Synchronized population oscillation of excitatory synaptic potentials dependent of calcium-induced calcium release in rat neocortex layer II/III neurons.

We examined the roles played by calcium-induced calcium release from ryanodine-sensitive calcium stores in induction of neocortical membrane potential oscillation by using caffeine, an agonist of ryanodine receptors. Intracellular recordings were made from neurons in layer II/III of rat visual cortex slices in a caffeine-containing medium. White matter stimulation initially evoked monophasic synaptic potentials. As low-frequency stimulation continued for over 10 min, an oscillating synaptic potential gradually became evoked, in which a paroxysmal depolarization shift was followed by a 8-10-Hz train of several depolarizing wavelets. This oscillating potential was not induced in a medium containing no caffeine with 2 or 0.5 mM [Mg2+](o). Under blockade of N-methyl-D-aspartate receptors, induction of this oscillating potential failed even with caffeine application. Experiments with the calcium store depletor, thapsigargin, revealed that this oscillating potential is induced in a manner dependent on intracellular calcium release. Dual intracellular recordings revealed that the oscillation was synchronized in pairs of layer II/III neurons. The oscillating potential was detectable by field potential recordings also, suggesting that the present oscillation seems to reflect a network property.