@article{3992, abstract = {Computing the volume occupied by individual atoms in macromolecular structures has been the subject of research for several decades. This interest has grown in the recent years, because weighted volumes are widely used in implicit solvent models. Applications of the latter in molecular mechanics simulations require that the derivatives of these weighted volumes be known. In this article, we give a formula for the volume derivative of a molecule modeled as a space-filling diagram made up of balls in motion. The formula is given in terms of the weights, radii, and distances between the centers as well as the sizes of the facets of the power diagram restricted to the space-filling diagram. Special attention is given to the detection and treatment of singularities as well as discontinuities of the derivative.}, author = {Edelsbrunner, Herbert and Koehl, Patrice}, issn = {0027-8424}, journal = {PNAS}, number = {5}, pages = {2203 -- 2208}, publisher = {National Academy of Sciences}, title = {{The weighted-volume derivative of a space-filling diagram}}, doi = {10.1073/pnas.0537830100}, volume = {100}, year = {2003}, } @article{4146, abstract = {During vertebrate gastrulation, highly coordinated cellular rearrangements lead to the formation of the three germ layers, ectoderm, mesoderm and endoderm. In zebrafish, silberblick (slb)/wnt11 regulates normal gastrulation movements by activating a signalling pathway similar to the Frizzled-signalling pathway, which establishes epithelial planar cell polarity (PCP) in Drosophila. However, the cellular mechanisms by which slb/wnt11 functions during zebrafish gastrulation are still unclear. Using high-resolution two-photon confocal imaging followed by computer-assisted reconstruction and motion analysis, we have analysed the movement and morphology of individual cells in three dimensions during the course of gastrulation. We show that in slb-mutant embryos, hypoblast cells within the forming germ ring have slower, less directed migratory movements at the onset of gastrulation. These aberrant cell movements are accompanied by defects in the orientation of cellular processes along the individual movement directions of these cells. We conclude that slb/wnt11-mediated orientation of cellular processes plays a role in facilitating and stabilising movements of hypoblast cells in the germ ring, thereby pointing at a novel function of the slb/wnt11 signalling pathway for the regulation of migratory cell movements at early stages of gastrulation.}, author = {Ulrich, Florian and Concha, Miguel and Heid, Paul and Voss, Ed and Witzel, Sabine and Roehl, Henry and Tada, Masazumi and Wilson, Stephen and Adams, Richard and Soll, David and Heisenberg, Carl-Philipp J}, issn = {1011-6370}, journal = {Development}, number = {22}, pages = {5375 -- 5384}, publisher = {Company of Biologists}, title = {{Slb/Wnt11 controls hypoblast cell migration and morphogenesis at the onset of zebrafish gastrulation}}, doi = {10.1242/dev.00758}, volume = {130}, year = {2003}, } @inproceedings{2337, author = {Lieb, Élliott H and Robert Seiringer}, editor = {Karpeshina, Yulia and Weikard, Rudi and Zeng, Yanni}, pages = {239 -- 250}, publisher = {American Mathematical Society}, title = {{Bose-Einstein condensation of dilute gases in traps }}, doi = {10.1090/conm/327/05818}, volume = {327}, year = {2003}, } @article{2354, abstract = {We investigate the ground state properties of a gas of interacting particles confined in an external potential in three dimensions and subject to rotation around an axis of symmetry. We consider the Gross-Pitaevskii (GP) limit of a dilute gas. Analysing both the absolute and the bosonic ground states of the system, we show, in particular, their different behaviour for a certain range of parameters. This parameter range is determined by the question whether the rotational symmetry in the minimizer of the GP functional is broken or not. For the absolute ground state, we prove that in the GP limit a modified GP functional depending on density matrices correctly describes the energy and reduced density matrices, independent of symmetry breaking. For the bosonic ground state this holds true if and only if the symmetry is unbroken.}, author = {Robert Seiringer}, journal = {Journal of Physics A: Mathematical and Theoretical}, number = {37}, pages = {9755 -- 9778}, publisher = {IOP Publishing Ltd.}, title = {{Ground state asymptotics of a dilute, rotating gas}}, doi = {10.1088/0305-4470/36/37/312}, volume = {36}, year = {2003}, } @article{2357, abstract = {The classic Poincaré inequality bounds the L q-norm of a function f in a bounded domain Ω ⊂ ℝ n in terms of some L p-norm of its gradient in Ω. We generalize this in two ways: In the first generalization we remove a set Τ from Ω and concentrate our attention on Λ = Ω \ Τ. This new domain might not even be connected and hence no Poincaré inequality can generally hold for it, or if it does hold it might have a very bad constant. This is so even if the volume of Τ is arbitrarily small. A Poincaré inequality does hold, however, if one makes the additional assumption that f has a finite L p gradient norm on the whole of Ω, not just on Λ. The important point is that the Poincaré inequality thus obtained bounds the L q-norm of f in terms of the L p gradient norm on Λ (not Ω) plus an additional term that goes to zero as the volume of Τ goes to zero. This error term depends on Τ only through its volume. Apart from this additive error term, the constant in the inequality remains that of the 'nice' domain Ω. In the second generalization we are given a vector field A and replace ∇ by ∇ + iA(x) (geometrically, a connection on a U(1) bundle). Unlike the A = 0 case, the infimum of ∥(∇ + iA)f∥ p over all f with a given ∥f∥ q is in general not zero. This permits an improvement of the inequality by the addition of a term whose sharp value we derive. We describe some open problems that arise from these generalizations.}, author = {Lieb, Élliott H and Robert Seiringer and Yngvason, Jakob}, journal = {Annals of Mathematics}, number = {3}, pages = {1067 -- 1080}, publisher = {Princeton University Press}, title = {{Poincaré inequalities in punctured domains}}, doi = {10.4007/annals.2003.158.1067 }, volume = {158}, year = {2003}, } @article{2358, abstract = {A study was conducted on the one-dimensional (1D) bosons in three-dimensional (3D) traps. A rigorous analysis was carried out on the parameter regions in which various types of 1D or 3D behavior occurred in the ground state. The four parameter regions include density, transverse, longitudinal dimensions and scattering length.}, author = {Lieb, Élliott H and Robert Seiringer and Yngvason, Jakob}, journal = {Physical Review Letters}, number = {15}, pages = {1504011 -- 1504014}, publisher = {American Physical Society}, title = {{One-dimensional Bosons in three-dimensional traps}}, doi = {10.1103/PhysRevLett.91.150401}, volume = {91}, year = {2003}, } @article{11766, abstract = {This paper studies the multicast routing and admission control problem on unit-capacity tree and mesh topologies in the throughput model. The problem is a generalization of the edge-disjoint paths problem and is NP-hard both on trees and meshes. We study both the offline and the online version of the problem: In the offline setting, we give the first constant-factor approximation algorithm for trees, and an -factor approximation algorithm for meshes. In the online setting, we give the first polylogarithmic competitive online algorithm for tree and mesh topologies. No polylogarithmic-competitive algorithm is possible on general network topologies (Lower bounds for on-line graph problems with application to on-line circuits and optical routing, in: Proceedings of the 28th ACM Symposium on Theory of Computing, 1996, pp. 531–540) and there exists a polylogarithmic lower bound on the competitive ratio of any online algorithm on tree topologies (Making commitments in the face of uncertainity: how to pick a winner almost every time, in: Proceedings of the 28th Annual ACM Symposium on Theory of Computing, 1996, pp. 519–530). We prove the same lower bound for meshes.}, author = {Henzinger, Monika H and Leonardi, Stefano}, issn = {0022-0000}, journal = {Journal of Computer and System Sciences}, number = {3}, pages = {567--611}, publisher = {Elsevier}, title = {{Scheduling multicasts on unit-capacity trees and meshes}}, doi = {10.1016/s0022-0000(03)00043-6}, volume = {66}, year = {2003}, } @inproceedings{11909, abstract = {This article presents a high-level discussion of some problems that are unique to web search engines. The goal is to raise awareness and stimulate research in these areas.}, author = {Henzinger, Monika H and Motwani, Rajeev and Silverstein, Craig}, booktitle = {18th International Joint Conference on Artificial Intelligence}, issn = {1045-0823}, location = {Acapulco, Mexico}, pages = {1573--1579}, publisher = {Association for Computing Machinery}, title = {{Challenges in web search engines}}, year = {2003}, } @article{12659, abstract = {For many years considerable efforts have been put into investigating and modelling hydrological processes of mountainous catchments. On the one hand, the complexity and intrinsically high variability of the involved processes as well as insufficient knowledge of the underlying physical mechanisms still induce large uncertainties in understanding observed phenomena and predicting the behaviour of the system. On the other hand, the demand for models that are able to simulate mountainous water resource systems is increasing because of the needs related to both water exploitation and water conservation, which clearly call for an integrated vision and modelling of these systems. Accordingly, this paper moves from a brief survey of the most significant achievements in mountain hydrology to discuss what could be future challenging issues related to the broader spectrum of questions, which hydrologic modelling of mountainous river systems may face in the next decades. Firstly, reference is made to existing methodologies for modelling alpine water systems, focussing on some specific aspects that provide a basis for the discussion of the weaknesses and perspectives of present simulation tools. The future is thus discussed, delineating some of the research challenges that may foster a comprehensive and integrated vision of water related issues in mountainous regions.}, author = {Burlando, Paolo and Pellicciotti, Francesca and Strasser, Ulrich}, issn = {2224-7955}, journal = {Hydrology Research}, number = {1}, pages = {47--74}, publisher = {IWA Publishing}, title = {{Modelling mountainous water systems between learning and speculating looking for challenges}}, doi = {10.2166/nh.2002.0004}, volume = {33}, year = {2002}, } @article{871, abstract = {BACKGROUND: Gene duplications have a major role in the evolution of new biological functions. Theoretical studies often assume that a duplication per se is selectively neutral and that, following a duplication, one of the gene copies is freed from purifying (stabilizing) selection, which creates the potential for evolution of a new function. RESULTS: In search of systematic evidence of accelerated evolution after duplication, we used data from 26 bacterial, six archaeal, and seven eukaryotic genomes to compare the mode and strength of selection acting on recently duplicated genes (paralogs) and on similarly diverged, unduplicated orthologous genes in different species. We find that the ratio of nonsynonymous to synonymous substitutions (Kn/Ks) in most paralogous pairs is <<1 and that paralogs typically evolve at similar rates, without significant asymmetry, indicating that both paralogs produced by a duplication are subject to purifying selection. This selection is, however, substantially weaker than the purifying selection affecting unduplicated orthologs that have diverged to the same extent as the analyzed paralogs. Most of the recently duplicated genes appear to be involved in various forms of environmental response; in particular, many of them encode membrane and secreted proteins. CONCLUSIONS: The results of this analysis indicate that recently duplicated paralogs evolve faster than orthologs with the same level of divergence and similar functions, but apparently do not experience a phase of neutral evolution. We hypothesize that gene duplications that persist in an evolving lineage are beneficial from the time of their origin, due primarily to a protein dosage effect in response to variable environmental conditions; duplications are likely to give rise to new functions at a later phase of their evolution once a higher level of divergence is reached.}, author = {Kondrashov, Fyodor and Rogozin, Igor and Wolf, Yuri and Koonin, Eugene}, issn = {1465-6906}, journal = {Genome Biology}, number = {2}, publisher = {BioMed Central}, title = {{Selection in the evolution of gene duplications }}, doi = {10.1186/gb-2002-3-2-research0008}, volume = {3}, year = {2002}, } @article{885, abstract = {We study fitness landscape in the space of protein sequences by relating sets of human pathogenic missense mutations in 32 proteins to amino acid substitutions that occurred in the course of evolution of these proteins. On average, ≈10% of deviations of a nonhuman protein from its human ortholog are compensated pathogenic deviations (CPDs), i.e., are caused by an amino acid substitution that, at this site, would be pathogenic to humans. Normal functioning of a CPD-containing protein must be caused by other, compensatory deviations of the nonhuman species from humans. Together, a CPD and the corresponding compensatory deviation form a Dobzhansky-Muller incompatibility that can be visualized as the corner on a fitness ridge. Thus, proteins evolve along fitness ridges which contain only ≈10 steps between sucessive corners. The fraction of CPDs among all deviations of a protein from its human ortholog does not increase with the evolutionary distance between the proteins, indicating that subtitutions that carry evolving proteins around these corners occur in rapid succession, driven by positive selection. Data on fitness of interspecies hybrids suggest that the compensatory change that makes a CPD fit usually occurs within the same protein. Data on protein structures and on cooccurrence of amino acids at different sites of multiple orthologous proteins often make it possible to provisionally identify the substitution that compensates a partiCUlar CPD.}, author = {Kondrashov, Alexey and Sunyaev, Shamil and Kondrashov, Fyodor}, issn = {0027-8424}, journal = {PNAS}, number = {23}, pages = {14878 -- 14883}, publisher = {National Academy of Sciences}, title = {{Dobzhansky-Muller incompatibilities in protein evolution}}, doi = {10.1073/pnas.232565499}, volume = {99}, year = {2002}, } @article{13438, abstract = {ICln is an ion channel identified by expression cloning using a cDNA library from Madin-Darby canine kidney cells. In all organisms tested so far, only one transcript for the ICln protein could be identified. Here we show that two splice variants of the ICln ion channel can be found in Caenorhabditis elegans. Moreover, we show that these two splice variants of the ICln channel protein, which we termed IClnN1 and IClnN2, can be functionally reconstituted and tested in an artificial lipid bilayer. In these experiments, the IClnN1-induced currents showed no voltage-dependent inactivation, whereas the IClnN2-induced currents fully inactivated at positive potentials. The molecular entity responsible for the voltage-dependent inactivation of IClnN2 is a cluster of positively charged amino acids encoded by exon 2a, which is absent in IClnN1. Our experiments suggest a mechanism of channel inactivation that is similar to the “ball and chain” model proposed for the Shaker potassium channel,i.e. a cluster of positively charged amino acids hinders ion permeation through the channel by a molecular and voltage-dependent interaction at the inner vestibulum of the pore. This hypothesis is supported by the finding that synthetic peptides with the same amino acid sequence as the positive cluster can transform the IClnN1-induced current to the current observed after reconstitution of IClnN2. Furthermore, we show that the nematode ICln gene is embedded in an operon harboring two additional genes, which we termed Nx and Ny. Co-reconstitution of Nx and IClnN2 and functional analysis of the related currents revealed a functional interaction between the two proteins, as evidenced by the fact that the IClnN2-induced current in the presence of Nx was no longer voltage-sensitive. The experiments described indicate that the genome organization in nematodes allows an effective approach for the identification of functional partner proteins of ion channels.}, author = {Fürst, Johannes and Ritter, Markus and Rudzki, Jakob and Danzl, Johann G and Gschwentner, Martin and Scandella, Elke and Jakab, Martin and König, Matthias and Oehl, Bernhard and Lang, Florian and Deetjen, Peter and Paulmichl, Markus}, issn = {0021-9258}, journal = {Journal of Biological Chemistry}, keywords = {Cell Biology, Molecular Biology, Biochemistry}, number = {6}, pages = {4435--4445}, publisher = {Elsevier}, title = {{ICln Ion channel splice variants in Caenorhabditis elegans}}, doi = {10.1074/jbc.m107372200}, volume = {277}, year = {2002}, } @article{1451, abstract = {Extending work of Bielawski-Dancer 3 and Konno 14, we develop a theory of toric hyperkähler varieties, which involves toric geometry, matroid theory and convex polyhedra. The framework is a detailed study of semi-projective toric varieties, meaning GIT quotients of affine spaces by torus actions, and specifically, of Lawrence toric varieties, meaning GIT quotients of even-dimensional affine spaces by symplectic torus actions. A toric hyperkähler variety is a complete intersection in a Lawrence toric variety. Both varieties are non-compact, and they share the same cohomology ring, namely, the Stanley-Reisner ring of a matroid modulo a linear system of parameters. Familiar applications of toric geometry to combinatorics, including the Hard Lefschetz Theorem and the volume polynomials of Khovanskii-Pukhlikov 11, are extended to the hyperkähler setting. When the matroid is graphic, our construction gives the toric quiver varieties, in the sense of Nakajima 17.}, author = {Hausel, Tamas and Sturmfels, Bernd}, issn = {1431-0635}, journal = {Documenta Mathematica}, number = {1}, pages = {495 -- 534}, publisher = {Deutsche Mathematiker Vereinigung}, title = {{Toric hyperkähler varieties}}, doi = {10.4171/DM/130}, volume = {7}, year = {2002}, } @misc{3508, abstract = {A method of automatic conversion of a physical object into a three-dimensional digital model. The method acquires a set of measured data points on the surface of a physical model. From the measured data points, the method reconstructs a digital model of the physical object using a Delaunay complex of the points, a flow strcuture of the simplicies in the Delaunay complex and retracting the Delaunay complex into a digital model of the physical object using the flow structure. The method then outputs the digital model of the physical object.}, author = {Edelsbrunner, Herbert and Fu, Ping}, title = {{Methods of generating three-dimensional digital models of objects by wrapping point cloud data points}}, year = {2002}, } @article{3621, abstract = {In 1991, Barton and Turelli developed recursions to describe the evolution of multilocus systems under arbitrary forms of selection. This article generalizes their approach to allow for arbitrary modes of inheritance, including diploidy, polyploidy, sex linkage, cytoplasmic inheritance, and genomic imprinting. The framework is also extended to allow for other deterministic evolutionary forces, including migration and mutation. Exact recursions that fully describe the state of the population are presented; these are implemented in a computer algebra package (available on the Web at http://helios.bto.ed.ac.uk/evolgen). Despite the generality of our framework, it can describe evolutionary dynamics exactly by just two equations. These recursions can be further simplified using a "quasi-linkage equilibrium" (QLE) approximation. We illustrate the methods by finding the effect of natural selection, sexual selection, mutation, and migration on the genetic composition of a population.}, author = {Kirkpatrick, Mark and Johnson, Toby and Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {4}, pages = {1727 -- 1750}, publisher = {Genetics Society of America}, title = {{General models of multilocus evolution}}, doi = {10.1093/genetics/161.4.1727}, volume = {161}, year = {2002}, } @article{3799, abstract = {GABAergic interneurones are diverse in their morphological and functional properties. Perisomatic inhibitory cells show fast spiking during sustained current injection, whereas dendritic inhibitory cells fire action potentials with lower frequency. We examined functional and molecular properties of K(+) channels in interneurones with horizontal dendrites in stratum oriens-alveus (OA) of the hippocampal CA1 region, which mainly comprise somatostatin-positive dendritic inhibitory cells. Voltage-gated K(+) currents in nucleated patches isolated from OA interneurones consisted of three major components: a fast delayed rectifier K(+) current component that was highly sensitive to external 4-aminopyridine (4-AP) and tetraethylammonium (TEA) (half-maximal inhibitory concentrations < 0.1 mM for both blockers), a slow delayed rectifier K(+) current component that was sensitive to high concentrations of TEA, but insensitive to 4-AP, and a rapidly inactivating A-type K(+) current component that was blocked by high concentrations of 4-AP, but resistant to TEA. The relative contributions of these components to the macroscopic K(+) current were estimated as 57 +/- 5, 25 +/- 6, and 19 +/- 2 %, respectively. Dendrotoxin, a selective blocker of Kv1 channels had only minimal effects on K(+) currents in nucleated patches. Coapplication of the membrane-permeant cAMP analogue 8-(4-chlorophenylthio)-adenosine 3':5'-cyclic monophosphate (cpt-cAMP) and the phosphodiesterase blocker isobutyl-methylxanthine (IBMX) resulted in a selective inhibition of the fast delayed rectifier K(+) current component. This inhibition was absent in the presence of the protein kinase A (PKA) inhibitor H-89, implying the involvement of PKA-mediated phosphorylation. Single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed a high abundance of Kv3.2 mRNA in OA interneurones, whereas the expression level of Kv3.1 mRNA was markedly lower. Similarly, RT-PCR analysis showed a high abundance of Kv4.3 mRNA, whereas Kv4.2 mRNA was undetectable. This suggests that the fast delayed rectifier K(+) current and the A-type K(+) current component are mediated predominantly by homomeric Kv3.2 and Kv4.3 channels. Selective modulation of Kv3.2 channels in OA interneurones by cAMP is likely to be an important factor regulating the activity of dendritic inhibitory cells in principal neurone-interneurone microcircuits.}, author = {Lien, Cheng and Martina, Marco and Schultz, Jobst and Ehmke, Heimo and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {405 -- 419}, publisher = {Wiley-Blackwell}, title = {{Gating, modulation and subunit composition of voltage-gated K(+) channels in dendritic inhibitory interneurones of rat hippocampus}}, doi = {10.1113/jphysiol.2001.013066}, volume = {538}, year = {2002}, } @article{3800, abstract = {Networks of GABAergic interneurons are of critical importance for the generation of gamma frequency oscillations in the brain. To examine the underlying synaptic mechanisms, we made paired recordings from "basket cells" (BCs) in different subfields of hippocampal slices, using transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the parvalbumin promoter. Unitary inhibitory postsynaptic currents (IPSCs) showed large amplitude and fast time course with mean amplitude-weighted decay time constants of 2.5, 1.2, and 1.8 ms in the dentate gyrus, and the cornu ammonis area 3 (CA3) and 1 (CA1), respectively (33-34 degrees C). The decay of unitary IPSCs at BC-BC synapses was significantly faster than that at BC-principal cell synapses, indicating target cell-specific differences in IPSC kinetics. In addition, electrical coupling was found in a subset of BC-BC pairs. To examine whether an interneuron network with fast inhibitory synapses can act as a gamma frequency oscillator, we developed an interneuron network model based on experimentally determined properties. In comparison to previous interneuron network models, our model was able to generate oscillatory activity with higher coherence over a broad range of frequencies (20-110 Hz). In this model, high coherence and flexibility in frequency control emerge from the combination of synaptic properties, network structure, and electrical coupling.}, author = {Bartos, Marlene and Vida, Imre and Frotscher, Michael and Meyer, Axel and Monyer, Hannah and Geiger, Jörg and Jonas, Peter M}, issn = {0027-8424}, journal = {PNAS}, number = {20}, pages = {13222 -- 13227}, publisher = {National Academy of Sciences}, title = {{Fast synaptic inhibition promotes synchronized gamma oscillations in hippocampal interneuron networks}}, doi = {10.1073/pnas.192233099}, volume = {99}, year = {2002}, } @article{3801, abstract = {To examine possible interactions between fast depression and modulation of inhibitory synaptic transmission in the hippocampus, we recorded from pairs of synaptically connected basket cells (BCs) and granule cells (GCs) in the dentate gyrus of rat brain slices at 34 degrees C. Multiple-pulse depression (MPD) was examined in trains of 5 or 10 inhibitory postsynaptic currents (IPSCs) evoked at frequencies of 10-100 Hz under several conditions that inhibit transmitter release: block of voltage-dependent Ca2+ channels by Cd2+ (10 microM), activation of gamma-amino-butyric acid type B receptors (GABA(B)Rs) by baclofen (10 microM) and activation of muscarinic acetylcholine receptors (mAchRs) by carbachol (2 microM). All manipulations led to a substantial inhibition of synaptic transmission, reducing the amplitude of the first IPSC in the train (IPSC1) by 72%, 61% and 29%, respectively. However, MPD was largely preserved under these conditions (0.34 in control versus 0.31, 0.50 and 0.47 in the respective conditions at 50 Hz). Similarly, a theta burst stimulation (TBS) protocol reduced IPSC1 by 54%, but left MPD unchanged (0.40 in control and 0.39 during TBS). Analysis of both fractions of transmission failures and coefficients of variation (CV) of IPSC peak amplitudes suggested that MPD had a presynaptic expression site, independent of release probability. In conclusion, different types of presynaptic modulation of inhibitory synaptic transmission converge on a reduction of synaptic strength, while short-term dynamics are largely unchanged.}, author = {Hefft, Stefan and Kraushaar, Udo and Geiger, Jörg and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 1}, pages = {201 -- 8}, publisher = {Wiley-Blackwell}, title = {{Presynaptic short-term depression is maintained during regulation of transmitter release at a GABAergic synapse in rat hippocampus}}, doi = {10.1113/jphysiol.2001.013455}, volume = {539}, year = {2002}, } @article{3802, abstract = {The presynaptic Ca2+ signal is a key determinant of transmitter release at chemical synapses. In cortical synaptic terminals, however, little is known about the kinetic properties of the presynaptic Ca2+ channels. To investigate the timing and magnitude of the presynaptic Ca2+ inflow, we performed whole-cell patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampus. MFBs showed large high-voltage-activated Ca(2+) currents, with a maximal amplitude of approximately 100 pA at a membrane potential of 0 mV. Both activation and deactivation were fast, with time constants in the submillisecond range at a temperature of approximately 23 degrees C. An MFB action potential (AP) applied as a voltage-clamp command evoked a transient Ca2+ current with an average amplitude of approximately 170 pA and a half-duration of 580 microsec. A prepulse to +40 mV had only minimal effects on the AP-evoked Ca2+ current, indicating that presynaptic APs open the voltage-gated Ca2+ channels very effectively. On the basis of the experimental data, we developed a kinetic model with four closed states and one open state, linked by voltage-dependent rate constants. Simulations of the Ca2+ current could reproduce the experimental data, including the large amplitude and rapid time course of the current evoked by MFB APs. Furthermore, the simulations indicate that the shape of the presynaptic AP and the gating kinetics of the Ca2+ channels are tuned to produce a maximal Ca2+ influx during a minimal period of time. The precise timing and high efficacy of Ca2+ channel activation at this cortical glutamatergic synapse may be important for synchronous transmitter release and temporal information processing.}, author = {Bischofberger, Josef and Geiger, Jörg and Jonas, Peter M}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {24}, pages = {10593 -- 10602}, publisher = {Society for Neuroscience}, title = {{Timing and efficacy of Ca(2+) channel activation in hippocampal mossy fiber boutons}}, doi = {10.1523/JNEUROSCI.22-24-10593.2002}, volume = {22}, year = {2002}, } @article{3919, abstract = {Hamilton's concept of local mate competition (LMC) is the standard model to explain female-biased sex ratios in solitary Hymenoptera. In social Hymenoptera, however, LMC has remained controversial, mainly because manipulation of sex allocation by workers in response to relatedness asymmetries is an additional powerful mechanism of female bias. Furthermore, the predominant mating systems in the social insects are thought to make LMC unlikely. Nevertheless, several species exist in which dispersal of males is limited and mating occurs in the nest. Some of these species, such as the ant Cardiocondyla obscurior, have evolved dimorphic males, with one morph being specialized for dispersal and the other for fighting with nest-mate males over access to females. Such life history, combining sociality and alternative reproductive tactics in males, provides a unique opportunity to test the power of LMC as a selective force leading to female-biased sex ratios in social Hymenoptera. We show that, in concordance with LMC predictions, an experimental increase in queen number leads to a shift in sex allocation in favour of non-dispersing males, but does not influence the proportion of disperser males. Furthermore, we can assign this change in sex allocation at the colony level to the queens and rule out worker manipulation.}, author = {Cremer, Sylvia and Heinze, Jürgen}, issn = {0962-8452}, journal = {Proceedings of the Royal Society of London Series B Biological Sciences}, number = {1489}, pages = {417 -- 422}, publisher = {Royal Society, The}, title = {{Adaptive production of fighter males: queens of the ant Cardiocondyla adjust the sex ratio under local mate competition}}, doi = {10.1098/rspb.2001.1892}, volume = {269}, year = {2002}, }