bluuebunny/crossref_metadata_2025 huggingface dataset:
The Evolution of Life History Parameters in Teleosts
Authors: Roff Derek A.
Published: November 2009

Empirical studies have shown that in teleosts there is a significant correlation between the life history parameters, age at first reproduction, natural mortality, and growth rate. In this paper 1 hypothesize that these correlations are the result of evolutionary adjustments due to the trade-off between reproduction, growth, and survival. A simple and reasonable assumption is that the costs of reproduction are sufficient to cause the ltmt function to decrease. A simple expression relating the age at first reproduction is derived from this assumption. This formula accounts for a statistically significant portion (60.6%) of the variation in age at first reproduction in 30 stocks of fish. To extend the model to predict the distribution of life history parameters across all teleosts, an explicit cost function is incorporated. The model is analyzed with respect to two fitness measures, the expected lifetime fecundity and malthusian parameter, r. In the first case it is shown that the optimal age at maturity, T, depends only on the natural mortality rate (M) and the growth rate (k). In the second case, T is a function of k and the logarithm of a parameter, In C; the latter is a product of egg and larval survival, maximum body length (Lx), and the proportionality coefficient of the fecundity/length function. Difficulties of measuring egg and larval survival make the testing of the latter case difficult for particular species. However, this method provides a simple formula for the computation of r; this is shown generally to be approximately zero, thereby adding strength to the assumptions of the first analysis. The distribution patterns of T on k and M on k are predicted and compared with the observed pattern. In general, the predictions are validated: however, certain combinations of k and ln C are shown to occur very infrequently. The prediction of such "empty" regions of the parameter space remains a challenge for future development of life history theory.
An Analysis of Morphometric Characters of Greenland Halibut (Reinhardtius hippoglossoides) in the Northwest Atlantic Using a Multivariate Analysis of Covariance
Authors: Bowering W. R.
Published: November 2009

Eleven morphometric characters were measured on samples of Greenland halibut (Reinhardtius hippoglossoides) from eight different areas of high Greenland halibut abundance throughout the Northwest Atlantic from Davis Strait to the northern Grand Bank. These data were then analysed using a multivariate analysis of covariance technique with the aim of using the results to delineate Greenland halibut stocks throughout the study area. The results suggested that each area examined may very well support a separate stock. However, given the state of knowledge of this resource, this was not believed to be truly the case. Alternative explanations for the results are discussed.
Estimating Stock Composition of Migrating Juvenile Fraser River (British Columbia) Sockeye Salmon, Oncorhynchus nerka, Using Parasites as Natural Tags
Authors: Bailey R. E. , Margolis L. , Groot C.
Published: November 2009

Simulated mixtures of juvenile sockeye salmon (Oncorhynchus nerka) were constructed using parasite data to represent proportionally the major component stocks of Fraser River and Lake Washington sockeye migrating within the Strait of Georgia, British Columbia, in 1982–84. Samples of migrating juveniles were also collected from Bedwell Harbour, South Pender Island, British Columbia, each year and analyzed for parasites and stock composition. The compositions of simulated and sample mixtures were estimated using a maximum likelihood stock composition model. Simulated mixture compositions were accurately estimated for most stocks for all year-classes. When significant misassignment occurred between stocks, the stocks were analyzed as a complex using the allocate-sum procedure. Sample mixture estimates correctly identified the dominant stock for each year-class, although for 1984 the dominant group was determined as a complex of three stocks because the individual stocks were not distinguishable. The results indicate that it is feasible to use parasites as natural tags to estimate stock compositions of migrating juvenile sockeye salmon in the Strait of Georgia.
Precision of Acoustic Fish Stock Estimates
Authors: MacLennan D. N. , MacKenzie I. G.
Published: November 2009

We derive efficient estimators of Q, the total fish quantity in an area sampled by acoustic survey, and the variance of Q. The estimators are valid when autocorrelation is insignificant, the nonzero samples have stationary statistics, and the distribution of the nonzero samples is normalised by a power transformation. Zero samples are treated separately, thus avoiding one source of nonstationarity. The Box–Cox test is applied to the nonzero data to determine the best λ to normalize the data through the transformation Z = (xλ− 1)/λ. Estimation formulae are presented for λ = 1/2, 1/3, 1/4, 1/6 and the log transform Z = log x which corresponds to λ = 0. Our methods have been applied to data from the 1984 and 1985 North Sea herring surveys. The sampling error is close to 25% in both years. Both the time between shoal encounters and the shoal size can be described by three-parameter Weibull distributions. Theoretical expressions for the mean fish quantity, and the variance of this mean, are presented as functions of the Weibull parameters. Computer simulations based on these distributions confirm the validity of the proposed estimation procedure. The estimators suggested by the Box–Cox test have the least bias. Other estimators exhibit severe bias. In particular, if log transforms are used when the data are not log-normally distributed and Box–Cox suggests λ>0, the mean fish quantity and its variance are both likely to be overestimated.
An Experimental Study of the Plankton Community Impacts of Two Omnivorous Filter-Feeding Cichlids, Tilapia galilaea and Tilapia aurea
Authors: Vinyard Gary L. , Drenner Ray W. , Gophen Moshe , Pollingher Utsa , Winkelman Dana L. , Hambright K. David
Published: November 2009

We conducted laboratory selective grazing experiments and outdoor mesocosm experiments assessing impacts of two cichlids, Tilapia galilaea and Tilapia aurea, on plankton from Lake Kinneret, Israel. Laboratory feeding rates of both fish increased for larger particles, reaching maximum values for zooplankton and Peridinium cinctum. Tilapia galilaea had higher feeding rates on Peridinium elpatiewsky and on intermediate-sized nanoplankton. Outdoor mesocosm experiments examining fish impacts on plankton community structure included two 21-d spring and summer experiments of replicated 2 × 2 factorial design (T. galilaea × T. aurea). Both fish suppressed crustaceans and rotifers. In the spring, fish also suppressed chlorophyll concentration and the dominant phytoplankter P. cinctum. In the summer, when nanoplankton dominated the phytoplankton and the smaller P. elpatiewsky was the most abundant dinoflagellate, only T. galilaea suppressed Peridinium spp., while presence of T. aurea was associated with increased chlorophyll concentration. Overall, T. galilaea suppressed more and enhanced fewer nanoplankton taxa than did T. aurea. Production of each fish species was lowest when both species were together, suggesting potential competition for plankton resources.
Accuracy of Pup Classifications and Its Effect on Population Estimates in the Hooded Seal (Cystophora cristata)
Authors: Stenson G. B. , Myers R. A.
Published: November 2009

Information from the classification of age-specific developmental stages has been used to adjust aerial survey estimates of pup production in a number of species of seals, including the hooded seal (Cystophora cristata). We test the assumption that hooded seal pups were accurately and consistently classified according to developmental stage and examine the consequences of misclassifications upon adjusted population estimates. We determined overall misclassification rates, the effect of survey height on classifications, and interobserver variability. At ice level, misclassifications rates were low (<3%). From an altitude of 30 m, newborn pups could not be classified correctly and misclassification rates for the two other stages of attended pups varied between 6.4 and 21.3%. There was no evidence of an overall bias in classifications or differences among observers although there was a significant interaction between day and stage. Individual pups appear to have been misclassified independently by each observer. Under actual survey conditions, observers classified a similar proportion of pups into each recognizable stage. The misclassification rates we observed did not significantly alter the previous population estimate. Methods for improving the current survey design include modifying classification criteria, providing observers with a period of on-ice training, and reducing the width of survey transects.
Emergence of Chironomidae (Diptera) in Fertilized and Natural Lakes at Saqvaqjuac, N.W.T.
Authors: Welch Harold E. , Jorgenson John K. , Curtis Martin F.
Published: November 2009

Chironomid emergence was quantified in four small lakes at Saqvaqjuac, N.W.T. (63°39′N), before and after lake fertilization. Emerging biomass responded immediately to increased phytoplankton production, reaching equilibrium the following year. Emergence from the reference lake was extremely variable, for no apparent reason. The emergence – phytoplankton production relationships found by Davies for the Experimental Lakes Area (~49°N) were generally valid for Saqvaqjuac lakes and Char Lake (74°42′), except that (1) biomass was better correlated than numbers because of increased mean size with increasing latitude and (2) total primary production was a better predictor than phytoplankton production alone because benthic photosynthesis increases with increasing latitude. Chironomid production seems to be a predictable function of total primary production throughout the latitudinal range of the small Canadian lakes examined.
Brood Mortality and Egg Predation by the Nemertean, Carcinonemertes epialti, on the Yellow Rock Crab, Cancer anthonyi, in Southern California
Authors: Shields Jeffrey D. , Okazaki Robert K. , Kuris Armand M.
Published: November 2009

Carcinonemertes epialti had a minimal impact on the egg mortality of a lightly infested population of a commercially important crab host, Cancer anthonyi. The nemertean had a high prevalence (> 97%) but was found at low intensities (mean intensity = 86.5 worms/pleopod, mean density = 0.3 worms/1000 eggs). Egg mortality varied from 0.0–30.5%, and was highly correlated with both worm intensity, and the timing of crab embryogenesis (mean mortality = 5.7%). Separate sites within the pleopod experienced different causal mechanisms of mortality. Mortality at the base of the pleopod was correlated with the presence, abundance, and immigration of C. epialti. Mortality at the tip of the pleopod was less correlated with worm abundance and was most likely a result of abrasion to the eggs or egg mass. Infestations of C. epialti varied between seasons and between host species. The worm was more abundant on host species that bred year-round (Cancer anthonyi and Hemigrapsus oregonensis); hence, infestation dynamics varied markedly between host species. In southern California, Cancer anthonyi was virtually always infested with C. epialti and is the most important host for the worm in this area.
Estimating the Density and Mortality of Juvenile Western Rock Lobsters (Panulirus cygnus) in Nursery Reefs
Authors: Phillips Bruce F.
Published: November 2009

Studies of juvenile rock lobsters (Panulirus cygnus) in the nursery reefs of Western Australia indicated that density-dependent processes on the reefs were the major determinant of year-class strengths of recruitment to the fishery. Reassessment of early data, plus additional information, indicates that these estimates may have been inaccurate. Alternative methods of estimating juvenile densities were examined; application of length–frequency analysis to calculate the age-classes; visual estimates, and single-night trapping. Length–frequency analysis indicated that either immigration onto the test reefs had occurred, or the data were inaccurate. Visual estimates and single-night trapping were more rapid and used less manpower and resources than mark–recapture methods, but the estimates were of unknown accuracy. No truly satisfactory method of making reliable estimates of either the density of natural mortality rate of juveniles in the nursery reefs is yet available. Nevertheless, the data on the levels of larval settlement and subsequent catches, suggest that density dependent processes probably have a significant effect on the levels of recruitment to the fishery, although the upper level to this recruitment has not been reached over the past 20 yrs.
Vertical Fine Structure of Particulate Matter and Nutrients in Sea Ice of the High Arctic
Authors: Smith Ralph E. H. , Harrison W. Glen , Harris Leslie R. , Herman Alex W.
Published: November 2009

The vertical fine structure of particulate matter and inorganic nutrients through the bottom layers of sea ice was determined at a site in the Canadian high arctic. Intense vertical gradients of chlorophyll a, nitrate, ammonium, nitrite, phosphate, and silicate developed in the lower 6 cm of the ice as ice algae attained standing crops of 250 mg∙m−2(up to 60 mg∙L−1) of chlorophyll a. Pigment and inorganic nutrient concentrations were closely correlated, and pools of inorganic nutrient were shown to exist in the particulate matter, suggesting that the extremely high dissolved nutrient concentrations in the bottom ice (e.g. up to 400 μmol∙L−1nitrate) were derived at least in part from leakage of algal intracellular pools. Nitrogen and phosphorus were present in excess of algal needs, but silicon may not have been. The ratios of particulate organic carbon to chlorophyll a and to particulate organic nitrogen increased from the ice–water interface upwards, consistent with a physiological response of the ice algae to the strong corresponding gradient of light availability. Although spatially compact, the assemblage of algae in the bottom ice inhabits a highly stratified environment.
Multivariate Approach to Study Species Assemblages at Large Spatiotemporal Scales: The Community Structure of the Epibenthic Fauna of the Estuary and Gulf of St. Lawrence
Authors: Ardisson P.-L. , Bourget E. , Legendre P.
Published: November 2009

We investigated hierarchical organization and spatiotemporal discontinuities in species abundances in the epibenthic community of the Estuary and Gulf of St. Lawrence. Quantitative samples were obtained from 1975 to 1984, on 161 collectors (navigation buoys) moored yearly from May through November. Maximum biomass values of the dominant species, common to all regions studied, were used to assess epibenthic community structure. Numerical methods were used to characterize spatial structure and temporal variability of the dominant assemblage. Spatially constrained clustering and ordination techniques revealed six broad biogeographic zones whose limits vary yearly. However, spatially unconstrained clustering and ordination techniques showed two major sets of non-continguous localities, each characterized by a singular biotic structure. Further, spatial autocorrelation analyses showed a significant relationship between biomass and geographic distance. The resulting spatial structure of biomass was dependent on the species considered. The multidimensional Mantel technique showed an 8-yr period of variation in community structure at large (whole system, Gulf) and intermediate (North Shore plus Lower North Shore) spatial scales. The amplitude and asymmetry of this temporal cycle increased as the spatial scale decreased. In spite of the observed discontinuous spatial patterns, the temporal oscillations in community structure detected at different spatial scales suggest that the Estuary-Gulf system responds to the external input of auxiliary energy as an integrated system.
Response of a Brook Trout (Salvelinus fontinalis) Population to a Reduction in Stream Benthos Following an Insecticide Treatment
Authors: Kreutzweiser D. P.
Published: November 2009

A forest stream was treated with permethrin to determine the response of brook trout to a reduction in the aquatic food resource following an insecticide treatment. The treatment resulted in massive invertebrate drift and significant reductions of benthos, but did not produce trout mortality or evidence of unusual behaviour. The density, population age structure, movement patterns, and condition of brook trout were not measurably affected by the permethrin treatment. The growth rates of 0 + and 1 + age-classes were significantly lower following the insecticide application than those of trout from the same age-classes of pretreatment years. This reduction in growth rate resulted in significantly smaller trout after treatment. A significant reduction in the growth of trout collected during the same period from a nearby untreated control stream indicated that unusually high summer temperatures were at least partially, if not entirely, responsible for the reduced growth rate of treated fish. Growth rates returned to or exceeded pretreatment levels by the overwinter period of the treatment year.
Effect of Fluoride Complexation on Aluminum Toxicity Towards Juvenile Atlantic Salmon (Salmo salar)
Authors: Wilkinson Kevin J. , Campbell Peter G. C. , Couture Pierre
Published: November 2009

In 7-d semistatic bioassays, fluoride complexation attenuated Al toxicity to juvenile Atlantic salmon (Salmo salar; age 1 +) and the accumulation of Al in gill tissue, but not to the extent predicted by the free-ion model of metal toxicity. Bioaccumulation and toxicity persisted even in the presence of an excess of the complexing ligand. An equilibrium model, involving the formation of a mixed ligand complex (F–Al–L-gill) at the gill surface, is proposed to explain this residual toxicity (L-gill = ligand at the gill surface). Exposure to Al, or to a combination of Al and F, led to a decrease in the plasma sodium levels even for sublethal conditions. Aluminum concentrations as low as 2 μM adversely affected the salmon. The similarity of the osmo-regulatory response to the H+-ion, to Al3+, and to Al(F)x suggested that the mechanism of toxicity in the presence of fluoride did not differ markedly from that observed by previous workers for salmonid species exposed to moderately acidic media containing Al but without added fluoride.
FREE FERMIONIC HETEROTIC MODEL BUILDING AND ROOT SYSTEMS
Authors: ROBINSON MATTHEW B. , CLEAVER GERALD B. , HUNZIKER MARKUS
Published: November 2009

We consider an alternative derivation of the GSO Projection in the free fermionic construction of the weakly coupled heterotic string in terms of root systems, as well as the interpretation of the GSO Projection in this picture. We then present an algorithm to systematically and efficiently generate input sets (i.e. basic vectors) in order to study landscape statistics with minimal computational cost. For example, the improvement at order 6 is ≈10-13 over a traditional brute force approach, and improvement increases with order. We then consider an example of statistics on a relatively simple class of models.
FRACTIONAL QUANTUM EULER–CAUCHY EQUATION IN THE SCHRÖDINGER PICTURE, COMPLEXIFIED HARMONIC OSCILLATORS AND EMERGENCE OF COMPLEXIFIED LAGRANGIAN AND HAMILTONIAN DYNAMICS
Authors: EL-NABULSI AHMAD RAMI
Published: November 2009

Fractional quantum Euler–Cauchy equation in the Schrödinger picture is derived from the fractional action-like variational approach recently introduced by the author. Many interesting consequences are revealed and explored, in particular the emergence of complexified harmonic oscillators, complexified Lagrangian and Hamiltonian and complexified fractional action integral.
THE STRENGTH OF FANO INTERFERENCE EFFECTS ON THE PROBE ABSORPTION IN ASYMMETRIC SEMICONDUCTOR QUANTUM WELLS
Authors: WANG ZHI-PING
Published: November 2009

We investigate the strength of Fano interference effects on the probe absorption spectra in asymmetric semiconductor quantum wells driven coherently by a probe laser field. We find that the probe absorption can be dramatically reduced due to the strength of the Fano interference, and the effect of the energy splitting on the probe absorption is also discussed. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength. Thus it may provide some possibilities for technological applications in optoelectronics and solid-state quantum information science.
A LIE SUPERALGEBRA AND CORRESPONDING HIERARCHY OF EVOLUTION EQUATIONS
Authors: WANG XIN-ZENG , DONG HUAN-HE
Published: November 2009

A Lie super algebra G is constructed and an isospectral problem with five potentials is designed. From there, a corresponding hierarchy of nonlinear evolution equations is derived and super-AKNS, super-TD, super-D-AKNS are deduced. Their super-Hamiltonian structure is established by making use of the supertrace identity, and they are intergrable in sense of Liouville.
THE INTERACTION BETWEEN THE DISLOCATION AND ELLIPTIC NOTCH IN ONE-DIMENSIONAL HEXAGONAL QUASI-CRYSTALS
Authors: LI LIAN HE , LIU GUAN TING
Published: November 2009

The interaction between the dislocation and elliptic notch in one-dimensional hexagonal quasi-crystals is considered. The explicit expressions of the complex potentials are derived by the conformal transformation method and the perturbation technique. Then the analytical expressions for the stresses and displacements can be determined. As a special case of the results, the solutions for the interaction between the Griffith crack and dislocation is observed. The stress intensity factor of crack and the force on dislocation are also obtained, which are very useful in practice.
ROBUST OBJECT TRACKING USING JOINT COLOR-TEXTURE HISTOGRAM
Authors: NING JIFENG , ZHANG LEI , ZHANG DAVID , WU CHENGKE
Published: November 2009

A novel object tracking algorithm is presented in this paper by using the joint color-texture histogram to represent a target and then applying it to the mean shift framework. Apart from the conventional color histogram features, the texture features of the object are also extracted by using the local binary pattern (LBP) technique to represent the object. The major uniform LBP patterns are exploited to form a mask for joint color-texture feature selection. Compared with the traditional color histogram based algorithms that use the whole target region for tracking, the proposed algorithm extracts effectively the edge and corner features in the target region, which characterize better and represent more robustly the target. The experimental results validate that the proposed method improves greatly the tracking accuracy and efficiency with fewer mean shift iterations than standard mean shift tracking. It can robustly track the target under complex scenes, such as similar target and background appearance, on which the traditional color based schemes may fail to track.
EVALUATIONS OF PARTICLE FILTER BASED HUMAN MOTION VISUAL TRACKERS FOR HOME ENVIRONMENT SURVEILLANCE
Authors: FONTMARTY MATHIAS , DANÈS PATRICK , LERASLE FRÉDÉRIC
Published: November 2009

This paper presents a thorough study of some particle filter (PF) strategies dedicated to human motion capture from a trinocular vision surveillance setup. An experimental procedure is used, based on a commercial motion capture ring to provide ground truth. Metrics are proposed to assess performances in terms of accuracy, robustness, but also estimator dispersion which is often neglected elsewhere. Relative performances are discussed through some quantitative and qualitative evaluations on a video database. PF strategies based on Quasi Monte Carlo sampling, a scheme which is surprisingly seldom exploited in the Vision community, provide an interesting way to explore. Future works are finally discussed.
DIRECTED CURRENT IN QUASI-ADIABATICALLY AC-DRIVEN NONLINEAR SYSTEMS
Authors: BUTTÀ PAOLO , NEGRINI PIERO
Published: November 2009

We rigorously prove the existence of directed transport for a certain class of ac-driven nonlinear one-dimensional systems, namely the generation of transport with a preferred direction in the absence of a net driving force.
A model of the isolated perfused rat small intestine
Authors: Lautenschläger Ingmar , Dombrowsky Heike , Frerichs Inéz , Kuchenbecker Solveig-Carolin , Bade Steffen , Schultz Holger , Zabel Peter , Scholz Jens , Weiler Norbert , Uhlig Stefan
Published: November 2009

Intestinal edema remains a serious clinical problem, and novel approaches to study its pathophysiology are needed. It was our aim to develop a long-term stable isolated perfused rat small bowel preparation permitting analysis of vascular, luminal, interstitial, and lymphatic compartments and to demonstrate the utility of this model by studying the effects of the proinflammatory mediator platelet-activating factor (PAF). A temperature-controlled chamber with an integrated balance was designed to perfuse isolated intestines through the mesenteric artery and the gut lumen. Steroids or oxygen carriers were not needed. Functional and morphological integrity of the tissue was preserved for several hours as confirmed by oxygen consumption, venous lactate-to-pyruvate ratio, arterial and venous pH, lactose digestion and galactose uptake, intravascular and luminal pressures, maintained fluid homeostasis, gut motility, and quantitative light microscopic analysis. Administration of PAF caused typical effects such as vasoconstriction, gut atony, and loss of galactose uptake. PAF also elicited a transient loss of 20% of the perfusate liquid from the mesenteric vascular bed, two-thirds of which were transferred to the lumen. All these responses were entirely reversible. This new model provides detailed insights into the physiology of the small intestine and will allow to study fundamental processes such as fluid homeostasis, barrier functions, transport mechanisms, and immune responses in this organ. Using this model, here we show a dramatic and yet reversible response of the rat small bowel to PAF, suggesting luminal water clearance as a novel safety factor in the intestine that may be of clinical relevance.
Mechanisms of lysophosphatidic acid (LPA) mediated stimulation of intestinal apical Cl−/OH− exchange
Authors: Singla Amika , Dwivedi Alka , Saksena Seema , Gill Ravinder K. , Alrefai Waddah A. , Ramaswamy Krishnamurthy , Dudeja Pradeep K.
Published: November 2009

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, is a natural component of food products like soy and egg yolk. LPA modulates a number of epithelial functions and has been shown to inhibit cholera toxin-induced diarrhea. Antidiarrheal effects of LPA are known to be mediated by inhibiting chloride secretion. However, the effects of LPA on chloride absorption in the mammalian intestine are not known. The present studies examined the effects of LPA on apical Cl−/OH− exchangers known to be involved in chloride absorption in intestinal epithelial cells. Caco-2 cells were treated with LPA, and Cl−/OH− exchange activity was measured as DIDS-sensitive 36Cl− uptake. Cell surface biotinylation studies were performed to evaluate the effect of LPA on cell surface levels of apical Cl−/OH− exchangers, downregulated in adenoma (DRA) (SLC26A3), and putative anion transporter-1 (SLC26A6). Treatment of Caco-2 cells with LPA (100 μM) significantly stimulated Cl−/OH− exchange activity. Specific agonist for LPA2 receptor mimicked the effects of LPA. LPA-mediated stimulation of Cl−/OH− exchange activity was dependent on activation of phosphatidylinositol 3-kinase/Akt signaling pathway. Consistent with the functional activity, LPA treatment resulted in increased levels of DRA on the apical membrane. Our results demonstrate that LPA stimulates apical Cl−/OH− exchange activity and surface levels of DRA in intestinal epithelial cells. This increase in Cl−/OH− exchange may contribute to the antidiarrheal effects of LPA.
IL-6 microinjected in the nucleus tractus solitarii attenuates cardiac baroreceptor reflex function in rats
Authors: Takagishi Miwa , Waki Hidefumi , Bhuiyan Mohammad E. R. , Gouraud Sabine S. , Kohsaka Akira , Cui He , Yamazaki Toshiya , Paton Julian F. R. , Maeda Masanobu
Published: November 2009

Recent gene array and molecular studies have suggested that an abnormal gene expression profile of interleukin-6 (IL-6) in the nucleus tractus solitarii (NTS), a pivotal region for regulating arterial pressure, may be related to the development of neurogenic hypertension. However, the precise functional role of IL-6 in the NTS remains unknown. In the present study, we have tested whether IL-6 affects cardiovascular control at the level of the NTS. IL-6 (1, 10, and 100 fmol) was microinjected in the NTS of Wistar rats (280–350 g) under urethane anesthesia. Although the baseline levels of arterial pressure and heart rate did not change following IL-6 injections, the cardiac baroreflex in response to increased arterial pressure was dose-dependently attenuated. In addition, IL-6 (100 fmol) microinjections also attenuated l-glutamate-induced bradycardia at the level of the NTS. Immunohistochemical detection of IL-6 in naïve rats demonstrated that it was predominantly observed in neurons within the brain stem, including the NTS. These findings suggest that IL-6 within the NTS may play an important role for regulating cardiovascular control via modulation of input signals from baroreceptor afferents. Whether the abnormal gene expression of IL-6 in the NTS is associated in a causal way with hypertension remains to be resolved.
Pregnancy restores insulin secretion from pancreatic islets in cafeteria diet-induced obese rats
Authors: Vanzela E. C. , Ribeiro R. A. , de Oliveira C. A. Machado , Rodrigues F. B. , Bonfleur M. L. , Carneiro E. M. , Souza K. L. A. , Boschero A. C.
Published: November 2009

Insulin resistance during pregnancy is counteracted by enhanced insulin secretion. This condition is aggravated by obesity, which increases the risk of gestational diabetes. Therefore, pancreatic islet functionality was investigated in control nonpregnant (C) and pregnant (CP), and cafeteria diet-fed nonpregnant (Caf), and pregnant (CafP) obese rats. Isolated islets were used for measurements of insulin secretion (RIA), NAD(P)H production (MTS), glucose oxidation (14CO2 production), intracellular Ca2+ levels (fura-2 AM), and gene expression (real-time PCR). Impaired glucose tolerance was clearly established in Caf and CafP rats at the 14th wk on a diet. Insulin secretion induced by direct depolarizing agents such as KCl and tolbutamide and increasing concentrations of glucose was significantly reduced in Caf, compared with C islets. This reduction was not observed in islets from CP and CafP rats. Accordingly, the glucose oxidation and production of reduced equivalents were increased in CafP islets. The glucose-induced Ca2+ increase was significantly lower in Caf and higher in CafP, compared with all other groups. CP and CafP islets demonstrated an increased Ca2+ oscillation frequency, compared with both C and Caf islets, and the amplitude of oscillations was augmented in CafP, compared with Caf islets. In addition, Cavα1.2 and SERCA2a mRNA levels were reduced in Caf islets. Cavα1.2, but not SERCA2a, mRNA was normalized in CafP islets. In conclusion, cafeteria diet-induced obesity impairs insulin secretion. This alteration is related to the impairment of Ca2+ handling in pancreatic islets, in especial Ca2+ influx, a defect that is reversed during pregnancy allowing normalization of insulin secretion.
Acute β-adrenergic stimulation does not alter mitochondrial protein synthesis or markers of mitochondrial biogenesis in adult men
Authors: Robinson Matthew M. , Richards Jennifer C. , Hickey Matthew S. , Moore Daniel R. , Phillips Stuart M. , Bell Christopher , Miller Benjamin F.
Published: November 2009

Exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) is dramatically inhibited in mice pretreated with a β-adrenergic receptor (β-AR) antagonist, suggesting that β-ARs play an important role in the regulation of skeletal muscle PGC-1α expression, and potentially, mitochondrial biogenesis. Accordingly, we hypothesized that acute β-AR stimulation would induce transcriptional pathways involved in skeletal muscle mitochondrial biogenesis in humans. Whole body protein turnover (WBPT), myofibrillar protein synthesis (MyPS), skeletal muscle mitochondrial protein synthesis (MiPS), and mitochondrial biogenic signaling were determined in samples of vastus lateralis obtained on two separate occasions in 10 young adult males following 1 h of continuous intravenous administration of saline (CON) or a nonspecific β-AR agonist [isoproterenol (ISO): 12 ng·kg fat free mass−1·min−1], combined with coinfusion of [1,2]13C-leucine. β-AR stimulation induced appreciable increases in heart rate and systolic blood pressure (both P < 0.001) but did not affect mitochondrial biogenic signaling (no change in PGC-1α, TFAM, NRF-1, NRF-2, COX, or NADHox expression via RT-PCR; P > 0.05). Additionally, MiPS [CON: 0.099 ± 0.028, ISO: 0.074 ± 0.046 (mean ± SD); P > 0.05] and MyPS (CON: 0.059 ± 0.008, ISO: 0.055 ± 0.009; P > 0.05), as well as measures of WBPT were unaffected. On the basis of this investigation, we conclude that acute intravenous β-AR stimulation does not increase mitochondrial protein synthesis or biogenesis signals in skeletal muscle.
Endothelin receptors: what's new and what do we need to know?
Authors: Watts Stephanie W.
Published: November 2009

Receptors are at the heart of how a molecule transmits a signal to a cell. Two receptor classes for endothelin (ET) are recognized, the ETAand ETBreceptors. Intriguing questions have arisen in the field of ET receptor pharmacology, physiology, and function. For example, a host of pharmacological studies support the interaction of the ETAand ETBreceptor in tissues (veins, arteries, bronchus, arterioles, esophagus), but yet few have been able to demonstrate direct ETA/ETBreceptor interaction. Have we modeled this interaction wrong? Do we have a truly selective ETAreceptor agonist such that we could selectively stimulate this important receptor? What can we learn from the recent phylogenic studies of the ET receptor family? Have we adequately addressed the number of biological molecules with which ET can interact to exert a biological effect? Recent mass spectrometry studies in our laboratory suggest that ET-1 interacts with other hereto unrecognized proteins. Biased ligands (ligands at the same receptor that elicit distinct signaling responses) have been discovered for other receptors. Do these exist for ET receptors and can we take advantage of this possibility in drug design? These and other questions will be posed in this minireview on topics on ET receptors.
Radiation-induced reductions in transporter mRNA levels parallel reductions in intestinal sugar transport
Authors: Roche Marjolaine , Neti Prasad V. S. V. , Kemp Francis W. , Agrawal Amit , Attanasio Alicia , Douard Véronique , Muduli Anjali , Azzam Edouard I. , Norkus Edward , Brimacombe Michael , Howell Roger W. , Ferraris Ronaldo P.
Published: November 2009

More than a century ago, ionizing radiation was observed to damage the radiosensitive small intestine. Although a large number of studies has since shown that radiation reduces rates of intestinal digestion and absorption of nutrients, no study has determined whether radiation affects mRNA expression and dietary regulation of nutrient transporters. Since radiation generates free radicals and disrupts DNA replication, we tested the hypotheses that at doses known to reduce sugar absorption, radiation decreases the mRNA abundance of sugar transporters SGLT1 and GLUT5, prevents substrate regulation of sugar transporter expression, and causes reductions in sugar absorption that can be prevented by consumption of the antioxidant vitamin A, previously shown by us to radioprotect the testes. Mice were acutely irradiated with137Cs gamma rays at doses of 0, 7, 8.5, or 10 Gy over the whole body. Mice were fed with vitamin A-supplemented diet (100× the control diet) for 5 days prior to irradiation after which the diet was continued until death. Intestinal sugar transport was studied at days 2, 5, 8, and 14 postirradiation. By day 8, d-glucose uptake decreased by ∼10–20% and d-fructose uptake by 25–85%. With increasing radiation dose, the quantity of heterogeneous nuclear RNA increased for both transporters, whereas mRNA levels decreased, paralleling reductions in transport. Enterocytes of mice fed the vitamin A supplement had ≥ 6-fold retinol concentrations than those of mice fed control diets, confirming considerable intestinal vitamin A uptake. However, vitamin A supplementation had no effect on clinical or transport parameters and afforded no protection against radiation-induced changes in intestinal sugar transport. Radiation markedly reduced GLUT5 activity and mRNA abundance, but high-d-fructose diets enhanced GLUT5 activity and mRNA expression in both unirradiated and irradiated mice. In conclusion, the effect of radiation may be posttranscriptional, and radiation-damaged intestines can still respond to dietary stimuli.
Rapid intravenous infusion of 20 ml/kg saline does not impair resting pulmonary gas exchange in the healthy human lung
Authors: Prisk G. Kim , Olfert I. Mark , Arai Tatsuya J. , Wagner Peter D. , Hopkins Susan R.
Published: November 2009

Rapid infusion of intravenous saline, a model of pulmonary interstitial edema, alters the distribution of pulmonary perfusion, raises pulmonary capillary blood volume, and increases bronchial wall thickness in humans. We hypothesized that infusion would disrupt pulmonary gas exchange by increasing ventilation/perfusion (V̇a/Q̇) inequality as opposed to a diffusive impairment in O2 exchange. Seven males (26 ± 3 yr; FEV1: 110 ± 16% predicted.) performed spirometry and had V̇a/Q̇ mismatch measured using the multiple inert gas elimination technique, before and after 20 ml/kg iv of normal saline delivered in ∼30 min. Infusion increased thoracic fluid content from transthoracic impedance by 12% ( P < 0.0001) and left FVC unchanged but reduced expiratory flows (FEF25–75 falling from 5.1 ± 0.4 to 4.2 ± 0.4 l/s, P < 0.05). However, V̇a/Q̇ mismatch as measured by the log standard deviation of the ventilation (LogSDV̇) and perfusion (LogSDQ̇) distributions remained unchanged; LogSDV̇: 0.40 ± 0.03 pre, 0.38 ± 0.04 post, NS; LogSDQ̇: 0.38 ± 0.03 pre, 0.37 ± 0.03 post, NS. There was no significant change in arterial Po2 (99 ± 2 pre, 99 ± 3 mmHg post, NS) but arterial Pco2 was decreased (38.7 ± 0.6 pre, 36.8 ± 1.2 mmHg post, P < 0.05). Thus, infusion compressed small airways and caused a mild degree of hyperventilation. There was no evidence for a diffusive limitation to O2 exchange, with the measured-predicted alveolar-arterial oxygen partial pressure difference being unaltered by infusion at FiO2 = 0.125 (4.3 ± 1.0 pre, 5.2 ± 1.0 post, NS). After infusion, the fraction of perfusion going to areas with V̇a/Q̇ < 1 was increased when a subject breathed a hyperoxic gas mixture [0.72 ± 0.06 (FiO2 = 0.21), 0.80 ± 0.06 (FiO2 = 0.30), P < 0.05] with similar effects on ventilation in the face of unchanged V̇a and Q̇. These results suggest active control of blood flow to regions of decreased ventilation during air breathing, thus minimizing the gas exchange consequences.
Interneuron Circuits Tune Inhibition in Retinal Bipolar Cells
Authors: Eggers Erika D. , Lukasiewicz Peter D.
Published: November 2009

While connections between inhibitory interneurons are common circuit elements, it has been difficult to define their signal processing roles because of the inability to activate these circuits using natural stimuli. We overcame this limitation by studying connections between inhibitory amacrine cells in the retina. These interneurons form spatially extensive inhibitory networks that shape signaling between bipolar cell relay neurons to ganglion cell output neurons. We investigated how amacrine cell networks modulate these retinal signals by selectively activating the networks with spatially defined light stimuli. The roles of amacrine cell networks were assessed by recording their inhibitory synaptic outputs in bipolar cells that suppress bipolar cell output to ganglion cells. When the amacrine cell network was activated by large light stimuli, the inhibitory connections between amacrine cells unexpectedly depressed bipolar cell inhibition. Bipolar cell inhibition elicited by smaller light stimuli or electrically activated feedback inhibition was not suppressed because these stimuli did not activate the connections between amacrine cells. Thus the activation of amacrine cell circuits with large light stimuli can shape the spatial sensitivity of the retina by limiting the spatial extent of bipolar cell inhibition. Because inner retinal inhibition contributes to ganglion cell surround inhibition, in part, by controlling input from bipolar cells, these connections may refine the spatial properties of the retinal output. This functional role of interneuron connections may be repeated throughout the CNS.
Chronotopically Organized Target-Distance Map in the Auditory Cortex of the Short-Tailed Fruit Bat
Authors: Hagemann Cornelia , Esser Karl-Heinz , Kössl Manfred
Published: November 2009

Topographic cortical representation of echo delay, the cue for target range, is an organizational feature implemented in the auditory cortices of certain bats dedicated to catch flying insects. Such cortical echo-delay maps provide a calibrated neural representation of object spatial distance. To assess general requirements for echo-delay computations, cortical delay sensitivity was examined in the short-tailed fruit bat Carollia perspicillata that uses frequency-modulated (FM) echolocation signals. Delay-tuned neurons with temporal specificity comparable to those of insectivorous bats are located within the high-frequency (HF) field of the auditory cortex. All recorded neurons in the HF field respond well to single pure-tone and FM-FM stimulus pairs. The neurons respond to identical FM harmonic components in echolocation pulse and delayed echo (e.g., FM2-FM2). Their characteristic delays (CDs) for low echo amplitudes range between 1 and 24 ms, which is comparable to other bat species. Maps of the topography of FM-FM neurons show that they are distributed across the entire HF area and organized along a rostrocaudal echo-delay axis representing object distance. Rostrally located neurons tuned to delays of 2–8 ms are overrepresented (66% of CDs). Neurons with longer delays (≥10 ms) are located throughout the caudal half of the HF field. The delay-sensitive chronotopic area covers ∼3.3 mm in rostrocaudal and ∼3.7 mm in dorsoventral direction, which is comparable or slightly larger than the size of cortical delay-tuned areas in insectivorous constant frequency bats, the only other bat species for which cortical chronotopy has been demonstrated. This indicates that chronotopic cortical organization is not only used exclusively for precise insect localization in constant frequency bats but could also be of advantage for general orientation tasks.
Compensatory Regulation of Cav2.1 Ca2+Channels in Cerebellar Purkinje Neurons Lacking Parvalbumin and Calbindin D-28k
Authors: Kreiner Lisa , Christel Carl J. , Benveniste Morris , Schwaller Beat , Lee Amy
Published: November 2009

Cav2.1 channels regulate Ca2+signaling and excitability of cerebellar Purkinje neurons. These channels undergo a dual feedback regulation by incoming Ca2+ions, Ca2+-dependent facilitation and inactivation. Endogenous Ca2+-buffering proteins, such as parvalbumin (PV) and calbindin D-28k (CB), are highly expressed in Purkinje neurons and therefore may influence Cav2.1 regulation by Ca2+. To test this, we compared Cav2.1 properties in dissociated Purkinje neurons from wild-type (WT) mice and those lacking both PV and CB (PV/CB−/−). Unexpectedly, P-type currents in WT and PV/CB−/−neurons differed in a way that was inconsistent with a role of PV and CB in acute modulation of Ca2+feedback to Cav2.1. Cav2.1 currents in PV/CB−/−neurons exhibited increased voltage-dependent inactivation, which could be traced to decreased expression of the auxiliary Cavβ2asubunit compared with WT neurons. Although Cav2.1 channels are required for normal pacemaking of Purkinje neurons, spontaneous action potentials were not different in WT and PV/CB−/−neurons. Increased inactivation due to molecular switching of Cav2.1 β-subunits may preserve normal activity-dependent Ca2+signals in the absence of Ca2+-buffering proteins in PV/CB−/−Purkinje neurons.
Combinatorial Responses Controlled by Synaptic Inhibition in the Cerebellum Granular Layer
Authors: Mapelli Jonathan , Gandolfi Daniela , D'Angelo Egidio
Published: November 2009

The granular layer of cerebellum has been long hypothesized to perform combinatorial operations on incoming signals. Although this assumption is at the basis of main computational theories of cerebellum, it has never been assessed experimentally. Here, by applying high-resolution voltage-sensitive dye imaging techniques, we show that simultaneous activation of two partially overlapping mossy fiber bundles (either with single pulses or high-frequency bursts) can cause combined excitation and combined inhibition, which are compatible with the concepts of coincidence detection and spatial pattern separation predicted by theory. Combined excitation appeared as an area in which the combination of two inputs is greater than the arithmetic sum of the individual inputs and was enhanced by γ-aminobutyric acid type A (GABAA) receptor blockers. Combined inhibition was manifest as an area where two inputs combined resulted in a reduction to less than half of the activity evoked from either one of the two inputs alone and was prevented by GABAA receptor blockers. The combinatorial responses occupied small granular layer regions (∼30 μm diameter), with combined inhibition being interspersed among extended areas of combined excitation. Moreover, the combinatorial effects lasted for tens of milliseconds and combined inhibition occurred only after termination of the stimuli. These combinatorial operations, if engaged by natural input patterns in vivo, may be important to influence incoming impulses organizing spatiotemporal spike sequences to be relayed to Purkinje cells.
Specific Roles of AMPA Receptor Subunit GluR1 (GluA1) Phosphorylation Sites in Regulating Synaptic Plasticity in the CA1 Region of Hippocampus
Authors: Lee Hey-Kyoung , Takamiya Kogo , He Kaiwen , Song Lihua , Huganir Richard L.
Published: November 2009

Activity-dependent changes in excitatory synaptic transmission in the CNS have been shown to depend on the regulation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). In particular, several lines of evidence suggest that reversible phosphorylation of AMPAR subunit glutamate receptor 1 (GluR1, also referred to as GluA1 or GluR-A) plays a role in long-term potentiation (LTP) and long-term depression (LTD). We previously reported that regulation of serines (S) 831 and 845 on the GluR1 subunit may play a critical role in bidirectional synaptic plasticity in the Schaffer collateral inputs to CA1. Specifically, gene knockin mice lacking both S831 and S845 phosphorylation sites (“double phosphomutants”), where both serine residues were replaced by alanines (A), showed a faster decaying LTP and a deficit in LTD. To determine which of the two phosphorylation sites was responsible for the phenotype, we have now generated two lines of gene knockin mice: one that specifically lacks S831 (S831A mutants) and another that lacks only S845 (S845A mutants). We found that S831A mutants display normal LTP and LTD, whereas S845A mutants show a specific deficit in LTD. Taken together with our previous results from the “double phosphomutants,” our data suggest that either S831 or S845 alone may support LTP, whereas the S845 site is critical for LTD expression.