High frequency activity preceding epileptic seizures

Abstract

High frequency activity (>100 Hz, HFA) is suggested to be related to seizure genesis, but the mechanism of the HFA is not clear. In the present work HFAs and epileptic features including electrographic seizures (trains of hypersynchronous population spikes lasting ~46 sec) and interictal discharges (abrupt potential deflections, ~40 ms) were induced in rat hippocampal slices by increasing potassium concentration in artificial cerebrospinal fluid (8-10 mM, ACSF). We demonstrated that 1) the HFA was formed mainly by synchronous firing of pyramidal neurons while a subset of interneurons might contribute the HFA; 2) the frequencies of the HFAs were region-specific (186 Hz in CA1 and 240 Hz in CA3), and seizures were present only in CA1; 3) build-up of HFA preceding seizures was observed and it was disrupted by refractory periods triggered by interictal discharges, which were abrupt potential deflections present between seizures every 0.8 sec; 4) interictal discharges have both pro- and anti-effects on seizure genesis, and the dual consequences might be due to modifying HFA; 5) synaptic transmission through glutamatergic and γ-aminobutyric acid-ergic synapses were not essential in HFA formation but they were related to the modulations of HFA. Our findings suggested the crucial role of HFA in the seizure genesis and the potential value in seizure prediction by monitoring the HFA.