title: Excitatory Postrhinal Projections to Principal Cells in the Medial Entorhinal Cortex.
abstract: The postrhinal cortex (POR) provides substantial input to the entorhinal cortex, mainly targeting superficial layers of the medial entorhinal cortex (MEC). Major inputs to POR originate in the visual and parietal cortex, thus providing neurons in MEC with a subset of cortical information relevant to their spatial firing properties. The POR takes a position that is comparable with that of the perirhinal cortex (PER) with regard to the lateral entorhinal cortex (LEC). Neurons in LEC and MEC show different functional properties likely reflecting differences in their respective inputs. Projections from PER to LEC exert a main inhibitory influence, which may relate to the sparse object-selective firing in LEC. In view of the continuous, spatially modulated firing properties of principal neurons in MEC, we tested in rats the hypothesis that projections from POR to MEC are functionally different from the PER-to-LEC counterpart in providing an excitatory drive to MEC. Our combined confocal and quantitative electron-microscopic observations indicated that POR projections target mainly principal cells in MEC, including neurons that project to the hippocampus. The ultrastructure of the majority of the synapses indicated that they are excitatory. Voltage-sensitive dye imaging in sagittal slices confirmed this morphologically derived conclusion, showing that the MEC network always responded with an overall depolarization, indicative for net excitatory transmission. In vitro single-cell recordings from principal cells showed only excitatory responses upon POR stimulation. These results show that POR provides an excitatory projection to MEC, differing fundamentally from the inhibitory projection of PER to LEC.
authors.affiliation: Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Noriko
authors.initials: N
authors.lastname: Koganezawa
authors.affiliation: Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Ragnhild
authors.initials: R
authors.lastname: Gisetstad
authors.affiliation: Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Ellen
authors.initials: E
authors.lastname: Husby
authors.affiliation: Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors.forename: Thanh P
authors.initials: TP
authors.lastname: Doan
authors.affiliation: Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway menno.witter@ntnu.no.
authors.forename: Menno P
authors.initials: MP
authors.lastname: Witter
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism; D016009:Chi-Square Distribution; D003911:Dextrans / Q000378:metabolism; D018728:Entorhinal Cortex / Q000166:cytology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology*; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009434:Neural Pathways / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D020318:Rats, Long-Evans; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D056969:Voltage-Sensitive Dye Imaging
chemical_list: D003911:Dextrans; C076397:biotinylated dextran amine; D001710:Biotin
keywords: excitation; lateral entorhinal cortex; memory; parahippocampal region; perirhinal cortex