To evaluate performance in a complex survival task, we studied the morphology of the Physarum plasmodium transportation network when presented with multiple separate food sources. The plasmodium comprises a network of tubular elements through which chemical nutrient, intracellular signals and the viscous body are transported and circulated. When three separate food sources were presented, located at the vertices of a triangle, the tubular network connected them via a short pathway, which was often analogous to the mathematically shortest route known as Steiner's minimum tree (SMT). The other common network shape had high fault tolerance against accidental disconnection of the tubes and was known as cycle (CYC). Pattern selection appeared to be a bistable system involving SMT and CYC. When more than three food sources were presented, the network pattern tended to be a patchwork of SMT and CYC. We therefore concluded that the plasmodium tube network is a well designed and intelligent system.

When two food sources are presented to the slime mold Physarum in the dark, a thick tube for absorbing nutrients is formed that connects the food sources through the shortest route. When the lightavoiding organism is partially illuminated, however, the tube connecting the food sources follows a different route. Defining risk as the experimentally measurable rate of light-avoiding movement, the minimum-risk path is exhibited by the organism, determined by integrating along the path. A model for an adaptive-tube network is presented that is in good agreement with the experimental observations. Introduction.-The plasmodium of Physarum polycephalum is an amoebalike organism with a body made up of a tubular network through which nutrients, signals, and body mass are transported. Studies of this organism have shown that it is able to determine the shortest path through a maze as well as ''solve'' other geometric puzzles [1][2][3]. In a maze, a starved organism forms a tube that connects food sources (FS) placed at the two exits of the maze via the shortest path, while nearly the entire protoplasm of the amoeba gathers over the two FS. The organism meets its physiological requirements in adopting this shape by absorbing nutrients from the FS as rapidly as possible while maintaining sufficient connectivity to permit intracellular communication. Such behavior in a primitive organism of this kind may offer insights into the evolutionary origins of biological information processing.Here we give the plasmodium a new type of task involving optimization behavior. Two separate FS are presented to the organism, which is illuminated by an inhomogeneous light field. Because the plasmodium is photophobic, tubes connecting the FS do not follow the simple shortest paths but form according to the illumination inhomogeneity. We report on the behavior of the organism under these conditions and discuss its physiological significance. We also propose a mathematical model for the cell dynamics and present a computational algorithm for its problem solving.Organism and methods.-The plasmodium of Physarum polycephalum, which regenerated from the sclerotia in ca. one-half day in the dark (25 C), was used in the experiments. A plastic film was placed onto a 1% agar gel, leaving a rectangular area (1 2 cm 2 ) of the gel uncovered. A few pieces (0:5 1 cm 2 ) of the regenerated plasmodium were placed in the rectangular area, and the preparation was placed in the dark for a few hours. The

The circadian pacemaker in the hypothalamic suprachiasmatic nucleus (SCN) is a hierarchical multioscillator system in which neuronal networks play crucial roles in expressing coherent rhythms in physiology and behavior. However, our understanding of the neuronal network is still incomplete. Intracellular calcium mediates the input signals, such as phase-resetting stimuli, to the core molecular loop involving clock genes for circadian rhythm generation and the output signals from the loop to various cellular functions, including changes in neurotransmitter release. Using a unique large-scale calcium imaging method with genetically encoded calcium sensors, we visualized intracellular calcium from the entire surface of SCN slice in culture including the regions where autonomous clock gene expression was undetectable. We found circadian calcium rhythms at a single-cell level in the SCN, which were topologically specific with a larger amplitude and more delayed phase in the ventral region than the dorsal. The robustness of the rhythm was reduced but persisted even after blocking the neuronal firing with tetrodotoxin (TTX). Notably, TTX dissociated the circadian calcium rhythms between the dorsal and ventral SCN. In contrast, a blocker of gap junctions, carbenoxolone, had only a minor effect on the calcium rhythms at both the single-cell and network levels. These results reveal the topological specificity of the circadian calcium rhythm in the SCN and the presence of coupled regional pacemakers in the dorsal and ventral regions. Neuronal firings are not necessary for the persistence of the calcium rhythms but indispensable for the hierarchical organization of rhythmicity in the SCN. yellow cameleon 3.60 | Nipkow-spinning disk confocal | adeno-associated virus | time-lapse imaging | acrophase map

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