bluuebunny/crossref_metadata_2025_split huggingface dataset:
MeV-Ion Microprobe Analyses of Whole Drosophila Suggest That Zinc and Copper Accumulation is Regulated Storage not Deposit Excretion
Authors: Schofield Robert M. S. , Postlethwait John H. , Lefevre Harlan W. 
Published: April 2021

ABSTRACT
We examined Drosophila spp. using a penetrative ion microprobe technique that allows us to quantify element contents in whole organs and organisms. Comparatively non-penetrative techniques, such as electron microscopy, could not have been used to make many of these measurements because material is lost during sectioning. We found that zinc was accumulated predominantly within a single organ: in the main segments of both the anterior and posterior Malpighian tubules. In contrast to zinc, iron and copper were more generally distributed throughout the body. Zinc concentrations as high as 2.8 % of dry mass were measured in cell-sized volumes of the Malpighian tubules. The large quantities of zinc (approximately 2×10−8 g in 8-day-old male adults) were sequestered by an unidentified mechanism. We found less than 1 % of the estimated amount of consumed zinc and copper in the abdomen of flies fed food containing several hundred parts per million dry mass of these metals. Our results are inconsistent with the detoxification hypothesis that predicts that a large proportion of the heavy metals passing through the gut are absorbed and stored permanently. We found for both zinc and copper that the quantity in the abdomen was not proportional to the concentration of these metals in the consumed food but was, instead, relatively invariant. For these reasons, we suggest that regulated biological availability, not detoxification, may be the primary benefit of zinc and copper storage.
Regulation of Ecdysis-Triggering Hormone Release by Eclosion Hormone
Authors: Kingan Timothy G. , Gray William , žitňan Duŝan , Adams Michael E. 
Published: April 2021

ABSTRACT
Ecdysis behavior in the tobacco hornworm Manduca sexta (Lepidoptera: Sphingidae) is triggered through reciprocal peptide signaling between the central nervous system and the epitracheal endocrine system. Recent evidence indicates that eclosion hormone may initiate endocrine events leading to ecdysis through its action on epitracheal glands to cause the release of ecdysis-triggering hormone (ETH). Here, we report that direct exposure of epitracheal glands to eclosion hormone in vitro leads to secretion of ETH. The threshold concentration of eclosion hormone needed to evoke release of ETH is approximately 3 pmol l−1. Eclosion hormone also induces elevation of cyclic GMP, but not cAMP, concentration in epitracheal glands at concentrations similar to those causing release of ETH. Both cGMP and 8-Br-cGMP mimic the secretory action of eclosion hormone. The sensitivity of the secretory response to eclosion hormone occurs during a narrow window of development, beginning approximately 8 h prior to pupal ecdysis. However, eclosion hormone can cause elevation of cGMP levels in epitracheal glands long before they acquire competence to release ETH, showing that the initial portion of the signal transduction cascade is in place early in development, but that the absence of a downstream step in the cascade prevents secretion. Measurements of cGMP levels in epitracheal glands during the ecdysis sequence show a sudden elevation some 30 min after the onset of pre-ecdysis, well after ETH secretion has been initiated. ETH secretion can therefore be viewed as a two-step process, beginning at pre-ecdysis when cGMP levels are relatively low, followed by a massive release resulting from a logarithmic elevation of cGMP levels.
Heart Rates and Abdominal Temperatures of Free-Ranging South Georgian Shags, Phalacrocorax Georgianus
Authors: Bevan R. M. , Boyd I. L. , Butler P. J. , Reid K. , Woakes A. J. , Croxall J. P. 
Published: April 2021

ABSTRACT
The South Georgian shag (Phalacrocorax georgianus) shows a remarkable diving ability comparable to that of penguins, yet nothing is known of the physiology of these birds. In this study, heart rates and abdominal temperatures were recorded continuously in four free-ranging South Georgian shags using an implanted data-logger. A time–depth recorder was also attached to the back of the implanted birds to record their diving behaviour.
The diving behaviour of the birds was essentially similar to that reported in other studies, with maximum dive durations for individual birds ranging between 140 and 287 s, and maximum depths between 35 and 101 m. The birds, while at the nest, had a heart rate of 104.0±13.1 beats min−1 (mean ± S.E.M.) and an abdominal temperature of 39.1±0.2 °C. During flights of 221±29 s, heart rate and abdominal temperature rose to 309.5±18.0 beats min−1 and 40.1±0.3 °C, respectively. The mean heart rate during diving, at 103.7±13.7 beats min−1, was not significantly different from the resting values, but the minimum heart rate during a dive was significantly lower at 64.8±5.8 beats min−1. The minimum heart rate during a dive was negatively correlated with both dive duration and dive depth. Abdominal temperature fell progressively during a diving bout, with a mean temperature at the end of a bout of 35.1±1.7 °C.
The minimum heart rate during diving is at a sub-resting level, which suggests that the South Georgian shag responds to submersion with the ‘classic’ dive response of bradycardia and the associated peripheral vasoconstriction and utilisation of anaerobic metabolism. However, the reduction in abdominal temperature may reflect a reduction in the overall metabolic rate of the animal such that the bird can remain aerobic while submerged.s
Muscle Power Output During Escape Responses in an Antarctic Fish
Authors: Franklin Craig E. , Johnston Ian A. 
Published: April 2021

ABSTRACT
Escape responses (C-shaped fast-starts) were filmed at 500 frames s−1 in the Antarctic rock cod (Notothenia coriiceps) at 0 °C. The activation and strain patterns of the superficial fast myotomal muscle were measured simultaneously using electromyography and sonomicrometry respectively. In order to bend the body into the initial C-shape, the muscle fibres in the rostral myotomes (at 0.35L, where L is total length) shortened by up to 13 % of their resting length at a maximum velocity of 1.68 fibre lengths s−1. During the contralateral contraction, muscle fibres were stretched (by 5 % and 7 % at 0.35L and 0.65L, respectively) and were activated prior to the end of lengthening, before shortening by up to 12 % of resting fibre length (peak-to-peak strain). Representative strain records were digitised to create cyclical events corresponding to the C-bend and contralateral contraction. Isolated fibres were subjected to the abstracted strain cycles and stimulated at the same point and for the same duration as occurs in vivo. During the early phase of shortening, muscle shortening velocity (V) increased dramatically whilst the load was relatively constant and represented a substantial fraction of the maximum isometric stress. Pre-stretch of active muscle was associated with significant force enhancement. For the contralateral contraction, V exceeded that predicted by the steady-state force–velocity relationship for considerable periods during each tailbeat, contributing to relatively high maximum instantaneous power outputs of up to 290 W kg−1 wet muscle mass. In vitro experiments, involving adjusting strain, cycle duration and stimulation parameters, indicated that in vivo muscle fibres produce close to their maximum power. During escape responses, the maximum velocity and acceleration recorded from the centre of gravity of the fish were 0.71±0.03 m s−1 and 17.1±1.4 m s−2, respectively (mean ± S.E.M., N=7 fish). Muscle performance was sufficient to produce maximum velocities and accelerations that were within the lower end of the range reported for temperate-zone fish.
How Does the Contractile Vacuole of Paramecium Multimicronucleatum Expel Fluid? Modelling The Expulsion Mechanism
Authors: Naitoh Yutaka , Tominaga Takashi , Ishida Masaki , Fok Agnes K. , Aihara Marilynn S. , Allen Richard D. 
Published: April 2021

ABSTRACT
To examine the forces needed for discharge of the fluid contents from the contractile vacuole of Paramecium multimicronucleatum, the time course of the decrease in vacuole diameter during systole (the fluid-discharging period) was compared with that of various vacuole discharge models. The observed time course did not fit that predicted by a model in which contraction of an actin–myosin network surrounding the vacuole caused discharge nor that predicted by a model in which the surface tension of the lipid bilayer of the vacuole caused discharge. Rather, it fitted that predicted by a model in which the cell’s cytosolic pressure was responsible for discharge. Cytochalasin B, an effective inhibitor of actin polymerization, had no effect on the in vivo time course of systole. An injection of a monoclonal antibody raised against the proton pumps of the decorated spongiomes (now known to be the locus of fluid segregation in P. multimicronucleatum) disrupted the decorated spongiomes and reduced the rate of fluid segregation, whereas it did not alter the time course of systole. We conclude that in P. multimicronucleatum the internal pressure of the contractile vacuole is caused predominantly by the cytosolic pressure and that the fluid-segregation mechanism does not directly affect the fluid-discharge mechanism. Elimination of this cytosolic pressure by rupturing the cell revealed the presence of a novel fluid-discharge mechanism, apparently centered in the vacuole membrane. The involvement of tubulation of the vacuole membrane as the force-generating mechanism for fluid discharge in disrupted cells is discussed.
Increased Concentrations of Haemolymph Mg2+ Protect Intracellular Ph and Atp Levels During Temperature Stress and Anoxia in the Common Shrimp Crangon Crangon
Authors: Sartoris F. J. , Pörtner H. O. 
Published: April 2021

ABSTRACT
The effects of temperature (0, 5, 10, 15 and 20 °C) and of anoxia (at 5 °C) on extracellular Mg2+ concentration ([Mg2+]e), intracellular pH (pHi) and ATP and lactate levels were investigated in intermoult adults of the common shrimp Crangon crangon. All animals caught in summer (summer animals) showed a slight but significant increase in [Mg2+]e at low temperatures. In contrast, at every temperature tested, a few of the animals caught in winter (winter animals) showed elevated [Mg2+]e during shortterm (4 h) but not during long-term (6 days) incubations. The reasons for the overshoot in Mg2+ concentrations in individual animals remain unexplained, but a protective effect of extracellular Mg2+ on intracellular pH and on ATP concentrations was visible at haemolymph Mg2+ concentrations above 15 mmol l−1. The influence of high extracellular [Mg2+] on pHi and intracellular ATP and lactate levels under normoxic and anoxic conditions was tested using an incubation medium containing 150–250 mmol l−1 Mg2+. When haemolymph Mg2+ levels were manipulated by exposure of the animal to high levels of Mg2+ in the external medium, animals with a haemolymph [Mg2+] below the threshold concentration of 15 mmol l−1 had significantly lower values of intracellular pH than animals with haemolymph [Mg2+] above 15 mmol l−1. In addition, the elevation of haemolymph [Mg2+] by incubation in high-[Mg2+] water prevented the drop in pHi and the rise in lactate levels induced by anoxia. The protective effect of high levels of extracellular Mg2+ did not depend upon the [Ca2+]/[Mg2+] ratio but only on [Mg2+]e. However, experiments with isolated muscle tissues showed no dependence of muscle intracellular pH on [Mg2+]e under both normoxic and anoxic conditions, leading to the conclusion that the protective effect is evoked via a central, possibly anaesthetising, effect of high [Mg2+]e. The dependence of pHi and muscle [ATP] on extracellular [Mg2+] resembles the protective effect of high Mg2+ levels on the post-ischaemic mammalian heart.
The Sub-Pulmonary Conus and the Arterial Anastomosis as Important Sites of Cardiovascular Regulation in the Crocodile Crocodylus Porosus
Authors: Axelsson Michael , Franklin Craig E. , Fritsche Regina , Grigg Gordon C. , Nilsson Stefan 
Published: April 2021

ABSTRACT
We present evidence to support the hypothesis that the arterial anastomosis and the cogteeth-like valves located in the sub-pulmonary conus in the right ventricle are important sites of cardiovascular regulation in the crocodile Crocodylus porosus. The influence of the arterial anastomosis on the development of the ‘foramen spike’ in the left aortic pressure trace, which occurs at the onset of diastole when the pressures in the right and left aortas become equal, and on gastrointestinal blood flow was examined in unanaesthetised C. porosus using blood vessel occluders. Measurements of blood flow in the arterial anastomosis showed that, during non-shunting conditions, there was a substantial systolic blood flow from the right aorta into the coeliac artery. The total coeliac artery blood flow was the sum of the anastomosis flow from the right aorta plus the left aortic flow originating from the right aorta via the foramen of Panizza during diastole. During mechanically induced pulmonary-to-systemic shunting, the anastomosis blood flow was reversed, with blood flowing from the left to the right aorta. The magnitude of the ‘foramen spike’ was directly related to the vascular resistance in the anastomosis. When vascular resistance in the anastomosis was high, such as during mechanical occlusion, there was an increase in the right aortic to left aortic pressure gradient during systole which resulted in an increase the foramen spike amplitude. Recordings of right intraventricular pressure in unanaesthetised C. porosus showed spontaneous changes in right intracardiac systolic pressure. The pressure recordings were biphasic, with the second contraction (isometric) being highly variable in size, indicating the control of pulmonary outflow resistance, possibly via the ‘cogteeth valves’ located in the sub-pulmonary conus in the right ventricle.
Temperature and Developmental Plasticity of Muscle Phenotype in Herring Larvae
Authors: Johnston Ian A. , Cole Nicholas J. , Vieira Vera L. A. , Davidson Irvine 
Published: April 2021

ABSTRACT
Myogenesis, the expression of myofibrillar protein isoforms and the development of muscle innervation were investigated in Clyde herring (Clupea harengus L.) in two successive spawning seasons at temperatures ranging from 5 °C to 15 °C. Myotube formation occurred in a rostral to caudal progression at similar somite stages at all temperatures. Superficial mononuclear muscle pioneer fibres were present at the horizontal septum. Myofibrillogenesis was retarded with respect to somite stage at low temperatures; for example, by the 50-somite stage, myofibrils were observed in the muscle pioneers of the first 31 somites at 12 °C, but only the first 20 somites at 5 °C. In the electron microscope, the earliest stages of myofibril assembly were observed in the muscle pioneer cells and in a proportion of the multinucleated myotubes within the same somite. By the end of somitogenesis, the density of myofibrils in the rostral myotomes was much higher at 15 °C than at 5 °C. Embryonic isoforms of myosin light chain 2 (LC2), troponin I and troponin T were identified in the presumptive white muscle using two-dimensional gel electrophoresis. Expression of the embryonic isoforms was gradually switched off during the larval stages. The size range over which embryonic isoforms were present was inversely related to rearing temperature. For example, the adult pattern of myosin LC2 expression was established at 11 mm total length (TL) at 15 °C, but not until 15 mm TL at 5 °C. Acetylcholinesterase staining was apparent at the myosepta in 31-somite stage embryos at 15 °C, but not until approximately the 40-somite stage at 5 °C. The red muscle fibres of larvae were initially innervated only at their myoseptal ends. The temperature at which the red muscle fibres became multiply innervated was inversely related to body size, occurring at 12–14 mm at 12 °C, but not until 16–19 mm at 5 °C. We conclude that the temperature during early development determines the relative timing and degree of expression of the myogenic programme, resulting in significant phenotypic variation in the swimming muscles of the larval stages. Our results highlight a potential mechanism whereby early thermal experience could influence survival and hence the strength of particular year classes of fish.
Control of Insect Ecdysis by a Positive-Feedback Endocrine System: Roles of Eclosion Hormone and Ecdysis Triggering Hormone
Authors: Ewer John , Gammie Stephen C. , Truman James W. 
Published: April 2021

ABSTRACT
A successful ecdysis in insects requires the precise coordination of behaviour with the developmental changes that occur late in a moult. This coordination involves two sets of endocrine cells: the peripherally located Inka cells, which release ecdysis triggering hormone (ETH), and the centrally located neurosecretory neurones, the VM neurones, which release eclosion hormone (EH). These two sets of endocrine cells mutally excite one another: EH acts on the Inka cells to cause the release of ETH. ETH, in turn, acts on the VM neurones to cause the release of EH. This positive-feedback relationship allows the Inka cells and the VM neurones to be the peripheral and central halves, respectively, of a decision-making circuit. Once conditions for both halves have been satisfied, their reciprocal excitation results in a massive EH/ETH surge in the blood as well as a release of EH within the central nervous system. This phasic signal then causes the tonic activation of a distributed network of peptidergic neurones that contain crustacean cardioactive peptide. The relationship of the latter cells to the subsequent maintenance of the ecdysis motor programme is discussed.
Energetic Consequences of Coordinating Wingbeat and Respiratory Rhythms in Birds
Authors: Funk Gregory D. , Valenzuela Ignacio J. , Milsom William K. 
Published: April 2021

ABSTRACT
The coordination of ventilatory and locomotor rhythms has been documented in many birds and mammals. It has been suggested that the physiological significance of such coordination is a reduction in the cost of ventilation which confers an energetic advantage to the animal. We tested this hypothesis by measuring the external work required to ventilate birds mechanically during simulated flight. Patterns of wing motion and breathing were produced in which the relationship between wing motion and breathing was in phase and out of phase with the relationship seen during normal flight. Differences between the energetic costs of in-phase versus out-of-phase synchronization were particularly large (26 %) in instances where locomotion and respiration frequency were synchronized at one breath per wingbeat. The saving (9 %) obtained from in-phase versus out-of-phase coordination at the 3:1 coordination ratio seen normally in free-flying Canada geese was smaller but still supported the hypothesis that there is a significant net saving obtained from reducing the mechanical interference between locomotion and ventilation by locomotor–respiratory coupling.
Adrenergic Stimulation of Sea Bream (Sparus Aurata) Red Blood Cells in Normoxia and Anoxia: Effects on Metabolism and on The Oxygen Affinity of Haemoglobin
Authors: Roig Teresa , Sánchez Josep , Tort Lluís , Altimiras Jordi , Bermúdez Jordi 
Published: April 2021

ABSTRACT
The metabolic response of sea bream (Sparus aurata) red blood cells to adrenergic stimulation was determined in normoxia and anoxia. In the presence of oxygen, red blood cells swelled and then recovered their resting volume. Continuous monitoring of oxygen uptake displayed the kinetics of the increase in the oxygen affinity of haemoglobin. Cell volume recovery correlated with an activation of ATP consumption, and the energy equilibrium was restored by increasing the rates of respiration and glycolysis. When the respiratory chain was blocked, adrenergic stimulation increased the rates of ATP consumption and glycolysis of red blood cells. Moreover, adrenergic stimulation of deoxygenated erythrocytes also increased cell volume but did not enhance glycolysis or ATP consumption, and the cells remained swollen. Our results suggest that there is an oxygen-linked signal transducer that activates ATP-consuming processes, provided that the adrenergic stimulation occurs in the presence of oxygen.
Cultured Branchial Epithelia From Freshwater Fish Gills
Authors: Wood Chris M. , Pärt Peter 
Published: April 2021

ABSTRACT
We have developed a method for the primary culture of gill epithelial cells from freshwater rainbow trout on permeable supports, polyethylene terephthalate membranes (‘filter inserts’). Primary cultures of gill cells (6–9 days in Leibowitz L-15 culture medium plus foetal bovine serum and glutamine) are trypsinized and the cells seeded onto the inserts. After 6 days of growth with L-15 medium on both surfaces (approximately isotonic to trout plasma), the cells form a tight epithelium as judged from a progressive rise in transepithelial resistance which reaches a stable plateau for a further 6 days, as long as L-15 exposure is continued on both surfaces. The cultured epithelium (approximately 8 μm thick) typically consists of 2–4 overlapping cell layers organized as in the lamellae in vivo, with large intercellular spaces, multiple desmosomes and putative tight junctions. The cells appear to be exclusively pavement-type cells with an apical surface glycocalyx, an abundance of rough endoplasmic reticulum, no selective DASPEI staining and relatively few mitochondria. Transepithelial resistance (approximately 3.5 kΩ cm2), permeability to a paracellular marker (polyethylene glycol-4000; 0.17×10−6 cm s−1) and unidirectional flux of Na+ and Cl− (approximately 300 nmol cm−2 h−1) all appear realistic because they compare well with in vivo values; net fluxes of Na+ and Cl− are zero. The preparation acidifies the apical medium, which accumulates a greater concentration of ammonia. Upon exposure to apical freshwater, resistance increases six-to elevenfold and a basolateral-negative transepithelial potential (TEP) develops as in vivo. These responses occur even when mannitol is used to prevent changes in apical osmotic pressure. Net Na+ and Cl− loss rates are low over the first 12 h (−125 nmol cm−2 h−1) but increase substantially by 48 h. The elevated resistance and negative TEP gradually attenuate but remain significantly higher than pre-exposure values after 48 h of apical freshwater exposure. The preparation may provide a valuable new tool for characterizing some of the mechanisms of active and passive ion transport in the pavement cells of the freshwater gill.