GABAergic Transmission and Chloride Equilibrium Potential Are Not Modulated by Pyruvate in the Developing Optic Tectum of Xenopus laevis Tadpoles

In the developing mammalian brain, gamma-aminobutyric acid (GABA) is thought to play an excitatory rather than an inhibitory role due to high levels of intracellular Cl− in immature neurons. This idea, however, has been questioned by recent studies which suggest that glucose-based artificial cerebrospinal fluid (ACSF) may be inadequate for experiments on immature and developing brains. These studies suggest that immature neurons may require alternative energy sources, such as lactate or pyruvate. Lack of these other energy sources is thought to result in artificially high intracellular Cl− concentrations, and therefore a more depolarized GABA receptor (GABAR) reversal potential. Since glucose metabolism can vary widely among different species, it is important to test the effects of these alternative energy sources on different experimental preparations. We tested whether pyruvate affects GABAergic transmission in isolated brains of developing wild type Xenopus tadpoles in vitro by recording the responsiveness of tectal neurons to optic nerve stimulation, and by measuring currents evoked by local GABA application in a gramicidin perforated patch configuration. We found that, in contrast with previously reported results, the reversal potential for GABAR-mediated currents does not change significantly between developmental stages 45 and 49. Partial substitution of glucose by pyruvate had only minor effects on both the GABA reversal potential, and the responsiveness of tectal neurons at stages 45 and 49. Total depletion of energy sources from the ACSF did not affect neural responsiveness. We also report a strong spatial gradient in GABA reversal potential, with immature cells adjacent to the lateral and caudal proliferative zones having more positive reversal potentials. We conclude that in this experimental preparation standard glucose-based ACSF is an appropriate extracellular media for in vitro experiments

Chirality Properties of Modeling Water in Different Aqueous Systems

The research addresses the problem of chirality existence in modeling water with various impurity molecules using new numerical algorithm of chirality determination. It is based on asymmetry analysis of molecular system composed of water molecules. The following molecular systems are investigated: (1) small water clusters such as (H2O)n, K+(H2O)m, and Na+(H2O)m (n = 4÷8, m = 5÷10) at temperature 1 K; (2) (H2O)n, K+(H2O)p, and Na+(H2O)p (n = 4÷9, p = 5÷8) at temperature 300 K; and (3) chiral biological molecules of L-valine, D-valine, L-glycerose, and D-glycerose and left or right water clusters (H2O)4 with water molecule’s shell with thickness varied from 4 to 14 Å with a step of 2 Å. The systems (1), (2) are investigated by Monte Carlo method and the interaction is simulated with Poltev-Malenkov potentials. Systems (3) are initiated using Solvate software, and then aqueous systems are optimized by the conjugate gradient algorithm using the MMFF94 potential. It is revealed that there is no predominance of right-handed or lefthanded substructures in all studied configurations of water molecules. But in small aqueous systems (2), (3), the number of types of water structures, taking into account chirality, depends on the presence of impurity ion and its type

Multivariate analysis of electrophysiological diversity of Xenopus visual neurons during development and plasticity

Abstract Biophysical properties of neurons become increasingly diverse over development, but mechanisms underlying and constraining this diversity are not fully understood. Here we investigate electrophysiological characteristics of Xenopus tadpole midbrain neurons across development and during homeostatic plasticity induced by patterned visual stimulation. We show that in development tectal neuron properties not only change on average, but also become increasingly diverse. After sensory stimulation, both electrophysiological diversity and functional differentiation of cells are reduced. At the same time, the amount of cross-correlations between cell properties increase after patterned stimulation as a result of homeostatic plasticity. We show that tectal neurons with similar spiking profiles often have strikingly different electrophysiological properties, and demonstrate that changes in intrinsic excitability during development and in response to sensory stimulation are mediated by different underlying mechanisms. Overall, this analysis and the accompanying dataset provide a unique framework for further studies of network maturation in Xenopus tadpoles

Diffusive dynamics and jamming in ensembles of robots with variable friction

In the present paper, we experimentally study the diffusive dynamics in ensembles of self-propelled and self-rotating bristle-bots. Considering the dependence of the system dynamics on the packing density of robots as well as on the friction between individual robots, we show that the friction slightly affects the diffusive dynamics but leads to a significant change in the jamming transition corresponding to the formation of rigid clusters of robots

Hafnia-yttria-alumina-silica based optical fibers with diminished mid-IR (> 2 mu m) loss

Fabrication details and basic characteristics of a set of novel multimode hafniayttria- alumina-silicate (HYAS) core-glass based fibers, one of which is co-doped with bismuth (Bi), for the mid-IR (> 2 mu m) spectral range are reported. It is demonstrated that fibers of this type possess low fundamental loss in the spectral range beyond 2 mu m, lowered by fewer times as compared to conventional silica-based ones, even at moderate (units of mol.%) co-doping with hafnium. This makes them attractive for versatile mid-IR applications. Furthermore, HYAS core-glass fiber co-doped with Bi is revealed to have all the signs of `active' (fluorescing) Bi-related centers, thus being suitable for lasing/amplifying in the nearIR spectral range. (C) 2017 Optical Society of Americ

Modeling on fluid flow and inclusion motion in centrifugal continuous casting strands

During the centrifugal continuous casting process, unreasonable casting parameters can cause violent level fluctuation, serious gas entrainment, and formation of frozen shell pieces at the meniscus. Thus, in the current study, a three-dimensional multiphase turbulent model was established to study the transport phenomena during centrifugal continuous casting process. The effects of nozzle position, casting and rotational speed on the flow pattern, centrifugal force acting on the molten steel, level fluctuation, gas entrainment, shear stress on mold wall, and motion of inclusions during centrifugal continuous casting process were investigated. Volume of Fluid model was used to simulate the molten steel-air two-phase. The level fluctuation and the gas entrainment during casting were calculated by user-developed subroutines. The trajectory of inclusions in the rotating system was calculated using the Lagrangian approach. The results show that during centrifugal continuous casting, a large amount of gas was entrained into the molten steel, and broken into bubbles of various sizes. The greater the distance to the mold wall, the smaller the centrifugal force. Rotation speed had the most important influence on the centrifugal force distribution at the side region. Angular moving angle of the nozzle with 8° and keeping the rotation speed with 60 revolutions per minute can somehow stabilize the level fluctuation. The increase of angular angle of nozzle from 8 to 18 deg and rotation speed from 40 to 80 revolutions per minute favored to decrease the total volume of entrained bubbles, while the increase of distance of nozzle moving left and casting speed had reverse effects. The trajectories of inclusions in the mold were irregular, and then rotated along the strand length. After penetrating a certain distance, the inclusions gradually moved to the center of billet and gathered there. More work, such as the heat transfer, the solidification, and the inclusions entrapment during centrifugal continuous casting, will be performed

Modeling human neurodevelopmental disorders in the Xenopus tadpole: from mechanisms to therapeutic targets

The Xenopus tadpole model offers many advantages for studying the molecular, cellular and network mechanisms underlying neurodevelopmental disorders. Essentially every stage of normal neural circuit development, from axon outgrowth and guidance to activity-dependent homeostasis and refinement, has been studied in the frog tadpole, making it an ideal model to determine what happens when any of these stages are compromised. Recently, the tadpole model has been used to explore the mechanisms of epilepsy and autism, and there is mounting evidence to suggest that diseases of the nervous system involve deficits in the most fundamental aspects of nervous system function and development. In this Review, we provide an update on how tadpole models are being used to study three distinct types of neurodevelopmental disorders: diseases caused by exposure to environmental toxicants, epilepsy and seizure disorders, and autism