Protective effect of hypothermia on hippocampal injury after 30 minutes of forebrain ischemia in rats is mediated by postischemic recovery of protein synthesis

Efficacy and Safety of Transnasal CoolStat Cooling Device to Induce and Maintain Hypothermia

Targeted temperature management (TTM) is recommended as a standard of care for postcardiac arrest patients. Current TTM methods have significant limitations to be used in an ambulatory setting. We investigated the efficacy and safety of a novel noninvasive transnasal evaporative cooling device (CoolStat™). Eleven Yorkshire pigs underwent hypothermia therapy using the CoolStat device. CoolStat induces evaporative cooling by blowing dehumidified ambient air over the nasal turbinates in a unidirectional fashion. CoolStat's efficacy and safety were assessed by applying different cooling strategies (groups A, B and C). In group A (efficacy study; n = 5, TTM for 8 hours), time to achieve brain target temperature (2°C reduction from baseline), and the percentage of time in which the temperature ranged within ±0.5°C after reaching the target temperature were investigated. In the safety assessment (groups B and C), two worst-case therapy situations were reproduced: in group B (n = 3), continuous maximum air flow (65 L/min) was applied without temperature control and, in group C (n = 3), subjects underwent 24-hour TTM (prolonged therapy). Hemodynamic and respiratory parameters, nasal mucosa integrity (endoscopic assessment), and other therapy-related adverse effects were evaluated. Efficacy study: CoolStat cooling therapy successfully induced and sustained managed hypothermia in all subjects. Brain target temperature was achieved in 0.5 ± 0.6 hours and kept within a ±0.5°C range for the therapy duration (99.9% ± 0.1%). All animals completed the safety studies. Maximum air flow (group B) and 24-hour (group C) therapies were well tolerated and no significant damage was observed on nasal mucosa for neither of the groups. CoolStat was able to efficiently induce and maintain hypothermia using unidirectional high flow of dry air into the nostrils of porcine models. CoolStat therapy was well tolerated and no damage to nasal mucosa was observed under either maximum air flow or prolonged therapy.

Temperature management for out-of-hospital cardiac arrest

More than 300,000 Americans suffer a cardiac arrest outside of the hospital each year and even among those who are successfully resuscitated and survive to hospital admission, outcomes remain poor. Temperature management (previously known as therapeutic hypothermia) is the only intervention that has been reproducibly demonstrated to ameliorate the neurologic injury that follows cardiac arrest. The results of a recent large randomized controlled trial have highlighted the uncertainty about temperature management strategies following cardiac arrest. This article reviews the issues and recommendations.

Regulation of mRNA following brain ischemia and reperfusion

There is growing appreciation that mRNA regulation plays important roles in disease and injury. mRNA regulation and ribonomics occur in brain ischemia and reperfusion (I/R) following stroke and cardiac arrest and resuscitation. It was recognized over 40 years ago that translation arrest (TA) accompanies brain I/R and is now recognized as part of the intrinsic stress responses triggered in neurons. However, neuron death correlates to a prolonged TA in cells fated to undergo delayed neuronal death (DND). Dysfunction of mRNA regulatory processes in cells fated to DND prevents them from translating stress-induced mRNAs such as heat shock proteins. The morphological and biochemical studies of mRNA regulation in postischemic neurons are discussed in the context of the large variety of molecular damage induced by ischemic injury. Open issues and areas of future investigation are highlighted. A sober look at the molecular complexity of ischemia-induced neuronal injury suggests that a network framework will assist in making sense of this complexity. The ribonomic network sits between the gene network and the various protein and metabolic networks. Thus, targeting the ribonomic network may prove more effective at neuroprotection than targeting specific molecular pathways, for which all efforts have failed to the present time to stop DND in stroke and after cardiac arrest. WIREs RNA 2017, 8:e1415. doi: 10.1002/wrna.1415 For further resources related to this article, please visit the WIREs website.

Cold stress protein RBM3 responds to temperature change in an ultra-sensitive manner in young neurons

Extremely mild hypothermia to 36.0 °C is not thought to appreciably differ clinically from 37.0 °C. However, it is possible that 36.0 °C stimulates highly sensitive hypothermic signaling mechanism(s) and alters biochemistry. To the best of our knowledge, no such ultra-sensitive pathway/mechanisms have been described. Here we show that cold stress protein RNA binding motif 3 (RBM3) increases in neuron and astrocyte cultures maintained at 33 °C or 36 °C for 24 or 48 h, compared to 37 °C controls. Neurons cultured at 36 °C also had increased global protein synthesis (GPS). Finally, we found that melatonin or fibroblast growth factor 21 (FGF21) augmented RBM3 upregulation in young neurons cooled to 36 °C. Our results show that a 1 °C reduction in temperature can induce pleiotropic biochemical changes by upregulating GPS in neurons which may be mediated by RBM3 and that this process can be pharmacologically mimicked and enhanced with melatonin or FGF21.

Effects of intraoperative external head cooling on short-term cognitive function in patients after coronary artery bypass graft surgery

The aim of study was to assess the effects of an intraoperative external head-cooling technique on cognitive dysfunction in the early postoperative period (at the 10th day) in patients after coronary artery bypass graft (CABG) surgery. Patients in Group H (n=25) were cooled with CPB and the intraoperative, external head-cooling technique, patients in Group C (n=25) were cooled only with cardiopulmonary bypass (CPB) to achieve mild hypothermia (33 - 34 °C). Cognitive function was analyzed before the operation and after the surgery using the Mini Mental State Examination (MMSE), the Modified Visual Reproduction Test from the Wechsler Memory Scale, Trail Making (A/B), WAIS--Digit Span (WDS) and WAIS Digit Symbol Substitution Test (WDSST). The incidence of cognitive impairment at the 10th day after the surgery was 36% (n=9) in Group H and 64% (n=16) in Group C (p=0.048). The temperature during the aortic cross-clamp period was associated with a lower rate of cognitive dysfunction (p=0.05, r(2)=0.09). The intraoperative, external head-cooling technique during the aortic cross-clamp period has a neuroprotective effect and leads to less short-term cognitive function impairment after CABG surgery.

Aortic Surgery without Infusion of Cardioplegic Solution at Total Circulatory Arrest

Background

Minimal infusion of cardioplegic solution (CPS) during aortic surgery using total circulatory arrest (TCA) may reduce several potential side effects: clamping on a diseased aorta, insult of coronary ostia, and edema.

Materials and Methods

From 2006 to 2009, 72 patients underwent aortic surgery without infusion of cardioplegic solution at the initiation of circulatory arrest. The diagnoses were acute aortic dissection (44), aneurysm (22), and intramural hematoma (6).

Results

The duration of TCA, the lowest nasopharyngeal temperature, bypass time, and aortic clamp time was 45 minutes, 16.4℃, 162 minutes, and 100 minutes, respectively. The amount of CPS was 1,050 mL, and 15 patients underwent surgery without CPS. The average inotrope score was 113 points (range, 6.25 to 5,048.5 points) corresponding to the dopamine infusion of 5 mcg/kg/min for 1 day. Seven patients showed a level of creatine kinase-MB above 50 ng/mL, postoperatively, compared with the average of 12.75 ng/mL. The ischemic change was found on electrocardiogram in 5 patients, postoperatively. There was no cardiac morbidity requiring mechanical assist. The average of intensive care unit stay and postoperative hospital stay was 40 hours (range, 15 to 482 hours) and 11 days, respectively.

Conclusion

Minimal infusion of only retrograde CPS during rewarming without initial infusion at TCA in aortic surgery is feasible and can be used with acceptable results.

Therapeutic applications of hypothermia in cerebral ischaemia

There is considerable experimental evidence that hypothermia is neuroprotective and can reduce the severity of brain damage after global or focal cerebral ischaemia. However, despite successful clinical trials for cardiac arrest and perinatal hypoxia-ischaemia and a number of trials demonstrating the safety of moderate and mild hypothermia in stroke, there are still no established guidelines for its use clinically. Based upon a review of the experimental studies we discuss the clinical implications for the use of hypothermia as an adjunctive therapy in global cerebral ischaemia and stroke and make some suggestions for its use in these situations.

Umbilical cord blood cell transplantation after brain ischemia--from recovery of function to cellular mechanisms

Cell transplantation has been proposed as a potential approach to the treatment of neurological disorders. One cell population of interest consists of human umbilical cord blood (hUCB) cells, which have previously been shown to be useful for reparative medicine in haematological diseases. However, hUCB cells are also capable of differentiating into various non-haematopoietic cells, including those of the neural lineage. Moreover, hUCB cells can secrete numerous neurotrophic factors and modulate immune function and inflammatory reaction. Several studies on animal models of ischemic brain injury have demonstrated the potential of hUCB cells to minimize damage and promote recovery after ischemic brain injury.This review focuses on the treatment of both stroke and perinatal hypoxic-ischemic brain injury using hUCB cells. We discuss the therapeutic effects demonstrated after hUCB cell transplantation and emphasize possible mechanisms counteracting pathophysiological events of ischemia, thus leading to the generation of a regenerative environment that allows neural plasticity and functional recovery. The therapeutic functional effects of hUCB cells observed in animal models make the transplantation of hUCB cells a promising experimental approach in the treatment of ischemic brain injury. Together with its availability, low risk of transplantation, immaturity of cells, and simple route of application, hUCB transplantation may stand a good chance of being translated into a clinical setting for the therapy of ischemic brain injury.

Temperature management in acute neurologic disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trials of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

Stem cells: implications in experimental ischaemic stroke therapy

Ischaemic stroke is a syndrome characterized by rapid onset of neurological injury due to interruption of blood flow to the brain. Widespread neuronal damage throughout the CNS has been shown to cause marked and multifarious functional impairments in the ischaemic brain. Recent advances as enumerated above have propelled acute ischaemic stroke management into a therapeutic era. However, once the damage from a stroke event has maximized, little can be done to recover premorbid function. Experimental animal data suggests that stem cell therapy may be an effective alternate to the conventional disease management strategies of ischaemic stroke. Therefore, the present review focuses on detailing the scope of stem cell therapy in the treatment of ischaemic stroke.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

Optimized and efficient preparation of astrocyte cultures from rat spinal cord

Astrocytes constitute a major class of glial cells in the CNS, and play crucial roles in physiological functioning, performance and maintenance of the CNS, as well as promotion of neuronal migration and maturation. Astrocytes have also been directly and indirectly implicated in the pathophysiology of various trauma occurrences, development of neurodegenerative diseases and nerve regeneration. To further understand mechanisms by which astrocytes elicit these effects, the first critical step in the study of astrocytes is the preparation of purified astrocytes cultures. Here we describe a simple and convenient procedure for producing rat primary astrocyte cultures of high purity, viability and proliferation. For astrocyte culture, we have optimized the isolation procedures and cultivation conditions including coating substrates, enzyme digestion, seeding density and composition of the culture medium. Using immunofluorescent antibodies against GFAP and OX-42 in combination of Hoechst 33342 fluorescent staining, we found that the purity of the astrocyte cultures was >99%. Astrocytes had high viability as measured by 3-(4, 5-dimethyl-2-yl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay. In addition, flow cytometric analysis was used to measure and observe variations in the cell cycle after 1-2 passages and proliferation of astrocytes was detected with a high percentage of cells stand in S+G(2)/M phase. Therefore, the method described here is ideal for experiments, which require highly pure astrocyte cultures.

Temperature Management in Acute Neurologic Disorders

Temperature management in acute neurologic disorders has received considerable attention in the last 2 decades. Numerous trials of hypothermia have been performed in patients with head injury, stroke, and cardiac arrest. This article reviews the physiology of thermoregulation and mechanisms responsible for hyperpyrexia. Detrimental effects of fever and benefits of normalizing elevated temperature in experimental models are discussed. This article presents a detailed analysis of trails of induced hypothermia in patients with acute neurologic insults and describes methods of fever control.

Delayed postconditionig initiates additive mechanism necessary for survival of selectively vulnerable neurons after transient ischemia in rat brain

1. The aim of this study was to validate the role of postconditioning, used 2 days after lethal ischemia, for protection of selectively vulnerable brain neurons against delayed neuronal death. 2. Eight, 10, or 15 min of transient forebrain ischemia in rat (four-vessel occlusion model) was used as initial lethal ischemia. Fluoro Jade B, the marker of neurodegeneration, and NeuN, a specific neuronal marker were used for visualization of changes 7 or 28 days after ischemia without and with delayed postconditioning. 3. Our results confirm that postconditioning if used at right time and with optimal intensity can prevent process of delayed neuronal death. At least three techniques, known as preconditioners, can be used as postconditioning: short ischemia, 3-nitropropionic acid and norepinephrine. A cardinal role for the prevention of death in selectively vulnerable neurons comprises synthesis of proteins during the first 5 h after postconditioning. Ten minutes of ischemia alone is lethal for 70% of pyramidal CA1 neurons in hippocampus. Injection of inhibitor of protein synthesis (Cycloheximide), if administered simultaneously with postconditioning, suppressed beneficial effect of postconditioning and resulted in 50% of CA1 neurons succumbing to neurodegeneration. Although, when Cycloheximide was injected 5 h after postconditioning, this treatment resulted in survival of 90% of CA1 neurons. 4. Though postconditioning significantly protects hippocampal CA1 neurons up to 10 min of ischemia, its efficacy at 15 min ischemia is exhausted. However, protective impact of postconditioning in less-sensitive neuronal populations (cortex and striatum) is very good after such a damaging insult like 15 min ischemia. This statement also means that up to 15 min of ischemia, postconditioning does not induce cumulation of injuries produced by the first and the second stress.

Attenuation of ischemia and/or reperfusion injury during myocardial infarction using mild hypothermia in rats: An immunohistochemical study of Bcl-2, Bax, Bak and TUNEL

The aim of the present study was to determine the beneficial effect of mild hypothermia during ischemia and/or reperfusion injury in myocardial infarction. Sprague-Dawley rats (400 +/- 20 g) were subjected to 30 min occlusion of the left coronary artery followed by 24 h reperfusion. Rats were divided into normothermic (NT; 37 degrees C) and hypothermic (HT; 34 degrees C) groups. In the HT group hypothermia was maintained during coronary occlusion and continued for 30 min following reperfusion. Histological analysis revealed dead cardiomyocytes and polymorphonuclear neutrophil infiltration after 24 h. Myocardial infarction, measured using an image analyzer, showed that the percentage area of infarction was significantly decreased in the HT group. Immunohistochemical analysis was carried out using antibodies against Bcl-2, Bax and Bak. DNA fragments were labeled in situ using the 3'-OH end-labeling method (TUNEL). In the HT group Bcl-2 was induced in many myocytes, whereas Bax and Bak were induced in only a few myocytes. A higher number of TUNEL-positive cells were recorded in the NT group than in the HT group, but these were more thinly scattered in the HT group. The expression pattern revealed that many myocytes could survive at the border zone in the HT group; in contrast, few myocytes in the NT group were able to survive. Our results suggest that mild hypothermia selectively interferes with, and mitigates, reperfusion injury.

Neurophysiological monitoring, magnetic resonance imaging, and histological assays confirm the beneficial effects of moderate hypothermia after epidural focal mass lesion development in rodents

OBJECTIVE

To assess the effects of moderate intraischemic hypothermia on neurophysiological parameters in an epidural balloon compression model in rats and to correlate the results with magnetic resonance imaging and histological findings.

METHODS

Neurophysiological monitoring included laser Doppler flow, tissue partial oxygen pressure, and intracranial pressure measurements and electroencephalographic assessments during balloon expansion, sustained inflation, and reperfusion. Moderate intraischemic cooling of animals was extended throughout the reperfusion period, and results were compared with those for normothermic animals. Moreover, histological morphometric and magnetic resonance imaging volumetric analyses of the lesions were performed.

RESULTS

Laser Doppler flow decreased slightly during ischemia (P < 0.05) in animals treated with hypothermia, and flow values demonstrated complete reperfusion, compared with incomplete flow restoration in untreated animals (P < 0.05). During ischemia, the tissue partial oxygen pressure was less than 4.3 mm Hg in both groups. After reperfusion, values returned to the normal range in both groups, but the tissue partial oxygen pressure in hypothermic animals was significantly higher (P = 0.042) and demonstrated 19% higher values, compared with normothermic animals, before rewarming. Moderate hypothermia attenuated a secondary increase in intracranial pressure (P < 0.05), and electroencephalographic findings indicated a trend toward faster recovery (P > 0.05) after reperfusion. Lesion size was reduced by 35% in magnetic resonance imaging volumetric evaluations and by 24.5% in histological morphometric analyses.

CONCLUSION

Intraischemic hypothermia improves cerebral microcirculation, attenuates a secondary increase in intracranial pressure, facilitates electroencephalographic recovery, and reduces the lesion size.

The Effects of Early Post-Traumatic Hyperthermia in Female and Ovariectomized Rats

Episodes of post-traumatic hyperthermia commonly occur in the head-injured patient population. Although post-traumatic hyperthermia has been shown to worsen outcome in experimental studies using male rats, the consequences of secondary hyperthermia following traumatic brain injury (TBI) have not been investigated in female animals. Thus, the purpose of this study was to examine the effects of post-traumatic hyperthermia after fluid-percussion (F-P) brain injury in intact and ovariectomized female rats. Thirty-eight female Sprague-Dawley rats were used in these experiments. Intact female rats underwent TBI followed 30 min later by a 4-h period of normothermia (37 degrees C) or brain hyperthermia (40 degrees C). Female rats that had been ovariectomized 10 days prior to TBI were also traumatized and followed by a period of normothermia or hyperthermia. At 72 h after TBI, rats were perfusion-fixed for quantitative histopathological and immunocytochemical evaluation. Following normothermic TBI, intact female rats demonstrated significantly smaller contusion volumes, decreased frequency of axonal beta-amyloid precursor protein (beta-APP) profiles, and greater numbers of NeuN-positive cortical neurons compared to traumatized ovariectomized females. Although post-traumatic hyperthermia increased contusion volume, cortical neuronal cell death and axonal damage in both intact and ovariectomized female groups, the effects of the induced hyperthermic period were more pronounced in ovariectomized animals. These findings demonstrate for the first time that post-traumatic hyperthermia worsens histopathological outcome in female rats, and that neural hormones, including estrogen and progesterone, may protect against secondary hyperthermic insults.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Therapeutic hypothermia

Hypothermia is common during anaesthesia and surgery owing to anaesthetic-induced inhibition of thermoregulatory control. Perioperative hypothermia is associated with numerous complications. However, for certain patient populations, and under specific clinical conditions, hypothermia can provide substantial benefits. Lowering core temperature to 32-34 degrees C may reduce cell injury by suppressing excitotoxins and oxygen radicals, stabilizing cell membranes, and reducing the number of abnormal electrical depolarizations. Evidence from animal studies indicates that even mild hypothermia provides substantial protection against cerebral ischaemia and myocardial infarction. Mild hypothermia has been shown to improve outcome after cardiac arrest in humans. Randomized trials are in progress to evaluate the potential benefits of mild hypothermia during aneurysm clipping and after stroke or acute myocardial infraction. However, as hypothermia can cause unwanted side-effects, further research is needed to better quantify the risks and benefits of therapeutic hypothermia.

Role of protein synthesis in the ischemic tolerance acquisition induced by transient forebrain ischemia in the rat

Although ischemic preconditioning of the heart and brain is a well-documented neuroprotective phenomenon, the mechanism underlying the increased resistance to severe ischemia induced by a preceding mild ischemic exposure remains unclear. In this study we have determined the effect of ischemic preconditioning on ischemia/reperfusion-associated translation inhibition in the neocortex and hippocampus of the rat. We studied the effect of the duration on the sublethal ischemic episode (3, 4, 5 or 8 min), as well as the amount of time elapsed between sublethal and lethal ischemia on the cell death 7 days after the last ischemic episode. In addition, the rate of protein synthesis in vitro and expression of the 72-kD heat shock protein (hsp) were determined under the different experimental conditions. Our results suggest that two different mechanisms are essential for the acquisition of ischemic tolerance, at least in the CA1 sector of hippocampus. The first mechanism implies a highly significant reduction in translation inhibition after lethal ischemia, especially at an early time of reperfusion, in both vulnerable and nonvulnerable neurons. For the acquisition of full tolerance, a second mechanism, highly dependent on the time interval between preconditioning (sublethal ischemia) and lethal ischemia, is absolutely necessary; this second mechanism involves synthesis of protective proteins, which prevent the delayed death of vulnerable neurons.

Effect of mild hypothermia on focal cerebral ischemia. Review of experimental studies

The purposes of this review are to clarify the effect of hypothermia therapy on focal cerebral ischemia in rats, and to consider the relevancy of its application to human focal cerebral ischemia. Since 1990, 26 reports confirming the brain-protecting effect of hypothermia in rat focal cerebral ischemia models have been published. Seventy-four experimental groups in these 26 reports were classified as having transient middle cerebral arterial occlusion (MCAO) with mild hypothermia (group A; 43 groups), permanent MCAO with mild hypothermia (group B; 14 groups), permanent MCAO with deep hypothermia (group C; 8 groups) and transient or permanent MCAO with mild hyperthermia (group D; 9 groups). The results were evaluated as the % infarct volume change caused by hypothermia or hyperthermia compared with the infarct volume in normothermic animals. The effectiveness was confirmed in 36 (83%) of the 43 groups in group A, 10 (71%) of the 14 in group B, and six (75%) of the eight in group C. The infarct volume of eight of the nine groups in group D was markedly aggravated. The percent infarct volume change was 55.3% +/- 27.1% in group A, 57.6% +/- 24.7% in group B, 60.8% +/- 45.5% in group C, and 189.7% +/- 89.4% in group D. For effective reduction of the infarct volume, hypothermia should be started during ischemia or within 1 h, at latest, after the beginning of reperfusion in the rat transient MCAO model. However, it is not clear whether this neuroprotective effect of hypothermia can also be observed in the chronic stage, such as several months later. Keeping the body temperature normothermic in order to avoid mild hyperthermia seems to be rather important for not aggravating cerebral infarction. Clinical randomized studies on the efficacy of mild hypothermia for focal cerebral ischemia and sophisticated mild hypothermia therapy techniques are mandatory.

Effect of intra-ischemic hypothermia on the expression of c-Fos and c-Jun, and DNA binding activity of AP-1 after focal cerebral ischemia in rat brain

It is unknown whether immediate early gene (IEG) induction and subsequent late gene regulation after ischemia is beneficial or deleterious. The aim of this study was to examine the effect of hypothermia on expression of c-Fos and c-Jun, and AP-1 DNA binding activity, after transient focal cerebral ischemia in rat brain, and clarify the role of IEGs and AP-1 after insults. Male Wistar rats underwent right middle cerebral artery occlusion for 1 h with the intraluminal suture method. During ischemia, animals were assigned to either normothermic (NT) or hypothermic (HT) groups. In the NT group, brain temperature was observed to spontaneously increase to 40 degrees C during ischemia. In the HT group, brain temperature decreased to 30 degrees C. Infarct volume in cortex was decreased in the HT group, compared with that in the NT group (P<0.001). Increased c-Fos immunoreactivity in the cortex was observed at 3 h after reperfusion in the HT, but not the NT group, while c-Jun expression was not affected by HT treatment. There was also a significant increase in AP-1 DNA binding activity at 3 h in the HT group when compared to the NT group (P<0.01). In conclusion, hypothermia decreased cerebral infarction in association with early increases in c-Fos expression and AP-1 DNA binding activity in peri-infarct cortex. It remains to be established whether such responses are a cause or consequence of cell survival, but these results clearly establish that altered transcription is a key feature of tissue spared following hypothermic focal ischemia.

Molecular mechanisms of cerebral ischemia-induced neuronal death

The mode of neuronal death caused by cerebral ischemia and reperfusion appears on the continuum between the poles of catastrophic necrosis and apoptosis: ischemic neurons exhibit many biochemical hallmarks of apoptosis but remain cytologically necrotic. The position on this continuum may be modulated by the severity of the ischemic insult. The ischemia-induced neuronal death is an active process (energy dependent) and is the result of activation of cascades of detrimental biochemical events that include perturbion of calcium homeostasis leading to increased excitotoxicity, malfunction of endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, alteration in proapoptotic gene expression, and activation of the effector cysteine proteases (caspases) and endonucleases leading to the final degradation of the genome. In spite of strong evidence showing that brain infarction can be reduced by inhibiting any one of the above biochemical events, such as targeting excitotoxicity, up-regulation of an antiapoptotic gene, or inhibition of a down-stream effector caspase, it is becoming clear that targeting a single gene or factor is not sufficient for stroke therapeutics. An effective neuroprotective therapy is likely to be a cocktail aimed at all of the above detrimental events evoked by cerebral ischemia and the success of such therapeutic intervention relies upon the complete elucidation of pathways and mechanisms of the cerebral ischemia-induced active neuronal death.

Long term production of reactive oxygen species during perinatal asphyxia in the rat central nervous system: effects of hypothermia

The formation of oxygen-derived free radicals in hypoxic and ischemic/reperfused brains has been proposed as an important step that links brain injury to neuronal death. Previously, we have demonstrated that reactive oxygen species (ROS) production was significantly increased in rat neostriatum during acute perinatal asphyxia (PA) in pups. In this article, we have studied the time course of ROS production in the neostriatum and neocortex of adult rats subjected to PA using electron spin resonance spectrometry (ESR) in order to record ROS production. Further more, we analyzed the actions of hypothermia on ROS release in pups and adult rats. We used for this study 6-month-old rats that suffered sub-severe and severe PA when they were pups. The most significant production of ROS was detected either in the neostriatum or neocortex at 19 and 20 min of PA. Hypothermia during 20 and 100 min at 15 degrees C prevented ROS formation either in pups and adult rats. These data further support the concept that free radicals may contribute to the brain injury alterations and that hypothermia can prevent long-term sequelae induced by PA.

Quantitative evaluation of the neuroprotective effects of hypothermia ranging from 34 degrees C to 31 degrees C on brain ischemia in gerbils and determination of the mechanism of neuroprotection

OBJECTIVE

The present study was designed to determine whether the predominant factor responsible for neuroprotection of hypothermia ranging from 31 to 34 degrees C is prolongation of onset of ischemic depolarization or suppression of neuronal injury during ischemic depolarization and to quantitatively determine the neuroprotective effects of hypothermia of 34 degrees C and 31 degrees C.

DESIGN

Prospective animal study.

SETTING

A university research laboratory.

SUBJECTS

Eighty-nine gerbils.

INTERVENTIONS

Bilateral common carotid arteries were occluded for 3-20 mins. The brain temperature was set at 37 degrees C, 34 degrees C, or 31 degrees C before and during ischemic depolarization.

MEASUREMENTS AND MAIN RESULTS

DC potentials were measured in the CA1 region, where histologic evaluation was performed 7 days later. Onset times of ischemic depolarization were 1.3 +/- 0.2, 1.6 +/- 0.4, and 2.4 +/- 0.7 mins at 37 degrees C, 34 degrees C, and 31 degrees C, respectively. The logistic regression curve demonstrated a close relationship between duration of ischemic depolarization and neuronal damage and showed a rightward shift by lowering the brain temperature. In the 37 degrees C, 34 degrees C, and 31 degrees C groups, the durations of ischemic depolarization causing 50% neuronal damage were estimated to be 8.0, 14.2, and 26.0 mins, respectively, and the ischemia times causing 50% neuronal damage were estimated to be 4.9, 8.1, and 14.2 mins, respectively.

CONCLUSIONS

The onset of ischemic depolarization was prolonged in the 34 degrees C and 31 degrees C groups by only 0.3 and 1.1 mins, respectively, compared with that in the 37 degrees C group. Most of the neuroprotection by hypothermia was attributed to the suppression of neuronal injury during ischemic depolarization, suggesting that hypothermia has neuroprotective effects if it is initiated during the ischemic depolarization period. The results also indicate that the neuroprotective effect at 31 degrees C is about three times greater than that at 34 degrees C and that neuronal cells can withstand 2.9 times longer duration of ischemia at 31 degrees C than at 37 degrees C.

Effects of mild and moderate hypothermia on apoptosis in neuronal PC12 cells

BACKGROUND

There is still a possibility that mild hypothermic therapy may be useful as a neuroprotective tool during the intraoperative period, although the mechanism of cerebral protection by mild hypothermia is not well understood. We hypothesized that mild hypothermia may be protective against cerebral ischaemia by inhibiting post-ischaemia apoptosis. In this study, we used serum-deprived PC12 cells as the neuronal apoptotic model and examined the direct effects of mild and moderate hypothermia.

METHODS

Apoptosis was induced by depriving the cell culture medium of serum, which is one of the most representative methods to induce apoptosis, but not necrosis, in PC12 cells. Effects of mild (35 and 33 degrees C) and moderate (31 and 29 degrees C) hypothermia on apoptosis were evaluated. Cytotoxicity (lactate dehydrogenase leakage) and the percentage of apoptotic cells (calculated by flow cytometry with propidium iodide) were evaluated 4 days after induction of apoptosis. As a control, cells without induction of apoptosis were incubated under the same conditions as the apoptosis group.

RESULTS

Without induction at 37 degrees C, cytotoxicity and the percentage of apoptotic cells were over 60 and 90%, respectively. At each temperature examined below 35 degrees C, significant decreases in cytotoxicity and the percentage of apoptotic cells were observed. Mean cytotoxicity at 31 and 29 degrees C was 50.2 (SD 4.2)% and 47.9 (4.4)%, respectively. The percentage of apoptotic cells at 31 and 29 degrees C was 42.5 (7.4)% and 36.5 (7.3)%, respectively. In the control group, cytotoxicity and the percentage of apoptotic cells were significantly higher at 29 degrees C than at 37 degrees C.

CONCLUSIONS

Mild and moderate hypothermia (29-35 degrees C) inhibited apoptosis, although hypothermia below 30 degrees C may induce apoptosis in intact cells.

Pharmacological correction of hypothermic P(50) shift does not alter outcome from focal cerebral ischemia in rats

Hypothermia decreases the arterial PO(2) at which hemoglobin is 50% saturated (P(50)), increasing hemoglobin O(2)-binding affinity. We used RSR13, a synthetic allosteric modifier of hemoglobin that increases P(50), to study the role of altered hemoglobin O(2)-binding affinity in mild hypothermic neuroprotection. RSR13 (150 mg/kg iv) restored P(50) to normothermic values. Rats underwent 70 min of middle cerebral artery occlusion (MCAO) at 30.0, 34.0, or 37.5 degrees C with hemoglobin saturation held at 98-100%. The 34.0 degrees C group received RSR13 or vehicle before ischemia. After 7 days of recovery, infarct volumes were reduced in all hypothermic groups, without evidence of a detrimental effect on infarct size or neurological score as a result of P(50) correction. To examine for a beneficial effect of P(50) correction, ischemia duration was increased to 120 min in rats maintained at 34.0 degrees C. Correction of P(50) by RSR13 did not alter cerebral infarct sizes or neurological scores. The decrease in P(50), caused by mild hypothermia, could not be associated with infarct size or neurological deficit resulting from ischemic brain hypoxia in rats.

Changes in the phosphorylation of initiation factor eIF-2alpha, elongation factor eEF-2 and p70 S6 kinase after transient focal cerebral ischaemia in mice

Mice were subjected to 60 min occlusion of the left middle cerebral artery (MCA) followed by 1-6 h of reperfusion. Tissue samples were taken from the MCA territory of both hemispheres to analyse ischaemia-induced changes in the phosphorylation of the initiation factor eIF-2alpha, the elongation factor eEF-2 and p70 S6 kinase by western blot analysis. Tissue sections from additional animals were taken to evaluate ischaemia-induced changes in global protein synthesis by autoradiography and changes in eIF-2alpha phosphorylation by immunohistochemistry. Transient MCA occlusion induced a persistent suppression of protein synthesis. Phosphorylation of eIF-2alpha was slightly increased during ischaemia, it was markedly up-regulated after 1 h of reperfusion and it normalized after 6 h of recirculation despite ongoing suppression of protein synthesis. Similar changes in eIF-2alpha phosphorylation were induced in primary neuronal cell cultures by blocking of endoplasmic reticulum (ER) calcium pump, suggesting that disturbances of ER calcium homeostasis may play a role in ischaemia-induced changes in eIF-2alpha phosphorylation. Dephosphorylation of eIF-2alpha was not paralleled by a rise in levels of p67, a glycoprotein that protects eIF-2alpha from phosphorylation, even in the presence of active eIF-2alpha kinase. Phosphorylation of eEF-2 rose moderately during ischaemia, but returned to control levels after 1 h of reperfusion and declined markedly below control levels after 3 and 6 h of recirculation. In contrast to the only short-lasting phosphorylation of eIF-2a and eEF-2, transient focal ischaemia induced a long-lasting dephosphorylation of p70 S6 kinase. The results suggest that blocking of elongation does not play a major role in suppression of protein synthesis induced by transient focal cerebral ischaemia. Investigating the factors involved in ischaemia-induced suppression of the initiation step of protein synthesis and identifying the underlying mechanisms may help to further elucidate those disturbances directly related to the pathological process triggered by transient cerebral ischaemia and leading to neuronal cell injury.

Perinatal brain injury

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 favor of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralization, 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 channels, 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 depolarization. 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 preischemic 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 postischemic 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. Interestingly, there is increasing evidence from recent clinical studies that perinatal brain damage is closely associated with ascending intrauterine infection before or during birth. However, a major part of this damage is likely to be of hypoxic-ischemic nature due to LPS-induced effects on fetal cerebral circulation. 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 intravenous administration of magnesium or postischemic induction of cerebral hypothermia.

Role of calcium in neuronal cell injury: which subcellular compartment is involved?

It is widely believed that calcium plays a primary role in the development of neuronal cell injury in different pathological states of the brain. Disturbances of calcium homeostasis may be induced in three different subcellular compartments, the cytoplasm, mitochondria or the endoplasmic reticulum (ER). The traditional calcium hypothesis holds that neuronal cell injury is induced by a marked increase in cytoplasmic calcium activity during stress (e.g., cerebral ischemia). Recently, this hypothesis has been modified, taking into account that under different experimental conditions the extent of cell injury does not correlate closely with calcium load or total calcium influx into the cell, and that neuronal cell injury has been found to be associated with both increases and decreases of cytoplasmic calcium activity. The mitochondrial calcium hypothesis is based on the observation that after a severe form of stress there is a massive influx of calcium ions into mitochondria, which may lead to production of free radicals, opening of the mitochondrial permeability transition (MPT) pore and disturbances of energy metabolism. However, it has still to be established whether drugs such as cyclosporin A are neuroprotective through their effect on MPT or through the blocking of processes upstream of MPT. The ER calcium hypothesis arose from the observation that ER calcium stores are depleted after severe forms of stress, and that the response of cells to disturbances of ER calcium homeostasis (activation of the expression of genes coding for ER resident stress proteins and suppression of the initiation of protein synthesis) resembles their response to a severe form of stress (e.g., transient ischemia) implying common underlying mechanisms. Elucidating the exact mechanisms of calcium toxicity and identifying the subcellular compartment playing the most important role in this pathological process will help to evaluate strategies for specific therapeutic intervention.

Immunohistochemical expression of Bcl-2, Bax and cytochrome c following focal cerebral ischemia and effect of hypothermia in rat

Recent studies suggest that mild hypothermia significantly alleviate damage following cerebral ischemia though the precise mechanism is poorly defined. In the present study, middle cerebral artery occlusion (MCAo) was induced in Sprague-Dawley (SD) rats for 1 h followed by varying periods of reperfusion. Cerebral infarcts identified by hematoxylin & eosin (H&E) staining revealed extensive lesion in normothermic (NT) 37 degrees C and small lesion in hypothermic (HT) 33 degrees C group of rats. Immunohistochemical analysis revealed Bcl-2 was induced in many neurons of HT group, while Bax and cytochrome c was induced in few neurons. In situ detection of DNA fragmentation using 3'-OH end labeling method (terminal dUTP nick-end labelling (TUNEL)) indicated, higher number of TUNEL-positive cells in NT group, but significantly decreased in HT group. The expression pattern revealed many neurons at the penumbra region could survive in HT group whereas, many neurons are committed to die in NT group. Our results suggest that hypothermia is selectively interfering at more than one place and providing protection.

Combination of intraischemic and postischemic hypothermia provides potent and persistent neuroprotection against temporary focal ischemia in rats

BACKGROUND AND PURPOSE

It is not known whether a combination of intraischemic and postischemic mild hypothermia provides extra neuroprotection and if so, whether the neuroprotection is persistent.

METHODS

Sixty-eight Sprague-Dawley rats were used. In group 1, ischemia and reperfusion were performed under normothermic (N) conditions (control, N-N). In group 2, ischemia was induced and maintained under hypothermic conditions (33 degrees C for 2 hours) and reperfusion was performed under normothermic conditions, H-N. In group 3, both ischemia and reperfusion were performed under hypothermic conditions for an additional 21 hours after the surgery, H-22H. In group 4, ischemia was induced and maintained under hypothermic conditions and reperfusion was performed under hypothermic conditions only for the initial 3 hours (H-3H). In group 5, ischemia was induced and maintained under normothermic conditions and reperfusion was performed under hypothermic conditions (33 degrees C) (N-22H). All rats were perfused 48 hours after the induction of ischemia. In addition, the normothermic or hypothermic therapy used for groups 1, 3, and 4 was performed again, and these rats were killed 30 days after the induction of ischemia. Furthermore, neurological deficits were monitored in groups N-N and H-22H for 4 weeks.

RESULTS

In the H-3H and H-22H groups, the total infarct volume was significantly reduced by 41% or 66%, respectively, assessed 48 hours after ischemia. The significant reduction in group H-22H was again confirmed 30 days after ischemia, ie, 50% reduction was observed. In contrast, the reduction in group H-3H (31%) was not significant. The neurological deficits were significantly more severe in the N-N group than in the H-22H group during week 4.

CONCLUSIONS

The neuroprotective effects against temporary focal ischemia evaluated by infarct volume and neurological functions by the combination therapy with intraischemic and prolonged postischemic mild hypothermia were persistent in rats. Appropriate design of mild hypothermia therapy extending into the late reperfusion period is important to maximize the neuroprotective effects of hypothermia.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

A novel Na+ and Ca2+ channel blocker, T-477, prevents brain edema following microsphere-induced permanent occlusion of cerebral arterioles in rats

One of the most common acute complications of stroke is brain edema. Treatment of edema is recommended when the condition of the patients is deteriorating. The present study was undertaken to evaluate the effect of T-477 [(R)-(+)-2-(4-chlorophenyl)-2,3-dihydro-4-diethyl aminoacetyl-4H-1,4-benzorthiazine hydrochloride], a novel neuronal Na+ and Ca2+ channel blocker, on brain edema in rats. Cerebral ischemia was induced by intra-arterial infusion of 1000 microspheres into the forebrain of freely moving rats, resulting in brain edema. T-477 was intravenously infused continuously for 24 h or twice for 3 h with a 3-h interval between infusions immediately after microsphere injection. T-477 dose-dependently inhibited the increase in brain water content by both infusion procedures; the inhibition was statistically significant at doses of 25 mg/kg per 24 h and 14 mg/kg per 9 h. Additionally, infusion of T-477 at a dose of 14 mg/kg per 9 h significantly inhibited the decrease in K content and the increase in Ca content of the forebrain. In conclusion, T-477 prevents brain edema following microsphere-induced cerebral embolism in rats.

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.

Neuroprotective effect of mild hypothermia cannot be explained in terms of a reduction of glutamate release during ischemia

An exogenous glutamate injection into the hypothermic hippocampal CA1 during 5-min ischemia produced the same extent of extracellular glutamate levels as observed in the normothermic CA1 during 5-min ischemia; however, neuronal death was not induced in the hypothermic CA1. Glutamate is released excessively into the extracellular space during ischemia, and is thought to induce brain injury by its neurotoxicity. It has been reported that the massive glutamate release is reduced by mild hypothermia, and it has been proposed that the reduction of ischemia-induced glutamate release exerts the neuroprotective effect on postischemic neuronal death. In the present study, to determine whether the neuroprotective effect of mild hypothermia on postischemic hippocampal CA1 neuronal death is due to the reduction of ischemia-induced glutamate release, gerbils were subjected to 5-min ischemia under hypothermic condition at 31 degrees C and were simultaneously injected exogenously with L-glutamate, so that the hypothermic CA1 around a microdialysis probe was exposed to the same extracellular glutamate levels as seen during normothermic ischemia, and the histological outcome was examined. An injection with 1 mM L-glutamate into the hypothermic CA1 during 5-min ischemia produced a similar extent of increased glutamate (17-fold increase) to that observed in the normothermic CA1 during 5-min ischemia (16-fold increase). However, neuronal death was not induced in the hypothermic CA1. This result indicates that the neuroprotective effect of mild hypothermia cannot be explained in terms of a reduction of glutamate release during ischemia.

Differential regulation of apoptosis-related genes in resistant and vulnerable subfields of the rat epileptic hippocampus

Animals exposed to kainic acid (KA) induced status epilepticus display a striking pattern of selective neuronal vulnerability in the hippocampus. Neurons in the hilus/CA3 and CA1 subfields appear particularly sensitive whereas dentate gyrus (DG) granule cells are resistant. The molecular basis for this differential susceptibility remains largely unknown. Recently, an involvement of nitric oxide, c-Jun amino-terminal kinases (JNK) and interleukin-1 beta converting enzyme (ICE)-related proteases has been proposed in KA induced neuronal cell death. In the present study, we have determined the regional expression of transcripts for two modulating genes operating in these pathways, i.e., the endogenous protein inhibitor of neuronal nitric oxide synthase (PIN), and a cytoplasmic inhibitor of the JNK signal transduction pathway, designated JNK interacting protein-1 (JIP-1) and of the gene for the apoptosis-executing protease Caspase-3 in KA-treated animals. The expression of PIN and JIP-1 was found significantly upregulated in granule cells of the resistant DG. In contrast, an induction of the ICE-related protease Caspase-3 was observed in vulnerable hippocampal regions, i.e. CA1, CA3 and hilus. These results point towards PIN and JIP-1 as antiapoptotic factors contributing to selective resistance of granule cells, whereas Caspase-3 may be involved in cell death of hippocampal CA1, CA3 and hilar neurons in the kainate epilepsy model.

Alterations in protein tyrosine kinase pathways following retinal vein occlusion in the rat

PURPOSE

To determine whether an experimental retinal vein occlusion in the rat activates protein tyrosine kinase pathways and increases angiogenic growth factors in the retina.

METHODS

Retinal vein occlusion (RVO) was induced in the rat retina with argon laser photocoagulation. Retinas were collected at 2 days, 1, 2, and 4 weeks after RVO and divided into halves: one half represented an area within the distribution of the occluded vein [RVO(IN)] and the other half represented an area outside the distribution of the occluded vein [RVO(OUT)]. RVO(IN) and (OUT) were examined by western blot analysis of tyrosine-phosphorylated proteins, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and 3 signal proteins in the tyrosine kinase pathways: phospholipase Cgamma (PLCgamma), phosphatidylinositol 3-kinase (PI3K), and mitogen-activated protein kinase (MAPK).

RESULTS

RVO caused a severe capillary nonperfusion in RVO(IN). Overall tyrosine-phosphorylated proteins were increased after RVO, especially in RVO(IN) at 2 days and 1 week. VEGF and bFGF were markedly increased in RVO(IN) at 2 days and 1 week. Tyrosine-phosphorylated PLCgamma, PI3K, and MAPK were also increased in RVO(IN) at these time points.

CONCLUSIONS

RVO caused an increase in overall protein tyrosine phosphorylation in the rat retina. This increase was associated with an increase in angiogenic growth factors (VEGF and bFGF). These results suggest that protein tyrosine kinase pathways are activated during retinal ischemia and may play a role in mitogenesis of vascular endothelial cells and other responses in the retina after RVO.

Disturbances of the functioning of endoplasmic reticulum: a key mechanism underlying neuronal cell injury?

Cerebral ischemia leads to a massive increase in cytoplasmic calcium activity resulting from an influx of calcium ions into cells and a release of calcium from mitochondria and endoplasmic reticulum (ER). It is widely believed that this increase in cytoplasmic calcium activity plays a major role in ischemic cell injury in neurons. Recently, this concept was modified, taking into account that disturbances occurring during ischemia are potentially reversible: it then was proposed that after reversible ischemia, calcium ions are taken up by mitochondria, leading to disturbances of oxidative phosphorylation, formation of free radicals, and deterioration of mitochondrial functions. The current review focuses on the possible role of disturbances of ER calcium homeostasis in the pathologic process culminating in ischemic cell injury. The ER is a subcellular compartment that fulfills important functions such as the folding and processing of proteins, all of which are strictly calcium dependent. ER calcium activity is therefore relatively high, lying in the lower millimolar range (i.e., close to that of the extracellular space). Depletion of ER calcium stores is a severe form of stress to which cells react with a highly conserved stress response, the most important changes being a suppression of global protein synthesis and activation of stress gene expression. The response of cells to disturbances of ER calcium homeostasis is almost identical to their response to transient ischemia, implying common underlying mechanisms. Many observations from experimental studies indicate that disturbances of ER calcium homeostasis are involved in the pathologic process leading to ischemic cell injury. Evidence also has been presented that depletion of ER calcium stores alone is sufficient to activate the process of programmed cell death. Furthermore, it has been shown that activation of the ER-resident stress response system by a sublethal form of stress affords tolerance to other, potentially lethal insults. Also, disturbances of ER function have been implicated in the development of degenerative disorders such as prion disease and Alzheimer's disease. Thus, disturbances of the functioning of the ER may be a common denominator of neuronal cell injury in a wide variety of acute and chronic pathologic states of the brain. Finally, there is evidence that ER calcium homeostasis plays a key role in maintaining cells in their physiologic state, since depletion of ER calcium stores causes growth arrest and cell death, whereas cells in which the regulatory link between ER calcium homeostasis and protein synthesis has been blocked enter a state of uncontrolled proliferation.

Mild hypothermia--a revived countermeasure against ischemic neuronal damages

Although hypothermia as a means of cerebral protection against and resuscitation from ischemic damage has a history of approximately six decades, extensive studies, both in basic and clinical fields, on the mechanisms, effects and methods of mild hypothermia at temperatures no less than 31 degrees C have started only in the last decade. In experiments on rodents, hypothermia in the postischemic period that is introduced up to several hours after reperfusion and is maintained for one day followed by a slow rewarming, significantly protects hippocampal neurons against damage. The mode of action of hypothermia is apparently non-specific and multi-focal in widely progressing cascade reactions in ischemic cells; namely, suppressing: (1) glutamate surge followed by; (2) intraneuronal calcium mobilization; (3) sustained activation of glutamate receptors; (4) dysfunction of blood brain barrier; (5) proliferation of microglial cells; and (6) production of superoxide anions and nitric oxide. In addition, mild hypothermia modulates processes in ischemic condition at the level of cell nucleus, such as the binding of transcription factor AP-1 to DNA, and ameliorates the depression of protein synthesis. This non-specific and widely affecting manner might explain why hypothermia is superior to any medicine developed. Recent clinical trials of mild hypothermia in various individual institutions have revealed significantly beneficial outcomes in some cases, along with an accumulation of practical knowledge of techniques and treatments. Large scale randomized studies involving multiple institutions as well as exchange of informations and ideas are needed for further development of hypothermia treatment.

Time-dependent changes in the ischemic forebrain following the microsphere-induced permanent occlusion of cerebral arterioles in rats

To evaluate the progression of brain edema without modification by the effect of anesthetics, we examined the local and permanent ischemia model in unanesthetized rats. The forebrain embolism was induced by intra-arterial infusion of microspheres of 50-microm diameter in freely moving rats. From 2 to 48 hr following the injection, the water-, Na- and Ca-contents progressively increased while the K content decreased in the microsphere-injected hemisphere. After the 3rd day, the water- and Na-contents gradually decreased and returned to the normal level on the 14th day. In contrast, the Ca level remained elevated even on the 56th day. The animals showed signs of neurological deficits 24 hr after the injection. In histopathological examination, large infarct areas were present in the microsphere-injected hemisphere after 24 to 48 hr. One to two weeks later, the lateral ventricle was expanded. Eight weeks after the injection, the ventricle remained expanded and newly developed infarct areas were observed in a scattered pattern around the fibrotic area. The results show the close correlation between the development of edema and the increase/decrease of Na/K contents from the onset to the recovery from edema, and their changes are similar to those in human stroke. This model enables us to evaluate not only the acute ischemic insult but also the chronic changes of the forebrain following the stroke.

Characterization of neuroprotection from excitotoxicity by moderate and profound hypothermia in cultured cortical neurons unmasks a temperature-insensitive component of glutamate neurotoxicity

Although profound hypothermia has been used for decades to protect the human brain from hypoxic or ischemic insults, little is known about the underlying mechanism. We therefore report the first characterization of the effects of moderate (30 degrees C) and profound hypothermia (12 degrees to 20 degrees C) on excitotoxicity in cultured cortical neurons exposed to excitatory amino acids (EAA; glutamate, N-methyl-D-aspartate [NMDA], AMPA, or kainate) at different temperatures (12 degrees to 37 degrees C). Cooling neurons to 30 degrees C and 20 degrees C was neuroprotective, but cooling to 12 degrees C was toxic. The extent of protection depended on the temperature, the EAA receptor agonist employed, and the duration of the EAA challenge. Neurons challenged briefly (5 minutes) with all EAA were protected, as were neurons challenged for 60 minutes with NMDA, AMPA, or kainate. The protective effects of hypothermia (20 degrees and 30 degrees C) persisted after rewarming to 37 degrees C, but rewarming from 12 degrees C was deleterious. Surprisingly, however, prolonged (60 minutes) exposures to glutamate unmasked a temperature-insensitive component of glutamate neurotoxicity that was not seen with the other, synthetic EAA; this component was still mediated via NMDA receptors, not by ionotropic or metabotropic non-NMDA receptors. The temperature-insensitivity of glutamate toxicity was not explained by effects of hypothermia on EAA-evoked [Ca2+]i increases measured using high- and low-affinity Ca2+ indicators, nor by effects on mitochondrial production of reactive oxygen species. This first characterization of excitotoxicity at profoundly hypothermic temperatures reveals a previously unnoticed feature of glutamate neurotoxicity unseen with the other EAA, and also suggests that hypothermia protects the brain at the level of neurons by blocking, rather than slowing, excitotoxicity.