On some computational results for single neurons' activity modeling

The classical Ornstein-Uhlenbeck diffusion neuronal model is generalized by inclusion of a time-dependent input whose strength exponentially decreases in time. The behavior of the membrane potential is consequently seen to be modeled by a process whose mean and covariance classify, it as Gaussian-Markov. The effect of the input on the neuron's firing characteristics is investigated by comparing the firing probability densities and distributions for such a process with the corresponding ones of the Ornstein-Uhlenbeck model. All numerical results are obtained by implementation of a recently developed computational method.     

Inhibition of human immunodeficiency virus type 1 Env-mediated fusion by DC-SIGN

DC-SIGN, a lectin expressed on dendritic cell and macrophage subsets, binds to human immunodeficiency virus Env glycoproteins, allowing capture of viral particles. Captured virions either infect target cells or are efficiently transmitted to lymphocytes. Cellular mechanisms underlying the effects of DC-SIGN remain poorly understood. Here we have analyzed the effects of DC-SIGN on viral entry and on syncytium formation induced by Env glycoproteins. The lectin enhanced susceptibility to viral infection and dramatically increased virion internalization. Captured virions accumulated in the vesicular pathway, and their access to the cytosol was altered. Strikingly, the presence of DC-SIGN on target cells inhibited their ability to form syncytia with Env-expressing cells. However, increasing CD4 surface levels on target cells alleviated this inhibitory effect of DC-SIGN. Moreover, the potency of the viral fusion inhibitor T-20 was not affected in DC-SIGN-expressing cells. Altogether, our results indicate that DC-SIGN exerts subtle and complex effects during early steps of HIV type 1 replication. DC-SIGN facilitates capture and accumulation of viral particles in a vesicular compartment and inhibits viral fusion. Competition between CD4 and DC-SIGN for Env binding likely affects virus access to the cytosol and syncytium formation.     

Prelude to a Kiss: Evidence for Mate Discrimination in the Striped Bark Scorpion, <Emphasis Type="Italic">Centruroides vittatus</Emphasis>

The scorpion, Centruroides vittatus, lives in groups, which may allow females to discriminate among mates. We examine possible female mate discrimination based on the duration of the kiss phase of courtship, during which sperm is transferred, and on the duration of the promenade a deux phase of courtship that precedes sperm transfer. Larger males spent less time during the promenade and more time during the kiss phases of courtship. We discuss the implications of this to sexual selection in scorpions.     

Transport of gamma-butyrobetaine in an Agrobacterium species isolated from soil.

An Agrobacterium sp. isolated from soil by selective growth on gamma-butyrobetaine (gamma-trimethylaminobutyrate) as the sole source of both carbon and nitrogen has been shown to possess an inducible transport system for this growth substrate. This transport system has a Kt of 0.5 microM and a maximal velocity of 3.8 nmol/min per mg (dry weight). The influx of gamma-butyrobetaine is optimal at pH 8.5 and operates against a concentration gradient. The transport system shows a high specificity for trimethylamine carboxylic acid molecules of defined chain length. gamma-Butyrobetaine uptake was significantly reduced in osmotically shocked cells and a gamma-butyrobetaine binding activity was detected in the crude shock fluid. This suggests a transport mechanism involving a periplasmic gamma-butyrobetaine binding protein.     

A Wiener-type neuronal model in the presence of exponential refractoriness

An instantaneous return process in the presence of random refractoriness for Wiener model of single neuron activity is considered. The case of exponential distributed refractoriness is analyzed and expressions for output distributions and interspike intervals density are obtained in closed form. A computational study is performed to elucidate the role played by the model parameters in affecting the firing probabilities and the interspike distribution.     

Anionic currents of chick sensory neurons are affected by a phospholipase A2 purified from the venom of the taipan snake.

A neurotoxic phospholipase A2 was purified from the venom of the taipan snake Oxyuranus scutellatus scutellatus by three consecutive chromatographic steps on ion exchange resins, followed by an affinity column prepared with a phosphatidylcholine derivative attached to Sepharose. The phospholipase was shown to be of type A2 (specific activity of 85 units/mg protein), and an apparent molecular weight of 16,000. Amino acid analysis shows the presence of approx. 150 residues with the N-terminal amino acid sequence: NLAQFGFMIRCANGGSRSALDYADYGC, different from all the phospholipases described until now. This enzyme is lethal to experimental mice (LD50 = 10 micrograms/20 g mouse weight) and affects ionic currents in chick (Gallus domesticus) dorsal root ganglion cells, measured by the whole-cell clamp technique. In symmetrical external/internal ionic solutions, after suppression of Na+, K+ and Ca2+ currents, external application of phospholipase at a low concentration (30 nM) was shown to increase the baseline current in a reversible manner. The augmented response was voltage-dependent and the effect was much greater for negative currents. In the presence of a salt gradient across the membrane (out 40 mM NaCl/in 140 mM CsCl), the current reversal potential revealed a shift in the positive direction typically due to Cl- ion flux through the membrane. External application of a 50 microM concentration of picrotoxin caused a reversible reduction of the phospholipase-induced chloride current. Moreover, no appreciable current block was detected after addition of 50 microM DIDS.     

Properties of quinoa and oat spaghetti loaded with carboxymethylcellulose sodium salt and pregelatinized starch as structuring agents

Spaghetti based on quinoa or oat were manufactured using two different structuring agents, carboxymethylcellulose sodium salt (CMC) and pregelatinized starch at three different percentages (0.1%, 0.2%, 0.3% and 10%, 20%, 30%, respectively). The dough rheological properties were determined using a capillary rheometer, the mechanical characteristics of dry spaghetti by a dynamic mechanical analyzer and the sensorial parameters by a trained panel. Elongational and shear viscosity declined or increased when CMC was added to quinoa and oat based dough, respectively. The stress at break for dry non-conventional spaghetti increased for oat spaghetti added with CMC and pregelatinized starch, whereas decreased for quinoa spaghetti. The sensorial parameters of dry and cooked spaghetti in quinoa and oat base were strongly affected by addition of CMC and pregelatinized starch as it was not possible to produce spaghetti in base either quinoa or oat without using the tested structuring agents.     

Length–weight and length–length relationships for four fish species of Upper Paranaíba river basin,Brazil

Here the length–weight and length–length relationships of four species are provided. Fishes were collected bimonthly from December 2015 to November 2016 with sieves and trawl net, with mesh size of 0.3 cm, in eight sites from the upper Paranaíba River basin, Southeastern Brazil. Fishes were measured (cm) and weighted (0.1 g) still in the field. First record of LWR and LLR are presented for three and four species, respectively.