Spontaneous epileptiform bursts and long-term potentiation in rat CA3 hippocampal slices induced by chaotic stimulation of mossy fibers

Abstract

The relation between long-term potentiation (LTP) and spontaneous rhythm in CA3 was investigated using rat hippocampal slices. Field potential response of CA3 to mossy fiber stimulation consisted of a mono-synaptic positive potential and subsequent poly-synaptic negative potentials. LTP of both field potentials was induced by chaotic mossy fiber stimulation. Although CA3 did not show any spontaneous rhythm before LTP induction in a normal perfusing medium, CA3 spontaneously caused epileptiform bursts after LTP induction by chaotic mossy fiber stimulation. The amplitude of those epileptiform bursts and the inter-burst interval were not uniform. After LTP induction, the cross-correlation function of spontaneous field potentials simultaneously recorded at two sites approximately 300 μm apart in CA3 showed a large central peak. This indicates that neuronal activity at two sites is synchronized. These results suggest that epileptiform bursts in CA3 are caused by synchronization of spontaneous CA3 pyramidal cell activity due to LTP induced by chaotic burst stimulation.