Abstract
In epilepsy patients, it is unknown who is at high-risk for SUDEP. Furthermore, the mechanism of how and why a patient cannot recover from the last generalized convulsive seizure (GCS) prior to SUDEP is unknown. We proposed that central chemosensing mechanisms are dysfunctional, and this contributes to SUDEP. Orexin has been implicated in chemosensing as a neuropeptide that aids to correct blood-gas instability, including hypercapnic and hypoxic/hypercapnic responses. The Kcna1-null mouse model of SUDEP is believed to be a high orexin model as, there is an increase in orexin the number of positive neurons by SD30 (an age relative to colony sudden death). Therefore, we hypothesized there is a dysfunction in orexin chemosensing in Kcna1-null mice that contributes to their risk for SUDEP. With a whole-body plethysmography approach, a novel test of anoxia-induced autoresuscitation (97%N2 and 3%CO2) was used to assess SUDEP risk. Kcna1-null mice at high-risk for SUDEP experienced higher autoresuscitation failure (5/7) as compared to age-matched wildtype mice (1/9) (p=0.04). Treatment of Kcna1-null mice at high-risk for SUDEP with an acute, systemic dose of the dual orexin receptor antagonist TCS1102 (100mg/kg i.p.) led to increased autoresuscitation success in 5/6 DORA-treated as compared to 3/8 vehicle-treated mice (DMSO) that was not significant (p=0.14). In a second approach using immunofluorescence, increased orexin influence was assessed at potential cardiorespiratory sites in the brainstem that may lead to dysfunction that contributes to SUDEP. This study examined if there is increased orexin innervation at three serotonin-rich sites: dorsal raphe, raphe magnus and raphe obscurus. No differences were observed across genotypes or within genotypes for orexin or tryptophan hydroxylase, an enzyme specific to serotonin cells that served as a serotonin cell marker. This study suggests that autoresuscitation is impaired in Kcna1-null mice at high-risk for SUDEP, and orexin may have a role in mediating the autoresuscitation response, which may not be occurring at the level of brainstem serotonin regions.