In situ hybridization analysis of c-fos and c-jun expression in the rat brain following transient forebrain ischemia

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.

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.

Molecular regulation of neuronal apoptosis

Apoptosis is a fundamental biological process used by all muticellular organisms to eliminate unwanted or superfluous cells, and is a prominent feature of normal neural development. Developmentally occurring neuronal apoptosis serves to match the number of neurons to the requirements of their synaptic targets and to rid the nervous system of inappropriate connections. While it is generally accepted that apoptosis is a "suicide program" inherent in all cells, the molecular basis of this program is just beginning to be unraveled. Evidence from numerous recent studies indicate that a variety of proteins are involved in the transmission of external signals to the cell-death machinery within the cell. This review describes many of the recent findings of the regulatory pathways and genes that have been implicated in the induction or suppression of apoptosis in neurons.

Immediate-early gene expression in the brain of the thiamine-deficient rat

Pyrithiamine-induced thiamine deficiency (PTD) in the rat is associated with neuronal loss in the thalamus and inferior colliculus. Recently, we were able to demonstrate the occurrence of apoptosis in the thalamus of these animals. Given that immediate-early genes (IEGs) participate in signal transduction pathways that mediate programmed cell death, the present study utilized in situ hybridization and immunohistochemistry to examine the expression of four IEGs (c-fos, c-jun, fos-B, and NGFI-A) during the progression of PTD. Elevated c-fos mRNA levels were initially observed in the posterior medial thalamus on d 12 of the deficiency. At the acute symptomatic stage (characterized by a loss of righting reflex on d 16-17), the posterior-medial thalamus exhibited increased mRNA for all genes examined, whereas the inferior colliculus demonstrated mRNA induction for c-fos, c-jun, and NGFI-A. Immunohistochemical analysis revealed that elevations of IEG mRNA associated with the acute symptomatic stage were consistently translated into protein in the thalamus. In contrast, whereas elevated Fos- and Jun-like immunoreactivity were detected in the inferior colliculus at this stage, NGFI-A-like immunoreactivity declined significantly below basal levels, suggesting a translational block. These results are consistent with our recent findings of apoptotic cell death, and indicate that differential patterns of IEG expression occur in the thalamus and inferior colliculus during PTD, which may contribute to the pathogenesis of this disorder.

Expression of Ca2+-dependent (classical) PKC mRNA isoforms after transient cerebral ischemia in gerbil hippocampus

Cerebral ischemia is known to modify the expression of genetic information in the brain. To complement this knowledge, in the present study we have estimated the expression of calcium- and phospholipid-dependent (classical) protein kinase C (c PKC) isoform mRNAs (alpha, beta1 and gamma) at different time following ischemia. Forebrain cerebral ischemia was performed on Mongolian gerbils by 5 minutes bilateral occlusion of common carotid arteries. At the pointed time the cytoplasmic RNA was extracted from hippocampus and the expression of PKC mRNA quantified by RT PCR technique using GAPDH expression as an internal standard. Results indicate that only one gamma isoform of cPKC mRNA expression becomes significantly modified in postischemic hippocampus. A transient increase up to 145% of control within the first 3 h was followed by its decline to 60-65% at a longer recirculation period. This lowered levels returned back to control at 72 h postischemic recovery. This result indicates that gamma PKC could be particularly sensitive to ischemic insult and would react in accordance with the other early signals determining ischemic outcome.

Forebrain expression of c-fos due to active maternal behaviour in lactating rats

To reveal brain sites simultaneously active during the expression of maternal behaviour in lactating rats, we used immunocytochemical visualization of the nuclear protein product Fos of the immediate-early gene c-fos as a marker of neuronal activity. After a 48 h separation from their litter, day 7 postpartum dams received a 1 h period of physical interaction with pups either capable or incapable of suckling, inaccessible pups in a wire-mesh box, an empty box, or no stimulation. Physical interaction with pups elicited high levels of pronurturant maternal behaviour (retrieval, licking, mouthing), and suckling elicited nursing behaviour as well. Exposure to the box, with or without pups, elicited high levels of investigatory sniffing, self-grooming, and general activity. Distal stimulation from pups did not differentially activate Fos in any of 20 sites, including olfactory-processing structures such as the piriform cortex and medial amygdala. Physical interaction with pups, with or without suckling, elicited higher levels of Fos-immunoreactive nuclei than that of other conditions in numerous sites, including many previously implicated in maternal behaviour (medial preoptic nucleus, nucleus accumbens, lateral septum, lateral habenula, and the bed nucleus of the stria terminalis). Similar group patterns of Fos expression also occurred in sites not previously implicated in maternal behaviour (somatosensory cortex and paraventricular thalamic nucleus). Interaction with nonsuckling pups elicited the highest levels of Fos in the cortical amygdala, whereas suckling did not activate higher Fos than nonsuckling interaction in any site included in this report, including hypothalamic nuclei involved in lactation (paraventricular, supraoptic, and arcuate). There was little or no Fos in cingulate cortex, olfactory tubercle, medial septum, medial habenula, or ventromedial hypothalamus. These data suggest that trigeminal stimuli received by lactating rats during the performance of pronurturant maternal behaviour promote cellular activity resulting in neuronal expression of c-fos in many forebrain sites including the medial preoptic nucleus, several sites connected with it that are part of the mesotelencephalic dopamine system, and in the somatosensory cortex. In contrast, in these forebrain sites suckling does not elicit greater levels of Fos than that seen in nonsuckled rats and distal stimuli from pups are ineffective in increasing Fos levels compared with non-stimulated controls.

Expression of nuclear redox factor ref-1 in the rat hippocampus following global ischemia induced by cardiac arrest

The Ref-1 protein is a bifunctional nuclear enzyme involved in repair of DNA lesions and in redox regulation of DNA-binding activity of AP-1 family members, such as Fos and Jun transcription factors. In the present study, we demonstrate by in situ hybridization that transient global ischemia induced by cardiac arrest activates ref-1 mRNA expression in the granular cells of the rat dentate gyrus after 6 h and in CA1 pyramidal neurons of the hippocampus proper after 24 h, respectively. Immunohistochemical analysis revealed nuclear accumulation of Ref-1 protein in granular cells of the ischemia-resistant dentate gyrus, whereas Ref-1 protein expression progressively decreased in vulnerable CA1 neurons of the post-ischemic hippocampus from 24 h onwards. At the same time point, intense nuclear c-Jun immunoreactivity was observed in both neuronal cell populations. Our data suggest that oxidative stress induced by ischemia-reperfusion may increase neuronal ref-1 expression. However, inability of ref-1 mRNA translation and nuclear translocation of encoded protein in CA1 pyramidal neurons may inhibit repair of oxidative DNA damage or cellular adaptive responses leading to delayed neuronal cell death.

Odor exposure reveals non-uniform expression profiles of c-Jun protein in rat olfactory bulb neurons

In the main olfactory bulb, neurons are arranged strategically in distinct layers among which translaminar synaptic transmission can be made from the superficial, sensory to the deep, output layers that account for the processing of olfactory information. To search for stimulus-transcription coupling thought to be operated differentially in several cell types, c-Jun expression was examined immunohistochemically in rat olfactory bulb following 30-min odor stimulation with acetic acid and 1-butanol. c-Jun was rapidly induced in neuronal cell nuclei belonging to periglomerular, tufted, mitral and granule cells. The disappearance of c-Jun, however, differed between each cell type. In the glomerular layer, the glomeruli composed of c-Jun-expressing periglomerular cells were seen. Different odors led to labeling of different sets of glomeruli. The labeled periglomerular cells disappeared within 2 h. In all the deeper layers, however, a rather homogeneous label was noted for the tufted, mitral and granule cells present throughout the olfactory bulb, regardless of the difference in odor. In tufted and mitral cells, the c-Jun expression persisted for 4 days after odor stimulation. In the granule cell layer, numerous granule cells increased c-Jun immunoreactivity which lasted for 1 day following odor application. In control rats which were given clean air, the basal amount of c-Jun expression was seen confined to scattered granule cells. The results suggest that c-Jun is expressed in a variety of odorant-stimulated bulb neurons with a time course being dependent on cell type.

Effect of electrical stimulation of the cerebral cortex on the expression of the Fos protein in the basal ganglia

The protein Fos is a transcription factor which is quickly induced in response to a variety of extracellular signals. Since this protein is expressed in a variety of neuronal systems in response to activation of synaptic afferents, it has been suggested that it might contribute to activity-dependent plasticity in neural networks. The present study investigated the effect of cortical electrical stimulation on the expression of Fos in the basal ganglia in the rat, a group of structures that participate in sensorimotor learning. Results show that the repetitive application of electrical shocks in restricted areas of the cerebral cortex induces an expression of Fos mostly confined to the striatum and the subthalamic nucleus. The induction which can be elicited from different cortical areas (sensorimotor, auditory and limbic areas) does not require particular temporal patterns of stimulation but rather depends on the total number of shocks delivered during a given period of time. Moreover, it appears to be rather independent of the number of spikes discharged by the activated cells. In the striatum, the distribution of immunoreactive neurons is precisely delineated and conforms to the known topographical organization of stimulated corticostriatal projections. As demonstrated using a variety of double labelling techniques (combination of the immunocytochemical detection of Fos with the autoradiography of mu opioid receptors, calbindin immunocytochemistry, in situ hybridization of preproenkephalin and preprotachykinin A messenger RNAs), striatal neurons which express Fos are mostly localized in the matrix compartment and concern equally enkephaline and substance P containing efferent neurons. In the subthalamic nucleus, Fos expression evoked by cortical stimulation is also confined to discrete regions of the nucleus, the localizations corresponding to the primary projection site of the stimulated cortical cells. These results indicate that in addition to its phasic synaptic influence on the basal ganglia, the cerebral cortex could exert a long-term effect on the functional state of this system via a genomic control. Since the basal ganglia are involved in sensorimotor learning and motor habit formation, it is tempting to speculate that the activity-dependent Fos induction at corticostriatal and subthalamic synapses may contribute to consolidate the functionality of the neuronal networks activated during the completion of given motor tasks.

Expression of c-fos and c-jun mRNA following transient retinal ischemia: an approach using ligation of the retinal central artery in the rat

The expression of the proto-oncogenes c-fos and c-jun was examined by in situ hybridization at various timepoints following transient retinal ischemia by means of ligation of the retinal central artery in the rat. Ischemia of 90-minute duration resulted in the degeneration of neurons in both the ganglion cell layer and the inner nuclear layer at 48 hours after reperfusion. The expression of c-fos and c-jun messenger RNA throughout the entire inner nuclear layer was transiently coinduced following 90-minute retinal ischemia with a peak at 1 hour after reperfusion. This expression was also found in the ganglion cell layer at 3 hours after reperfusion. Weak signals for c-fos and c-jun mRNA were observed at 24 hours after reperfusion and returned to near control levels by 48 hours. c-jun protein expression was detected in the ganglion cell layer, the middle of the inner nuclear layer, and optic nerve head at 3 hours, but not 1 hour, after lethal ischemia/reperfusion; however, c-fos protein expression was not detected after reperfusion. Whereas no neuronal degenerative changes were found at 7 days after 30-minute ischemic retina, c-fos and c-jun messenger RNA were also induced at 1 hour postreperfusion. To our knowledge, this study is the first report to show expression patterns of immediate-early genes after retinal ischemia/reperfusion. These results suggest that changes in expression of c-fos and c-jun after transient retinal ischemia are similar to those after transient brain ischemia, and the selective occlusion of the central retinal artery will provide a useful model for studying ischemic neuronal degeneration in vivo in the rat retina.

Subarachnoid hemorrhage induces c-fos, c-jun and hsp70 mRNA expression in rat brain

To detect stress responses of the brain to subarachnoid hemorrhage (SAH), we investigated the expression of immediate early genes (IEGs) and hsp70 mRNA by in situ hybridization. Experimental SAH was produced in 49 rats by endovascular penetration. We also monitored the intracranial pressure (ICP) changes. The genes c-fos and c-jun were induced in the cerebral cortex, hippocampus and dentate gyrus in the penetrated side. mRNA coding for hsp70 was induced in the cerebral cortex, hippocampus, thalamus, hypothalamus and caudoputamen in the penetrated side and extended to the contralateral hemisphere. IEGs in the cerebral cortex were completely blocked by MK-801 pretreatment, but hsp70 mRNA was not. This suggests that the expression of IEGs correlates with spreading depression. The IEGs and hsp70 expression may reflect the severity of SAH impact and relate to the mechanisms of symptomatic vasospasm.

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.

In vivo hypoxia-induced neuronal damage in dentate gyrus of rat hippocampus: changes in NMDA receptors and the effect of MK-801

Hypoxia is a major cause of ischaemia-induced neuronal damage. In the present study, we examined the effects of in vivo hypoxia on N-methyl-D-aspartate receptors (NMDAR) in the rat hippocampus. This model of in vivo hypoxia involved placing rats in a hypoxic chamber containing 5% O2 and 95% N2 for 30 min. In the hippocampus, neuronal cells in the CA3, the hilus of the dentate gyrus and the dentate gyrus (DG) were damaged. In the CA1, which is known to be vulnerable to ischaemic damage, neuronal cells did not show hypoxia-induced damage. In vivo hypoxia-induced damage caused morphological changes in neuronal cells, such as shrunken, spindle or triangular shapes accompanied by pyknotic nuclei, but did not induce the loss of neuronal cells. On the other hand, the number of binding sites for [3H]-1-[1-(2-thienyl)cyclohexyl]-3,4-piperidine hydrochloride (TCP) gradually decreased on and after 7 days, and then maximally decreased by 25% at 21 days after hypoxia. The number of NMDAR1-immunopositive cells was decreased by 22% in the DG, but was unchanged in the CA3. Furthermore, we examined the effect of a non-competitive NMDA antagonist, (+)-5-methyl-10, 11-dihydro-5H-dibenzo[a,b] cyclohepten-5,10-imine hydrogen maleate (MK-801), on against in vivo hypoxia. The administration of MK-801 (3 mg/kg, i.p.), 30 min before hypoxia treatment, partly protected against neuronal damage in the DG, but not in the CA3. These results suggest that hypoxia-induced neuronal damage in the DG involves, in part, the activation of NMDAR.

NMDA receptor overstimulation triggers a prolonged wave of immediate early gene expression: relationship to excitotoxicity

Exposure of the rodent striatum to quinolinic acid (QA, N-methyl-D-aspartate receptor agonist) induces immediate early gene (IEG; c-fos, c-jun, jun-B, zif/268) expression that may extend 12-24 h after injection. In order to determine the specificity of the prolonged IEG response to the QA injection, the temporal pattern of c-fos mRNA expression was examined during the first 4 h after administration of saline or QA (40 micrograms). As early as 30 min after intrastriatal injection, both saline and QA increased c-fos mRNA levels. In the saline group, this increase in IEG expression was only transient and returned to baseline by 1 h. In contrast, c-fos mRNA levels within QA-injected animals continued to rise significantly at 1 and 4 h. In a second experiment, rats received 4 ng to 40-micrograms injections of QA followed by sacrifice at 6 h to determine if increasing QA doses caused the appearance of the prolonged IEG response phase. The prolonged IEG response was evident at 6 h only in animal groups that received higher dose ranges (4-40 micrograms) of QA. A final experiment was undertaken to determine if blockage of NMDA receptor stimulation would also inhibit the prolonged IEG response at 6 h in relationship to neuronal sparing evidenced at 24 h post-QA injection. The NMDA receptor antagonist, MK-801, blocked the prolonged IEG response at 6 h following QA (40 micrograms) injection while also preventing striatal neuropeptide mRNA decline by 24 h. Delaying the MK-801 administration for 1-2 h post-QA injection revealed that the intensity of the prolonged IEG mRNA response may be predictive of neuronal demise within the QA lesion site. These results suggest that prolonged IEG expression is associated with QA excitotoxicity of the rodent striatum and subsequent neuronal degeneration.

At least three neurotransmitter systems mediate a stress-induced increase in c-fos mRNA in different rat brain areas

1. Protooncogene c-fos mRNA levels were determined in the rat cerebral cortex, hippocampus, and cerebellum after exposure to a combined forced swimming and confinement stress. The stress resulted in an increase in c-fos mRNA levels in all three brain areas. 2. In an effort to elucidate the neurotransmitter systems involved in this stress-induced increase, animals were injected, prior to exposure to the stress, with either diazepam, MK-801, or propranolol. 3. In both the cerebral cortex and the hippocampus the stress-induced increase in c-fos mRNA was inhibited by MK-801, suggesting that it is mediated via NMDA receptors. In the hippocampus, propranolol had a similar effect, indicating that beta-adrenergic receptors are also involved in the stress-induced increase in c-fos mRNA. 4. On the other hand, the increase in c-fos mRNA produced by the stress of the injection was inhibited in the cerebral cortex by diazepam or propranolol and in the hippocampus only by diazepam. Furthermore, administration of MK-801 resulted in an increase in c-fos mRNA in the hippocampus of the nonstressed animals. In the cerebellum no one of the three drugs employed affected c-fos mRNA levels in either stressed or nonstressed animals. 5. Our results thus show that various forms of stress activate, in different brain areas, neurons with either NMDA, beta-adrenergic, and/or GABA-A receptors.

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.

Prolongation and enhancement of postischemic c-fos expression after fasting

BACKGROUND AND PURPOSE

A rapid but transient expression of c-fos after cerebral ischemia has been extensively documented. However, the mechanism of this induction and whether induction of c-fos is neuroprotective or detrimental to the brain after ischemia is presently not clear. Fasting before transient cerebral ischemia has been shown to reduce delayed neuronal necrosis and infarct volume. The purpose of the present study was to examine the effect of preischemic fasting for 24 hours on the expression of c-fos after transient focal cerebral ischemia.

METHODS

Focal cerebral ischemia was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries for 60 minutes. Male Long-Evans rats weighting 250 to 300 g were randomly divided into two groups: fed (control group) and food deprived for 24 hours (fasted group) before ischemic surgery. Infarct volumes were measured on the basis of triphenyltetrazolium chloride-delineated infarct areas, and plasma glucose levels were determined by the glucose oxidase method. Temporal and spatial expression of c-fos was assessed by Northern blot analysis, in situ hybridization, and immunohistochemistry.

RESULTS

Fasting for 24 hours before 60 minutes of ischemia resulted in a 26.6% decrease in preischemic plasma glucose levels and a 74.5% reduction in infarct volumes in the fasted group compared with the control group. A rapid but transient induction of c-fos mRNA was observed in the ischemic cortex in control animals after 60 minutes of ischemia. Fasting not only prolonged but also enhanced the intensity of c-fos expression in the ischemic cortex. Regional c-fos expression was also different between these two groups.

CONCLUSIONS

The results support the contention that c-fos expression may be compatible with its purported neuroprotective role in selected experimental paradigms. The signaling mechanisms underlying the effect of fasting and subsequent lowering of plasma glucose levels on postischemic c-fos expression remain to be explored.

The anti-craving drug acamprosate reduces c-fos expression in rats undergoing ethanol withdrawal

Acamprosate (Ca salt of N-acetylhomotaurine) is a novel anti-craving substance which a double-blind placebo-controlled study has proven to be therapeutically useful in the prevention of relapses in weaned alcoholics. In the present study the expression of the immediate-early gene c-fos in rat hippocampal and cerebellar neurons was used to monitor the modulatory effect of acamprosate on neuronal excitability during ethanol withdrawal. Several hybridization techniques were employed to investigate the effect of acamprosate on c-fos expression. Acamprosate (200 mg/kg; intraperitoneally) reduced the elevated c-fos mRNA levels in the hippocampus and the cerebellum following 24 h of ethanol withdrawal, or the application of the convulsant pentylenetetrazole. The effect of ethanol withdrawal on c-fos expression was more pronounced in the cerebellum than in the hippocampus. In the hippocampus (CA1) and the cerebellum acamprosate alone induced a significant increase in c-fos expression in drug-naive animals. Only in the hippocampus did co-administration of pentylenetetrazole during ethanol withdrawal induce a further increase in c-fos expression. The present findings support the notion that acamprosate elicits its preventive effect on relapse by reducing the hyperexcitability of central neurons during withdrawal, following long-term ethanol consumption.

Differential effects of haloperidol and two anxiolytic drugs, buspirone and lesopitron, on c-Fos expression in the rat striatum and nucleus accumbens

We have studied the effects of the neuroleptic haloperidol and the non-benzodiazepine anxiolytics buspirone and lesopitron on the expression of c-Fos immunoreactivity in the rat forebrain. Haloperidol and buspirone administration resulted in a significant quantitative increase in the number of Fos-immunoreactive neurons in the lateral striatum and a presumable qualitative increase in the nucleus accumbens. In contrast, lesopitron did not lead to a significant increase in the c-Fos expression in the striatum. The induction of c-Fos immunoreactivity by buspirone is compatible with an interaction of this compound with D2 dopamine receptors, as documented for haloperidol. The lack of effects after lesopitron administration suggests that, in contrast with buspirone, this compound has no dopaminergic blocking activity.

Expression of c-fos and fos-B proteins following transient forebrain ischemia: effect of hypothermia

Immediate early genes are induced by transient global ischemia. Using immunohistochemistry we studied the effect of intraischemic hypothermia (30 degrees C) on the expression of c-fos and fos-B proteins following 10 min forebrain ischemia in the gerbil. Postischemia (PI) periods of 1 hour (h), 6 h, 1 day (d) and 2 d and nonischemic controls were examined in normothermic and hypothermic brains. In normothermic ischemic brains, marked expression of c-fos occurred in the dentate gyrus after 1 h PI which extended to CA2-4 regions by 6 h. Hypothermia hastened the time course of c-fos expression as it was expressed simultaneously in the dentate gyrus as well as CA2-4 regions after only 1 h, and by 6 h the expression remained only in the CA2-4 regions and not the dentate gyrus in hypothermic ischemic brains. There was no difference in its expression between normothermic and hypothermic brains in the 1 d and 2 d PI animals. Somewhat similar changes were noted in fos-B expression. In normothermic ischemic brains fos-B was induced in the dentate gyrus by 1 h PI, and by 6 h it extended to involve CA1-4 cells. The hypothermic ischemic brains showed faster induction of fos-B so that the dentate gyrus as well as CA1-4 regions were immunopositive at 1 h PI. There was no difference in its expression between normothermic and hypothermic brains in the subsequent PI periods of 6 h, 1 d and 2 d. The shift towards faster sequential induction of these genes by hypothermia in ischemic brains may be indicative of preservation of or faster recovery of mechanisms involved in intracellular signalling.

Disturbances of calcium homeostasis within the endoplasmic reticulum may contribute to the development of ischemic-cell damage

It is widely accepted that disturbances of calcium homeostasis play a key role in the development of cell damage produced by transient cerebral ischemia. It is believed that the sharp increase in cytosolic calcium activity during ischemia activates a cascade of calcium-dependent metabolic processes which ultimately destroy the integrity of the cell. However, it has never been taken into account that ischemic cell damage may, at least in part, be caused by a disturbance of calcium homeostasis within the endoplasmic reticulum after transient cerebral ischemia. In fact, depletion of the endoplasmic reticulum from calcium induces metabolic changes resembling, in many respects, those produced by transient cerebral ischemia: it causes an inhibition of the activity of the eucaryotic initiation factor elF-2 alpha (by phosphorylation), a disaggregation of polyribosomes and thus an inhibition of global protein synthesis, and an increased expression of certain genes such as transcription factors (c-fos and c-jun) and the glucose-related protein grp78. Finally, a depletion of calcium in the endoplasmic reticulum induces tissue damage within the brain and triggers apoptosis in neuronal and non-neuronal cells. It is therefore concluded that cell damage induced by transient ischemia may, at least in part, be caused by a disturbance of calcium homeostasis within the endoplasmic reticulum.

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.

PRL-1, a protein tyrosine phosphatase, is expressed in neurons and oligodendrocytes in the brain and induced in the cerebral cortex following transient forebrain ischemia

Protein tyrosine phosphorylation is thought to play an important role in the regulation of neural function. We reported previously that CL100, a cytoplasmic type protein tyrosine phosphatase (PTP), was induced after transient forebrain ischemia. In the present study, changes in the mRNA levels after ischemia of PRL-1, a cytoplasmic type PTP and immediate-early gene similar to CL100, was examined. In situ hybridization histochemistry showed that PRL-1 mRNA was expressed in normal adult rats in neurons and oligodendrocytes in widespread regions including the cerebral cortex, hippocampus and cerebellum. PRL-1 mRNA was expressed in the developing brains on embryonic days 15 and 19 and postnatal day 1. Northern blot analysis showed that PRL-1 mRNA was induced from 6 h to 9 h after reperfusion in the cerebral cortex of postischemic rats. These findings suggest that PRL-1 plays a role in neurons and oliogodendrocytes, and that expression of PRL-1 mRNA is regulated by a mechanism different from those of other immediate-early genes such as c-fos and c-jun.

Global ischemia induces immediate-early genes encoding zinc finger transcription factors

Ischemia induces immediate-early genes (IEGs) in brain. Since prolonged expression of some IEGs may precede neuronal death, some researchers have suggested that these IEGs mediate neuronal death. We therefore examined the effect of 5 and 10 min of global ischemia on the expression of the IEGs NGFI-A, NGFI-B, NGFI-C, egr-2, egr-3, and Nurr1 in gerbil brain. All of the IEGs were induced after 30 min of reperfusion in the hippocampus. Most of them were induced in several other regions as well, including cortex, hypothalamus, thalamus, and amygdala. The acute IEG induction decreased in most brain areas by 2-6 h. However, at 24 h following 5 min of ischemia NGFI-A continued to be expressed in the CA1 region and dentate gyrus. In the dentate gyrus, NGFI-C continued to be expressed for 24 h and egr-3 for as long as 72 h. In other brain areas, all of the IEGs returned to control levels by 72 h except in CA1, where most messenger RNA (mRNA) levels were decreased; this decrease correlated with marked neuronal loss. The persistent expression of NGFI-A in CA1 neurons destined to die and the persistent expression of NGFI-A, NGFI-C, and egr-3 genes in dentate granule cell neurons that survive may indicate that some transcription factors modulate cell death whereas others support cell survival when expressed for prolonged periods. The protein products of several transcription factors, including c-fos, are known to downregulate their own expression. The persistent expression of NGFI-A in the CA1 neurons destined to die could therefore be due to ischemia-induced transcriptional activation caused by, e.g., increased intracellular calcium levels plus a lack of negative feedback caused by the blockade of the translation of NGFI-A mRNA into protein.

Cyclin D1 messenger RNA is induced in microglia rather than neurons following transient forebrain ischaemia

Following 30 min of forebrain ischaemia in the rat, delayed neuronal death occurs in the CA1 sector of the hippocampus within two to three days, whereas neurons in other selectively vulnerable regions, such as the dorsolateral striatum, die within 6-12 h. In this study, we investigated cyclin D1 expression, which codes for a regulatory protein in cell cycle regulation, but it is also induced in sympathetic neurons undergoing programmed cell death. Cyclin D1 messenger RNA could not be detected by in situ hybridization techniques in brains of control rats, but was found at one and two days after ischaemia in regions of the dorsolateral striatum with neuronal degeneration. DNA fragmentation in this region, identified by the terminal transferase biotinylated-UTP nick end labelling (TUNEL) procedure, was observed from 6 h after ischaemia onward. In the hippocampus, increased levels of cyclin D1 messenger RNA were found at two and three days after ischaemia in the striatum pyramidale of the CA1 sector. This expression was associated with the occurrence of neuronal damage and TUNEL-stained neurons. By seven days cyclin D1 messenger RNA was found in hardly any brain structure. There was no temporospatial overlap of cyclin D1 expression with the expression of the immediate-early genes c-fos, c-jun, and mkp-1, a result which is clearly distinct from findings in sympathetic ganglion neurons undergoing programmed cell death. These results do not suggest a role for cyclin D1 in neuronal cell death following transient forebrain ischaemia. The similarity of the cyclin D1 expression profile with that of the microglia-specific CR3 complement receptor beta-subunit messenger RNA, and the results of combined in situ hybridization and microglia-specific immunohistochemistry suggest that microglia are the source of cyclin D1 messenger RNA in the postischaemic brain. Since cyclin D1 codes for a critical regulatory protein for progression of the G0 to G1 phase in the cell cycle and we did not observe prominent occurrence of DNA fragmentation in microglial cells in the hippocampus at time points when cyclin D1 messenger RNA was found, we suggest that cyclin D1 induction is involved in the onset of microglial cell proliferation.

Selective c-Jun overexpression is associated with ionizing radiation-induced apoptosis in the developing cerebellum of the rat

Immunohistochemistry to Bcl-2, Bax, c-Myc, c-Fos, Fos-related, c-Jun, Jun B and Jun D was used to study the involvement of these factors in ionizing radiation-induced apoptosis in the cerebellum of the developing rat. Selective c-Jun overexpression was observed during the whole process of radiation-induced cell death. Furthermore, c-Jun overexpression was restricted to apoptotic cells, as shown by double labeling with the method of in situ labeling of nuclear DNA fragmentation and c-Jun immunohistochemistry. This is the first in vivo evidence that selective c-Jun overexpression is associated with apoptotic cell death in the developing nervous system following ionizing radiation.

Evidence for apoptotic cell death in the choroid plexus following focal cerebral ischemia

Focal cerebral ischemia in rats subjected to middle cerebral artery (MCA) occlusion results in apoptotic DNA fragmentation and activation of putative cell death effector genes in neurons and functional impairment of the plexus choroideus. In the present study we investigated whether cerebral ischemia may induce apoptotic cell death in the choroid plexus. Using in situ end-labeling by terminal transferase and fluorescein-dUTP, nuclear DNA breaks were detected in the choroid plexus of the lateral ventricle of the ischemic hemisphere after 6 h but not after 1.5 h of MCA occlusion. Intense cytoplasmic immunostaining for pro-apoptotic Bax protein and moderate immunolabeling for Bcl-X was observed in the epithelium of the choroid plexus of the lateral and third ventricles. However, constitutive expression of Bax and Bcl-X proteins in the plexus choroideus did not change significantly following focal ischemia. Thus, cells of the choroid plexus may die by apoptosis after several hours of cerebral ischemia. Modulation of cell death effector genes of the bcl-2 family however, may not be required for apoptotic cell death to occur.

Ontogenetic differences in energy metabolism and inhibition of protein synthesis in hippocampal slices during in vitro ischemia and 24 h of recovery

The present study was designed to clarify whether ontogenetic differences in the vulnerability of the brain towards hypoxic-ischemic insults are only caused by the low cerebral energy demand of immature animals or whether there are additional mechanisms, such as protein synthesis (PSR), that may be involved in this phenomenon. We therefore measured tissue levels of adenylates and PSR in hippocampal slices from immature (E40) and mature (E60) guinea pigs fetuses and from adult guinea pigs during in vitro ischemia and 24 h of recovery using a recently modified method. Hippocampal slices were incubated in a temperature controlled flow-through chamber, gassed with 95% O2/5% CO2. In vitro ischemia was induced by transferring slices to a glucose-free artificial cerebrospinal fluid (aCSF) equilibrated with 95% N2/5% CO2. The duration of ischemia ranged from 10 to 40 min. Adenylates were measured by HPLC after extraction with perchloric acid. PSR was evaluated as the incorporation rate of [14C]leucine into proteins. Under control conditions, tissue levels in adenylates did not change, whereas PSR increased slightly in hippocampal slices from mature fetuses and adult animals during a 24-h control incubation period. In slices from immature fetuses ATP levels were only maintained for 2 h. During in vitro ischemia the decline in ATP, total adenylate pool, and adenylate energy charge was much slower in slices from immature fetuses than in slices from mature fetuses or adults. After in vitro ischemia, ATP and the total adenylate pool did not completely recover in mature fetuses and adults, whereas adenylate energy charge almost returned to control values independently of the developmental stage. Two hours after in vitro ischemia PSR was undisturbed in slices from immature fetuses, but severely inhibited in slices from mature fetuses and adults. With ongoing recovery, PSR in mature fetuses returned to control values, while in adults it was still inhibited even 24 h after in vitro ischemia. From these results we conclude that hippocampal slices prepared from mature guinea pig fetuses as well as from adult guinea pigs can be held metabolically stable during long-term incubation using a recently modified technique. However, in slices from immature fetuses a stable energy state could not be maintained for more than 2 h. We further conclude that postischemic disturbances in PSR closely reflect the ontogenetic changes in the vulnerability of the brain to ischemia and that low energy metabolism is certainly not the only cause of the increased vulnerability of the fetal brain to ischemia.

Ischemia and lesion induced imbalances in cortical function

Cortical structures are often critically affected by ischemic and traumatic lesions which may cause transient or permanent functional disturbances. These disorders consist of changes in the membrane properties of single cells and alterations in synaptic network interactions within and between cortical areas including large-scale reorganizations in the representation of the peripheral input. Prominent functional modifications consisting of massive membrane depolarizations, suppression of intracortical inhibitory synaptic mechanisms and enhancement of excitatory synaptic transmission can be observed within a few minutes following the onset of cortical hypoxia or ischemia and probably represent the trigger signals for the induction of neuronal hyperexcitability, irreversible cellular dysfunction and cell death. Pharmacological manipulation of these early events may therefore be the most effective approach to control ischemia and lesion induced disturbances and to attenuate long-term neurological deficits. The complexity of secondary structural and functional alterations in cortical and subcortical structures demands an early and powerful intervention before neuronal damage expands to intact regions. The unsatisfactory clinical experience with calcium and N-methyl-D-aspartate antagonists suggests that this result might be achieved with compounds that show a broad spectrum of actions at different ligand-activated receptors, voltage-dependent channels and that also act at the vascular system. Whether the same therapy strategies developed for the treatment of ischemic injury in the adult brain may be applied for the immature cortex is questionable, since young cortical networks with a high degree of synaptic plasticity reveal a different response pattern to hypoxic and ischemic insults. Age-dependent molecular biological, morphological and physiological parameters contribute to an enhanced susceptibility of the immature brain to these noxae during early ontogenesis and have to be investigated in more detail for the development of adequate clinical therapy.

Molecular correlates of delayed neuronal death following transient forebrain ischemia in the rat

Following transient forebrain ischemia selective and delayed neuronal degeneration occurs in the CA1 sector of the hippocampus. It is presently unclear whether this cell death is related to programmed cell death (PCD), which occurs in neurons during development of the CNS. Recently, the expression of various genes, such as c-fos, c-jun mkp-1, cyclin D1, and hsp70 was found to be associated with PCD in model systems. We and others have described that these genes are also upregulated in the hippocampus following ischemia. Most notably, c-fos, c-jun, and hsp70 are expressed specifically in CA1 neurons at survival times shortly preceding cell degeneration in rat models of global ischemia. In addition, the gene products could be detected by immunohistochemical methods, despite a general impairment of protein synthesis. These finding are especially relevant, since recent report suggests a functional role for Fos family proteins and c-jun in PCD in neurons of the superior cervical ganglion. These results could be indicative for the occurrence of a PCD-related program in CA1 neurons ad corroborate several other lines of evidences, such as occurrence of DNA fragmentation. Clearly, further studies are necessary to elucidate the functional role of the gene inductions following ischemia in vivo.

Heat-shock protein and C-fos expression in focal microvascular brain damage

Cortical brain damage was produced in rats by a focal pulse from a Nd-YAG laser, and evolution of the lesion was evaluated at 30 min, and 2, 8, and 24 h with respect to microvascular perfusion, blood-brain barrier (BBB) permeability, and expression of both the heat-shock/stress protein, hsp72, and the c-fos proto-oncogene transcription factor. A double-labeling fluorescence technique employing intravenously injected Evans blue albumin (EBA) and fluorescein-labeled dextran was used to map and measure BBB damage and microvascular perfusion in fresh frozen brain sections. Hsp72 and c-fos mRNAs were localized by in situ hybridization, and the respective proteins were identified by immunocytochemistry. Parallel sections were stained for glial fibrillary acidic protein and for routine histologic examination. Striking hsp72 mRNA expression was evident by 2 h in an approximately 300 microns wide rim surrounding an area of expanding BBB damage. Increased hsp72 mRNA was observed only in regions of preserved microcirculation, where the hsp72 protein was subsequently localized exclusively in the vasculature at 24 h after the insult. Hsp72-positive endothelial cells spanned the narrow margin between the lesion and histologically normal, glial fibrillary acidic protein (GFAP)-positive cortical tissue. There was no hsp72 expression in the area of subcortically migrating edema fluid. Inductions of c-fos mRNA and Fos protein were not strikingly evident around the focal brain lesion, but were observed transiently throughout the injured hemisphere at 30 min and 2.5 h, respectively, indicating that spreading depression was triggered by the focal injury. These results are in striking contrast to those previously obtained from studies of models of focal ischemic or traumatic brain injury, which are characterized by a complex pattern of glial and neuronal hsp72 expression in the periphery of an infarct, and which suggest that the tightly demarcated lesion produced by the Nd-YAG laser lacks these components of graded injury that are evident following other types of focal brain damage.

Deafferentiation-induced c-fos gene expression in subthalamic nucleus and substantia nigra reticulata is reduced by non-NMDA receptor antagonist

Molecular events underlying the mechanism by which brain injury elicits delayed transneuronal degeneration of neurons remote from the site of initial injury are not well understood. In rats, acute injury of the caudate nucleus (CN) and globus pallidus (GP) by local injection of excitotoxic ibotenic acid (IA) or by transient forebrain ischemia resulted in delayed cell death of neurons in the substantia nigra reticulata (SNr). To elucidate the involvement of glutamate receptor mediated hyperactivity of neurons produced by loss of inhibitory inputs in this delayed degeneration of SNr neurons, the region-specific expression of an immediate early gene, c-fos, and the effect of glutamate receptor antagonists on the c-fos expression were examined by using immunocytochemical and in situ hybridization analysis. Following unilateral IA-injection into the CN and GP, a robust expression of c-fos mRNA and Fos protein was induced specifically in neurons of both subthalamic nucleus (STN) and SNr deafferented by the IA-lesions 36 h after IA-injection. The delayed expression of Fos-protein in SNr neurons lasted for 48 h longer than that in STN neurons. Following unilateral IA-injection confined to the CN, an intense but short-term expression of Fos-protein was exhibited only in neurons of the deafferented SNr. c-fos mRNA and Fos protein were not expressed in neurons of the substantia nigra compacta at any time points examined. The induction of c-fos mRNA and Fos protein in neurons of the STN and SNr following IA-lesions of the CN and GP was reduced markedly by non-NMDA receptor antagonist (GYKI52466), but not by NMDA receptor antagonist (MK-801). The region-specific c-fos expression implies that deprivation of inhibitory afferents (disinhibition) due to destruction of presynaptic neurons can induce increased activity of postsynaptic neurons. The effect of GYKI52466 on the c-fos gene expression in neurons of the deafferented STN and SNr suggests that activation of non-NMDA receptors may be involved in a pathophysiological cascade for the transneuronal degeneration of SNr neurons.

Age-related changes in composition of transcription factor, AP-1 complex in the rat brain

We examined age-related changes in composition of transcription factor, activator protein-1 (AP-1) which binds to TPA responsive element (TRE) in the non-stimulated rat brain, using electrophoretic mobility-shift assay with immunodepletion/supershift assay. The total TRE-binding activity in the frontal cortex and the hippocampus of the aged rats markedly decreased to 66% and 43%, respectively, and TRE-bindings of AP-1 in both regions also decreased to 82% and 66%, respectively, with aging. Jun-Jun dimers accounted for approximately half of the total TRE-bindings and 80-90% of the AP-1 bindings, while there were fewer Fos-Jun dimers, in both examined regions of the non-stimulated adult. The proportion of active Fos-Jun heterodimers in the frontal cortex increased to up to half of the AP-1 bindings in the aged rats, indicating that cortical AP-1-related transcription may increase with aging even under the non-stimulated condition. In the hippocampus, inactive Jun-Jun homodimers became predominant in AP-1 with aging. This regional diversity of age-related changes in the composition of AP-1 in the brain may be related to changes or dysfunction in neuronal signal transduction in the aged.

Homolateral cerebrocortical changes in neuropeptide and receptor expression after minimal cortical infarction

A cortical infarct of 2 mm diameter was obtained in the parietal cortex after a craniotomy, disruption of the dura mater and topical application of 3 M KCl. It has been shown previously that the presence of a small cortical infarct induces an increase in immediate early gene messenger RNA expression followed by an increase in neuropeptide and glutamic acid decarboxylase messenger RNA expression. Glutamate, acting at N-methyl-D-aspartate receptors, is held responsible for these changes, since they are blocked by pretreatment with dizocilpine. In the present study, we have analysed the consequences of the dramatic changes in messenger RNA expression on the level of immediate early gene products c-fos and zif 268, and on that of neuropeptides by using immunohistochemistry. After just 1 h, an increase in c-fos- and zif 268-like immunoreactivity is observed in the entire cortical hemisphere homolateral to the infarct, and is no longer detected after 6 h. An increase in cholecystokinin octapeptide-, substance P-, neuropeptide Y- and somatostatin-like immunoreactivity is observed in the entire cortical hemisphere homolateral to the infarct after three days, and is no longer detected after 30 days. To investigate if these dramatic increases in neuropeptide immunoreactivities may have functional consequences, we studied the level of cholecystokinin receptors by autoradiographic binding using [125I]cholecystokinin-8S and in situ hybridization for the detection of cholecystokinin-b receptor messenger RNA. A decrease in cholecystokinin binding sites and cholecystokinin-b receptor messenger RNA is observed in the entire cortical hemisphere homolateral to the infarct after three days, and is no longer detected after nine days. This study shows that a topical stimulation has diffuse effects, reaching regions far from the site of the lesion, and some of them are still strongly present after nine days. The increase in neuropeptide messenger RNAs is followed by an increase in the protein products of these genes, which may modify the neurotransmission. As a corollary to this, a decrease in cholecystokinin binding sites occurs. This may have further consequences on signal transduction pathways. This decrease in cholecystokinin binding sites is associated with a decrease in the cholecystokinin-b receptor messenger RNA, and this is the first example of a decrease in messenger RNA levels in this experimental model.

c-fos and HSP70 gene expression in rat brains in high gravitation-induced cerebral ischemia

Previous studies have shown that brief exposures of rodents to high gravitational forces (+Gz) in a specifically designed centrifuge cause global cerebral ischemia. In the present study, the effect of +Gz exposure to +22.5Gz for 15 to 60 s on c-fos and HSP70 gene expression was examined. Northern and RT-PCR analyses to total RNA isolated from brains of rats in different post-exposure times revealed a significant, time-dependent increase in the c-fos mRNA level which returned to near normal by 180 min. The HSP70 mRNA level was increased two-fold at 30 min post exposure, and remained elevated until 180 min. The transient stimulation of c-fos and HSP70 gene expression should serve as useful biomarkers for hypergravic stress on the brain. The present results should aid in design of future experiments in our understanding of the pathophysiology of the high +Gz challenges.

Biphasic expression of the fos and jun families of transcription factors following transient forebrain ischaemia in the rat. Effect of hypothermia

Transient global ischaemia induces the expression of immediate early genes. Using in situ hybridization, the expression of c-fos, fosB, fra-1, fra-2, c-jun and junB was studied after 15 min of normothermic and hypothermic (33 degrees C) transient forebrain ischaemia in the rat, induced by common carotid occlusion combined with systemic hypotension. Two phases of induction of the immediate early genes were observed. The early phase, peaking at 1-2 h of reperfusion, was dominated by marked expression in the dentate gyrus. The second phase, with maximal expression at 12-36 h of reperfusion, was observed particularly in the vulnerable CA1 and CA3 regions. Hypothermia increased the early induction of one of the genes studied, signifying a differential effect of hypothermia upon the signal transduction mechanisms activating these genes. The late induction occurred earlier after hypothermic than after normothermic ischaemia. The early expression of immediate early genes is due to the rapid activation of cytosolic response elements caused by the ischaemic insult. We suggest that the late induction is a stress signal for activation of repair processes, analogous to the cellular response seen after UV light-induced DNA damage. The relatively fast induction of the immediate early genes following hypothermic ischaemia may reflect a faster resumption of normal intracellular signalling, enhancing neuronal recovery.

Amino acid uptake in ischemically compromised brain tissue

BACKGROUND AND PURPOSE

Multitracer positron emission tomography (PET) was used to investigate local amino acid accumulation in brain tissue surrounding focal ischemia.

METHODS

PET using 15O-labeled oxygen and water for measuring cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF), C15O for determination of blood volume (CBV) and calculation of oxygen extraction fraction, and L-[11C]methylmethionine (11C-MET) for the assessment of amino acid accumulation was applied in 14 patients (mean age, 52 +/- 9.1 years) with acute ischemic hemispheric stroke. Two multitracer PET studies were completed, the first 8 to 24 hours after onset of neurological symptoms and the follow-up study 14 +/- 1 days after the ischemic attack. Functional changes were compared with morphological damage on cranial CT or MRI. Three-dimensional matching and volume of interest evaluation procedures were used to study 11C-MET accumulation in relation to various physiological variables in infarcted and noninfarcted tissue.

RESULTS

Compared with contralateral mirror regions, initially increased regional 11C-MET uptake (21.2 +/- 10.9%, P < .001) was found in patchy areas in the immediate vicinity of infarction as well as in distant areas within the same hemisphere. In those areas, regional CBF (-11.4 +/- 21.2%, P < .01) and oxygen extraction fraction (2.8 +/- 29.1%, P = NS) were highly variable, and regional CMRO2 was preserved or slightly reduced (-12.4 +/- 16.0%, P < .001). CBF data comprised severely ischemic as well as high values (14.6 to 64.2 mL/100 g per minute). Cranial CT and coregistered MRI in five patients demonstrated preserved morphology. In all peri-infarct areas (n = 62), the 11C-MET uptake showed a positive correlation with delta CMRO2 as the relative improvement of ipsilateral CMRO2 between the two PET studies (r = .378, P < .01). Particularly in areas with increased oxygen extraction fraction (n = 42), the 11C-MET uptake showed a mild correlation with CMRO2 at follow-up measurement (r = .31, P < .05). In all peri-infarct areas, 11C-MET uptake showed a negative correlation with oxygen extraction fraction (r = -.672, P < .001) and a positive correlation with CBF (r = .4, P = .001). In all infarcted and peri-infarct areas, normalized initial 11C-MET uptake was positively correlated with CMRO2 at follow-up (r = .603, P < .001).

CONCLUSIONS

Focal increases of 11C-MET uptake seen in this study were generally mild. They might be seen in the core of ischemia, indicating breakdown of the blood-brain barrier with poor tissue prognosis, but they also frequently occurred during or after ischemic compromise in surviving brain tissue surrounding focal cerebral infarction, perhaps representing alterations of amino acid transport or protein synthesis in brain tissue with a favorable prognosis.

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.

Cellular responses to experimental brain injury

Little is known regarding the molecular (genomic) events associated with the pathophysiology of traumatic brain injury (TBI). This review focusses on the experimental efforts to date elucidating the acute alterations in expression of immediate early genes (IEGs), heat shock proteins (HSPs) and cytokines following experimental brain injury. The immediate early genes, c-fos, c-jun and junB were observed to be bilaterally induced in the cortex and hippocampus as early as 5 min following lateral fluid-percussion (FP) brain injury in the rat. While levels of c-fos and junB mRNA returned to control levels by 2h, c-jun mRNA remained elevated up to 6h post-injury. Increased levels of mRNA for the inducible heat-shock protein (hsp72) were observed up to 12h following injury and were restricted to the cortex ipsilateral to the impact site. Mild induction of the glucose-regulated proteins (grp78 and grp94), which share sequence homology with hsp72, was apparent in the ipsilateral cortex. The cytokines IL-1 beta and TNF alpha were induced at 1h following FP brain injury and remained elevated up to 6h post-injury. These data, while indicative of the complex genomic response to TBI, are also suggestive of the trauma-induced activation of multiple signal transduction pathways.

Differential time courses of c-fos mRNA expression in hippocampal subfields following acquisition and recall testing in mice

Spatio-temporal patterns of c-fos mRNA expression were studied in the mouse brain following the partial acquisition of an appetitive conditioning task in a Skinner box. We used two experimental situations: during the initial acquisition of the task (acquisition paradigm) and during the retention test (recall paradigm). In both paradigms the in situ hybridization signal was exclusively located in the hippocampal formation and the posterior cingulate cortex. However, the time-dependent pattern of expression was quite different according to the experimental situation: mRNA levels peaked at 90 min post-test in both paradigms but returned to basal (control) level by 180 min in the acquisition group, while in CA3 and DG subfields, high levels of mRNA expression were maintained at 180 min in the recall group. Taken together these results suggest that the IEG c-fos is implicated in the different phases of post-acquisition memory processes and involve a differential spatio-temporal regulation of its expression in hippocampal subfields.

Induction of c-fos and c-jun gene products and heat shock protein after brief and prolonged cerebral ischemia in gerbils

BACKGROUND AND PURPOSE

Proto-oncogene activation and induction of heat shock protein (HSP) occur in response to various stimuli to brain, but the role in neuronal survival after cerebral ischemia remains uncertain. We compared the extent of insults and induction of c-fos and c-jun gene products (c-FOS and c-JUN) as well as HSP in ischemic and postischemic gerbil brains immunohistochemically.

METHODS

Common carotid arteries of Mongolian gerbils were occluded for 5 or 15 minutes and recirculated for 0 minutes to 7 days. Antibodies for c-FOS, c-JUN, and HSP 70 were used for immunohistochemistry, and positive reactions were semiquantitatively analyzed. The presence of ischemic and postischemic lesions was ascertained with an antibody for microtubule-associated proteins.

RESULTS

After ischemia for 15 minutes and reperfusion, c-FOS was induced promptly after 1 to 6 hours in pyramidal cells of the CA3 and CA4 regions, while c-JUN became visible in the same areas after recirculation for 4 to 48 hours. HSP 70 was detected after recirculation for 24 hours in the CA3 region. In layers I and II of the cerebral cortex, c-FOS and c-JUN peaked at 3 hours and HSP 70 at 96 hours. Induction of these proteins was absent or negligible in the areas that developed ischemic or postischemic lesions, including the subiculum-CA1 and CA1 regions of the hippocampus and layers III/IV and Vb/VI of the cerebral cortex. After shorter ischemia for 5 minutes and reperfusion, c-FOS and c-JUN were rapidly induced at 15 minutes to 1 hour except for the subiculum-CA1 and CA1 regions of the hippocampus. Induction of HSP 70 did not occur for 24 hours and was noted only in the hippocampus.

CONCLUSIONS

Induction of c-FOS and c-JUN occurred in the areas surviving after transient cerebral ischemia, but the extent of induction and the latent period varied depending on the duration of the insult and the location. In the areas with ischemic or postischemic damage detected by loss of the reaction for microtubule-associated proteins, the induction of c-FOS and c-JUN was either absent or minimal, suggesting that active induction of those immediate early gene products occurred early in surviving neurons. On the other hand, the induction of HSP 70 did not occur until reperfusion for 24 hours and actively occurred only in the areas with earlier induction of c-FOS and/or c-JUN, suggesting that the induction of HSP 70 occurred in neurons that survived to that point, but it did not participate in early responses for neuronal survival after global cerebral ischemia.

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.

Immunocytochemical and in situ hybridization approaches to the optimization of brain slice preparations

Methods are described for determining the expression of specific mRNAs and proteins in brain slices, in order to elucidate changes in gene expression during preparation of vibratome slices from hippocampus of adult rats. In situ hybridization with 35S-labeled oligonucleotides was used to evaluate the level and distribution of c-fos and hsp72 mRNAs in 15-microns frozen sections prepared from these slices. Commercially available antibodies were used to examine the distribution of induced Fos and Jun proto-oncogenes as well as expression of the neuronal cytoskeletal protein, microtubule-associated protein 2 (MAP2), in 50-microns vibratome sections from immersion-fixed slices. These studies confirm the induction of c-fos and hsp72 mRNAs during routine incubation, as previously observed in hippocampal slices obtained with a tissue chopper and incubated under somewhat different conditions, indicating that such responses are likely to be common features of many slice preparations. Accumulation of Fos and Jun immunoreactivities in neurons and glia was generally consistent with the distribution of c-fos mRNA induction observed in slices, and the neuronal component of this response was comparable to the expression of these proteins observed after transient ischemia in vivo. MAP2 immunoreactivity detected in the dendritic processes of neurons tended to show an increase in staining intensity during slice incubation, although loss of dendritic staining in specific regions was occasionally observed in association with the absence of Fos and Jun expression and histological evidence of neuron damage. These results support the use of MAP2 immunoreactivity as a sensitive indicator of neuronal integrity in slices.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear-envelope nucleoside triphosphatase kinetics and mRNA transport following brain ischemia and reperfusion

STUDY HYPOTHESIS

We attempted to determine whether the reduced egress of mRNA from brain nuclei following in vivo ischemia and reperfusion is caused by direct damage to the nuclear pore-associated NTPase that impairs the system for nuclear export of polyadenylated, or poly(A)+, mRNA.

DESIGN

Prospective animal study.

INTERVENTIONS

NTPase activity and poly(A)+ mRNA transport were studied in nuclear envelope vesicles (NEVs) prepared from canine parietal cortex isolated after 20 minutes of ischemia or 20 minutes of ischemia and 2 or 6 hours of reperfusion.

RESULTS

Brain NEV NTPase Michaelis-Menten constant (Km) and maximum uptake velocity (Vmax) and the ATP-stimulated poly(A)+ mRNA egress rates were not significantly affected by ischemia and reperfusion. In vitro exposure of the NEVs to the OH. radical-generating system completely abolished NTPase activity.

CONCLUSION

We conclude that brain ischemia and reperfusion do not induce direct inhibition of nucleocytoplasmic transport of poly(A)+ mRNA. This suggests that the nuclear membrane is not exposed to significant concentrations of OH. radical during reperfusion.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.