Ventilatory physiology of the numbat (<Emphasis Type="Italic">Myrmecobius fasciatus</Emphasis>)

This study examines the ventilatory physiology of the numbat (Myrmecobius fasciatus), a small to medium-sized (550 g) termitivorous marsupial. Ventilatory parameters at thermoneutrality reflect the slightly low (83% of predicted) basal metabolic rate of the numbat, with ventilation frequency (ƒ_R; 30.6±3.65 breaths min^–1), tidal volume [V_T; 6.0±0.66 ml at body temperature and pressure, saturated (BTPS)] and consequently minute volume (V_I; 117.7±15.22 ml min^–1; BTPS) all being 80–87% of that expected for a marsupial of similar body mass. Oxygen extraction was 27.7±1.37% in the thermoneutral zone. As is typical of marsupials, numbats accommodated increased oxygen consumption rates at ambient temperatures (T _a) below the thermoneutral zone by increasing minute volume (up to 411.2±43.98 ml min^–1; BTPS at T _a=10 °C) rather than oxygen extraction. Minute volume at 10 °C increased more by changes in ventilation frequency (up to 45.5±4.85 breaths min^–1) than tidal volume (9.4±1.03 ml, BTPS), as is also typical for a small-medium sized marsupial.Abbreviations BMR basal metabolic rate - BTPS body temperature and pressure, saturated - EO ₂ oxygen extraction - ƒ _R ventilation frequency - STPD standard temperature and pressure, dry - T _a ambient temperature - T _b body temperature - TNZ thermoneutral zone - V _I minute volume - V _T tidal volume - O ₂ oxygen consumption rate Communicated by I.D. Hume     

Cardiorespiratory reflexes and aquatic surface respiration in the neotropical fish tambaqui (<Emphasis Type="Italic">Colossoma macropomum</Emphasis>): acute responses to hypercarbia

We examined the cardiorespiratory responses to 6 h of acute hypercarbia (1, 2.5, and 5% CO₂) in intact and gill-denervated (bilateral denervation of branchial branches of cranial nerves IX and X) tambaqui, Colossoma macropomum. Intact fish exposed to 1 and 2.5% CO₂ increased respiratory frequency (f_R) and ventilation amplitude (V_AMP) slowly over a 1- to 3-h period. Denervated fish did not show this response, suggesting that tambaqui possess receptors in the gills that will produce excitatory responses to low levels of hypercarbia (1 and 2.5% CO₂) if the exposure is prolonged. The cardiac response to stimulation of these receptors with this level of CO₂ was a tachycardia and not a bradycardia. During exposure to 5% CO₂, intact fish increased f_R and V_AMP, and showed a pronounced bradycardia after 1 h. After 2 h, the heart rate (f_H) started to increase, but returned to control values after 6 h. In denervated fish, the increase in f_R was abolished. The slow increase in V_AMP and the bradycardia were not abolished, suggesting that these changes arose from extra-branchial receptors. Neither intact nor denervated fish developed the swelling of the lower lip or performed aquatic surface respiration, even after 6 h, suggesting that these are unique responses to hypoxia and not hypercarbia.Abbreviations ASR aquatic surface respiration - f_H heart frequency - f_R respiratory frequency - V_AMP ventilation amplitude - _TOT total ventilation     

Teratological studies of prenatal exposure of mice to a 20 kHz sawtooth magnetic field

In order to evaluate the importance of gestational age in possible effects due to exposure to a 20 kHz sawtooth magnetic field, pregnant ICR mice at gestational 2.5-15.5 days post-coitus, which is the most sensitive stage for the induction of major congenital malformations, were exposed in a carrousel irradiator. The mice were exposed to a 20 kHz intermediate frequency (IF) sawtooth magnetic field had a 6.5 microT peak intensity for 8 h/day. The animals were sacrificed on the 18th day of gestation; and the fetuses were examined for mortality, growth retardation, changes in head size, and other morphological abnormalities. From the above conditions, it is concluded that the exposure to a 20 kHz sawtooth magnetic field with 6.5 microT peak intensity does not inflict any adverse effect on fetuses of pregnant mice.     

60 Hz electric field upregulates cytosolic Ca2+ level in mouse splenocytes stimulated by lectin

The effect of a 60 Hz electric field (EF) on alteration of cytosolic free Ca2+ level ([Ca2+]c) was examined in mouse splenocytes stimulated by lectins, namely concanavalin A (ConA) or phytohemagglutinin. In order to understand the role of EF on alterations in [Ca2+]c and to determine whether EF exposure increased cell mortality the splenocytes were cultured under the 60 Hz EFs producing current densities of 6 or 60 microA/cm2 for 30 min or 24 h. Cell mortality was less than 2% in experimental all conditions. [Ca2+]c in the splenocyte was not changed by the 6 microA/cm2 exposure alone, while a lectin-induced [Ca2+]c elevation in the EF exposed cells was significantly higher than that of the sham exposed cells (P <.05: ANOVA, P <.05: paired t-test). Moreover, the enhanced increase of [Ca2+]c in the EF exposed, lectin stimulated cells was only observed in the presence of extracellular Ca2+. The EF dependent upregulation of [Ca2+]c persisted after EF exposure (P <.05: paired t-test). The results clearly indicate that Ca2+ influx across the plasma membrane is responsible for the enhanced increase of [Ca2+]c in the EF exposed, lectin stimulated cells and that EF has persistent effect on the cells. Although the precise mechanisms of the EF dependent upregulation of [Ca2+]c is not fully elucidated, the present results demonstrate that the 60 Hz EF (6 microA/cm2) affects [Ca2+]c during cell activation via a Ca2+ influx pathway induced by lectin stimulation.     

In vitro exposure apparatus for ELF magnetic fields

For in vitro studies on the effect of extremely low frequency (ELF) magnetic field exposures in different laboratories, a programmable, high precision exposure system enabling blinded exposures has been developed and fully characterized. It is based on two shielded 4 coil systems that fit inside a commercial incubator. The volume of uniform B field exposure with 1% field tolerance is 50% larger compared to a Merrit 4 coil system with the same coil volume. The uncertainties for the applied magnetic fields have been specified to be less than 4%. The computer controlled apparatus allows signal waveforms that are composed of several harmonics, blind protocols, monitoring of exposure and environmental conditions and the application of B fields up to 3.6 mT root-mean-square amplitude. Sources of artifacts have been characterized: sham isolation >43 dB, parasitic incident E fields <1 V/m, no recognizable temperature differences in the media for exposure or sham state, and vibrations of the mechanically decoupled dish holder <0.1 m/s(2) (= 0.01 g), which is only twice the sham acceleration background level produced by the incubator and fan vibrations.     

Genome size variation in Central European species of Cirsium (Compositae) and their natural hybrids

BACKGROUND AND AIMS: Nuclear DNA amounts of 12 diploid and one tetraploid taxa and 12 natural interspecific hybrids of Cirsium from 102 populations in the Czech Republic, Austria, Slovakia and Hungary were estimated. METHODS: DAPI and PI flow cytometry were used. KEY RESULTS: 2C-values of diploid (2n = 34) species varied from 2.14 pg in C. heterophyllum to 3.60 pg in C. eriophorum (1.68-fold difference); the 2C value for the tetraploid C. vulgare was estimated at 5.54 pg. The DNA contents of hybrids were located between the values of their putative parents, although usually closer to the species with the smaller genome. Biennial species of Cirsium possessed larger nuclear DNA amounts than their perennial relatives. Genome size was negatively correlated with Ellenberg's indicator values for continentality and moisture and with eastern limits of distribution. A negative relationship was also detected between the genome size and the tendency to form natural interspecific hybrids. On the contrary, C-values positively corresponded with the spinyness (degree of spinosity). AT frequency ranged from 48.38 % in C. eriophorum to 51.75 % in C. arvense. Significant intraspecific DNA content variation in DAPI sessions was detected in C. acaule (probably due to the presence of B-chromosomes), and in tetraploid C. vulgare. Only the diploid level was confirmed for the Pannonian C. brachycephalum, generally considered to be tetraploid. In addition, triploidy was discovered for the first time in C. rivulare. CONCLUSIONS: Considerable differences in nuclear DNA content exist among Central European species of Cirsium on the diploid level. Perennial soft spiny Cirsium species of wet habitats and continental distributions generally have smaller genomes. The hybrids of diploid species remain diploid, and their DNA content is smaller than the mean of the parents. Species with smaller genomes produce interspecific hybrids more frequently.     

Structural characterization of the fusion core in syncytin, envelope protein of human endogenous retrovirus family W

Syncytin is a captive retroviral envelope protein, possibly involved in the formation of the placental syncytiotrophoblast layer generated by trophoblast cell fusion at the maternal-fetal interface. We found that syncytin and type I viral envelope proteins shared similar structural profiling, especially in the regions of N- and C-terminal heptad repeats (NHR and CHR). We expressed the predicted regions of NHR (41aa) and CHR (34aa) in syncytin as a native single chain (named 2-helix protein) to characterize it. 2-Helix protein exists as a trimer and is highly alpha-helix, thermo-stable, and denatured by low pH. NHR and CHR could form a protease-resistant complex. The complex structure built by the molecular docking demonstrated that NHR and CHR associated in an antiparallel manner. Overall, the 2-helix protein could form a thermo-stable coiled coil trimer. The fusion core structure of syncytin was first demonstrated in endogenous retrovirus. These results support the explanation how syncytin mediates cytotrophoblast cell fusion involved in placental morphogenesis.     

Attachment Sites and Frequency Distribution of Erythraeid Mites, Leptus Indianensis (Acari: Prostigmata), Ectoparasitic on Harvestmen, Leiobunum Formosum (Opiliones)

Host attachment sites and frequency distribution of parasitism were investigated for the larval erythraeid mite Leptus indianensis parasitising a sample of 500 harvestmen, Leiobunum formosum in Tennessee, USA. A significant difference was found in the number of mites attached to different body segments of the harvestmen with the greatest number of mites attached to femurs I–IV. Scanning electron microscopy revealed that the mites attached to smooth areas of the host integument between rows of stout setae. The frequency distribution of mites parasitising the harvestman population was highly clumped (Coefficient of Dispersion=3.34) with a relatively small number of hosts being parasitised by most of the mites.     

Parameter Estimation Methods for Single Neuron Models

With the advancement in computer technology, it has become possible to fit complex models to neuronal data. In this work, we test how two methods can estimate parameters of simple neuron models (passive soma) to more complex ones (neuron with one dendritic cylinder and two active conductances). The first method uses classical voltage traces resulting from current pulses injection (time domain), while the second uses measures of the neuron's response to sinusoidal stimuli (frequency domain). Both methods estimate correctly the parameters in all cases studied. However, the time-domain method is slower and more prone to estimation errors in the cable parameters than the frequency-domain method. Because with noisy data the goodness of fit does not distinguish between different solutions, we suggest that running the estimation procedure a large number of times might help find a good solution and can provide information about the interactions between parameters. Also, because the formulation used for the model's response in the frequency domain is analytical, one can derive a local sensitivity analysis for each parameter. This analysis indicates how well a parameter is likely to be estimated and helps choose an optimal stimulation protocol. Finally, the tests suggest a strategy for fitting single-cell models using the two methods examined.     

不同沙地生境下黄柳(Salix gordejevii)种群若干数量特征的比较研究

对分布于３种不同沙地生境（半固定沙丘、固定沙丘、丘间低地）黄柳灌丛的个体形态、生长和群体数量特征进行了比较研究,同时测定了灌丛下草本层植物种类组成及频率。结果显示：分布于丘间低地的黄柳灌丛当年枝平均长度增加缓慢,短枝条的比例较高,枝长频度分布（当年枝）峰值偏左,分枝也较多,叶片短而狭,长宽比大;与之相比,分布于半固定沙丘上的灌丛当年枝平均长度增加较快,长枝条比例较高,枝长频度分布趋于正态分布,分枝