Synthesis of a stress protein following transient ischemia in the gerbil

Predictive Value of Heat-Shock Protein Gene Expression on Severe Neonatal Hypoxic-Ischemic Encephalopathy

This study aims to evaluate significant gene expression in severe hypoxic ischemic encephalopathy (HIE) in newborns, which can be used as a predictable measure for high-risk HIE infants. The study prospectively recruited 77 inborn near-term or term HIE newborns between January 2018 and December 2020. We measured six different genes within 6 h of life among the HIE infants and compared the gene levels between the mild- and severe-HIE groups. Among these, 64 HIE infants (83.1%) did not receive therapeutic hypothermia (TH) because they were categorized as mild HIE, and the 13 remaining (16.9%) infants were categorized as ≥ moderate-HIE group and received TH. More abnormal MRI findings, seizure, and use of anti-convulsant were more found in the ≥ moderate = HIE group along with longer mechanical ventilation days and hospitalization. Heat-shock protein 70 family 1 A (HSPA1A) and serpin family H member 1 (SERPINH1) genes, which encode heat-shock protein (HSP) 70 and 47, respectively, were significantly elevated in the ≥ moderate-HIE, seizure, and abnormal MRI groups. HSP 70 and 47 were significantly elevated in the severe-HIE group, possibly playing protective roles in inhibiting exacerbated neuroinflammation and maintaining a cellular homeostasis. At 18–24 months, ≥ moderate-HIE group manifested a significant language delay.

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.

Ischemic tolerance in the brain: endogenous adaptive machinery against ischemic stress

Although more than 100 drugs have been examined clinically, tissue plasminogen activator remains the only drug approved for the treatment of acute ischemic stroke. Since the discovery of ischemic tolerance, it has been widely recognized that the brain possesses an endogenous protective machinery to protect against ischemic stress. Recent studies have clarified that both the upregulation of neuroprotective signaling and the downregulation of inflammatory or apoptotic pathways are involved equally in the acquisition of ischemic tolerance. The triggering stimuli for ischemic stresses are divided into hypoxic, oxidant/inflammatory, and glutamate stress. Glutamate stress, particularly the synaptic stimulation of the N-methyl-D-aspartate receptor, leads to activation of the cAMP response element-binding protein, which could subsequently induce gene expression of several neuroprotective molecules. Gene reprogramming and metabolic downregulation are intimately involved in ischemic tolerance as well as in hibernation and hypothermia. Micro-RNAs may be a key player for tuning the level of gene expression in ischemic tolerance. Future research should be performed to investigate the most effective combination for brain protection, enhancement of cell survival signaling, and inhibition of the inflammatory or apoptotic pathways.

Osteogenic differences in cultured rat periosteal cells under hypoxic and normal conditions

The aim of the present study was to investigate the osteogenic capability of rat calvarial periosteal cells in hypoxic conditions in vitro. Periosteum was obtained from the calvarial bone of Sprague-Dawley rats. Following primary tissue culture, subcultured cells were used in hypoxic or normal conditions. On days 1, 2, 3 and 4 following the cell culture, cell proliferation and mRNA and protein expression levels were evaluated. No significant difference in the cell proliferation rate was found between the normal and hypoxic condition groups. The hypoxic condition group exhibited a stronger expression of hypoxia-inducible factor (HIF)1α, vascular endothelial growth factor (VEGF), Runx2, alkaline phosphatase (ALP), bone sialoprotein (BSP), osteocalcin (OCN) and periostin at the mRNA level compared to that of the normal condition group. The hypoxic condition group also exhibited a stronger expression of HIF1α, VEGF, bone morphogenetic protein (BMP)2, Runx2, ALP and BSP at the protein level compared to that of the normal condition group. In conclusion, periosteal cells cultured in hypoxic conditions demonstrated activated osteogenic capability in vitro.

Induction of heat shock proteins for protection against oxidative stress

Heat shock proteins (Hsps) have been studied for many years and there is now a large body of evidence that demonstrates the role of Hsp upregulation in tissue and cell protection in a wide variety of stress conditions. Oxidative stress is known to be involved in a number of pathological conditions, including neurodegeneration, cardiovascular disease and stroke, and even plays a role in natural aging. In this review we summarize the current understanding of the role of Hsps and the heat shock response (HSR) in these pathological conditions and discuss the therapeutic potential of an Hsp therapy for these disorders. However, although an Hsp based therapy appears to be a promising approach for the treatment of diseases that involve oxidative damage, there are some significant hurdles that must be overcome before this approach can be successful. For example, to be effective an Hsp based therapy will need to ensure that the upregulation of Hsps occurs in the right place (i.e. be cell specific), at the right time and to a level and specificity that ensures that all the important binding partners, namely the co-chaperones, are also present at the appropriate levels. It is therefore unlikely that strategies that involve genetic modifications that result in overexpression of specific Hsps will achieve such sophisticated and coordinated effects. Similarly, it is likely that some pharmaceutical inducers of Hsps may be too generic to achieve the desired specific effects on Hsp expression, or may simply fail to reach their target cells due to delivery problems. However, if these difficulties can be overcome, it is clear that an effective Hsp based therapy would be of great benefit to the wide range of depilating conditions in which oxidative stress plays a critical role.

Cellular responses of rat periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate the responses of periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro.

MATERIAL AND METHODS

Periodontal ligament fibroblasts were isolated from rat incisors. In the hypoxia group, cells were incubated in 2% O(2) for 1-3 d. In the re-oxygenation group, cells were first incubated under the same conditions as the hypoxia group for 24 h and then were returned to normoxic conditions and cultured for 1-2 additional days.

RESULTS

Proliferation ratios increased in all groups in a time-dependent manner. Proliferation ratios in both the hypoxia and re-oxygenation groups were significantly higher than in the control group on days 2 and 3. Alkaline phosphatase activity was significantly higher in the hypoxia group than in the control and the re-oxygenation groups. The expression of bone sialoprotein mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. The expression of vascular endothelial growth factor mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. In the re-oxygenation group, the level of expression of bone sialoprotein mRNA and vascular endothelial growth factor mRNA were similar to those of the control group. The expression of heat shock protein 70 mRNA in the hypoxia group was similar to that in the control group, whereas in the re-oxygenation group it was statistically higher than in the other groups.

CONCLUSION

These results suggest that periodontal ligament cells maintain their osteogenic ability in hypoxia and re-oxygenation conditions in vitro.

Irreversible translation arrest in the reperfused brain

Irreversible translation arrest occurs in reperfused neurons that will die by delayed neuronal death. It is now recognized that suppression of protein synthesis is a general response of eukaryotic cells to exogenous stressors. Indeed, stress-induced translation arrest can be viewed as a component of cell stress responses, and consists of initiation, maintenance, and termination phases that work in concert with stress-induced transcriptional mechanisms. Within this framework, we review translation arrest in reperfused neurons. This framework provides a basis to recognize that phosphorylation of the alpha subunit of eukaryotic initiation factor 2 is the initiator of translation arrest, and a key marker indicating activation of neuronal stress responses. However, eIF2 alpha phosphorylation is reversible. Other phases of stress-induced translation arrest appear to contribute to irreversible translation arrest specifically in ischemic vulnerable neuron populations. We detail two lines of evidence supporting this view. First, ischemia, as a stress stimulus, induces irreversible co-translational protein misfolding and aggregation after 4 to 6 h of reperfusion, trapping protein synthesis machinery into functionally inactive protein aggregates. Second, ischemia and reperfusion leads to modifications of stress granules (SGs) that sequester functionally inactive 48S preinitiation complexes to maintain translation arrest. At later reperfusion durations, these mechanisms may converge such that SGs become sequestered in protein aggregates. These mechanisms result in elimination of functionally active ribosomes and preclude recovery of protein synthesis in selectively vulnerable neurons. Thus, recognizing translation arrest as a component of endogenous cellular stress response pathways will aid in making sense of the complexities of postischemic translation arrest.

Effects of Triflusal and Aspirin in a Rat Model of Cerebral Ischemia

Background and Purpose— Neuroinflammation plays a critical role in the pathogenesis of cerebral ischemia. Triflusal, a selective cyclooxygenase-2, and its active metabolite 3-hydroxy-4-trifluoromethylbenzoic acid may inhibit apoptosis and inflammation after cerebral ischemia. An in vivo model of cerebral ischemia was used to investigate the effects of triflusal and aspirin treatment on infarct volume, and inflammation after cerebral ischemia in the rat.

Methods— Male Wistar rats were subjected to a permanent right-sided middle cerebral artery occlusion. Rats received oral administration of either triflusal or aspirin. After 3 days after surgery, immunostaining was used to detect neuroinflammatory cells and molecules, and infarct volumes were measured.

Results— Both triflusal and aspirin at a dose of 30 mg/kg but not 10 mg/kg significantly reduced infarct volume compared with vehicle treatment. Middle cerebral artery occlusion resulted in increased astrocyte and heat shock protein-27 (Hsp27) immunostaining in the ipsilateral cortex. Triflusal (30 mg/kg) or aspirin treatment (30 mg/kg) did not reduce the levels of GFAP or Hsp27 immunostaining. Triflusal (30 mg/kg) also significantly decreased the protein levels of IL-Iβ but not nuclear factor kappa B or tumor necrosis factor-α in the cortex ipsilateral to the middle cerebral artery occlusion.

Conclusions— The results suggest that triflusal and aspirin appear to be equally neuroprotective against middle cerebral artery occlusion-induced cerebral ischemia. Therefore, strong rationale exists to continue the neuroprotective examination of triflusal in brain injury.

Isolation and characterization of LCHN: a novel factor induced by transient global ischemia in the adult rat hippocampus

Using mRNA differential display to identify cerebral ischemia-responsive mRNAs, we isolated and cloned a cDNA derived from a novel gene, that has been designated LCHN. Antisense mRNA in situ hybridization and immunoblotting confirmed LCHN expression to be induced in the rat hippocampus following transient forebrain ischemia. The deduced amino acid sequence of the novel LCHN cDNA contains an open reading frame of 455 amino acids, encoding a protein with a predicted molecular mass of approximately 51 kDa. Although LCHN is highly conserved between rat, mouse, and human, the deduced amino acid sequence of LCHN does not possess significant homology to other known genes. LCHN immunoreactivity is detected within the somatodendritic compartment of neurons, is also present on dendritic growth cones, but is not detected on astrocytes. The induction of LCHN in the hippocampus following ischemic injury may have functional consequences, as the ectopic over-expression of LCHN generated neurons with longer and more branched axons and dendrites. Taken together, these data suggest that LCHN could play a role in neuritogenesis, as well as in neuronal recovery and/or restructuring in the hippocampus following transient cerebral ischemia.

Morphohistological Change and Expression of HSP70, Osteopontin and Osteocalcin mRNAs in Rat Dental Pulp Cells with Orthodontic Tooth Movement

Morphological change and expression of osteopontin, osteocalcin, and HSP70 mRNAs in rat dental pulp cells with experimental orthodontic tooth movement were investigated. Elastic rubber blocks, 0.65 mm in thickness, were inserted between the maxillary first and second molars in rats. In addition to morphological observations of HE staining and TUNEL staining at days 3, 7, 14 and 28 after insertion of elastic rubber blocks, expression of HSP70, osteopontin and osteocalcin mRNAs was also analyzed using quantitative RT-PCR with a LightCycler. Morphologically, proliferation and vasodilation of capillaries was evident in the pulp at days 3 and 7, and a sparse odontoblast layer and apoptosis in the pulp were observed at days 7 and 14 after rubber block insertion. Expression of HSP70, osteopontin and osteocalcin mRNAs in the experimental groups was higher than that in the control group at all time points. This suggests that orthodontic tooth movement causes degenerative changes and apoptosis in pulp cells, while pulp homeostasis is maintained at the genetic level.

Effect of ischemic preconditioning on cerebral blood flow after subsequent lethal ischemia in gerbils

Ischemic tolerance, the phenomenon where a sublethal ischemic preconditioning protects the brain against a subsequent lethal ischemia, has been widely studied. Studies have been done on cerebral blood flow levels prior to the lethal ischemia, but the hemodynamic pattern after global ischemia with ischemic preconditioning has not been reported. Sequential changes in regional cerebral blood flow (rCBF) in gerbil hippocampus after 5 min global ischemia with or without 2 min ischemic preconditioning were studied to determine if ischemic preconditioning affects rCBF. Four different treatments were given: (1) sham-operated, (2) 2 min ischemia, (3) non-preconditioned, and (4) preconditioned. Groups (1) and (2) (both groups n = 5) were given a 24-h recovery period and the rCBF was measured for baseline values. 24 h after sham-operation (3) and 2 min ischemia (4), gerbils were subjected to 5 min ischemia followed by 1 h, 6 h, 1-day or 7-day reperfusion periods (all groups n = 5). Although no regional difference was observed in the recovery pattern of rCBF, the values of rCBF were significantly higher in the preconditioned group throughout whole brain regions including hippocampus. These results indicate that ischemic preconditioning facilitated the recovery of rCBF after 5 min global ischemia. It needs further study to determine whether the protecting effects of preconditioning relate to the early recovery of rCBF or not. However, our results could be interpreted that the early recovery of rCBF may lead to benefits for cell survival in the CA1 neuron, probably facilitating other protecting mechanisms.

Differential effects of sublethal ischemia and chemical preconditioning with 3-nitropropionic acid on protein expression in gerbil hippocampus

Pretreatment with a low dose of 3-nitropropionic acid (3-NPA) has been shown to induce ischemic tolerance in the gerbil hippocampus. It is well known that sublethal (2-min) ischemia also induces ischemic tolerance. To investigate the acquisition of ischemic tolerance with 3-NPA, we examined the protein expression after 3-NPA treatment in comparison with sublethal ischemia. Immunohistochemical studies revealed intense expression of Bcl-2 and Bcl-xL in the hippocampal CA1 area after 3-NPA treatment. Furthermore, the time course of the expression of Bcl-xL showed a similar pattern to the acquisition of ischemic tolerance by 3-NPA treatment. The induction of Bcl-xL occurred in the hippocampal CA1 area at 24 h after 3-NPA treatment, and significant induction was observed at 48 h. Western blot analysis of hippocampus harvested 48 h after the pretreatment, showed that the expression of Bcl-2 and Bcl-xL was significantly increased by either 3-NPA treatment or 2-min ischemia. However, PMCA1 and HSP70 protein expression increased only in the sublethal ischemia treated group. The difference between 3-NPA treated group and control group was not statistically significant. These results suggest that Bcl-2 and Bcl-xL are essential for acquisition of ischemic tolerance, while HSP70 and PMCA1 play important roles in the enhancement of ischemic tolerance.

Tissue preconditioning may explain concentric lesions in Baló's type of multiple sclerosis

Lesions of Baló's concentric sclerosis are characterized by alternating layers of myelinated and demyelinated tissue. The reason for concentric demyelination in this variant of multiple sclerosis is unclear. In the present study we investigated the immunopathology in autopsy tissue of 14 patients with acute multiple sclerosis or fulminant exacerbations of chronic multiple sclerosis with Baló-type lesions in the CNS, focusing on the patterns of tissue injury in actively demyelinating lesions. We found that all active concentric lesions followed a pattern of demyelination that bears resemblances to hypoxia-like tissue injury. This was associated with high expression of inducible nitric oxide synthase in macrophages and microglia. At the edge of active lesions and, less consistently, in the outermost layer of preserved myelin, proteins involved in tissue preconditioning, such as hypoxia-inducible factor 1alpha and heat-shock protein 70, were expressed mainly in oligodendrocytes and to a lesser degree also in astrocytes and macrophages. Due to their neuroprotective effects, the rim of periplaque tissue, where these proteins are expressed, may be resistant to further damage in an expanding lesion and may therefore remain as a layer of preserved myelinated tissue.

ORP150 ameliorates ischemia/reperfusion injury from middle cerebral artery occlusion in mouse brain

The 150-kDa oxygen-regulated protein (ORP150), a novel stress protein localized to the endoplasmic reticulum (ER), is induced by hypoxia/ischemia. To determine the role of ORP150 in cerebral infarction following ischemia/reperfusion, ORP150 transgenic (TG) and knockout (KO) mice were subjected to 1 or 3 h of middle cerebral artery (MCA) occlusion followed by reperfusion for 24 h. At 24 h after 1 h of occlusion, significantly less infarct volume was evident in cerebral cortex, but not in striatum, in ORP150TG than ORP150KO mice (P<0.001). Infarct volume did not differ significantly between these groups at 24 h after 3 h of occlusion. Immunohistochemical reactivity for microtubule-associated protein (MAP)2 in the MCA territory was lost in ORP150KO mice at 24 h after 1 h of occlusion. In contrast, MAP2 staining still was present in the affected cortex of ORP150TG mice, where markedly enhanced ORP150 immunoreactivity was demonstrated. MAP2 staining had disappeared from the affected area at 24 h after 3 h of occlusion in both groups, but astrocytic ORP150 reactivity was preserved in the ORP150TG group. At 6 h after 1-h occlusion, when MAP2 staining was evident in the affected cortex, some cortical neurons of the TG mice were reactive for Bcl-xS/L. Thus, ORP150 may be cytoprotective against ischemia/reperfusion injury via reduction of ER stress and probably also inhibition of apoptosis.

Altered epithelial density and expansion of bulbar projections of a discrete HSP70 immunoreactive subpopulation of rat olfactory receptor neurons in reconstituting olfactory epithelium following exposure to methyl bromide

A previously described subpopulation of rat olfactory receptor neurons, the 2A4(+)ORNs, is 1) distinguished by intense constitutive cytoplasmic immunoreactivity to antibodies to the 70-kD heat shock protein (HSP70); 2) occurs sparsely but consistently through ventral and lateral olfactory epithelium (OE); and 3) projects to just two to three consistently located glomeruli in each olfactory bulb (OB) (Carr et al. [1994] J Comp Neurol 348:150-160). Immunoreactivity appears not to be stress-related. To examine the persistence of these features following destruction and reconstitution of the OE, rats were subjected to methyl bromide-induced OE lesion (Schwob et al. [1995] J Comp Neurol 59:15-37; Schwob et al. [1999] J Comp Neurol 412:439-457] and their OE and OBs examined with antibodies to HSP70 6-10.5 weeks postlesion. Lesioned OE showed significantly increased 2A4(+)ORN densities but no alteration of 2A4(+)ORN zonal distribution. The OBs of lesioned animals showed marked expansions of 2A4(+)ORN bulbar projections, with 2-15-fold increases in numbers of glomeruli showing 2A4(+)axons, and projection expansions were greater in animals maintained on chronic food restriction prior to lesioning. Examination of archival 5-month post-MeBr lesion material indicates that altered projection patterns are maintained.

Correlation between delayed neuronal cell death and selective decrease in phosphatidylinositol 4-kinase expression in the CA1 subfield of the hippocampus after transient forebrain ischemia

Transient forebrain ischemia induces a delayed neuronal death in the CA1 area of the hippocampus. However, the mechanism leading to this phenomenon has yet to be established. The authors used an mRNA differential-display method to isolate genes for which mRNA levels change only in the hippocampus during ischemia/reperfusion. They succeeded in identifying the product of one down-regulated gene as phosphatidylinositol 4-kinase (PI 4-K). Compared with control levels, PI 4-K mRNA expression in the hippocampus, but not the cerebral cortex, was significantly decreased by 30% and about 80% 1 and 7 days after ischemia/reperfusion, respectively. Interestingly, PI 4-K and PI bisphosphate levels were selectively decreased in the CA1 region, but not other regions, whereas TUNEL-positive cells could be detected 3 days after ischemia. Consistent with these results, PI 4-K expression was suppressed by hypoxia in SK-N-MC neuroblastoma cells before loss of cell viability. Overexpression of wild-type PI 4-K, but not the kinase-negative mutant of PI 4-K (K1789A), recovered the loss of viability induced by hypoxia. These findings strongly suggest that a prior decrease in PI 4-K and PI bisphosphate levels caused by brain ischemia/hypoxia is partly involved in delayed neuronal cell death.

Pulp cell responses during hypoxia and reoxygenation in vitro

The purpose of this study was to investigate pulp cell responses during hypoxia and reoxygenation. Pulp tissues obtained from beagle dogs were cultured. In the control group, pulp cells were incubated in normoxic conditions (20% O2) for 1-4 d. In the hypoxia group, pulp cells were incubated under hypoxic conditions (2% O2) for 1-4 d. In the reoxygenation group, pulp cells were first incubated under hypoxic conditions for 24 h, and were then incubated in normoxic conditions (20% O2) for one to three additional days. Cell viability, MTT (3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction assay, cellular proliferation, and alkaline phosphatase (ALPase) activity were determined. Expression of heat shock protein 70 (HSP70) and vascular endothelial growth factor (VEGF) was analysed by Western blotting. Hypoxia inducible factor-1alpha (HIF-1alpha) in pulp cells was analysed by reverse transcriptase polymerase chain reaction (RT-PCR). The cell growth rate and ALPase activity were significantly higher in the hypoxia group than in the control group. After reoxygenation, cellular proliferation and ALPase activity decreased to the level of the control group while HSP70 expression increased. Hypoxia inducible factor-1alpha expression was detected in pulp cells, and VEGF expression (which is regulated by HIF-1alpha) increased under hypoxic conditions. These results suggest that dynamic responses to hypoxia and reoxygenation occur in pulp cells.

Repeated cerebral ischemia induced hippocampal cell death and impairments of spatial cognition in the rat

We developed a method of causing strong ischemic insult only in vulnerable nerve cells, such as hippocampal cells, without causing hemiplegia or difficulty in moving, by repeating cerebral ischemia for a brief time with a short interval periods. The rats subjected to 10 min of cerebral ischemia exhibited no impairment of spatial cognition at the test trial 7 days after final reperfusion. However, when the 10 min ischemia was repeated twice with a 1 hr interval, the rats exhibited a significant decrease in number of correct choices and increase in number of errors. Three times of repeated cerebral ischemia also induced a significant decrease in the number of correct choices and increase in the number of errors, but there were some rats showing motor difficulty. Cell death was typically observed in the CA1 layer of the hippocampus of rats subjected twice to 10 min of cerebral ischemia. Hippocampal and cortical acetylcholine (ACh) release weas transiently increased during the first and second 10 minutes of ischemia and normalized immediately after recirculation; thereafter, ACh release from these areas gradually decreased and showed a significantly low level at 7 days after recirculation. These results suggest that the repeated cerebral ischemia-induced impairment of spatial memory may be due to the dysfunction of hippocampal and cortical ACh systems and hippocampal cell death. The repeated cerebral ischemia model which produces cell death and ACh dysfunction in the hippocampus is thought to be useful for evaluating new drugs for the treatment of cerebrovascular dementia.

Passage of spermidine across the blood-brain barrier in short recirculation periods following global cerebral ischemia: effects of mild hyperthermia

Transport of a polyamine (PA), spermidine (SPMD) into rat brain at various early postischemic periods was studied. Rats underwent 20 min of four-vessel occlusion (4VO) followed by 5, 10, 30 and 60 min of recirculation (RC) periods with natural brain temperature. 3H-aminoisobutyricacid (AIB) and 14C-SPMD were utilised to search dual functions of the blood-brain barrier (BBB); barrier and carrier functions, respectively. Unidirectional blood-to-brain transfer constant (Kin) was calculated for AIB and SPMD in four brain regions-parieto-temporal cortex, striatum, hippocampus and cerebellum. Kin for SPMD ranged between 1.2+/-0.3 x 10(3) ml g(-1) min(-1) (for striatum) and 2.2+/-0.4 x 10(3) ml g(-1) min(-1) (for cerebellum) in controls. Kin for AIB showed similar values. At 5 and 10 min RC periods, Kin for both substances increased in a non-specific manner in all brain regions studied. In the cortex, Kin for SPMD at 5 and 10 min RC periods were 3.2+/-0.4 x 10(3) and 2.9+/-0.3 x 10(3) ml g(-1) min(-1), respectively, and found to be maximum with respect to other brain regions studied. 30 and 60 min RC groups showed specific transport for SPMD, whilst there were no changes for Kin for AIB, in all brain regions studied. Hippocampus showed the maximum increase in Kin SPMD at 60 min RC (2.7+/-0.3 x 10(3) ml g(-1) min(-1)), corresponding to a percentage rise of 121%. Intraischemic mild brain hyperthermia (39 degrees C) gave rise to a striking increase in Kin at 60 min postischemia for both substances. These results suggest that there is a specific transport of SPMD into brain at 30 and 60 min RC periods following 20 min of forebrain ischemia. Moreover, dual functions of the BBB were perturbed with intracerebral mild hyperthermia during ischemia.

Increase in Specific Proteins and mRNAs Following Transient Anoxia - Aglycaemia in Rat CA1 Hippocampal Slices

Incorporation of [35S]methionine into proteins and two-dimensional gel autoradiograms was used to characterize early post-anoxia - aglycaemia protein synthesis in the CA1 area of rat hippocampal slices maintained in vitro. We have compared the effects of 3 - 4 min and 5 - 10 min insults, since the former but not the latter produces a reversible block of synaptic transmission (see companion paper). An insult of between 3 min 30 s and 4 min induces a transient increase in the labelled proteins during the first hour of reoxygenation, as compared to control. The increase in protein synthesis is conspicuous for several proteins, including actin, alpha-tubulin and heat-shock proteins (hsp70c and hsp90), as determined by immunoblotting. In the case of alpha-tubulin, we show with in situ hybridization and polymerase chain reaction procedures that the increase in protein synthesis is associated with a marked increase in the expression of the corresponding messenger RNAs. The results demonstrate that, in addition to regulatory proteins such as hsps, the synthesis of several polypeptides, including those associated with the cytoskeleton, is altered in anoxic damage.

Ischemic depolarization monitoring: evaluation of protein synthesis in the hippocampal CA1 after brief unilateral ischemia in a gerbil model

OBJECT

The authors investigate whether depolarization monitoring is an accurate index of ischemic damage in a gerbil model of unilateral ischemia and assess the effects of brief cerebral ischemia on protein synthesis in this model.

METHODS

The authors evaluate the relationship between the duration of ischemic depolarization caused by unilateral carotid artery occlusion and ischemia-induced neuronal damage in the CA1 subregion 7 days after ischemia. When the depolarization period exceeded 210 seconds, some neuronal damage was detected, and almost complete neuronal damage was observed when the period exceeded 400 seconds. Uptake of [14C]valine was evaluated in ischemic and nonischemic CA1 subregions. Disturbances in protein synthesis were seen in all animals subjected to sublethal ischemia (< or = 210-second depolarization) after a 10-minute recirculation, and after 2 and 6 hours of recirculation in animals with 90 seconds or more of depolarization. Inhibition of protein synthesis was proportional to the length of the depolarization period. After 1 and 3 days of recirculation, protein synthesis returned to near normal, and some animals with depolarizations greater than 180 to 210 seconds showed an increase in protein synthesis. Protein synthesis in all animals returned to normal levels after 7 days of recirculation.

CONCLUSIONS

In this study the authors demonstrate that monitoring of ischemic depolarization is a useful method to predict neuronal damage in the hippocampal CA1 in this model, and they identify subtle changes in protein synthesis after brief ischemia. Sublethal ischemia was divided into three categories by its depolarization period (< 90 seconds, 90-180 seconds, and > 180-210 seconds) with regard to changes in protein synthesis.

Preoperative stress conditioning prevents paralysis after experimental aortic surgery: increased heat shock protein content is associated with ischemic tolerance of the spinal cord

BACKGROUND

All forms of surgical therapy are stressful and injurious. The problems of paralysis, renal dysfunction, and colonic ischemia associated with aortic occlusion are due to acute ischemia-reperfusion injury at the cellular level. Acute-anterior spinal cord ischemia is the most devastating outcome of these iatrogenic-ischemic events. The majority of surgical procedures are performed electively and therefore provide an opportunity to preoperatively condition the patient to minimize these ischemia-related morbidities.

OBJECTIVES

We sought to determine whether acute spinal cord injury associated with aortic occlusion can be prevented by induction of the cellular stress response by means of preoperative administration of whole-body hyperthermia or stannous chloride.

METHODS

The study consisted of an experimental rabbit model of infrarenal aortic occlusion for 20 minutes at normothermic body temperature.

RESULTS

Control rabbits experienced an 88% (7/8) incidence of paralysis after spinal cord ischemia induced by 20 minutes of aortic occlusion, whereas animals treated preoperatively with either whole-body hyperthermia (0/9) or stannous chloride (0/4) never became paralyzed (P <.001 for control vs treated groups). Ischemic protection of the spinal cord was associated with increased content of stress proteins within tissues of pretreated animals.

CONCLUSION

Prior induction of the heat shock response in the whole animal will increase the content of stress proteins within the spinal cord and other tissues and result in the prevention of hind-limb paralysis associated with aortic occlusion. We have designated the preoperative induction of the cellular stress response for the prevention of ischemic tissue injury stress conditioning. We suggest that stress-conditioning protocols represent the opportunity to practice preventative medicine at the molecular level.

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.

Neuroprotective effects of bilobalide, a component of the Ginkgo biloba extract (EGb 761), in gerbil global brain ischemia

The neuroprotective effect of Ginkgo biloba extract (EGb 761) against ischemic injury has been demonstrated in animal models. In this study, we compared the protective effect of bilobalide, a purified terpene lactone from EGb 761, and EGb 761 against ischemic injury. We measured neuronal loss and the levels of mitochondrial DNA (mtDNA)-encoded cytochrome oxidase (COX) subunit III mRNA in vulnerable hippocampal regions of gerbils. At 7 days of reperfusion after 5 min of transient global forebrain ischemia, a significant increase in neuronal death and a significant decrease in COX III mRNA were observed in the hippocampal CA1 neurons. Oral administration of EGb 761 at 25, 50 and 100 mg/kg/day and bilobalide at 3 and 6 mg/kg/day for 7 days before ischemia progressively protected CA1 neurons from death and from ischemia-induced reductions in COX III mRNA. In addition, both bilobalide and EGb 761 protected against ischemia-induced reductions in COX III mRNA in CA1 neurons prior to their death, at 1 day of reperfusion. These results suggest that oral administration of bilobalide and EGb 761 protect against ischemia-induced neuron death and reductions in mitochondrial gene expression.

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

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

Minimal ischaemic neuronal damage and HSP70 expression in MF1 strain mice following bilateral common carotid artery occlusion

Investigation into the influence of specific genes and gene products upon the pathophysiology of cerebral ischaemia has been greatly enhanced by the use of genetically modified mice. A simple model of global cerebral ischaemia in mouse is bilateral common carotid artery occlusion (BCCAo) and the neuropathological impact of BCCAo has been investigated in several mouse strains. Bilateral carotid occlusion produces extensive neuronal damage in C57Bl/6J strain mice and this damage is linked to posterior communicating artery (PcomA) hypoplasticity in the circle of Willis. In the present study, we investigated the effect of BCCAo in MF1 strain mice and compared them with C57Bl/6J mice. The neuropathological consequences of BCCAo were assessed using standard histochemical staining and heat shock protein 70 (HSP70) immunohistochemical staining (to demarcate cells that had been ischaemically stressed). The effect of BCCAo on mean arterial blood pressure (MABP) was also measured. The plasticity of the circle of Willis was recorded using carbon black perfusion. MF1 mice displayed significantly less ischaemic neuronal damage and HSP70 immunoreactivity compared to C57Bl/6J mice following 10-20 min BCCAo. Moreover, ischaemic neuronal damage and HSP70 immunoreactivity in MF1 mice subjected to extended BCCAo (25-45 min) was never as extensive or widespread as that observed in C57Bl/6J mice after 20 min BCCAo. MABP in MF1 mice (102+/-5 mmHg) was significantly higher than in C57Bl/6J mice (87+/-5) during 20 min BCCAo. MABP in MF1 mice during 20 and 40 min (103+/-12 mmHg) BCCAo remained above pre-occlusion values for the entire occlusion period. MF1 mice had significantly greater circle of Willis plasticity (more PcomAs) than C57Bl/6J mice did. These data indicate that MF1 mice are less susceptible to BCCAo than C57Bl/6J mice and that this could be due to maintained increases in MABP during BCCAo and the lower prevalence of abnormalities of the circle of Willis in MF1 mice.

Decrease in level of APG-2, a member of the heat shock protein 110 family, in murine brain following systemic administration of kainic acid

APG-2 belongs to the heat shock protein 110 family. Although kainic acid (KA)-induced seizures are known to elicit expression of inducible heat shock protein 70 (HSP70) in the brain, no investigation has been carried out on the APG-2 level after excitatory amino acid-induced seizures. By means of an immunoblot assay, we determined the levels of HSP70 and APG-2 in discrete brain structures of mice after a single intraperitoneal injection of KA or N-methyl-D-aspartic acid (NMDA). APG-2 level was significantly decreased in frontal cortex, hippocampus, and striatum three days after the administration of KA, while HSP70 level was increased in these regions following the administration. In any of these regions, APG-2 levels were returned to the control levels 10 days after the administration. However, no significant changes were observed in levels of both HSP70 and APG-2 in hypothalamus, midbrain, medulla-pons, and cerebellum of the mice. By contrast, NMDA administration did not significantly affect both levels in any of the regions examined. These findings indicate that the transient decrease in APG-2 expression is one of the intracellular events elicited by signals peculiar to KA, but not by those peculiar to NMDA, in telencephalon of murine brain.

Intracellular Ca(2+) changes induced by in vitro ischemia in rat retinal slices

The effect of ischemia on intracellular Ca(2+)concentration [[Ca(2+)](i)] in retinal slices was investigated. [Ca(2+)](i)in each layer of the retina was determined from fluorescence images in rat retinal slices loaded with fura2-AM. Ischemic like conditions were imposed on the retinal slice in vitro by perfusion with an oxygen/glucose deprived solution. All measurements were taken at 25 degrees C except when temperature dependence was examined. In response to 100 m M K(+)or 0.2 m M glutamate under normoxic conditions, the [Ca(2+)](i)increase was higher in the inner retinal layers. Fifteen min ischemia evoked an increase in Ca(2+)levels in all layers of the retina, and the rates of increase were especially high in the outer/inner segment layer and the outer nuclear layer. Ischemia in the absence of extracellular Ca(2+)also induced a Ca(2+)rise, but at lower rates than with standard ischemia. Intermittent ischemia, composed of three 15 min bursts of ischemia at 10 min intervals, promoted the Ca(2+)rise. There was a more marked rise in [Ca(2+)](i)when the temperature was increased to 29 or 33 degrees C. Thus, in the rat retinal slice, in vitro ischemia evoked a more marked Ca(2+)rise in the outer retina, which was in contrast to the Ca(2+)responses to glutamate or high K(+). The rates of increase in [Ca(2+)](i)with ischemia were larger at higher temperatures, and intermittent ischemia also promoted the Ca(2+)rise. These increases appear to be derived from predominant influx of extracellular Ca(2+)rather than release of intracellular Ca(2+)stores.

Regulation of pp60(c-src) synthesis in rat hippocampal slices by in vitro ischemia and glucocorticoid administration

Corticosteroids, released from the adrenal gland in response to stress, bind to receptors that act as transcription factors to alter gene expression and, subsequently, protein synthesis. Using [(35)S]-methionine-cysteine incorporation to measure protein synthesis in hippocampal slices incubated under ischemic conditions, synthesis of 60 kDa and 78 kDa proteins decreases 4 hr after in vivo administration of corticosterone to rats. The former protein has been identified by immunoblotting and immunoprecipitation to be the proto-oncogene, pp60(c-src). In the absence of prior glucocorticoid administration, ischemic conditions increase the amount of immunoreactive pp60(c-src) in membranes of hippocampal slices. Chronic exposure to elevated titers of glucocorticoids has been demonstrated to result in cell loss as well as in reduced neuronal plasticity and regeneration. Given the involvement of pp60(c-src) in synaptic plasticity and cell growth, glucocorticoid-mediated reduction in its synthesis is a potential molecular marker for stress-induced alterations in brain function.

Establishment of a local cooling model against spinal cord ischemia representing prolonged induction of heat shock protein

OBJECTIVES

Paraplegia is one of the serious complications of thoracoabdominal aortic operations. Regional hypothermia protects against spinal cord ischemia although the protective mechanism remains unknown. We attempted to create a simple model of local cooling under transient spinal cord ischemia and evaluated the effect using functional and histologic findings.

METHODS

Male domesticated rabbits were divided into 3 groups: control, normothermic group (group N), and local hypothermic group (group H). A balloon catheter was used for spinal cord ischemia by abdominal aortic clamping. A cold pack attached to the lumbar region could lower the regional cord temperature initially. Neurologic function was evaluated by the Johnson score. Cell damage was analyzed by observing motor neurons with the use of hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated deoxy-uracil triphosphate biotin in situ nick end labeling (TUNEL), and immunoreactivity of heat shock protein.

RESULTS

Physiologic estimation showed that local hypothermia improved the functional deficits (group N, 1.3 +/- 0.9; group H, 4.9 +/- 0.3; P =.0020). Seven days after reperfusion, there was a significant difference in the motor neuron numbers between groups N and H (group N, 7.2 +/- 1.9; group H, 20.4 +/- 3.2; P =.0090). The number of TUNEL-positive motor neurons was reduced significantly (group N, 7.2 +/- 2.4; group H, 1.0 +/- 0.7; P =.0082). Heat shock protein immunoreactivity was prolonged up to 2 days after reperfusion in the hypothermic group.

CONCLUSIONS

These results suggest that local hypothermia extended the production of heat shock protein in spinal cord motor neurons after reperfusion and inhibited their apoptotic change.

Induction of the HSP110/105 family in the rat hippocampus in cerebral ischemia and ischemic tolerance

Recently, the authors isolated a novel gene of the HSP110 family, ischemia responsive protein 94 kDa (irp94), and demonstrated the expression of this gene after transient forebrain ischemia. In the current study, the authors investigated the expression profiles of all HSP110 family members including hsp110/105 and osp94/apg-1, after transient forebrain ischemia using rat four-vessel occlusion model. Among three members of the HSP110 family, induction of hsp110/105 was the most prominent after ischemia. hsp110/105 mRNA expression was clearly enhanced from 4 to 24 hours after a 6-minute or longer ischemic period. First, hsp110/105 mRNA expression was induced in the dentate gyrus, and later in the pyramidal layer. HSP110/105 protein expression also was enhanced by a 6-minute or longer period of ischemia. Profiles of HSP110/105 expression after ischemia were similar to those of inducible HSP70. After transient forebrain ischemia for 10 minutes, HSP110/105 protein was induced in the dentate gyrus and the CA3 pyramidal layer, but not in the CA1 pyramidal neurons. However, 6 minutes of ischemia induced the HSP110/105 protein, as well as the HSP70 protein, in the CA1 region. CA1 pyramidal neurons expressing HSP110/105 acquired tolerance against subsequent severe ischemia. In conclusion, HSP110/105 showed the most prominent induction after ischemia among the three HSP110 gene family members. Colocalization of HSP110/105 and HSP70 in the CA1 neurons that acquired tolerance suggested that induced HSP110/105 might contribute to ischemic tolerance together with HSP70.

Induction of heat shock proteins and motor function deficits after focal cerebellar injury

A weight drop model of focal cerebellar injury was used to identify heat shock protein induction and motor function deficits in the anesthetized, adult male, Sprague-Dawley rat. All animals were trained on a beam walking test prior to surgery. Groups of animals received severe, mild or sham weight drop injury to the lateral/paravermal region of the cerebellum. The mild and sham-injured animals showed no motor deficits in the beam walking test, whereas animals with severe cerebellar injury showed significant motor deficits in the beam walking test that approached recovery of motor function 20 days after injury. Following severe injury, induction of heat shock protein of 27kDa was observed in Purkinje cells and in neurons of the deep cerebellar nuclei, as well as Bergmann glial cells, glial cells located in the granule cell layer and the underlying white matter. Following mild injury, heat shock protein of 27kDa induction was observed in Purkinje cells and glial cells, but not in neurons of the deep cerebellar nuclei. The labeled Purkinje cells were widely distributed in the ipsilateral cerebellar cortex. Many of the glial cells that were immunostained with heat shock protein of 27kDa co-localized with cells immunoreactive for glial fibrillary acidic protein. After severe injury, heat shock protein of 72kDa was localized mainly in granule cells at the site of the trauma and in the ipsilateral deep cerebellar nuclei whereas, after mild injury, light labeling was observed only in the granule cell layer. The results demonstrate that focal cerebellar injury has profound effects on motor behavior and induces different families of heat shock proteins in specific groups of neurons and glial cells in the cerebellum.

Attenuation of ischemic brain edema and cerebrovascular injury after ischemic preconditioning in the rat

Ischemic preconditioning (IPC) induces neuroprotection to subsequent severe ischemia, but its effect on the cerebrovasculature has not been studied extensively. This study evaluated the effects of IPC on brain edema formation and endothelial cell damage that follows subsequent permanent focal cerebral ischemia in the rat. Transient (15 minute) middle cerebral artery occlusion (MCAO) was used for IPC. Three days after IPC or a sham operation, permanent MCAO was induced. Twenty-four hours after permanent MCAO, neurologic deficit, infarction volume, and water and ion content were evaluated. Six hours post-ischemia, blood-brain barrier (BBB) permeability was examined using [3H]-inulin. Water, ion contents, and BBB permeability were assessed in three zones (core, intermediate, and outer) depending on their relation to the MCA territory. Heat shock protein 70 (HSP70) was also examined as a potential marker of vascular injury. The model of IPC significantly reduced brain infarction and neurologic deficit. Compared with a sham operation, IPC also significantly attenuated brain edema formation in the intermediate (sham and IPC water contents: 5.99+/-0.65 vs. 4.99+/-0.81 g/g dry weight; P < 0.01) and outer zones (5.02+/-0.48 vs. 4.37+/-0.42 g/g dry weight; P < 0.01) of the ipsilateral hemisphere but not in the core zone. Blood-brain barrier disruption assessed by [3H]-inulin was significantly attenuated in the IPC group and the number of blood vessels that displayed HSP70 immunoreactivity was also reduced. Thus, IPC significantly attenuates ischemic brain edema formation, BBB disruption, and, as assessed by HSP70, vascular injury. Understanding the mechanisms involved in IPC may provide insight into methods for preserving cerebrovascular function during ischemia.

Chemical preconditioning with 3-nitropropionic acid in gerbil hippocampal slices: therapeutic window and the participation of adenosine receptor

Ischemic tolerance induced by a subtoxic dose of neurotoxin, 3-nitropropionic acid (3-NPA), was recently reported as "chemical preconditioning." We electrophysiologically investigated the therapeutic window and the effect via action at the adenosine receptor using a gerbil hippocampal slice model of the tolerance phenomenon. 3-NPA at the dose of 4 mg/kg was administered intraperitoneally at 3, 24, and 72 h prior to slice preparation. Prolonged delay to hypoxic depolarization (HD) and improvement of the field excitatory postsynaptic potential recovery following a fixed period of hypoxia (8 min) were observed in the groups pretreated at 3 and 24 h compared with the control (P < 0.05). Correlation between the delay to HD and the recovery was highly significant (r = 0.37, P < 0.001). These effects were completely reversed by administration of theophylline (20 mg/kg), an adenosine receptor blocker. These findings indicate that chemical preconditioning with 3-NPA induces early onset (3 h) and long-lasting (24 h) tolerance of hypoxic damage to excitatory synaptic mechanisms in the hippocampus by delayed calcium entry, and the activation of adenosine receptor contributes to this neuroprotective effect.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.

The role of volume transmission of adaptogenic signals in forming the adaptive reactions of the brain

This review presents published data and results from our own studies providing evidence for the important role of volume, non-synaptic transmission of adaptogenic signals in the mechanisms forming the long-term adaptive reactions of the brain. The importance of chemical factors involved in volume transmission and secreted by cells in this process is discussed. Special attention is paid to peptides-possible mediators of volume transmission of adaptive-type signals. Evidence has been obtained for the presence of peptides and their role in the mechanism of development of adaptive brain reactions of different origins, especially those arising in response to tetanic stimulation of neurons and transient hypoxic stress. An original method for testing for the effects of neuromodulator factors released by cells in donor slices subjected to these treatments on recipient slices was used to show that these factors had pronounced effects on synaptic transmission and could induce long-term potentiation of synaptic transmission, protecting against functional derangements due to prolonged anoxia. Blockade of protein synthesis in donor slices subjected to adaptogenic treatments suppressed the appearance of these effects. The review concludes with a discussion of the mechanisms of interaction of the synaptic and volume transmission of signals involved in forming long-term adaptive brain reactions.

Hypothermia during reperfusion after asphyxial cardiac arrest improves functional recovery and selectively alters stress-induced protein expression

This study examined whether prolonged hypothermia induced 1 hour after resuscitation from asphyxial cardiac arrest would improve neurologic outcome and alter levels of stress-related proteins in rats. Rats were resuscitated from 8 minutes of asphyxia resulting in cardiac arrest. Brain temperature was regulated after resuscitation in three groups: normothermia (36.8 degrees C x 24 hours), immediate hypothermia (33 degrees C x 24 hours, beginning immediately after resuscitation), and delayed hypothermia (33 degrees C x 24 hours, beginning 60 minutes after resuscitation). Mortality and neurobehavioral deficits were improved in immediate and delayed hypothermia rats relative to normothermia rats. Furthermore, both immediate and delayed hypothermia improved neuronal survival in the CA1 region of the hippocampus assessed at 14 days. In normothermia rats, the 70-kDa heat shock protein (Hsp70) and 40-kDa heat shock protein (Hsp40) were increased within 12 hours after resuscitation in the hippocampus. Delayed hypothermia attenuated the increase in Hsp70 levels in the hippocampus but did not affect Hsp70 induction in the cerebellum. Hippocampal expression of Hsp40 was not affected by hypothermia. These data indicate that prolonged hypothermia during later reperfusion improves neurologic outcome after experimental global ischemia and is associated with selective changes in the pattern of stress-induced protein expression.

Constitutive expression of the 25-kDa heat shock protein Hsp25 reveals novel parasagittal bands of purkinje cells in the adult mouse cerebellar cortex

Despite the reported absence of the 25-kDa heat shock protein Hsp25 in the rodent cerebellum, we have determined that Hsp25 is constitutively expressed in a subset of Purkinje cells in the adult cerebellum of the mouse. No other cerebellar neurons are Hsp25 immunoreactive, but there is weak staining associated with blood vessels. In the vermis, Hsp25-immunoreactive Purkinje cells are confined to two regions: one in lobules VI/VII, the other in lobules IX/X. In each region, only a subset of the Purkinje cells is immunoreactive. These cells are grouped in five parasagittal bands arranged symmetrically about the midline. The boundaries of these expression domains correspond to transverse zones previously inferred from other expression patterns. A third Hsp25-immunopositive domain is seen in the paraflocculus and flocculus. Again, only a subset of Purkinje cells within the paraflocculus and flocculus express Hsp25, revealing three distinct bands. Previous descriptions of compartmentation antigens have not differentiated between adult populations of Purkinje cells in these regions, suggesting that Hsp25 is a novel compartmentation antigen in the adult cerebellum.

Stress proteins as molecular markers of neurotoxicity

In response to many environmental and pathophysiologic stressful stimuli, cells undergo a stress response characterized by induction of a variety of proteins, including the heat shock protein family. The inducible heat shock protein 70 (hsp70) is believed to participate in an array of cellular activities, including cytoprotection. Normal brain cells have little detectable hsp70 RNA or protein. However, following a stressful condition hsp70 mRNA and protein are induced in different cell types depending on the severity and the nature of the stimulus. The induction of hsp70 protein correlates with the regional and cellular vulnerability to a particular injury as identified by standard histologic methods. The pattern of hsp70 expression differs in response to various neurotoxic stimuli, including hyperthermia, ischemia, seizures, hemorrhage, and N-methyl-D-aspartate receptor antagonist administration. Hsp70 expression is a useful marker of cellular injury and may help to identify previously unrecognized areas of vulnerability in the nervous system after a neurotoxic stimulus. Hsp70 may also play a neuroprotective role in the brain.

Glucocorticoids regulate the synthesis of HSP27 in rat brain slices

Using mild heat shock of rat brain slices as a model for cellular insult, corticosteroid-mediated regulation of protein synthesis has been investigated. Following a single in vivo injection of rats with corticosterone or the Type II glucocorticoid receptor agonist, RU-28362, synthesis of a 28 kDa protein is elevated in cerebellar slices which are subsequently incubated in vitro at 39 degrees C for 3 h. Immunoblotting of proteins subsequent to separation by two-dimensional gel electrophoresis has identified this glucocorticoid-sensitive protein to be the small molecular weight heat-shock protein, HSP27. Synthesis of the major heat-shock proteins, HSP70 and HSP90, is not glucocorticoid-sensitive. When animals are sacrificed at either 4 h following an aldosterone injection or at 24 h following a corticosterone injection, the synthesis of HSP27 in cerebellar slices is decreased. Treatment of adrenalectomized rats with either corticosterone, RU-28362 or aldosterone produces increased synthesis of HSP27. With duration of heat shock, there is a transient increase in the synthesis of HSP27 after 2 h at 39 degrees C in slices from the cerebral cortex, with a more sustained synthesis of HSP27 in cerebellar slices. In hippocampal slices, HSP27 is rarely present. The upregulated synthesis of HSP27 in the cerebellum following an acute exposure to stress-like elevations in corticosterone titers may contribute to the relative resistance of this brain region to cellular insults.

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.

NMDA receptor antagonism, but not AMPA receptor antagonism attenuates induced ischaemic tolerance in the gerbil hippocampus

Recent studies have shown that a brief 'pre-conditioning' ischaemic insult reduces the hippocampal cell death caused by a subsequent more severe test insult. In the present studies, we have examined the effects of the non-competitive NMDA receptor antagonist ((5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine, MK-801) a competitive NMDA receptor antagonist, LY202157, AMPA receptor antagonist ((3S,4aR,6R,8aR)-6-[2-(1(2)H-tetrazole-5-yl)]decahydroiso quinoline-3-carboxylic acid, LY293558), a non-competitive AMPA receptor antagonist ((-)-1-(4-amino-phenyl)-4-methyl-7,8-methylenedioxy-4,5-dihydro-3-acetyl -2,3-benzodiazepine, LY300164), and a mixed NMDA/AMPA receptor antagonist, LY246492, in a gerbil model of ischaemic tolerance. Ischaemic tolerance was induced by subjecting gerbils to a 2-min 'pre-conditioning' ischaemia (bilateral carotid occlusion) 2 days prior to a 3-min test ischaemia. The effects of MK-801 (2 mg/kg i.p.), LY293558 (20 mg/kg i.p., followed by 4 x 10 mg/kg at 3 h intervals), LY300164 (4 x 10 mg/kg i.p. at 1 h intervals), LY246492 (40 mg/kg i.p., followed by 4 x 20 mg/kg i.p. at 3 h intervals) and LY202157 (30 mg/kg i.p., followed by 4 x 15 mg/kg i.p. at 2 h intervals) were then examined in this model. Initial dosing commenced 30 min prior to the 2-min 'pre-conditioning' ischaemia. Results indicated that a 2-min 'pre-conditioning' ischaemia produced ischaemic tolerance in all cases. The non-competitive NMDA receptor antagonist, MK-801, produced a significant (P < 0.01) reduction in the induced tolerance, while the competitive NMDA receptor antagonist, LY202157, also attenuated (P < 0.05) the induction of tolerance. In contrast, two AMPA receptor antagonists (LY293558 and LY300164) and a mixed NMDA/AMPA receptor antagonist (LY246492) had no effect on the induction of tolerance. These results suggest that NMDA receptor activation, but not AMPA receptor activation is involved in the phenomenon of ischaemic tolerance.

HSP70 expression is increased during the day in a diurnal animal, the golden-mantled ground squirrel Spermophilus lateralis

Heat shock protein 70 (HSP70) gene expression was studied in a seasonal hibernator, the diurnal ground squirrel, Spermophilus lateralis. RNA transcripts of 2.7 and 2.9 kb hybridizing to an HSP70 cDNA were expressed in both brain and peripheral tissues of pre-hibernation euthermic animals; higher levels of expression were observed during the day than during nighttime samples. A decline in the expression of both transcripts occurred in all tissues examined during hibernation that remained low throughout the hibernation season, including the interbout euthermic periods and regardless of time of day. Quantitative comparisons showed pre-hibernation nighttime HSP70 expression to be as low as that observed during hibernation, despite the drastic increase in metabolic state and nearly 30 degrees C difference in body temperature. In contrast to HSP70, some mRNAs, such as beta-actin and HSP60, remained relatively constant, while others, such as glyceraldehyde 3-phosphate dehydrogenase, increased in specific tissues during the hibernation season. These results indicate that the expression of a highly conserved gene involved in protection from cellular stress, HSP70, can vary with an animal's arousal state.

Activation of Arc gene, a dendritic immediate early gene, by middle cerebral artery occlusion in rat brain

The effect of middle cerebral artery (MCA) occlusion on the activity-regulated cytoskeleton-associated protein (Arc) mRNA expression has been investigated using in situ hybridization. It was induced in the extensive regions of cerebral cortex, medial striatum, and distant areas such as the ipsilateral lateral septal nucleus, bilateral hippocampal formation and contralateral amygdala following MCA occlusion. In the hippocampal formation, it was induced in the granule cell layer and the stratum pyramidale at 1 h and in the molecular layer and in the stratum oriens and stratum radiatum bilaterally at 4 h. MK-801 pretreatment strongly attenuated the induction of Arc mRNA. The present results suggest that Arc may play an important role in the neuronal plasticity through NMDA activation following focal cerebral ischemia.

Calpastatin is up-regulated in response to hypoxia and is a suicide substrate to calpain after neonatal cerebral hypoxia-ischemia

In a model of cerebral hypoxia-ischemia in the immature rat, widespread brain injury is produced in the ipsilateral hemisphere, whereas the contralateral hemisphere is left undamaged. Previously, we found that calpains were equally translocated to cellular membranes (a prerequisite for protease activation) in the ipsilateral and contralateral hemispheres. However, activation, as judged by degradation of fodrin, occurred only in the ipsilateral hemisphere. In this study we demonstrate that calpastatin, the specific, endogenous inhibitor protein to calpain, is up-regulated in response to hypoxia and may be responsible for the halted calpain activation in the contralateral hemisphere. Concomitantly, extensive degradation of calpastatin occurred in the ipsilateral hemisphere, as demonstrated by the appearance of a membrane-bound 50-kDa calpastatin breakdown product. The calpastatin breakdown product accumulated in the synaptosomal fraction, displaying a peak 24 h post-insult, but was not detectable in the cytosolic fraction. The degradation of calpastatin was blocked by administration of CX295, a calpain inhibitor, indicating that calpastatin acts as a suicide substrate to calpain during hypoxia-ischemia. In summary, calpastatin was up-regulated in areas that remain undamaged and degraded in areas where excessive activation of calpains and infarction occurs.