Abstracts

Rationale: Although early-life seizures may be harmful and increase the risk of epilepsy later in life, postnatal seizures acquired due to asphyxia or other early traumas may lead to tolerance to prepare the brain from the impact of a subsequent injury. Previously, we demonstrated that postnatal (P) P20 juvenile rats are sensitive to CA1 injury following a single injection of kainic acid (KA) (1xKA) but resistant to this damage when the animals have a history of two prior seizures on P6 and P9 (3xKA). We hypothesized that the two earlier seizures, in the neonatal period, led to neuroprotection via a pre-conditioning mechanism involving attenuation of Ca2 currents and induction of survival signaling pathways. Methods: The CA1 was microdissected away from the other hippocampal subregions and total RNA was extracted, subjected to RT-PCR then hybridized with a rat microarray platform to identify genes involved in the protective effects produced by multiple early-life seizures. Ca2 influx with FURA 2-AM imaging was used to monitor glutamatergic receptor efficacy after 1xKA vs. 3xKA. Results: Microarray results indicated that over 13,000 genes were regulated in the CA1 after a single seizure induced in the juvenile period, but also that a large percentage of them were differentially regulated if the animals had a history of two neonatal seizures. Of the total number of altered genes only 11 were commonly decreased and 389 were commonly increased. Examples of protective genes that were up-regulated after 3xKA were anti-apoptotic Bcl-2 gene members and adaptor proteins such as adaptor protein complex AP-1, sigma 1 adaptor protein, phosphotyrosine interaction, and adaptor-related protein complex 3, mu 2 subunit. Differential regulation of cytokines also favored protection. Annexins and S100 proteins two large, but distinct, calcium-binding protein families were differentially regulated; annexin 3 was increased after 3xKA but not after 1xKA. Calmodulin 2 was decreased after 1xKA but increased after 3xKA. Ca2 imaging studies also showed that N-methyl-D-aspartate (NMDA) responses were enhanced at 5 hrs after 1xKA but these elevations were attenuated after 3xKA. Conclusions: Described changes may contribute to early-life seizure-induced pre-conditioning and neruroprotection. This could be achieved by reduced glutamate receptor-mediated Ca2 permeability of the hippocampus and redirecting apoptotic pathways.