Dysregulation of an Inhibitory-serotonergic Circuit in a Mouse Model of Dravet Syndrome
Abstract number :
3.017
Submission category :
1. Basic Mechanisms / 1B. Epileptogenesis of genetic epilepsies
Year :
2024
Submission ID :
79
Source :
www.aesnet.org
Presentation date :
12/9/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Evan Rosenberg, MD, PhD – The University of Pennsylvania Perelman School of Medicine
Clara Wang, BS – The University of Pennsylvania School of Arts and Sciences
Frances Jensen, MD – Perelman School of Medicine at the University of Pennsylvania
Ethan Goldberg, MD, PhD – Children's Hospital of Philadelphia
Rationale: Dravet Syndrome (DS) is a form of drug-resistant epilepsy in both children and adults, caused by variants in the
SCN1A gene encoding the voltage-gated sodium channel α subunit Nav1.1. Recent promising clinical trials led to FDA approval of the serotonin (5-HT)-boosting agent fenfluramine for treatment of seizures in DS patients. Despite this, the circuit basis for the seizure-reducing effects of serotonergic agents remains poorly understood.
Methods: We explored the effect of Nav1.1 deletion in the bidirectional dorsal raphe nucleus (DRN) to medial prefrontal cortex (mPFC) circuit utilizing electrophysiology, optogenetics, immunohistochemistry, and optical imaging. Experiments were performed in a mouse model of DS (Scn1a+/- mice harboring an exon 1 deletion leading to a null allele) at both early (postnatal, P16-21) and later (P35-56) time points. The DS mouse was then crossed to a double transgenic line harboring a floxed Ai14D/TdTomato reporter crossed to either ePET-Cre (to label serotonergic neurons) or PV-Cre (to label parvalbumin-positive interneurons). We then examined the receptor-, cell-, and age-specific mechanisms by which 5-HT regulates excitability in DS mice compared to WT controls.
Results: Using immunohistochemical analysis, we found that the DRN comprises medial ePET-Cre positive 5-HT as well as lateral parvalbumin (PV) containing neurons, with a subset of neurons co-expressing 5-HT and PV. PV interneurons in the DRN demonstrated enriched Nav1.1 expression in the axon initial segment relative to 5-HT-positive/PV-negative neurons. Compared to PV interneurons, DRN 5-HT principal neurons demonstrated distinct passive and active electrophysiological properties. Nav1.1 deletion in Scn1a+/- mice severely impaired firing in DRN PV-positive/5-HT-negative interneurons, mildly disrupted firing of neurons co-expressing 5-HT and PV, and spared changes in firing of 5-HT-positive/PV-negative principle neurons at P16-21. mPFC PV interneurons in Scn1a+/- mice had impaired firing at later (P35-56), but not earlier (P16-21) time points.
Conclusions:
We found that loss of Nav1.1 causes age- and region-specific changes to the DRN-mPFC microcircuit in the DS mouse model. We predict that Nav1.1 deletion causes marked impairment of DRN PV+ interneurons, which might dysregulate endogenous release of 5-HT from principal cells in the DRN. In addition, we discovered that PV interneurons in mPFC demonstrate impairment at later developmental time points in contrast to what has been observed previously in neocortex and hippocampus. This data reveals complex dysfunction of the DRN-mPFC circuit in Dravet syndrome, with potential implications for regulation of endogenous 5-HT release.
Funding:
This work is supported by NIH NINDS R01 NS110869 (EG), R25 NS065745 (ECR) and the Louis H Castor, M.D., Undergraduate Research Grant and Frances Velay Fellowship from Penn CURF (CW).
Basic Mechanisms