Intrinsic Projections of Layer Vb Neurons to Layers Va, III, and II in the Lateral and Medial Entorhinal Cortex of the Rat

Publication date: 3 July 2018

Source: Cell Reports, Volume 24, Issue 1

Author(s): Shinya Ohara, Mariko Onodera, Øyvind W. Simonsen, Rintaro Yoshino, Hiroyuki Hioki, Toshio Iijima, Ken-Ichiro Tsutsui, Menno P. Witter

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.

Graphical Abstract

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