Abstracts

Rationale: CNS infections are a major risk factor for the development of temporal lobe epilepsy, a form of epilepsy that is often drug resistant. Post-infection epileptogenesis is not well understood, partly due to the lack of an animal model that accurately reproduces the pathologic and phenotypic features of human encephalitis-induced epilepsy. We have recently reported that in the subpopulation of the Theiler’s virus-infected mice that exhibit acute post-infection seizures, 50% go onto have spontaneous seizures 2 months following infection (see poster of Kerry Ann Stewart). The current study examines the frequency, amplitude, total charge transfer, and kinetics of miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) in hippocampal brain slices prepared from TMEV-infected and saline injected C57BL/6 mice at least 2 months following infection. Methods: Mice were intracerebrally injected with either PBS or TMEV (2 x 10 PFU). Hippocampal brain slices were cut to a thickness of 300 μm. Whole-cell patch-clamp recordings were made of CA3 hippocampal neurons in Ringer’s solution containing CNQX (10 μM) and APV (50 μM) for recording IPSCs or picrotoxon (50μM) for recording EPSCs. The internal pipette solution was composed of (in mM): 130 CsCl, 1 NaCl, 5 EGTA, 10 HEPES, 1 MgCl2 1 CaCl2, 5 QX314, and 2 ATP. Experiments were performed in voltage clamp with the holding potential set at -70 mV. After baseline activity was established, the same solution, but now containing TTX (1 μM), was washed on for 15 min. Recordings of 3 min were made before and after TTX application. Measurements of mIPSC and mEPSC number, amplitude, total charge transfer, rise time, and decay time were made. Results: Recordings of mIPSCs made from PBS-injected (N=8) and virus-injected-mice (N=10) revealed no significant difference between average frequency, amplitude, total charge transfer, or rise time. However, normalized cumulative distributions for decay times for both PBS-injected (8844 mIPSCs) and virus-injected mice (9980 mIPSCs) revealed a significant increase of decay times in the virus-injected mice (χ-square test, p=0.003). While recording of mEPSCs from PBS-injected (N=5) and virus-injected (N=10) mice found no difference in average mEPSC rise time, number, and peak amplitude, significant increases were found in average mEPSC total charge transfer (t-test, p=0.01) and decay time (t-test, p=0.01). Conclusions: These findings give support for the use of the Theiler’s virus infected B6 mice as a novel model of infection-induced epilepsy. The changes of both excitatory and inhibitory transmission in the CA3 region of hippocampus suggest network disturbances that might lead to, or exacerbate, seizure activity. These observations are analogous to those observed in other animal models of epilepsy, and suggest that virally induced epilepsies might result from similar changes in hippocampal networks. Acknowledgment We thank the CURE and Margolis Foundation's for the support of this work.