Monosynaptic activation of CA3 by the medial perforant path.
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.
Wu
K
K
Departments of Physiology and Clinical Neurological Sciences, The University of Western Ontario, London, Canada.
Leung
L S
LS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D018891:Dentate Gyrus / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials; D019580:Perforant Pathway / Q000502:physiology*; D051381:Rats; D011930:Reaction Time / Q000502:physiology; D013569:Synapses / Q000502:physiology*