Intrinsic Projections of Layer Vb Neurons to Layers Va, III, and II in the Lateral and Medial Entorhinal Cortex of the Rat
Shinya Ohara,
Mariko Onodera,
Øyvind W. Simonsen,
Rintaro Yoshino,
Hiroyuki Hioki,
Toshio Iijima,
Ken-Ichiro Tsutsui,
Menno P. Witter
Affiliations
Shinya Ohara
Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, 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, 7489 Trondheim, Norway
Mariko Onodera
Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
Øyvind W. Simonsen
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, 7489 Trondheim, Norway
Rintaro Yoshino
Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
Hiroyuki Hioki
Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan; Department of Cell Biology and Neuroscience, Juntendo University Graduate School of Medicine, Tokyo 113-8421, Japan
Toshio Iijima
Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
Ken-Ichiro Tsutsui
Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai 980-8577, Japan
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, 7489 Trondheim, Norway; Corresponding author
Summary: Layer V of the entorhinal cortex (EC) receives input from the hippocampus and originates main entorhinal outputs. The deep-sublayer Vb, immunopositive for the transcription factor Ctip2, is thought to be the main recipient of hippocampal projections, whereas the superficial-sublayer LVa, immunonegative for Ctip2, originates the main outputs of EC. This disrupts the proposed role of EC as mediating hippocampal-cortical interactions. With the use of specific (trans)synaptic tracing approaches, we report that, in medial entorhinal cortex, layer Vb neurons innervate neurons in layers Va, II, and III. A similar circuitry exists in the lateral entorhinal cortex. We conclude that EC-layer Vb neurons mediate two circuits in the hippocampus-memory system: (1) a hippocampal output circuit to telencephalic areas by projecting to layer Va and (2) a feedback projection, sending information back to the EC-hippocampal loop via neurons in layers II and III. : Ohara et al. demonstrate the intrinsic connectivity of layer Vb neurons of both the medial and lateral entorhinal cortex. Layer Vb neurons are key elements of two circuits in the hippocampus-memory system: a hippocampal-output circuit and a feedback loop to the hippocampus. Keywords: parahippocampus, rodent, interlaminar connectivity, hippocampal-entorhinal connections, hippocampal-cortical connections
