Differences in sensitivity to the convulsant pilocarpine in substrains and sublines of C57BL/6 mice

Abstract

In rodents, the cholinomimetic convulsant pilocarpine is widely used to induce status epilepticus (SE), followed by hippocampal damage and spontaneous recurrent seizures, resembling temporal lobe epilepsy. This model has initially been described in rats, but is increasingly used in mice, including the C57BL/6 (B6) inbred strain. In the present study, we compared the effects of pilocarpine in three B6 substrains (B6JOla, B6NHsd and B6NCrl) that were previously reported to differ in several behavioral and genetic aspects. In B6JOla and B6NHsd, only a small percentage of mice developed SE independently of whether pilocarpine was administered at high bolus doses or with a ramping up dosing protocol, but mortality was high. The reverse was true in B6NCrl, in which a high percentage of mice developed SE, but mortality was much lower compared to the other substrains. However, in subsequent experiments with B6NCrl mice, striking differences in SE induction and mortality were found in sublines of this substrain coming from different barrier rooms of the same vendor. In B6NCrl from Barrier #8, administration of pilocarpine resulted in a high percentage of mice developing SE, but mortality was low, whereas the opposite was found in B6NCrl mice from four other barriers of the same vendor. The analysis of F1 mice from a cross of female Barrier 8 pilocarpine-susceptible mice with resistant male mice from another barrier (#9) revealed that F1 male mice were significantly more sensitive to pilocarpine than the resistant parental male mice whereas female F1 mice were not significantly different from resistant Barrier 9 females. These observations strongly indicate X-chromosome linked genetic variation as the cause of the observed phenotypic alterations. To our knowledge, this is the first report which demonstrates that not only the specific B6 substrain but also sublines derived from the same substrain may markedly differ in their response to convulsants such as pilocarpine. As the described differences have a genetic basis, they offer a unique opportunity to identify the genes and pathways involved and contribute to a better understanding of the underlying molecular mechanisms of seizure susceptibility.

Prevention or Modification of Epileptogenesis after Brain Insults: Experimental Approaches and Translational Research

“…These data indicate that genetic differences in outbred rat strains may contribute to variations between experimental data in post-SE models of SE. Similar differences between strains and substrains have also been reported for TLE models in mice (Schauwecker, 2002;Borges et al, 2003;Mü ller et al, 2009c).…”

Pilocarpine-Induced Convulsive Activity Is Limited by Multidrug Transporters at the Rodent Blood-Brain Barrier

“…FVB/N mice appear to exhibit high vulnerability compared with other inbred (C57BL/6) or outbred strains (CD1, NMRI) (Chen et al, 2005). Conversely, C57BL/6 mice are highly resistant to pilocarpine in terms of SE induction (Borges et al, 2003;Müller et al, 2009;Bankstahl et al, 2012). In view of the present results, these strain differences might be explained in part by different transporter expression levels at the blood-brain barrier, leading to mouse strain-dependent brain uptake of pilocarpine.…”

“…Unfortunately, SE induction and survival rates can dramatically differ not only between rodent strains (Chen et al, 2005;Winawer et al, 2007a,b), but also between animals of the same strain bred by different vendors and even between inbred mice originating from different breeding rooms of the same vendor (Borges et al, 2003;Bankstahl et al, 2009Bankstahl et al, , 2012Müller et al, 2009). The mechanisms underlying this variable efficacy of pilocarpine are unknown.…”

Refinement of a model of acquired epilepsy for identification and validation of biomarkers of epileptogenesis in rats

“…2-4. subsidiaries of Harlan used previously by us. There is obviously a disadvantage of using outbred strains for epilepsy models, although similar differences can also occur in inbred rodent strains because of epigenetic or environmental factors [35,36].…”