Induction of c-fos, junB, c-jun, and hsp70 mRNA in cortex, thalamus, basal ganglia, and hippocampus following middle cerebral artery occlusion

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.

Effects of transient global ischemia and kainate on poly(ADP-ribose) polymerase (PARP) gene expression and proteolytic cleavage in gerbil and rat brains

Poly (ADP-ribose) polymerase (PARP) is involved in various cellular functions, including DNA repair, the cell cycle and cell death. While PARP activation could play a critical role in repairing ischemic brain damage, PARP inactivation caused by caspase 3-cleavage may also be important for apoptotic execution. In this study we investigated the effects of transient global ischemia and kainic acid (KA) neurotoxicity, in gerbil and rat brains, respectively, on PARP gene expression and protein cleavage. PARP mRNA increased in the dentate gyrus of gerbil brains 4 h after 10 min of global ischemia, which returned to basal levels 8 h after ischemia. KA injection (10 mg/kg) also induced a marked elevation in PARP mRNA level selectively in the dentate gyrus of rat brains 1 h following the injection, which returned to basal levels 4 h after the injection. These observations provide the first evidence of altered PARP gene expression in brains subjected to ischemic and excitotoxic insults. Using both monoclonal and polyclonal antibodies to PARP cleavage products, little evidence of significant PARP cleavage was found in gerbil brains within the first 3 days after 10 min of global ischemia. In addition, there was little evidence of significant PARP cleavage in rat brains within 2 days after kainate (KA) injection. Though these findings show that caspase induced PARP cleavage is not substantially activated by global ischemia and excitotoxicity in whole brain, the PARP mRNA induction could suggest a role for PARP in repairing DNA following brain injury.

High resolution magnetic resonance angiography non-invasively reveals mouse strain differences in the cerebrovascular anatomy in vivo

High resolution magnetic resonance angiography (MRA) revealed highly variable arterial cerebrovascular structures in mice from different strains and within the same strain. C57Black/6 mice presented small unilateral anastomoses between the posterior cerebral and the superior cerebellar arteries. Well developed, either unilateral or bilateral, posterior communicating arteries (PcomA) were detected on CBA mice. The arterial structure of CD1 mice ranged from no detectable anastomoses to well developed, unilateral PcomAs. SV-129 mice showed significantly shorter middle cerebral arteries compared to the other strains, and clear bilateral anastomoses between the posterior cerebral and the superior cerebellar arteries. Because of its non-invasiveness, MRA may be of importance in murine stroke studies by enabling the selection of animals and/or the side for performing the surgical intervention, and the verification of its success. Magn Reson Med 44:252-258, 2000.

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.

Multiple molecular penumbras after focal cerebral ischemia

Though the ischemic penumbra has been classically described on the basis of blood flow and physiologic parameters, a variety of ischemic penumbras can be described in molecular terms. Apoptosis-related genes induced after focal ischemia may contribute to cell death in the core and the selective cell death adjacent to an infarct. The HSP70 heat shock protein is induced in glia at the edges of an infarct and in neurons often at some distance from the infarct. HSP70 proteins are induced in cells in response to denatured proteins that occur as a result of temporary energy failure. Hypoxia-inducible factor (HIF) is also induced after focal ischemia in regions that can extend beyond the HSP70 induction. The region of HIF induction is proposed to represent the areas of decreased cerebral blood flow and decreased oxygen delivery. Immediate early genes are induced in cortex, hippocampus, thalamus, and other brain regions. These distant changes in gene expression occur because of ischemia-induced spreading depression or depolarization and could contribute to plastic changes in brain after stroke.

Neurons in layer III of the entorhinal cortex. A role in epileptogenesis and epilepsy?

A preferential lesion of neurons in layer III of the entorhinal cortex (EC) is often observed in patients suffering from temporal lobe epilepsy and in several animal models of the disease. This lesion is duplicated in rats by a focal, intra-entorhinal injection of the "indirect" excitotoxin aminooxyacetic acid (AOAA), providing a model that can be used to study the mechanisms underlying seizure-induced cell death and epilepsy. Doomed neurons in the EC and in several associated limbic structures show pathological changes within hours after the AOAA injection, but GABAergic neurons in layer III of the EC are quite resistant. This pattern of neuron loss eventually results in hippocampal and entorhinal hyperexcitability. Notably, the seizure-induced death of layer III neurons in the EC can be attenuated by eliminating the prominent excitatory input from the presubiculum. Taken together, these results suggest opportunities to target parahippocampal structures for the treatment of temporal lobe epilepsy.

Brain plasticity and stroke rehabilitation. The Willis lecture

Neuronal connections and cortical maps are continuously remodeled by our experience. Knowledge of the potential capabilityof the brain to compensate for lesions is a prerequisite for optimal stroke rehabilitation strategies. Experimental focal cortical lesions induce changes in adjacent cortex and in the contralateral hemisphere. Neuroimaging studies in stroke patients indicate altered poststroke activation patterns, which suggest some functional reorganization. To what extent functional imaging data correspond to outcome data needs to be evaluated. Reorganization may be the principle process responsible for recovery of function after stroke, but what are the limits, and to what extent can postischemic intervention facilitate such changes? Postoperative housing of animals in an enriched environment can significantly enhance functional outcome and can also interact with other interventions, including neocortical grafting. What role will neuronal progenitor cells play in future rehabilitation-stimulated in situ or as neural replacement? And what is the future for blocking neural growth inhibitory factors? Better knowledge of postischemic molecular and neurophysiological events, and close interaction between basic and applied research, will hopefully enable us to design rehabilitation strategies based on neurobiological principles in a not-too-distant future.

Induction of cyclooxygenase-2 messenger RNA after transient and permanent middle cerebral artery occlusion in rats: comparison with c-fos messenger RNA by using in situ hybridization

OBJECT

Recently, two different cyclooxygenase (COX) genes, COX-1 and -2, were identified. In this study, topographic and chronological profiles of COX-2 messenger (m)RNA and c-fos mRNA expression were investigated using in situ hybridization after focal cerebral ischemia.

METHODS

Rats undergoing permanent ischemia were decapitated at 30 and 90 minutes and at 2, 4, 8, and 24 hours after middle cerebral artery (MCA) occlusion, and rats undergoing transient ischemia were decapitated at 4, 8, and 24 hours after MCA occlusion that lasted for either 30 or 90 minutes. After brief transient MCA occlusion, c-fos mRNA was induced in the whole MCA territory, adjacent cortex (cingulate cortex), and distant brain regions such as the hippocampus and substantia nigra. In contrast, COX-2 mRNA was not induced in the ischemic core (lateral striatum) but only in the penumbral area (MCA cortex). Long transient and permanent MCA occlusion did not induce c-fos and COX-2 mRNAs in the ischemic core but strongly induced both mRNAs in the penumbral area (medial striatum and periphery of MCA cortex) and adjacent cortex (cingulate cortex). In brain regions distant from the ischemic territory, although c-fos mRNA was induced in the thalamus, substantia nigra, and hippocampus after extended transient and permanent occlusion, COX-2 mRNA was only induced in the bilateral hippocampi. The induction of COX-2 mRNA persisted in all locations even at 24 hours after MCA occlusion.

CONCLUSIONS

The distribution of COX-2 mRNA induction was apparently different from that of c-fos mRNA after MCA occlusion. These results pertaining to COX-2 mRNA agree well with the previous observations of changes in prostaglandin metabolism induced by focal cerebral ischemia. However, whether this induction of the COX-2 gene contributes to the histopathological outcome of cerebral ischemia remains to be elucidated.

Temporal profile and cellular localization of interleukin-6 protein after focal cerebral ischemia in rats

Although interleukin-6 (IL-6) has various neuroprotective effects against cerebral ischemia, the topographic distribution and cellular source of IL-6 after cerebral ischemia remain unclear. In the current study, the localization of IL-6 protein was immunohistochemically examined in rats after 3.5, 12, 24, and 48 hours of reperfusion after 1.5 hours of middle cerebral artery occlusion. Middle cerebral artery occlusion was induced by the intraluminal suture method. The specificity of the anti-IL-6 antibody used in the current study was confirmed by Western blot analysis and an immunoabsorption test. To identify the cellular source, lectin histochemical study and immunohistochemical study with microtubule-associated protein-2, ED1, and glial fibrillary acidic protein also were carried out. The sham group did not show any clear IL-6 immunoreactivity. After 3.5 hours of reperfusion, IL-6 immunoreactivity was first detected on the reperfused side, and it was upregulated, especially in the periinfarct region, after 24 hours of reperfusion. Also, IL-6 was expressed after 3.5 hours of reperfusion in the contralateral cerebral cortex and bilateral hippocampi. Double staining showed that the cells containing IL-6 were neurons and round-type microglia, not astrocytes. The current findings suggest that IL-6 expression in ischemically threatened neurons and reactive microglia is closely associated with brain tissue neuroprotective mechanisms against cerebral ischemia.

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.

NBPA: a cerebral ischaemic protective agent

1. NBPA is a derivative of 3-n-butylpathalide isolated from Apium granolens Linn. 2. At concentrations ranging from 6 x 10(-6) to 10(-6) mol/L, NBPA inhibited the L-type calcium current in guinea-pig myocardial cells and cultured human neuroblastoma cells. 3. At 10(-6) mol/L, NBPA markedly inhibited calcium-dependent and -independent release of glutamate from synaptosomes. 4. The [31P] nuclear magnetic resonance spectrum has shown that pretreatment with NBPA at 15 mg/kg, i.p., improved energy metabolism. 5. In situ hybridization has shown that 10 and 20 mg/kg, i.p., NBPA prior to cerebral artery occlusion can accelerate the expression of heat shock protein 70 mRNA and inhibit c-fos mRNA expression. 6. It has been shown that NBPA decreases the nitric oxide content and bc nitric oxide synthase (NOS) activity in the global cerebral ischaemia-reperfusion model in rats. In addition, it has been shown that NBPA significantly inhibits the expression of inducible NOS protein.

High-resolution magnetic resonance angiography of the mouse brain: application to murine focal cerebral ischemia models

Three-dimensional time-of-flight high-resolution magnetic resonance angiography was applied to visualize the cerebral vasculature of the mouse brain. In normal mice, angiograms of good quality, showing the essential details of the arterial cerebrovascular anatomy, could be obtained in only 2.5 min without the use of contrast agents. Signals from slowly flowing blood, e.g., in veins, could also be detected after administration of a blood pool contrast agent. The technique was applied to mouse models of permanent and transient brain ischemia, involving the occlusion of the middle cerebral artery. High-resolution magnetic resonance angiography proved to be a very useful tool for verifying the success of the occlusion in these models.

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.

Transient MRI-detected water apparent diffusion coefficient reduction correlates with c-fos mRNA but not hsp70 mRNA induction during focal cerebral ischemia in rats

Cerebral ischemia induces immediate early genes such as c-fos and stress genes such as hsp70. In this study, the spatial relationships between c-fos and hsp70 mRNA expression and changes detectable with diffusion and perfusion magnetic resonance (MR) imaging were examined. The middle cerebral artery (MCA) of young adult rats was occluded for 30 or 60 min. Diffusion MR (D-MR) images were acquired continuously during the ischemic period and dysprosium-contrast perfusion (P-MR) images were acquired at the end of the ischemic period. C-fos and hsp70 mRNA expression were examined with in situ hybridization. The most significant finding of this work was that for both durations of ischemia, c-fos induction was observed in cortical and sub-cortical regions exhibiting a transient reduction in the apparent diffusion coefficient of water (ADC). Transients which occurred on a time scale of 3 min may have been caused by spreading depression. Those occurring on a 10-min time scale may have been caused by an initial reduction in blood flow with occlusion that was followed by an ischemia-induced increase in collateral blood flow. P-MR imaging showed that perfusion in c-fos positive regions was higher than in regions with persistently reduced ADC. Hsp70 induction did not correlate with transient ADC reduction. It was induced in the MCA territory in regions showing persistent ADC changes, with induction being greatest at the periphery of these regions. It was also induced in regions that exhibited both spontaneous reversal of the diffusion changes and decreased perfusion.

DNA cleavage and proteolysis of microtubule-associated protein 2 after cerebral ischemia of different severity

We report temporal profiles of cytoplasmic proteolysis and genomic DNA cleavage after cerebral ischemia of different severity in gerbils. Global forebrain ischemia by bilateral common carotid artery occlusion for 5 min with reperfusion, severe unilateral hemispheric ischemia by unilateral common carotid artery occlusion for 30 min with reperfusion, and complete ischemia by decapitation were used. The hippocampus was examined for proteolysis by using immunohistochemistry for microtubule-associated protein 2, DNA cleavage by using in situ nick-end labelling, and nuclear morphology by Hematoxylin staining. During evolution of delayed neuronal death after transient forebrain ischemia, loss of the immunoreaction for microtubule-associated protein 2 occurred almost in parallel with DNA cleavage in the CA1 region. In contrast, disappearance of the immunoreaction for microtubule-associated protein 2 was much faster than genomic DNA cleavage after unilateral hemispheric ischemia and reperfusion. The microtubule-associated protein 2 immunoreactivity was completely lost before development of changes in nuclear morphology or DNA cleavage after complete ischemia. The present study demonstrated the differences between necrosis and delayed neuronal death, but the nuclear morphology in the latter was not exactly the same as seen in apoptosis. Some elements of both necrotic and apoptotic machineries may work following transient ischemia, and the degree of ischemic insult may determine the character of cell death process.

Suppression of post-ischemic-induced fos protein expression by an antisense oligonucleotide to c-fos mRNA leads to increased tissue damage

Activation of c-fos, an immediate early gene, and the subsequent upregulation of Fos protein expression occur following neural injury, including focal cerebral ischemia (fci). Fos and Jun form a heterodimer known as activator protein 1, which regulates the expression of many late effector genes. To study the downstream effects of c-fos expression following ischemia, we suppressed the translation of c-fos by administering an antisense oligonucleotide (AO) to c-fos mRNA. Eighteen hours prior to fci, male, Long Evans (LE) rats received intraventricular injections of AO, mismatched AO (MS) or artificial cerebrospinal fluid (aCSF). Fci was induced by permanent right middle cerebral artery occlusion. At 24-h post-occlusion, neurological function was assessed, and the animals were sacrificed. The brains were removed and stained with triphenyltetrazolium chloride for infarct volume determination. Fos immunohistochemistry was performed in separate animals to determine the effects of treatment on Fos expression number of Fos positive cells. AO administration reduced the number of cells with fci-induced Fos expression by approximately 75%. No differences in neurological scores existed between any of the groups. AO-treated LE developed larger infarcts (40.1+/-1.0%, mean+/-S.D., p<0.001) than MS- or aCSF-treated controls (34.3+/-1.0%, 34.6+/-1.0%, respectively). These results suggest that c-fos activation and subsequent Fos protein expression exerts a neuroprotective effect, which is likely via upregulation of neurotrophins, following focal cerebral ischemia. This response, among others, may contribute to brain adaptation to injury that underlies functional recovery after stroke.

Overexpression of thioredoxin in transgenic mice attenuates focal ischemic brain damage

Thioredoxin (TRX) plays important biological roles both in intra- and extracellular compartments, including in regulation of various intracellular molecules via thiol redox control. We produced TRX overexpressing mice and confirmed that there were no anatomical and physiological differences between wild-type (WT) mice and TRX transgenic (Tg) mice. In the present study we subjected mice to focal brain ischemia to shed light on the role of TRX in brain ischemic injury. At 24 hr after middle cerebral artery occlusion, infarct areas and volume were significantly smaller in Tg mice than in WT mice. Moreover neurological deficit was ameliorated in Tg mice compared with WT mice. Protein carbonyl content, a marker of cellular protein oxidation, in Tg mice showed less increase than did that of WT mice after the ischemic insult. Furthermore, c-fos expression in Tg mice was stronger than in WT mice 1 hr after ischemia. Our results suggest that transgene expression of TRX decreased ischemic neuronal injury and that TRX and the redox state modified by TRX play a crucial role in brain damage during stroke.

Primary cortical glial reaction versus secondary thalamic glial response in the excitotoxically injured young brain: microglial/macrophage response and major histocompatibility complex class I and II expression

The excitatory amino acid analog, N-methyl-D-aspartate, was injected intracortically into nine-day-old rats. Resulting axon-sparing lesions in the developing sensorimotor cortex, which secondarily affect thalamic neurons that become deprived of cortical targets, provide an experimental model for the study of the glial response in distantly affected areas. The microglial/macrophage response was studied using tomato lectin histochemistry and major histocompatibility complex I and II immunocytochemistry. Blood-brain barrier integrity was evaluated. In the cortical lesion site, where blood-brain barrier breakdown occurs, the rapid microglial response was restricted to the degenerating area. Microglial changes were first seen at 4 h post-injection, peaking at days 3-5. Reactive microglia changed morphology, increased tomato lectin binding and expressed major histocompatibility complex I. Additionally, some cells expressed major histocompatibility complex II. In the secondarily affected thalamus, the microglial response was not as pronounced as in the cortex, was first seen at 10 h post-injection and peaked at days 3-5. Reactive microglia showed a bushy morphology, were intensely lectin positive and expressed major histocompatibility complex I. The exceptional response of the nine-day-old brain to cortical lesions makes this model an interesting tool for studying the implications of microglial major histocompatibility factor expression in still enigmatic processes such as wound healing and plasticity.

Immunohistochemical analysis of cyclic AMP response element binding protein phosphorylation in focal cerebral ischemia in rats

Phosphorylation of cyclic AMP response element binding protein (CREB) is one of the most important mechanisms controlling various gene transcriptions. In the present study, the phosphorylation of CREB was examined immunohistochemically at 24 h of recirculation following 1.5 h of middle cerebral artery occlusion (MCAO) in rats. MCAO was induced by the intraluminal suture method. The infarct core revealed a significant reduction in the number of immunoreactive cells with the anti-phosphorylated CREB and with the anti-CREB antibody, which binds to both unphosphorylated and phosphorylated CREB. In contrast, the peri-infarct area exhibited a marked increase in the number of immunopositive cells as well as in the intensity of nuclear staining with each antibody, so that almost all of the cells expressing CREB demonstrated phosphorylation of CREB. On the other hand, about half of the CREB immunopositive cells reacted weakly with the anti-phosphorylated CREB antibody in the sham group. These findings indicated that the expression as well as phosphorylation of CREB protein was significantly activated in the regions surrounding the infarct area. Since phosphorylation of CREB has recently been implicated in signal transductions that promote the survival and differentiation of neurons, the present data suggest that tissue repair mechanisms may be markedly activated in the peri-infarct area.

Biochemical and molecular characteristics of the brain with developing cerebral infarction

1. We review the biochemical and molecular changes in brain with developing cerebral infarction, based on recent findings in experimental focal cerebral ischemia. 2. Occlusion of a cerebral artery produces focal ischemia with a gradual decline of blood flow, differentiating a severely ischemic core where infarct develops rapidly and an area peripheral to the core where the blood flow reduction is moderate (called penumbra). Neuronal injury in the penumbra is essentially reversible but only for several hours. The penumbra area tolerates a longer duration of ischemia than the core and may be salvageable by pharmacological agents such as glutamate antagonists or prompt reperfusion. 3. Upon reperfusion, brain cells alter their genomic properties so that protein synthesis becomes restricted to a small number of proteins such as stress proteins. Induction of the stress response is considered to be a rescue program to help to mitigate neuronal injury and to endow the cells with resistance to subsequent ischemic stress. The challenge now is to determine how the neuroprotection conferred by prior sublethal ischemia is achieved so that rational strategies can be developed to detect and manipulate gene expression in brain cells vulnerable to ischemia. 4. Expansion of infarction may be caused by an apoptotic mechanism. Investigation of apoptosis may also help in designing novel molecular strategies to prevent ischemic cell death. 5. Ischemia/reperfusion injury is accompanied by inflammatory reactions induced by neutrophils and monocytes/macrophages infiltrated and accumulated in ischemic areas. When the role of the inflammatory/immune systems in ischemic brain injury is revealed, new therapeutic targets and agents will emerge to complement and synergize with pharmacological intervention directed against glutamate and Ca2+ neurotoxicity.

Attenuated c-fos mRNA induction after middle cerebral artery occlusion in CREB knockout mice does not modulate focal ischemic injury

To elucidate the mechanism of ischemia-induced signal transduction in vivo, we investigated the effect of the targeted disruption of the alpha and delta isoforms of the cAMP-responsive element-binding protein (CREB) on c-fos and heatshock protein (hsp) 72 gene induction. Permanent focal ischemia was induced by occlusion of the middle cerebral artery of the CREB mutant mice (CREB(-/-), n = 5) and the wild-type mice (n = 6). Three hours after onset of ischemia, the neurologic score was assessed and pictorial measurements of ATP and cerebral protein synthesis (CPS) were carried out to differentiate between the ischemic core (where ATP is depleted), the ischemic penumbra (where ATP is preserved but CPS is inhibited), and the intact tissue (where both ATP and CPS are preserved). There were no significant differences in neurologic score or in ATP, pH, and CPS between the two groups, suggesting that the sensitivity of both strains to ischemia is the same. Targeted disruption of the CREB gene significantly attenuated c-fos gene induction in the periischemic ipsilateral hemisphere but had no effect on either c-fos or hsp72 mRNA expression in the penumbra. The observations demonstrate that CREB expression, despite its differential effect on c-fos, does not modulate acute focal ischemic injury.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Recruitment of several neuroprotective pathways after permanent focal ischemia in mice

After an ischemic episode induced by the electrocoagulation of the left middle cerebral artery (MCA) in mouse, neurons within the damaged territory die either by an apoptotic or by a necrotic process. Most of the cortical neurons within the ischemic area display both morphological and biochemical signs of programmed cell death: nuclear condensation, DNA degradation, formation of apoptotic bodies, and glutathione depletion. In fact, apoptosis essentially contributes to the expansion of the ischemic lesion and the maximum of damaged territory is reached 24 h postocclusion. Several potentially neuroprotective pathways have been evidenced in different experimental models of ischemia including the activation of antioxidant enzyme activities and/or the recruitment of neurotrophic as well as antiapoptotic factors. In our model of permanent focal ischemia induced by MCA occlusion, we measured the temporal synthesis of nerve growth factor (NGF) and examined the status of antioxidant enzymes as well as Bcl-2 antiapoptotic product. We detected in both cortices a transient increase of NGF which peaks at 6 h. Moreover, we reported that glutathione peroxidase is recruited with a time course which parallels NGF synthesis. Finally, we observed the induction of Bcl-2 in safe neurons; this may represent a self-protective response against ischemia-induced apoptosis. We provide evidence that in a model of permanent focal ischemia, several neuroprotective pathways could be coactivated.

Expression of immediate early gene c-fos in rat brain following increased intracranial pressure

No attention has been given to an influence of the intracranial pressure (ICP) elevation on the brain at the level of the gene. In the present study, we originally attempted to evaluate the molecular biological changes of the brain, especially the expression of c-fos mRNA as a marker of cellular response, caused by increased ICP. Our results confirm that the neurons and non-neuronal cells are well able to tolerate the stress of increased ICP at the level of the gene, under the condition that cerebral blood flow (CBF) is maintained. A severe increase in ICP, which reduces CBF, enhances the c-fos mRNA expression in a similar fashion as in a forebrain ischemia model, except in the choroid plexus.

Decreased expression of bcl-2 and bcl-x mRNA coincides with apoptosis following intracerebral administration of 3-nitropropionic acid

The mitochondrial toxin, 3-nitropropionic acid (3-NP), is an irreversible inhibitor of succinate dehydrogenase that induces apoptosis in vitro and in vivo. We injected 3-NP into the striatum of rats to examine the potential role of Bcl-2 or Bcl-x, proteins that can inhibit apoptosis, in brain injury due to 3-NP. Electrophoretic examination of striatal tissue indicated that 3-NP induced internucleosomal fragmentation typical of apoptosis. There was also histologic evidence of apoptosis based on staining by the terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) method. Apoptosis was first observed 6 h after injection, was maximal at 1 day, and was still observed on day 7. Expression of bcl-2, bcl-x, and c-jun mRNA expression was evaluated 1, 3, 6, and 12 h and 1, 3, 5, and 7 days after injection using in situ hybridization. Both bcl-2 and bcl-x mRNA expression in the striatum decreased starting at 6 h and continued to 5 days after injection. This was in contrast to an apparent increase in c-jun expression. The similarity in the time course of apoptosis to that of suppression of bcl-2 and bcl-x mRNA suggests that changes in expression of these genes may contribute to apoptosis following 3-NP injection.

Ischemic preconditioning and brain tolerance: temporal histological and functional outcomes, protein synthesis requirement, and interleukin-1 receptor antagonist and early gene expression

BACKGROUND AND PURPOSE

A short duration of ischemia (ie, ischemic preconditioning [PC]) can provide significant brain protection to subsequent ischemic events (ie, ischemic tolerance [IT]). The present series of studies was conducted to characterize the temporal pattern of a PC paradigm, to systematically evaluate the importance of protein synthesis in PC-induced IT, and to explore candidate gene expression changes associated with IT.

METHODS

Temporary middle cerebral artery occlusion (MCAO) (10 minutes) was used for PC. Various periods of reperfusion (ie, 2, 6, and 12 hours and 1, 2, 7, 14, and 21 days) were allowed after PC and before permanent MCAO (PMCAO) (n=7 to 9 per group) to establish IT compared with non-PC (sham-operated) rats (n=22). Infarct size, forelimb and hindlimb motor function, and cortical perfusion (laser-Doppler flowmetry; n=9 per group) were measured after PMCAO. The effects of the protein synthesis inhibitor cycloheximide administered just before PC (n= 13 to 17) or administered long after PC but just before PMCAO (n=7 to 8) on IT were also determined. Interleukin- receptor antagonist mRNA (reverse transcriptase and polymerase chain reactions [n=20] and Northern analysis [n=50]) and protein expression (immunohistochemistry [n=16]) after PC and early response gene expression (Northern analysis [n=16]) after PMCAO in PC animals were determined.

RESULTS

Hemispheric infarct was significantly (P<0.01) reduced only if PC was performed 1 day (decreased 58.4%), 2 days (decreased 58.1%), or 7 days (decreased 59.4%) before PMCAO. PC significantly (P<0.01) reduced neurological deficits (similar to reductions in infarct size). Cycloheximide eliminated ischemic PC-induced IT effects on both brain injury and neurological deficits if administered before PC (P<0.05) but not if administered long after PC but before PMCAO. PC did not produce any significant brain injury, alter cortical blood flow after PMCAO, or produce contralateral cortical neuroprotection. Interleukin-1 receptor antagonist mRNA and protein expression were increased significantly (P<0.01) only during the IT period. PC rats also exhibited a significant (P<0.01) reduction in c-fos and zif268 mRNA expression after PMCAO.

CONCLUSIONS

PC is a powerful inducer of ischemic brain tolerance as reflected by preservation of brain tissue and motor function. PC induces IT that is dependent on de novo protein synthesis. New protein(s) that occurs at the PC brain site 1 to 7 days after PC contributes to the neuroprotection. Those proteins that are produced after the more severe PMCAO in PC animals apparently do not contribute to IT. The PC-induced IT is also associated with increased expression of the neuroprotective protein interleukin-1 receptor antagonist and a reduced postischemic expression of the early response genes c-fos and zif268. (Stroke. 1998;29:1937-1951.)

Differential induction of immediate early gene mRNAs following cryogenic and impact trauma with/without craniotomy in rats

Expression of immediate early gene (IEG) mRNAs following traumatic brain injury in 3 different models-cryogenic injury, impact injury with craniotomy and impact injury without craniotomy-was investigated using in situ hybridization. Cryogenic brain injury resulted in c-fos and c-jun mRNA expression throughout the ipsilateral cortex, piriform cortex and dentate gyrus on the injured side, with peak at 30 min to 1 h post-injury. Impact injury with craniotomy was associated with hybridization signals in the same areas and also in the subcortical white matter or ependyma underlying the impact site at 30 min post-injury. The expression was rather more prolonged than with cryogenic injury. Impact injury without craniotomy induced the expression of both mRNAs throughout the ipsilateral cortex, piriform cortex and dentate gyrus at 30 min post-injury, but this was promptly attenuated by 1 h post-injury, except for bilateral elevation in the dentate gyrus. The present study, thus, demonstrated that regional and temporal expression of IEG mRNAs is influenced by the intensity, quality and manner of application of the insult. Differences in the expression of IEGs may alter the late response gene expression and affect the succeeding events.

The influence of delayed postischemic hyperthermia following transient focal ischemia: alterations of gene expression

We have recently shown that moderate hyperthermia, even if delayed, markedly enlarges the volume of an acute ischemic infarct. In the current study, we used in situ hybridization autoradiography to assess the effects of delayed hyperthermia on the regional expression of messenger RNA (mRNA) for the immediate early genes c-fos and c-jun, the inducible heat-shock protein 70 (hsp70) and glial fibrillary acid protein (GFAP) following 1 h of transient middle cerebral artery occlusion (MCAo) produced in rats by the insertion of an intraluminal suture. Sham-occluded rats were also studied. One day after MCAo, rats were placed into a heating chamber, where cranial temperature was either maintained at 37-38 degrees C (normothermic group) or was elevated to 40 degrees C (hyperthermic group) for 3 h. At either 2 or 24 h thereafter, brains were studied by in situ hybridization. Low-level constitutive c-fos and c-jun expression in sham-occluded rats was unaffected by delayed temperature manipulation. Prior MCAo decreased c-fos and c-jun mRNA in the affected striatum and overlying cortex. In rats studied 2 h after delayed hyperthermia, however, c-fos mRNA was markedly increased in ipsilateral cingulate cortex. By contrast, the pattern of c-jun mRNA was similar in rats with prior MCAo irrespective of delayed normothermia or hyperthermia: increased expression involved ipsilateral cingulate and paramedian cortical areas. Bilateral increases in hsp70 expression were produced by hyperthermia alone, and hsp70 mRNA was densely increased throughout the ischemic cortex and striatum following MCAo, while delayed hyperthermia altered this pattern by extending the zone of increased hsp70 message to cingulate and paramedian cortical areas at 2 h. GFAP mRNA was decreased within the previously ischemic field but increased in surrounding regions. The induction of c-fos and hsp70 message in tissue regions abutting zones of enhanced injury in brains with delayed postischemic hyperthermia indicates that these zones have been additionally stressed: these gene responses may possibly contribute to the protection of these threatened regions.

A reproducible model of middle cerebral artery occlusion in mice: hemodynamic, biochemical, and magnetic resonance imaging

A reproducible model of thread occlusion of the middle cerebral artery (MCA) was established in C57 Black/6J mice by matching the diameter of the thread to the weight of the animals. For this purpose, threads of different diameter (80 to 260 microns) were inserted into the MCA of animals of different weights (18 to 33 g), and the success of vascular occlusion was evaluated by imaging the ischemic territory on serial brain sections with carbon black. Successful occlusion of the MCA resulted in a linear relationship between body weight and thread diameter (r = 0.46, P < 0.01), allowing precise selection of the appropriate thread size. Laser-Doppler measurements of CBF, neurological scoring, and 2,3,5-triphenyltetrazolium chloride staining confirmed that matching of animal weight and suture diameter produced consistent cerebral infarction. Three hours after MCA occlusion, imaging of ATP, tissue pH, and cerebral protein synthesis allowed differentiation between the central infarct core, in which ATP was depleted, and a peripheral penumbra with reduced protein synthesis and tissue acidosis but preserved ATP content. Perfusion deficits and ischemic tissue alterations could also be detected by perfusion- and diffusion-weighted magnetic resonance imaging, demonstrating the feasibility of dynamic evaluations of infarct evolution. The use of multiparametric imaging techniques in this improved MCA occlusion model opens the way for advanced pathophysiological studies of stroke in gene-manipulated animals.

Reduction of cortical infarction and impairment of apoptosis in NGF-transgenic mice subjected to permanent focal ischemia

The neuroprotective potential of the nerve growth factor (NGF) against permanent ischemic brain damage has been investigated in vivo using NGF-transgenic (tg) mice. The expression of the transgene is driven by part of the promoter of the proto-oncogene c-fos, which belongs to the first set of genes activated after brain ischemic insult. Wild-type (wt) mice and tg mice were subjected to permanent focal ischemia induced by electrocoagulation of the middle cerebral artery. Twenty four hours (h) after the ischemic shock, when compared to wt, tg mice displayed a 40% reduction of the infarcted area, which lasted up to 1 week. However, infarcted brain areas were similar in wt and tg mice within the first hours post-occlusion, indicating that NGF acted to block the progression of neuronal damage. Kinetics of NGF synthesis assessed by ELISA was in good agreement with the observed neuroprotective effect, since NGF content peaked 6 h post-ischemia. This was further correlated with the time-course of c-Fos immunoreactivity, detectable only from 6 h post-ischemia. The neuroprotective effect of NGF involved the impairment of apoptotic cell death, as evidenced by a marked decrease of the number of apoptotic profiles inside the ischemic zone in tg mice. These results underline the potential of c-fos-NGF-tg mice to study in vivo the molecular and cellular mechanisms of the NGF-induced neuroprotective effect against ischemic damage.

A strain-independent postnatal neurodegeneration in mice lacking the EGF receptor

Mice lacking the epidermal growth factor receptor (EGFR) exhibit strain-dependent phenotypes ranging from placental to postnatal skin, lung and brain defects. After birth, all mutant mice develop a progressive neurodegeneration in the frontal cortex, olfactory bulb and thalamus, characterized by massive apoptosis and upregulation of c-fos. These defects occur in a strain-independent manner, since neither rescue of the placental phenotype by aggregation of diploid 129/Sv EGFR mutant and tetraploid wild-type embryos, nor promotion of lung maturation by transplacental dexamethasone administration alters the course of neurodegeneration. VEGF is not induced during the degenerative process, excluding hypoxia and ischemia as causes of cell death. A migratory disorder is detected in the hippocampus with nests of ectopic neurons, which are also apoptotic. Cerebral cortices from EGFR mutants contain lower numbers of GFAP positive astrocytes, which display reduced proliferation in vitro. Since EGFR is expressed in the affected cell-types, these results define a specific function for EGFR in the proliferation and/or differentiation of astrocytes and in the survival of postmitotic neurons.

Redox control of neuronal damage during brain ischemia after middle cerebral artery occlusion in the rat: immunohistochemical and hybridization studies of thioredoxin

Thioredoxin (TRX) is a small, multifunctional protein with a redox-active site and multiple biological functions that include reducing activity for reactive oxygen intermediates. We assayed TRX and TRX mRNA by immunohistochemical methods and hybridization experiments in the rat brain after middle cerebral artery (MCA) occlusion. During ischemia, the immunoreactivity for TRX decreased; it disappeared after MCA occlusion in the ischemic regions. It rapidly decreased and nearly disappeared at 4 and 16 hours after MCA occlusion in the lateral striatum and frontoparietal cortex, respectively. On the other hand, in the perifocal ischemic region, the penumbra, TRX immunoreactivity began to increase 4 hours after MCA occlusion and continued to increase until 24 hours after occlusion. In hybridization experiments, TRX mRNA decreased and nearly disappeared 4 hours after MCA occlusion in the lateral striatum. In the frontoparietal cortex, it decreased until 24 hours after MCA occlusion. In the perifocal ischemic region, TRX mRNA began to increase 4 hours after MCA occlusion and continued to increase until 24 hours. Northern blot analysis showed that total TRX mRNA in the operated hemispheres was induced from 8 hours and increased until 24 hours after the surgical procedures. We previously reported that recombinant TRX promotes the in vitro survival of primary cultured neurons. We now suggest that TRX in the penumbra has neuroprotective functions and that decreased levels of TRX in the ischemic core modify neuronal damage during focal brain ischemia.

Blood-brain barrier disruption, HSP70 expression and apoptosis due to 3-nitropropionic acid, a mitochondrial toxin

3-Nitropropionic acid (3-NP), a mitochondrial toxin, induces apoptosis in the striatum. We wanted to determine if there was a relationship between mitochondrial dysfunction, disruption of the blood-brain barrier (BBB), and apoptosis. BBB disruption following intrastriatal injection of 3-NP was assessed by Evans blue leakage, brain water content, and by the expression of the 70 kDa heat shock protein (HSP70) and mRNA. Apoptosis was assessed by in situ terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) and gel electrophoresis to detect internucleosomal DNA fragmentation. Microscopic evidence of Evans blue leakage due to 3-NP was present only 3 hr after injection. Both internucleosomal DNA fragmentation and TUNEL-labeling did not appear until 24 hr after injection. HSP70 (protein and mRNA) was also elevated by 24 hr. There was a quantitative increase in Evans blue leakage and brain water content due to 3-NP by 3 days after injection. Our results suggest that BBB disruption is an early event followed by increased HSP70 expression and apoptosis. We speculate that 3-NP damages endothelial cells, leading to vasogenic edema and apoptosis.

Induction of ornithine decarboxylase mRNA in transient focal cerebral ischemia in the rat

We used in situ hybridization to localize the long-term changes in ornithine decarboxylase (ODC) expression after a 90 min occlusion of the middle cerebral artery (MCAO) in the rat. The ODC mRNA was induced in the ipsilateral dentate gyrus (DG) and throughout the ischemic cortex at 12 h and still at 3 days after reperfusion. The induction was blocked by an N-methyl-D-aspartate (NMDA) receptor antagonist suggesting that ODC induction is NMDA receptor-mediated. The long-lasting up-regulation detected in regions where no cellular damage usually occurs, favors the hypothesis that ODC expression does not contribute to neuronal death after stroke.

Transient middle cerebral artery occlusion by intraluminal suture: I. Three-dimensional autoradiographic image-analysis of local cerebral glucose metabolism-blood flow interrelationships during ischemia and early recirculation

Using autoradiographic image-averaging strategies, we studied the relationship between local glucose utilization (LCMRglc) and blood flow (LCBF) in a highly reproducible model of transient (2-hour) middle cerebral artery occlusion (MCAO) produced in Sprague-Dawley rats by insertion of an intraluminal suture coated with poly-L-lysine. Neurobehavioral examination at 60 minutes after occlusion substantiated a high-grade deficit in all animals. In two subgroups, LCBF was measured with 14C-iodoantipyrine at either 1.5 hours of MCAO, or at 1 hour of recirculation after suture removal. In two other matched subgroups, LCMRglc was measured with 14C-2-deoxyglucose at 1.5 to 2.25 hours of MCAO, and at 0.75 to 1.5 hours of recirculation after 2 hours of MCAO. Average image data sets were generated for LCBF, LCMRglc, and the LCMRglc/LCBF ratio for each study time. Middle cerebral artery occlusion for 2 hours induced graded LCBF decrements affecting ipsilateral cortical and basal ganglionic regions. After 1 hour of recirculation, LCBF in previously ischemic neocortical regions increased by 40% to 200% above ischemic levels, but remained depressed, on average, at about 40% of control. By contrast, frank hyperemia was noted in the previously ischemic caudoputamen. Mean cortical LCBF values during MCAO correlated highly with their respective LCBF values after 1 hour of recirculation (R = 0.93), suggesting that post-ischemic LCBF recovery is related to the depth of ischemia. Despite focal ischemia, LCMRglc during approximately 2 hours of MCAO was preserved, on average, at near-normal levels; but following approximately 1 h of recirculation, LCMRglc became markedly depressed (on average, 55% of control in previously densely ischemic cortical regions). Regression analysis indicated that this depressed glucose utilization was determined largely by the intensity of antecedent ischemia. By pixel analysis, the ischemic core (defined as LCBF 0% to 20% of control) comprised 33% of the ischemic hemisphere, and the penumbra (LCBF 20% to 40%) accounted for 26%. The penumbra was concentrated at the coronal poles of the ischemic lesion and formed a thin shell around the central ischemic core. During 2 hours of MCAO, the LCMRglc/LCBF ratio within the ischemic penumbra was increased four-fold above normal (average, 179 umol/100 mL). In marked contrast, after approximately 1 h recirculation, this uncoupling had almost completely subsided. The companion study (Zhao et al., 1997) further analyzes these findings in relation to patterns of infarctive histopathology.

NGFI-B, c-fos, and c-jun mRNA expression in mouse brain after acute carbon monoxide intoxication

The expression of immediate early genes (IEG) has been documented in the brain after various kinds of insults such as ischemia and hypoxia. To determine whether acute carbon monoxide intoxication (ACOI) might trigger IEG expression, adult ddY mice were subjected to carbon monoxide exposure at a rate of 30 mL/min for 35 seconds. The levels of NGFI-B, c-fos, and c-jun mRNA were determined by Northern blot analysis. A time-course study in the cerebral cortex indicated that the induction of NGFI-B, c-fos, and c-jun mRNA started as early as 15 minutes, reached a peak at 30 minutes, and returned to the basal level at 1 hour after the ACOI. In addition, the temporal feature of the induction of these IEG mRNA in the hippocampus was very similar to that in the cerebral cortex. Examination of brain regions at 30 minutes after the ACOI revealed a significant induction of NGFI-B mRNA in the cerebellum, thalamus-hypothalamus, brainstem. as well as in the cortex and hippocampus, but not in the striatum or olfactory bulb. Furthermore, the neuroanatomical distribution of c-fos mRNA at 30 minutes after the ACOI was very similar to that of the NGFI-B mRNA. The widespread distribution of these IEG in the brain, especially in the cerebellum and brainstem, indicates that the major cause for the triggering of IEG expression in the brain by the ACOI might be a diffuse hypoxia. These findings show for the first time the temporal and spatial expression of IEG in the brain after ACOI.

Histological markers of neuronal, axonal and astrocytic changes after lateral rigid impact traumatic brain injury

The model of lateral, rigid impact traumatic brain injury is widely used but remains relatively poorly characterized by comparison with fluid percussion injury models. Thus, whilst the gross morphological changes that occur over the short- and long-term post-injury have been described, more subtle measures of neuronal injury and activation, and markers of axonal and glial reactions have not been investigated, complicating interpretation of data from this model. To address this issue, a variety of neurohistological markers were examined in adult male rats which had been subjected to open brain, lateral rigid impact injury. A piston device was unilaterally driven 3.0 mm into the somatosensory cortex at a speed of 3.2 m/s. Neuronal activation evidenced by Fos-like immunoreactivity showed a complex pattern at 3 h after injury which appeared to be related both to proximity to the impact site and cortical efferent connectivity. At 24 h after injury, acid fuchsin staining demonstrated dying neurons in the margin of the injury and in ipsilateral hippocampus and dorsal thalamus. Injured cells identified by heat-shock protein immunoreactivity showed a similar distribution. Axonal injury demonstrated with 68 kDa neurofilament immunoreactivity was more widely distributed. Less axonal damage was found with increasing distance from the injury site. At 7 days post-injury, glial fibrillary acidic protein immunoreactive astrocytes were prolific in the ipsilateral thalamus, hippocampus and striatum and throughout the injured cortex. In general, controlled, lateral rigid impact injury provides a more focused injury than is seen with lateral fluid percussion which may have implications for the behavioral deficits seen in this injury model.

Expression of zinc finger immediate early genes in rat brain after permanent middle cerebral artery occlusion

The prolonged expression of the leucine zipper fos/jun immediate early genes (IEG) has been correlated with neuronal death after cerebral ischemia. In this study, the expression of six zinc finger IEG was examined using in situ hybridization in adult rats after middle cerebral artery occlusion (MCAO) with the suture model. NGFI-A, NGFI-B, NGFI-C, egr-2, egr-3, and Nurr1 mRNA were all induced throughout the ipsilateral cortex at 1 hour to 12 hours after MCAO. The cortical induction for most of the genes was greatest in the anterior cingulate and the anterior cerebral artery (ACA) and middle cerebral artery (MCA) transition zone. All of the zinc finger IEG were induced at 1 hour in all regions of hippocampus. NGFI-A and NGFI-B were induced in ipsilateral thalamus. Within areas of infarction, the basal IEG mRNA expression, and expression of the housekeeping gene cyclophilin A mRNA, decreased below control levels by 12 hours after the ischemia. Immediate early gene expression outside areas of infarction returned to control levels in most brain regions by 24 hours except for egr-3, which continued to be induced in the MCA/ ACA transition zone for 24 hours, and NGFI-A, which continued to be expressed in specific regions of the thalamus for 72 hours. The induction of these IEG in the cortex is likely caused by ischemia-induced cortical spreading depression, with the hippocampal and thalamic IEG induction being caused by activation of efferent cortical pathways to these regions. The prominent induction of NGFI-B, NGFI-C, egr-2, and egr-3 in the anterior cingulate cortex, the ACA/MCA transition zone, and medial striatum could reflect the ischemic regions around MCA infarcts. The prolonged NGFI-A expression observed in thalamus in this study, and in CA1 of hippocampus after global ischemia in the gerbil in a previous study, suggests that the prolonged NGFI-A, expression could be the result of or the cause of the delayed cell death. Prolonged NGFI-A expression, like c-fos and c-jun, seems to provide a marker for slowly dying neurons.

The heat shock stress response after brain lesions: induction of 72 kDa heat shock protein (cell types involved, axonal transport, transcriptional regulation) and protein synthesis inhibition

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or dic as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity.

Expression of basic fibroblast growth factor mRNA after transient focal ischemia: comparison with expression of c-fos, c-jun, and hsp 70 mRNA

We have reported that basic fibroblast growth factor (bFGF) prevents retrograde degeneration of thalamic neurons after middle cerebral artery (MCA) occlusion. To identify the protective mechanism of bFGF, we examined bFGF mRNA expression in a model of transient focal ischemia with in situ hybridization. Compared to c-fos, c-jun, and hsp 70 mRNA expression, upregulation of the bFGF mRNA expression was delayed until 6 h after reperfusion. By 12 h, bFGF mRNA was markedly induced in the peri-infarcted cortex, cingulate cortex, and peri-infarcted white matter. At 24 h and 2 days the induction of bFGF mRNA in these regions persisted, and disappeared by 5 day. The quantitative assessment of bFGF mRNA expression revealed that optical density ratios of the cingulate gyrus and the caudoputamen were significantly higher at 12 h, 24 h, and 2 d after reperfusion than those in sham controls. Microscopic observation indicated bFGF mRNA signals were present in several types of cortical cells, including neurons and nonneuronal cells. Since intrinsic bFGF, released from the damaged tissue, can influence the healing response through receptors upregulated by injury, it is reasonable that this pattern of bFGF mRNA expression parallels the bFGFR mRNA expression previously reported.

Effects of neuroprotective dose of fructose-1,6-bisphosphate on hypoxia-induced expression of c-fos and hsp70 mRNA in neonatal rat cerebrocortical slices

In situ hybridization (ISH) measurements of c-fos and hsp70 expression were made in brain slice studies of hypoxia, with or without fructose-1,6-bisphosphate (FBP) pretreatment. Each experiment used eighty 350 microns thick cerebrocortical slices, obtained from twenty 7-day old rats. Thirty minute periods of hypoxia were followed by 8 h of hyperoxic perfusion. Slices were removed at eight predetermined times, and processed for ISH and immunohistochemistry. In three of six hypoxia experiments, slices were pretreated for 60 min with 2 mM FBP, a condition known to maintain ATP level in brain slices during hypoxia. In three other hypoxia experiments slices received no pretreatment. In two control experiments slices were perfused for 11.5 h without hypoxia. In control experiments, hsp70 mRNA was barely detectable in slices at all times, although moderate c-fos mRNA expression occurred at 1 h after decapitation. Hypoxia produced a modest but statistically significant increase in c-fos mRNA and hsp70 mRNA induction 4 h following reoxygenation. At all times after hypoxia, FBP pretreatment reduced expression of c-fos and hsp70 mRNA. The absence of hsp70 mRNA in control slices suggests that intracellular protein denaturation was minimal in this preparation. In slices made hypoxic, the decrease in c-fos and hsp70 mRNA caused by FBP pretreatment suggests ameliorated progression towards injury. Immunohistochemistry showed no HSP70 protein at any time following hypoxia, with or without FBP pretreatment, presumably due to delayed HSP70 protein synthesis, or to a block in translation, as observed in vivo in other studies.

Expression of NGFI-B mRNA in a rat focal cerebral ischemia-reperfusion model

Cerebral ischemia is known to induce the expression of several immediate early genes (IEGs), including c-fos and c-jun, which subsequently regulate a number of late effector genes. In this study, we examined the expression of NGFI-B (or nur 77) mRNA in a rat focal cerebral ischemia-reperfusion model. NGFI-B is a member of the IEGs which encodes for a nuclear receptor and is rapidly induced by nerve growth factor (NGF). Northern blot analysis showed a rapid but transient enhancement of NGFI-B mRNA, a peak level for which was observed at 30 min of reperfusion following 60 min ischemic insult. At the peak level, quantitative analysis of the blot indicated a 12-fold and 4-fold increase of NGFI-B mRNA in the ischemic cortex and ipsilateral hippocampus, respectively, as compared to the sham-operated control. No apparent changes in mRNA levels were observed within contralateral sites of the cortex. Results from in situ hybridization showed that severe ischemia (60 min) resulted in a marked increase of NGFI-B mRNA throughout the entire ischemic cerebral cortex. The increase was particularly notable in the frontal, occipital, perirhinal and piriform cortical regions and in the dentate gyrus and CAI-3 regions of the ipsilateral hippocampus. A marked induction was also noted in the ipsilateral caudate putamen. Unlike the induction profile of NGFI-B mRNA, severe ischemia resulted in bilateral increases of its family gene, NGFI-A mRNA. The spatial induction profile is similar to that of NGFI-B mRNA in both hemispheres, except within the region of the contralateral dentate gyrus which showed low levels of NGFI-A mRNA. The expression pattern of NGF and BDNF mRNA, upstream genes of NGFI-B, were also examined. Interestingly the temporal and spatial expression patterns of BDNF mRNA were very similar to that of NGFI-A mRNA under the same conditions, whereas increased NGF and NGFI-B mRNA were observed only in the ipsilateral hemisphere. It is likely that multiple and/or overlapping pathways are activated subsequent to ischemic challenge which in turn are crucial for cel survival and/or functional recovery following focal cerebral ischemia.

Specific induction of protein kinase C delta subspecies after transient middle cerebral artery occlusion in the rat brain: inhibition by MK-801

Protein kinase C (PKC) consists of a family of closely related Ca2+/phospholipid-dependent phosphotransferase isozymes, most of which are present in the brain and are differentially activated by second messengers. Calcium-dependent PKC activity may cause neuronal degeneration after ischemic insult. PKC is also involved in trophic-factor signaling, indicating that activity of some PKC subspecies may be beneficial to the injured brain. Therefore, we screened long-term changes in the expression of multiple PKC subspecies after focal brain ischemia. Middle cerebral artery occlusion was produced by using an intraluminal suture for 30 min of 90 min. In in situ hybridization experiments, mRNA levels of PKC alpha, -beta, -gamma, -delta, -epsilon, and -zeta were decreased in the infarct core 4 hr after ischemia and were lost completely 12 hr after ischemia. In areas surrounding the core, PKC delta mRNA was specifically induced 4, 12, and 24 hr after ischemia in the cortex. At 3 and 7 d, the core and a rim around it showed increased mRNA levels of PKC delta. No other subspecies were induced. At 2 d, immunoblotting demonstrated increased levels of PKC delta protein in the perifocal tissue, and immunocytochemistry revealed an increased number of PKC delta-positive neurons in the perifocal cortex. In the core, PKC delta-positive macrophages and endothelial cells were seen. Pretreatment with MK-801, an NMDA antagonist, inhibited cortical PKC delta mRNA induction. The data show that focal brain ischemia induces PKC delta mRNA and protein but not other PKC subspecies through the activation of NMDA receptors and that the upregulation lasts for several days in neurons of the perifocal zone.

DNA fragmentation and HSP70 protein induction in hippocampus and cortex occurs in separate neurons following permanent middle cerebral artery occlusions

DNA nick end-labeling (TUNEL) and heat shock protein (HSP)70 immunocytochemistry were performed on the same brain sections 1 (n = 6), 3 (n = 12), and 7 (n = 7) days following permanent middle cerebral artery (MCA) occlusions produced in adult rats using the endovascular carotid suture method. In the cortex at 1 and 3 days following MCA occlusions, HSP70 immunoreactive neurons were located outside areas of infarction and showed little evidence of DNA fragmentation. HSP70-stained cortical neurons were intermingled with TUNEL cells near the infarct, but extended for greater distances away from the infarct. DNA fragmentation occurred in CA1 hippocampal neurons in 39% of the animals at 1 and 3 days following ipsilateral MCA occlusion. Bilateral DNA fragmentation occurred in CA1 neurons in one subject. HSP70 protein was expressed in CA1 hippocampal neurons in nine of 18 (50%) animals at 1 and 3 days following MCA occlusions, including all animals that exhibited hippocampal DNA fragmentation. Three animals had bilateral expression of HSP70 in CA1 neurons. Cells that stained for either HSP70 protein or DNA fragmentation existed in close proximity to one another. Approximately 5-7% of HSP70-stained cells were TUNEL stained and 3% of TUNEL-positive cells also stained for HSP70. There was no HSP70 staining or DNA fragmentation in the brains of sham-operated controls (n = 4) or in the brains of animals 7 days following MCA occlusions. These data suggest that ischemic cells capable of translating HSP70 protein generally do not undergo DNA fragmentation. These data support the concept that most HSP70 protein-containing neurons in the cortical "penumbra" and hippocampus survive ischemic injury and are "reversibly injured." It is shown that CA1 hippocampal pyramidal neurons die or are reversibly injured in approximately 50% of animals following permanent MCA occlusions. Although the mechanism of this hippocampal injury is unknown, it could relate to transynaptic activation of N-methyl-D-aspartate (NMDA) receptors that mediate induction of early genes in hippocampus.

Global ischemia induces apoptosis-associated genes in hippocampus

Using in situ hybridization, Northern blotting and RT-PCR we studied the post-ischemic expression of bcl-2, bcl-x, bax and ICE. One day following 5 min or 10 min of global ischemia bcl-2 and bcl-x mRNAs were induced in CA1 hippocampal pyramidal neurons while bax was unchanged. By 72 h after ischemia the expression of bcl-2, bcl-x and bax mRNAs decreased in CA1. The large isoform of bcl-x (bcl-xL), detected using RT-PCR, decreased in whole hippocampus by 24-72 h after ischemia relative to the putative short (bcl-xS) and transmembrane deleted (bcl-x delta TM) forms. Oligonucleotides to interleukin-1 beta convertase (ICE), which detected the expected 2-kb transcript and two lesser 1.5- and 3-kb hybridizing species, demonstrated slight mRNA induction in the CA1 region at 72 h following ischemia. DNA nick end-labeling at 3 days following ischemia showed DNA fragmentation in neurons limited to the CA1 region of hippocampus following 5 min ischemia, while DNA fragmentation was detected in CA1, CA3, dentate gyrus and cortical neurons following 10 min ischemia. The data support the view that hippocampal neurons might undergo an apoptosis-like death after global ischemia. Since global ischemia decreases total protein synthesis especially in the CA1 region, the increases in bcl-2 mRNA levels may not necessarily lead to increased Bcl-2 protein levels. This may explain why the CA1 neurons die despite the prominent induction of the protective bcl-2 gene. The observed decrease by 24 h in the bcl-xL/bcl-xS ratio which preceded DNA fragmentation may participate in the cell death produced by ischemia. However, because of the ischemia-induced decrease in total protein synthesis, the decreased bcl-xL/bcl-xS ratio does not necessarily lead to a changed ratio in the amount of the appropriate proteins. Since ICE-like mRNA was induced at 72 h when the CA1 neurons were dead, the significance of this ICE-like mRNA induction remains unclear.

Computer-assisted image-averaging strategies for the topographic analysis of in situ hybridization autoradiographs

We report the application of a computer-based image-averaging strategy to the quantitative topographic analysis of in situ hybridization autoradiographs, based upon a disparity-analysis algorithm. We illustrate this approach for a representative antisense riboprobe-the astrocytic marker, glial fibrillary acid protein (GFAP)-in the setting of fluid-percussion brain injury in rats. Sequential coronal autoradiographs in individual animals are first digitized and aligned by disparity analysis. Next, coronal sections of all brains of a given experimental group are placed in register with one another, using a common anatomic reference level. One brain of the series serves as a template, and corresponding sections of other brains are mapped into its contour at each level. In this manner, average and standard deviation image data sets may be generated. With thresholding techniques, individual data sets can be dichotomized with respect to a chosen threshold, and frequency maps can be generated at each coronal level, displaying numbers of brains showing supra-threshold levels of mRNA at each pixel location. Pixel-by-pixel statistical comparison of data sets obtained under two different conditions (e.g., 30 min vs. 24 h following brain trauma) is then feasible. A digitized functional-anatomic brain atlas may be fitted to the images to assist analysis. Computer-based image analysis of in situ hybridization autoradiographs greatly extends the utility and applicability of this technique.

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

BACKGROUND

Cerebral ischemia is a potent modulator of gene expression. Immediate early genes undergo rapid induction after both global and focal cerebral ischemia. Many immediate early genes code for transcription factors. Additional genes, including those encoding for neurotrophic factors and neurotransmitter systems, are induced in a delayed fashion after cerebral ischemia. The functional significance of early and late gene regulation after cerebral ischemia requires further investigation. These changes may be beneficial (friend) or detrimental (foe). Many of the genes are likely neuroprotective and important for recovery, but others may be involved in ischemic cell death mediated by apoptosis.

SUMMARY OF REVIEW

We review evidence that supports the hypothesis that cell death after cerebral ischemia occurs through the dual pathways of ischemic necrosis and apoptosis.

CONCLUSIONS

Gene regulation, including immediate early genes, is required for programmed neuronal death after trophic factor deprivation and is predicted to be involved in apoptosis triggered by cerebral ischemia. Novel therapies following cerebral ischemia may be directed at genes mediating either recovery or apoptosis.

Altered expression of Bcl-2, Bcl-X, Bax, and c-Fos colocalizes with DNA fragmentation and ischemic cell damage following middle cerebral artery occlusion in rats

Permanent occlusion of the middle cerebral artery in rats was used to assess the effects of focal ischemia on the expression of members of the bcl-2 family which have been implicated in the regulation of programmed cell death. Intraluminal occlusion of one middle cerebral artery for 6 h resulted in histologically detectable brain damage within the ipsilateral caudate putamen, basolateral cortex and parts of the thalamus. In the infarcted basolateral cortex and thalamus fragmentation of DNA was detected in many nuclei using in-situ end-labeling of DNA breaks by terminal transferase, whereas only scattered labeled nuclei were visible in the infarcted caudate putamen. Immunohistochemical analysis revealed activation of c-Fos in the infarcted cortex and thalamus and in the non-infarcted cingulate cortex as has been shown by others. A decrease in immunoreactivity for Bcl-2, and Bcl-X and an increase in immunostaining for Bax was observed exclusively in neurons within the ischemic cortex and thalamus. Within the infarcted caudate putamen, however, protein levels of all bcl-2 family members declined and c-Fos remained absent. By reverse transcription and polymerase chain reaction it was demonstrated that levels of bcl-2 mRNA markedly decreased in the ipsilateral hemisphere, whereas the amount of bax mRNA was elevated. These findings suggest that a shift in the ratio of cell death repressor Bcl-2 to cell death effector Bax and a concomitant activation of c-Fos may contribute to neuronal apoptosis in the infarcted thalamus and cortex.