1999 Fiscal Year Final Research Report Summary
Analysis using optical recording for synaptic plasticity of non-LTP type in hippocampal slices
| Project/Area Number |
09480227
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Neuroscience in general
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| Research Institution | Gunma University, School of Medidcine |
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Principal Investigator |
SEKINO Yuko Gunma Univ. Shc. Med. Dept. of Neurobiology and Behavior, Assist. Professor, 医学部, 講師 (70138866)
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| Co-Investigator(Kenkyū-buntansha) |
SHIRAO Tomoaki Gunma Univ. Shc. Med. Dept. of Neurobiology and Behavior, Professor, 医学部, 教授 (20171043)
HAYASHI Kensuke Gunma Univ. Shc. Med. Dept. of Neurobiology and Behavior, Research Associate (50218567)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Hippocampus / Optical Recording / Adenosine / LTP / CA2 / CA3a |
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| Research Abstract |
Using optical and field potential recordings, we have shown that there were two distinguished patterns of signal propagation, CA3-CA1 and CA3-CA2-CA1, in oblique slices obtained from rat hippocampus ; the, and the slow propagation. In the fast propagation, activity flowed directly from CA3 to the stratum radiatum of CA1, and in the slow propagation optical signals were generated in CA2 before spreading to CA1. Our data reveal that CA2 neurons can transmit delayed excitatory signals to CA1 neurons. We therefore conclude that consideration of electrical signal propagation through the hippocampus should include flow through the CA2 region in addition to the traditional dentate gyrus-CA3-CA1 trisynaptic circuit. When slices were treated with an adenosine antagonist (2 μM 8-CPT), population spikes (PSs) were recorded in the stratum pyramidale of CA1 and CA2 in almost all of transverse slices, where no PS was recorded without 8-CPT in most cases. This data indicated that there is strong puri
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nergic inhibition in CA2/CA3a and suggest that CA2 cells act as a gate of signal propagation in the transverse plane of hippocampus.
We further described the immunocytochemical distribution of adenosine A1 receptors in the rat hippocampus. Adenosine A1 receptor-like immunoreactivity was seen on the cell soma and dendrites of pyramidal cells and the cell soma and proximal part of dendrites of granule cells, but not on glial cells. In the adult rat hippocampus, rostrocaudal inspection revealed that immunoreactivity in CA2/CA3a was greatest. Confocal microscopy revealed differences in the staining patterns for the adenosine A1 receptor and synaptophysin, a marker of presynaptic terminals. This suggests that the adenosine A1 receptor might have postsynaptic physiological functions. Double-labeling of adenosine A1 receptors and anterogradely labeled fibers from the supramammillary nucleus showed that the fibers from the supramammillary nucleus terminate directly on the cell soma of the A1 receptor immunopositive neurons in CA2/CA3a and the dentate gyrus.
These results indicate that the adenosine A1 receptor in CA2/CA3a and the dentate gyrus are in a position to regulate hippocampal theta activity and that resultant strong synaptic depression in CA2/CA3a could play a role in regulating the intrinsic signal flow between CA3 and CA1. Less
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