Abstracts

Rationale: Dravet syndrome (DS) is severe form of epilepsy with a high risk for sudden unexpected death in epilepsy (SUDEP).  Although cardiac failure is considered to be the root cause of SUDEP in DS, it is also well known that respiratory dysfunction can cause cardiac problems.  Despite this, few studies have characterized respiratory activity in mouse models of DS, and thus it is not known whether disordered breathing contributes to SUDEP in DS.   DS is most commonly caused by mutations in Scn1A, a gene that encodes the voltage gated Na+ channel (Nav1.1) that is predominantly expressed in inhibitory neurons. Inhibitory neurons regulate breathing at multiple levels of the respiratory circuit including respiratory chemoreceptors, neurons that regulate depth and frequency of breathing in response to changes in CO2/H+.  Therefore, we hypothesize that loss-of-function mutations in Scn1A will disrupt inhibitory control of chemoreceptor function to cause abnormal breathing and subsequent cardiac dysfunction and premature death. Methods: We use the cre-lox system to conditionally expressahuman DS-associated loss-of-function Scn1A mutation (A1783V) selectively in inhibitory neurons (Scn1AA1783V).  At the cellular level, we use electrophysiological techniques to characterize intrinsic electrical properties and CO2/H+-sensitivity of chemosensitive neurons and inhibitory neurons located in a brainstem respiratory center known as the retrotrapezoid nucleus (RTN) in brain slices from control and Scn1AA1783V mice.  At the network level, we use slice-patch electrophysiology to characterize excitatory and inhibitory synaptic drive to chemosensitive RTN neurons tissue from each genotype.  At the whole animal level, we use whole-body plethysmography to assess baseline breathing and the ventilatory response to CO2 in control and Scn1AA1783V mice.  All experiments are performed in neonatal pups (10-15 days of age) results are analyzed by t-test or two-way RM-ANOVA and Tukey’s multiple comparison test as appropriate.(p < 0.05). Results: We found that a subset of inhibitory neurons in slices from control mice are inhibited by CO2/H+ (n=16,p A1783V/+ mice have reduced basal activity (n=12,p=0.02), as expected for loss of a Na+ channel. Also, found that Scn1AA1783V/+ mice exhibit severe hypoventilation under basal conditions(n=10,p 2/H+ (n=10,p < 0.05), and die prematurely(n=37).   Conclusions: We provide the first characterization of breathing in a mouse model of DS.  We show at cell, network and whole animal levels that loss of Scn1A function in inhibitory neurons disruption of respiratory chemoreception and may contribute to premature death in a mouse model of DS.   Funding: American Epilepsy Society Predoctoral Research Fellowship