Hippocampal-medial entorhinal circuit is differently organized along the dorsoventral axis in rodents
Shinya Ohara,
Märt Rannap,
Ken-Ichiro Tsutsui,
Andreas Draguhn,
Alexei V. Egorov,
Menno P. Witter
Affiliations
Shinya Ohara
Laboratory of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan; Kavli Institute for Systems Neuroscience, Center for Computational Neuroscience, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, NTNU Norwegian University of Science and Technology, Trondheim, Norway; PRESTO, Japan Science and Technology Agency (JST), Tokyo, Japan
Märt Rannap
Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
Ken-Ichiro Tsutsui
Laboratory of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan
Andreas Draguhn
Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany
Alexei V. Egorov
Institute of Physiology and Pathophysiology, Medical Faculty, Heidelberg University, Heidelberg, Germany; Corresponding author
Menno P. Witter
Kavli Institute for Systems Neuroscience, Center for Computational Neuroscience, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, NTNU Norwegian University of Science and Technology, Trondheim, Norway; Corresponding author
Summary: The general understanding of hippocampal circuits is that the hippocampus and the entorhinal cortex (EC) are topographically connected through parallel identical circuits along the dorsoventral axis. Our anterograde tracing and in vitro electrophysiology data, however, show a markedly different dorsoventral organization of the hippocampal projection to the medial EC (MEC). While dorsal hippocampal projections are confined to the dorsal MEC, ventral hippocampal projections innervate both dorsal and ventral MEC. Further, whereas the dorsal hippocampus preferentially targets layer Vb (LVb) neurons, the ventral hippocampus mainly targets cells in layer Va (LVa). This connectivity scheme differs from hippocampal projections to the lateral EC, which are topographically organized along the dorsoventral axis. As LVa neurons project to telencephalic structures, our findings indicate that the ventral hippocampus regulates LVa-mediated entorhinal-neocortical output from both dorsal and ventral MEC. Overall, the marked dorsoventral differences in hippocampal-entorhinal connectivity impose important constraints on signal flow in hippocampal-neocortical circuits.
