Long-term expression of Fos-related antigen and transient expression of delta FosB associated with seizures in the rat hippocampus and striatum

Effect of repeated seizures on spatial exploration and immediate early gene expression in the hippocampus and dentate gyrus

Immediate early genes (IEGs) are coordinately activated in response to neuronal activity and can cause activation of secondary response genes that modulate synaptic plasticity and mediate long-lasting changes in behaviour. Excessive neuronal stimulation induced by epileptic seizures induce rapid and dramatic changes in IEG expression. Although the impact of acute seizure activity on IEG expression has been well studied, less is known about the long-term effects of chronic seizures on IEG induction during seizure free periods where behavioural and cognitive impairments are frequently observed in people with epilepsy and in animal models of epilepsy. The present study sought out to examine the impact of chronic pentylenetetrazole evoked seizures (PTZ kindling) on spatial exploration induced in IEG expression (c-Fos, ΔFosB, Homer1a, Egr1, Npas4, Nr4a1) in the hippocampus (CA1 and CA3 subfields) and dentate gyrus of rats. Male rats underwent two weeks of PTZ kindling (every 2 days) or received vehicle injections and were placed into a novel open field arena for 30 min either 24 hrs or 4 weeks after the last treatment. Although exploratory activity was similar between PTZ kindled and vehicle controls when examined 24 hrs after the last treatment, we observed a significant reduction in spatial exploration induced expression of c-Fos, Egr1, and ΔFosB in the hippocampus and dentate gyrus, and reduced expression of Nr4a1 in the dentate gyrus and Homer1a in the hippocampus only. When testing was conducted after a 4-week recovery period, only c-Fos continued to show reduced expression after exposure a novel environment in previously PTZ kindled animals. Interestingly, these animals also showed reduced activity in the center region of the open field suggestive of heightened anxiety-like behaviour. Collectively, these results suggest that repeated seizures may lead to longterm downregulation in hippocampal IEG expression that can extend into seizure free periods thereby providing a critical mechanism for the development of cognitive and behavioural deficits that arise during chronic epilepsy

c-Fos and FosB/ΔFosB colocalizations in selected forebrain structures after olanzapine, amisulpride, aripiprazole, and quetiapine single administration in rats preconditioned by two different mild stressors sequences

OBJECTIVE

Olanzapine (OLA), amisulpride (AMI), aripiprazole (ARI), and quetiapine (QUE) belong to antipsychotics, which administration represents still most reliable way for the treatment of schizophrenic and bipolar disorders. The intention of the present study was to explore whether the acute administration of a particular antipsychotic, indicated by the presence of c-Fos, will: a) stimulate neurons already activated by a long lasting homogeneous or heterogeneous stress preconditioning, indicated by the FosB/ΔFosB (ΔFosB) expression, or b) have a stimulatory effect only on a not activated, so called silent neurons. The pattern of ΔFosB and c-Fos spatial relationship was investigated in three forebrain structures, including the septal ventrolateral nucleus (seVL), the striatal dorsolateral area (stDL), and the shell of the nucleus accumbens (shell).

METHODS

The rats were divided into 10 groups and exposed to two types of stressors. Half of them was exposed to a sequence of homogeneous stressor - handling (HDL) and the other half to a heterogeneous stressor (CMS) daily for 20 days. CMS consisted of five types of stressors: crowding, air-puff, wet bedding, predator stress, and forced swimming applied in an unexpected order. On the 21st day of the experiment, the rats were free of the stress exposure and on the 22nd day, both groups of animals receive a single intraperitoneal injection of vehicle (4% DMSO in saline, 0.1 ml/100 g) or OLA (5 mg/kg), AMI (20 mg/kg), ARI (10 mg/kg), and QUE (15 mg/kg). 90 min after the drugs administration the animals were transcardially perfused, brains removed, cut into 30 µm thick coronal sections, and double stained: first with ΔFosB antibody linked with Alexa488 fluorescent dye and second with c-Fos antibody linked to Alexa596 one. Quantitative evaluation of ΔFosB and c-Fos colocalizations was performed on fluorescence photomicrographs transformed into a final picture containing only yellow, green, and red colored circles.

RESULTS

The data of this investigation demonstrate that ΔFosB and c-Fos colocalizations occurred in each of the three areas investigated, i.e. seVL, stDL, and shell ones, in both HDL as well as CMS preconditioned rats. The levels of ΔFosB and c-Fos colocalizations varied in the individual forebrain areas studied. From the total 22 areas measured, level of c-Fos colocalization prevailed over ΔFosB in 18 ones. However, neither c-Fos nor ΔFosB reached 100% level of colocalization in any of the forebrain areas investigated.

CONCLUSION

The present findings indicate that ΔFosB and c-Fos colocalizations occurred in each of the three areas investigated, i.e. seVL, stDL, and shell, in both HDL and CMS preconditioned rats, whereas the parallel occurrence of free c-Fos as well as c-Fos colocalized with ΔFosB might speak out for a possible involvement of the c-Fos activated by antipsychotics applied in dual, i.e. short- and long-lasting, functions.

Hypothalamic Astrocytes Respond to Gastric Mucosal Damage Induced by Restraint Water-Immersion Stress in Rat

Restraint water-immersion stress (RWIS), a compound stress model, includes both psychological and physical stimulation. Studies have shown that neurons in the hypothalamus are involved in RWIS, but the role of astrocytes and the interactions between astrocytes and neurons in RWIS are not clear. Here, we tested our hypothesis that hypothalamus astrocytes are involved in RWIS and interact with neurons to regulate gastric mucosal damage induced by RWIS. The expression of Glial fibrillary acidic protein (GFAP) and c-Fos in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) significantly increased following the RWIS. GFAP and c-Fos expression are similar in the temporal pattern, peaked at 1 h after the RWIS, then reduced gradually, and reached a maximal level again at 5 h which show “double-peak” characteristics. Intracerebroventricular administration of astroglial toxin L-a-aminoadipate (L-AA) and c-Fos antisense oligodeoxy nucleotides (ASO) both decreased RWIS-induced gastric mucosal damage. Results of immunohistochemistry assay revealed that both L-AA and ASO decreased the activation of astrocytes and neurons in the hypothalamus by RWIS. These results showed that hypothalamus neuron-astrocyte “network” involved in gastric mucosal damage induced by RWIS. This study may offer theoretical basis for some novel therapeutic strategies for RWIS-induced gastric ulcers.

Adolescent exposure to cocaine increases anxiety-like behavior and induces morphologic and neurochemical changes in the hippocampus of adult rats

Repeated exposure to cocaine during adolescence may affect both physical and psychological conditions in the brain, and increase the risk of psychiatric disorders and addiction behaviors in adulthood. Adolescence represents a critical development period for the hippocampus. Moreover, different regions of the hippocampus are involved in different functions. Dorsal hippocampus (dHP) has been implicated in learning and memory, whereas ventral hippocampus (vHP) plays an important role in emotional processing. In this study, the rats that were exposed to cocaine during adolescence (postnatal days, P28-P42) showed higher anxiety-like behavior in the elevated plus maze test in adulthood (P80), but displayed normal spatial learning and memory in the Morris water maze test. Furthermore, repeated exposure to cocaine during adolescence lead to alterations in morphology of pyramidal neurons, activities of astrocytes, and levels of proteins that involved in synaptic transmission, apoptosis, inflammation and addiction in both dHP and vHP of adult rats. These findings suggest that repeated exposure to cocaine during adolescence in rats may elicit morphologic and neurochemical changes in the hippocampus when the animals reach adulthood. These changes may contribute to the increased susceptibility for psychiatric disorders and addiction seen in adults.

Exposure to extremely low frequency magnetic fields induces fos-related antigen-immunoreactivity via activation of dopaminergic d1 receptor

We previously demonstrated that repeated exposure to extremely low frequency magnetic fields (ELF-MF) increases locomotor activity via stimulation of dopaminergic D1 receptor (J. Pharmacol. Sci., 2007;105:367-371). Since it has been demonstrated that activator protein-1 (AP-1) transcription factors, especially 35-kDa fos-related antigen (FRA), play a key role in the neuronal and behavioral adaptation in response to various stimuli, we examined whether repeated ELF-MF exposure induces FRA-immunoreactivity (FRA-IR) in the striatum and nucleus accumbens (striatal complex) of the mice. Repeated exposure to ELF-MF (0.3 or 2.4 mT, 1 h/day, for consecutive fourteen days) significantly induced hyperlocomotor activity and FRA-IR in the striatal complex in a field intensity-dependent manner. ELF-MF-induced FRA-IR lasted for at least 1 year, while locomotor activity returned near control level 3 months after the final exposure to ELF-MF. Pretreatment with SCH23390, a dopaminergic D1 receptor antagonist, but not with sulpiride, a dopaminergic D2 receptor antagonist, significantly attenuated hyperlocomotor activity and FRA-IR induced by ELF-MF. Our results suggest that repeated exposure to ELF-MF leads to prolonged locomotor stimulation and long-term expression of FRA in the striatal complex of the mice via stimulation of dopaminergic D1 receptor.

Delayed wave of c-Fos expression in the dorsal hippocampus involved specifically in persistence of long-term memory storage

Memory formation is a temporally graded process during which transcription and translation steps are required in the first hours after acquisition. Although persistence is a key characteristic of memory storage, its mechanisms are scarcely characterized. Here, we show that long-lasting but not short-lived inhibitory avoidance long-term memory is associated with a delayed expression of c-Fos in the hippocampus. Importantly, this late wave of c-Fos is necessary for maintenance of inhibitory avoidance long-term storage. Moreover, inhibition of transcription in the dorsal hippocampus 24 h after training hinders persistence but not formation of long-term storage. These findings indicate that a delayed phase of transcription is essential for maintenance of a hippocampus-dependent memory trace. Our results support the hypothesis that recurrent rounds of consolidation-like events take place late after learning in the dorsal hippocampus to maintain memories.

Late expression of FosB transcription factor in 4-aminopyridine-induced seizures in the rat cerebral cortex

In this study, the immunolocalization of FosB transcription factor was investigated in acute and chronic experimental models of seizures induced by 4-aminopyridine. Wistar rats were injected intraperitoneally daily with 5mg/kg 4-aminopyridine for 1, 4, 8 and 12 days and sacrificed 24h after the last injection. Corresponding control groups received the solvent of 4-aminopyridine. Immunohistochemistry revealed an increase in FosB immunolabelling in the frontal cortex in 4-aminopyridine-treated animals compared to controls, both in acute and chronic time course groups. The dentate gyrus displayed elevated FosB immunopositivity only after repeatedly applied convulsant (4-aminopyridine), i.e. following 4, 8 and 12 days of treatment, but no significant immunolocalization was observed in the hippocampus proper. The neuronal localization of FosB after 12 days of 4-aminopyridine-induced convulsions was analysed by means of FosB-parvalbumin double immunolabelling. The increased number of double-labelled cells was significant in the frontal cortex, hilum of the dentate fascia and region CA1 of the hippocampus. We conclude that the studied neocortical and allocortical areas showed a different pattern of FosB immunolocalization, which suggests a relative deficiency of transcriptional regulation in the Ammon's horn and may be responsible for distinct response to seizure-induced cellular insult.

Regulation of fosB and DeltafosB mRNA expression: in vivo and in vitro studies

The transcription factor DeltaFosB, a truncated splice isoform of FosB, accumulates in brain after several types of chronic stimulation. This accumulation is thought to be mediated by the unique stability of DeltaFosB compared to all other Fos family proteins. The goal of the present study was to determine if the relative expression of the two fosB isoforms is also regulated at the mRNA level, thereby further contributing to the selective accumulation of DeltaFosB after chronic stimulation. First, unlike the protein, the half-life of DeltafosB mRNA is only slightly longer than that of full-length fosB mRNA both in cultured cells in vitro and in the brain in vivo. Additionally, similar to c-fos, both fosB isoforms are induced abundantly in striatum after acute administration of amphetamine or stress, and partially desensitize after chronic exposures. Surprisingly, the relative ratio of DeltafosB to fosB mRNA increases most significantly after acute, not chronic, stimulation. Finally, overexpression of polypyrimidine tract binding protein (PTB1), which regulates RNA splicing, in cultured cells decreases the relative expression of DeltafosB compared to fosB mRNA. Together, these findings suggest that splicing of fosB pre-mRNA is regulated by the quantity of unspliced transcript available to the splicing machinery. These data provide fundamental information concerning the generation of DeltafosB mRNA, and indicate that the selective accumulation of DeltaFosB protein with chronic stimulation does not involve its preferential generation by RNA splicing.

Regulation of DeltaFosB transcriptional activity by Ser27 phosphorylation

The transcription factor, DeltaFosB, is an important mediator of the long-term plasticity induced in brain by chronic exposure to drugs of abuse, stress, or several other psychoactive stimuli. We have previously demonstrated that the casein kinase 2 (CK2)-mediated phosphorylation of a highly conserved N-terminal serine (Ser27) plays a critical role in regulating DeltaFosB's unusual stability, while it does not affect that of the full-length FosB protein. In the present study, we analysed whether CK2 and Ser27 phosphorylation also play a role in regulating DeltaFosB's transcriptional activity. Our findings indicate that CK2 activation increases DeltaFosB's transactivation potential, while CK2 inhibition decreases it. Further, we show that preventing Ser27 phosphorylation by mutating the site to Ala results in a significant decrease in DeltaFosB transactivation, without affecting DeltaFosB's subcellular localization or DNA-binding affinity. In contrast, Ser27 does not seem to play a role in the transactivation potential of full-length FosB. These findings constitute the first evidence of a role for phosphorylation in DeltaFosB's transcriptional activity.

Regulation of DeltaFosB stability by phosphorylation

The transcription factor DeltaFosB (also referred to as FosB2 or FosB[short form]) is an important mediator of the long-term plasticity induced in brain by chronic exposure to several types of psychoactive stimuli, including drugs of abuse, stress, and electroconvulsive seizures. A distinct feature of DeltaFosB is that, once induced, it persists in brain for relatively long periods of time in the absence of further stimulation. The mechanisms underlying this apparent stability, however, have remained unknown. Here, we demonstrate that DeltaFosB is a relatively stable transcription factor, with a half-life of approximately 10 h in cell culture. Furthermore, we show that DeltaFosB is a phosphoprotein in brain and that phosphorylation of a highly conserved serine residue (Ser27) in DeltaFosB protects it from proteasomal degradation. We provide several lines of evidence suggesting that this phosphorylation is mediated by casein kinase 2. These findings constitute the first evidence that DeltaFosB is phosphorylated and demonstrate that phosphorylation contributes to its stability, which is at the core of its ability to mediate long-lasting adaptations in brain.

ΔFosB: a molecular switch for long-term adaptation in the brain

DeltaFosB is a unique transcription factor that plays an essential role in long-term adaptive changes in the brain associated with diverse conditions, such as drug addiction, Parkinson's disease, depression, and antidepressant treatment. It is induced in brain, in a region- and cell-type-specific manner by many types of chronic perturbations. Once induced, it persists for long periods of time due to its unusual stability. The transcriptional effects of DeltaFosB are complex, because the protein can function as both a transcriptional activator and repressor. Progress has been made in identifying specific target genes for DeltaFosB and in relating some of these genes to DeltaFosB's cellular and behavioral actions. Future studies will help us to better understand the biochemical basis of DeltaFosB's unique stability, as well as the precise molecular pathways through which this transcription factor produces its complex effects on neuronal plasticity and complex behavior.

Fos and FRA protein expression in rat precerebellar structures during the Neurolab Space Mission

Changes in gene expression were examined in precerebellar structures during and after space flight. These structures included the inferior olive (IO), the source of climbing fibers, and the lateral reticular nucleus (LRt) and basilar pontine nuclei (PN), sources of mossy fibers. We examined two immediate early gene products with two different time courses of expression: Fos, which persists only for a few (6-8)h after activation and FRA expression, which lasts for longer periods of time, i.e. hours and/or days after activation. Gravity effects on Fos and FRA gene expression were evident in vestibular and visual areas of the IO, including the dorsomedial cell column, the beta subnucleus and the dorsal cap of Kooy of the medial nucleus (which projects to the flocculonodular lobe, i.e. to the vestibular area of the IO involved in the olivary control of the vestibulo-ocular reflex (VOR)). Gene expression also affected the subnuclei A, B, and C and the caudal part of the medial IO. These olivary regions do not receive vestibular afferents, but rather spinal afferents, and are particularly involved in the olivary control of the vestibulospinal reflex (VSR). Changes in Fos expression were also observed in the LRt and the PN. We suggest that sensory substitution, in which signals produced by a subject's own activity replace activity normally provided by macular stimulation, contributes to the recovery of microgravity-related postural and motor deficits. While no consistent increases in FRA expression occurred in vestibular IO regions 24h after launch, consistent increases in FRA expression occurred 24h after landing. We hypothesize that this asymmetrical pattern of gene expression resulted from (i). tonic microgravity experienced after launch counteracting the effects of increased phasic gravitational forces experienced during launch, and (ii). the tonic gravitational field experienced after landing potentiating the effects of increased phasic gravitational forces experienced during landing. The specificity of these results is demonstrated by an absence of direct gravity-related changes in Fos expression in other precerebellar structures such as the external cuneate nucleus, group X, and the dorsal column nuclei that transmit exteroceptive and proprioceptive signals to thalamic nuclei and somatosensory areas of the cerebral cortex. The gravity-related Fos and FRA expression changes in the IO and the LRt seen here are of interest in view of the important role their projections play in adaptive gain changes of the VOR and VSR during sustained visuo-vestibular and neck-vestibular stimulation.

Sudden and unexpected death in epilepsy (SUDEP): evidence of acute neuronal injury using HSP-70 and c-Jun immunohistochemistry

Post-mortem and neuropathological examination in sudden and unexpected death in epilepsy (SUDEP) shows no specific lesions and the exact cause and mechanism of death in these cases remains undetermined. There is clinical evidence to support the fact that SUDEP is a seizure-mediated event, and patients with poorly controlled seizures are at higher risk. We aimed to identify any evidence of acute neuronal injury in SUDEP cases at post-mortem to support that a recent seizure had occurred. We analysed the distribution and frequency of heat shock protein (HSP)-70 and c-Jun immunopositive neurones in the hippocampus in 18 SUDEP cases and 22 control cases, both markers being nonspecific but early and reliable indicators of acute neuronal injury. Post-mortem control groups included patients with epilepsy with cause of death other than SUDEP (including status epilepticus and accidental death), and patients with sudden cardiac death without an epilepsy history. An additional surgical control group included patients with refractory epilepsy and hippocampal sclerosis who had undergone temporal lobectomy. Semiquantitative analysis of the distribution of HSP-70 staining showed significantly more SUDEP cases with positively labelled neurones in hippocampal subfields compared to epilepsy and cardiac post-mortem controls (P < 0.001) but not compared to the epilepsy surgical controls (P = 0.4). No significant difference in immunostaining patterns between groups was seen in the parahippocampal gyrus with HSP-70 or with c-Jun in either the hippocampus or parahippocampal gyrus regions. The detection of HSP-70 positive neurones in the hippocampus in SUDEP is supportive of ante-mortem neuronal injury including a recent seizure prior to death.

Spatial and temporal profile of haloperidol-induced immediate-early gene expression and phosphoCREB binding in the dorsal and ventral striatum of amphetamine-sensitized rats

To determine if D(2) dopamine receptor-mediated nuclear signaling is altered during the development of amphetamine sensitization, we examined the expression of immediate-early gene (IEG) products, Fos, Jun, and Fos-related antigen (FRA), in both controls and amphetamine-sensitized rats after a challenge with the D(2) antagonist haloperidol. When chronic saline- or amphetamine (5 mg/kg, i.p. for 14 days)-treated rats were challenged with 2 mg/kg haloperidol at withdrawal day 3 (w3), more 35-kDa FRA was induced in the ventral striatum of the control group than in the amphetamine-treated rats. In contrast, more Jun and 35-kDa FRA were expressed in the ventral striatum of the amphetamine-treated group than in the controls when haloperidol was given at w10. Topographical analyses indicate that the decrease in FRA immunoreactive neuronal density in amphetamine-treated rats at w3 were located in the dorsolateral caudate/putamen and the nucleus accumbens shell and core subregions. Conversely, the increase in Jun-immunoreactive neurons in amphetamine-treated rats at w10 was observed in the dorsolateral caudate/putamen; in the case of the FRAs, the increase was observed in the nucleus accumbens shell. In addition, the time-dependent profile of IEG expression paralleled the activation of an upstream regulator, cAMP-response element binding protein, in the ventral striatum after haloperidol treatment. These neurochemical changes may be associated with behavioral plasticity, since amphetamine-treated rats displayed a lower amount of locomotor activity when exposed to a novel environment at w3, but had recovered at w10. Overall, the current study reveals that there is a distinct temporal and spatial profile of haloperidol-induced IEG expression and/or CREB phosphorylation in amphetamine-treated rats, suggesting that there is a critical transition between the early and late withdrawal periods.

Immediate early gene expression in the vestibular nuclei and related vegetative areas in rats during space flight

Changes in neuronal activity resulting in somatic and vegetative deficits occur during different space flight conditions. Immediate early genes (IEGs: c-fos and Fos-related antigen [FRA]) are useful indicators of changes in neuronal activity and plasticity. They are induced within minutes of several extracellular stimulations, while the corresponding proteins persist for hours (Fos) or days (FRAs). Changes in IEG expression are likely to contribute to adaptation to microgravity and readaptation to the terrestrial environment. During the NASA Neurolab Mission (STS-90), changes in IEG expression were studied in adult male albino rats (Fisher 344) sacrificed at flight day (FD) 2 (24 h after launch), FD14 and at similar time points after re-entry (R + 1, 24 h after re-entry, and R + 13). These time points were chosen to maximize the probability of detecting changes in IEG expression related to changes in gravitational fields occurring during the mission, e.g. (i) increase in gravitational force from 1 to 3 g during the launch, before reaching about 0 g at FD2; (ii) adaptation to 0 g at FD14; (iii) increase in gravity from 0 to approximately 1.5-1.8 g before reaching 1 g at R + 1; and (iv) readaptation to 1 g at R + 13. Fos- and FRA-positive cells were identified in the brainstem of flight rats and ground-based controls using immunocytochemistry. With respect to control rats, the number of labeled cells increased in flight animals in the medial and spinal vestibular nuclei (but not in the lateral vestibular nucleus) at FD2, decreased at FD14, greatly increased at R + 1 and returned to baseline levels at R + 13. Similar changes in IEG expression were also observed in the nucleus of the solitary tract, the area postrema and the central nucleus of the amygdala. In particular, in these vegetative areas the number of Fos-positive cells decreased in flight rats with respect to controls at FD14, i.e. after exposure to 0 g, but significantly increased at R + 1, i.e. after return to 1 g. Thus, altered gravitational fields produced molecular changes in vestibular nuclei controlling somatic functions, as well as in related medullary and basal forebrain structures regulating vegetative functions.

Fos-related antigens are involved in the transcriptional responses of locus coeruleus neurons to altered gravitational fields in rats

Locus coeruleus (LC) neurons, which have widespread projections to the whole brain, respond to natural stimulation of macular receptors. Using immunocytochemistry we investigated whether rats exposed to altered gravitational fields showed changes in Fos and Fos-related antigen (FRA) protein levels in the LC. Fos protein is induced very rapidly and returns to basal levels within hours after stimulation, while FRAs persist for days or weeks after induction. Adult male albino rats (Fisher 344) were sacrificed at different time points during a space flight (NASA Neurolab Mission, STS-90) and the numbers of Fos- and FRA-positive cells in the LC were counted and compared to those in ground-based control rats. No significant changes in Fos protein expression were detected in the LC under different space flight conditions. In contrast, the number of FRA-positive cells increased on average to 167% of that of the controls at FD2, i.e. when gravity increased from 1 to 3 g during the launch before reaching about 0 g. FRA-labeled neurons then decreased to 46% of control values at FD14, i.e. after adaptation to 0 g, but increased again to 317% of control values at R + 1, when the animals were exposed to an increase in gravitational force from 0 to 1.5-1.8 g before reaching 1 g during landing. The number of labeled cells was 193% of the control values at R + 13, i.e. after readaptation to 1 g. Thus gravitational force appears to be very effective in inducing a long-term increase in FRA protein expression in the LC. Because activity in the noradrenergic LC neurons may increase Fos expression in several target structures, we postulate that the long-lasting induction of FRAs in the LC at FD2, and more prominently at R + 1, may contribute to the long-term molecular changes which probably occur in the brain during adaptation to 0 g and readaptation to 1 g.

Jun, Fos and Krox in the thalamus after C-fiber stimulation: coincident-input-dependent expression, expression across somatotopic boundaries, and nucleolar translocation

Expression of the inducible transcription factors Jun, Fos and Krox is commonly used to map neurons in the brain that are activated by sensory inputs. However, some neurons known to be electrically excited by such inputs do not always express these factors. In particular, stimulation of hindlimb sensory nerve C-fibers induces expression of c-Fos in the medial thalamus (the mediodorsal, intermediodorsal, centrolateral and centromedial), but not in the lateral thalamus (the ventroposterolateral, ventroposteromedial and posterior group). We hypothesized that c-Fos expression might only occur in these lateral areas after more complex stimulation patterns, or that only other transcription factors can be induced in these areas by such stimuli. Thus we examined the effects of single, repeated and coincident C-fiber inputs on expression of six inducible transcription factors in the medial, lateral and reticular thalamus of the rat. A weak C-fiber input caused by noxious mechanical stimulation of the skin of one hindpaw did not induce expression of c-Fos, FosB, Krox-20 or Krox-24; but it did reduce the basal expressions of c-Jun and JunD in both the medial and lateral areas. An intense input produced by electrical stimulation of all the C-fibers in one sciatic nerve also failed to induce expression of c-Fos, FosB, Krox-20 or Krox-24 in the medial or lateral areas. However, in the medial thalamus it increased c-Jun and reduced the basal expression of JunD, whereas in the lateral thalamus it had no effect on c-Jun but again reduced the basal expression of JunD. With repeated stimulation, i.e. when the noxious stimulus was applied to the contralateral hindpaw 6 h after the sciatic stimulation, there was again no induction of c-Fos, FosB or Krox-20 in the medial thalamus; but there was an increase in c-Jun and Krox-24, and a decrease in JunD levels. In the lateral thalamus the repeated stimulation again failed to induce c-Fos, but the expressions of FosB, c-Jun and Krox-24 were increased, and that of JunD was again reduced. With coincident stimulation, i.e. when a stimulus was applied to each hindpaw simultaneously, c-Fos and Krox-24 remained absent; but there was a marked induction of FosB and Krox-20, a strong repression of c-Jun, and no effect or a reduction of the basal levels of JunD. This coincident stimulation also caused FosB to appear in the nucleolus of many thalamic neurons. MK-801, but not L-NAME, blocked all these changes. In summary, noxious stimulation affects the expression of all transcription factors in the medial, lateral and reticular thalamus in a complex manner depending upon the inducible transcription factor considered, the thalamic nucleus, and the stimulation paradigm. The expression of some transcription factors uniquely after simultaneous inputs suggests they act as coincidence detectors at the gene level.

Kainate-induced genes in the hippocampus: lessons from expression patterns

Kainate, the analog of the excitatory amino acid L-glutamate, upon binding to non-NMDA glutamate receptors, causes depolarization of neurons followed by severe status epilepticus, neurodegeneration, plasticity and gliosis. These events are best observed in hippocampus, the limbic structure implicated in learning and long-term memory formation. Neurons in all hippocampal structures undergo hyper-activation, however, whereas the cells in the CA subfields degenerate within 2--3 days following the application of kainate, the granule cells of the dentate gyrus are resistant to any form of neurodegeneration and even initiate new synaptic contacts. These physiological and histological changes are modulated by short-term and long-term alterations in gene expression. Perhaps close examination of the changing spatio-temporal patterns of mRNAs of various genes may help in generating a clearer picture of the molecular events leading to complex cognitive functions.

Decreased c-fos expression in experimental neonatal hydrocephalus: evidence for reduced neuronal activation

Although neonatal hydrocephalus often results in residual neurological impairments, little is known about the cellular mechanisms responsible for these deficits. The immediate early gene, fos (c-fos), functions as a “third messenger” to regulate protein synthesis and is a good marker for neuronal activation. To identify functional changes in neurons at the cellular level, the authors quantified fos RNA expression and localized fos protein in the H-Tx rat model of congenital hydrocephalus. Tissue samples from sensorimotor and auditory regions were obtained from hydrocephalic rats and age-matched, normal litter mates at 1, 6, 12, and 21 days of age (four-six animals in each group) and processed for immunohistochemical analysis of fos and Northern blot analysis of RNA. At 12 days of age, hydrocephalic animals exhibited significant decreases in the ratio of fos immunoreactive cells to Nissl-stained neurons from both cortical regions, but no statistical differences were noted in fos expression. At 21 days of age, both the ratio of fos immunoreactive cells to Nissl-stained neurons and fos expression decreased significantly. The number of fos-positive neurons decreased in all cortical layers but was most prominent in layers V through VI. This decrease did not appear to be caused by neuronal death because examination of Nissl-stained sections revealed many viable neurons within the areas where fos immunoreactivity was absent. These results suggest that progressive neonatal hydrocephalus reduces the capacity for neuronal activation in the cerebral cortex, primarily in those neurons that provide corticofugal projections, and that this impairment may begin during relatively early stages of ventriculomegaly.

DeltaFosB: a molecular mediator of long-term neural and behavioral plasticity

DeltaFosB, a member of the Fos family of transcription factors, is derived from the fosB gene via alternative splicing. Just as c-Fos and many other Fos family members are induced rapidly and transiently in specific brain regions in response to many types of acute perturbations, novel isoforms of DeltaFosB accumulate in a region-specific manner in brain uniquely in response to many types of chronic perturbations, including repeated administration of drugs of abuse or of antidepressant or antipsychotic treatments. Importantly, once induced, these DeltaFosB isoforms persist in brain for relatively long periods due to their extraordinary stability. Mice lacking the fosB gene show abnormal biochemical and behavioral responses to chronic administration of drugs of abuse or antidepressant treatments, consistent with an important role for DeltaFosB in mediating long-term adaptations in the brain. More definitive evidence to support this hypothesis has recently been provided by inducible transgenic mice, wherein biochemical and behavioral changes, which mimic the chronic drug-treated state, are seen upon overexpression of DeltaFosB in specific brain regions. This evolving work supports the view that DeltaFosB functions as a type of 'molecular switch' that gradually converts acute responses into relatively stable adaptations that underlie long-term neural and behavioral plasticity to repeated stimuli.

Long-term increase of Sp-1 transcription factors in the hippocampus after kainic acid treatment

Systemic administration of kainic acid (KA), a glutamate receptor agonist, causes robust seizures and has been used as an excellent rodent model for human temporal lobe epilepsy. Recently, we have demonstrated that a single injection of KA increases the steady-state levels of proenkephalin (PENK) mRNA in the rat hippocampus for at least one year. However, the molecular mechanisms underlying this long-term increase in PENK mRNA levels have not been clearly defined. To determine the possible involvement of the Sp-1 transcription factors in this regulation, electrophoresis mobility-shift assays were used to study the expression of Sp-1 factors in the hippocampus after KA treatment. The results showed that there are long-lasting increases in Sp-1 DNA-binding activity. The Sp-1 DNA-binding complexes were only competed by the non-radioactive Sp-1 element and not by ENKCRE2, AP-1 or CRE elements, indicating the specificity of Sp-1 DNA-binding activity. Since the expression of Sp-1 parallels the time course of long-lasting increase in the expression of PENK mRNA and mossy fiber sprouting after KA treatment, we hypothesize that the increase in Sp-1 activity may be associated with the long-term changes in the plasticity of hippocampal function after KA-induced seizures.

Essential role of the fosB gene in molecular, cellular, and behavioral actions of chronic electroconvulsive seizures

The role of Fos-like transcription factors in neuronal and behavioral plasticity has remained elusive. Here we demonstrate that a Fos family member protein plays physiological roles in the neuronal, electrophysiological, and behavioral plasticity associated with repeated seizures. Repeated electroconvulsive seizures (ECS) induced isoforms of DeltaFosB in frontal cortex, an effect that was associated with increased levels of the NMDA receptor 1 (NMDAR1) glutamate receptor subunit. Induction of DeltaFosB and the upregulation of NMDAR1 occurred within the same neurons in superficial layers of neocortex. Activator protein-1 (AP-1) complexes composed of DeltaFosB were bound to a consensus AP-1 site in the 5'-promoter region of the NMDAR1 gene. The upregulation of NMDAR1 was absent in mice with a targeted disruption of the fosB gene. In addition, repeated ECS treatment caused progressively shorter motor seizures (tolerance) in both rats and wild-type mice, as well as reduced NMDA-induced inward currents in pyramidal neurons from superficial layers of the neocortex of wild-type mice. These behavioral and electrophysiological effects were also significantly attenuated in fosB mutant mice. These findings identify fosB gene products as transcription factors critical for molecular, electrophysiological, and behavioral adaptations to motor seizures.

Behavioural sensitization in 6-hydroxydopamine-lesioned rats is related to compositional changes of the AP-1 transcription factor: evidence for induction of FosB- and JunD-related proteins

Rats with unilateral dopamine denervation exhibit turning behaviour in response to the selective D1 agonist SKF 38393 only after a previous exposure to dopamine agonists. We demonstrate here that this 'priming' phenomenon is related to both an increased expression of the pre-existing AP-1 complex and the occurrence of novel AP-1 complexes which are formed by FosB- and JunD-related proteins. While the former protein is expressed as a consequence of the dopamine denervation, the latter is related to the first exposure to a dopamine agonist. Pre-treatment with MK-801, an antagonist for glutamatergic receptors, prevents both the priming development and the AP-1 compositional changes. Rotational behaviour induced by SKF 38393 closely correlates with the presence of the priming AP-1 complexes, regardless of the capability of the D1 agonist to induce the immediate-early gene cFos.