Predominant expression of nuclear activator protein-1 complex with DNA binding activity following systemic administration of N-methyl-D-aspartate in dentate granule cells of murine hippocampus

Neuroprotective effects of isoliquiritigenin against cognitive impairment via suppression of synaptic dysfunction, neuronal injury, and neuroinflammation in rats with kainic acid-induced seizures

Epileptogenesis is a dynamic process initiated by insults to brain and commonly accompanied by cognitive impairment. Isoliquiritigenin (ISL), a flavonoid in licorice, has a broad spectrum of biological effects including anti-inflammatory and antioxidant activities. However, the protective effects of ISL against cognitive impairment in epileptic processes and the underlying molecular mechanism are not well understood. To address these questions, we established an reproducible seizure model by intracerebroventricular injection of kainic acid (KA) in 21-day-old rats; ISL was intraperitoneally administered three times prior to KA injection, and changes in cognitive function; synaptic plasticity; neuronal injury; number of glial cells; and expression of pro-inflammatory cytokines and nuclear factor-like (NRF)2 signaling and NACHT, LRR, and PYD domains-containing protein (NLRP)3 inflammasome components in the hippocampus were examined. Rats with KA-induced seizures showed longer average escape latency and decreases in the number of platform crossings and average time spent in the target quadrant in the Morris water maze; ISL pretreatment reversed this decline in cognitive impairment and increased the protein levels of synaptophysin, postsynaptic density-95 and brain-derived neurotrophic factor while reducing the number of Fluoro Jade B-positive cells, microglia, and astrocytes; cleaved-Caspase-3 and -9 protein levels; and tumor necrosis factor-α, interleukin (IL)-1β, and IL-18 production. It also enhanced the nuclear localization of NRF2, hemeoxygenase-1, and NAD(P)H:quinone oxidoreductase (NQO) 1, and reversed the upregulation of NLRP3 inflammasome components NLRP3 and Caspase-1 induced by KA injection. Thus, ISL protects against cognitive impairment in KA-induced epileptic processes possibly through regulation of NRF2 signaling and the NLRP3 inflammasome pathway.

Organic cation transporter-mediated ergothioneine uptake in mouse neural progenitor cells suppresses proliferation and promotes differentiation into neurons

The aim of the present study is to clarify the functional expression and physiological role in neural progenitor cells (NPCs) of carnitine/organic cation transporter OCTN1/SLC22A4, which accepts the naturally occurring food-derived antioxidant ergothioneine (ERGO) as a substrate in vivo. Real-time PCR analysis revealed that mRNA expression of OCTN1 was much higher than that of other organic cation transporters in mouse cultured cortical NPCs. Immunocytochemical analysis showed colocalization of OCTN1 with the NPC marker nestin in cultured NPCs and mouse embryonic carcinoma P19 cells differentiated into neural progenitor-like cells (P19-NPCs). These cells exhibited time-dependent [³H]ERGO uptake. These results demonstrate that OCTN1 is functionally expressed in murine NPCs. Cultured NPCs and P19-NPCs formed neurospheres from clusters of proliferating cells in a culture time-dependent manner. Exposure of cultured NPCs to ERGO or other antioxidants (edaravone and ascorbic acid) led to a significant decrease in the area of neurospheres with concomitant elimination of intracellular reactive oxygen species. Transfection of P19-NPCs with small interfering RNA for OCTN1 markedly promoted formation of neurospheres with a concomitant decrease of [³H]ERGO uptake. On the other hand, exposure of cultured NPCs to ERGO markedly increased the number of cells immunoreactive for the neuronal marker βIII-tubulin, but decreased the number immunoreactive for the astroglial marker glial fibrillary acidic protein (GFAP), with concomitant up-regulation of neuronal differentiation activator gene Math1. Interestingly, edaravone and ascorbic acid did not affect such differentiation of NPCs, in contrast to the case of proliferation. Knockdown of OCTN1 increased the number of cells immunoreactive for GFAP, but decreased the number immunoreactive for βIII-tubulin, with concomitant down-regulation of Math1 in P19-NPCs. Thus, OCTN1-mediated uptake of ERGO in NPCs inhibits cellular proliferation via regulation of oxidative stress, and also promotes cellular differentiation by modulating the expression of basic helix-loop-helix transcription factors via an unidentified mechanism different from antioxidant action.

Glutamate preferentially suppresses osteoblastogenesis than adipogenesis through the cystine/glutamate antiporter in mesenchymal stem cells

We have shown that glutamate (Glu) signaling machineries, such as receptors (GluR) and transporters, are functionally expressed by mesenchymal stem cells, in addition to by their progeny cells such as osteoblasts and chondrocytes. Sustained exposure to Glu induced significant decreases in alkaline phosphatase (ALP) staining and osteoblastic marker gene expression in the mesenchymal C3H10T1/2 stem cells infected with runt-related transcription factor-2 (Runx2) adenovirus, without markedly affecting Oil Red O staining for adipocytes in cells cultured with adipogenic inducers. In cells with Runx2 adenovirus, the cystine/Glu antiporter substrate cystine significantly prevented the decreases by Glu in both ALP staining and osteoblastic marker gene expression, with GluR agonists being ineffective. In cells with Runx2 adenovirus, Glu significantly decreased [14C]cystine uptake, intracellular glutathione (GSH) level, Runx2 recruitment to osteocalcin promoter and nuclear Runx2 protein level, respectively. Cystine again significantly prevented the decreases by Glu in both GSH levels and Runx2 recruitment. In mouse bone marrow stromal cells, Glu and a GSH depleter significantly decreased ALP staining without affecting Oil Red O staining. Knockdown of the cystine/Glu antiporter led to markedly decreased ALP staining and GSH levels, with concomitant prevention of the decrease by Glu, in cells with Runx2 adenovirus. These results suggest that Glu may play a role as a negative regulator at an early differentiation stage into osteoblasts than adipocytes through a mechanism relevant to nuclear translocation of Runx2 after regulation of intracellular GSH levels by the cystine/Glu antiporter expressed in mesenchymal stem cells.

Possible promotion of neuronal differentiation in fetal rat brain neural progenitor cells after sustained exposure to static magnetism

We have previously shown significant potentiation of Ca(2+) influx mediated by N-methyl-D-aspartate receptors, along with decreased microtubules-associated protein-2 (MAP2) expression, in hippocampal neurons cultured under static magnetism without cell death. In this study, we investigated the effects of static magnetism on the functionality of neural progenitor cells endowed to proliferate for self-replication and differentiate into neuronal, astroglial, and oligodendroglial lineages. Neural progenitor cells were isolated from embryonic rat neocortex and hippocampus, followed by culture under static magnetism at 100 mT and subsequent determination of the number of cells immunoreactive for a marker protein of particular progeny lineages. Static magnetism not only significantly decreased proliferation of neural progenitor cells without affecting cell viability, but also promoted differentiation into cells immunoreactive for MAP2 with a concomitant decrease in that for an astroglial marker, irrespective of the presence of differentiation inducers. In neural progenitors cultured under static magnetism, a significant increase was seen in mRNA expression of several activator-type proneural genes, such as Mash1, Math1, and Math3, together with decreased mRNA expression of the repressor type Hes5. These results suggest that sustained static magnetism could suppress proliferation for self-renewal and facilitate differentiation into neurons through promoted expression of activator-type proneural genes by progenitor cells in fetal rat brain.

Neurogenesis mediated by gamma-aminobutyric acid and glutamate signaling

In this review, we will summarize our ongoing studies on the functionality of both gamma-aminobutyric acid (GABA) and glutamate receptors expressed by undifferentiated neural progenitor cells isolated from embryonic rodent brains. Cells were cultured with growth factors for the formation of round spheres by clustered cells under floating conditions, whereas a reverse transcription polymerase chain reaction analysis revealed expression of mRNA for particular subtypes of different ionotropic and metabotropic GABA and glutamate receptors in undifferentiated progenitors and neurospheres. Moreover, sustained exposure to either GABAergic or glutamatergic agonists not only modulated the size of neurospheres formed, but also affected spontaneous and induced differentiation of neural progenitor cells into particular progeny cell lineages such as neurons and astroglia. Both GABA and glutamate could play a pivotal role in the mechanisms underlying proliferation for self-replication along with the determination of subsequent differentiation fate toward particular progeny lineages through activation of their receptor subtypes functionally expressed by undifferentiated neural progenitor cells. Accordingly, neurogenesis seems to be also under control by GABAergic and glutamatergic signaling in developing brains as seen with neurotransmission in adult brains.

Promotion of neuronal differentiation through activation of N-methyl-D-aspartate receptors transiently expressed by undifferentiated neural progenitor cells in fetal rat neocortex

Neural progenitor cell is a generic term for undifferentiated cell populations composed of neural stem, neuronal progenitor, and glial progenitor cells with abilities for self-renewal and multipotentiality. In this study, we have attempted to evaluate the possible functional expression of N-methyl-D-aspartate (NMDA) receptors by neural progenitor cells prepared from neocortex of 18-day-old embryonic rats. Cells were cultured in the presence of basic fibroblast growth factor (bFGF) for different periods up to 12 days under floating conditions. Reverse transcription-polymerase chain reaction and fluorescence imaging analyses revealed transient expression of functional NMDA receptors in neurospheres formed by clustered progenitors during the culture with bFGF. A similarly potent increase was seen in the fluorescence intensity after brief exposure to NMDA in cells differentiated after the removal of bFGF under adherent conditions, and an NMDA receptor antagonist invariably prevented these increases by NMDA. Moreover, sustained exposure to NMDA not only inhibited the formation of neurospheres when exposed for 10 days from day 2 to day 12 but also promoted spontaneous and induced differentiation of neurospheres to cells immunoreactive for a neuronal marker protein on immunocytochemistry and Western blotting analyses. These results suggest that functional NMDA receptors may be transiently expressed to play a role in mechanisms underlying the modulation of proliferation along with the determination of subsequent differentiation fate toward a neuronal lineage in neural progenitor cells of developing rat neocortex.

Activation of GABA(A) receptors facilitates astroglial differentiation induced by ciliary neurotrophic factor in neural progenitors isolated from fetal rat brain

Immunocytochemical analysis confirmed the validity of isolation procedures of neural progenitors capable of self-replication and differentiation from discrete fetal rat brain structures. A reverse transcription-polymerase chain reaction analysis revealed the expression of particular GABA(A) receptor (GABA(A)R), GABA(B)R-1 and GABA(C)R, but not GABA(B)R-2, subunits in neocortical cells before commitment. Sustained exposure to the GABA(A)R agonist muscimol at 100 mumol/L led to significant increases in the mitochondrial activity and the total areas of neocortical neurospheres formed during the cultivation for 12 days in a manner sensitive to a GABA(A)R antagonist, with lactate dehydrogenase release being unchanged. Moreover, prior sustained exposure to muscimol significantly facilitated the subsequent expression of an astroglial marker protein in cells differentiated by ciliary neurotrophic factor (CNTF) toward an astroglial lineage, with a concomitant decrease in the neuronal marker protein expression, in an antagonist-sensitive manner on Western blotting analysis. However, muscimol failed to significantly affect the expression of both marker proteins in cells differentiated in either the presence or absence of all-trans-retinoic acid. These results suggest that prior activation of GABA(A)R may preferentially facilitate the commitment by CNTF of neural progenitor cells toward an astroglial lineage after simulation of the self-replication activity in the developing rat brain.

Novel interaction between HMGA1a and StIP1 in murine terminally differentiated retina

High mobility group protein A1a (HMGA1a) is expressed at high levels in embryonic cells and has been implicated in their transcriptional regulation. However, it has been reported that high levels of HMGA1a expression are normally detected in the photoreceptor of adult (terminally differentiated cells) murine retina. We showed that biochemical purification of the recombinant HMGA1a binding activity in nuclear fractions from murine retina, but not from hippocampus, resulted in STAT3 interacting protein 1 (StIP1) that formed a novel complex with HMGA1a, STAT3 and homeodomain-interacting protein kinase 2 (HIPK2). While StIP1 expressions in brain, liver, lung, heart, skeletal muscle, spleen and thymus have previously been demonstrated, this is the first report that StIP1 was expressed in nuclear fractions from murine retina, and that in murine retina there are several novel complexes of transcriptional regulators consisting of HMGA1a, StIP1, STAT3 and HIPK2.

Down-regulation of norepinephrine transporter function induced by chronic administration of desipramine linking to the alteration of sensitivity of local-anesthetics-induced convulsions and the counteraction by co-administration with local anesthetics

Alterations of norepinephrine transporter (NET) function by chronic inhibition of NET in relation to sensitization to seizures induce by cocaine and local anesthetics were studied in mice. Daily administration of desipramine, an inhibitor of the NET, for 5 days decreased [(3)H]norepinephrine uptake in the P2 fractions of hippocampus but not cortex, striatum or amygdalae. Co-administration of lidocaine, bupivacaine or tricaine with desipramine reversed this effect. Daily treatment of cocaine increased [(3)H]norepinephrine uptake into the hippocampus. Daily administration of desipramine increased the incidence of appearance of lidocaine-induced convulsions and decreased that of cocaine-induced convulsions. Co-administration of lidocaine with desipramine reversed the changes of convulsive activity of lidocaine and cocaine induced by repeated administration of desipramine. These results suggest that down-regulation of hippocampal NET induced by chronic administration of desipramine may be relevant to desipramine-induced sensitization of lidocaine convulsions. Inhibition of Na(+) channels by local anesthetics may regulate desipramine-induced down-regulation of NET function. Repeated administration of cocaine induces up-regulation of hippocampal NET function. Desipramine-induced sensitization of lidocaine seizures may have a mechanism distinct from kindling resulting from repeated administration of cocaine.

In vivo treatment with the K+ channel blocker 4-aminopyridine protects against kainate-induced neuronal cell death through activation of NMDA receptors in murine hippocampus

Activation of NMDA receptors has been shown to induce either neuronal cell death or neuroprotection against excitotoxicity in cultured neurons in vitro. To elucidate in vivo neuroprotective role of NMDA receptors, we investigated the effects of activation of NMDA receptors by endogenous glutamate on kainate-induced neuronal damage to the mouse hippocampus in vivo. The systemic administration of the K+ channel blocker 4-aminopyridine (4-AP, 5 mg/kg, i.p.) induced expression of c-Fos in the hippocampal neuronal cell layer, which expression was completely abolished by the noncompetitive NMDA receptor antagonist MK-801, thus indicating that the administration of 4-AP would activate NMDA receptors in the hippocampal neurons. The prior administration of 4-AP at 1 h to 1 day before significantly prevented kainate-induced pyramidal cell death in the hippocampus and expression of pyramidal cells immunoreactive with an antibody against single-stranded DNA. Further immunohistochemical study on deoxyribonuclease II revealed that the pretreatment with 4-AP led to complete abolition of deoxyribonuclease II expression induced by kainate in the CA1 and CA3 pyramidal cells. The neuroprotection mediated by 4-AP was blocked by MK-801 and by the adenosine A1 antagonist 8-cyclopenthyltheophylline. Taken together, in vivo activation of NMDA receptors is capable of protecting against kainate-induced neuronal damage through blockade of DNA fragmentation induced by deoxyribonuclease II in the murine hippocampus.

Nuclear condensation of cyclic adenosine monophosphate responsive element-binding protein in discrete murine brain structures

We have directed a polyclonal antibody against an oligo-peptide (123-136) of the transcription factor cyclic AMP responsive element-binding protein (CREB) including the serine residue at 133. Rabbit sera were purified by ammonium sulfate precipitation, followed by affinity chromatography to homogeneity on one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified antibody not only induced marked supershift of CREB binding, without affecting binding of activator protein-1 on gel retardation electrophoresis, but also differentiated between CREB and CREB phosphorylated at serine133 in brain nuclear fractions on Western blotting. Immunoreactive CREB was detected in both cytosolic and nuclear fractions of discrete murine brain structures but was more highly condensed in cerebellum than in neocortex and hippocampus. Incubation of brain nuclear fractions led to a marked export of immunoreactive CREB in a temperature-dependent manner, whereas the temperature-dependent export activity was significantly lower in cerebellum than in other brain structures. Suppression of general new protein synthesis by cycloheximide (500 mg/kg, i.p.) in vivo resulted in a significant decrease in the nuclear CREB level, with a concomitant increase in the cytosolic level in hippocampus, but not in cerebellum. These results suggest that the nuclear export activity might vary from region to region in murine brains through a hitherto unidentified mechanism other than the nuclear localization signal, to result in different nuclear condensation ratios for subsequent elicitation of differential transcriptional activities by the constitutive transcription factor CREB in the nucleus.

Possible involvement of the expression and phosphorylation of N-Myc in the induction of HMGA1a by hypoxia in the human neuroblastoma cell line

Increased expression of N-Myc and expression of the high mobility group protein A1a (HMGA1a) were observed in the nuclei of SK-N-SH cells following exposure to hypoxia. These observations were accompanied by the appearance of additional high molecular weight bands, which were eliminated by pretreatment with alkaline phosphatase. Immunoprecipitation showed phosphorylation of serine, threonine and tyrosine residues of N-Myc in the nucleus. These results suggest that hypoxia-induced signals in SK-N-SH cells lead to persistent expression of HMGA1a, which may induce expression of the transcription factor N-Myc, and that phosphorylation at serine, threonine and tyrosine residues of N-Myc occurs at an early stage after stimulation. Such signal consolidation processes could play a role in neuronal survival after hypoxia in neurons.

Transcriptional Regulation of Neuronal Genes and Its Effect on Neural Functions: Gene Expression in Response to Static Magnetism in Cultured Rat Hippocampal Neurons

We have previously shown a marked but transient increase in DNA binding of the nuclear transcription factor activator protein-1 after brief exposure to static magnetic fields in cultured rat hippocampal neurons, suggesting that exposure to static magnetism would lead to long-term consolidation as well as amplification of different functional alterations through modulation of de novo protein synthesis at the level of gene transcription in the hippocampus. Hippocampal neurons were cultured under sustained exposure to static magnetic fields at 100 mT, followed by extraction of total RNA for differential display (DD) analysis using random primers. The first and the second DD polymerase chain reaction similarly showed the downregulation of particular genes in response to sustained magnetism. Nucleotide sequence analysis followed by BLASTN homology searching revealed high homology of these 2 DD-PCR products to the 3' non-coding regions of the mouse basic helix-loop-helix transcription factor ALF1 and that of histone H3.3A, respectively. On Northern blot analysis using the 2 cloned differentially expressed fragments labeled with [alpha-(32)P]dCTP by the random primer method, a marked decrease was seen in expression of mRNA for ALF1 and histone H3.3A in hippocampal neurons cultured under sustained exposure to static magnetic fields at 100 mT. It thus appears that static magnetism may modulate cellular integrity and functionality through expression of a variety of responsive genes required for gene transcription and translation, proliferation, differentiation, maturation, survival, and so on in cultured rat hippocampal neurons.

Glutamate receptor-mediated regulation of c-fos expression in cultured microglia

It has been recently shown that the expression of various types of neurotransmitter receptors is not restricted to neurons but also observed in a majority of glial cells. However, their function in glial cells is not known well in both physiological and pathological conditions. Here, we investigated the role of glutamate receptor on c-fos gene expression in primary cultured and BV-2 microglia. Our results demonstrated that both c-fos mRNA and protein were dramatically induced following treatment with various glutamate receptor agonists (500muM); N-methyl-d-aspartic acid, kainic acid, (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and (RS)-3,5-dihydroxyphenylglycine. The responses were significantly suppressed by specific antagonists and also by calcium chelating agents EGTA and BAPTA-AM. Our results suggest that glutamate receptor activation regulates c-fos gene expression by modifying intracellular calcium levels in microglia. These findings might provide an insight in to understanding the function of microglial glutamate receptors in neuron-to-glial interaction under the excitotoxic conditions.

Regulation of neuronal differentiation by N-methyl-D-aspartate receptors expressed in neural progenitor cells isolated from adult mouse hippocampus

In vitro culture of neural progenitor cells isolated from adult murine hippocampus according to the Percoll density gradient method resulted in formation of round spheres not immunoreactive to microtubule-associated protein-2 (MAP-2) or glial fibrillary acidic protein in the presence of basic fibroblast growth factor within 12 days in vitro (DIV). Reverse-transcription PCR analysis revealed constitutive expression in these neurospheres of different subunits required for assembly of functional heteromeric N-methyl-D-aspartate (NMDA) receptor channels. Immunocytochemical analysis confirmed expression of NR1, NR2A, and NR2B subunits in neurospheres cultured for 4-12 DIV. Brief (5 min) exposure to NMDA induced marked expression of c-Fos, Fos-B, Fra-2, and c-Jun proteins in neurospheres cultured for 12 DIV 2 hr later. The NMDA receptor antagonist dizocilpine markedly inhibited expression of both c-Jun and c-Fos proteins in NMDA-exposed neurospheres. Sustained exposure to NMDA not only markedly inhibited neurosphere formation by 12 DIV when exposed from 4-12 DIV, but also resulted in facilitation of subsequent differentiation of neurospheres exposed to all-trans retinoic acid to cells immunoreactive to both neuron-specific enolase and neuronal nuclei, in addition to MAP-2, as revealed by Western blot and immunocytochemistry analyses. These results suggest that functional heteromeric NMDA receptors may be expressed constitutively in neural progenitor cells before differentiation to play a crucial role in commitment and differentiation to neurons in adult murine hippocampus.

Novel function of PS2V: change in conformation of tau proteins

Neurofibrillary tangles (NFTs) are associated with many neurodegenerative disorders, such as Alzheimer's disease (AD). The major components of NFTs are hyper-phosphorylated tau proteins. The alternatively spliced form of the presenilin-2 (PS2) gene (PS2V) has been observed in sporadic AD brains. However, it is not known whether there is a relationship between tau aggregation/hyper-phosphorylation and PS2V expression. In this manuscript, we make the first report of PS2V alterations in the conformation of the tau protein (unknown form of tau) in the human neuroblastoma cell line.

Enhanced binding activity of nuclear antioxidant-response element through possible formation of Nrf2/Fos-B complex after in vivo treatment with kainate in murine hippocampus

To evaluate whether in vivo glutamate signals modulate signaling processes mediated by antioxidant-response element (ARE), we examined ARE binding in nuclear extracts from the hippocampus after in vivo treatment of mice with kainate. Enhancement of ARE binding was found at 2 h to 3 days after kainate treatment. Supershift analysis indicated possible involvement of Nrf2, Fos-B, and c-Fos in ARE binding in hippocampal nuclear extracts obtained from kainate-treated animals. On super-supershift analysis by combination of these antibodies, ARE probe/protein complex was shifted by the anti-Fos-B antibody alone, but not by the anti-c-Fos antibody alone, and further addition of the anti-Nrf2 antibody dramatically eliminated binding of the complex shifted by the anti-Fos-B antibody in hippocampal nuclear extracts from kainate-treated animals. Kainate treatment induced a profound increase in levels of c-Fos and Fos-B, without markedly affecting that of Nrf2 in nuclear extracts from the hippocampus. Co-localization of Nrf2 with both Fos-B and c-Fos was found in neuronal cell layers of the hippocampus in kainate-treated animals. RT-PCR analysis revealed that kainate treatment increases glutathione-S-transferase mRNA level in the hippocampus. Taken together, kainate signals may enhance nuclear ARE binding through an interaction between constitutive Nrf2 with inducible Fos-B expressed in murine hippocampus.

Fos-B expression is required for polyamine-induced increase in nuclear activator protein-1 DNA binding in discrete structures of murine brain

Spermidine (SPD) and spermine (SPN) have been shown to be endogenous agonists for N-methyl-D-aspartate (NMDA) receptors that could lead to expression of the nuclear transcription factor activator protein-1 (AP1) complex in the mammalian central nervous system both in vitro and in vivo. In nuclear extracts of murine whole brain, AP1 DNA binding increased significantly in a concentration-dependent manner with the addition of either SPD or SPN at a concentration range of 50-500 microM. Similarly, the nuclear proteins histone and dephosphorylated casein, but not phosphorylated casein, significantly increased AP1 DNA binding alone but in the presence of either SPD or SPN did not increase further binding. By contrast, another endogenous polyamine, putrescine, significantly prevented AP1 DNA binding increases by histone and dephosphorylated casein, but did not by itself significantly alter binding. Invariably, SPD and SPN effected significantly increased AP1 DNA binding in neocortex, hippocampus, striatum, midbrain, hypothalamus and cerebellum, but not in medulla-pons and spinal cord. Supershift and Western blotting analyses revealed relatively high constitutive expression of Fos-B protein in neocortex and hippocampus, but not in medulla-pons and spinal cord. Immunoprecipitation of Fos-B led to complete abolition of the ability of SPN and SPD to increase AP1 DNA binding in neocortical and hippocampal nuclear extracts. These results suggest that expression of Fos-B protein may be required for modulation of nuclear gene transcription by both SPD and SPN through stimulation DNA-binding activity of AP1 complex in murine central structures.

In vivo neuroprotective role of NMDA receptors against kainate-induced excitotoxicity in murine hippocampal pyramidal neurons

Activation of NMDA receptors has been shown to induce either neuronal cell death or neuroprotection against excitotoxicity in cultured cerebellar granule neurons in vitro. We have investigated the effects of pretreatment with NMDA on kainate-induced neuronal cell death in mouse hippocampus in vivo. The systemic administration of kainate (30 mg/kg), but not NMDA (100 mg/kg), induced severe damage in pyramidal neurons of the hippocampal CA1 and CA3 subfields 3-7 days later, without affecting granule neurons in the dentate gyrus. An immunohistochemical study using an anti-single-stranded DNA antibody and TdT-mediated dUTP nick end labeling analysis both revealed that kainate, but not NMDA, induced DNA fragmentation in the CA1 and CA3 pyramidal neurons 1-3 days after administration. Kainate-induced neuronal loss was completely prevented by the systemic administration of NMDA (100 mg/kg) 1 h to 1 day previously. No pyramidal neuron was seen with fragmented DNA in the hippocampus of animals injected with kainate 1 day after NMDA treatment. The neuroprotection mediated by NMDA was prevented by the non-competitive NMDA receptor antagonist MK-801. Taken together these results indicate that in vivo activation of NMDA receptors is capable of protecting against kainate-induced neuronal damage through blockade of DNA fragmentation in murine hippocampus.

Induced HMGA1a expression causes aberrant splicing of Presenilin-2 pre-mRNA in sporadic Alzheimer's disease

The aberrant splicing isoform (PS2V), generated by exon 5 skipping of the Presenilin-2 (PS2) gene transcript, is a diagnostic feature of sporadic Alzheimer's disease (AD). We found PS2V is hypoxia-inducible in human neuroblastoma SK-N-SH cells. We purified a responsible trans-acting factor based on its binding to an exon 5 fragment. The factor was identified as the high mobility group A1a protein (HMGA1a; formerly HMG-I). HMGA1a bound to a specific sequence on exon 5, located upstream of the 5' splice site. HMGA1a expression was induced by hypoxia and the protein was accumulated in the nuclear speckles with the endogenous splicing factor SC35. Overexpression of HMGA1a generated PS2V, but PS2V was repressed by cotransfection with the U1 snRNP 70K protein that has a strong affinity to HMGA1a. HMGA1a could interfere with U1 snRNP binding to the 5' splice site and caused exon 5 skipping. HMGA1a levels were significantly increased in the brain tissue from sporadic AD patients. We propose a novel mechanism of sporadic AD that involves HMGA1a-induced aberrant splicing of PS2 pre-mRNA in the absence of any mutations.

A dissociation of gamma-butyrolactone-induced absence seizure and CRE- and AP-1 DNA-binding activities in the developing rat brain

Generalized absence epilepsy is a neurological childhood disorder which is characterized by behavioral arrest with staring and by 3 Hz spike and wave discharges (SWDs) in the electroencephalogram (EEG). In the present study, we investigated the correlation between behavioral and EEG changes and nuclear cAMP-responsive element (CRE)- and activator protein-1 (AP-1) DNA-binding activities during gamma-butyrolactone (GBL)-induced absence seizure in the developing rat brain. In the adult postnatal day 60 (P60) rat brain, both the transcription factor activation and absence seizure in behavior and EEG were simultaneously induced 15 min after GBL injection. In the infant P20 rat or young P40 rat, a higher sensitivity to GBL induced absence epilepsy in behavior and EEG 10-15 min after injection compared with that of adult rat. By contrast, no significant increase of CRE- and AP-1 DNA-binding activities could be seen in the infant thalamus. A significant increase in CRE- and AP-1 DNA-binding activities first occurred in the P30-40 young thalamus at 30 and 90 min, respectively, after GBL injection. Such a dissociation of high inducibility of behavior and EEG changes and low inducibility of CRE- and AP-1 DNA-binding activities in the infant or young rat clearly indicates that the activation of nuclear CRE- and AP-1 DNA-binding activities is a late occurring phenomenon with a different developmental maturation of thalamocortical circuit compared with absence seizure.

Modulation of DNA binding of nuclear transcription factors with leucine-zipper motifs by particular endogenous polyamines in murine central and peripheral excitable tissues

Transcriptional regulation is one of the most important functions of polyamines in the nucleus of eukaryotic cells. The addition of the endogenous polyamines spermine and spermidine markedly increased DNA binding activity of the transcription factor activator protein-1 (AP1) in a concentration-dependent manner at a concentration range of 50 to 500 microM in nuclear extracts of murine whole brain when determined in the absence of added MgCl(2) on gel retardation electrophoresis. Similar but less potent potentiation was seen with DNA binding of cAMP responsive element binding protein (CREB), while both polyamines were ineffective in affecting that of c-Myc irrespective of the addition of MgCl(2). Unlabeled AP1 probe was invariably more potent in competing for AP1 binding than unlabeled CREB probe in either the presence or absence of spermine and spermidine. In addition to whole brain, both polyamines significantly increased AP1 binding in retina, adrenal and pituitary, without significantly affecting that in spleen. Moreover, ultraviolet and circular dichroism spectra analyses revealed that these two polyamines induced DNA topological transition of AP1 probe under the conditions favorable for the increase in AP1 binding. These results suggest that both spermine and spermidine may modulate gene transcription through cis- and trans-actions on AP1 binding in the nucleus in murine central and peripheral structures with high excitability.

Possible regulation by N-methyl-d-aspartate receptors of proliferative progenitor cells expressed in adult mouse hippocampal dentate gyrus

An immunohistochemical technique was employed to analyze mechanisms underlying modulation by N-methyl-d-aspartate (NMDA) receptors of proliferation of neural progenitor cells in adult mouse brain. The systemic administration of NMDA at 100 mg/kg resulted in marked expression of c-Fos, Fra-2 and c-Jun proteins in the granule cell layers of the dentate gyrus in murine hippocampus 2 h later, followed by a significant reduction of the incorporation of 5-bromo-2'-deoxyuridine (BrdU) in a manner sensitive to the antagonist dizocilpine 2 days after administration. The administration of NMDA also suppressed constitutive expression of both nestin and proliferating cell nuclear antigen (PCNA) in the dentate granule cells 2 days later, without markedly affecting cell viability for up to 8 weeks after administration. In the subventricular zone and olfactory bulb, however, NMDA failed to affect either the incorporation of BrdU or the expression of nestin and PCNA. The NR1 subunit was highly expressed in the dentate gyrus in addition to the stratum oriens in the hippocampus, but not in the subventricular zone and olfactory bulb. These results suggest that NMDA receptors may play a role crucial for maintenance of the integrity and function of proliferative neural progenitor cells through expression of the nuclear transcription factor activator protein-1 in granule cells of the dentate gyrus in adult mouse brain.

Nuclear transcription factors in the hippocampus

In the mammalian hippocampus, there is a trisynaptic loop that has been often referred to in studies on learning and memory mechanisms and their physiological correlate, the long-term potentiation (LTP). The three sets of synapses are formed by the fibers of perforant pathway terminating on granule cells and by the mossy fibers and Schaeffer collaterals making connections with the pyramidal cells. Each of the three types of synapses can develop LTP. LTP is accompanied by changes in gene expression and it is the nuclear transcription, involving specific transcription factors, that is the starting point for the series of biological amplifications and consolidations both necessary for such sustained changes. The transcription factors are proteins that control gene expression, development and functional formation in every eukaryotic cell. Two categories of transcription factors have been defined to date: general factors that comprise at least 20 proteins to form multiple preinitiation complex at the TATA box (TATA rich sequence) or regulatory factors that bind to promoter or enhancer regions at specific sites on the DNA close to, or distant from, the TATA box. Transcription factors have been divided into five different major classes according to unique protein motifs. These include basic domain, zinc-finger, helix-turn-helix, beta-Scaffold factors with minor groove contacts and other transcription factors not specifically classified. Much evidence has been accumulating in favor of the participation of several transcription factors in the consolidation of memory in the mammalian hippocampus following a spatial memory task. It is, therefore, of great importance that the involvement of transcription factors in de novo protein synthesis relevant to the synaptic mechanisms that mediate the formation of long-term memory should be summarized and discussed. No specific correlation between transduction of extracellular signals and expression of nuclear transcription factors, however, has been demonstrated to date.

Transcription factors and drugs in the brain

In mammalian cells, protein de novo synthesis is mainly regulated at the stage of gene transcription by RNA polymerase II in the nucleus. Transcription factors are proteins that bind to the specific nucleotide sequences at promoter or enhancer regions on target genes to control the transcription of mRNA from genomic DNA. In this article, we have outlined the signal responsiveness of different transcription factors to particular drugs in the brain. Nuclear transcription factors rapidly respond to a variety of extracellular signals carried by neurotransmitters, hormones and autacoids as a third messenger in frequent situations. Translated proteins are responsible for a number of physiological and pathological events for a long period in the brain. We have also discussed possible involvement of transcription factors in molecular mechanisms underlying development of tolerance and dependence to drugs following acute and chronic administration.

Localization of activator protein-1 complex with DNA binding activity in mitochondria of murine brain after in vivo treatment with kainate

To elucidate mechanisms underlying mitochondrial dysfunctions induced by glutamate, we have examined the effects of in vivo treatment with the ionotropic glutamate receptor agonist kainate on localization of the transcription factor activator protein-1 (AP-1) in mitochondria as well as nuclei of murine brain. A systemic administration of kainate dramatically enhanced AP-1 DNA binding in both mitochondrial and nuclear extracts of mouse cerebral cortex and hippocampus 1 hr to 3 d later. Unlabeled AP-1 probe selectively competed for AP-1 DNA binding in mitochondrial extracts of cortex and hippocampus obtained from mice injected with kainate. Supershift and immunoblotting analyses revealed participation of c-Fos, Fos-B, and Jun-B proteins in potentiation by kainate of mitochondrial AP-1 DNA binding in cortex and hippocampus. An immunohistochemical study demonstrated marked expression by kainate of c-Fos protein in the pyramidal and dentate granular layers, whereas an immunoelectron microscopic analysis showed localization of c-Fos protein within mitochondria, as well as nuclei, of the CA1 pyramidal and dentate granular cells in hippocampus obtained 2 hr after the administration of kainate. Mitochondrial AP-1 DNA binding was inhibited by particular unlabeled oligonucleotides containing sequences similar to the AP-1 site found in the noncoding region of mitochondrial DNA. Kainate markedly potentiated binding of radiolabeled oligonucleotide probes containing sequences effective in competing for AP-1 DNA binding in hippocampal mitochondrial extracts. These results suggest that kainate may facilitate expression of the AP-1 complex and subsequent translocation into mitochondria to participate in mechanisms associated with transcriptional regulation of mitochondrial DNA in murine hippocampus.

Activator protein-1 complex expressed by magnetism in cultured rat hippocampal neurons

Brief exposure for 15 min to static magnetic filed at 100 mT led to marked but transient potentiation of binding of a radiolabeled probe for activator protein-1 (AP1) in immature cultured rat hippocampal neurons with high expression of growth-associated protein-43. Immunoblotting and supershift analyses revealed that brief exposure to static magnetic field increased AP1 DNA binding through expression of Fra-2, c-Jun, and Jun-D proteins in immature cultured hippocampal neurons. Significantly less potent increases were seen in both intracellular free Ca(2+) concentration and AP1 binding following the addition of N-methyl-d-aspartate in these immature neurons exposed to magnetism 24 h before. These results suggest that brief exposure to weak static magnetic field may lead to desensitization of NMDA receptor channels through modulation of de novo synthesis of particular inducible target proteins at the level of gene transcription by the AP1 complex expressed in the nucleus of immature cultured rat hippocampal neurons.

Potentiation of nuclear activator protein-1 DNA binding following brief exposure to N-methyl-D-aspartate in immature cultured rat hippocampal neurons

Similar potentiation was seen with the nuclear transcription factor activator protein-1 (AP1) binding in rat hippocampal neurons cultured for 3 and 9 DIV, when determined immediately after exposure to 500 microM N-methyl-D-aspartate (NMDA) for 60-120 min. Growth-associated protein-43 was markedly expressed in hippocampal neurons cultured for 3-5 DIV, with a decline up to 9 DIV. In immature neurons cultured for 3 DIV, NMDA was effective in significantly potentiating AP1 binding even in the presence of Mg(2+) with less potency than in the absence of Mg(2+) when determined immediately after sustained exposure for 120 min. When determined 120 min after brief exposure for 5 min, by contrast, NMDA significantly potentiated AP1 binding at a range of 100-500 microM only in the absence of Mg(2+) in immature neurons cultured for 3 DIV. At least 60 min was required for significant potentiation of AP1 binding as an interval between brief exposure and subsequent cell harvest. Dizocilpine abolished the potentiation determined 120 min after brief exposure to 500 microM NMDA, and both dantrolene and nifedipine were similarly effective in significantly preventing the potentiation at 10-50 microM. These results suggest that NMDA may potentiate AP1 binding following a sustained increase in intracellular free Ca(2+) concentrations through influxes across NMDA-operated and L-type voltage-sensitive Ca(2+) channels, in addition to release from intracellular Ca(2+) stores, in immature cultured rat hippocampal neurons.

Nuclear degradation of particular Fos family members expressed following injections of NMDA and kainate in murine hippocampus

Transient glutamate signaling often leads to long lasting and permanent alterations of a variety of cellular functions through particular membrane receptors in the brain. For elucidation of mechanisms underlying long-term consolidation of transient extracellular signals, we have examined expression and degradation of particular Fos family member proteins required for assembly to the nuclear transcription factor activator protein-1 in this study. Transcription factors could modulate the activity of RNA polymerase II responsible for the formation of mRNA from genomic DNA in the nucleus and therefore regulate de novo synthesis of particular target functional proteins. Mice were intraperitoneally injected with 100 mg/kg N-methyl-D-aspartic acid (NMDA) or 40 mg/kg kainic acid (KA), followed by homogenization of hippocampus in the presence of different protease and phosphatase inhibitors 2 h after administration, and subsequent preparation of nuclear and cytosolic fractions. The systemic administration of both NMDA and KA induced marked expression of particular Fos family members, including c-Fos and Fra-2 proteins, in hippocampal nuclear and cytosolic fractions. Incubation at 30 degrees C for 1 to 18 h led to differential degradation profiles of each Fos family member protein in nuclear fractions in a manner peculiar to the individual excitants. Degradation rate was also affected by dialysis and subsequent addition of inhibitors for phosphatases and proteases. These results suggest that in vivo NMDA and KA signals may additionally modulate the activity of heterologous machineries responsible for breakdown of each Fos family member in a unique manner in nuclear fractions, rather than cytosolic fractions, of murine hippocampus.

Differential postreceptor signaling events triggered by excitotoxic stimulation of different ionotropic glutamate receptors in retinal neurons

The aim of this work was to investigate whether excitotoxicity induced by overstimulation of different ionotropic glutamate receptors could trigger different intracellular signaling cascades. Cultured chick neuronal retina cells, essentially amacrine-like, were particularly sensitive to the toxicity induced by non-NMDA glutamate receptor agonists. One hour stimulation with 100 microM kainate induced a reduction of cell viability of about 44%, as assessed by the MTT test 24 hr after stimulation. Kainate-induced toxicity was mediated through AMPA receptors. Glutamate (100 microM, 1 hr) reduced cell viability by 26%, essentially acting through N-methyl-D-aspartate receptors. Five hours after stimulation, neuronal retina cells had an apoptotic-like nuclear morphology. In retinal neurons, the excitotoxic stimulation, with either glutamate or kainate, induced a calcium-dependent enhancement of the DNA-binding activity of the activating protein-1 (AP-1) transcription factor, which was maximal 2 hr after stimulation. Glutamate induced a greater increase in the AP-1 DNA-binding activity than did kainate. Supershift assays using antibodies directed against different members of the Fos and Jun protein families showed that the AP-1 complex in retinal neurons includes proteins of the Fos family, namely, Fra-2, c-Jun, and Jun D. The DNA-binding activity of the nuclear factor-kappaB transcription factor was not significantly changed upon excitotoxic stimulation with any agonist. Stimulation of glutamate receptors with 100 microM kainate or 100 microM glutamate for 2 min was sufficient to induce the activation of the extracellular signal-regulated kinase (ERK). Inhibition of the ERK activation with the MEK inhibitors U 0126 and PD 98059 increased the toxicity induced by kainate but was without effect on the toxicity induced by glutamate. These results indicate that, although stimulation with both glutamate receptor agonists increased ERK phosphorylation, only kainate-induced ERK activation correlates with the activation of a survival signaling pathway. Our results suggest that, in chick embryo retinal neurons, the signaling pathways that mediate excitotoxic cell death and neuroprotection are stimulus specific.

Decrease in level of APG-2, a member of the heat shock protein 110 family, in murine brain following systemic administration of kainic acid

APG-2 belongs to the heat shock protein 110 family. Although kainic acid (KA)-induced seizures are known to elicit expression of inducible heat shock protein 70 (HSP70) in the brain, no investigation has been carried out on the APG-2 level after excitatory amino acid-induced seizures. By means of an immunoblot assay, we determined the levels of HSP70 and APG-2 in discrete brain structures of mice after a single intraperitoneal injection of KA or N-methyl-D-aspartic acid (NMDA). APG-2 level was significantly decreased in frontal cortex, hippocampus, and striatum three days after the administration of KA, while HSP70 level was increased in these regions following the administration. In any of these regions, APG-2 levels were returned to the control levels 10 days after the administration. However, no significant changes were observed in levels of both HSP70 and APG-2 in hypothalamus, midbrain, medulla-pons, and cerebellum of the mice. By contrast, NMDA administration did not significantly affect both levels in any of the regions examined. These findings indicate that the transient decrease in APG-2 expression is one of the intracellular events elicited by signals peculiar to KA, but not by those peculiar to NMDA, in telencephalon of murine brain.

Degradation of c-Fos protein expressed by N-methyl-D-aspartic acid in nuclear fractions of murine hippocampus

In both nuclear and cytosolic fractions of murine hippocampus, constitutive expression was seen with Fra-2 protein, but not with other Fos family members tested including c-Fos, Fos-B and Fra-1 proteins. Fos-B protein was only detected in nuclear fractions. The systemic administration of N-methyl-D-aspartic acid (NMDA) induced marked and transient expression of c-Fos protein, but not other family members, in both hippocampal fractions 2 h later. In vitro incubation at 30 degrees C led to more rapid degradation of inducible c-Fos protein than constitutive Fra-2 protein in nuclear fractions obtained 2 h after the administration of NMDA, without significantly affecting that of both member proteins in cytosolic fractions. The addition of phosphatase inhibitors significantly delayed the initial degradation rate of inducible c-Fos protein, with concomitant facilitation of that of constitutive Fra-2 protein, in nuclear fractions. The addition of protease inhibitors also delayed the initial degradation of constitutive Fra-2 protein, without markedly altering that of inducible c-Fos protein, in nuclear fractions. Immunoprecipitation analysis revealed that NMDA induced phosphorylation of c-Fos protein on tyrosine residues in nuclear fractions to a lesser extent than that on serine residues 2 h after administration. These results suggest that NMDA signals may be propagated to the nucleus to induce both expression and degradation of c-Fos protein through a molecular mechanism associated with phosphorylation on serine and/or tyrosine residues in murine hippocampus.

Differential in vitro degradation of particular Fos family members expressed by kainic acid in nuclear and cytosolic fractions of murine hippocampus

Mice were injected with kainic acid (KA) at a convulsive dose, followed by homogenization of the hippocampus in the presence of different protease and phosphatase inhibitors, and subsequent preparation of nuclear and cytosolic fractions. An intraperitoneal injection of KA resulted in marked expression of particular Fos family members, including c-Fos, Fra-2, and Fos-B, but not Fra-1 proteins, in both fractions 2 to 18 h after administration. These fractions were individually incubated at 30 degrees C for 1 to 18 h for determination of in vitro degradation. Similarly rapid degradation was seen with c-Fos protein between nuclear fractions obtained 2 and 18 h after administration, while no significant degradation was found for c-Fos protein in cytosolic fractions obtained 2 h after administration during incubation. By contrast, in vitro incubation led to rapid degradation of c-Fos protein in cytosolic fractions obtained 18 h after administration. Degradation profiles were peculiar to each member protein in nuclear and cytosolic fractions obtained 2 and 18 h after administration. Dialysis prevented degradation of c-Fos protein in nuclear fractions without markedly affecting that in cytosolic fractions in a manner independent of the time after administration. The addition of inhibitors for phosphatases, but not for proteases, accelerated the degradation of c-Fos protein in nuclear fractions previously dialyzed. These results suggest that in vivo KA signals may modulate heterologous machineries responsible for breakdown of each Fos family member in a unique manner in nuclear fractions, rather than cytosolic fractions, of murine hippocampus.

Consolidation of transient ionotropic glutamate signals through nuclear transcription factors in the brain

Long-lasting alterations of neuronal functions could involve mechanisms associated with consolidation of transient extracellular signals through modulation of de novo synthesis of particular functional proteins in the brain. In eukaryotes, protein de novo synthesis is mainly under the control at the level of gene transcription by transcription factors in the cell nucleus. Transcription factors are nuclear proteins with an ability to recognize particular core nucleotides at the upstream and/or downstream of target genes, and thereby to modulate the activity of RNA polymerase II that is responsible for the formation of mRNA from double stranded DNA. Gel retardation electrophoresis is widely employed for conventional detection of DNA binding activities of a variety of transcription factors with different protein motifs. Extracellular ionotropic glutamate (Glu) signals lead to rapid and selective potentiation of DNA binding of the nuclear transcription factor activator protein-1 (AP1) that is a homo- and heterodimeric complex between Jun and Fos family members, in addition to inducing expression of the corresponding proteins, in a manner unique to each Glu signal in murine hippocampus. Therefore, extracellular Glu signals may be differentially transduced into the nucleus to express AP1 with different assemblies between Jun and Fos family members, and thereby to modulate de novo synthesis of the individual target proteins at the level of gene transcription in the hippocampus. Such mechanisms may be operative on synaptic plasticity as well as delayed neuronal death through consolidation of alterations of a variety of cellular functions induced by transient extracellular signals in the brain.

Effects of glutathione depletion by 2-cyclohexen-1-one on excitatory amino acids-induced enhancement of activator protein-1 DNA binding in murine hippocampus

We have investigated the role of glutathione in mechanisms associated with excitatory amino acid signaling to the nuclear transcription factor activator protein-1 (AP1) in the brain using mice depleted of endogenous glutathione by prior treatment with 2-cyclohexen-1-one (CHX). In the hippocampus of animals treated with CHX 2 h before, a significant increase was seen in enhancement of AP1 DNA binding when determined 2 h after the injection of kainic acid (KA) at low doses. The sensitization to KA was not seen in animals injected with CHX 24 h before, in coincidence with the recovery of glutathione contents to the normal levels. By contrast, CHX did not significantly affect the potentiation by NMDA of AP1 binding under any experimental conditions. Prior treatment with CHX resulted in facilitation of behavioral changes induced by KA without affecting those induced by NMDA. These results suggest that endogenous glutathione may be at least in part involved in molecular mechanisms underlying transcriptional control by KA, but not by NMDA, signals of cellular functions.

Differential expression and phosphorylation of particular fos family members by kainate in nuclear and cytosolic fractions of murine hippocampus

An i.p. injection of kainate resulted in severe losses of neuronal cells stained by Cresyl Violet in the CA1 and CA3 pyramidal layers of the murine hippocampus within two weeks, without affecting those in the dentate granule layer up to six weeks. Immunohistochemical analysis revealed marked and predominant expression of Fos family members, including c-Fos, Fos-B and Fra-2 proteins, in the dentate granule layer of the hippocampus, but not in the pyramidal layers, 2-18h after administration. Immunoblotting experiments showed that kainate induced more potent expression of c-Fos protein in nuclear fractions obtained 2h after injection than those obtained 18h later, with similar expression between cytosolic fractions obtained 2 and 18h after administration. Both Fos-B and Fra-2 proteins were more potently expressed in nuclear and cytosolic fractions 18h after administration than 2h when determined on immunoblotting analysis. Two-dimensional electrophoresis revealed expression of several proteins immunoreactive to the anti-c-Fos antibody with different isoelectric points in response to kainate in nuclear and cytosolic fractions of the hippocampus for 2-18h after a single injection. Immunoprecipitation analysis using the anti-c-Fos antibody showed phosphorylation of c-Fos protein on serine residues in hippocampal nuclear fractions 2h after administration, with additional phosphorylation on tyrosine residues 18h later. Prior treatment of the protein synthesis inhibitor cycloheximide prevented the expression of immunoreactivities to the anti-c-Fos antibody detected on two-dimensional electrophoresis in hippocampal nuclear fractions obtained 2h after administration.These results suggest that in vivo kainate signals may lead to persistent expression of the transcription factor activator protein-1 that consists of different Fos family members, as well as of c-Fos protein phosphorylated on serine and/or tyrosine residues, at an early stage after administration. Such signal consolidation processes could play a role in mechanisms associated with neuronal survival after kainate in the dentate granular layer of murine hippocampus.