Hippocampal Organization of Spatial Map

2018 Fiscal Year Research-status Report

• Project/Area Number: 18K03168
• Research Institution: University of Tsukuba
• Principal Investigator: Pavlides C 筑波大学, 人間系, 教授 (50712808)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: Hippocampus / fear memory / spatial memory / immediate early genes / Zif268 / functional organization

Outline of Annual Research Achievements

The proposed studies were aimed at determining neuronal functional organization in the hippocampus for fear memory. Previously, we observed a topographic organization in the hippocampus in animals engaged in both spatial as well as sequential order memory tasks. That is, pyramidal cells in the dorsal hippocampus formed clusters of a few adjacent active cells. This is contrary to the prevalent view of a random, distributed organization. However, the previous studies included only the dorsal hippocampus and using 2-D analysis. For the present studies, the behavioral paradigm was fear conditioning (another hippocampus dependent task), and we performed a 3-D reconstruction of the entire hippocampus. Based on previous reports showing that the proximal and distal parts of the hippocampus may be organized differently both in terms of inputs as well as functionally, we analyzed each subregion separately in terms of topographic organization.
To allow for better 3-D imaging we initially tried to use a tissue clearing method (Cubic) that would allow us to visualize the entire hippocampus without sectioning. In our hands, however, this proved not to be a suitable solution. Granted this method has certain advantages, it produced significant tissue swelling which did not allow for precise reconstruction of the topographic organization. Instead we switched back to sectioning of the brain tissue and fluorescent immunohistochemistry (IHC).

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

Thus far, we have completed one set of experiments in animals trained in contextual fear conditioning and have processed the dorsal hippocampus for Zif268 IHC. 3-D analysis revealed that a cluster type organization took place both in the dorsal proximal-distal and longitudinal axis (Arai and Pavlides, 2019a; Arai and Pavlides, 2019b). Using a 3-D reconstruction we also observed clustering in the longitudinal axis of the dorsal hippocampus (Arai and Pavlides, 2018). This study is still preliminary in that more subjects will have to be included. Further, we would like to compare functional organization using contextual (hippocampus dependent) and cued (hippocampus independent) tasks.

Strategy for Future Research Activity

During the second year of funding, we will complete the ongoing experiments to include a larger number of subjects as well as cued conditioned groups. Further, we will image both proximal-distal parts of CA1 and CA3 and dorsal-ventral sections. The main objective of the second year will be to use optogenetic stimulation to activate/suppress entorhinal cortex afferents to hippocampus to determine effects on neuronal functional organization and behaviors. We have started with viral injections to optimize parameters - including volume and brain sites. We have also started with microprobe surgeries to determine effectiveness of optogenetic stimulation parameters. The experiments should be completed during the second year.

Causes of Carryover

Part of the funds were to be used for the purchase of Virus constructs as well as confocal microscopy time, both of which are rather expensive. We are getting to that part of the studies in the second year. Therefore, the funds will be used during the second year of funding. Also, both the immunohistochemistry and optogenetic stimulation will require substantial supplies, especially since the number of animals to be used and brain tissue to be processed will be substantially more than in the previous year.

Research Products

• [Journal Article] Hippocampal functional organization: A microstructure of the place cell network encoding space. (2019)
  • Author(s): Pavlides, C., Donishi, T., Ribeiro, S., Mello, C.V., Blanco, W., and Ogawa, S.
  • Journal Title: Neurobiology of Learning and Memory Volume: 161 Pages: 122-134
  • DOI: doi: 10.1016/j.nlm.2019.03.010.113
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Fear memory consolidation in sleep requires protein kinase A. (2018)
  • Author(s): Cho, J., Sypniewski, K.A., Arai, S., Yamada, K., Ogawa, S., and Pavlides, C.
  • Journal Title: Learning and Memory Volume: 25 Pages: 241-246.
  • DOI: 10.1101/lm.046458.117.
  • Peer Reviewed / Open Access
• [Presentation] Hippocampal Functional Organization in Fear Memory. (2019)
  • Author(s): Arai, S. and Pavlides, C.
  • Organizer: The 30th meeting of the Japanese Society for Behavioral Neuroendocrinology
• [Presentation] Memory Consolidation in Sleep (2019)
  • Author(s): Pavlides, C.
  • Organizer: The Third Sino-Japan session: Symposium on the Frontier of Behavioral Neuroendocrinology.
  • Int'l Joint Research / Invited
• [Presentation] Hippocampal Functional Organization in Contextual Fear Memory Task. (2019)
  • Author(s): Arai, S. and Pavlides, C.
  • Organizer: The 42nd Annual meeting of the Japan Neuroscience Society
• [Presentation] Functional 3D-Reconstruction of the Hippocampus in a Spatial Memory Task. (2018)
  • Author(s): Arai, S. and Pavlides, C.
  • Organizer: The 41st Annual meeting of the Japan Neuroscience Society