Molecular and cellular basis: insights from experimental models of Dravet syndrome.

Dravet syndrome is caused by mutations of the SCN1A gene that encodes voltage-gated sodium channel alpha-1 subunit. SCN1A-knock-in mouse with a disease-relevant nonsense mutation that we generated well reproduced the disease phenotypes. Both homozygous and heterozygous knock-in mice developed epileptic seizures within the first postnatal month. In heterozygotes, trains of evoked action potentials in fast-spiking, inhibitory cells exhibited pronounced spike amplitude decrement late in the burst but not in pyramidal neurons. Furthermore, our immunohistochemical studies showed that in wild-type mice Nav1.1 is expressed in parvalbumin-positive inhibitory interneurons (PV cells), dominantly in its axons and moderately in somata, and not expressed in pyramidal cells nor other types of interneurons including somatostatin-positive and calretinin-positive cells. These results so far suggest that Nav1.1 expression is largely confined to PV cells and plays critical roles in their spike output, and that impaired function of PV cells would be the cellular basis of Dravet syndrome.