title: Two reentrant pathways in the hippocampal-entorhinal system.
abstract: The entorhinal cortex has long been recognized as an important interface between the hippocampal formation and the neocortex. The notion of bidirectional connections between the entorhinal cortex and the hippocampal formation have led to the suggestion that hippocampal output originating in CA1 and subiculum may reenter hippocampal subfields via the entorhinal cortex. To investigate this, we used simultaneous multi-site field potential recordings and current source density analysis in the entorhinal cortex and hippocampal formation of the rat in vivo. Under ketamine/xylazine anesthesia, we found that repetitive stimulation of subiculum or Schaffer collaterals facilitated entorhinal responses, such that a population spike appeared in layer III. In addition, a current sink in stratum lacunosum-moleculare of area CA1 was found, that followed responses in the entorhinal cortex, indicating reentrance into this area. Responses indicating reentrance in the dentate gyrus were not found under ketamine/xylazine anesthesia, but were readily evoked under urethane anesthesia. Reentrance into CA1 was also encountered under urethane anesthesia. These results suggest that parallel, but possibly functionally distinct, connections are present between the output of the hippocampal formation and cells in layers III and II of the entorhinal cortex that project to area CA1 and the dentate gyrus, respectively.
authors.affiliation: Swammerdam Institute of Life Sciences, Section Neurobiology, University of Amsterdam, Graduate School of Neurosciences Amsterdam, Amsterdam, The Netherlands. fkloos@mit.edu
authors.forename: Fabian
authors.initials: F
authors.lastname: Kloosterman
authors.forename: Theo
authors.initials: T
authors.lastname: van Haeften
authors.forename: Fernando H
authors.initials: FH
authors.lastname: Lopes da Silva
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology; D018891:Dentate Gyrus / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D018728:Entorhinal Cortex / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006624:Hippocampus / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D007649:Ketamine / Q000494:pharmacology; D008568:Memory / Q000502:physiology; D009434:Neural Pathways / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014520:Urethane / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology
chemical_list: D014991:Xylazine; D014520:Urethane; D007649:Ketamine