Expression Of Inducible Transcription Factors Research Articles

RETRACTED: Genomic Decoding of Neuronal Depolarization by Stimulus-Specific NPAS4 Heterodimers

Cells regulate gene expression in response to salient external stimuli. In neurons, depolarization leads to the expression of inducible transcription factors (ITFs) that direct subsequent gene regulation. Depolarization encodes both a neuron's action potential (AP) output and synaptic inputs, via excitatory postsynaptic potentials (EPSPs). However, it is unclear if distinct types of electrical activity can be transformed by an ITF into distinct modes of genomic regulation. Here, we show that APs and EPSPs in mouse hippocampal neurons trigger two spatially segregated and molecularly distinct induction mechanisms that lead to the expression of the ITF NPAS4. These two pathways culminate in the formation of stimulus-specific NPAS4 heterodimers that exhibit distinct DNA binding patterns. Thus, NPAS4 differentially communicates increases in a neuron's spiking output and synaptic inputs to the nucleus, enabling gene regulation to be tailored to the type of depolarizing activity along the somato-dendritic axis of a neuron.

ANG III induces expression of inducible transcription factors of AP-1 and Krox families in rat brain

In addition to rapid responses comprising increases in blood pressure, drinking, and stimulation of natriuresis, ANG II induces the expression of transcription factors (TF) in the central nervous system. The ANG II metabolite ANG III (ANG 2-8) has been demonstrated to exert physiological effects similar to those of ANG II. We aimed to determine 1) whether ANG III induces TF expression in the brain, 2) which ANG II (AT) receptor subtype is involved, and 3) whether the two peptides, ANG II and ANG III, differ in their efficacy to stimulate TF expression. ANG II (100 pmol), ANG III (100 pmol), or vehicle was injected into the lateral brain ventricle of conscious rats alone or in combination with the AT(1) receptor antagonist losartan (10 nmol), the AT(2) receptor antagonist PD-123319 (5 nmol), or the aminopeptidase inhibitor amastatin (10 nmol). Similar to ANG II, ANG III induced the expression of c-Fos, c-Jun, and Krox-24 in four brain regions, subfornical organ, median preoptic area, paraventricular nucleus, and supraoptic nucleus of the hypothalamus, with the same efficacy. This effect was AT(1) receptor mediated. Pretreatment with amastatin reduced the expression of TF in response to ANG II, indicating that this expression is partly mediated by ANG III. Interestingly, the AT(2) receptor antagonist PD-123319 alone slightly enhanced the expression of c-Fos, c-Jun, and Krox-24 in different populations of neurons of the paraventricular nucleus. These data indicate that different populations of neurons in the paraventricular nucleus are tonically inhibited by AT(2) receptors under physiological conditions.

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

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

Involvement of adrenoceptors in the angiotensin II-induced expression of inducible transcription factors in the rat forebrain and hypothalamus

Angiotensin II (Ang II) acts as a neuromodulator/neurotransmitter in specific brain nuclei involved in the regulation of blood pressure and volume homeostasis. It also induces a highly differentiated transcription factor expression in these nuclei. We investigated whether adrenoceptors, which modulate other central actions of angiotensin II like the vasopressin release, also play a role in the AT1 receptor-mediated expression of the transcription factors (TF) c-Fos, c-Jun and Krox-24 in the rat brain. Ang II, injected intracerebroventricularly, induced the expression of c-Fos, c-Jun and Krox-24 in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. Pretreatment with the α1-adrenoceptor antagonist, prazosin, significantly inhibited the Ang II-induced transcription factor expression in the SON and PVN. The α2-adrenoceptor antagonist, yohimbine, also reduced Ang II-stimulated transcription factors significantly in both nuclei. This inhibition was mainly localized in vasopressinergic magnocellular neurons in both nuclei. The β-adrenoceptor antagonist, propranolol, did not influence the Ang II-induced expression of TF. Our results show that both, Ang II-induced vasopressin release and transcription factor expression, involve the same neuronal connections in the brain, implicating that the signal transduction pathways leading to the two different effects are at least to a certain degree convergent.

Effect of repetitive icv injections of ANG II on c-Fos and AT(1)-receptor expression in the rat brain.

ANG II has been implicated in neuroplastic processes via stimulation of inducible transcription factors (ITF) in the brain. In the present study, we investigated the effects of acute vs. repetitive once daily intracerebroventricular injections of ANG II for 7 days on the expression of ITF and constitutive transcription factor (CTF) and the AT1 receptor in the median preoptic area (MnPO), the subfornical organ (SFO), and the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). After repetitive injections, the expression of c-Fos declined by approximately 50% in MnPO, SFO, PVN, and SON compared with controls injected once. The desensitization of c-Fos occurred on the transcriptional level as shown in the SON by RT-PCR. Apart from a novel expression of c-Jun in the SON, the ITF c-Jun, JunB, JunD, and Krox-24 did not change after repetitive stimulation. Neither were the CTF, calcium response element binding protein, activating transcription factor 2, and serum response factor altered after repetitive vs. single injections of ANG II. The AT1 receptor was coexpressed with c-Fos/c-Jun. Immunohistochemical stainings suggest an increase in AT1-receptor number in MnPO, SFO, PVN, and SON on chronic stimulation compared with once-injected controls. These findings demonstrate that repetitive periventricular stimulation with ANG II essentially alters the expression of transcription factors compared with acute stimulation and suggest c-Fos and c-Jun as major intermediates of the AT1-receptor transcription.

Interactive effects of nicotine and alcohol co-administration on expression of inducible transcription factors in mouse brain.

Nicotine and alcohol are abused substances that are often used concurrently. Despite their combined usage, little is known about how they interact to produce changes in behavior and neural activity. Two experiments were conducted to identify interactions on both behavior and neural targets resulting from the co-administration of nicotine and alcohol. In Experiment 1, male C57BL/6J mice were administered saline, alcohol (2.4 g/kg, i.p.), nicotine (0.5 mg/kg, i.p.) or an alcohol/nicotine mixture and returned to their home cage. In Experiment 2, a higher dose of nicotine (1.0 mg/kg, i.p.) was included and animals were exposed to a novel environment. Several behavioral measures were analysed during novelty exposure. Immunohistochemical detection of inducible transcription factors (c-Fos and Egr1) was used in both experiments to identify changes in neural activation. Behavioral results suggested that the drugs were interacting in the production of behaviors. In particular, alcohol produced locomotor stimulation while it suppressed counts of rearing and leaning. When co-administered, nicotine appeared to counteract the alcohol-enhanced locomotor activity. Several brain regions were observed to have altered transcription factor expression in response to the different drug treatments, including amygdalar, hippocampal and cortical subregions. In a subset of these brain areas, nicotine and alcohol counteracted one another in the expression of transcription factors. These results identify several interactive target sites within the hippocampus, extended amygdala and cortical regions. The interactions appear to be a result of antagonizing actions of nicotine and alcohol. Finally, the results suggest that the combined use of nicotine and alcohol may offset the effects of the drug administered independently.

Jun, Fos and Krox in the hippocampus after noxious stimulation: simultaneous-input-dependent expression and nuclear speckling

Stimulation of sensory C-fibres produces extensive expression of the Fos, Jun and Krox families of inducible transcription factors (ITFs) in many nociceptive CNS areas [28]. In the hippocampus, however, c-Fos is only weakly induced by such stimulation, and expression of the other ITFs has not been studied. Here we examine the effects of single, repeated and simultaneous C-fibre inputs on ITF expressions in the rat hippocampus. A brief, strong electrical stimulation of sciatic nerve C-fibres induced little or no expression of c-Fos or Krox-20. In contrast, FosB was induced and continued to rise in all areas, whereas the basal expressions of c-Jun and Krox-24 were initially reduced but then returned during the subsequent 36 h. A weak noxious cutaneous stimulus applied to one hindpaw induced only weak expressions of the ITFs. However, if the sciatic stimulation was applied contralaterally and 6 h beforehand, this weak stimulus strongly induced Krox-24, but not other ITFs, i.e. there was a potentiation of Krox-24 expression. When these two stimuli were applied simultaneously a few c-Fos labelled cells did appear, and there was and an increased Krox-24 expression. There was also a strong potentiation of FosB and a strong reduction in c-Jun expression. This simultaneous stimulation was the only type of stimulation to induce expression of Krox-20. Also after simultaneous stimulation the majority of the nuclear labelling for FosB, but not of the other ITFs, had a speckled appearance. MK-801 blocked these changes in ITF expressions, but it could also cause the C-fibre stimulations to induce c-Fos and c-Jun in specific areas of the hippocampus. Thus C-fibre stimulation does affect transcription factor activity in the hippocampus; and the strong responses of some ITFs to simultaneous inputs points to their having a role as ‘genetic coincidence detectors’ in the hippocampus.

ITF expression in mouse brain during acquisition of alcohol self-administration

Expression of inducible transcription factors (ITFs) c-Fos and FosB was investigated during acquisition of alcohol drinking in C57BL/6J mice. A slight but statistically significant increase in c-Fos expression was found in the Edinger–Westphal nucleus (EW) of animals consuming 2% ethanol/10% sucrose for the first time. Stronger expression of c-Fos in EW was found in animals repeatedly consuming ethanol-containing solutions. These findings underscore the potential importance of EW in alcohol-related behaviors.

ITF mapping after drugs of abuse: pharmacological versus perceptional effects

Analysis of inducible transcription factors (ITFs) expression is often applied to map drug-induced changes of neuronal activity in brain. Administration of cocaine and alcohol induces ITFs in a large number of brain structures. However, induction of ITFs in a brain region does not necessarily indicate a pharmacological effect of the drug in this brain region. Many of the brain regions could be activated by secondary effects. Perception of stimulus properties of the drug or locomotor effects of the drug are possible secondary effects. Anesthesia can block induction of ITFs by cocaine and alcohol suggesting that ITF expression in a majority of brain regions is more sensitive to secondary effects than to pharmacological effects of these drugs. In agreement with this hypothesis is our finding that the majority of brain regions responding with ITF expression to alcohol administration do not respond to voluntary alcohol self-administration in animals. Only a few brain regions show similar ITF induction after both administration and self-administration of this drug. Presumably these brain regions could be responding to pharmacological effects of alcohol. Given the low resolution of invasive techniques, ITF mapping experiments will continually contribute to our understanding of mechanisms of drug addiction and alcoholism.

Cocaine- and alcohol-mediated expression of inducible transcription factors is blocked by pentobarbital anesthesia

Identifying the neurocircuitry involved in behavioral responses to drugs of abuse is an important step towards understanding the mechanisms of drug addiction. The present study sought to distinguish brain regions involved in pharmacological effects of cocaine and ethanol from secondary effects by administering these drugs in the presence or absence of pentobarbital anesthesia. Changes in neuronal activity were assessed by immunohistochemical analysis of expression of an inducible transcription factor (ITF), c-Fos, in the brain of rats habituated to repeated pentobarbital anesthesia or saline administration. Cocaine administration (15 mg/kg, i.v.) in non-anesthetized animals produced a strong induction of c-Fos in the striatum and large number of other brain areas. Ethanol administration (2 g/kg, i.p.) induced c-Fos in a smaller number of characteristic brain areas, including the central nucleus of amygdala and paraventricular nucleus of hypothalamus. However, neither of these drugs was able to induce c-Fos in pentobarbital-anesthetized rats (50 mg/kg, i.v.). The suppressive effects of pentobarbital were not specific to c-Fos, such that pentobarbital also suppressed expression of ITFs FosB and Egr1 in the striatum of cocaine-treated rats. On the other hand, pentobarbital by itself strongly induced c-Fos expression in the lateral habenula of saline-, cocaine-, and ethanol-injected rats. It is not clear whether the suppressive effects of anesthesia on ITF expression in other areas are mediated by activation of lateral habenula, or are independent of this event. Our data suggest that in the absence of conscious awareness of drug-associated cues, cocaine and alcohol activate only a fraction of the neural elements engaged in the unanesthetized state.

Exploration of a novel environment leads to the expression of inducible transcription factors in barrel-related columns

Tactile information acquired through the vibrissae is of high behavioral relevance for rodents. Numerous physiological studies have shown adaptive plasticity of cortical receptive field properties due to stimulation and/or manipulation of the whiskers. However, the cellular mechanisms leading to these plastic processes remain largely unknown. Although genomic responses are anticipated to take place in this sequel, virtually no data so far exist for freely behaving animals concerning this issue. Thus, adult rats were placed overnight in an enriched environment and most of them were also subjected to clipping of different sets of whiskers. This type of stimulation led to a specific and statistically significant increase in the expression of the protein products of the inducible transcription factors c-Fos, JunB, inducible cyclic-AMP early repressor and Krox-24 (also frequently named Zif268 or Egr-1), but not c-Jun. The response was found in columns of the barrel cortex corresponding to the stimulated vibrissae; it displayed a layer-specific pattern. However, no induction of transcription factors was observed in the subcortical relay stations of the whisker-to-barrel pathway, i.e. the trigeminal nuclei and the ventrobasal complex. These results strongly suggest that a coordinated transcriptional response is initiated in the barrel cortex as a consequence of processing of novel environmental stimuli.

Alcohol drinking produces brain region-selective changes in expression of inducible transcription factors

Mapping the effects of alcohol consumption on neural activity could provide valuable information on mechanisms of alcohol's effects on behavior. The present study sought to identify effects of alcohol consumption on expression of inducible transcription factors (ITFs) in mouse brain. C57BL/6J mice were trained to consume 10% ethanol/10% sucrose solution during a 30-min limited access period. Control animals were given access to 10% sucrose solution or water. Following the final day of the procedure, animals were sacrificed and immunohistochemical analyses were performed for three ITFs (c-Fos, FosB, and Zif268). Alcohol-consuming animals had increased ITF expression in several brain areas. Specifically, c-Fos was significantly induced in the nucleus accumbens core (AcbC), the medial posteroventral portion of the central nucleus of the amygdala (CeMPV), and the Edinger–Westphal nucleus (EW). Expression of c-Fos was significantly lower in the dentate gyrus of alcohol-consuming animals vs. sucrose-consuming animals. However, it was not significantly different from the water controls. Induction of c-Fos in AcbC, CeMPV and EW was significantly related to blood alcohol concentrations (BAC). Furthermore, FosB expression in the CeMPV and the EW was also significantly higher in the alcohol-consuming animals vs. water controls. FosB expression in the EW was significantly related to BAC. The significance of these results is two-fold. First, our experiments demonstrate that ITF mapping is an effective strategy in identifying alcohol-induced changes following voluntary consumption. Second, they suggest a relationship between ITF expression in AcbC, CeMPV and EW and the level of alcohol intoxication.

A double dissociation within the hippocampus of dopamine D 1/D 5 receptor and β-adrenergic receptor contributions to the persistence of long-term potentiation

We compared the effects of the D 1/D 5 receptor antagonist SCH-23390 with the β-adrenergic receptor antagonist propranolol on the persistence of long-term potentiation in the CA1 and dentate gyrus subregions of the hippocampus. In slices, SCH-23390 but not propranolol reduced the persistence of long-term potentiation in area CA1 without affecting its induction. The drugs exerted reverse effects in the dentate gyrus, although in this case the induction of long-term potentiation was also affected by propranolol. The lack of effect of SCH-23390 on the induction and maintenance of long-term potentiation in the dentate gyrus was confirmed in awake animals. The drug also had little or no effect on the expression of inducible transcription factors. In area CA1 of awake animals, SCH-23390 blocked persistence of long-term potentiation beyond 3 h, confirming the results in slices. To rule out a differential release of catecholamines induced by our stimulation protocols between brain areas, we compared the effects of the D 1/D 5 agonist SKF-38393 with the β-adrenergic agonist isoproterenol on the persistence of a weakly induced, decremental long-term potentiation in CA1 slices. SKF-38393 but not isoproterenol promoted greater persistence of long-term potentiation over a 2-h period. In contrast, isoproterenol but not SKF-38392 facilitated the induction of long-term potentiation. These data demonstrate that there is a double dissociation of the catecholamine modulation of long-term potentiation between CA1 and the dentate gyrus, suggesting that long-term potentiation in these brain areas may be differentially consolidated according to the animal's behavioural state.

Effects of mild traumatic brain injury on immunoreactivity for the inducible transcription factors c-Fos, c-Jun, JunB, and Krox-24 in cerebral regions associated with conditioned fear responding

We have previously demonstrated that mild traumatic brain injury (TBI) of the right parietal cortex results in a relatively selective deficit in conditioned fear responding. However, this behavioural deficit is very consistent and unrelated to the extent of the cortical necrotic lesion. We were therefore interested in determining if other brain regions might show a consistent response to mild TBI, and therefore, more reliably relate to the behavioural change. Increased expression of inducible transcription factors (ITFs) has been used to study which brain regions respond to a variety of events. In the present study, we examined the expression patterns of immunoreactivity (IR) for four ITFs (c-Fos, c-Jun, JunB, and Krox-24) at 3 h after mild fluid percussion TBI. Changes in ITF expression were only observed ipsilateral to the side of TBI. The clearest changes were observed in brain regions known to be involved in conditioned fear responding, such as the amygdala complex and hippocampal formation and several cortical regions. In contrast, no changes in IR for any of the ITFs were observed in the striatum, nucleus accumbens, nucleus basalis magnocellularis, septum or periacqueductal grey. Unlike the extent of visible damage to the cortex at the site of impact, the overexpression of ITFs showed a notable consistency between animals subjected to TBI. This consistency in regions known to be involved in conditioned fear responding (i.e., amygdala complex and hippocampal formation) lead us to suggest that it is these changes, rather than the more variable cortical necrotic lesion, that is responsible for the behavioural deficits we observe following mild TBI. Importantly, our results demonstrate that like the hippocampus, the amygdala is a sub-cortical structure particularly sensitive to the effects of mild brain trauma and underline the fact that cerebral regions distant from the location of the fluid impact can be affected.

Angiotensin peptides and inducible transcription factors.

Transcription factors are DNA-binding proteins which are able to identify specific nucleotide sequences and by binding to them may regulate the expression of genes at the level of transcription. In addition to the general transcription factors, which are basically the same for each gene transcribed by eukaryotic RNA polymerase II, more than 100 specific transcription factors have been identified so far. These specific transcription factors regulate the expression patterns of various sets of inducible genes during growth and development and enable the adjustment of cells and tissues to environmental changes. Especially the AP-1 proteins have found increasing interest, since members of these families such as c-Fos and c-Jun seem to be involved in trophic changes in peripheral organs. Many studies have also used them as marker proteins for activated neurons in the central nervous system to identify functional pathways and connections between brain nuclei. The renin-angiotensin system is implicated both in the hormonal and the central regulation of blood pressure and volume homeostasis. By binding to their specific receptors angiotensin peptides, namely angiotensin (Ang) II, have also been reported to induce the expression of a variety of inducible transcription factors (ITF) of the AP-1 and other families in peripheral organs such as kidney and blood vessels and in specific brain regions. By activating ITF, transient ligand receptor signals are transformed into long-lasting genetic changes. While the Ang II induced expression of ITF in peripheral organs seems to be associated with trophism, the physiological significance of this expression in brain nuclei with their postmitotic cells is much less clear. This contribution reviews the Ang II induced ITF expression in various tissues and discusses the possible physiological and pathophysiological consequences of the resulting changes in genetic patterns.

Central angiotensin AT1 and muscarinic receptors in ITF expression on intracerebroventricular NaCl.

In the present study, we investigated the expression pattern of the inducible transcription factors (ITF) c-Fos, c-Jun, JunB, JunD, and Krox-24 following intracerebroventricular injections of hyperosmolar saline (0.2, 0.3, and 0.6 M NaCl) and its mediation via angiotensin and/or muscarinic receptors. c-Fos, c-Jun, and Krox-24 were differentially expressed in organum vasculosum laminae terminalis, median preoptic area, subfornical organ (SFO), and paraventricular and supraoptic nuclei. Expression of c-Fos and c-Jun was inhibited by pretreatment with the angiotensin AT1 receptor antagonist losartan (10 and 20 nmol icv) following 0.20 and 0.30 M saline. Pretreatment with atropine (15 nmol icv) inhibited the 0.30 and 0.60 M NaCl-induced expression of c-Fos, c-Jun, and Krox-24 in all areas except the SFO. Coexpression of the ITF with vasopressin and oxytocin, the major effector peptides in osmoregulation, was demonstrated, implying the corresponding genes as putative target genes of the ITF. The results show a highly differentiated ITF expression pattern in the brain mediated by angiotensinergic and muscarinergic pathways, suggesting a finely tuned regulation of target genes.

Expression of c- jun, junB, c- fos, fra-1 and fra-2 mRNA in the rat brain following seizure activity and axotomy

The present study has investigated the congruence of mRNA induction and protein expression of inducible transcription factors (ITFs). The patterns of c- jun, junB, c- fos, fra-1 and fra-2 mRNAs were studied by radioactive and non-radioactive in situ hybridization in the adult rat brain following kainate-induced seizure activity and axotomy. In the same animals, the expression of c-Jun, JunB and c-Fos proteins was compared with the respective mRNA signals. Using radioactive labeled probes all investigated mRNAs showed an onset within 1 h after systemic kainate application and the maximal levels were generally reached after 3 h. Each mRNA displayed a specific temporo-spatial expression pattern. Whereas fra-1 and fra-2 were restricted to the hippocampus, c- jun, junB and c- fos were additionally induced in the cortex, amygdala and thalamus. The areas with maximal labeling were the dentate gyrus and the hippocampal CA1 and CA3 subfields. The expression patterns between c- jun, junB and c- fos mRNA were virtually congruent with the respective protein. Labeling of the junB and fra-2 probes with digoxigenin yielded similar results. Twenty-four hours, 3 and 10 days following transection of the medial forebrain bundle and the mamillo-thalamic tract, high levels of c- jun mRNA (either digoxigenin or radioactive labeled probes) and protein were seen in the axotomized neurons of the substantia nigra pars compacta and mamillary body whereas the other mRNAs studied and the JunB or c-Fos proteins could not be detected. These findings demonstrate that mRNAs encoding for ITFs are translated into the respective proteins following excitotoxic seizures and axotomy, and that the antisera used for immunocytochemistry yield specific expression patterns of homologous proteins.

BDNF restores the expression of Jun and Fos inducible transcription factors in the rat brain following repetitive electroconvulsive seizures.

The expression of inducible transcription factors was studied following repetitive electroconvulsive seizures (ECS), c-Fos, c-Jun, JunB, and JunD immunoreactivities were investigated following a single (1 x ECS) or repetitive ECS evoked once per day for 4, 5, or 10 days (4 x ECS, 5 x ECS, or 10 x ECS). Animals were killed 3 or 12 h following the last ECS. Three hours after 1 x ECS, c-Fos was expressed throughout the cortex and hippocampus. After 5 x ECS and 10 x ECS, c-Fos was reexpressed in the CA4 area, but was completely absent in the other hippocampal areas and cortex. In these areas, c-Fos became only reinducible when the time lag between two ECS stimuli was 5 days. In contrast to c-Fos, intense JunB expression was inducible in the cortex and hippocampus, but not CA4 subfield, after 1 x ECS, 5 x ECS, and 10 x ECS. Repetitive ECS did not effect c-Jun and JunD expression. In a second model of systemic excitation of the brain, repetitive daily injection of kainic acid for 4 days completely failed to express c-Fos, c-Jun, and JunB after the last application whereas injection of kainic acid once per week did not alter the strong expressions compared to a single application of kainic acid. In order to study the maintenance of c-Fos expression during repetitive seizures, brain-derived neurotrophic factor (BDNF) was applied in parallel for 5 or 10 days via miniosmotic pumps and permanent cannula targeted at the hippocampus or the parietal cortex. Infusion of BDNF completely reinduced c-Fos expression during 5 x ECS or 10 x ECS in the cortex ipsilaterally to the cannula and, to a less extent, also increased the expression of c-Jun and JunB when compared to saline-treated controls. BDNF had no effect on the expression patterns in the hippocampus. ECS with or without BDNF infusion did not change the expression patterns of the constitutive transcription factors ATF-2, CREB, and SRF. These data demonstrate that various transcription factors substantially differ in their response to acute and chronic neural stimulation. Repetitive pathophysiological excitation decreases the transcriptional actions of neurons over days in the adult brain, and this decrement can be prevented by BDNF restoring the neuroplasticity at the level of gene transcription.

Differential time course of angiotensin-induced AP-1 and Krox proteins in the rat lamina terminalis and hypothalamus

We studied the time course of expression of the inducible transcription factors (ITF) c-Fos, FosB, c-Jun, JunB, JunD, Krox-20 and Krox-24, induced by a single intracerebroventricular injection of angiotensin II, in the subfornical organ (SFO), median preoptic nucleus (MnPO) paraventricular nucleus (PVN) and supraoptic nucleus (SON). c-Fos and Krox-24 were expressed rapidly in neurons of all four areas but completely disappeared after 4 h. FosB showed a delayed but persistent expression between 4 h and 24 h in the MnPO and PVN. c-Jun was induced in the MnPO, SFO and PVN after 1.5 h and in the SON after 4 h. JunB was selectively expressed in the MnPO and SFO and the level of JunD did not change. The expression of the pre-existing transcription factors SRF, CREB and ATF-2 which contribute to the transcriptional control of jun, fos and krox genes, was not affected by Ang II. Thus, we could show for the first time that an acute stimulation of AT receptors results in continual changes in ITF expression over 24 h.

Cycloheximide phase-shifts, but does not prevent, de novo Krox-24 protein expression

Previous studies show that focal hippocampal injury transiently increases NMDA receptor-dependent expression of inducible transcription factors (ITFs including Krox-24) in rat dentate gyrus neurons. Furthermore, pretreatment with the protein synthesis inhibitor, cycloheximide (CHX), prevents de novo ITF protein expression 1 h post-injury. Here, we further characterize the effects of a single pretreatment dose of CHX on injury-induced expression of Krox-24 and show that CHX pretreatment phase-shifts (delays), but does not prevent, de novo expression of Krox-24 in hippocampal dentate gyrus neurons following injury. This may have implications for studies which use CHX pretreatment to examine the role of gene expression and de novo protein synthesis in long-term memory formation, the stabilization of long-term potentiation, kindling and neuronal injury.