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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Syst. Neurosci. | doi: 10.3389/fnsys.2019.00038

Organization of posterior parietal – frontal connections in the rat

 Grethe M. Olsen1, 2,  Karoline Hovde1, 2, Hideki Kondo1, 2, 3,  Teri Sakshaug1, 2, Hanna H. Sømme1, 2,  Jonathan R. Whitlock1, 2 and  Menno P. Witter1, 2*
  • 1Kavli Institute for Systems Neuroscience, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Norway
  • 2Egil and Pauline Braathen and Fred Kavli Centre for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Norway
  • 3Cold Spring Harbor Laboratory, United States

Recent investigations of the rat posterior parietal cortex (PPC) suggest that this region plays a central role in action control together with the frontal cortical areas. Posterior parietal-frontal cortical connections have been described in rats, but little is known about whether these connections are topographically organized as in the primate. Here we injected retrograde and anterograde tracers into subdivisions of PPC as well as the frontal midline and orbital cortical areas to explore possible topographies within their connections. We found that PPC projects to several frontal cortical areas, largely reciprocating the densest input received from the same areas. All PPC subdivisions are strongly connected with the secondary motor cortex (M2) in a topographically organized manner. The medial subdivision (mPPC) has a dense reciprocal connection with the most caudal portion of M2 (cM2), whereas the lateral subdivision (lPPC) and the caudolateral subdivision (PtP) are reciprocally connected with the intermediate rostrocaudal portion of M2 (iM2). Sparser reciprocal connections were seen with anterior cingulate area 24b. mPPC connects with rostral, and lPPC and PtP connect with caudal parts of 24b, respectively. There are virtually no connections with area 24a, nor with prelimbic or infralimbic cortex. PPC and orbitofrontal cortices are also connected, showing a gradient such that mPPC entertains reciprocal connections mainly with the ventral orbitofrontal cortex, whereas lPPC and PtP are preferentially connected with medial and central portions of ventrolateral orbitofrontal cortex, respectively. Our results thus indicate that the connections of PPC with frontal cortices are organized in a topographical fashion, supporting functional heterogeneity within PPC and frontal cortices.

Keywords: anterograde tracer injections, retrograde tracer injections, Immunohistochemistry, Cingulate cortex, Motor Cortex, orbitofrontal cortex, Posterior parietal cortex, AB_2307337

Received: 26 May 2019; Accepted: 29 Jul 2019.

Copyright: © 2019 Olsen, Hovde, Kondo, Sakshaug, Sømme, Whitlock and Witter. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Menno P. Witter, Kavli Institute for Systems Neuroscience, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, 7030, Sør-Trøndelag, Norway, menno.witter@ntnu.no