Homeostatic Activity-Dependent Tuning of Recurrent Networks for Robust Propagation of Activity.

UNLABELLED: Developing neuronal networks display spontaneous bursts of action potentials that are necessary for circuit organization and tuning. While spontaneous activity has been shown to instruct map formation in sensory circuits, it is unknown whether it plays a role in the organization of motor networks that produce rhythmic output. Using computational modeling, we investigate how recurrent networks of excitatory and inhibitory neuronal populations assemble to produce robust patterns of unidirectional and precisely timed propagating activity during organism locomotion. One example is provided by the motor network inDrosophilalarvae, which generates propagating peristaltic waves of muscle contractions during crawling. We examine two activity-dependent models, which tune weak network connectivity based on spontaneous activity patterns: a Hebbian model, where coincident activity in neighboring populations strengthens connections between them; and a homeostatic model, where connections are homeostatically regulated to maintain a constant level of excitatory activity based on spontaneous input. The homeostatic model successfully tunes network connectivity to generate robust activity patterns with appropriate timing relationships between neighboring populations. These timing relationships can be modulated by the properties of spontaneous activity, suggesting its instructive role for generating functional variability in network output. In contrast, the Hebbian model fails to produce the tight timing relationships between neighboring populations required for unidirectional activity propagation, even when additional assumptions are imposed to constrain synaptic growth. These results argue that homeostatic mechanisms are more likely than Hebbian mechanisms to tune weak connectivity based on spontaneous input in a recurrent network for rhythm generation and robust activity propagation. SIGNIFICANCE STATEMENT: How are neural circuits organized and tuned to maintain stable function and produce robust output? This task is especially difficult during development, when circuit properties change in response to variable environments and internal states. Many developing circuits exhibit spontaneous activity, but its role in the synaptic organization of motor networks that produce rhythmic output is unknown. We studied a model motor network, that when appropriately tuned, generates propagating activity as during crawling inDrosophilalarvae. Based on experimental evidence of activity-dependent tuning of connectivity, we examined plausible mechanisms by which appropriate connectivity emerges. Our results suggest that activity-dependent homeostatic mechanisms are better suited than Hebbian mechanisms for organizing motor network connectivity, and highlight an important difference from sensory areas.This work was supported by Cambridge Overseas Research Fund, Trinity College, and Swartz Foundation to J.G. and Wellcome Trust VIP funding to J.F.E. through Program Grant WT075934 to Michael Bate and Matthias Landgraf. J.G. is also supported by Burroughs-Wellcome Fund Career Award at the Scientific Interface.This is the final version of the article. It first appeared from the Society for Neuroscience via https://doi.org/10.1523/JNEUROSCI.2511-15.201

Slow dynamics and strong finite-size effects in many-body localization with random and quasiperiodic potentials

We investigate charge relaxation in disordered and quasiperiodic quantum wires of spinless fermions (t -V model) at different inhomogeneity strength W in the localized and nearly localized regime. Our observable is the time-dependent density correlation function, Phi(x, t), at infinite temperature. We find that disordered and quasiperiodic models behave qualitatively similar: Although even at longest observation times the width Delta x(t) of Phi(x, t) does not exceed significantly the noninteracting localization length, xi(0), strong finite-size effects are encountered. Our findings appear difficult to reconcile with the rare-region physics (Griffiths effects) that often is invoked as an explanation for the slow dynamics observed by us and earlier computational studies. Motivated by our numerical data we discuss a scenario in which the MBL-phase splits into two subphases: in MBLA Delta x(t) diverges slower than any power, while it converges towards a finite value in MBLB. Within the scenario the transition between MBLA and the ergodic phase is characterized by a length scale, xi, that exhibits an essential singularity In xi similar to 1/vertical bar W - W-c1 vertical bar. Relations to earlier numerics and proposals of two-phase scenarios will be discussed

Development of connectivity in a motoneuronal network in Drosophila larvae.

BACKGROUND: Much of our understanding of how neural networks develop is based on studies of sensory systems, revealing often highly stereotyped patterns of connections, particularly as these diverge from the presynaptic terminals of sensory neurons. We know considerably less about the wiring strategies of motor networks, where connections converge onto the dendrites of motoneurons. Here, we investigated patterns of synaptic connections between identified motoneurons with sensory neurons and interneurons in the motor network of the Drosophila larva and how these change as it develops. RESULTS: We find that as animals grow, motoneurons increase the number of synapses with existing presynaptic partners. Different motoneurons form characteristic cell-type-specific patterns of connections. At the same time, there is considerable variability in the number of synapses formed on motoneuron dendrites, which contrasts with the stereotypy reported for presynaptic terminals of sensory neurons. Where two motoneurons of the same cell type contact a common interneuron partner, each postsynaptic cell can arrive at a different connectivity outcome. Experimentally changing the positioning of motoneuron dendrites shows that the geography of dendritic arbors in relation to presynaptic partner terminals is an important determinant in shaping patterns of connectivity. CONCLUSIONS: In the Drosophila larval motor network, the sets of connections that form between identified neurons manifest an unexpected level of variability. Synapse number and the likelihood of forming connections appear to be regulated on a cell-by-cell basis, determined primarily by the postsynaptic dendrites of motoneuron terminals.L.C. was supported by a Fyssen Foundation post-doctoral fellowship. This work was supported by a Biotechnology and Biological Sciences Research Council (UK) grant (BB/I022414/1) to M.L., a Wellcome Trust Programme Grant (WT075934) to Michael Bate and M.L., a Grass Foundation fellowship to A.S.M., and a Sir Isaac Newton Trust grant to A.S.M. and M.L. The work benefited from facilities supported by a Wellcome Trust Equipment Grant (WT079204) and contributions by the Sir Isaac Newton Trust in Cambridge.This paper was originally published in Current Biology (Couton L, Mauss AS, Yunusov T, Diegelmann S, Evers JF, Landgraf M, Current Biology 2015, 25, 568–576, doi:10.1016/j.cub.2014.12.056

Fast imaging of live organisms with sculpted light sheets.

Light-sheet microscopy is an increasingly popular technique in the life sciences due to its fast 3D imaging capability of fluorescent samples with low photo toxicity compared to confocal methods. In this work we present a new, fast, flexible and simple to implement method to optimize the illumination light-sheet to the requirement at hand. A telescope composed of two electrically tuneable lenses enables us to define thickness and position of the light-sheet independently but accurately within milliseconds, and therefore optimize image quality of the features of interest interactively. We demonstrated the practical benefit of this technique by 1) assembling large field of views from tiled single exposure each with individually optimized illumination settings; 2) sculpting the light-sheet to trace complex sample shapes within single exposures. This technique proved compatible with confocal line scanning detection, further improving image contrast and resolution. Finally, we determined the effect of light-sheet optimization in the context of scattering tissue, devising procedures for balancing image quality, field of view and acquisition speed.This work was funded by grants from the Wellcome Trust, the Medical Research Council, the CamBridgeSense network, Carlsberg Foundation, the Alzheimer Research UK Trust and the Biotechnology and Biological Sciences Research Council and the Wolfson Foundation.This is the final version of the article. It first appeared at http://dx.doi.org/10.1038/srep09385

Density Propagator for Many-Body Localization: Finite-Size Effects, Transient Subdiffusion, and Exponential Decay

We investigate charge relaxation in quantum wires of spinless disordered fermions (t-V model). Our observable is the time-dependent density propagator Pi(epsilon)(x.t), calculated in windows of different energy density epsilon of the many-body Hamiltonian and at different disorder strengths W, not exceeding the critical value W-c. The width Delta x(epsilon) (t) of Pi(epsilon)(x,t) exhibits a behavior d ln Delta x(epsilon) (t) / d ln t = beta(epsilon)(t) where the exponent function beta(epsilon)(t) less than or similar to 1/2 is seen to depend strongly on L at all investigated parameter combinations. (i) We confirm the existence of a region in phase space that exhibits subdiffusive dynamics in the sense that beta(epsilon)(t) < 1/2 in a large window of times. However, subdiffusion might possibly be transient, only, finally giving way to a conventional diffusive behavior with beta(epsilon) = 1/2. (ii) We cannot confirm the existence of many-body mobility edges even in regions of the phase diagram that have been reported to be deep in the delocalized phase. (iii) (Transient) subdiffusion 0 < beta(epsilon)(t) less than or similar to 1/2 coexists with an enhanced probability for returning to the origin. Pi(epsilon),(0,t) decaying much slower than 1/Delta x(epsilon) (t) Correspondingly, the spatial decay of Pi(epsilon)(x,t) is far from Gaussian, being exponential or even slower. On a phenomenological level, our findings are broadly consistent with the effects of strong disorder and (fractal) Griffiths regions

The baculovirus Ac108 protein is a per os infectivity factor and a component of the ODV entry complex

Wild-type ODVs (Wt) have an intact ODV entry complex in their envelope and are orally infectious towards insect larvae (left panel). In the absence of Ac108 (mut ac108), the stable core is still present but nevertheless fails to form an entry complex, affecting the ODV oral infectivity (right panel). The components of the core complex are depicted in yellow and the loosely associated components are depicted in red. PIF7 is depicted in green as its affinity with the complex is currently not known.Baculoviruses orally infect insect larvae when they consume viral occlusion bodies (OBs). OBs consist of a crystalline protein matrix in which the infectious virus particles, the occlusion-derived viruses (ODVs), are embedded. The protein matrix dissolves in the alkaline environment of the insect's midgut lumen. The liberated ODVs can then infect midgut endothelial cells through the action of at least nine different ODV-envelope proteins, called per os infectivity factors (PIFs). These PIF proteins mediate ODV oral infectivity, but are not involved in the systemic spread of the infection by budded viruses (BVs). Eight of the known PIFs form a multimeric complex, named the ODV entry complex. In this study, we show for Autographa californica multiple nucleopolyhedrovirus that mutation of the ac108ORF abolishes the ODV oral infectivity, while production and infectivity of the BVs remains unaffected. Furthermore, repair of the ac108 mutant completely recovered oral infectivity. With an HA-tagged repair mutant, we were able to demonstrate by Western analysis that the Ac108 protein is a constituent of the ODV entry complex, where the formation was abolished in the absence of this protein. Based on these results, we conclude that ac108 encodes a per os infectivity factor (PIF9) that is also an essential constituent of the ODV entry complex.</p

Reactive Oxygen Species Mediate Activity-Regulated Dendritic Plasticity Through NADPH Oxidase and Aquaporin Regulation

Neurons utilize plasticity of dendritic arbors as part of a larger suite of adaptive plasticity mechanisms. This explicitly manifests with motoneurons in the Drosophila embryo and larva, where dendritic arbors are exclusively postsynaptic and are used as homeostatic devices, compensating for changes in synaptic input through adapting their growth and connectivity. We recently identified reactive oxygen species (ROS) as novel plasticity signals instrumental in this form of dendritic adjustment. ROS correlate with levels of neuronal activity and negatively regulate dendritic arbor size. Here, we investigated NADPH oxidases as potential sources of such activity-regulated ROS and implicate Dual Oxidase (but not Nox), which generates hydrogen peroxide extracellularly. We further show that the aquaporins Bib and Drip, but not Prip, are required for activity-regulated ROS-mediated adjustments of dendritic arbor size in motoneurons. These results suggest a model whereby neuronal activity leads to activation of the NADPH oxidase Dual Oxidase, which generates hydrogen peroxide at the extracellular face; aquaporins might then act as conduits that are necessary for these extracellular ROS to be channeled back into the cell where they negatively regulate dendritic arbor size

Kajian Potensi Energi Arus Laut Sebagai Energi Alternatif Untuk Pembangkit Listrik Di Perarian Selat Lembeh, Sulawesi Utara

Kebutuhan akan energi listrik terus mengalami peningkatan dan sumber energi utamanya adalah energi konvensional yang ketersediannya terbatas di alam, untuk itu diperlukan adanya pencarian sumber energi lain yang terbarukan. Selat Lembeh merupakan wilayah perairan sempit yang berada di antara Laut Maluku yang dipengaruhi oleh massa air dari Pasifik dan Laut Sulawesi yang dipengaruhi oleh massa air dari Hindia. Penelitian ini bertujuan untuk mengetahui karakteristik arus laut serta mengetahui potensi arus laut sebagai sumber energi alternatif pembangkit listrik. Pengolahan data terdiri dari analisa data arus dan pasang surut, pemodelan numerik, dan menghitung estimasi rapat daya. Penelitian ini menggunakan metode kuantitatif dan penentuan lokasi dengan sampling area. Berdasarkan hasil penelitian, rapat daya terbesar yang dihasilkan yaitu pada musim barat, sebesar 120,02 kW/m2

Effects of pollen species composition on the foraging behaviour and offspring performance of the mason bee Osmia bicornis (L.)

The effects of floral species composition on offspring performance of solitary bees are rarely studied under conditions where foraging behaviour of mothers is allowed to play a role. In a semi-field experiment, we restricted foraging choices of the polylectic mason bee Osmia bicornis L. to flower species belonging to plant families presumably used to different extent: Borago officinalis L. (Boraginaceae), Centaurea cyanus L. (Asteraceae) and Brassica napus L. (Brassicaceae). We quantified the foraging behaviour and brood cell production by mother bees, and compared the quality of offspring in pure and mixed flower species stands. Offspring survival in pure stands was expected to reflect the mothers’ foraging preferences in the mixed stand. Pure stands of B. napus supported highest offspring survival, body mass and fraction of females produced. Offspring survival on C. cyanus and B. officinalis was very low. Larval mortality occurred earlier in brood cells provided with B. officinalis pollen than in brood cells provided with C. cyanus pollen suggesting different effects of pollen quality on early larval and later development. The time spent on different foraging activities correlated with lifetime reproductive output. However, in mixed stands, the proportion of time the bees were foraging on the different flower species did not differ significantly. Foraging behaviour may therefore not generally be a good proxy for the quality of floral resources for offspring production. Our results suggest that resources collected from one plant species may influence the usefulness of resources from another plant species. Bees may therefore overcome potentially deleterious effects of the suboptimal resources by mixing low- and high-quality resources. This may help generalist bees, such as O. bicornis, to cope with an unpredictable environment