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

Differential roles of NR2A- and NR2B-containing NMDA receptors in activity-dependent brain-derived neurotrophic factor gene regulation and limbic epileptogenesis

Fleeting activation of NMDA receptors (NMDARs) induces long-term modification of synaptic connections and refinement of neuronal circuits, which may underlie learning and memory and contribute to pathogenesis of a diversity of neurological diseases, including epilepsy. Here, we found that NR2A and NR2B subunit-containing NMDARs were coupled to distinct intracellular signaling, resulting in differential BDNF expression and extracellular signal-regulated kinase 1/2 (ERK1/2) activation. Selective activation of NR2A-containing NMDARs increased BDNF gene expression. Activation of NR2B-containing NMDARs led to ERK1/2 phosphorylation. Furthermore, selectively blocking NR2A-containing NMDARs impaired epileptogenesis and the development of mossy fiber sprouting in the kindling and pilocarpine rat models of limbic epilepsy, whereas inhibiting NR2B-containing NMDARs had no effects in epileptogenesis and mossy fiber sprouting. Interestingly, blocking either NR2A- or NR2B-containing NMDARs decreased status epilepticus-induced neuronal cell death. The specific requirement of NR2A and its downstream signaling for epileptogenesis implicates attractive new targets for the development of drugs that prevent epilepsy in patients with brain injury.

Effects of Manganese Complexes of Curcumin and Diacetylcurcumin on Kainic Acid-Induced Neurotoxic Responses in the Rat Hippocampus

This study aimed to investigate the mechanism underlying the protective effects of manganese complexes of curcumin (Cp-Mn) and diacetylcurcumin (DiAc-Cp-Mn) on kainic acid (KA)-induced excitotoxicity in the rat hippocampus. Systemic injection of KA (10 mg/kg, i.p.) caused seizures and increased the expression of neurotoxic markers, immediate early genes [c-jun, cyclooxygenase 2 (COX-2), brain-derived neurotrophic factor (BDNF), and heat shock protein 70 (hsp70)] and a delayed response gene [inducible nitric oxide synthase (iNOS)], which were measured at 6 and 72 h after KA injection, respectively, in the hippocampus. Pretreatment with Cp-Mn (50 mg/kg, i.p.) and DiAc-Cp-Mn (50 mg/kg, i.p.) but not with curcumin (50 mg/kg, i.p.) delayed the onset of KA-induced seizure without affecting the seizure score. KA injection induced c-Fos immunoreactivity in DG, CA1, and CA3 hippocampal regions, the expression of which peaked at 6 h after injection. Cp-Mn and DiAc-Cp-Mn treatment significantly decreased c-Fos expression elicited by KA. Moreover, Cp-Mn and DiAc-Cp-Mn administration suppressed the KA-induced expression of c-jun, COX-2, BDNF, and iNOS mRNA, whereas curcumin attenuated only iNOS mRNA expression. No compounds tested had an effect on KA-induced hsp70 expression. It is therefore likely that in addition to radical scavenging and SOD-like activities, the suppression of potential neuronal injury marker expression by Cp-Mn and DiAc-Cp-Mn, contributes to the neuroprotective activities of these compounds, which are superior to those of curcumin, on KA-induced excitotoxicity in the hippocampus. These results suggest the beneficial effects of Cp-Mn, and DiAc-Cp-Mn on the treatment of excitotoxicity-induced neurodegenerative diseases.

Increased estrogen receptor beta expression correlates with decreased spine formation in the rat hippocampus

Estrogens play an important role in the brain function acting through two receptor types, ERalpha and ERbeta, both well-recognized as transcription factors. In this study, we investigated the ERbeta mRNA and protein levels in the rat hippocampus by using two in vivo models that are known to affect synapse formation. Natural estrous-proestrous cycle was used as a model in which a marked decrease in the density of hippocampal synapses was previously observed between proestrus and estrus. We have found that ERbeta mRNA and protein were displayed in high levels in the estrus and in low levels in the proestrous phase. By applying kainic acid (KA) to adult rats, we demonstrated that up-regulation of ERbeta mRNA and protein in hippocampal CA regions was vulnerable to KA-induced excitotoxicity. Furthermore, we note a concomitant decrease of ERbeta in the excitotoxicity-resistant denate gyrus that undergoes intense plastic changes, including synaptogenesis. These data suggested that decreases in ERbeta expression correlated with increase in synapse formation. This notion has been tested in vitro in hippocampal cultures, in which overexpression of ERbeta by means of gene transfection resulted in the lowering of the dendritic spine density that was elevated by estrogen. In summary, our results suggest that ERbeta inhibits synapse formation in hippocampal neurons.

Ketogenic diet decreases the level of proenkephalin mRNA induced by kainic acid in the mouse hippocampus

The ketogenic diet (KD) has been used to control medically refractory epilepsy in children for more than 80 years. Despite the clinical efficacy of the KD, its underlying bases are still obscure. Previous work from our laboratory has established that the KD has an antiepileptic and neuroprotective effect in the kainic acid (KA)-induced seizure model. The neuronal excitation caused by KA leads to increases in the expression of a variety of genes, including immediate-early genes and opioid peptides derived from proenkephalin (PENK) and prodynorphin (PDYN). In particular, the up-regulated PENK gene that is induced by KA in the hippocampal dentate granule cells has proconvulsant properties. PENK is regulated by the c-jun amino-terminal kinase (JNK) signaling pathway, the crucial role of which is involved in the regulation of transcription factors, such as Jun and Fos. In the present study, we examined the effect of the KD on the increase of PENK, Fos, Jun, AP-1 DNA-binding activity and JNK gene expression induced by KA in the mouse hippocampus. Using in situ hybridization and northern blot analysis, we found that the KD significantly decreases the level of PENK gene expression induced by KA of the granular cells in the hippocampus. In addition, we have also found that KD diminished KA-induced AP-1 DNA-binding activity, Fos and Jun expression, and phoshorylated form of the three types of JNKs. These results suggest that the KD suppresses KA-induced activation of JNK signaling pathways, followed by a decrease of PENK gene expression in the hippocampus, thereby resulting in antiepileptic effects.

Sustained activation of Akt by melatonin contributes to the protection against kainic acid-induced neuronal death in hippocampus

In the present study, the underlying protective mechanism of melatonin on kainic acid (KA)-induced excitotoxicity was examined in the hippocampus of mice. KA, administered intracerebroventricularly (i.c.v.), induced marked neuronal cell death with concurrent microglial activation and subsequent induction of inducible nitric oxide synthase (iNOS) in the hippocampus. Histopathological analysis demonstrated that melatonin (10 mg/kg), administered 1 hr prior to KA, attenuated KA-induced death of pyramidal neurons in the CA3 region. Melatonin obviously suppressed KA-induced microglial activation and consequent iNOS expression that were determined by increased immunoreactivities of microglial marker OX-6 and iNOS, respectively. Increased phosphorylation of Akt in pyramidal neurons was observed as early as 2 hr after administration of melatonin. Further, melatonin resulted in increased expression of astroglial glial cell line-derived neurotrophic factor (GDNF), which started to appear approximately 6 hr after administration of melatonin. The results of the present study demonstrate that melatonin exerts its neuroprotective action against KA-induced excitotoxicity both through the activation of neuronal Akt and via the direct action on hippocampal neurons and through the increased expression of astroglial GDNF, which subsequently activates neuronal PI3K/Akt pathway. Therefore, the present study suggests that melatonin, pineal secretory product, is potentially useful in the treatment of acute brain pathologies associated with excitotoxic neuronal damage such as epilepsy, stroke, and traumatic brain injury.

Epileptogenesis-related genes revisited

The main goal of this study was to identify common features in the molecular response to epileptogenic stimuli across different animal models of epileptogenesis. Therefore, we compared the currently available literature on the global analysis of gene expression following epileptogenic insult to search for (i) highly represented functional gene classes (GO terms) within data sets, and (ii) individual genes that appear in several data sets, and therefore, might be of particular importance for the development of epilepsy due to different etiologies. We focused on two well-described models of brain insult that induce the development of spontaneous seizures in experimental animals: status epilepticus and traumatic brain injury. Additionally, a few papers describing gene expression in rat and human epileptic tissue were included for comparison. Our analysis revealed that epileptogenic insults induce significant changes in gene expression within a subset of pre-defined GO terms, that is, in groups of functionally linked genes. We also found individual genes for which expression changed across different models of epileptogenesis. Alterations in gene expression appear time-specific and underlie a number of processes that are linked with epileptogenesis, such as cell death and survival, neuronal plasticity, or immune response. Particularly, our analysis highlighted alterations in gene expression in glial cells as well as in genes involved in the immune response, which suggests the importance of gliosis and immune reaction in epileptogenesis.

A conserved mRNA expression profile of SREB2 (GPR85) in adult human, monkey, and rat forebrain

SREB is a subfamily of G-protein-coupled receptors, which consists of SREB1 (GPR27), SREB2 (GPR85), and SREB3 (GPR173). Its high evolutionary conservation and predominant expression in the CNS suggest that SREB family members and their undiscovered ligand(s) may have significant functions in the nervous system. SREB2 is the most conserved receptor throughout vertebrate evolution. As a first step in understanding the function of the SREB family, we have determined the anatomical gene expression profile of SREB2 in adult human, monkey, and rat forebrain using in situ hybridization histochemistry. The expression pattern of SREB2 mRNA was well conserved across three mammalian species. SREB2 mRNA was expressed in neurons throughout the brain and the most abundant expression was detected in the hippocampal dentate gyrus in all species examined. The areas expressing high levels of SREB2 mRNA overlap with brain structures known to possess high levels of plasticity, namely, the hippocampal formation, olfactory system, and supraoptic and paraventricular nuclei. Further, the anatomical expression of SREB1 and SREB3 overlapped with that of SREB2 in the adult monkey brain. Together, these data suggest a possible link between SREB family and neural plasticity, which may explain its extremely high conservation throughout vertebrate evolution.

Effects of ryanodine receptor activation on neurotransmitter release and neuronal cell death following kainic acid-induced status epilepticus

Dynamic changes in intracellular free Ca(2+) concentration play a crucial role in various neural functions. The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and the ryanodine (Ry) receptor (RyR) are involved in Ca(2+)-induced Ca(2+)-release (CICR). Recent studies have shown that type 3 IP3R is highly expressed in rat hippocampal neurons after kainic acid (KA)-induced seizures and that dantrolene, a RyR antagonist, reduces KA-induced neuronal cell death. We investigated the RyR-associated effects of CICR agents on basal and K(+)-evoked releases of GABA and glutamate in rat hippocampus and the changes in expression of mRNA for RyRs in mouse brain after KA-induced seizures. The stimulatory effect of Ry on releases of GABA and glutamate was concentration-dependent in a biphasic manner. The inflection point in concentration-response curves for Ry on GABA release was lower than that for glutamate in both basal and K(+)-evoked conditions, suggesting that hyperactivation of RyR-associated CICR produces the imbalance between GABAergic and glutamatergic transmission. Following KA-induced seizures, transient up-regulation of brain-type RyR mRNA was observed in the hippocampal CA3 region and striatum, and signals for c-Fos mRNA increased transiently in the hippocampus, dentate gyrus and deeper layers of the neocortex. Thereafter, some dead neurons with single-stranded DNA (ssDNA) immunoreactive fragmented nuclei appeared in these areas. These findings suggest that intracellular Ca(2+) release via the RyR might be one of the mechanisms involved in KA-induced neuronal cell death.

Kainic acid (KA)-induced Ca2+/Calmodulin-dependent protein kinase II (CaMK II) expression in the neurons, astrocytes and microglia of the mouse hippocampal CA3 region, and the phosphorylated CaMK II only in the hippocampal neurons

In the present study, we investigated the role of Ca2+/calmodulin-dependent protein kinase II (CaMK II) and which types of neuronal cells contain CaMK II and phosphorylated CaMK II (p-CaMK II) in the CA3 hippocampal region of mice using confocal immunofluorescence study. KA increased the CaMK II, p-CaMK II, glial fibrillary acidic protein (GFAP) and complement receptor type 3 (OX-42) immunoreactivities (IR) at 30 min after KA treatment in mouse hippocampal area. In studies, nevertheless KA-induced CaMK II is expressed in neurons or astrocytes or microglia, p-CaMK II is expressed only in neurons. Thus, our results suggest that the activated CaMK II in early time may be performed important roles only in neurons but not in the astrocytes and microglia.

Role of nicotinic acetylcholine receptors in the regulation of kainic acid-induced hippocampal cell death in mice

Kainic acid (KA) is a well-known excitatory, neurotoxic substance. In mice, morphological damage of hippocampus induced by KA administered intracerebroventricularly (i.c.v.) was markedly concentrated on the CA3 pyramidal neurons. In the present study, the possible role of nicotinic acetylcholine receptors (nAchRs) in hippocampal cell death induced by KA (0.1 microg) administered i.c.v. was examined. Methyllycaconitine (MC; nAchRs antagonist, 20 microg) attenuated KA-induced CA3 pyramidal cell death. KA increased immunoreactivities (IRs) of phorylated extracellular signal-regulated kinase (p-ERK; at 30 min), p-CaMK II (at 30 min), c-Fos (at 2 h), c-Jun (at 2 h), glial fibrillary acidic protein (GFAP at 1 day), and the complement receptor type 3 (OX-42; at 1 day) in hippocampal area. MC attenuated selectively KA-induced p-CaMK II, GFAP and OX-42 IR in the hippocampal CA3 region. Our results suggest that p-CaMK II may play as an important regulator responsible for the hippocampal cell death induced by KA administered i.c.v. in mice. Reactive astrocytes, which was meant by GFAP IR, and activated microglia, which was meant by OX-42 IR, may be a good indicator for measuring the cell death in hippocampal regions by KA-induced excitotoxicity. Furthermore, it is implicated that niconitic receptors appear to be involved in hippocampal CA3 pyramidal cell death induced by KA administered i.c.v. in mice.

Gene expression profiles in microdissected neurons from human hippocampal subregions

Pyramidal neurons in hippocampal subregions are selectively vulnerable in certain disease states. To investigate, we tested the hypothesis that selective vulnerability in human hippocampus is related to regional differences in neuronal cell death and cell receptor gene expression in CA1 vs. CA3 subregions. We used laser capture microdissection to remove approximately 600 CA1 and 600 CA3 pyramidal neurons each from five fresh-frozen normal post-mortem brains, extracted total RNA and double-amplified mRNA. This was reverse transcribed and labeled for hybridization onto human cDNA array chips containing probes to 10,174 genes and unknown ESTs. RNA from additional microdissections was pooled for replicate hybridizations and quantitative RT-PCR validation. Gene expression differences were few (< 1%). We found 43 enriched genes in CA1 neuronal samples that included peripheral benzodiazipine receptor-associated protein, nicotinic cholinergic receptor, two chemokine receptors (CCR1 and CCR5) and several transcriptional factors. We found 17 enriched genes in the CA3 neuronal samples that included fibroblast growth factor receptor and prostaglandin-endoperoxide synthase 1. We found no differential gene expression for 23 calcium channel proteins; nine transporter proteins; 55 cell death and apoptotic regulator proteins; and an additional 497 cell receptors, including 24 glutamate receptors. Quantitative RT-PCR of four differentially expressed genes confirmed the microarray data. The results confirm the ability to examine gene expression profiles in microdissected neurons from human autopsy brain. They show only minor gene expression differences between two distinct neuronal populations in the hippocampus and suggest that selective hippocampal vulnerability is due to factors other than intrinsic differential expression in glutamate receptors and cell death genes.

Zac1 is up-regulated in neural cells of the limbic system of mouse brain following seizures that provoke strong cell activation

Zac1, a new zinc-finger protein that regulates both apoptosis and cell cycle arrest, is abundantly expressed in many proliferative/differentiation areas during brain development. In the present work, we studied Zac1 gene expression and protein in experimental seizure models following i.p. injection of pentylenetetrazole (PTZ) or kainic acid (KA). Following KA treatment, an early and intense up-regulation of Zac1 is detected in the limbic areas, such as the hippocampus, cortex and amygdaloid and hypothalamic nuclei. Pre-treatment with MK-801, an antagonist of the NMDA receptors, fully blocks the effect of KA in the hippocampus, whereas it only attenuates KA-induced Zac1 up-regulation in the other areas of the limbic system. A reduced induction is obtained with PTZ-treated animals, specifically in the entorhinal and piriform cortices as well as in amygdaloid and hypothalamic nuclei. Thus, Zac1 is highly induced in the seizure models that generate strong neuronal stimulation and/or extensive cell damage (cell death), reinforcing its putative role in the control of the cell cycle and/or apoptosis. Moreover, strong induction is observed in the granular cells of the dentate gyrus (which are resistant to neurodegeneration) and in some glial cells of the dentate gyrus and subventricular zone, suggesting that Zac1 may be implicated in the mechanisms of neural plasticity following injury.

Inactivation of glycogen synthase kinase-3β protects against kainic acid-induced neurotoxicity in vivo

Many neurodegenerative diseases involve oxidative stress and excitotoxic cell death. In an attempt to further elucidate the signal transduction pathways involved in the cell death/cell survival associated with excitotoxicity, we have used an in vivo model of excitotoxicity employing kainic acid (KA)-induced neurotoxicity. Here, we show that extracellular signal-related kinase (ERK) 2, but not ERK 1, is phosphorylated and thereby activated in the hippocampus and cerebellum of kainic acid-treated mice. Phosphorylation and hence inactivation of glycogen synthase kinase 3beta (GSK-3beta), a general survival factor, is often a downstream consequence of mitogen-activated protein kinase pathway activation. Indeed, GSK-3beta phosphorylation occurred in response to kainic acid exclusively in the affected hippocampus, but not as a consequence of ERK activation. This may represent a compensatory attempt at self-protection by the cells in this particular brain region. A role for GSK-3beta inhibition in cell survival was further supported by the fact that pharmacological inhibition of GSK-3beta using lithium chloride was protective against kainic acid-induced excitotoxicity in hippocampal slice cultures. This work supports a role for GSK-3beta in cell death in response to excitotoxins in vivo and further confirms that GSK-3beta plays a role in cell death/cell survival pathways.

Roles of adenosine receptors in the regulation of kainic acid-induced neurotoxic responses in mice

Kainic acid (KA) is a well-known excitatory and neurotoxic substance. In ICR mice, morphological damage of hippocampus induced by KA administered intracerebroventricularly (i.c.v.) was markedly concentrated on the hippocampal CA3 pyramidal neurons. In the present study, the possible role of adenosine receptors in hippocampal cell death induced by KA (0.1 microg) administered i.c.v. was examined. It has been shown that 3,7-dimethyl-1-propargylxanthine (DMPX; A2 adenosine receptors antagonist, 20 microg) reduced KA-induced CA3 pyramidal cell death. KA dramatically increased the phosphorylated extracellular signal-regulated kinase (p-ERK) immunoreactivities (IR) in dentate gyrus (DG) and mossy fibers. In addition, c-Jun, c-Fos, Fos-related antigen 1 (Fra-1) and Fos-related antigen 2 (Fra-2) protein levels were increased in hippocampal area in KA-injected mice. DMPX attenuated KA-induced p-ERK, c-Jun, Fra-1 and Fra-2 IR. However, 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine (PACPX; A1 adenosine receptor antagonist, 20 microg) did not affect KA-induced p-ERK, c-Jun, Fra-1 and Fra-2 IR. KA also increased the complement receptor type 3 (OX-42) IR in CA3 region of hippocampus. DMPX, but not PACPX, blocked KA-induced OX-42 IR. Our results suggest that p-ERK and c-Jun may function as important regulators responsible for the hippocampal cell death induced by KA administered i.c.v. in mice. Activated microglia, which was detected by OX-42 IR, may be related to phagocytosis of degenerated neuronal elements by KA excitotoxicity. Furthermore, it is implicated that A2, but not A1, adenosine receptors appear to be involved in hippocampal CA3 pyramidal cell death induced by KA administered i.c.v. in mice.

Brain-derived neurotrophic factor signaling modifies hippocampal gene expression during epileptogenesis in transgenic mice

Brain-derived neurotrophic factor (BDNF) regulates neuronal survival, differentiation and plasticity. It has been shown to promote epileptogenesis and transgenic mice with decreased and increased BDNF signaling show opposite alterations in epileptogenesis. However, the mechanisms of BDNF action are largely unknown. We studied the gene expression changes 12 days after kainic acid-induced status epilepticus in transgenic mice overexpressing either the functional BDNF receptor trkB or a dominant-negative truncated trkB. Epileptogenesis produced marked changes in expression of 27 of 1090 genes. Cluster analysis revealed BDNF signalling-mediated regulation of functional gene classes involved in cellular transport, DNA repair and cell death, including kinesin motor kinesin family member 3A involved in cellular transport. Furthermore, the expression of cytoskeletal and extracellular matrix components, such as tissue inhibitor of metalloproteinase 2 was altered, emphasizing the importance of intracellular transport and interplay between neurons and glia during epileptogenesis. Finally, mice overexpressing the dominant-negative trkB, which were previously shown to have reduced epileptogenesis, showed a decrease in mRNAs of several growth-associated genes, including growth-associated protein 43. Our data suggest that BDNF signaling may partly mediate the development of epilepsy and propose that regrowth or repair processes initiated by status epilepticus and promoted by BDNF signaling may not be as advantageous as previously thought.

Matrix metalloproteinases and their endogenous inhibitors in neuronal physiology of the adult brain

More than 20 matrix metalloproteinases (MMPs) and four of their endogenous tissue inhibitors (TIMPs) act together to control tightly temporally restricted, focal proteolysis of extracellular matrix. In the neurons of the adult brain several components of the TIMP/MMP system are expressed and are responsive to changes in neuronal activity. Furthermore, functional studies, especially involving blocking of MMP activities, along with the identification of MMP substrates in the brain strongly suggest that this enzymatic system plays an important physiological role in adult brain neurons, possibly being pivotal for neuronal plasticity.

Identification and analysis of plasticity-induced late-response genes

The excitatory neurotransmitter, glutamate, activates N-methyl-d-aspartate (NMDA) receptors to induce long-lasting synaptic changes through alterations in gene expression. It is believed that these long-lasting changes contribute to learning and memory, drug tolerance, and ischemic preconditioning. To identify NMDA-induced late-response genes, we used a powerful gene-identification method, differential analysis of primary cDNA library expression (DAzLE), and cDNA microarray from primary cortical neurons. We report here that a variety of genes, which we have named plasticity-induced genes (PLINGs), are up-regulated with differential expression patterns after NMDA receptor activation, indicating that there is a broad and dynamic range of long-lasting neuronal responses that occur through NMDA receptor activation. Our results provide a molecular dissection of the activity-dependent long-lasting neuronal responses induced by NMDA receptor activation.

Chromatin remodeling and neuronal response: multiple signaling pathways induce specific histone H3 modifications and early gene expression in hippocampal neurons

Plasticity in gene expression is achieved by a complex array of molecular mechanisms by which intracellular signaling pathways directly govern transcriptional regulation. In addition to the remarkable variety of transcription factors and co-regulators, and their combinatorial interaction at specific promoter loci, the role of chromatin remodeling has been increasingly appreciated. The N-terminal tails of histones, the building blocks of nucleosomes, contain conserved residues that can be post-translationally modified by phosphorylation, acetylation, methylation and other modifications. Depending on their nature, these modifications have been linked to activation or silencing of gene expression. We wanted to investigate whether neuronal stimulation by various signaling pathways elicits chromatin modifications that would allow transcriptional activation of immediate early response genes. We have analysed the capacity of three drugs - SKF82958 (a dopaminergic receptor agonist), pilocarpine (a muscarinic acetylcholine receptor agonist) and kainic acid (a kainate glutamate receptor agonist) - to induce chromatin remodeling in hippocampal neurons. We show that all stimulations induce rapid, transient phosphorylation of histone H3 at serine 10. Importantly, the same agonists induce rapid activation of the mitogen-activated protein kinase pathway with similar kinetics to extracellular-regulated-kinase phosphorylation. In the same neurons where this dynamic signaling cascade is activated, there is induction of c-fos transcription. Histone H3 Ser10 phosphorylation is coupled to acetylation at the nearby Lys14 residue, an event that has been linked to local opening of chromatin structure. Our results underscore the importance of dynamic chromatin remodeling in the transcriptional response to various stimuli in neuronal cells.

Inducible cAMP early repressor (ICER) in the nervous system - a transcriptional regulator of neuronal plasticity and programmed cell death

The acronym ICER (inducible cAMP early repressor) refers to a group of four proteins produced from the CREM/ICER gene due to use of an internal promoter (P2) placed in an intron of the CREM (cAMP responsive element modulator) gene. The ICER proteins contain DNA binding/leucine zipper domains that make them endogenous inhibitors of transcription driven by CREB (cAMP responsive element binding protein) and its cognates, CREM and ATF-1 (activating transcription factor-1). ICER expression is inducible in the brain and in neuronal culture by a variety of stimuli. As a CREB antagonist, ICER appears to be of pivotal importance in neuronal plasticity and programmed cell death.

Role of glutamate receptors and an on-going protein synthesis in the regulation of phosphorylation of Ca2+/calmodulin-dependent protein kinase II in the CA3 hippocampal region in mice administered with kainic acid intracerebroventricularly

In an immunohistochemical study, kainic acid (KA, 0.1 microg) administered intracerebroventricularly (i.c.v.) dramatically increased the expression of Ca2+/calmodulin-dependent protein kinase II (CaMK II) and the phosphorylation of CaMK II (p-CaMK II) in the CA3 hippocampal region of mice. Pre-treatment with cycloheximide (a protein synthesis inhibitor; 200 mg/kg) intraperitoneally prevented the expression of CaMK II and phosphorylation of CaMK II induced by KA. In addition, pre-treatment with MK-801 ((5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine; an NMDA receptor blocker, 1 microg, i.c.v.) or CNQX (6-cyano-7-nitroquinoxaline-2,3-dione; a non-NMDA receptor blocker, 0.5 microg, i.c.v.) attenuated the p-CaMK II, but not CaMK II, expression induced by KA. Our results suggest that KA administered supraspinally induces CaMK II and the phosphorylation of CaMK II expression in the CA3 hippocampal region, for which an on-going protein synthesis is needed. Furthermore, both NMDA and non-NMDA receptors appear to be involved in supraspinally administered KA-induced phosphorylation of CaMK II.

Two previously undescribed members of the mouse CPEB family of genes and their inducible expression in the principal cell layers of the hippocampus

Cytoplasmic polyadenylation element-binding (CPEB) proteins control polyadenylation-induced translation in early development. Studies in oocytes led to the delineation of Xenopus CPEB, the first member of the family to be identified, and its mouse homologue mCPEB-1. Recently, a second mouse family member, mCPEB-2, has been described in germ cells. Increasing evidence also implicates CPEB proteins as being important in the hippocampus, where these proteins are thought to regulate local protein synthesis and synaptic plasticity. We therefore carried out a systematic screen for CPEB genes in the mouse brain and report two previously undescribed gene family members: mCPEB-3 and -4. We next examined the expression of all four genes in the hippocampus and found that mCPEB-1, -2, and -4 transcripts are expressed in the principal cell layer in the CA3 and CA1 region and in the dentate gyrus of the hippocampus. mCPEB-3 was barely expressed in naïve animals but together with mCPEB-4 was strongly up-regulated after injection of kainate to initiate seizure activity. Whereas mCPEB-1 is regulated by the Aurora kinase, mCPEB-2, -3, and -4 do not contain Aurora kinase phosphorylation sites. However, alternative splice isoforms of mCPEB-2, -3, and -4 encode the so-called B region with phosphorylation sites for cAMP-dependent protein kinase, calcium/calmodulin-dependent protein kinase II, and S6 kinase. Only isoforms that encode the B region were expressed in the principal cell layer. Coexpression of mCPEB-1 and the B region-containing splice isoforms suggests that a variety of different signaling pathways can recruit CPEB activity in hippocampal neurons.

Inducible cAMP early repressor, an endogenous antagonist of cAMP responsive element-binding protein, evokes neuronal apoptosis in vitro

Active CREB (cAMP responsive element-binding protein) transcription factor is crucial for neuronal survival. Several members of the CREM/ICER (cAMP responsive element modulator/inducible cAMP early repressor) protein family may act as endogenous CREB antagonists. However, their involvement in a process of programmed cell death remains unexplored. Here we report that ICER may play such a role in neuronal apoptosis because it is upregulated in apoptotic neurons in vitro, and overexpression of ICER, delivered in adenoviral vector, evokes programmed cell death of three different kinds of cultured neurons, namely those derived from hippocampal dentate gyrus, cerebral cortex, and superior cervical ganglion. Reporter gene assay with a promoter containing a CREB-responsive sequence revealed a decrease in both basal and induced CRE-dependent gene expression in neurons overexpressing ICER. Finally, the level of expression of the anti-apoptotic protein Bcl-2, a well known CREB target, was markedly diminished in ICER-treated neurons. We suggest that the naturally occurring CREB functional antagonist ICER may have a specific function in programmed cell death of neurons, probably by silencing the expression of anti-apoptotic genes.

Cycloheximide inhibits neurotoxic responses induced by kainic acid in mice

In the present study, we examined the effect of cycloheximide on various pharmacological responses induced by kainic acid (KA) administered intracerebroventricularly (i.c.v.) in mice. In a passive avoidance test, a 20-min cycloheximide (200mg/kg, i.p.) pretreatment prevented the memory impairment induced by KA. The morphological damage induced by KA (0.1microg) in the hippocampus was markedly concentrated in the CA3 pyramidal neurons and cycloheximide effectively prevented the KA-induced pyramidal cell death in CA3 hippocampal region. In immunohistochemical study, KA dramatically increased the phosphorylation of extracellular signal-regulated protein kinase (p-ERK), c-Jun N-terminal kinase 1 (p-JNK1), and calcium/calmodulin-dependent protein kinase II (p-CaMK II). Cycloheximide attenuated the increased p-ERK, p-JNK1, and p-CaMK II levels induced by KA. Furthermore, cycloheximide inhibited the increased c-Fos and c-Jun protein expression levels induced by KA in the hippocampus. The activation of microglia was detected in KA-induced CA3 cell death region by immunostaining with a monoclonal antibody against the OX-42. Cycloheximide inhibited KA-induced increase of OX-42 immunoreactivity. Our results suggest that the increased expression of the c-Fos, c-Jun, and phosphorylation of ERK, JNK1, and CaMK II proteins may play important roles in the memory impairment and the cell death in CA3 region of the hippocampus induced by i.c.v. KA administration in mice. Furthermore, the activated microglia may be related to phagocytosis of degenerated neuronal elements induced by KA.

cDNA profiling of epileptogenesis in the rat brain

Symptomatic temporal lobe epilepsy typically develops in three phases: brain insult --> latency period (epileptogenesis) --> recurrent seizures (epilepsy). We hypothesized that remodeling of neuronal circuits underlying epilepsy is associated with altered gene expression during epileptogenesis. Epileptogenesis was induced by electrically triggered status epilepticus (SE) in rats. Animals were continuously monitored with video-EEG, and the hippocampus and temporal lobe were collected either during epileptogenesis (1, 4 and 14 days) or after the first spontaneous seizures (14 days) for cDNA array analysis. Altogether, 282 genes had altered expression, from which 87 were in the hippocampus and 208 in the temporal lobe (overlap in 13). Assessment of hippocampal gene expression during epileptogenesis indicated that 37 genes were altered in the 1-day group, 12 in the 4-day group and 14 in the 14-day epileptogenesis group. There were 42 genes with altered expression in the 14-day epilepsy group. In the temporal lobe, the number of genes with altered expression was 29 in the 1-day group, 155 in the 4-day group, 32 in the 14-day epileptogenesis group and 62 in the 14-day epilepsy group. Products of the altered genes are involved in neuronal plasticity, gliosis, organization of the cytoskeleton or extracellular matrix, cell adhesion, signal transduction, regulation of cell cycle, and metabolism. As most of these genes have not previously been implicated in epileptogenesis or epilepsy, these data open new avenues for understanding the molecular basis of epileptogenesis and provide new targets for rational development of anti-epileptogenic treatments for patients with an elevated risk of epileptogenesis after brain injury.

Dantrolene protects neurons against kainic acid induced apoptosis in vitro and in vivo

Apoptotic cell death induced by kainic acid (KA) in cultures of rat cerebellar granule cells (CGC) and in different brain regions of Wistar rat pups on postnatal day 21 (P21) was studied. In vitro, KA (100-500 microM) induced a concentration-dependent loss of cell viability in MTT assay and cell death had apoptotic morphology as studied by chromatin staining with propidium iodide (PI). In vivo, twenty-four hours after induction of status epilepticus (SE) by an intraperitoneal KA injection (5 mg/kg) we quantified apoptotic cells in hippocampus (CA1 and CA3), parietal cortex and cerebellum using PI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. We report that dantrolene, a specific ryanodine receptor antagonist, was able to significantly reduce the apoptotic cell death in CGC cultures and in hyppocampal CA1 and parietal cortex regions. Our finding can be valuable for neuroprotective therapy strategies in patients with repeated generalized seizures or status epilepticus.

Status Epilepticus Induces Changes in the Expression and Localization of Endogenous Palmitoyl-Protein Thioesterase 1

Kainic acid (KA)-induced experimental epilepsy, a model of excitotoxicity, leads to selective neuronal death and synaptic restructuring. We used this model to investigate the effects of neuronal hyperactivation on palmitoyl-protein thioesterase 1 (PPT1), the deficiency of which causes drastic neurodegeneration. Immunological stainings showed that epileptic seizures in adult rats led to a progressive and remarkable increase of PPT1 in limbic areas of the brain. Within 1 week, the maximal expression was observed in CA3 and CA1 pyramidal neurons of the hippocampus. In the surviving pyramidal neurons, PPT1 localized in vesicular structures in cell soma and neuritic extensions. After seizures, colocalization of PPT1 with synaptic membrane marker (NMDAR2B) was enhanced. Further, synaptic fractionation revealed that after seizures PPT1 was readily observed on the presynaptic side of synaptic junction. These data suggest that PPT1 may protect neurons from excitotoxicity and have a role in synaptic plasticity.

Matrix metalloproteinase-9 undergoes expression and activation during dendritic remodeling in adult hippocampus

Neurons of adult brain are able to remodel their synaptic connections in response to various stimuli. Modifications of the peridendritic environment, including the extracellular matrix, are likely to play a role during synapse remodeling. Proteolytic disassembly of ECM is a complex process using the regulated actions of specific extracellular proteinases. One of best-characterized families of matrix-modifying enzymes is the matrix metalloproteinase (MMP) family. Here, we describe changes in the expression and function of two well known MMPs, MMP-9 and MMP-2, in adult rat brain before and after systemic administration of the glutamate receptor agonist kainate. Kainate application results in enhanced synaptic transmission and seizures followed by selective tissue remodeling, primarily in hippocampal dentate gyrus. MMP-9 but not MMP-2 was highly expressed by neurons in normal adult rat brain. MMP-9 protein was localized in neuronal cell bodies and dendrites. Kainate upregulated the level of MMP-9 mRNA and protein within hours after drug administration. This was followed several hours later by MMP-9 enzymatic activation. Within hippocampus, MMP-9 mRNA and activity were increased selectively in dentate gyrus, including its dendritic layer. In addition, MMP-9 mRNA levels decreased in areas undergoing neuronal cell loss. This unique spatiotemporal pattern of MMP-9 expression suggests its involvement in activity-dependent remodeling of dendritic architecture with possible effects on synaptic physiology.