Theta oscillation in somata and dendrites of hippocampal pyramidal cells in vivo: activity-dependent phase precession of action potentials. Hippocampus 8:244–261

ABSTRACT: Theta frequency field oscillation reflects synchronized synaptic potentials that entrain the discharge of neuronal populations within the D100–200 ms range. The cellular-synaptic generation of theta activity in the hippocampus was investigated by intracellular recordings from the somata and dendrites of CA1 pyramidal cells in urethane-anesthetized rats. The recorded neurons were verified by intracellular injection of biocytin. Transition from non-theta to theta state was charac-terized by a large decrease in the input resistance of the neuron (39 % in the soma), tonic somatic hyperpolarization and dendritic depolarization. The probability of pyramidal cell discharge, as measured in single cells and from a population of extracellularly recorded units, was highest at or slightly after the negative peak of the field theta recorded from the pyramidal layer. In contrast, cyclic depolarizations in dendrites corre-sponded to the positive phase of the pyramidal layer field theta (i.e. the hyperpolarizing phase of somatic theta). Current-induced depolarizatio