Abstracts

To investigate the association between semaphorin 3F-neuropilin-2 (Sema3F-Npn-2) signaling and epilepsy, using knockout mice.
To determine hippocampal involvement in seizures of [italic]sema3F [/italic]knockout mice, using depth wire recording.
Sema3F-Npn-2 signaling is required for the proper targeting of the infrapyramidal tract in the hippocampus ^{[sahay, Tessier-Lavigne][sub].[/sub]} In epilepsy models there is a dramatic decrease in semaphorin levels ^{[Barnes, Holtmaat][sub]. [/sub]}These observations along with the known histopathology of hippocampal sclerosis (mossy fiber sprouting), the observed phenotype of the [italic]sema3F [/italic]knockout mouse (staring) and the localization of Sema3F ligand and Npn-2 receptor in synaptic-rich areas of the hippocampus, prompted us to hypothesize that: 1) [italic]Sema3F [/italic]and [italic]npn-2[/italic] knockouts have epilepsy. 2) This may be temporal lobe epilepsy. 3) These mice may serve as new models for epileptogenesis. So far, we have shown that [italic]sema3F [/italic]knockouts have epilepsy ^{[Sahay 2005][sub]. [/sub]}Here, we heve further pursued objective 1 by examining the association of neuropilin-2 and epilepsy and objective 2 by performing depth wire recordings in [italic]sema3F [/italic]knockouts to evaluate the role of the hippocampus in their seizures. Depth electrodes were implanted into the hippocampus of knockout mice and wild-type controls using a stereotaxic manipulator. Histology confirmed depth wire placement in the hippocampus. EEG and behavior were monitored daily. Seizure susceptibility was assessed by PTZ. Scalp EEG recordings suggest that [italic]npn-2[/italic] knockout mice have epileptic seizures manifested by staring episodes. Additionally, behavioral monitoring indicate that [italic]npn-2[/italic] knockout mice have significantly fewer exploratory episodes (p=0.012) and significantly more stationary episodes (p=0.005) compared to wild-type controls.
We have simultaneously recorded EEG from the hippocampus and scalp. H[amp]E staining of brain slices showed depth wire placement in the CA3 region. Administration of PTZ produced seizures in wild-types and [italic]sema3F[/italic] knockouts. The first epileptiform EEG change was hippocampal for both. However, this early hippocampal EEG change occurred significantly earlier in the [italic]sema3F[/italic] knockout mouse, suggesting increased susceptibility to seizures (p=0.007). Most notably, the time between the early hippocampal EEG change and the subsequent scalp EEG change was significantly greater in [italic]sema3F[/italic] knockouts than in wild-types in whom the temporal and scalp epileptiform EEG changes were nearly simultaneous (p=0.04). [italic]npn-2 [/italic]knockout mice show epileptic behavior and develop seizures, thereby buttressing the relationship between loss of Sema3F-Npn-2 signaling and epilepsy.
Depth EEG recordings and PTZ tests indicate that seizures in [italic]sema3F[/italic] knockout mice occur earlier in the hippocampus and persist there longer prior to spreading to the scalp, suggesting a hippocampal focus. Frther studies may provide insight into cellular mechanisms of epileptogenesis.