A neuroprotected state can be acquired by preconditioning brain with a stimulus that is subthreshold for damage (tolerance). Acquisition of tolerance involves coordinate, bi-directional changes to gene expression levels and the re-programmed phenotype is determined by the preconditioning stimulus. While best studied in ischemic brain there is evidence brief seizures can confer tolerance against prolonged seizures (status epilepticus). Presently, we developed a model of epileptic preconditioning in mice and used microarrays to gain insight into the transcriptional phenotype within the target hippocampus at the time tolerance had been acquired. Epileptic tolerance was induced by an episode of non-damaging seizures in adult C57Bl/6 mice using a systemic injection of kainic acid. Neuron and DNA damage-positive cell counts 24 h after status epilepticus induced by intraamygdala microinjection of kainic acid revealed preconditioning given 24 h prior reduced CA3 neuronal death by ~45% compared with non-tolerant seizure mice. Microarray analysis of over 39,000 transcripts (Affymetrix 430 2.0 chip) from microdissected CA3 subfields was undertaken at the point at which tolerance was acquired. Results revealed a unique profile of small numbers of equivalently up-and down-regulated genes with biological functions that included transport and localization, ubiquitin metabolism, apoptosis and cell cycle control. Select microarray findings were validated post hoc by real-time polymerase chain reaction and Western blotting. The present study defines a paradigm for inducing epileptic preconditioning in mice and first insight into the global transcriptome of the seizure-damage refractory brain.
Keywordsepilepsy; transcriptome; kainic acid; tolerance; neuroprotection; apoptosis Stressful and potentially noxious insults that are subthreshold for damage are capable of rendering brain refractory to damage incurred by a subsequent, prolonged and otherwise harmful stressor (Dirnagl et al., 2003). This process, termed preconditioning, is a highly conserved endogenous mechanism by which brain can protect itself (tolerance) (Chen and Simon, 1997 Tolerance in brain was originally identified as a gene synthesis-dependent process that took 1-3 days to be acquired in vivo (Kitagawa et al., 1991;Simon et al., 1993;Chen et al., 1996). The process is highly conserved, being readily elicited in numerous rat and mouse models of ischemic brain injury (Dirnagl et al., 2003;Gidday, 2006;Stenzel-Poore et al., 2007). It may also have clinical relevance as evinced by more favorable outcomes in patients experiencing transient ischemic attacks prior to a large stroke (Weih et al., 1999). Preconditioning can also be induced by other brain insults including seizure (Sasahira et al., 1995;Najm et al., 1998;El Bahh et al., 2001;Borges et al., 2007) and certain chemicals/drugs (Rosenzweig et al., 2004), and cross-tolerance whereby ischemic and other paradigms are combined has also been reported in rodents (Plamondon et al., 1999;Towfighi et al., 1999).Mi...
