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Temporal analysis of P15 hippocampus in kainate-induced seizures. Koh-2K08NS002068-04

ABSTRACT: Early childhood convulsions have been correlated with hippocampal neuron loss in patients with intractable temporal lobe epilepsy. Using a "two-hit" rat seizure model, we have shown that animals subjected to kainate (KA)- or hypoxia-induced seizures during early postnatal period showed no cell death, yet sustained more extensive neuronal death after second seizures in adulthood. An early life seizure, without causing overt cellular injury, predisposes the brain to the damaging effect of seizures in later life. Cellular and molecular changes that accompany early seizures and that lead to subsequent epileptogenesis and increased susceptibility to seizure-induced neuronal injury, however, remain poorly understood. We propose to investigate age-specific, time-dependent changes in gene expression that may underlie this priming effect of early-life seizures. We will determine the sequence of gene expression pattern in the hippocampus at various times following KA induced seizures at postnatal day (P) 15. Previous studies have shown that AMPA receptor subtype of glutamate receptors play a crucial role in the age-specific vulnerability and in the long-term epileptogenic effects of perinatal hypoxia seizures. We found that AMPA receptor antagonists block the increased susceptibility caused by early life seizures to later seizures and seizure-induced brain damage. We hypothesize that an alteration of AMPA receptor composition is one of many changes caused by early-life seizures that leads to an increase in Ca2+ permeability, which then results in cascade of downstream events and modifies array of gene expression that promote epileptogenesis and susceptibility to neuronal death in later life. We will examine three time points: 1hr, 72 hr, and 15 days following systemic KA-induced seizures at P15 as we have previously observed structural changes within the hippocampus at these time points. Within an hour of KA seizures, a marked swelling of dendrites, disassembly of dendritic microtubules and glycogen depletion are observed by electron microscopy. Within 5 days, basal dendrites of CA3 hippocampal pyramidal neurons show abnormal spine morphology and decreased branching pattern. 15 days after the seizures, aberrant growth of mossy fibers in the CA3 stratum oriens is observed in animals exposed to KA. Ten hippocampi will be pooled from five animals treated with KA (3mg/kg i.p.) and from five littermate controls injected with PBS. Animals will be decapitated and hippocampi will be rapidly dissected from the brain, flash frozen in liquid nitrogen, and stored at -80C until extraction of total RNA, which will be sent to the center. We will provide 4 tissue samples-2 controls and 2 KA, each a pool of five animals - for each time points. Mixing tissues from multiple rats will normalize single nucleotide polymorphisms and tissue heterogeneity. Keywords: time-course

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE1831 | GEO | 2004/10/14

SECONDARY ACCESSION(S): PRJNA104753

REPOSITORIES: GEO

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Project description:Early childhood convulsions have been correlated with hippocampal neuron loss in patients with intractable temporal lobe epilepsy. Using a "two-hit" rat seizure model, we have shown that animals subjected to kainate (KA)- or hypoxia-induced seizures during early postnatal period showed no cell death, yet sustained more extensive neuronal death after second seizures in adulthood. An early life seizure, without causing overt cellular injury, predisposes the brain to the damaging effect of seizures in later life. Cellular and molecular changes that accompany early seizures and that lead to subsequent epileptogenesis and increased susceptibility to seizure-induced neuronal injury, however, remain poorly understood. We propose to investigate age-specific, time-dependent changes in gene expression that may underlie this priming effect of early-life seizures. We will determine the sequence of gene expression pattern in the hippocampus at various times following KA induced seizures at postnatal day (P) 15. Previous studies have shown that AMPA receptor subtype of glutamate receptors play a crucial role in the age-specific vulnerability and in the long-term epileptogenic effects of perinatal hypoxia seizures. We found that AMPA receptor antagonists block the increased susceptibility caused by early life seizures to later seizures and seizure-induced brain damage. We hypothesize that an alteration of AMPA receptor composition is one of many changes caused by early-life seizures that leads to an increase in Ca2+ permeability, which then results in cascade of downstream events and modifies array of gene expression that promote epileptogenesis and susceptibility to neuronal death in later life. We will examine three time points: 1hr, 72 hr, and 15 days following systemic KA-induced seizures at P15 as we have previously observed structural changes within the hippocampus at these time points. Within an hour of KA seizures, a marked swelling of dendrites, disassembly of dendritic microtubules and glycogen depletion are observed by electron microscopy. Within 5 days, basal dendrites of CA3 hippocampal pyramidal neurons show abnormal spine morphology and decreased branching pattern. 15 days after the seizures, aberrant growth of mossy fibers in the CA3 stratum oriens is observed in animals exposed to KA. Ten hippocampi will be pooled from five animals treated with KA (3mg/kg i.p.) and from five littermate controls injected with PBS. Animals will be decapitated and hippocampi will be rapidly dissected from the brain, flash frozen in liquid nitrogen, and stored at -80C until extraction of total RNA, which will be sent to the center. We will provide 4 tissue samples-2 controls and 2 KA, each a pool of five animals - for each time points. Mixing tissues from multiple rats will normalize single nucleotide polymorphisms and tissue heterogeneity.

Project description:Neuropsychiatric consequences of poorly controlled seizures that begin in childhood can be devastating. School failure or behavioral difficulty in a child with epilepsy is common and can become the focus of concern for families. Current antiepileptic drugs compound problems with their CNS side effects; effective therapy is currently limited as little is known about the cellular and molecular changes caused by seizures in the developing brain. This study will investigate transcriptional regulation induced by early-life seizures and explore alternative nonpharmacological therapeutic strategies in reversing damages of early-life seizures. We will study the therapeutic efficacy of environmental enrichment in reducing seizure-induced neuronal injury and in modifying gene expression alterations. We will explore molecular mechanisms underlying the beneficial effects of enriched environment and examine how different genes act in concert to influence the outcome of seizure-induced damage. To test the effect of environmental enrichment in modifying KA seizure-induced alterations in gene expression. We hypothesize that environmental enrichment enhances plastic, homeostatic response of immature brain to excessive, dysregulating seizure activity and protect against maladaptive response of developing animals to seizures. After inducing seizures by systemic injection of KA (8 mg/kg) or PBS injections (control) at P20, we will randomly assign P21 male Long Evans rats to 4 groups: enrichment housing (control-enriched; SE-enriched) or to standard vivarium cages (control; SE). Sixteen animals (8 control-enriched; 8 SE-enriched) will be housed as a group in a plastic rectangular cage measuring 115cm x 80 cm containing a running wheel, tunnels, rubber balls, a maze, a mirror, and a clock with a cyclist pendulum. Control and KA will be housed individually in a standard cage. Four litters will be used for each run of experiment and the experiment will be repeated once to obtain 16 animals per group. At P30, 240 h after KA or PBS, animals will be deeply anesthetized with isoflurane, decapitated for total RNA preparation (half brain for each, n = 12 per group). Total RNA will be isolated from each hippocampus individually, and equal amounts of RNA from 4 hippocampi will be pooled for each Genechip. Three independent hybridizations will be performed per condition (total of 12 Genechip Rat Expression Set 230).

Project description:Microarray profiling was used to investigate gene expression in the hypoxic seizure model of acquired epilepsy in the rat, with the aim of characterizing functional pathways which are persistently activated or repressed during epileptogenesis. Hippocampal and cortical tissues were transcriptionally profiled over a one week period following an initial series of seizures induced by mild hypoxia at post-natal day 10 (P10), and the gene expression data was then analyzed with a focus on gene set enrichment analysis, an approach which emphasizes regulation of entire pathways rather than of individual genes. Animals were subjected to one of three conditions, control condition with no exposure to hypoxia, hypoxic seizures, and hypoxic seizures followed by treatment with the AMPAR antagonist NBQX, a compound tentatively proposed to be a modulator of epileptogenesis. Gene expression in the control samples was found to be consistent with known processes of neuronal maturation in the rat for the given time window. The hypoxic seizure response was found to be saliently enriched for components of the PI3K/mTOR and Wnt signaling pathways, alongside gene sets representative of glutamatergic, synaptic and axonal processes, perhaps regulated as a downstream consequence of activation of these pathways. Wnt signaling components were also found enriched in the more specifically epileptogenic NBQX-responsive gene set. While activation of the mTOR pathway is consistent with its known role in epileptogenesis and strengthens the case for mTOR or PI3K pathway inhibitors as potential anti-epileptogenic drugs, investigation of the role of Wnt signaling and the effect of cognate inhibitors offers a parallel avenue of research toward anti-epileptogenic treatment. Cohorts of ten days old (P10) rat pups were subjected to one of three experimental conditions: 1) a control sham treatment inducing no hypoxic seizures (noHS), 2) a treatment under hypoxia inducing hypoxic seizures (HS), in which each animal underwent a 15 minutes passage at 5% O2, and 3) a treatment with hypoxia inducing hypoxic seizures, followed by four intra-peritoneal injections of NBQX over a 48 h period, starting at 30 minutes post-hypoxia (HS+NBQX). Control vehicle injections of DMSO were performed for the animals under the noHS and HS conditions. Time of occurrence and number of seizures for the animals undergoing hypoxia were recorded and analyzed. Times to the first seizure were found to be exponentially distributed, with mean time to first seizure of 114 seconds, and total count of seizures occurring in the 15 minute hypoxic interval was found to be approximately normally distributed, with mean count 10.6 and standard deviation 2.9. For each treatment condition, cohorts of 4 to 6 rat pups were killed at five sampling times spanning 1 hour to 1 week post-hypoxia (1h, 6h, 12h, 48h, 168h post-hypoxia), for a total of 75 animals sacrificed. Whole cortex and hippocampi were extracted from the sacrificed animals and separately profiled on two Affymetrix high-throughput plate microarrays after RNA quality control, resulting in a total of 144 CEL files encapsulating the gene expression data. The 144 CEL files, generated from scans of the individual microarrays on the two 96-well Affymetrix HT Rat Focus Arrays, were processed according to the MAS5 algorithm, resulting for each input CEL file in output of 24,249 probeset-level intensities and corresponding absent/present calls. For each processed scan, two summary statistics, consisting of the total number of present calls on the chip, and the 75th percentile of present call intensities, were then computed. A quality control step was performed by inspecting for outlier scans in the space of these two statistics (no outliers were found). Additional visual inspection of a heat map of clustered profiles identified a potential tissue assignment swap between two samples, which were conservatively eliminated from further analysis. The resulting 142 quality-controlled profiles were then assembled into a single data matrix, and normalized to each other by linear rescaling of all probeset intensities so as to bring the 75th percentile of present call intensities on all chips to a single common value. These processing steps, and most of the subsequent analyses discussed here, were done using the Gecko gene expression analysis platform (Theilhaber et al., 2004). Additional analyses were performed using the R statistical tools framework (R Development Core Team 2008).

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Temporal analysis of P15 hippocampus in kainate-induced seizures. Koh-2K08NS002068-04

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