Abstracts

Rationale: Although rises in intracellular calcium [Ca2+]i can eventually kill neurons recent evidence shows that Ca2+ can also prevent neurons from dying under numerous conditions. For example, postnatal (P) P20 juvenile rats are sensitive to CA1 cell body damage following a single injection of kainic acid (KA) (1xKA) but resistant to this injury when animals have a history of two earlier neonatal seizures on P6 and P9 (3xKA). We hypothesized that the two earlier seizures led to the neuroprotection by a pre-conditioning mechanism. Methods: Our previously established model of early-life kainate (KA)-induced status epilepticus, single (1x KA) vs. multiple (3x KA) seizures was employed (Liu et al., Seizure. 15, 2006). The Golgi method was used to analyze changes in morphology by measuring dendritic branch number and length and spine density. Gene regulation with microarray technology was used to identify genes involved in the protective effects; and Ca2+ influx with FURA 2-AM imaging was used to monitor glutamatergic receptor efficacy in the CA1 after 1xKA vs. 3xKA. Results: Golgi staining showed partial sparing of dendritic spines and branching on CA1 pyramidal neurons after 3xKA. After 2xKA and the same delay, a sparse number of CA1 neurons were injured at cell level, reduced branch length was measured and partial pruning of spines occurred. Immunohistochemistry revealed acute decreases in N-methy-D-aspartate (NMDA) immunoprotein in CA1 neurons at 24 hrs after KA injection. Microarrays showed a large number of transcripts were differentially up-regulated or down-regulated. For example, distinct calcium-binding protein families annexin 3 and certain anti-apoptotic Bcl-2 gene members were increased after 3xKA but not after 1xKA. Ca2+ imaging studies also showed that NMDA responses were enhanced at 5 hrs after 1xKA but these elevations were attenuated after 3xKA. Conclusions: Results indicate that different changes in morphology occur depending upon when seizures begin and that partial pruning and reduction in excitatory synapses may protect against subsequent insults. It also appears that certain calcium binding and proto-oncogene proteins may contribute to protection mechanisms by reducing glutamate receptor mediated Ca2+ permeability of the hippocampus and redirecting apoptotic pathways.