Abstracts

Seizures are associated with hyper-synchronous electrical activity in the EEG recordings. However, the network dynamics at the single neuron level during the development and maintenance of seizures remains largely unknown. In this study we studied the firing behavior of single neurons, and monitored synchronization between the different recorded neurons during developing and ongoing seizures evoked by pilocarpine and picrotoxin., Multi-electrode extra-cellular recordings of single units and local field potentials were performed from the hippocampus of anesthsized (urethane) and awake rats under control conditions and after administration of pilocarpine and picrotoxin. The two convulsants were administered either by systemic (I.P.) or local (intra-hippocampal) injection. In addition simultaneous intracellular whole-cell recordings were performed., Immediately after administration of pilocarpine and picrotoxin, prior to initiation of clinical or electrographic seizures, the frequency of spikes decreased, and synchronization between neurons, as measured by the cross-correlogram, markedly diminished or disappeared all together. In contrast after clinical and electrographic seizures initiated the frequency of spikes gradually increased, neurons tended to fire in bursts and the inter-neuron synchronization markedly increased. The cross-correlograms during the clinical seizure revealed higher values and wider time-windows as compared to control conditions. Similar results were obtained in anesthetized and awake rats; in systemic (I.P.) and local intra-hippocampal administration of the convulsants, and with pilocarpine and picrotoxin. Simultaneous intracellular whole-cell recording from anesthetized rats demonstrated the intracellular correlate of developing seizures., In this study we showed that during the development of pharmacologically induced seizures synchronization of firing between different neurons in the hippocampus decreased dramatically, while only later during clinical seizures inter-neuronal synchronization gradually increased. These findings may promote our understanding of the network dynamics responsible for seizure initiation and maintenance. Moreover, in future it may serve as the basis for detection of impending seizures in human patients., (Supported by ISF foundation; Rapapport family Foundation.)