Role of brainstem cardiorespiratory neurons in SUDEP

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Sudden Unexpected Death in Epilepsy (SUDEP) is defined as the sudden, unexpected, and unexplained death of a person with epilepsy. SUDEP accounts for between 8 and 17% of all epilepsy-related deaths, rising to 50% in patients for which current therapies are ineffective. Amongst all neurological conditions, it is second only to stroke for number of life-years lost. Increasing evidence supports apnea (breathing cessation) as the primary cause of death following a seizure. Apnea and oxygen desaturation have been reported in a large percentage of patients during and after convulsive seizures, and of the 9 SUDEP cases that were monitored by video-EEG in epilepsy monitoring units (EMUs) at the time of death, all involved respiratory arrest occurring before terminal asystole (MORTEMUS study). A better understanding of the key processes involved in respiratory dysfunction and subsequent SUDEP would allow for the development of novel rescue therapies. SUDEP occurs across numerous epilepsy populations. One such vulnerable population are patients with SCN8A epileptic encephalopathy (EE), who have a gain of function mutation in the NaV1.6 sodium channel. Our mice models harbor Scn8a mutations identified in patients that suffered SUDEP, and produce many of the clinical symptoms of the patients, including spontaneous generalized tonic-clonic seizures, apnea, and SUDEP. Using these clinically relevant mice models we will test our CENTRAL HYPOTHESIS that SUDEP occurs when breathing ceases after a seizure, as a result of constant tonic inspiratory activity, and failure of breathing recovery is due to impaired cardiorespiratory homeostasis. AIM 1: We will determine the role of the Bötzinger complex (BötC) and retrotrapezoid nucleus (RTN) brainstem neurons on coordinating inspiratory activity during seizure-induced apnea using optogenetic techniques. AIM 2: Epilepsy patients at risk for SUDEP have impaired central chemosensitivity. We show that our SCN8A EE mice also have impaired central chemosensitivity. We propose to assess in vivo CO2-sensitivity at developmental time points leading up to SUDEP and determine if inhibition of sodium channel (INa) currents can rescue CO2-sensitivity. We will determine changes in RTN neurons to determine their CO2/H+-sensitivity, intrinsic excitability, and INa currents. Finally, we will use shRNA to knockdown NaV1.6 in the RTN and assess its contribution to in vivo CO2- sensitivity and SUDEP. AIM 3: Impaired cardiac control is a contributor of SUDEP, and we find that bradycardia occurs immediately prior to SUDEP. We will determine in vivo parasympathetic cardiac drive leading up to SUDEP and determine effects of INa inhibition. We will make recordings from parasympathetic cardiovagal neurons and determine the effects of NaV1.6 knockdown on bradycardia and SUDEP. These studies will significantly impact our current understanding of the cardiorespiratory alterations that lead to SUDEP and could provide important insight into novel therapeutic targets to prevent SUDEP.