Plant Physiology LEAF SHEATHS AND THE INHIBITION O F GERMINATION OF YOUNG AXILLARY BUDS IN SUGARCANE(')S(2)

ABSTRACT The younger parts of field-grown stalks of the sugarcane variety Co 205, with spindle included but with leaf blades trimmed back, were grown in distilled water in the dark. .When sheaths were left intact, few buds germinated; axillary shoots developed only from mature nodes. When sheaths were removed, many more buds germinated; axillary shoots developed from both older immature and mature nodes. The results, applied to normal stalk development, suggest that the sheath helps to control tillering. Germination of young bdds could, be inhibited by the sheath when the sheath is tight as around upper cylindrical nodes, but not when the sheath is loose as around lower obconic nodes at the base of the stalk

Interactions between vaccinia virus and sensitized macrophages in vitro

The action of peritoneal exudate cells (PEC) from normal and vaccinia virus infected mice on infectious vaccinia virus particles was investigatedin vitro. PEC from immune mice showed a significantly higher infectivity titre reduction (virus clearance, VC) than normal cells. This effect could be clearly attributed to the macrophage. Vaccinia virus multiplied in PEC from normal animals while there was no virus propagation in cells from immunized mice. The release of adsorbed or engulfed virus was reduced significantly in PEC from immunized animals. Anti-vaccinia-antibodies seem to activate normal macrophages to increased virus clearance. This stimulating effect was demonstrable only in the IgG fraction of the antiserum. The activity of macrophages from mice injected three times over a period of 14 days with vaccinia virus could be entirely blocked with anti-mouse-IgG, while PEC from mice injected one time six days previously were not inhibited

Modelling physical characteristics of river habitats

The physical characteristics of river habitats constitute the setting in which fluvial biota dwell and thrive. Determining the spatial and temporal patterns of physical habitat characteristics and the main factors that control them is extremely important to increase the efficiency of river management, conservation, and restoration. This study determined spatial patterns of physical habitat characteristics for Atlantic and Mediterranean rivers in northern Spain and developed a river classification based on hydromorphological characteristics. Data gathered from almost 600 sites following a modified version of the River Habitat Survey methodology were used. In addition to the usual River Habitat Survey variables, the sequence of hydromorphologic units (i.e., areas exhibiting similar hydraulic characteristics, in terms of water velocity and depth), water depths, and widths were recorded. Unmodified reaches were selected computing the Habitat Modification Score. Multiple Linear Regression models were employed to test relationships between Principal Component Analyses that summarized physical river habitat characteristics with ecological relevance and environmental variables (i.e., climate, topography, land cover, and geology) at different spatial scales and used to predict physical habitat attributes for all river reaches. The density of hydromorphologic units, flow turbulence, substrate size, and channel dimensions were able to discriminate river classes within the river network, with topography being the main environmental driver of habitat characteristics (although climate, geology, and land cover were also relevant). This classification scheme could constitute a useful tool to restore physical habitat conditions in modified river reaches.info:eu-repo/semantics/acceptedVersio

How Noisy Adaptation of Neurons Shapes Interspike Interval Histograms and Correlations

Channel noise is the dominant intrinsic noise source of neurons causing variability in the timing of action potentials and interspike intervals (ISI). Slow adaptation currents are observed in many cells and strongly shape response properties of neurons. These currents are mediated by finite populations of ionic channels and may thus carry a substantial noise component. Here we study the effect of such adaptation noise on the ISI statistics of an integrate-and-fire model neuron by means of analytical techniques and extensive numerical simulations. We contrast this stochastic adaptation with the commonly studied case of a fast fluctuating current noise and a deterministic adaptation current (corresponding to an infinite population of adaptation channels). We derive analytical approximations for the ISI density and ISI serial correlation coefficient for both cases. For fast fluctuations and deterministic adaptation, the ISI density is well approximated by an inverse Gaussian (IG) and the ISI correlations are negative. In marked contrast, for stochastic adaptation, the density is more peaked and has a heavier tail than an IG density and the serial correlations are positive. A numerical study of the mixed case where both fast fluctuations and adaptation channel noise are present reveals a smooth transition between the analytically tractable limiting cases. Our conclusions are furthermore supported by numerical simulations of a biophysically more realistic Hodgkin-Huxley type model. Our results could be used to infer the dominant source of noise in neurons from their ISI statistics

Towards Critical Human Resource Management Education (CHRME): a sociological imagination approach

This article explores the professional standing of the discipline of human resource management (HRM) in business schools in the post-financial crisis period. Using the prism of the sociological imagination, it explains the learning to be gained from teaching HRM that is sensitive to context, power and inequality. The context of crisis provides ideal circumstances for critical reflexivity and for integrating wider societal issues into the HRM curriculum. It argues for Critical Human Resource Management Education or CHRME, which, if adopted, would be an antidote to prescriptive practitioner-oriented approaches. It proceeds to set out five principles for CHRME: using the ‘sociological imagination’ prism; emphasizing the social nature of the employment relationship; investigating paradox within HRM; designing learning outcomes that encourage students to appraise HRM outcomes critically; and reflexive critique. Crucially, CHRME offers a teaching strategy that does not neglect or marginalize the reality of structural power, inequality and employee work experiences

An Allograft Glioma Model Reveals the Dependence of Aquaporin-4 Expression on the Brain Microenvironment

Aquaporin-4 (AQP4), the main water channel of the brain, is highly expressed in animal glioma and human glioblastoma in situ. In contrast, most cultivated glioma cell lines don’t express AQP4, and primary cell cultures of human glioblastoma lose it during the first passages. Accordingly, in C6 cells and RG2 cells, two glioma cell lines of the rat, and in SMA mouse glioma cell lines, we found no AQP4 expression. We confirmed an AQP4 loss in primary human glioblastoma cell cultures after a few passages. RG-2 glioma cells if grafted into the brain developed AQP4 expression. This led us consider the possibility of AQP4 expression depends on brain microenvironment. In previous studies, we observed that the typical morphological conformation of AQP4 as orthogonal arrays of particles (OAP) depended on the extracellular matrix component agrin. In this study, we showed for the first time implanted AQP4 negative glioma cells in animal brain or flank to express AQP4 specifically in the intracerebral gliomas but neither in the extracranial nor in the flank gliomas. AQP4 expression in intracerebral gliomas went along with an OAP loss, compared to normal brain tissue. AQP4 staining in vivo normally is polarized in the astrocytic endfoot membranes at the glia limitans superficialis and perivascularis, but in C6 and RG2 tumors the AQP4 staining is redistributed over the whole glioma cell as in human glioblastoma. In contrast, primary rat or mouse astrocytes in culture did not lose their ability to express AQP4, and they were able to form few OAPs

Adaptation and Selective Information Transmission in the Cricket Auditory Neuron AN2

Sensory systems adapt their neural code to changes in the sensory environment, often on multiple time scales. Here, we report a new form of adaptation in a first-order auditory interneuron (AN2) of crickets. We characterize the response of the AN2 neuron to amplitude-modulated sound stimuli and find that adaptation shifts the stimulus–response curves toward higher stimulus intensities, with a time constant of 1.5 s for adaptation and recovery. The spike responses were thus reduced for low-intensity sounds. We then address the question whether adaptation leads to an improvement of the signal's representation and compare the experimental results with the predictions of two competing hypotheses: infomax, which predicts that information conveyed about the entire signal range should be maximized, and selective coding, which predicts that “foreground” signals should be enhanced while “background” signals should be selectively suppressed. We test how adaptation changes the input–response curve when presenting signals with two or three peaks in their amplitude distributions, for which selective coding and infomax predict conflicting changes. By means of Bayesian data analysis, we quantify the shifts of the measured response curves and also find a slight reduction of their slopes. These decreases in slopes are smaller, and the absolute response thresholds are higher than those predicted by infomax. Most remarkably, and in contrast to the infomax principle, adaptation actually reduces the amount of encoded information when considering the whole range of input signals. The response curve changes are also not consistent with the selective coding hypothesis, because the amount of information conveyed about the loudest part of the signal does not increase as predicted but remains nearly constant. Less information is transmitted about signals with lower intensity

A discrete time neural network model with spiking neurons II. Dynamics with noise

We provide rigorous and exact results characterizing the statistics of spike trains in a network of leaky integrate and fire neurons, where time is discrete and where neurons are submitted to noise, without restriction on the synaptic weights. We show the existence and uniqueness of an invariant measure of Gibbs type and discuss its properties. We also discuss Markovian approximations and relate them to the approaches currently used in computational neuroscience to analyse experimental spike trains statistics.Comment: 43 pages - revised version - to appear il Journal of Mathematical Biolog