Abstracts

RATIONALE: Dentate granule cell neurogenesis and axon outgrowth are associated with both hippocampal development and models of temporal lobe epilepsy, raising the possibility that mechanisms underlying network alterations during epileptogenesis overlap with those utilized during development. Based on this hypothesis, we are characterizing gene expression in the dentate gyrus during epileptogenesis and development to identify genes and gene families exhibiting similar patterns of regulation during these processes.
METHODS: Adult rats received pilocarpine to induce SE using a standard protocol, and were killed 14 days later. Hippocampi were dissected, sliced into 600 [mu]m sections, and subfields were dissected for collection of dentate gyrus tissue. Similar sacrifice and dissection procedures were followed for postnatal day 3 and control adult rats. Total RNA was isolated from tissue samples and applied to DNA oligonucleotide microarrays (Affymetrix, Santa Clara, CA) to survey the expression levels of more than 8,000 genes.
RESULTS: Of the 4168 detectable gene sequences, 171 sequences were up- or down-regulated during epileptogenesis, and 51 of these were similarly regulated during development. Many of the genes regulated during epileptogenesis fell into specific categories of gene product function, including cellular proliferation and fate determination, calcium regulation, and composition of the extracellular matrix. In the latter category, a number of genes were identified, including the anti-adhesive extracellular matrix component SPARC (also referred to as osteonectin or BM-40) and SC1, a secreted glycoprotein that shares partial sequence homology with SPARC. Despite their previously characterized similarities in structure and function, DNA microarray data indicated that SPARC mRNA is increased in the post-SE dentate gyrus while SC1 message levels decline. [italic]In situ[/italic] hybridization studies verified that SPARC and SC1 are differentially regulated in the dentate gyrus following SE.
CONCLUSIONS: The high percentage of genes that were similarly regulated during development and epileptogenesis provides further support to the concept that developmental mechanisms contribute to network alterations associated with epileptogenesis. Furthermore, the coordinated and differential expression of multiple genes implicated in the composition of the extracellular matrix following SE suggests that regulation of the extracellular matrix may play an important role in epilepsy-associated network plasticity.
Support: NIH RO1NS39950 and State of California grant to UCSF for alcohol and substance abuse research.