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
Bradley P.
Wyble,1
Christiane
Linster,1,2 and
Michael E.
Hasselmo2
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.
