Increases in the threshold for the development of epileptiform activity in field CA1 of Krushinskii-Molodnika rat hippocampal slices as an adaptive protective mechanism.

Studies were carried out into the chances of developing epileptiform activity in the neuronal network of hippocampal field CA1 in normal (Wistar) rats and in rats genetically predisposed to audiogenic convulsions (Krushinskii-Molodkina rats). The development of epileptiform activity was assessed in terms of the reduction in the threshold for development trains of epileptiform discharges in field CA1 of hippocampal slices, which were induced using episodic increases in the extracellular K+ concentration ([K+]0) or decreases in the extracellular Mg2+ concentration ([Mg2+]0). These experiments showed that the threshold for the development of trains of epileptiform discharges increased in field CA1 of hippocampal slices of Krushinskii-Molodkina rats, while the excitability of glutamatergic Schaffer collaterals/commissural fibers was decreased. In addition, Krushinskii-Molodkina rats showed no long-term potentiation of glutamatergic synaptic transmission or potentiation of the EPSP-spike system in pyramidal neurons, induced in field CA1 of hippocampal slices in Wistar rats by reductions in [Mg2+]0 and increases in [K+]0 respectively. It is suggested that this underlies the operation of an adaptive protective mechanism preventing the propagation of convulsive activity in the Krushinskii-Molodkina rat brain.