Convective exchange between the nose and the atmosphere

It is generally accepted that there is little rebreathing of gas exhaled through the nose. A detailed physical model system has been used to quantify and identify the mechanisms responsible for this phenomenon. By the use of a cast of the upper respiratory tract and oscillating flows with a Reynolds number of 500 and nondimensional frequency of 1.6, corresponding to quiet tidal breathing through the nose, dye dilution measurements indicated an efficiency of tidal exchange of 0.95. Flow visualization studies performed to trace the expiratory flow, as well as the streamlines during steady inspiratory flow, support the hypothesis that the high efficiency of exchange is due to radical differences in the velocity fields between inspiratory and expiratory phases of this oscillatory flow. These findings confirm that convective gas exchange between the nose and the atmosphere is highly efficient; however, the underlying mechanism responsible for this exchange also maximizes the exposure of the respiratory system to aerosols contained in the ambient atmosphere.     

Passage of uncharged dextrans from blood to lung lymph in awake sheep

To examine how molecular size alone influences the passage of macromolecules from the pulmonary microcirculation into lymph collected from the caudal mediastinal lymph node of the sheep, we infused polydisperse uncharged [3H]dextrans intravenously at a constant rate over a period of 7.5 h in nine awake sheep with lung lymph fistulas. Lymph and plasma were collected during hours 5.5-7.5 of the infusions, and the [3H]dextrans were separated by molecular sieve chromatography into fractions that ranged from 1.6 to 8.4 nm in effective molecular (Stokes-Einstein) radius. Lymph-to-plasma (L/P) ratios for [3H]dextrans were near 1.0 at 1.6-nm radius, decreased with increasing molecular size, and approached zero at radii above 5.0 nm. We confirmed that these L/P ratios represented steady-state values by extending the duration of the infusion to approximately 30 h in two of the nine sheep and finding that the L/P ratios remained unchanged. These results were consistent with molecular sieving through a homoporous membrane with cylindrical pores of 5.0-nm radius. We also found that the L/P ratio for albumin [0.76 +/- 0.13 (SE)] in five of the same sheep was much higher than that for the [3H]dextran fraction of the same effective molecular radius [0.11 +/- 0.02 (SE)]. These results suggest that the movement of macromolecules from the pulmonary microcirculation into pulmonary lymph collected from the caudal mediastinal node of the sheep is influenced by both molecular size and molecular charge and that, compared with uncharged dextrans, the steady-state passage of anionic endogenous proteins from plasma to lymph is enhanced.     

Activation of neurons in the rostral ventrolateral medulla increases bronchomotor tone in dogs.

Previous work from this laboratory has demonstrated that the chemical activation of cell bodies in the caudal ventrolateral medulla of chloralose-anesthetized dogs decreased bronchomotor tone by withdrawing cholinergic input to airway smooth muscle. In the present study we determined the bronchomotor responses to microinjection of DL-homocysteic acid (100 mM; 25-50 nl) into the rostral ventrolateral (RVL) medulla of chloralose-anesthetized dogs. Total lung resistance was used as a functional index of bronchomotor tone. Microinjection of DL-homocysteic acid into the 20 sites located in the lateral aspect of the RVL medulla increased both total lung resistance [from 6.5 +/- 0.4 to 9.1 +/- 0.8 (SE) cmH2O.l-1.s; P less than 0.05] and mean arterial pressure (from 125 +/- 5 to 148 +/- 8 mmHg; P less than 0.05). Microinjection of this amino acid into nine sites located in the medial aspect of the RVL medulla increased mean arterial pressure (from 130 +/- 6 to 153 +/- 6 mmHg; P less than 0.05) but had no effect on total lung resistance. We confirmed in three sites that the increase in total lung resistance evoked by microinjection of DL-homocysteic acid was accompanied by an increase in tracheal smooth muscle tension. The increase in total lung resistance evoked by DL-homocysteic acid was not affected by beta-adrenergic blockade but was abolished by muscarinic blockade.     

Dispersal and dormancy strategies among insect species competing for a pulsed resource

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Peribacteroid space acidification: a marker of mature bacteroid functioning in Medicago truncatula nodules

Legumes form a symbiotic interaction with Rhizobiaceae bacteria, which differentiate into nitrogen‐fixing bacteroids within nodules. Here, we investigated in vivo the pH of the peribacteroid space (PBS) surrounding the bacteroid and pH variation throughout symbiosis. In vivo confocal microscopy investigations, using acidotropic probes, demonstrated the acidic state of the PBS. In planta analysis of nodule senescence induced by distinct biological processes drastically increased PBS pH in the N₂‐fixing zone (zone III). Therefore, the PBS acidification observed in mature bacteroids can be considered as a marker of bacteroid N₂ fixation. Using a pH‐sensitive ratiometric probe, PBS pH was measured in vivo during the whole symbiotic process. We showed a progressive acidification of the PBS from the bacteroid release up to the onset of N₂ fixation. Genetic and pharmacological approaches were conducted and led to disruption of the PBS acidification. Altogether, our findings shed light on the role of PBS pH of mature bacteroids in nodule functioning, providing new tools to monitor in vivo bacteroid physiology.     

Cold‐induced expression of diapause in Praon volucre: fitness cost and morpho‐physiological characterization

Cold exposure (2°C for 7 days) in constant darkness at mummy stage induces diapause expression in 9% of the Praon volucre Haliday population. Diapausing parasitoids show a significant delay in emergence time compared with nondiapausing counterparts. A diapause‐mediated polyphenism is observed in mummy colour, with diapausing mummies being clearly darker than nondiapausing ones. The diapause status of dark mummies is confirmed by a significant reduction in metabolic rate. Diapausing parasitoids also display specific morphological characteristics: they are heavier (fresh and dry mass) and accumulate larger fat reserves than nondiapausing counterparts. The diapause status is associated with a fitness cost in terms of adult longevity. There is no evidence of diapause‐related change in supercooling ability.     

One hundred years of instability in ensiferan relationships

Although Ensifera is a major insect model group, its phylogenetic relationships have been understudied so far. Few phylogenetic hypotheses have been proposed, either with morphological or molecular data. The largest dataset ever used for phylogeny reconstruction on this group is molecular (16S rRNA, 18S rRNA and 28S rRNA sequences for 51 ensiferan species), which has been used twice with different resultant topologies. However, only one of these hypotheses has been adopted commonly as a reference classification. Here we re‐analyse this molecular dataset with different methods and parameters to test the robustness and the stability of the adopted phylogeny. Our study reveals the instability of phylogenetic relationships derived from this dataset, especially for the deepest nodes of the group, and suggests some guidelines for future studies. The comparison between the different classifications proposed in the past 70 years for Ensifera and our results allows the identification of potential monophyletic clades (katydids, mole crickets, scaly crickets + Malgasia, true crickets, leaf roller crickets, cave crickets) and the remaining unresolved clades (wetas, Jerusalem crickets and most of the highest rank clades) in Ensifera phylogeny.     

Effects of relative humidity and buffer additives on the contact printing of microarrays by quill pins

DNA microarrays printed with quill pins exhibit significant variation in probe DNA spots. Interspot variations and nonuniform distribution of probe within spots are major sources of experimental uncertainty in microarray analysis. To gain better insight into the sources of variation, we analyzed 450 consecutive depositions printed at relative humidities between 40 and 80% using three print buffers. Increasing relative humidity improved printing performance by delaying pin failure but did not reduce the variability in spot characteristics. Adding either betaine or dimethyl sulfoxide (DMSO) to the print buffer also improved quill pin performance. Least interspot variation was observed with the DMSO additive printed at 80% relative humidity, but this additive also resulted in the greatest intraspot variation. Least intraspot variation was observed with 1.5M betaine printed at 60% relative humidity, but these conditions produced microarrays with high interspot variability. Evaporation of printing solution from the quill reservoir appeared to be the primary cause of interspot and intraspot variations. Our studies indicate that relative humidity and printing solution additives reduce evaporation. Based on the spot variability requirements for a particular application, humidity and additives may be chosen to optimize either inter- or intraspot variability.     

Molecular beacon sequence design algorithm

A method based on Web-based tools is presented to design optimally functioning molecular beacons. Molecular beacons, fluorogenic hybridization probes, are a powerful tool for the rapid and specific detection of a particular nucleic acid sequence. However, their synthesis costs can be considerable. Since molecular beacon performance is based on its sequence, it is imperative to rationally design an optimal sequence before synthesis. The algorithm presented here uses simple Microsoft Excel formulas and macros to rank candidate sequences. This analysis is carried out using mfold structural predictions along with other free Web-based tools. For smaller laboratories where molecular beacons are not the focus of research, the public domain algorithm described here may be usefully employed to aid in molecular beacon design.