Spontaneous hyperpolarizations in pyramidal cells of chronically stimulated rabbit hippocampus.

Abstract

Through daily electrical stimulation of one of the hippocampi in the rabbit, EEG spikes were kindled in both hippocampi. Such hippocampi (termed kindled hippocampi) were studied with the microelectrode in acute experiments. Electrical activities of the kindled hippocampus were characterized by spontaneous occurrence of hyperpolarizing potentials of various magnitudes (3-27 mV) and various durations (50-600 ms) in the pyramidal cell. These hyperpolarizations were never preceded by a prolonged spike burst. They could occur with no preceding depolarizations. They consisted of 2 components, i.e., Cl-dependent (somatic inhibitory postsynaptic potential) and Cl-non-dependent (dendritic hyperpolarization) components. They were the main abnormal events occurring within the pyramidal cell of the kindled hippocampus, and were probably the intracellular correlates of the EEG spikes.