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Two reentrant pathways in the hippocampal-entorhinal system
Fabian Kloosterman1, Theo van Haeften, Fernando H Lopes da Silva
1Swammerdam Institute of Life Sciences, Section Neurobiology, University of Amsterdam, Graduate School of Neurosciences Amsterdam, Amsterdam, The Netherlands. fkloos@mit.edu
Hippocampus
|September 25, 2004
Summary
This study investigated hippocampal reentrance into the entorhinal cortex. Findings suggest parallel pathways exist for information flow between the hippocampal formation and entorhinal cortex.
Area of Science:
- Neuroscience
- Neuroanatomy
Background:
- The entorhinal cortex (EC) is a critical interface between the hippocampal formation (HF) and the neocortex.
- Bidirectional connections suggest hippocampal output may reenter HF subfields via the EC.
Purpose of the Study:
- To investigate the reentrance of hippocampal output into HF subfields through the EC.
- To explore the functional connectivity between the HF and EC.
Main Methods:
- Simultaneous multi-site field potential recordings in rats.
- In vivo current source density analysis of the EC and HF.
- Repetitive stimulation of subiculum and Schaffer collaterals under different anesthesia conditions (ketamine/xylazine and urethane).
Main Results:
- Repetitive stimulation facilitated entorhinal responses, with population spikes in layer III.
- Evidence of reentrance into CA1 was observed, indicated by a current sink in stratum lacunosum-moleculare following EC responses.
- Reentrance into the dentate gyrus was not observed under ketamine/xylazine but was evoked under urethane anesthesia.
Conclusions:
- Parallel connections exist between HF output and EC layers III and II.
- These pathways project to CA1 and the dentate gyrus, respectively.
- The findings suggest distinct functional roles for these reentrant pathways.