A network mechanism underlying hippocampal seizure-like synchronous oscillations.

The hippocampus is a remarkable neural structure that displays a variety of synchronous oscillations that may be physiological or pathophysiological, such as theta rhythms and epileptic seizures. Electrically induced seizure-like afterdischarges are an excellent system for elucidating the network mechanisms underlying neuronal synchronization and rhythm generation of epileptic synchronous oscillations in extremely hyperactive hippocampal networks. In this Update Article, we review key findings of studies on these electrically induced seizure-like afterdischarges in vitro. During these afterdischarges, GABAergic responses become transiently depolarizing and even excitatory as chloride rapidly accumulates postsynaptically in pyramidal cells. Glutamate and potassium enhance this transient GABAergic excitation. Neuronal synchronization of afterdischarge is achieved by GABAergic and glutamatergic excitation of pyramidal cells and interneurons localized in the stratum pyramidale and stratum oriens. Rhythm generation in seizure-like synchronous oscillations is not yet understood but is the subject of intensive study.