Abstracts

Rationale: Dravet syndrome (DS) is a rare childhood epilepsy disorder resulting in spontaneous, recurrent seizures and behavioral co-morbidities. A successful drug screening model should recapitulate the phenotypes observed in a clinical setting. A floxed stop Scn1a-A1783V mouse was evaluated with chronic video-EEG to assess the frequency of spontaneous seizures over 30 days. The seizure history and frequency observed in this study aids in determining the sample sizes and experimental timeline needed for preclinical drug studies. Additionally, in an attempt to better understand the behavioral co-morbidities associated with this particular model, hyperactivity and anxiety-like behaviors were measured using the open field paradigm. Overall, this study contributed to our understanding of the model and its validity in preclinical drug discovery. Methods: We employed both male and female offspring of a Scn1a-A1783V (Jax stock #026133) and a Sox2-cre mouse. The heterozygous offspring of these mice express the missense mutation, A1783V, in cre-expressing tissue. Scn1a positive mice (n=12) and wild type littermates (n=9) were implanted at P30-P35 with a bipolar electrode (PlasticsOne) over the cortex. A ground electrode was placed over the cerebellum. Mice recovered from surgery for 7 days and then were tethered for 24h/day, 7d/week video-EEG recording. Recordings were collected over 30 days. Electrographic seizures were defined as sharp-wave discharges, with amplitudes at least 2x the height of baseline and lasting more than 5 seconds, followed by post-ictal depression. Each electrographic seizure was evaluated via video recording for the matching behavioral seizure by an experimenter blinded to genotype. While DS is a childhood epilepsy, for the purpose of this study, mice were implanted approximately 1-2 weeks post-weaning. In a separate cohort, behavioral co-morbidities were assessed at P21-28 in both heterozygous (n=14) and wild type littermates (n=16) with the open field paradigm. Movement was automatically detected and recorded in a 60 cm x 60 cm open field arena enclosed with Plexiglass (Fusion S v1.1, AccuScan Instruments, Columbus Ohio) for 10 minutes. The behaviors scored include the total distance traveled (cm), average speed (cm/s) and time spent in the center zone(s). Results: Scn1a mice exhibited recurrent, spontaneous seizures over the course of 30 days. Daily seizure burden varied for individual mice, but overall, Scn1a mice had, on average, 1.02 ± 0.1 (mean ± SEM) generalized, tonic-clonic seizures per day, while wild type littermates had no evidence of seizure activity. Average seizure duration was 30.8 ± 0.4 s. In addition, interictal spikes were commonly observed in only heterozygous mice. A separate cohort of P21-28 Scn1a and age matched wild type littermates were assessed using the open field paradigm. Scn1a mice traveled significantly farther and faster and spent significantly less time in the center of the open field than their wild type littermates (p = 0.02, p=0.02, p< 0.0001, respectively, Mann-Whitney Test). Conclusions: These results demonstrate this mouse model of DS has spontaneous, recurrent seizures. Furthermore, the results from the open field paradigm strongly suggest these mice have increased thigmotaxis and anxiety-like behavior, recapitulating co-morbidities seen in a clinical setting. Overall, the mouse model of DS used in this characterization study may be suitable for preclinical drug discovery. Funding: HHSN271201600048C (KW)