title: Parahippocampal and retrosplenial connections of rat posterior parietal cortex.
abstract: The posterior parietal cortex has been implicated in spatial functions, including navigation. The hippocampal and parahippocampal region and the retrosplenial cortex are crucially involved in navigational processes and connections between the parahippocampal/retrosplenial domain and the posterior parietal cortex have been described. However, an integrated account of the organization of these connections is lacking. Here, we investigated parahippocampal connections of each posterior parietal subdivision and the neighboring secondary visual cortex using conventional retrograde and anterograde tracers as well as transsynaptic retrograde tracing with a modified rabies virus. The results show that posterior parietal as well as secondary visual cortex entertain overall sparse connections with the parahippocampal region but not with the hippocampal formation. The medial and lateral dorsal subdivisions of posterior parietal cortex receive sparse input from deep layers of all parahippocampal areas. Conversely, all posterior parietal subdivisions project moderately to dorsal presubiculum, whereas rostral perirhinal cortex, postrhinal cortex, caudal entorhinal cortex and parasubiculum all receive sparse posterior parietal input. This indicated that the presubiculum might be a major liaison between parietal and parahippocampal domains. In view of the close association of the presubiculum with the retrosplenial cortex, we included the latter in our analysis. Our data indicate that posterior parietal cortex is moderately connected with the retrosplenial cortex, particularly with rostral area 30. The relative sparseness of the connectivity with the parahippocampal and retrosplenial domains suggests that posterior parietal cortex is only a modest actor in forming spatial representations underlying navigation and spatial memory in parahippocampal and retrosplenial cortex. © 2017 Wiley Periodicals, Inc.
authors.affiliation: The Faculty of Medicine, Kavli Institute for Systems Neuroscience, Centre for Neural Computation, Egil and Pauline Braathen and Fred Kavli Centre for Cortical Microcircuits, NTNU - Norwegian University of Science and Technology, Postbox 8905, 7491, Trondheim, Norway.
authors.forename: Grethe M
authors.initials: GM
authors.lastname: Olsen
authors.affiliation: Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Katahira 2-1-1, Aoba-Ku, Sendai, 980-8577, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Ohara
authors.affiliation: Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Katahira 2-1-1, Aoba-Ku, Sendai, 980-8577, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Iijima
authors.affiliation: The Faculty of Medicine, Kavli Institute for Systems Neuroscience, Centre for Neural Computation, Egil and Pauline Braathen and Fred Kavli Centre for Cortical Microcircuits, NTNU - Norwegian University of Science and Technology, Postbox 8905, 7491, Trondheim, Norway.
authors.forename: Menno P
authors.identifier: 0000-0003-0285-1637
authors.initials: MP
authors.lastname: Witter
mesh_terms: D000818:Animals; D005260:Female; D006624:Hippocampus / Q000166:cytology*; D008297:Male; D056347:Neuroanatomical Tract-Tracing Techniques; D020534:Parahippocampal Gyrus / Q000166:cytology*; D010296:Parietal Lobe / Q000166:cytology*; D000071039:Perirhinal Cortex / Q000166:cytology*; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D014793:Visual Cortex / Q000166:cytology*
keywords: AB_10073917; AB_2298772; anterograde tracing; immunohistochemistry; rabies virus tracing; retrograde tracing; spatial navigation