Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Division of Brain Circuits, National Institute for Basic Biology, Okazaki, Japan
Kenta Kobayashi
Section of Viral Vector Development, National Institute for Physiological Sciences, Okazaki, Japan
Masamichi Ohkura
Brain and Body System Science Institute, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
Junichi Nakai
Brain and Body System Science Institute, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Division of Brain Circuits, National Institute for Basic Biology, Okazaki, Japan
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.
