1,646 research outputs found
Mechanisms of neuro- and cytotoxicity of local anesthetics and their adjuvants
No full textPlaatselijke verdovingsmiddelen zetten een mechanisme in gang waarbij zenuwcellen zichzelf vernietigen. Dit kan leiden tot zenuwschade. Stevens wilde achterhalen hoe die zenuwschade ontstaat. Hij toont aan dat alle gangbare plaatselijke verdovingsmiddelen een soort zelfmoordmechanisme van zenuwcellen in gang zetten. Om de kans op deze schade te beperken, worden plaatselijke verdovingsmiddelen vaak met andere middelen gemengd. Het merendeel van deze middelen is onschadelijk. Stevens spoorde twee middelen op die de zenuwschade verergerden. Het onderzoek is uitgevoerd in celculturen, maar Stevens raadt nu al aan om deze middelen niet bij plaatselijke verdoving te gebruiken
Edward F. Stevens Correspondence
No full textEntries include a handwritten biographical sketch and a biographical lecture and traveling museum advertisement of a New England flying Santa and the president of the Boston Author\u27s Club, with the photographic image of Snow at the ship\u27s wheel and a list of publications
Quantitative analysis of snoRNA association with pre-ribosomes and release of snR30 by Rok1 helicase
No full textIn yeast, three small nucleolar RNAs (snoRNAs) are essential for the processing of pre-ribosomal RNA—U3, U14 and snR30—whereas 72 non-essential snoRNAs direct site-specific modification of pre-rRNA. We applied a quantitative screen for alterations in the pre-ribosome association to all 75 yeast snoRNAs in strains depleted of eight putative helicases implicated in 40S subunit synthesis. For the modification-guide snoRNAs, we found no clear evidence for the involvement of these helicases in the association or dissociation of pre-ribosomes. However, the DEAD box helicase Rok1 was required specifically for the release of snR30. Point mutations in motif I, but not in motif III, of the helicase domain of Rok1 impaired the release of snR30, but this was less marked than in strains depleted of Rok1, and resulted in a dominant-negative growth phenotype. Dissociation of U3 and U14 from pre-ribosomes is also dependent on helicases, suggesting that release of the essential snoRNAs might differ mechanistically from release of the modification-guide snoRNAs. Keywords: ribosome biogenesis; RNA helicase; snoRN
At limits of life: multidisciplinary insights reveal environmental constraints on biotic diversity in continental Antarctica
No full textData source: Supporting information, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0044578#s5Multitrophic communities that maintain the functionality of the extreme Antarctic terrestrial ecosystems, while the simplest of any natural community, are still challenging our knowledge about the limits to life on earth. In this study, we describe and interpret the linkage between the diversity of different trophic level communities to the geological morphology and soil geochemistry in the remote Transantarctic Mountains (Darwin Mountains, 80uS). We examined the distribution and diversity of biota (bacteria, cyanobacteria, lichens, algae, invertebrates) with respect to elevation, age of glacial drift sheets, and soil physicochemistry. Results showed an abiotic spatial gradient with respect to the diversity of the organisms across different trophic levels. More complex communities, in terms of trophic level diversity, were related to the weakly developed younger drifts (Hatherton and Britannia) with higher soil C/N ratio and lower total soluble salts content (thus lower conductivity). Our results indicate that an increase of ion concentration from younger to older drift regions drives a succession of complex to more simple communities, in terms of number of trophic levels and diversity within each group of organisms analysed. This study revealed that integrating diversity across multi-trophic levels of biotic communities with abiotic spatial heterogeneity and geological history is fundamental to understand environmental constraints influencing biological distribution in Antarctic soil ecosystems.Catarina Magalhães, Mark I. Stevens, S. Craig Cary, Becky A. Ball, Bryan C. Storey, Diana H. Wall, Roman Tűrk and Ulrike Ruprech
Intern experience with William F. Guyton & Associates: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical referencesThis report is a review of the author's experience as an intern with
William F. Guyton & Associates. William F. Guyton & Associates is a consulting
groundwater hydrology firm with offices in Austin and Houston, Texas. The intern worked at the
main office in Austin for the duration of the internship. The author worked on a variety of
projects during the internship. These projects encompassed general groundwater studies,
computer simulation, technical analyses of aquifer parameters, and inspection of water well
construction and testing. General groundwater studies involved the collection of water well
construction and chemical analyses data. The author wrote several computer codes to handle
basic computations, and the author used several existing finite difference codes to simulate
groundwater movement. The technical analyses of pumping test data were analyzed by the author
to determine aquifer parameters. The field work involved on-site inspection of water well
construction and involved quality control of the pumping test after construction. The author
interacted with various agencies of the state and federal government. This interaction was
necessary to many of the projects. The collection of water well data and the use of the finite
difference codes gave the author the opportunity to obtain knowledge of the daily operations
of these agencies
Crystal Structures of Two Rat MHC Class Ia (RT1-A) Molecules that are Associated Differentially with Peptide Transporter Alleles TAP-A and TAP-B
No full textAntigenic peptides are loaded onto class I MHC molecules in the endoplasmic reticulum (ER) by a complex consisting of the MHC class I for Chemical Biology, The heavy chain, beta(2)-microglobulin, calreticulin, tapasin, Erp57 (ER60) and the transporter associated with antigen processing (TAP). While most mammalian species transport these peptides into the ER via a single allele of TAP, rats have evolved different TAPs, TAP-A and TAP-B, that are present in different inbred strains. Each TAP delivers a different spectrum of peptides and is associated genetically with distinct subsets of MHC class Ia alleles, but the molecular basis for the conservation (or co-evolution) of the two transporter alleles is unknown. We have determined the crystal structures of a representative of each MHC subset, viz RT1-A(a) and RT1-A1(c), in association with high-affinity nonamer peptides. The structures reveal how the chemical properties of the two different rat MHC F-pockets match those of the corresponding C termini of the peptides, corroborating biochemical data on the rates of peptide-MHC complex assembly. An unusual sequence in RT1-Al-c leads to a major deviation from the highly conserved beta(3)/alpha(1) loop (residues 40-59) conformation in mouse and human MHC class I structures. This loop change contributes to profound changes in the shape of the A-pocket in the peptide-binding groove and may explain the function of RT1-A1(c) as an inhibitory natural killer cell ligand.NCI NIH HHS [CA58896]; NIMH NIH HHS [MH19185
Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (Gobiomorphus cotidianus) – implications for incipient speciation in island freshwater fish species
No full textBackground: Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.
Results: Microchemical analyses of otolith isotopes (Sr-88, Ba-137 and Ca-43) differentiated migratory and non-migratory stocks of the New Zealand endemic Gobiomorphus cotidianus McDowall (Eleotridae). Samples were taken from two rivers, one lake and two geographically-separated outgroup locations. Meristic analyses of oculoscapular lateral line canals documented a gradual reduction of these structures in the non-migratory populations. Amplified fragment length polymorphism (AFLP) fingerprints revealed considerable genetic isolation between migratory and non-migratory populations. Temporal differences in reproductive timing (migratory = winter spawners, non-migratory = summer spawners; as inferred from gonadosomatic indices) provide a prezygotic reproductive isolation mechanism between the two ecotypes.
Conclusion: This study provides a holistic look at the role of diadromy in incipient speciation of island freshwater fish species. All four analytical approaches (otolith microchemistry, morphology, spawning timing, population genetics) yield congruent results, and provide clear and independent evidence for the existence of distinct migratory and non-migratory ecotypes within a river in a geographically confined range. The morphological changes within the non-migratory populations parallel interspecific patterns observed in all non-migratory New Zealand endemic Gobiomorphus species and other derived gobiid taxa, a pattern suggesting parallel evolution. This study indicates, for the first time, that distinct ecotypes of island freshwater fish species may be formed as a consequence of loss of migration and subsequent diversification. Therefore, if reproductive isolation persists, these processes may provide a mechanism to facilitate speciation
Pyloric caecal morphology of brook charr, Salvelinus fontinalis, in relation to diet
No full textBrook charr, Salvelinus fontinafis, shifts its diet from zoobenthos to pelagic prey when living sympatrically with white sucker, Catostomus commersoni, in lakes of the Laurentian Shield. We tested the hypothesis that this diet difference would have a significant impact on their pyloric caecal morphology in 5 lakes containing allopatric brook charr populations and 6 other lakes containing both brook charr and white sucker. We observed that the mean length of the most posterior caecum of charr was significantly greater in sympatry than in allopatry (8 f 1SD: 9.91+ 1.12mm versus 8.44 f 0.67mm). This is equivalent to an increase of 18% of total pyloric caecal mass (dry weight) in sympatric brook charr. These results indicate that this response to differences in diet, well known in birds, also occurs in fish.Source type: Electronic(1
A Study of Cattle "Temperament" and its Measurement
No full textAuthor Institution: State Normal School, Stevens Point, Wisconsi
The partitioning of oxygen uptake from air and from water by the large obligate air-breathing teleost pirarucu (Arapaima gigas)
No full textPirarucu, weighing 2 to 3 kg, ventilated their gills 16to 24 times per minute and ventilated their lungs every 1to 2 min. Average oxygen uptake from water was 23 mg. h ' .kg-l; average oxygen uptake from air was 80 mgh-'.kg-'. That is, in normoxic water they obtain about 75% of their oxygen from air, and never less than 50% from air. In hypoxic water the fraction from air increases, ultimately to 100%in anoxic water.Source type: Print(0
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