bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of Na+ transport across leech skin by peptide hormones and neurotransmitters
Authors: Milde Helga , Weber Wolf-Michael , Salzet Michel , Clauss Wolfgang 
Published: April 2021

ABSTRACT
An increase in intracellular cyclic AMP concentration stimulates transepithelial Na+ transport across the skin of the leech Hirudo medicinalis, but it is unclear how cytosolic cyclic AMP levels are elevated in vivo. In search of this external stimulus, we performed Ussing chamber experiments to test several peptide hormones and neurotransmitters for their effect on Na+ transport across leech dorsal integument. Although all the peptide hormones under investigation significantly affected ion transport across leech integument, none of them mimicked the effect of an experimental rise in intracellular cyclic AMP level. The invertebrate peptides conopressin and angiotensin II amide inhibited short-circuit-current-(Isc) and amiloride-sensitive Na+ transport (Iamil), although to slightly different degrees. The vertebrate peptide hormones 8-arginine-vasopressin and 8-lysine-vasopressin both produced an inhibition of Iamil comparable with that caused by angiotensin II amide. However, 8-lysine-vasopressin reduced Isc, whereas 8-arginine-vasopressin induced a moderate increase in Isc. The neurotransmitter dopamine, which occurs in the leech central nervous system in relatively large amounts, and its precursor L-dopamine both induced large decreases in Isc and Iamil. However, the reactions evoked by the catecholamines showed no pronounced similarity to the effects of intracellular cyclic AMP. Two other neurotransmitters known to occur in leeches, serotonin (5-hydroxytryptamine) and γ-n-aminobutyric acid (GABA), had no influence on transepithelial ion transport in leech skin.
Hydrodynamic Drag of Diving Birds: Effects Of Body Size, Body Shape And Feathers At Steady Speeds
Authors: Lovvorn James R. , Liggins Geoffrey A. , Borstad Matthias H. , Calisal Sander M. , Mikkelsen Jon 
Published: April 2021

ABSTRACT
For birds diving to depths where pressure has mostly reduced the buoyancy of air spaces, hydrodynamic drag is the main mechanical cost of steady swimming. Drag is strongly affected by body size and shape, so such differences among species should affect energy costs. Because flow around the body is complicated by the roughness and vibration of feathers, feathers must be considered in evaluating the effects of size and shape on drag. We investigated the effects of size, shape and feathers on the drag of avian divers ranging from wing-propelled auklets weighing 75 g to foot-propelled eiders weighing up to 2060 g. Laser scanning of body surfaces yielded digitized shapes that were averaged over several specimens per species and then used by a milling machine to cut foam models. These models were fitted with casts of the bill area, and their drag was compared with that of frozen specimens. Because of the roughness and vibration of the feathers, the drag of the frozen birds was 2–6 times that of the models. Plots of drag coefficient (CD) versus Reynolds number (Re) differed between the model and the frozen birds, with the pattern of difference varying with body shape. Thus, the drag of cast models or similar featherless shapes can differ both quantitatively and qualitatively from that of real birds. On the basis of a new towing method with no posts or stings that alter flow or angles of attack, the dimensionless CD/Re curves differed among a size gradient of five auklet species (75–100 g) with similar shapes. Thus, extrapolation of CD/Re curves among related species must be performed with caution. At lower speeds, the CD at a given Re was generally higher for long-necked birds that swim with their neck extended (cormorants, grebes, some ducks) than for birds that swim with their head retracted (penguins, alcids), but this trend was reversed at high speeds. Because swimming birds actually travel at a range of instantaneous speeds during oscillatory strokes, species variations in drag at different speeds must be considered in the context of accelerational stroking.
The Influence of Stimulus and Background Colour on Signal Visibility in the Lizard Anolis Cristatellus
Authors: Fleishman Leo J. , Persons Matthew 
Published: April 2021

ABSTRACT
Anoline lizards communicate with visual displays in which they open and close a colourful throat fan called the dewlap. We used a visual fixation reflex as an assay to test the effects of stimulus versus background chromatic and brightness contrast on the probability of detecting a moving coloured (i.e. dewlap-like) stimulus in Anolis cristatellus. The probability of stimulus detection depended on two additive visual-system channels, one responding to brightness contrast and one responding to chromatic contrast, independent of brightness. The brightness channel was influenced only by wavelengths longer than 450 nm and probably received input only from middle- and/or long-wavelength photoreceptors. The chromatic contrast channel appeared to receive input from three, or possibly four, different classes of cone in the anoline retina, including one with peak sensitivity in the ultraviolet. We developed a multi-linear regression equation that described most of the results of this study to a reasonable degree of accuracy. In the future, this equation could be used to predict the relative visibility of different-coloured stimuli in different habitat light conditions, which should be very useful for testing hypotheses that attempt to relate habitat light conditions and visual-system response to the evolution of signal design.
The Guidance of Desert Ants by Extended Landmarks
Authors: Collett T. S. , Collett M. , Wehner R. 
Published: April 2021

ABSTRACT
Desert ants (Cataglyphis fortis) were trained to follow a fixed route around a barrier to a feeder. Their homeward trajectories were recorded on a test field containing a similar barrier, oriented either as in training or rotated through 22 or 45 °. Under one set of experimental conditions, the homeward trajectories rotated with the orientation of the barrier, implying that the visual features of this extended landmark can determine the route independently of compass cues: the barrier provided a ‘visual scene’ that controlled the trajectories of the ants. Under other conditions, the trajectories after rotation were a compromise between the habitual compass direction and the direction with respect to the rotated barrier.
Trajectories were determined primarily by the visual scene when ants were allowed to return close to the nest before being caught and tested. The compromise trajectories were observed when ants were taken from the feeder. It seems that ants exhibit at least two separate learnt responses to the barrier: (i) a habitual compass direction triggered by the sight of the barrier and (ii) a visual scene direction that is compass-independent. We suggest that the weighting accorded to these different learnt responses changes with the state of the path integration system.
Changes in the Thoracic Temperature of Honeybees While Receiving Nectar From Foragers Collecting at Different Reward Rates
Authors: Farina Walter M. , Wainselboim Alejandro J. 
Published: April 2021

ABSTRACT
Mouth-to-mouth food exchange in eusocial insects (trophallaxis) contributes to the organization of complex social activities. In the case of honeybees, foragers returning from a nectar source transfer the food collected to receiver colony-mates through oral contact. Previous studies have shown that the speed of nectar transfer within each contact (unloading rate) increases when foragers return from feeding sites with higher profitability, i.e. with more concentrated sugar solutions or higher solution flow rates. However, there is no evidence that the nectar unloading rate is actually evaluated by hive-mates during food exchange. To investigate this, trophallaxis between donor bees returning from a feeder with different flow rates of sucrose solution (range 1.0–8.2 μl min−1 of 50 % w/w sucrose solution) and receiver hive-mates was studied by combining behavioural and infrared thermal analysis.
The results show that when foraging bees returned from a feeder delivering a higher flow rate they initiated unloading at higher thoracic temperatures and transferred the solution at higher speed. During these food exchanges, the thoraces of receiver bees warmed up faster in proportion to increasing forager temperature and unloading rate. Therefore, whatever the variable actually evaluated by receivers (mostly nectar processors, i.e. bees that handle nectar in the hive) during trophallaxis (unloading rate and/or donor thoracic temperature), they raised their activity level in proportion to that of the foragers. In this way, receiver bees will intensify their nectar processing when nectar foragers return from more profitable sites.
Seasonal Change in the Capacity for Supercooling By Neonatal Painted Turtles
Authors: Packard Gary C. , Packard Mary J. , Mcdaniel Leonard L. 
Published: April 2021

ABSTRACT
Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest where they completed incubation the preceding summer. This facet of their natural history commonly causes neonates in northerly populations to be exposed in mid-winter to ice and cold, which many animals survive by remaining unfrozen and supercooled. We measured the limit of supercooling in samples of turtles taken shortly after hatching and in other samples after 2 months of acclimation (or acclimatization) to a reduced temperature in the laboratory or field. Animals initially had only a limited capacity for supercooling, but they acquired an ability to undergo deeper supercooling during the course of acclimation. The gut of most turtles was packed with particles of soil and eggshell shortly after hatching, but not after acclimation. Thus, the relatively high limit of supercooling for turtles in the days immediately after hatching may have resulted from the ingestion of soil (and associated nucleating agents) by the animals as they were freeing themselves from their eggshell, whereas the relatively low limit of supercooling attained by acclimated turtles may have resulted from their purging their gut of its contents. Parallels may, therefore, exist between the natural-history strategy expressed by hatchling painted turtles and that expressed by numerous terrestrial arthropods that withstand the cold of winter by sustaining a state of supercooling.
Behavioral recovery from spinal cord injury following delayed application of polyethylene glycol
Authors: Borgens Richard B. , Shi Riyi , Bohnert Debra 
Published: April 2021

SUMMARYTopical application of the hydrophilic polymer polyethylene glycol (PEG) to isolated adult guinea pig spinal cord injuries has been shown to lead to the recovery of both the anatomical integrity of the tissue and the conduction of nerve impulses through the lesion. Furthermore, a brief (2 min) application of the fusogen (Mr 1800, 50 % w/v aqueous solution) to the exposed spinal cord injury in vivo can also cause rapid recovery of nerve impulse conduction through the lesion in association with functional recovery. Behavioral recovery was demonstrated using a long-tract, spinal-cord-dependent behavior in rodents known as the cutaneus trunci muscle (CTM) reflex. This reflex is observed as a contraction of the skin of the back in response to tactile stimulation. Here, we confirm and extend these preliminary observations. A severe compression/contusion injury to the exposed thoracic spinal cord of the guinea pig was performed between thoracic vertebrae 10 and 11. Approximately 7 h later, a topical application of PEG was made to the injury (dura removed) for 2 min in 15 experimental animals, and levels of recovery were compared with those of 13 vehicle-treated control animals. In PEG-treated animals, 93 % recovered variable levels of CTM functioning and all recovered some level of conduction through the lesion, as measured by evoked potential techniques. The recovered reflex was relatively normal compared with the quantitative characteristics of the reflex prior to injury with respect to the direction, distance and velocity of skin contraction. Only 23 % of the control population showed any spontaneous CTM recovery (P=0.0003) and none recovered conduction through the lesion during the 1 month period of observation (P=0.0001). These results suggest that repair of nerve membranes by polymeric sealing can provide a novel means for the rapid restoration of function following spinal cord injury.
Three-dimensional morphometry of spinal cord injury following polyethylene glycol treatment
Authors: Duerstock Bradley S. , Borgens Richard B. 
Published: April 2021

SUMMARYWe are developing a novel means of restoring function after severe acute spinal cord injury. This involves a brief application of polyethylene glycol (PEG) to the site of injury. In the companion paper, we have shown that a delayed application of PEG can produce strikingly significant physiological and behavioral recovery in 90–100 % of spinal-cord-injured guinea pigs. In the present paper, we used three-dimensional computer reconstructions of PEG-treated and sham-treated spinal cords to determine whether the pathological character of a 1-month-old injury is ameliorated by application of PEG. Using a novel isocontouring algorithm, we show that immediate PEG treatment and treatment delayed by up to 7 h post-injury statistically increased the volume of intact spinal parenchyma and reduced the amount of cystic cavitation. Furthermore, in PEG-treated animals, the lesion was more focal and less diffuse throughout the damaged segment of the spinal cord, so that control cords showed a significantly extended lesion surface area. This three-dimensional computer evaluation showed that the functional recovery produced by topical application of a hydrophilic polymer is accompanied by a reduction in spinal cord damage.
Amino acid modulation of in vivo intestinal zinc absorption in freshwater rainbow trout
Authors: Glover Chris N. , Hogstrand Christer 
Published: April 2021

SUMMARY
The composition of the intestinal lumen is likely to have considerable influence upon the absorption, and consequently the nutrition and/or toxicity, of ingested zinc in aquatic environments, where zinc is both a nutrient and a toxicant of importance. The effects of amino acids upon intestinal zinc uptake in freshwater rainbow trout (Oncorhynchus mykiss) were studied using an in vivo perfusion technique. The presence of histidine, cysteine and taurine had distinct modifying actions upon quantitative and qualitative zinc absorption, compared to perfusion of zinc alone. Alterations in zinc transport were not correlated with changes in levels of free zinc ion. The chemical nature of the zinc–amino acid chelate, rather than the chelation itself, appeared to have the most important influence upon zinc absorption. l-histidine, despite a strong zinc-chelating effect, maintained quantitative zinc uptake at control (zinc alone) levels. This effect correlated with the formation of Zn(His)2 species. d-histidine at a luminal concentration of 100 mmol l–1 significantly enhanced subepithelial zinc accumulation, but reduced the fraction of zinc that was retained and absorbed by the fish. The possibility of a Zn(His)2-mediated pathway for intestinal uptake is discussed. l-cysteine specifically stimulated the accumulation of zinc post-intestinally, an effect attributed to enhanced zinc accumulation in the blood. Taurine increased subepithelial zinc accumulation, but decreased the passage of zinc to post-intestinal compartments. Amino acids are proposed to have important roles in modifying intestinal zinc uptake with potential implications for environmental toxicity as well as aquaculture.
Circadian rhythm of acidification in insect vas deferens regulated by rhythmic expression of vacuolar H+-ATPase
Authors: Bebas Piotr , Cymborowski Bronislaw , Giebultowicz Jadwiga M. 
Published: April 2021

SUMMARYRecent studies have demonstrated that the peripheral tissues of vertebrates and invertebrates contain circadian clocks; however, little is known about their functions and the rhythmic outputs that they generate. To understand clock-controlled rhythms at the cellular level, we investigated a circadian clock located in the reproductive system of a male moth (the cotton leaf worm Spodoptera littoralis) that is essential for the production of fertile spermatozoa. Previous work has demonstrated that spermatozoa are released from the testes in a daily rhythm and are periodically stored in the upper vas deferens (UVD). In this paper, we demonstrate a circadian rhythm in pH in the lumen of the UVD, with acidification occurring during accumulation of spermatozoa in the lumen. The daily rhythm in pH correlates with a rhythmic increase in the expression of a proton pump, the vacuolar H+-ATPase (V-ATPase), in the apical portion of the UVD epithelium. Rhythms in pH and V-ATPase persist in light/dark cycles and constant darkness, but are abolished in constant light, a condition that disrupts clock function and renders spermatozoa infertile. Treatment with colchicine impairs the migration of V-ATPase-positive vesicles to the apical cell membrane and abates the acidification of the UVD lumen. Bafilomycin, a selective inhibitor of V-ATPase activity, also prevents the decline in luminal pH. We conclude that the circadian clock generates a rhythm of luminal acidification by regulating the levels and subcellular distribution of V-ATPase in the UVD epithelium. Our data provide the first evidence for circadian control of V-ATPase, the fundamental enzyme that provides the driving force for numerous secondary transport processes. They also demonstrate how circadian rhythms displayed by individual cells contribute to the synchrony of physiological processes at the organ level.
Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia
Authors: Frick N. T. , Wright P. A. 
Published: April 2021

SUMMARY
At a field site in Belize, mangrove killifish Rivulus marmoratus inhabit hypersaline waters (up to 48 ‰) containing approximately 1 mmol l–1 ammonia. We tested the hypotheses that R. marmoratus modify their nitrogen metabolism and excretion (i) by accumulating free amino acids (FAAs) and urea in the tissues during hyperosmotic stress and (ii) by shifting to ureotelism and accumulating FAAs during hyperammonia stress. Urea excretion (JUrea) (but not ammonia excretion, JAmm) displayed a diurnal pattern, with significantly less (75 %) urea excreted at night than during the day in both laboratory-reared clones and wild-caught killifish. When fish were exposed to hypersaline conditions (45 ‰ sea water), JUrea was significantly reduced and tissue urea and FAA levels were elevated compared with those of control fish (15 ‰ sea water). When R. marmoratus were exposed to 0, 1, 2, 5 and 10 mmol l–1 NH4Cl (pH 8) for 48 h, no differences were found in JUrea. Remarkably, prolonged exposure (10 days) to 5 mmol l–1 NH4Cl (pH 8) did not result in an elevation of tissue ammonia levels. In addition, tissue urea and total FAA levels did not differ between control and ammonia-exposed fish after ⩾4 days. We propose that the euryhaline R. marmoratus retain urea and FAAs within their tissues in response to extreme osmotic stress. In contrast to many ammonia-tolerant fishes, R. marmoratus do not shift to ureotelism during prolonged hyperammonia stress, nor do they convert nitrogenous wastes into FAAs. The data suggest that killifish continue to eliminate ammonia despite an unfavourable blood-to-water gradient, thereby avoiding accumulation of ammonia.
Nitrogen metabolism and excretion in the mangrove killifishRivulus marmoratusII. Significant ammonia volatilization in a teleost during air-exposure
Authors: Frick N. T. , Wright P. A. 
Published: April 2021

SUMMARYThe mangrove killifish Rivulus marmoratus can tolerate prolonged periods of air-exposure (&gt;1 month). During these periods of emersion, we hypothesized that R. marmoratus would convert potentially toxic ammonia into urea and free amino acids (FAAs). In air-exposed fish, both ammonia (JAmm) and urea (JUrea) excretion continued at approximately 57 % and 39 %, respectively, of submerged rates. Remarkably, approximately 42 % of the total ammonia excreted during air-exposure was through NH3 volatilization. Ammonia did not accumulate in whole-body tissues of air-exposed fish, but levels of both urea and some FAAs (primarily alanine and glutamine) were up to twofold higher after 10 days. The activities of the ornithine–urea cycle enzymes carbamoyl phosphate synthetase III and ornithine transcarbamylase increased (by approximately 30 % and 36 %, respectively) in whole-body tissues of air-exposed fish, while levels of arginase remained unchanged. The activities of enzymes involved in amino acid and oxidative metabolism were not significantly different between control and air-exposed fish. Partitioning of the anterior and posterior ends of immersed fish revealed that just over half (57 %) of the total nitrogen (ammonia+urea) was excreted through the anterior end of the fish, presumably via the branchial tissues, while emersed fish increased excretion via the posterior end (kidney+skin). R. marmoratus do not undergo a shift towards ureotelism during air-exposure. Rather, we propose that R. marmoratus are able to survive on land for extended periods without significant ammonia accumulation because they continuously release ammonia, partially by NH3 volatilization.
The mechanics of wave-swept algae
Authors: Denny Mark , Gaylord Brian 
Published: April 2021

SUMMARYWave-swept marine algae must contend with the hydrodynamic forces imposed by extreme water velocities. Nonetheless, they seldom have a shape that appears streamlined and they are constructed of weak, compliant materials. How do they survive? The answer is complex, but a coherent story is beginning to emerge. The combined effect of frond shape and material properties ensures that algae are flexible. In small individuals, flexibility allows the plant to reorient and reconfigure in flow, thereby assuming a streamlined shape and reducing the applied hydrodynamic force. In large individuals, flexibility allows fronds to `go with the flow', a strategy that can at times allow the plant to avoid hydrodynamic forces but may at other times impose inertial loads. Our understanding of algal mechanics is such that we can begin to predict the survivorship of algae as a function of size, spatial distribution and wave climate.
Mitochondrial ATP-sensitive K+ channels influence force development and anoxic contractility in a flatfish, yellowtail flounderLimanda ferruginea, but not Atlantic codGadus morhuaheart
Authors: MacCormack Tyson J. , Driedzic William R. 
Published: April 2021

SUMMARYThe influence of ATP-sensitive K+ channels (KATPchannels) on cardiac performance during anoxia and reoxygenation was investigated in two species of fish showing different cardiac responses to anoxia. Force production in isometrically contracting ventricular muscle preparations from yellowtail flounder is potentiated at the onset of anoxia,while force immediately declines in Atlantic cod preparations. Glibenclamide,a general KATP blocker, impaired oxygenated force development in yellowtail flounder heart but was without effect on cod preparations. The mitochondrial KATP (mKATP)-specific blocker 5-hydroxydecanoic acid (5HD) improved oxygenated force production in yellowtail flounder heart without influencing contractility during anoxia or reoxygenation. The specific mKATP agonist diazoxide preserved resting tension and eliminated anoxic force potentiation in yellowtail flounder heart preparations. Neither 5HD nor diazoxide affected contractility in cod ventricle preparations. Results indicate that KATP channels can modulate contractility in yellowtail flounder heart and are potentially important in cardiac hypoxia survival in this species.