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
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.

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Teaser

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.


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