bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diet-induced plasticity in the taste system of an insect: localization to a single transduction pathway in an identified taste cell
Authors: Glendinning John I. , Ensslen Sonya , Eisenberg Michal E. , Weiskopf Phoebe 
Published: April 2021

ABSTRACT
We studied exposure-induced sensitivity changes in an identified taste cell from Manduca sexta, a herbivorous caterpillar. This taste cell occurs within the lateral styloconic sensillum and responds selectively to compounds that humans characterize as bitter (e.g. caffeine, salicin and aristolochic acid). We made extracellular recordings from several classes of identified taste cell within the lateral sensillum, both before and after dietary exposure (for 48 h) to a suprathreshold concentration of caffeine, salicin or aristolochic acid. Our results revealed (1) that dietary exposure to caffeine desensitized the bitter-sensitive taste cell to caffeine, whereas dietary exposure to salicin or aristolochic acid did not desensitize the same taste cell to salicin or to aristolochic acid; (2) that dietary exposure to caffeine failed to alter the responsiveness of the sugar-, salt- or inositol-sensitive taste cells within the same sensillum; that the caffeine-induced desensitization phenomenon generalized to salicin, a compound that stimulates the same transduction pathway as caffeine, but not to aristolochic acid, a compound that stimulates a different pathway; and that chronically stimulating the lateral sensillum with caffeine, in the absence of ingestion, was sufficient to induce desensitization. We conclude that caffeine causes desensitization through a direct effect on a single transduction pathway within the bitter-sensitive taste cell.
Effect of low ambient mineral concentrations on the accumulation of calcium, magnesium and phosphorus by early life stages of the air-breathing armoured catfish Megalechis personata (Siluriformes: Callichthyidae)
Authors: Mol Jan H. , Atsma Wim , Flik Gert , Bouwmeester Hans , Osse Jan W. M. 
Published: April 2021

ABSTRACT
The accumulation of calcium, magnesium and phosphorus was measured during an 8-week period in the early life stages of the air-breathing armoured catfish Megalechis personata acclimated to low-mineral fresh water (0.073 mmol l−1 calcium, 0.015 mmol l−1 magnesium, &lt;0.001 mmol l−1 phosphate) and high-mineral fresh water (0.59 mmol l−1 calcium, 1.94 mmol l−1 magnesium, &lt;0.001 mmol l−1 phosphate). The fish accumulated calcium twice as fast and phosphorus 1.5 times as fast in low-mineral fresh water (LMF) as in high-mineral fresh water (HMF), while the rate of accumulation of magnesium did not differ in LMF and HMF. The difference in the rates of accumulation of calcium and phosphorus between LMF and HMF was independent of the growth performance (food intake) in LMF and HMF. The mineral content of young M. personata from natural swamps and rainforest creeks in Suriname followed the LMF accumulation curves. The transition from aquatic respiration to bimodal respiration in the third week after hatching did not affect rates of mineral accumulation. The high rates of accumulation of calcium and magnesium of M. personata in LMF of 654 and 58 μmol h−1 kg−1, respectively, exceed the rates of uptake of calcium and magnesium of teleosts reported in the literature. The high rates of mineral accumulation in the early life stages of M. personata reflect the exponential growth during the first 8 weeks after hatching and the requirements of the juveniles while building their dermal armour. M. personata is well-adapted to neotropical fresh waters with an extremely low mineral content. The accumulation of calcium and phosphorus is discussed in relation to the function of the bony armour of M. personata.
The roles of the sun and the landscape in pigeon homing
Authors: Wallraff Hans G. , Chappell Jackie , Guilford Tim 
Published: April 2021

ABSTRACT
It seems reasonable to assume that pigeons use visual features in the landscape for orientation when they are homing over familiar terrain. Experimental evidence to prove or disprove this possibility is, however, difficult to obtain. Here, we link the problem with the observation that deflections of initial orientation caused by clock-shift are often smaller than predicted on a pure sun compass basis. We substantiate the hypothesis that consistently reduced deflections and increased angular scatter occur only when pigeons are released in familiar areas where a remembered pattern of landscape features can conflict with the position of the sun. Repeated releases of the same individuals under clock-shift, or elimination of non-visual navigational clues (odours), appear to strengthen the conflicting influence of familiar visual landmarks. Accelerated returns of birds allowed to preview the surrounding familiar scenery before release also support the conclusion that the visual environment is included in the homing system of pigeons. The landscape, however, not only helps home-finding, if it is familiar, but may also have a distracting influence that contributes to the great variability of initial orientation patterns.
Muscle dynamics in skipjack tuna: timing of red muscle shortening in relation to activation and body curvature during steady swimming
Authors: Shadwick Robert E. , Katz Stephen L. , Korsmeyer Keith E. , Knower Torre , Covell James W. 
Published: April 2021

ABSTRACT
Cyclic length changes in the internal red muscle of skipjack tuna (Katsuwonus pelamis) were measured using sonomicrometry while the fish swam in a water tunnel at steady speeds of 1.1–2.3 L s−1, where L is fork length. These data were coupled with simultaneous electromyographic (EMG) recordings. The onset of EMG activity occurred at virtually the same phase of the strain cycle for muscle at axial locations between approximately 0.4L and 0.74L, where the majority of the internal red muscle is located. Furthermore, EMG activity always began during muscle lengthening, 40–50 ° prior to peak length, suggesting that force enhancement by stretching and net positive work probably occur in red muscle all along the body. Our results support the idea that positive contractile power is derived from all the aerobic swimming muscle in tunas, while force transmission is provided primarily by connective tissue structures, such as skin and tendons, rather than by muscles performing negative work.
We also compared measured muscle length changes with midline curvature (as a potential index of muscle strain) calculated from synchronised video image analysis. Unlike contraction of the superficial red muscle in other fish, the shortening of internal red muscle in skipjack tuna substantially lags behind changes in the local midline curvature. The temporal separation of red muscle shortening and local curvature is so pronounced that, in the mid-body region, muscle shortening at each location is synchronous with midline curvature at locations that are 7–8 cm (i.e. 8–10 vertebral segments) more posterior. These results suggest that contraction of the internal red muscle causes deformation of the body at more posterior locations, rather than locally. This situation represents a unique departure from the model of a homogeneous bending beam, which describes red muscle strain in other fish during steady swimming, but is consistent with the idea that tunas produce thrust by motion of the caudal fin rather than by undulation of segments along the body.
Effects of sustained swimming on hepatic glucose production of rainbow trout
Authors: Shanghavi Deena S. , Weber Jean-Michel 
Published: April 2021

ABSTRACT
The rate of hepatic glucose production (Raglucose) was measured by continuous infusions of 6-[3H]glucose in live rainbow trout (Oncorhynchus mykiss) before, during and after swimming for 3 h at 1.5 body lengths s−1 in a swim tunnel. Contrary to expectation, we found that sustained swimming causes a 33 % decline in the Ra,glucose of trout (from 7.6±2.1 to 5.1±1.3 μmol kg−1 min−1, means ± S.E.M., N=7), even though exercise of the same intensity elicits a two-to fourfold increase in all the mammalian species investigated to date. Measurements of catecholamine levels show that circulating [epinephrine] decreases by 30 % during exercise (from 4.7±0.3 to 3.3±0.4 nmol l−1, N=8), suggesting that this hormone is partly responsible for controlling the decline in Raglucose. The inhibiting effect of swimming on hepatic glucose production persists for at least 1 h after the cessation of exercise. In addition, rainbow trout can maintain a steady blood glucose concentration throughout sustained exercise by closely matching hepatic glucose production with peripheral glucose utilization, even though this species is generally considered to be a poor glucoregulator. This study provides the first continuous measurements of glucose kinetics during the transition from rest to work in an ectotherm and it suggests that circulating glucose is not an important fuel for aerobic locomotion in trout.
The control of blood pressure during external hypercapnia in the rainbow trout (Oncorhynchus mykiss)
Authors: Perry S. F. , Fritsche R. , Hoagland T. M. , Duff D. W. , Olson K. R. 
Published: April 2021

ABSTRACT
Adult freshwater rainbow trout (Oncorhynchus mykiss) were exposed acutely (approximately 20 min) in a stepwise manner to increasing levels of environmental carbon dioxide ranging between 1.7 and 9.0 mmHg (0.23–1.2 kPa). Experiments were performed to examine, for the first time, the influence of hypercapnic acidosis on aspects of cardiovascular physiology including blood pressure, cardiac output and vascular resistance. Fish displayed dose (water CO2 partial pressure) -dependent increases in ventral aortic (13–39 %) and dorsal aortic (17–54 %) blood pressures that reflected marked increases in systemic vascular resistance (16–78 %); branchial vascular resistance was unaffected by hypercapnia. At the highest level of hypercapnia (9.0 mmHg), central venous pressure was significantly elevated by 54 %. Although cardiac output remained constant, heart rate was significantly lowered by 4–7 beats min−1 at the two highest levels of hypercapnia. To determine whether the cardiovascular responses to hypercapnia were being blunted by the stepwise increase in external , a separate group of fish was exposed directly to a single step of hypercapnia (water 8.0 mmHg). The cardiovascular responses were similar to those exhibited by the more gradually exposed fish except that central venous pressure did not increase and the extent of the bradycardia was greater (13 beats min−1).
After confirming the effectiveness of yohimbine in blocking the vasoconstrictory α-adrenoreceptors of the systemic vasculature, this antagonist was used as a tool to assess the importance of α-adrenoreceptor stimulation in promoting the cardiovascular responses during hypercapnia. Prior treatment of fish with yohimbine prevented the increased blood pressures and systemic vascular resistance during hypercapnia but did not influence the CO2-induced bradycardia. Plasma levels of catecholamines did not change during hypercapnia, and therefore the stimulation of the systemic α-adrenoreceptors presumably reflected increased sympathetic nerve activity.
To determine whether the cardiovascular changes elicited by hypercapnia were related to acidosis-induced hypoxaemia, fish were exposed to hypoxia in a stepwise manner (water 65–151 mmHg). The cardiovascular responses to hypoxia were markedly different from those to hypercapnia and consisted of pronounced increases in systemic and branchial vascular resistance, but only at the most severe level of hypoxia; ventral and dorsal aortic pressures were unaffected. The differences between the responses to hypercapnia and hypoxia, coupled with the smaller reductions in blood oxygen content during hypercapnia, support the hypothesis that the cardiovascular responses to CO2 are direct and are unrelated to hypoxaemia.
Increases in tissue free amino acid levels in response to prolonged emersion in marine crabs: an ammonia-detoxifying process efficient in the intertidal Carcinus maenas but not in the subtidal Necora puber
Authors: Durand Fabrice , Chausson Fabienne , Regnault Michèle 
Published: April 2021

ABSTRACT
Carcinus maenas and Necora puber were exposed to air for 72 h and 18 h, respectively, at 18 °C. Changes in the free amino acid (FAA) content of their muscle, hepatopancreas and haemolymph were recorded during air-exposure and subsequent reimmersion. Muscle and hepatopancreas urate contents and haemolymph serum protein levels were also measured during emersion.
In air-exposed C. maenas, the muscle FAA pool increased significantly within the first 24 h of emersion. This increase was due to an increase in the non-essential amino acid (NEAA) pool only; the essential amino acid (EAA) pool did not change. In haemolymph, the EAA pool decreased during the first 24 h of emersion, whereas the FAA and NEAA pools did not change. However, in this compartment, glutamine levels increased throughout the air-exposure period. No significant changes in FAA, NEAA and EAA contents of the hepatopancreas were observed during the 72 h emersion.
In air-exposed N. puber, the FAA pools of muscle and hepatopancreas did not change, although changes in the levels of some amino acids were observed during the 18 h emersion period. In this species, large increases in both the NEAA and EAA pools in the haemolymph were recorded. High levels of urate were observed in the muscle and hepatopancreas of immersed N. puber, but no significant changes occurred during emersion. In contrast, immersed C. maenas exhibited low levels of urate in both compartments, and hepatopancreas urate levels increased slightly during emersion. Haemolymph protein content did not change in air-exposed N. puber, whereas it increased in the haemolymph of 72 h emersed C. maenas.
The origin of newly formed NEAAs and their role in ammonia detoxification, particularly in C. maenas, which is able to regulate its internal ammonia levels during such a prolonged emersion, are discussed.
Expression of membrane transporters in cane toad Bufo marinus oocytes
Authors: Markovich Daniel , Regeer Ralf R. 
Published: April 2021

ABSTRACT
Membrane transport proteins (transporters and ion channels) have been extensively expressed in amphibian oocytes. The aims of this study were to determine whether oocytes from the cane toad Bufo marinus could be used as an alternative expression system to the broadly used Xenopus laevis oocytes. mRNAs encoding plasma membrane transporters NaSi-1 and sat-1 (sulphate transporters), NaDC-1 (dicarboxylate transporter), SGLT-1 (Na+/glucose cotransporter) and rBAT and 4F2 hc (amino acid transporters) were injected into B. marinus oocytes. All led to significant induction of their respective transport activities. Uptake rates were comparable with those in X. laevis oocytes, with the exception of rBAT, which was able to induce amino acid uptake only in X. laevis oocytes, suggesting that rBAT may require an endogenous X. laevis oocyte protein that is absent from B. marinus oocytes. Transport kinetics were determined for the NaSi-1 cotransporter in B. marinus oocytes, with identical results to those obtained in X. laevis oocytes. NaSi-1 specificity for the Na+ cation was determined, and the anions selenate, molybdate, tungstate, oxalate and thiosulphate could all inhibit NaSi-1-induced sulphate transport. This study demonstrates that cane toad oocytes can be used successfully to express plasma membrane proteins, making this a viable heterologous system for the expression of proteins.
Ultrastructural observations of adherent cell pairs in Hydra vulgaris
Authors: Takaku Yasuharu , Hariyama Takahiko , Kurachi Masashi , Tsukahara Yasuo 
Published: April 2021

ABSTRACT
Previous morphological studies of cell sorting in Hydra vulgaris have considered only clusters of cells. Here, we present ultrastructural observations on the adherent region of cell pairs brought into contact (following dissociation) using a three-dimensional laser manipulator. There was a much larger area of close membrane contact between endodermal cell pairs in comparison with ectodermal cell pairs. Separation distances between membranes were categorized into three classes: closest distance (&lt;4 nm); medium distance (5–25 nm); and cleavage (&gt;25 nm). The sum of distances in the closest and medium categories as a proportion of total contact length was significantly greater (P&lt;0.01) for endodermal cells (49.0±6.5 %) than for ectodermal cells (26.7±4.4 %). In intact Hydra, this sum of distances was also significantly greater for endodermal cells, indicating that newly adherent cells, even after adhesion for only 10 min, display similar morphological characteristics to cells in intact Hydra. This suggests that close membrane contacts contribute to differential cell adhesion, which may form the basis of the cell sorting process.
Roots as a site of hydrogen sulfide uptake in the hydrocarbon seep vestimentiferan Lamellibrachia sp.
Authors: Julian David , Gaill Françoise , Wood Eric , Arp Alissa J. , Fisher Charles R. 
Published: April 2021

ABSTRACT
Vestimentiferan tubeworms have no mouth or gut, and the majority of their nutritional requirements are provided by endosymbiotic bacteria that utilize hydrogen sulfide oxidation to fix CO2 into organic molecules. It has been assumed that all vestimentiferans obtain the sulfide, O2 and CO2 needed by the bacteria across the plume (gill) surface, but some live in locations where very little sulfide is available in the sea water surrounding the plume. We propose that at least some of these vestimentiferans can grow a posterior extension of their body and tube down into the sea-floor sediment, and that they can use this extension, which we call the ‘root’, to take up sulfide directly from the interstitial water. In this study of the vestimentiferan Lamellibrachia sp., found at hydrocarbon seeps in the Gulf of Mexico at depths of approximately 700 m, we measured seawater and interstitial sulfide concentrations in the hydrocarbon seep habitat, determined the structural characteristics of the root tube using transmission electron microscopy, characterized the biochemical composition of the tube wall, and measured the sulfide permeability of the root tube. We found that, while the sulfide concentration is less than 1 μmol l−1 in the sea water surrounding the gills, it can be over 1.5 mmol l−1 at a depth of 10–25 cm in sediment beneath tubeworm bushes. The root tube is composed primarily of giant β-chitin crystallites (12–30 % of total mass) embedded in a protein matrix (50 % of total mass). Root tubes have a mean diameter of 1.4 mm, a mean wall thickness of 70 μm and can be over 20 cm long. The tubeworm itself typically extends its body to the distal tip of the root tube. The root tube wall was quite permeable to sulfide, having a permeability coefficient at 20 °C of 0.41×10−3 cm s−1, with root tube being 2.5 times more permeable to sulfide than trunk tube of the same diameter. The characteristics of the root suggest that it reaches down to the higher sulfide levels present in the deeper sediment and that it functions to increase the surface area available for sulfide uptake in a manner analogous to a respiratory organ.
Cardiovascular responses to adenosine in the antarctic fish Pagothenia borchgrevinki
Authors: Sundin Lena , Axelsson Michael , Davison William , Forster Malcolm E. 
Published: April 2021

ABSTRACT
We have investigated the effects of adenosine on the cardiovascular system of the Antarctic fish Pagothenia borchgrevinki. Continuous measurements of ventral and dorsal aortic blood pressures, heart rate (fH) and ventral aortic blood flow (cardiac output, Q̇) were made using standard cannulation techniques and a single-crystal Doppler flowmeter. On line measurements of arterial were made using an oxygen electrode connected to an extracorporeal loop.
Adenosine (10 nmol kg−1) and the specific A1-receptor agonist N6-cyclopentyladenosine (CPA) elicited biphasic changes in the branchial and systemic resistances. While there was an initial decrease in the branchial resistance followed by an increase, the opposite was true for the systemic response. The resistance changes were significantly attenuated by aminophylline (a P1-receptor antagonist) and 8-cyclopentyltheophylline (CPT; an A1-receptor antagonist). In addition, adenosine induced an aminophylline-sensitive decrease in the arterial . The reduction was attenuated when pre-injection arterial was low.
Adenosine and CPA also caused a marked reduction in fH, with CPA being more potent. The bradycardia was blocked by aminophylline and CPT, demonstrating an involvement of A1 receptors in this response.
The mechanics of sound production in the puff adder Bitis arietans (Serpentes: viperidae) and the information content of the snake hiss
Authors: Young Bruce A. , Nejman Nancy , Meltzer Karen , Marvin Jessica 
Published: April 2021

ABSTRACT
Puff adders (Bitis arietans), like many other snakes, hiss as part of their defensive repertoire. In B. arietans, the hisses have a clear quadraphasic pattern consisting of an initial exhalatory hiss, a brief transitional pause, an inhalatory hiss and a rest or breath-holding phase. Simultaneous recordings of body diameter, electrical activity in the intrinsic laryngeal musculature, airflow through the nasal passageway and sound production revealed that the anterior respiratory tract plays a passive role in hissing and that the costal pump is responsible for generating the quadraphasic pattern. During hissing, B. arietans uses the same mechanics previously described for normal respiratory ventilation in snakes. Analyses of artificial hisses reveal that the anterior respiratory tract of B. arietans has little ability to modify an exhalant airstream acoustically. The combination of the simple ventilatory mechanics used during hissing and the lack of acoustic modification of the exhalant airstream results in the production of an acoustically simple hiss. Cross-correlation matrix analyses of a variety of snake hisses showed a high degree of acoustic similarity between the sounds, almost approaching the levels determined for white noise. This high level of acoustic similarity reflects the low level of acoustic specialization within the sounds produced by snakes and the low potential for encoded information content.
The relationship between mechanical work and energy expenditure of locomotion in horses
Authors: Minetti A. E. , Ardigò L. P. , Reinach E. , Saibene F. 
Published: April 2021

ABSTRACT
Three-dimensional motion capture and metabolic assessment were performed on four standardbred horses while walking, trotting and galloping on a motorized treadmill at different speeds. The mechanical work was partitioned into the internal work (WINT), due to the speed changes of body segments with respect to the body centre of mass, and the external work (WEXT), due to the position and speed changes of the body centre of mass with respect to the environment. The estimated total mechanical work (WTOT=WINT+WEXT) increased with speed, while metabolic work (C) remained rather constant. As a consequence, the ‘apparent efficiency’ (effAPP=WTOT/C) increased from 10 % (walking) to over 100 % (galloping), setting the highest value to date for terrestrial locomotion. The contribution of elastic structures in the horse’s limbs was evaluated by calculating the elastic energy stored and released during a single bounce (WEL,BOUNCE), which was approximately 1.23 J kg−1 for trotting and up to 6 J kg−1 for galloping. When taking into account the elastic energy stored by the spine bending and released as WINT, as suggested in the literature for galloping, WEL,BOUNCE was reduced by 0.88 J kg−1. Indirect evidence indicates that force, in addition to mechanical work, is also a determinant of the metabolic energy expenditure in horse locomotion.