Immediate early gene expression in response to cerebral ischemia. Friend or foe?

Neuroprotective gene expression profiles in ischemic cortical cultures preconditioned with IGF-1 or bFGF

The mechanisms underlying growth factor preconditioning of neurons are only partially elucidated, and no studies have been conducted in this area using a gene profiling approach. We used cDNA microarrays to compare the transcriptional profiles of cells preconditioned either with insulin-like growth factor I (IGF-1) or basic fibroblast growth factor (bFGF), to identify differentially regulated genes that may function in growth factor signaling, response to oxygen-glucose deprivation (OGD), and most importantly, cell survival. Primary rat cortical cultures were treated with bFGF or IGF-1 for 2, 24, or 24 h followed by OGD for 90 min, and compared with cells that were subject to OGD without growth factor pretreatment. Although the majority of surveyed genes were unchanged in all experimental treatments, 175 genes (10% of the cDNAs on the chip) were found to be differentially regulated in at least one of the treatment conditions. Hierarchical clustering of these 175 genes was used to identify four expression clusters: IGF-1 regulated, bFGF regulated, OGD regulated, and putative neuroprotective genes. Further analysis using realtime RT-PCR confirmed that we had identified genes that are regulated by single growth factors, as well as several more that are co-regulated by both IGF-1 and bFGF. These genes can influence neuronal survival by affecting diverse pathways such as growth factor signal transduction (CD44, DTR, DUSP6, EPS8, IGFBP3), DNA repair and transcription (FOXJ1), metabolic homeostasis (RASA1, SHMT2), cytoskeletal stability (MSN, MAPT) and cholesterol biosynthesis (FDFT1, FDPS).

Ischemic preconditioning or heat shock pretreatment ameliorates neuronal apoptosis following hypothermic circulatory arrest

OBJECTIVE

Hypothermic circulatory arrest has been widely used in complex cardiac and aortic surgery. Stroke and/or neurologic injury can occur after prolonged hypothermic circulatory arrest, possibly due to apoptosis. Ischemic preconditioning has been widely used as a neuroprotective tool, but its application in neuronal injury under hypothermic circulatory arrest has never been studied.

METHODS

Forty male New Zealand white rabbits were placed on closed-chest cardiopulmonary bypass, subjected to hypothermic circulatory arrest, and rewarmed to normothermia. Experimental groups were treated with heat shock or ischemic preconditioning before hypothermic circulatory arrest. Hippocampal CA1 neurons were analyzed histopathologically. Apoptosis was confirmed by TUNEL assay and Western blot analysis, and serum S-100beta levels, c-Fos and Bcl-2 antibodies, and caspase-3 and heat shock protein 70 levels were measured.

RESULTS

After 2-hour hypothermic circulatory arrest and 4-hour reperfusion, apoptosis was observed in hippocampal CA1 neurons with elevation of serum S-100beta levels, which could be ameliorated by ischemic preconditioning or heat shock manipulations. TUNEL-positive nuclear expression of caspase-3 increased after hypothermic circulatory arrest (3.08% +/- 0.71%, P <.001) and was diminished with ischemic preconditioning (1.61% +/- 0.42%) and heat shock (1.72% +/- 0.38%) manipulations. Ischemic preconditioning or heat shock manipulations produced diverse patterns of heat shock protein 70, c-Fos, and Bcl-2 protein expression, suggesting that these manipulations provide neuroprotection via different pathways.

CONCLUSIONS

Ischemic preconditioning and heat shock can attenuate hippocampal CA1 neuronal apoptosis after prolonged hypothermic circulatory arrest under cardiopulmonary bypass. The expression of heat shock protein 70 may not play a major role in the first window of ischemic preconditioning-induced neuroprotection.

Overexpression of genes in the CA1 hippocampus region of adult rat following episodes of global ischemia

Ischemic stress is associated with marked changes in gene expression in the hippocampus--albeit little information exists on the activation of nonabundant genes. We have examined the expression of several known genes and identified novel ones in the adult rat hippocampus after a mild, transient, hypovolemic and hypotensive, global ischemic stress. An initial differential screening using a prototype array to assess gene expression after stress followed by a suppression subtractive hybridization protocol and cDNA microarray revealed 124 nonoverlapped transcripts predominantly expressed in the CA1 rat hippocampus region in response to ischemic stress. About 78% of these genes were not detected with nonsubtracted probes. Reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization on these 124 transcripts confirmed the differential expression of at least 83. Most robustly expressed were gene sequences NFI-B, ATP1B1, RHOGAP, PLA2G4A, BAX, CASP3, P53, MAO-A, FRA1, HSP70.2, and NR4A1 (NUR77), as well as sequence tags of unknown function. New stress-related genes of similar functional motifs were identified, reemphasizing the importance of functional grouping in the analysis of multiple gene expression profiles. These data indicate that ischemia elicits expression of an array of functional gene clusters that may be used as an index for stress severity and a template for target therapy design.

Altered biosynthesis of neuropeptide processing enzyme carboxypeptidase E after brain ischemia: molecular mechanism and implication

In this study, using both in vivo and in vitro ischemia models, the authors investigated the impact of brain ischemia on the biosynthesis of a key neuropeptide-processing enzyme, carboxypeptidase E (CPE). The response to brain ischemia of animals that lacked an active CPE was also examined. Combined in situ hybridization and immunocytochemical analyses for CPE showed reciprocal changes of CPE mRNA and protein, respectively, in the same cortical cells in rat brains after focal cerebral ischemia. Western blot analysis revealed an accumulation of the precursor protein of CPE in the ischemic cortex in vivo and in ischemic cortical neurons in vitro. Detailed metabolic labeling experiments on ischemic cortical neurons showed that ischemic stress caused a blockade in the proteolytic processing of CPE. When mice lacking an active CPE protease were subjected to a sublethal episode of focal cerebral ischemia, abundant TUNEL-positive cells were seen in the ischemic cortex whereas only a few were seen in the cortex of wild-type animals. These findings suggest that ischemia has an adverse impact on the neuropeptide-processing system in the brain and that the lack of an active neuropeptide-processing enzyme exacerbates ischemic brain injury.

Integrated technology for evaluation of brain function and neural plasticity

The study of neural plasticity has expanded rapidly in the past decades and has shown the remarkable ability of the developing, adult, and aging brain to be shaped by environmental inputs in health and after a lesion. Robust experimental evidence supports the hypothesis that neuronal aggregates adjacent to a lesion in the sensorimotor brain areas can take over progressively the function previously played by the damaged neurons. It definitely is accepted that such a reorganization modifies sensibly the interhemispheric differences in somatotopic organization of the sensorimotor cortices. This reorganization largely subtends clinical recovery of motor performances and sensorimotor integration after a stroke. Brain functional imaging studies show that recovery from hemiplegic strokes is associated with a marked reorganization of the activation patterns of specific brain structures. To regain hand motor control, the recovery process tends over time to bring the bilateral motor network activation toward a more normal intensity/extent, while overrecruiting simultaneously new areas, perhaps to sustain this process. Considerable intersubject variability exists in activation/hyperactivation pattern changes over time. Some patients display late-appearing dorsolateral prefrontal cortex activation, suggesting the development of "executive" strategies to compensate for the lost function. The AH in stroke often undergoes a significant "remodeling" of sensory and motor hand somatotopy outside the "normal" areas, or enlargement of the hand representation. The UH also undergoes reorganization, although to a lesser degree. Although absolute values of the investigated parameters fluctuate across subjects, secondary to individual anatomic variability, variation is minimal with regards to interhemispheric differences, due to the fact that individual morphometric characters are mirrored in the two hemispheres. Excessive interhemispheric asymmetry of the sensorimotor hand areas seems to be the parameter with highest sensitivity in describing brain reorganization after a monohemispheric lesion, and mapping motor and somatosensory cortical areas through focal TMS, fMRI, PET, EEG, and MEG is useful in studying hand representation and interhemispheric asymmetries in normal and pathologic conditions. TMS and MEG allow the detection of sensorimotor areas reshaping, as a result of either neuronal reorganization or recovery of the previously damaged neural network. These techniques have the advantage of high temporal resolution but also have limitations. TMS provides only bidimensional scalp maps, whereas MEG, even if giving three-dimensional mapping of generator sources, does so by means of inverse procedures that rely on the choice of a mathematical model of the head and the sources. These techniques do not test movement execution and sensorimotor integration as used in everyday life. fMRI and PET may provide the ideal means to integrate the findings obtained with the other two techniques. This multitechnology combined approach is at present the best way to test the presence and amount of plasticity phenomena underlying partial or total recovery of several functions, sensorimotor above all. Dynamic patterns of recovery are emerging progressively from the relevant literature. Enhanced recruitment of the affected cortex, be it spared perilesional tissue, as in the case of cortical stroke, or intact but deafferented cortex, as in subcortical strokes, seems to be the rule, a mechanism especially important in early postinsult stages. The transfer over time of preferential activation toward contralesional cortices, as observed in some cases, seems, however, to reflect a less efficient type of plastic reorganization, with some aspects of maladaptive plasticity. Reinforcing the use of the affected side can cause activation to increase again in the affected side with a corresponding enhancement of clinical function. Activation of the UH MI may represent recruitment of direct (uncrossed) corticospinal tracts and relate more to mirror movements, but it more likely reflects activity redistribution within preexisting bilateral, large-scale motor networks. Finally, activation of areas not normally engaged in the dysfunctional tasks, such as the dorsolateral prefrontal cortex or the superior parietal cortex in motor paralysis, might reflect the implication of compensatory cognitive strategies. An integrated approach with technologies able to investigate functional brain imaging is of considerable value in providing information on the excitability, extension, localization, and functional hierarchy of cortical brain areas. Deepening knowledge of the mechanisms regulating the long-term recovery (even if partial), observed for most neurologic sequelae after neural damage, might prompt newer and more efficacious therapeutic and rehabilitative strategies for neurologic diseases.

Electro-acupuncture preconditioning abrogates the elevation of c-Fos and c-Jun expression in neonatal hypoxic-ischemic rat brains induced by glibenclamide, an ATP-sensitive potassium channel blocker

This study aimed to clarify the neuroprotective mechanism of electro-acupuncture (EA) preconditioning on hypoxic-ischemic brain injury (HIBI). Using Western blot, the expression of c-fos protein (c-Fos) and c-jun protein (c-Jun) induced by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker was examined from cerebral cortical and hippocampal samples in neonatal hypoxic-ischemic rats, with or without EA preconditioning. EA was performed on Hegu (LI4), a well-known acupoint commonly used in Oriental medicine for the treatment of neuronal injury resulting from hypoxia-ischemia (HI). Preconditioned rats were treated with either diazoxide, a K(ATP) channel opener, glibenclamide, or sterile saline injected into the left lateral ventricle (i.c.v.), with or without EA administration before HI insult. Interestingly, low c-Fos and c-Jun expressions were found both in diazoxide and EA groups, 24 h after HI. Furthermore, significant differences in relative optical density (ROD) were found between glibenclamide and HI control groups (P< or =0.05), as well as between the group administered glibenclamide after EA and the HI control group (P< or =0.05). However, the level of c-Fos and c-Jun expression in the group administered glibenclamide after EA was significantly lower than in the glibenclamide group (P< or =0.05). The present findings indicate that the effectiveness of EA preconditioning against HIBI may be mediated via the opening of K(ATP) channels.

Treatment with the snail peptide CGX-1007 reduces DNA damage and alters gene expression of c-fos and bcl-2 following focal ischemic brain injury in rats

Delayed cell death following ischemic brain injury has been linked to alterations in gene expression. In this study we have evaluated the upregulation of several genes associated with delayed cell death (c-fos, bax, and bcl-2) during the initial 24 h of transient middle cerebral artery occlusion (MCAo) in the rat and the effects of postinjury treatment with the NR2B subunit specific NMDA receptor antagonist CGX-1007 (Conantokin-G, Con-G). C-fos mRNA levels peaked at 1 h postinjury in both cortical and subcortical ischemic brain regions (30-fold increase), remained elevated at 4 h and returned to within normal, preinjury levels 24 h postinjury. The increase in mRNA levels correlated to increased protein expression in the entire ipsilateral hemisphere at 1 h. Regions of necrosis at 4 h were void of C-Fos immunoreactivity with continued upregulation in surrounding regions. At 24 h, loss of C-Fos staining was observed in the injured hemisphere except for sustained increases along the border of the infarct and in the cingulate cortex of vehicle treated rats. CGX-1007 treatment reduced c-fos expression throughout the infarct region by up to 50%. No significant differences were measured in either bcl-2 or bax mRNA expression between treatment groups. However, at 24 h postinjury CGX-1007 treatment was associated with an increase in Bcl-2 immunoreactivity that correlated to a reduction in DNA fragmentation. In conclusion, CGX-1007 effectively attenuated gene expression associated with delayed cell death as related to a neuroprotective relief of cerebral ischemia.

Effects of postischemic environment on transcription factor and serotonin receptor expression after permanent focal cortical ischemia in rats

Housing rats in an enriched environment improves functional outcome after ischemic stroke, this may reflect neuronal plasticity in brain regions outside the lesion. Which components of the enriched environment that are of greatest importance for recovery after brain ischemia is uncertain. We have previously found that enriched environment and social interaction alone both improve functional recovery after focal cerebral ischemia, compared with isolated housing with voluntary wheel-running. In this study, the aim was to separate components of the enriched environment and investigate the effects on some potential mediators of improved functional recovery; such as the inducible transcription factors nerve growth factor-induced gene A (NGFI-A) and NGFI-B, and the glucocorticoid and serotonin systems. After permanent middle cerebral artery occlusion, rats were divided into four groups: individually housed with no equipment (deprived group), individually housed with free access to a running wheel (running group), housed together in a large cage with no equipment (social group) or in a large cage furnished with exchangeable bars, chains and other objects (enriched group). mRNA expression of inducible transcription factors, serotonin and glucocorticoid receptors was determined with in situ hybridisation 1 month after cerebral ischemia. Rats housed in enriched or social environments showed significantly higher mRNA expression of NGFI-A and NGFI-B in cortical regions outside the lesion and in the CA1 (cornu ammonis region of the hippocampus), compared with isolated rats with or without a running wheel. NGFI-A and NGFI-B mRNA expression in cortex and in CA1 was significantly correlated to functional outcome. 5-Hydroxytryptamine receptor 1A (5-HT(1A)) mRNA expression and binding, as well as 5-HT(2A) receptor mRNA expression were decreased in the hippocampus (CA4 region) of the running wheel rats. Mineralocorticoid receptor gene expression was increased in the dentate gyrus amongst wheel-running rats. No group differences were found in plasma corticosterone levels or mRNA levels of glucocorticoid receptor, corticotropin-releasing hormone, 5-HT(2C) or c-fos. In conclusion, we have found that social interaction is a major component of the enriched environment regarding the effects on NGFI-A and NGFI-B expression. These transcription factors may be important mediators of improved functional recovery after brain infarctions, induced by environmental enrichment.

Antiactin-targeted immunoliposomes ameliorate tissue plasminogen activator-induced hemorrhage after focal embolic stroke

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) is limited by serious risks of intracerebral hemorrhage. In this study, the authors show that a novel antiactin-targeted immunoliposome significantly reduced tPA-induced hemorrhage in an established rat model of embolic focal stroke. Spontaneously hypertensive rats were subjected to focal ischemia using homologous blood clot emboli. Delayed administration of tPA (10 mg/kg, 6 hours after ischemia) induced intracerebral hemorrhage at 24 hours. In control rats treated with tPA plus vehicle, hemorrhage volumes were 9.0 +/- 2.4 uL (n = 7). In rats treated with tPA plus antiactin immunoliposomes, hemorrhage volumes were significantly reduced to 4.8 +/- 2.7 uL (n = 8, P < 0.05). No significant effects were seen when rats were treated with tPA plus a nontargeted liposome (7.8 +/- 2.1 uL, n = 9). Fluorescent immunohistochemistry showed that rhodamine-labeled targeted liposomes colocalized with vascular structures in ischemic brain that stained positive for endothelial barrier antigen, a marker of cerebral endothelial cells. These data suggest that immunoliposomes may ameliorate vascular membrane damage and reduce hemorrhagic transformation after thrombolytic therapy in cerebral ischemia.

Dynamic expression of p38beta MAPK in neurons and astrocytes after transient focal ischemia

Here we report the dynamically regulated expression of p38beta MAPK isoform in specific subsets of cells in postischemic brain. The activity of p38beta MAPK in the postischemic brain revealed biphasic induction at 30 min and 4 days after 1 h MCAO. During the early surge period, p38beta MAPK was preferentially localized in the nucleus and dendrites of neurons in the future infarction area, while during the delayed surge p38beta MAPK was heavily induced in reactive astrocytes in penumbra. The temporally and spatially regulated pattern of p38beta MAPK expression in the postischemic brain suggests distinct roles of p38beta MAPK in neuronal death and in the astrocyte activation.

Fos protein expression following acute administration of diethyldithiocarbamate in rats

Dithiocarbamates are compounds commonly used in medicine and in agriculture and their prolonged use is known to result in neurotoxicity. Whether this response may be related to early gene expression has not been investigated. We have addressed this issue by mapping Fos expression in rats acutely injected with diethyldithiocarbamate (DDTC) and correlating these data to neural damage in the hippocampus as determined by pyknotic nuclei count. In comparison to saline injected rats, DDTC treatment induced a marked Fos expression in most brain regions at 1 and 3 h. In the hippocampus, a high Fos expression was followed by a variable number of pyknotic nuclei at 6 h, depending on the subregion. The data suggest that, in this model of neurotoxicity, c-fos induction does not reflect a cell commitment to die or survive, but rather a cell response to the DDTC-induced oxidative disorder.

Arrest of apoptosis in auditory neurons: implications for sensorineural preservation in cochlear implantation

HYPOTHESIS

The JNK/c-Jun cell death pathway is a major pathway responsible for the loss of oxidative stress-damaged auditory neurons.

BACKGROUND

Implantation of patients with residual hearing accentuates the need to preserve functioning sensorineural elements. Although some auditory function may survive electrode insertion, the probability of initiating an ongoing loss of auditory neurons and hair cells is unknown. Cochlear implantation can potentially generate oxidative stress, which can initiate the cell death of both auditory neurons and hair cells.

METHODS

Dissociated cell cultures of P4 rat auditory neurons identified the apoptotic pathway initiated by oxidative stress insults (e.g., loss of trophic factor support) and characterized this pathway by arresting translation of pathway-specific mRNA with antisense oligonucleotide treatment and with the use of pathway specific inhibitors. The presence or absence of apoptosis-specific protein and changes in the level of neuronal survival measured the efficacy of these interventional strategies.

RESULTS

These in vitro studies identified the JNK/c-Jun cascade as a major initiator of apoptosis of auditory neurons in response to oxidative stress. Neurons pretreated with c-jun antisense oligonucleotide and exposed to high levels of oxidative stress were rescued from apoptosis, whereas neurons in treatment control cultures died. Treatment of oxidative-stressed cultures with either curcumin, a MAPKKK pathway inhibitor, or PD-098059, a MEK1 inhibitor, blocked loss of neurons via the JNK/c-Jun apoptotic pathway.

CONCLUSION

Blocking the JNK/c-Jun cell death pathway is a feasible approach to treating oxidative stress-induced apoptosis within the cochlea and may have application as an otoprotective strategy during cochlear implantation.

Signal transduction and neurosurvival in experimental models of brain injury

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

Transient forebrain ischemia alters the mRNA expression of methyl DNA-binding factors in the adult rat hippocampus

We have examined how transient cerebral ischemia affects the mRNA expression of a family of methyl CpG-binding domain (MBD)-containing factors in the rat hippocampus. Our results show that each member of this family is affected by cerebral ischemia challenge, but with differing patterns of responsiveness. At 3, 6 and 12 h following reperfusion, MeCP2 and MBD1 expression is maintained at control levels throughout the hippocampus. At 24 h, MeCP2 and MBD1 are induced in both the CA1 and CA3 subfields. This delayed pattern of induction is in contrast to the responses of MBD2 and MBD3. Both MBD2 and MBD3 display significant changes in expression at early times following reperfusion, although their changes are opposite in direction. MBD2 expression is induced throughout the hippocampal formation at 6 h, and remains elevated at 12 and 24 h. MBD3 expression decreases as early as 3 h following insult in the CA3 and dentate gyrus, and the decreased expression remains in the vulnerable CA1 subfield at 6, 12, and 24 h. Taken together, these results are the first to illustrate that the expression of methyl DNA-binding factors are affected by challenges to the brain, and they also illustrate that each methyl DNA-binding factor responds differently to cerebral ischemic challenge. As each of these family members is associated either directly or indirectly with the inhibition of gene transcription, our results suggest that following cerebral ischemia the normal pattern of transcriptional inhibition provided by these factors may be altered in the hippocampus.

Ischemia-reperfusion-related repair deficit after oxidative stress: implications of faulty transcripts in neuronal sensitivity after brain injury

Diseases of the heart are the No. 1 killer in industrialized countries. Brain injury can develop as a result of cerebral ischemia-reperfusion due to stroke (brain attack) and other cardiovascular diseases. Learning about the disease is the best way to reduce disability and death. We present here whether gene repair activities are associated with neuronal death in an ischemia-reperfusion model that simulates stroke in male Long-Evans rats. This experimental stroke model is known to induce necrosis in the ischemic cortex. Cerebral ischemia causes overactivation of membrane receptors and accumulation of extracellur glutamate and intracellular calcium, which activates neuronal nitric oxide synthase, causing damage to lipids, proteins, and nucleic acids, and reduces energy sources with consequent functional deterioration, leading to cell death. Restoration processes normally repair genes with few errors. However, ischemia elevates oxidative DNA lesions despite these repair mechanisms. These episodes concurrently occur with the induction of immediate-early genes that critically activate other late genes in the signal transduction pathway. Damage, repair, and transcription of the c-FOS gene are presented here as examples, because Fos peptide, one of the components of activator protein 1, activates nerve growth factor and repair mechanisms. The results of our studies show that treatments with 7-nitroindazole, a specific inhibitor of nitric oxide synthase known to attenuate nitric oxide, oxidative DNA lesions, and necrosis, increase intact c-fos mRNA levels after stroke. This suggests that the accuracy of gene expression could be accounted for the recovery of cellular function after cerebral injury.

Transcripts of damaged genes in the brain during cerebral oxidative stress

Recent studies using ischemia/reperfusion models of brain injury suggest that there is a period of time during which the formation of oxidative DNA lesions (ODLs) exceeds removal. This interval is a window of opportunity in which to study the effect of gene damage on gene expression in the brain, because the presence of excessive ODLs mimics a deficiency in gene repair, which has been shown to be associated with neurological disorders. Evidence from studies using similar models indicates that expression of faulty transcripts from ODL-infested genes and non-sense mutation in repaired genes occur before the process of cell death. Preventing the formation of ODLs and enhancing ODL repair are shown to increase the expression of intact transcripts and attenuate cell death. Understanding this mechanism could lead to the development of therapeutic techniques (physiologic, pharmacological, and/or genomic) that can enhance recovery.

DNA microarray analysis of cortical gene expression during early recirculation after focal brain ischemia in rat

Focal brain ischemia is followed by changes in gene expression as reflected by altered mRNA levels. DNA microarray analysis can be used to survey thousands of genes for differential expression triggered by ischemic metabolic stress. In this study, Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) using an intravascular poly-L-lysine-coated filament, and brains were removed after 3 h of recirculation for mRNA isolation. A differential measurement of mRNAs from post-ischemic and sham control animals was performed using the Mouse UniGene 1 microarray. Established values for differential expression were used (> or =1.7 or < or =-1.7 fold), and hits (n=2-3 arrays) divided into known 'ischemia-hypoxia response' genes and 'newly connected' annotated genes. n=28 ischemia-hypoxia response genes were up-regulated and n=6 were down-regulated. Regulated genes comprised immediate early genes, heat shock proteins, anti-oxidative enzymes, trophic factors, and genes involved in RNA metabolism, inflammation and cell signaling. Based on the ability of the microarray to replicate known changes in gene expression, n=35 newly connected genes were found up-regulated and n=41 down-regulated. DNA microarray analysis allows one to develop novel working hypotheses for responses to brain ischemia based on the regulation of annotated genes.

Environmental influences on functional outcome after a cortical infarct in the rat

The effect of postoperative housing conditions on functional outcome and brain-derived neurotrophic factor (BDNF) gene expression was evaluated 1 month after a distal ligation of the right middle cerebral artery (MCA) in spontaneously hypertensive rats. Two days postoperatively the rats were randomized into four groups; individually housed with no equipment (deprived group), individually housed with free access to a connected running wheel (running group), housed together in a large cage with no equipment (social group) or in the same size of cage furnished with bars, chains and various things to manipulate (enriched group). The enriched rats had significantly higher scores when crossing a rotating horizontal rod than deprived and running rats. The social group performed significantly better than the deprived group. The BDNF gene expression in the ipsi- and contralateral cortex, thalamus, hippocampus and cerebellum did not significantly differ between the groups. The weight of the adrenal glands was significantly increased in running rats suggesting that postischemic running may be stressful. We conclude that the beneficial effect of postischemic environmental enrichment is likely to be a combination of social and various physical activities, and that BDNF gene expression 1 month after a cortical infarct did not correlate with functional outcome.

Arachidonate release and c-fos expression in various models of hypoxia and hypoxia-hypoglycemia in retinoic acid differentiated neuroblastoma cells

Hypoxia-hypoglycemia has played an important role in inducing both phospholipase A2 activation and the expression of the early gene c-fos, in the neuroblastoma cell line SK-N-BE, after it has been differentiated by retinoic acid. Under hypoxic-hypoglycemic conditions, arachidonic acid release has found to be significant after 30 min, whereas c-fos expression has required at least 4 h. This model has been obtained by adding glycolytic inhibitor 2-deoxyglucose to the culture and by placing cells in an atmosphere containing 100% N2 for different time periods. This condition has been compared with two different models: NaCN and nitrogen have been used as hypoxic stimuli, without inhibiting the glycolytic pathway, but the same cell cultures have been used. Cell viability and the fall of cellular ATP levels have been evaluated in all the models, in order to monitor and compare the hypoxic cellular damage. Phospholipase A2 activation has been found to be significant in all conditions, even if to a different extent; but only hypoxia combined with the inhibition of the glycolytic pathway, has induced a significant expression of c-fos. It is very difficult to study hypoxic stimuli in 'in vitro' systems. Our study has compared three different models and the one combining gaseous hypoxia and hypoglycemic conditions seems to be very effective in stimulating early events involved in hypoxic phenomena such as phospholipase activation and the expression of the early gene c-fos.

Blockade of A(2A) adenosine receptors leads to c-fos inhibition in a rat model of brain ischemia

Adenosine plays an important role in cerebral ischemia by acting on its own receptors, in particular the A(2A)receptor. Its activation leads to excitatory amino acid release thus contributing to the ischemic damage. Blockade by specific antagonists may protect against cytotoxic injury. Our study was aimed to investigate the effect of the blockade of A(2A)receptors, by Sch 58261, on the expression of the early gene c-fos, in a model of permanent middle cerebral artery occlusion (pMCAo), in rats. In the pMCAo model, ischemia was induced in the right hemisphere whereas the contralateral one was considered the control. In our study, we have compared pMCAo rats, pMCAo rats treated with Sch 58261 and sham operated ones.C-fos was markedly expressed in the ischemic hemispheres, whereas lower levels were detected in the contralateral ones of the ischemic animals. The lowest bands were observed in sham operated rats. After treatment with Sch 58261, a considerable reduction in c-fos expression was observed in the ischemic hemispheres, whereas a limited effect was detected in the others. Our results suggest that inhibition of immediate-early gene expression by the A(2A)receptors antagonist Sch 58261 may contribute to its neuroprotective activity.

Synergistic induction of HSP40 and HSC70 in the mouse hippocampal neurons after cerebral ischemia and ischemic tolerance in gerbil hippocampus

An ischemia-induced gene was screened using a differential display technique in mouse transient forebrain ischemia. One of the ischemia-responsive clones was found to encode mouse hsp40. HSP40 has a critical regulatory function in the HSC70 ATPase activity. Expression of hsp40 mRNA was low in the nonischemic mouse hippocampus, but it was significantly upregulated 4 hr after ischemia by Northern blot analysis. In situ hybridization analysis revealed hsp40 mRNA induction in the neuron. HSP40 protein expression was also enhanced in the pyramidal and dentate granular neurons from 2 to 4 days after ischemia. The temporal expression and distribution profile of HSC70 protein was similar to that of HSP40, and both proteins were colocalized in ischemic hippocampal neurons. In the gerbil transient forebrain ischemia model, both HSP40 and HSC70 proteins were expressed strongly in ischemia-resistant CA3 neurons and dentate granule cells 1 day after 5 min ischemia, but were not expressed in vulnerable CA1 neurons. However, both proteins were in parallel expressed in the tolerance-acquired CA1 neurons. Based on the current observation that both HSP40 and HSC70 proteins were synergistically expressed in the ischemia-resistant and tolerance-acquired neurons, cochaperone HSP40 may play a significant role against postischemic neuronal response and lead to cell survival through interaction with simultaneously induced HSC70.

Altered expression of the neuropeptide-processing enzyme carboxypeptidase E in the rat brain after global ischemia

Carboxypeptidase E, an exoprotease involved in the processing of bioactive peptides released by a regulated secretory pathway, was identified in a subtractive complementary DNA library derived from an ischemic rat brain by differential screening. In situ hybridization and immunocytochemical analysis showed the presence of carboxypeptidase E messenger RNA and protein in the cerebral cortex, thalamus, striatum, and hippocampus of a healthy rat brain. After 15 minutes of transient global ischemia followed by 8 hours of reperfusion, increased levels of carboxypeptidase E messenger RNA and protein were observed in the hippocampal CA1 and CA3 regions and in the cortex, as detected by Northern and Western blot analyses and in situ hybridization. After extended reperfusion (24 to 72 hours), both carboxypeptidase E messenger RNA and protein levels were decreased. The ischemia-induced changes in carboxypeptidase E expression suggest that this enzyme may play a role in modulating the brain's response to ischemia.

Differential effects of ischemia and reperfusion on c-Jun N-terminal kinase isoform protein and activity

Activation of the c-Jun N-terminal (JNK) or stress-activated protein kinases (SAPK) is associated with a wide range of disparate cellular responses to extracellular stimuli, including either induction of or protection from apoptosis. This study investigates the effect of ischemia and reperfusion on JNK isoform activities using a reversible rabbit spinal cord ischemia model. High basal JNK activity, attributed to the p46 JNK1 isoform, was expressed in the CNS of untreated rabbits. JNK activity decreased in the lumbar spinal cord of rabbits occluded for 15-60 min. During reperfusion animals occluded for 15 min recovered neurological function and JNK activity returned to normal levels. In contrast animals occluded for 60 min remained permanently paraplegic and JNK activity was half the control activity after 18 h of reperfusion. In these animals proteolytic fragments of JNK1 and JNK3 were observed and protein levels, but not activity, of JNK isoforms increased in a detergent-insoluble fraction. Two novel c-Jun (and ATF-2) kinase activities increased during reperfusion of animals occluded for 60 min. An activity designated p46(slow) was similar in M(r) to a JNK2 isoform induced in these animals. A second 30-kDa activity associated with the detergent-insoluble fraction co-migrated with a JNK3 N-terminal fragment. The results show that JNK1 is active in the normal CNS and increased activity is not associated with durations of ischemia and reperfusion that induce cell death. However, specific JNK isoform activation may participate in the cell death pathways as increased activity of novel c-Jun (ATF-2) kinase activities was observed in paraplegic animals.

Temporospatial expression of HSP72 and c-JUN, and DNA fragmentation in goat hippocampus after global cerebral ischemia

The role of gene induction (expression of HSP72 and c-JUN proteins) and delayed ischemic cell death (in situ labeling of DNA fragmentation) have been investigated in the goat hippocampus after transient global cerebral ischemia. The animals were subjected to 20-min ischemia (bilateral occlusion of the external carotid arteries plus bilateral jugular vein compression) and allowed to reperfuse for 2 h, and then 1, 3, and 7 days. Histological signs of cell loss were not found in the hippocampus at 2 h, 1 day, or 3 days of reperfusion. However, such an ischemic insult produced extensive, selective, and delayed degeneration in the hippocampus, as 68% of the neurons in CA1 had died at 7 days, but cell loss was not detected in CA3 and dentate gyrus fields. Concomitantly, a high percentage of TUNEL-positive CA1 neurons (60+/-9%, mean +/- SEM) was seen at 7 days, but not at the earlier time points. Mild induction of HSP72 was detected in the goat hippocampus after ischemia. The maximum percentage of HSP72-positive neurons (10-15%) was shown at 3 days of reperfusion and was concentrated mainly in the CA3 field, subiculum, and hilus, rather than in the CA1 field, whereas HSP72 expression was hardly detected at 7 days. At this later time point, scattered induction of nuclear c-JUN was found in a few neurons. The results show that: 1) postischemic delayed neuronal death selectively affects the CA1 field in the goat hippocampus, a phenomenon which seems to take longer to develop than in previously reported rodent models; and 2) postischemic expression of c-JUN does not appear to be related to cell death or survival, while the inability of most CA1 neurons to express HSP72 could contribute to neuronal death.

The role of proteolytic enzymes in focal ischaemic brain damage

Although various neuroprotective and fibrinolytic drugs are currently under evaluation in the acute stages of ischaemic stroke, their therapeutic potential is likely to be limited by unwanted side effects and a narrow time window of opportunity for intervention. Proteolytic enzymes are involved in the catabolism of peptide neurotransmitters and structural cellular proteins in normal brain and have been implicated in the pathogenesis of neurodegenerative disorders. We hypothesised that activation of these enzymes might also play a crucial role in effecting ischaemic neuronal injury, thereby providing a potential site for therapeutic intervention in human stroke. Focal cerebral ischaemia was induced by thermocoagulation of the left middle cerebral artery in aged (30 month) male Wistar rats who were pre-treated with saline or the competitive N-methyl-D-Aspartate antagonist D-CPP-ene, which has been shown to be neuroprotective in young animal models of stroke. Major protease activities were analysed in the left (ischaemic) and right (non-ischaemic) hemispheres, following tissue homogenisation. Data have been analysed using Mann-Whitney tests and are presented as means +/- standard errors. Enzyme activity decreased in ischaemic brain; for example, the mean activity of dipeptidyl aminopeptidase I was 23 +/- 3 and 43 +/- 6 nmol substrate/hour/ml brain extract in the left and right hemispheres respectively (n = 10, p < 0.05). Ischaemic neuronal injury is not effected by the early activation of proteolytic enzymes and protease inhibitors are therefore unlikely to be of benefit in human stroke.

A metabotropic glutamate receptor antagonist, alpha-methyl-4-carboxyphenylglycine, attenuates immediate early gene mRNA expression following traumatic injury in cultured rat cortical glial cells

The effects of three glutamate receptor antagonists, (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate (MK-801) for the N-methyl-D-aspartate receptor, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f] quinoxaline-7-sulfonamide (NBQX) for the alpha-amino-3-hydroxy-5methyl-4-isoxazole propionate /kinate receptor and (S)-alpha-methyl-4-carboxyphenylglycine (MCPG) for the metabotropic receptor, on c-fos and c-jun mRNA expression were investigated in cultured cortical glial cells following traumatic scratch injury. Expression of the two genes along the edges of wounds detected by in situ hybridization was not affected by MK-801 and NBQX. However, 100 and 500 microM of MCPG remarkably reduced the hybridization signals for both c-fos and c-jun mRNAs. The present results suggest that group I metabotropic glutamate receptors might have some association with immediate early gene induction after in vitro traumatic injury in glial cells.

Differential cellular expression of tumor necrosis factor-alpha and Type I tumor necrosis factor receptor after transient global forebrain ischemia

We examined the expression of tumor necrosis factor-alpha (TNF-alpha) and the Type I tumor necrosis factor receptor, (TNFR1), in relation to c-fos, a known regulator gene of immediate cellular responses, after an extended period of global ischemia. The number of TNF-alpha mRNA expressing cells peaked in most brain areas after 8 h of reperfusion. Significant increases in TNFR1 mRNA expression were evident in the cortex at 2 and 8 h of reperfusion and after 8 h of reperfusion in the CA3/CA4 region of the hippocampus. Transient neuronal c-fos mRNA expression preceded these responses. TNF-alpha immunoreactivity was seen in neurons>>>oligodendrocytes=perivascular cells=ependymal cells=vessel wall structures. After ischemia/reperfusion, increased TNF-alpha immunoreactivity was evident only in oligodendrocytes. TNFR1 immunoreactivity in sham brains manifested in bundles of cellular fibers of variable length and thickness. In post-ischemic brains, immunoreactivity in these cellular processes representing mainly astroglial extensions was suppressed at 2 h but recovered partially by 8 and 24 h of reperfusion. In contradiction, transient ischemia-induced TNFR1 immunoreactivity was observed in somas of large cortical neurons, in activated microglia/macrophages, perivascular and endothelial cells.Taken together, the increase in neuronal TNF-alpha mRNA appeared not to be followed by substantial translation to protein in the cerebral tissue after an extended period of global ischemia. However, there was increased neuronal TNFR1 immunostaining in conjunction with increased immunostaining for TNF-alpha in oligoglial elements, which suggests signaling to neurons by enhanced oligoglial TNF-alpha.

Early c-Fos induction after cerebral ischemia: a possible neuroprotective role

The role of c-Fos in neurodegeneration or neuroprotection after cerebral ischemia is controversial. To investigate whether early c-Fos induction after ischemia is associated with neuroprotection, rats were subjected to 10 minutes of transient forebrain ischemia and c-Fos expression was examined. Resistant dentate granule cells and neurons in CA2-4 displayed more robust immunoreactivity than vulnerable neurons in the CA1 region of hippocampus during early hours of reperfusion. By 6 hours after reperfusion, c-Fos immunoreactivity was greatly diminished in all areas of the hippocampus. Administration of N-acetyl-O-methyldopamine (NAMDA), a compound previously shown to protect CA1 neurons against ischemia, increased c-Fos immunoreactivity in the CA1 vulnerable region at 6 hours after ischemia and protected SK-N-BE(2)C neurons from oxygen glucose deprivation. Further in vitro study showed that NAMDA potentiated phorbol-12 myristate-13 acetate (PMA)-induced c-Fos expression, AP1 binding activity, and late gene expression determined by chloramphenicol acetyltransferase (CAT) activity from AP1 containing tyrosine hydroxylase promoter-CAT fusion gene in SK-N-BE(2)C neurons. In vivo and in vitro results showed that a neuroprotectant, NAMDA, in concert with another stimulus (for example, ischemia or PMA) up-regulates c-Fos expression and suggested that the early rise of NAMDA-induced c-Fos expression in vulnerable CA1 neurons may account for neuroprotection by means of up-regulating late gene expression for survival.

Neuronal NOS inhibitor that reduces oxidative DNA lesions and neuronal sensitivity increases the expression of intact c-fos transcripts after brain injury

In response to oxidative stress, the ischemic brain induces immediate early genes when its nuclear genes contain gene damage. Antioxidant that reduces gene damage also reduces cell death. To study the mechanism of neuronal sensitivity, we investigated the transcription of the c-fos gene after brain injury of the ischemia-reperfusion type using focal cerebral ischemia-reperfusion in Long-Evans hooded rats. We observed a significant (p < 0.01) increase in c-fos mRNA in the ischemic cortex immediately after brain injury. However, the c-fos transcript was sensitive to RNase A protection assay (RPA) upon reperfusion. The transcript became significantly resistant to RPA (42%, p < 0.03) when 3-bromo-7-nitroindazole (25 mg/kg, i.p.), known to abolish nitric oxide, gene damage and neuronal sensitivity, was injected. Our data suggest that neuronal nitric oxide synthase and aberrant mRNA from genes with oxidative damage could be associated with neuronal sensitivity.

Molecular mechanisms of ischemic neuronal injury

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.

Early and delayed induction of immediate early gene expression in a novel focal cerebral ischemia model in the rat

This study aimed at evaluating changes in expression of immediate early genes in a new photothrombotic focal ischemia model that exhibits late spontaneous reperfusion and morphological restoration in the region-at-risk within the cerebral cortex. Gene expression was studied with Northern blots, in situ hybridization and immunohistochemistry. At early time points (1-4 h), nerve growth factor-induced gene A and B, and c-fos mRNAs, were quickly induced throughout the ipsilateral cortex, with no obvious differences between the region-at-risk and remote cortical areas. High concentrations of nerve growth factor-induced gene A and c-Fos proteins were present within the region-at-risk even when cortical cerebral blood flow was as low as 40% of control values. At 4 h the nerve growth factor-induced gene A mRNA and protein expression was significantly decreased in the hippocampus vs. naive controls. However, a small decrease was also found in sham-operated and anaesthetized controls. A late induction, at 5 days, of c-fos and nerve growth factor-induced gene B mRNAs was seen bilaterally in the hippocampus and also, in the case of nerve growth factor induced-gene B, in the contralateral cortex. A complex pattern of changes in immediate early gene expression occurs after reversible focal cortical ischemia. This may be important for tissue recovery as well as neuropsychiatric symptoms after stroke.

Activation of mitogen-activated protein kinases after permanent cerebral artery occlusion in mouse brain

The purpose of this study was to examine the activation, topographic distribution, and cellular location of three mitogen-activated protein kinases (MAPKs) after permanent middle cerebral artery occlusion (MCAO) in mice. Phosphorylated MAPKs expression in the ischemic region was quantified using Western blot analysis and localized immunohistochemically using the diaminobenzide staining and double-labeled immunostaining. Extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2), p38 mitogen-activated protein (p38), and c-Jun NH2-terminal kinase or stress-activated protein kinase (SAPK/JNK) were initially activated at 30 minutes, 10 minutes, and 5 minutes, respectively, after focal cerebral ischemia. Peak expression represented a 2.7-fold, 3.7-fold, and 4.8-fold increase in each of these MAPKs, respectively. The immunohistochemical expressions of ERK1, ERK2, p38, and SAPK/JNK protein paralleled the Western blot analysis results. Double-labeled immunofluorescent staining demonstrated that the neurons and astrocytes expressed ERK1, ERK2, p38, and SAPK/JNK during the early time points after MCAO. The current results demonstrate that brain damage after ischemia rapidly triggers time-dependent ERK1, ERK2, p38, and SAPK/ JNK phosphorylation, and reveals that neurons and astrocytes are involved in the activation of the MAPK pathway. This very early expression of MAPKs suggests that MAPKs may be closely involved in signal transduction during cerebral ischemia.

Increased binding activity at an antioxidant-responsive element in the metallothionein-1 promoter and rapid induction of metallothionein-1 and -2 in response to cerebral ischemia and reperfusion

Metallothioneins (MTs) are cysteine-rich metal-binding proteins that are potentially involved in zinc homeostasis and free radical scavenging. The expression pattern of MT-1 and the binding activity of various MT-1 promoter elements were investigated after mild focal cerebral ischemia in the rat. Transient focal ischemia was induced by occluding both common carotid arteries and the right middle cerebral artery for 30 min. By the use of real-time quantitative PCR, a 10-fold increase in MT-1 and -2 mRNA levels was found in the cortex 24 hr after reperfusion. In situ hybridization and immunocytochemistry showed a rapid increase in MT-1 and -2 mRNA and MT protein in endothelial cells of microvessels at 6 hr after reperfusion, followed by an increased expression in astrocytes of the infarcted cortex at 24 hr after reperfusion. The early increase in MT expression preceded an increase in cerebral edema measured with T2-weighted magnetic resonance imaging. Gel shift assays were performed on nuclear extracts prepared from cortices before and at 6 and 24 hr after reperfusion. Increased binding activity was found at an antioxidant/electrophilic response element (ARE) sequence in the MT-1 promoter at 6 hr with a lower and variable binding activity at 24 hr after reperfusion. Constitutive binding activity was found for Sp1 and a metal response element in the MT-1 promoter that did not increase after ischemia and reperfusion. This study suggests a role of ARE-binding proteins in inducing cerebral MT-1 expression and implicates MT-1 as one of the early detoxifying genes in an endogenous defense response to cerebral ischemia and reperfusion.

Müller cells in the preconditioned retinal ischemic injury rat

The role of Müller cells in the preconditioned retinal ischemic injury rat was investigated. In anesthetized Sprague Dawley rats, retinal ischemia for 5 minutes constituted the preconditioning stimulus for the left eye. After 24 hours, both eyes were clamped for 60 minutes. In 30, 60, 90, and 120, minutes and 1 day, 3 days, and 7 days after ischemia, electroretinograms were recorded, and the eyeballs were enucleated. After fixation with 4% paraformaldehyde, the avidin-biotin-peroxidase technique was applied to show glutamine synthetase (GS) and glial fibrillary acidic protein (GFAP). Furthermore, for the solubilized retinas, Western blot analysis and enzyme-linked immunosorbent assay were performed to detect GS and GFAP in the extracts. Preconditioning performed 24 hours before ischemia significantly improved the recovery of the a-, and b-waves 1 day after 60 minute ischemia. In the 30, 60, 90, and 120 minutes after ischemia, the recovery of the a-wave only was observed. There was a nonsignificant trend toward greater recovery in the first 120 minutes after 60 minute ischemia, especially in the b-wave. GS immunoreactivity had no significant difference between non-preconditioned and preconditioned groups 30, 60, 90, and 120 minutes after ischemia. In 1 day after ischemia, GS immunoreactivity decreased in both groups. In 3 and 7 days after ischemia, GS immunoreactivity recovered only in the preconditioned group. The retinas at 3 and 7 days after 1 hour of ischemia showed increased GFAP immunoreactivity in the non-preconditioned group. In the preconditioned group, only slight GFAP immunoreactivity was observed. These results suggested that the mechanism of preconditioned retinal ischemia may be related to Müller cells in the retina.

Environmental influence on brain-derived neurotrophic factor messenger RNA expression after middle cerebral artery occlusion in spontaneously hypertensive rats

Enriched environment significantly enhances postischemic functional outcome. We have tested the hypothesis that housing in enriched environment stimulates gene expression for brain-derived neurotrophic factor. After ligation of the middle cerebral artery in male spontaneously hypertensive rats, they were housed in individual cages for 30h, then housed either in standard cages or in an enriched environment. The rats were killed two to 30days after the ischemic event. Cryostat coronal sections through the dorsal hippocampus (Bregma -3.3) were processed for in situ hybridization using a rat-brain-derived neurotrophic factor messenger RNA antisense oligonucleotide probe. Postischemic gene expression was significantly higher in standard rats than in enriched rats in contralateral and peri-infarct cortex and in most parts of the hippocampus two, three and 12days after the ischemic event, with a trend for higher-than-baseline levels in standard rats and lower-than-baseline levels in enriched rats. At 20 and 30days the values for both groups were below baseline levels. Contrary to our hypothesis, gene expression in rats postoperatively housed in enriched environment was significantly lower than in standard rats at a time when other studies have reported hyperexcitability in the ipsilateral and contralateral cortex. Should the low messenger RNA levels correspond to low protein synthesis, this might indicate that dampening of the early postischemic hyperexcitability may be beneficial. Low levels in both groups at 20 and 30days may correspond to loss of callosal connections in the opposite hemisphere and to horizontal cortical connections in the lesioned hemisphere.

Transient spinal cord ischemia in rat: the time course of spinal FOS protein expression and the effect of intraischemic hypothermia (27 degrees C)

1. In the present study, we characterize the time course of spinal FOS protein expression after transient noninjurious (6-min) or injurious (12-min) spinal ischemia induced by inflation of a balloon catheter placed into the descending thoracic aorta. In addition, this work examined the effects of spinal hypothermia on FOS expression induced either by ischemia or by potassium-evoked depolarization (intrathecal KCl). 2. Short-lasting (6-min) spinal ischemia evoked a transient FOS protein expression. The peak expression was seen 2 hr after reperfusion in all laminar levels in lumbosacral segments. At 4 hr of reperfusion, more selective FOS expression in spinal interneurons localized in the central part of laminae V-VII was seen. At 24 hr no significant increase in FOS protein was detected. 3. After 12 min of ischemia and 2 hr of reflow, nonspecific FOS expression was seen in both white and gray matter, predominantly in nonneuronal elements. Intrathecal KCl-induced FOS expression in spinal neurons in the dorsal horn and in the intermediate zone. Spinal hypothermia (27 degrees C) significantly suppressed FOS expression after 6 or 12 min of ischemia but not after KCl-evoked depolarization. 4. Data from the present study show that an injurious (but not noninjurious) interval of spinal ischemia evokes spinal FOS protein expression in glial cells 2 hr after reflow. The lack of neuronal FOS expression corresponds with extensive neuronal degeneration seen in this region 24 hr after reflow. Noninjurious (6-min) ischemia induced a transient, but typically neuronal FOS expression. The significant blocking effect of hypothermia (27 degrees C) on the FOS induction after ischemia but not after potassium-evoked depolarization also suggests that simple neuronal depolarization is a key trigger in FOS induction.

Temporary middle cerebral artery occlusion in the rat: consistent protocol for a model of stroke and reperfusion

The intraluminal suture method of middle cerebral artery occlusion (MCAO) in the rat (the suture model) is a model of stroke which readily lends itself to studying the pathophysiology of post-ischaemic reperfusion. Unfortunately, variability of outcome has compromised the potential of the model, but systematic studies might characterize a consistent protocol. Therefore, the clinical and neuropathological outcome of temporary MCAO and reperfusion in the suture model were systematically investigated. Two hours or 4 h of MCAO were employed, measuring the extent of infarction at 24 h with triphenyltetrazolium chloride or at 72 h with histopathological techniques. Outcome was compared in three rat strains. Following 2 h of MCAO, motor function improved during reperfusion in Sprague-Dawley, but not in Wistar or Fischer-344 rats. All Sprague-Dawley and Wistar rats survived the protocol to 72 h, but 33% of Fischer-344 rats died. The extents of infarction and oedema were greater and less variable in Wistar and Fischer-344 than Sprague-Dawley rats, and in all three strains, the extent of infarction increased with reperfusion time. Following 4 h of MCAO, there was no improvement in motor function during reperfusion in Sprague-Dawley rats, and mortality was high at 24 h in Wistar (33%) and Fischer-344 rats (83%). Outcome was only pursued in Sprague-Dawley rats to 72 h, where the extent of infarction was quite variable. It was concluded that the extent and variability of outcome following temporary MCAO in the suture model is strain-dependent, and a consistent protocol with zero mortality was found in Wistar rats using 2 h of MCAO and 70 h of reperfusion.

Cerebral ischemia: gene activation, neuronal injury, and the protective role of antioxidants

A large number of gene products appear after an ischemic insult making it difficult to decipher which genes are involved in tissue injury. Reactive oxygen species (ROS) can influence gene expression and have a role in the events that lead to neuronal death. In global cerebral ischemia the oxidative responsive transcription factor, NF-kappa B, is persistently activated in neurons that are destined to die. There are several potential routes through which NF-kappa B can act to induce neuronal death, including production of death proteins and an aborted attempt to reenter the cell cycle. NF-kappa B is only transiently activated in neurons that survive. Persistent NF-kappa B activation can be blocked by antioxidants, which suggests that the neuroprotective effect of antioxidants may be due to inhibiting activation of NF-kappa B.

Oxidative DNA damage precedes DNA fragmentation after experimental stroke in rat brain

Experimental stroke using a focal cerebral ischemia and reperfusion (FCIR) model was induced in male Long-Evans rats by a bilateral occlusion of both common carotid arteries and the right middle cerebral artery for 30-90 min, followed by various periods of reperfusion. Oxidative DNA lesions in the ipsilateral cortex were demonstrated using Escherichia coli formamidopyrimidine DNA N-glycosylase (Fpg protein)-sensitive sites (FPGSS), as labeled in situ using digoxigenin-dUTP and detected using antibodies against digoxigenin. Because Fpg protein removes 8-hydroxy-2'-deoxyguanine (oh8dG) and other lesions in DNA, FPGSS measure oxidative DNA damage. The number of FPGSS-positive cells in the cortex from the sham-operated control group was 3 +/- 3 (mean +/- SD per mm(2)). In animals that received 90 min occlusion and 15 min of reperfusion (FCIR 90/15), FPGSS-positive cells were significantly increased by 200-fold. Oxidative DNA damage was confirmed by using monoclonal antibodies against 8-hydroxy-guanosine (oh8G) and oh8dG. A pretreatment of RNase A (100 microg/ml) to the tissue reduced, but did not abolish, the oh8dG signal. The number of animals with positive FPGSS or oh8dG was significantly (P<0.01) higher in the FCIR group than in the sham-operated control group. We detected few FPGSS of oh8dG-positive cells in the animals treated with FCIR of 90/60. No terminal UTP nicked-end labeling (TUNEL)-positive cells, as a detection of cell death, were detected at this early reperfusion time. Our data suggest that early oxidative DNA lesions elicited by experimental stroke could be repaired. Therefore, the oxidative DNA lesions observed in the nuclear and mitochondrial DNA of the brain are different from the DNA fragmentation detected using TUNEL.

What animal models have taught us about the treatment of acute stroke and brain protection

Stroke research has progressed in leaps and bounds in the past decades. A driving force is the increasing availability of new research tools in this field (eg, animal stroke models). Animal stroke models have been extensively applied to advance our understanding of the mechanisms of ischemic brain injury and to develop novel therapeutic strategies for reducing brain damage after a stroke. Animal stroke models have been useful in characterizing the molecular cascades of injury processes. These "injury pathways" are also the targets of therapeutic interventions. The major achievements made in the past 2 decades applying animal stroke models include 1) the identification of the mediator role of excitotoxin and oxygen free radicals in ischemic brain injury; 2) the confirmation of apoptosis as a major mechanism of ischemic cell death; 3) the characterization of postischemic gene expression; 4) the delineation of postischemic inflammatory reaction; 5) the application of transgenic mice to confirm the roles of purported mediators in ischemic brain injury; 6) development of novel magnetic resonance imaging sequences for early noninvasive detection of ischemic brain lesions; and, 7) the development of novel therapeutic strategies based on preclinical findings derived from animal stroke models.

Reduction of tissue plasminogen activator-induced hemorrhage and brain injury by free radical spin trapping after embolic focal cerebral ischemia in rats

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) remains complicated by serious risks of cerebral hemorrhage and brain injury. In this study, a novel model of tPA-induced hemorrhage was used in spontaneously hypertensive rats to examine the correlates of hemorrhage, and test methods of reducing hemorrhage and brain injury. Homologous blood clot emboli were used to occlude the middle cerebral artery in spontaneously hypertensive rats, and delayed administration of tPA (6 hours postischemia) resulted in high rates of cerebral hemorrhage 24 hours later. Compared with untreated rats, tPA significantly increased hemorrhage volumes by almost 85%. Concomitantly, infarction and neurological deficits were worsened by tPA. A parallel experiment in normotensive Wistar-Kyoto rats showed markedly reduced rates of hemorrhage, and tPA did not significantly increase hemorrhage volumes. To examine whether tPA-induced hemorrhage was caused by the delayed onset of reperfusion per se, another group of spontaneously hypertensive rats was subjected to focal ischemia using a mechanical method of arterial occlusion. Delayed (6 hours) reperfusion via mechanical means did not induce hemorrhage. However, administration of tPA plus delayed mechanical reperfusion significantly increased hemorrhage volumes. Since reperfusion injury was implicated, a final experiment compared outcomes in spontaneously hypertensive rats treated with tPA plus the free radical spin trap alpha-phenyl tert butyl nitrone (alpha-PBN) versus tPA alone. tPA-induced hemorrhage volumes were reduced by 40% with alpha-PBN, and infarction and neurological deficits were also decreased. These results indicate that (1) blood pressure is an important correlate of tPA-induced hemorrhage, (2) tPA interacts negatively with reperfusion injury to promote hemorrhage, and (3) combination therapies with anti-free radical treatments may reduce the severity of tPA-induced hemorrhage and brain injury after cerebral ischemia.

Molecular cloning and characterization of Amida, a novel protein which interacts with a neuron-specific immediate early gene product arc, contains novel nuclear localization signals, and causes cell death in cultured cells

Amida was isolated by the yeast two-hybrid system as a novel protein which associated with Arc, a non-transcriptional immediate early gene specific to the brain. Amida was confirmed to be associated with Arc in vitro and in vivo. Amida shows no homology to known proteins. Amida is ubiquitously expressed, although it is abundant in the brain. A transfection study revealed that Amida was localized in the nucleus and after 72 h the transfected cells underwent apoptosis. Furthermore, we found two nuclear localization signals and a domain needed for interacting with Arc was encompassed by two nuclear localization signals. Co-transfection experiment with Amida and Arc suggested that Amida transported Arc into the nucleus and negatively regulated Amida-induced cell death. These results indicate that Arc together with Amida may modulate cell death in the brain.

Biology of ischemic cerebral cell death

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

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.

Environmental influence on gene expression and recovery from cerebral ischemia

An emerging concept in neurobiology is that the adult brain retains a capacity for plasticity and functional reorganization throughout the life span. Experimental data from electrophysiological, morphological and behavioral studies have documented experience dependent plasticity in the intact and injured adult brain. Neuroimaging clinical studies indicate altered post stroke functional activation patterns, usually including activation of the intact hemisphere. However, there is some disagreement regarding their functional significance and longitudinal studies correlating outcome and activation pattern are needed to solve some controversies. Postoperative housing of rats in activity stimulating environment after ligation of the middle cerebral artery significantly enhances outcome. Gene expression for brain derived neurotrophic factor and Ca2+/calmodulin-dependent protein kinase II, two substances with potential role in brain plasticity, show different patterns in animals housed in standard and in enriched environment. The functional significance of altered gene expression needs to be evaluated.

Environmental enrichment alters nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression after middle cerebral artery occlusion in rats

Housing rats in an enriched environment after focal brain ischemia improves functional outcome without changes in infarct volume, suggesting neuroplastic changes outside the lesion. In this study, permanent occlusion of the middle cerebral artery was followed by housing in an enriched or a standard environment. Nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression were determined by in situ hybridization two to 30 days after middle cerebral artery occlusion. Stroke induced a decrease in nerve growth factor-induced gene A messenger RNA expression in cortical areas outside the ischemic lesion and in the CA1 subregion of the hippocampus two to three days after ischemia. This decrease was more prolonged with environmental enrichment, lasting until 20 days. However, 30 days after focal cerebral ischemia, environmental enrichment increased nerve growth factor-induced gene A expression compared to standard housing. A reduction of hippocampal glucocorticoid receptor (type II) messenger RNA two to 12 days after stroke in standard housed rats was restored by environmental enrichment. These data suggest that improved functional outcome induced by environmental enrichment after middle cerebral artery occlusion is associated with dynamically altered expression of nerve growth factor-induced gene A messenger RNA in brain regions outside the ischemic lesion, and sustained levels of hippocampal glucocorticoid receptor messenger RNA expression.