bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnesium Transport in Freshwater Teleosts
Authors: Bijvelds Marcel J. C. , Van Der Velden Joan A. , Kolar Zvonimir I. , Flik Gert 
Published: April 2021

ABSTRACT
The magnesium handling of freshwater teleost fish is discussed, with an emphasis on the role of branchial, intestinal and renal transport. In response to the eminent threat of constant diffusive losses of minerals such as magnesium, freshwater fish have developed efficient mechanisms for magnesium homeostasis. Magnesium losses are overcome by the uptake of magnesium from the food, making the intestine an important route for magnesium uptake. Some evidence suggests that intestinal magnesium uptake in fish is a regulated, cellular process. The ambient water is an additional magnesium source for fish, implicating the gills as a secondary route for magnesium uptake. Certainly, in some species, direct uptake from the water, probably via branchial routes, ameliorates the effects of a low-magnesium diet. The hard tissues, representing over 50 % of the total body magnesium pool, form a reservoir from which magnesium can be recruited to perform its functions in the cellular metabolism of soft tissues such as muscle. In fish, as in terrestrial vertebrates, the balance of a variety of elements becomes disturbed when the magnesium homeostasis of the soft tissues is disrupted. However, fish appear to be less sensitive than terrestrial vertebrates to these perturbations. Magnesium is reabsorbed in the kidneys to minimise losses. For renal cells, part of a cellular pathway has been elucidated that would allow absorptive magnesium transport (a magnesium conductive pathway in renal brush-border membranes). In some euryhaline teleosts, the kidneys appear to switch instantaneously to rapid magnesium secretion upon magnesium loading, a response common to marine fish that are threatened by diffusive magnesium entry. This enigmatic mechanism underlies the capacity of some euryhaline species to acclimate rapidly to sea water. Despite the progress made over the last decade, much of the cellular and molecular basis of magnesium transport in the gills, intestine and kidneys remains obscure. The application of fluorescent, radioactive and molecular probes, some of which have only recently become available, may yield rapid progress in the field of magnesium research.
Kinetic Analysis of a Signal-Transduction Pathway by Time-Resolved Somatic Complementation of Mutants
Authors: Starostzik Christine , Marwan Wolfgang 
Published: April 2021

ABSTRACT
Sensory control of sporulation in Physarum polycephalum plasmodia is mediated by a branched signal-transduction pathway that integrates blue light, far-red light, heat shock and the starvation state. Mutants defective in the pathway were isolated and three phenotypes obtained: blue-blind, general-blind and light-independent sporulating. When plasmodia of the blue-blind mutant Blu1 were exposed to a pulse of blue light and subsequently fused to non-induced wild-type plasmodia, the resulting heterokaryons sporulated, indicating a functional blue-light photoreceptor in the mutant. When the general-blind mutant Nos1 was fused to a wild-type plasmodium which had been induced by light, sporulation of the heterokaryon was blocked. However, the dominant inhibition of sporulation by Nos1 was gradually lost with increasing time between induction by light and time of fusion, suggesting that Nos1 can be bypassed by the time-dependent formation of a downstream signal-transduction intermediate. Phenotype expression in constitutively sporulating (Cos) mutants depended on starvation. The Cos2 product was titrated by fusing mutant plasmodia of different sizes to wild-type plasmodia of constant size and analysing the sporulation probability of the resulting heterokaryon. The titration curve indicates that a small change in the amount of Cos2 product can cause sporulation. We conclude that somatic complementation analysis allows the time-resolved evaluation of the regulatory function of mutations in a signal-transduction pathway without prior cloning of the gene. This shortcut allows us to characterize many mutants quickly and to select those for molecular analysis that display a well-defined regulatory function.
Organic Matrix Synthesis in the Scleractinian Coral Stylophora Pistillata: Role in Biomineralization and Potential Target of the Organotin Tributyltin
Authors: Allemand Denis , Tambutté Éric , Girard Jean-Pierre , Jaubert Jean 
Published: April 2021

ABSTRACT
The kinetics of organic matrix biosynthesis and incorporation into scleractinian coral skeleton was studied using microcolonies of Stylophora pistillata. [14C]Aspartic acid was used to label the organic matrix since this acidic amino acid can represent up to 50 mol % of organic matrix proteins. External aspartate was rapidly incorporated into tissue protein without any detectable lag phase, suggesting either a small intracellular pool of aspartic acid or a pool with a fast turn-over rate. The incorporation of 14C-labelled macromolecules into the skeleton was linear over time, after an initial delay of 20 min. Rates of calcification, measured by the incorporation of 45Ca into the skeleton, and of organic matrix biosynthesis and incorporation into the skeleton were constant. Inhibition of calcification by the Ca2+ channel inhibitor verapamil reduced the incorporation of organic matrix proteins into the skeleton. Similarly, organic matrix incorporation into the skeleton, but not protein synthesis for incorporation into the tissue compartment, was dependent on the state of polymerization of both actin and tubulin, as shown by the sensitivity of this process to cytochalasin B and colchicin. These drugs may inhibit exocytosis of organic matrix proteins into the subcalicoblastic space. Finally, inhibition of protein synthesis by emetin or cycloheximide and inhibition of N-glycosylation by tunicamycin reduced both the incorporation of macromolecules into the skeleton and the rate of calcification. This suggests that organic matrix biosynthesis and its migration towards the site of calcification may be a prerequisite step in the calcification process. On the basis of these results, we investigated the effects of tributyltin (TBT), a component of antifouling painting known to interfere with biomineralization processes. Our results have shown that this xenobiotic significantly inhibits protein synthesis and the subsequent incorporation of protein into coral skeleton. This effect was correlated with a reduction in the rate of calcification. Protein synthesis was shown to be the parameter most sensitive to TBT (IC50=0.2 µmol l−1), followed by aspartic acid uptake by coral tissue (IC50=0.6 µmol l−1), skeletogenesis (IC50=3 µmol l−1) and Ca2+ uptake by coral tissue (IC50=20 µmol l−1). These results suggest that the mode of action of TBT on calcification may be the inhibition of organic matrix biosynthesis.
Diving Speeds and Angles of a Gyrfalcon (Falco Rusticolus)
Authors: Tucker Vance A. , Cade Tom J. , Tucker Alice E. 
Published: April 2021

ABSTRACT
An optical tracking device recorded the three-dimensional paths of 11 dives by a 1.02 kg gyrfalcon, trained to dive to a falconer. The dives started at altitudes up to 500 m above the ground and were inclined at angles of 17–62 ° from the horizontal. The falcon controlled its speed during the dives, rather than simply falling from the sky, and the dives had three phases. During the first (acceleration) phase, the falcon accelerated to speed limits between 52 and 58 m s−1 in the seven fastest dives, evidently with minimum drag, because its accelerations were close to those predicted from theory for minimum drag. The falcon then began a constant-speed phase by increasing drag by a factor of 1.3–4.8 while still 100–350 m above the ground in most dives. The constant-speed phase lasted no more than a few seconds, and the falcon then began a deceleration phase by increasing its drag further, this time by factors of 1.7–3.2, and decelerating with a mean value of −0.95 times gravitational acceleration.
During all three phases, the dive angle was nearly constant or increased during the deceleration phase, and the falcon made no changes in its body shape that were obvious through the tracking device telescope except to reduce its wing span as it accelerated. The falconer, however, was close to the falcon at the end of the dive and could see that, during the deceleration phase, the falcon held its wings in a cupped position, apparently with a high angle of attack and therefore high drag. At the end of the deceleration phase, the falcon dropped its legs, spread its toes and finally spread its wings as it approached the falconer.
Although the speeds reported here are the fastest ever measured with known accuracy in animals, the falcon could theoretically have reached more than 70 m s−1 if it had continued to accelerate with minimum drag until close to the ground. Even at this speed, it would have had enough altitude to pull out of the dive before crashing into the ground. Several authors have estimated that diving falcons reach speeds of more than 70 m s−1, and wild falcons may reach such speeds when they make long, steep dives upon birds flying high in the air.
Mechanics and Energetics of Human Locomotion on Sand
Authors: Lejeune T. M. , Willems P. A. , Heglund N. C. 
Published: April 2021

ABSTRACT
Moving about in nature often involves walking or running on a soft yielding substratum such as sand, which has a profound effect on the mechanics and energetics of locomotion. Force platform and cinematographic analyses were used to determine the mechanical work performed by human subjects during walking and running on sand and on a hard surface. Oxygen consumption was used to determine the energetic cost of walking and running under the same conditions. Walking on sand requires 1.6–2.5 times more mechanical work than does walking on a hard surface at the same speed. In contrast, running on sand requires only 1.15 times more mechanical work than does running on a hard surface at the same speed. Walking on sand requires 2.1–2.7 times more energy expenditure than does walking on a hard surface at the same speed; while running on sand requires 1.6 times more energy expenditure than does running on a hard surface. The increase in energy cost is due primarily to two effects: the mechanical work done on the sand, and a decrease in the efficiency of positive work done by the muscles and tendons.
Effects of Buoyancy on the Diving Behavior of Northern Elephant Seals
Authors: Webb P. M. , Crocker D. E. , Blackwell S. B. , Costa D. P. , Boeuf B. J. Le 
Published: April 2021

ABSTRACT
Marine mammals experience radical seasonal changes in body composition, which would be expected to affect their buoyancy in the water. The aim of this study was to examine the relationship between such changes in buoyancy and diving behavior in northern elephant seals Mirounga angustirostris. This was achieved by modifying the buoyancy of 13 juvenile elephant seals translocated from Año Nuevo State Reserve, CA, USA, and released at various sites in Monterey Bay, CA, USA. The buoyancy of each seal was calculated and was increased or decreased using syntactic foam or lead weights, and their diving behavior was recorded as they returned to Año Nuevo. The seals were divided into three groups: increased buoyancy (B+), reduced buoyancy (B−) and control seals (Bc). Mean descent rates were 0.77±0.3 m s−1 for the B+ seals, 0.82±0.2 m s−1 for the control seals and 0.87±0.3 m s−1 for the B-seals, and were significantly different. Mean ascent rates for the three treatments were 0.82±0.3 m s−1 for the B+ seals, 0.86±0.3 m s−1 for the control seals and 0.82±0.3 m s−1 for the B− seals. All the B+ seals ascended faster than they descended, while four of the five B− seals descended faster than they ascended. There was a significant negative correlation between buoyancy and descent rate, with less buoyant seals descending faster than more buoyant seals. There was, however, no correlation between ascent rate and buoyancy. This suggests that seals may use negative buoyancy to drift passively during descent, but that all seals may swim continuously during ascent. There was a significant correlation between buoyancy and the drift descent rate of C-type drift dives, including upwards drift in the most buoyant seal. Buoyancy was not correlated with diving depth, trip duration, dive duration or surface-interval duration. This study demonstrates that buoyancy plays a significant role in shaping diving behavior in northern elephant seals and that elephant seals may adjust their behavior to suit their buoyancy, rather than adjusting their buoyancy to suit a dive. This study also validated the truncated cones method of calculating body composition in this species by comparing it with body composition determined using tritium dilution.
Programmed Cell Death Specifically Eliminates one Part of a Locust Pleuroaxillary Muscle after the Imaginal Moult
Authors: Meuser Susanne , Pflüger Hans-Joachim 
Published: April 2021

ABSTRACT
In the hemimetabolous insect Locusta migratoria, fundamental restructuring occurs at the transition from flightless nymph to flight-capable adult. This transition involves all components of the flight circuit, which is present but not used for flight in nymphs. The meso- and metathoracic pleuroaxillary muscles, M85 and M114 respectively, constitute one component of this circuit. In the adult locust, these are flight-steering muscles, but their function in the nymph is as yet unknown. Our study reveals that adult and nymphal metathoracic pleuroaxillary muscles M114 differ profoundly. The nymphal muscle contains the distinct part M114c in addition to parts M114a and M114b characteristic of the adult. The contractions of M114c are slow and long-lasting, corresponding to its long sarcomeres and slow form of ATPase, and contrast with the adult muscle parts M114a and M114b in all of these features. We demonstrate a hormone-dependent degeneration of M114c after the adult moult. This degeneration can be blocked by actinomycin D and cycloheximide. It may thus be termed genetically programmed cell death, triggered after the adult moult and, as demonstrated here, functioning via the ATP-dependent ubiquitin pathway. Given the defined onset of degeneration after the adult moult, it is possible that M114c may fulfil a specific function in nymphs, during or shortly after moulting.
Locust Dorsal Unpaired Median (Dum) Neurones Directly Innervate And Modulate Hindleg Proprioceptors
Authors: Bräunig Peter , Eder Matthias 
Published: April 2021

ABSTRACT
A subgroup of the large efferent octopaminergic dorsal unpaired median (DUM) neurones of the third thoracic ganglion, the DUM3,4,5 neurones, directly innervates the tendons of certain proprioceptors of the locust hindleg, the so-called strand receptors. The terminals of the DUM neurones occur in regions of the strands that also contain the dendrites of the mechanoreceptive sensory cells. Both stimulation of the DUM3,4,5 neurones and bath application of octopamine change the responses of strand receptor units to mechanical stimulation. In both situations, most single strand receptor units show an increased response to mechanical stimulation. Some units, however, decrease their sensitivity to mechanical stimulation in response to octopamine application or DUM neurone stimulation.
Synaptic Activation Of Efferent Neuromodulatory Neurones In The Locust Schistocerca Gregaria
Authors: Baudoux Sylvie , Burrows Malcolm 
Published: April 2021

ABSTRACT
The segmental ganglia of the locust contain efferent neuromodulatory neurones with cell bodies at the dorsal midline and axons that supply muscles and other tissue on both sides of the body. These are the dorsal unpaired median (DUM) neurones. Intracellular recordings were made from pairs of known metathoracic efferent DUM neurones in locusts in which all nerves were intact and in isolated metathoracic ganglia. The 19 metathoracic, efferent DUM neurones were identified according to the nerve roots through which their axons emerge from the ganglion. The synaptic potentials in these DUM neurones have been analysed to investigate how these neurones are activated and how their spikes are controlled.
The degree of correlation between the synaptic potentials in particular pairs of neurones was quantified using a correlation analysis. This allowed the population of DUM neurones to be divided into three subsets that also map onto an anatomical grouping based on the distribution of their axons in the lateral nerves: (i) DUM1 neurones (DUMDL and DUM1b); (ii) DUM3 and DUM3,4 neurones; and (iii) DUM3,4,5, DUM5b neurones and DUMETi. Individual neurones within each subset showed strong correlations between their synaptic potentials, in both intact locusts and isolated ganglia, and tended to spike at the same time. Neurones in different subsets had few synaptic potentials in common and tended to spike independently. The persistence of common synaptic potentials in neurones of the three subsets in isolated ganglia indicates that they are derived from neurones within the metathoracic ganglion.
The DUM neurones that had many common synaptic potentials in a quiescent locust responded in similar ways to mechanosensory stimulation of different parts of the body. DUM3,4,5 and DUM5 neurones gave the clearest and most consistent responses to stimulation of mechanoreceptors on either hind leg. DUM3 and DUM3,4 neurones responded variably, but usually with a hyperpolarisation. DUM1 neurones were rarely excited by mechanosensory stimuli but, like the preceding group, their responses were dependent upon whether the locust was moving its legs.
These results lend further support to the idea that there is a subdivision of action amongst this population of DUM neurones, with those supplying the same targets being driven by the same presynaptic local neurones.
Hypoxia Elicits an Increase in Pulmonary Vasculature Resistance in Anaesthetised Turtles (Trachemys Scripta)
Authors: Crossley Dane , Altimiras Jordi , Wang Tobias 
Published: April 2021

ABSTRACT
In mammals and birds, low oxygen levels in the lungs cause a constriction of the pulmonary vasculature. This response is locally mediated and is considered to be important for local matching of perfusion and ventilation. It is not known whether reptiles respond in a similar fashion. The present study describes the effects of altering lung oxygen levels (at a constant of 0.03) on systemic and pulmonary blood flows and pressures in anaesthetised (Nembumal, 50 mg kg−1) and artificially ventilated turtles Trachemys scripta. During severe hypoxia (1.5–3 kPa ), pulmonary blood flow decreased in all animals; systemic blood flow increased, resulting in an increased net right-to-left shunt blood flow. The redistribution of blood flows was associated with reciprocal changes in the vascular resistances within the pulmonary and the systemic circulations (Rpul and Rsys, respectively). At 1.5 kPa O2, Rpul increased from 0.09±0.01 to 0.15±0.03 kPa ml−1 min kg during normoxia (means ±1 S.E.M., N=5). Concurrently, Rsys tended to decrease from a normoxic value of 0.12±0.01 to 0.09±0.02 kPa ml−1 min kg (P=0.08). The effects of hypoxia on the haemodynamic variables persisted following atropinisation (1 mg kg−1) and cervical vagotomy, suggesting that the increased Rpul during hypoxia is locally mediated. This study therefore demonstrates that turtles exhibit hypoxic pulmonary vasoconstriction, although the threshold is low compared with that of mammals.
Roles of Eyes, Leg Proprioceptors and Statocysts in the Compensatory Eye Movements of Freely Walking Land Crabs (Cardisoma Guanhumi)
Authors: Paul Herbert , Barnes W. Jon P. , Varjú Dezsö 
Published: April 2021

ABSTRACT
The compound eyes, the canal organs of the statocysts and proprioceptors in the legs all generate compensatory eye movements in the horizontal plane in the land crab Cardisoma guanhumi. Frequency analyses of the compensatory eye reflexes elicited by each of these inputs show that visual (V) and proprioceptive (P) reflexes respond best below 0.1 Hz, while statocyst (S) reflexes only achieve a high gain above this frequency. They thus increase the range of frequencies over which compensation can occur.
Eye and body movements were recorded in an arena under all possible combinations of crabs seeing or blind (V+ or V−), with or without statocysts (S+ or S−) and freely walking or passively transported on a trolley (P+ or P−). Intact crabs (V+S+P+) show good stabilisation of the eyes in space, the only movements with respect to external coordinates being saccadic resetting movements (fast phases of nystagmus). The eyes thus compensate well for body turns, but are unaffected by translatory movements of the body and turns that are not accompanied by a change in the orientation of the long axis of the body in space. In the absence of any one sense, compensation for rotation is significantly impaired, whether measured by the increase in the width of the histograms of changes in the angular positions of the eyes in space (ΔϕE), by the mean angular velocity of the eyes (slope of regression line, mE) with respect to the angular velocity of the body (mB) or by response gain plotted against angular acceleration of body turn (a). The absence of two senses reduces the crab’s ability to compensate still further, with the statocyst-only condition (V−S+P−) being little better than the condition when all three senses are absent (V−S−P−).
Such multisensory control of eye compensation for body rotation is discussed both in terms of making use of every available cue for reducing retinal slip and in making available the information content of the optic flow field.
Regulation of Muscle Mitochondrial Design
Authors: Moyes Christopher D. , Battersby Brendan J. , Leary Scot C. 
Published: April 2021

ABSTRACT
Mitochondria are responsible for the generation of ATP to fuel muscle contraction. Hypermetabolic stresses imposed upon muscles can lead to mitochondrial proliferation, but the resulting mitochondria greatly resemble their progenitors. During the mitochondrial biogenesis that accompanies phenotypic adaptation, the stoichiometric relationships between functional elements are preserved through shared sensitivities of respiratory genes to specific transcription factors. Although the properties of muscle mitochondria are generally thought to be highly conserved across species, there are many examples of mitochondrial differences between muscle types, species and developmental states and even within single cells. In this review, we discuss (1) the nature and regulation of gene families that allow coordinated expression of genes for mitochondrial products and (2) the regulatory mechanisms by which mitochondrial differences can arise over physiological and evolutionary time.
Decay Of Ca2+ and Force Transients in Fast- and Slow-Twitch Skeletal Muscles from the Rat, Mouse and Etruscan Shrew
Authors: Wetzel Petra , Gros Gerolf 
Published: April 2021

ABSTRACT
Isometric single-twitch force and intracellular Ca2+ transients were recorded simultaneously, using fura-2, from slow- and fast-twitch muscle fibres of the rat, mouse and Etruscan shrew Suncus etruscus. In the slow-twitch rat soleus, force half-relaxation time was three times longer than the 50 % decay time of the fura-2 signal. In contrast, in the fast-twitch extensor digitorum longus muscles of all three animals, muscle relaxation preceded Ca2+ decay. It is proposed that this surprising property of fast-twitch muscles is due to their pCa–tension curve, which is shifted to the right compared with that of slow-twitch muscle.