Abstracts

Rationale: Inbred strains of mice exhibit large differences regarding susceptibility to experimentally-induced seizures which, in a controlled environment, are mediated primarily by genetic variation. Previously, we have used C57BL/6J (B6) and DBA/2J (D2) inbred strains to map and identify candidate genes for analysis in human epilepsy. The present study describes a new genetic model based on mouse strains related to B6 and D2, but which may have an enhanced potential to identify additional seizure susceptibility genes. Methods: Parental C57BL/10SnJ (B10) and C57BL/KsJ (BK) mice, as well as mice from F1 and F2 intercross generations, were tested for maximal electroshock seizure threshold (MEST). MEST was determined by giving mice a single daily shock via earclip electrodes starting at 20 mA (60 Hz, 0.2 sec) and increasing current 2 mA per day until a maximal seizure was elicited. Mice were euthanized following determination of MEST and tissue harvested for DNA extraction. Results: Results confirmed the large strain difference in MEST that we reported previously and also revealed an effect of gender in the B10 strain. MEST values (mean ± SD, given in mAmp) were: B10 females: 75 ± 4, B10 males: 82 ± 8; BK females 28 ± 2, BK males 31 ± 5 (n = 20-25 per group). B10 x BK F1 mice exhibited a phenotype intermediate between the parental strains: F1 females: 49 ± 177 4 (n = 12), F1 males: 57 ± 7 (n = 20). Similarly, F2 intercross mice exhibited an intermediate phenotype, but with greater variability reflecting the magnitude of the overall genetic influence: F2 females: 52 ± 13 (n = 75), F2 males: 58 ± 15 (n = 81). Conclusions: MEST exhibits a polygenic inheritance pattern in this cross with a combination of genetic effects. Heritability estimation indicates that over 75% of the variance in the F2 population is due to the influence of genetic polymorphism. F2 mice exhibiting the most “extreme” phenotype at both ends of the quantitative trait distribution (~20% lowest and highest MEST values) were selected for use in a first-pass genome scan to be conducted on the Illumina platform (377 SNP panel). Results will allow chromosomal localization of the genes that mediate the major difference in seizure susceptibility between B10 and BK mice and may lead ultimately to identification of new candidate genes for translation to clinical studies of epilepsy.