Abstracts

Rationale: Previous study shows that treatment with neuraminidase (NEU), the key enzyme which cleaves sialic acids, exerted powerful anticonvulsive action in vitro and in vivo. In contrast blockade of endogenous NEU by specific blocker N-Acetyl-2,3-dehydro-2-deoxyneuraminic acid (NADNA) significantly reduces seizure threshold and aggravates hippocampal seizures in vivo. The goal of the present study is to investigate the role of endogenous NEU in morphological and electrophysiological characteristics and seizure susceptibility of pyramidal CA1 layer in cultured rat hippocampal slices. Methods: Extracellular field potentials were recorded from pyramidal CA1 layer in cultured rat hippocampal slices. The level of sialylation was estimated using SNA-I (horseradish peroxidase conjugated) and toluidine blue staining. Morphological characteristics of synapses were estimated using electron microscopy. Results: Histochemical studies show that incubation of slices with NADNA results in significant increasing in the level of sialylation of the hippocampal tissue. To study an effect of NADNA on the net hippocampal activity we used two models of seizures. We show that treatment with NADNA increases duration and frequency of seizure-like activity induced by gabazine. Using low magnesium model of epilepsy we show that seizures recorded from hippocampal slices pretreated with NADNA have recurrent cycles of activity which contained in sequence: initial burst, tonic activity, tonic-clonic activity and clonic activity. On the contrary in the untreated slices we did not find any regular sequences and only tonic-clonic and clonic activities were found. In slices treated in 2mM NADNA density of perforated synapses in CA1 stratum radiatum was 7.6±0.5/100mkm2 which significantly more then the amount of perforated synapses in control untreated slices (4.1±0.4/ 100µm2). Coincubation slices with NADNA and 5mM Ca2 eliminated effect of NEU blocker on the synaptic density in CA1 stratum radiatum. Conclusions: Our studies show that downregulation of endogenous NEU leads to increasing of synaptogenesis in hippocampus. Experiments with high concentrations of calcium suggest this process is activity dependent. Also our data indicate that shape of synchronization could be influenced by amount of active NEU in neuronal tissue (Supported by Christopher Donalty and Kyle Coggins Memorial grant).