Abstracts

Rationale: Sudden Unexplained Death in Epilepsy (SUDEP) is a leading cause of mortality across epilepsy disorders. SUDEP affects up to 50% of patients with Dravet syndrome (DS), a genetic epilepsy syndrome caused primarily by a mutation in the SCN1A gene. The mechanism of SUDEP is not fully understood. We hypothesize that seizure- and post-ictal hypoxia-induced inflammation becomes excessive and dysregulated within the nucleus tractus solitarius (NTS), a medullary nucleus that regulates cardiorespiratory function. Microglia and astrocytes have been implicated in adaptive ventilatory responses in the NTS following low oxygen conditions. Both glial types become activated following CNS insults, change their morphology and function, and become primary producers of pro-inflammatory cytokines such as TNFα and IL-6. Though inflammation is homeostatic and necessary to recover from insults, we propose that such overwhelming inflammation in a region of the brain crucial for respiration prevents normal glia-mediated compensatory breathing mechanisms following a seizure. Understanding the role of brainstem microglia and astrocytes in inflammation and respiratory regulation in Dravet syndrome may provide insight into a potential mechanism of SUDEP in this population.

Methods: A Dravet syndrome mouse model expressing a heterozygous mutation in the sodium channel gene Scn1a^A1783V/WT (Het) was used and compared with wild-type (WT) controls. Whole body plethysmography (WBP) studies allowed evaluation of respiration in P30-40 Het and WT following induction of 6 Hz seizure. The mRNA expression of pro-inflammatory cytokines TNFα and IL-6 were determined in the forebrain and brainstem using qPCR in P25-30 Het vs. WT mice to evaluate inflammation. To determine intrinsic NTS neuronal excitability of P25-35 Het vs. WT mice, electrophysiologic methods were used. The tractus solitarius (TS), a fiber bundle that innervates the NTS, was stimulated and extracellular field excitatory post-synaptic potential (fEPSP) was recorded in the NTS. The input/output relationship was assessed and compared for both groups of mice.

Results: WBP studies revealed that at baseline, Hets had greater tidal volume and expiratory volume compared to WT. Following induced seizure, Hets had shorter end inspiratory pause than WT. The mRNA of TNFa and IL-6 were upregulated in the brainstem of Hets compared to the brainstem of WT. We have been able to record fEPSPs in the NTS and hypothesize that for a given stimulus intensity, the fEPSP recorded in Hets will be lower than in WT. These experiments are in progress.

Conclusions: Inflammation is greatest in the Het brainstem, suggesting that inflammation may be involved in the dysregulated respiration observed in Hets at baseline and following a seizure. Further studies will allow us to better evaluate the role of inflammation in central respiration in this DS model.

Funding: Please list any funding that was received in support of this abstract.: This project was supported by the Dravet Syndrome Foundation.