bluuebunny/crossref_metadata_2025 huggingface dataset:
What single‐channel analysis tells us of the activation mechanism of ligand‐gated channels: the case of the glycine receptor
Authors: Sivilotti Lucia G.
Published: September 2009

Glycine receptors are, in several ways, the member of the nicotinic superfamily that is best‐suited for single‐channel recording. That means that they are ideal for testing ideas about how activation proceeds in a ligand‐gated ion channel from the binding of the agonist to the opening of the channel. This review describes the quantitative characterization by single‐channel analysis of a novel activation mechanism for the glycine receptor. The favourable properties of the glycine receptor allowed the first detection of a conformation change that follows the binding of the agonist but precedes the opening of the channel. We used the term ‘flipping’ to describe this pre‐opening conformational change. The ‘flipped’ state has a binding affinity higher than the resting state, but lower than the open state. This increased affinity presumably reflects a structural change near the agonist binding site, possibly the ‘capping’ of the C‐loop. The significance of the ‘flip’ activation mechanism goes beyond understanding the behaviour and the structure–function relation of glycine channels, as this mechanism can be applied also to other members of the superfamily, such as the muscle nicotinic receptor. The ‘flip’ mechanism has thrown light on the question of why partial agonists are not efficacious at keeping the channel open, a question that is fundamental to rational drug design. In both muscle nicotinic and glycine receptors, partial agonists are as good as full agonists at opening the channel once flipping has occurred, but are not as effective as full agonists in eliciting this early conformational change.
Activation of native TRPC1/C5/C6 channels by endothelin‐1 is mediated by both PIP3and PIP2in rabbit coronary artery myocytes
Authors: Saleh Sohag N. , Albert Anthony P. , Large William A.
Published: September 2009

We investigate activation mechanisms of native TRPC1/C5/C6 channels (termed TRPC1 channels) by stimulation of endothelin‐1 (ET‐1) receptor subtypes in freshly dispersed rabbit coronary artery myocytes using single channel recording and immunoprecipitation techniques. ET‐1 evoked non‐selective cation channel currents with a unitary conductance of 2.6 pS which were not inhibited by either ETAor ETBreceptor antagonists, respectively BQ‐123 and BQ788, when administered separately. However, in the presence of both antagonists, ET‐1‐evoked channel activity was abolished indicating that both ETAand ETBreceptor stimulation activate this conductance. Stimulation of both ETAand ETBreceptors evoked channel activity which was inhibited by the protein kinase C (PKC) inhibitor chelerythrine and by anti‐TRPC1 antibodies indicating that activation of both receptor subtypes causes TRPC1 channel activation by a PKC‐dependent mechanism. ETAreceptor‐mediated TRPC1 channel activity was selectively inhibited by phosphoinositol‐3‐kinase (PI‐3‐kinase) inhibitors wortmannin (50 nm) and PI‐828 and by antibodies raised against phosphoinositol‐3,4,5‐trisphosphate (PIP3), the product of PI‐3‐kinase‐mediated phosphorylation of phosphatidylinositol 4,5‐bisphosphate (PIP2). Moreover, exogenous application of diC8‐PIP3stimulated PKC‐dependent TRPC1 channel activity. These results indicate that stimulation of ETAreceptors evokes PKC‐dependent TRPC1 channel activity through activation of PI‐3‐kinase and generation of PIP3. In contrast, ETBreceptor‐mediated TRPC1 channel activity was inhibited by the PI‐phospholipase C (PI‐PLC) inhibitor U73122. 1‐Oleoyl‐2‐acetyl‐sn‐glycerol (OAG), an analogue of diacylglycerol (DAG), which is a product of PI‐PLC, also activated PKC‐dependent TRPC1 channel activity. OAG‐induced TRPC1 channel activity was inhibited by anti‐phosphoinositol‐4,5‐bisphosphate (PIP2) antibodies and high concentrations of wortmannin (20 μm) which depleted tissue PIP2levels. In addition exogenous application of diC8‐PIP2activated PKC‐dependent TRPC1 channel activity. These data indicate that stimulation of ETBreceptors evokes PKC‐dependent TRPC1 activity through PI‐PLC‐mediated generation of DAG and requires a permissive role of PIP2. In conclusion, we provide the first evidence that stimulation of ETAand ETBreceptors activate native PKC‐dependent TRPC1 channels through two distinct phospholipids pathways involving a novel action of PIP3, in addition to PIP2, in rabbit coronary artery myocytes.
Randomized Controlled Study Investigating Viral Suppression and Serological Response following Pre-S1/Pre-S2/S Vaccine Therapy Combined with Lamivudine Treatment in HBeAg-Positive Patients with Chronic Hepatitis B
Authors: Hoa Pham Thi Le , Huy Nguyen Tien , Thu Le The , Nga Cao Ngoc , Nakao Kazuhiko , Eguchi Katsumi , Chi Nguyen Huu , Hoang Bui Huu , Hirayama Kenji
Published: September 2009

The aim of the current study was to evaluate viral suppression following combined treatment with an S/pre-S1/pre-S2 vaccine and lamivudine in patients with chronic hepatitis B. We established a randomized, controlled clinical trial to compare the responses of three different treatment groups: those receiving vaccine monotherapy, lamivudine monotherapy, or combination treatment. Viral response was evaluated via hepatitis B virus (HBV) DNA suppression using different levels of classification. Seroconversion was evaluated via HBeAg loss, HBeAg seroconversion, HBsAg loss, and anti-HBs response. We found that the group receiving combination treatment demonstrated a significant increase in viral suppression over that for the lamivudine or vaccine monotherapy group, although the HBeAg seroconversion rate was not different. This enhanced suppression effect in the combination group was reversed after the discontinuation of vaccine treatment, suggesting that booster doses are required for a sustained viral response. Anti-HBs was detected in 55/120 vaccine recipients, but only 3 patients demonstrated HBsAg loss, indicating that the vaccine-induced anti-HBs was unable to completely neutralize HBsAg in the serum. At the study end point, anti-HBs responders showed significantly higher HBeAg seroconversion rates, greater suppression of HBV DNA levels, and a lower median reduction in HBV DNA levels than those of anti-HBs nonresponders. Our results suggest that combined treatment with the vaccine and lamivudine was significantly more effective than lamivudine monotherapy in the short term and was especially successful in producing viral suppression and an enhanced anti-HBs antibody response.
In Vitro Activities of Piperaquine, Lumefantrine, and Dihydroartemisinin in Kenyan
Plasmodium falciparum
Isolates and Polymorphisms in
p
fcrt
and
p
fmdr1
Authors: Mwai Leah , Kiara Steven M. , Abdirahman Abdi , Pole Lewa , Rippert Anja , Diriye Abdi , Bull Pete , Marsh Kevin , Borrmann Steffen , Nzila Alexis
Published: September 2009

We have analyzed the in vitro chemosensitivity profiles of 115 Kenyan isolates for chloroquine (CQ), piperaquine, lumefantrine (LM), and dihydroartemisinin in association with polymorphisms in
pfcrt
at codon 76 and
pfmdr
1
at codon 86, as well as with variations of the copy number of
pfmdr
1
. The median drug concentrations that inhibit 50% of parasite growth (IC
50
s) were 41 nM (interquartile range [IQR], 18 to 73 nM), 50 nM (IQR, 29 to 96 nM), 32 nM (IQR, 17 to 46 nM), and 2 nM (IQR, 1 to 3 nM) for CQ, LM, piperaquine, and dihydroartemisinin, respectively. The activity of CQ correlated inversely with that of LM (
r
2
= −0.26;
P
= 0.02). Interestingly, parasites for which LM IC
50
s were higher were wild type for
pfcrt
-76
and
pfmdr
1
-
86
. All isolates had one
pfmdr
1
copy. Thus, the decrease in LM activity is associated with the selection of wild-type
pfcrt
-
76
and
pfmdr
1
-
86
parasites, a feature that accounts for the inverse relationship between CQ and LM. Therefore, the use of LM-artemether is likely to lead to the selection of more CQ-susceptible parasites.
The Antituberculosis Drug Pyrazinamide Affects the Course of Cutaneous Leishmaniasis In Vivo and Increases Activation of Macrophages and Dendritic Cells
Authors: Mendez Susana , Traslavina Ryan , Hinchman Meleana , Huang Lu , Green Patricia , Cynamon Michael H. , Welch John T.
Published: September 2009

Antileishmanial therapy is suboptimal due to toxicity, high cost, and development of resistance to available drugs. Pyrazinamide (PZA) is a constituent of short-course tuberculosis chemotherapy. We investigated the effect of PZA on
Leishmania major
promastigote and amastigote survival. Promastigotes were more sensitive to the drug than amastigotes, with concentrations at which 50% of parasites were inhibited (MIC
50
) of 16.1 and 8.2 μM, respectively (48 h posttreatment). Moreover, 90% of amastigotes were eliminated at 120 h posttreatment, indicating that longer treatments will result in parasite elimination. Most strikingly, PZA treatment of infected C57BL/6 mice resulted in protection against disease and in a 100-fold reduction in the parasite burden. PZA treatment of J774 cells and bone marrow-derived dendritic cells and macrophages increased interleukin 12, tumor necrosis factor alpha, and activation marker expression, as well as nitric oxide production, suggesting that PZA enhances effective immune responses against the parasite. PZA treatment also activates dendritic cells deficient in Toll-like receptor 2 and 4 expression to initiate a proinflammatory response, confirming that the immunostimulatory effect of PZA is directly caused by the drug and is independent of Toll-like receptor stimulation. These results not only are strongly indicative of the promise of PZA as an alternative antileishmanial chemotherapy but also suggest that PZA causes collateral immunostimulation, a phenomenon that has never been reported for this drug.
Antiapoptotic Proteins Bcl-2 and Bcl-X
L
Inhibit
Clostridium difficile
Toxin A-Induced Cell Death in Human Epithelial Cells
Authors: Matte Isabelle , Lane Denis , Côté Élodie , Asselin Ann-Élise , Fortier Louis-Charles , Asselin Claude , Piché Alain
Published: September 2009

It has been well established that
Clostridium difficile
toxin A (TcdA) induces cell death in human epithelial cells. However, the mechanism of TcdA-induced cell death remains to be fully characterized. Here, we show that TcdA induces dose-dependent cell death in ovarian carcinoma and colonic carcinoma cell lines. TcdA-mediated cell death, as well as caspase 8 and caspase 3 activation, were specifically abrogated by anti-toxin antibodies. Although caspase 8 and caspase 3 were activated by TcdA in OVCAR3 ovarian carcinoma and T84 colonic cancer cells, pancaspase and caspase 8, 3, and 9 inhibitors did not block TcdA-induced cell death. In contrast, tumor necrosis factor-related apoptosis-inducing ligand-induced cell death was nearly completely blocked by caspase inhibitors in OVCAR3 cells. In these cells, TcdA induces the mitochondrial pathway of apoptosis, as demonstrated by changes in mitochondrial outer membrane permeabilization (MOMP). Furthermore, overexpression of the antiapoptotic proteins Bcl-2 and Bcl-X
L
significantly inhibited TcdA-induced cell death, as well as TcdA-induced MOMP. Conversely, small interfering RNA-mediated inhibition of Bcl-X
L
in TcdA-resistant SKOV3ip1 cells enhanced TcdA-induced cell death. Overexpression of the antiapoptotic proteins Bcl-2 and Bcl-X
L
in T84 cells also inhibited TcdA-induced cell death. Altogether, our data demonstrate that TcdA induces cell death in both ovarian and colonic cancer cells preferentially via the mitochondrial pathway of apoptosis by a death receptor-independent and a caspase-independent mechanism. This process is regulated by antiapoptotic members of the Bcl-2 family.
Toll-Like Receptor Signaling in Airborne
Burkholderia thailandensis
Infection
Authors: West T. Eoin , Hawn Thomas R. , Skerrett Shawn J.
Published: September 2009

Melioidosis is a tropical disease endemic in southeast Asia and northern Australia caused by the gram-negative soil saprophyte
Burkholderia pseudomallei
. Although infection is often systemic, the lung is frequently involved.
B. thailandensis
is a closely related organism that at high doses causes lethal pneumonia in mice. We examined the role of Toll-like receptors (TLRs), essential components of innate immunity, in vitro and in vivo during murine
B. thailandensis
pneumonia. TLR2, TLR4, and TLR5 mediate NF-κB activation by
B. thailandensis
in transfected HEK293 or CHO cells. In macrophages, TLR4 and the adaptor molecule MyD88, but not TLR2 or TLR5, are required for tumor necrosis factor alpha production induced by
B. thailandensis
. In low-dose airborne infection, TLR4 is needed for early, but not late, bacterial containment, and MyD88 is essential for control of infection and host survival. TLR2 and TLR5 are not necessary to contain low-dose infection. In high-dose airborne infection, TLR2 deficiency confers a slight survival advantage. Lung and systemic inflammatory responses are induced by low-dose inhaled
B. thailandensis
independently of individual TLRs or MyD88. These findings suggest that redundancy in TLR signaling or other MyD88-dependent pathways may be important in pneumonic
B. thailandensis
infection but that MyD88-independent mechanisms of inflammation are also activated. TLR signaling in
B. thailandensis
infection is substantially comparable to signaling induced by virulent
B. pseudomallei
. These studies provide additional insights into the host-pathogen interaction in pneumonic
Burkholderia
infection.
OmpA of Uropathogenic
Escherichia coli
Promotes Postinvasion Pathogenesis of Cystitis
Authors: Nicholson Tracy F. , Watts Kristin M. , Hunstad David A.
Published: September 2009

Type 1 pilus directs bladder epithelial binding and invasion by uropathogenic
Escherichia coli
(UPEC) in the initial stage of cystitis, but the bacterial determinants of postinvasion events in the pathogenesis of cystitis are largely undetermined. We show here that the UPEC outer membrane protein A (OmpA), a monomeric, major, integral protein component of the bacterial outer membrane, functions as a critical determinant of intracellular virulence for UPEC, promoting persistent infection within bladder epithelium. Using a murine urinary tract infection (UTI) model, we demonstrate that whereas deletion of the UPEC
ompA
gene did not disrupt initial epithelial binding and invasion by UPEC, it did preclude completion of the intracellular bacterial community (IBC) pathway, accompanied by diminishing bacterial loads in the bladder. This defect in epithelial persistence of the
ompA
mutant was enhanced in competitive infections with wild-type UPEC. Microscopic examinations revealed that the
ompA
mutant formed significantly fewer IBCs, and those that were initiated were unable to progress past the early stages of maturation. These defects could be corrected by complementation of
ompA
. In addition, expression of
ompA
during wild-type UTI was sharply increased at time points correlated with IBC development and the arrival of host immune effector cells. Our findings establish OmpA as a key UPEC virulence factor that functions after epithelial invasion to facilitate IBC maturation and chronic bacterial persistence.
Bacterial Growth Rate and Host Factors as Determinants of Intracellular Bacterial Distributions in SystemicSalmonella entericaInfections
Authors: Grant Andrew J. , Foster Gemma L. , McKinley Trevelyan J. , Brown Sam P. , Clare Simon , Maskell Duncan J. , Mastroeni Pietro
Published: September 2009

Bacteria of the speciesSalmonella entericacause a range of life-threatening diseases in humans and animals worldwide. The within-host quantitative, spatial, and temporal dynamics ofS. entericainteractions are key to understanding how immunity acts on these infections and how bacteria evade immune surveillance. In this study, we test hypotheses generated from mathematical models of in vivo dynamics ofSalmonellainfections with experimental observation of bacteria at the single-cell level in infected mouse organs to improve our understanding of the dynamic interactions between host and bacterial mechanisms that determine net growth rates ofS. entericawithin the host. We show that both bacterial and host factors determine the numerical distributions of bacteria within host cells and thus the level of dispersiveness of the infection.
Rhodococcus equiVirulence-Associated Protein A Is Required for Diversion of Phagosome Biogenesis but Not for Cytotoxicity
Authors: von Bargen Kristine , Polidori Marco , Becken Ulrike , Huth Gitta , Prescott John F. , Haas Albert
Published: September 2009

Rhodococcus equiis a gram-positive facultative intracellular pathogen that can cause severe bronchopneumonia in foals and AIDS patients. Virulence is plasmid regulated and is accompanied by phagosome maturation arrest and host cell necrosis. A replacement mutant in the gene for VapA (virulence-associated protein A), a major virulence factor ofR. equi, was tested for its activities during macrophage infection. Early in infection, phagosomes containing thevapAmutant did not fuse with lysosomes and did not stain with the acidotropic fluor LysoTracker similar to those containing virulent wild-typeR. equi. However,vapAmutant phagosomes had a lower average pH. Late in infection, phagosomes containing thevapAmutant were as frequently positive for LysoTracker as phagosomes containing plasmid-cured, avirulent bacteria, whereas those with virulent wild-typeR. equiwere still negative for the fluor. Macrophage necrosis after prolonged infection with virulent bacteria was accompanied by a loss of organelle staining with LysoTracker, suggesting that lysosome proton gradients had collapsed. ThevapAmutant still killed the macrophages and yet did not affect the pH of host cell lysosomes. Hence, VapA is not required for host cell necrosis but is required for neutralization of phagosomes and lysosomes or their disruption. This is the first report of anR. equimutant with altered phagosome biogenesis.
Particulate Phosphorus Dynamics in Headwater Streams
Authors: Prairie Yves T. , Kalff Jacob
Published: September 2009

We examined the dynamics of particulate phosphorus (PP) in seven headwater streams of southern Quebec draining catchments differing in size, extent of forest cover, and stream channel gradient. The extent of forest cover can be used to predict average [PP]. The magnitude of the temporal fluctuations (variance) in [PP] was strongly related to mean levels. While most streams showed positive relationships between discharge and [PP] in rain events, inverse relations were observed in two streams and possibly the result of the rapid exhaustion of PP. Inverse relationships were also seen in these two streams for samples collected outside rain events. We present a model based on channel gradient and extent of forest cover to predict the slope coefficient of [PP]–discharge relationships and also the occurrence of very rapid exhaustion. We then extend this model to include the influence of precipitation history and catchment size on [PP] in headwater streams. This model accounted for 60% of the variation of the pooled observations from all seven streams and is comparable in predictive power with stream-specific models published elsewhere in the literature.
Influence of Lake Morphometry on the Response of Submerged Macrophytes to Sediment Fertilization
Authors: Duarte Carlos M. , Kalff Jacob
Published: September 2009

The influence of lake morphometry on the growth of submerged macrophytes in response to sediment fertilization was studied at sites of varying bottom slope (steep to gentle), wave exposure (high to low), and depth (1.0 and 2.5 m) in Lake Memphremagog (Quebec–Vermont). The biomass increases were on average 2.1 times greater for fertilized plants than for the paired controls. The extent of the growth response was greatest at the 1.0-m sites. The smaller response at the 2.5-m sites was further decreased as exposure to waves increased. The smaller response at 2.5 m (depth of maximum biomass) suggests that factors such as light limitation, length of the growing season, and littoral slope, but not sediment nutrient levels, limit submerged biomass there. The importance of the physical factors appears to increase as the biomass increases. "Overwintering" plants showed greater response to fertilization than those growing from seeds. Overall, the extent of the growth response to sediment fertilization depends on the energy environment (i.e. depth, wave exposure, and slope) of the littoral. The influence of these physical factors explains previous difficulties in finding strong correlations between nutrient levels and the growth of submerged macrophytes.
Sequential Decision Plans in Monitoring Benthic Macroinvertebrates: Cost Savings, Classification Accuracy, and Development of Plans
Authors: Jackson John K. , Resh Vincent H.
Published: September 2009

Sequential decision plans provide a statistical approach that can reduce the number of benthic sample units needed to classify a site as impacted or unimpacted, thus reducing the cost of using benthic macroinvertebrates in water quality assessment programs. These plans require information about unimpacted and impacted conditions, the mathematical distribution of the data, and acceptable risks of classification error. A large benthic data set (n = 55) was used for simulations that created and tested sequential decision plans. Using 10–60% reductions in species richness, mayfly (Cinygmula) population density, and species diversity as definitions of impact in the simulations, the average number of sample units processed for identification of the unimpacted reference site was reduced (compared with fixed sample-size methods that are commonly used) by 50–64% for species richness, 59–79% for density estimates, and 51–55% for species diversity. Unimpacted data sets were initially classified as representing impacted conditions in 0–5% of the cases. If classifications are to be interpreted properly, sampling error and spatial and temporal variation in biological parameters must be considered when sequential decision plans are created.
Relationships Between Concentrations of Sedimentary Variables and Trophic State in Florida Lakes
Authors: Brenner Mark , Binford Michael W.
Published: September 2009

Midlake sediment samples from 97 Florida lakes were analyzed for organic matter (LOI 550 °C), carbonate (LOI 550–990 °C), total C, N, and P, and pigment (SCDU665) content. We used simple correlation and multiple regression to examine relationships between concentrations of selected sediment constituents, or their ratios, and trophic state (Carlson's TSI) of the overlying waters. Simple concentrations of sediment variables are poor predictors of TSI. The best simple correlation relates N per gram of organic matter to TSI–Chl a but explains only 27% of the variance in trophic state. The best multiple regression model incorporates five independent sediment variables and accounts for 43% of the variance in TSI–Chl a. Reasons for the poor relationships include (1) interlake variation in the dilution of organic matter and pigments by allochthonous inorganics, (2) variation among lakes in the diagenesis of surface sediments, (3) differential contributions of insoluble, large particulate, inorganic P, and (4) failure of open-water TSI measures to account for contributions to sediments from littoral and allochthonous sources.
Influence of Seasonal River Discharge on Survival of Juvenile Atlantic Salmon Salmo Salar
Authors: Gibson R. J. , Myers R. A.
Published: September 2009

The effects of winter and summer river discharge on the survival of eggs and underyearlings of Atlantic salmon (Salmo salar) were examined in six rivers of Newfoundland and New Burnswick where stock–recruitment relationships were available. There were positive relationships between either winter discharge or temperature and survival of underyearling salmon for five rivers. For all rivers combined, survival and winter discharge were related (P < 0.05). The hypothesis that summer discharge was unrelated to survival could not be rejected. However, there was evidence that summer discharge enhances survival in the Miramichi and Northwest Miramichi rivers of New Brunswick.
Potential Contribution of Natural Hydrocarbon Seepage to Benthic Productivity and the Fisheries of Atlantic Canada
Authors: Levy E. M. , Lee K.
Published: September 2009

Bacterial processes involving methane and other low molecular weight hydrocarbons may be a substantial contribution to the overall benthic productivity in areas where natural seepage from the seabed occurs. This process may be sufficiently extensive on the continental shelf off the east coast of Canada to be of importance to the fishery.
Seasonal and Interannual Variability of Current, Temperature and Salinity off Southwest Nova Scotia
Authors: Smith Peter C.
Published: September 2009

Strong annual signals are found in temperature, salinity, and current measurements at two sites off Cape Sable, Nova Scotia. Differences in means and annual cycles indicate that the along-isobath current is not controlled by wind stress at these time scales. The phase of the primary peak of freshwater runoff into the Gulf of St. Lawrence (RIVSUM) is consistent with the advection of a salinity minimum to Cape Sable at an average speed of 6 km∙d−1, but the secondary peak is not observed and may be masked by the seasonal inflow of slope water into the Gulf of Maine via Northeast Channel. A diffusive model, forced by air–sea interaction, provides a reasonable fit to the annual temperature cycles with vertical diffusivities of 15–50 × 10−4 m2∙s−1. Correlations between residual longshore wind stress and along-isobath current, deep salinity, and temperature are consistent with wind-driven upwelling. Furthermore, warm-core rings in the slope water sometimes enhance onshore heat and salt fluxes to create positive temperature and salinity anomalies off Cape Sable, especially in late summer. February ocean temperature anomalies to 50 m are related to winter-average cross-shore wind (and related heat flux residuals), but do not persist on seasonal time scales.
Particle Drift in the Surface Layer off Southwest Nova Scotia; Description and Evaluation of a Model
Authors: Page Fred H. , Smith Peter C.
Published: September 2009

A two-dimensional (horizontal) surface layer particle dispersion model for the Southwest Nova Scotia region is described and evaluated. The model is based on a barotropic M2 tidal model and wind-driven response model. It includes a constant residual current field plus time varying M2 tidal and wind-driven currents. Tidal currents are shown to cause particle trajectories to vary with the time of particle release. Constant winds are shown to have an important influence on particle trajectories, although periodic winds have little effect. Comparisons between simulated particle trajectories and satellite-tracked drogue trajectories show the model can qualitatively reproduce drogue trajectories on the western, but not on the eastern portion of Browns Bank. However, the model consistently underestimates the observed displacements. These discrepancies are probably due to (1) unmodeiled baroclinic components of the circulation and/or (2) the inability of the model to resolve strong topographic gradients and the resulting rectified currents over the steep flanks of the Bank. The use of a previous empirically-defined circulation does not significantly improve the model's performance.
Stage Dependent Vertical Distribution of Haddock (Melanogrammus aeglefinus) Eggs in a Stratified Water Column: Observations and Model
Authors: Page Fred H. , Frank Kenneth T. , Thompson Keith R.
Published: September 2009

The depth distribution of four development stages of haddock (Melanogrammus aeglefinus) eggs was measured during May 1984 in a continuously stratified water column over Browns Bank. The egg profile varied with development. Early stage eggs were most concentrated near the sea surface whereas late stage eggs were distributed uniformly over depth or had a subsurface maximum. In order to explain the shape of these profiles a one-dimensional (vertical) advection–diffusion model including density stratification was used. Model egg profiles compared favourably with observed profiles and indicate that a large proportion (>30%) of haddock eggs are below the Ekman depth (δe. This proportion increases as the eggs develop. For example more than 50% of the stage III and IV eggs are below δe. Surface drift bottles and other indicators of the very near surface wind-driven transport would appear to be poor indicators of egg transport in haddock and possibly several other species, such as Atlantic cod (Gadus morhua) and mackerel (Scomber scombrus).
Survival and Abundance of Young Atlantic Cod (Gadus morhua) and Haddock (Melanogrammus aeglefinus) as Indicators of Year-class Strength
Authors: Campana Steven E. , Frank Kenneth T. , Hurley Peter C. F. , Koeller Peter A. , Page Fred H. , Smith Peter C.
Published: September 2009

To identify the life history stage(s) most influential in determining yearclass strength, we constructed and analyzed survival curves of the 1983, 1984, and 1985 cohorts of cod and haddock off Southwest Nova Scotia relative to their physical and biological environment. Relative abundance of each Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) yearclass was not reflected by egg or larval abundance in any year examined. However, abundance of both pelagic and settled juveniles did appear to reflect yearclass strength. Egg and larval mortality could not be consistently linked with advection from the spawning site, and did not covary with subsequent recruitment. In both species, mortality between the larval and juvenile stage was inversely correlated with yearclass strength, but sources of the mortality could not be identified. Larval growth was inversely related to mortality of the early larval stage and independent of larval abundance. However, juvenile growth was proportional to mortality and inversely related to abundance. Despite early life coexistence and similarities in spawning time and location, the relative yearclass strengths of cod and haddock in Southwest Nova Scotia were different, suggesting that the timing of local physical and biological events may play an important role in the recruitment success of these stocks.
Modelling the Initiation of Spring Phytoplankton Blooms: a Synthesis of Physical and Biological Interannual Variability off Southwest Nova Scotia, 1983–85
Authors: Perry R. Ian , Hurley Peter C. F. , Smith Peter C. , Koslow J. Anthony , Fournier Robert O.
Published: September 2009

Chlorophyll and nitrate data from monthly surveys off southwest Nova Scotia indicate the spring phytoplankton bloom began near the end of March of each year, occurring early (late) in 1984 (1983). The highest chlorophyll biomass(all months) was found in 1985. Using survey data, the Sverdrup hypothesis for the initiation of the bloom was tested by comparing the critical depth, Zcr, for net phytoplankton production to the observed mixed-layer depth, Zmix. Survey median Zcr/Zmix were consistently less than 1 until May, suggesting that observed blooms were initiated by events outside the specific survey periods. Results of a mixed-layer model incorporating surface heating, differential advection and turbulent dissipation by wind and tide showed reasonable agreement with observed mixed depths, and patterns of the mean (modelled) mixed-layer light intensity are significantly correlated with observed chlorophyll biomass. In 1983 and 1984, mean light intensities first exceeded the critical value for a bloom to occur in late March. In 1985, transient periods of stratification in mid-February and early March produced intensities greater than the critical value. These events, together with higher nitrate concentrations and lower Zooplankton biomass, appear to be responsible for the high chlorophyll biomass observed in 1985.
Periphyton Responses to Higher Trophic Levels and Light in a Shaded Stream
Authors: Hill Walter R. , Harvey Bret C.
Published: September 2009

The effects of higher trophic levels on benthic primary producers were examined in the context of light limitation in a shaded headwater stream. Abundance (presence or absence) of a predatory fish Semotilus atromaculatus and a grazing snail Elimia clavaeformis were manipulated with in situ Plexiglas channels, while spatial variability in ambient light was related to variability in primary productivity among channels. Indirect effects of fish on periphyton were insignificant, possibly because grazers that are vulnerable to fish predation were scarce during the experiment, or because fish preyed upon other predators of grazers. Snails had compensatory effects within the periphyton: they diminished biomass and productivity in the loosely attached layer, but stimulated productivity in the tightly attached layer. Snails appeared to mitigate shading of the tightly attached layer by the loosely attached layer. Benthic primary productivity was highly correlated with ambient light levels, accounting for 42% of the variability in total (loosely and tightly attached layers combined) primary productivity. Multiple regression analysis indicated that fish and snail effects on total primary productivity were minor compared to light effects. These results suggest that light availability controls realized as well as potential production in this unproductive stream.
Migratory Catch-Age Analysis
Authors: Quinn II Terrance J. , Deriso Richard B. , Neal Philip R.
Published: September 2009

We review techniques for estimating the abundance of migratory populations and develop a new technique based on catch-age data from geographic regions and our earlier technique, catch-age analysis with auxiliary information (Deriso et al. 1985, 1989). Data requirements are catch-age data over several years, some auxiliary information, and migration rates among regions. The model, containing parameters for year-class abundance, age selectivity, full-recruitment fishing mortality, and catchability, is fitted to data with a nonlinear least squares algorithm. We present a measurement error model and a process error model and favor the process error model because all model parameters can be jointly estimated. By application to data on Pacific halibut, the process error model converges readily and produces estimates with no significant bias. These estimates have relatively high precision compared to those from analyses which did not incorporate migration information. The error structure used in a model has a more significant impact on parameter estimates than migration rates. A sensitivity study of migration rates shows sensitivity of the order of the rates themselves.
Effects of Diet or Liming on Steroid Hormone Metabolism and Reproduction in Atlantic Salmon (Salmo salar) Held in an Acidic River
Authors: Sangalang G. B. , Freeman H. C. , Uthe J. F. , Sperry L. S.
Published: September 2009

Attempts to avert the impacts of an acidic river environment on Atlantic salmon (Salmo salar) were carried out in 1985 and 1986. Salmon were held in the Westfield River (pH 4.7–5.2) and the nearby Medway River (pH 5.3–5.6) during their sexual maturation. A diet containing 3% NaCl was fed to the Westfield salmon in 1985. Marble chips were used to elevate the pH of Westfield River water in 1986. Fish fed the salt diet had higher peak levels of plasma sex hormones, higher fecundity, greater incidence of spawners, lower egg mortality, and less weight loss than fish fed a commercial trout diet. The reproductive performance of fish held in limed water (pH 5.1–5.9) almost attained the level observed in the Medway (control) fish. Limestone treatment stimulated early peaking of blood androgen levels, testosterone, and 11-ketotestosterone in Westfield males, and 17α, 20β-dihydroxy-4-pregnen-3-one, a follicular mediator of gonadotropin, in a few Westfield females. The head kidneys produced more cortisol and corticosterone in all Westfield fish in both years compared to Medway fish. The results suggest that neither dietary salt nor liming completely prevented the decline of reproductive performance and the alteration of steroid hormone metabolism in salmon.
Morphometric Effects of Low pH and Limed Water on the Gills of Atlantic Salmon (Salmo salar)
Authors: Jagoe Charles H. , Haines Terry A.
Published: September 2009

Gills from adult Atlantic salmon held in water from an acid river (Westfield River, Queens County, Nova Scotia; mean pH 4.8) were compared to gills from fish held in the same water treated with limestone (mean pH 5.5) and gills from fish held in a nearby control river (Medway River; mean 5.4). Morphometric analysis showed that fish held in the acidic water had more gill chloride cells and mucous cells than those held in the limed water or the control river. The difference in chloride cell number was due to increased numbers of the cells on the primary lamellar epithelium; numbers of cells on the secondary lamellae did not increase with acid exposure. Male fish were found to have more chloride cells on their secondary lamellae than female fish. Chloride cells were larger and more nearly spherical in shape in the fish exposed to low pH water. The liming treatment was partially effective in preventing changes in gill histology. Changes in size, shape, and number of chloride cells probably represent a response of increasing ionic uptake to offset the losses of ions occurring during low pH stress.
Onshore Movements of Atlantic Mackerel (Scomber scombrus) in the Northern Gulf of St. Lawrence: Associations with Wind-Forced Advections of Warmed Surface Waters
Authors: Castonguay Martin , Rose George A. , Leggett William C.
Published: September 2009

We employed fisheries acoustic techniques to assess the distribution and relative abundance of Atlantic mackerel (Scomber scombrus) at high resolution at Brador Bay in the northern Gulf of St. Lawrence in 1985 and 1986. These data were used to test the hypotheses that (1) onshore movements of mackerel are associated with wind-forced advections of heated surface waters and (2) mackerel are confined to waters having temperatures [Formula: see text]. Increased mackerel densities or "mackerel events" followed landward advections of heated surface waters in both 1985 and 1986. Landward advections of surface waters, and mackerel events, followed alongshore wind stress from the northeast. In our daytime observations, mackerel tended to concentrate in waters having temperatures of approximately 4 °C, near bottom, beneath warmer surface waters. However, the overall probability of mackerel occurrence inshore was much greater when near-bottom waters were warmer [Formula: see text]. Mackerel densities were not correlated with salinities, cross-shore winds, or currents but were negatively correlated with Atlantic cod (Gadus morhua) densities within the study site.
Acute Handling Stress Alters Hepatic Glycogen Metabolism in Food-Deprived Rainbow Trout (Oncorhynchus mykiss)
Authors: Vijayan M. M. , Moon T. W.
Published: September 2009

Acute handling stress resulted in significant elevation of plasma cortisol and lactate concentrations within 30 min in both fed and food-deprived rainbow trout (Oncorhynchus mykiss), indicating a typical stress response. Plasma glucose levels rose immediately (30 min) poststress in the food-deprived group, while there was a delayed response (2 h) in the fed group. The low liver glycogen content and total glycogen phosphorylase (GPase) and glycogen synthase (GSase) activities in the food-deprived group indicated an overall depression in glycogen metabolism. Acute handling stress maintained liver glycogen stores for up to 4 h in the food-deprived group, but the combined effects of limited substrate and increased energy demand necessitated mobilization of liver glycogen in the food-deprived group, but not in the fed group. This increased glycogen mobilization in the food-deprived group coincided with a secondary elevation in plasma cortisol concentration 4 h poststress. The results indicated that food-deprived rainbow trout were more sensitive to stress of handling and mobilized glycogen stores to meet the energy demand imposed by the stressor. The elevated plasma cortisol levels noted during acute handling stress could play an important role in energy partitioning, metabolically adapting the fish to handling stress.
Influence of Dietary Protein and Lipid on Nitrogen and Energy Losses in Lake Trout,Salvelinus namaycush
Authors: Jayaram Muthanna G. , Beamish F. W. H.
Published: September 2009

Nitrogen and energy loss in fecal and nonfecal excretions by lake trout, Salvelinus namaycush (171–268 g), varied directly with dietary protein (40 and 50% dry weight) and inversely with lipid (10 and 20%) among four test diets. Diets high in lipid increased dry matter digestibility resulting in reduced nitrogen and energy loss in feces. NH3-N constituted 74.0–93.0% of total N excreted in fasted (4–12 d) and fed trout, while urea-N constituted 4.6–17.8% of total N. Excretion of urea-N was high in fish fed the high-lipid diet, particularly when dietary protein was also high. Total N and NH3-N excretion rose to peak values between 4 and 12 h after feeding and thereafter declined to prefeeding levels by 24 h. Urea-N excretion rates varied significantly following ingestion of all but one (50% protein, 20% lipid) test diet, reaching peak values between 4 and 12 h. In fasted fish, total N and NH3-N excretions were significantly low and failed to show a daily pattern; the urea-N excretion rate was significantly high compared with fish fed diets 1, 2, and 3 and followed a daily pattern of change. On average, a larger proportion (13–25%) of food energy is lost through nitrogenous excretion than in the feces (8–22%).
Life Cycle Patterns, Density, and Frequency of Deformities in Chironomus Larvae (Diptera: Chironomidae) over a Contaminated Sediment Gradient
Authors: Urk Geert van , Kerkurm Frans C. M. , Smit Henk
Published: September 2009

Along a gradient of contamination in Lake Vossemeer (where contaminated sediments from the River Rhine are deposited out), Chironomus cf. plumosus larvae occurred at lower population densities and with higher frequencies of deformities as the contamination levels increased. At the least polluted sites, the frequency of larval deformities was elevated only slightly compared with reference levels. At these sites, C. cf. plumosus had a bivoltine life cycle and overwintered in the fourth larval instar stage. At moderately contaminated sites, the percentage of prepupal larvae was significantly lower in spring and the development of pupae delayed by 2 wk. At heavily contaminated sites, larval densities were strongly reduced and no pupae were observed at all. Under such conditions, population density seems to be a suitable additional indicator of toxic stress. The frequency of deformed larvae was higher from November to April than from July to October. Maximum frequencies were observed during emergence of the overwintering generation, suggesting that the period between February and April may be the most suitable period for the assessment of this parameter.
Effects of Sediment Transport on Survival of Salmonid Embryos in a Natural Stream: A Simulation Approach
Authors: Lisle Thomas E. , Lewis Jack
Published: September 2009

A model is presented that simulates the effects of streamflow and sediment transport on survival of salmonid embryos incubating in spawning gravels in a natural channel. Components of the model include a 6-yr streamflow record, an empirical bedload-transport function, a relation between transport and infiltration of sandy bedload into a gravel bed, effects of fine-sediment infiltration on gravel properties, and functions relating embryo survival to gravel properties. High-flow events drive temporal variations in survival; cross-channel variations in bedload transport cause spatial variations. Expected survival, as a result, varies widely from year to year and between spawning runs in a single year. Alternative functions from previous research that relate survival to fine-sediment concentration in spawning gravel and to intergravel rates of flow yield categorically different results. The relative uncertainty of the components of this model indicates that the greatest research needs are to understand how sediment transport affects the intergravel environment and how these changes affect embryo development and survival.
Patterns in Coastal Migration and Stock Structure of Capelin (Mallotus villosus)
Authors: Nakashima Brian S.
Published: September 2009

Approximately 57 500 mature capelin (Mallotus villosus) were tagged with external tags from 1983 to 1988 along the southeast and east coasts of Newfoundland to determine inshore migration patterns and to reexamine the current belief that two separate capelin stocks spawn on east coast beaches. Capelin released in a particular bay were recaptured from the same bay or locations further north. Upstream migration using the Labrador Current was hypothesized as a directional clue to the prespawning migration. Capelin caught in one stock area were recaptured in another area, indicating that mature capelin from the Northeast Newfoundland – Labrador and Northern Grand Bank – Avalon stocks mix and migrate north together. The distribution and mixture of pre-spawning fish inshore as described by tag returns have implications on how capelin resources should be surveyed, assessed, and managed.
ROUGH VOLTERRA EQUATIONS 1: THE ALGEBRAIC INTEGRATION SETTING
Authors: DEYA AURÉLIEN , TINDEL SAMY
Published: September 2009

We define and solve Volterra equations driven by an irregular signal, by means of a variant of the rough path theory called algebraic integration. In the Young case, that is for a driving signal with Hölder exponent γ > 1/2, we obtain a global solution, and are able to handle the case of a singular Volterra coefficient. In case of a driving signal with Hölder exponent 1/3 < γ < 1/2, we get a local existence and uniqueness theorem. The results are easily applied to the fractional Brownian motion with Hurst coefficient H > 1/3.
EVALUATION AND MINIMIZATION OF GEOMETRIC RECONSTRUCTION ERRORS IN FEM MODELS GENERATED FROM CT-SCAN IMAGES
Authors: BOCCACCIO ANTONIO , LAMBERTI LUCIANO , PAPPALETTERE CARMINE , QUAGLIARELLA LIVIO
Published: September 2009

CAD reconstruction of anatomical regions from computerized tomography (CT) scans is a very common approach in orthopaedic biomechanics. The CAD model is discretized into finite volume sub-domains and finite element (FE) analyses are performed in order to predict the distribution of stresses generated by applied loads. However, quality and reliability of numerical results depend on the level of accuracy reached in the meshing process. This paper analyzes some critical parameters that may affect the overall efficiency of the CT–FEM transformation process: scan threshold range, object size, and complexity. An optimization procedure for minimizing geometric errors on size and shape of reconstructed objects is presented. Finally, accuracy of stress predictions is evaluated for FE models that include known amounts of geometric errors. Compression and bending loads are considered. Results show that geometric and stress errors rapidly decrease as the objects to be reconstructed become larger in size. Optimal threshold ranges can be identified clearly for both an epoxy-resin benchmark model and a real bone specimen cut from a human lumbar vertebra. This allows geometric errors to be reduced significantly.
A NOTE ON HILBERT TERNARY ALGEBRAS
Authors: Bahmani Fatemeh
Published: September 2009

We show that every simple abelian real Hilbert ternary algebra is isomorphic to the algebra of Hilbert-Schmidt operators between two real, complex or quaternionic Hilbert spaces, up to a positive multiple of the inner product.
A COLLECTION OF PROBLEMS ON SPECTRALLY BOUNDED OPERATORS
Authors: Mathieu Martin
Published: September 2009

We discuss several open problems on spectrally bounded operators, some new, some old, adding in a few new insights.