Developmental changes in brain activity of heterozygous Scn1a knockout rats

Mayu Tahara; Norimichi Higurashi; Junichi Hata; Masako Nishikawa; Ken Ito; Shinichi Hirose; Takehito Kaneko; Tomoji Mashimo; Tetsushi Sakuma; Takashi Yamamoto; Hirotaka James Okano

doi:10.3389/fneur.2023.1125089

Developmental changes in brain activity of heterozygous Scn1a knockout rats

Front Neurol. 2023 Mar 14:14:1125089. doi: 10.3389/fneur.2023.1125089. eCollection 2023.

Authors

Mayu Tahara^{1

2}, Norimichi Higurashi¹, Junichi Hata^{2

3}, Masako Nishikawa⁴, Ken Ito^{1

2}, Shinichi Hirose⁵, Takehito Kaneko⁶, Tomoji Mashimo⁷, Tetsushi Sakuma⁸, Takashi Yamamoto⁸, Hirotaka James Okano²

Affiliations

¹ Department of Pediatrics, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan.
² Division of Regenerative Medicine, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan.
³ Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa-ku, Tokyo, Japan.
⁴ Clinical Research Support Center, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan.
⁵ General Medical Research Center, School of Medicine, Fukuoka University, Fukuoka, Japan.
⁶ Division of Fundamental and Applied Sciences, Graduate School of Science and Engineering, Iwate University, Morioka, Japan.
⁷ Division of Animal Genetics, Laboratory Animal Research Center, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan.
⁸ Division of Integrated Sciences for Life, Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan.

Abstract

Introduction: Dravet syndrome (DS) is an infantile-onset developmental and epileptic encephalopathy characterized by an age-dependent evolution of drug-resistant seizures and poor developmental outcomes. Functional impairment of gamma-aminobutyric acid (GABA)ergic interneurons due to loss-of-function mutation of SCN1A is currently considered the main pathogenesis. In this study, to better understand the age-dependent changes in the pathogenesis of DS, we characterized the activity of different brain regions in Scn1a knockout rats at each developmental stage.

Methods: We established an Scn1a knockout rat model and examined brain activity from postnatal day (P) 15 to 38 using a manganese-enhanced magnetic resonance imaging technique (MEMRI).

Results: Scn1a heterozygous knockout (Scn1a ^+/-) rats showed a reduced expression of voltage-gated sodium channel alpha subunit 1 protein in the brain and heat-induced seizures. Neural activity was significantly higher in widespread brain regions of Scn1a ^+/- rats than in wild-type rats from P19 to P22, but this difference did not persist thereafter. Bumetanide, a Na⁺-K⁺-2Cl^- cotransporter 1 inhibitor, mitigated hyperactivity to the wild-type level, although no change was observed in the fourth postnatal week. Bumetanide also increased heat-induced seizure thresholds of Scn1a ^+/- rats at P21.

Conclusions: In Scn1a ^+/- rats, neural activity in widespread brain regions increased during the third postnatal week, corresponding to approximately 6 months of age in humans, when seizures most commonly develop in DS. In addition to impairment of GABAergic interneurons, the effects of bumetanide suggest a possible contribution of immature type A gamma-aminobutyric acid receptor signaling to transient hyperactivity and seizure susceptibility during the early stage of DS. This hypothesis should be addressed in the future. MEMRI is a potential technique for visualizing changes in basal brain activity in developmental and epileptic encephalopathies.

Keywords: Dravet syndrome (DS); bumetanide (BTN); developmental and epileptic encephalopathy (DEE); functional neuroimaging; gamma-aminobutyric acid (GABA).

Associated data

figshare/10.6084/m9.figshare.12894698

Grants and funding

This work was supported in part by the JSPS KAKENHI Grants JP20H03630 and JP20H03651 (SH), JP26461552, JP18K07802, and JP21K07780 (NH); AMED Grant JP21ek0109505 (SH) and JP22bm0804023h0003 (NH); grants from the Science Research Promotion Funds (G19001 and G20001) (SH); research grants from Kawano Masanori Memorial Public Interest Incorporated Foundation for Promotion of Pediatrics (NH and MT), The Mother and Child Health Foundation (NH), and The Japan Epilepsy Research Foundation (NH).