bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of the Asc System and Na+/K+ Pump Activities in Brown Trout (Salmo Trutta) Hepatocytes
Authors: Gallardo M. A. , Pesquero J. , Esteve M. , Canals P. , Sánchez J. 
Published: April 2021

ABSTRACT
The present study investigates the regulation of Na+/K+ pump activity and alanine uptake in trout hepatocytes. Pump activity increased when cells were incubated in an amino-acid-free medium, while it was reduced in cells from fasted animals. Short-term exposure (3 h) to glucagon modified the activity of the pump in a complex seasonally dependent pattern: in experiments carried out in autumn and winter there was some inhibition, while in spring the pump was activated by this hormone.
Pharmacological modification of levels of two intracellular signal transducers, namely cyclic AMP and Ca2+, always led to a reduction in pump activity. These experiments were conducted in May, when activation of the pump by glucagon exposure occurred. There is no apparent explanation for the mechanism by which this hormone modifies the activity of the pump. Glucagon also regulates the activity of system ASC (a Na+-dependent amino acid carrier with short-chain neutral amino acids as preferred substrates). This regulation also showed a seasonally dependent pattern, although the pattern was opposite to that found for the regulation of Na+/K+ pump activity.
Homing Behaviour of Pigeons Subjected to Unilateral Zinc Sulphate Treatment of Their Olfactory Mucosa
Authors: Benvenuti Silvano , Gagliardo Anna 
Published: April 2021

ABSTRACT
Pigeons were made anosmic by unilateral treatment of their olfactory mucosa with a zinc sulphate solution and by plugging the contralateral nostril. In a series of releases at unfamiliar sites, 55–79 km from the home loft, the experimental birds’ homing behaviour was compared with that of two control groups: unmanipulated control birds, and birds subjected to unilateral zinc sulphate treatment and equipped with an ipsilateral nasal plug. The experimental pigeons exhibited homing behaviour – in terms of both homeward initial orientation and homing performance – significantly poorer than that of both unmanipulated and treated control pigeons. In addition, the homing behaviour of the treated controls turned out to be only slightly, and not significantly, poorer than that of the unmanipulated birds. The results show that the impaired homing capabilities of the zinc-sulphate-treated birds are due to the lack of navigational information and not to non-specific brain damage caused by the experimental treatment.
Leucokinin Increases Paracellular Permeability in Insect Malpighian Tubules
Authors: Wang Steven , Rubenfeld Ari B. , Hayes Timothy K. , Beyenbach Klaus W. 
Published: April 2021

ABSTRACT
There are two major transport pathways across epithelia: a transcellular pathway through cells and a paracellular pathway between cells. Previous electrophysiological studies in mosquito Malpighian tubules suggested that the neuropeptide leucokinin-VIII (LK-VIII) increases the chloride permeability of the paracellular pathway. To test the effect of LK-VIII on the paracellular pathway further, we measured transepithelial permeabilities of inulin and sucrose in isolated Malpighian tubules from the mosquito Aedes aegypti. Cell membranes are impermeable to inulin and sucrose, leaving the paracellular pathway as the only route for their transepithelial permeation. LK-VIII (10−6 mol l−1) significantly increased transepithelial permeability to both inulin (by 73.8 %) and sucrose (by 32.4 %) in parallel with a significant increase in rates of transepithelial fluid secretion (by 75–90 %). Cyclic adenosine monophosphate (cyclic AMP, 10−4 mol l−1), which is known to stimulate transcellular transport, also increased rates of transepithelial fluid secretion (by 57–59 %), but it did so without increasing the permeability to sucrose and inulin. Thus, LK-VIII increases the permeability of the paracellular pathway whereas cyclic AMP does not.
Heart and Respiratory Rates and Their Significance for Convective Oxygen Transport Rates in the Smallest Mammal, the Etruscan Shrew Suncus Etruscus
Authors: Jürgens Klaus D. , Fons Roger , Peters Thomas , Sender Susanne 
Published: April 2021

ABSTRACT
Heart and respiratory rates of the smallest mammal (mean adult body mass 2 g), the Etruscan shrew Suncus etruscus, were determined at rest and under stress conditions. Heart rate was obtained from electrocardiograms (ECGs), recorded via foot electrodes. The mean ± S.D. heart rate of resting animals (ambient temperature 22 °C) was 835±107 min−1, the mean maximal rate amounted to 1093±235 min−1. The highest single value recorded was 1511 min−1, which is the highest heart rate reported so far for an endotherm. The respiratory rate was also obtained from ECG recordings, which showed the electrical activity of the breathing muscles during inhalation, and additionally by recording the movements of the thoracic wall with a laser autofocus system. The mean resting respiratory rate was 661±93 min−1, the mean maximal rate was 758±109 min−1 and the highest single value recorded was 894 min−1. At 22 °C, the specific oxygen consumption rate is 67 times higher in resting S. etruscus than in resting humans. Under these conditions, the respiratory rate of the shrew is 47 times higher but the heart rate only 12 times higher than in man. Therefore, to achieve an adequate circulatory oxygen transport rate, the product of relative stroke volume and arterio–venous O2 difference has to be 5.6 times higher in the shrew than in man, whereas for an appropriate ventilatory oxygen transport rate the product of relative tidal volume and oxygen extraction has to be only 1.4 times higher in this small insectivore than in man. The maximal possible oxygen transport rates of the ventilatory and the circulatory system have been estimated and compared with the diffusional transport capacity of the lung. These rates amount to approximately 1000 ml O2 kg−1 min−1. According to our results and data in the literature, an aerobic scope of 7–10 seems to be realistic for the Etruscan shrew.
Transmission Of Vibration Across Honeycombs And Its Detection By Bee Leg Receptors
Authors: Sandeman D. C. , Tautz J. , Lindauer M. 
Published: April 2021

ABSTRACT
Vibration of the rims of open cells in a honeycomb, applied in the plane of the comb face, is transmitted across the comb. Attenuation or amplification of the vibratory signal depends on its frequency and on the type of comb. In general, framed combs, both large and small, strongly attenuate higher frequencies, whereas these are amplified in small open combs. The very poor transmission properties of the large framed combs used in commercial hives may explain the bees’ habit of freeing an area of comb from the frame in those areas used for dancing. Extracellular electrical recordings from the leg of a honeybee detect large action potentials from receptors that monitor extension of the tibia on the femur. Measurements of threshold displacement amplitudes show these receptors to be sensitive to low frequencies. The amplification properties of unframed combs extend the range of these receptor systems to include frequencies that are emitted by the bee during its dance, namely the 15 Hz abdomen waggle and 250 Hz thorax vibration.
Effects Of Ca2+ On Oxidative Phosphorylation In Mitochondria From The Thermogenic Organ Of Marlin
Authors: O’Brien John , Block Barbara A. 
Published: April 2021

ABSTRACT
Mitochondria from the muscle-derived thermogenic (heater) organ and oxidative red muscle of the blue marlin (Makaira nigricans) were studied in order to evaluate aspects of the mechanism of thermogenesis in heater tissue. We investigated whether short-term Ca2+-induced uncoupling of mitochondria contributes to the thermogenic cycle of the heater organ by enhancing the respiration rate. Specific electrodes were used to obtain simultaneous measurements of oxygen consumption and Ca2+ fluxes on isolated mitochondria, and the effects of various concentrations of Ca2+ on respiration rates and the ADP phosphorylated/atomic oxygen consumed (P/O) ratio were examined. Addition of Ca2+ in excess of 10 µmol l−1 to respiring heater organ or red muscle mitochondria partially inhibited state 3 respiration and reduced the P/O ratio, indicating that the mitochondria were partially uncoupled. These effects were blocked by 2 µmol l−1 Ruthenium Red. In heater organ mitochondria, state 3 respiration rate and the P/O ratio were not significantly reduced by 1µmol l−1 free Ca2+, a concentration likely to be near the maximum achieved in a stimulated cell. This indicates that transient increases in cytosolic Ca2+ concentration may not significantly reduce the P/O ratio of heater organ mitochondria. The activity of 2-oxoglutarate dehydrogenase in heater organ mitochondria was stimulated by approximately 15 % by Ca2+ concentrations between 0.2 and 1 µmol l−1. These results suggest that heater organ mitochondria are able to maintain a normal P/O ratio and should maintain ATP output during transient increases in Ca2+ concentration, supporting a model in which an ATP-consuming process drives thermogenesis. Activation of mitochondrial dehydrogenases by low levels of Ca2+ may also enhance respiration and contribute to thermogenesis.
Optomotor Behaviour in Xenopus Laevis Tadpoles as a Measure of the Effect of Gravity on Visual and Vestibular Neural Integration
Authors: Pronych Scott P. , Souza Kenneth A. , Neff Anton W. , Wassersug Richard J. 
Published: April 2021

ABSTRACT
The ability of aquatic vertebrates to maintain their position requires integration of visual and vestibular sensory information. To understand better how aquatic animals integrate such information, we measured the optomotor behaviour of Xenopus laevis tadpoles raised in growth chambers in microgravity (&lt;10−3g), normal gravity (1 g), hypergravity (3 g) and on a slowly rotating clinostat (simulated microgravity). The goal of this research was to determine how development in an altered gravitational force field affects the visual-and vestibular-dependent behaviour of tadpoles. This research represents the first time that the optomotor behaviour of an organism raised from fertilization in microgravity has been tested.
Significant differences were observed in the optomotor behaviour among the four gravity treatments. When first exposed to normal gravity, the microgravity-raised tadpoles exhibited the strongest (or most positive) optomotor behaviour, while the 3 g centrifuge tadpoles showed no optomotor response. Some abnormal behaviours (such as erratic swimming, lying motionless and abnormal swimming posture) were observed in the tadpoles raised in altered gravity on the initial day of testing. One day later, the tadpoles raised in hypergravity did not differ significantly in their optomotor behaviour from control tadpoles raised in normal gravity. However, tadpoles raised in microgravity still displayed an exaggerated optomotor response.
One week after the tadpoles had been introduced to normal gravity, there was no longer a significant difference in optomotor behaviour among the different gravity treatments. This convergence of optomotor behaviour by tadpoles from the different treatments reflects the acclimation of their vestibular systems to normal gravity.
Excretion and Distribution of Ammonia and the Influence of Boundary Layer Acidification in Embryonic Rainbow Trout (Oncorhynchus Mykiss)
Authors: Rahaman-Noronha E. , O’Donnell M. J. , Pilley C. M. , Wright P. A. 
Published: April 2021

ABSTRACT
This study examined ammonia excretion by embryos of the rainbow trout (Oncorhynchus mykiss). The distribution of ammonia in relation to the H+ distribution and electrical potential was determined. The influence of the pH of the unstirred layer (USL) of water next to the external surface of the embryo was also assessed. Eyed-up embryos (35–40 days post-fertilization) were exposed to various external water conditions [pH 6.0, pH 10.0, 1.6 mmol l−1 NaCl, 0.0 mmol l−1 NaCl, 0.2 mmol l−1 NH4Cl, 2.5 mmol l−1 borax buffer (Na2B4O7.10H2O), 2.5 mmol l−1 Hepes, 0.1 mmol l−1 amiloride] for 30 min and ammonia excretion rates, ammonia concentration in the perivitelline fluid (PVF) and yolk, and the pH of the PVF, yolk and USL were measured. The rate of ammonia excretion was dependent, in part, on the partial pressure gradient of NH3 from the PVF to the USL. Exposure to water of pH 6 increased, whereas NH4Cl or pH 10 exposure decreased, ammonia excretion rates. Elevated external Na+ levels also influenced the rate of ammonia excretion, but neither Na+-free water nor amiloride had any effect. The distribution of ammonia between the PVF and USL was dependent on the H+ distribution, but ammonia was distributed according to the electrical potential between the PVF and yolk. The USL was 0.32 pH units more acidic than the bulk water. Addition of buffer to the external water eliminated the acid USL and decreased ammonia excretion rates. We conclude that rainbow trout embryos excrete ammonia primarily as NH3, but when external Na+ levels are elevated, ammonia excretion may be independent of the gradient. The acidic USL next to the chorion probably facilitates NH3 diffusion by maintaining the through the conversion of NH3 to NH4+ upon entry into the USL.
The Respiratory Development of Atlantic Salmon: I. Morphometry of Gills, Yolk Sac and Body Surface
Authors: Wells Patrick R. , Pinder Alan W. 
Published: April 2021

ABSTRACT
During development from larva to juvenile in Atlantic salmon, Salmo salar, there is a change in the anatomical potential for gas exchange among gills, body skin and yolk sac as the larvae resorb yolk, grow and develop gills. Newly hatched Atlantic salmon have poorly developed gills but do have a high skin area to mass ratio and a large well-vascularized yolk sac. Cutaneous surfaces accounted for over 95 % of the total area available for respiration in newly hatched Atlantic salmon (body mass 0.032–0.060 g). The branchial contribution to total area increased rapidly, however, so that by the end of yolk absorption (body mass 0.19–0.23 g) it constituted 22 % of the total area and overtook cutaneous surface area between 5 and 6 g wet body mass. Harmonic mean diffusion distance across the skin increased through development from 20 μm at hatch (14 μm across the yolk sac) to 70 μm in an 11 g fish. Diffusion distances across both the filaments and lamellae of the gills decreased through development, from 3.7 to 2.4 μm for lamellae and from 14.5 to 10.8 μm for filaments.
The total anatomical diffusion factor (ADF, mass-specific surface area per unit diffusion distance) remained constant over early development and appeared to be higher than in adult fish. The distribution of ADF changed over early development from 50 % yolk sac, 42 % body surface and 8 % branchial in newly hatched fish to 68 % branchial and 32 % cutaneous at the end of yolk resorption. Generally, early post-hatch development of gills, ADF and some cutaneous surfaces showed high mass exponents. After yolk resorption (body mass 0.2 g), however, these coefficients were lower and closer to unity. The change in scaling at the end of yolk resorption in this study may reflect the completion of larva to juvenile metamorphosis in Atlantic salmon. Comparison between our data and values in the literature suggests that the timing of gill development is related more to developmental stage than to body size.
Hummingbird Hovering Performance in Hyperoxic Heliox: Effects of Body Mass and Sex
Authors: Chai Peng , Harrykissoon Rajesh , Dudley Robert 
Published: April 2021

ABSTRACT
Owing to their small size and hovering locomotion, hummingbirds are the most aerobically active vertebrate endotherms. Can hyperoxia enhance the flight performance of this highly oxygen-dependent group? Hovering performance of ruby-throated hummingbirds (Archilochus colubris) was manipulated non-invasively using hyperoxic but hypodense gas mixtures of sea-level air combined with heliox containing 35 % O2. This manipulation sheds light on the interplay among metabolic power input, mechanical power output and aerodynamic force production in limiting flight performance. No significant differences in flight mechanics and oxygen consumption were identified between hyperoxic and normoxic conditions. Thus, at least in the present experimental context, hyperoxia did not change the major metabolic and mechanical parameters; O2 diffusive capacities of the respiratory system were probably not limiting to a significant extent. Compared with hummingbirds in our previous studies, the present experimental birds were heavier, had resultant shorter hover-feeding durations and experienced aerodynamic failure at higher air densities. Because hummingbirds have relatively stable wingbeat frequencies, modulation of power output was attained primarily through variation in stroke amplitude up to near 180 °. This result indicates that maximum hovering performance was constrained geometrically and that heavier birds with greater fat loads had less margin for enhancement of power production. Sexual dimorphism in flight adaptation also played a role, with males showing more limited hovering capacities, presumably as a trade-off for increased maneuverability.
Wingbeat Frequency and the Body Drag Anomaly: Wind-Tunnel Observations on a Thrush Nightingale (Luscinia Luscinia) And a Teal (Anas Crecca)
Authors: Pennycuick C. J. , Klaassen Marcel , Kvist Anders , lindström Åke 
Published: April 2021

ABSTRACT
A teal (Anas crecca) and a thrush nightingale (Luscinia luscinia) were trained to fly in the Lund wind tunnel for periods of up to 3 and 16 h respectively. Both birds flew in steady flapping flight, with such regularity that their wingbeat frequencies could be determined by viewing them through a shutter stroboscope. When flying at a constant air speed, the teal’s wingbeat frequency varied with the 0.364 power of the body mass and the thrush nightingale’s varied with the 0.430 power. Both exponents differed from zero, but neither differed from the predicted value (0.5) at the 1 % level of significance. The teal continued to flap steadily as the tunnel tilt angle was varied from —1 ° (climb) to +6 ° (descent), while the wingbeat frequency declined progressively by about 11 %. In both birds, the plot of wingbeat frequency against air speed in level flight was U-shaped, with small but statistically significant curvature. We identified the minima of these curves with the minimum power speed (Vmp) and found that the values predicted for Vmp, using previously published default values for the required variables, were only about two-thirds of the observed minimum-frequency speeds. The discrepancy could be resolved if the body drag coefficients (CDb) of both birds were near 0.08, rather than near 0.40 as previously assumed. The previously published high values for body drag coefficients were derived from wind-tunnel measurements on frozen bird bodies, from which the wings had been removed, and had long been regarded as anomalous, as values below 0.01 are given in the engineering literature for streamlined bodies. We suggest that birds of any size that have well-streamlined bodies can achieve minimum body drag coefficients of around 0.05 if the feet can be fully retracted under the flank feathers. In such birds, field observations of flight speeds may need to be reinterpreted in the light of higher estimates of Vmp. Estimates of the effective lift:drag ratio and range can also be revised upwards. Birds that have large feet or trailing legs may have higher body drag coefficients. The original estimates of around CDb=0.4 could be correct for species, such as pelicans and large herons, that also have prominent heads. We see no evidence for any progressive reduction of body drag coefficient in the Reynolds number range covered by our experiments, that is 21 600–215 000 on the basis of body cross-sectional diameter.
in vivo Length Oscillations of Indirect Flight Muscles in The Fruit Fly Drosophila Virilis
Authors: Chan Wai Pang , Dickinson Michael H. 
Published: April 2021

ABSTRACT
We have used high-speed video microscopy to measure in vivo length oscillations of the indirect flight muscles of the fruit fly Drosophila virilis during tethered flight. The changes in muscle strain were measured by tracking the deformation of the thoracic exoskeleton at the origin and insertion of both the dorsal longitudinal (DLM) and the dorsal ventral (DVM) muscles. The mean peak-to-peak strain amplitudes were found to be 3.5 % for the DLMs and 3.3 % for the DVMs, although the strain amplitude within individual cycles ranged from 2 to 5 %. These values are consistent with the small number of previous measurements of indirect flight muscle strain in other insects, but almost an order of magnitude greater than the strain amplitudes used in most biophysical studies of skinned Drosophila fibers. The results suggest that serial compliance within this sarcomere would need to relieve approximately 70 % of the total strain in order for individual crossbridges to remain attached throughout a complete contraction–extension cycle.
Aerodynamic Characteristics of the Wings and Body of a Dragonfly
Authors: Okamoto Masato , Yasuda Kunio , Azuma Akira 
Published: April 2021

ABSTRACT
The aerodynamic characteristics of the wings and body of a dragonfly and of artificial wing models were studied by conducting two types of wind-tunnel tests and a number of free-flight tests of gliders made using dragonfly wings. The results were consistent between these different tests. The effects of camber, thickness, sharpness of the leading edge and surface roughness on the aerodynamic characteristics of the wings were characterized in the flow field with Reynolds numbers (Re) as low as 103 to 104.
Dynamic Anatomical Study Of Cardiac Shunting In Crocodiles Using High-Resolution Angioscopy
Authors: Axelsson Michael , Franklin Craig E. , Löfman Carl O. , Nilsson Stefan , Grigg Gordon C. 
Published: April 2021

ABSTRACT
Prolonged submergence imposes special demands on the cardiovascular system. Unlike the situation in diving birds and mammals, crocodilians have the ability to shunt blood away from the lungs, despite having an anatomically divided ventricle. This remarkable cardiovascular flexibility is due in part to three anatomical peculiarities: (1) an ‘extra’ aorta (the left aorta) that leaves the right ventricle and allows the blood from the right ventricle to take an alternative route into the systemic circulation instead of going to the lungs; (2) the foramen of Panizza, an aperture that connects the right and left aortas at their base immediately outside the ventricle; and (3) a set of connective tissue outpushings in the pulmonary outflow tract in the right ventricle. Using high-resolution angioscopy, we have studied these structures in the beating crocodile heart and correlated their movements with in vivo pressure and flow recordings. The connective tissue outpushings in the pulmonary outflow tract represent an active mechanism used to restrict blood flow into the lungs, thus creating one of the conditions required for a right-to-left shunt. We observed that the foramen of Panizza was obstructed by the medial cusp of the right aortic valve during most of systole, effectively differentiating the left and right aortic blood pressure. During diastole, however, the foramen remained open, allowing pressure equilibration between the two aortas. Contrary to current theories, we found that the left aortic valves were unable to cover the foramen of Panizza during any part of the cardiac cycle, supporting the reversed foramen flow hypothesis. This would ensure a supply of blood to the coronary and cephalic circulation during a complete shut-down of the left side of the heart, such as might occur during prolonged submergence.