Studies on cultured Schwann cells: the induction of myelin synthesis, and the control of their proliferation by a new growth factor

We have recently described the use of immunological methods to identify and purify rat Schwann cells. In dissociated cultures of neonatal sciatic nerve, all of the cells can be identified by antigenic criteria as either Schwann cells or fibroblasts. The fibroblasts may be removed by treatment with antiserum to the Thy-1 antigen and complement. The purified Schwann cells have been used to study the regulation of the expression of myelin components, and the stimulation of Schwann cell division by a soluble growth factor. Among the components of myelin, we have concentrated on the peripheral myelin glycoprotein P_0, which constitutes 50–60% of the protein in peripheral myelin. We have studied the distribution of P_0 in vitro and in vivo by immunofluorescence, immuno-autoradiography on SDS gels, and solid-phase radioimmunoassay. Our results support the hypothesis that P_0 is induced specifically as a consequence of the interaction between the Schwann cell and the myelinated type of axon. The level of P_0 in the myelin membrane is at least 1000-fold higher than in the Schwann cell membrane. Purified Schwann cells divide very slowly in a conventional tissue culture medium. This has allowed us to purify a new growth factor from extracts of brain and pituitary, tentatively named Glial Growth Factor (GGF). The activity resides in a basic protein with a native molecular weight of 6 × 10^4 daltons and a subunit molecular weight of 3 × 10^4 daltons, which is active at levels comparable to those of epidermal growth factor. GGF is mitogenic for Schwann cells, astrocytes and muscle fibroblasts

A Characterization of the Brightness Oscillations During Thermonuclear Bursts From 4U 1636-536

The discovery of nearly coherent brightness oscillations during thermonuclear X-ray bursts from six neutron-star low-mass X-ray binaries has opened up a new way to study the propagation of thermonuclear burning, and may ultimately lead to greater understanding of thermonuclear propagation in other astrophysical contexts, such as in Type Ia supernovae. Here we report detailed analyses of the ~580 Hz brightness oscillations during bursts from 4U 1636-536. We investigate the bursts as a whole and, in more detail, the initial portions of the bursts. We analyze the ~580 Hz oscillations in the initial 0.75 seconds of the five bursts that were used in a previous search for a brightness oscillation at the expected ~290 Hz spin frequency, and find that if the same frequency model describes all five bursts there is insufficient data to require more than a constant frequency or, possibly, a frequency plus a frequency derivative. Therefore, although it is appropriate to use an arbitrarily complicated model of the ~580 Hz oscillations to generate a candidate waveform for the ~290 Hz oscillations, models with more than two parameters are not required by the data. For the bursts as a whole we show that the characteristics of the brightness oscillations vary greatly from burst to burst. We find, however, that in at least one of the bursts, and possibly in three of the four that have strong brightness oscillations throughout the burst, the oscillation frequency reaches a maximum several seconds into the burst and then decreases. This behavior has not been reported previously for burst brightness oscillations, and it poses a challenge to the standard burning layer expansion explanation for the frequency changes.Comment: 18 pages including three figures, uses aaspp4.sty, submitted to The Astrophysical Journal on April

Formation of Compact Stellar Clusters by High-Redshift Galaxy Outflows II: Effect of Turbulence and Metal-Line Cooling

In the primordial universe, low mass structures with virial temperatures less than 10$^{4}$ K were unable to cool by atomic line transitions, leading to a strong suppression of star formation. On the other hand, these "minihalos" were highly prone to triggered star formation by interactions from nearby galaxy outflows. In Gray & Scannapieco (2010), we explored the impact of nonequilibrium chemistry on these interactions. Here we turn our attention to the role of metals, carrying out a series of high-resolution three-dimensional adaptive mesh refinement simulations that include both metal cooling and a subgrid turbulent mixing model. Despite the presence of an additional coolant, we again we find that outflow-minihalo interactions produce a distribution of dense, massive stellar clusters. We also find that these clusters are evenly enriched with metals to a final abundance of Z $\approx$ 10$^{-2}$ Z$_{\odot}$. As in our previous simulations, all of these properties suggest that these interactions may have given rise to present-day halo globular clusters.Comment: 14 pages, 8 figures, Accepted to Ap

Scientific investigations in the Gulf of Mexico and Caribbean Sea during the 1974-1975 Calypso cruise, parts 1 and 2

The distribution and concentrations of the standing crop of phytoplankton and nutrient salts in the Gulf of Mexico and the Caribbean Sea were investigated to provide ground truth for correlating temperature and chlorophyll-a measurements with observations from NASA U-2 aircraft equipped with specially designed sensors for measuring ocean color phenomena. The physical, chemical, and biological data obtained is summarized. Sampling procedures and methods used for determining plant pigments, species composition of phytoplankton, nutrient salt analysis, and the euphotic zones are described

On the Scale Dependence of Foraging in Terrestrial Herbivores

Meaningful modeling of the spatial and trophic dynamics of terrestrial herbivores demands understanding of the constraints and fitness objectives that presumably underlie behavior. This is complex in terrestrial herbivores, because of scale-dependent constraints on nutrient or energy gain. Mechanistic processes of forage cropping, forage mastication, movements between feeding stations, and forage digestion each have unique constraints that apply on different time, size, and spatial scales. Moreover, competing activities are rarely taken into account. Experimental testing of foraging objectives is therefore clouded by uncertainty regarding which time scale is most relevant from the animal’s perspective, leading to confusion and misrepresentation in the foraging literature. We illustrate these arguments from both theoretical and empirical points of view, based on our work with wild ungulates as well as the contemporary literature

Optimisation of patch distribution strategies for AMR applications

As core counts increase in the world's most powerful supercomputers, applications are becoming limited not only by computational power, but also by data availability. In the race to exascale, efficient and effective communication policies are key to achieving optimal application performance. Applications using adaptive mesh refinement (AMR) trade off communication for computational load balancing, to enable the focused computation of specific areas of interest. This class of application is particularly susceptible to the communication performance of the underlying architectures, and are inherently difficult to scale efficiently. In this paper we present a study of the effect of patch distribution strategies on the scalability of an AMR code. We demonstrate the significance of patch placement on communication overheads, and by balancing the computation and communication costs of patches, we develop a scheme to optimise performance of a specific, industry-strength, benchmark application

Effective antiprotease-antibiotic treatment of experimental anthrax

BACKGROUND: Inhalation anthrax is characterized by a systemic spread of the challenge agent, Bacillus anthracis. It causes severe damage, including multiple hemorrhagic lesions, to host tissues and organs. It is widely believed that anthrax lethal toxin secreted by proliferating bacteria is a major cause of death, however, the pathology of intoxication in experimental animals is drastically different from that found during the infectious process. In order to close a gap between our understanding of anthrax molecular pathology and the most prominent clinical features of the infectious process we undertook bioinformatic and experimental analyses of potential proteolytic virulence factors of B. anthracis distinct from lethal toxin. METHODS: Secreted proteins (other than lethal and edema toxins) produced by B. anthracis were tested for tissue-damaging activity and toxicity in mice. Chemical protease inhibitors and rabbit immune sera raised against B. anthracis proteases were used to treat mice challenged with B. anthracis (Sterne) spores. RESULTS: B. anthracis strain delta Ames (pXO1(-), pXO2(-)) producing no lethal and edema toxins secrets a number of metalloprotease virulence factors upon cultivation under aerobic conditions, including those with hemorrhagic, caseinolytic and collagenolytic activities, belonging to M4 and M9 thermolysin and bacterial collagenase families, respectively. These factors are directly toxic to DBA/2 mice upon intratracheal administration at 0.5 mg/kg and higher doses. Chemical protease inhibitors (phosphoramidon and 1, 10-phenanthroline), as well as immune sera against M4 and M9 proteases of B. anthracis, were used to treat mice challenged with B. anthracis (Sterne) spores. These substances demonstrate a substantial protective efficacy in combination with ciprofloxacin therapy initiated as late as 48 h post spore challenge, compared to the antibiotic alone. CONCLUSION: Secreted proteolytic enzymes are important pathogenic factors of B. anthrasis, which can be considered as effective therapeutic targets in the development of anthrax treatment and prophylactic approaches complementing anti-lethal toxin therapy

Spatial heterogeneity and irreversible vegetation change in semi-arid grazing systems

Recent theoretical studies have shown that spatial redistribution of surface water may explain the occurrence of patterns of alternating vegetated and degraded patches in semiarid grasslands. These results implied, however, that spatial redistribution processes cannot explain the collapse of production on coarser scales observed in these systems. We present a spatially explicit vegetation model to investigate possible mechanisms explaining irreversible vegetation collapse on coarse spatial scales. The model results indicate that the dynamics of vegetation on coarse scales are determined by the interaction of two spatial feedback processes. Loss of plant cover in a certain area results in increased availability of water in remaining vegetated patches through run-on of surface water, promoting within-patch plant production. Hence, spatial redistribution of surface water creates negative feedback between reduced plant cover and increased plant growth in remaining vegetation. Reduced plant cover, however, results in focusing of herbivore grazing in the remaining vegetation. Hence, redistribution of herbivores creates positive feedback between reduced plant cover and increased losses due to grazing in remaining vegetated patches, leading to collapse of the entire vegetation. This may explain irreversible vegetation shifts in semiarid grasslands on coarse spatial scales