Abstracts

The pathogenesis of temporal lobe epilepsy (TLE) is characterized by activity-dependent changes in synaptic plasticity. Certain forms of synaptic plasticity have been shown to depend on modifications of the presynaptic release machinery. However, our knowledge about the underlying molecular mechanisms and the role of the presynaptic release machinery in functional changes that underlie epileptic activity at the level of the synapse is very limited. Therefore, we have analyzed whether the expression patterns of components of the presynaptic release machinery are altered in different stages of an experimental model of temporal lobe epilepsy. We have furthermore characterized knock-out mice deficient for three proteins that are integral components of the release machinery, RIM1[alpha], RIM2[alpha] or Synaptotagmin 10 (Syt 10), in an experimental model of TLE., Status epilepticus (SE) was induced by systemic application of pilocarpine to rats as well as to three mutant mouse lines . Changes in mRNA levels were analyzed by Real-time PCR and in situ hybridization (ISH). Seizure susceptibility was determined after induction of SE. The frequency and severity of chronic recurrent seizures was analyzed with a telemetric EEG system (DSI) and parallel video analysis. To study hippocampal damage, the amount of segmental hippocampal loss of neurons and gliosis were analyzed in wild-type and knock-out mice after SE., To investigate changes in the mRNA expression level of various components of the presynaptic release machinery hippocampal subregions (dentate gyrus (DG), CA3 and CA1) were isolated from rats 4, 6 and 8 hours and 5 and 28 days after SE induced by pilocarpine. Analysis of these samples by Real-time PCR, ISH and Affymetrix-Micro-Arrays showed distinct changes in the expression patterns of several constituents of the release machinery; e.g. Syt 10 could not be detected in the CA1 region of control rats/mice, neither by single cell PCR nor by ISH, however, its mRNA was strongly expressed in CA1 cells 6 h after SE.
To study if ablation of individual components of the presynaptic release machinery affects epileptogenesis we are analyzing three mutant mouse lines in the pilocarpine model of TLE: knock-out mice for the active zone proteins RIM1[alpha] and RIM2[alpha], which exhibit defects in short- and long-term synaptic plasticity, and Syt 10, whose mRNA expression is induced by seizures. So far the results obtained by Video- and EEG-Monitoring of these animals suggest that RIM1[alpha] knock-out mice have a higher susceptibility to seizures than wild-type littermates (n=5). Furthermore, the latency to the first seizue and to SE seem to be reduced., Our results suggest that components of the presynaptic release machinery are modified during epileptogenesis, may play a pathogenetic role and constitute targets for new therapeutic approaches in TLE., (Supported by DFG (SFB TR3, Emmy-Noether-Program), BONFOR.)