Segregation of Seizure Traits in C57 Black Mouse Substrains Using the Repeated-Flurothyl Model

Abstract

Identifying the genetic basis of epilepsy in humans is difficult due to its complexity, thereby underlying the need for preclinical models with specific aspects of seizure susceptibility that are tractable to genetic analyses. In the repeated-flurothyl model, mice are given 8 flurothyl-induced seizures, once per day (the induction phase), followed by a 28-day rest period (incubation phase) and final flurothyl challenge. This paradigm allows for the tracking of multiple phenotypes including: initial generalized seizure threshold, decreases in generalized seizure threshold with repeated flurothyl exposures, and changes in the complexity of seizures over time. Given the responses we previously reported in C57BL/6J mice, we analyzed substrains of the C57BL lineage to determine if any of these phenotypes segregated in these substrains. We found that the generalized seizure thresholds of C57BL/10SNJ and C57BL/10J mice were similar to C57BL/6J mice, whereas C57BL/6NJ and C57BLKS/J mice showed lower generalized seizure thresholds. In addition, C57BL/6J mice had the largest decreases in generalized seizure thresholds over the induction phase, while the other substrains were less pronounced. Notably, we observed only clonic seizures during the induction phase in all substrains, but when rechallenged with flurothyl after a 28-day incubation phase, ∼80% of C57BL/6J and 25% of C57BL/10SNJ and C57BL/10J mice expressed more complex seizures with tonic manifestations with none of the C57BL/6NJ and C57BLKS/J mice having complex seizures with tonic manifestations. These data indicate that while closely related, the C57BL lineage has significant diversity in aspects of epilepsy that are genetically controlled. Such differences further highlight the importance of genetic background in assessing the effects of targeted deletions of genes in preclinical epilepsy models.

GABAergic Neuron-Specific Loss of Ube3a Causes Angelman Syndrome-Like EEG Abnormalities and Enhances Seizure Susceptibility

“…Latencies to seizure following an initial exposure to the putative GABA A R antagonist, flurothyl, provide a reliable index of seizure threshold in naïve mice, and flurothyl seizures are highly penetrant regardless of genetic background (Krasowski, 2000; Kadiyala et al, 2014). We therefore used flurothyl to test seizure susceptibility in congenic C57BL/6 Ube3a FLOX/p+ ::NEX-Cre mice (Figure 4A 1 and 4B).…”

The relevance of inter- and intrastrain differences in mice and rats and their implications for models of seizures and epilepsy

“…2) [116]. Such differences further highlight the importance of genetic background in assessing the effects of genes in preclinical epilepsy models.…”

“…These differences in GST and seizure phenotype between these closely related strains of C57BL mice demonstrate the power of the genetic background on seizure measurements. Data are modified from Kadiyala et al [116]. …”

Dissociation of spontaneous seizures and brainstem seizure thresholds in mice exposed to eight flurothyl‐induced generalized seizures

“…A single flurothyl seizure was induced on day 28 (flurothyl rechallenge/retest) to determine the final seizure phenotype. Flurothyl‐induced seizures were behaviorally graded on a scale of 1 to 7 . Briefly, grades 1 and 2 were clonic‐forebrain seizures, whereas grades 3–7 were tonic‐brainstem seizure behaviors (Table ) …”

“…Mice were~8 weeks old when seizure testing began, consistent with previous studies utilizing the repeated-flurothyl model. [10][11][12][13]15,16,[23][24][25] All mice were provided complete access to food and water on a standard 12-h light/dark cycle with lights off at 7 p.m. All experimental procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of Albany Medical College and were in compliance with the National Institutes of Health's Guide for the Use and Care of Laboratory Animals.…”