AUTHOR=Ohara Shinya , Gianatti Michele , Itou Kazuki , Berndtsson Christin H. , Doan Thanh P. , Kitanishi Takuma , Mizuseki Kenji , Iijima Toshio , Tsutsui Ken-Ichiro , Witter Menno P. TITLE=Entorhinal Layer II Calbindin-Expressing Neurons Originate Widespread Telencephalic and Intrinsic Projections JOURNAL=Frontiers in Systems Neuroscience VOLUME=13 YEAR=2019 URL=https://www.frontiersin.org/journals/systems-neuroscience/articles/10.3389/fnsys.2019.00054 DOI=10.3389/fnsys.2019.00054 ISSN=1662-5137 ABSTRACT=

In the present study we provide the first systematic and quantitative hodological study of the calbindin-expressing (CB+) principal neurons in layer II of the entorhinal cortex and compared the respective projections of the lateral and medial subdivisions of the entorhinal cortex. Using elaborate quantitative retrograde tracing, complemented by anterograde tracing, we report that the layer II CB+ population comprises neurons with diverse, mainly excitatory projections. At least half of them originate local intrinsic and commissural projections which distribute mainly to layer I and II. We further show that long-range CB+ projections from the two entorhinal subdivisions differ substantially in that MEC projections mainly target field CA1 of the hippocampus, whereas LEC CB+ projections distribute much more widely to a substantial number of known forebrain targets. This connectional difference between the CB+ populations in LEC and MEC is reminiscent of the overall projection pattern of the two entorhinal subdivisions.