Mapping a mouse limbic seizure susceptibility locus on chromosome 10.

PURPOSE: Mapping seizure susceptibility loci in mice provides a framework for identifying potentially novel candidate genes for human epilepsy. Using C57BL/6J × A/J chromosome substitution strains (CSS), we previously identified a locus on mouse chromosome 10 (Ch10) conferring susceptibility to pilocarpine, a muscarinic cholinergic agonist that models human temporal lobe epilepsy by inducing initial limbic seizures and status epilepticus (status), followed by hippocampal cell loss and delayed-onset chronic spontaneous limbic seizures. Herein we report further genetic mapping of pilocarpine quantitative trait loci (QTLs) on Ch10. METHODS: Seventy-nine Ch10 F(2) mice were used to map QTLs for duration of partial status epilepticus and the highest stage reached in response to pilocarpine. Based on those results we created interval-specific congenic lines to confirm and extend the results, using sequential rounds of breeding selectively by genotype to isolate segments of A/J Ch10 genome on a B6 background. KEY FINDINGS: Analysis of Ch10 F(2) genotypes and seizure susceptibility phenotypes identified significant, overlapping QTLs for duration of partial status and severity of pilocarpine-induced seizures on distal Ch10. Interval-specific Ch10 congenics containing the susceptibility locus on distal Ch10 also demonstrated susceptibility to pilocarpine-induced seizures, confirming results from the F(2) mapping population and strongly supporting the presence of a QTL between rs13480781 (117.6 Mb) and rs13480832 (127.7 Mb). SIGNIFICANCE: QTL mapping can identify loci that make a quantitative contribution to a trait, and eventually identify the causative DNA-sequence polymorphisms. We have mapped a locus on mouse Ch10 for pilocarpine-induced limbic seizures. Novel candidate genes identified in mice can be investigated in functional studies and tested for their role in human epilepsy.

Increased seizure severity and seizure-related death in mice lacking HCN1 channels.

Persistent down-regulation in the expression of the hyperpolarization-activated HCN1 cation channel, a key determinant of intrinsic neuronal excitability, has been observed in febrile seizure, temporal lobe epilepsy, and generalized epilepsy animal models, as well as in patients with epilepsy. However, the role and importance of HCN1 down-regulation for seizure activity is unclear. To address this question we determined the susceptibility of mice with either a general or forebrain-restricted deletion of HCN1 to limbic seizure induction by amygdala kindling or pilocarpine administration. Loss of HCN1 expression in both mouse lines is associated with higher seizure severity and higher seizure-related mortality, independent of the seizure-induction method used. Therefore, down-regulation of HCN1 associated with human epilepsy and rodent models may be a contributing factor in seizure behavior.