Abstracts

Rationale: There exists a gap in knowledge of medications that could prevent sudden unexpected death in epilepsy (SUDEP). Recent data suggests that SUDEP is related to spreading depression (SD), a self-propagating wave of depolarization in the cerebral cortex (Aiba I and Noebels JL, Sci Transl Med, 2015). Our Mashl+/- model of Alternating Hemiplegia of Childhood (AHC) shows increased predisposition to SD and SUDEP. SD has been shown to be propagated by NMDA receptor activation, and dextromethorphan (DXM), which has anti-NMDA blocking properties, has been shown to attenuate DXM. Thus our aim was to study DXM’s effects on SD and SUDEP in our animal model.  Methods: Experiment 1: We compared the frequency of SUDEP during 4 quarters of life in the Mashl+/- model. Experiment 2: 4 groups were studied to observe the in vivo effects of DXM. 2 groups of WT and 2 groups of Mashl+/- mice, one of each receiving vehicle and one of each receiving DXM (20 mg/kg). Animals underwent vestibular stimulation once/day for 10 days 20 minutes after receiving vehicle/DXM. Then animals were subjected to flurothyl-induced seizures. Experiment 3: To examine DXM’s effects in vitro, brain slices from WT and Mashl+/- animals were subjected to spreading depression using high concentrations of KCl and treated with various concentrations of DXM. Results: Experiment 1: Mortality was significantly higher in the second quarter of life of Mashl+/- mice: n = 39, P < 0.05, x2 test (7/39 in the 1st quarter; 16/39 in the 2nd; 11/39 in the 3rd; and 5/39 in the 4th). Spontaneous recurrent seizures were observed in 3/22 (14%) Mashl+/- mice as compared to 0/40 (0%) WT mice. Experiment 2: After undergoing vestibular stimulation, all Mashl+/- mice had seizures irrespective of whether they received DXM or vehicle. Preliminary results showed a trend that DXM treatment decreases seizure latency in both WT and Mashl+/- mice (WT, n = 2, P = 0.058; Mashl+/-, n = 2, P = 0.052). Experiment 3: Spreading depression duration was significantly inhibited at high concentrations of DXM in WT animal brain slices (P = 0.050), however no such effect was observed in Mashl+/- slices. Spreading depression amplitude remained unaffected in both WT and Mashl+/- slices. Conclusions: 1) SUDEP occurred most commonly during the second quarter of life and by virtue of the occurrence of stimulus induced seizures this model can be used as model to screen for potential anti-SUDEP medications. 2) DXM offered no protection against death and SD in vivo. 3) Unlike previous studies in adult mice, we did not find any protective effect of DXM in vitro.  Funding: This work was supported by The Duke Institute for Brain Sciences (DIBS) Fund number 4510874, Duke Fund numbers 4410161 and 3912247, The Duke Translational Research Institute (DTRI) Grant SOMVP-2012, and a grant from a Cure AHC Foundation (MAM).