Changes in extracellular Ca2+ and K+ activity accompanying hippocampal discharges

Publisher Website
Google Scholar
Abstract
In rats under urethane anaesthesia, changes in the extracellular activities of K+ and Ca2+ (aK and aCa) evoked by fimbrial or entorhinal stimulation and recorded in area CA3 with ion-selective microelectrodes are maximal in the pyramidal cell layers. With 10/s stimulation, aK increases by 6-9 mM whereas aCa falls by 0.5-1.0 mM. In contrast with the increase in aK, which is distributed over a wide range of depth, the reduction in aCa is particularly sharply limited to the level of pyramidal cell bodies. It is regularly associated with a negative afterpotential in the extracellular field, which presumably reflects a large postsynaptic Ca2+ inward current, apparently predominant in the cell bodies. Repetitive stimulation sometimes evokes spreading depressionlike swings in potential, which are seen only near the pyramidal stratum and are accompanied by massive increases in aK (to 30-40 mM) and falls in aCa (to < 0.1 mM). A large Ca2+ influx into pyramidal cells may be of significance for "plastic" aspects of hippocampal function and when excessive, as during repetitive convulsive activity, may be responsible for the necrosis of CA3 neurons.