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Autistic-like behavior, spontaneous seizures, and increased neuronal excitability in a Scn8a mouse model

Abstract

Patients with SCN8A epileptic encephalopathy exhibit a range of clinical features, including multiple seizure types, movement disorders, and behavioral abnormalities, such as developmental delay, mild-to-severe intellectual disability, and autism. Recently, the de novo heterozygous SCN8A R1620L mutation was identified in an individual with autism, intellectual disability, and behavioral seizures without accompanying electrographic seizure activity. To date, the effects of SCN8A mutations that are primarily associated with behavioral abnormalities have not been studied in a mouse model. To better understand the phenotypic and functional consequences of the R1620L mutation, we used CRISPR/Cas9 technology to generate mice expressing the corresponding SCN8A amino acid substitution. Homozygous mutants exhibit tremors and a maximum lifespan of 22 days, while heterozygous mutants (RL/+) exhibit autistic-like behaviors, such as hyperactivity and learning and social deficits, increased seizure susceptibility, and spontaneous seizures. Current clamp analyses revealed a reduced threshold for firing action potentials in heterozygous CA3 pyramidal neurons and reduced firing frequency, suggesting that the R1620L mutation has both gain- and loss-of-function effects. In vivo calcium imaging using miniscopes in freely moving RL/+ mutants showed hyperexcitability of cortical excitatory neurons that is likely to increase seizure susceptibility. Finally, we found that oxcarbazepine and Huperzine A, a sodium channel blocker and reversible acetylcholinesterase inhibitor, respectively, were capable of conferring robust protection against induced seizures in RL/+ mutants. This mouse line will provide the opportunity to better understand the range of clinical phenotypes associated with SCN8A mutations and to develop new therapeutic approaches.

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Fig. 1: Generation and characterization of the R1620L line.
Fig. 2: RL/+ mutants exhibit abnormal behaviors.
Fig. 3: RL/+ mutants exhibit greater susceptibility to induced seizures.
Fig. 4: RL/+ mutants exhibit significantly increased neural excitability and seizure susceptibility.
Fig. 5: Oxcarbazepine and Huperzine A increase resistance to 6 Hz- and PTZ-induced seizures in RL/+ mutants.

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Acknowledgements

The authors would like to acknowledge Dr. Mike Epstein for guidance on statistical analyses and Cheryl Strauss for editorial assistance.

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JCW and AE designed the research studies and wrote the manuscript. JCW generated the mice with contribution from JTT. JCW performed the seizure and behavior experiments with contribution from JTT. SFG, LC, KD, XX, and ALG performed the slice electrophysiology and calcium imaging. GASI performed the Western blot analyses and nerve conduction velocity experiments. SP and SMG performed pain analysis. SFG, KD, GASI SMG, XX, and ALG contributed to editing the manuscript.

Corresponding author

Correspondence to Jennifer C. Wong.

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Wong, J.C., Grieco, S.F., Dutt, K. et al. Autistic-like behavior, spontaneous seizures, and increased neuronal excitability in a Scn8a mouse model. Neuropsychopharmacol. (2021). https://doi.org/10.1038/s41386-021-00985-9

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