Transient hyperthermia protects against subsequent forebrain ischemic cell damage in the rat

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.

Modulation of renal cell injury by heat shock proteins: lessons learned from the immature kidney

The mechanisms that underlie tolerance to injury in immature animals and tissues have been a subject of interest since 1670. Observations in neonatal units that premature infants are less prone to develop acute renal failure than adults in critical care units have prompted a series of investigations. Although initially attributed to metabolic adaptation such as increased glycolytic capacity and preservation of high energy phosphate, more recent studies have indicated a prominent role for the heat shock response. Observed modulations of injury by heat shock proteins in the immature kidney have significant implications for advancement of our understanding of renal cell injury in both adults and children.

Heat shock inhibits both aminoglycoside- and cisplatin-induced sensory hair cell death

Human hearing and balance impairments are often attributable to the death of sensory hair cells in the inner ear. These cells are hypersensitive to death induced by noise exposure, aging, and some therapeutic drugs. Two major classes of ototoxic drugs are the aminoglycoside antibiotics and the antineoplastic agent cisplatin. Exposure to these drugs leads to hair cell death that is mediated by the activation of specific apoptotic proteins, including caspases. The induction of heat shock proteins (HSPs) in response to cellular stress is a ubiquitous and highly conserved response that can significantly inhibit apoptosis in some systems by inhibiting apoptotic proteins. Induction of HSPs occurs in hair cells in response to a variety of stimuli. Given that HSPs can directly inhibit apoptosis, we hypothesized that heat shock may inhibit apoptosis in hair cells exposed to ototoxic drugs. To test this hypothesis, we developed a method for inducing HSP expression in the adult mouse utricle in vitro. In vitro heat shock reliably produces a robust up-regulation of HSP-70 mRNA and protein, as well as more modest up-regulation of HSP-90 and HSP-27. The heat shock does not result in death of hair cells. Heat shock has a significant protective effect against both aminoglycoside- and cisplatin-induced hair cell death in the utricle preparation in vitro. These data indicate that heat shock can inhibit ototoxic drug-induced hair cell death, and that the utricle preparation can be used to examine the molecular mechanism(s) underlying this protective effect.

Cerebral preconditioning and ischaemic tolerance

Adaptation is one of physiology's fundamental tenets, operating not only at the level of species, as Darwin proposed, but also at the level of tissues, cells, molecules and, perhaps, genes. During recent years, stroke neurobiologists have advanced a considerable body of evidence supporting the hypothesis that, with experimental coaxing, the mammalian brain can adapt to injurious insults such as cerebral ischaemia to promote cell survival in the face of subsequent injury. Establishing this protective phenotype in response to stress depends on a coordinated response at the genomic, molecular, cellular and tissue levels. Here, I summarize our current understanding of how 'preconditioning' stimuli trigger a cerebroprotective state known as cerebral 'ischaemic tolerance'.

A Sick Eye in a Sick Body? Systemic Findings in Patients with Primary Open-angle Glaucoma

Despite intense research, the pathogenesis of primary open-angle glaucoma (POAG) is still not completely understood. There is ample evidence for a pathophysiological role of elevated intraocular pressure; however, several systemic factors may influence onset and progression of the disease. Systemic peculiarities found in POAG include alterations of the cardiovascular system, autonomic nervous system, immune system, as well as endocrinological, psychological, and sleep disturbances. An association between POAG and other neurodegenerative diseases, such as Alzheimer disease and Parkinson disease, has also been described. Furthermore, the diagnosis of glaucoma can affect the patient's quality of life. By highlighting the systemic alterations found in POAG, this review attempts to bring glaucoma into a broader medical context.

Effect of repetitive ischemic preconditioning on spinal cord ischemia in a rabbit model

A completely randomized controlled study based on a rabbit model was designed to study the effect of repetitive ischemic preconditioning (IPC) on a spinal cord ischemic reperfusion injury. Twenty four white adult Japanese rabbits were randomly assigned to one of the 3 groups (n = 8 per group): Group I: sham-operation group, Group II: ischemic reperfusion group, and, Group III: IPC group. Spinal cord ischemia was induced by infra-renal aortic cross-clamp for 45 min in Group II. Before 45 min ischemia, the rabbits in Group III underwent four cycles of IPC (5 min of ischemia followed by 5 min of reperfusion). Post-operative neurological function, electromyography (EMG) of rear limbs, and spinal cord histopathological changes were measured. The concentrations of calcium, magnesium, copper, and zinc in spinal cord were measured in the 7th day. The neurological function and histopathological changes in Group II were significantly different from those in Group I or Group III (P < 0.05 or 0.01). There was a more significant change of EMG in Group II than that in Group III (P < 0.05). The concentrations of calcium and copper in Group II were significantly higher (P < 0.05 or 0.01), but magnesium and zinc were significantly lower (P < 0.05) than those in Group I. Calcium and copper in Group II were significantly higher (P < 0.05), but zinc was significantly lower (P < 0.01) than those in Group III. In conclusion, repetitive IPC can protect rabbit spinal cord from ischemic reperfusion injury in a timely manner, which is associated with corrections of imbalance of calcium, magnesium, copper, and zinc in the ischemic region.

Mechanisms of Brain Injury after Global Cerebral Ischemia

Cerebral ischemia results in a rapid depletion of energy stores that triggers a complex cascade of cellular events such as cellular depolarization and Ca2+ influx, resulting in excitotoxic cell death. The critical determinant of severity of brain injury is the duration and severity of the ischemic insult and early restoration of CBF. Induced therapeutic hypothermia following CA is the only strategy that has demonstrated improvement in outcomes in prospective, randomized clinical trials. Although pharmacologic neuro-protection has been disappointing thus far in a variety of experimental animal models, further research efforts are directed at using some agents that demonstrate marginal or moderate efficacy in combination with hypothermia. Although the signal transduction pathways and intracellular molecular events during cerebral ischemia and reperfusion are complex, potential therapeutic neuroprotective strategies hold promise for the future.

Effect of acute hypoxic preconditioning on qEEG and functional recovery after cardiac arrest in rats

Acute hypoxic preconditioning (AHPC) can confer neuroprotection from global cerebral ischemia such as cardiac arrest. We hypothesize that acute neuroprotection by AHPC will be detected early by quantitative EEG (qEEG) entropy analysis after asphyxial cardiac arrest (aCA). Cerebral ischemia lowers EEG signal randomness leading to low entropy. A qEEG entropy index defined as the duration when the entropy measure is 15% below uninjured baseline entropy is used as a measure of injury. We compared 3 groups of adult Wistar rats: (1) untreated controls that were subjected to 5 min of aCA and were resuscitated (n = 5); (2) AHPC-treated group with 10% FI O2 for 30 min, then 25 min of room air, 5 min of aCA followed by resuscitation (n = 5); and (3) a surgical sham group (no aCA) (n = 3). Functional outcome was assessed by neurodeficit score (NDS) which consisted of level of consciousness, cranial nerve, motor-sensory function, and simple behavioral tests (best = 100 and brain dead = 0). We found that increasing entropy index of injury at 0-5 h from return of spontaneous circulation (ROSC) is associated with worsening NDS at 24 h (linear regression: r = 0.81, P < 0.001). The NDS of the group sham (84.7 +/- 2.8) (mean +/- SEM) and AHPC group (84.6 +/- 2.9, P > 0.05) was better than control injury group (52.2 +/- 8.4, P < 0.05) (ANOVA with Tukey test). We therefore conclude that AHPC confers acute neuroprotection at 24 h, which was detected by qEEG entropy during the first 5 h after injury.

Proteome analysis of cortical neuronal cultures following cycloheximide, heat stress and MK801 preconditioning

Studying endogenous neuroprotective mechanisms induced by preconditioning may provide drug leads to reduce ischemic neuronal death. In this study, we used 2-DE to examine protein expression following cycloheximide, heat stress, and MK801 preconditioning in rat cortical neuronal cultures. Of 150 differentially expressed protein spots selected for identification the protein or tentative protein(s) were identified in 84 cases, representing 50 different proteins. Different protein spots representing the same protein or closely related protein(s) occurred for 21 of the identified proteins and are likely to represent PTMs or proteolytic fragments of the protein. Six protein spots (actin, elongation factor 1-alpha 1, peptidyl-prolyl cis-transisomerase A, Cu/Zn superoxide dismutase, stathmin, tropomyosin) were differentially expressed in all three preconditioning treatments. Twenty-seven protein spots were differentially expressed in two preconditioning treatments, while 51 spots were differentially expressed in one treatment. Three proteins heterogeneous nuclear ribonucleoproteins A2/B1, mitochondrial stress-70 protein, and tropomyosin were detected in control neuronal cultures, but not following one or more preconditioning treatments, while a posttranslational modified form of the voltage dependent anion channel 1 was only detected following cycloheximide preconditioning. In summary, this study has revealed multiple protein changes potentially involved in neuroprotective and neurodamaging pathways, which require further characterization.

Differences in infarct evolution between lipopolysaccharide-induced tolerant and nontolerant conditions to focal cerebral ischemia

OBJECT

Although brain tissue may be protected by previous preconditioning, the temporal evolution of infarcts in such preconditioned brain tissue during focal cerebral ischemia is largely unknown. Therefore, in this study the authors engaged in long-term observation with magnetic resonance (MR) imaging to clarify the difference in lesion evolution between tolerant and nontolerant conditions.

METHODS

Bacterial lipopolysaccharide (LPS; 0.9 mg/kg) was administered intravenously to induce cross-ischemic tolerance. Focal cerebral ischemia was induced 72 hours later in spontaneously hypertensive rats. Serial brain MR images were obtained 6 hours, 24 hours, 4 days, 7 days, and 14 days after ischemia by using a 7.05-tesla unit. Lesion-reducing effects were evident 6 hours after ischemia in the LPS group. Preconditioning with LPS does not merely delay but prevents ischemic cell death by reducing lesion size. Lesion reduction was a sustained effect noted up to 14 days after ischemia. Reduction of local cerebral blood flow (ICBF) in the periinfarct area was significantly inhibited in the LPS group, which was correlated with endothelial nitric oxide synthase (eNOS) expression.

CONCLUSIONS

Significant preservation of ICBF in the periinfarct area, which is relevant to sustained upregulation of eNOS, could be a candidate for the long-term inhibiting effect on infarct evolution in the LPS-induced tolerant state.

Evidence for a Role of Second Pathophysiological Stress in Prevention of Delayed Neuronal Death in the Hippocampal CA1 Region

In ischemic tolerance experiment, when we applied 5-min ischemia 2 days before 30-min ischemia, we achieved a remarkable (95.8%) survival of CA1 neurons. However, when we applied 5-min ischemia itself, without following lethal ischemia, we found out 45.8% degeneration of neurons in the CA1. This means that salvage of 40% CA1 neurons from postischemic degeneration was initiated by the second pathophysiological stress. These findings encouraged us to hypothesize that the second pathophysiological stress used 48 h after lethal ischemia can be efficient in prevention of delayed neuronal death. Our results demonstrate that whereas 8 min of lethal ischemia destroys 49.9% of CAI neurons, 10 min of ischemia destroys 71.6% of CA1 neurons, three different techniques of the second pathophysiological stress are able to protect against both: CA1 damage as well as spatial learning/memory dysfunction. Bolus of norepinephrine (3.1 micromol/kg i.p.) used two days after 8 min ischemia saved 94.2%, 6 min ischemia applied 2 days after 10 min ischemia rescued 89.9%, and an injection of 3-nitropropionic acid (20 mg/kg i.p.) applied two days after 10 min ischemia protected 77.5% of CA1 neurons. Thus, the second pathophysiological stress, if applied at a suitable time after lethal ischemia, represents a significant therapeutic window to opportunity for salvaging neurons in the hippocampal CA1 region against delayed neuronal death.

Heat shock proteins: new keys to the development of cytoprotective therapies

All cells, from bacterial to human, have a common, intricate response to stress that protects them from injury. Heat shock proteins (Hsps), also known as stress proteins and molecular chaperones, play a central role in protecting cellular homeostatic processes from environmental and physiologic insult by preserving the structure of normal proteins and repairing or removing damaged ones. An understanding of the interplay between Hsps and cell stress tolerance will provide new tools for treatment and drug design that maximise preservation or restoration of health. For example, the increased vulnerability of tissues to injury in some conditions, such as ageing, diabetes mellitus and menopause, or with the use of certain drugs,, such as some antihypertensive medications, is associated with an impaired Hsp response. Additionally, diseases that are associated with tissue oxidation, free radical formation, disorders of protein folding, or inflammation, may be improved therapeutically by elevated expression of Hsps. The accumulation of Hsps, whether induced physiologically, pharmacologically, genetically, or by direct administration of the proteins, is known to protect the organism from a great variety of pathological conditions, including myocardial infarction, stroke, sepsis, viral infection, trauma, neurodegenerative diseases, retinal damage, congestive heart failure, arthritis, sunburn, colitis, gastric ulcer, diabetic complications and transplanted organ failure. Conversely, lowering Hsps in cancer tissues can amplify the effectiveness of chemo- or radiotherapy. Treatments and agents that induce Hsps include hyperthermia, heavy metals (zinc and tin), salicylates, dexamethasone, cocaine, nicotine, alcohol, alpha-adrenergic agonists, PPAR-gamma agonists, bimoclomol, geldanamycin, geranylgeranylacetone and cyclopentenone prostanoids. Compounds that suppress Hsps include quercetin (a bioflavinoid), 15-deoxyspergualin (an immunosuppressive agent) and retinoic acid. Researchers who are cognisant of the Hsp-related effects of these and other agents will be able to use them to develop new therapeutic paradigms.

Transient hyperthermia protects against subsequent seizures and epilepsy-induced cell damage in the rat

Many mild preconditioning stress conditions, including physical and metabolic injuries, increase the resistance of neurons to subsequent more severe stresses of the same or different type. This "tolerance phenomenon" lasts one to several weeks, providing a unique opportunity to investigate endogenous neuroprotective mechanisms. The aim of this study was to find a physiological and easily applicable preconditioning stimulus able to confer protection against convulsant-induced neuronal damage and seizures. We found that moderate transient hyperthermic preconditioning markedly reduced kainic-acid-induced neuronal cell loss and attenuated susceptibility to bicuculline-induced seizures. Prevention of cell damage (approximately 50%) was efficient both in vitro in organotypic hippocampal slice cultures and in vivo in adult rats. This protection lasted about 1 week and peaked 3 to 5 days after pretreatment. Unraveling the mechanisms of heat shock preconditioning-induced protection against epilepsy should lead to the development of new therapeutic strategies.

Inhibitory effects of long-term administration of ferulic acid on astrocyte activation induced by intracerebroventricular injection of beta-amyloid peptide (1-42) in mice

Accumulating evidence indicates that glial cells are actively involved in the pathogenesis of Alzheimer's disease. We recently reported protective effects of long-term administration of ferulic acid against learning and memory deficit induced by centrally administered beta-amyloid peptide (Abeta)1-42 in mice. In that report, we found that the Abeta1-42-induced increases in immunoreactivities of glial fibrillary acidic protein, the astrocyte marker, and interleukin(IL)-1beta in the hippocampus are also suppressed by pretreatment with ferulic acid. In the present study, we aimed to further characterize the effect of long-term administration of ferulic acid on the centrally administered Abeta1-42-induced activation of glial cells in mice. Mice were allowed free access to drinking water (control) or water containing ferulic acid (0.006%) for 4 weeks, and then Abeta1-42 (410 pmol) was administered via intracerebroventricular injection. Intracerebroventricularly injected Abeta1-42 induced an increase in immunoreactivities of endothelial nitric oxide synthase (eNOS) and 3-nitrotyrosine (3-NT) in the activated astrocytes in the hippocampus. Pretreatment of ferulic acid for 4 weeks prevented the Abeta1-42-induced increase in eNOS and 3-NT immunoreactivities. Administration of ferulic acid per se induced a transient and slight increase in eNOS immunoreactivity in the hippocampus on day 14, which returned to basal levels on day 28. Intracerebroventricularly injected Abeta1-42 also increased interleukin-1alpha(IL-1alpha) immunoreactivity in the hippocampus, which was also suppressed by pretreatment with ferulic acid. These results demonstrate that long-term administration of ferulic acid induces suppression of the centrallly injected Abeta1-42-induced activation of astrocytes which is suggested to underlie the protective effect of ferulic acid against Abeta1-42 toxicity in vivo.

Expression of Hsp72 in lymphocytes in patients with febrile convulsion

The pathophysiology of febrile convulsion, the most common childhood neurologic disease, remains unclear. In this study, we investigated what role a heat shock protein plays in this disease. We enrolled eight boys and two girls with febrile convulsion and 10 age-matched healthy controls. We did a biosynthetic evaluation of both groups by separating lymphocytes and measuring the expression of heat shock protein 72 before and after heat shock treatment. Before the treatment, both groups were found to have small amounts of constitutive heat shock protein 72. Afterwards, its expression increased in both groups, and no statistical difference was found between the increases in the two groups. In addition, there was no obvious difference in the susceptibility to produce heat shock proteins. However, the febrile convulsion group was found to have a significant decrease in phosphorylation of heat shock protein 72. These results suggest the possible involvement of post-translational modification of heat shock proteins, most likely phosphorylation, in the pathogenesis of febrile convulsion.

Ischemic preconditioning procedure induces behavioral deficits in the absence of brain injury?

Preconditioning describes a phenomenon whereby a sub-injury inducing insult can protect against a later larger injury. Thus, short-term cerebral ischemia can protect against a prolonged ischemia (ischemic preconditioning). This study examines rats undergoing ischemic preconditioning to test whether preconditioning may cause changes in behavior even though they do not cause an identifiable brain lesion. Rats had a transient (15 minutes) middle cerebral artery occlusion or a sham occlusion. Forelimb placing and forelimb use asymmetry tests were used to assess behavioral deficits. Brain histology, microglia activation, heat shock protein and ferritin levels were also examined. Ischemic preconditioning did not cause brain infarction, but induced behavioral changes. There were no significant differences between ischemic preconditioning and sham rats in the two behavioral tests at day one. However, the ischemic preconditioning group showed impaired forelimb placing at days 3, 7 and 14 (p<0.05). That group also had a significant (p<0.05) behavioral deficit in the forelimb use asymmetry test at days 3 and 7 (but not 14). Our present study demonstrated that a behavioral deficit occurred in ischemic preconditioning. This raises the question of whether induction of protective mechanisms by preconditioning stimuli necessarily involves some form of brain injury, detectable by changes in behavior though not by a lesion. This would be consistent with data suggesting that brain injury can initiate mechanisms potentially favorable to neuroplasticity and neuroprotection.

Upregulation of HSP by geranylgeranylacetone protects the cochlear lateral wall from endotoxin-induced inflammation

We investigated whether an acyclic polyisoprenoid antiulcer drug, geranylgeranylacetone (GGA), induces the expression of HSP70 in the rat cochlea. Immunoblotting revealed upregulation of HSP70 in the cochlea at 12 h after transtympanic (local) or oral (systemic) administration of GGA, and this increased at 24 h after administration. Positive immunohistochemical staining of HSP70 was observed in the hair cells, the spiral ganglion, the stria vascularis, the spiral ligament, and the perivascular portion of modiolar vessels. We therefore subsequently studied the effects of GGA as an HSP-inducer on inner ear trauma due to inflammation. Damage to the lateral wall due to inflammation induced by lipopolysaccharide inoculation was protected against by pretreatment with GGA, as assessed physiologically by measurement of cochlear blood flow and morphologically by electron microscopy. The results of the present study suggest that GGA can protect the cochlea against other injuries including those induced by noise, ototoxic drugs, and ischemia by upregulating HSP70.

Heat shock treatment protects osmotic stress-induced dysfunction of the blood-brain barrier through preservation of tight junction proteins

The blood-brain barrier (BBB) is a specialized structure in the central nervous system (CNS), which participates in maintenance of a state of cerebrospinal fluid homeostasis. The endothelial cells of the cerebral capillaries and the tight junctions between them form the basis of the BBB. Research has shown that destruction of the BBB is associated with diseases of the CNS. However, there is little research on how the BBB might be protected. In this study, we used a high osmotic solution (1.6 M D-mannitol) to open the BBB of rats and Evans blue dye as a macromolecular marker. The effect of heat shock treatment was evaluated. The results show that increased synthesis of heat shock protein 72 (Hsp72) was induced in the heated group only. BBB permeability was significantly less in the heat shock-treated group after hyperosmotic shock. The major tight junction proteins, occludin and zonula occludens (ZO)-1, were significantly decreased after D-mannitol treatment in the nonheated group, whereas they were preserved in the heated group. The coimmunoprecipitation studies demonstrated that Hsp72 could be detected in the precipitates of brain extract interacting with anti-ZO-1 antibodies as well as those interacting with anti-occludin antibodies in the heated group. We conclude that the integrity of tight junctions could be maintained by previous heat shock treatment, which might be associated with the increased production of Hsp72.

Induction of neuronal tolerance by electroconvulsive shock in rats subjected to forebrain ischemia

We have examined ischemic tolerance induced by electroconvulsive shock before exposure to forebrain ischemia. Subjects were 40 rats, which were randomly allocated to control, single ECS (sECS), repeated ECS (rECS) or sham group. sECS group and rECS group received ECS only once 2 days before the subsequent 8-min forebrain ischemia and once a day for 9 consecutive days until 2 days before the exposure to ischemia, respectively. Forebrain ischemia was produced by modified bilateral carotid artery occlusion technique. Control group underwent brain ischemia without ECS pretreatment. Sham group received ECS without following exposure to ischemia. Pyramidal cell injury of the hippocampal CA1 sector was microscopically examined on the 7th day after the ischemic exposure or the sham operation. Damage of the pyramidal cells was assessed by the injury ratio, which was ratio of non-viable pyramidal cells to the whole pyramidal cells. The injury ratios of CA1 pyramidal cells in sECS, rECS and control groups were 30.5 +/- 10.8 (n=10), 42.3 +/- 18.4% (n=10) and 90.4 +/- 2.9% (n=9), respectively. The injury ratios in sECS and rECS groups were lower than the ratio in control group (p<0.01), while the ratios of sECS and rECS groups were not different. The pyramidal cells in sham group were intact. Our results indicate that both preconditionings of sECS and rECS have a potency to induce delayed tolerance against temporary forebrain ischemia, though the potency was not different between sECS and rECS. Electroconvulsive shock may be added to the list of preconditioning stimuli to protect brain against ischemic neuronal damage.

A new model of ischemic preconditioning using young adult hippocampal slice cultures

In ischemic preconditioning (IPC), brief sublethal ischemia protects neurons from a subsequent lethal ischemia. In vivo models faithfully display preconditioning, yet, these models are technically challenging, time-consuming and expensive. In vitro models of preconditioning have also been developed that are technically easier and less expensive. A drawback of pre-existing in vitro models is that since susceptibility to ischemic injury is age-dependent; neuroprotection is being studied in neurons that have intrinsic resistance to oxygen-glucose deprivation (OGD). This study introduces a new in vitro model of ischemic preconditioning in hippocampal slice cultures isolated from 20-30-day-old rats. Slice cultures show a high susceptibility and sharp thresholds toward ischemia that is comparable to that found in vivo. A 5-min OGD treatment was not neurotoxic to young adult slice cultures, while a 10-min OGD treatment was neurotoxic. In addition, the sublethal 5-min OGD treatment protected against a 10-min OGD treatment that was delivered 24 h later. Neuroprotection was seen in preconditioned slice cultures stained with propidium iodide (PI) or with antisera against the neuron-specific antigen NeuN. Energy failure is hypothesized to trigger ischemic preconditioning and a 5-min OGD treatment induced transient energy failure in young adult slice cultures. This model may assist in the search for new therapeutics for the prevention and/or treatment of stroke.

Reduced tolerance of immature renal tubules to anoxia by HSF-1 decoy

Immature animals demonstrate an amplified heat shock response following a variety of insults compared with that seen in mature animals (M). The potential role of the heat shock response in modulating immature tolerance to injury was compared between rat pups, 10 postnatal days of age (P10), and M. Baseline levels of the heat shock transcription factor (HSF-1) were substantially elevated in P10 compared with M animals. In uninjured P10 pups, HSF-1 level was comparable to that of M animals subjected to 45 min of ischemia. As anticipated, the integrity of suspensions of tubules exposed to anoxia was preserved in P10 animals (23% LDH release) compared with M (40%), P < 0.01. The effect of targeted inhibition of HSF-1 on tubular integrity was studied using a cyclic oligonucleotide decoy. The HSF-1 decoy increased the severity of anoxic injury in P10 pups to a level comparable with M animals. LDH release was 33% in decoy-treated P10 tubules compared with 40% in M. When P10 tubules were treated with scrambled decoy, resistance to anoxia remained intact (24%). The increased vulnerability of the tubular suspension to injury was specific to the HSF-1 decoy and proportional to the dose of decoy applied. This study demonstrates maturation in the abundance of HSF-1 in the immature rat kidney. The loss of resistance of immature tubules to anoxia with specific inhibition of HSF-1 may be due to its effect on the heat shock response or other signaling pathways of critical pathobiological importance in renal cell injury.

Spreading depression induces long-lasting brain protection against infarcted lesion development via BDNF gene-dependent mechanism

Preconditioning the rat brain with spreading depression for 48 h induces potent ischemic tolerance (infarct tolerance) after an interval of 12-15 days, consequently reducing the infarcted lesion size in the acute phase following focal cerebral ischemia. However, persistence of the morphological and functional neuroprotection has not yet been proven. We tested whether tolerance-derived neuroprotection against focal cerebral ischemia persists or merely delays the progress of cerebral infarction. Prolonged spreading depression was induced in mice by placing a depolarized focus with intracerebral microinfusion of KCl for 24 h; after intervals of 3, 6, 9 or 12 days, temporary focal ischemia was imposed. In the analysis of the infarcted lesion volume 24 h after ischemia, groups with 6 or 9 day interval demonstrated significantly smaller lesion volume compared to time-matched vehicle control group (P=0.002). Significant reduction in cerebral infarction was also observed at the chronic phase, namely 14 days after ischemia (33% reduction) (P=0.021) accompanied with less severe neurological deficits (38% reduction) (P=0.020). Using this technique, we also investigated if the mice with targeted disruption of a single BDNF allele (heterozygous BDNF-deficient mice) can gain the same potency of tolerance as the wild mice. In the result on infarcted lesion volumes following temporary focal ischemia, potent tolerance developed in the wild type (35% reduction) (P=0.007) but not in the heterozygous BDNF-deficient mice (<19% reduction) (P=0.155), indicating that BDNF expression level following spreading depression is contributing to infarct tolerance development.

Scopolamine-induced amnesia can be prevented by heat shock pretreatment in rats

The current study used the passive avoidance test to examine whether heat shock pretreatment has an effect on the memory impairment induced by scopolamine. Heat shock protein (HSP) 72 overexpression was detected in different brain structures in rats 16 h after heat shock treatment, but not in rats receiving no heat shock or 48 h after heat shock treatment. The step-through latency of either pre- or post-training administration of scopolamine in rats 16 h after heat shock treatment was significantly higher than those of the rats receiving no heat shock or 48 h after heat shock treatment. However, rats, 16 h after heat shock treatment and having been given scopolamine, performed no better than rats treated only with scopolamine. Hence, the present results indicate that heat shock has a protective, but not therapeutic, effect on the memory impairment induced by scopolamine by overexpression of HSP72 in rat brain.

Sleep deprivation prior to transient global cerebral ischemia attenuates glial reaction in the rat hippocampal formation

This study was aimed to ascertain the effect of sleep deprivation on subsequent cerebral ischemia in the rat hippocampal formation. Seven days after transient global cerebral ischemia induced by four-vessel occlusion method, most of the pyramidal cells in the hippocampal CA1 subfield underwent disruption and pyknosis as detected by cresyl violet staining. With OX-42, OX-18, OX-6 and ED1 immunohistochemistry, robust microglia/macrophage reactions were observed in the CA1 and dentate hilus. The majority of reactive microglia was rod-shaped, bushy or amoeboidic cells bearing hypertrophic processes. Astrocytes also displayed hypertrophic processes, whose immunostaining for glial fibrillary acidic protein was markedly enhanced. The ischemia-induced neuronal damage and glial reactions, however, were noticeably attenuated in rats subjected to pretreatment with sleep deprivation for five consecutive days. The most drastic effect was the diminution of OX-18, OX-6 and ED1 immunoreactivities, suggesting that the immune potentiality and/or phagocytosis of these cells was suppressed by prolonged sleep deprivation prior to ischemic insult. It is postulated that sleep deprivation may have a preconditioning influence on subsequent lethal cerebral ischemia. Hence, sleep deprivation may be considered as a therapeutic strategy in brain ischemic damage.

Hypothermic preconditioning induces rapid tolerance to focal ischemic injury in the rat

Stressful, preconditioning stimuli can elicit rapid and delayed forms of tolerance to ischemic injury. The identification and characterization of preconditioning stimuli that are effective, but relatively benign, could enhance the clinical applicability of induced tolerance. This study examines the efficacy of brief hypothermia as a preconditioning stimulus for inducing rapid tolerance. Rats were administered hypothermic preconditioning or sham preconditioning and after an interval of 20-120 min were subjected to transient focal ischemia using a three-vessel occlusion model. The volume of cerebral infarction was measured 24 h or 7 days after ischemia. In other experiments, the depth or duration of the hypothermic stimulus was manipulated, or a protein synthesis inhibitor (anisomycin) was administered. Twenty minutes of hypothermia delivered 20 or 60 (but not 120) min prior to ischemia significantly reduces cerebral infarction. The magnitude of protection is enhanced with deeper levels of hypothermia, but is not affected by increasing the duration of the hypothermic stimulus. Treatment with a protein synthesis inhibitor does not block the induction of rapid tolerance. Hypothermic preconditioning elicits a rapid form of tolerance to focal ischemic injury. Unlike delayed tolerance induced by hypothermia, rapid tolerance is not dependent on either de novo protein synthesis or the duration of the preconditioning stimulus. These findings suggest that the mechanisms underlying rapid and delayed tolerance induced by hypothermia differ fundamentally. Brief hypothermia could provide a rapid means of inducing transient tissue protection in the context of predictable ischemic events.

Ischemic tolerance and endogenous neuroprotection

Practically any stimulus capable of causing injury to a tissue or organ can, when applied close to (but below) the threshold of damage, activate endogenous protective mechanisms--thus potentially lessening the impact of subsequent, more severe stimuli. A sub-threshold ischemic insult applied to the brain, for example, activates certain cellular pathways that can help to reduce damage caused by subsequent ischemic episodes--a phenomenon known as 'ischemic preconditioning' (IP) or 'ischemic tolerance' (IT). Although investigated for some time in model organisms, IP/IT has recently been shown in human brain. This opens a window into endogenous neuroprotection and, potentially, a window of opportunity to utilize these mechanisms in the clinic to treat patients with stroke and other CNS disorders.

Hyperthermic pre-conditioning protects retinal neurons from N-methyl-D-aspartate (NMDA)-induced apoptosis in rat

Glutamate-induced excitotoxicity is associated with a selective loss of retinal neurons after retinal ischemia and possibly in glaucoma. Since heat shock protein (HSP) 70 is known to play a protective role against ischemic neuronal injury, which is also linked to excitotoxicity, we studied the expression of inducible (HSP72) and constitutive (HSC70) forms of HSP70 in apoptosis of retinal ganglion cells (RGCs) after intravitreal injection of 8 nmoles N-methyl-D-aspartate (NMDA), a glutamate receptor agonist. Approximately 18 h after NMDA injection, there were increased numbers of TUNEL-positive cells and cells with elevated HSP72 immunoreactivity in the retinal ganglion cell layer (RGCL), but there were no noticeable changes in HSC70 immunoreactivity. These HSPs positive cells were also Thy-1 positive, a marker for RGCs. Hyperthermic pre-conditioning, which is known to induce HSPs, given 6 or 12 h prior to NMDA injection ameliorated neuronal loss in the RGCL as counted 7 days after NMDA injection but pre-conditioning at 18 h prior to NMDA injection did not have any ameliorative effect. Quercetin, an inhibitor of HSP synthesis, abolished the ameliorative effect of hyperthermic pre-conditioning. Pre-conditioning elevated HSP72 but not HSC70 immunoreactivity and reduced the number of TUNEL-positive cells in the RGCL at 18 h. Our results suggest that intravitreal injection of NMDA induces an up-regulation of HSP72 in a time-dependent manner but not HSC70 in RGCs, indicating a stress response of HSP72 in RGCs and other inner retinal neurons after exposure to NMDA. Hyperthermic pre-conditioning given within a therapeutic window is neuroprotective to the retina against NMDA-induced excitotoxicity, likely by inhibiting apoptosis through the modulation of HSP72 expression.

Signal transduction and neurosurvival in experimental models of brain injury

Brain injury and neurodegenerative disease are linked by their primary pathological consequence-death of neurons. Current approaches for the treatment of neurodegeneration are limited. In this review, we discuss animal models of human brain injury and molecular biological data that have been obtained from their analysis. In particular, signal transduction pathways that are associated with neurosurvival following injury to the brain are presented and discussed.

Epsilon PKC is required for the induction of tolerance by ischemic and NMDA-mediated preconditioning in the organotypic hippocampal slice

Glutamate receptors and calcium have been implicated as triggering factors in the induction of tolerance by ischemic preconditioning (IPC) in the brain. However, little is known about the signal transduction pathway that ensues after the IPC induction pathway. The main goals of the present study were to determine whether NMDA induces preconditioning via a calcium pathway and promotes translocation of the protein kinase C epsilon (epsilonPKC) isozyme and whether this PKC isozyme is key in the IPC signal transduction pathway. We corroborate here that IPC and a sublethal dose of NMDA were neuroprotective, whereas blockade of NMDA receptors during IPC diminished IPC-induced neuroprotection. Calcium chelation blocked the protection afforded by both NMDA and ischemic preconditioning significantly, suggesting a significant role of calcium. Pharmacological preconditioning with the nonselective PKC isozyme activator phorbol myristate acetate could not emulate IPC, but blockade of PKC activation with chelerythrine during IPC blocked its neuroprotection. These results suggested that there might be a dual involvement of PKC isozymes during IPC. This was corroborated when neuroprotection was blocked when we inhibited epsilonPKC during IPC and NMDA preconditioning, and IPC neuroprotection was emulated with the activator of epsilonPKC. The possible correlation between NMDA, Ca2+, and epsilonPKC was found when we emulated IPC with the diacylglycerol analog oleoylacetyl glycerol, suggesting an indirect pathway by which Ca2+ could activate the calcium-insensitive epsilonPKC isozyme. These results demonstrated that the epsilonPKC isozyme played a key role in both IPC- and NMDA-induced tolerance.

The adaptive effects of hypoxic preconditioning of brain neurons

Prophylactic transient hypoxia (preconditioning) increased neuron resistance to subsequent induction of severe hypoxia. Published data and results obtained by the authors on the molecular-cellular mechanisms of hypoxic preconditioning are presented. The roles of intracellular signal transduction, genome function, stress proteins, and neuromodulatory peptides in this process are discussed. The roles of glutamatergic as well as calcium and phosphoinositide regulatory systems and neuromodulatory factors as components of "volume" signal transmission are analyzed in hypoxic preconditioning-associated induction of functional tolerance mechanisms against the acute harmful effects of hypoxia on neurons in olfactory slices.

Ischemic tolerance

A brief period of cerebral ischemia confers transient tolerance to a subsequent ischemic challenge in the brain. This phenomenon of ischemic tolerance has been confirmed in various animal models of forebrain ischemia and focal cerebral ischemia. Since the ischemic tolerance afforded by preceding ischemia can bring about robust protection of the brain, the mechanism of tolerance induction has been extensively studied. It has been elucidated that ischemic tolerance protects neurons, and at the same time, it preserves brain function. Further experiments have shown that metabolic and physical stresses can also induce cross-tolerance to cerebral ischemia, but the protection by cross-tolerance is relatively modest. The underlying mechanism of ischemic tolerance still is not fully understood. Potential mechanisms may be divided into two categories: (1) A cellular defense function against ischemia may be enhanced by the mechanisms inherent to neurons. They may arise by posttranslational modification of proteins or by expression of new proteins via a signal transduction system to the nucleus. These cascades of events may strengthen the influence of survival factors or may inhibit apoptosis. (2) A cellular stress response and synthesis of stress proteins may lead to an increased capacity for health maintenance inside the cell. These proteins work as cellular "chaperones" by unfolding misfolded cellular proteins and helping the cell to dispose of unneeded denatured proteins. Recent experimental data have demonstrated the importance of the processing of unfolded proteins for cell survival and cell death. The brain may be protected from ischemia by using multiple mechanisms that are available for cellular survival. If tolerance induction can be manipulated and accelerated by a drug treatment that is safe and effective enough, it could greatly improve the treatment of stroke.

Brain genomic response following hypoxia and re-oxygenation in the neonatal rat. Identification of genes that might contribute to hypoxia-induced ischemic tolerance

Hypoxic preconditioning (8% O2, 3 h) produces tolerance 24 h after hypoxic-ischemic brain injury in neonatal rats. To better understand the ischemic tolerance mechanisms induced by hypoxia, we used oligonucleotide microarrays to examine genomic responses in neonatal rat brain following 3 h of hypoxia (8% O2) and either 0, 6, 18, or 24 h of re-oxygenation. The results showed that hypoxia-inducible factor (HIF)-1- but not HIF-2-mediated gene expression may be involved in brain hypoxia-induced tolerance. Among the genes regulated by hypoxia, 12 genes were confirmed by real time reverse transcriptase-PCR as follows: VEGF, EPO, GLUT-1, adrenomedullin, propyl 4-hydroxylase alpha, MT-1, MKP-1, CELF, 12-lipoxygenase, t-PA, CAR-1, and an expressed sequence tag. Some genes, for example GLUT-1, MT-1, CELF, MKP-1, and t-PA did not show any hypoxic regulation in either astrocytes or neurons, suggesting that other cells are responsible for the up-regulation of these genes in the hypoxic brain. These genes were expressed in normal and hypoxic brain, heart, kidney, liver, and lung, with adrenomedullin, MT-1, and VEGF being prominently induced in brain by hypoxia. These results suggest that a number of endogenous molecular mechanisms may explain how hypoxic preconditioning protects against subsequent ischemia, and may provide novel therapeutic targets for treatment of cerebral ischemia.

Characteristics of hypothermic preconditioning influencing the induction of delayed ischemic tolerance

OBJECT

A brief period of hypothermia has recently been shown to induce delayed tolerance to ischemic brain injury. This form of tolerance is initiated several hours after hypothermic preconditioning (HPC) and persists for a few days. Hypothermia-induced tolerance could provide a means for limiting cellular injury during predictable periods of ischemia, such as those that occur during many surgical procedures. The purpose of this study was to characterize the parameters of HPC that regulate the induction of delayed tolerance.

METHODS

The general design of the experiments was to perform HPC or a sham procedure on adult Sprague-Dawley rats. Twenty-four hours later, the animals were subjected to a transient period of ischemia induced by a 1-hour period of three-vessel occlusion. Infarct volume was assessed 24 hours postischemia. In the first series of experiments, the depth of global (that is, whole-body) HPC was set at 25.5, 28.5, or 31.5 degrees C, and the duration of HPC was fixed at 20 minutes. In the second series of experiments, the duration of global HPC was set at 20, 60, 120, or 180 minutes, and the depth of HPC was set at 33 or 34.5 degrees C. In the third series of experiments, focal HPC was administered by selectively cooling the head to achieve a cortical temperature of 28.5 or 31.5 degrees C for 20 minutes, with the duration of HPC fixed at 20 minutes. The magnitude of tolerance induced by HPC was dependent on the depth and duration of the hypothermic stimulus. The parameters of hypothermia that are capable of inducing tolerance are similar to, or less severe than, those already in clinical use during intraoperative procedures. Focal cooling was as effective as global cooling for eliciting tolerance, indicating that it is possible to establish tolerance while limiting the potential complications of systemic hypothermia.

CONCLUSIONS

The results of these experiments indicate that HPC may provide an effective and safe means for limiting cellular injury resulting from predictable periods of central nervous system ischemia.

Stress protection by a fluorescent Hsp27 chimera that is independent of nuclear translocation or multimeric dissociation

A chimeric protein consisting of enhanced green fluorescent protein (EGFP) fused to the N-terminus of human Hsp27 conferred stress protection in human A549 lung carcinoma and murine L929 cells that were stably transfected to express the chimera constitutively. The resultant protection was comparable with that in the same cell lines when they were transfected to express corresponding levels of Hsp27. Unlike L929 cells, A549 cells exhibit endogenous Hsp27 expression, whose expression was inhibited in proportion to the amount of fluorescent chimera expressed, suggesting that the A549 cells recognized the latter as Hsp27. Upregulation of Hsp27 or chimeric Hsp27 in all transfected cell lines (stable or transient transfection) caused no measurable change in cellular glutathione levels, indicating that glutathione played no role in the stress protection associated with either protein. Chimeric Hsp27 had a monomeric molecular weight of 55 kDa (that of Hsp27 plus EGFP) in both cell types and formed a 16-mer complex twice as massive as that formed by Hsp27. Heat shock or sodium arsenite induced phosphorylation of both chimeric Hsp27 and Hsp27, which resulted in the disaggregation of Hsp27 multimers in both cell types and disaggregation of 20% of the chimeric multimers in L929 cells. But chimeric Hsp27 multimers did not disaggregate after stress in A549 cells. Epifluorescence and confocal microscopy demonstrated that chimeric Hsp27 was restricted to the cytoplasm under normal growth conditions and after heat shock in all cells. This study supports the conclusions that Hsp27 stress protection requires neither its translocation into the nucleus nor the dissociation of its multimeric complex. Furthermore, it demonstrates that fluorescent chimeras of heat shock proteins can be functional and used to observe the protein's distribution within living cells.

A 72 kDa heat shock protein is protective against the selective vulnerability of CA1 neurons and is essential for the tolerance exhibited by CA3 neurons in the hippocampus

The correlation between the expression of a 72 kDa heat shock protein and vulnerability of hippocampal CA1, CA3, and dentate gyrus regions to glutamate toxicity was investigated using a highly specific antisense oligonucleotide technique. Glutamate (1 mM, 15 min) caused region-dependent neuronal damage in cultured hippocampal slices 24 h after exposure and the most severe damage was observed in CA1. When slices were heat-shocked (43.5 degrees C, 30 min) before exposure to glutamate, neuronal damage in CA1 was attenuated. The strongest protection was observed when the interval between the heat shock and the exposure to glutamate was 3 days, which coincided with the maximal induction of a 72 kDa heat shock protein in neurons. When the expression of a 72 kDa heat shock protein was suppressed by the antisense oligonucleotide, the protective effect of the heat shock was completely inhibited. Glutamate itself also induced a 72 kDa heat shock protein in neurons, region-dependently, 24 h after the exposure. The signal of a 72 kDa heat shock protein in CA3 and dentate gyrus was significantly stronger than that in CA1. When the antisense oligonucleotide was applied, the damage in CA3 and dentate gyrus was exaggerated dose-dependently, and this effect was more remarkable in CA3 than in the dentate gyrus. Based on these data, we concluded that: (i) a 72 kDa heat shock protein has a protective effect against the selective vulnerability of CA1 neurons, (ii) a 72 kDa heat shock protein is an essential factor for the tolerance exhibited by CA3 neurons, and (iii) dentate gyrus tolerance is based on mechanisms other than those mediated through a 72 kDa heat shock protein.

Neuroprotective effects of hyperthermic preconditioning on infarcted volume after middle cerebral artery occlusion in rats: role of adenosine receptors

OBJECTIVE

There are still only a limited number of studies regarding the neuroprotective effects of hyperthermic preconditioning on regional brain ischemia or regarding the role of adenosine A1 receptors in such pretreatment. We examined the effects of hyperthermic pretreatment on infarcted volume after middle cerebral artery occlusion (MCAO), as well as the contribution of A1 receptors, to the responses in rats.

DESIGN

Prospective, randomized animal study.

SETTINGS

An animal research laboratory in a medical university.

SUBJECTS

Male Wistar rats (200-250 g).

INTERVENTION

All animals were anesthetized with isoflurane during each pretreatment, as well as for MCAO. The animals were assigned as follows: (i) sham-control group (n = 8), which was maintained at normothermia (37 +/- 0.2 degrees C pericranial temperature) for 15 mins, then kept in an awake state for 0.5, 3, 6, 18, 24, or 48 hrs before 2-hr MCAO; (ii) hyperthermia group (n = 8), which was subjected to 42 +/- 0.5 degrees C for 15 mins, and then received the same treatment as the sham group; (iii) DPCPX (a selective central adenosine receptor antagonist)-treated control group, which was given the agent before normothermia pretreatment, then kept for a recovery time of 0.5 or 24 hrs (n = 8 in each group) before MCAO; (iv) DPCPX plus hyperthermia-treated group, which was administered the agent at the same dose as the control before hyperthermic exposure, then selected for each recovery time (n = 8 in each group) before MCAO; (v) DPCPX-ischemic group, to which the agent was administered before MCAO (n = 8); and (vi) vehicle-ischemic group, in which peanut oil as a vehicle, instead of DPCPX, was injected before MCAO (n = 8). Values are expressed as mean +/- se. Statistical analysis was done by analysis of variance, followed by Scheffe's F test, Mann-Whitney U test, or the chi-square test as appropriate (p <.05).

MAIN RESULTS

The infarcted volume in hyperthermic animals kept for 18 or 24 hrs before the occlusion procedure was significantly smaller than in the sham controls, but not in rats kept for 0.5, 3.0, 6.0, and 48 hrs. DPCPX partially reversed the reduction in infarcted volume that was induced by hyperthermic preconditioning after focal ischemia, whereas the agent itself did not affect the volume after ischemia.

CONCLUSION

These data indicate that hyperthermic pretreatment reduces the effects on MCAO-induced cerebral infarction, possibly via a partial mediation of the central adenosine receptors in the brain. The results also suggest a need for further studies to define the relationship between heat shock proteins and central adenosine receptors in preconditioning.

Polyunsaturated fatty acids induce ischemic and epileptic tolerance

The findings reported in this work show that pretreatment with polyunsaturated fatty acids, particularly linolenic acid, present in vegetable oils, can provide a potent tolerance against neurodegeneration in two models of neuronal death-generating treatments such as kainic acid injection and global ischemia. Rats were injected i.v. with 500 nmol/kg of linolenic acid as long as 3 days prior to 6 min global ischemia or received an injection of linolenic acid as long as 3 days prior to a dose of 7.5 mg/kg kainic acid. Neuronal degeneration, assessed by analysis of neuronal density on Cresyl Violet-stained hippocampal sections, was significantly reduced in linolenic acid-treated rats (94-85% of cell survival in the ischemic model and 99-79% of cell survival in the epileptic model in respective CA1 and CA3 subfields). The neuroprotection observed following the injection of linolenic acid 3 days prior to induction of a severe ischemic or epileptic challenge was associated with the induction of the neuroprotective HSP70 heat shock protein within the time window of protection. The injection of 500 nmol/kg of linolenic acid induced a maximal HSP70 expression of 387% at 72 h. In contrast, the overexpression of one well-known protein inducer of neuronal cell death, Bax, which is induced by both ischemic and kainic acid-induced epileptic insults, was prevented by linolenic acid in the 3-day window of protection. These results strengthen the idea of an interesting potential therapeutical value of polyunsaturated fatty acids in neuronal protection.

Normobaric hypoxia induces tolerance to focal permanent cerebral ischemia in association with an increased expression of hypoxia-inducible factor-1 and its target genes, erythropoietin and VEGF, in the adult mouse brain

Tolerance to cerebral ischemia is achieved by preconditioning sublethal stresses, such as ischemia or hypoxia, paradigms in which the decrease of O2 availability may constitute an early signal inducing tolerance. In accordance with this concept, this study shows that hypoxia induces tolerance against focal permanent ischemia in adult mice. Normobaric hypoxia (8% O2 of 1-hour, 3-hour, or 6-hour duration), performed 24 hours before ischemia, reduces infarct volume by approximately 30% when compared with controls. To elucidate the mechanisms underlying this neuroprotection, the authors investigated the effects of preconditioning on cerebral expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and its target genes, erythropoietin and vascular endothelial growth factor (VEGF). Hypoxia, whatever its duration (1 hour, 3 hours, 6 hours), rapidly increases the nuclear content of HIF-1alpha as well as the mRNA levels of erythropoietin and VEGF. Furthermore, erythropoietin and VEGF are upregulated at the protein level 24 hours after 6 hours of hypoxia. The authors' findings show that (1) hypoxia elicits a delayed, short-lasting (<72 hours) tolerance to focal permanent ischemia in the adult mouse brain; (2) HIF-1 target genes could contribute to the establishment of tolerance; and (3) this model might be a useful paradigm to further study the mechanisms of ischemic tolerance, to identify new therapeutic targets for stroke.

Geldanamycin induces heat shock proteins in brain and protects against focal cerebral ischemia

Geldanamycin (GA), a benzoquinone ansamycin, binds Hsp90 in vitro, releases heat shock factor (HSF1) and induces heat shock proteins (Hsps). Because viral and transgenic overexpression of Hsps protects cells against ischemia in vitro, we hypothesized that GA would protect brain from focal ischemia by inducing Hsps in vivo. Adult male Sprague-Dawley rats were subjected to 2-hour middle cerebral artery occlusions (MCAO) using the suture technique followed by 22-h reperfusions. GA or vehicle was injected into the lateral cerebral ventricles (i.c.v) 24 h before ischemia. Geldanamycin at 1 microg/kg decreased infarct volumes by 55.7% (p < 0.01) and TUNEL-positive cells by 30% in cerebral cortex. GA also improved behavioral outcomes (p < 0.01) and reduced brain edema (p < 0.05). Western blots showed that the 1 microg/kg GA dose induced Hsp70 and Hsp25 protein 8.2-fold and 2.7-fold, respectively, by 48 h following administration. Immunocytochemistry showed that GA induced Hsp70 in neurons and Hsp25 in glia and arteries in cortex, hippocampus, hypothalamus, and other brain regions. GA reduced co-immunoprecipitation of HSF1 with Hsp90 in brain tissue homogenates, promoted HSE-binding of HSF in brain nuclear extracts using gel shift assays, and increased luciferase reporter gene transcription for the Hsp70 promoter in PC12 cells. The data show that geldanamycin protects brain from focal ischemia and that this may be due, at least in part, to geldanamycin stimulation of heat shock gene transcription.

Cerebral glucose utilization in transgenic mice overexpressing heat shock protein 70 is altered by dizocilpine

Heat shock protein (HSP70), a member of the 70 kDa HSP superfamily, has been widely implicated in the cellular stress response to numerous insults. HSP70 may be a significant factor in cell survival following stresses such as cerebral ischaemia. The precise mechanisms by which HSP70 facilitates cell survival remain unclear. The aim of this study was to ascertain whether any differences in local cerebral glucose utilization (LCGU) existed between transgenic mice overexpressing HSP70 (HSP70 Tg) and wild- type littermate (WT) mice. LCGU was assessed using (14)C-2-deoxyglucose in HSP70 Tg and WT mice under basal conditions (intraperitoneal injection of saline) and during metabolic activation produced by NMDA receptor blockade (intraperitoneal injection of dizocilpine, 1 mg/kg). No significant alterations in LCGU were observed between saline injected HSP70 Tg and WT mice in any of the 35 brain regions analyzed. Dizocilpine injection produced significant heterogeneous alterations in LCGU in HSP70 Tg mice (24 of 35 brain regions) and in WT mice (22 of 35 brain regions) compared with saline injected mice. The distribution of altered LCGU produced by dizocilpine was similar in HSP70 Tg and WT mice. However in five brain regions, dizocilpine injected HSP70 Tg mice displayed significantly altered LCGU compared to dizocilpine injected WT mice (anterior thalamic nucleus +27%, dorsal CA1 stratum lacunosum molecularae +22%, dorsal CA1 stratum oriens + 14%, superior olivary body -26%, and the nucleus of the lateral lemniscus -16%). These data highlight that while overexpression of HSP70 transgene does not significantly alter LCGU in the basal state, mice overexpressing the HSP70 transgene respond differently to metabolic stress produced by NMDA receptor blockade in some important brain regions.

Evaluation of preconditioning treatments to protect near-pure cortical neuronal cultures from in vitro ischemia induced acute and delayed neuronal death

We evaluated the efficacy of cycloheximide, heat stress, NMDA receptor blockade (MK801/AP-5), oxygen--glucose deprivation, hypoxia, hypothermia and TNFalpha preconditioning to protect cortical neurons from in vitro ischemic insults that result in acute necrotic and delayed apoptotic neuronal death. Preconditioning treatments were performed 22--24 h before in vitro ischemia. In vitro ischemia was carried out in 96-well microtitre strip-plates by washing neuronal cultures with a balanced salt solution containing 25 mM 2-deoxy-D-glucose and incubating in an anaerobic chamber. Glutamate receptor blockers were present during in vitro ischemia to induce delayed neuronal death. Cycloheximide, heat stress, MK801 and oxygen--glucose deprivation preconditioning were neuroprotective in both acute and delayed in vitro ischemic neuronal death models. AP-5 preconditioning and a 12 h post-MK801 preconditioning interval protected neurons from acute ischemic neuronal death only. Hypoxia, TNFalpha and hypothermic preconditioning provided no neuronal protection in the in vitro ischemia models. This study has confirmed for the first time that several preconditioning treatments can protect neurons from in vitro ischemia induced acute necrotic and delayed apoptotic neuronal death. In addition, a unique feature of this study is the finding that preconditioning could be induced in near-pure primary cortical neuronal cultures, thus confirming that ischemic tolerance is an intrinsic property of neurons and provides a simplified culture system for identifying neuroprotective proteins.

Optic nerve protection, regeneration, and repair in the 21st century: LVIII Edward Jackson Memorial lecture

PURPOSE

To present the current status and clinical implications of optic nerve protection, repair, and regeneration after experimental injury in mammals, including nonhuman primates.

DESIGN

Optic nerve and neuro-ophthalmology experimental study review.

METHOD

Synthesis of experimental data regarding experimental studies of optic nerve protection, repair, and regeneration.

RESULTS

Under certain conditions, mammalian retinal ganglion cells can be prevented from dying despite injury to the cell bodies or their axons, injured mammalian retinal ganglion cells whose axons have degenerated can be induced to extend new axons, and regenerating axons can reach their correct targets in the central nervous system. In addition, stem cells can be induced to become retinal ganglion cells.

CONCLUSIONS

It may soon be possible to preserve and restore vision in persons whose sight is threatened or has been lost from disease or damage to the optic nerve.

Mn-SOD and Bcl-2 expression after repeated hyperbaric oxygenation

To clarify the mechanism of ischemic tolerance induced by HBO, we investigated the effect of HBO on immunoreactivity to Bcl-2 and Bax, apoptosis-regulating protein, or Mn-SOD, a radical scavenging system, in the CA1 sector of the gerbil hippocampus. Pretreatment comprising, five sessions at 2 ATA (atmosphere absolute) every other day, but not that comprising, ten sessions at 3 ATA every day, caused significant increases in Bcl-2 and Mn-SOD immunoreactivity in the CA1 sector compared with in the sham pretreatment group. No significant differences in Bax immunoreactivity and neuronal density in the CA1 hippocampal neurons was observed between the groups. These results suggest that protection against mitochondrial alterations after ischemia through Mn-SOD and/or Bcl-2 expression is related to the ischemic tolerance induced by repeated HBO pre-treatment.

Activation of the nuclear factor-kappaB is a key event in brain tolerance

The transcription factor nuclear factor-kappaB (NFkappaB) is an ubiquitously expressed inducible regulator of a broad range of genes and plays a pivotal role in cell death and survival pathways. Three models of brain tolerance (ischemic, epileptic, and polyunsaturated fatty acid-induced preconditioning), known to confer resistance to neurons against ischemia or status epilepticus, were used to determine whether NFkappaB mediated the late preconditioning. A sublethal 3 min ischemia, a dose of 5 mg/kg kainic acid (KA5) or 500 nmol of linolenic acid (LIN500) led to a rapid increase of NFkappaB DNA-binding activity and nuclear translocation of p65 and p50 subunits of NFkappaB in neurons. Pretreatment with the NFkappaB inhibitor diethyldithiocarbamate or kappaB decoy DNA blocked the increased DNA-binding activity and the nuclear translocation of NFkappaB and abolished the neuroprotective effects of different delayed preconditionings against severe ischemia or epilepsy. The inhibition of NFkappaB observed in rats preconditioned with 3 min ischemia, KA5 or LIN500 treatments compared with ischemic or epileptic controls was correlated with the prevention of the inducible degradation of the inhibitory protein IkappaBalpha. Preconditioning probably inhibits the activation of NFkappaB by interfering with a pathway that leads to the direct transcriptional activation of IkappaBalpha by NFkappaB itself. The present work provides evidence that activation of NFkappaB is a crucial step in the signal transduction pathway that underlies the development of brain tolerance and may open new strategies in the prevention of cerebral diseases, such as ischemia or epilepsy.

Preferential conditions for and possible mechanisms of induction of ischemic tolerance by repeated hyperbaric oxygenation in gerbil hippocampus

OBJECTIVE

We reported previously that repeated hyperbaric oxygenation (HBO) as pretreatment induced ischemic tolerance in the gerbil hippocampus. This study was conducted to determine the preferential conditions for induction of ischemic tolerance by HBO and the mechanism of this induction through immunohistochemical analysis of Bcl-2, Bax, and manganese superoxide dismutase expression.

METHODS

Five-minute forebrain ischemia was produced in gerbils after pretreatment with 2 atmospheres absolute (ATA) HBO once every other day for one, three, or five sessions, 2 ATA hyperbaric air once every other day for five sessions, or 3 ATA HBO once daily for 10 sessions. Histological examinations were then performed. Two days after pretreatment with 2 ATA HBO once every other day for five sessions or with 3 ATA HBO once daily for 10 sessions, sections were analyzed immunohistochemically.

RESULTS

Pretreatment with 2 ATA HBO once every other day for three or five sessions induced ischemic tolerance; however, pretreatment with 2 ATA HBO for one session, 2 ATA hyperbaric air once every other day for five sessions, or 3 ATA HBO once daily for 10 sessions did not. Pretreatment with 2 ATA HBO once every other day for five sessions, but not with 3 ATA HBO once daily for 10 sessions, significantly increased Bcl-2 and manganese superoxide dismutase immunoreactivity in the CA1 sector.

CONCLUSION

These results suggest that protection against mitochondrial alterations after ischemia through manganese superoxide dismutase and/or Bcl-2 expression may be related to induction of ischemic tolerance by repeated HBO pretreatment.