Plasticity-Driven Self-Organization under Topological Constraints Accounts for Non-random Features of Cortical Synaptic Wiring

Understanding the structure and dynamics of cortical connectivity is vital to understanding cortical function. Experimental data strongly suggest that local recurrent connectivity in the cortex is significantly non-random, exhibiting, for example, above-chance bidirectionality and an overrepresentation of certain triangular motifs. Additional evidence suggests a significant distance dependency to connectivity over a local scale of a few hundred microns, and particular patterns of synaptic turnover dynamics, including a heavy-tailed distribution of synaptic efficacies, a power law distribution of synaptic lifetimes, and a tendency for stronger synapses to be more stable over time. Understanding how many of these non-random features simultaneously arise would provide valuable insights into the development and function of the cortex. While previous work has modeled some of the individual features of local cortical wiring, there is no model that begins to comprehensively account for all of them. We present a spiking network model of a rodent Layer 5 cortical slice which, via the interactions of a few simple biologically motivated intrinsic, synaptic, and structural plasticity mechanisms, qualitatively reproduces these non-random effects when combined with simple topological constraints. Our model suggests that mechanisms of self-organization arising from a small number of plasticity rules provide a parsimonious explanation for numerous experimentally observed non-random features of recurrent cortical wiring. Interestingly, similar mechanisms have been shown to endow recurrent networks with powerful learning abilities, suggesting that these mechanism are central to understanding both structure and function of cortical synaptic wiring.     

Feinstruktur der Protonephridien von Paromalostomum proceracauda (Plathelminthes,Macrostomida)

Zusammenfassung Die Protonephridien von Paromalostomum proceracauda bestehen aus je einem Terminalkomplex und einem ausleitenden Kanal. Jeder Terminalkomplex setzt sich aus drei multiciliären Terminalzellen mit jeweils separatem Filtrationsapparat zusammen; die Zellen sind gestaffelt hintereinander angeordnet und bilden ein gemeinsames Reusenlumen. Der Nephridialkanal, der nicht an der Ultrafiltration, sondern nur an Resorptionsvorgängen beteiligt ist, besteht aus mindestens zwei röhrenförmigen, hintereinander liegenden ciliären Zellen. Die jeweils letzte Kanalzelle bildet auch den Nephridialporus. Proximal sind die Protonephridien bis zur Basis der Epidermis vollständig von einer interzellulären Matrix umhüllt.

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Fine structure of the protonephridia of Paromalostomum proceracauda (Plathelminthes, Macrostomida)

Summary The protonephridia of Paromalostomum proceracaud consist, respectively, of a terminal complex and a draining canal. Each terminal complex is composed of three multiciliary terminal cells with separate filtration apparatuses; the cells are staggered, forming a joint basket lumen. The nephridial canal consists of two or more tube-shaped ciliary cells, which are arranged in series; these cells do not participate in ultrafiltration but in resorption processes. The last canal cell also forms the nephroporus. Up to the epidermis, the protonephridia are proximally surrounded by an intercellular matrix.

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Abkürzungen cw Cilienwurzel - ep Epidermiszelle - i Interzellularsubstanz - k Kanalzelle - kl Kanallumen - l Leptotrichien - m Muskulatur des Hautmuskelschlauches - n Kern einer Terminaloder Kanalzelle - r Reusenapparat - rl Reusenlumen - rs Reusenstab - t1, 2, 3 Terminalzelle 1, 2, 3 - v Vakuole     

Functional characterization of the Staphylococcus carnosus SecA protein in Escherichia coli and Bacillus subtilissecA mutant strains

Abstract The cell wall of Candida albicans contains mannoproteins that are covalently associated with β-1,6-glucan. When spheroplasts were allowed to regenerate a new cell wall, initially non-glucosylated cell wall proteins accumulated in the medium. While the spheroplasts became osmotically stable, β-1,6-glucosylated proteins could be identified in their cell wall by SDS-extraction or β-1,3-glucanase digestion. At later stages of regeneration, β-1,3-glucosylated proteins were also found. Hence, incorporation of proteins into the cell wall is accompanied by extracellular coupling to β-1,6-/β-l,3-glucan. The SDS-extractable glucosylated proteins probably represent degradation products of wall proteins rather than their precursors. Tunicamycin delayed, but did not prevent the formation of β-1,6-glucosylated proteins, demonstrating that β-1,6-glucan is not attached to N -glycosidic side-chains of wall proteins.     

Über den »Cytotropismus« der Furchungszellen des Grasfrosches (Rana fusca)

Ohne ZusammenfassungNr. VIII der fortlaufenden, in verschiedene Zeitschriften vertheilten Serie von des Verfassers »Beiträgen zur Entwickelungsmechanik des Embryo«.     

Eine neue Weide aus dem Staate Washington

Ohne Zusammenfassung     

Distinct binding sites of Ala48-hirudin1-47 and Ala48-hirudin48-65 on alpha-thrombin

The interaction of alpha-thrombin with Ala48-hirudin, Ala48-hirudin1-47, and Ala48-hirudin48-65 was analyzed. Mutations at Pro48 were found to cause only slight changes in the kon (human: 3.1 +/- 0.3 x 10(8) M-1 s-1; bovine: 1.03 +/- 0.3 x 10(8) M-1 s-1) and koff (human: 0.4 +/- 0.2 x 10(-3) s-1; bovine: 2.9 +/- 0.4 x 10(-3) s-1) rate constants for the formation of the thrombin-hirudin complex. The amino-terminal fragment Ala48-hirudin1-47 containing the three disulfide bridges and the carboxyl-terminal fragment Ala48-hirudin48-65 were derived from the Ala48 mutant by proteolysis with endoproteinase Lys-C. These fragments inhibit bovine alpha-thrombin clotting activity with IC50 values of 0.6 and 4.9 microM, respectively (2.4 nM for r-hirudin). By mapping the interaction of Ala48-hirudin-derived fragments with bovine alpha-thrombin by limited proteolysis with trypsin and pancreatic elastase distinct binding sites for each fragment were determined. The carboxyl-terminal fragment was found to bind to the proposed anion-binding exosite in the region B62-74, whereas the amino-terminal fragment binds to a region around the elastase cleavage site at residues 150-151 of the alpha-thrombin B-chain.     

Bemerkungen zur Analyse des Reizgeschehens und der funktionellen Anpassung sowie zum Anteil dieser Anpassung an der Entwicklung des Reiches der Lebewesen

Ohne Zusammenfassung     

Die Speicherung von Trypanblau in der Golgisubstanz in glatten und quergestreiften Muskelfasern

Ohne Zusammenfassung     

The dependency of the size-growth relationship of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in forest stands on long-term site conditions, drought events, and ozone stress

Against a backdrop of increasing climate change, the effects of site conditions, drought events and ozone stress on the size-growth relationship in Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) stands are analyzed. The size-growth relationship is represented by a straight line defined by intercept and slope of a simple linear equation with stem diameter at height 1.30 m as independent variable and annual stem diameter increment at height 1.30 as dependent variable. On the basis of 64 long-term experimental plots dating back to 1871 and representing an ecological gradient from fertile to poor sites, it is shown that poorer sites exhibit shallower slopes of the linear size-growth relationships than fertile sites. Annual measurements of the size-growth relationship, including the extremely dry years of 1976 and 2003, also showed that lower stand growth rates result in shallower size-growth relationship slopes. By comparing stands with and without experimental twice-ambient ozone exposure between 2000 and 2007, it was found that ozone stress can significantly reduce the slope of the size-growth relationship. This indicates that limiting site condition, whether acute or chronic in nature, distinctly reduces the superiority of tall trees, and that a lower degree of resource limitation increases the steepness of the size-growth relationship. The causes for this behavior and the consequences for stand dynamics, silvicultural treatment and prognostication by models are discussed.