Frequency dependent information flow from the entorhinal cortex to the
hippocampus.
Tengis Gloveli, Dietmar Schmitz, Ruth M. Empsonõ and Uwe Heinemann.
Institute of Physiology at the Charit‚, Department of Neurophysiology,
Humboldt University, Berlin, Tucholskystr. 2, 10117 Berlin, Germany.
APStracts 4:0245N, 1997.
ABSTRACT
Storage and retrieval of information in the hippocampus is dependent on
information transfer from the entorhinal cortex (EC). We studied how the
separate pathways from layer II and III of the EC to the hippocampus are
selected for information transfer during repetitive synaptic stimulation.
Intracellular recordings were made from EC layer II and III projection cells
in horizontal combined EC-hippocampal slices. Synaptic responses to
stimulation of deep layers or the lateral EC with stimulus intensities about
70% of that required to elicit an action potential were analyzed during short
trains of repetitive stimulation. The threshold intensities for induction of
action potentials were in layer II cells 8.2ñ3.8 V, significantly larger than
4.4ñ1.5 V in type 1 and 5.2ñ3.3 V in type 2 layer III cells, respectively.
During repetitive subthreshold stimulation with frequencies below 5 Hz the
pathway from the EC layer II remained quiet and was preferentially activated
with stimulation frequencies above 5 Hz. In contrast, the EC layer III cells
responded preferentially to low stimulus frequencies (<10 Hz) and became
strongly inhibited when synaptically stimulated with frequencies above 10 Hz.
Interestingly, during stimulus frequencies between 5 and 10 Hz the likelihood
that both layer II and III cells fire were large. Thus, a frequency switch
operates in the entrohinal cortex regulating output of layer II and III cells
to the hippocampus. We suggest that such frequency dependent regulation of
information flow presents a new principle of neuronal information processing.
Received 5 May 1997; accepted in final form 4 September 1997.
APS Manuscript Number J355-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997