The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 2138-2144
Copyright ©2000 by the American Physiological Society

Size of CA1-Evoked Synaptic Potentials Is Related to Theta Rhythm Phase in Rat Hippocampus

 ¹Department of Psychology, Harvard University, Cambridge 02138; and  ²Department of Psychology, Boston University, Boston, Massachusetts 02215

Wyble, Bradley P., Christiane Linster, and Michael E. Hasselmo. Size of CA1-Evoked Synaptic Potentials Is Related to Theta Rhythm Phase in Rat Hippocampus. J. Neurophysiol. 83: 2138-2144, 2000. Cholinergic and GABAergic neurons projecting to the hippocampus fire with specific phase relations to theta rhythm oscillations in the electroencephalogram (EEG). To determine if this phasic input has an impact on synaptic transmission within the hippocampus, we recorded evoked population excitatory postsynaptic potential (EPSPs) during different phases of theta rhythm by using techniques similar to those described in Rudell and Fox. Synaptic potentials elicited by stimulation of region CA3 of the contralateral hippocampus were recorded in region CA1 and CA3. In these experiments, the initial slope of evoked potentials showed a change in magnitude during different phases of the theta rhythm recorded in the dentate fissure, with individual trials showing an average of 9.5% change in slope of potentials, and the average across all experiments showing a change of 7.8%. Evoked potentials were maximal 18° after the positive peak of the dentate fissure theta EEG. These potentials were also smaller by 18.2% during theta as opposed to non-theta states. Phasic changes in modulation of synaptic transmission could contribute to phase precession of hippocampal place cells and could enhance storage of new sequences of activity as demonstrated by computational models.