Correlation of song frequency and body weight in passerine birds

Summary Frequency analysis of the songs of 90 European passerine species shown a correlation with body weight. In a number of species a dependence on habitat was found.     

The contribution of Shaker K+ channels to the information capacity of Drosophila photoreceptors

An array of rapidly inactivating voltage-gated K+ channels is distributed throughout the nervous systems of vertebrates and invertebrates. Although these channels are thought to regulate the excitability of neurons by attenuating voltage signals, their specific functions are often poorly understood. We studied the role of the prototypical inactivating K+ conductance, Shaker, in Drosophila photoreceptors by recording intracellularly from wild-type and Shaker mutant photoreceptors. Here we show that loss of the Shaker K+ conductance produces a marked reduction in the signal-to-noise ratio of photoreceptors, generating a 50% decrease in the information capacity of these cells in fully light-adapted conditions. By combining experiments with modelling, we show that the inactivation of Shaker K+ channels amplifies voltage signals and enables photoreceptors to use their voltage range more effectively. Loss of the Shaker conductance attenuated the voltage signal and induced a compensatory decrease in impedance. Our results demonstrate the importance of the Shaker K+ conductance for neural coding precision and as a mechanism for selectively amplifying graded signals in neurons, and highlight the effect of compensatory mechanisms on neuronal information processing.     

Bose-Einstein condensation of the triplet states in the magnetic insulator TlCuCl3

Bose-Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled to form a dimer in a crystalline network: the dimer ground state is a spin singlet (total spin zero), separated by an energy gap from the excited triplet state (total spin one). In these dimer compounds, Bose-Einstein condensation becomes theoretically possible. At a critical external magnetic field, the energy of one of the Zeeman split triplet components (a type of boson) intersects the ground-state singlet, resulting in long-range magnetic order; this transition represents a quantum critical point at which Bose-Einstein condensation occurs. Here we report an experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals. We verify unambiguously the theoretically predicted gapless Goldstone mode characteristic of the Bose-Einstein condensation of the triplet states.     

Controlled collisions for multi-particle entanglement of optically trapped atoms

Entanglement lies at the heart of quantum mechanics, and in recent years has been identified as an essential resource for quantum information processing and computation. The experimentally challenging production of highly entangled multi-particle states is therefore important for investigating both fundamental physics and practical applications. Here we report the creation of highly entangled states of neutral atoms trapped in the periodic potential of an optical lattice. Controlled collisions between individual neighbouring atoms are used to realize an array of quantum gates, with massively parallel operation. We observe a coherent entangling-disentangling evolution in the many-body system, depending on the phase shift acquired during the collision between neighbouring atoms. Such dynamics are indicative of highly entangled many-body states; moreover, these are formed in a single operational step, independent of the size of the system.     

A first-generation linkage disequilibrium map of human chromosome 22

DNA sequence variants in specific genes or regions of the human genome are responsible for a variety of phenotypes such as disease risk or variable drug response. These variants can be investigated directly, or through their non-random associations with neighbouring markers (called linkage disequilibrium (LD)). Here we report measurement of LD along the complete sequence of human chromosome 22. Duplicate genotyping and analysis of 1,504 markers in Centre d'Etude du Polymorphisme Humain (CEPH) reference families at a median spacing of 15 kilobases (kb) reveals a highly variable pattern of LD along the chromosome, in which extensive regions of nearly complete LD up to 804 kb in length are interspersed with regions of little or no detectable LD. The LD patterns are replicated in a panel of unrelated UK Caucasians. There is a strong correlation between high LD and low recombination frequency in the extant genetic map, suggesting that historical and contemporary recombination rates are similar. This study demonstrates the feasibility of developing genome-wide maps of LD.     

Intraaxonal iodate inhibits sodium inactivation

Zusammenfassung Iodat (IO ₃ ^– )-Ionen hemmen den Inaktivierungsvorgang des Natriumsystems, falls sie intraaxonal durch Diffusion vom abgeschnittenen Ende einer markhaltigen Froschnervenfaser her ans Innere der Schnürringmembran gelangen. Mit der Spannungsklemme erhält man dann in TEA-Ringer eine Strom-Spannungskurve des Natriumsystems auch mit lang dauernden Potentialänderungen. In der Stromklemme lassen sich unter diesen Umständen Aktionspotentiale mit Dauern bis zu 1 min registrieren.

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Dedicated to Prof. A. vonMuralt on the occasion of his 70th birthday.

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Sponsored by the Deutsche Forschungsgemeinschaft Sonderforschungsbereich 38 — Membranforschung.     

Prey localization by surface wave ray-tracing: Fish track bugs like oceanographers track storms

Summary Surface-feeding fish accurately determine direction and distance to the center of a concentric wave stimulus, even if only a single, short lasting wave train is presented^1,2. It has been suggested that one cue used by these fish to localize the wave center is the distance dependent frequency modulation of the initial part of a wave stimulus^3,4. Here we show how the distance information contained in the fractional frequency change of a capillary wave group can be decoded. We suggest that wave source localization in surface-feeding fish in part is based on a principal similar to that used by oceanographers to track storms by the frequency change of forerunners of swell.     

Oxygen equilibrium ofPriapulus hemerythrin

Summary The hemerythrin-containing coelomic fluid ofPriapulus caudatus shows a relatively low O₂ affinity (half-saturation O₂ tension P₅₀=8 mm at 10 °C) and a low O₂ capacity (near 1 vol.%). O₂ affinity is independent of pH but shows a large temperature sensitivity. A major role as a continuous O₂ transporter seems to be excluded.Acknowledgments. A major part of this work was carried out at the Kristineberg Marine Laboratory, Fiskebäckskil (Sweden) and in the Zoophysiology Department, Aarhus Universitet (Denmark).     

An actin-destabilizing factor is present in human plasma

Summary Plasma and serum of humans or experimental animals contain a factor which destabilizes F-actin. The factor has no DNAse or thrombin activity and after incubation with F-actin does not modify the position of the actin band on a SDS polyacrylamide gel. Hence it probably depolymerizes F-actin.Acknowledgment. This work was supported by the Swiss National Science Foundation, grant No.3.692-0.76. We thank Drs M. Crippa and C.A. Bouvier for measuring the DNAse and thrombin activities. The technical help of Mrs M. Redard and A. De Almeida and the photographic work of Mr J.-C. Rumbeli and Mr E. Denkinger are gratefully acknowledged.