Research ArticleEpilepsy

Spreading depolarization in the brainstem mediates sudden cardiorespiratory arrest in mouse SUDEP models

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Science Translational Medicine  08 Apr 2015:
Vol. 7, Issue 282, pp. 282ra46
DOI: 10.1126/scitranslmed.aaa4050

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Subduing SUDEP (sudden unexplained death in epilepsy)

Patients with uncontrolled epilepsy can have a seizure at any time and—even worse—also face an increased risk of sudden death: SUDEP (sudden unexplained death in epilepsy). Aiba and Noebels now report that genetically controlled sensitivity to inactivation of the heart and respiratory control centers of the brain may underlie SUDEP. After a seizure, epileptic mice with mutations in certain ion channels can show a massive depolarization in the brainstem, which shuts down the cardiorespiratory control centers, causing sudden death. Mutation in a modifier gene prevented the mortality. The authors attribute the susceptibility to so-called spreading depression to the mutated ion channels and suggest that similar channel variations in humans may increase the risk of seizure-induced death. Ultimately, genetic analysis could predict which patients are at the highest risk of SUDEP.

Abstract

Cardiorespiratory collapse after a seizure is the leading cause of sudden unexpected death in epilepsy (SUDEP) in young persons, but why only certain individuals are at risk is unknown. To identify a mechanism for this lethal cardiorespiratory failure, we examined whether genes linked to increased SUDEP risk lower the threshold for spreading depolarization (SD), a self-propagating depolarizing wave that silences neuronal networks. Mice carrying mutations in Kv1.1 potassium channels (−/−) and Scn1a sodium ion channels (+/R1407X) phenocopy many aspects of human SUDEP. In mutant, but not wild-type mice, seizures initiated by topical application of 4-aminopyridine to the cortex led to a slow, negative DC potential shift recorded in the dorsal medulla, a brainstem region that controls cardiorespiratory pacemaking. This irreversible event slowly depolarized cells and inactivated synaptic activity, producing cardiorespiratory arrest. Local initiation of SD in this region by potassium chloride microinjection also elicited electroencephalographic suppression, apnea, bradycardia, and asystole, similar to the events seen in monitored human SUDEP. In vitro study of brainstem slices confirmed that mutant mice had a lower threshold for SD elicited by metabolic substrate depletion and that immature mice were at greater risk than adults. Deletion of the gene encoding tau, which prolongs life in these mutants, also restored the normal SD threshold in Kv1.1-mutant mouse brainstem. Thus, brainstem SD may be a critical threshold event linking seizures and SUDEP.

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