Temperature modulation of ischemic neuronal death and inhibition of calcium/calmodulin-dependent protein kinase II in gerbils

Optimal Temperature Management During Cardiopulmonary Bypass: Warm, Cold, or Tepid?

Hypothermia permitted the advent of cardiac surgery and is considered by many the mainstay of cerebral protection during cardiopulmonary bypass (CPB). How ever, some clinicians have questioned the importance of reduced temperatures during CPB and advocate "normo thermic" heart surgery. Hypothermia (mild, moderate, and profound) provides protection during periods of inadequate oxygen delivery by at least two mecha nisms. First, metabolic rate is directly related to tempera ture ; therefore, reduced temperatures increase toler ance to inadequate oxygen delivery. Q10 values (the ratio of metabolic rates at temperature X°C and tempera ture X°C - 10°C) are controversial and are reported as varying between 2.0 and 5.0. During profound hypother mia (temperature = 17°C), metabolic requirements are 10% to 15% of normothermic values. Second, reduced temperatures (even minimal reductions [34°C to 35°C]) attenuate the release of glutamate and other excitatory amines from ischemic neuronal cells. This phenomenon is thought to play an important role in hypothermic cerebral protection. Many investigators have assessed the impact of normothermic temperatures on cerebral outcomes in cardiac surgery patients. Although seem ingly conflicting conclusions are reported, this much is clear: cerebral temperatures in excess of 37°C exacer bate ischemic injury and even mild hypothermia re duces central nervous system damage in the ischemic brain.

Review : Neuroprotection in Brain Ischemia: An Update (Part II

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated the pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches to achieve neuroprotection of the acutely ischemic brain that are directed at specific injury mechanisms. In the second portion of this two-part review, the following potential therapeutic approaches to acute ischemic injury are considered: 1) modulation of nonglutamatergic neurotransmission, including monoaminergic systems (dopamine, norepinephrine, serotonin), γ-aminobutyric acid, and adenosine; 2) mild-to-moderate therapeutic hypothermia; 3) calcium channel antagonism; 4) an tagonism of oxygen free radicals; 5) modulation of the nitric oxide system; 6) antagonism of cytoskeletal proteolysis; 7) growth factor administration; 8) therapy directed at cellular mediators of injury; and 9) the rationale for combination pharmacotherapy. The Neuroscientist 1:164-175, 1995

Neurologic Injury Associated with Rewarming from Hypothermia: Is Mild Hypothermia on Bypass Better than Deep Hypothermic Circulatory Arrest?

Many known risk factors for adverse cardiovascular and neurological outcomes in children with congenital heart defects (CHD) are not modifiable; however, the temperature and blood flow during cardiopulmonary bypass (CPB), are two risk factors, which may be altered in an attempt to improve long-term neurological outcomes. Deep hypothermic circulatory arrest, traditionally used for aortic arch repair, has been associated with short-term and long-term neurologic sequelae. Therefore, there is a rising interest in using moderate hypothermia with selective antegrade cerebral blood flow on CPB during aortic arch repair. Rewarming from moderate-to-deep hypothermia has been shown to be associated with neuronal injury, neuroinflammation, and loss of cerebrovascular autoregulation. A significantly lesser degree of rewarming is required following mild (33-35°C) hypothermia as compared with moderate (28-32°C), deep (21-27°C), and profound (less than 20°C) hypothermia. Therefore, we believe that mild hypothermia is associated with a lower risk of rewarming-induced neurologic injury. We hypothesize that mild hypothermia with selective antegrade cerebral perfusion during CPB for neonatal aortic arch repair would be associated with improved neurologic outcome.

Therapeutic hypothermia applicable to cardiac surgery

OBJECTIVE

To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH.

DATABASES USED

Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded.

CONCLUSIONS

Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Effects of hypothermia combined with neural stem cell transplantation on recovery of neurological function in rats with spinal cord injury

The microenvironment of the injured spinal cord is hypothesized to be involved in driving the differentiation and survival of engrafted neural stem cells (NSCs). Hypothermia is known to improve the microenvironment of the injured spinal cord in a number of ways. To investigate the effect of NSC transplantation in combination with hypothermia on the recovery of rat spinal cord injury, 60 Sprague-Dawley female rats were used to establish a spinal cord hemisection model. They were divided randomly into three groups: A, spinal cord injury group; B, NSC transplantation group; and C, NSC transplantation + hypothermia group. At 1, 2, 4, 6 and 8 weeks post-injury, the motor function of all animals was evaluated using the Basso, Beattie and Besnaham locomotor scoring system and the inclined plane test. At 4 weeks post-transplantation, histological analysis and immunocytochemistry were performed. At 8 weeks post-transplantation, horseradish peroxidase nerve tracing and transmission electron microscopy were conducted to observe axonal regeneration. The outcome of hind limb motor function recovery in group C significantly surpassed that in group B at 4 weeks post-injury (P<0.05). Recovery was also observed in group A, but to a lesser degree. For the pathological sections no neural axonal were observed in group A. A few axon-like structures were observed in group B and more in group C. Horseradish peroxidase-labeled neurofibers and bromodeoxyuridine-positive cells were observed in the spinal cords of group C. Fewer of these cells were found in group B and fewer still in group A. The differences among the three groups were significant (P<0.05). Using transmission electron microscopy, newly formed nerve fibers and myelinated nerve fibers were observed in the central transverse plane in groups B and C, although these nerve fibers were not evident in group A. In conclusion, NSC transplantation promoted the recovery of hind limb function in rats, and combination treatment with hypothermia produced synergistic effects.

The many faces of calmodulin in cell proliferation, programmed cell death, autophagy, and cancer

Calmodulin (CaM) is a ubiquitous Ca(2+) receptor protein mediating a large number of signaling processes in all eukaryotic cells. CaM plays a central role in regulating a myriad of cellular functions via interaction with multiple target proteins. This review focuses on the action of CaM and CaM-dependent signaling systems in the control of vertebrate cell proliferation, programmed cell death and autophagy. The significance of CaM and interconnected CaM-regulated systems for the physiology of cancer cells including tumor stem cells, and processes required for tumor progression such as growth, tumor-associated angiogenesis and metastasis are highlighted. Furthermore, the potential targeting of CaM-dependent signaling processes for therapeutic use is discussed.

Influence of Fever and hospital-acquired infection on the incidence of delayed neurological deficit and poor outcome after aneurysmal subarachnoid hemorrhage

Although fever and infection have been implicated in the causation of delayed neurological deficits (DND) and poor outcome after aneurysmal subarachnoid hemorrhage (SAH), the relationship between these two often related events has not been extensively studied. We reviewed these events through of our retrospective database of patients with SAH. Multivariate logistic regression was used to determine independent predictors of DND and poor outcome. A total of 186 patients were analyzed. DND was noted in 76 patients (45%). Fever was recorded in 102 patients (55%); infection was noted in 87 patients (47%). A patient with one infection was more likely to experience DND compared to a patient with no infections (adjusted OR 3.73, 95% CI 1.62, 8.59). For those with more than two infections the likelihood of DND was even greater (adjusted OR 4.24, 95% CI 1.55, 11.56). Patients with 1-2 days of fever were less likely to have a favorable outcome when compared to their counterparts with no fever (adjusted OR 0.19, 95% CI 0.06, 0.62). This trend worsened as the number of days febrile increased. These data suggest that the presence of infection is associated with DND, but that fever may have a stronger independent association with overall outcome.

Hypothermia enhances the colocalization of calmodulin kinase IIα with neuronal nitric oxide synthase in the hippocampus following cerebral ischemia

Hypothermia has been shown to have neuroprotective effects against neurotrauma and cerebrovascular disease. Cerebral ischemia induces the activation of calcium/calmodulin kinase II (CaM-KII), which modulates many enzymes. We have previously demonstrated that CaM-KIIα downregulates neuronal nitric oxide synthase (nNOS) activity. However, precise details regarding the neuroprotective mechanism of hypothermia largely remain to be elucidated. Therefore, in this study, we investigated the neuroprotective mechanism of hypothermia, focusing on the association between CaM-KIIα and nNOS in CA1 hippocampus after focal cerebral ischemia in mice. The temperature was maintained at normothermia (36.5-37.5°C) or mild hypothermia (31.5-32.5°C) during these procedures. Focal cerebral ischemia induced significant dissociation of CaM-KIIα from nNOS in the CA1 hippocampus but not in the cerebral cortex under normothermia. Hypothermia did not change the expression of nNOS, but it significantly induced the colocalization of CaM-KIIα with nNOS in CA1 hippocampus immediately after cerebral ischemia. These results presumably result in the attenuation of nNOS activity and could contribute to the tolerance to post-ischemic damage. This effect could be one of the neuroprotective mechanisms of hypothermia.

HIV and SIV induce alterations in CNS CaMKII expression and activation: a potential mechanism for cognitive impairment

The molecular mechanisms underlying learning and memory impairment in patients with HIV-associated neurological disease have remained unclear. Calcium/calmodulin-dependent kinase II (CaMKII) has key roles in synaptic potentiation and memory storage in neurons and also may have immunomodulatory functions. To determine whether HIV and simian immunodeficiency virus (SIV) induce alterations in CaMKII expression and/or activation (autophosphorylation) in the brain, we measured CaMKII alterations by quantitative immunoblotting in both an in vitro HIV/neuronal culture model and in vivo in an SIV-infected macaque model of HIV-associated neurological damage. Using primary rat hippocampal neuronal cultures treated with culture supernatants harvested from HIV-1-infected human monocyte-derived macrophages (HIV/MDM), we found that CaMKII activation declined after exposure of neurons to HIV/MDM. Consistent with our in vitro measurements, a significant decrease in CaMKII activation was present in both the hippocampus and frontal cortex of SIV-infected macaques compared with uninfected animals. In SIV-infected animals, total CaMKII expression in the hippocampus correlated well with levels of synaptophysin. Furthermore, CaMKII expression in both the hippocampus and frontal cortex was inversely correlated with viral load in the brain. These findings suggest that alterations in CaMKII may compromise synaptic function in the early phases of chronic neurodegenerative processes induced by HIV.

Small temperature variations alter edaravone-induced neuroprotection of cortical cultures exposed to prolonged hypoxic episodes

BACKGROUND

Edaravone, a free radical scavenger, has been shown to be neuroprotective in vivo and in vitro. However, the impact of small temperature variations on its neuroprotective actions remains unknown.

METHODS

We examined the degree of neuroprotection conferred by various concentrations of edaravone on cortical cultures exposed to prolonged hypoxia (24 h) under three conditions: mild hypothermia (32 degrees C), normothermia (37 degrees C), and mild hyperthermia (39 degrees C). The survival of cortical neurones from E16 Wistar rats (SR) was evaluated using photomicrographs taken before and after exposure to hypoxia.

RESULTS

The mean survival of neurones exposed to hypoxia at normothermia was 14.7 (sem 1.8)%. The addition of 50 microM edaravone significantly improved the mean survival to 40.5 (4.7)%. This improvement was noted at higher doses of edaravone (5 microM < or =) but not at lower doses (< or =500 nM). With mild hypothermia and prolonged hypoxia without edaravone, neuroprotection was significantly improved with a mean survival of 63.0 (5.2)%. This neuroprotective effect was not enhanced with the addition of edaravone, even at the highest dose. Hypoxia-induced neurotoxicity was aggravated by mild hyperthermia as reflected by a mean survival of 9.1 (2.1)%. However, higher concentrations of edaravone inhibited the deleterious effect of mild hyperthermia, thereby demonstrating a significant neuroprotective effect. The survival of neurones subjected to both hyperthermia and edaravone was the same as that of neurones exposed to normothermia and edaravone.

CONCLUSIONS

Temperature is a potential factor in determining whether edaravone confers a neuroprotective effect when applied during prolonged hypoxic insults.

Hyperthermia Exacerbates Ischaemic Brain Injury

Hyperthermia frequently occurs in stroke patients. Hyperthermia negatively correlates with clinical outcome and adversely effects treatment regiments otherwise successful under normothermic conditions. Preclinical studies also demonstrate that hyperthermia converts salvageable penumbra to ischaemic infarct. The present article reviews the knowledge accumulated from both clinical and preclinical studies about hyperthermia and ischaemic brain injury, examines current treatment strategies and discusses future research directions.

Protection in animal models of brain and spinal cord injury with mild to moderate hypothermia

For the past 20 years, various laboratories throughout the world have shown that mild to moderate levels of hypothermia lead to neuroprotection and improved functional outcome in various models of brain and spinal cord injury (SCI). Although the potential neuroprotective effects of profound hypothermia during and following central nervous system (CNS) injury have long been recognized, more recent studies have described clinically feasible strategies for protecting the brain and spinal cord using hypothermia following a variety of CNS insults. In some cases, only a one or two degree decrease in brain or core temperature can be effective in protecting the CNS from injury. Alternatively, raising brain temperature only a couple of degrees above normothermia levels worsens outcome in a variety of injury models. Based on these data, resurgence has occurred in the potential use of therapeutic hypothermia in experimental and clinical settings. The study of therapeutic hypothermia is now an international area of investigation with scientists and clinicians from every part of the world contributing to this important, promising therapeutic intervention. This paper reviews the experimental data obtained in animal models of brain and SCI demonstrating the benefits of mild to moderate hypothermia. These studies have provided critical data for the translation of this therapy to the clinical arena. The mechanisms underlying the beneficial effects of mild hypothermia are also summarized.

Induced hypothermia in acute ischemic stroke

BACKGROUND

Induced hypothermia is a promising neuroprotective treatment for acute ischemic stroke. Data from both global and focal ischemia animal models have been encouraging. However, only a few small clinical studies have investigated its use in humans.

OBJECTIVE

To review the background, possible mechanisms of action, and the preclinical and clinical data supporting the neuroprotective role of induced hypothermia following acute ischemic stroke.

METHODS

A literature search was performed using the PubMed database. Only papers in English were reviewed.

RESULTS/CONCLUSIONS

Induced hypothermia is effective as a neuroprotectant in animal models of acute ischemic stroke. Its multimodal mechanism of action makes it a very attractive method of neuroprotection. Although human studies suggest it is safe and feasible, larger randomized controlled trials are necessary to address clinical efficacy and to refine the methods and parameters of induced hypothermia protocols.

Ischemia and status epilepitcus result in enhanced phosphorylation of calcium and calmodulin-stimulated protein kinase II on threonine 253

Ca2+-stimulated protein kinase II (CaMKII) is critically involved in the regulation of synaptic function and is implicated in the neuropathology associated with ischemia and status epilepticus (SE). The activity and localization of CaMKII is regulated by multi-site phosphorylation. In the present study we investigated the effects of global ischemia followed by reperfusion and of SE on the phosphorylation of CaMKII on T253 in rat forebrains and compared this to the phosphorylation of T286. Both ischemia and SE resulted in marked increases in the phosphorylation of T253, and this was particularly marked in the postsynaptic density (PSD). Phosphorylation of T286 decreased rapidly towards basal levels following ischemia whereas phosphorylation of T253 remained elevated for between 1 and 6 h before decreasing to control values. Following SE, phosphorylation of T253 remained elevated for between 1 and 3 h before decreasing to control levels. In contrast, phosphorylation of T286 remained elevated for at least 24 h following the termination of SE. Total CaMKII associated with PSDs transiently increased 10 min following ischemia, but only several hours following SE. The results demonstrate that phoshorylation of CaMKII on T253 is enhanced following both ischemia/reperfusion and SE and indicate that the phosphorylation of T253 and T286 are differentially regulated.

Phosphorylation of Calcium Calmodulin—Dependent Protein Kinase II following Lateral Fluid Percussion Brain Injury in Rats

Traumatic brain injury (TBI) can dramatically increase levels of intracellular calcium ([Ca(2+)](i)). One consequence of increased [Ca(2+)](i) would be altered activity and function of calcium-regulated proteins, including calcium-calmodulin-dependent protein kinase II (CaMKII), which is autophosphorylated on Thr(286)(pCaMKII(286)) in the presence of calcium and calmodulin. Therefore, we hypothesized that TBI would result in increased levels of pCaMKII(286), and that such increases would occur early after injury in brain regions known to be damaged following lateral fluid percussion TBI (i.e., hippocampus and cortex). In order to test this hypothesis, immunostaining of CaMKII was examined in rat hippocampus and cortex after lateral fluid percussion (LFP) injury using an antibody directed against pCaMKII(286). LFP injury produced a marked increase in pCaMKII(286) immunostaining in the hippocampus and overlying cortex 30 min after TBI. The pattern of increased immunostaining was uneven, and unexpectedly absent in some hippocampal CA3 pyramidal neurons. This suggests that phosphatase activity may also increase following TBI, resulting in dephosphorylation of pCaMKII(286) in subpopulations of CA3 pyramidal neurons. Western blotting confirmed a rapid increase in levels of pCaMKII(286) at 10 and 30 min after brain injury, and that it was transient and no longer significantly elevated when examined at 3, 8, and 24 h. These results demonstrate that TBI alters the autophosphorylation state of CaMKII, an important neuronal regulator of critical cell functions, including enzyme activities, cell structure, gene expression, and neuronal plasticity, and provide a molecular mechanism that is likely to contribute to cell injury and impaired plasticity after TBI.

Molecular targets in cerebral ischemia for developing novel therapeutics

Cerebral ischemia (stroke) triggers a complex series of biochemical and molecular mechanisms that impairs the neurologic functions through breakdown of cellular integrity mediated by excitotoxic glutamatergic signalling, ionic imbalance, free-radical reactions, etc. These intricate processes lead to activation of signalling mechanisms involving calcium/calmodulin-dependent kinases (CaMKs) and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). The distribution of these transducers bring them in contact with appropriate molecular targets leading to altered gene expression, e.g. ERK and JNK mediated early gene induction, responsible for activation of cell survival/damaging mechanisms. Moreover, inflammatory reactions initiated at the neurovascular interface and alterations in the dynamic communication between the endothelial cells, astrocytes and neurons are thought to substantially contribute to the pathogenesis of the disease. The damaging mechanisms may proceed through rapid nonspecific cell lysis (necrosis) or by active form of cell demise (apoptosis or necroptosis), depending upon the severity and duration of the ischemic insult. A systematic understanding of these molecular mechanisms with prospect of modulating the chain of events leading to cellular survival/damage may help to generate the potential strategies for neuroprotection. This review briefly covers the current status on the molecular mechanisms of stroke pathophysiology with an endeavour to identify potential molecular targets such as targeting postsynaptic density-95 (PSD-95)/N-methyl-d-aspartate (NMDA) receptor interaction, certain key proteins involved in oxidative stress, CaMKs and MAPKs (ERK, p38 and JNK) signalling, inflammation (cytokines, adhesion molecules, etc.) and cell death pathways (caspases, Bcl-2 family proteins, poly (ADP-ribose) polymerase-1 (PARP-1), apoptosis-inducing factor (AIF), inhibitors of apoptosis proteins (IAPs), heat shock protein 70 (HSP70), receptor interacting protein (RIP), etc., besides targeting directly the genes itself. However, selecting promising targets from various signalling cascades, for drug discovery and development is very challenging, nevertheless such novel approaches may lead to the emergence of new avenues for therapeutic intervention in cerebral ischemia.

Cellular mechanisms of neuronal damage from hyperthermia

Hyperthermia can cause brain damage and also exacerbate the brain damage produced by stroke and amphetamines. The developing brain is especially sensitive to hyperthermia. The severity of, and mechanisms underlying, hyperthermia-induced neuronal death depend on both temperature and duration of exposure. Severe hyperthermia can produce necrotic neuronal death. For a window of less severe heat stresses, cultured neurons exhibit a delayed death with apoptotic characteristics including cytochrome c release and caspase activation. Little is known about mechanisms of hyperthermia-induced damage upstream of these late apoptotic effects. This chapter considers several possible upstream mechanisms, drawing on both in vivo and in vitro studies of the nervous system and other tissues. Hyperthermia-induced damage in some non-neuronal cells includes endoplasmic reticular stress due to denaturing of nascent polypeptide chains, as well as nuclear and cytoskeletal damage. Evidence is presented that hyperthermia produces mitochondrial damage, including depolarization, in cultured mammalian neurons.

Hyperthermia and central nervous system injury

Fever is a common occurrence in patients following brain and spinal cord injury (SCI). In intensive care units, large numbers of patients demonstrate febrile periods during the first several days after injury. Over the last several years, experimental studies have reported the detrimental effects of fever in various models of central nervous system (CNS) injury. Small elevations in temperature during or following an insult have been shown to worsen histopathological and behavioral outcome. Thus, the control of fever after brain or SCI may improve outcome if more effective strategies for monitoring and treating hyperthermia were developed. Because of the clinical importance of fever as a potential secondary injury mechanism, mechanisms underlying the detrimental effects of mild hyperthermia after injury have been evaluated. To this end, studies have shown that mild hyperthermia (>37 degrees C) can aggravate multiple pathomechanisms, including excitotoxicity, free radical generation, inflammation, apoptosis, and genetic responses to injury. Recent data indicate that gender differences also play a role in the consequences of secondary hyperthermia in animal models of brain injury. The observation that dissociations between brain and body temperature often occur in head-injured patients has again emphasized the importance of controlling temperature fluctuations after injury. Thus, increased emphasis on the ability to monitor CNS temperature and prevent periods of fever has gained increased attention in the clinical literature. Cooling blankets, body vests, and endovascular catheters have been shown to prevent elevations in body temperature in some patient populations. This chapter will summarize evidence regarding hyperthermia and CNS injury.

Neurotoxic zinc translocation into hippocampal neurons is inhibited by hypothermia and is aggravated by hyperthermia after traumatic brain injury in rats

Hypothermia reduces excitotoxic neuronal damage after seizures, cerebral ischemia and traumatic brain injury (TBI), while hyperthermia exacerbates damage from these insults. Presynaptic release of ionic zinc (Zn2+), translocation and accumulation of Zn2+ ions in postsynaptic neurons are important mechanisms of excitotoxic neuronal injury. We hypothesized that temperature-dependent modulation of excitotoxicity is mediated in part by temperature-dependent changes in the synaptic release and translocation of Zn2+. In the present studies, we used autometallographic (AMG) and fluorescent imaging of N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ) staining to quantify the influence of temperature on translocation of Zn2+ into hippocampal neurons in adult rats after weight drop-induced TBI. The central finding was that TBI-induced Zn2+ translocation is strongly influenced by brain temperature. Vesicular Zn2+ release was detected by AMG staining 1 h after TBI. At 30 degrees C, hippocampus showed almost no evidence of vesicular Zn2+ release from presynaptic terminals; at 36.5 degrees C, the hippocampus showed around 20% to 30% presynaptic vesicular Zn2+ release; and at 39 degrees C vesicular Zn2+ release was significantly greater (40% to 60%) than at 36.5 degrees C. At 6 h after TBI, intracellular Zn2+ accumulation was detected by the TSQ staining method, which showed that Zn2+ translocation also paralleled the vesicular Zn2+ release. Neuronal injury, assessed by counting eosinophilic neurons, also paralleled the translocation of Zn2+, being minimal at 30 degrees C and maximal at 39 degrees C. We conclude that pathological Zn2+ translocation in brain after TBI is temperature-dependent and that hypothermic neuronal protection might be mediated in part by reduced Zn2+ translocation.

Physiology and clinical relevance of induced hypothermia

Experimental evidence and clinical experience suggest that mild hypothermia protects numerous tissues from damage during ischemic insult. However, the extent to which hypothermia becomes a valued therapeutic option will depend on the clinician's ability to rapidly reduce core body temperature and safely maintain hypothermia. To date, general anesthesia is the best way to block autonomic defenses during induction of mild-to-moderate hypothermia; unfortunately, general anesthesia is not an option in most patients likely to benefit from therapeutic hypothermia. Induction of hypothermia in awake humans is complicated by both the technical difficulties related to thermal manipulation and the remarkable efficacy of thermoregulatory defenses, especially vasoconstriction and shivering. The most effective thermal manipulation devices are generally invasive and, therefore, more prone to complications than surface methods. In an effort to inhibit thermoregulation in awake humans, several agents have been tested either alone or in combination with each other. For example, the combination of meperidine and buspirone has already been applied to facilitate induction of hypothermia in human trials. However, pharmacological induction of thermoregulatory tolerance to cold without excessive sedation, respiratory depression, or other serious toxicity remains a major focus of current therapeutic hypothermia research.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

The effects of temperature on hypoxic-ischemic brain injury

Over the past 15 years it has been recognized that the temperature of the brain has an important influence on the extent of brain injury that follows intervals of hypoxia-ischemia. Available data in animals and humans show that brain injury is worsened when fever is superimposed on an ischemic event. Furthermore, data in neonates and adults strongly suggest a neuroprotective role for modest hypothermia (temperature reductions of 1 to 6 degrees C) applied during or following ischemia or hypoxia-ischemia. This article provides an overview of the effects of brain temperature, including its role in the development of brain injury, mechanisms of brain injury which may be temperature sensitive, the regulation of brain temperature, thermal characteristics during brain cooling, and current clinical investigations that use temperature as a therapeutic modality.

Phosphorylation of neuronal nitric oxide synthase at Ser847 by CaM-KII in the hippocampus of rat brain after transient forebrain ischemia

The authors previously demonstrated that Ca2+/calmodulin (CaM)-dependent protein kinase IIalpha (CaM-KIIalpha) can phosphorylate neuronal nitric oxide synthase (nNOS) at Ser847 and attenuate NOS activity in neuronal cells. In the present study, they established that forebrain ischemia causes an increase in the phosphorylation of nNOS at Ser847 in the hippocampus. This nNOS phosphorylation appeared to be catalyzed by CaM-KII: (1) it correlated with the autophosphorylation of CaM-KIIalpha; (2) it was blocked by the CaM-KII inhibitor, KN-93; and (3) nNOS and CaM-KIIalpha were found to coexist in the hippocampus. Examination of the spatial relation between nNOS and CaM-KIIalpha in the brain revealed coexistence in the hippocampus but not in the cortex during reperfusion, with a concomitant increase in autophosphorylation of CaM-KIIalpha. The phosphorylation of nNOS at Ser847 probably takes place in nonpyramidal hippocampal neurons, which increased after 30 minutes of reperfusion in the hippocampus, whereas no significant increase was detected in the cortex. An intraventricular injection of KN-93 significantly decreased the phosphorylation of nNOS in the hippocampus. These results point to CaM-KII as a protein kinase, which by its colocalization may attenuate the activity of nNOS through its Ser847 phosphorylation, and may thus contribute to promotion of tolerance to postischemic damage in hippocampal neurons.

Calcium/calmodulin-dependent kinase II phosphorylation of the GABAA receptor alpha1 subunit modulates benzodiazepine binding

gamma-Aminobutyric acid (GABA) is the primary neurotransmitter that is responsible for the fast inhibitory synaptic transmission in the central nervous system. A major post-translational mechanism that can rapidly regulate GABAAR function is receptor phosphorylation. This study was designed to test the effect of endogenous calcium and calmodulin-dependent kinase II (CaM kinase II) activation on both allosteric modulator binding and GABAA receptor subunit phosphorylation. Endogenous CaM kinase II activity was stimulated, and GABAA receptors were subsequently analyzed for bothallosteric modulator binding properties and immunoprecipitated and analyzed for subunit phosphorylation levels. A significant increase in allosteric-modulator binding of the GABAAR was observed under conditions maximal for CaM kinase II activation. In addition, CaM kinase II activation resulted in a direct increase in phosphorylation of the GABAA receptor alpha1 subunit. The data suggest that the CaM kinase II-dependent phosphorylation of the GABAA receptor alpha1 subunit modulated allosteric modulator binding to the GABAA receptor.

Persistent phosphorylation of synaptic proteins following middle cerebral artery occlusion

Transient cerebral ischemia following 1 to 2 hours of middle cerebral artery occlusion (MCAO) in the rat leads to infarction, which can be diminished by synaptic transmission modulators, implying aberrant cell signaling in the pathogenetic process. The authors report here changes in the levels of tyrosine phosphorylated proteins (PTyr) and calcium calmodulin kinase II (CaMKII) phosphorylation of Thr 286, in synaptosomal, particulate, and cytosolic fractions of different cortical areas following 1 or 2 hours of MCAO, or 2 hours of MCAO followed by 2 hours of reperfusion. At the end of 2-hour MCAO, PTyr, and in particular the pp180, indicative of NR2A/B subunit, increased in the synaptosomal fraction in less ischemic areas while it decreased in more severe ischemic regions. During reperfusion, phosphorylation increased at least 2-fold in all reperfused areas. During 2 hours of MCAO, the phosphorylation of CaMKII increased 8- to 10-fold in the synaptosomal fraction in all ischemic brain regions. During reperfusion, the phospho-CaMKII levels remained elevated by approximately 300% compared with the contralateral hemisphere (control). There was no increase in phospho-CaMKII in the cytosolic fraction at any time during or following ischemia in any of the brain regions examined. The authors conclude that both tyrosine kinase coupled pathways, as well as CaMKII-mediated cellular processes associated with synaptic activity, are strongly activated during and particularly following MCAO. These results support the hypothesis that aberrant cell signaling may contribute to ischemic cell death and dysfunction, and that selective modulators of cell signaling may be targets for pharmacological intervention against ischemic brain damage.

Baclofen is neuroprotective and prevents loss of calcium/calmodulin-dependent protein kinase II immunoreactivity in the ischemic gerbil hippocampus

Excessive release of glutamate during transient cerebral ischemia initiates a cascade of events that leads to the delayed and selective death of neurons located in the hippocampus. Activity of calcium calmodulin kinase II (CaM kinase), a protein kinase critical to neuronal functioning, disappears following ischemia. The in vivo link between glutamate excitoxicity and alterations in CaM kinase activity has not been extensively studied. Baclofen, a selective gamma-aminobutyric acid (GABA)(B) receptor agonist, has been shown to inhibit glutamate release. The present study evaluated the neuroprotective efficacy of this compound and assessed early changes in hippocampal-dependent behaviors and CaM kinase immunoreactivity following transient cerebral ischemia. Baclofen (50 mg/kg) prevented both the loss of hippocampal CA1 pyramidal cells and the reduction in hippocampal CaM kinase immunoreactivity observed in control animals following ischemic insult. Cerebral ischemia produced a significant increase in working memory errors; however, baclofen failed to attenuate this memory deficit. Results confirm that baclofen is neuroprotective and support a link between glutamate excitotoxicity and reductions in CaM kinase immunoreactivity.

Hypothermic treatment restores glucose regulated protein 78 (GRP78) expression in ischemic brain

Mild hypothermia is a well-known method of reducing brain damage caused by traumatic, hypoxic, and ischemic injury. To elucidate the neuroprotective mechanism induced by hypothermic treatment, we compared gene expression profiles in the hippocampus of gerbils rendered ischemic for 15 min and then reperfused for 3 h under conditions of normothermia (37+/-0.5 degrees C) or hypothermic treatment (34+/-0.5 degrees C). Using the differential display method, we observed significantly reduced expression of the 78 kDa glucose regulated protein (GRP78), in ischemic gerbil hippocampus that underwent normothermic reperfusion, but normal GRP78 expression in animals that underwent hypothermic reperfusion. In situ hybridization and Northern blot analysis showed GRP78 mRNA expression was reduced in the CA1 region of the hippocampus under normothermic conditions, but was not reduced under hypothermic conditions. Western blot analysis also showed the levels of immunoreactive GRP78 protein decreased in neurons of the hippocampal CA-1 region under normothermia, but not under hypothermic treatments. Furthermore, adenovirus-mediated overexpression of GRP78 protects rat hippocampal neurons from cell death and inhibits the rise in intracellular calcium concentration normally induced by hydrogen peroxide. These results suggest that reduction in GRP78 expression contributes to cell damage in the ischemic brain and that hypothermia-mediated restoration of GRP78 expression is one mechanism that enhances neuronal survival.

Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia

Mild hypothermia protects the brain against experimental ischemia, but the reasons are not well known. We examined whether the protective effects of mild hypothermia could be correlated with alterations in expression of Bcl-2, an anti-apoptotic protein in a rat model of transient global ischemia. Following 10 min of forebrain ischemia, hippocampal neurons were examined 72 h later for survival, expression of Bcl-2 family proteins and apoptosis. Intraischemic mild hypothermia was applied for 3 h (33 degrees C, isch-33) or normal body temperature was maintained (37 degrees C, isch-37). Survival of CA1 neurons was significantly improved in the isch-33 group compared to the isch-37 group (90 vs. 53% survival; P<0.01). The proportion of Bcl-2-positive cells among surviving CA1 neurons in the isch-33 group was increased compared to that of sham and isch-37 groups (P<0.01). Bax expression in CA1 was no different between sham and isch-33 groups, but was significantly decreased in isch-37 (P<0.05). TUNEL staining was positive in many isch-37 CA1 neurons, but absent in isch-33. Utilizing electron microscopy, more cells meeting criteria for apoptosis were observed in the isch-37 than isch-33. These data suggest that mild hypothermia attenuates apoptotic death, and that this protection may be related to increases in Bcl-2.

Hypothermia on NO-mediated neurogenic relaxation and on hypoxic inhibition in the response of canine cerebral arteries

Cerebral arteries are innervated by nitric oxide (NO)-mediated vasodilator nerves, and hypoxia has been shown to attenuate neurogenic vasorelaxation. The present study examines the effects of hypothermia on neurogenic vasorelaxation and on the hypoxia-induced inhibition of the neurogenic vasorelaxation response. In isolated canine cerebral arteries, relaxant responses to transmural electrical stimulation (5 Hz for 40 s), mediated via NO synthesized from L-arginine, were not influenced by lowering the bathing media temperature from 37 degrees C to 30 degrees C but were attenuated at 25 degrees C. On the other hand, relaxations caused by nicotine and exogenous NO were not significantly attenuated but were prolonged by cooling to 25 degrees C. The responses associated with nerve stimulation by electrical pulses or nicotine were depressed by hypoxia (from about 500 mmHg of partial O2 pressure to about 45 mmHg) under normothermia. However, hypothermia at 25 degrees C prevented the inhibition by hypoxia of the neurogenic relaxation. It is concluded that the hypothermia-induced inhibition in the response to electrical nerve stimulation is not associated with a decreased synthesis and release of NO in vasodilator nerves nor with a reduced ability of smooth muscle to relax in response to NO. Interference with the propagation of action potentials might be involved in the inhibition via a fall of temperature. The fact that the hypoxia-induced impairment of vasodilator nerve function was prevented by cooling may partially explain the efficacy of hypothermia in protecting against ischemic neuronal injury in the brain.

Hyperthermia in the neurosurgical intensive care unit

OBJECTIVE

In patients with traumatic or ischemic brain injury, hyperthermia is thought to worsen the neurological injury. We studied fever in the neurosurgical intensive care unit (ICU) population using a definition common to surgical practice (rectal temperature >38.5 degrees C). We sought to determine fever incidence, fever duration, and peak temperature and to quantify the use of antipyretic therapy. We also attempted to determine the patient subgroups that are at highest risk for development of fever.

METHODS

In a retrospective chart review of a 6-month period, all febrile episodes that occurred in a consecutive series of neurosurgical ICU patients in a university hospital setting were studied. A febrile episode was defined as a rectal temperature of at least 38.5 degrees C; an episode lasted until the temperature fell below this threshold.

RESULTS

The 428 patients studied had 946 febrile episodes. Fever occurred in 47% of patients, with a mean of 4.7 febrile episodes in each febrile patient. Fevers occurred in more than 50% of patients who were admitted to the ICU for subarachnoid hemorrhage, a central nervous system infection, seizure control, or hemorrhagic stroke, but they occurred in only 27% of patients admitted for spinal disorders. Fevers occurred in 15% of the patients who stayed in the ICU less than 24 hours, but in 93% of those who remained longer than 14 days. Despite the use of antipyretic therapy for 86% of the febrile episodes, 57% lasted longer than 4 hours and 5% lasted longer than 12 hours.

CONCLUSION

Fever is common in critically ill neurosurgical patients, especially those with a prolonged length of stay in the ICU or a cranial disease. If hyperthermia worsens the functional outcome after a primary ischemic or traumatic injury, as has been suggested by several studies of stroke patients, treatment of fever is a clinical issue that requires better management.

Cardiopulmonary cerebral resuscitation using emergency cardiopulmonary bypass, coronary reperfusion therapy and mild hypothermia in patients with cardiac arrest outside the hospital

OBJECTIVES

The purpose of this study was to evaluate the efficacy of an alternative cardiopulmonary cerebral resuscitation (CPCR) using emergency cardiopulmonary bypass (CPB), coronary reperfusion therapy and mild hypothermia.

BACKGROUND

Good recovery of patients with out-of-hospital cardiac arrest is still inadequate. An alternative therapeutic method for patients who do not respond to conventional CPCR is required.

METHODS

A prospective preliminary study was performed in 50 patients with out-of-hospital cardiac arrest meeting the inclusion criteria. Patients were treated with standard CPCR and, if there was no response, by emergency CPB plus intra-aortic balloon pumping. Immediate coronary angiography for coronary reperfusion therapy was performed in patients with suspected acute coronary syndrome. Subsequently, in patients with systolic blood pressure above 90 mm Hg and Glasgow coma scale score of 3 to 5, mild hypothermia (34 C for at least two days) was induced by coil cooling. Neurologic outcome was assessed by cerebral performance categories at hospital discharge.

RESULTS

Thirty-six of the 50 patients were treated with emergency CPB, and 30 of 39 patients who underwent angiography suffered acute coronary artery occlusion. Return of spontaneous circulation and successful coronary reperfusion were achieved in 92% and 87%, respectively. Mild hypothermia could be induced in 23 patients, and 12 (52%) of them showed good recovery. Factors related to a good recovery were cardiac index in hypothermia and the presence of serious complications with hypothermia or CPB.

CONCLUSIONS

The alternative CPCR demonstrated an improvement in the incidence of good recovery. Based upon these findings, randomized studies of this hypothermia are needed.

Subcellular distribution and autophosphorylation of calcium/calmodulin-dependent protein kinase II-alpha in rat hippocampus in a model of ischemic tolerance

A brief period of sublethal ischemia induces resistance to a subsequent, otherwise lethal, ischemic insult, a process named ischemic tolerance or preconditioning. A persistently disturbed cell signaling during reperfusion after cerebral ischemia has been proposed to contribute to ischemic cell death. Here, we report on the effect of ischemic preconditioning on the levels of the regulatory alpha-subunit of calcium/calmodulin protein kinase II and its phosphorylation in the hippocampal CA1 region. We found that during and following lethal cerebral ischemia, calcium/calmodulin protein kinase II-alpha is persistently translocated to cell membranes, where it becomes phosphorylated at threonine 286. In contrast, in the preconditioned brains the translocation and phosphorylation are transient and return to preischemic values after one day of reperfusion. At this time of reperfusion, the total level of calcium/calmodulin protein kinase II-alpha is significantly lower in preconditioned animals compared to the sham and non-conditioned animals. After one day of reperfusion, the level of calcium/calmodulin protein kinase II-alpha messenger RNA decreases in the non-conditioned brains, whereas it is unchanged in preconditioned brains. We conclude that, during and after ischemia, calcium/calmodulin protein kinase II-alpha is translocated to cell membranes and becomes phosphorylated at threonine 286. This could detrimentally influence cell survival by changing receptor function and ion channel conductance. Ischemic preconditioning prevents the persistent presence of calcium/calmodulin protein kinase II-alpha at cell membranes, presumably by enhancing its degradation, which could be part of a neuroprotective mechanism of ischemic tolerance.

Differential fall in ATP accounts for effects of temperature on hypoxic damage in rat hippocampal slices

Intracellular recordings, ATP and cytosolic calcium measurements from CA1 pyramidal cells in rat hippocampal slices were used to examine the mechanisms by which temperature alters hypoxic damage. Hypothermia (34 degrees C) preserved ATP (1.7 vs. 0.8 nM/mg) and improved electrophysiologic recovery of the CA1 neurons after hypoxia; 58% of the neurons subjected to 10 min of hypoxia (34 degrees C) recovered their resting and action potentials, while none of the neurons at 37 degrees C recovered. Increasing the glucose concentration from 4 to 6 mM during normothermic hypoxia improved ATP (1.3 vs. 0.8 nM/mg) and mimicked the effects of hypothermia; 67% of the neurons recovered their resting and action potentials. Hypothermia attenuated the membrane potential changes and the increase in intracellular Ca(2+) (212 vs. 384 nM) induced by hypoxia. Changing the glucose concentration in the artificial cerebrospinal fluid primarily affects ATP levels during hypoxia. Decreasing the glucose concentration from 4 to 2 mM during hypothermic hypoxia worsened ATP, cytosolic Ca(2+), and electrophysiologic recovery. Ten percent of the neurons subjected to 4 min of hypoxia at 40 degrees C recovered their resting and action potentials; this compared with 60% of the neurons subjected to 4 min of normothermic hypoxia. None of the neurons subjected to 10 min of hypoxia at 40 degrees C recovered their resting and action potentials. Hyperthermia (40 degrees C) worsens the electrophysiologic changes and induced a greater increase in intracellular Ca(2+) (538 vs. 384 nM) during hypoxia. Increasing the glucose concentration from 4 to 8 mM during 10 min of hyperthermic hypoxia improved ATP (1.4 vs. 0.6 nM/mg), Ca(2+) (267 vs. 538 nM), and electrophysiologic recovery (90 vs. 0%). Our results indicate that the changes in electrophysiologic recovery with temperature are primarily due to changes in ATP and that the changes in depolarization and Ca(2+) are secondary to these ATP changes. Both primary and secondary changes are important for explaining the improved electrophysiologic recovery with hypothermia.

Altered mRNA expression for brain-derived neurotrophic factor and type II calcium/calmodulin-dependent protein kinase in the hippocampus of patients with intractable temporal lobe epilepsy

The expression of brain-derived neurotrophic factor and the alpha subunit of calcium/calmodulin-dependent protein kinase II mRNA in hippocampi obtained during surgical resections for intractable temporal lobe epilepsy were examined. Both calcium/calmodulin-dependent protein kinase II and brain-derived neurotrophic factor are localized heavily within the hippocampus and have been implicated in regulating hippocampal activity (Kang and Schuman [1995] Science 267:1658-1662; Suzuki [1994] Intl J Biochem 26:735-744). Also, the autocrine and paracrine actions of brain-derived neurotrophic factor within the central nervous system make it a likely candidate for mediating morphologic changes typically seen in the epileptic hippocampus. Quantitative assessments of mRNA levels in epileptic hippocampi relative to autopsy controls were made by using normalized densitometric analysis of in situ hybridization. In addition, correlations between clinical data and mRNA levels were studied. Relative to autopsy control tissue, decreased hybridization to mRNA of the alpha subunit of calcium/calmodulin-dependent protein kinase II and increased hybridization to brain-derived neurotrophic factor mRNA were found throughout the granule cells of the epileptic hippocampus. There also was a significant negative correlation between the duration of epilepsy and the expression of mRNA for brain-derived neurotrophic factor. These results are similar qualitatively to those found in animal models of epilepsy and suggest that chronic seizure activity in humans leads to persistent alterations in gene expression. Furthermore, these alterations in gene expression may play a role in the etiology of the epileptic condition.

Status epilepticus results in an N-methyl-D-aspartate receptor-dependent inhibition of Ca2+/calmodulin-dependent kinase II activity in the rat

Status epilepticus is a major medical emergency that results in significant alteration of neuronal function. Status epilepticus involves seizure activity recurring frequently enough to induce a sustained alteration in brain function. This study was initiated to investigate how status epilepticus affects the activity of calcium and calmodulin-dependent kinase II in the brain. Calcium and calmodulin-dependent kinase II is a neuronally enriched signal transducing system involved in the regulation of neurotransmitter synthesis and release, cytoskeletal function, gene transcription, neurotransmitter receptor function and neuronal excitability. Therefore, alteration of this signal transduction system would have significant physiological effects. Status epilepticus was induced in rats by pilocarpine injection, allowed to progress for 60 min and terminated by repeated diazepam injections. Animals were killed at specific time-points and examined for calcium and calmodulin-dependent kinase II activity. Calcium and calmodulin-dependent kinase II activity was significantly reduced in cerebral cortex and hippocampal homogenates obtained from status epilepticus rats when compared with control animals. Once established, the status epilepticus-induced inhibition of calcium and calmodulin-dependent kinase II activity was observed at all time-points tested following the termination of seizure activity. However, calcium and calmodulin-dependent kinase II activity was not significantly decreased in thalamus and cerebellar homogenates. In addition, status epilepticus-induced inhibition of calcium and calmodulin-dependent kinase II activity was dependent upon activation of N-methyl-D-aspartate subtype of glutamatergic receptors. Thus, status epilepticus induced a significant inhibition of calcium and calmodulin-dependent kinase II activity that involves N-methyl-D-aspartate receptor activation. The data support the hypothesis that inhibition of calcium and calmodulin-dependent kinase II activity may be involved in the alteration of neuronal function following status epilepticus.

Body temperature correlates with functional outcome and the lesion size of cerebral infarction

INTRODUCTION

Experimental studies have demonstrated that mild hyperthermia exacerbates ischemia-induced neuronal injury.

MATERIAL AND METHODS

We examined the relationship between body temperature and functional outcome in 183 patients suffering from cerebral infarction, and admitted within 24 h from the onset of stroke. Patients' functional capacities in daily life were evaluated by Rankin's score before the attack (RS0), on the day of admission (RS1), and 3 months after the onset of stroke (RS90).

RESULTS

RS90 showed an independent correlation with RS0, RS1, age, infarct size and maximum body temperature recorded within the first 7 days from the onset of stroke by multivariate analysis. History of previous cerebrovascular accidents, atrial fibrillation, hemorrhagic transformation, infection, and a hypothalamic lesion showed significant associations with RS90 by the Mann-Whitney U-test, but not by multivariate analysis. Infarct size correlated with body temperature, atrial fibrillation, and hemorrhagic transformation.

CONCLUSION

Body temperature correlated well with both functional outcome and infarct size in patients with an acute cerebral infarction.

Biology of ischemic cerebral cell death

With the approval of alteplase (tPA) therapy for stroke, it is likely that combination therapy with tPA to restore blood flow, and agents like glutamate receptor antagonists to halt or reverse the cascade of neuronal damage, will dominate the future of stroke care. The authors describe events and potential targets of therapeutic intervention that contribute to the excitotoxic cascade underlying cerebral ischemic cell death. The focal and global animal models of stroke are the basis for the identification of these events and therapeutic targets. The signalling pathways contributing to ischemic neuronal death are discussed based on their cellular localization. Cell surface signalling events include the activities of both voltage-gated K+, Na+, and Ca2+ channels and ligand-gated glutamate, gamma-aminobutyric acid and adenosine receptors and channels. Intracellular signalling events include alterations in cytosolic and subcellular Ca2+ dynamics, Ca2+ -dependent kinases and immediate early genes whereas intercellular mechanisms include free radical formation and the activation of the immune system. An understanding of the relative importance and temporal sequence of these processes may result in an effective stroke therapy targeting several points in the cascade. The overall goal is to reduce disability and enhance quality of life for stroke survivors.

Pathophysiology of perinatal brain damage

Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favour of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralisation, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na(+)/K(+) pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channel, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarisation. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to pre-ischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the post-ischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of i.v. administration of magnesium or post-ischemic induction of cerebral hypothermia.

Global ischemia-induced inhibition of the coupling ratio of calcium uptake and ATP hydrolysis by rat whole brain microsomal Mg(2+)/Ca(2+) ATPase

Ischemia is associated with a loss of cytosolic calcium homeostasis. Intracellular stores, particularly in endoplasmic reticulum, are critical for the maintenance of calcium homeostasis. Recent studies have shown that ischemia significantly inhibited microsomal calcium uptake mediated by Mg(2+)/Ca(2+) ATPase, the major mechanism of endoplasmic reticulum calcium sequestration. This study was initiated to determine whether the decreased calcium uptake caused by ischemia was the result of inhibition of Mg(2+)/Ca(2+) ATPase activity or an uncoupling of calcium uptake from ATP hydrolysis. The microsomal Mg(2+)/Ca(2+) ATPase specific inhibitor thapsigargin partially inhibited ATPase activity and completely inhibited calcium uptake. ATPase inhibited by thapsigargin was considered microsomal Mg(2+)/Ca(2+) ATPase. Ischemia from 5 to 60 min had no significant effect on thapsigargin sensitive ATPase activity. However, under identical conditions, increasing ischemia from 5 to 60 min significantly inhibited microsomal calcium uptake. Comparing calcium uptake to ATP hydrolysis as ischemia increased from 5 to 60 min revealed that the coupling ratio of calcium molecules sequestered to ATP molecules hydrolyzed became significantly decreased. The results demonstrated that the effect of ischemia on microsomal calcium uptake was mediated by an uncoupling of calcium transport from Mg(2+)/Ca(2+) ATPase activity.

Cerebral blood flow does not mediate the effect of brain temperature on recovery of extracellular potassium ion activity after transient focal ischemia in the rat

Temperature plays an important role in determining outcome following both global and focal brain ischemia. After focal ischemia, the degree of infarction decreases with mild hypothermia and increases with mild hyperthermia. In this study, brain extracellular potassium ion activity and local cerebral blood flow were measured in cerebral cortex during 60 min of middle cerebral artery occlusion and 60 min of re-perfusion. Brain temperature was maintained at 32-34 degrees C (mild hypothermia), 35.5-36.5 degrees C (normothermia), or 37.5-38.5 degrees C (mild hyperthermia) throughout ischemia and re-perfusion. In normothermic animals and to a greater degree in hyperthermic animals, extracellular potassium ion activity showed delayed secondary elevation above pre-ischemia values within 40-60 min after re-perfusion. No secondary elevation of extracellular potassium ion activity was observed in hypothermic animals. There was no difference in cortical blood flow among groups with varying brain temperature, indicating that delayed deterioration of brain potassium ion homeostasis was not caused by temperature dependent alteration of cerebral blood flow. The data suggest that loss of potassium ion homeostasis during re-perfusion after focal cerebral ischemia is caused by cellular rather than vascular dysfunction and may reflect secondary inhibition of energy metabolism.

Separation of radiolabeled orthophosphate and adenosine 5'-triphosphate by 20% polyacrylamide gel electrophoresis: an assay for brain microsomal Mg2+/Ca2+ ATPase activity

Measuring orthophosphate is an important tool in biochemical analyses used to study membrane transport ATPases essential for calcium homeostasis. Current techniques involve extraction of radioactive phosphate with organic solvents, a technique that results in large quantities of hazardous radioactive waste. Other colorimetric assays are less sensitive and are complicated by interference of background absorbance from membrane tissue and unutilized ATP. This report describes a unique assay for the detection of inorganic phosphate and its application to the study of rat brain microsomal Mg2+/Ca2+ ATPase from a membrane fraction. The technique involves the separation of radioactive phosphate from unused gamma-radiolabeled ATP by resolution on 20% polyacrylamide gels. Both are visualized with X-ray film and quantitated by liquid scintillation counting after extraction from the gels. The assay can detect as little as 4.1 pmol of radiolabeled ATP and ATPase activity in 3.5 ng/microliter of membrane protein. This method offers the advantage of simultaneous quantitation of radiolabeled ATP and radioactive orthophosphate without the generation of large quantities of radioactive waste. The results demonstrate the development of a novel assay procedure for quantitating orthophosphate that is extremely sensitive, reproducible, and applicable to the study of any phosphate liberating enzyme.

Postischemic hyperthermia exacerbates neurologic injury after deep hypothermic circulatory arrest

BACKGROUND

Aggressive surface warming is a common practice in the pediatric intensive care unit. However, recent rodent data emphasize the protective effect of mild (2 degrees - 3 degrees C) hypothermia after cerebral ischemia. This study evaluates different temperature regulation strategies after deep hypothermic circulatory arrest with a survival piglet model.

METHODS

Fifteen piglets were randomly assigned to 3 groups. All groups underwent 100 minutes of deep hypothermic circulatory arrest at 15 degrees C. Brain temperature was maintained at 34 degrees C for 24 hours after cardiopulmonary bypass in group I, 37 degrees C in group II, and 40 degrees C in group III. Neurobehavioral recovery was evaluated daily for 3 days after extubation by neurologic deficit score (0, normal; 500, brain death) and overall performance category (1, normal; 5, brain death). Histologic examination was assessed for hypoxic-ischemic injury (0, normal; 5, necrosis) in a blinded fashion.

RESULTS

All results are expressed as mean +/- standard deviation. Recovery of neurologic deficit score (12.0 +/- 17.8, 47.0 +/- 49.95, 191.0 +/- 179.83; P = .05 for group I vs III), overall performance category (1.0 +/- 0.0, 1.4 +/- 0.6, 2.8 +/- 1.3; P < .05 for group I vs III), and histologic scores (0.0 +/- 0.0, 1.0 +/- 1.2, 2.8 +/- 1.8; P < .05 for group I vs III cortex) were significantly worse in hyperthermic group III. These findings were associated with a significantly lower cytochrome aa3 recovery determined by near-infrared spectroscopy in group III animals (P = .0041 for group I vs III). No animal recovered to baseline electroencephalographic value by 48 hours after deep hypothermic circulatory arrest. Recovery was significantly delayed in the hyperthermic group III animals, with a lower amplitude 14 hours after the operation, which gradually increased with time (P < .05 for group III vs groups I and II).

CONCLUSIONS

Mild postischemic hyperthermia significantly exacerbates functional and structural neurologic injury after deep hypothermic circulatory arrest and should therefore be avoided.

Modulation of GABAergic receptor binding by activation of calcium and calmodulin-dependent kinase II membrane phosphorylation

gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system (CNS). Because of the important role that GABA plays in the CNS, alteration of GABAA receptor function would significantly affect neuronal excitability. Protein phosphorylation is a major mechanism for regulating receptor function in the brain and has been implicated in modulating GABAA receptor function. Therefore, this study was initiated to determine the role of calmodulin-dependent kinase II (CaM kinase II) membrane phosphorylation on GABAA receptor binding. Synaptosomal membrane fractions were tested for CaM kinase II activity towards endogenous substrates. In addition, muscimol binding was evaluated under equilibrium conditions in synaptosomal membrane fractions subjected to either basal (Mg2+ alone) or maximal CaM kinase II-dependent phosphorylation. Activation of endogenous CaM kinase II-dependent phosphorylation resulted in a significant enhancement of the apparent Bmax for muscimol binding without significantly altering the apparent binding affinity. The enhanced muscimol binding could be increased further by the addition of exogenous CaM kinase II to synaptosomal membrane fractions. Co-incubation with inhibitors of kinase activity during the phosphorylation reactions blocked the CaM kinase II-dependent increase in muscimol binding. The data support the hypothesis that activation of CaM kinase II-dependent phosphorylation caused an increased GABAA receptor binding and may play an important role in modulating the function of this inhibitory receptor/chloride ion channel complex.

Postischemic hyperthermia increases expression of hsp72 mRNA after brief ischemia in the gerbil

Brain temperature during ischemia critically determines insult severity, and temperature changes during recirculation may also affect subsequent injury. We have examined the impact of postischemic temperature on induction of the 70 kDa stress protein, hsp72, after brief ischemia in the gerbil. Animals were subjected to 2 min ischemia after which they were maintained under continuous halothane anesthesia during 3 h recirculation, and were either kept normothermic or subjected to hyperthermia comparable to that which occurs spontaneously in gerbils released from anesthesia immediately after the occlusion. Quantitative in situ hybridization showed striking dependence of hsp72 induction on postischemic hyperthermia. This result establishes that delayed temperature-sensitive signals mediate this injury-associated transcriptional response, and demonstrates that postischemic temperature must be carefully monitored in studies of gene expression and induced tolerance employing brief ischemic insults.

Hypothermia attenuates the activation of protein kinase C in focal ischemic rat brain: dual autoradiographic study of [3H]phorbol 12,13-dibutyrate and iodo[14C]antipyrine

Using phorbol 12,13-dibutyrate (PDBu) autoradiography, we investigated the effect of hypothermia or protein kinase C (PKC) activation in rat brain 2 h after focal ischemia. In normothermia, a significant increase of PDBu binding was observed in ischemic brain. Hypothermia suppressed the increase of PDBu binding in degree and extent. These observations suggest that intraischemic hypothermia attenuates the activation of PKC, and this may in part be participate in the protective effect of hypothermia.