Research reportGeneration and characterization of pilocarpine-sensitive C57BL/6 mice as a model of temporal lobe epilepsy

C57BL/6 (B6) is the most widely used inbred mouse strain, but its use in epilepsy research is compromised by low sensitivity to various convulsants, including pilocarpine. We recently identified a subline of B6NCrl mice in a barrier (#8) of a German vendor (Charles River) that was much more sensitive to status epilepticus (SE) induction than B6NCrl mice from four other barriers of the same vendor and other B6 substrains. Breeding experiments indicated that the observed differences have a genetic basis, thus offering a unique opportunity to identify the genes and pathways involved and contributing to a better understanding of the underlying molecular mechanisms of seizure susceptibility. Since the pilocarpine-sensitive B6 subline (B6NCrl#8) is not further available from the breeder, we decided to generate a new highly pilocarpine-sensitive B6NCrl subline by crossing female B6NCrl#8 mice with male F1 hybrids. Further sister-brother mating of the resulting F2 generation generated a highly susceptible F3 generation. Similar to B6NCrl#8 mice, mice from the F3 generation were significantly more susceptible to SE induction than any other B6 substrain, including B6J (JAX) mice, which were particularly insensitive to seizure induction. In contrast to the marked inter-subline differences in susceptibility to induction of SE, B6 sublines did not differ in the long-term consequences of SE, i.e., development of spontaneous seizures and neurodegeneration in the hippocampus, although hippocampal damage was much less severe than previously reported for other mouse strains. We have started to search for genetic loci underlying the high seizure susceptibility of B6NCrl#8 and filial generations obtained by cross-breeding with this B6 subline. Further characterization of the genetic variations underlying high susceptibility to convulsants such as pilocarpine will facilitate our understanding of the pathomechanisms involved in the evolution of single seizures to a self-sustained SE and provide new opportunities for interventions.

► C57BL/6 (B6) mice are commonly considered insensitive to convulsants. ► However, B6 substrains and sublines markedly differ in sensitivity to pilocarpine. ► B6J (JAX) mice have the lowest sensitivity, while a subline of B6NCrl is very sensitive. ► Further breeding of these B6NCrl mice results in a highly sensitive F3 generation. ► We have started to use these mice for identifying genetic determinants of seizure susceptibility.