Abstracts

Inheritance patterns between mouse strains suggest that a robust genetic influence determines individual susceptibility to kainic acid-induced hippocampal cell death. FVB/N and C57BL/6 mice exhibit differential susceptibility to kainate-induced cell death, with FVB/N being sensitive and C57BL/6 mice relatively resistant. In previous studies, phenotypic assessment of cell death in (F1 X FVB/N)N2 backcross progeny suggested that differences in apparent cell death are conferred by a single gene locus (Schauwecker, 2003b). To define the genetic contributions affecting individual differences in kainate-induced cell death susceptibility, a genome-wide scan was performed on N2 backcross populations to map quantitative trait loci for kaiante-induced cell death susceptibility. An N2 backcross was constructed using the C57BL/6 and FVB/N strains as progenitors. Mice were injected with kainate and observed for 3-4 hours for the onset and extent of seizures. To determine whether seizure severity correlates with excitotoxic neuronal loss, morphological analysis was performed. Seven days following administration of kainate, a total of 331 N2 offspring were perfused and assessed for susceptibility to kainate-induced cell death. Following the phenotypic testing, quantitative trait linkage analysis was performed using information derived from a genome scan of 87 polymorphic microsatellite markers spanning the whole genome, Chromosome Y excepted. Linkage between kainate-induced cell death susceptibility and marker loci was analyzed by the computer program MapManager QTX. Statistical mapping yielded significant evidence (LOD scores[gt]2.3) for quantitative trait loci (QTLs) on Chromosomes 4, 15, and 18, which together explain roughly 25% of the phenotypic variance in this model. We detected the locus of greatest effect on distal Chromosome 18 (LOD=4.9). We subsequently controlled for two markers that flank the Chr 18 locus and used composite interval mapping to search for other loci that may have additive effects. No additional QTLs were mapped in models that fix the identified QTL. In order to show conclusively that cell death susceptibility can simply be predicted by the genotype across one of our critical intervals when it is inherited, we constructed a congenic strain by moving the Chr 18 C57BL/6 region into the FVB/N strain. Damage was significantly reduced in the congenic strain that contained the C57BL/6 resistant region in a FVB/N strain. This study provides evidence for the genetic control of seizure-induced cell death susceptibility in mice and identifies individual susceptibility loci. These QTLs may ultimately lead to the identification of genes influencing individual differences in kainate-induced cell death threshold in mice and aid in the discovery of novel neuroprotective agents. (Supported by NIH grant NS38696 to PES.)