Topographical and laminar organization of subicular projections to the parahippocampal region of the rat

Authors

  • Fabian Kloosterman,

    1. Swammerdam Institute of Life Sciences, Section of Neurobiology, University of Amsterdam, Graduate School of Neurosciences Amsterdam, NL-1098 SM Amsterdam, The Netherlands
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  • Menno P. Witter,

    Corresponding author
    1. Department of Anatomy, VU University Medical Center, Research Institute of Neurosciences, Graduate School of Neurosciences Amsterdam, NL-1081 BT Amsterdam, The Netherlands
    • Department of Anatomy, VU University Medical Center, Research Institute of Neurosciences, Graduate School of Neurosciences Amsterdam, Van der Boechorststraat 7 NL-1081 BT Amsterdam, The Netherlands
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  • Theo Van Haeften

    1. Department of Anatomy, VU University Medical Center, Research Institute of Neurosciences, Graduate School of Neurosciences Amsterdam, NL-1081 BT Amsterdam, The Netherlands
    2. Department of Biochemistry, Cell Biology and Histology, Faculty of Veterinary Medicine, University of Utrecht, NL-3508 TD Utrecht, The Netherlands
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Abstract

In this study, we analyzed in detail the topographic organization of the subiculoparahippocampal projection in the rat. The anterograde tracers Phaseolus vulgaris leucoagglutinin-L and biotinylated dextran amine were injected into the subiculum at different septotemporal and transverse levels. Deep layers of the ento-, peri-, and postrhinal cortices are the main recipients of subicular projections, but in all cases we noted that a small fraction of the projections also terminates in the superficial layers II and III. Analysis of the fiber patterns in the parahippocampal region revealed a topographic organization, depending on the location of the cells of origin along both the transverse and the septotemporal axes of the subiculum. Projections originating from subicular cells close to CA1, i.e., proximal part of subiculum, terminate exclusively in the lateral entorhinal cortex and in the perirhinal cortex. In contrast, projections from cells closer to the subiculum-presubiculum border, i.e., distal part of subiculum, terminate in the medial entorhinal cortex and in the postrhinal cortex. In addition, cells in septal portions of the subiculum project to a lateral band of entorhinal cortex parallel to the rhinal sulcus and to peri- or postrhinal cortices, whereas cells in more temporal portions project to more medial parts of the entorhinal cortex. These results indicate that subicular projections to the parahippocampal region precisely reciprocate the known inputs from this region to the hippocampal formation. We thus suggest that the reciprocal connectivity between the subiculum and the parahippocampal region is organized as parallel pathways that serve to segregate information flow and thus maintain the identity of processed information. Although this parallel organization is comparable to that of the CA1-parahippocampal projections, differences exist with respect to the degree of collateralization. J. Comp. Neurol. 455:156–171, 2003. © 2002 Wiley-Liss, Inc.

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