Memantine for prevention of spinal cord injury in a rabbit model

Evaluation of spinal cord protective threshold of serum memantine, an NMDA receptor antagonist, in a rabbit model of paraplegia

Purpose

To evaluate the threshold of serum memantine for prevention of spinal cord injury (SCI) in a rabbit paraplegic model.

Methods

Forty-two New Zealand white rabbits were divided into 7 groups. Preoperatively, oral memantine was given starting from 60 mg OD for 7 days in the initial group, then reducing the dose and/or duration to 60 mg OD for 5 days, 30 mg OD for 5 days, 30 mg OD for 3 days, 15 mg OD for 3 days, 30 mg single dose, and 60 mg single dose, in subsequent 6 groups. A paraplegic model was created by clamping both infrarenal aorta and inferior vena cava (IVC) for 45 min. Motor evoked potentials (MEPs), modified Tarlov score (0-5), serum memantine concentration, and histopathology of the spinal cord were evaluated.

Results

Half of all rabbits (21/42) showed spinal protection. Receiver operating characteristic (ROC) curve analysis showed serum level of 4.5 ng/ml as a cutoff value for spinal protection (sensitivity 86%, specificity 62%, area under the curve (AUC) 0.785, P = .002). Sixteen rabbits had serum level ≥ 4.5 ng/ml (group A), with 26 rabbits having < 4.5 ng/ml (group B). Further comparison was done between groups A and B. The mean modified Tarlov score at 6, 24, 48, and 72 h was 4.5 ± 0.9 and 2.4 ± 1.6, in groups A and B, respectively (P < .001). The modified Tarlov score showed positive correlation with serum memantine level (Spearman's rho = 0.618, P = .01). Results of MEP and histopathology were significantly better for group A.

Conclusions

We showed that memantine is protective against SCI at serum levels ≥ 4.5 ng/ml in a rabbit model; thus, it can be a potential adjunct for spinal protection during thoracic/thoracoabdominal aortic surgeries.

Effects of D‑Ala2, D‑Leu5‑Enkephalin pre‑ and post‑conditioning in a rabbit model of spinal cord ischemia and reperfusion injury

It has recently been revealed that during the aorta-clamped period, D-Ala², D-Leu⁵-Enkephalin (DADLE) infusion can protect the spinal cord against ischemia and reperfusion (I/R) injury. However, the protective effects of DADLE administration prior to ischemia or at the time of early reperfusion have not yet been investigated. Drug pre- or post-conditioning can serve as a more valuable clinical strategy. Therefore, the present study was designed to investigate the neuroprotective effect of DADLE infusion at different time intervals in order to determine the optimum time point for ischemic spinal cord protection. A total of 40 New Zealand white rabbits were randomly divided into 5 groups: Sham-operated (Sham), normal saline pre-conditioning (NS), DADLE per-conditioning (D_per), DADLE pre-conditioning (D_pre) and DADLE post-conditioning (D_post). All animals were subjected to spinal cord ischemia for 30 min followed by 48 h reperfusion. Hind limb motor functions were assessed according to the Tarlov criterion when the animals regained consciousness, 6, 24 and 48 h after reperfusion. Histological analysis and the number of viable α-motor neurons were also used to assess the extent of spinal cord injury. Compared with the NS group, the Tarlov scores and the number of normal neurons were significantly higher in the D_per group (P<0.05), which were consistent with the results of a previous study. In addition, the paraplegia rate and loss of normal motor neurons were lower in the DADLE per- and post-conditioning groups compared with the DADLE pre-conditioning; however, these were not statistically significant. DADLE 0.05 mg/kg administration at three time points all mitigated normal motor neuron injury in the anterior horn and decreased the paraplegia rates in rabbits. The therapeutic benefits appeared best in the post-conditioning group with DADLE, and worst in the pre-conditioning group.

The Effects of Memantine on Glutamic Receptor-Associated Nitrosative Stress in a Traumatic Brain Injury Rat Model

BACKGROUND

The main aim of this study is to elucidate whether the neuroprotective effect of memantine, a noncompetitive N-methyl-d-aspartate receptor 2B (NR2B) antagonist, affects neuronal nitrosative stress, apoptosis, and NR2B expression and improves functional outcomes.

METHODS

Immediately after the onset of fluid percussion traumatic brain injury (TBI), anesthetized male Sprague-Dawley rats were divided into sham-operated, TBI + vehicle, and TBI + memantine groups. TBI rats were treated with a memantine intraperitoneal injection dose of 20 mg/kg intraperitoneally and then 1 mg/kg every 12 hours intraperitoneally for 6 doses. The motor function, proprioception, infarction volume, and neuronal apoptosis were then measured. Immunofluorescence was used to evaluate astrogliosis, microgliosis, nitrosative stress, and NR2A and NR2B expression in cortical cells. All the parameters were assessed 72 hours after TBI.

RESULTS

Compared with the sham-operated controls, the TBI-induced motor and proprioception deficits, and increased infraction volume after TBI were significantly attenuated by memantine therapy. The TBI-induced neuronal apoptosis, astrogliosis, and microgliosis, the numbers of neuronal NO synthase and 3-nitro-l-tyrosine expression in neurons, and inducible NO synthase expression in microglia and astrocyte cells in the ischemic cortex after TBI were significantly improved by memantine therapy. Simultaneously, without affecting the NR2A expression in neuronal cells, the NR2B expression significantly decreased after memantine therapy, as evaluated by an immunofluorescence stain.

CONCLUSIONS

Intraperitoneal injection of memantine in the acute stage may ameliorate TBI in rats by affecting NR2B expression and decreasing neuronal apoptosis and nitrosative stress in the injured cortex. These effects might represent 1 mechanism by which functional recovery occurred.

Changes in transcranial electrical motor-evoked potentials during the early and reversible stage of permanent spinal cord ischemia predict spinal cord injury in a rabbit animal model

The present study examined changes in the transcranial electrical motor-evoked potentials (TceMEP) waveform to predict neurological deficits and histopathological changes during the early and reversible stage of different levels of permanent spinal cord ischemic injury in a rabbit animal model. A total of 24 New Zealand rabbits were randomly divided into four groups of 6 rabbits each. Group 1 underwent a ligation of the lumbar artery at three levels (L1-L3), group 2 underwent a ligation of the lumbar artery at four levels (L1-L4) and group 3 underwent a ligation of the lumbar artery at five levels (L1-L5). The sham group contained 6 rabbits and did not receive ligation. TceMEP was recorded within 5 min of ligation and, 2 days later, motor function was assessed and the spinal cords were removed for histological examination. Following spinal cord injury, the relationship between variations in the TceMEP waveform and motor function and pathological damage was analyzed. It was observed that the amplitude of TceMEP began to decrease within 1 min of lumbar artery ligation and that the amplitude stabilized within 5 min. These amplitude changes that occurred within 5 min of different levels of permanent spinal cord ischemic injury were positively related to changes in motor function following recovery from anesthesia and 2 days after ligation. The Pearson correlation coefficient was 0.980 and 0.923 for these two time points, respectively (P<0.001). In addition, the amplitude changes were positively related to pathological damage, with a Pearson correlation coefficient of 0.945 (P<0.001). The results of the present study suggested that amplitude changes in TceMEP are particularly sensitive to ischemia. Ischemia may be detected within 1 min and the amplitude changes begin to stabilize within 5 min following ligation of the lumbar artery. The use of intraoperative monitoring of TceMEP allows for the detection of spinal cord ischemic injury with no time delay, which may allow for protective measures to be taken to prevent the occurrence of irreversible spinal cord injury.

Specific combinations of ion channel inhibitors reduce excessive Ca2+ influx as a consequence of oxidative stress and increase neuronal and glial cell viability in vitro

Combinations of Ca²⁺ channel inhibitors have been proposed as an effective means to prevent excess Ca²⁺ flux and death of neurons and glia following neurotrauma in vivo. However, it is not yet known if beneficial outcomes such as improved viability have been due to direct effects on intracellular Ca²⁺ concentrations. Here, the effects of combinations of Lomerizine (Lom), 2,3-dioxo-7-(1H-imidazol-1-yl)6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate (YM872), 3,5-dimethyl-1-adamantanamine (memantine (Mem)) and/or adenosine 5'-triphosphate periodate oxidized sodium salt (oxATP) to block voltage-gated Ca²⁺ channels, Ca²⁺ permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, NMDA receptors and purinergic P2X₇ receptors (P2X₇R) respectively, on Ca²⁺ concentration and viability of rat primary mixed cortical (MC) cultures exposed to hydrogen peroxide (H₂O₂) insult, were assessed. The contribution of ryanodine-sensitive intracellular stores to intracellular Ca²⁺ concentration was also assessed. Live cell calcium imaging revealed that a 30min H₂O₂ insult induced a slow increase in intracellular Ca²⁺, in part from intracellular sources, associated with loss of cell viability by 6h. Most combinations of inhibitors that included oxATP significantly decreased Ca²⁺ influx and increased cell viability when administered simultaneously with H₂O₂. However, reductions in intracellular Ca²⁺ concentration were not always linked to improved cell viability. Examination of the density of specific cell subpopulations demonstrated that most combinations of inhibitors that included oxATP preserved NG2+ non-oligodendroglial cells, but preservation of astrocytes and neurons required additional inhibitors. Olig2⁺ oligodendroglia and ED-1⁺ activated microglia/macrophages were not preserved by any of the inhibitor combinations. These data indicate that following H₂O₂ insult, limiting intracellular Ca²⁺ entry via P2X₇R is generally associated with increased cell viability. Protection of NG2+ non-oligodendroglial cells by Ca²⁺ channel inhibitor combinations may contribute to observed beneficial outcomes in vivo.

Methodology of motor evoked potentials in a rabbit model

Spinal cord ischemia (SCI) is a devastating complication of aortic operations. Neuromonitoring using motor evoked potentials (MEPs) is a sensitive modality to detect SCI in humans. We describe a leporine SCI model using MEPs to test pharmaceutical therapeutics and other neuroprotective adjuncts. In 80 rabbits, methods to obtain MEPs in normotensive and ischemic rabbits were developed. The effects of isoflurane, propofol, apnea, and hypotension on lower extremity MEPs were studied. Lower extremity MEPs disappear upon SCI induction in 78 of 78 (100 %) rabbits. Prior to SCI induction and during apneic episodes, lower extremity MEPs were lost in all (100 %) and upper extremity MEPs in one (25 %). Isoflurane was used in four experiments, with loss of lower extremity MEPs in all four (100 %) and loss of upper extremity MEPs in zero. With propofol upper extremity, MEPs were obtainable in 80 of 80 rabbits (100 %) and lower extremity MEPs in 78 of 80 rabbits (97.5 %) prior to SCI induction. The presence of these lower extremity MEPs prior to SCI induction was not correlated with systolic or diastolic blood pressure. Disappearance of MEPs occurred in all 45 rabbits with postoperative lower extremity impairment. MEPs in the leporine model correlate closely with paraplegia. MEPs are influenced by inhaled anesthetics and apnea but not by hypotension alone. Propofol anesthesia provides reliable MEPs. This study provides the basis for a reproducible model of SCI to be used for novel therapeutic drug development.

NMDA Receptor Antagonist Attenuates Bleomycin-Induced Acute Lung Injury

Background

Glutamate is a major neurotransmitter in the central nervous system (CNS). Large amount of glutamate can overstimulate N-methyl-D-aspartate receptor (NMDAR), causing neuronal injury and death. Recently, NMDAR has been reported to be found in the lungs. The aim of this study is to examine the effects of memantine, a NMDAR channel blocker, on bleomycin-induced lung injury mice.

Methods

C57BL/6 mice were intratracheally injected with bleomycin (BLM) to induce lung injury. Mice were randomized to receive saline, memantine (Me), BLM, BLM plus Me. Lungs and BALF were harvested on day 3 or 7 for further evaluation.

Results

BLM caused leukocyte infiltration, pulmonary edema and increase in cytokines, and imposed significant oxidative stress (MDA as a marker) in lungs. Memantine significantly mitigated the oxidative stress, lung inflammatory response and acute lung injury caused by BLM. Moreover, activation of NMDAR enhances CD11b expression on neutrophils.

Conclusions

Memantine mitigates oxidative stress, lung inflammatory response and acute lung injury in BLM challenged mice.

Curcumin protects against ischemic spinal cord injury: The pathway effect

Inducible nitric oxide synthase and N-methyl-D-aspartate receptors have been shown to participate in nerve cell injury during spinal cord ischemia. This study observed a protective effect of curcumin on ischemic spinal cord injury. Models of spinal cord ischemia were established by ligating the lumbar artery from the left renal artery to the bifurcation of the abdominal aorta. At 24 hours after model establishment, the rats were intraperitoneally injected with curcumin. Reverse transcription-polymerase chain reaction and immunohistochemical results demonstrated that after spinal cord ischemia, inducible nitric oxide synthase and N-methyl-D-aspartate receptor mRNA and protein expression significantly increased. However, curcumin significantly decreased inducible nitric oxide synthase and N-methyl-D-aspartate receptor mRNA and protein expression in the ischemic spinal cord. Tarlov scale results showed that curcumin significantly improved motor function of the rat hind limb after spinal cord ischemia. The results demonstrate that curcumin exerts a neuroprotective fect against ischemic spinal cord injury by decreasing inducible nitric oxide synthase and N-methyl-D-aspartate receptor expression.

Memantine alleviates brain injury and neurobehavioral deficits after experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) causes brain injury via glutamate excitotoxicity, which leads to an excessive Ca(2+) influx and this starts an apoptotic cascade. Memantine has been proven to reduce brain injury in several types of brain insults. This study investigated the neuro-protective potential of memantine after SAH and explored the underlying mechanisms. An endovascular perforation rat model of SAH was used and Sprague-Dawley rats were randomized into sham surgery, SAH + vehicle, and SAH + memantine groups. The effects of memantine on SAH were evaluated by assessing the neuro-behavioral functions, blood-brain barrier (BBB) permeability and neuronal cell preservation. The mechanisms of action of memantine, with its N-methyl-D-aspartate (NMDA) antagonistic characteristics on nitric oxide synthase (NOS) expression and peroxynitrite formation, were also investigated. The apoptotic cascade after SAH was suppressed by memantine. Neuronal NOS (nNOS) expression, peroxynitrite formation, and subsequent oxidative/nitrosative stress were also reduced. Memantine effectively preserved BBB integrity, rescued neuronal injury, and improved neurological outcome in experimental SAH. Memantine has neuro-protective potential in experimental SAH and may help combat SAH-induced brain damage in the future.

Paraplegia prevention by oral pretreatment with memantine in a rabbit model

OBJECTIVE

To evaluate the role of memantine (N-methyl-d-aspartate receptor antagonist) pretreatment for the prevention of spinal cord ischemia after infrarenal aortic clamping in a rabbit model.

METHODS

Thirty New Zealand White rabbits were divided into 5 different groups of 6 rabbits. Groups 60-7 and 60-5 received oral memantine 60 mg once a day for 7 and 5 days, respectively, and groups 30-5 and 30-3 received oral memantine 30 mg once a day for 5 and 3 days, respectively, all before surgery. Group C (control) received normal feeds without memantine. A paraplegic model was created by clamping both the aorta and the inferior vena cava infrarenally and just proximal to their bifurcations for 45 minutes. The modified Tarlov score, motor evoked potential (MEP), serum memantine concentration, and histopathology of the spinal cord were evaluated.

RESULTS

The mean modified Tarlov scores were 4.2±1.3, 4.3±1.0, 4.2±1.3, 4.3±1.2, and 0.8±1.6 in groups 60-7, 60-5, 30-5, 30-3, and C, respectively at 6, 24, 48, and 72 hours (P<.009 for individual groups vs control). Percentage amplitude loss of MEP by the end of surgery was 29.5%±46.3%, 11.9%±28.0%, 30.0%±46.8%, 16.7%±40.8%, and 81.8%±40.3% for the 5 groups, respectively (P=.049). After declamping, MEP reappeared in 83%, 100%, 83%, 83%, and 33% of cases in the 5 groups, respectively (P=.073). The serum memantine level was similar in the 4 memantine groups. Spinal cords were normal in most of the rabbits in groups 60-7, 60-5, 30-5, and 30-3, but severely ischemic in most of the rabbits in group C (P=.041).

CONCLUSIONS

Oral memantine pretreatment is protective against spinal cord ischemia, and can be an additional strategy for the prevention of paraplegia during thoracoabdominal aortic surgeries.

Dose-effects of aorta-infused clenbuterol on spinal cord ischemia-reperfusion injury in rabbits

Background

The β₂ adrenergic receptor (β₂AR) plays an important role in ischemia-reperfusion (I/R) injury in various organs. Recently, a selective β₂AR agonist clenbuterol was suggested to protect against cerebral I/R injury. This study was designed to investigate changes of β₂ARs after spinal cord I/R injury and dose-effects of aorta-infused clenbuterol on spinal cord I/R injury in rabbits.

Methods

Spinal cord ischemia was induced in New Zealand white rabbits by infrarenal abdominal aortic occlusion with a balloon catheter for 30 minutes except the sham group. During occlusion, nothing (I/R group), normal saline (NS group) or clenbuterol at different doses of 0.005, 0.01, 0.05, 0.1, 0.5, or 1 mg/kg (C_0.005, C_0.01, C_0.05, C_0.1, C_0.5, and C₁ groups) was infused into the occluded aortic segments. The hemodynamic data, blood glucose and serum electrolytes were measured during experimental period. Neurological function was assessed according to the modified Tarlov scales until 48 hours after reperfusion. After that, the lumbar spinal cord was harvested for β₂AR immunohistochemistry and histopathologic evaluation in the anterior horns.

Results

The β₂AR expression in the anterior horns of the spinal cord was significantly higher in the I/R group than in the sham group. Tarlov scores and the number of viable α-motor neurons were higher in C_0.01-C_0.5 groups than in the NS group, C_0.005 and C₁ groups and were highest in the C_0.1 group. Hypotension and hyperglycemia were found in the C₁ group.

Conclusion

β₂ARs in the anterior horn were upregulated after spinal cord I/R injury. Aortic-infused clenbuterol (0.01–0.5 mg/kg) can attenuate spinal cord I/R injury dose-dependently during the ischemic period. The Optimal dosage was 0.1 mg/kg. Activation of β₂AR could be a new therapeutic strategy for the treatment of spinal cord I/R injury.

Effects of hyperbaric oxygen therapy after spinal cord injury: systematic review

OBJECTIVE: to conduct a systematic review of experimental and clinical studies evaluating the effect of hyperbaric oxygen therapy on the spinal cord injury. METHODS: ninety-three studies were identified in the database Pubmed. Among these, through a set of inclusion/exclusion criteria, 11 articles published between 1963 and 2009 were selected. In the nine experimental studies, different ways to apply the treatment were observed. The measured outcomes were: functional, histological, biochemical and electrophysiological. RESULTS: in most of the studies, the results show recovery of locomotor function, histology and/or biochemical features. Regarding the two studies in clinical samples, the results are controversial. The samples are heterogeneous and the application of hyperbaric oxygen therapy is not the same for all patients in each study. CONCLUSION: considering the results of this review, further studies are necessary to define the role of hyperbaric oxygen therapy in acute spinal cord injury.

Neuroprotective effects of memantine in a mouse model of retinal degeneration induced by rotenone

This is the first report of the in vivo effectiveness of memantine as a neuroprotective agent against rotenone-induced retinal toxicity. We tested the hypothesis that uncompetitive NMDAR blockade with memantine prevents mitochondrial dysfunction-related neurodegeneration in vivo, using a mouse model of retinal ganglion cell layer (GCL) degeneration induced by rotenone, a mitochondrial complex I inhibitor. Rotenone induced an increase in cell death and oxidative stress in GCL compared to controls, and these changes were prevented by the co-administration of memantine. The neurotoxic effect of rotenone was also reflected as a decrease in total cell density in GCL and GCL+nerve fiber layer thickness. These changes were also prevented by co-administration of memantine in a dose-dependent manner. In addition, memantine induced an increase in long-term retinal energy metabolic capacity. The results suggest that NMDAR activation contributes to cell death induced by mitochondrial dysfunction and that uncompetitive NMDAR blockade may be used as a neuroprotective strategy against mitochondrial dysfunction in neurodegenerative diseases.

Protective effect of sildenafil (Viagra) in transient spinal cord ischemia

Prospective study of the neuroprotective activity of sildenafil in a rat spinal ischemia model. The present study involved 21 male Sprague-Dawley rats. The animals were divided into 3 groups. Physiological serum was administered intraperitoneally to the 8 rats in the control group at the beginning of reperfusion for a period of 20 min after abdominal aortal occlusion. Sildenafil (Viagra) was administered as a single 10-mg/kg/day intraperitoneal dose to the 8 rats in the sildenafil group at the beginning of reperfusion after 20 min of abdominal aortal occlusion. No occlusion was performed and no agent was administered to the 5 rats in the sham group, but the abdominal aorta was reached by means of surgical intervention. Before the animals were sacrificed, several physiological and biochemical parameters were investigated, preoperative and postoperative motor functions were also assessed, and somatosensory evoked potential (SEP) monitoring and histopathological examinations were carried out. No differences were found between the physiological and biochemical parameters in each of the 3 groups. Neurological scoring performed after reperfusion demonstrated a significant improvement in the neurological results relative to those of the control group over 48 h in subjects that received sildenafil. These animals also showed better 24-hour SEP results, measured in terms of extended latency and decreased amplitude, than the control animals. A histopathological study showed reduced ischemic symptoms in rats that received sildenafil compared with those in the control group. However, no anomalies were observed in the sham group with respect to the histopathological and neurological findings. These results indicate that neurological damage due to spinal-cord ischemia-reperfusion injury can be reduced by sildenafil.

Potential role of N-methyl-D-aspartate receptors as executors of neurodegeneration resulting from diverse insults: focus on memantine

Glutamatergic neurotransmission is critical to normal learning and memory and when the activity of glutamate neurons becomes excessive, or the normal function of its primary receptors becomes dysfunctional, this may lead to pathological changes associated with age-related neurodegenerative diseases. Anomalous glutamatergic activity associated with Alzheimer's disease may be due to a postsynaptic receptor and downstream defects that produce inappropriately timed or sustained glutamate activation of N-methyl-D-aspartate receptors, leading to neuronal injury and death and cognitive deficits associated with dementia. The mechanisms leading to the condition of chronically depolarized membranes on vulnerable neurons in the Alzheimer's disease brain are likely due to a complex interaction between oxidative stress, mitochondrial failure, chronic brain inflammation and the presence of amyloid-beta and hyperphosphorylated-tau; each of these factors are highly interrelated with each other and are discussed with an emphasis upon potential therapeutic mechanisms underlying the neuroprotective actions of memantine.

Combined neuroprotective effects of celecoxib and memantine in experimental intracerebral hemorrhage

Memantine, a N-methyl-D-aspartate (NMDA) receptor antagonist, inhibits hematoma expansion and celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, reduces perihematomal inflammation in intracerebral hemorrhage. We examined whether the combination treatment has additive effects in experimental intracerebral hemorrhage (ICH). ICH was induced using stereotaxic infusion of collagenase into brains of adult rats. After the induction of ICH, rats were treated with intraperitoneal injection of memantine (20 mg/kg), celecoxib (20 mg/kg) or both agents. Only vehicles were administrated in rats of the control group. Results showed that the combination treatment of memantine and celecoxib reduced both hematoma volume and brain edema. Combination treatment also induced the better functional recovery with further attenuation of cerebral inflammation and apoptosis compared to the control group. When compared to the single agent groups, the combination treatment showed better effects in neuroprotection and anti-inflammation. These results suggest the feasible combined application of memantine and celecoxib in ICH treatment.

MK-801 improves neurological and histological outcomes after spinal cord ischemia induced by transient aortic cross-clipping in rats

BACKGROUND

Glutamergic excitotoxicity has been shown to play a deleterious role in the pathophysiology of ischemic spinal cord injury (ISCI). The aim of this study was to investigate the neuroprotective effect of a single dose of MK-801, an antiexcitotoxic drug, in a rat model of ISCI.

METHODS

Ischemic spinal cord injury was induced for 17 minutes in Sprague-Dawley rats using direct aortic arch, just proximal to the left common carotid artery, plus left subclavian artery cross-clamping through a left-sided limited thoracotomy. Study groups were as follows: control group (n = 8) receiving only vehicle and experimental group (n = 8) receiving a single dose of MK-801 (1 mg/kg IV) 10 minutes before aortic clamping. Neurological examination was performed at 6 hours, 24 hours, and daily up to 96 hours. Rats were sacrifice at methylprenisolone socium succinate 96 hours, and spinal cords were removed for histopathology.

RESULTS

All the control rats had severe permanent neurological deficits after ISCI, whereas the MK-801-treated rats had statistically (P < .05) better neurological outcome and good recovery. Histopathology revealed severe neuronal necrosis in the lumbar gray matter of control rats, whereas MK-801-treated rats showed mild injury.

CONCLUSION

These results demonstrate that combined temporary clipping of the aortic arch (just proximal to the left common carotid artery) plus left subclavian artery for 17 minutes reproduces reliable paraplegia, and a single dose of MK-801 given before ISCI provides significant neuroprotection.

Is intrathecal magnesium sulfate safe and protective against ischemic spinal cord injury in rabbits?

We performed three sets of experiments to investigate the safety of intrathecal magnesium and to determine its optimal dose for protection, if any, against ischemic spinal cord injury in rabbits. First, we examined neurotoxicity of 0.3, 1, 2, or 3 mg/kg of magnesium sulfate (n = 6 each). Significant sensory dysfunction was observed in the 3-mg/kg group 7 days after administration. Motor dysfunction was found in two rabbits in both the 2- and 3-mg/kg groups. The area of destruction in laminae V-VII was observed in one, two, and one rabbit in the 1-, 2-, and 3-mg/kg groups, respectively. Second, we investigated the temporal profile (6 h, 48 h, and 96 h [n = 3 each]) of histopathologic changes after 3 mg/kg of magnesium sulfate and confirmed similar changes in the rabbits with motor dysfunction at 48 and 96 h. Third, we evaluated the effects of 0.3 mg/kg or 1 mg/kg of magnesium sulfate or saline (n = 6 each) administered before ischemia on hindlimb motor function and histopathology after spinal cord ischemia (15 min). Magnesium did not improve neurologic or histopathologic outcome 96 h after reperfusion. The results indicate that intrathecal magnesium has a risk of neurotoxicity and shows no evidence of protective effects against ischemic spinal cord injury.

Protective effect of D-003 on experimental spinal cord ischemia in rabbits

D-003 is a natural mixture of long chain aliphatic acids isolated and purified from sugar cane wax. It possesses antiplatelet and antithrombotic effects as well as decreases plasma and serum levels of thromboxane B(2) (TxB(2)), meanwhile significantly and markedly raises prostacyclin (PgI(2)) levels in rats. This study was undertaken to investigate the effects of D-003 on spinal cord injury in rabbits. New Zealand rabbits were treated during 10 days with D-003 (25 and 200 mg kg(-1)) and ASA (2 mg kg(-1)) before spinal cord ischemia. Animals were subjected to 20 min of aortic occlusion and 24h of reperfusion. Clinical symptoms and histopathological changes of spinal cord were observed. The PgI(2) levels in thoracic aorta were quantified by bioassay. D-003 (25 and 200 mg kg(-1)) significantly increased the mean scores reached 4h after reperfusion, although no dose relation was observed. Twenty-four hours after reperfusion, no deaths occurred in both sham and D-003 treated groups, meanwhile in positive controls and ASA the mortality rate was 38.5% and 7.69% respectively. In addition, 100% of sham, 69% and 77% of rabbits treated with D-003 at 25 and 200 mg kg(-1), respectively, did not show histopathological changes. By the contrary, 100% of positive control animals showed severe damage and ASA-treated rabbits showed only a partial protection. Animals treated with both doses of D-003 showed PgI(2) levels significantly larger than those of positive and negative controls, an effect dose-related, while ASA 2 mg kg(-1) did not change PgI(2) values. The increase of PgI(2) levels achieved in the D-003 treated animals could be an important mechanism in the protection against the spinal cord ischemia.

Ischémie médullaire

Traditional data and recent advances in the field of spinal cord ischemia are reviewed, with special attention to clinical and radiological features, as well as underlying etiology, outcome, and pathophysiology. Acute spinal cord ischemia includes arterial and venous infarction and global ischemia resulting from cardiac arrest or severe hypotension. MRI has become the technique of choice for the imaging diagnosis of spinal cord infarction. Correlation of clinical and MRI data has allowed diagnosis of clinical syndromes due to small infarcts in the central or peripheral arterial territory of the spinal cord. Diffusion-weighted MR imaging may increase the sensitivity and specificity for diagnosis of acute spinal cord infarction. Diagnosis of venous spinal cord infarction remains difficult. As for global ischemia, neuropathological studies demonstrated a great sensitivity of spinal cord to ischemia, with selective vulnerability of lumbosacral neurons. Chronic spinal cord ischemia results in a syndrome of progressive myelopathy. The cause is usually an arteriovenous malformation. Most often, diagnosis may be suspected on MRI, leading to diagnostic, and eventually therapeutic, spinal angiography.

The role of pharmacology in spinal cord protection during thoracic aortic reconstruction

Surgery of the thoracic aorta continues to have a significant risk of neurologic complication. Several strategies to minimize this risk are emerging. Pharmacologic protection from these complications continues to be researched, but at this point few medications are being used clinically. This article reviews the pathophysiology of ischemic spinal cord injury and summarizes the investigational pharmacology that may prevent these serious complications.

Neuroprotection by memantine against neurodegeneration induced by beta-amyloid(1-40)

Progressive neuronal loss and cognitive decline in Alzheimer's disease (AD) might be aggravated by beta-amyloid-enhanced excitotoxicity. Memantine is an uncompetitive NMDA receptor antagonist under clinical development for the treatment of AD. Memantine has neuroprotective actions in several in vitro and in vivo models. In the present study, we determined whether memantine protected against beta-amyloid induced neurotoxicity and learning impairment in rats. Twenty Sprague-Dawley rats received vehicle or vehicle plus memantine (steady-state plasma concentrations of 2.34+/-0.23 microM, n=10) s.c. by osmotic pump for 9 days. After 2 days of treatment, 2 microl of water containing beta-amyloid 1-40 [Abeta(1-40)] were injected into the hippocampal fissure. On the ninth day of treatment, animals were sacrificed, and morphological and immunohistochemical techniques were used to determine the extent of neuronal degeneration and astrocytic and microglial activation in the hippocampus. Psychomotor activity and spatial discrimination were tested on the eighth day of treatment. Abeta(1-40), but not water, injections into hippocampus led to neuronal loss in the CA1 subfield, evidence of widespread apoptosis, and astrocytic and microglial activation and hypertrophy. Memantine treated animals had significant reductions in the amount of neuronal degeneration, pyknotic nuclei, and GFAP immunostaining as compared with vehicle treated animals. These data suggest that memantine, at therapeutically relevant concentrations, can protect against neuronal degeneration induced by beta-amyloid.

Reduction of spinal cord injury with pentobarbital and hypothermia in a rabbit model

OBJECTIVES

to evaluate the effects of hypothermia and pentobarbital on spinal cord ischaemia induced in a rabbit model.

MATERIALS AND METHODS

thirty-two rabbits, allocated into four equal groups, had the infrarenal aorta clamped distal to the left renal artery and above the iliac bifurcation for 40 min. Groups 3 and 4 had infusion of 15 mg/kg of pentobarbital intravenously for 5 min, 15 min before the cross-clamping. Groups 2 and 4 had infusion of 20 ml of Ringer's lactate (LR) solution at 3 degrees C for 3 min during aortic cross clamp into the isolated aortic segment. Group 1 was untreated and served as control. Postoperative functions of spinal cord were assessed.

RESULTS

paraplegia occurred in all rabbits in Group 1, in one in each of Groups 2 and 3, whereas no paraplegia was observed in Group 4. In addition 2 and 3 animals of Groups 2 and 3, respectively revealed varying degree of neurological disturbances, whereas all animals of Group 4 had normal function. This difference between Groups 2, 3, and 4 vs Group 1 was significant (p<0.002). So was the difference between Groups 2 and 4 (p=0.03), whereas the difference between Groups 3 and 4 was not significant.

CONCLUSIONS

hypothermia and pentobarbital was more effective than hypothermia alone for prevention of spinal cord ischaemia in a rabbit model.

Pentoxifylline reduces biochemical markers of ischemia-reperfusion induced spinal cord injury in rabbits

STUDY DESIGN

Occlusion of the infrarenal abdominal aorta with administration of pentoxifylline was applied to adult rabbits, followed by removal of aortic clamp and reperfusion. Tissue levels of cytokines, lipid peroxides, and antioxidant enzymes were assayed and compared within groups.

OBJECTIVES

To examine the effect of pentoxifylline (PTX) on cytokine levels, lipid peroxidation, and antioxidant enzymes in a rabbit model of spinal cord ischemia-reperfusion injury induced by aortic occlusion.

SETTING

Isparta, Turkey.

METHODS

Rabbits were randomly allocated into four groups of sham laparotomy (SHAM), sham laparotomy with PTX administration (SHAM+PTX), aortic occlusion and reperfusion (AOR), aortic occlusion and reperfusion with PTX administration (AOR+PTX). An intravenous bolus of 50 mg/kg PTX was given just before aortic cross clamping. An atraumatic microvascular clamp was then placed on the abdominal aorta immediately distal to the left renal artery for 30 min. PTX was infused at a rate of 0.5 mg/kg/min during the aortic occlusion. Animals were subjected to 120 min of reperfusion after removal of the aortic clamp. All animals were sacrificed at the end of reperfusion. The lumbosacral segments of spinal cords were quickly harvested and stored at -78 degrees C for biochemical assays of IL-6, TNF-alpha, MDA, SOD, and CAT levels. Differences among groups were analyzed by one-way analysis of variance followed by a post hoc Tukey's honestly significant difference test.

RESULTS

No differences in mean levels of IL-6, TNF-alpha, MDA, SOD, and CAT were noted between SHAM and SHAM+PTX groups (P>0.05). There was a significant increase in all biochemical parameters in the AOR group (P<0.05). Administration of PTX significantly attenuated the levels of all biochemical parameters in the AOR+PTX group (P<0.05).

CONCLUSION

PTX pretreatment attenuated ischemia-reperfusion induced spinal cord injury in a rabbit model, in terms of biochemical parameters of ischemia and reperfusion.

Reduction of ischemic spinal cord injury by dextrorphan: comparison of several methods of administration

OBJECTIVES

We investigated the effect of dextrorphan, an N -methyl-D -aspartate receptor antagonist, on the reduction of ischemic spinal cord injury and the safe clamping time after various methods of administration.

METHODS

Spinal cord ischemia was induced in New Zealand White rabbits by infrarenal aortic clamping and animals were divided into 5 groups. Group A (n = 15) received simple clamping. Groups B (n = 20) and C (n = 35) received dextrorphan pretreatment (10 mg/kg), followed by continuous intravenous or intra-aortic infusion (1 mg/min), respectively. Group D (n = 25) received the same dextrorphan pretreatment and bolus intra-aortic injection at clamping (1 mg per minute of clamping time). Group E (n = 15) received bolus intrathecal injection of dextrorphan (0.2 mg/kg). Each dextrorphan-treated group had a small group of control animals (n = 5). The neurologic status was assessed by the Johnson score (5 = normal, 0 = paraplegic) 48 hours after unclamping, and animals were put to death for histopathologic examination.

RESULTS

All dextrorphan-treated groups showed better neurologic function than the respective control animals (P <.001 vs groups B, C, and D; P =.014 vs group E). The order of efficacy of dextrorphan (as revealed by the average of neurologic status) was as follows: group C > group D (P =.017, after 50 minutes of clamping), group D > group B (P =.014, after 45 minutes of clamping), and group B > group E (P <.001, after 40 minutes of clamping). Histopathologic findings did not necessarily correspond with hind-limb neurologic function.

CONCLUSIONS

Dextrorphan reduced the physical findings associated with ischemic spinal cord injury, and continuous intra-aortic infusion prolonged the safe clamping time significantly more than delivery by other routes.

Neuroprotection by memantine, a non-competitive NMDA receptor antagonist after traumatic brain injury in rats

This study investigated whether memantine, a non-competitive NMDA receptor antagonist is neuroprotective after traumatic brain injury (TBI) induced in adult rats with a controlled cortical impact device. TBI led to significant neuronal death in the hippocampal CA2 and CA3 regions (by 50 and 59%, respectively), by 7 days after the injury. Treatment of rats with memantine (10 and 20 mg/Kg, i.p.) immediately after the injury significantly prevented the neuronal loss in both CA2 and CA3 regions. This is the first study showing the neuroprotective potential of memantine to prevent the TBI-induced neuronal damage.

The N-methyl-D-aspartate antagonist memantine has no neuroprotective effect during hypothermic circulatory arrest: a study in the chronic porcine model

BACKGROUND

Glutamate excitotoxicity has an important role in the development of brain injury after prolonged hypothermic circulatory arrest. The goal of the present study was to determine the potential efficacy of memantine, an N -methyl-D -aspartate receptor antagonist, to mitigate cerebral injury after hypothermic circulatory arrest.

METHODS

Twenty pigs (23-33 kg) were randomly assigned to receive memantine (5 mg/kg) or placebo in a blinded fashion before a 75-minute period of hypothermic circulatory arrest at 20 degrees C. Hemodynamic, electroencephalographic, and metabolic monitoring were carried out. The intracerebral concentrations of glucose, lactate, glutamate, and glycerol were measured by means of enzymatic methods on a microdialysis analyzer. Daily behavioral assessment was performed until the animals died or were put to death on day 7. Histologic analysis of the brain was carried out in all animals.

RESULTS

In the memantine group, 5 of 10 animals survived 7 days compared with 9 of 10 in the placebo group. The median behavioral score at day 7 was 3.5 in the memantine group and 7.5 in the placebo group (P >.2). Among the surviving animals, medians were 9.0 and 8.0 on day 7 (P >.2), respectively. The medians of recovered electroencephalographic bursts were equal in both groups. The median of total histopathologic score was 16 in the memantine group and 14 in the placebo group (P >.2). There was a negative correlation between glutamate levels and electroencephalographic burst recovery (tau = -0.377, P =.043). A positive correlation was found between the highest individual glutamate value and histopathologic score (tau = 0.336, P =.045).

CONCLUSIONS

The present study demonstrates that memantine has no neuroprotective effect after hypothermic circulatory arrest in the pig. In addition, we have shown the accuracy of cerebral glutamate measurements to predict histopathologic injury after hypothermic ischemia.

The effects of FK506 on neurologic and histopathologic outcome after transient spinal cord ischemia induced by aortic cross-clamping in rats

Spinal cord injury is a devastating complication of thoracoabdominal aortic surgery. We investigated the effect of the immunosuppressant FK506, a macrolide antibiotic demonstrated to have neuroprotective effects in cerebral ischemia models, in a rat model of transient spinal cord ischemia. Spinal cord ischemia was induced in anesthetized rats by using direct aortic arch plus left subclavian artery cross-clamping through a limited thoracotomy. Experimental groups were as follows: sham-operation; control, receiving only vehicle; FK506 A, receiving FK506 (1 mg/kg IV) before clamping; and FK506 B, receiving FK506 (1 mg/kg IV) at the onset of reperfusion. Neurologic status was assessed at 24 h and then daily up to 96 h with a 0 to 6 scale (0, normal function; 6, severe paraplegia). Rats were randomly killed at 24, 48, or 96 h, and spinal cords were harvested for histopathology. Physiologic variables did not differ significantly among experimental groups. All control rats suffered severe and definitive paraplegia. FK506-treated rats had significantly better neurologic outcome compared with control. Histopathologic analysis disclosed severe injury in the lumbar gray matter of all control rats, whereas most FK506-treated rats had less injury. These data suggest that FK506 can improve neurologic recovery and attenuate spinal cord injury induced by transient thoracic aortic cross-clamping.

IMPLICATIONS

A single dose-injection of the immunosuppressant FK506 significantly improved neurologic outcome and attenuated spinal cord injury induced by transient thoracic aortic cross-clamping in the rat.

Hyperbaric oxygen therapy given 30 minutes after spinal cord ischemia attenuates selective motor neuron death in rabbits

OBJECTIVE

Spinal cord ischemia sometimes causes paraplegia because the spinal motor neuron cells are vulnerable to ischemia. Although various protective remedies for spinal cord injury have been reported, there have been few established clinical methods. Although hyperbaric oxygen (HBO) has been used clinically as a treatment for ischemia, the reason for its effectiveness is still uncertain because sufficient experimental data are lacking.

DESIGN

Prospective, randomized, controlled study.

SETTING

Experimental animal research laboratory in a university research center.

SUBJECTS

Twenty-three Japanese white rabbits, weighing 2-3 kg.

INTERVENTIONS

A modified rabbit spinal cord ischemia model of infrarenal aortic occlusion for 15 mins was employed. Rabbits were randomly assigned to four groups; the rabbits in group A did not undergo ischemic insults (n = 5). The rabbits in groups B and C underwent ischemic insult for 15 mins, followed by 1 hr of HBO treatment at 3 atm absolute with 100% oxygen at 30 mins (n = 6) or 6 hrs (n = 7) after reperfusion, respectively. The rabbits in group D underwent ischemic insult for 15 mins without HBO treatment (n = 5).

MEASUREMENTS AND MAIN RESULTS

We observed neurologic functions for 14 days. The sections of the spinal cords were stained with hematoxylin and eosin, and the number of spinal motor neurons in ventral region was counted by light microscopy. All rabbits in groups A and B could stand, whereas all rabbits in groups C and D showed irreversible paraplegia on days 2 and 14 after reperfusion. Spinal motor neurons in ventral gray matter in groups C and D decreased significantly compared with those in groups A and B.

CONCLUSIONS

HBO therapy shortly after ischemic insult had protective effects against ischemic spinal cord damage. However, delayed treatment with HBO did not change the prognosis.

Pharmacologic neuroprotection in experimental spinal cord ischemia: a systematic review

Various surgical procedures may cause temporary interruption of spinal cord blood supply and may result in irreversible ischemic injury and neurological deficits. The cascade of events that leads to neuronal death following ischemia may be amenable to pharmacological manipulations that aim to increase the tolerable duration of ischemia. Many agents have been evaluated in experimental spinal cord ischemia (SCI). In order to investigate whether an agent is available that justifies clinical evaluation, the literature on pharmacological neuroprotection in experimental SCI was systematically reviewed to assess the neuroprotective efficacy of the various agents. In addition, the strength of the evidence for neuroprotection was investigated by analyzing the methodology. The authors used a systematic review to conduct this evaluation. The included studies were analyzed for neuroprotection and methodology. In order to be able to compare the various agents for neuroprotective efficacy, relative risks and confidence intervals were calculated from the data in the results sections. A total of 103 studies were included. Seventy-nine different agents were tested. Only 14 of the agents tested did not afford protection at all. A large variation was observed in the experimental models to produce SCI. This variation limited comparison of the individual agents. In 48 studies involving 31 single agents, the relative risks and confidence intervals could be calculated. An analysis of the methodology revealed poor temperature management and lack of statistical power in the majority of the 103 studies. The results suggest that numerous agents may protect the spinal cord from transient ischemia. However, poor temperature management and lack of statistical power severely weakened the evidence. Consequently, clinical evaluation of pharmacological neuroprotection in surgical procedures that carry a risk of ischemic spinal cord damage is not justified on the basis of this study.

Ischemic spinal cord injury induced by aortic cross-clamping: prevention by riluzole

OBJECTIVE

Recent studies confirmed the deleterious role of glutamate in the pathophysiology of spinal cord ischemia induced by aortic cross-clamping. We investigated the effect of riluzole, an anti-glutamate drug, in a rat model of spinal cord ischemia.

MATERIALS AND METHODS

Spinal cord ischemia was induced in normothermia for 14 min in Sprague-Dawley rats using direct aortic arch plus left subclavian artery cross-clamping through a limited thoracotomy. Experimental groups were as follows: sham-operation (n=15), control (n=15) receiving only vehicle, riluzole (n=15) receiving riluzole (4 mg/kg) before clamping and at the onset of reperfusion. Separate animals were used for monitoring physiologic parameters in the sham-operation (n=3), control (n=5), and riluzole (n=5) groups. Neurologic status was assessed at 6, 24 h, and then daily up to 96 h. Rats were randomly killed at 24, 48, or 96 h (n=5 for each time). Spinal cords were harvested for histopathology, immunohistochemistry for microtubule-associated protein 2 (MAP-2), TUNEL staining, and analysis of DNA fragmentation by agarose gel electrophoresis.

RESULTS

All sham-operated rats had a normal neurologic outcome, whereas all control rats suffered severe and definitive paraplegia. Riluzole-treated rats had significantly better neurologic function compared to the control. Histopathology disclosed severe neuronal necrosis in the lumbar gray matter of control rats, whereas riluzole-treated rats suffered usually mild to moderate injury. Riluzole particularly prevented motor neurons injury. MAP-2 immunoreactivity was completely lost in control rats, whereas it was preserved either completely or partly in riluzole-treated rats. TUNEL staining revealed numerous apoptotic neurons scattered within the whole gray matter of control rats. Riluzole prevented or dramatically attenuated apoptotic neuronal death in treated rats. DNA extracted from lumbar spinal cords of sham-operated and riluzole-treated rats exhibited no laddering, whereas spinal cords from control rats showed DNA laddering with fragmentation into approximately 180 multiples of base pairs.

CONCLUSIONS

Riluzole may protect the spinal cord in a setting of severe ischemia by preventing neuronal necrosis and apoptosis. This drug may therefore be considered for clinical use during 'high risk' surgical procedures on the thoracoabdominal aorta.

Hypothermic retrograde venous perfusion with adenosine cools the spinal cord and reduces the risk of paraplegia after thoracic aortic clamping

OBJECTIVE

We evaluated the utility of retrograde venous perfusion to cool the spinal cord and protect neurologic function during aortic clamping. We hypothesized that hypothermic adenosine would preserve the spinal cord during ischemia.

METHODS

Six swine (group I) underwent thoracic aortic occlusion for 30 minutes at normothermia. Group II animals underwent spinal cooling by retrograde perfusion of the paravertebral veins with hypothermic (4 degrees C) saline solution during aortic occlusion. The spinal cords of group III animals were cooled with a hypothermic adenosine solution in a similar fashion. Intrathecal temperature was monitored and somatosensory evoked potentials assessed the functional status of spinal pathways.

RESULTS

Spinal cooling without systemic hypothermia significantly improved neurologic Tarlov scores in group III (4.8 +/- 0.2) and group II (3.8 +/- 0.4) when compared with group I scores (1.3 +/- 0.6) (P <.001). Furthermore, 5 of the 6 animals in group III displayed completely normal neurologic function, whereas only one animal in group II and no animals in group I did (P =.005). Somatosensory evoked potentials were lost 10.6 +/- 1.4 minutes after ischemia in group I. In contrast, spinal cooling caused rapid cessation of neural transmission with loss of somatosensory evoked potentials at 6.9 +/- 1.2 minutes in group II and 7.0 +/- 0.8 minutes in group III (P =.06). Somatosensory evoked potential amplitudes returned to 85% of baseline in group III and 90% of baseline in group II compared with only 10% of baseline in group I (P =.01).

CONCLUSIONS

We conclude that retrograde cooling of the spinal cord is possible and protects against ischemic injury and that adenosine enhances this effect. The efficacy of this method may be at least partly attributed to a more rapid reduction in metabolic and electrical activity of the spinal cord during ischemia.