Abstracts

Purkinje Cell-specific scn1b Knockout Causes Cellular Hypoexcitability and Associative Learning Disabilities Modeling Developmental and Epileptic Encephalopathies

Abstract number : 1.023
Submission category : 1. Basic Mechanisms / 1B. Epileptogenesis of genetic epilepsies
Year : 2024
Submission ID : 728
Source : www.aesnet.org
Presentation date : 12/7/2024 12:00:00 AM
Published date :

Authors :
Presenting Author: F. Isaac Guillén, MS – Dell Medical School / Department of Neurology

Shao-Ying Cheng, PhD – University of Texas at Austin
Hiroshi Nishiyama, PhD – University of Texas at Austin
MacKenzie Howard, PhD – Dell Medical School

Rationale: Developmental and epileptic encephalopathies (DEEs) are pediatric disorders characterized by a broad range of neurodevelopmental disabilities and medically refractory epilepsy. Loss of function of SCN1B causes DEEs, including Dravet syndrome, that typically include severe motor dysfunction, autistic features, and deficits of learning, memory, and cognition.

SCN1B plays key roles in development as a cell adhesion molecule and gene expression regulator, and control of neuronal physiology as an auxiliary ion channel subunit. Scn1b knockout mice exhibit cell-specific changes to neural excitability and ataxia. But due to severe progressive seizures, health deterioration, and early mortality, they can’t be used to study mature brain function or behavior. Thus there is a major gap in understanding, and ability to study, mechanisms of SCN1B-DEE disabilities.

Most DEE research focuses on seizures in hippocampus, cortex, and thalamus, but many of the most impactful and persistent DEE disabilities localize to cerebellum. Scn1b is highly expressed in cerebellum and known to play some role in the specialized physiology of Purkinje cells (PCs). Here, we tested the hypothesis that Scn1b regulation of PC physiology is necessary for maintenance of cerebellar output and associative memory governed by cerebellum.


Methods: Mice were Scn1bflox/flox;Ai14+;Pcp2-Cre on congenic C57Bl6/J backgrounds. Pcp2 expresses Cre, thus excising Scn1b, specifically in PCs (hereafter: PC-Scn1b KO). Cre- littermates were controls. Ai14+ provided fluorescent indication of Cre expression.

Whole cell current clamp recordings were made from PCs in acute vermis and paravermis cerebellar slices from adult (12 wk) mice. Intrinsic properties and spontaneous and evoked action potentials were quantified.

Associative cerebellar learning was measured with eyeblink conditioning in adult mice. Awake, head-fixed mice were shown a light (condition stimulus, CS) followed immediately by a noxious (non-painful) air puff to the eye (unconditional stimulus, US). Over training sessions, mice typically learn to close their eye in response to the CS. Fractional eye closure (FEC) during CS was quantified.

Results: Scn1b loss caused profound and progressive PC hypoexcitability (Fig. 1). PC-Scn1b KO PCs had significant decreases in spike input/output functions (p< 0.001; RM-ANOVA) and increases in rheobase (p< 0.0001; t-test).

Cerebellar associative learning was abolished by PC-specific Scn1b loss (Fig. 2). Most control mice learned the eyeblink task, but learning was completely absent in PC-Scn1b KO mice (p< 0.0001; RM-ANOVA).


Conclusions: Our data show that Scn1b is a key regulator of PC excitability and necessary for associative learning in adult brain. PC-specific loss of Scn1b is sufficient to disrupt physiology and cause severe changes to cerebellar control of a broad range of neurological systems governing motor, social, and cognitive behavior. This study validates a novel model for, and suggests potential mechanisms underlying, a range of DEE neurodevelopmental disabilities.


Funding: Funded by a Dravet Syndrome Foundation Research Grant and NIH/NINDS R01 NS112500.

Basic Mechanisms