Topological constraints on spiral wave dynamics in spherical geometries with inhomogeneous excitability

We analyze the way topological constraints and inhomogeneity in the excitability influence the dynamics of spiral waves on spheres and punctured spheres of excitable media. We generalize the definition of an index such that it characterizes not only each spiral but also each hole in punctured, oriented, compact, two-dimensional differentiable manifolds and show that the sum of the indices is conserved and zero. We also show that heterogeneity and geometry are responsible for the formation of various spiral wave attractors, in particular, pairs of spirals in which one spiral acts as a source and a second as a sink -- the latter similar to an antispiral. The results provide a basis for the analysis of the propagation of waves in heterogeneous excitable media in physical and biological systems.Comment: 5 pages, 6 Figures, major revisions, accepted for publication in Phys. Rev.

Correction of the toxic effect of cyclophosphamide on hemopoiesis in animals with lewis lung carcinoma using low-molecular-weight sodium alginate

The influence of low-molecular-weight sodium alginate, which is administered as an isolated agent and in combination with cyclophosphamide, on the parameters of peripheral blood and bone marrow was studied in mice with Lewis lung carcinoma. It was shown that administration of sodium alginate with a molecular weight of 1–10 and 20–30 kDa to tumor-bearing animals prevents bone marrow failure by activating the process of regeneration of granulocytic hemopoietic stem cells that are damaged by a single injection or repetitive injections of a cytostatic agent, due to stimulation of the clonal activity of granulocytopoiesis precursors. As a result, this treatment prevents the progression of leukopenia

New biological model of moderate inhibition of tumor and metastases growth with prolonged leukopenia in mice

A new biological model of moderate inhibition of tumor growth and metastases with prolonged leukopenia on C57BI/6 mice with the Lewis Lung Carcinoma was designed. The model was created by the injection of cyclophosphamide (dose 83.3 mg/kg) on 6th, 12th, 18th days after tumor cells transplantation on animals. Experiment showed that 3-fold cyclophosphamide use leads to growth of primary tumor and metastases inhibition. Tumor growth inhibition was 34 % on 21st day after cyclophosphamide inject. The number of metastases decreased by 4.7 times (p < 0,01). Metastatic area reduced. Metastasis frequency made 100 %. In addition, the course of cyclophosphamide application caused inhibition of granulocytic and lymphoid hematopoiesis. The reducing the number of segmented neutrophils and lymphocytes was showed on the 3rd day after 1, 2 and 3 injections of cyclophosphamide. The model can be used to study the efficacy of drugs in tumor therapy and in correction of such toxic manifestation of chemotherapy as leukopenia

On Propagation of Excitation Waves in Moving Media: The FitzHugh-Nagumo Model

BACKGROUND: Existence of flows and convection is an essential and integral feature of many excitable media with wave propagation modes, such as blood coagulation or bioreactors. METHODS/RESULTS: Here, propagation of two-dimensional waves is studied in parabolic channel flow of excitable medium of the FitzHugh-Nagumo type. Even if the stream velocity is hundreds of times higher that the wave velocity in motionless medium (), steady propagation of an excitation wave is eventually established. At high stream velocities, the wave does not span the channel from wall to wall, forming isolated excited regions, which we called "restrictons". They are especially easy to observe when the model parameters are close to critical ones, at which waves disappear in still medium. In the subcritical region of parameters, a sufficiently fast stream can result in the survival of excitation moving, as a rule, in the form of "restrictons". For downstream excitation waves, the axial portion of the channel is the most important one in determining their behavior. For upstream waves, the most important region of the channel is the near-wall boundary layers. The roles of transversal diffusion, and of approximate similarity with respect to stream velocity are discussed. CONCLUSIONS: These findings clarify mechanisms of wave propagation and survival in flow

BIOLOGICAL EFFECTS OF THE NEW SILVER-CONTAINING POLYMER NANOCOMPOSITE

In the materials there are presented, results of the synthesis and biological testing of the new nanocomposite which, contains silver nanoparticles incapsulated. in the synthetic polymer poly-1-vinyl-1,2,4-triazole. The synthesis method, of silvercontaining polymere nanocomposite is shown. With the use of modern equipment evidence of the nanocomposite with the size of 2-10 nm silver production, are substinated. It was revealed, that the new nanocomposite causes slight changes in the tissue structure of experimental animals internal organs and biochemical shift that is characteristic for the compensatory-adaptive reactions development. There are presented, the results of the silver nanoparticles distribution, mainly in the kidney and. liver tissue

A cross-scale analysis to understand and quantify the effects of photosynthetic enhancement on crop growth and yield across environments

Abstract Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying the importance of individual and multiple manipulations on the seasonal biomass growth and yield performance of target crops across variable production environments is limited. Using a state-of-the-art cross-scale model in the APSIM platform we predicted the impact of altering photosynthesis on the enzyme-limited (Ac) and electron transport-limited (Aj) rates, seasonal dynamics in canopy photosynthesis, biomass growth, and yield formation via large multiyear-by-location crop growth simulations. A broad list of promising strategies to improve photosynthesis for C3 wheat and C4 sorghum were simulated. In the top decile of seasonal outcomes, yield gains were predicted to be modest, ranging between 0% and 8%, depending on the manipulation and crop type. We report how photosynthetic enhancement can affect the timing and severity of water and nitrogen stress on the growing crop, resulting in nonintuitive seasonal crop dynamics and yield outcomes. We predicted that strategies enhancing Ac alone generate more consistent but smaller yield gains across all water and nitrogen environments, Aj enhancement alone generates larger gains but is undesirable in more marginal environments. Large increases in both Ac and Aj generate the highest gains across all environments. Yield outcomes of the tested manipulation strategies were predicted and compared for realistic Australian wheat and sorghum production. This study uniquely unpacks complex cross-scale interactions between photosynthesis and seasonal crop dynamics and improves understanding and quantification of the potential impact of photosynthesis traits (or lack of it) for crop improvement research

Diffusion in crowded biological environments: applications of Brownian dynamics

Biochemical reactions in living systems occur in complex, heterogeneous media with total concentrations of macromolecules in the range of 50 - 400 mgml. Molecular species occupy a significant fraction of the immersing medium, up to 40% of volume. Such complex and volume-occupied environments are generally termed 'crowded' and/or 'confined'. In crowded conditions non-specific interactions between macromolecules may hinder diffusion - a major process determining metabolism, transport, and signaling. Also, the crowded media can alter, both qualitatively and quantitatively, the reactions in vivo in comparison with their in vitro counterparts. This review focuses on recent developments in particle-based Brownian dynamics algorithms, their applications to model diffusive transport in crowded systems, and their abilities to reproduce and predict the behavior of macromolecules under in vivo conditions

Abnormal reward prediction-error signalling in antipsychotic naive individuals with first-episode psychosis or clinical risk for psychosis.

Ongoing research suggests preliminary, though not entirely consistent, evidence of neural abnormalities in signalling prediction errors in schizophrenia. Supporting theories suggest mechanistic links between the disruption of these processes and the generation of psychotic symptoms. However, it is unknown at what stage in the pathogenesis of psychosis these impairments in prediction-error signalling develop. One major confound in prior studies is the use of medicated patients with strongly varying disease durations. Our study aims to investigate the involvement of the meso-cortico-striatal circuitry during reward prediction-error signalling in earliest stages of psychosis. We studied patients with first-episode psychosis (FEP) and help-seeking individuals at-risk for psychosis due to sub-threshold prodromal psychotic symptoms. Patients with either FEP (n = 14), or at-risk for developing psychosis (n = 30), and healthy volunteers (n = 39) performed a reinforcement learning task during fMRI scanning. ANOVA revealed significant (p < 0.05 family-wise error corrected) prediction-error signalling differences between groups in the dopaminergic midbrain and right middle frontal gyrus (dorsolateral prefrontal cortex, DLPFC). FEP patients showed disrupted reward prediction-error signalling compared to controls in both regions. At-risk patients showed intermediate activation in the midbrain that significantly differed from controls and from FEP patients, but DLPFC activation that did not differ from controls. Our study confirms that FEP patients have abnormal meso-cortical signalling of reward-prediction errors, whereas reward-prediction-error dysfunction in the at-risk patients appears to show a more nuanced pattern of activation with a degree of midbrain impairment but preserved cortical function