2016 Fiscal Year Research-status Report
Neural network organization of the spatial map
| Project/Area Number |
15K13157
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| Research Institution | University of Tsukuba |
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Principal Investigator |
Pavlides C 筑波大学, 人間系, 教授 (50712808)
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| Project Period (FY) |
2015-04-01 – 2018-03-31
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| Keywords | hippocampus / memory / place cells / episodic memory / immediate early genes |
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| Outline of Annual Research Achievements |
It is well known that the hippocampus is involved in various functions including spatial navigation, and declarative memory. Still little is known of the functional neuronal organization of this structure to encode for any of these tasks. Previously, we determined that the hippocampus is functionally organized in neuronal clusters to encode for space (Pavlides, et al., submitted). We observed a similar type organization in a sequential order, odor discrimination task, as well as a novel object recognition task (Cho, et al. 2014; manuscript in preparation). Based on these findings, we hypothesized that a "cluster-type" organization is a basic unit of hippocampal function. The studies during the previous funding period were aimed at testing this hypothesis, by determining whether a similar organization is present for contextual fear memory for which the hippocampus is involved. For this we are using the immediate early gene Zif268 as an indicator of neuronal activity. We have recently completed these experiments. The results, thus far, show that in the dorsal hippocampal CA3 field pyramidal cells form clusters with a few adjacent active Zif268 expressing cells, similar to the spatial task. However, there was no significant difference in the CA1 field. This suggests that although a cluster type organization may be a functional unit in the hippocampus, there may exist a region specificity for different tasks. We are in the process of finalizing the data analysis and presenting the results (Cho, et al., 2017; Japanese Neuroscience Society. Chiba, Japan).
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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
The behavioral (fear conditioning) experiments were straightforward and a standard procedure in our laboratory, therefore, they presented no problems. The anatomical studies are also straightforward in terms of the immunohistochemical labeling of cells, brain imaging, etc. The data analysis, on the other hand, has proven to be very time consuming requiring careful discrimination of labeled cells, their distribution and possible clustering. Proving that the clustering we observed does not occur randomly requires conducting various simulation models, which we lacked the expertise in and thus took a considerable time to perform. As part of the proposed studies, we would like to assess whether the same or different cell clusters encode different behaviors or memories. This requires performing double labeling of cells using two different IEG’s and the cat-FISH method. We are in the process of using this method, although we do not have final results yet. We have also adapted a fluorescence labeling method to label different IEG’s which may also allow us to do double labeling. This method produces a lot more distinct labeling of active cells and thus will provide more convincing results. Furthermore, using this method we should be able to perform 3-D reconstructions of the entire hippocampus, which is one of the objectives of the studies.
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| Strategy for Future Research Activity |
The planned studies are aimed at determining the validity of the cell clusters. In the initial experiments, it was essential to test the hypothesis that cell clusters constitute a functional unit in the hippocampus. This was done by using different hippocampus dependent tasks and determining that the clusters occur in each case. Having observed that this is indeed the case, we will proceed to manipulate different hippocampal inputs (e.g., medial or lateral entorhinal cortex, amygdala, etc) by temporary inactivation (e.g., muscimol, lidocaine) and analyze how it may affect the observed clusters. Each of these inputs provides different types of information (e.g., spatial, emotional, etc) and may affect the clusters differentially. These initial studies should provide direct proof that the clusters indeed encode different types of information. In future studies we can attempt to activate/inactivate specific cell population in the medial or lateral entorhinal cortex, using more modern techniques (i.e., adeno-associated virus (AAV) neuronal infection; ontogenetic stimulation) and determine how this may affect functional neuronal organization.
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| Causes of Carryover |
During the past funding period a significant amount of effort and time was spent optimizing the immunohistochemical methods as well as data analysis/computer simulation, etc, which require somewhat less funds. In the next funding period a larger number of experiments will be performed which will require more animals, and supplies. The immunohistochemical studies will require the purchasing of various IEG probes, as well as other supplies which are rather expensive. Furthermore, a number of studies will be coming to completion and will be submitted for publication as well as meeting attendance for the dissemination of the results.
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| Expenditure Plan for Carryover Budget |
The funds will be used for animal purchases, immunohistochemical and other basic laboratory supplies, meeting attendance as well as publication costs.
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Research Products
(4 results)
