Abstracts

Prolonged seizures during childhood can lead to neuropsychiatric consequences including memory impairment, learning disability, and behavioral problems. No effective post-seizure treatment exists to prevent this neurological insult. Using kainic acid (KA)-induced seizures, a rat model of temporal lobe epilepsy, we have demonstrated a reversal of seizure-induced decrease in exploratory behavior in open field testing of young rats by exposure to an enriched environment for 7-10 days after KA. These behavioral changes were accompanied by transcriptional alterations of genes involved in proliferation, long-term potentiation, and memory consolidation including [italic]Arc[/italic], [italic]Homer1a[/italic], and [italic]Egr1[/italic]. The expression of these genes were decreased after KA-induced seizure but significantly increased after post-seizure exposure to an enriched environment. To demonstrate a causal role for these genes in alleviating seizure-induced behavioral deficits, we have delivered recombinant adeno-associated virus (rAAV2) containing [italic]Arc[/italic] into the hippocampus of young rats after KA-induced seizure and assessed the subsequent behavioral effects., [italic]Arc, Homer1a[/italic], and [italic]Egr1[/italic] were cloned into AAV2 shuttle vectors and high-titer rAAV2 vectors were produced by the CMRC Viral Vector Core. Long-Evans male rats were injected either with PBS or KA at postnatal day 21 (P21) and divided into 5 groups (KA-ARC, PBS-ARC, KA-GFP, PBS-GFP, PBS-No Surgery). One day later, rAAV2-Arc or rAAV2-GFP was stereotactically injected into the hippocampus of anesthetized rats in the surgical groups. Rats underwent the open field test at P28, 35, and 42. Animals were sacrificed at P44 and brains were immediately flash-frozen. 40[mu]m cryostat sections were cut and processed for quantitative real-time RT-PCR (qRT-PCR), in situ hybridization (ISH), immunocytochemistry (ICC), and western blot., In the open field test, KA-ARC animals explored significantly more than KA surgical controls (two-way ANOVA, [italic]p[/italic]=0.0196, [italic]n[/italic]=8). By the third week of open field testing, a 1.6-fold increase in exploratory behavior of KA-ARC rats compared to KA controls was paralleled by a [gt]2.5-fold increase in [italic]Arc[/italic] mRNA (qRT-PCR, [italic]p[/italic]=0.0013, [italic]n[/italic]=8) and a 2-fold increase of Arc protein in western blot with Arc antibody. Shown by ISH and ICC, [italic]Arc[/italic] mRNA and protein were primarily localized to the dentate granule cells of the hippocampus. Exploratory behavior significantly correlated with [italic]Arc[/italic] mRNA expression seen in qRT-PCR ([italic]r[/italic]=0.701, [italic]p[/italic]=0.0012, [italic]n[/italic]=18)., Expression of [italic]Arc[/italic] mRNA and protein was increased by injection of rAAV2-Arc into rat brain, which led to an improvement in exploratory behavior after KA-induced seizure. These results demonstrate that [italic]Arc[/italic] expression can reverse seizure-induced behavioral impairments. Future [italic]in vivo[/italic] studies injecting viral vectors containing [italic]Egr1[/italic] and [italic]Homer1a[/italic] into rat brain will elucidate whether these genes will also afford protection against behavioral deficits after seizure., (Supported by Child Neurology Foundation, K02NS048237.)