GABA-enhanced collective behavior in neuronal axons underlies persistent gamma-frequency oscillations

Gamma (30–80 Hz) oscillations occur in mammalian electroencephalogram in a manner that indicates cognitive relevance. In vitro models of gamma oscillations demonstrate two forms of oscillation: one occurring transiently and driven by discrete afferent input and the second occurring persistently in response to activation of excitatory metabotropic receptors. The mechanism underlying persistent gamma oscillations has been suggested to involve gap-junctional communication between axons of principal neurons, but the precise relationship between this neuronal activity and the gamma oscillation has remained elusive. Here we demonstrate that gamma oscillations coexist with high-frequency oscillations (>90 Hz). High-frequency oscillations can be generated in the axonal plexus even when it is physically isolated from pyramidal cell bodies. They were enhanced in networks by nonsomatic -aminobutyric acid type A (GABAA) receptor activation, were modulated by perisomatic GABAA receptor-mediated synaptic input to principal cells, and provided the phasic input to interneurons required to generate persistent gamma-frequency oscillations. The data suggest that high-frequency oscillations occurred as a consequence of random activity within the axonal plexus. Interneurons provide a mechanism by which this random activity is both amplified and organized into a coherent network rhythm

Expression of connexins in human preimplantation embryos in vitro

Intercellular communication via gap junctions is required to coordinate developmental processes in the mammalian embryo. We have investigated if the connexin (Cx) isoforms known to form gap junctions in rodent preimplantation embryos are also expressed in human embryos, with the aim of identifying species differences in communication patterns in early development. Using a combination of polyA PCR and immunocytochemistry we have assessed the expression of Cx26, Cx31, Cx32, Cx40, Cx43 and Cx45 which are thought to be important in early rodent embryos. The results demonstrate that Cx31 and Cx43 are the main connexin isoforms expressed in human preimplantation embryos and that these isoforms are co-expressed in the blastocyst. Cx45 protein is expressed in the blastocyst but the protein may be translated from a generally low level of transcripts: which could only be detected in the PN to 4-cell embryos. Interestingly, Cx40, which is expressed by the extravillous trophoblast in the early human placenta, was not found to be expressed in the blastocyst trophectoderm from which this tissue develops. All of the connexin isoforms in human preimplantation embryos are also found in rodents pointing to a common regulation of these connexins in development of rodent and human early embryos and perhaps other species

A role for fast rhythmic bursting neurons in cortical gamma oscillations in vitro

Basic cellular and network mechanisms underlying gamma frequency oscillations (30–80 Hz) have been well characterized in the hippocampus and associated structures. In these regions, gamma rhythms are seen as an emergent property of networks of principal cells and fast-spiking interneurons. In contrast, in the neocortex a number of elegant studies have shown that specific types of principal neuron exist that are capable of generating powerful gamma frequency outputs on the basis of their intrinsic conductances alone. These fast rhythmic bursting (FRB) neurons (sometimes referred to as "chattering" cells) are activated by sensory stimuli and generate multiple action potentials per gamma period. Here, we demonstrate that FRB neurons may function by providing a large-scale input to an axon plexus consisting of gap-junctionally connected axons from both FRB neurons and their anatomically similar counterparts regular spiking neurons. The resulting network gamma oscillation shares all of the properties of gamma oscillations generated in the hippocampus but with the additional critical dependence on multiple spiking in FRB cells

Multiple mitochondrial introgression events and heteroplasmy in trypanosoma cruzi revealed by Maxicircle MLST and next generation sequencing

Background Mitochondrial DNA is a valuable taxonomic marker due to its relatively fast rate of evolution. In Trypanosoma cruzi, the causative agent of Chagas disease, the mitochondrial genome has a unique structural organization consisting of 20–50 maxicircles (∼20 kb) and thousands of minicircles (0.5–10 kb). T. cruzi is an early diverging protist displaying remarkable genetic heterogeneity and is recognized as a complex of six discrete typing units (DTUs). The majority of infected humans are asymptomatic for life while 30–35% develop potentially fatal cardiac and/or digestive syndromes. However, the relationship between specific clinical outcomes and T. cruzi genotype remains elusive. The availability of whole genome sequences has driven advances in high resolution genotyping techniques and re-invigorated interest in exploring the diversity present within the various DTUs. Methodology/Principal Findings To describe intra-DTU diversity, we developed a highly resolutive maxicircle multilocus sequence typing (mtMLST) scheme based on ten gene fragments. A panel of 32 TcI isolates was genotyped using the mtMLST scheme, GPI, mini-exon and 25 microsatellite loci. Comparison of nuclear and mitochondrial data revealed clearly incongruent phylogenetic histories among different geographical populations as well as major DTUs. In parallel, we exploited read depth data, generated by Illumina sequencing of the maxicircle genome from the TcI reference strain Sylvio X10/1, to provide the first evidence of mitochondrial heteroplasmy (heterogeneous mitochondrial genomes in an individual cell) in T. cruzi. Conclusions/Significance mtMLST provides a powerful approach to genotyping at the sub-DTU level. This strategy will facilitate attempts to resolve phenotypic variation in T. cruzi and to address epidemiologically important hypotheses in conjunction with intensive spatio-temporal sampling. The observations of both general and specific incidences of nuclear-mitochondrial phylogenetic incongruence indicate that genetic recombination is geographically widespread and continues to influence the natural population structure of TcI, a conclusion which challenges the traditional paradigm of clonality in T. cruzi

Characterization of the anticipated synchronization regime in the coupled FitzHugh--Nagumo model for neurons

We characterize numerically the regime of anticipated synchronization in the coupled FitzHugh-Nagumo model for neurons. We consider two neurons, coupled unidirectionally (in a master-slave configuration), subject to the same random external forcing and with a recurrent inhibitory delayed connection in the slave neuron. We show that the scheme leads to anticipated synchronization, a regime in which the slave neuron fires the same train of pulses as the master neuron, but earlier in time. We characterize the synchronization in the parameter space (coupling strength, anticipation time) and introduce several quantities to measure the degree of synchronization.Comment: 8 pages. Proceedings of the conference on "Stochastic Systems: From Randomness to"Complexit

The optimization problem of the shaped knife profiling

Проаналізовано переваги та недоліки процесу гарячого поділу безперервнолитої квадратної заготовки на ножицях з фасонними ножами. Відзначається доцільність проведення теоретичних досліджень розділових операцій на ножицях з використанням методу скінченних елементів (МСЕ). Метою даної роботи було визначення оптимальної форми профілювання фасонного ножа для поділу квадратної заготовки в гарячому стані шляхом математичного моделювання на базі МСЕ. Представлено методику проведення досліджень, що включали два етапи. На першому етапі використовували математичне моделювання відповідно до плану повного факторного експерименту 24 згідно виробничих умов реалізації процесу з ножами що мали значення кута розкриття ножів 90…98° та ухилу контактних поверхонь 3…11°. При обробці даних моделювання були отримані три відносних параметра, два з яких характеризують зминання (затяжка) і загин кінців розкату, і ще один – ромбічність торцевої поверхні. Для кожного з параметрів, отримані лінійні рівняння регресії як функція температури різання та розмірів заготовок, величини кута розкриття ножів та ухилу контактних поверхонь. На другому етапі дослідження вирішували оптимізаційну задачу пошуку мінімуму цільової функції – ромбічності. За результатами відзначено, що оптимальні значення профілювання ножів залежать від вимог, що висуваються до якості зрізу. Введено фактор граничного відхилення зминання і загину кінців, встановлений діапазон його значень та проаналізовано вплив на оптимальні параметри. Запропоновано величини кута розкриття ножів та ухилу контактних поверхонь, за умови мінімізації граничного відхилення зминання і загину кінців у досліджуваних діапазонах температур та розмірів заготовок. Отримано залежності параметрів профілювання ножів від граничного відхилення зминання і загину кінців заготовок після поділу. Результати роботи можуть бути рекомендовані для використання при прийнятті проектно-конструкторських і технологічних рішень в питаннях гарячого розділення безперервнолитої квадратної заготовки фасонними ножами на кут.The advantages and disadvantages of the process of separation in hot condition of billet with square shape by special profiled knives were analyzed. There is expediency of carrying out theoretical researches the separating operations by shears based on finite elements method (FEM) is noted. The purpose of the work was to determine the optimal shape for make form a profiled knife for separating a square billet in a hot state by simulating based on the FEM. A methodology of study realization consisting of two stages is presented. At the first stage, simulating was used in accordance with the plan of the full factorial experiment 24 according to the technological environment for the process implementation with knives having a knife opening angle of 90...98° and a contact surface inclination of 3...11°. At the processing the simulation results, three relative parameters were obtained. Two parameters characterize the crumpling (tightening) and bending of the billet ends, and one more – the rhomboidity of the end surface. For each of the parameters, the linear regression equations obtained as a function of cutting temperature and billet sizes, the knife opening angle and contact surface inclination. At the second stage of the study, the optimization problem of determining the minimum of the objective function – rhomboidity – was solved. According to the results, it was noted that the optimal values of the profiling of knives depend on the requirements for the quality of the cut. The factor of the maximum deviation of crumpling and bending of the ends is introduced. The range of its values is established and the influence on the optimal parameters is analyzed. The values of the knife opening angle and contact surface inclination are proposed, provided that the maximum deviation of the crumpling and bending of the ends, at the studied temperature ranges and sizes of the billets, is minimized. The dependences of the optimal parameters of the profiling of knives on the maximum deviation of the crumpling and bending of the ends of the billets after separation are obtained. Results of work can be recommended for use to get solutions in design and technology questions of hot separation square billet by profiled knife on the angle

Searching for faint companions with VLTI/PIONIER. I. Method and first results

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. Aims. We search for low-mass companions around a few bright stars using different strategies, and determine the dynamic range currently reachable with PIONIER. Methods. Our method is based on the closure phase, which is the most robust interferometric quantity when searching for faint companions. We computed the chi^2 goodness of fit for a series of binary star models at different positions and with various flux ratios. The resulting chi^2 cube was used to identify the best-fit binary model and evaluate its significance, or to determine upper limits on the companion flux in case of non detections. Results. No companion is found around Fomalhaut, tau Cet and Regulus. The median upper limits at 3 sigma on the companion flux ratio are respectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on the search region extending from 5 to 100 mas. Our observations confirm that the previously detected near-infrared excess emissions around Fomalhaut and tau Cet are not related to a low-mass companion, and instead come from an extended source such as an exozodiacal disk. In the case of del Aqr, in 30 min of observation, we obtain the first direct detection of a previously known companion, at an angular distance of about 40 mas and with a flux ratio of 2.05e-2 \pm 0.16e-2. Due to the limited u,v plane coverage, its position can, however, not be unambiguously determined. Conclusions. After only a few months of operation, PIONIER has already achieved one of the best dynamic ranges world-wide for multi-aperture interferometers. A dynamic range up to about 1:500 is demonstrated, but significant improvements are still required to reach the ultimate goal of directly detecting hot giant extrasolar planets.Comment: 11 pages, 6 figures, accepted for publication in A&

Constraining the Exozodiacal Luminosity Function of Main-sequence Stars: Complete Results from the Keck Nuller Mid-infrared Surveys

Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near-and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 µm spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 µm instrumental bandwidth. Based on the 8-9 µm data alone, which provide the highest signal-to-noise measurements, only one star shows a large excess imputable to dust emission (η Crv), while four more show a significant (> 3σ) excess: β Leo, β UMa, ζ Lep, and y Oph. Overall, excesses detected by KIN are more frequent around A-type stars than later spectral types. Astatistical analysis of the measurements further indicates that stars with known far-infrared (y ≥ 70 µm) excesses have higher exozodiacal emission levels than stars with no previous indication of a cold outer disk. This statistical trend is observed regardless of spectral type and points to a dynamical connection between the inner (zodi-like) and outer (Kuiper-Belt-like) dust populations. The measured levels for such stars are clustering close to the KIN detection limit of a few hundred zodis and are indeed consistent with those expected from a population of dust that migrated in from the outer belt by Poynting-Robertson drag. Conversely, no significant mid-ilinfrared excess is found around sources with previously reported near-infrared resolved excesses, which typically have levels of the order of 1% over the photospheric flux. If dust emission is really at play in these near-infrared detections, the absence of a strong mid-infrared counterpart points to populations of very hot and small (submicron) grains piling up very close to the sublimation radius. For solar-type stars with no known infrared excess, likely to be the most relevant targets for a future exo-Earth direct imaging mission, we find that their median zodi level is 12±24 zodis and lower than 60 (90) zodis with 95% (99%) confidence, if a lognormal zodi luminosity distribution is assumed