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Séminaire impromptu - Hokkaido University Mini-Symposium

Abstract :

Thursday March 13, starting at 14:00 in the CGFB:
14:00 - 14:45: Prof.Tomomi Nemoto and Kohei Otomo: Improving in vivo two-photon and confocal microscopy with novel laser technology
14:45 - 15:30: Prof. Toshiyuki Nakagaki: Physical ethology of an amoeba of Physarum plasmodium: Networking the spatially distributed food-sources

 14h00    Improving in vivo two-photon and confocal microscopy with novel laser technology (Tomomi Nemoto )

“In vivo” two-photon microscopy (TPLSM) has revealed vital information on neural activity for brain function, even in light of its limitation in imaging events at depths greater than a several hundred micrometers from the brain surface. To break the limit of this penetration depth, we introduced a novel light source based on a semiconductor laser [1]. The light source successfully visualized not only cortex layer V pyramidal neurons spreading to all cortex layers at a superior S/N ratio, but visualize hippocampal CA1 neurons in young adult mice [2]. These results indicate that the penetration depth of this laser was ~1.4 mm. In vivo TPLSM with a laser emitting a longer wavelength might give us insights on activities of neurons in the cortex or the hippocampus. This deep imaging method could be applicable to other living organs including tumor tissues. In addition, we developed liquid crystal devices to convert linearly polarized beams (LP) to vector beams [3]. A liquid device generated a vector beam called higher-order radially polarized (HRP) beam, that enabled that each of the aggregated 0.17 μm beads was distinguished individually, whereas in conventional confocal microscopy or TPLSM they could not. We also visualized the finer structures of networks of filamentous cytoskeleton microtubule fluorescently-labeled in the COS-7, and primary culture of mouse neurons. Moreover, by taking an advantage of the LCDs that can utilize various wavelengths including near-infrared, we could employ an HRP beam for improving TPLSM. An HRP beam visualized fine intracellular structures not only in fixed cells stained with various dyes, but also in living cells expressing a fluorescent protein [4]. HRP beam also visualized finer structures of microtubules in fixed cells. Here, we will discuss these improvements and future application on the basis of our recent data.

References: [1] H. Yokoyama, et al., “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers”, Opt. Express, 6, 17752 (2008). [2] R. Kawakami, et al., “Visualizing hippocampal neurons with in vivo two-photon microscopy using a 1030 nm picosecond pulse laser” , Sci. Rep. , 3, 1014 (2013). [3] Y. Kozawa, et al., “Lateral resolution enhancement of laser scanning microscopy by a higher-order radially polarized mode beam”, Opt. Express, 19, 15947 (2011). [4] S. Ipponjima, et al., "Improvement of lateral resolution and extension of depth of field in two-photon microscopy by a higher-order radially polarized beam", Microscopy, in press (2013)

14h45  Physical ethology of an amoeba of Physarum plasmodium: Networking the spatially distributed food-sources (Toshiyuki Nakagaki)

Capacity of information processing in an amoeboid organism is higher than we had thought. The organism is the plasmodium of Physarum polycephalum (true slime mold), which is a large aggregate of protoplasm with a large number of nuclei. The organism found the optimal path when it obtained the multiple locations of food[1]. A simple mathematical model for the path finding was proposed in terms of differential equations. As well as the path-finding ability, the organism was able to anticipate the next timing of periodic environmental change after experienced some periodic changes of environment[2], and to show a kind of behaviors that seemed to be ' indecisive ' when it encountered the presence of a chemical repellent, quinine[3]. We indicated that a simple dynamics was enough to reproduce these observed behaviors. In this talk, we focus on the networking capacity[1,4-7]. We show that the Physarum can be used as a model experimental system to gain insight into the rules governing de-centralized, self-organized, adaptive network development. This simple biological system can establish networks with comparable efficiency, fault-tolerance and cost to real-world infrastructure networks, in this case judged in comparison to the Tokyo rail system. When many small food sources were presented at various positions that corresponded to geographical locations of cities, Physarum made a tube network among the food sources. We have therefore developed a biologically-inspired mathematical model that captures adaptive network formation in Physarum with a minimal set of equations. We anticipate that this model encapsulates the core mechanisms needed for adaptive network development, and should have wide applicability to guide network construction in other domains.

References: 1. A. Tero, et al. : “Rules for biologically-inspired adaptive network design”, Science, 327 : 439-442 (2010) 2. T. Saigusa, et al. : "Amoebae anticipate periodic events", Phys. Rev. Lett., Vol. 100, 018101 (2008) 3. T. Nakagaki, et al. : "Minimum-risk path finding by an adaptive amoebal network", Phys. Rev. Lett., Vol. 99, 068104 (2007) 4. T. Nakagaki, et al. : Computational ability of cells based on cell dynamics and adaptability, Vol. 27, 57-81 (2009) 5. K. Ueda, et al. : “Mathematical model for contemplative amoeboid locomotion”, Phys. Rev. E, 83, 021916 (2011). 6. L. Heaton, B. et al. : "Analysis of fungal network", Fungal Biol. Rev., Vol. 26, 12-29 (2012). 7. Qi Ma et al.: "Current reinforced random walks for constructing transport network", The Royal Soc. Interface, Vol. 10, 20120864 (2013).



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