Abstracts

Audiogenic seizures were induced ino mice carrying the human SCN8A encephalopathy mutation p.Asn1768Asp (N1768D; “D/+ mice”) using a 15 kHz pure tone. Video, electroencephalogram (EEG), electrocardiogram (ECG), and breathing via whole body plethysmography were recorded before, during, and immediately after stimulation of seizures.

To test the necessity of ictal activity from upper motor neurons in the motor cortex are required for generating ictal apnea, we expressed iDREADD receptors in cortical excitatory neurons of D/+ mice and injected CNO i.p. prior to inducing seizures with a 15 kHz pure tone (Figure 1A). Under control conditions, seizures presented with the usual tonic phase apnea and spike wave discharges (SWDs) in the motor cortex (Figures 1B-D). CNO administration robustly inhibited the SWDs, but the tonic phase and apnea were not affected (Figures 1C-E). The effect of all doses of CNO on ECoG power was significantly greater than the effect on apnea (p = 0.0001, 2-way ANOVA).

We implanted fiberoptic ferrules bilaterally into the Bötzinger Complex (BötC) of mice that express Channelrhodopsin2 (ChR2) under the vesicular GABA transporter (VGAT; “VGAT-ChR2” mice) that were crossed with D/+ mice (Figure 2A). The goal of the experiment is to photostimulate BötC during ictal apnea to inhibit tonic inspiratory activity and produce expiration (Figure 2A). Seizures were evoked using a 15 kHz pure tone (Figures 2B-D). Trains of light pulses (50 ms pulses, 5 mW of 473 nm light) were evoked repetitively during ictal apnea (Figures 1C & D). However, this did not recover normal breathing rhythm and apnea duration was no different for any photostimulation paradigm versus control (p = 0.7892, F =  0.1747, One-Way ANOVA; Figure 1E). Although breathing was not affected during seizures, the effects on baseline breathing were substantial; for example, inspiration was inhibited for a full 10 second photostimulation train (Figure 2F).