Comparison of hydrogen clearance and 14C-antipyrine autoradiography in the measurement of spinal cord blood flow after severe impact injury

Meglumine cyclic adenylate improves cardiovascular hemodynamics and motor-function in a rat model of acute T4 thoracic spinal cord injury

STUDY DESIGN

Animal experimental study.

OBJECTIVES

Spinal cord injury (SCI) at or above the T6 level causes cardiovascular dysfunction. Maintaining cAMP levels with cAMP analogs can facilitate neurological recovery. In the present study, the effects of meglumine cyclic adenylate (MCA), a cAMP analog and approved cardiovascular drug, on cardiovascular and neurological recovery in acute T4-SCI in rats were investigated.

SETTING

Hospital in Kunming, China.

METHODS

Eighty rats were randomly allocated to five groups, and groups A-D received SCI: (A) a group administered MCA at 2 mg/kg/d iv qd, (B) a group administered dopamine at 2.5 to 5 μg/kg/min iv to maintain mean arterial pressure above 85 mm Hg, (C) a group administered atropine at 1 mg/kg iv bid, (D) a group receiving an equal volume of saline iv qd for 3 weeks after SCI and (E) a group undergoing laminectomy only. The cardiovascular and behavioral parameters of the rats were examined, and spinal cord tissues were processed for hematoxylin and eosin staining, Nissl staining, electron microscopy, and analysis of cAMP levels.

RESULTS

Compared with dopamine or atropine, MCA significantly reversed the decrease in cAMP levels in both myocardial cells and the injured spinal cord; improved hypotension, bradycardia and behavioral parameters at 6 weeks; and improved spinal cord blood flow and histological structure at 7 days post-SCI. The regression analysis suggested spinal cord motor-function improved as decreased heart rate and mean arterial pressure were stopped post-SCI.

CONCLUSIONS

MCA may be an effective treatment for acute SCI by sustaining cAMP-dependent reparative processes and improving post-SCI cardiovascular dysfunction.

SPONSORSHIP

N/A.

Safe range of shortening the middle thoracic spine, an experimental study in canine

PURPOSE

To determine the safe range of shortening the spinal column at middle thoracic spine and to observe the changes in blood-spinal cord barrier (BSCB), microglia/macrophage activation and inducible nitric oxide synthase (iNOS) activity after shortening-induced spinal cord injury.

METHODS

Dogs were allocated to four groups. Group A (control) underwent laminectomy of T7 without shortening the spinal column. Groups B, C and D had 1/3, 1/2, and 2/3 of T7 resected, respectively, followed by spinal shortening. Somatosensory evoked potential (SSEP) and hind-limb function were recorded periodically for 14 days after operation. Spinal cord blood flow (SCBF) and BSCB were detected at the acute phase of shortening. Microglia/macrophage reactions and iNOS activity were observed by immunohistochemistry.

RESULTS

Shortening of 1/3 of a vertebral height caused no significant changes in SSEP and hind-limb function after operation, whereas shortening of 1/2 of the height caused SSEP abnormality and paraparesis, and severe neurologic deficit of hind-limb was observed when the shortening reached 2/3 of the height. SCBF increased temporarily and showed a trend of recovery when the shortening was within 1/2 of a vertebral segment height. When it reached 1/2 or 2/3 of the height, SCBF at 6 h post-operation was 86.33% or 74.95% of the baseline, and an increasing BSCB permeability was observed. In the subsequent 7 days, obvious activation of macrophage and increased number of iNOS-positive cells were observed.

CONCLUSION

It is safe to shorten the spinal cord within 1/3 of a vertebral height in middle thoracic spine under two-segment laminectomy in canine. The BSCB disruption, macrophage activation, and increased iNOS activity were observed in the acute phase of the injury. These slides can be retrieved under Electronic Supplementary Material.

Changes in Pressure, Hemodynamics, and Metabolism within the Spinal Cord during the First 7 Days after Injury Using a Porcine Model

Traumatic spinal cord injury (SCI) triggers many perturbations within the injured cord, such as decreased perfusion, reduced tissue oxygenation, increased hydrostatic pressure, and disrupted bioenergetics. While much attention is directed to neuroprotective interventions that might alleviate these early pathophysiologic responses to traumatic injury, the temporo-spatial characteristics of these responses within the injured cord are not well documented. In this study, we utilized our Yucatan mini-pig model of traumatic SCI to characterize intraparenchymal hemodynamic and metabolic changes within the spinal cord for 1 week post-injury. Animals were subjected to a contusion/compression SCI at T10. Prior to injury, probes for microdialysis and the measurement of spinal cord blood flow (SCBF), oxygenation (in partial pressure of oxygen; PaPO₂), and hydrostatic pressure were inserted into the spinal cord 0.2 and 2.2 cm from the injury site. Measurements occurred under anesthesia for 4 h post-injury, after which the animals were recovered and measurements continued for 7 days. Close to the lesion (0.2 cm), SCBF levels decreased immediately after SCI, followed by an increase in the subsequent days. Similarly, PaPO₂ plummeted, where levels remained diminished for up to 7 days post-injury. Lactate/pyruvate (L/P) ratio increased within minutes. Further away from the injury site (2.2 cm), L/P ratio also gradually increased. Hydrostatic pressure remained consistently elevated for days and negatively correlated with changes in SCBF. An imbalance between SCBF and tissue metabolism also was observed, resulting in metabolic stress and insufficient oxygen levels. Taken together, traumatic SCI resulted in an expanding area of ischemia/hypoxia, with ongoing physiological perturbations sustained out to 7 days post-injury. This suggests that our clinical practice of hemodynamically supporting patients out to 7 days post-injury may fail to address persistent ischemia within the injured cord. A detailed understanding of these pathophysiological mechanisms after SCI is essential to promote best practices for acute SCI patients.

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

The authors present a review of spinal cord blood supply, discussing the anatomy of the vascular system and physiological aspects of blood flow regulation in normal and injured spinal cords. Unique anatomical functional properties of vessels and blood supply determine the susceptibility of the spinal cord to damage, especially ischemia. Spinal cord injury (SCI), for example, complicating thoracoabdominal aortic aneurysm repair is associated with ischemic trauma. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic SCI causes complex changes in spinal cord blood flow, which are closely related to the severity of injury. Manipulating physiological parameters such as mean arterial blood pressure and intrathecal pressure may be beneficial for patients with an SCI. Studying the physiopathological processes of the spinal cord under vascular compromise remains challenging because of its central role in almost all of the body's hemodynamic and neurofunctional processes.

Perfusion CT measurements in healthy cervical spinal cord: feasibility and repeatability of the study as well as interchangeability of the perfusion estimates using two commercially available software packages

Our purpose was to examine the feasibility and reproducibility of perfusion CT studies in the cervical spinal cord and the interchangeability of the values obtained by two post-processing methods. The perfusion CT studies of 40 patients with neck tumours were post-processed using two software packages (Software-1: deconvolution-based analysis with adiabatic tissue homogeneity approach and Software-2: maximum-slope-model with Patlak analysis). Eight patients were examined twice for assessing the reproducibility of the technique. Two neuroradiologists separately post-processed the images with two arterial input functions (AIFs): (1) the internal carotid artery (ICA) and (2) the vertebral artery (VA). Maps of blood flow (F) in ml/min/100 g, blood volume (V) in ml/100 g, mean transit time (MTT) in seconds (s) and permeability (PS) in ml/min/100 g were generated. The mean F, V, MTT and PS (Software-1) with VA-AIF and ICA-AIF were 8.93, 1.12, 16.3, 1.88 and 8.57, 1.19, 16.85 and 1.94, respectively. The reproducibility of the techniques was satisfactory, while the V and MTT values (in Software-1) and the F and V values (in Software-2) were dependent on the site of the AIF (p >or= 0.03 and p=0.02, respectively). The interobserver agreement was very good. The significant differences in measurements for a single patient (%) using Software-1/Software-2 were +/-120%/110%, 90%/80%, 180% and 250%/130% for F, V, MTT and PS, respectively. Only F and PS values in the healthy tissue seemed to be interchangeable. Our results were in essential agreement with those derived by invasive measurements in animals. The cervical spine perfusion CT studies are feasible and reproducible. The present knowledge has to be validated with studies in spinal cord tumours in order to decide the usefulness of the perfusion CT in this field.

Quantitative measurement of spinal cord blood volume in humans using vascular-space-occupancy MRI

Although perfusion is of major interest for many spinal cord disorders, there is no established, reproducible technique for evaluating blood flow or blood volume of the spinal cord in humans. Here the first report of in vivo measurement of human spinal cord blood volume (scBV) is presented. An FDA-approved contrast agent, Gd-DTPA, was used as an intravascular agent for the cord parenchyma, and pre-/post-contrast vascular-space-occupancy (VASO) MRI experiments were performed to obtain a quantitative estimation of scBV in mL blood/100 mL tissue. VASO MRI was used because it does not rely on knowledge of an arterial input function, it avoids the imaging artifacts of single-shot echo planar imaging approaches, and it requires only relatively simple and direct calculations for scBV quantification. Preliminary tests at 1.5 T and 3 T gave mean +/- SD scBV values of 4.3 +/- 0.7 ml/100 mL tissue (n = 6) and 4.4 +/- 0.7 ml/100 mL tissue (n = 4), respectively, consistent with the expectation that the scBV values would not be field-dependent.

Perfusion-weighted magnetic resonance imaging of the spinal cord in cervical spondylotic myelopathy

Principles of echo shifting with a train of observations was used to perform magnetic susceptibility-weighted magnetic resonance imaging with bolus-tracking in 14 patients with spondylotic myelopathy to assess changes in perfusion parameters of the spinal cord before and after decompression surgery for cervical spondylotic myelopathy. The mean transit time (MTT), bolus arrival time (T0), and time to peak (TTP) were obtained from regions of interest (ROIs) and assessed as the ratio between the spinal cord and the pons (MTT index = MTT(ROI)/MTT(pons), T0 index = T0(ROI)/T0(pons), TTP index = TTP(ROI)/TTP(pons)). The patients were divided into two groups according to percentage improvement on the Neurosurgical Cervical Spine Scale. The MTT index in patients with good recovery (> or =50%) was significantly reduced. The T0 index and TTP index showed no significant change in both groups. Reduction of MTT index may indicate improved perfusion of the spinal cord following surgery for cervical spondylotic myelopathy.

Changes in masseter muscle blood flow during voluntary isometric contraction in humans

The effect of jaw clenching on local blood flow in the masseter muscle was measured using the hydrogen clearance method in 13 healthy subjects. Sustained isometric masseter-muscle contraction levels of 25 and 50% of maximum voluntary contraction (MVC) were investigated. The blood flow at 25% MVC before contraction, during contraction and after contraction was 12.3 +/- 10.9, 19.2 +/- 12.1 and 78.8 +/- 63.9 mL min(-1) (100 g)(-1) (mean +/- s.d.), respectively. At 50% MVC, it was 14.2 +/- 12.9, 18.6 +/- 10.0 and 80.1 +/- 61.8, respectively. The volume of blood flow was significantly greater after contraction as compared with before contraction at both levels (P < 0.0001) and there was no significant difference between before and during contraction periods (P = 0.17: 25% MVC; P = 0.38: 50% MVC). At 50% MVC blood flow before contraction and the difference in blood flow before and during contraction showed significant negative correlation (r = -0.636, P < 0.02). When the volume of blood flow was low before contraction it tended to increase during contraction and decreased when it was high before contraction. These findings indicate that blood flow in the masseter muscle during sustained isometric contraction is affected by the condition of contraction and may be influenced by the muscle region. It was also indicated that the blood flow during high level contraction was influenced by the volume of blood flow before contraction. Clinically, our findings may help to understand pathological changes which may lead to chronic masticatory muscle pain.

P2X7 receptor inhibition improves recovery after spinal cord injury

Secondary injury exacerbates the extent of spinal cord insults, yet the mechanistic basis of this phenomenon has largely been unexplored. Here we report that broad regions of the peritraumatic zone are characterized by a sustained process of pathologic, high ATP release. Spinal cord neurons expressed P2X7 purine receptors (P2X7R), and exposure to ATP led to high-frequency spiking, irreversible increases in cytosolic calcium and cell death. To assess the potential effect of P2X7R blockade in ameliorating acute spinal cord injury (SCI), we delivered P2X7R antagonists OxATP or PPADS to rats after acute impact injury. We found that both OxATP and PPADS significantly improved functional recovery and diminished cell death in the peritraumatic zone. These observations demonstrate that SCI is associated with prolonged purinergic receptor activation, which results in excitotoxicity-based neuronal degeneration. P2X7R antagonists inhibit this process, reducing both the histological extent and functional sequelae of acute SCI.

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.

Influence of posttraumatic hypoxia on behavioral recovery and histopathological outcome following moderate spinal cord injury in rats

Pulmonary dysfunction leading to secondary hypoxia is a common complication of spinal cord injury (SCI). The purpose of this study was to clarify the behavioral and histopathological consequences of posttraumatic hypoxia in an established model of traumatic SCI. Forty-five female Sprague-Dawley rats were randomly assigned to one of four groups, including (1) laminectomy and normoxia (n = 10), (2) laminectomy and hypoxia (n = 11), (3) NYU weight-drop and normoxia (n = 12), and (4) NYU weight-drop and hypoxia (n = 11). For these studies, a moderate injury was induced by adjusting the height of the weight drop (10 g) to 12.5 mm above the exposed spinal cord (T10). Immediately after injury, PaO2 in the hypoxic rats was kept between 30 and 35 mm Hg for 30 min. PaO2 in the normoxic group was maintained over 100 mm Hg, while PaCO2 in all rats was maintained at 35-40 mm Hg. The behavior of the rats was checked every 7 days using the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale. Rats were sacrificed at 8 weeks for quantitative histopathological analysis of lesion areas. During the hypoxic insults, the mean arterial blood pressure dropped in both sham control and weight-drop rats (p < 0.01). At the end of the 8-week monitoring period, BBB scores were 12.5 +/- 3.1 (mean +/- SEM) and 14.2 +/- 3.4 in the normoxic and hypoxic traumatized rats, respectively. No significant difference between the traumatized groups was documented with BBB monitoring. In contrast, the percent of gray matter necrosis at the impact epicenter was significantly increased in hypoxic versus normoxic SCI rats (p < 0.01). These data demonstrate that posttraumatic hypoxia complicated by mild hypotension aggravates the histopathological consequences of SCI and further emphasize the need to control for secondary hypoxic insults after experimental and clinical SCI. Potential explanations for the lack of a correlation between the behavioral and histopathological findings are discussed.

Evidence that nitric oxide- and opioid-containing interneurons innervate vessels in the dorsal horn of the spinal cord of rats

In the dorsal horn of the spinal cord, activation of small fibre nociceptive afferents leads to the release of nitric oxide and enkephalins by interneurons. In this work we encountered unexpected relationships among local spinal cord dorsal horn blood flow, specific forms of afferent input, nitric oxide and intrinsic opioids. Selective rises in rat lumbar dorsal cord blood flow using laser Doppler flowmetry and microelectrode hydrogen clearance polarography were generated by ipsilateral, 'nociceptive' low (3 Hz) frequency stimulation of sciatic afferents. Inhibitors of nitric oxide synthase (NOS) prevented rises in flow during stimulation without influencing baseline flow. Ipsilateral hindpaw intradermal injection of capsaicin, a nociceptive activator, also generated large rises in flow sensitive to NOS inhibition. During NOS blockade or morphine administration there were unexpected acute declines in the dorsal cord blood flow strictly confined to low frequency stimulation epochs. This acute vasoconstrictive effect was prevented by administration of an opioid receptor antagonist. Using immunohistochemistry, terminals apparently innervating dorsal spinal cord blood vessels were labelled with antibodies against neuronal NOS and met-enkephalin. We conclude that local nitric oxide and opioids, probably from interneurons, have competitive actions on dorsal horn microvessels once interneurons are activated during a nociceptive barrage. Collateral innervation of blood vessels may explain this property.

Noncontusive segmental spinal cord injury using radiofrequency current

OBJECTIVE

To develop a nondisruptive model for the study of spinal cord injury.

METHODS

A 2-MHz radiofrequency heating chamber was mounted over the rat T13-L1 vertebral column via a short dorsal incision. Epidural temperature at chamber level was monitored via a small proximal laminotomy. Forty-three rats were studied using time-temperature heating regimens from 45 to 48.5 degrees C and 4 to 15 minutes. A blinded numerical hind limb impairment score (Neurologic Impairment Score) was determined at intervals up to 2 weeks after injury. Segmental spinal cord blood flow was measured using [14C]butanol tissue uptake in injured and control rats.

RESULTS

Above the injury threshold, increasing the time-temperature regimens was associated with a progressively worse Neurologic Impairment Score (r = 0.73-0.87 up to 24 hours after injury). Cord blood flow was unchanged at 2 hours but was 44% depressed at the injury level 6 hours after injury (p < 0.01). Histologically, injury extended minimally beyond the injured segment. Vascular thrombosis was not seen.

CONCLUSION

This comparatively noninvasive model does not mechanically disrupt cord components and results in progressive neurologic impairment that correlates with the time-temperature regimen used for injury. It should be useful in identifying secondary phenomena that worsen functional status after cord trauma.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

Interstitial and tissue cations and electrical potential after experimental spinal cord injury

Interstitial and tissue cations and electrical potential were studied in an experimental model of spinal cord contusion injury in anaesthetised cats. Measurements of interstitial ion activity in the grey matter at the injury site (with ion-selective electrodes), showed a decrease of sodium and calcium, an increase of potassium, a small acidification and a negative shift in the electrical potential 5 min after injury. The interstitial ionic changes were completely reversible within 90 min following injury. Measurements of the ion content in a tissue sample from the injury site (flame photometry) showed an increase of sodium and calcium and a decrease of potassium 5 min after injury. The magnitude of the post-injury sodium change was much larger than the potassium change, both for interstitial and tissue measurements. Treatment of the animals with the calcium entry blocker flunarizine before the injury did not influence the magnitude of post-injury interstitial calcium decrease but significantly increased the rate of subsequent recovery. Pre-injury flunarizine treatment also significantly increased the recovery rate of the electrical potential. The experiments suggest the occurrence of a net ionic shift towards the intracellular space, which may contribute to oedema formation in the very early post-injury period. The post-injury decrease of interstitial calcium activity is probably not mediated by flunarizine-sensitive calcium entry mechanisms; such mechanisms may, however, be involved in the subsequent recovery period for interstitial calcium activity. Calcium ions may be involved in the recovery process of the negative electrical potential after injury.

Effect of U-50488h, a selective opioid kappa receptor agonist, on vascular injury after spinal cord trauma

U-50488H, a selective opioid kappa receptor agonist has been shown to be a neuroprotective agent in animal models of spinal cord injury. The mechanism of action of U-50488H is not known. Methylprednisolone, the only neuroprotective drug proven in patients with acute spinal cord injury may prevent the secondary injury after an initial trauma. Secondary vascular injury develops after experimental spinal cord trauma. In this study we examined the effects of U-50488H on post-traumatic vascular injury based on the measurement of vascular permeability, edema and neutrophil infiltration in a rat spinal cord injury model. Vascular permeability was assessed by vascular extravasation of fluorescein isothiocyanate conjugated dextran (FITC-D), a macromolecular tracer. Tissue edema was determined by percentage water content and neutrophil infiltration by myeloperoxidase (MPO) activity, a marker enzyme for neutrophils. U-50488H at doses of 5, 10, 20 and 40 mg/kg i.p. administered twice (0.5 h before and 0.5 h after trauma) reduced vascular permeability in a dose-dependent manner. More frequent dosing (10 mg/kg, 0.5 h before and 0.5, 2, 8 and 22 h after injury) reduced vascular permeability 24 h after injury. U-50488H also reduced edema formation but did not affect neutrophil infiltration. Results from this study raise the possibility that the neuroprotective effect of U-50488H involves a secondary vascular event.

Methylprednisolone treatment of experimental spinal cord injury

Lipid peroxidation has been identified as a deleterious consequence of contusive spinal cord trauma and of thermal injury. The L3-L6 spinal cord segment was thermally injured using a radiofrequency heating chamber mounted on the vertebral column of anesthetized rats. Hind limb function was assessed 2 hours later. A bolus of methylprednisolone (MP, 30 mg/kg) was then given intravenously, followed by 5.4 mg/kg/hr MP for 6 or 24 hours. Cord water content and regional spinal cord blood flow (RSCBF, 14C-butanol distribution) were measured at seven cord levels after function had been reassessed following treatment. Untreated rats were given vehicle. The study was randomized and blinded.

RESULTS

Edema in heated segments was progressive over 24 hours, but was the same in treated vs untreated rats. RSCBF in heated segments was the same in treated vs uninjured controls at 6 and 24 hours. In untreated rats, RSCBF in the heated segment was elevated by 30% at 6 hours, but was the same as uninjured control by 24 hours. In the unheated segments of untreated rats, RSCBF was elevated at 24 hours. At 24 hours, RSCBF was lower in treated vs untreated rats at all levels, including the heated one. Limb function deteriorated equivalently in both groups.

CONCLUSION

MP obviated the early rise in RSCBF in heated segments and the elevations in RSCBF in uninjured segments, but had no effect on cord edema or on limb function.

A preliminary report on the use of laser-Doppler flowmetry during tethered spinal cord release

Neurological deterioration in the tethered cord syndrome has been postulated to result from a compromise of blood flow in the distal spinal cord. In order to evaluate vascular perfusion in human subjects, a new technique of laser-Doppler flowmetry was used to monitor continuously the microcirculation of the distal spinal cord during surgery for tethered cord release in 10 children. For further comparison, five children undergoing selective dorsal rhizotomy were also monitored. In the tethered cord syndrome group, spinal cord blood flow before untethering was a mean of 12.6 ml/min per 100 g of tissue and increased in all cases after release to a mean of 29.4 ml/min per 100 g of tissue. All patients improved neurologically. The selective dorsal rhizotomy group had a preoperative mean spinal cord blood flow of 30.8 ml/min per 100 g of tissue, which was not altered by the operative procedure. Significant improvement occurs in distal spinal cord blood flow after tethered cord release, which may be representative of an important mechanism in the pathophysiology of the tethered cord syndrome.

Effect of flunarizine and methylprednisolone on functional recovery after experimental spinal injury

The effect of flunarizine and methylprednisolone on the recovery of somatosensory evoked potentials (SEPs) was evaluated in an experimental model of spinal cord impact injury in anesthetized cats. In addition, the effect of flunarizine on posttraumatic spinal cord blood flow (SCBF) (using the hydrogen clearance technique) and interstitial calcium and potassium activity (ion-selective electrodes) was investigated. After the injury (600 g.cm), SEPs disappeared, followed by a spontaneous recovery to 17% of the preinjury amplitude at the end of the 4 h observation period. Flunarizine treatment (0.1 mg/kg IV, given 5 and 120 min after injury) resulted in a significantly improved recovery of SEPs, reaching 52% of the preinjury amplitude. Methylprednisolone treatment (30 mg/kg IV, given 5 min after injury) resulted in a 30% recovery level, significantly better than in untreated animals but significantly inferior to flunarizine treatment. Combination of both treatments resulted in a 62% recovery level, significantly better than after methylprednisolone treatment alone. Flunarizine treatment had no significant effect on the postinjury evolution of SCBF and interstitial potassium activity; it did, however, significantly accelerate the recovery of interstitial calcium activity, which sharply decreased immediately after injury. It is concluded that intravenous administration of the calcium entry blocker flunarizine improves the functional recovery of the spinal cord in the acute phase after experimental spinal impact injury. The observed improvement is not achieved by an effect on local blood flow but is possibly related to an inhibitory effect of the drug on cellular calcium entry.

In vivo angiogenesis by platelet-derived wound-healing formula in injured spinal cord

In vivo angiogenesis was investigated using platelet-derived wound-healing formula (PDWHF) in the injured cat spinal cord. Twenty-two gauge teflon sheaths, which had been coated with PDWHF-Hydron or only with Hydron, were inserted into the spinal cords of cats and the injured cats were maintained for 3 weeks. Selection of PDWHF-Hydron or Hydron was double blinded. The PDWHF-Hydron group showed notable neovascularization as well as dilation around the injury site, and this was statistically significant when compared to the control group. PDWHF seems to play a role in the healing processes of spinal cord injury and may have important interactions with other growth factors and in particular neurogenic growth factor.

The effect of growth factor formula (platelet derived wound healing formula) in experimental spinal cord injuries

The main purpose of this study was to investigate the usefulness of platelet derived wound healing formula (PDWHF) in the treatment of experimentally induced spinal cord injuries in cats. The injury model in ten adult cats consisted of the placement of three 22-gauge Teflon catheter sheaths into the spinal cord at the L2 level. Treatment consisted of coating these sheaths with PDWHF in Hydron. Three animals were used as controls. In the 7 remaining cats, treatment was double blinded. Cats were sacrificed at 3 weeks after injury and injured spinal cord segments were excised for histologic evaluation. Electrophysiologic and clinical motor function were evaluated throughout a period of observation. Evoked potentials in both the treated and control groups indicated incomplete spinal cord lesions due to insertion of the needles. There did not appear to be any significant improvement or difference in the evoked response and clinical function as a result of treatment with PDWHF. The histological findings in the PDWHF-treated group showed significant new vessel formation as well as dilation and around the injury site. This neovascularization, both qualitative and quantitative, was noted in the treatment group. This information, with a limited injury and very simple delivery system for growth factor, would suggest there is definite neovascularization occurring as a result of this treatment and this may be useful in the subsequent wound healing response such as axonal growth and scar tissue formation.

Kininogen and kinin in experimental spinal cord injury

Activation of the kallikrein-kinin system has been implicated in the pathogenesis of vasogenic brain edema and posttraumatic vascular injury. We determined the levels of kininogen and kinin in an experimental spinal cord injury model in the rat. Kininogen content in traumatized cord segments increased in a time-dependent manner. Western blot analysis showed that the kininogen in traumatized cord comigrates with 68K low-molecular-weight kininogen or T-kininogen. Trypsin treatment of the kininogen in traumatized cord released both bradykinin and T-kinin, which were separated by HPLC and quantified with a kinin radioimmunoassay. Endogenous kinin levels in the frozen spinal cord also increased up to 40-fold 2 h after injury as compared with controls. The results demonstrate an increased accumulation of kininogen and its conversion to vasoactive kinins in experimental spinal cord injury.

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 multimolecular cascade of spinal cord injury. Studies on prostanoids, calcium, and proteinases

Experimental spinal cord injury in animals induced by weight drop produces neurological deficit and paralysis. Correlation of the progressive morphological changes in the lesion by both light and electron microscopy with the biochemical alterations revealed ischemia, edema, hemorrhage, tissue necrosis, granular changes in axons, vesicular degeneration of myelin and axonal calcification. The biochemical pathology was that of degradation of axonal (neurofilaments) and myelin proteins (MBP and PLP) with increased activities of proteolytic enzymes and particularly the neutral proteinase. The level of total calcium increased progressively in the lesion to a peak at 8 hrs. and subsequently remained constant thereafter. The capacity of calcium for activating proteinases and lipases and fostering the degradation of axon and myelin proteins as well as the liberation of arachidonic acid required for the synthesis of prostanoids must be relevant. An increased production of prostanoids is indicated by elevation of thromboxane (TxB2), a stable metabolite of TXA2 at 1 hour after injury. The 6-keto-PG1(1)a was also increased but to a lesser extent. We suspect that the activation of arachidonic acid metabolism contributes to post-traumatic vascular injury and the progressive ischemia. These putative roles for calcium in proteolysis and lipolysis, inducing degradation of macromolecules and production of prostanoids which initiate edema, lysolecithin a myelinolytic factor and mitochondrial dysfunction in spinal cord injury are discussed.

Potassium and calcium changes in injured spinal cords

In previous studies, we found large rises in extracellular potassium activity ([K+]e) and falls in extracellular Ca2+ activity ([Ca2+]e) in injured spinal cords. [K+]e recovered rapidly at the impact site within 2 h but ischemia onset at 2-3 h paradoxically did not cause further [K+]e rises. [Ca2+]e, in contrast, remained depressed for long periods of time, suggesting either an effective block of Ca diffusion to the injury site or a deep Ca2+ sink at the impact site. To resolve questions raised by the [K+]e and [Ca2+]e recovery patterns, we used atomic absorption spectroscopy to measure spatial distributions of tissue concentrations of K ([K]t) and Ca ([Ca]t) in cat spinal cords injured by a standardized contusion, compared with uninjured controls. At the impact site, [K]t fell to 51% and 35% of control at 1 and 3 h. The K content of cord surrounding the impact site did not change significantly at 1 h, but K gains in surrounding cord at 3 h approximated K losses from the impact site. The K results indicate that contusion disrupts greater than 80% of cells at the impact site with K loss to adjacent cord, blood, and cerebrospinal fluid. Such losses may explain why subsequent ischemia at the impact site did not cause [K+]e rises. [Ca]t at the impact site increased to 37% and 59% above control at 1 and 3 h. The Ca gain at the impact site exceeded the amount of free extracellular Ca2+ available before injury within 2 cm of the impact site. At 1 h, the Ca lost in cord surrounding the impact site approximated the Ca gain at the impact site. These findings indicate that Ca accumulated at the impact site comes largely from surrounding cord. We propose that Ca sequestration by inorganic phosphates causes a deep Ca sink at the impact site.

Vascular permeability in experimental spinal cord injury

Following spinal cord injury in rats there was a time-dependent change of vascular permeability as reflected by extravasation of 125I-labelled serum albumin. The change of vascular permeability correlated with tissue calcium and water accumulation suggesting that cord exposure to plasma calcium as a consequence of vascular injury may contribute to the progressive post-traumatic cord necrosis.

Videodensitometric estimation of the protective effect of hyperbaric oxygen in the ischemic gerbil brain

To verify its protective effect on the ischemic mammalian brain, hyperbaric oxygen was administered to six groups of carotid-ligated gerbils. The outcome was evaluated clinically and by a colorimetric videodensitometry technique by comparing differences in the interhemispheric color density through the translucent intact cranium. It was found that there was a graded decrease in interhemispheric differences with increasing exposure to hyperbaric oxygen (the appearance of the ischemic hemisphere increasingly approached that of normal brain). This correlated with the incidence of ischemia in each group.

Spinal cord and cerebral blood flow responses to subarachnoid injection of local anesthetics with and without epinephrine

Subarachnoid anesthesia with lidocaine, mepivacaine, or tetracaine with and without added epinephrine (1:100 000) produced no demonstrable changes in average cerebral (CBF) or segmental spinal cord blood flow (SCBF) in 38 cats anesthetized with pentobarbital. Blood flow was measured by the injection of radioactive microspheres. Seven groups of cats received either lidocaine 15 mg, lidocaine 15 mg with epinephrine, mepivacaine 10 mg, mepivacaine 10 mg with epinephrine, tetracaine 5 mg, tetracaine 5 mg with epinephrine, or saline with epinephrine 1:100 000. Mean arterial pressure (MAP) decreased significantly (P less than 0.05) in Groups I-VI. Added epinephrine had no effect on the decrease in MAP. Amplitude of the somatosensory cortical evoked response decreased significantly in Groups I-VI, but did not change from control in Group VII. No significant change in CBF or SCBF was demonstrated in any group at any time. Plasma lidocaine and mepivacaine levels were significantly less at 5 min after subarachnoid injection in the groups receiving epinephrine compared to those not receiving epinephrine (P less than 0.05). The data appear to support the hypothesis of a vasoconstrictive reduction in systemic absorption of intrathecal local anesthetics, but suggest that significant segmental spinal cord ischemia does not occur. Maintenance of total flow in the face of a decrease in MAP suggests that autoregulation in brain and spinal cord may be maintained. Changes in regional SCBF or CBF may have been present but were not examined in this study. Further studies of brain and spinal cord blood flow dynamics, regional flow changes, and regulation of flow after intrathecal agents are necessary.

Differential effects of transection of the spinal cord and splanchnic nerve on adrenal tyrosine hydroxylase and catecholamines

The role of spinal pathways in the regulation of adrenal medullary tyrosine hydroxylase and catecholamines was studied in adult rats subjected to spinal cord transection at the third thoracic level. In these animals the sympathoadrenal preganglionic neurons were isolated from their supraspinal afferents. This treatment led after three days to a progressive reduction of tyrosine hydroxylase activity and dopamine content (as compared to unoperated controls) until at least the 10th day. The results of the administration of dexamethasone or adrenocorticotropic hormone to spinalized rats suggest that in these animals glucocorticoid hypersecretion is not involved in the decline of adrenal tyrosine hydroxylase and that in fact adrenocorticotropic hormone supplementation can prevent it. A neurogenic origin for the depression of adrenomedullary function is favoured because unilateral splanchnicotomy (which by itself does not affect adrenal tyrosine hydroxylase), prior to cord section, prevented the diminution of tyrosine hydroxylase activity in the denervated gland. The decline of adrenal tyrosine hydroxylase and dopamine after spinal section may result from a decrease of modulatory impulses to the adrenal from decentralized sympathoadrenal preganglionic neurons in the isolated cord, following the loss of a descending facilitation of these neurons and/or the release of a segmental interneuronal inhibition of these neurons from a descending inhibitory influence. Such descending pathways may decussate partially below the low cervical level because rats with hemisection of the cord at C6-C7 exhibited no decline of adrenal tyrosine hydroxylase or of dopamine measured on either side seven days postoperatively.

Failure of nimodipine to reverse acute experimental spinal cord injury

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

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

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

Failure of tetracaine to reverse spinal cord injury in the cat

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

Comparative studies of regional CNS blood flow and evoked potentials in the cat. Effects of hypotensive ischemia on somatosensory evoked potentials in cerebral cortex and spinal cord

Functional resistance to graded hypotensive ischemia of various segments of the somatosensory pathway was determined in anesthetized cats by repeated concurrent recordings of regional blood flow measured by hydrogen clearance, and evoked potentials (EPs), of dorsal horn of lumbar spinal cord and cerebral cortex. During normal resting CNS blood flow (CBF), there were significant successive reductions of EP amplitudes, recorded from presynaptic spinal components (634, 424-949 microV; re-linearized mean and 95% confidence limits of log-transformed data) compared to postsynaptic spinal (359, 247-522 microV) and presynaptic cortical (50, 32-79 microV) and to postsynaptic cortical components (33, 22-50 microV). During ischemia amplitudes of EPs in spinal cord and cerebral cortex showed significantly different behaviors. The presynaptic spinal component was virtually independent of regional blood flow down to 12 percent of resting values, the postsynaptic cortical component exhibited strongest positive correlations (r = 0.45) with flow. In both regions postsynaptic amplitude was more sensitive to flow changes than respective presynaptic amplitudes. Despite similar regression coefficients for intermediate segments of somatosensory pathway, only postsynaptic spinal components were significantly correlated (r = 0.40) with regional flow. Presynaptic cortical amplitudes were variable and no significant flow dependence was demonstrated. Results suggested that in comparable degrees of regional ischemia of CNS functional integrity is determined by numbers of synaptic transmissions involved locally. Comparatively simple structures, e.g. the spinal cord, are less susceptible to ischemia and complex neuronal networks, e.g. the cerebral cortex, are more susceptible.

Control of blood flow in the cat spinal cord

Spinal cord blood flow (SCBF) and the effect of end-tidal CO2 concentration (ETCO2) on SCBF (CO2 reactivity) were studied in the lumbar spinal cord of cats by means of the hydrogen-clearance technique Hydrogen gas was administered by inhalation, and its level in spinal cord tissue was estimated amperometrically with small (75 micrometers) platinum electrodes. The average SCBF's at normocapnia (ETCO2 = 4%) of the ventral horn gray matter and of the white matter at several locations were 43.2 and 16.2 ml . 100 gm-1 . min-1, respectively. For gray and white matter, the values of CO2 reactivity, estimated by the coefficient of the regression of SCBF (ml . 100 gm-1 . min-1) on ETCO2 (ml . 100 ml-1) were 11.6 and 2.1, respectively. No differences in SCBF or CO2 reactivity were observed between intact animals kept under N2O-O2 ventilation and decerebrated animals with no anesthesia. After an acute spinal section, ventral horn SCBF and CO2 reactivity (measured eight segments below the cordotomy) were not altered, in spite of the profound neural depression present (that is, spinal shock). Orthodromic (dorsal root) stimulation of the ventral horn neurons induced an average increase in blood flow of 128% above control values. Antidromic (ventral root) motoneuron activation failed to produce any significant changes in ventral horn blood flow.

Combined PGI2, indomethacin, and heparin improves neurological recovery after spinal trauma in cats

Anesthetized cats were subjected to standardized cervical spinal trauma produced by a modification of the Allen weight-dropping method. One hour after injury, animals were randomly allocated to one of three treatment groups, in which they received 1) saline, 2) naloxone, or 3) combined treatment, consisting of indomethacin, heparin, and prostacyclin (PGI2). Treatment was continued for 4 hours. Neurological function was evaluated weekly by a neurologist unaware of the treatment group, and was graded by means of a scale modified from that of Tarlov. Functional recovery in animals receiving combined drug therapy was significantly better than in saline-treated control animals, and was similar to that observed in naloxone-treated animals. The findings are discussed with respect to "blood-damaged tissue interaction" and may have implications both with regard to the pharmacological management of acute spinal injury and to the mechanism of action of opiate antagonists.

A precise and sensitive method for measurement of spinal cord blood flow

Spinal cord blood flow can be accurately and rapidly measured in rabbits by intravenous injection of [14C]iodoantipyrine, collection of sequential arterial samples, and abrupt termination of blood flow to the spinal cord by severing the aorta with a previously implanted ligature. The radioactive tracer concentrations in arterial and spinal cord samples can be rapidly measured in a scintillation counter. The spinal cord blood flow can then be calculated from these blood and tissue tracer concentrations. This method is suitable for use in anesthetized or unanesthetized small animals.

Effect of high-dose corticosteroid therapy on blood flow, evoked potentials, and extracellular calcium in experimental spinal injury

High-dose methylprednisolone (15 to 30 mg/kg), administered 45 minutes after severe contusion injury (400 gm-cm) to cat spinal cords, rapidly reverses the typical posttraumatic ischemia that occurs in spinal injuries. White matter blood flow improves despite the systemic hypotension associated with bolus intravenous injections of such massive corticosteroid doses. In addition, this treatment facilitates extracellular calcium ionic recovery in contused spinal cords, and salvages evoked potential activity that is lost in untreated cats. These data suggest that high-dose corticosteroid treatment causes local vasodilation of spinal cord blood vessels. The consequent blood flow increase may account for the beneficial effects of high-dose corticosteroid treatment on both functional recovery and histopathological appearance of injured spinal cords.

The effect of blood transfusion, dopamine, and gamma hydroxybutyrate on posttraumatic ischemia of the spinal cord

Posttraumatic spinal cord blood flow (SCBF) was assessed after elevating the mean systemic arterial pressure (mSAP) with a blood transfusion, or with an infusion of dopamine. The effect of the anesthetic agent, gamma hydroxybutyrate, was also assessed. Flows were measured using the 14C-antipyrine autoradiographic method. Animals were injured at T-1 by acute compression of the spinal cord with a clip exerting a pressure of 175 gm. Uninjured animals, with mSAP's of 120.0 +/- 17.0 mm Hg, had gray and white matter flows of 74.2 +/- 22.3 and 18.7 +/- 6.7 ml/100 gm/min, respectively, while injured untreated animals had mSAP's of 82.5 +/- 14.1 mm Hg and gray and white matter flows of 13.3 +/- 12.1 and 3.9 +/- 3.9 ml/100 gm/min, respectively, at the injury site. Blood transfusion raised the mSAP's to 127.5 +/- 13.7 mm Hg in the injured animals and doubled the flows in gray and white matter to 25.6 +/- 30.2 and 6.3 +/- 6.4 ml/100 gm/ml, respectively. Dopamine did not have as beneficial an effect as blood transfusion on either the mSAP (101.0 +/- 16.7 mm Hg) or the SCBF (gray and white matter flows of 18.4 +/- 12.4 and 5.8 +/- 5.9 ml/100 gm/min). Gamma hydroxybutyrate (GHB) had almost no effect on the mSAP or SCBF of normal animals, and in injured animals produced only a unilateral increase in flow on the less severely injured side, without affecting the mSAP.

Oxygenated fluorocarbon perfusion as treatment of acute spinal cord compression injury in dogs

Experiments were conducted to determine the therapeutic value of subarachnoid perfusion of the traumatized dog spinal cord with the fluorocarbon, Fluosol-DA (20%). Control dogs without lesions, but which had durotomy, subarachnoid catheter placement, and saline irrigation for 4 hours, did not have any residual neurological deficit. A series of 41 dogs underwent an acute spinal cord compression using an epidural balloon inflated to a pressure of 160 mm Hg and maintained for 1 hour. Treatment included durotomy only (11 dogs), durotomy with saline perfusion at room temperature (15 dogs), and durotomy with oxygenated Fluosol-DA perfusion at room temperature (15 dogs). The dogs underwent daily grading of neurological status for a 60-day period. Dogs undergoing perfusion of the spinal cord with either saline or oxygenated Fluosol-DA had significantly improved motor recovery (p less than 0.004) compared with dogs undergoing durotomy only. Perfusion with oxygenated Fluosol-DA resulted in significantly better motor recovery (p less than 0.05) than did perfusion with normal saline. Microscopic examination of the traumatized spinal cords failed to reveal a substantial difference between the three groups. However, dogs with better functional results tended to have less destruction of the white matter. Hemorrhagic necrosis of the central gray matter was consistently observed in all traumatized spinal cords.

Spinal trauma: pharmacological evidence for vasoconstrictor activity in cerebrospinal fluid

Cerebrospinal fluid from six cases of acute spinal trauma collected 0--6 days after injury was examined for vasoconstrictor activity using both human isolated cerebral arteries and animal tissues. The cerebrospinal fluid of four out of six patients was vasoactive. The identities of the vasoconstrictor substances were not established, but experiments with pharmacological antagonists showed that arterial contractions were not due to serotonin, histamine, noradrenaline, acetylcholine or angiotensin II, substances which are known potent spastic agents on cerebral arteries. Our findings would explain by the mechanism of arterial spasm, principally in the anterior spinal artery, the neuropathological appearance of central haemorrhagic necrosis in spinal cord injury. The infarction of the core of the spinal cord could be caused by vasoconstrictor substances, reported here, in the cerebrospinal fluid after spinal injury. If the identities of the substances could be established, drug therapy to prevent or relieve the spasm would be possible.