Abstracts

Rationale: Mutations in NaV1.1 sodium channel have been implicated in multiple epileptic encephalopathies. SMEI, an infantile onset severe epileptic syndrome, is caused by loss of function mutations in the Scn1a gene resulting in haploinsufficiency of its gene product, NaV1.1 channels. We have developed a mouse model of SMEI by targeted disruption of Scn1a. Heterozygous (Scn1a+/-) mice develop spontaneous seizures after P21. Homozygous null (Scn1a-/-) mice have frequent spontaneous seizures beginning on P10 and die by P15. In human SMEI, multiple generalized and focal seizure types begin in infancy. Febrile seizures including status epilepticus are frequent and may be the initial seizure type. In this study we characterize the electrographic and behavioral properties of spontaneous and temperature-induced seizures in the SMEI mouse model.Methods: Postnatal day 14 mice were anesthetized with ketamine and xylazine and implanted with thin platinum wire electrodes. Active electrodes were placed through a small hole in each of the four quadrants of the skull. A reference electrode was placed at the vertex and a ground wire was placed subcutaneously over posterior head. The wires were fixed in place with cyanoacrylate glue. After recovery from anesthesia on the same day, referential digital video-EEG recording was performed at 200 Hz in a temperature-controlled chamber. Rectal temperature probes were placed to monitor body core temperature. Recordings were performed for 5-10 min at baseline temperature. Subsequently, the chamber temperature was increased to 44° C, and the body temperature increased by approximately 0.3 deg per min. Spontaneous seizures were recorded in a similar way without raising the chamber temperature.Results: Scn1a+/- mice did not show spontaneous epileptiform activity at baseline temperature in 5 to 10 min recordings. As the temperature was elevated, epileptic activity consisting of multifocal sharp and slow waves was seen. Further increases in body temperature resulted in seizures characterized by stiffening followed by hypermotor activity that correlated with rhythmic spike and wave on EEG. In contrast, inter-ictal EEGs from Scn1a-/- mice contained frequent spontaneous epileptiform activity at baseline temperature. Seizures included clonic forepaw movement followed by rhythmic clonic head and trunk movements. Bilateral anterior spike and wave initially appeared at 3 Hz, increasing to 7-8 Hz, and spreading to involve all head regions. Increasing the temperature increased the frequency and duration of seizures. Scn1a+/+ mice did not show inter-ictal epileptiform activity or spontaneous seizures at normal or elevated temperatures. Conclusions: Using simultaneous video-EEG recording we demonstrated that Scn1a+/- mice have temperature-induced seizures, recapitulating the human phenotype. Scn1a-/- mice show spontaneous epileptic activity and seizures at baseline temperature representing a more severe phenotype.