Abstracts

Rodents experience severe hippocampal damage after a kainate-induced status epilepticus (SE). However, if rats are preconditioned by a short duration of kainate-induced seizures (20 min.) one and two days before a prolonged SE, neuronal damage can be prevented (Zhang et al., 2002, J. Neurosci. 22: 6052-61). The goal of this study is to identify genes that are specifically expressed after preconditioning and might protect neurons from injury. For preconditioning rats were injected on day -2 and -1 with kainate (12-15 mg/kg i.p.) and after 20 min. of seizure activity pentobarbital (40 mg/kg i.p.) was injected to stop seizures. To confirm the neuroprotective effect of preconditioning, some rats were injected with kainate on day 0 and status epilepticus was induced. These rats were sacrificed 3 d after SE and neuronal damage was evaluated by Fluoro-Jade staining. We compared the mRNA expression profiles of 3 different hippocampal cell populations from 8 preconditioned and 8 control (non-preconditioned) rats, using Affymetrix 230A microarrays. RNA was extracted and amplified from cells one day after the second preconditioning seizure harvested by laser capture microscopy from the dentate granule cell layer, the CA3 and the CA1 pyramidal cell layer. Hippocampal neuronal damage was observed by Fluoro-Jade labeling 3 days after kainate-induced SE (N=3 rats). In contrast, in rats that were preconditioned prior to SE (N=3) Fluoro-Jade-labeled cells were found in several brain areas but not the hippocampus, confirming that preconditioning is neuroprotective in the hippocampus. Microarray analysis revealed that more genes were significantly changed after preconditioning in the dentate granule cell layer (1231 genes), than in the CA1 (116) and CA3 (48) pyramidal cell layer (fig 1, false discovery rate 5%). Eleven genes were found to be significantly changed in all 3 cell populations, including neuropeptide Y (NPY), which is known to be upregulated by seizures.[figure1]Fig 1 shows the number of commonly changed genes after preconditioning in the 3 areas examined. Although CA3 and CA1 pyramidal cells are protected by brief preconditioning seizures, by far the most extensive changes in gene expression occurred in dentate granule cells, indicating that the dentate gyrus may be most critical in the neuroprotective effect of preconditioning. Among the genes changed after preconditioning in all 3 main hippocampal neuronal cell layers NPY is likely to play a role in preconditioning due to its anticonvulsant properties. Other promising genes will be validated and evaluated for their neuroprotective potential. (Supported by CURE (KB), NINDS (RD))