Shulou(Shulou.com)11/24 Report--

Thanks to CTOnews.com netizens Xing Han roaming clues delivery! CTOnews.com, February 28, according to the website of the College of Future Technology of Peking University, the Cheng Heping-Wang Aimin team of Peking University published an article online in Nature-method (Nature Methods) on February 23, reporting that a miniaturized three-photon microscope weighing only 2.17g realized functional imaging of the whole cerebral cortex and hippocampal neurons of free-walking mice for the first time. It opens a new research paradigm to reveal the neural mechanism in the deep structure of the brain.

▲ mice wearing a miniaturized three-photon microscope. The picture is from the website of the School of Future Technology, Peking University. According to the same introduction, the hippocampus, located under the cortex and corpus callosum, plays an important role in the consolidation of short-term memory to long-term memory, spatial memory and emotional coding. In rodent models, the hippocampus is more than one millimeter deep from the brain surface. Because the brain tissue, especially the corpus callosum, has the optical properties of high scattering to light, breaking the imaging depth limit has been a great challenge for neuroscientists for a long time. Previous miniature single-photon and miniature multiphoton microscopes are unable to penetrate the whole cortex and directly image the hippocampus without damage.

CTOnews.com learned from the website of the School of Future Technology of Peking University that the latest miniaturized three-photon microscope of Peking University has broken through the imaging depth limit of the previous miniaturized multiphoton microscope: the light path excited by the microscope can penetrate the entire mouse cerebral cortex and corpus callosum to directly observe and record the CA1 subregion of the hippocampus of mice. the maximum imaging depth of calcium signal of neurons can reach 1.2 mm. The depth of vascular imaging can reach 1.4 mm. In addition, in terms of phototoxicity, whole-skin calcium signal imaging requires only a few milliwatts, while hippocampal calcium signal imaging only needs 20 to 50 milliwatts, which is much lower than the safe threshold of tissue injury. Therefore, the miniature three-photon microscope can continuously observe the functional activity of neurons for a long time without obvious photobleaching and light damage.

▲ miniature three-photon microscopic imaging records the structural and functional dynamics of mouse cerebral cortex L1-L6 and hippocampal CA1. This breakthrough benefits from a new optical configuration design. Through the simulation of the layered scattering model of cortex, white matter and hippocampus, it is found that the fluorescence signal is in a state of random scattering when it reaches the brain surface from deep tissue, which reduces the fluorescence collection efficiency of microscopic objective lens and greatly limits the depth of imaging. In order to solve this problem, the classical Abbe condenser structure is introduced into the configuration design: the compact connection of the miniature Abbe condenser and the simplified infinite object lens can improve the transmission efficiency of the scattered light, and the partial reuse of the Abbe condenser and the micro tube mirror in the excitation light path can further simplify the structure and reduce the loss. In general, the scattering fluorescence collection efficiency of the new miniaturized microscope has been improved exponentially.

At the same time, using a miniature three-photon microscope, the authors studied the coding mechanism of neurons in the sixth layer of mouse parietal cortex in the sensory motor process of grasping jelly beans: it was found that about 37% of the neurons were active before the grab and were the most active during the grab. About 5.6% of the neurons became active after the grab, indicating that different neurons were involved in different stages of coding. This result shows the application potential of miniaturized three-photon microscope in brain science research.

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