title: Impaired excitability of somatostatin- and parvalbumin-expressing cortical interneurons in a mouse model of Dravet syndrome.
abstract: Haploinsufficiency of the voltage-gated sodium channel NaV1.1 causes Dravet syndrome, an intractable developmental epilepsy syndrome with seizure onset in the first year of life. Specific heterozygous deletion of NaV1.1 in forebrain GABAergic-inhibitory neurons is sufficient to cause all the manifestations of Dravet syndrome in mice, but the physiological roles of specific subtypes of GABAergic interneurons in the cerebral cortex in this disease are unknown. Voltage-clamp studies of dissociated interneurons from cerebral cortex did not detect a significant effect of the Dravet syndrome mutation on sodium currents in cell bodies. However, current-clamp recordings of intact interneurons in layer V of neocortical slices from mice with haploinsufficiency in the gene encoding the NaV1.1 sodium channel, Scn1a, revealed substantial reduction of excitability in fast-spiking, parvalbumin-expressing interneurons and somatostatin-expressing interneurons. The threshold and rheobase for action potential generation were increased, the frequency of action potentials within trains was decreased, and action-potential firing within trains failed more frequently. Furthermore, the deficit in excitability of somatostatin-expressing interneurons caused significant reduction in frequency-dependent disynaptic inhibition between neighboring layer V pyramidal neurons mediated by somatostatin-expressing Martinotti cells, which would lead to substantial disinhibition of the output of cortical circuits. In contrast to these deficits in interneurons, pyramidal cells showed no differences in excitability. These results reveal that the two major subtypes of interneurons in layer V of the neocortex, parvalbumin-expressing and somatostatin-expressing, both have impaired excitability, resulting in disinhibition of the cortical network. These major functional deficits are likely to contribute synergistically to the pathophysiology of Dravet syndrome.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; and.
authors.forename: Chao
authors.initials: C
authors.lastname: Tai
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; andMedicinal Safety Research Laboratories, Daiichi Sankyo Co., Ltd., Tokyo 134-8630, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Abe
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; and.
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Westenbroek
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; and.
authors.forename: Todd
authors.initials: T
authors.lastname: Scheuer
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; and wcatt@uw.edu.
authors.forename: William A
authors.initials: WA
authors.lastname: Catterall
mesh_terms: D000200:Action Potentials; D000818:Animals; D004195:Disease Models, Animal; D004831:Epilepsies, Myoclonic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D059330:GABAergic Neurons / Q000378:metabolism* / Q000473:pathology; D005786:Gene Expression Regulation; D051379:Mice; D008817:Mice, Mutant Strains; D062550:NAV1.1 Voltage-Gated Sodium Channel / Q000096:biosynthesis / Q000235:genetics; D019579:Neocortex / Q000378:metabolism* / Q000473:pathology; D010320:Parvalbumins / Q000096:biosynthesis* / Q000235:genetics; D017966:Pyramidal Cells / Q000378:metabolism* / Q000473:pathology; D013004:Somatostatin / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D062550:NAV1.1 Voltage-Gated Sodium Channel; D010320:Parvalbumins; C568249:Scn1a protein, mouse; D013004:Somatostatin