Increase in rat spinal cord blood flow with the calcium channel blocker, nimodipine

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

Management of Thoracic Aneurysm

A review of the literature on the management of thoracic aneurysm is presented. These patients have various comorbid conditions and need thorough work-ups. Aneurysms can be classified according to shapes and locations. Various methods to maintain hemodynamic stability with adequate endorgan perfusion are presented. The success of the operation depends upon preoperative anticipation and preparation for adequate organ perfusion and hemodynamic stability along with good communication between the anesthesiologist and the surgical team.

Intravenous infusion of magnesium chloride improves epicenter blood flow during the acute stage of contusive spinal cord injury in rats

Vasospasm, hemorrhage, and loss of microvessels at the site of contusive or compressive spinal cord injury lead to infarction and initiate secondary degeneration. Here, we used intravenous injection of endothelial-binding lectin followed by histology to show that the number of perfused microvessels at the injury site is decreased by 80-90% as early as 20 min following a moderate T9 contusion in adult female rats. Hemorrhage within the spinal cord also was maximal at 20 min, consistent with its vasoconstrictive actions in the central nervous system (CNS). Microvascular blood flow recovered to up to 50% of normal volume in the injury penumbra by 6 h, but not at the epicenter. A comparison with an endothelial cell marker suggested that many microvessels fail to be reperfused up to 48 h post-injury. The ischemia was probably caused by vasospasm of vessels penetrating the parenchyma, because repeated Doppler measurements over the spinal cord showed a doubling of total blood flow over the first 12 h. Moreover, intravenous infusion of magnesium chloride, used clinically to treat CNS vasospasm, greatly improved the number of perfused microvessels at 24 and 48 h. The magnesium treatment seemed safe as it did not increase hemorrhage, despite the improved parenchymal blood flow. However, the treatment did not reduce acute microvessel, motor neuron or oligodendrocyte loss, and when infused for 7 days did not affect functional recovery or spared epicenter white matter over a 4 week period. These data suggest that microvascular blood flow can be restored with a clinically relevant treatment following spinal cord injury.

Mechanisms of injury and emergency care of acute spinal cord injury in dogs and cats

OBJECTIVES

To review the literature in regards to the pathophysiology of acute spinal cord injury, and to describe current concepts in regards to patient assessment, diagnostic, and therapeutic measures with a special emphasis on emergency and critical care considerations.

ETIOLOGY

Acute spinal cord injury occurs in 2 phases. The primary injury occurs at the time of initial injury and may include intervertebral disk herniation, vertebral fracture or luxation, penetrating injury, and vascular anomalies such as fibrocartilaginous embolic myelopathy. Secondary injury occurs following primary injury and is multifactorial encompassing numerous biochemical and vascular events that result in progression of injury.

DIAGNOSIS

The diagnosis is based on history and physical examination findings. A neurologic examination should be performed following initial patient assessment and stabilization. Further diagnostics to characterize acute spinal injury include radiographs and advanced imaging modalities such as myelography, computed tomography, or magnetic resonance imaging.

THERAPY

Initial treatment should focus on addressing the patient's cardiovascular and respiratory system. Supportive measures to support systemic perfusion are vital to minimizing secondary injury. Specific therapy toward minimizing secondary injury in veterinary medicine remains controversial, especially in regards to the utilization of methylprednisolone. Other therapies are either in need of additional research or have failed to document clinical difference.

PROGNOSIS

The prognosis for acute spinal injury is varied and is dependent upon the presence of concurrent trauma, location, and type of primary injury sustained, and extent of neurologic impairment at the time of initial presentation. The etiology of the underlying trauma is of great importance in determining prognosis and outcome. Loss of deep pain is generally accepted as a poor prognostic indicator; however, even these patients can recover depending on their response to treatment.

Low-dose L-arginine administration increases microperfusion of hindlimb muscle without affecting blood pressure in rats

The objective of this work was to evaluate the influence of exogenous L-arginine on the capillary blood flow of peripheral tissues of normotensive subjects. Rats were anesthetized with sodium pentobarbital, and the blood flow of femoral, dorsal, and ventral skin and gastrocnemius and soleus muscle was measured by laser Doppler flow and microsphere methods to compare the blood flow before and after the L-arginine infusion. L-arginine lowered the mean blood pressure in a dose-dependent manner, but a statistically significant reduction in mean blood pressure was detected only at a high dose of 500 mg/kg of body weight. The significant blood flow increment was detected after the L-arginine infusion at doses of 50 and 150 mg/kg without causing hypotension. Nicardipine, a calcium channel blocker, also increased the skin blood flow, but the blood flow increment and blood pressure fall were comparable. A significant increment in microperfusion was detected in gastrocnemius, soleus muscle, and ventral skin compared with control group by the microsphere method. No adverse effects were observed during L-arginine and microsphere infusion. The present work indicates that l-arginine infusion increases muscle capillary blood flow in rats that are not performing exercise. Supplementation with l-arginine might provide additional blood flow at rest and during exercise and result in the improvement of muscle performance and exercise capacity.

The effects of calcium channel antagonist nimodipine on end-plate vascularity of the degenerated intervertebral disc in rats

The vascular channels at the end-plate of the intervertebral disc are very important in maintaining a healthy disc. With age, a reduction of the nutrition of the avascular nucleus pulposus is inevitable. On the other hand the calcium channel antagonist nimodipine has been shown to have a positive effect on blood flow in the region of the vertebral end-plate. To evaluate the effects of nimodipine on the end-plate vascularity in the degenerative discs, we have produced an experimental disc degeneration and evaluated the radiological and histopathological features of the end-plate of the degenerated discs. Adult rats were divided into 3 groups: control (n=5), operated degeneration (n=5), and nimodipine treatment (n=5). Using a posterior approach, a cut was made parallel to the end-plates in the posterior annulus fibrosus in 5 consecutive intervertebral discs between the 5th and 10th vertebral segments of the tails of adult Swiss Albino rats. At 8 weeks, 5 of these animals were treated with nimodipine. In each experimental group, 1 animal was examined using computed tomography (CT) to study the density of the cartilage end-plate of the disc. Then, the animals were sacrificed for subsequent histopathological evaluation. We found that the vascular channel counts and percentage areas from animals treated with nimodipine were higher than from both the non-operative control and operated degeneration groups, although these were not statistically different. Accordingly, the profile of the density histogram in the nimodipine-treated group showed a wide plateau, indicating an increase in the vascularity in this region. From our results, we suggest that nimodipine enhances vascularisation of the cartilage end-plate in the disc. It is possible that the increased proportion of vascular contacts at the end-plate has a beneficial effect in the nutrition of the disc. However, further experimental studies will be needed to determine the validity of this statement in animals or human beings.

Acute spinal cord injury, part II: contemporary pharmacotherapy

Spinal cord injury (SCI) remains a common and devastating problem of modern society. Through an understanding of underlying pathophysiologic mechanisms involved in the evolution of SCI, treatments aimed at ameliorating neural damage may be developed. The possible pharmacologic treatments for acute spinal cord injury are herein reviewed. Myriad treatment modalities, including corticosteroids, 21-aminosteroids, opioid receptor antagonists, gangliosides, thyrotropin-releasing hormone (TRH) and TRH analogs, antioxidants and free radical scavengers, calcium channel blockers, magnesium replacement therapy, sodium channel blockers, N -methyl-D-aspartate receptor antagonists, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid-kainate receptor antagonists, modulators of arachadonic acid metabolism, neurotrophic growth factors, serotonin antagonists, antibodies against inhibitors of axonal regeneration, potassium channel blockers (4-aminopyridine), paclitaxel, clenbuterol, progesterone, gabexate mesylate, activated protein C, caspase inhibitors, tacrolimus, antibodies against adhesion molecules, and other immunomodulatory therapy have been studied to date. Although most of these agents have shown promise, only one agent, methylprednisolone, has been shown to provide benefit in large clinical trials. Given these data, many individuals consider methylprednisolone to be the standard of care for the treatment of acute SCI. However, this has not been established definitively, and questions pertaining to methodology have emerged regarding the National Acute Spinal Cord Injury Study trials that provided these conclusions. Additionally, the clinical significance (in contrast to statistical significance) of recovery after methylprednisolone treatment is unclear and must be considered in light of the potential adverse effects of such treatment. This first decade of the new millennium, now touted as the Decade of the Spine, will hopefully witness the emergence of universal and efficacious pharmacologic therapy and ultimately a cure for SCI.

Autoradiographic [3H]nimodipine distribution after experimental spinal cord injury in rats

Because of its potential for augmentation of blood flow and protection of neurons after neurological insult, nimodipine has been investigated as a treatment of spinal cord injury (SCI). The results have been inconsistent, possibly because of poor delivery of nimodipine to the injured spinal cord. The following study was designed to determine the delivery of nimodipine to the injured spinal cord. It was also hoped that information about the temporal and spatial pattern of binding of nimodipine after SCI might further elucidate the relationship between calcium channel activation and injury. Fourteen female Wistar rats were divided into three groups: control (n = 3), 30 min post-SCI (n = 6); and 4 h post-SCI (n = 5). The injury was produced by acute clip compression for 1 min at T1. [3H]Nimodipine was administered 5 min after laminectomy in the control group, and at the above-specified times after injury in the SCI groups. The drug was then allowed to equilibrate for 30 min before the animals were killed. The spatial patterns and concentrations of [3H]nimodipine in various segments of the spinal cord were autoradiographically determined. The highest concentrations of [3H]nimodipine were at the injury site after SCI. Also, the mean [3H]nimodipine concentrations in all sites in each animal were higher in the injury groups than in the control group (p < 0.05). This study indicates that delivery of this agent to the injured cord is possible, and provides evidence of widespread Ca2+ channel activation in the first 4 h after injury.

Effect of nimodipine and N-acetylcysteine on lipid peroxidation after experimental spinal cord injury

The effectiveness of nimodipine and N-acetylcysteine in experimental spinal cord injury was evaluated by measuring tissue lipid peroxidation levels of the damaged spinal cords 1 hour after the injury We used the clip compression method to produce acute spinal cord injury in 40 female Sprague-Dawley rats were used. The rats were divided into four groups of 10 each. Lipid peroxidation was assessed by measuring the tissue content of malonil dialdehyde (MDA). In group 3, nimodipine, and in group 4, N-acetylcysteine, was administered i.p. as a single dose immediately after the injury. The rats were sacrificed 1 hour after clip application. The tissue mean MDA content was 3,992 micromol MDA/gww in group 1 (sham operated), 10,192 micromol MDA/gww in group 2 (trauma), 10,449 micromol MDA/gww in group 3 (nimodipine treatment) and 9,009 micromol MDA/gww in group 4 (N-acetylcysteine treatment). These results demonstrated that a single dose of nimodipine and N-acetylcysteine had no effect on peroxidation of lipid membranes in the early period of experimental spinal cord injury.

Spinal cord blood flow and pathophysiological changes after transient spinal cord ischemia in cats

OBJECTIVE

The goal was to study the hemodynamics and regional pathophysiological changes in the spinal cord after transient vascular occlusion in cats.

METHODS

We measured spinal cord blood flow (SCBF) continuously in the lumbar region with a laser-doppler flowmeter, before, during, and after spinal cord ischemia induced by balloon occlusion of the thoracic aorta, in 24 cats (divided into three groups) and simultaneously recorded the evoked spinal cord potentials (ESPs). In each group (n = 8), 10-, 20-, and 30-minute ischemic loading was performed. All animals were evaluated neurologically 36 hours later, and then their spinal cords were examined histologically.

RESULTS

The amplitude of ESPs decreased 10 minutes and disappeared 20 minutes after occlusion. SCBF increased to as much as 2 times the control values after reperfusion and decreased gradually in all groups. Then, in all animals in the 10-minute group and six animals in the 20-minute group, SCBF returned to the control values, which were subsequently maintained throughout the experiment, and ESPs returned to normal patterns within 1 hour. For all animals in the 30-minute group and two in the 20-minute group, hypoperfusion after recirculation, irreversible amplitude changes in ESPs, postischemic paraparesis, and pathological ischemic changes in the lower thoracic and lumbar spinal segments were recognized.

CONCLUSION

Our results showed that > 20-minute occlusion of the thoracic aorta in cats resulted in irreversible spinal perfusion disorders and that the monitoring of SCBF and ESPs could be useful for predicting potential neurological deficits. Furthermore, postischemic hypoperfusion may have an important role in the development of secondary spinal cord ischemia, resulting in severe neurological dysfunction. This observation suggested the possibility of therapeutic modification of the secondary processes inducing hypoperfusion after spinal ischemia.

Anoxic injury in the rat spinal cord: pharmacological evidence for multiple steps in Ca(2+)-dependent injury of the dorsal columns

To examine anoxic injury in spinal cord white matter, we studied axonal conduction in the dorsal columns during and following a standard 60 min anoxic insult at 36 degrees C. Perfusion of the spinal cord in 0-Ca2+ Ringer solution resulted in significantly improved recovery of the compound action potential. Similarly, removal of Na+ from the perfusate resulted in significantly improved recovery of conduction in dorsal column axons. Exposure of the anoxic spinal cord to the Na+ channel blocker tetrodotoxin (TTX), the Na-Ca exchange blockers benzamil and bepridil, Na(+)-H+ exchange blockers amiloride and harmaline, and perfusion in Ringer solution with pH adjusted to 6.4, all resulted in improved recovery. The tertiary anesthetics procaine and lidocaine, as well as phenytoin and carbamazepine, also resulted in improved recovery of compound action potential amplitude after 60 min of anoxia. These results demonstrate that a significant component of irreversible loss of conduction, following anoxic injury of the dorsal columns, is Ca(2+)-dependent. Moreover, these results demonstrate that TTX-inhibitable Na+ channels participate in the pathophysiology of anoxic injury in spinal cord white matter, and indicate that reverse Na-Ca exchange provides a route for at least part of the damaging influx of Ca2+ into an intracellular compartment in anoxic spinal cord white matter. Our results also suggest that extracellular acidosis may have a protective effect on anoxic spinal cord white matter, and support the hypothesis that anoxic injury of spinal cord white matter may involve the Na(+)-H+ exchanger.

Clinical potential for the use of neuroprotective agents. A brief overview

"Stroke treatment seems to be entering a golden age ...." Fisher's observation not only applies to ischemic stroke, but to all the conditions described above, and in the future, possibly (and quite speculatively), to other neurologic diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, even radiation therapy and Bell's palsy. Physicians must sharpen their criteria for decisions regarding therapy and must" ... be prepared to accept what is actually known from scientific data ... rather than to rely on instinct, clinical impression, or the need to do something rather than nothing."

Effect of nimodipine or methylprednisolone on recovery from acute experimental spinal cord injury in rats

The purpose of the present study was to examine the behavioral, electrophysiologic, and anatomic responses to nimodipine or methylprednisolone treatment of acute experimental spinal cord injury. Four groups of rats were injured at T1 by compressing the cord with a 52-g clip for 1 minute. The treatments were begun 15 minutes after injury, and the animals were observed thereafter for 8 weeks. Nimodipine 0.02 mg/kg/h intravenously (iv) for 8 hours with adjuvant albumen volume expansion, followed by 20 mg/kg nimodipine enterally three times per day for 7 days, produced a moderately better composite score comprising four endpoint parameters than the other treatments which consisted of nimodipine iv for 8 hours only, methylprednisolone 30 mg/kg iv bolus followed by 5.4 mg/kg/h iv for 8 hours, or control.

Limiting ischemic spinal cord injury using a free radical scavenger 21-aminosteroid and/or cerebrospinal fluid drainage

Traumatic spinal cord injury occurs in two phases: biomechanical injury, followed by ischemia and reperfusion injury. Biomechanical injury to the spinal cord, preceded or followed by various pharmaceutical manipulations or interventions, has been studied, but the ischemia/reperfusion aspect of spinal cord injury isolated from the biomechanical injury has not been previously evaluated. In the current study, ischemia to the lumbar spinal cord was induced in albino rabbits via infrarenal aortic occlusion, and two interventions were analyzed: the use of U74006F (Tirilazad mesylate), a 21-aminosteroid, and cerebrospinal fluid (CSF) drainage. These treatment modalities were tested alone or in combination. In Phase 1 of this study, the rabbits received 1.0 mg/kg of Tirilazad or an equal volume of vehicle (controls) prior to the actual occlusion, three doses of Tirilazad (1 mg/kg each) during the occlusion, then several doses after the occlusion. Of the Tirilazad-treated animals, 30% became paraplegic while 70% of the control animals became paraplegic. Phase 2 involved the same doses of Tirilazad as in Phase 1 and, in addition, CSF pressure monitoring and drainage were performed. The paraplegia rate was 79% in the control animals, 36% in the group receiving Tirilazad alone, 25% in the group with CSF drainage alone, and 20% in the Tirilazad plus CSF drainage group. This rate also correlated with changes noted in CSF pressure; both Tirilazad administration alone and CSF drainage alone induced a decrease in CSF pressure and the two combined produced a further decrease. There was marked improvement in the perfusion pressure when using Tirilazad alone, CSF drainage alone, and Tirilazad therapy in combination with CSF drainage, with the last group producing the largest increase. This change in CSF pressure and perfusion pressure correlated with improved functional neurological outcome. Pathological examination revealed that Tirilazad therapy reduced the extensive and diffuse neuronal, glial, and endothelial damage to (in its most severe form) a more patchy focal region of damage in the gray matter. Cerebrospinal fluid drainage resulted in pyknosis of some motor neurons, and some eosinophilia. The combination of CSF drainage and Tirilazad administration resulted in the least abnormality, with either normal or near-normal spinal cords. It is concluded that Tirilazad administration decreased CSF pressure during spinal cord ischemia and reperfusion and, like CSF drainage, increased and improved the perfusion pressure to the spinal cord, decreased spinal cord damage, and improved functional outcome.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of flunarizine on neurological recovery and spinal cord blood flow in experimental spinal cord ischemia in rabbits

BACKGROUND AND PURPOSE

The lipophilic calcium channel antagonist flunarizine has been demonstrated to be neuroprotective in several models of cerebral ischemia. Ischemic spinal cord injury may have a similar pathophysiology and hence may respond in a similar fashion. This study was designed to investigate the effects of pretreatment with flunarizine on systemic hemodynamics, spinal cord blood flow, and neurological recovery in a rabbit model of ischemic spinal cord injury.

METHODS

New Zealand White rabbits were anesthetized with ketamine and xylazine and instrumented for systemic blood pressure monitoring and spinal cord blood flow measurements using the microsphere method. After pretreatment with flunarizine or vehicle, ischemic spinal cord injury was created selectively in the caudal regions of the spinal cord by cross-clamping the abdominal aorta for a period of 25 minutes. Spinal cord blood flow was measured before, during, and 15 minutes after cross-clamp removal. Animals were allowed to recover and were graded neurologically at 18 and 24 hours after ischemia.

RESULTS

Flunarizine injection was associated with hypotension that was both transient and dose related. Animals pretreated with flunarizine 0.4 mg/kg had significantly improved neurological recovery scores at 18 hours after ischemia (P = .017) compared with vehicle controls. At 24 hours this effect was lessened (P = .095); however, 60% of flunarizine-treated animals retained their ability to hop, whereas all of the vehicle-treated animals were nonambulatory.

CONCLUSIONS

Flunarizine has a protective effect on neurological recovery after experimental ischemic spinal cord injury. The therapeutic window is narrow, and dosing is limited by untoward hypotension. The mechanism of protection likely involves inhibition of pathological cytosolic calcium accumulation rather than a direct effect on vascular smooth muscle.

Spinal cord blood flow and evoked potential responses after treatment with nimodipine or methylprednisolone in spinal cord-injured rats

This study examined the effect of nimodipine or methylprednisolone on spinal cord blood flow (SCBF) and electrophysiological function after spinal cord injury in rats. Three groups of male rats (n = 10 per group) were injured by compression of the cord at T1 for 1 minute with a 52-g clip. The hydrogen clearance technique was used to measure SCBF at the T1 segment. Motor and somatosensory evoked potentials were recorded. SCBF and evoked potentials were measured before injury and again at approximately 1 and 2.5 hours after injury. The methylprednisolone group received a bolus of methylprednisolone (30 mg/kg) at 5 minutes after injury and then at 15 minutes after injury, the group received an infusion of methylprednisolone at 5.4 mg/kg per hour. The nimodipine group received placebo at 5 minutes and then received an infusion of nimodipine at 0.02 mg/kg per hour at 15 minutes. The placebo group received placebo at both times. Physiological parameters were closely monitored and maintained within the normal range. Albumin was administered after injury to maintain mean arterial blood pressure at or above 80 mm Hg. The infusions were continued for approximately 3 hours after spinal cord injury. SCBF was not significantly different between the experimental groups at either 1 or 2.5 hours postinjury (P = 0.16 and 0.71, respectively), and evoked potential responses did not return in any rat at any time after injury. Thus, this experiment failed to demonstrate an improvement in SCBF or electrophysiological function with either drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the calcium channel antagonist nimodipine after experimental spinal cord injury

The cortical somatosensory evoked potentials (CSEPs) were recorded to determine if the administration of nimodipine improves axonal function after spinal cord injury. Animals receiving a 52 g compression injury (a moderately severe injury) for 5 minutes were randomly allocated to one of five treatment groups. Each group was given an infusion of one of the following nimodipine regiments over 2 hours, commencing 1 hour before compression: placebo (n = 20), 0.5 micrograms/kg (n = 10), 0.25 micrograms/kg (n = 20), 0.125 micrograms/kg (n = 10), and 0.25 micrograms/kg + Hetstarch (n = 10). In the control group, 65% of animals lost the CSEPs immediately after the injury with almost all (95%) of these regaining the CSEPs within 15 minutes after decompression of the spinal cord. In the treated groups, the rate of the CSEP loss was highest in the 0.5 micrograms/kg group. This group also had the lowest CSEP recovery. The proportion of the CSEP loss was essentially the same for the other nimodipine-treated groups, although it seemed that there was an increasing number of nonresponses with increasing the nimodipine dose. Our data indicate lack of any beneficial effects of nimodipine on axonal function as measured by evoked activities in experimental spinal cord injury.

[Effects of continuous administration of nimodipine during the acute phase of spinal cord injury in baboons]

This study was carried out to assess the putative improvement of spinal cord blood flow obtained with a calcium channel blocker after acute spinal cord injury in ten baboons. The injury was generated by compressing the cord at L1 level for 5 seconds with a balloon catheter inflated to 2 bars with Ringer's solution. Subsequently, five monkeys received a saline infusion, and five others a nimodipine infusion (0.04 mg.kg-1 x h-1), for seven days. Spinal cord blood flow (SCBF) was measured using a scanographic technique with stable xenon. Somatosensory evoked potentials (SEP), magnetic resonance imaging (MRI) and a histological study of the spine were carried out a different times of the study. SCBF and SEP were recorded before injury. Thereafter SCBF was measured every thirty minutes during the four hours following the injury, as well as on day 7. SEP and MRI were recorded on days 1 and 7. The histological study was carried out on the eighth day. Three spinal cord and vertebral segments were collected, fixed, sliced and stained. SCBF before injury was not significantly different in either group (39.8 +/- 15.9 ml x 100 g-1 x min-1 for the treatment group 40.9 +/- 16.3 ml x 100 g-1 x min-1 for the control group). During the injury, there were major variations between animals. The results were expressed as percentages of each animal's control SCBF (before injury). Immediately after injury, SCBF increased in both groups. However, in the control group, SCBF decreased more than in the treatment group on the seventh day after injury (80 to 90% vs 25 to 50%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Further studies of nimodipine in experimental spinal cord injury in the rat

Previously in our laboratory, nimodipine was effective in reversing posttraumatic ischemia and promoting electrophysiologic recovery in a rat spinal cord injury (SCI) model. However, these beneficial effects were achieved when nimodipine was combined with adjuvant therapy to reverse posttraumatic hypotension, by either volume expansion or vasopressor therapy. The present experiments determined if nimodipine alone can increase spinal cord blood flow (SCBF) and improve function after SCI. The hydrogen clearance technique was used to measure SCBF, and motor and somatosensory evoked potentials (MEP and SSEP) were used to quantitate electrophysiologic function. SCBF, MEP, and SSEP were recorded before and after a 52 g clip compression injury at the T1 segment and then repeated after a 35 minute infusion of nimodipine. Twenty-five rats were allocated randomly to five equal groups, each of which received 35 minute infusions of one of the following doses of nimodipine: (1) 0 mg/kg, (2) 0.005 mg/kg, (3) 0.01 mg/kg, (4) 0.025 mg/kg, or (5) 0.05 mg/kg. SCBF decreased after injury in all groups, and there was no increase in SCBF after nimodipine infusion in any group. MEP and SSEP were abolished by the injury in all rats, and there was no recovery of the evoked potentials in any group. It is concluded that adjuvant therapy for posttraumatic hypotension may be necessary for nimodipine to improve SCBF and promote recovery of function in the injured spinal cord.

Spinal cord injury in rats: inability of nimodipine or anti-neutrophil serum to improve spinal cord blood flow or neurologic status

The role of a calcium-mediated increase in vascular resistance and of vascular damage caused by polymorphonuclear leukocytes (PMNLs) in the development of neurologic deficit and disturbance of spinal cord circulation following spinal cord compression was studied in the rat. Spinal cord injury was induced by 5 min of compression with a load of 35 g on a 2.2 X 5.0 mm compression plate. This caused transient paraparesis. The rats received either the calcium receptor antagonist nimodipine or an anti-rat neutrophil serum (ANS). Nimodipine was infused i.v. for 4 h in an amount of 1.5 micrograms/kg/min starting 60 min after trauma. The number of circulating PMNLs was depleted by intraperitoneal injection of an ANS raised in sheep given 12 h before trauma. This caused a reduction to about 2% of the pre-ANS value. Controls received saline or normal sheep serum. The motor performance was assessed daily on the inclined plane. On day one, the day after injury, the capacity angle had decreased from about 63 degrees preoperatively to close to 32 degrees in the experimental groups. There was then a slow improvement in both the control and experimental groups and on day 4 the capacity angle was close to 43 degrees in all 3 groups. Spinal cord blood flow, as measured with the 14C-iodoantipyrine autoradiography method, was similar in all groups on day 4. As neither the neurologic dysfunction nor the spinal cord blood flow was affected by post-trauma treatment with nimodipine or pretreatment with ANS, the possibility that calcium-mediated vasoconstriction or PMNLs play a role in the development of posttraumatic neurologic disability was not supported by this study.

Spinal cord blood flow and systemic blood pressure after experimental spinal cord injury in rats

We looked at the relation between systemic arterial blood pressure and recovery from spinal cord injury by inducing both hypertension and hypotension in 25 rats randomly allocated to five equal groups. The rats received no injury, a mild (2.3-g), or a severe (53.0-g) spinal cord injury lasting 1 minute. We used the hydrogen clearance technique to measure spinal cord blood flow at the injury site (T1) and at an adjacent site (C6). Mean systemic arterial blood pressure was either increased with adrenaline or decreased by phlebotomy in 20-mm-Hg intervals except for the severe-injury group, in which the posttraumatic pressure could only be increased with adrenaline. Spinal cord blood flow remained constant in the no-injury group between 81 and 180 mm Hg. After a mild injury, induced moderate hypertension (121-140 mm Hg) improved spinal cord blood flow significantly, whereas hypotension decreased it in a linear fashion. Severe injury caused a marked decrease in spinal cord blood flow and mean systemic arterial blood pressure. Even extreme hypertension (161-180 mm Hg) induced by adrenaline did not significantly increase spinal cord blood flow at T1 but caused hyperemia at C6 due to loss of autoregulation. In conclusion, normotension should be attempted, irrespective of the severity of spinal cord injury. Induced hypertension after severe spinal cord injury was not beneficial in improving spinal cord blood flow at the injury site while potentially increasing hemorrhage and edema.

Nicardipine after spinal cord compression in the lamb

To study the effects of the calcium channel blocker nicardipine on spinal cord blood flow and spinal evoked potentials, the following study was undertaken. After cord compression, which was productive of paraparesis, nicardipine was administered intravenously in 10 anesthetized lambs. Ten control animals were subjected to compression but received saline instead. Nicardipine produced a significant decrease in mean arterial pressure when compared to the control group. Thirty minutes after compression, spinal cord blood flow also was lower in the nicardipine group compared with controls. Spinal evoked potentials did not recover after compression in either group.

Acute injury to the central nervous system

Central nervous system (CNS) trauma is divided into brain and spinal cord injury. A basic understanding of the pathophysiology of CNS trauma helps the practitioner more accurately evaluate, treat, and prognose cases of CNS trauma. The progressive nature of CNS injuries and the contribution of microvascular ischemic are explored.

Effect of nimodipine-associated hypotension on recovery from acute spinal cord injury in cats

The effect of nimodipine on acute spinal cord trauma was studied in cats. Spinal evoked responses (SERs) were abolished after weight drop injury of 100 g-cm. All control animals showed spontaneous recovery of spinal cord function as measured by SERs. Treatment with a moderate intravenous dose of nimodipine resulted in a 32% drop in systemic blood pressure and delay in or failure of spinal cord recovery. We concluded that in this model, nimodipine treatment had deleterious effect on the spinal cord recovery due to the significant associated hypotension. It is likely that marked hypotension in the case of traumatic loss of autoregulation overrides the expected nimodipine-related increase in spinal cord blood flow with resultant additional ischemic damage.

Effect of a calcium channel blocker on posttraumatic spinal cord blood flow

The normal rat spinal cord blood flow (SCBF) has been shown to increase after administration of nimodipine, a calcium channel blocker. The present study investigates the capability of nimodipine to improve SCBF, as measured by the hydrogen clearance technique, after a 53.0-gm clip compression injury to the T-1 segment of the rat spinal cord. The profound drop in mean systemic arterial blood pressure (MSAP) after cervical cord injury precluded any improvement in posttraumatic SCBF by nimodipine alone. Hence, in a randomized controlled study with five rats per group, pressor agents (whole blood, angiotensin, or adrenaline) were infused to maintain MSAP between 100 and 120 mm Hg after injury. Control animals received only a saline infusion. Nimodipine at the optimal dose found in normal animals (1.5 microgram/kg/min) was added to the pressor agents. The MSAP and other physiological parameters were measured in rats receiving the pressor agents only and in those receiving pressor agents combined with nimodipine. In rats receiving whole blood, angiotensin, or adrenaline the posttraumatic MSAP improved to between 100 and 120 mm Hg, but there was no improvement in SCBF compared to the saline group. The addition of nimodipine decreased MSAP and SCBF in all groups except those animals also receiving adrenaline, where the MSAP was maintained at 109 +/- 5 mm Hg. In these animals a significant increase in posttraumatic SCBF from 16.5 +/- 2.1 to 20.2 +/- 2.3 ml/100 gm/min (mean +/- standard error of the mean) occurred at the site of injury with the addition of nimodipine. The maintenance of an adequate MSAP by a pressor agent was crucial for nimodipine to improve posttraumatic SCBF by its ability to dilate the spinal vascular bed. Adrenaline was the only pressor agent that could fulfill the above criteria, although other pressor agents need to be investigated. Experiments are underway with the combination of adrenaline and nimodipine to further verify these encouraging results demonstrating an improvement in posttraumatic ischemia of the spinal cord.

A microcomputer system for on-line collection of blood flow and related physiological data

A multi-disciplinary approach is described for the development of a microcomputer based on-line data collection system for blood flow experiments. Well designed software provides a flexible approach to data collection, which is particularly suited to blood flow research laboratories. The choice of well supported hardware ensures ease of development with minimum time and cost.