Requirement for nitric oxide activation of p21(ras)/extracellular regulated kinase in neuronal ischemic preconditioning

Involvement of Ras in survival responsiveness to nitric oxide toxicity in pheochromocytoma cells

Nitric oxide (NO) plays a key role in attenuation of tumor growth by activated macrophages that generate large amount of cytotoxic/cytostatic free radicals. However, some tumor cells may survive from NO cytotoxicity and continue to proliferate to malignant tumors. Since a protooncogene product Ras was shown to be activated by NO, this study investigated the involvement of Ras in the cell survival in response to NO cytotoxicity in pheochromocytoma (PC12) cells. Treatment with Ras inhibitor or constitutive expression of dominant negative Ras markedly increased NO-induced cell death. NO-resistant PC12 cells (PC12-NO-R) exhibited higher steady state Ras activity than the parental PC12 cells. Inducible expression using tetracycline-on (Tet-on) system of Ras mutants (dominant negative Ras or dominant active Ras) demonstrated that blockade of Ras activity increased NO-induced cell death whereas enhancement of Ras activity attenuated NO-induced cell death. Furthermore, inducible expression of NO-insensitive mutant Ras selectively increased cellular vulnerability to NO but not to ROS. NO, Ras inhibitor and extracellular signal-regulated kinase (Erk) blocker synergistically increased cell death. These observations suggest that Ras activity may be a critical factor for survival response of tumor cells to NO toxicity and pharmacological agents affecting Ras activity may enhance efficacy of NO-mediated tumor therapies.

Improvement in neuronal survival after ischemic preconditioning in hippocampal slice cultures

The main goals of the current study were to assess: (a) whether a sublethal ischemic insult could protect the CA1 subregion of the hippocampus in organotypic slices against a lethal ischemic insult; and (b) whether this protection is long lasting as determined with an accurate immunohistochemical neuronal marker, NeuN. Hippocampal slice cultures were grown for 12-14 days in vitro. Slices were exposed either to oxygen/glucose deprivation (OGD) for 45 min (ischemia), or OGD for 15 min (ischemic preconditioning), 48 h prior to 45 min OGD, or were untreated (sham). Cell death was estimated by propidium iodide fluorescence 1 day after OGD and by NeuN immunohistochemistry 7 days after OGD. Image analysis was employed to measure the relative optical density of the NeuN-signal in all groups. After ischemia, damaged neurons were shrunken or lost and NeuN immunoreactivity was reduced. Relative optical density of NeuN (ROD [NeuN]) was 0.193+/-0.015 in control (sham) (n=9). In slices that underwent ischemia, ROD [NeuN] declined to 0.108+/-0.018 (n=5) in CA1 (*P<0.05 ROD [NeuN] in preconditioned slice cultures was 0.190+/-0.037 (76% higher than the ischemia group). Similar results were found after measuring PI fluorescence. In the CA1 sub-region, PI fluorescence was about 13, 47 and 17% in the sham, ischemic and IPC groups, respectively. We suggest that the immunohistochemical approach validates the dye uptake method used in slice cultures and yields quantitative data specific for neurons. We also conclude that the organotypic hippocampal slice model is useful for studying delayed ischemic preconditioning that is maintained for hours or days after the preconditioning event.

Analysis of 106 kb of contiguous DNA sequence from the D genome of wheat reveals high gene density and a complex arrangement of genes related to disease resistance

Vast differences exist in genome sizes of higher plants; however, gene count remains relatively constant among species. Differences observed in DNA content can be attributed to retroelement amplification leading to genome expansion. Cytological and genetic studies have demonstrated that genes are clustered in islands rather than distributed at random in the genome. Analysis of gene islands within highly repetitive genomes of plants like wheat remains largely unstudied. The objective of our work was to sequence and characterize a contiguous DNA sequence from chromosome IDS of Aegilops tauschii. An RFLP probe that maps to the Lr21 region of IDS was used to isolate a single BAC. The BAC was sequenced and is 106 kb in length. The contiguous DNA sequence contains a 46-kb retroelement-free gene island containing seven coding sequences. Within the gene island is a complex arrangement of resistance and defense response genes. Overall gene density in this BAC is 1 gene per 8.9 kb. This report demonstrates that wheat and its relatives do contain regions with gene densities similar to that of Arabidopsis.

Neuroprotection by hypoxic preconditioning requires sequential activation of vascular endothelial growth factor receptor and Akt

Hypoxic preconditioning provides protection against ischemic brain lesions in animal models of cerebral ischemia-hypoxia. To analyze the underlying molecular mechanisms, we developed an in vitro model of hypoxic neuroprotection in cerebellar granule neurons (CGN) by reducing the oxygen tension to 1-5% for 1-24 hr. Exposure to 5% O2 for 9 hr resulted in reduction of cell death after potassium deprivation, treatment with 100 microm glutamate, or 500 microm 3-nitroproprioninc acid (3-NP) by 46, 22, and 55%, respectively. Shorter (1 or 3 hr) or longer (>12 hr) intervals or pretreatment with lower oxygen tension failed to rescue CGN from death. In contrast, toxicity of four different chemotherapeutic drugs [1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, cisplatine, topotecane, and vincristine] was unaffected by hypoxic preconditioning. The induction of protective effects was dependent on new protein synthesis. Protein levels of B-cell lymphoma protein-2 (BCL-2), BCL-x(L/S), heat shock protein 70/90, and BCL-2-associated death protein remained unaltered. CGN incubated at 5% O2 for 9 hr showed increased levels of the vascular endothelial growth factor (VEGF), the VEGF receptor-2 (VEGFR-2), phosphorylated Akt/protein kinase B (PKB), and extracellular signal-regulated kinase 1 (ERK1). Incubation with a neutralizing anti-VEGF antibody, a monoclonal antibody to VEGFR-2, wortmannin, or antisense-Akt/PKB, but not treatment with U0126, an ERK-inhibitor, reverted the resistance acquired by hypoxic preconditioning. Inhibition of VEGFR-2 blocked the activation of Akt/PKB. Finally, pretreatment with recombinant VEGF resulted in a hypoxia-resistant phenotype in the absence of hypoxic preconditioning. Our data are indicating a sequential requirement for VEGF/VEGFR-2 activation and Akt/PKB phosphorylation for neuronal survival mediated by hypoxic preconditioning and propose VEGF as a hypoxia-induced neurotrophic factor.

Activation of adenosine triphosphate-sensitive potassium channels confers protection against rotenone-induced cell death: therapeutic implications for Parkinson's disease

It is anticipated that further understanding of the protective mechanism induced by ischemic preconditioning will improve prognosis for patients of ischemic injury. It is not known whether preconditioning exerts beneficial actions in neurodegenerative diseases, in which ischemic injury plays a causative role. Here we show that transient activation of ATP-sensitive potassium channels, a trigger in ischemic preconditioning signaling, confers protection in PC12 cells and SH-SY5Y cells against neurotoxic effect of rotenone and MPTP, mitochondrial complex I inhibitors that have been implicated in the pathogenesis of Parkinson's disease. The degree of protection is in proportion to the bouts of exposure to an ATP-sensitive potassium channel opener, a feature reminiscent of ischemic tolerance in vivo. Protection is sensitive to a protein synthesis inhibitor, indicating the involvement of de novo protein synthesis in the protective processes. Pretreatment of PC12 cells with preconditioning stimuli FeSO(4) or xanthine/xanthine oxidase also confers protection against rotenone-induced cell death. Our results demonstrate for the first time the protective role of ATP-sensitive potassium channels in a dopaminergic neuronal cell line against rotenone-induced neurotoxicity and conceptually support the view that ischemic preconditioning-derived therapeutic strategies may have potential and feasibility in therapy for Parkinson's disease.

Isoflurane induced prolonged protection against cerebral ischemia in mice: a redox sensitive mechanism?

We here demonstrate that general anesthesia with isoflurane can have profound effects on the brain of mice long after the anesthetic has been discontinued. Three hours of exposure to 1% isoflurane induced rapid and longlasting protection against 60 min transient focal cerebral ischemia induced by filament occlusion of the middle cerebral artery (MCAO). Mean infarct volumes were significantly smaller in animals pretreated with isoflurane 0, 12, and 24 h before MCAO (-38%, -31%, -24%, respectively). Mild hypoxia (17% O(2)) during or 5 mg/kg desferrioxiamine administered at the onset of isoflurane pretreatment completely abrogated the development of delayed tolerance (12 h) against focal cerebral ischemia, suggesting that the signaling of delayed protection induced by isoflurane is sensitive to the intracellular oxygenation state.

Genetic mapping of the Lr20-Pm1 resistance locus reveals suppressed recombination on chromosome arm 7AL in hexaploid wheat

The Lr20-Sr15-Pm1 resistance locus in hexaploid wheat confers resistance to three different fungal wheat pathogens (leaf rust, stem rust, and powdery mildew). It was previously localized in the distal region of chromosome arm 7AL. As a first step towards the isolation of this complex locus, we performed molecular mapping of the Lr20 and Pm1 genes in three F2 populations. In two populations, a cluster of 8 and 12 markers, respectively, cosegregated with the resistance genes. In a third population based on a cross between a susceptible lr20 mutant and a resistant cultivar, all clustered markers were monomorphic. However, in this population the recombination frequency proximal to the Lr20 gene was up to 60 times higher, indicating that the complete genetic linkage of the clustered markers is not due to a close physical linkage of the probes but is caused by suppressed recombination. This was supported by the analysis of Triticum monococcum BAC clones where no physical linkage between cosegregating probes was observed. Suppressed recombination at the Lr20-Pm1 locus is likely the result of an alien introgression of chromatin from an unidentified wild relative species or is due to chromosomal rearrangements.

Genomic targeting and high-resolution mapping of the domestication gene Q in wheat

The Q locus is largely responsible for the domestication of bread wheat. Q confers the free-threshing character of the spike and influences other important agronomic traits. Using chromosome deletion lines, Q was placed on the physical map within a submicroscopic segment of the long arm of chromosome 5A. We targeted markers to the segment by comparative mapping of anonymous RFLP clones, AFLP, and mRNA differential display analysis of deletion lines 5AL-7 and -23, which have deletion breakpoints that flank the Q locus. Differentially expressed sequences detected fragments at various loci on group 5 chromosomes suggesting that Q may be a regulatory gene. We identified 18 markers within the Q gene deletion interval and used them to construct a genetic linkage map of the region in F2 populations derived from chromosome 5A disomic substitution lines. The genetic map corresponding to the deletion segment was 20-cM long, and we identified markers as close as 0.7 cM to the Q gene. An estimate of base pairs per centimorgan within the region is 250 kb/cM, an 18-fold increase in recombination compared with the genomic average. Genomic targeting and high-density mapping provide a basis for the map-based cloning of the Q gene.

Tolerance against ischemic neuronal injury can be induced by volatile anesthetics and is inducible NO synthase dependent

BACKGROUND AND PURPOSE

We tested whether volatile anesthetics induce neuroprotection that is maintained for a prolonged time.

METHODS

Rats were pretreated for 3 hours with 1 minimal anesthetic concentration of isoflurane or halothane in normal air (anesthetic preconditioning [AP]). The animals were subjected to permanent middle cerebral artery occlusion (MCAO) at 0, 12, 24, or 48 hours after AP. Halothane-pretreated animals were subjected to MCAO 24 hours after AP. Histological evaluation of infarct volumes was performed 4 days after MCAO. Cerebral glucose utilization was measured 24 hours after AP with isoflurane. Primary cortical neuronal cultures were exposed to 1.4% isoflurane for 3 hours. Oxygen-glucose deprivation (OGD) was performed 24 hours after AP. Injury was assessed 24 hours later by measuring the release of lactate dehydrogenase into the medium 24 hours after OGD.

RESULTS

Isoflurane anesthesia at 0, 12, and 24 hours before MCAO or halothane anesthesia 24 hours before MCAO significantly reduced infarct volumes (125+/-42 mm3, P=0.024; 118+/-51 mm3, P=0.008; 120+/-49 mm3, P=0.009; and 121+/-48 mm3, P=0.018, respectively) compared with control volumes (180+/-51 mm3). Three hours of isoflurane anesthesia in rats did not have any effect on local or mean cerebral glucose utilization measured 24 hours later. Western blot analysis from cortical extracts of AP-treated animals revealed an increase of the inducible NO synthase (iNOS) protein beginning 6 hours after AP. The iNOS inhibitor aminoguanidine (200 mg/kg IP) eliminated the infarct-sparing effect of AP. In cultured cortical neurons, isoflurane exposure 24 hours before OGD decreased the OGD-induced release of lactate dehydrogenase by 49% (P=0.002).

CONCLUSIONS

Pretreatment with volatile anesthetics induces prolonged neuroprotection in vitro and in vivo, a process in which iNOS seems to be critically involved.

Activation of Erk1/2 and Akt in astrocytes under ischemia

Substantial evidence has shown that extracellular signal-regulated kinases 1 and 2 (Erk1/2) and serine/threonine kinase (Akt) play important roles in regulating cell survival. We examined the activities of these kinases in astrocytes under ischemia in an anaerobic chamber. The level of phosphorylated Erk1/2 in astrocytes began to increase after 1 h ischemia, reached a maximum after 4 h ischemia, before decreasing from 5 to 6 h. Akt was activated later than Erk1/2. It was significantly increased after 4 h ischemia before declining steadily afterwards. Lactate dehydrogenase (LDH) assay and Hoechst nucleic staining indicated that U0126, which inhibits Erk1/2 phosphorylation, enhanced ischemia-induced cell death, whereas LY294002, which inhibits Akt phosphorylation, delayed cell death. These effects were dose-dependent. At 4 and 6 h ischemia, U0126-treated astrocytes expressed a lower level of Bcl-2 than controls. In contrast, LY294002-treated astrocytes expressed a higher level of Bcl-2 than controls as shown by Western blots. Bcl-x(L) expression level was not affected by either treatment. These data suggest that activation of the MAPK/Erk1/2 pathway might protect astrocytes from ischemic injury, but activation of the PI3-K/Akt pathway does not. The effect may involve Bcl-2 but not Bcl-x(L) expression.

Role of mitogen- and stress-activated kinases in ischemic injury

Protein kinase-mediated signaling cascades constitute the major route by which cells respond to their extracellular environment. Of these, three well-characterized mitogen-activated protein kinase (MAPK) signaling pathways are those that use the extracellular signal-regulated kinase (ERK1/2) or the stress-activated protein kinase (p38/SAPK2 or JNK/SAPK) pathways. Mitogenic stimulation of the MAPK-ERK1/2 pathway modulates the activity of many transcription factors, leading to biological responses such as proliferation and differentiation. In contrast, the p38/SAPK2 and JNK/SAPK (c-Jun amino-terminal kinase/stress-activated protein kinase) pathways are only weakly, if at all, activated by mitogens, but are strongly activated by stress stimuli. There is now a growing body of evidence showing that these kinase signaling pathways become activated following a variety of injury stimuli including focal cerebral ischemia. Whether their activation, however, is merely an epiphenomenon of the process of cell death, or is actually involved in the mechanisms underlying ischemia-induced degeneration, remains to be fully understood. This review provides an overview of the current understanding of kinase pathway activation following cerebral ischemia and discusses the evidence supporting a role for these kinases in the mechanisms underlying ischemia-induced cell death.

Neuroprotection and P450 2C11 upregulation after experimental transient ischemic attack

BACKGROUND AND PURPOSE

Transient ischemic attack (TIA) is a risk factor for stroke. However, TIA may also serve as a preconditioning stimulus, reducing damage from subsequent stroke. We tested the hypothesis that experimental TIA induces expression of P450 2C11, an arachidonic acid epoxygenase that produces vasodilator epoxyeicosatrienoic acids, leading to increased tissue perfusion and reduced stroke damage.

METHODS

Wistar rats underwent three 10-minute middle cerebral artery occlusions (TIA) or sham surgery. Three days later, animals were subjected to 2-hour middle cerebral artery occlusion and 24 hours of reperfusion. Brains were stained with 2,3,5-triphenyltetrazolium chloride for infarct size measurement or processed for quantification of P450 2C11 mRNA and protein with the use of RNase protection assay and Western blotting. Regional cerebral blood flow (CBF) at the end of 2-hour ischemia was measured in separate groups of rats with iodoantipyrine autoradiography.

RESULTS

Cerebral infarct was reduced by >50% in TIA- versus sham-preconditioned animals. 2C11 mRNA and protein were increased in ipsilateral hemisphere by 3 days after TIA but not sham surgery. Induction of 2C11 by TIA was also evident in ipsilateral hemisphere at 24 hours after 2-hour middle cerebral artery occlusion and 24 hours of reperfusion. End-ischemic regional CBF was not different between TIA- and sham-pretreated groups.

CONCLUSIONS

We conclude that experimental TIA induces ischemic tolerance by a mechanism temporally linked to upregulation of P450 2C11. Enzyme induction does not attenuate ischemic severity by amplifying end-ischemic CBF.

Transforming growth factor-beta 1 increases bad phosphorylation and protects neurons against damage

Despite the characterization of neuroprotection by transforming growth factor-beta1 (TGF-beta1), the signaling pathway mediating its protective effect is unclear. Bad is a proapoptotic member of the Bcl-2 family and is inactivated on phosphorylation via mitogen-activated protein kinase (MAPK). This study attempted to address whether MAPK signaling and Bad phosphorylation were influenced by TGF-beta1 and, furthermore, whether these two events were involved in the antiapoptotic effect of TGF-beta1. We found a gradual activation of extracellular signal-regulated kinase 1/2 (Erk1/2) and MAPK-activated protein kinase-1 (also called Rsk1) and a concomitant increase in Bad phosphorylation at Ser(112) in mouse brains after adenovirus-mediated TGF-beta1 transduction under nonischemic and ischemic conditions induced by transient middle cerebral artery occlusion. Consistent with these effects, the ischemia-induced increase in Bad protein level and caspase-3 activation were suppressed in TGF-beta1-transduced brain. Consequently, DNA fragmentation, ischemic lesions, and neurological deficiency were significantly reduced. In cultured rat hippocampal cells, TGF-beta1 inhibited the increase in Bad expression caused by staurosporine. TGF-beta1 concentration- and time-dependently activated Erk1/2 and Rsk1 accompanied by an increase in Bad phosphorylation. These effects were blocked by U0126, a mitogen-activated protein kinase/Erk kinase 1/2 inhibitor, suggesting an association between Bad phosphorylation and MAPK activation. Notably, U0126 and a Rsk1 inhibitor (Ro318220) abolished the neuroprotective activity of TGF-beta1 in staurosporine-induced apoptosis, indicating that activation of MAPK is necessary for the antiapoptotic effect of TGF-beta1 in cultured hippocampal cells. Together, we demonstrate that TGF-beta1 suppresses Bad expression under lesion conditions, increases Bad phosphorylation, and activates the MAPK/Erk pathway, which may contribute to its neuroprotective activity.

Possible roles of nitric oxide in the physiology and pathophysiology of the mammalian cochlea

Nitric oxide (NO) has been implicated as a mediator of vasodilation and neurotransmission in the mammalian cochlea. This is demonstrated by the presence of nitric oxide synthase (NOS) and nitric oxide (NO) in the blood vessels and the organ of Corti in the cochlea. It is not certain if the neurons in the spiral ganglion produce NO since no fluorescent signal could be detected by 4,5-diaminofluorescein diacetate (DAF-2DA), a fluorescent indicator of NO. To determine if NO/peroxynitrite plays any role in neurodestruction observed in ischemic cochlea of the guinea pig, the effects of NO donors, such as S-nitrosocysteine (S-NC) and nitroglycerine (NTG); peroxynitrite generators, such as 3-morpholinosydnonimine (SIN-1); peroxynitrite inhibitors, such as superoxide dismutase plus catalase (SOD/Cat); and NOS inhibitors, such as N(G)-nitro-L-arginine methyl ether (L-NAME) were tested on normal and ischemic cochleae. The level of NO in the cochlea after 20 to 120 minutes of ischemia was indicated by measurement of nitrites/nitrates in the perilymph. The evidence gathered from these experiments indicates that NO or peroxynitrite is not necessarily destructive to auditory hair cells, and in fact, exogenous NO may protect neural structures in the cochlea from damage under ischemic conditions.

Desferrioxamine induces delayed tolerance against cerebral ischemia in vivo and in vitro

The widely prescribed drug desferrioxamine is a known activator of the hypoxia-inducible transcription factor 1 (HIF-1) and the subsequent transcription of erythropoietin. In the brain, HIF-1 is a master switch of the transcriptional response to hypoxia, whereas erythropoietin is a potent neuroprotectant. The authors show that desferrioxamine dose-dependently and time-dependently induces tolerance against focal cerebral ischemia in rats and mice, and against oxygen-glucose deprivation in purified cortical neurons. Desferrioxamine induced HIF-1 DNA binding and transcription of erythropoietin in vivo, the temporal kinetics of which were congruent with tolerance induction. Desferrioxamine is a promising drug for the induction of tolerance in humans when ischemia can be anticipated.

Thrombin-receptor activation and thrombin-induced brain tolerance

The authors previously found that pretreatment with a low dose of thrombin attenuates the brain edema induced by a large dose of thrombin or an intracerebral hemorrhage, and reduces infarct volume after focal cerebral ischemia (i.e., thrombin preconditioning). This study investigated whether thrombin preconditioning is caused by activation of the thrombin receptor, also called protease-activated receptor. In the in vivo studies, thrombin-induced brain tolerance was eliminated by RPPGF (Arg-Pro-Pro-Gly-Phe), a thrombin-receptor antagonist. Pretreatment with a thrombin-receptor agonist reduced the amount of edema induced by a large dose of thrombin infused into the ipsilateral basal ganglia 7 days later (81.3 +/- 0.7% vs. 82.6 +/- 0.8% in the control, P < 0.05). In the in vitro study, low doses of thrombin (1 or 2 U/mL) did not induce cell death. However, doses greater than 5 U/mL resulted in dose-dependent lactate dehydrogenase release (P < 0.01). Thrombin and thrombin receptor-activating peptide preconditioning reduced lactate dehydrogenase release induced by a high dose of thrombin (10 and 20 U/mL), whereas RPPGF blocked the effect of thrombin preconditioning in vitro. Western blots indicated that p44/42 mitogen-activated protein kinases were activated after thrombin preconditioning. Finally, inhibition of p44/42 mitogen-activated protein kinases activation by PD98059 abolished the thrombin-preconditioning effect. Results indicate that thrombin-induced brain tolerance is in part achieved through activation of the thrombin receptor. Activation of the thrombin receptor in the brain may be neuroprotective. The protective effect of thrombin preconditioning is achieved through the p44/42 mitogen-activated protein kinase signal-transduction pathway.

Mitogen-activated protein kinase inhibition in traumatic brain injury: in vitro and in vivo effects

The authors provide the first in vitro and in vivo evidence that perturbations in mitogen-activated protein kinase (MAPK) signal-transduction pathways are involved in the pathophysiology of traumatic brain injury. In primary rat cortical cultures, mechanical trauma induced a rapid and selective phosphorylation of the extracellular signal-regulated kinase (ERK) and p38 kinase, whereas there was no detectable change in the c-jun N-terminal kinase (JNK) pathway. Treatment with PD98059, which inhibits MAPK/ERK 1/2, the upstream activator of ERK, significantly increased cell survival in vitro. The p38 kinase and JNK inhibitor SB203580 had no protective effect. Similar results were obtained in vivo using a controlled cortical impact model of traumatic injury in mouse brain. Rapid and selective upregulation occurred in ERK and p38 pathways with no detectable changes in JNK. Confocal immunohistochemistry showed that phospho-ERK colocalized with the neuronal nuclei marker but not the astrocytic marker glial fibrillary acidic protein. Inhibition of the ERK pathway with PD98059 resulted in a significant reduction of cortical lesion volumes 7 days after trauma. The p38 kinase and JNK inhibitor SB203580 had no detectable beneficial effect. These data indicate that critical perturbations in MAPK pathways mediate cerebral damage after acute injury, and further suggest that ERK is a novel therapeutic target in traumatic brain injury.

Cross-tolerance to otherwise lethal N-methyl-D-aspartate and oxygen-glucose deprivation in preconditioned cortical cultures

In vitro ischemic preconditioning induced by subjecting rat cortical cultures to nonlethal oxygen-glucose deprivation protects against a subsequent exposure to otherwise lethal oxygen-glucose deprivation. We provide evidence that attenuation of the postsynaptic N-methyl-D-aspartate (NMDA) receptor- and Ca(2+)-dependent neurotoxicity underlies oxygen-glucose deprivation tolerance. It is demonstrated that extended tolerance to otherwise lethal NMDA or oxygen-glucose deprivation can be induced by either of their sublethal forms of preconditioning. These four pathways are linked, since NMDA receptor blockade during preconditioning by oxygen-glucose deprivation eliminates tolerance. These results suggest that NMDA tolerance, induced by nonlethal activation of these receptors during oxygen-glucose deprivation preconditioning, underlies oxygen-glucose deprivation tolerance. Several neurotoxic downstream Ca(2+)-dependent signaling events specifically linked to NMDA receptor activation are attenuated during otherwise lethal oxygen-glucose deprivation in preconditioned cultures. Specifically, calpain activation, as well as degradation of microtubule-associated protein-2 and postsynaptic density-95, are attenuated 2 h following otherwise lethal NMDA treatment alone or oxygen-glucose deprivation in preconditioned cultures. Formation of microtubule-associated protein-2-labeled dendritic varicosities is also attenuated in preconditioned cultures within 1 h of lethal oxygen-glucose deprivation or NMDA application. Intracellular Ca(2+) levels, measured using the high- or low-affinity dyes Fluo-4 (K(d) approximately equal 345 nM) or Fluo-4FF (K(d) approximately equal 9.7 microM) respectively, are markedly attenuated during lethal oxygen-glucose deprivation in preconditioned cultures.Collectively, the results suggest the attenuation of the postsynaptic NMDA-mediated component of otherwise lethal oxygen-glucose deprivation through the suppression of Ca(2+)-dependent neurotoxic signaling, a mechanism that is initially induced by transient nonlethal activation of this receptor during ischemic preconditioning.

Cortical spreading depression transiently activates MAP kinases

Cortical spreading depression (CSD) has been shown to have neuroprotective effects when administered in advance of cerebral ischemia. The mechanism by which CSD induces its neuroprotective effect however remains to be elucidated. Since MAP kinases have been shown to impart neuroprotection in ischemic preconditioning paradigms, we attempted to determine the role CSD may have in the activation of MAPK. We show that CSD is capable of increasing the phosphorylation of ERK in a MEK-dependent manner. This phosphorylation is, however, transient, as phosphorylated ERK levels return to control levels 45 min after 2 h of CSD elicitation. Immunohistochemical analysis reveals that the phosphorylated form of ERK is located ubiquitously in cells of the CSD-treated cortex while CSD-elicited MEK phosphorylation resides solely in the nuclei. These data suggest that CSD may act via the MAP kinase pathways to mediate preconditioning.

Altered extracellular signal-regulated kinase signal transduction by the muscarinic acetylcholine and metabotropic glutamate receptors after cerebral ischemia

To determine whether muscarinic acetylcholine receptors (mAChR) in the post-ischemic hippocampus may be involved in altered extracellular signal-regulated kinases (ERK) signal transduction, we have investigated changes in the activity of ERK1/2 induced by a muscarinic agonist, carbachol. Cerebral ischemia was produced in the rat by injecting 900 microspheres (48 microm in diameter) into the right internal carotid artery. Applying carbachol to the contralateral hippocampal slices from ischemic rats increased the phosphorylation of ERK1/2 but did not increase phosphorylation in the ipsilateral hippocampus. Analysis of M(1) mAChR binding showed that there was no significant difference in the number and K(d) values between the hippocampi from naïve and ischemic rats. Immunoblotting analysis showed no significant difference in the amount of M(1) mAChR in both hemispheres. In contrast to carbachol stimulation, the protein kinase C activator induced an activation of ERK1/2 in the ipsilateral hippocampus. This increase was shown to occur in neurons by immunofluorescence colocalization study. Carbachol-stimulated tyrosine phosphorylation of the G alpha(q/11), inositol 1,4,5-trisphosphate formation, and association of G alpha(q/11) with phospholipase C beta 1 were attenuated in the ipsilateral hippocampus. We also found that stimulation of group I metabotropic glutamate receptors, which are linked to G alpha(q/11), failed to increase in phosphorylation of ERK1/2 in the ipsilateral hippocampus. These results suggest that failure in receptor-mediated tyrosine phosphorylation of the G alpha(q/11) subunit and a defect in receptor-G alpha(q/11-)effector coupling in the ischemic hippocampus may be involved in alterations of ERK signal transduction.

Ischemic preconditioning acts upstream of GluR2 down-regulation to afford neuroprotection in the hippocampal CA1

Animals subjected to sublethal transient global ischemia (ischemic preconditioning) exhibit neuroprotection against subsequent global ischemia-induced neuronal death in the hippocampal CA1 (ischemic tolerance). The molecular mechanisms underlying ischemic tolerance are unclear. Here we report that ischemic preconditioning induced a small, transient down-regulation of GluR2 mRNA expression and greatly attenuated subsequent ischemia-induced GluR2 mRNA and protein down-regulation and neuronal death. Ischemic preconditioning and GluR2 antisense knockdown acted synergistically to increase cell death. Sublethal antisense knockdown did not protect against subsequent ischemic insults or antisense knockdown. These findings indicate that ischemic preconditioning acts at step(s) upstream from suppression of GluR2 gene expression to afford neuroprotection and implicate transcriptional regulation of GluR2 expression in the adaptive mechanisms associated with ischemic tolerance.

Genetic and physical mapping of Lrk10-like receptor kinase sequences in hexaploid oat (Avena sativa L.)

Oat receptor-like kinase gene sequences, homologous to the Lrk10 gene from wheat (Triticum aestivum L.), were mapped in oat (Avena sativa L.). PCR primers designed from the wheat Lrk10 were used to produce ALrk10 from oat. Two DNA sequences, ALrk1A1 and ALrk4A5, were produced from primers designed from coding and noncoding regions of ALrk10. Their use as RFLP probes indicated that the kinase genes mapped to four loci on different hexaploid oat 'Kanota' x 'Ogle' linkage groups (4_12, 5, 6, and 13) and to a fifth locus unlinked to other markers. Three of these linkage groups contain a region homologous to the short arm of chromosome I of wheat and the fourth contains a region homologous to chromosome 3 of wheat. Analysis with several nullisomics of oat indicated that two of the map locations are on satellite chromosomes. RFLP mapping in a 'Dumont' x 'OT328' population indicated that one map location is closely linked to Pg9, a resistance gene to oat stem rust (Puccinia graminis subsp. avenae). Comparative mapping indicates this to be the region of a presumed cluster of crown rust (Puccinia coronata subsp. avenae) and stem rust resistance genes (Pg3, Pg9, Pc44, Pc46, Pc50, Pc68, Pc95, and PcX). The map position of several RGAs located on KO6 and KO3_38 with respect to Lrk10 and storage protein genes are also reported.

TNF-alpha-induced tolerance to ischemic injury involves differential control of NF-kappaB transactivation: the role of NF-kappaB association with p300 adaptor

Preconditioning with sublethal ischemia results in natural tolerance to ischemic stress, where multiple mediators of ischemic damage are simultaneously counteracted. Tumor necrosis factor alpha (TNF-alpha) has been implicated in development of ischemic tolerance. Using cellular models of ischemic tolerance, we have demonstrated that an effector of TNF-alpha-induced preconditioning is ceramide, a sphingolipid messenger in TNF-alpha signaling. TNF-alpha/ceramide-induced preconditioning protected cultured neurons against ischemic death and cultured astrocytes against proinflammatory effects of TNF-alpha. TNF-alpha activates a transcription factor NF-kappaB that binds promoters of multiple genes, thus ensuring pleiotropic effects of TNF-alpha. We describe here a mechanism that allows selective suppression of TNF-alpha/NF-kappaB-induced harmful genes in preconditioned cells while preserving cytoprotective responses. We demonstrate that in astrocytes activation of an adhesion molecule ICAM-1 by TNF-alpha is regulated through association of the phosphorylated p65 subunit of NF-kappaB with an adapter protein, p300, and that in preconditioned cells p65 remains unphosphorylated and ICAM-1 transcription is inhibited. However, TNF-alpha-activated transcription of a protective enzyme, MnSOD, does not depend on p300 and does not become inhibited in preconditioned cells. This new understanding of TNF-alpha-induced adaptation to ischemic stress and inflammation could suggest novel avenues for clinical intervention during ischemic and inflammatory diseases.

Increased neuronal hypoxic tolerance induced by repetitive chemical hypoxia

To investigate the effects of time interval and cumulative dosage of repetitive mild cellular hypoxia on shape of neurodegeneration and neuroprotection in mice, population spike amplitude (PSA) was measured during hypoxia and posthypoxic recovery in hippocampal slices from untreated control and mice pretreated in vivo with a single or repeatedly intraperitoneal injection of 3-nitropropionate (3-NP). Posthypoxic recovery of PSA was dose-dependent in single pretreated slices, with maximal recovery on pretreatment attained with 20 mg/kg 3-NP (82 +/- 32%, P < 0.01). Upon 5 and 9 treatments with 20 mg/kg 3-NP (dosage interval 3 days), PSA recovered to (38 +/- 9)% with the difference being not significant vs control group and (72 +/- 45)% with the difference being significant (P < 0.05 to control, P < 0.05 to 5 treatments), respectively. In contrast, with 2 days time interval, recovery after 5 and 9 treatments was (30 +/- 25)% and (16 +/- 14)%, respectively (without significant difference from control). Continued neuroprotection was also observed upon increase of dosage interval to 4 and 5 days. It was suggested that repetitive chemical hypoxia is a model for neurodegenerative disease and continued neuroprotection depending on time interval between repetitive hypoxic episodes rather than cumulative dosage. At appropriate time intervals increased neuronal hypoxic tolerance could be induced with number of hypoxic episodes.

Neuronal survival and cell death signaling pathways

Neuronal viability is maintained through a complex interacting network of signaling pathways that can be perturbed in response to a multitude of cellular stresses. A shift in the balance of signaling pathways after stress or in response to pathology can have drastic consequences for the function or the fate of a neuron. There is significant evidence that acutely injured and degenerating neurons may die by an active mechanism of cell death. This process involves the activation of discrete signaling pathways that ultimately compromise mitochondrial structure, energy metabolism and nuclear integrity. In this review we examine recent evidence pertaining to the presence and activation of anti- and pro-cell death regulatory pathways in nervous system injury and degeneration.

Extracellular signal-regulated kinase and c-Jun N-terminal protein kinase in ischemic tolerance

The alterations and involvement of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK) activation were examined in the hippocampal CA1 region in a rat model of global brain ischemic tolerance. Western blotting study showed that ERK activation (diphosphorylation) level was decreased (3.75-, 0.56-, and 0.23-fold vs sham control) and JNK activation level was increased (3.82-, 4.63-, and 5.30-fold vs sham control) 3 days after more severe ischemic insults (6 min, 8 min, and 10 min of ischemia, respectively). These alterations were significantly prevented by pretreatment with preconditioning ischemia, which also provided neuronal protection against ischemic injury. Inhibition of ERK activation after preconditioning ischemia by PD98059, a specific ERK kinase inhibitor, significantly prevented the inhibitory effects of preconditioning ischemia on both JNK activation and ischemic injury. The results suggest that ERK activation after preconditioning ischemia may result in the prevention of JNK activation and thus be involved in the protective responses in ischemic tolerance in hippocampal CA1 region.

Isoform-specific membrane translocation of protein kinase C after ischemic preconditioning

Mild cerebral anoxic/ischemic/stress insults promote 'tolerance' and thereby protect the brain from subsequent 'lethal' anoxic/ischemic insults. We examined whether specific activation of PKC alpha, delta, epsilon, or zeta isoforms is associated with ischemic preconditioning (IPC) in rat brain. IPC was produced by a 2-minute global cerebral ischemia. Membrane and cytosolic fractions of the hippocampi were immunoblotted using specific antibodies for PKCalpha, delta, epsilon, and zeta. PKCalpha showed a significant translocation to the membrane fraction from 30 min to 4 h and PKCdelta at 4 h following IPC. In contrast, the membrane/cytosol ratio of PKCepsilon showed a tendency to decrease at 30 min and 8 h, and the membrane/cytosol ratio of PKCzeta was significantly decreased from 30 min to 24 h following IPC. These findings indicate PKC isoform-specific membrane translocations in the hippocampus after brief global brain ischemia and suggest that activation of PKCalpha and PKCdelta may be associated with IPC-induced tolerance in the rat hippocampus.

Bax and caspases are inhibited by endogenous nitric oxide in dorsal root ganglion neurons in vitro

Axotomised dorsal root ganglia (DRG) neurons show an increased expression of neuronal nitric oxide synthase (nNOS) compared with neurons from the intact ganglia. Increased nNOS expression resulted in synthesis of nitric oxide (NO) and the subsequent activation of cGMP in satellite glia cells surrounding the DRG neuron soma. In dissociated DRG we have demonstrated that the increase in nNOS expression is regulated by nerve growth factor and that the subsequent inhibition of NO production or cGMP synthesis precipitates apoptosis of neurons expressing nNOS and some non-nNOS neurons. Hence, NO or the NO-cGMP cascade appears to have a neuroprotective action in trophic factor-deprived DRG neurons. In the present study, using immunocytochemistry, we have investigated some of the factors associated with apoptosis that are activated when nNOS activity is blocked with NOS inhibitor in DRG neurons in vitro. Marked elevation of bax was observed within a few hours of NOS inhibition in nNOS containing neurons, whereas pretreatment of cultures with l-arginine completely abolished this effect in almost all nNOS neurons and 8-bromo-cGMP in some neurons. The apoptosis precipitated by NOS inhibition was also partially prevented by a number of caspase inhibitors; of those a caspase-9 blocker was the most effective. These observations further support the neuroprotective role of NO/NO-cGMP in stressed DRG neurons in an autocrine fashion that involves the suppression of bax, caspase-3 and -9 activation.

Transient cerebral ischemia increases tyrosine phosphorylation of the synaptic RAS-GTPase activating protein, SynGAP

Cerebral ischemia results in activation of the mitogen-activated protein kinase pathway and increased tyrosine phosphorylation of proteins associated with postsynaptic densities (PSDs). The authors investigated the possible relation between these events by determining the effect of ischemia on tyrosine phosphorylation of the brain-specific, PSD-enriched, Ras-GTPase activating protein, SynGAP. Transient (15 minutes) global ischemia was produced in rats by 4-vessel occlusion and PSDs prepared from forebrains immediately after ischemia or at 20 minutes, 1 hour, or 24 hours of reperfusion. Tyrosine phosphorylation of SynGAP was elevated relative to sham-operated controls by 20 minutes of reperfusion and remained elevated for at least 24 hours. Tyrosine phosphorylation of SynGAP also increased in CA1 and CA3/DG subfields of the hippocampus. Enhanced tyrosine phosphorylation of SynGAP was not accompanied by a change in PSD RasGAP activity. SynGAP bound to the SH2 domains of Src and Fyn in a tyrosine phosphorylation-dependent fashion, and this interaction increased after ischemia. SynGAP binds to the PDZ domains of PSD-95/SAP90 and coimmunoprecipitated with PSD-95. The coimmunoprecipitation of SynGAP with PSD-95 decreased after ischemia. The results indicate that changes in the properties and interactions of SynGAP may be involved in the neuropathology of ischemia.

Minocycline provides neuroprotection against N-methyl-D-aspartate neurotoxicity by inhibiting microglia

Glutamate excitotoxicity to a large extent is mediated through activation of the N-methyl-D-aspartate (NMDA)-gated ion channels in several neurodegenerative diseases and ischemic stroke. Minocycline, a tetracycline derivative with antiinflammatory effects, inhibits IL-1beta-converting enzyme and inducible nitric oxide synthase up-regulation in animal models of ischemic stroke and Huntington's disease and is therapeutic in these disease animal models. Here we report that nanomolar concentrations of minocycline protect neurons in mixed spinal cord cultures against NMDA excitotoxicity. NMDA treatment alone induced microglial proliferation, which preceded neuronal death, and administration of extra microglial cells on top of these cultures enhanced the NMDA neurotoxicity. Minocycline inhibited all these responses to NMDA. Minocycline also prevented the NMDA-induced proliferation of microglial cells and the increased release of IL-1beta and nitric oxide in pure microglia cultures. Finally, minocycline inhibited the NMDA-induced activation of p38 mitogen-activated protein kinase (MAPK) in microglial cells, and a specific p38 MAPK inhibitor, but not a p44/42 MAPK inhibitor, reduced the NMDA toxicity. Together, these results suggest that microglial activation contributes to NMDA excitotoxicity and that minocycline, a tetracycline derivative, represents a potential therapeutic agent for brain diseases.

Neuronal protein kinase signaling cascades and excitotoxic cell death

Perturbation of normal survival mechanisms may play a role in a large number of disease processes. Glutamate neurotoxicity, particularly when mediated by the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors, has been hypothesized to underlie several types of acute brain injury, including stroke. Several neurological insults linked to excessive release of glutamate and neuronal death result in tyrosine kinase activation, including p44/42 mitogen activated protein (MAP) kinase. To further explore a role for MAP kinase activation in excitotoxicity, we used a novel tissue culture model to induce neurotoxicity. Removal of the endogenous blockade by Mg2+ of the NMDA receptor in cultured hippocampal neurons triggers a self perpetuating cycle of excitotoxicity, which has relatively slow onset, and is critically dependent on NMDA receptors and activation of voltage gated Na+ channels. These injury conditions led to a rapid phosphorylation of p44/42 that was blocked by MAP kinase kinase (MEK) inhibitors. MEK inhibition was associated with protection against synaptically mediated excitotoxicity. Interestingly, hippocampal neurons preconditioned by a sublethal exposure to Mg(2+)-free conditions were rendered resistant to injury induced by a subsequently longer exposure to this insult; the preconditioning effect was MAP kinase dependent. The MAP kinase signaling pathway can also promote polypeptide growth factor mediated neuronal survival. MAP kinase regulated pathways may act to promote survival or death, depending upon the cellular context in which they are activated.

Effects of nitric oxide on normal and ischemic cochlea of the guinea pig

To determine whether nitric oxide (NO)/peroxynitrite plays any role in neurodestruction observed in ischemic cochlea of the guinea pig, the effects of NO donors like S-nitrosocysteine (S-NC) and nitroglycerin (NTG), peroxynitrite generators like 3-morpholinosydnonimine (SIN-1), peroxynitrite inhibitors like superoxide dismutase plus catalase (SOD/Cat), as well as NOS inhibitors like N(G)-nitro-l-arginine methyl ether (L-NAME), were tested on normal and ischemic cochleae. Various concentrations of S-NC and SIN-1 were introduced into the perilymphatic space of normal guinea pig cochlea. Quantitative scanning electron microscopy of inner and outer hair cells was carried out 2 days later. To determine the level of NO in the cochlea after 20 to 120 min of ischemia, nitrites/nitrates in the perilymph were measured. The effects of NO on the ischemic cochlea were tested by infusion of SOD/Cat, L-NAME, S-NC, and NTG into the perilymphatic space just before decapitation. Introduction of fixative into the cochlea was delayed for 15 min to investigate the effects of the chemicals on nerve endings at the base of inner hair cells. The results showed that the level of nitrites/nitrates tended to decline with increasing time of ischemia. There was no significant hair cell loss in the cochleae treated with SIN-1 or S-NC. At 15 min after ischemia, most of the nerve endings at the base of the inner hair cells were protected from damage when 1 mM S-NC or NTG was infused into the perilymph. Taken together, the results indicate that NO/peroxynitrite is unlikely to be involved in the neurodestruction in the ischemic cochlea. In fact, exogenous NO may have a neural protective effect.

Inhibition of neuronal nitric oxide synthase results in neurodegenerative changes in the axotomised dorsal root ganglion neurons: evidence for a neuroprotective role of nitric oxide in vivo

In axotomised adult rat dorsal root ganglion (DRG), many neurons show a marked increase in expression of neuronal nitric oxide synthase (nNOS). It has been established that NO functions as a neuron-glial signalling molecule by generating cGMP in glia cells that surround the neuron in DRG. Furthermore, in cultures of dissociated DRG deprived of nerve growth factor, many neurons expressed nNOS and cGMP and subsequently died if either enzyme's activity was inhibited suggesting that NO-cGMP pathway could be neuroprotective in stressed DRG neurons. This has now been tested in vivo. It was found, 10 days after sciatic axotomy that nNOS was expressed in 36% of DRG neurons in the L5 and L6 ganglia giving rise to the damaged nerve, compared with 6% in contralateral ganglia. Almost all nNOS neurons and 24% of non-nNOS neurons expressed c-Jun in their nuclei. Ten days following axotomy, treatment with the relatively selective nNOS-blocker, 1-(2-trifluoromethylphenyl) imidazole (TRIM), caused morphology changes in approximately 50% of neurons that consisted of vacuolations, blebbing and highly irregular cell boundaries. Sham operated, TRIM treated, nerve-sectioned, vehicle treated, and controls did not show these changes. These observations further support the view that NO could be neuroprotective in some injured/stressed primary sensory neurons.

Cell-cycle arrest in TrkA-expressing NIH3T3 cells involves nitric oxide synthase

We have examined nerve growth factor (NGF)-triggered signaling in two NIH3T3 cell lines exogenously expressing the NGF receptor, TrkA. TRK1 cells cease to proliferate and extend long processes in response to NGF, while E25 cells continue to proliferate in the presence of NGF. These two cell lines express similar levels of TrkA and respond to NGF with rapid elevation of mitogen-activated protein kinase (MAPK) activity. MAPK activation is slightly more sustained for E25 cells than for TRK1 cells, although sustained activation of MAPK has been suggested to cause cell-cycle arrest. As judged by NADPH-diaphorase staining, nitric oxide synthase (NOS) activity is increased in TRK1 cells upon exposure to NGF. In contrast, diaphorase staining in E25 cells is unaffected by NGF treatment. Immunocytochemistry shows that levels of the brain NOS (bNOS) isoform are increased in TRK1, but not E25, cells exposed to NGF. Furthermore, Western blots show that NGF elevated cyclin-dependent kinase inhibitor, p21(WAF1), in TRK1 cells only. NGF-induced p21(WAF1) expression, cell-cycle arrest and process extension are abolished by N-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NOS. The inactive enantiomer, D-NAME, did not inhibit these responses. Furthermore, even though E25 cells do not respond to NGF or nitric oxide donors, they do undergo a morphological change in response to NGF plus a nitric oxide donor. Therefore, NOS and p21(WAF1) are induced only in the TrkA-expressing NIH3T3 cell line that undergoes cell-cycle arrest and morphological changes in response to NGF. These results demonstrate that sustained activation of MAPK is not the sole determining factor for NGF-induced cell-cycle arrest and implicate NO in the cascade of events leading to NGF-induced morphological changes and cell-cycle arrest.

Nitric oxide and nitric oxide synthase in Huntington's disease

Nitric oxide (NO) is a biologically active inorganic molecule produced when the semiessential amino acid l-arginine is converted to l-citrulline and NO via the enzyme nitric oxide synthase (NOS). NO is known to be involved in the regulation of many physiological processes, such as control of blood flow, platelet adhesion, endocrine function, neurotransmission, neuromodulation, and inflammation, to name only a few. During neuropathological conditions, the production of NO can be either protective or toxic, dependent on the stage of the disease, the isoforms of NOS involved, and the initial pathological event. This paper reviews the properties of NO and NOS and the pathophysiology of Huntington's disease (HD). It discusses ways in which NO and NOS may interact with the protein product of HD and reviews data implicating NOS in the neuropathology of HD. This is followed by a synthesis of current information regarding how NO/NOS may contribute to HD-related pathology and identification of areas for potential future research.

The concept of cellular "fight-or-flight" reaction to stress

As animals respond to environmental stress with a set of default reactions described as the "fight-or-flight" response, so do epithelial and endothelial cells when they are confronting stressors in their microenvironment. This review will summarize a growing body of data suggesting the existence of a set of stereotypical cellular reactions to stress, provide some examples of diseases that are characterized by excessive flight reactions, describe the cellular mechanisms whereby the fight-or-flight reaction is accomplished, as well as cellular mechanisms triggering either fight or flight. It is proposed that cell-matrix adhesion is a sensitive indicator of the severity of stress. This indicator is interfaced with several default programs for cellular survival or death, thus dictating the fate of the cell. Some diagnostic and therapeutic applications of the concept, presently used and potentially useful, are outlined. The essential feature of this concept is its ability to categorize cellular events in terms of either type of default reaction, predict the details of each, and potentially exploit them clinically.

Activation of p44/42 mitogen activated protein kinases in thrombin-induced brain tolerance

BACKGROUND

Our recent studies have shown that prior intracerebral injection of a low dose of thrombin attenuates the brain edema formation that results from either an intracerebral hematoma, an intracerebral injection of a large dose of thrombin or cerebral ischemia. The aim of the current study is to investigate whether thrombin-induced tolerance (thrombin preconditioning; TPC) is associated with activation of p44/42 mitogen activated protein (MAP) kinases.

METHODS

This study contained three parts. In the first, rats received an intracerebral infusion of either saline or one unit thrombin (the TPC dose) into the right caudate nucleus. After 1, 3 and 7 days, the rats will be killed and brains used to detect p44/42 MAP kinases activation using Western blot analysis and immunohistochemistry. In the second and third parts, rats received intracerebral infusions of either vehicle, one unit thrombin (TPC) or one unit thrombin and 5 nmol PD 098059. These rats were either killed to detect kinases activation after 24 h or received a second intracerebral infusion of five-unit thrombin 7 days later with brain edema being assessed after a further 24 h.

RESULTS

Western blot analysis demonstrated that p44/42 MAP kinases were activated in the ipsilateral basal ganglia after the intracerebral infusion of thrombin one unit. Cells immunoreactive for activated p44/42 MAP kinases were found in the ipsilateral basal ganglia and ipsilateral cortex. PD 098059, a MAP kinase kinase inhibitor, abolished thrombin-induced activation of p44/42 MAP kinases. TPC suppressed thrombin-induced brain edema while PD 098059 blocked this protective effect. The water contents in the ipsilateral basal ganglia 24 h after infusion of thrombin five units were 82.6+/-0.8%, 79.2+/-0.4% and 81.8+/-1.9% in the control, TPC alone and TPC plus PD 098059 groups, respectively.

CONCLUSION

Thrombin can activate p44/42 MAP kinases within the brain and the protective effects of thrombin preconditioning on brain edema formation are related to this activation.

Cell permeable exogenous ceramide reduces infarct size in spontaneously hypertensive rats supporting in vitro studies that have implicated ceramide in induction of tolerance to ischemia

Previous work in primary cell culture has shown that TNF-alpha and ceramide are involved in the signaling that induces tolerance to brain ischemia (Ginis et al., 1999; Liu et al., 2000). To validate the in vitro studies, the authors administered cell permeable analogs of ceramides intracisternally or intravenously to examine their effect on neuroprotection after focal cerebral ischemia. Permanent middle cerebral artery occlusion (MCAO) was performed in spontaneously hypertensive rats. Infarct volumes were assessed at 24 hours after surgery. D-erythro-N-acetylsphingosine (C2-ceramide) or its vehicle was infused intracisternally for 1 hour before MCAO. In a second set of studies, D-erythro-N-octanoylsphingosine (C8-ceramide) or its vehicle was injected intravenously 48 or 24 hours before MCAO to mimic preconditioning (PC) and was also injected 5 minutes after MCAO. C2-ceramide infusion significantly reduced infarct volumes by approximately 14% (P < 0.05). C8-ceramide injection reduced infarct volumes approximately 17% compared with controls. This effect was constant and significant compared with controls over the time periods examined (P < 0.01). This work supports findings in primary brain cell cultures that implicate ceramide as a downstream signal that is proximate to development of tolerance to brain ischemia. Because the degree of protection represents approximately 50% of the maximal infarct reduction observed in this model, there are probably additional signaling pathways that subserve tolerance.

Preconditioning with spreading depression activates specifically protein kinase Cdelta

Preconditioning with brief ischemia or spreading depression (SD) confers tolerance in cortical neurons to subsequent episode of ischemia. In myocardium a similar preconditioning is achieved by mechanisms, which are mediated by protein kinase C (PKC) alpha, delta, epsilon or zeta isoform. We induced SD by cortical application of KCl in the rat and analyzed cortical tissues after recovery of 30 min, 4 h and 12 h. While no changes at protein levels or activity of PKCalpha, epsilon or zeta were detected, a considerable increase in membrane translocation of PKCdelta was seen at 30 min and 12 h. A significant increase at mRNA level, protein amount and autophosphorylation at 12 h confirmed the late activation of PKCdelta, which may be involved in neuronal protection by preconditioning.

Mitogen-activated protein kinases and cerebral ischemia

Mitogen-activated protein kinases (MAPKs) have crucial roles in signal transduction from the cell surface to the nucleus and regulate cell death and survival. Recent papers support the hypothesis that neuronal apoptosis and cerebral ischemia induce the robust activation of MAPK cascades. Although extracellular signal-regulated kinases pathways promote cell survival and proliferation, and c-Jun N-terminal protein kinases/p38 pathways induce apoptosis in general, the roles of MAPK cascades in neuronal death and survival seem to be complicated and altered by the type of cells and the magnitude and timing of insults. Some specific inhibitors of MAPK cascades provide important information in clarifying the roles of each molecule in neuronal death and survival, but the results are still controversial. Further studies are necessary to elucidate the activated signal transduction upstream and downstream of the cascades in cerebral ischemia, and to define the crosstalk between the cascades and other signaling pathways, before MAPK cascades can be candidate molecules in the treatment of cerebral ischemia.

Potentiation by histamine of synaptically mediated excitotoxicity in cultured hippocampal neurones: a possible role for mast cells

Excessive glutamatergic neurotransmission, particularly when mediated by the N:-methyl-D-aspartate (NMDA) subtype of glutamate receptor, is thought to underlie neuronal death in a number of neurological disorders. Histamine has been reported to potentiate NMDA receptor-mediated events under a variety of conditions. In the present study we have utilized primary hippocampal neurone cultures to investigate the effect of mast cell-derived, as well as exogenously applied, histamine on neurotoxicity evoked by excessive synaptic activity. Exposure of mature cultures for 15 min to an Mg(2+)-free/glycine-containing buffer to trigger synaptic transmission through NMDA receptors, caused a 30-35% neuronal loss over 24 h. When co-cultured with hippocampal neurones, activated mast cells increased excitotoxic injury to 60%, an effect that was abolished in the presence of histaminase. Similarly, addition of histamine during magnesium deprivation produced a concentration-dependent potentiation (+ 60%; EC(50) : 5 microM) of neuronal death which was inhibited by sodium channel blockers and NMDA receptor antagonists, although this effect did not involve known histamine receptors. The histamine effect was further potentiated by acidification of the culture medium. Cultures 'preconditioned' by sublethal (5 min) Mg(2+) deprivation exhibited less neuronal death than controls when exposed to a more severe insult. NMDA receptor activation and the extracellular regulated kinase cascade were required for preconditioning neuroprotection. The finding that histamine potentiates NMDA receptor-mediated excitotoxicity may have important implications for our understanding of conditions where enhanced glutamatergic neurotransmission is observed in conjunction with tissue acidification, such as cerebral ischaemia and epilepsy.

Piroxicam and NS-398 rescue neurones from hypoxia/reoxygenation damage by a mechanism independent of cyclo-oxygenase inhibition

We studied whether NS-398, a selective cyclo-oxygenase-2 (COX-2) enzyme inhibitor, and piroxicam, an inhibitor of COX-2 and the constitutively expressed COX-1, protect neurones against hypoxia/reoxygenation injury. Rat spinal cord cultures were exposed to hypoxia for 20 h followed by reoxygenation. Hypoxia/reoxygenation increased lactate dehydrogenase (LDH) release, which was inhibited by piroxicam (180-270 microM) and NS-398 (30 microM). Cell counts confirmed the neuroprotection. Western blotting revealed no COX-1 or COX-2 proteins even after hypoxia/reoxygenation. Production of prostaglandin E2 (PGE2), a marker of COX activity, was barely measurable and piroxicam and NS-398 had no effect on the negligible PGE2 production. Hypoxia/reoxygenation increased nuclear factor-kappa B (NF-kappaB) binding activity, which was inhibited by piroxicam but not by NS-398. AP-1 binding activity after hypoxia/reoxygenation was inhibited by piroxicam but strongly enhanced by NS-398. However, both COX inhibitors induced activation of extracellular signal-regulated kinase (ERK) in neurones and phosphorylation of heavy molecular weight neurofilaments, cytoskeletal substrates of ERK. It is concluded that piroxicam and NS-398 protect neurones against hypoxia/reperfusion. The protection is independent of COX activity and not solely explained by modulation of NF-kappaB and AP-1 binding activity. Instead, piroxicam and NS-398-induced phosphorylation through ERK pathway may contribute to the increased neuronal survival.

NO activation of fos promoter elements requires nuclear translocation of G-kinase I and CREB phosphorylation but is independent of MAP kinase activation

We have shown that nitric oxide (NO) regulates c-fos gene expression via cGMP-dependent protein kinase (G-kinase), but NO's precise mechanism of action is unclear. We now demonstrate that: (1) NO targets two transcriptional elements in the fos promoter, i.e., the fos AP-1 binding site and the cAMP-response element (CRE); (2) NO activation of these two enhancer elements requires the CRE binding protein CREB because a dominant negative CREB fully inhibits NO transactivation of reporter genes whereas dominant negative Fos or CCAAT enhancer binding proteins have no effect; (3) CREB is phosphorylated by G-kinase in vitro and its phosphorylation increases in vivo when G-kinase is activated either directly by cGMP or indirectly by NO via soluble guanylate cyclase; (4) NO activation of fos promoter elements requires nuclear translocation of G-kinase but not activation of mitogen-activated protein kinases.

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.

Infarct tolerance accompanied enhanced BDNF-like immunoreactivity in neuronal nuclei

A prolonged period (48 h) of cortical spreading depression (CSD) induced resistance against severe focal cerebral ischemia (infarct tolerance), however, the mechanism behind this is unknown. The infarct tolerance was a transient phenomenon; the resistance increased linearly for the initial 12 days, peaking from 12 to 15 days after a preconditioning of CSD, and was decreased thereafter. This study examined the time course of brain-derived neurotrophic factor (BDNF), heat shock protein (hsp)27 and 70, and glial fibrillary acidic protein (GFAP) expressions after CSD in the brain. Immunohistochemical expression of BDNF, hsp27, hsp70, or GFAP following a prolonged period of CSD induced by KCl-infusion, or following NaCl-infusion was analyzed by regional densitometry for 24 days in the rat neocortex. In addition, BDNF protein was measured quantitatively by two-site ELISA assay in the neocortex (n=6 at each time point). The GFAP expression was elevated in astrocytes (compared to the normal level of immunodensity) during the period peaking on day 3-6 following the CSD. The hsp27 immunoreactivity was also elevated in astrocytes from day 1 to 12 peaking on day 1 and 6, but there was no expression of hsp70 during the period following CSD. The immunoreactivity for BDNF was elevated in neurons from day 0 to 18 peaking on day 1 and 6. The protein levels of BDNF in the neocortex were significantly elevated from day 0 to 12 peaking on days 0 and 6 (compared to the normal level) (P<0.05). Using a laser-scanning confocal imaging system, the BDNF-like immunoreactivity in neuronal nuclei was found to increase linearly peaking on day 12, which correlated well with the development of infarct tolerance. The intranuclear increase in BDNF-like protein might contribute to the induction of infarct tolerance in the brain.

Hypoxia/hypoglycemia-induced amino acid release is decreased in vitro by preconditioning

The aim of this study was to investigate the effects of preconditioning on amino acid neurotransmitter release, induced by hypoxia/hypoglycaemia, from rat brain cortical slices. Tissue, perfused with artificial cerebrospinal fluid (aCSF) at 37 degrees C with zero glucose and gassed with 95% nitrogen and 5% carbon dioxide, showed a fivefold increase in glutamate release with little effect on gamma-aminobutyric acid (GABA) release. Preconditioning, with three 5-min periods of hypoxia/hypoglycaemia preceding continuous hypoxia/hypoglycaemia, significantly decreased glutamate release whilst significantly elevating GABA release. These results suggest that GABA may reduce the release of glutamate and consequently decrease the neurotoxic effects of glutamate.

Sustained activation of p42/p44 mitogen-activated protein kinase during recovery from simulated ischaemia mediates adaptive cytoprotection in cardiomyocytes

Delayed cytoprotection (preconditioning) occurs 24 h after sublethal simulated ischaemia and reperfusion (SI/R) in neonatal rat ventricular cardiomyocytes. SI/R was used to investigate the role of activation of mitogen-activated protein kinases (MAPKs), stress-activated protein kinases (SAPKs) and phosphoinositide 3-kinase-dependent protein kinase B (PKB)/Akt in cytoprotection. SI resulted in transient dual (Thr/Tyr) phosphorylation of p42/p44-MAPK and p38-MAPK, weak phosphorylation of p46/p54-SAPK, but no phosphorylation of PKB. 'Reperfusion' caused further transient phosphorylation of p38-MAPK, but sustained phosphorylation of p42/p44-MAPK (lasting 4 h) and of Ser(473) of PKB (lasting 2 h). Furthermore, SI/R (24 h) induced delayed protection against lethal SI, as determined by an increase in cell viability ¿bioreduction of MTT [3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide]¿ and a decrease in cell injury (release of creatine kinase). Both protection and phosphorylation of p42/p44-MAPK were blocked by the MEK-1/2 (MAPK/Erk kinase-1/2) inhibitor PD98059 (50 microM) when given during SI/R, but not when given during SI alone. The p38-MAPK inhibitor SB203580 (10 microM) blocked the p38-MAPK-dependent phosphorylation of activating transcription factor 2 in vitro, and the phosphoinositide 3-kinase inhibitor wortmannin (100 nM) blocked PKB phosphorylation on Ser(473). However, neither SB203580 nor wortmannin had any effect on delayed protection. Therefore sustained activation of p42/p44-MAPK during simulated 'reperfusion' following sublethal SI mediates preconditioning in cardiomyocytes independently of transient activation of p38-MAPK or sustained activation of PKB.