Increased intracerebral excitatory amino acids and nitric oxide after hypothermic circulatory arrest

Lidocaine for postoperative pain after cardiac surgery: a systematic review

OBJECTIVE

Lidocaine is one of the most widely used local anesthetics with well-known pharmacological properties. The purpose of this systematic review is to investigate the effects of lidocaine on postoperative pain scores and recovery after cardiac surgery.

METHODS

A comprehensive database search was conducted by a reference librarian for randomized clinical trials (RCT) from January 1, 1980 to September 1, 2019. Eligible study designs included randomized controlled trials of lidocaine for postoperative pain management in adults undergoing cardiac surgery. After removal of duplicates, 947 records were screened for eligibility and 3 RCTs met inclusion criteria.

RESULTS

Sources of bias were identified in 2 of 3 RCTs. Lidocaine was administered intravenously, topically, and intrapleurally. Key findings included [1] 2% lidocaine placed topically on chest tube prior to intraoperative insertion was associated with significantly lower pain scores and lower cumulative doses of fentanyl; and [2] 2% lidocaine administered intrapleurally was associated with significantly lower pain scores and significant improvements in pulmonary mechanics. Lidocaine infusions were not associated with significant changes in pain scores or measures of recovery. No significant associations were observed between lidocaine and overall mortality, hospital length of stay or ICU length of stay. No data were reported for postoperative nausea and vomiting or arrhythmias.

CONCLUSIONS

Due to the favorable risk profile of topical lidocaine and the need for further advancements in the postoperative care of adults after cardiac surgery, topically administered lidocaine could be considered for incorporation into established postoperative recovery protocols.

Selective cerebral perfusion prevents abnormalities in glutamate cycling and neuronal apoptosis in a model of infant deep hypothermic circulatory arrest and reperfusion

Deep hypothermic circulatory arrest is often required for the repair of complex congenital cardiac defects in infants. However, deep hypothermic circulatory arrest induces neuroapoptosis associated with later development of neurocognitive abnormalities. Selective cerebral perfusion theoretically provides superior neural protection possibly through modifications in cerebral substrate oxidation and closely integrated glutamate cycling. We tested the hypothesis that selective cerebral perfusion modulates glucose utilization, and ameliorates abnormalities in glutamate flux, which occur in association with neuroapoptosis during deep hypothermic circulatory arrest. Eighteen infant male Yorkshire piglets were assigned randomly to two groups of seven (deep hypothermic circulatory arrest or deep hypothermic circulatory arrest with selective cerebral perfusion for 60 minutes at 18℃) and four control pigs without cardiopulmonary bypass support. Carbon-13-labeled glucose as a metabolic tracer was infused, and gas chromatography-mass spectrometry and nuclear magnetic resonance were used for metabolic analysis in the frontal cortex. Following 2.5 h of cerebral reperfusion, we observed similar cerebral adenosine triphosphate levels, absolute levels of lactate and citric acid cycle intermediates, and carbon-13 enrichment among three groups. However, deep hypothermic circulatory arrest induced significant abnormalities in glutamate cycling resulting in reduced glutamate/glutamine and elevated γ-aminobutyric acid/glutamate along with neuroapoptosis, which were all prevented by selective cerebral perfusion. The data suggest that selective cerebral perfusion prevents these modifications in glutamate/glutamine/γ-aminobutyric acid cycling and protects the cerebral cortex from apoptosis.

Molecular mechanisms and cell signaling of 20-hydroxyeicosatetraenoic acid in vascular pathophysiology

Cytochrome P450s enzymes catalyze the metabolism of arachidonic acid to epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid and hydroxyeicosatetraeonic acid (HETEs). 20-HETE is a vasoconstrictor that depolarizes vascular smooth muscle cells by blocking K+ channels. EETs serve as endothelial derived hyperpolarizing factors. Inhibition of the formation of 20-HETE impairs the myogenic response and autoregulation of renal and cerebral blood flow. Changes in the formation of EETs and 20-HETE have been reported in hypertension and drugs that target these pathways alter blood pressure in animal models. Sequence variants in CYP4A11 and CYP4F2 that produce 20-HETE, UDP-glucuronosyl transferase involved in the biotransformation of 20-HETE and soluble epoxide hydrolase that inactivates EETs are associated with hypertension in human studies. 20-HETE contributes to the regulation of vascular hypertrophy, restenosis, angiogenesis and inflammation. It also promotes endothelial dysfunction and contributes to cerebral vasospasm and ischemia-reperfusion injury in the brain, kidney and heart. This review will focus on the role of 20-HETE in vascular dysfunction, inflammation, ischemic and hemorrhagic stroke and cardiac and renal ischemia reperfusion injury.

Protective Effects of Danhong Injection against Cerebral Damage during On-Pump Coronary Artery Bypass Graft Surgery

To explore the protective effects of Danhong injection against cerebral damage during on-pump coronary artery bypass graft surgery and its mechanism. Methods. Fifty patients scheduled for on-pump CABG surgery were randomly divided into Danhong injection group (group D) and control group (group C). Group D was given Danhong injection while group C was given the same volume of normal saline when the artery was cut open. Jugular bulb blood right before the operation began (T1), when body temperature rewarming to 36°C (T2), 30 min after the termination of cardiopulmonary bypass (T3), and 6 hrs after the termination of CPB (T4) was collected. The superoxide dismutase activity by using xanthine oxidase method and concentration determination of malondialdehyde were examined. Results. In group C, SOD activity was less at T2–T4 than at T1. It was also less active comparatively in group D at T2–T4. The MDA concentration increased in both groups but was more obvious in group C. Levels of TNF-α, IL-6, IL-8, and IL-10 increased in both groups C and D at T3 and T4, compared to T1. Conclusions. Danhong injection shows significant protective effects against cerebral damage during on-pump coronary artery bypass graft surgery.

Relative Higher Hematocrit Attenuates the Cerebral Excitatory Amino Acid Elevation Induced by Deep Hypothermic Circulatory Arrest in Rats

Hemodilution is a commonly used technique in cardiopulmonary bypass (CPB) and deep hypothermic circulation arrest (DHCA). Our previous study showed that lower hematocrit aggravated the brain injury after DCHA. Because the excitatory amino acids are critical pathways of ischemic neuronal damage, the purpose of the present study was to investigate the effects of different degrees of hemodilution on the excitatory amino acid content in different brain areas after DHCA Adult Sprague-Dawley rats were randomly divided into four groups: group I hematocrit (Hct) 10% (H1), group II Hct 20% (H2), group III Hct 30% (H3), and control group (C). All animals except those in the control group underwent DHCA at 18°C for 90 minutes. Different degrees of hemodilution were accomplished by changing the composition and volume of the priming solution used in CPB. High-performance liquid chromatography was used to determine the concentration of glutamate (Glu), aspartate (Asp), glycine (Gly), gamma-aminobutyric acid (GABA), and taurine (Tau) in the cerebral cortex, hippocampus, and thalamus. We found that the concentration of these five amino acids in the hippocampus and cortex were all increased after DHCA. Glu, Asp, and Gly in the hippocampus and cortex were significantly lower in the Hct 30% group than in the other two groups (p<0.05). There was no significant difference in the GABA and Tau concentrations among the three groups. In summary, excitatory amino acids increased significantly after DHCA, and relative higher hematocrit attenuates this response.

Brief review on systematic hypothermia for the protection of central nervous system during aortic arch surgery: a double-sword tool?

Antegrade selective cerebral perfusion in conjunction with hypothermia attenuate postoperative neurological injury, which in turn still remains the main cause of mortality and morbidity following aortic arch surgery. Hypothermic circulatory arrest however could be a useful tool during arch surgery, surgery for chronic thromboembolic disease, air on the arterial line during CPB, during cavotomy for extraction of renal cell carcinoma with level IV extension, or when dealing with difficult trauma to the SVC or IVC. Cerebral protective effects with hypothermic procedures including inhibition of neuron excitation, and discharge of excitable amino acids, and thereby, prevention of an increase in intercellular calcium ions, hyperoxidation of lipids in cell membranes, and free radical production.The authors are briefly discussing the fundamental principles of using hypothermia as an adjunct tool of the cardiothoracic surgeon's practice. The relationship between temperature, flow, metabolic requirements and adverse effects is addressed.

Preventive effect of gastrodin on cognitive decline after cardiac surgery with cardiopulmonary bypass: a double-blind, randomized controlled study

Cognitive decline is a common complication after cardiac surgery with cardiopulmonary bypass (CPB), but as such no pharmacological therapy has been shown to be efficacious in preventing the decline. However, gastrodin has been shown to have multi-pharmacological effects on neurological functions. We undertook this study to test the hypothesis that gastrodin would potentially prevent CPB-associated neurocognitive decline. We randomly assigned 200 patients undergoing mitral valve replacement surgery to receive either gastrodin (40 mg/kg) or saline after the induction of anesthesia and subsequently evaluated cognitive function before surgery, at discharge, and at 3rd month after surgery by using a battery of five neurocognitive tests, or adverse effects of gastrodin postoperatively. Neurocognitive decline in postoperative function was defined as a drop of 1 SD or more in the scores on tests of any one of the four domains of cognitive function. Cognitive decline occurred in 9% of the patients in the gastrodin group in contrast to 42% in the control group (P<0.01) at discharge. Cognitive outcome could be determined at 3rd month in 87 patients in the gastrodin group and 89 in the control group. Cognitive decline was detected in 6% in the gastrodin group and 31% in the control group (P<0.01). The incidences of possible adverse effects were similar between two groups. These results indicate that gastrodin is an effective and a safe drug for the prevention of neurocognitive decline in patients undergoing mitral valve replacement surgery with CPB.

Glutamate excitotoxicity mediates neuronal apoptosis after hypothermic circulatory arrest

BACKGROUND

Prolonged hypothermic circulatory arrest results in neuronal cell death and neurologic injury. We have previously shown that hypothermic circulatory arrest causes both neuronal apoptosis and necrosis in a canine model. Inhibition of neuronal nitric oxide synthase reduced neuronal apoptosis, while glutamate receptor antagonism reduced necrosis in our model. This study was undertaken to determine whether glutamate receptor antagonism reduces nitric oxide formation and neuronal apoptosis after hypothermic circulatory arrest.

METHODS

Sixteen hound dogs underwent 2 hours of circulatory arrest at 18 degrees C and were sacrificed after 8 hours. Group 1 (n = 8) was treated with MK-801, 0.75 mg/kg intravenously prior to arrest followed by 75 microg/kg/hour infusion. Group 2 dogs (n = 8) received vehicle only. Intracerebral levels of excitatory amino acids and citrulline, an equal coproduct of nitric oxide, were measured. Apoptosis, identified by hematoxylin and eosin staining and confirmed by electron microscopy, was blindly scored from 0 (normal) to 100 (severe injury), while nick-end labeling demonstrated DNA fragmentation.

RESULTS

Dogs in groups 1 and 2 had similar intracerebral levels of glutamate. However, MK-801 significantly reduced intracerebral glycine and citrulline levels compared with hypothermic circulatory arrest controls. The MK-801 significantly inhibited apoptosis (7.92 +/- 7.85 vs 62.08 +/- 6.28, group 1 vs group 2, p < 0.001).

CONCLUSIONS

Our results showed that glutamate receptor antagonism significantly reduced nitric oxide formation and neuronal apoptosis. We provide evidence that glutamate excitotoxicity mediates neuronal apoptosis in addition to necrosis after hypothermic circulatory arrest. Clinical glutamate receptor antagonists may have therapeutic benefits in ameliorating both types of neurologic injury after hypothermic circulatory arrest.

Overactivation of poly(adenosine phosphate-ribose) polymerase 1 and molecular events in neuronal injury after deep hypothermic circulatory arrest: study in a rabbit model

OBJECTIVE

Although deep hypothermic circulatory arrest has been known to induce neuronal injury, the molecular mechanism of this damage has not been identified. We studied the key molecular mediators through cellular energy failure, excitotoxicity, and overactivation of poly(adenosine diphosphate-ribose) polymerase 1 in brain tissues of a rabbit model of deep hypothermic circulatory arrest similar to clinical settings.

METHODS

We established 2 models of cardiopulmonary bypass (n = 15) and deep hypothermic circulatory arrest (n = 15) associated with cerebral microdialysis in rabbits. Deep hypothermic circulatory arrest lasted for 60 minutes. The measurements of glucose, lactate, pyruvate, and glutamate collected by means of microdialysis were quantified by using a microdialysis analyzer and high-performance liquid chromatography. The overactivation of poly(adenosine diphosphate-ribose) polymerase 1 was assessed by detecting immunostaining of poly(adenosine diphosphate-ribose). Histologic studies were used to identify neuronal morphologic changes and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling staining and poly(adenosine diphosphate-ribose) polymerase 1 Western blotting were used to identify apoptotic cells and early apoptotic signals.

RESULTS

Deep hypothermic circulatory arrest significantly increased the lactate/pyruvate and lactate/glucose ratios and the glutamate value, whereas cardiopulmonary bypass did not (P < .05). Deep hypothermic circulatory arrest significantly increased the numbers of poly(adenosine diphosphate-ribose)-positive and apoptotic neurons compared with cardiopulmonary bypass (P < .05). The cleavage of poly(adenosine diphosphate-ribose) polymerase 1 was only found in the deep hypothermic circulatory arrest group. More injured neurons were found in the deep hypothermic circulatory arrest group (histologic scores, P < .05).

CONCLUSIONS

This study demonstrated that deep hypothermic circulatory arrest results in an overactivation of poly(adenosine diphosphate-ribose) polymerase 1, and that there were molecular events consisting of cellular energy failure, excitotoxicity, overactivation of poly(adenosine diphosphate-ribose) polymerase 1, and necrosis and/or apoptosis in neuronal injury.

Motor impairment and neuronal damage following hypothermia in tropical amphibians

Although the induction of mild to moderate cerebral hypothermia in mammals can have neuroprotective activity, some deleterious effects have been described when inducing deep hypothermia during cooling of the brain. In the spinal cord, rapid deep cooling can induce seizure activity accompanied by release of the excitatory neurotransmitters, glutamate and aspartate. We used cold-sensitive tropical amphibians as a model to determine (a) the critical temperature inside the central nervous system necessary to induce seizures during rapid cooling; (b) the survival rate during slow deep cooling of the whole animal; and (c) whether deep cooling can cause neuronal cell damage. Seizures induced by deep rapid (<or=3 min) cooling of the spinal cord began when a critical temperature of 10.4 degrees C was reached. During slow (>or=30 min) deep cooling of the whole animal (12 h at 2-3 degrees C), around 70% of animals died. Spinal reflexes were enhanced when temperatures within the spinal cord reached between 9.0 degrees C and 11.6 degrees C. A fivefold increase in blood glucose level was observed during slow deep cooling. Recovery after slow deep cooling was accompanied by motor impairment and the main histological findings were condensation of the cytoplasm and nuclear pyknosis. Severe neuronal cell damage was characterized by swelling, vacuolated cytoplasm with distended neuronal bodies. These results indicate that deep cooling can easily induce neuronal cell damage in the central nervous system of cold-sensitive animals. They also warn us to the potential sequels associated with the use of deep brain cooling as a neuroprotective strategy.

Noninvasive assessment of brain injury in a canine model of hypothermic circulatory arrest using magnetic resonance spectroscopy

BACKGROUND

Studies have confirmed the neuroprotective effect of diazoxide in canines undergoing hypothermic circulatory arrest (HCA). A decreased N-acetyl-asparate:choline (NAA:Cho) ratio is believed to reflect the severity of neurologic injury. We demonstrated that noninvasive measurement of NAA:Cho with magnetic resonance spectroscopy facilitates assessment of neuronal injury after HCA and allows for evaluation of neuroprotective strategies.

METHODS

Canines underwent 2 hours of HCA at 18 degrees C and were observed for 24 hours. Animals were divided into three groups (n = 15 in each group): normal (unoperated), HCA (HCA only), and HCA+diazoxide (pharmacologic treatment before HCA). The NAA:Cho ratios were obtained 24 hours after HCA by spectroscopy. Brains were immediately harvested for fresh tissue NAA quantification by mass spectrometry. Separate cohorts of HCA (n = 16) and HCA+diazoxide (n = 23) animals were kept alive for 72 hours for daily neurologic assessment.

RESULTS

Cortical NAA:Cho ratios were significantly decreased in HCA versus normal animals (1.01 +/- 0.29 versus 1.31 +/- 0.23; p = 0.004), consistent with severe neurologic injury. Diazoxide pretreatment limited neurologic injury versus HCA alone, reflected in a preserved NAA:Cho ratio (1.21 +/- 0.27 versus 1.01 +/- 0.29; p = 0.05). Data were substantiated with fresh tissue NAA extraction. A significant decrease in cortical NAA was observed in HCA versus normal (7.07 +/- 1.9 versus 8.54 +/- 2.1 micromol/g; p = 0.05), with maintenance of normal NAA levels after diazoxide pretreatment (9.49 +/- 1.1 versus 7.07 +/- 1.9 micromol/g; p = 0.0002). Clinical neurologic scores were significantly improved in the HCA+diazoxide group versus HCA at all time points.

CONCLUSIONS

Neurologic injury remains a significant complication of cardiac surgery and is most severe after HCA. Magnetic resonance spectroscopy assessment of NAA:Cho ratios offers an early, noninvasive means of potentially evaluating neurologic injury and the effect of neuroprotective agents.

Neonatal Brain Protection and Deep Hypothermic Circulatory Arrest: Pathophysiology of Ischemic Neuronal Injury and Protective Strategies

Deep hypothermic circulatory arrest (DHCA) has been used for the past 50 years in the surgical repair of complex congenital cardiac malformations and operations involving the aortic arch; it enables the surgeon to achieve precise anatomical reconstructions by creating a bloodless operative field. Nevertheless, DHCA has been associated with immediate and late neurodevelopmental morbidities. This review provides an overview of the pathophysiology of neonatal hypoxic brain injury after DHCA, focusing on cellular mechanisms of necrosis, apoptosis, and glutamate excitotoxicity. Techniques and strategies in neonatal brain protection include hypothermia, acid base blood gas management during cooling, and pharmacologic interventions such as the use of volatile anesthetics. Surgical techniques consist of intermittent cerebral perfusion during periods of circulatory arrest and continuous regional brain perfusion.

Serial proton magnetic resonance spectroscopy of the brain in children undergoing cardiac surgery

We used proton magnetic resonance spectroscopy to study 11 children (age < 8 years) with congenital heart disease undergoing cardiopulmonary bypass to determine whether low (10 +/- 4; n = 6) vs high (20 +/- 4; n = 5) perfusate hematocrits during bypass resulted in changes in brain metabolites which correlate with neurologic injury. Long and short echo time single voxel magnetic resonance spectroscopy in occipital gray matter and neurologic assessment were performed preoperatively and 2 and 5 days postoperatively. We also determined whether prolonged periods at low flow rates during bypass affected spectroscopy variables. We found no significant differences in metabolite ratios between the low vs high hematocrit groups or the lower vs higher flow rate groups (repeated measures analysis of variance of observation ranks converted to normal scores). However, our study was limited by statistical power due to the small sample size, therefore no conclusions could be made. Additional studies involving a greater number of patients are necessary. In all 11 children, magnetic resonance spectroscopy detected a significant decrease in brain N-acetyl-aspartate, and increases in myoinositol and glutamate/glutamine after surgery (Quade test) demonstrating that magnetic resonance spectroscopy is sensitive in detecting subtle postoperative changes in brain metabolites.

Mitochondrial ATP-sensitive potassium channel activation protects cerebellar granule neurons from apoptosis induced by oxidative stress

BACKGROUND AND PURPOSE

Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels are present in the brain, and several reports have shown that mitoK(ATP) channel openers protect the brain against ischemic injury. However, the precise mechanisms of this protection are not well established. We hypothesized that mitoK(ATP) channel openers prevent apoptosis by preserving mitochondrial membrane potential.

METHODS

We investigated the effect of mitoK(ATP) channel openers on apoptosis induced by oxidative stress using cultured cerebellar granule neurons.

RESULTS

The mitoK(ATP) channel opener diazoxide (100 micromol/L) significantly suppressed the number of cells with terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive nuclei and the increase in caspase-3 activity induced by 20 micromol/L H2O2. Diazoxide and another opener, pinacidil, prevented the loss of mitochondrial inner membrane potential (Delta(Psi)m) induced by H2O2. These effects were abolished by 5-hydroxydecanoate (500 micromol/L), a mitoK(ATP) channel blocker. Cyclosporin A and bongkrekic acid, inhibitors of the mitochondrial permeability transition pore, also prevented Delta(Psi)m loss, confirming the involvement of the mitochondrial permeability transition in the apoptotic cascade in neurons. Furthermore, diazoxide prevented the increase in extracellular glutamate concentration induced by H2O2, but this effect was not attributable to activation of surface K(ATP) channels.

CONCLUSIONS

MitoK(ATP) channel openers inhibited apoptosis by preserving mitochondrial inner membrane potential. These beneficial effects may suggest a possible new target for neuroprotection.

Failure of retrograde cerebral perfusion to attenuate metabolic changes associated with hypothermic circulatory arrest

OBJECTIVES

Although retrograde cerebral perfusion has become a popular adjunctive technique and may improve cerebral ischemic tolerance during hypothermic circulatory arrest, direct cerebral metabolic benefit has yet to be demonstrated in human subjects. We investigated the post-arrest metabolic phenomena with and without retrograde cerebral perfusion in patients.

METHODS

In a prospective randomized trial, 42 patients undergoing aortic surgery requiring hypothermic circulatory arrest were allocated to receive hypothermic circulatory arrest alone (n = 21) or hypothermic circulatory arrest with additional retrograde cerebral perfusion (n = 21). Circulatory arrest was commenced at 15 degrees C, and retrograde perfusion was instituted through the superior vena cava at a maximum jugular bulb pressure of 25 mm Hg. Transcranial, paired, repeated samples of the arterial and jugular bulb blood were analyzed for oxygen and glucose. Velocity in the right middle cerebral artery was also measured simultaneously.

RESULTS

There were 3 (7.1%) deaths and 3 (7.1%) episodes of neurologic deficit. Mean bypass and circulatory arrest duration (in minutes) were similar between groups (P =.4 and.14). The mean retrograde perfusion duration was 23 minutes. Post-arrest nasopharyngeal temperature was similar (15.3 degrees C vs. 15.3 degrees C). Retrograde perfusion did not affect post-arrest oxygen extraction, glucose extraction, or jugular bulb Po(2). There was no immediate lactate release immediately after hypothermic circulatory arrest.

CONCLUSIONS

Retrograde cerebral perfusion did not influence immediate post-arrest nasopharyngeal temperature or cerebral metabolic recovery. The low jugular bulb Po(2) suggests equivalent ischemia. These findings cast doubt on the effectiveness of retrograde cerebral perfusion as a metabolic adjunct to hypothermic circulatory arrest.

Pharmacologically induced preconditioning with diazoxide: a novel approach to brain protection

BACKGROUND

Ischemic preconditioning is an endogenous mechanism whereby brief periods of ischemia render neurons resistant to subsequent lethal insults. This protection appears to alter cellular apoptosis and can be induced by potassium channel openers acting on the inner membrane of the mitochondria (mitoK(ATP)). To test the hypothesis that pharmacologic preconditioning could provide neuroprotection, the mitoK(ATP) opener diazoxide was used in a canine model of brain injury induced by hypothermic circulatory arrest (HCA).

METHODS

Seventeen dogs were placed on cardiopulmonary bypass (CPB) and cooled to 18 degrees C. After 2 hours of HCA, animals were rewarmed and weaned from CPB. Six dogs received intravenous diazoxide (2.5 mg/kg bolus 15 minutes prior to CPB, then 0.5 mg/min until circulatory arrest, then restarted for the first hour of rewarming). Six animals received vehicle only. Five received diazoxide and the mitoK(ATP) blocker 5-hydroxydecanoate (5-HD). Using a modified Pittsburgh Canine Neurological Scoring System (0 = normal, 500 = brain death), animals were evaluated every 24 hours for 3 days. The brains were removed and histologic sections of four regions characteristically injured in this model were scored (0 = no injury, 4 = infarction) by a neuropathologist in a blinded fashion.

RESULTS

Clinical scoring showed marked improvement in the diazoxide group at 48 hours (101 +/- 10.5 vs 165 +/- 14.8, p < 0.01) and 72 hours (54 +/- 9.3 vs 137 +/- 12.1, p < 0.01). This neuroprotection was attenuated when 5-HD was concomitantly administered. Three of four brain regions typically injured in this model (cortex, hippocampus, and entorhinal cortex) had significant neuron preservation in the diazoxide group. Likewise, combined region scores were significantly improved in the treatment group (1.18 +/- 0.2 vs 2.46 +/- 0.2, p < 0.01).

CONCLUSIONS

Pretreatment with diazoxide resulted in significant improvement in both clinical neurologic scores and histopathology in our model of HCA. This suggests that pharmacologic preconditioning with the mitoK(ATP) channel opener diazoxide may offer effective neuroprotection during HCA.

Cerebral effects of cold reperfusion after hypothermic circulatory arrest

OBJECTIVES

This study was undertaken to explore whether an interval of cold reperfusion can improve cerebral outcome after prolonged hypothermic circulatory arrest.

METHODS

Sixteen pigs (27-30 kg) underwent 90 minutes of circulatory arrest at a brain temperature of 20 degrees C. Eight animals were rewarmed immediately after hypothermic circulatory arrest (controls), and 8 were reperfused for 20 minutes at 20 degrees C and then rewarmed (cold reperfusion). Electrophysiologic recordings, fluorescent microsphere determinations of cerebral blood flow, calculations of cerebral oxygen consumption, and direct measurements of intracranial pressure (millimeters of mercury) were obtained at baseline (37 degrees C), before hypothermic circulatory arrest, after discontinuing circulatory arrest at 37 degrees C deep brain temperature, and at 2, 4, and 6 hours thereafter. Histopathologic features and percent brain water were determined after the animals were sacrificed.

RESULTS

Cerebral blood flow and oxygen consumption decreased during cooling: cerebral oxygen consumption returned to baseline levels after 4 hours, but cerebral blood flow remained depressed until 6 hours in both groups. Cold reperfusion failed to improve electrophysiologic recovery or to reduce brain weight, but median intracranial pressure increased significantly less after cold reperfusion than in controls (P =.02). Although no significant difference in the incidence of histopathologic abnormalities between groups was found, all 3 animals with an intracranial pressure of more than 15 mm Hg after immediate rewarming had histopathologic lesions, and high intracranial pressure was more prevalent among all animals with subsequent histopathologic lesions (P =.03).

CONCLUSIONS

Cold reperfusion significantly inhibited the rise in intracranial pressure seen in control pigs after 90 minutes of circulatory arrest at 20 degrees C, suggesting that cold reperfusion may decrease cerebral edema and thereby improve outcome after prolonged hypothermic circulatory arrest.

Exogenous aspartate neurotoxicity in the spinal cord under metabolic stress in vivo

BACKGROUND

Considerable evidence exists that neurotoxicity of excitatory amino acids is related to the neuronal injury, including paraplegia. However, little is known about aspartate neurotoxicity in the spinal cord in vivo. We evaluated the detrimental effects of exogenous aspartate on spinal cord neurons under metabolic stress.

METHODS

New Zealand white rabbits underwent an infrarenal aortic isolation. Group A animals (n = 7) received segmental aspartate 50 mmol/L) infusion for 10 minutes. Group B animals (n = 7) received saline as a negative control. Group C animals (n = 5) received segmental aspartate 100 mmol/L) infusion for 5 minutes. Group D animals (n = 7) were pretreated with segmental infusion of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptan-5,10-imine (MK-801) (6 mg/kg), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist for 1 minute, followed by segmental infusion of aspartate (50 mmol/L) for 9 minutes. Group E animals (n = 7) received vehicle only, followed by aspartate (50 mmol/L) infusion as a control of group D. Neurologic status was assessed at 12, 24, and 48 hours after operation using the Tarlov score.

RESULTS

Group A animals exhibited paraplegia or paraparesis with marked neuronal necrosis. Group B and C animals recovered fully. Group D animals showed significantly better neurologic function (p = 0.0007) compared with group E animals that exhibited paraplegia or paraparesis.

CONCLUSIONS

Exogenous aspartate can have detrimental effects on spinal cord neurons under metabolic stress. This model may be useful in assaying neuronal injury mediated by NMDA receptor in vivo.

Effects of a traditional Chinese medicine, Qing Nao Yi Zhi Fang, on glutamate excitotoxicity in rat fetal cerebral neuronal cells in primary culture

Qing Nao Yi Zhi Fang (QNYZ), a traditional Chinese medicine, has been developed as a drug to be used for the prevention and treatment of vascular dementia. However, the mechanisms by which this drug affects vascular dementia remain unknown. We examined the effects of QNYZ serum on glutamate excitotoxicity in rat fetal cerebral neuronal cells in primary culture. Exposure of neuronal cells to glutamate leads to a decrease in the activities of cholinesterase, superoxide dismutase, and streptoavidin peroxidase, and an increase in lactate dehydrogenase release. These enzyme activities were restored to the levels in untreated cells by the addition of QNYZ serum. QNYZ serum suppressed the increased nitric oxide production induced by glutamate and prevented glutamate-mediated apoptosis. QNYZ serum also improved mitochondrial energy metabolism after glutamate exposure. These findings suggest that QNYZ has protective effects against glutamate-mediated excitotoxicity in neuronal cells during ischemic brain injury.