2017 Fiscal Year Annual Research Report
Time-window of NMDA receptor-dependent LTP during memory formation, consolidation and recall
| Project/Area Number |
16H02455
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| Research Institution | Kyoto University |
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Principal Investigator |
林 康紀 京都大学, 医学研究科, 教授 (90466037)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | 記憶学習 / 長期記憶 / 記憶固定化 / 細胞骨格 / 光増感法 / 樹状突起スパイン / シナプス可塑性 |
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| Outline of Annual Research Achievements |
How synaptic plasticity contributes to memory consolidation is of great scientific interest. LTP is characterized by increase in synaptic response sustaining more than hours and implicated in learning. This long-term stabilization of synaptic transmission is based on morphological change in synaptic structures. Dendritic spine is an actin-rich structure in which actin exists in either filamentous or globular form at its dynamic equilibrium. In the initial phase of LTP, cofilin (CFL), an actin-binding protein, is transported to the spine and forms a stable complex with F-actin. Therefore, proper modulation of cofilin activity is crucial in LTP, eventually in formation of memory. In order to elucidate the role of cofilin in memory formation, we developed a novel method to control the activity of cofilin optogenetically, in vivo. We found that 559 nm LASER irradiation on a dendritic spine expressing cofilin fused with SuperNova, a GFP-family protein which generates reactive oxygen species (ROS) within their close range by light irradiation, results in inactivation of cofilin. When cofilin-SuperNova was expressed in neuron, optical inactivation of cofilin shrinks dendric spines specifically after LTP. We then expressed CFL-SN in mouse hippocampus by injecting AAV-floxed-CFL-SN into CA1 region of CaMKII-Cre mouse. When LASER was irradiated after learning, mice with CFL-SN expression showed impaired memory recall, indicating cofilin activity following learning was crucial in memory consolidation. Therefore, cofilin-SuperNova is a versatile method to elucidate memory mechanism.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Generally the experiments are working as hypothesized. Followed by laser irradiation 10 min after LTP induction, the spine volume decreased. The same effect was also observed up to 30 after LTP induction but not 50 min after. Furthermore, the laser irradiation on the spine 1 min before sLTP had no effect on the spine enlargement. These results indicate cofilin is critical for maintenance of LTP up to 30 min after induction.
We confirmed electrically recorded LTP is canceled by the LASER. Illumination 10 min after HFS decreased EPSP slope. LTP could be induced again 40 min after CALI and potentiation of EPSP was observed, indicating the cancellation of LTP by CALI is not due to non-specific impairment in synaptic transmission.
To test this system in memory formation, we expressed CFL-SN in hippocampal neurons by injecting AAV-floxed-CFL-SN into CA1 region of CaMKII-Cre mouse, then implanted an optical fiber above the virus injection region. Memory was examined by Inhibitory Avoidance (IA) task. Memory was not impaired just by overexpress of CFL-SN in CA1 neuron. In contrast, memory was significantly impaired when 593 nm laser light was delivered 2 min after an electrical shock at day 1. On the other hand, memory was not impaired when the light delivered 1 min before the electrical shock. Illumination 2 hours after the shock had no effect on memory. These data are consistent with those from slice culture. This new method can specifically erase memory shortly (2 min) after memory formation without any effect on subsequent induction of memory.
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| Strategy for Future Research Activity |
We will move on to CALI in cortical area. We will start from anterior cingulate cortex, which has been implicated in memory consolidation and recall. We will express CFL-SN using AAV vector and induce CALI at different time point after learning. We will also test the possibility that memory is consolidated during sleep by carrying out CALI during sleep.
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