Two-photon calcium imaging of the medial prefrontal cortex and hippocampus without cortical invasion

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Abstract

In vivo two-photon calcium imaging currently allows us to observe the activity of multiple neurons up to ~900 µm below the cortical surface without cortical invasion. However, many important brain areas are located deeper than this. Here, we used an 1100 nm laser that underfilled the back aperture of the objective together with red genetically encoded calcium indicators to establish two-photon calcium imaging of the intact mouse brain and detect neural activity up to 1200 μm from the cortical surface. This imaging was obtained from the medial prefrontal cortex (the prelimbic area) and the hippocampal CA1 region. We found that neural activity before water delivery repeated at a constant interval was higher in the prelimbic area than in layer 2/3 of the secondary motor area. Reducing the invasiveness of imaging is an important strategy to reveal the intact brain processes active in cognition and memory.

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Masashi Kondo

Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-8818-8316
Kenta Kobayashi

Section of Viral Vector Development, National Institute for Physiological Sciences, Okazaki, Japan

Competing interests
The authors declare that no competing interests exist.
Masamichi Ohkura

Brain Science Institute, Saitama University, Saitama, Japan

Competing interests
The authors declare that no competing interests exist.
Junichi Nakai

Brain Science Institute, Saitama University, Saitama, Japan

Competing interests
The authors declare that no competing interests exist.
Masanori Matsuzaki

Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan

For correspondence
mzakim@m.u-tokyo.ac.jp

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0003-3872-4322

Funding

Ministry of Education, Culture, Sports, Science, and Technology (Grant-in-Aids for Scientific Research on Innovative Areas (15H01455))

Masanori Matsuzaki

Ministry of Education, Culture, Sports, Science, and Technology (Grant-in-Aids for Scientific Research on Innovative Areas (17H06309))

Masanori Matsuzaki

Ministry of Education, Culture, Sports, Science, and Technology (Grant-in-Aids for Scientific Research (A) (15H02350))

Masanori Matsuzaki

Takeda Science Foundation

Masanori Matsuzaki

Japan Agency for Medical Research and Development (The Strategic Research Program for Brain Sciences)

Masanori Matsuzaki

Japan Agency for Medical Research and Development (The program for Brain Mapping by Integrated Neurotechnologies for Disease Studies (Brain/MINDS))

Masanori Matsuzaki

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: All animal experiments were approved by the Institutional Animal Care and Use Committee of The University of Tokyo, Japan (Medicine-P16-012).

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.