibited a profound increase in water content. Light microscopy revealed a significant expansion of the spinal cord as compared to controls. The swelling was most pronounced in the gray matter on the injured side. Electron microscopy showed distorted neurons, swollen astrocytes and extracellular edema in the gray matter in and around the primary lesion. There was also a sponginess in the surrounding white matter with disruption of myelin, collapsed axons and widened periaxonal spaces. Pretreatment of the rats with p-CPA significantly reduced the swelling of the injured spinal cord and there was no visible expansion. The ipsilateral edema in the central gray matter was considerable less pronounced as compared to that in untreated animals. The increase in water content was less than 1% in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

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.