Post-ischemic and kainic acid-induced c-fos protein expression in the rat hippocampus

Effect of salvia miltiorrhiza bunge on cerebral infarct in ischemia-reperfusion injured rats

According to the theory of traditional Chinese medicine, cerebral infarction results from blood stasis, and the method of quickening the blood and dispelling stasis is used to treat cerebral infarct. salvia miltorrhiza bunge (SM) is a Chinese herb, which is considered to have an action of quickening the blood and dispelling stasis, and is frequently used to treat related disorders of blood stasis such as cerebrovascular accident and ischemic heart disease. The aim of the present study was to investigate the effect of SM on cerebral infarct in ischemia-reperfusion injured rats. A total of 30 Sprague-Dawley (SD) rats were studied. A model of focal cerebral infarct was developed by occluding both common carotid arteries and the right middle cerebral artery for 90 minutes. After 24 hours reperfusion, the rats were killed and the brain tissue was stained with 2, 3, 5-triphenyl-tetrazolium chloride (TTC). The areas of cerebral infarct were calculated, and lumino-chemiluminesence (CL) counts and lucigenin-CL counts of peripheral blood taken at this time were measured. The changes in the area of cerebral infarct were used as an index to evaluate the effect of SM on cerebral infarct. The results indicated that pretreatment with intraperitoneal injection of 30 mg/kg and 15 mg/kg SM reduced the area of cerebral infarct and also reduced the luminol-CL counts of peripheral blood in ischemia-reperfusion injured rats. This study has demonstrated that SM can reduce the area of cerebral infarct in ischemia-reperfusion injured rats, suggesting it may be useful in the treatment of cerebral infarct in humans. The therapeutic effect of SM may be partly due to its free radical scavenging activities.

Acupuncture modulates expressions of nitric oxide synthase and c-Fos in hippocampus after transient global ischemia in gerbils

The effects of acupuncture on the expressions of nitric oxide synthase (NOS) and c-Fos in the hippocampus of gerbils after transient ischemia were investigated via nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and Fos immunohistochemistry. In animals of the ischemia-induction groups, both common carotid arteries were occluded for 5 minutes. Animals of the acupunctued groups were given acupunctural treatment at Zusanli twice daily for 9 consecutive days. Acupuncture was shown to decrease NADPH-d and c-Fos levels in both the sham-operation group and the ischemia-induction group. These results suggest that acupuncture modulates the expressions of NOS and c-Fos in the hippocampus.

Anticonvulsive and free radical scavenging activities of Gastrodia elata Bl. in kainic acid-treated rats

Gastrodia elata Bl. (GE) is a traditional Chinese herb that is commonly used in Chinese communities to treat convulsive disorders such as epilepsy. The purpose of the present study was to determine the anticonvulsive and free radical activities of GE in rats. In vitro studies were conducted by using brain tissue from 6 male Sprague-Dawley (SD) rats treated with 120 microg/ml of kainic acid (KA), with or without the addition of various concentrations of GE. In vivo studies were conducted in a total of 30 male SD rats divided into 5 groups of 6 rats which were treated as follows: 1) the normal group received an intraperitoneal injection (i.p.) of PBS (Phosphate buffer saline, 1 ml/kg); 2) the control group received KA (12 mg/kg) i.p.; 3) the GE 1.0 group received oral administration of GE 1.0 g/kg 30 min prior to KA administration; 4) the GE 0.5 group received oral administration of GE 0.5 g/kg 30 min prior to KA administration; 5) the PH group received oral administration of phenytoin 20 mg/kg 30 min prior to KA administration. Seizures were verified by behavioral observations, electroencephalograph (EEG) and electromyography (EMG). Lipid peroxide levels in the rat brain, luminol chemiluminescence (CL) and lucigenin-CL in the peripheral blood were measured simultaneously after behavioral observations. The results indicate that GE administration significantly reduced KA-induced lipid peroxide levels in vitro. Oral administration of GE 1.0 g/kg and phenytoin 20 mg/kg significantly reduced counts of wet dog shakes (WDS), paw tremor (PT) and facial myoclonia (FM) in KA-treated rats. In addition, oral administration of GE 1.0 g/kg significantly delayed the onset of WDS, from 30 min in the control group to 46 min in the 0.5 g/kg group, and 63 min in the GE 1.0 g/kg group. A significantly reduced level of lipid peroxides in the rat brain was found in the GE 1.0 g/kg, 0.5 g/kg, and phenytoin 20 mg/kg groups. The GE 1.0 g/kg group showed significant reduction of luminol-CL and lucigenin-CL counts in the peripheral blood compared to the control group. The results of the present study demonstrate that GE has anticonvulsive and free radical scavenging activities. Further studies are needed to determine the clinical effectiveness of GE as an anticonvulsant in humans.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

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

Anticonvulsive and free radical scavenging actions of two herbs, Uncaria rhynchophylla (MIQ) Jack and Gastrodia elata Bl., in kainic acid-treated rats

Uncaria rhynchophylla (Miq.) Jack (UR) and Gastrodia elata BI. (GE) are traditional Chinese herbs that are usually used in combination to treat convulsive disorders, such as epilepsy, in China. The aim of this study was to compare the anticonvulsive and free radical scavenging activities of UR alone and UR in combination with GE in rats. For the in vitro studies, brain tissues from 6 male Sprague-Dawley (SD) rats were treated with 120 microg/ml kainic acid (KA), with or without varied concentrations of UR or UR plus GE. For the in vivo studies, male SD rats (6 per group) received intraperitoneal (i.p.) injection of KA 12 mg/kg to induce epileptic seizures and generation of free radicals, with or without oral administration of UR 1 g/kg alone or UR 1 g/kg plus GE 1 g/kg. Epileptic seizures were verified by behavioral observations, and electroencephalography (EEG) and electromyography (EMG) recordings. These results showed that UR alone decreased KA-induced lipid peroxide levels in vitro, whereas UR plus GE did not produce a greater effect than UR alone. UR significantly reduced counts of wet dog shakes (WDS), paw tremor (PT) and facial myoclonia (FM) in KA-treated rats and significantly delayed the onset time of WDS, from 27 min in the control group to 40 min in the UR group. UR plus GE did not inhibit seizures more effectively than UR alone, but did further prolong the onset time of WDS to 63 min (P < 0.05 vs. UR alone). UR alone reduced the levels of free radicals in vivo, as measured by lipid peroxidation in the brain and luminol-chemiluminescence (CL) counts and lucigenin-CL counts in the peripheral whole blood, but the combination of GE and UR did not reduce free radical levels more markedly than UR alone. In conclusion, our results indicate that UR has anticonvulsive and free radical scavenging activities, and UR combined with GE exhibit greater inhibition on the onset time of WDS than UR alone. These findings suggest that the anticonvulsive effects of UR and GE may be synergistic. However, the mechanism of interaction between UR and GE remains unknown.

Systematic expression of immediate early genes and intensive astrocyte activation induced by intrastriatal ferrous iron injection

The potential role(s) of transitional metals such as iron have been implicated in neurodegeneration through biochemical processes, particularly oxidative stress. We injected ferrous chloride (FeCl2) and ferric chloride (FeCl3) into the striatonigral system of Sprague-Dawley rats to investigate the biological and toxic effects of ferrous iron in the central nervous system. When FeCl2 was injected into the ventral midbrain, rats showed a characteristic behavior which indicated ipsilateral dopaminergic hyperactivity. FeCl2 injection into the striatum induced a dose-dependent damage, the activation of astrocytes and recruitment of macrophage/microglia at the injected site. Interestingly, the activation of astrocytes was also observed in the anatomically remote areas such as the ipsilateral subthalamic nucleus and pars reticulata of the substantia nigra after 1 week. Expression of immediate early genes (IEGs; c-fos and NGFI-A) was observed in the cortex, thalamic nuclei, subthalamic nucleus, pars reticulata of the substantia nigra, lateral and medial geniculate bodies on the ipsilateral side from 3 to 15 h after FeCl2 injection. Pre-treatment with dimethyl sulfoxide, a hydroxyl radical scavenger, prevented FeCl2-induced expression of IEGs in the thalamic nuclei and geniculate bodies, but not in the cerebral cortex. On the other hand, the effects of FeCl3 were faint and limited on IEGs expression and tissue damage. These results suggest that ferrous iron affects the nervous system vigorously, possibly yielding free radicals such as hydroxyl radicals, and could be one of the important candidates for neurodegenerative diseases under the state in which acclimating systems for iron toxicity are disrupted.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Delayed induction of JunB precedes CA1 neuronal death after global ischemia in the gerbil

The immediate early genes (IEGs), c-jun, junB and c-fos are expressed after global ischemia in the gerbil. The role of these genes remains unclear. Whilst moderate ischemia (7 min) causes delayed CA1 neuronal death, pre-conditioning with mild ischemia (2 min) neuroprotects the CA1 subfield. This differential response allows the specific expression patterns of IEGs to be associated with either delayed neuronal death, or cell survival, depending upon the insult severity. Using a graded insult strategy we have shown that (1) early IEG expression is prominent in the neuronal layers of the CA3, hilar and dentate regions, and (2) a delayed, secondary wave of JunB expression is localized to the selectively vulnerable CA1 neuronal layer after moderate ischemia. This expression precedes the histological and histochemical features of neuronal death. Delayed JunB expression was not observed in animals subject to 2 min ischemia. The glial fibrillary acidic protein (GFAP) promotor possesses an AP-1 binding site, the target for IEG dimers. To examine the possible link between IEG expression and astrocyte activation the transcriptional activation of GFAP was assessed. GFAP mRNA was evident within 8 h of ischemia after both insults. The extent of the astrocytic reaction was dependent upon the severity of the ischemia. The temporospatial distribution of IEG and GFAP expression differed, indicating that glial activation is unlikely to be regulated by the hippocampal expression of IEGs. We conclude that early IEG expression is involved in signalling mechanisms that invoke neuroprotective effects in the dentate and CA3 regions, and that delayed JunB expression in the CA1 subfield is associated with neuronal death, and may be involved in the commitment or execution phases of cell death. Early astrocytic responses may play a role in the mechanism of ischaemic tolerance.

Ischemia-induced CA1 neuronal death is preceded by elevated FosB and Jun expression and reduced NGFI-A and JunB levels

Alterations in levels of the immediate-early gene (IEG) proteins Fos, FosB, DeltaFosB, Jun, JunB, JunD, and NGFI-A were investigated in rat hippocampus by immunohistochemistry 2, 12, 24, and 48 h after forebrain ischemia. Transient global ischemia of 20 min, produced by four vessel occlusion (4-VO), elicited different patterns of IEG expression in vulnerable CA1 and more resilient CA3 neurons. Cell counts revealed that except for JunD and NGFI-A, immunoreactivity for all examined IEGs was initially elevated by forebrain ischemia in both CA1 and CA3 hippocampal subfields. However, distinct patterns of IEG expression became evident in these regions at later time points. The pivotal difference was the persistence of ischemia-induced elevations of FosB and Jun expression in the CA1 region of the hippocampus. Unlike CA3 neurons, where IEG immunoreactivity had subsided to basal levels by 24-48 h, CA1 neurons continued to display increased FosB- and Jun-like immunoreactivity 48 h post-ischemia. Western blot analysis revealed that elevated expression of both FosB and DeltaFosB-like proteins were responsible for the immunohistochemical detection of enhanced FosB-like immunoreactivity in CA1 neurons at 48 h. These findings are consistent with recent in vitro studies that implicate FosB and Jun in gene signalling pathways responsible for programmed cell death. In contrast to FosB and Jun, JunB expression declined significantly below basal levels in CA1 neurons at 48 h, yet remained unaltered in CA3 neurons. Given that JunB can inhibit the transactivating properties of Jun, decreased JunB levels may contribute to the apoptotic death of CA1 neurons by enhancing the transcriptional regulating activity of Jun. Also notable at 48 h was the complete loss of constitutive NGFI-A expression from CA1 neurons of ischemic animals. These findings suggest that persistent elevations in FosB and Jun expression, concurrent with reductions in JunB and NGFI-A levels, contribute to the apoptotic death of CA1 neurons after forebrain ischemia.

Platelet-derived growth factor-BB, but not -AA, prevents delayed neuronal death after forebrain ischemia in rats

Our previous studies demonstrated coordinate expression of platelet-derived growth factor (PDGF) -B chain and beta-receptor in neurons at risk in the rat brain with focal ischemia. To clarify a role of the -B chain in the brain further, we examined whether PDGF-A or -B chain protects CA1 pyramidal neurons from delayed neuronal death after forebrain ischemia in rats. Pretreatment with PDGF-BB, but not -AA, at 120 ng/d for 2 days until forebrain ischemia was performed markedly ameliorated delayed neuronal death in CA1 pyramidal neurons on day 7 after ischemia. This neuroprotective effect of PDGF-BB was dose-dependent, and pretreatment with PDGF-BB at 240 ng/d showed almost complete inhibition of delayed neuronal death. In contrast, posttreatment with PDGF-BB at 120 ng/d starting 20 minutes after ischemia demonstrated no significant neuroprotective effect. The current study established marked neuroprotective actions of PDGF-BB in ischemic neuronal damage.

Immediate early gene expression and delayed cell death in limbic areas of the rat brain after kainic acid treatment and recovery in the cold

Systemic injection of kainic acid (KA) results in characteristic behaviors and programmed cell death in some regions of the rat brain. We used KA followed by recovery at 4 degrees C to restrict damage to limbic structures and compared patterns of immediate early gene (IEG) expression and associated DNA binding activity in these damaged areas with that in spared brain regions. Male Wistar rats were injected with KA (12 mg/kg, i.p.) and kept at 4 degrees C for 5 h. This treatment reduced the severity of behaviors and restricted damage (observed by Nissl staining) to the CA1 and CA3 regions of the hippocampus and an area including the entorhinal cortex. DNA laddering, characteristic of apoptosis, was first evident in the hippocampus and the entorhinal cortex 18 and 22 h after KA, respectively. The pattern of IEG mRNA induction fell into three classes: IEGs that were induced in both damaged and spared areas (c-fos, fos B, jun B, and egr-1), IEGs that were induced specifically in the damaged areas (fra-2 and c-jun), and an IEG that was significantly induced by saline injection and/or the cold treatment (jun D). The pattern of immunoreactivity closely followed that of mRNA expression. Binding to the AP-1 and EGR DNA consensus sequences increased in all three regions studied. This study describes a unique modification of the animal model of KA-induced neurotoxicity which may prove a useful tool for dissecting the molecular cascade that ultimately results in programmed cell death.

Selective neuronal vulnerability in the hippocampus--a role for gene expression?

Proposed mechanisms of neurodegeneration focus generally on the triggering of toxic biochemical pathways by an increased intracellular concentration of Ca2+. Recent evidence also suggests that Ca2+ causes transcriptional activation of so-called 'cell-death genes'. Efforts to elucidate the basis of selective vulnerability have relied on animal models of delayed neuronal death in the hippocampus. Biochemical and morphological data indicate that delayed neuronal death is a form of programmed cell death, or apoptosis. Observations that specific genes are activated transcriptionally for prolonged times in neuronal populations that are undergoing delayed death suggest that active gene expression is part of the neuronal-death cascade. Although a direct causal role remains to be proven, evidence implicates certain genes in neuronal-death pathways.

The role of inducible transcription factors in apoptotic nerve cell death

Recent studies have shown that certain types of nerve cell death in the brain occur by an apoptotic mechanism. Researchers have demonstrated that moderate hypoxic-ischemic (HI) episodes and status epilepticus (SE) can cause DNA fragmentation as well as other morphological features of apoptosis in neurons destined to die, whereas more severe HI episodes lead to neuronal necrosis and infarction. Although somewhat controversial, some studies have demonstrated that protein synthesis inhibition prevents HI-and SE-induced nerve cell death in the brain, suggesting that apoptotic nerve cell death in the adult brain is de novo protein synthesis-dependent (i.e., programmed). The identity of the proteins involved in HI-and SE-induced apoptosis in the adult brain is unclear, although based upon studies in cell culture, a number of potential cell death and anti-apoptosis genes have been identified. In addition, a number of studies have demonstrated that inducible transcription factors (ITFs) are expressed for prolonged periods in neurons undergoing apoptotic death following HI and SE. These results suggest that prolonged expression of ITFs (in particular c-jun) may form part of the biological cascade that induces apoptosis in adult neurons. These various studies are critically discussed and in particular the role of inducible transcription factors in neuronal apoptosis is evaluated.

Reexpression of developmentally regulated MAP2c mRNA after ischemia: colocalization with hsp72 mRNA in vulnerable neurons

Levels of mRNAs encoding the microtubule-associated proteins MAP2b and MAP2c as well as the 70-kDa stress protein [72-kDa heat shock protein (hsp72)] were evaluated in postischemic rat brain by in situ hybridization with oligonucleotide probes corresponding to the known rat sequences. Rats were subjected to 10-min cardiac arrest, produced by compression of major thoracic vessels, followed by resuscitation. The normally expressed MAP2b mRNA showed transient twofold elevations in all hippocampal neuron populations at 6-h recirculation, followed by a return to control levels by 24 h. MAP2b hybridization was progressively lost thereafter from the vulnerable CA1 and outer cortical layers, preceding both the fall in immunoreactive MAP2b and the eventual cell loss in these regions. The depletion of MAP2b mRNA coincided with an increase in the alternatively spliced MAP2c in vulnerable regions during 12-48 h of recirculation, precisely overlapping the late component of hsp72 expression that persisted in these cell populations. Previous studies have suggested that the initial induction of hsp72 provides an index of potential postischemic injury in neuron populations that may or may not be injured, while lasting hsp72 mRNA expression is associated with cell damage. In contrast, the present results demonstrate that MAP2c expression under these conditions occurs uniquely in neuron populations subject to injury. Available evidence suggests that MAP2c expression represents a plastic response in subpopulations of neurons that will survive in these regions, although it remains to be explicitly determined whether it may also be transiently expressed in dying cells. In any case, these observations demonstrate that reexpression of developmentally regulated MAP2c mRNA is a relatively late postischemic response in vulnerable cell populations, indicating that pathways regulating MAP2 splicing may be closely associated with mechanisms of neuron injury and/or recovery.

Modulation of ischemic signal by antagonists of N-methyl-D-aspartate, nitric oxide synthase, and platelet-activating factor in gerbil hippocampus

Cerebral ischemia in the gerbil results in early hippocampal changes, which include transient activation and/or translocation of protein kinase C (PKC), increased enzymatic activity of ornithine decarboxylase (ODC), and elevated DNA binding ability of activator protein-1 (AP1). The time-course of all three of these postischemic responses was found to be almost parallel, peaking at 3 hr after the ischemic insult. The effectiveness of known modulators of postischemic morphological outcome (MK-801, L-NAME, and gingkolides BN 52020 and BN 52021) in counteracting the induction of PKC, ODC, and AP1 formation was tested. These drugs were administrated as followed: MK-801 (a noncompetitive inhibitor of NMDA channel), 0.8 mg/kg i.p., 30 min before ischemia, and 5 min after the insult; L-NAME (competitive inhibitor of NO synthase), 10 mg/kg i.p., 30 min before ischemia, and 5 mg/kg, 5 min after ischemia; BN52020 and BN52021 (inhibitors of platelet-activating factor: PAF receptors) were administered as a suspension in 5% ethanol in water by oral route, 10 mg/kg for 3 days before ischemia. Three of these drugs, MK-801, L-NAME, and BN52021, significantly reduced ischemia-elevated activity of PKC and ODC, whereas AP1 formation was only partially attenuated. Our observations implicate the existence of different mechanism(s) for postischemic PKC and ODC activation, which in turn is engaged in AP1 induction.

NMDA receptor-mediated expression of Fos protein in the rat striatum following methamphetamine administration: relation to behavioral sensitization

In order to clarify the possible involvement of N-methyl-D-aspartate (NMDA) receptors in mediating striatal Fos protein induction and behavioral sensitization after methamphetamine administration, we examined the effects of non-competitive NMDA receptor antagonist MK-801 on these phenomena in rats. A single administration of 1.0 and 5.0 mg/kg methamphetamine resulted in a dose-dependent increase in Fos-immunoreactive cells in the medial striatum. Prior exposure to 5.0 mg/kg methamphetamine enhanced ipsilateral rotational behavior in response to subsequent methamphetamine administration in unilateral nigral-lesioned rats (sensitization). Pretreatment with 1.0 mg/kg MK-801 completely prevented both the expression of striatal Fos protein and the development of acute behavioral sensitization following a single injection of 5.0 mg/kg methamphetamine. These results suggest that NMDA receptor-mediated mechanisms contribute to the expression of striatal Fos protein associated with behavioral sensitization that follows exposure to methamphetamine.

Coexpression of c-fos and hsp70 mRNAs in gerbil brain after ischemia: induction threshold, distribution and time course evaluated by in situ hybridization

Levels of mRNAs encoding the proto-oncogene, c-fos, and the 70 kDa stress protein, hsp70, were evaluated in gerbil brain following transient cerebral ischemia of varied duration by in situ and blot hybridization techniques. Blots of total hippocampal RNA obtained after 5 min ischemic insults confirmed a characteristic, transient time course of c-fos expression with a striking elevation within 1 h and a return to control levels by 3 h recirculation. Hsp70 hybridization was significant at 1 h and continued to increase until 3-6 h after the insult. Striking accumulation of c-fos mRNA was detected within 15 min recirculation in dentate granule cells, persisting through 1 h, and a weaker signal was evident in CA1 and CA3 pyramidal neurons of hippocampus, as well as in prepiriform/entorhinal cortex and neocortical regions, during the same interval. Hsp70 hybridization showed an identical distribution at 1 h recirculation. Ischemic insults of 1 min duration resulted in no detectable increase of either mRNA, while 2 min ischemia resulted in changes comparable to those seen after 5 min insults. This common threshold corresponds to the ischemic interval required for energy depletion and resultant failure of intracellular ion homeostasis. In contrast, expression of hsp70 mRNA was not observed under conditions of brief depolarization accompanying cortical or hippocampal spreading depression that were shown to induce c-fos. A delayed component of c-fos mRNA expression was not detected in this model, while persistent hsp70 hybridization, restricted to hippocampal CA1 neurons, was evident at 48 h after either 2 min or 5 min ischemic insults. The parallels in c-fos and hsp70 mRNA expression during early recirculation suggest that overlapping mechanisms triggered following postischemic depolarization contribute to their induction after transient ischemia.

Immediate-early gene protein expression in neurons undergoing delayed death, but not necrosis, following hypoxic-ischaemic injury to the young rat brain

A unilateral hypoxia-ischaemia (HI) 21-day-old rat preparation was used to assess the effects of HI on the expression of the immediate-early gene proteins (IEGPs) c-Fos/FRAs, Fos B, c-Jun, Jun B, Jun D, Krox 20, Krox 24, and on the mRNA for the neurotrophic factor, brain-derived neurotrophic factor (BDNF). Moderate HI (15 min hypoxia) produced delayed, selective neuronal death and was associated with a rapid induction of c-Fos, Fos B, Jun B, Jun D, and c-Jun proteins, but not Krox 20 protein or BDNF mRNA, in neurons on the side of HI and also a delayed expression of c-Jun (and to a lesser extent c-Fos/FRA's and Fos B) 24-48 h after HI in neurons that underwent delayed neuronal death. Krox 24 showed an initial induction followed by a long-lasting suppression of its expression in regions undergoing cell loss. Severe HI (60 min hypoxia) resulted in seizures and rapid neuronal loss and infarction (necrotic cell death) on the side of HI, and was associated with early induction of c-Fos, Fos B, c-Jun, Jun B, Jun D, Krox 20 and Krox 24 protein and BDNF mRNA in neurons on the non-ligated side of the brain. Fos, c-Jun, Jun B, Jun D and Krox 24, but not Krox 20, Fos B, or BDNF mRNA, were also induced in non-nerve cells on the damaged side of the brain after both moderate and severe HI, and many of these cells appeared to be dividing. Thus, moderate HI induces IEGP's in neurons and non-nerve cells in damaged regions, whereas severe HI induces IEGP's and BDNF in non-damaged regions. c-Jun (and to a lesser extent c-Fos/FRA's) showed a prolonged expression in neurons undergoing delayed, but not necrotic, cell death suggesting that they may be involved in the biochemical cascade that causes selective delayed neuronal death. BDNF was not induced by HI, and therefore, does not appear to play an endogenous neuroprotective role in the CNS.

Differential expression of the immediate early genes c-fos, c-jun, junB, and NGFI-B in the rat brain following transient forebrain ischemia

The temporospatial expression pattern of four immediate early genes (IEGs) (c-fos, c-jun, junB, NGFI-B) following 30 min of global ischemia was investigated in rat brains by in situ hybridization and immunohistochemistry (c-fos). All examined IEG mRNAs, as well as Fos-like immunoreactivity, increased transiently in vulnerable and resistant brain regions following ischemia, but the induction profiles were distinct. Ischemia caused a post-ischemic early-onset, transient c-fos induction in wide-spread regions, as well as a late-onset induction restricted to vulnerable regions. Late-onset c-fos induction was observed in the CA1 region and the ventral thalamus but not in the striatum or neocortex, where neurons degenerate at a quicker pace. After recirculation, c-jun mRNA appeared to be initially coinduced with c-fos mRNA, but c-jun mRNA levels remained elevated or increased in various regions, including all vulnerable regions, when c-fos mRNA had already declined to near basal levels. Compared to c-fos and c-jun, junB induction was less pronounced and confined largely to the dentate gyrus. NGFI-B mRNA increased moderately and only in brain regions exhibiting the most dramatic c-fos increases and with similar kinetics. The differential activation of the investigated IEGs suggests that rather complex long-term adaptive processes may be initiated at the genomic level after global ischemia. The present findings provide further evidence that the activation of IEGs forms part of the brain's metabolic response to ischemia, but no simple correlation appears to exist between the induction of the investigated IEGs and the phenomenon of selective vulnerability.

Calcium-mediated mechanisms of ischemic injury and protection

Our understanding of calcium's role in cerebral ischemia continues to evolve from the initial recognition that it may be harmful to the ischemic cell. A multitude of experiments have supported the hypothesis that excessive influx of calcium into the cell under ischemic conditions is a major mechanism of cell injury and death. Pharmacological intervention to restore cellular calcium homeostasis is protective in many models of cell anoxia. Principle routes of calcium entry are the voltage-sensitive (VSCC) and N-methyl-D-aspartate linked receptor operated (ROCC) calcium channels. Regional variations in channel densities have been described and it is now known that these classes of channels are located in different regions of the neurons. Activation of both channel types has been identified in in vivo models of cerebral ischemia. Although the ROCC is predominant in number, the VSCC appears to activate at higher cerebral blood flow values suggesting that it is an earlier conduit for calcium than the glutamate-driven ROCC. Intracellular calcium is well recognized as a second messenger system and there is increasing appreciation that it induces immediate early genes (IEG). Since IEGs function as transcriptional regulating factors, the differential expression of specific target genes may be of importance for determining death or survival of the ischemic tissue.

Differential transcription and translation of immediate early genes in the gerbil hippocampus after transient global ischemia

Excitotoxic activation of glutamate receptors is thought to be a key event for the molecular pathogenesis of postischemic delayed neuronal death of CA-1 neurons in the gerbil hippocampus. Glutamate receptor stimulation also causes induction of transcription factors that belong to the class of immediate early genes. We examined the expression of six different immediate early genes in the gerbil hippocampus after transient global ischemia. Comparative analysis of c-fos and Krox-24 expression was carried out in the same animals at the transcriptional and translational level by in situ hybridization and immunocytochemistry. Postischemic synthesis of four additional immediate early gene (IEG)-encoded proteins (FOS-B, c-JUN, JUN-B, and JUN-D) was investigated by immunocytochemistry at recirculation intervals between 1 and 48 h. After 5 min of ischemia, transcription of c-fos and Krox-24 mRNA was induced in all hippocampal subpopulations with peak expression at 1 h after recirculation. In vulnerable CA-1 neurons, increased transcription of c-fos and Krox-24 was not followed by translation into protein. Induction of immediate early gene-encoded proteins was restricted to neuronal populations less vulnerable to brief ischemia and identified neurons that are targets of glutamate receptor-mediated neurotoxicity but that are destined to survive. Our data indicate an asynchronous synthesis and persistence of individual IEG-encoded proteins in these neurons. The staggered induction implies that combinatorial changes of transcription factors allow a differential postischemic regulation of target gene expression both spatially and over time.

Cycloheximide prevents kainate-induced neuronal death and c-fos expression in adult rat brain

The present study was directed at evaluating the possible involvement of protein synthesis in excitotoxin-induced neuronal damage and prolonged expression of the proto-oncogene, c-fos. Kainic acid-induced seizure activity elicited varying degrees of neuronal damage and cell loss in selectively vulnerable regions of the adult rat limbic system. Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter behavioral seizure characteristics, but markedly attenuated damage to susceptible neuronal populations. A prolonged increase in c-fos mRNA was observed by in situ hybridization up to 16 h after the onset of seizures in regions exhibiting neuronal death. Pretreatment with cycloheximide did not affect the transient induction of c-fos observed in numerous structures, but significantly reduced the prolonged expression of c-fos mRNA in kainate-vulnerable regions. Despite producing massive seizure activity, systemic kainic acid administration during the early postnatal period did not induce any neuronal death, and did not result in prolonged c-fos expression in any brain structures. The developmental onset of selective neuronal vulnerability coincided with that of prolonged c-fos expression in susceptible neuronal populations. In adult rats, seizure activity induced by pentylenetetrazole did not produce neuronal damage nor did it produce prolonged c-fos expression. These results not only demonstrate that kainate-induced neurotoxicity and the prolonged expression of c-fos are both prevented by cycloheximide, but also strengthen idea that prolonged c-fos expression is a marker of neuronal death.

Impairment of Fos protein formation in the rat infarct borderzone by MK-801, but not by NBQX

In the present immunocytochemical study, we investigated the mechanism of Fos protein induction and the regional distribution of the Fos protein in brains of spontaneously hypertensive rats subjected to 2 h of permanent middle cerebral artery occlusion (MCAO). Rats were administered either saline or a glutamate receptor antagonist; the non-competitive NMDA receptor antagonist MK-801 or the AMPA receptor antagonist NBQX which are known to be able to reduce infarct size in MCA occluded rats. The saline treated rats showed presence of Fos protein in nerve cell nuclei throughout the cortical and striatal infarct borderzone, but no staining in the infarct core or contralateral hemisphere. MK-801 almost totally abolished this expression of Fos protein whereas NBQX had no significant effect on Fos protein expression. It is suggested that the Fos protein induction is due to repeated spreading depressions mediated by NMDA receptors in the infarct borderzone, and that Fos protein due to its persistence in the tissue can be used as a histochemical marker of borderzone tissue at risk for eventually becoming recruited in the infarct.

Brain injury and repair mechanisms: the potential for pharmacologic therapy in closed-head trauma

Rotational acceleration from closed-head trauma produces shear-strain brain injury at the interface of gray and white matter. The initial injury is followed by progressive damage involving three key phenomena: progression of subtle focal axonal damage to axonal transection between six and 12 hours after injury, progressive development of tissue microhemorrhages between 12 and 96 hours after injury, and development of tissue and cerebral spinal fluid lactic acidosis that does not appear to be explained by trauma-induced tissue depolarization, activation of phospholipases and the release of free arachidonic acid, radical generation by metabolism of arachidonate, and lipid peroxidation with consequent membrane degradation and partial mitochondrial uncoupling. Because of terminal differentiation, neurons may have a limited membrane repair capability that might be stimulated by growth factors. Other potential therapeutic interventions include calmodulin inhibitors, iron chelators, and free radical scavengers.

Suppression of protein synthesis in the reperfused brain

BACKGROUND

Brain ischemia and reperfusion produce profound protein synthesis alterations, the extent and persistence of which are dependent on the nature of the ischemia, the brain region, the cell layer within a region, and the particular proteins studied. After transient ischemia, most brain regions recover their protein synthesis capability; however, recovery in the selectively vulnerable areas is poor. It is unknown whether this phenomenon itself provokes or is a consequence of the process of neuronal death.

SUMMARY OF REVIEW

Protein synthesis suppression during ischemia is due to energy depletion, but this is quickly reversed upon recirculation. Reperfusion does not appear to damage DNA or transcription mechanisms, although there are changes in the profile of transcripts being made. Similarly, purified ribosomes isolated from reperfused brains can make the normal repertoire of proteins and heat-shock proteins. However, during early reperfusion, newly synthesized messenger RNAs appear to accumulate in the nucleus; this alteration in RNA handling could reflect disruption at any of several steps, including posttranscriptional processing, nuclear pore transport, cytoskeletal binding, or formation of the translation initiation complex. Another mechanism that may be responsible for protein synthesis suppression during late reperfusion is progressive membrane destruction, with consequent shifts in the concentration of ions crucial for ribosomal function.

CONCLUSIONS

Protein synthesis suppression after ischemia likely involves a progression of multiple mechanisms during reperfusion. Although the recent work reviewed here offers new insight into the potential mechanisms disrupting protein synthesis, detailed understanding will require further investigation.

Switch in glutamate receptor subunit gene expression in CA1 subfield of hippocampus following global ischemia in rats

Severe, transient global ischemia of the brain induces delayed damage to specific neuronal populations. Sustained Ca2+ influx through glutamate receptor channels is thought to play a critical role in postischemic cell death. Although most kainate-type glutamate receptors are Ca(2+)-impermeable, Ca(2+)-permeable kainate receptors have been reported in specific kinds of neurons and glia. Recombinant receptors assembled from GluR1 and/or GluR3 subunits in exogenous expression systems are permeable to Ca2+; heteromeric channels containing GluR2 subunits are Ca(2+)-impermeable. Thus, altered expression of GluR2 in development or following a neurological insult or injury to the brain can act as a switch to modify Ca2+ permeability. To investigate the molecular mechanism underlying delayed postischemic cell death, GluR1, GluR2, and GluR3 gene expression was examined by in situ hybridization in postischemic rats. Following severe, transient forebrain ischemia GluR2 gene expression was preferentially reduced in CA1 hippocampal neurons at a time point that preceded their degeneration. The switch in expression of kainate/AMPA receptor subunits coincided with the previously reported increase in Ca2+ influx into CA1 cells. Timing of the switch indicates that it may play a causal role in postischemic cell death.

Influence of medial septal cholinoceptive cells on c-Fos-like proteins induced by soman

The effects of intraseptal application of atropine on c-fos proto-oncogene expression related to soman treatment were studied by immunohistochemistry for c-Fos-like proteins. In control rats, 2 h after the onset of convulsion, c-Fos-like immunoreactivity was intense in the piriform and entorhinal cortices, but also in the cingulate, frontoparietal and retrosplenial cortices. In addition, the staining was moderate in the hypothalamus, amygdala and fascia dentata. The intraseptal application of atropine, which prevented soman-induced convulsions, reduced or even blocked c-Fos-like protein production related to soman treatment. This inhibition of Fos induction was significant in most of the limbic structures but also in non-limbic areas. The data in this study strongly suggest that the cholinergic cells of the medial septal area play a key role in soman-induced seizures, and confirm that c-Fos-like protein induction is closely related to neuronal hyperactivity.

Induction of FOS and JUN proteins after focal ischemia in the rat: differential effect of the N-methyl-D-aspartate receptor antagonist MK-801

FOS and JUN proteins are transcription factors thought to be involved in coupling neuronal excitation to target gene expression. Cortical infarction of consistent size and location was produced by irradiating the rat brain with Xenon light through the intact skull for 20 min following systemic injection of the photo-sensitizing dye, rose bengal. To investigate the time course and distribution pattern of five cellular immediate early gene (IEG)-encoded proteins after focal ischemia, the expression of c-FOS, FOS B, c-JUN, JUN B and JUN D was studied immunocytochemically in sham-operated control animals and at different postischemic time intervals up to 24 h. A separate group of animals was pretreated with the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801. Photochemically induced focal ischemia caused a rapid induction of FOS and JUN proteins in the entire ipsilateral cortex apart from the ischemic focus. Immunoreactivity in the ipsilateral subcortical gray and white matter and in the entire contralateral hemisphere was indistinguishable from control animals. Individual IEG-encoded proteins were sequentially induced with increased levels of immunoreactivity persisting for different time periods up to 24 h. c-FOS, FOS B, c-JUN and JUN B exhibited a characteristic distribution pattern as reflected by different staining intensities in individual cortical layers. The rapid IEG induction in the entire ipsilateral sensorimotor and limbic structure-associated cortices after photochemically induced infarction most likely reflects spreading depression caused by ischemia and mediated by NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)