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Na(v)1.1 localizes to axons of parvalbumin-positive inhibitory interneurons: a circuit basis for epileptic seizures in mice carrying an Scn1a gene mutation.

Ikuo Ogiwara, Hiroyuki Miyamoto, Noriyuki Morita, Nafiseh Atapour, Emi Mazaki, Ikuyo Inoue, Tamaki Takeuchi, Shigeyoshi Itohara, Yuchio Yanagawa, Kunihiko Obata, Teiichi Furuichi, Takao K Hensch, Kazuhiro Yamakawa

J. Neurosci., 2007 May 30 , 27, 5903-14

Loss-of-function mutations in human SCN1A gene encoding Na(v)1.1 are associated with a severe epileptic disorder known as severe myoclonic epilepsy in infancy. Here, we generated and characterized a knock-in mouse line with a loss-of-function nonsense mutation in the Scn1a gene. Both homozygous and heterozygous knock-in mice developed epileptic seizures within the first postnatal month. Immunohistochemical analyses revealed that, in the developing neocortex, Na(v)1.1 was clustered predominantly at the axon initial segments of parvalbumin-positive (PV) interneurons. In heterozygous knock-in mice, trains of evoked action potentials in these fast-spiking, inhibitory cells exhibited pronounced spike amplitude decrement late in the burst. Our data indicate that Na(v)1.1 plays critical roles in the spike output from PV interneurons and, furthermore, that the specifically altered function of these inhibitory circuits may contribute to epileptic seizures in the mice.