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Electrophysiological characterization of interlaminar entorhinal connections: an essential link for re-entrance in the hippocampal–entorhinal system

Authors

  • Fabian Kloosterman,

    1. Swammerdam Institute of Life Sciences, Section Neurobiology, University of Amsterdam, Graduate School of Neurosciences Amsterdam, Amsterdam, The Netherlands
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    • *

      Present address: Picower Center for Learning and Memory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building E18-366, Cambridge, MA 02139.

  • Theo Van Haeften,

    1. Department of Biochemistry, Cell Biology and Histology, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands
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  • Menno P. Witter,

    1. Department of Anatomy, VU University Medical Center, Research Institute Neurosciences, Graduate School of Neurosciences Amsterdam, Amsterdam, The Netherlands
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  • Fernando H. Lopes da Silva

    1. Swammerdam Institute of Life Sciences, Section Neurobiology, University of Amsterdam, Graduate School of Neurosciences Amsterdam, Amsterdam, The Netherlands
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: Dr Fabian Kloosterman, at *present address below.
E-mail: fkloos@mit.edu

Abstract

The hippocampal formation communicates with the neocortex mainly through the adjacent entorhinal cortex. Neurons projecting to the hippocampal formation are found in the superficial layers of the entorhinal cortex and are largely segregated from the neurons receiving hippocampal output, which are located in deep entorhinal layers. We studied the communication between deep and superficial entorhinal layers in the anaesthetized rat using field potential recordings, current source density analysis and single unit measurements. We found that subiculum stimulation was able to excite entorhinal neurons in deep layers. This response was followed by current sinks in superficial layers. Both responses were subject to frequency dependent facilitation, but not depression. Selective blockade of deep layer responses also abolished subsequent superficial layer responses. This clearly demonstrates a functional deep-to-superficial layer communication in the entorhinal cortex, which can be triggered by hippocampal output. This pathway may provide a means by which processed hippocampal output is integrated or compared with new incoming information in superficial entorhinal layers, and it constitutes an important link in the process of re-entrance of activity in the hippocampal–entorhinal network, which may be important for consolidation of memories or retaining information for short periods.

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