Time course of energy perturbation after compression trauma to the spinal cord: an experimental study in the rat using microdialysis

Persistent oppression and simple decompression both exacerbate spinal cord ascorbate levels

Background: Surgical decompression after acute spinal cord injury has become the consensus of orthopaedic surgeons. However, the choice of surgical decompression time window after acute spinal cord injury has been one of the most controversial topics in orthopaedics. Objective: We apply an online electrochemical system (OECS) for continuously monitoring the ascorbate of the rats' spinal cord to determine the extent to which ascorbate levels were influenced by contusion or sustained compression. Methods: Adult Sprague-Dawley rats (n=10) were instrumented for ascorbate concentration recording and received T11 drop spinal cord injury (SCI). The Group A (n=5) were treated with immediately decompression after SCI. The Group B (n=5) were contused and oppressed until 1 h after the injury to decompress. Results: The ascorbate level of spinal cord increased immediately by contusion injury and reached to 1.62 μmol/L ± 0.61 μmol/L (217.30% ± 95.09% of the basal level) at the time point of 60 min after the injury. Compared with the Group A, the ascorbate level in Group B increased more significantly at 1 h after the injury, reaching to 3.76 μmol/L ± 1.75 μmol/L (430.25% ± 101.30% of the basal level). Meanwhile, we also found that the decompression after 1 hour of continuous compression will cause delayed peaks of ascorbate reaching to 5.71 μmol/L ± 2.69 μmol/L (627.73% ± 188.11% of the basal level). Conclusion: Our study provides first-hand direct experimental evidence indicating ascorbate is directly involved in secondary spinal cord injury and exhibits the dynamic time course of microenvironment changes after continuous compression injury of the spinal cord.

The influence of time from injury to surgery on motor recovery and length of hospital stay in acute traumatic spinal cord injury: an observational Canadian cohort study

To determine the influence of time from injury to surgery on neurological recovery and length of stay (LOS) in an observational cohort of individuals with traumatic spinal cord injury (tSCI), we analyzed the baseline and follow-up motor scores of participants in the Rick Hansen Spinal Cord Injury Registry to specifically assess the effect of an early (less than 24 h from injury) surgical procedure on motor recovery and on LOS. One thousand four hundred and ten patients who sustained acute tSCIs with baseline American Spinal Injury Association Impairment Scale (AIS) grades A, B, C, or D and were treated surgically were analyzed to determine the effect of the timing of surgery (24, 48, or 72 h from injury) on motor recovery and LOS. Depending on the distribution of data, we used different types of generalized linear models, including multiple linear regression, gamma regression, and negative binomial regression. Persons with incomplete AIS B, C, and D injuries from C2 to L2 demonstrated motor recovery improvement of an additional 6.3 motor points (SE=2.8 p<0.03) when they underwent surgical treatment within 24 h from the time of injury, compared with those who had surgery later than 24 h post-injury. This beneficial effect of early surgery on motor recovery was not seen in the patients with AIS A complete SCI. AIS A and B patients who received early surgery experienced shorter hospital LOS. While the issues of when to perform surgery and what specific operation to perform remain controversial, this work provides evidence that for an incomplete acute tSCI in the cervical, thoracic, or thoracolumbar spine, surgery performed within 24 h from injury improves motor neurological recovery. Early surgery also reduces LOS.

A characterization of white matter pathology following spinal cord compression injury in the rat

Our laboratory has previously described the characteristics of neuronal injury in a rat compression model of spinal cord injury (SCI), focussing on the impact of this injury on the gray matter. However, white matter damage is known to play a critical role in functional outcome following injury. Therefore, in the present study, we used immunohistochemistry and electron microscopy to examine the alterations to the white matter that are initiated by compression SCI applied at T12 vertebral level. A significant loss of axonal and dendritic cytoskeletal proteins was observed at the injury epicenter within 1day of injury. This was accompanied by axonal dysfunction, as demonstrated by the accumulation of β-amyloid precursor protein (β-APP), with a peak at 3days post-SCI. A similar, acute loss of cytoskeletal proteins was observed up to 5mm away from the injury epicenter and was particularly evident rostral to the lesion site, whereas β-APP accumulation was prominent in tracts proximal to the injury. Early myelin loss was confirmed by myelin basic protein (MBP) immunostaining and by electron microscopy, which also highlighted the infiltration of inflammatory and red blood cells. However, 6weeks after injury, areas of new Schwann cell and oligodendrocyte myelination were observed. This study demonstrates that substantial white matter damage occurs following compression SCI in the rat. Moreover, the loss of cytoskeletal proteins and accumulation of β-APP up to 5mm away from the lesion site within 1day of injury indicates the rapid manner in which the axonal damage extends in the rostro-caudal axis. This is likely due to both Wallerian degeneration and spread of secondary cell death, with the latter affecting axons both proximal and distal to the injury.

Surgical treatment for acute spinal cord injury study pilot study #2: evaluation of protocol for decompressive surgery within 8 hours of injury

Acute spinal cord injury (SCI) is a major public health problem for which there is still only limited treatment available. The National Acute Spinal Cord Injury Study-2 (NASCIS-2) and -3 clinical trials demonstrated that the use of acute pharmacotherapy with methylprednisolone can attenuate the secondary injury cascade if administered within 8 hours of acute SCI. However, no trial has been performed to examine whether acute surgical decompressive procedures within this critical 8-hour time window can improve patients' neurological outcome. The purpose of the current prospective Surgical Treatment for Acute Spinal Cord Injury Study (STASCIS) pilot study was to determine the feasibility of obtaining a radiological diagnosis of spinal canal compromise of 25% or more and to perform spinal cord (C3-T1) decompressive procedures by 8 hours postinjury. One of the following three decompressive methods was used: 1) traction alone; 2) traction and surgery; or 3) surgery alone. Twenty-six patients from eight North American centers were entered into the study between 1996 and 1997. Significant difficulties were encountered in many centers in performing immediate magnetic resonance imaging examination in patients with acute SCI. Fewer than 10% of acute cervical SCI patients could be enrolled into this protocol mainly because the combination of the required time for rescue, resuscitation, transport, imaging study, and surgical preparation exceeded the 8-hour injury-to-decompressive surgery window. Eleven patients underwent decompressive procedures initially by being placed in traction at a mean time of 10.9 hours postinjury. Those patients not undergoing this procedure underwent decompressive surgery at a mean time of 40.1 hours. However, the surgical decompressive procedure was completed within 12 hours in seven patients. As a result of these findings, several major changes have been made to the STASCIS protocol for early decompressive therapy.

Role of acid-sensing ion channel 1a in the secondary damage of traumatic spinal cord injury

OBJECTIVE

To determine the cellular and molecular mechanisms by which acid-sensing ion channel 1a (ASIC1a) plays its role in the secondary injury after traumatic spinal cord injury (SCI), and validate the neuroprotective effect of ASIC1a suppression in SCI model in vivo.

BACKGROUND

Secondary damage after traumatic SCI contributes to the exacerbation of cellular insult and thereby contributes to spinal cord dysfunction. However, the underlying mechanisms remain largely unknown. Acidosis is commonly involved in the secondary injury process after the injury of central nervous system, but whether ASIC1a is involved in secondary injury after SCI is unclear.

METHODS

Male Sprague-Dawley rats were subjected to spinal contusion using a weight-drop injury approach. Western blotting and immunofluorescence assays were used to observe the change of ASIC1a expression after SCI. The TUNEL staining in vivo as well as the cell viability and death assays in spinal neuronal culture were employed to assess the role of ASIC1a in the secondary spinal neuronal injury. The electrophysiological recording and Ca(2+) imaging were performed to reveal the possible underlying mechanism. The antagonists and antisense oligonucleotide for ASIC1a, lesion volume assessment assay and behavior test were used to estimate the therapeutic effect of ASIC1a on SCI.

RESULTS

We show that ASIC1a expression is markedly increased in the peri-injury zone after traumatic SCI. Consistent with the change of ASIC1a expression in injured spinal neurons, both ASIC1a-mediated whole-cell currents and ASIC1a-mediated Ca(2+) entry are significantly enhanced after injury. We also show that increased activity of ASIC1a contributes to SCI-induced neuronal death. Importantly, our results indicate that down-regulation of ASIC1a by antagonists or antisense oligonucleotide reduces tissue damage and promotes the recovery of neurological function after SCI.

CONCLUSION

This study reveals a cellular and molecular mechanism by which ASIC1a is involved in the secondary damage process after traumatic SCI. Our results suggest that blockade of Ca(2+) -permeable ASIC1a may be a potential neuroprotection strategy for the treatment of SCI patients.

Stress-resistant neural stem cells positively influence regional energy metabolism after spinal cord injury in mice

The importance of stem cells to ameliorate the devastating consequences of traumatic injuries in the adult mammalian central nervous system calls for improvements in the capacity of these cells to cope, in particular, with the host response to the injury. We have previously shown, however, that in the acutely traumatized spinal cord local energy metabolism led to decreased ATP levels after neural stem cell (NSC) transplantation. As this might counteract NSC-mediated regenerative processes, we investigated if NSC selected for increased oxidative stress resistance are better suited to preserve local energy content. For this purpose, we exposed wild-type (WT) NSC to hydrogen peroxide prior to transplantation. We demonstrate here that transplantation of WT-NSC into a complete spinal cord compression injury model even lowers the ATP content beyond the level detected in spinal cord injury-control animals. Compared to WT-NSC, stress-resistant (SR) NSC did not lead to a further decrease in ATP content. These differences between WT- and SR-NSC were observed 4 h after the lesion with subsequent transplantation. At 24 h after lesioning, these differences were no more as obvious. Thus, in contrast to native NSC, transplantation of NSC selected for oxidative stress resistance can positively influence local energy metabolism in the first hours after spinal cord compression. The functional relevance of this observation has to be tested in further experiments.

Spinal cord injury: a systematic review of current treatment options

BACKGROUND

Spinal cord injury (SCI) is a devastating event often resulting in permanent neurologic deficit. Research has revealed an understanding of mechanisms that occur after the primary injury and contribute to functional loss. By targeting these secondary mechanisms of injury, clinicians may be able to offer improved recovery after SCI.

QUESTIONS/PURPOSES

In this review, we highlight advances in the field of SCI by framing three questions: (1) What is the preclinical evidence for the neuroprotective agent riluzole that has allowed this agent to move into clinical trials? (2) What is the preclinical evidence for Rho antagonists that have allowed this group of compounds to move into clinical trials? (3) What is the evidence for early surgical decompression after SCI?

METHODS

We conducted a systematic review of MEDLINE and EMBASE-cited articles related to SCI to address these questions.

RESULTS

As a result of an improved understanding of the secondary mechanisms of SCI, specific clinical strategies have been established. We highlight three strategies that have made their way from bench to bedside: the sodium-glutamate antagonist riluzole, the Rho inhibitor Cethrin, and early surgical decompression. Each of these modalities is under clinical investigation. We highlight the fundamental science that led to this development.

CONCLUSIONS

As our understanding of the fundamental mechanisms of SCI improves, we must keep abreast of these discoveries to translate them into therapies that will hopefully benefit patients. We summarize this process of bench to bedside with regard to SCI.

The human G93A-SOD1 mutation in a pre-symptomatic rat model of amyotrophic lateral sclerosis increases the vulnerability to a mild spinal cord compression

Background

Traumatic injuries can undermine neurological functions and act as risk factors for the development of irreversible and fatal neurodegenerative disorders like amyotrophic lateral sclerosis (ALS). In this study, we have investigated how a mutation of the superoxide dismutase 1 (SOD1) gene, linked to the development of ALS, modifies the acute response to a gentle mechanical compression of the spinal cord. In a 7-day post-injury time period, we have performed a comparative ontological analysis of the gene expression profiles of injured spinal cords obtained from pre-symptomatic rats over-expressing the G93A-SOD1 gene mutation and from wild type (WT) littermates.

Results

The steady post-injury functional recovery observed in WT rats was accompanied by the early activation at the epicenter of injury of several growth-promoting signals and by the down-regulation of intermediate neurofilaments and of genes involved in the regulation of ion currents at the 7 day post-injury time point. The poor functional recovery observed in G93A-SOD1 transgenic animals was accompanied by the induction of fewer pro-survival signals, by an early activation of inflammatory markers, of several pro-apoptotic genes involved in cytochrome-C release and by the persistent up-regulation of the heavy neurofilament subunits and of genes involved in membrane excitability. These molecular changes occurred along with a pronounced atrophy of spinal cord motor neurones in the G93A-SOD1 rats compared to WT littermates after compression injury.

Conclusions

In an experimental paradigm of mild mechanical trauma which causes no major tissue damage, the G93A-SOD1 gene mutation alters the balance between pro-apoptotic and pro-survival molecular signals in the spinal cord tissue from the pre-symptomatic rat, leading to a premature activation of molecular pathways implicated in the natural development of ALS.

Intrathecal lactate concentration and spinal cord injury in thoracoabdominal aortic surgery

OBJECTIVE

The aim of this study was to evaluate the role of lactate as an early predictor of spinal cord injury during thoracoabdominal aortic aneurysm repair.

DESIGN

Observational study.

SETTING

University hospital.

PARTICIPANTS

Sixteen consecutive patients (10 men and 6 women) scheduled to undergo thoracoabdominal aortic aneurysm repair were enrolled in the study. All patients were affected by atherosclerotic aneurysmal pathology.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During surgery, the authors simultaneously withdrew samples of cerebrospinal fluid and arterial blood to evaluate pO(2), pCO(2), pH, and lactate concentration. Samples were collected at 5 fixed times during and after surgery: T1 (before aortic cross-clamping), T2 (15 minutes after clamping), T3 (just before unclamping), T4 (end of surgery), and T5 (4 hours after the end of surgery). Lactate levels in cerebrospinal fluid rose consistently during aortic cross-clamping (T1 = 1.89 mmol/L, T2 = 2.21 mmol/L, T3 = 2.88 mmol/L, T4 = 3.655 mmol/L, and T5 = 3.16 mmol/L). Lactate concentrations in the cerebrospinal fluid were significantly higher in the 4 patients who developed neurologic injury, even at T1 (before surgery), than in those who did not end in spinal cord injury with the 4 highest values belonging to the 4 patients who later developed spinal cord injury.

CONCLUSIONS

This study has the potential to elucidate the time course of early lactate level elevation during thoracoabdominal aortic aneurysm repair and its clinical use in predicting the development of postoperative spinal cord injury.

Timing of decompressive surgery of spinal cord after traumatic spinal cord injury: an evidence-based examination of pre-clinical and clinical studies

While the recommendations for spine surgery in specific cases of acute traumatic spinal cord injury (SCI) are well recognized, there is considerable uncertainty regarding the role of the timing of surgical decompression of the spinal cord in the management of patients with SCI. Given this, we sought to critically review the literature regarding the pre-clinical and clinical evidence on the potential impact of timing of surgical decompression of the spinal cord on outcomes after traumatic SCI. The primary literature search was performed using MEDLINE, CINAHL, EMBASE, and Cochrane databases. A secondary search strategy incorporated articles referenced in prior meta-analyses and systematic and nonsystematic review articles. Two reviewers independently assessed every study with regard to eligibility, level of evidence, and study quality. Of 198 abstracts of pre-clinical studies, 19 experimental studies using animal SCI models fulfilled our inclusion and exclusion criteria. Despite some discrepancies in the results of those pre-clinical studies, there is evidence for a biological rationale to support early decompression of the spinal cord. Of 153 abstracts of clinical studies, 22 fulfilled the inclusion and exclusion criteria. While the vast majority of the clinical studies were level-4 evidence, there were two studies of level-2b evidence. The quality assessment scores varied from 7 to 25 with a mean value of 12.41. While 2 of 22 clinical studies assessed feasibility and safety, 20 clinical studies examined efficacy of early surgical intervention to stabilize and align the spine and to decompress the spinal cord; the most common definitions of early operation used 24 and 72 h after SCI as timelines. A number of studies indicated that patients who undergo early surgical decompression can have similar outcomes to patients who received a delayed decompressive operation. However, there is evidence to suggest that early surgical intervention is safe and feasible and that it can improve clinical and neurological outcomes and reduce health care costs. Based on the current clinical evidence using a Delphi process, an expert panel recommended that early surgical intervention should be considered in all patients from 8 to 24 h following acute traumatic SCI.

Effect of decompression on complete spinal cord injury in rats

To examine whether spinal cord decompression improves functional recovery and decreases lesion volumes in paraplegic (not paraparetic) rats and, if so, at what postoperative time it is most efficacious. The spinal cords of 63 female rats were compressed at T9 with Yasargil clips. Rats were assigned randomly to five different treatment groups of 3 s, 1 hr, 6 hr, 3 weeks, and 10 weeks. Locomotor behavior scoring was based on the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale (Ohio State University, Columbus, OH) motor scores. Comparing five groups, the mean BBB was statistically higher in the 3-s group (P < 0.05). Comparison of progressive changes in BBB in each group revealed statistically meaningful improvement in the 3-s group, too. Spared surface area of spinal cord was 81.5 +/- 4.9% in 3-s group and 10.8 +/- 1.4% in the delayed groups of decompression (P = 0.039). Rats undergoing immediate decompression showed significantly better functional recovery and smaller lesion volumes.

The characteristics of neuronal injury in a static compression model of spinal cord injury in adult rats

Studies of spinal cord injury using contusion (impact) injury paradigms have shown that neuronal death is an acute event that is largely over within 24 h. However, much less is known about cell death following compression injury, despite compression being a key component of natural spinal injuries. We have therefore used neuronal nuclei (NeuN) immunostaining to examine the spatiotemporal pattern of neuronal loss after static compression injury in adult rats. 3D reconstruction was used to reveal the full effect of the injury. Neuronal loss at the injury epicentre, assessed by NeuN immunostaining, amounted to 44% at 1 day but increased to 73% at 3 days and 81% at 1 month. Neuronal loss was also seen 5 mm rostral and caudal to the epicentre, but was not significant until 3 days. NeuN loss was greatest in the ventral horns and in the intermediate grey matter, with the lateral dorsal horns relatively spared. Cystic cavities formed after injury, but were not evident until 4 weeks and were small in size. In contrast to the slow profile of neuronal loss, the compression injury also evoked a transient expression of activating transcription factor-3 (ATF3) and activated c-Jun in neurons. ATF3 expression peaked at 3 days and declined at 7 days. Our spatiotemporal analysis of compression injury shows that neuronal loss is much more protracted than in contusion injury, and highlights the potential for neuroprotective strategies. This study is also the first indication of ATF3 involvement in spinal cord injury.

Assessment of three year experience of a strategy for patient selection and timing of operation in the management of acute thoracic and lumbar spine fractures: a prospective study

BACKGROUND

The purpose of this article is to report experience gained over three years of the use of a protocol for patient selection and timing of operation for acute thoracic and lumbar fractures.

METHOD

At admission, all patients underwent neurological and imaging exams. All patients with a spinal cord lesion scored as ASIA A at any level inferior to T10 and as ASIA B, C or D at any level, were categorized as emergency and operated on within eight hours from trauma. ASIA A cases in the T1-T10 tract and ASIA E cases at any level were treated in the ordinary operative work schedule.

FINDINGS

Ninety-four patients with surgically treated lumbar or thoracic fractures took part in this study. On the imaging studies, 12 patients were classified as A, 50 as B and 32 as C following the AO classification. At the neurological exam, 39 patients were scored as ASIA A, nine as B, six as C, two as D and 38 as E. At follow-up, of the 39 patients scored as ASIA A, 13 (33%) improved at least one grade and of the 17 scored as ASIA B, C or D, 11 (64.7%) improved. None of the 38 patients scored as ASIA E deteriorated.

CONCLUSIONS

The findings show that the strategy in the protocol was safe and followed by satisfactory rates of neurological outcome. Larger prospective studies, preferably randomized, are needed to establish definitively its place in the management of patients with spinal injury.

The timing of surgical intervention in the treatment of spinal cord injury: a systematic review of recent clinical evidence

STUDY DESIGN

Evidence-based literature review.

OBJECTIVE

To provide updated evidence-based recommendations regarding spinal cord decompression in patients with acute spinal cord injury (SCI).

SUMMARY OF BACKGROUND DATA

It is controversial whether early decompression following SCI conveys a benefit in neurologic outcome.

METHODS

MEDLINE search of experimental and clinical studies showing the effect of decompression on neurologic outcome following SCI. We focused on articles published within the last 10 years, with a particular emphasis on research conducted within the past 5 years.

RESULTS

A total of 66 articles were retrieved. Animal studies consistently show that neurologic recovery is enhanced by early decompression. There was 1 randomized controlled trial that showed no benefit to early (<72 hours) decompression. Several recent prospective series suggest that early decompression (<72 hours) can be performed safely and may improve neurologic outcomes. A recent systematic review showed that early decompression (<24 hours) resulted in statistically better outcomes compared to both delayed decompression and conservative treatment.

CONCLUSIONS

There are currently no standards regarding the role and timing of decompression in acute SCI. We recommend urgent decompression of bilateral locked facets in a patient with incomplete tetraplegia or in a patient with SCI with neurologic deterioration. Urgent decompression in acute cervical SCI remains a reasonable practice option and can be performed safely. There is emerging evidence that surgery within 24 hours may reduce length of intensive care unit stay and reduce post-injury medical complications.

Regional energy metabolism following short-term neural stem cell transplantation into the injured spinal cord

Stem cells have been shown to partly restore central nervous system (CNS) function after transplantation into the injured CNS. However, little is known about their influence on acute energy metabolism after spinal cord injury. The present study was designed to analyze regional changes in energy metabolites. Young adult mice were subjected to laminectomy with subsequent hemisection at the L2/3 vertebral level. Immediately thereafter a stable clone of murine neural stem cells (NSCs) was injected into the lesion site. After 4 and 24 h, spinal cords were removed and ATP, glucose, and lactate were analyzed by a bioluminescence approach in serial sections and compared to a laminectomized (intact control), hemisected-only or hemisected vehicle-injected control group. At both time points, ATP content of the hemisected group in the tissue segments adjacent to the lesion was increased when compared to the laminectomized control. At the lesion site ATP content decreased significantly at 24 h in the cell-transplanted group when compared to the laminectomized control group. Glucose content decreased at the lesion site and in segments adjacent to the lesion at both time points and in all experimental groups when compared to the laminectomized control group. Lactate content decreased significantly at 4 h in the caudal segments of the vehicle-injected group and in both adjacent segments of the transplanted group when compared to the laminectomized control. At the lesion site, lactate content decreased significantly at 4 and 24 h in the cell-transplanted group, when compared to the laminectomized control. The area of ATP decline at the lesion site 24 h postinjury was significantly lower in the vehicle control group as compared to the hemisected or transplanted group. The decrease in glucose combined with an increase in ATP in the lesion-adjacent segments may indicate that the tissue responds with an increased use of glucose to support itself with sufficient ATP. The significant decrease in glucose, lactate, and ATP in the cell-transplanted group at 24 h may indicate a high metabolic need of the stem cells. The lower area of ATP decline 24 h after vehicle administration suggests that the vehicle solution washes out toxic mediators, thus ameliorating hemisection-dependent secondary tissue damage.

The role and timing of early decompression for cervical spinal cord injury: update with a review of recent clinical evidence

It remains controversial whether early decompression following spinal cord injury conveys a benefit in neurological outcome. The goal of this paper is to provide evidence-based recommendations regarding spinal cord decompression in patients with acute spinal cord injury. We performed a Medline search of experimental and clinical studies reporting on the effect of decompression on neurological outcome following spinal cord injury. Animal studies consistently show that neurological recovery is enhanced by early decompression. One randomized controlled trial showed no benefit to early (<72 h) decompression, however, several recent prospective series suggest that early decompression (<12 h) can be performed safely and may improve neurological outcomes. A recent meta-analysis showed that early decompression (<24 h) resulted in statistically better outcomes compared to both delayed decompression and conservative management. Currently, there are no standards regarding the role and timing of decompression in acute spinal cord injury. We recommend urgent decompression of bilateral locked facets in patients with incomplete tetraplegia or in patients with spinal cord injury experiencing neurological deterioration. Urgent decompression in acute cervical spinal cord injury remains a reasonable practice option and can be performed safely.

Increased protein oxidation and decreased creatine kinase BB expression and activity after spinal cord contusion injury

Traumatic injury to the spinal cord triggers several secondary effects, including oxidative stress and compromised energy metabolism, which play a major role in biochemical and pathological changes in spinal cord tissue. Free radical generation and lipid peroxidation have been shown to be early events subsequent to spinal cord injury. In the present study, we demonstrated that protein oxidation increases in rat spinal cord tissue after experimental injury. As early as h after injury, the level of protein carbonyls at the injury epicenter was significantly higher than in control (169%, p < 0.05) and increased gradually over the next 4 weeks to 1260% of control level. Both caudal and rostral parts of the injured spinal cord demonstrated a mild increase of protein carbonyls by 4 weeks postinjury (135-138%, p < 0.05). Immunocytochemical analysis of protein carbonyls in the spinal cord cross-sections showed increased protein carbonyl immunoreactivity in the epicenter section compared to rostral and caudal sections of the same animal or control laminectomy animals. Increased protein carbonyl formation in damaged spinal cord tissue was associated with changes in activity and expression of an oxidative sensitive enzyme, creatine kinase BB, which plays an important role in the maintenance of ATP level in the CNS tissue. Damage to CK function in the CNS may severely aggravate the impairment of energy metabolism. The results of our study indicate that events associated with oxidative damage are triggered immediately after spinal cord trauma but continue to occur over the subsequent 4 weeks. These results suggest that antioxidant therapeutic strategies may be beneficial to lessen the consequences of the injury and potentially improve the restoration of neurological function.

The role and timing of decompression in acute spinal cord injury: what do we know? What should we do?

The management of acute spinal cord injury has traditionally concentrated on preventative measures as well as, for the better part of the previous century, conservative care. Pharmacologic interventions, in particular intravenous methylprednisolone therapy, have shown modest improvements in clinical trials and are still undergoing evaluation. More recent interest has focused on the role of surgical reduction and decompression, particularly "early" surgery. A review of the current evidence available in the literature suggests that there is no standard of care regarding the role and timing of surgical decompression. There are insufficient data to support overall treatment standards or guidelines for this topic. There are, however, Class II data indicating that early surgery (<24 hours) may be done safely after acute SCI. Furthermore, there are Class III data to suggest a role for urgent decompression in the setting of 1) bilateral facet dislocation and 2) incomplete spinal cord injury with a neurologically deteriorating patient. Whereas there is biologic evidence from experimental studies in animals that early decompression may improve neurologic recovery after SCI, the relevant time frame in humans remains unclear. To date, the role of decompression in patients with SCI is only supported by Class III and limited Class II evidence and accordingly can be considered only a practice option. Accordingly, there is a strong rationale to undertake prospective, controlled trials to evaluate the role and timing of decompression in acute SCI.

Release of glutamate, nitric oxide and prostaglandin E2 and metabolic activity in the spinal cord of rats following peripheral nociceptive stimulation

Peripheral tissue injury and inflammation may result in a facilitated spinal nociceptive transmission and central sensitization. Particularly, nitric oxide (NO) and prostaglandins (PGs) have been shown to be key mediators involved in the induction and maintenance of this state. By means of spinal cord microdialysis we have determined interstitial glutamate, NO (NO2-/NO3-), PGE2, glycerol, glucose and lactate concentrations in the dorsal horns of the spinal cord following peripheral nociceptive stimulation to gain further insight into the link between excitatory neurotransmitters and metabolic functions in the spinal cord during nociception. Formalin and zymosan injection into one hind paw evoked a biphasic release of glutamate and NO with the glutamate peaks preceding those of NO. Moreover, zymosan induced a biphasic increase of interstitial glycerol concentrations accompanied by an increase of interstitial lactate indicating metabolic disturbances. In contrast, formalin injection led to an elevation of dialysate glucose concentrations which may be interpreted as an indication of enhanced metabolic activity. The sequential release of glutamate and NO in the dorsal horns of the spinal cord in response to peripheral nociceptive stimulation supports the theory that NO may act as a retrograde transmitter. The metabolic changes observed after formalin and zymosan injection suggest that an intense peripheral nociceptive stimulation may not only activate but also disturb metabolic activity and possibly membrane integrity in the spinal cord.

Free radical pathways in CNS injury

Free radicals are highly reactive molecules implicated in the pathology of traumatic brain injury and cerebral ischemia, through a mechanism known as oxidative stress. After brain injury, reactive oxygen and reactive nitrogen species may be generated through several different cellular pathways, including calcium activation of phospholipases, nitric oxide synthase, xanthine oxidase, the Fenton and Haber-Weiss reactions, by inflammatory cells. If cellular defense systems are weakened, increased production of free radicals will lead to oxidation of lipids, proteins, and nucleic acids, which may alter cellular function in a critical way. The study of each of these pathways may be complex and laborious since free radicals are extremely short-lived. Recently, genetic manipulation of wild-type animals has yielded species that over- or under-express genes such as, copper-zinc superoxide dismutase, manganese superoxide dismutase, nitric oxide synthase, and the Bcl-2 protein. The introduction of the species has improved the understanding of oxidative stress. We conclude here that substantial experimental data links oxidative stress with other pathogenic mechanisms such as excitotoxicity, calcium overload, mitochondrial cytochrome c release, caspase activation, and apoptosis in central nervous system (CNS) trauma and ischemia, and that utilization of genetically manipulated animals offers a unique possibility to elucidate the role of free radicals in CNS injury in a molecular fashion.

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 reactive oxygen species in membrane phospholipid breakdown and energy perturbation after traumatic brain injury in the rat

Interstitial glycerol may be a useful marker for posttraumatic and postischemic membrane phospholipid (PL) breakdown. Degradation of membrane PLs is thought to be triggered by both calcium and reactive oxygen species (ROS)-mediated mechanisms and to be associated with disturbed energy metabolism. In this study, we investigated the temporal changes of interstitial glycerol, lactate, and glucose after traumatic brain injury in the rat and the effect of pretreatment with the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN; 30 mg/kg i.v.). Microdialysate was sampled continuously in 10-min fractions from 1 h before, until 2 h after a cortical contusion injury produced by the weight-drop technique. The maximal concentration of interstitial glycerol (a ninefold increase) was seen 10-30 min after trauma and subsided during the following 2 h, but remained above base line as compared to sham operated animals. Concomitantly, there was an increase in interstitial lactate (fivefold) and a fall in interstitial glucose, indicating a posttraumatic energy perturbation. PBN treatment significantly attenuated the interstitial accumulation of glycerol and lactate. The results support the concept that ROS are involved in posttraumatic membrane PL breakdown and that PBN improves mitochondrial function after CNS injury. Monitoring of interstitial glycerol with microdialysis may be a valuable tool for studies on membrane PL degradation and the efficacy of neuroprotective drugs in acute CNS injury.

Pretreatment with alpha-phenyl-N-tert-butyl-nitrone (PBN) improves energy metabolism after spinal cord injury in rats

We evaluated in rats, the effect of the spin trap alpha-phenyl-N-tert-butyl nitrone (PBN) on energy metabolism after severe spinal cord injury (SCI). A laminectomy of vertebrae Th7 and Th8 was made. A probe was inserted in a dorsal horn, and microdialysis was performed for 1.5 h before and 4 h after applying severe compression (4.5 g/mm2) for 5 min. Thirty minutes before trauma 30-mg/kg PBN or saline was given intravenously and a second dose of 10 mg/kg after 3 h. Microdialysis samples were collected at intervals of 10 min and analysed by high performance liquid chromatography. As reported previously there was a severalfold rise of lactate after trauma. The mean level of lactate was consistently lower in animals pretreated with PBN, but the difference was statistically significant between the groups only at 200 min after trauma. Lactate normalized more rapidly in PBN pretreated animals. In saline-treated rats, hypoxanthine quickly rose and reached a maximum 23 times above basal level 20 min after trauma, while the rise was 14 times in PBN pretreated rats. The increase of hypoxanthine was significantly lower and normalized more rapidly in PBN pretreated animals. This study suggests that PBN pretreatment attenuates lactic acidosis and improves energy metabolism after severe SCI. The effect may, at least partly, reflect amelioration of radical induced mitochondrial dysfunction.

Independent depressive mechanisms of GABA and (+/-)-8-hydroxy-dipropylaminotetralin hydrobromide on young rat spinal axons

We compared the effect of GABA and the serotonin receptor agonist (+/-)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OH-DPAT) on compound action potential amplitudes, latency, and conduction velocity in the spinal cord isolated from young (eight to 13-day-old) Long-Evans hooded rats. Supramaximally activated conducting action potentials and extracellular K+ activity were recorded with microelectrodes from the cuneatus-gracilis fasciculi and corticospinal tract. In the cuneatus-gracilis fasciculi, 8-OH-DPAT (10(-4) M) significantly reduced response amplitudes by 26.1 +/- 10.3% (mean +/- S.D., P < 0.0001, paired t-test, n = 27) and increased latencies by 20.3 +/- 7.9% (P < 0.0001). GABA (10(-4) M) reduced/amplitudes by 31.7 +/- 15.0% (P < 0.0001, n = 28) and increased latencies by 6.1 +/- 5.4% (P < 0.0001). However, neither GABA nor 8-OH-DPAT significantly altered conduction velocities, suggesting that the latency shifts are due to changes in activation time and not conduction velocity. In cortical spinal tract, 8-OH-DPAT (10(-4) M) depressed response amplitudes by 18.9 +/- 9.6% (P < 0.05, n = 5), increased latencies by 23.3 +/- 7.2% (P < 0.0001), but reduced conduction velocities by 19.9 +/- 10.2%. GABA (10(-4) M) reduced amplitudes by 16.4 +/- 7.5% (P < 0.01, n = 5), increased latencies by 5.3 +/- 2.3% (P < 0.05), and did not change conduction velocities. Bicuculline or picrotoxin blocked the GABA effects but did not affect the 8-OH-DPAT effects on both tracts. The potassium channel blocker tetraethylammonium did not alter the 8-OH-DPAT effects. The Na+/K(+)-ATPase inhibitor ouabain (10(-6) M) markedly enhanced the depressive GABA effects from 27.9 +/- 12.0% to 49.4 +/- 24.5% (P < 0.01, n = 9), but had no effect on 8-OH-DPAT-mediated effects. These results suggest that GABA and serotonin agonists depress axonal excitability through different and independent mechanisms.

Changes of extracellular levels of amino acids after graded compression trauma to the spinal cord: an experimental study in the rat using microdialysis

We evaluated in rats, the time course of changes in extracellular levels of amino acids, lactate and pyruvate, which ensued spinal cord compression of mild, moderate, and severe degrees. The neurochemical findings measured by HPLC were compared with known outcome measures of this model. A laminectomy of vertebrae Th7 and Th8 was made and a microdialysis probe was inserted in one dorsal horn. Fluid samples were collected at intervals of 10 min. Dialysate lactate and lactate/pyruvate ratios increased in proportion to the severity of injury, suggesting a progressive derangement of energy metabolism. Mild trauma, with no neurologic deficits, did not induce any remarkable change of amino acids, but taurine values were temporarily slightly elevated. Moderate trauma, leading to transient paraparesis, resulted in a transient rise of glutamate and taurine. Severe trauma resulting in paraplegia of the hind limbs induced profound changes of extracellular amino acids. Glutamate and aspartate rose 5-6 times above basal level. There were marked elevations of taurine, glycine, arginine, alanine, asparagine, histidine, serine, threonine, and tyrosine after this degree of trauma. Glutamate, aspartate, and taurine returned to the basal level within 50 min, whereas most of the other amino acids remained elevated throughout the experiment. Thus, we found profound disturbances of extracellular amino acids and energy metabolites. The elevations of glutamate and aspartate correlated with previously recorded data on neurological outcome. The composition of the early extracellular edema showed marked temporal changes related to the severity of impact. Future studies regarding treatment of traumatic edema should focus on its chemical composition as well as its volume since such edema is not uniform in composition.

Spinal cord lactate concentration during chemical stimulation of the nucleus tractus solitarii in anesthetized rats

This study was conducted to determine the mechanism of spinal cord blood flow (SCBF) decrease following the nucleus tractus solitarii (NTS) activation. In urethane-anesthetized, paralyzed and artificially ventilated rats, neurons in the NTS were chemically stimulated by microinjection of L-glutamate (1.7 nmol; 50 nl) and the lactate concentration, one of indicators of local neuronal metabolism, in the spinal cord was monitored in real time using an enzyme electrode. Before the chemical stimulation study, the responses of the enzyme electrode and its specificity were tested in vitro and in vivo. The electrode responded to step changes in lactate concentration and a calibration plot and regression line were obtained in vitro. The lactate concentration was significantly (P < 0.01) increased during induced apnea in vivo (n = 8). The lactate concentration in the spinal cord was not significantly changed by chemical stimulation of the NTS when arterial blood pressure (ABP) remained above the lower limit of spinal cord autoregulation (n = 21). When chemical stimulation of the NTS decreased ABP to below the lower limit of autoregulation (n = 18), the lactate concentration in the spinal cord was significantly (P < 0.01) increased. This may only be due to hypotensive effects because the lactate concentration was also significantly (P < 0.01) increased when the ABP was passively decreased below the lower limit of autoregulation by controlled hemorrhage in intact (n = 11) and sinoaortic denervated rats (n = 10). Intravenous lactate injection produced no significant increase in the current from the enzyme electrode in the spinal cord (n = 4). Using the electrode with inactivated enzyme solution, the current from the electrode did not change with the increase in lactate in the spinal cord. These findings indicate that the enzyme electrode can detect rapid changes of lactate, a product of anaerobic metabolism. These results also indicate that the spinal cord vasoconstrictor response elicited by chemical stimulation of the NTS, which was performed above the lower limit of spinal cord autoregulation in our previous study, may be due to neurogenic regulatory mechanism, but not to the secondary effects of changes in metabolism.