A numerical model of expired flow in a monoalveolar lung model subjected to pressure ramps

A numerical investigation of pulmonary flow properties was carried out in a monoalveolar model composed of a balloon and a compliant tube in series, subjected to pressure ramps. The flow is shown to become quickly limited by a wave-speed mechanism, occurring at the peak flow. The critical point then travels upstream, while the main part of the exit flow rate is provided by the tube collapse. After the critical flow period, the flow becomes subcritical and viscous effects are predominant in the deeply collapsed tube.     

The Human Obesity Gene Map: The 1996 Update

An update of the human obesity gene map up to October 1996 is presented. Evidence from Mendelian disorders exhibiting obesity as a clinical feature, single-gene mutation rodent models, quantitative trait loci uncovered in crossbreeding experiments with mouse, rat, and pig models, association and case-control studies with candidate genes, and linkage studies with genes and other markers is reviewed. All chromosomal locations of the animal loci are converted into human genome locations based on syntenic relationships between the genomes. A complete listing of all these loci reveals that only 4 of the 24 human chromosomes are not yet represented, i.e., 9, 18, 21, and Y. Several chromosome arms are characterized by the presence of several putative loci. The following arms include at least three such loci: 1p, 1q, 3p, 4q, 6p, 7q, 8p, 8q, 11p, 11q, 15q, 20q, and Xq. Studies with negative association and linkage results are also reviewed.     

Variability in the transmission efficiency of potyviruses by different clones ofAphis gossypii

A sample of seventy-twoAphis gossypii Glover (Homoptera: Aphididae) clones was collected in south-eastern France. The efficiency of these clones to transmit a potyvirus (papaya ringspot virus T-strain) was assessed in controlled conditions. In a first screening, the virus was transmitted by all clones and a 3.5-fold difference between the most and least efficient clones was obtained. During subsequent trials, which were carried out to confirm the differences in the transmission efficiency of these clones, only one clone proved to be more efficient than the others. This difference appeared consistent over a 1-year period, and was also confirmed with 4 other related potyviruses.

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Résumé Un échantillon de 72 clones deA. gossypii a été collecté dans le Sud-Est de la France. L'efficacité de transmission d'un potyvirus (PRSV-T) a été mesurée en conditions contr?lées pour chacun de ces clones. Un premier screening a permis de montrer que tous les clones transmettaient ce virus, et qu'un rapport de 3,5 existait entre l'efficacité de transmission du clone le plus efficace et celle du clone le moins efficace. Au cours des essais ultérieurs destinés à confirmer ces différences, un seul clone s'est montré significativement plus efficace que les autres. Cette différence s'est maintenue pendant la période d'essais (1 an). Elle s'est reproduite avec 4 autre potyvirus apparentés.

     

Muscarinic receptor binding in rat brain using the agonist, [3H]cis methyldioxolane

Muscarinic receptor binding was measured in rat forebrain preparations using the muscarinic agonist, [³H]cis methyldioxolane ([³H]CD). The results of equilibrium binding studies using [³H]CD concentrations between 0.5–64 nM showed that [³H]CD binding did not saturate in this concentration range, although the binding isotherm was concave downward. Nonlinear regression analysis of the binding data revealed the presence of two populations of muscarinic receptors having dissociation constants of 1.83 and 123 nM and binding capacities of 85 and 1320 fmol/mg protein, respectively. Competitive inhibition experiments showed that [³H]CD binding was readily displaced by several muscarinic agonists and antagonists. The stereospecificity of [³H]CD binding was demonstrated in competitive inhibition experiments using the stereoisomers of benzetimide and acetyl-β-methylcholine. Dexetimide was 10,000 times more potent than levetimide and l-acetyl-β-methylcholine was 520 times more potent than d-acetyl-β-methylcholine. A variety of nonmuscarinic cholinergic drugs were not effective at inhibiting [³H]CD binding at a concentration of 10 μM.     

Alloparental feeding in Adélie penguins: why is it uncommon?

We investigated alloparental interactions and conditions which could facilitate or prevent the expression of alloparental behaviours in Adélie penguins (Pygoscelis adeliae), a long-lived seabird which nests in high-density colonies around Antarctica. Observation sessions were carried out during the crèche stage on 48 identified pairs and 50 identified chicks in a 217-nest subcolony. As the season progressed, young were fed less often by their own parents because these were increasingly absent from the breeding site and less responsive to their offspring’s solicitations. As a consequence, young and particularly those with a low body mass, coming from a two-chick brood, opted for gradually soliciting more from other adults to obtain food, preferentially those nesting in their direct vicinity. Unsuccessful breeders represented a low and constant part of the adult population and were not specifically solicited by unrelated young. Despite the increasing chick demand, only 4.1% (3 out of 73) of alloparental solicitations resulted in feeding, which is negligible compared to parental feeding. To investigate factors that could trigger the appearance of alloparental care, we carried out comparisons with king (Aptenodytes patagonicus) and emperor penguins (Aptenodytes forsteri) which represent the closest species for which data on alloparental behaviour were available. Our results show different trends to those observed in these species and three factors may explain the low occurrence of alloparental behaviour in Adélie penguins: (1) the low and constant proportion of unsuccessful breeders, (2) the absence of chick selectivity towards unsuccessful breeders, and (3) the late period of chick accessibility for potential alloparents.     

Evolutionary temperature compensation of carbon fixation in marine phytoplankton

The efficiency of carbon sequestration by the biological pump could decline in the coming decades because respiration tends to increase more with temperature than photosynthesis. Despite these differences in the short‐term temperature sensitivities of photosynthesis and respiration, it remains unknown whether the long‐term impacts of global warming on metabolic rates of phytoplankton can be modulated by evolutionary adaptation. We found that respiration was consistently more temperature dependent than photosynthesis across 18 diverse marine phytoplankton, resulting in universal declines in the rate of carbon fixation with short‐term increases in temperature. Long‐term experimental evolution under high temperature reversed the short‐term stimulation of metabolic rates, resulting in increased rates of carbon fixation. Our findings suggest that thermal adaptation may therefore have an ameliorating impact on the efficiency of phytoplankton as primary mediators of the biological carbon pump.     

Taxol suppresses dynamics of individual microtubules in living human tumor cells

Microtubules are intrinsically dynamic polymers, and their dynamics play a crucial role in mitotic spindle assembly, the mitotic checkpoint, and chromosome movement. We hypothesized that, in living cells, suppression of microtubule dynamics is responsible for the ability of taxol to inhibit mitotic progression and cell proliferation. Using quantitative fluorescence video microscopy, we examined the effects of taxol (30-100 nM) on the dynamics of individual microtubules in two living human tumor cell lines: Caov-3 ovarian adenocarcinoma cells and A-498 kidney carcinoma cells. Taxol accumulated more in Caov-3 cells than in A-498 cells. At equivalent intracellular taxol concentrations, dynamic instability was inhibited similarly in the two cell lines. Microtubule shortening rates were inhibited in Caov-3 cells and in A-498 cells by 32 and 26%, growing rates were inhibited by 24 and 18%, and dynamicity was inhibited by 31 and 63%, respectively. All mitotic spindles were abnormal, and many interphase cells became multinucleate (Caov-3, 30%; A-498, 58%). Taxol blocked cell cycle progress at the metaphase/anaphase transition and inhibited cell proliferation. The results indicate that suppression of microtubule dynamics by taxol deleteriously affects the ability of cancer cells to properly assemble a mitotic spindle, pass the metaphase/anaphase checkpoint, and produce progeny.     

Effects of glutamine, proline, histidine and betaine on post-thaw motility of stallion spermatozoa

The supplementation of the freezing diluent with 3 amino acids (glutamine, proline and histidine) and 1 amino acid-related compound (betaine) in preserving stallion spermatozoa diluted in INRA82 extender containing 2.5% (v/v) glycerol and 2% (v/v) egg yolk (control extender) during freezing and thawing was studied at 0, 40, 80, 120 and 160 mM in 20 split ejaculates (10 stallions x 2 ejaculates; Experiment 1). Glutamine and proline were studied at 0, 10, 20, 30, 40, 50, 60, 70 and 80 mM in 20 split ejaculates (10 stallions x 2 ejaculates; Experiment 2). In each experiment, spermatozoa were evaluated after thawing by computer automated sperm analyzer. The percentage of motile spermatozoa (faster than 30 microns/sec) was assessed. In addition, the velocity of the average path (VAP), the straight line velocity (VSL), the curvilinear velocity (VCL) and the amplitude of the lateral head displacement (ALH) were also measured. In Experiment 1, only glutamine (40 mM) significantly improved sperm motility (56.0% +/- 3.0 vs 49.7% +/- 1.6; P < 0.05) compared with the control extender, while velocities were unaffected at concentrations of 40 to 120 mM. However, at 160 mM, a significant decrease in motility and velocity was observed for all amino acids. In Experiment 2, motility in glutamine (range 41.1% +/- 3.8%; 42.4% +/- 3.6) and proline (43.0% +/- 3.7; 45.6% +/- 3.8) extenders compared with the control (34.7% +/- 1.6) was improved significantly (P < 0.05). Sperm velocity was improved at concentrations higher than 40 mM glutamine and 50 mM proline.