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Brain Res. 1998 Jun 22;797(1):35-41.

Monosynaptic activation of CA3 by the medial perforant path.

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  • 1Departments of Physiology and Clinical Neurological Sciences, The University of Western Ontario, London, Canada.


The functional projection of the medial perforant path (MPP) to different CA3 subfields was studied in urethan-anesthetized rats using current source density analysis. MPP stimulation resulted in an early-latency (presumed monosynaptic) sink with onset of 2-3 ms at the distal apical dendritic layer of CA3 (stratum lacunosum molecule) and a long-latency (presumed disynaptic, >7 ms) sink at stratum lucidum and radiatum of CA3. The population spike (onset 5. 3-6.1 ms), a sink at CA3 pyramidal cell layer, was observed 67% of the time (12 of 18 rats) in CA3a, 44% (8 of 18) in CA3b and 58% (7 of 12 rats) in CA3c following MPP stimulation. Population spike was not observed during presumed disynaptic excitation of CA3. Both early-latency sink (excitatory postsynaptic potential) and population spike in CA3 revealed robust paired-pulse facilitation (PPF). In contrast, little PPF was found for the MPP-evoked excitatory sink at the middle molecular layer of the dentate gyrus. The data suggested that the entorhinal cortex provides a strong monosynaptic excitation of different subfields of CA3. A direct entorhinal to CA3 input bypasses the dentate gyrus and may play a role in normal hippocampal signal processing and neural plasticity.

Copyright 1998 Elsevier Science B.V. All rights reserved.

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