Impairment of Sharp-Wave Ripples in a Murine Model of Dravet Syndrome

Christine S. Cheah, Brian N. Lundstrom, William A. Catterall, John C. Oakley

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Dravet syndrome (DS) is a severe early-onset epilepsy associated with heterozygous loss-of-function mutations in SCN1A Animal models of DS with global Scn1a haploinsufficiency recapitulate the DS phenotype, including seizures, premature death, and impaired spatial memory performance. Spatial memory requires hippocampal sharp-wave ripples (SPW-Rs), which consist of high-frequency field potential oscillations (ripples, 100-260 Hz) superimposed on a slower SPW. Published in vitro electrophysiologic recordings in DS mice demonstrate reduced firing of GABAergic inhibitory neurons, which are essential for the formation of SPW-R complexes. Here, in vivo electrophysiologic recordings of hippocampal local field potential in both male and female mice demonstrate that Scn1a haploinsufficiency slows intrinsic ripple frequency and reduces the rate of SPW-R occurrence. In DS mice, peak ripple-band power is shifted to lower frequencies, average intertrough intervals of individually detected ripples are slower, and the rate of SPW-R generation is reduced, while SPW amplitude remains unaffected. These alterations in SPW-R properties, in combination with published reductions in interneuron function in DS, suggest a direct link between reduced inhibitory neuron excitability and impaired SPW-R function. A simple interconnected, conductance-based in silico interneuron network model was used to determine whether reduced sodium conductance is sufficient to slow ripple frequency, and stimulation with a modeled SPW demonstrates that reduced sodium conductance alone is sufficient to slow oscillatory frequencies. These findings forge a potential mechanistic link between impaired SPW-R generation and Scn1a mutation in DS mice, expanding the set of disorders in which SPW-R dysfunction contributes to impaired memory.SIGNIFICANCE STATEMENT Disruption of sharp-wave ripples, a characteristic hippocampal rhythm coordinated by the precise timing of GABAergic interneurons, impairs spatial learning and memory. Prior in vitro patch-clamp recordings in brain slices from genetic mouse models of Dravet syndrome (DS) reveal reduced sodium current and excitability in GABAergic interneurons but not excitatory cells, suggesting a causal role for impaired interneuron activity in seizures and cognitive impairment. Here, heterozygous Scn1a mutation in DS mice reduces hippocampal sharp-wave ripple occurrence and slows internal ripple frequency in vivo and a simple in silico model demonstrates reduction in interneuron function alone is sufficient to slow model oscillations. Together, these findings provide a plausible pathophysiologic mechanism for Scn1a gene mutation to impair spatial memory.

Original languageEnglish (US)
Pages (from-to)9251-9260
Number of pages10
JournalThe Journal of neuroscience : the official journal of the Society for Neuroscience
Volume39
Issue number46
DOIs
StatePublished - Nov 13 2019

Keywords

  • channelopathy
  • Dravet syndrome
  • epilepsy comorbidity
  • learning and memory
  • Scn1a
  • sharp-wave ripple

ASJC Scopus subject areas

  • Neuroscience(all)

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