Numerical simulations of the pulsating flow of cerebrospinal fluid flow in the cervical spinal canal of a Chiari patient

The flow of cerebrospinal fluid (CSF) in a patient-specific model of the subarachnoid space in a Chiari I patient was investigated using numerical simulations. The pulsating CSF flow was modeled using a time-varying velocity pulse based on peak velocity measurements (diastole and systole) derived from a selection of patients with Chiari I malformation. The present study introduces the general definition of the Reynolds number to provide a measure of CSF flow instability to give an estimate of the possibility of turbulence occurring in CSF flow. This was motivated by the fact that the combination of pulsating flow and the geometric complexity of the spinal canal may result in local Reynolds numbers that are significantly higher than the commonly used global measure such that flow instabilities may develop into turbulent flow in these regions. The local Reynolds number was used in combination with derived statistics to characterize the flow. The results revealed the existence of both local unstable regions and local regions with velocity fluctuations similar in magnitude to what is observed in fully turbulent flows. The results also indicated that the fluctuations were not self-sustained turbulence, but rather flow instabilities that may develop into turbulence. The case considered was therefore believed to represent a CSF flow close to transition.     

Gene flow from transgenic rice to red rice (Oryza sativa L.) in the field

In this study, we simulate a transgenic rice crop highly infested with red rice to examine transgene transfer from a transgenic line (A2504) resistant to glufosinate ammonium to cohabitant red rice. The red rice was sown along with the transgenic line at the highest density found in naturally infested crops in the region. Agricultural practices similar to those used to control red rice infestation in northern Italy rice fields were used to reproduce the local rice production system. During the first 2 years, the field was treated with herbicide at the appropriate time; in the first year the dosage of herbicide was three times the recommended amount. In this first year, detectable red rice plants that escaped herbicide treatment were manually removed. Nevertheless, two herbicide‐resistant hybrid plants (named 101 and 104) were identified in the experimental field during the second year of cultivation. Phenotypic and molecular characterisation suggests the hybrid nature of these two plants, deriving from crossing events involving A2504, respectively, with red rice (plant 101) and the buffer cultivar Gladio (plant 104). The progeny of two subsequent generations of the two plants were examined and the presence of the transgene detected, indicating stable transfer of the transgene across generations. In conclusion, despite control methods, red rice progeny tolerant to the herbicide can be expected following use of transgenic rice and, consequently, difficulties in controlling this weed with chemicals will emerge in a relatively short time.     

Chemiluminescence determination of fluoroquinolone antibiotics using a soluble manganese (IV)-sulphite system.

The reaction of soluble manganese (IV) with sulphite in acidic condition was found to elicit weak chemiluminescence (CL). The CL signal was remarkably enhanced in the presence of three fluoroquinolones, viz. norfloxacin, ofloxacin and ciprofloxacin. Based on these observations, a new flow-injection CL method was developed for the determination of these fluoroquinolones. The method allows determination in the range 5.0 x 10(-8)-1.0 x 10(-6) mol/L for norfloxacin, 1.0 x 10(-7)-8.0 x 10(-6) mol/L for ofloxacin and 1.0 x 10(-7)-3.0 x 10(-5) mol/L for ciprofloxacin, with detection limits of 3 x 10(-8) mol/L, 5 x 10(-8) mol/L and 3 x 10(-8) mol/L, respectively. The method was applied to the determination of fluoroquinolones in pharmaceutical preparations.     

构建医患和谐：大型医院图书馆的医学信息服务的“三个面向”

针对临床医疗引发的医患矛盾,从医学信息服务角度提出了以面向医院管理层、临床医务人员和患者的医学信息服务来化解矛盾,阐述了大型医院图书馆以医学信息服务为纽带,构建医患和谐的工作要点。     

Functional comparison of hemoglobin purified by different methods and their biophysical implications

Hemoglobin (Hb) that is purified from red blood cells (RBCs) is commonly subjected to harsh processing conditions, such as high temperatures and extensive column separation, which may damage the Hb by altering the heme prosthetic group and/or the Hb protein structure. In this study, bovine and human Hb purified by tangential flow filtration (TFF) was compared to commercial preparations of human Hb (Hemosol, Inc., Toronto, Canada) and bovine Hb (Biopure, Inc., Cambridge, MA). Purified Hbs were characterized by measuring their overall purity (SDS–PAGE, SEC, and ESI‐MS), susceptibility to oxidation (k_ox), responses to physiological conditions (pH, [Cl^?], [IHP], and T), and ligand binding kinetics (O₂, NO, and CO). All Hbs evaluated possessed comparable biophysical properties, however, a small amount of catalase was detected in the TFF‐purified Hbs that reduced the rate of autoxidation. Mass changes observed by mass spectrometry suggest that structural alterations may be introduced into Hbs that are purified by extensive chromatographic separations. These results demonstrate that TFF is a suitable process for the purification of Hb from RBCs with a quality equivalent to that of commercial Hb preparations that employ more extensive purification strategies. This work also shows that TFF can yield highly pure Hb which can be used for Hb‐based O₂ carrier synthesis. Biotechnol. Bioeng. 2010; 106: 76–85. © 2010 Wiley Periodicals, Inc.     

Temporal and spatial genetic structure in Vitellaria paradoxa (shea tree) in an agroforestry system in southern Mali

Ten microsatellite loci were used to investigate the impact of human activity on the spatial and temporal genetic structure of Vitellaria paradoxa (Sapotaceae), a parkland tree species in agroforestry systems in southern Mali. Two stands (forest and fallow) and three cohorts (adults, juveniles and natural regeneration) in each stand were studied to: (i) compare their levels of genetic diversity (gene diversity, HE; allelic richness, Rs; and inbreeding, FIS); (ii) assess their genetic differentiation (FST); and (iii) compare their levels of spatial genetic structuring. Gene diversity parameters did not vary substantially among stands or cohorts, and tests for bottleneck events were nonsignificant. The inbreeding coefficients were not significantly different from zero in most cases (FIS = -0.025 in forest and 0.045 in fallow), suggesting that the species is probably outbreeding. There was a weak decrease in F(IS) with age, suggesting inbreeding depression. Differentiation of stands within each cohort was weak (FST = 0.026, 0.0005, 0.010 for adults, juveniles and regeneration, respectively), suggesting extensive gene flow. Cohorts within each stand were little differentiated (FST = -0.001 and 0.001 in forest and fallow, respectively). The spatial genetic structure was more pronounced in fallow than in forest where adults showed no spatial structuring. In conclusion, despite the huge influence of human activity on the life cycle of Vitellaria paradoxa growing in parkland systems, the impact on the pattern of genetic variation at microsatellite loci appears rather limited, possibly due to the buffering effect of extensive gene flow between unmanaged and managed populations.     

Mutational analysis of the stability of the H2A and H2B histone monomers

The eukaryotic histone heterodimer H2A-H2B folds through an obligatory dimeric intermediate that forms in a nearly diffusion-limited association reaction in the stopped-flow dead time. It is unclear whether there is partial folding of the isolated monomers before association. To address the possible contributions of structure in the monomers to the rapid association, we characterized H2A and H2B monomers in the absence of their heterodimeric partner. By far-UV circular dichroism, the H2A and H2B monomers are 15% and 31% helical, respectively—significantly less than observed in X-ray crystal structures. Acrylamide quenching of the intrinsic Tyr fluorescence was indicative of tertiary structure. The H2A and H2B monomers exhibit free energies of unfolding of 2.5 and 2.9 kcal mol^− 1, respectively; at 10 μM, the sum of the stability of the monomers is ∼ 60% of the stability of the native dimer. The helical content, stability, and m values indicate that H2B has a more stable, compact structure than H2A. The monomer m values are larger than expected for the extended histone fold motif, suggesting that the monomers adopt an overly collapsed structure. Stopped-flow refolding—initiated from urea-denatured monomers or the partially folded monomers populated at low denaturant concentrations—yielded essentially identical rates, indicating that monomer folding is productive in the rapid association and folding of the heterodimer. A series of Ala and Gly mutations were introduced into H2A and H2B to probe the importance of helix propensity on the structure and stability of the monomers. The mutational studies show that the central α-helix of the histone fold, which makes extensive intermonomer contacts, is structured in H2B but only partially folded in H2A.     

Genetic structure of populations of the closely related species of Melanopsis (Gastropoda: Cerithiacea) in Israel

Population genetic structure in the species of Melanopsis were studied by means of cellulose acetate gel allozyme electrophoresis, on 26 Melanopsis populations from Israel: six of Melanopsis buccinoidea Olivier, 1801, eight of Melanopsis saulcyi Bourguignat, 1853, one of Melanopsis meiostoma Heller et Sivan, 2000 , 11 of Melanopsis costata Olivier, 1804, represented by two subspecies: M. costata costata Olivier, 1804 and M. costata jordanica Roth, 1839. 14 loci (nine polymorphic) were scorable: Aat, Alp, Est-1, Est-2, Gpi, Hbdh, Idh-1, Idh-2, Iddh, Mdh, Mdhp, Mpi, Pgdh, Pgm. Gametic disequilibrium was postulated. D-statistics was computed, indicating limited migration, not epistatic selection as the source of disequilibrium. Exact multilocus and multipopulation tests showed a statistically significant heterozygote deficit in 18 populations and seven polymorphic loci. Inbreeding, Wahlund's effect and codominant mode of selection were postulated as causing homozygote excess. Mantel test indicated a statistically significant association between the pairwise θ and geographic distance, and no association between Nm and the geographic distance. The mean gene flow estimates Nm, derived from either θ or private alleles technique, were consistent. Hierarchical F-statistics showed slight differences between the taxa. The process of speciation within the genus seems not yet completed.     

MATING SYSTEM AND ASYMMETRIC HYBRIDIZATION IN A MIXED STAND OF EUROPEAN OAKS

The sessile (Quercus petraea [Matt.] Liebl.) and pedunculate (Quercus robur L.) oaks are two closely related species having a wide sympatric distribution over Europe. Under natural conditions, they frequently form mixed forests, where hybridization is suspected to occur. In this paper, two different approaches have been applied to the study of the mating system and the interspecific gene flow in a mixed stand formed by the two species. The mating systems of both species have been studied separately by means of the mixed-mating model. The relative contribution of the parental species to the progenies have been estimated with two different methods. The first uses the admixture model. The second is an extension of the mixed-mating model and subdivides the outcrossing rate into intra- and interspecific components. The two species were almost completely outcrossing. This high level of outcrossing and interspecific gene flow could play an important role in the maintenance of the genetic diversity in these long-lived forest tree species. The contribution of the sessile oak to the pedunculate oak progenies varied from 17% to 48%. In contrast, ovules of sessile oak trees appear to be preferentially fertilized by other extreme sessile genotypes. We suggest that interspecific and directional gene flow was responsible for such patterns. Pedunculate oak is considered as a pioneer species and is progressively replaced by sessile oak. Our present findings add a further genetic component to this succession scheme, suggesting that unidirectional gene flow reinforces succession between the two species.     

Shrinking genomes? Evidence from genome size variation in Crepis (Compositae)

Large-scale surveys of genome size evolution in angiosperms show that the ancestral genome was most likely small, with a tendency towards an increase in DNA content during evolution. Due to polyploidisation and self-replicating DNA elements, angiosperm genomes were considered to have a 'one-way ticket to obesity' (Bennetzen & Kellogg 1997). New findings on how organisms can lose DNA challenged the hypotheses of unidirectional evolution of genome size. The present study is based on the classical work of Babcock (1947a) on karyotype evolution within Crepis and analyses karyotypic diversification within the genus in a phylogenetic context. Genome size of 21 Crepis species was estimated using flow cytometry. Additional data of 17 further species were taken from the literature. Within 30 diploid Crepis species there is a striking trend towards genome contraction. The direction of genome size evolution was analysed by reconstructing ancestral character states on a molecular phylogeny based on ITS sequence data. DNA content is correlated to distributional aspects as well as life form. Genome size is significantly higher in perennials than in annuals. Within sampled species, very small genomes are only present in Mediterranean or European species, whereas their Central and East Asian relatives have larger 1C values.