bluuebunny/crossref_metadata_2025_split huggingface dataset:
NO2− uptake and HCO3− excretion in the intestine of the European flounder (Platichthys flesus)
Authors: Grosell M. , Jensen F. B. 
Published: April 2021

ABSTRACT
Ion transport across isolated intestinal segments from the European flounder (Platichthys flesus) was studied with the primary aim of evaluating the mechanisms of nitrite (NO2−) uptake and HCO3− excretion. A double-radiolabelling technique was applied to monitor unidirectional Cl− and Na+ influx. Furthermore, net fluxes of NO2−, HCO3−, Cl−, Na+ and water were recorded. NO2− uptake was inhibited by mucosal application of bumetanide (10−4 mol l−1) but not DIDS (10−3 mol l−1), suggesting that NO2− is transported across the intestine via the Na+/K+/2Cl− cotransporter rather than via a Cl−/HCO3− exchanger. In addition to transport via the Na+/K+/2Cl− cotransporter, NO2− uptake may also occur through the Na+/Cl− cotransporter and by conductive transport. NO2−and Cl− influx rates seemed to reflect their mucosal concentrations, and NO2− did not influence unidirectional influx or net flux of Cl−. HCO3− efflux was significantly reduced in the presence of 10−3 mol l−1 DIDS in the mucosal solution. This may indicate the presence of an apical Cl−/HCO3− exchanger in the intestinal epithelium, which would not comply with the current model of HCO3− excretion in the intestine of marine teleost fish. An alternative model of HCO3− excretion across the intestinal epithelium is proposed.
The vibrational startle response of the desert locust Schistocerca gregaria
Authors: Friedel Thomas 
Published: April 2021

ABSTRACT
Substratum vibrations elicit a fast startle response in unrestrained quiescent desert locusts (Schistocerca gregaria). The response is graded with stimulus intensity and consists of a small, rapid but conspicuous movement of the legs and body, but it does not result in any positional change of the animal. With stimuli just above threshold, it begins with a fast twitch of the hindlegs generated by movements of the coxa–trochanter and femur–tibia joints. With increasing stimulus intensity, a rapid movement of all legs may follow, resulting in an up–down movement of the whole body.
The magnitude of both the hindleg movement and electromyographic recordings from hindleg extensor and flexor tibiae muscles increases with stimulus amplitude and reaches a plateau at vibration accelerations above 20 m s−2 (peak-to-peak). Hindleg extensor and flexor tibiae muscles in unrestrained animals are co-activated with a mean latency of 30 ms. Behavioural thresholds are as low as 0.47 m s−2 (peak-to-peak) at frequencies below 100 Hz but rise steeply above 200 Hz. The response habituates rapidly, and inter-stimulus intervals of 2 min or more are necessary to evoke maximal reactions.
Intracellular recordings in fixed (upside-down) locusts also revealed co-activation of both flexor and extensor motor neurones with latencies of approximately 25 ms. This shows that the neuronal network underlying the startle movement is functional in a restrained preparation and can therefore be studied in great detail at the level of identified neurones.
Lactate transport across sarcolemmal vesicles isolated from rainbow trout white muscle
Authors: Laberee Karen , Milligan C. Louise 
Published: April 2021

ABSTRACT
Rainbow trout (Oncorhynchus mykiss) retain the majority of lactate produced during exhaustive exercise within white muscle. Previous studies have suggested that this retention is partially via a re-uptake of released lactate. The purpose of this work was to study lactate uptake using trout white muscle sarcolemmal vesicles. Lactate uptake by trout white muscle is partially through a low-affinity, high-capacity carrier (apparent Km=55.6 mmol l−1 and Vmax= 44.5 nmol mg−1 protein min−1). At high concentrations (20 and 50 mmol l−1), pyruvate partially (up to 39 %) inhibited lactate uptake, suggesting the involvement of a monocarboxylate carrier. The anion transport inhibitor 4-acetoamido-4′-isothiocyanstilbene-2,2′-disulphonic acid (SITS) and the monocarboxylate transport inhibitor α-cyano-4-hydroxycinnamate (CHC) stimulated apparent lactate uptake. The model developed suggests that lactate is taken up by the vesicles, at least in part by a pyruvate-sensitive monocarboxylate carrier, and that its subsequent efflux is inhibited by SITS and CHC, suggesting that lactate export from trout white muscle is also carrier-mediated.
Migratory directions of free-flying birds versus orientation in registration cages
Authors: Nievergelt Fränzi , Liechti Felix , Bruderer Bruno 
Published: April 2021

ABSTRACT
Good conditions for migration may promote offshore flights in nocturnal autumn migrants at the northern border of the Mediterranean Sea, whereas unfavourable conditions may induce flights along the coast. These predictions were tested by performing orientation cage experiments and making simultaneous observations of free-flying birds using a tracking radar. The flight directions of free-flying birds were mainly towards southwest and did not differ between overcast and clear sky conditions. The caged birds, however, tended towards southwest under clear sky and showed a more scattered distribution in the southwest and southeast quadrants under overcast conditions. Similar directional scatter occurred when the cage experiments were performed late at night. In contrast, free-flying birds shifted their flight direction towards west as night progressed to avoid flights across the sea. Flight directions observed by radar shifted slightly towards west as the season progressed owing to more frequent southeasterly winds. In orientation cages, however, directional preference was scattered towards southwest and southeast in the early migratory season and became unimodal (southwest) at the peak of the season; this change was not caused by different species composition. Consequently, there is a general coincidence of flight directions and directional preferences in orientation cages, but interpretations of results from orientation cages must allow for the possibility that experimental directions are different from migratory directions of free-flying birds, particularly under suboptimal migratory conditions.
Seasonal and temperature effects on the adrenergic responses of Arctic charr (Salvelinus alpinus) erythrocytes
Authors: Lecklin Tiina , Nikinmaa Mikko 
Published: April 2021

ABSTRACT
In the present study, we have examined the adrenergic responses of Arctic charr (Salvelinus alpinus) erythrocytes acclimated to different temperatures (2, 8 and 14 °C) during different seasons. We measured the changes in cellular water and ion contents after noradrenaline stimulation using different noradrenaline concentrations and external pH values. Furthermore, the effects of acute temperature changes on the magnitude of the adrenergic response were studied. The adrenergic response of Arctic charr erythrocytes showed pronounced seasonal variation. The [Na+]/[Cl−] accumulation ratio after adrenergic stimulation was greatest in May, indicating an enhanced activity of the Na+/H+ exchanger. The noradrenaline-induced change in [Na+]i was greatest in spring. In addition to a seasonal effect, the exchanger seemed to be most active in erythrocytes from charr acclimated to low temperature (2 °C) early in May: the EC50 value was lower and the calculated maximal increase in [Na+]i was greater in the 2 °C-acclimated group than in the other acclimation groups. In contrast, acclimation to different temperatures did not affect these responses (measured at a constant temperature) in February. An acute temperature change has a smaller effect on the adrenergic response of Arctic charr erythrocytes than on rainbow trout (Oncorhynchus mykiss) erythrocytes.
Cell-derived stiffening and plasticizing factors in sea cucumber (Cucumaria frondosa) dermis
Authors: Koob Thomas J. , Koob-Emunds Magdalena M. , Trotter John A. 
Published: April 2021

ABSTRACT
The stiffness of holothurian dermis can be altered experimentally in vitro by changing the concentration of extracellular Ca2+. Previous experiments with Cucumaria frondosa have established that these Ca2+ effects are due to Ca2+-dependent cellular processes rather than to direct effects of Ca2+ on the extracellular matrix. The present report describes two protein factors that are released from cells of C. frondosa dermis by membrane lysis and that directly alter the stiffness of the extracellular matrix. One factor, isolated from the inner dermis, increased tissue stiffness in the absence of Ca2+. The second factor, from the outer dermis, decreased tissue stiffness in the presence of normal Ca2+ levels. The relative abundance of these two factors in the inner and outer dermis suggests the possibility that the cells that control tissue stiffness are spatially segregated. Both factors were partially purified under non-denaturing conditions by anion-exchange and gel-filtration chromatography. The partially purified protein preparations retained biological activity. These results suggest that the stiffness of sea cucumber dermis is regulated by cell-mediated secretion of either the stiffening or plasticizing protein and that alterations in dermis stiffness brought about by manipulation of Ca2+ levels are mediated by effects on secretion of one or both of these proteins.
Locomotor forces on a swimming fish: three-dimensional vortex wake dynamics quantified using digital particle image velocimetry
Authors: Drucker Eliot G. , Lauder George V. 
Published: April 2021

ABSTRACT
Quantifying the locomotor forces experienced by swimming fishes represents a significant challenge because direct measurements of force applied to the aquatic medium are not feasible. However, using the technique of digital particle image velocimetry (DPIV), it is possible to quantify the effect of fish fins on water movement and hence to estimate momentum transfer from the animal to the fluid. We used DPIV to visualize water flow in the wake of the pectoral fins of bluegill sunfish (Lepomis macrochirus) swimming at speeds of 0.5–1.5 L s−1, where L is total body length. Velocity fields quantified in three perpendicular planes in the wake of the fins allowed three-dimensional reconstruction of downstream vortex structures. At low swimming speed (0.5 L s−1), vorticity is shed by each fin during the downstroke and stroke reversal to generate discrete, roughly symmetrical, vortex rings of near-uniform circulation with a central jet of high-velocity flow. At and above the maximum sustainable labriform swimming speed of 1.0 L s−1, additional vorticity appears on the upstroke, indicating the production of linked pairs of rings by each fin. Fluid velocity measured in the vicinity of the fin indicates that substantial spanwise flow during the downstroke may occur as vortex rings are formed. The forces exerted by the fins on the water in three dimensions were calculated from vortex ring orientation and momentum. Mean wake-derived thrust (11.1 mN) and lift (3.2 mN) forces produced by both fins per stride at 0.5 L s−1 were found to match closely empirically determined counter-forces of body drag and weight. Medially directed reaction forces were unexpectedly large, averaging 125 % of the thrust force for each fin. Such large inward forces and a deep body that isolates left-and right-side vortex rings are predicted to aid maneuverability. The observed force balance indicates that DPIV can be used to measure accurately large-scale vorticity in the wake of swimming fishes and is therefore a valuable means of studying unsteady flows produced by animals moving through fluids.
Tail kinematics of the chub mackerel Scomber japonicus: testing the homocercal tail model of fish propulsion
Authors: Gibb Alice C. , Dickson Kathryn A. , Lauder George V. 
Published: April 2021

ABSTRACT
Scombrid fishes possess a homocercal caudal fin with reduced intrinsic musculature and dorso–ventrally symmetrical external and internal morphology. Because of this symmetrical morphology, it has often been assumed that scombrid caudal fins function as predicted by the homocercal tail model. According to that model, the caudal fin moves in a dorso–ventrally symmetrical manner and produces no vertical lift during steady swimming. To test this hypothesis, we examined the tail kinematics of chub mackerel, Scomber japonicus (24.8±1.3 cm total length, L). Markers were placed on the caudal fin to identify specific regions of the tail, and swimming chub mackerel were videotaped from lateral and posterior views, allowing a three-dimensional analysis of tail motion. Analysis of tail kinematics suggests that, at a range of swimming speeds (1.2–3.0 L s−1), the dorsal lobe of the tail undergoes a 15 % greater lateral excursion than does the ventral lobe. Lateral excursion of the dorsal tail-tip also increases significantly by 32 % over this range of speeds, indicating a substantial increase in tail-beat amplitude with speed. In addition, if the tail were functioning in a dorso–ventrally symmetrical manner, the tail should subtend an angle of 90 ° relative to the frontal (or xz) plane throughout the tail beat. Three-dimensional kinematic analyses reveal that the caudal fin actually reaches a minimum xz angle of 79.8 °. In addition, there is no difference between the angle subtended by the caudal peduncle (which is anterior to the intrinsic tail musculature) and that subtended by the posterior lobes of the tail. Thus, asymmetrical movements of the tail are apparently generated by the axial musculature and transmitted posteriorly to the caudal fin. These results suggest that the caudal fin of the chub mackerel is not functioning symmetrically according to the homocercal model and could produce upward lift during steady swimming.
Circadian oscillation of sensitivity of spider eyes: diurnal and nocturnal spiders
Authors: Yamashita Shigeki , Nakamura Takiko 
Published: April 2021

ABSTRACT
The circadian oscillation of sensitivity of the anterior median eye of a nocturnal spider Araneus ventricosus and that of a diurnal spider Menemerus confusus were examined by recording electroretinograms. The anterior median eye of Araneus ventricosus showed a marked circadian oscillation of sensitivity, but that of Menemerus confusus showed no circadian oscillation.
Inositol-1,4,5-trisphosphate and inositol-1,3,4,5-tetrakisphosphate are second messenger targets for cardioactive neuropeptides encoded on the fmrfamide gene
Authors: Willoughby Debbie , Yeoman Mark S. , Benjamin Paul R. 
Published: April 2021

ABSTRACT
This paper examines the importance of the calcium-mobilizing inositol phosphate pathway in mediating the effects of FMRFamide and its gene-related neuropeptides on the myogenic heart beat of the pond snail Lymnaea stagnalis. These peptides are encoded on a single exon of the FMRFamide gene and mediate diverse physiological effects in the isolated heart. The rate of production of inositol-1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol-1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4], measured using an HPLC method, were both significantly elevated in a concentration-dependent manner by FMRFamide (and were also elevated by FLRFamide). The threshold for increasing inositol phosphate production was low (100 pmol l−1) with a peak response occurring at 1 μmol l−1 FMRFamide. The shape of the dose–response curve for FMRFamide-induced elevation of heart-beat frequency, obtained in pharmacological experiments on the isolated whole heart, was similar to that for stimulation of inositol phosphate levels in homogenized heart tissue. FMRFamide and Ins(1,4,5)P3 produced similar effects on the rate of heart beat in permeabilized whole hearts. In addition, the phospholipase C inhibitor, neomycin (2.5 mmol l−1), blocked the stimulatory effects of FMRFamide on Ins(1,4,5)P3 production in heart homogenate, and attenuated the excitatory effects of this neuropeptide in the isolated heart. The ‘isoleucine’ pentapeptides, EFLRIamide and pQFYRIamide, also encoded by the FMRFamide gene, produced no significant effects on inositol phosphate production when applied alone or in combination with FMRFamide. These results suggested that FMRFamide (and FLRFamide), but not EFLRIamide and pQFYRIamide, mediated their main effects on heart beat via the inositol phosphate pathway. The fifth peptide, SEQPDVDDYLRDVVLQSEEPLY (‘SEEPLY’) had no effect when applied alone but appeared to modulate the effects of FMRFamide by delaying the time-to-peak of the Ins(1,4,5)P3 response from 5 s to 20 s by an unknown mechanism.
Cyclic AMP is involved in cardioregulation by multiple neuropeptides encoded on the FMRFamide gene
Authors: Willoughby Debbie , Yeoman Mark S. , Benjamin Paul R. 
Published: April 2021

ABSTRACT
We have used a combination of biochemical and pharmacological techniques to investigate the role of the cyclic nucleotides, 3′,5′-cyclic adenosine monophosphate (cyclic AMP) and 3′,5′-cyclic guanosine monophosphate (cyclic GMP), in mediating the cardioregulatory effects of FMRFamide and other neuropeptides encoded on exon II of the FMRFamide gene of Lymnaea stagnalis. The ‘isoleucine’ peptides (EFLRIamide and pQFYRIamide) produced complex biphasic effects on the frequency, force of contraction and tonus of the isolated heart of L. stagnalis, which were dependent on adenylate cyclase (AC) activity of the heart tissue. At a control rate of cyclic AMP production of ⩽ 10 pmoles min−1 mg−1 protein, the ‘isoleucine’ peptides produced a significant increase in AC activity in heart membrane preparations. This suggested that the enhanced AC activity is responsible for the stimulatory effects of the ‘isoleucine’ peptides on frequency and force of contraction of heart beat. This excitation sometimes followed an initial ‘inhibitory phase’ where the frequency of beat, force of contraction and tonus of the heart were reduced by the ‘isoleucine’ peptides. Hearts that showed the inhibitory phase of the ‘isoleucine’ response, but characteristically lacked the delayed excitatory phase, were found to have high levels of membrane AC activity ⩾10 pmoles min−1 mg−1 protein in controls. Application of the ‘isoleucine’ peptides to membrane homogenate preparation from these hearts failed to increase AC activity. The addition of FMRFamide produced significant increases in the rate of cyclic AMP production in the heart membrane preparations, which could account, at least in part, for the cardioexcitatory effects of this peptide in the isolated whole heart. A membrane-permeable cyclic AMP analogue (8-bromo-cyclic AMP) and an AC activator (forskolin) were also cardioexcitatory. The peptide SEEPLY had no effects on the beat properties of the isolated heart and did not alter AC activity. The activity of the membrane-bound (particulate) guanylate cyclase (GC) was not significantly affected by any of the peptides.
A point-mass model of gibbon locomotion
Authors: Bertram John E. A. , Ruina Andy , Cannon C. E. , Chang Young Hui , Coleman Michael J. 
Published: April 2021

ABSTRACT
In brachiation, an animal uses alternating bimanual support to move beneath an overhead support. Past brachiation models have been based on the oscillations of a simple pendulum over half of a full cycle of oscillation. These models have been unsatisfying because the natural behavior of gibbons and siamangs appears to be far less restricted than so predicted. Cursorial mammals use an inverted pendulum-like energy exchange in walking, but switch to a spring-based energy exchange in running as velocity increases. Brachiating apes do not possess the anatomical springs characteristic of the limbs of terrestrial runners and do not appear to be using a spring-based gait. How do these animals move so easily within the branches of the forest canopy? Are there fundamental mechanical factors responsible for the transition from a continuous-contact gait where at least one hand is on a hand hold at a time, to a ricochetal gait where the animal vaults between hand holds? We present a simple model of ricochetal locomotion based on a combination of parabolic free flight and simple circular pendulum motion of a single point mass on a massless arm. In this simple brachiation model, energy losses due to inelastic collisions of the animal with the support are avoided, either because the collisions occur at zero velocity (continuous-contact brachiation) or by a smooth matching of the circular and parabolic trajectories at the point of contact (ricochetal brachiation). This model predicts that brachiation is possible over a large range of speeds, handhold spacings and gait frequencies with (theoretically) no mechanical energy cost. We then add the further assumption that a brachiator minimizes either its total energy or, equivalently, its peak arm tension, or a peak tension-related measure of muscle contraction metabolic cost. However, near the optimum the model is still rather unrestrictive. We present some comparisons with gibbon brachiation showing that the simple dynamic model presented has predictive value. However, natural gibbon motion is even smoother than the smoothest motions predicted by this primitive model.
Patterned activation of unpaired median neurons during fictive crawling in Manduca sexta larvae
Authors: Johnston R. M. , Consoulas C. , Pflüger H.-J. , Levine R. B. 
Published: April 2021

ABSTRACT
The unpaired median neurons are common to the segmental ganglia of many insects. Although some of the functional consequences of their activation, among them the release of octopamine to modulate muscle contraction, have been described, less is understood about how and when these neurons are recruited during movement. The present study demonstrates that peripherally projecting unpaired median neurons in the abdominal and thoracic ganglia of the larval tobacco hornworm Manduca sexta are recruited rhythmically during the fictive crawling motor activity that is produced by the isolated central nervous system in response to pilocarpine. Regardless of the muscles to which they project, the efferent unpaired median neurons in all segmental ganglia are depolarized together during the phase of the crawling cycle when the thoracic leg levator motoneurons are active. During fictive crawling, therefore, the unpaired median neurons are not necessarily active in synchrony with the muscles to which they project. The rhythmical synaptic drive of the efferent unpaired median neurons is derived, at least in part, from a source within the subesophageal ganglion, even when the motor pattern is evoked by exposing only the more posterior ganglia to pilocarpine. In pairwise intracellular recordings from unpaired median neurons in different ganglia, prominent excitatory postsynaptic potentials, which occur with an anterior-to-posterior delay in both neurons, are seen to underlie the rhythmic depolarizations. One model consistent with these findings is that one or more neurons within the subesophageal ganglion, which project posteriorly to the segmental ganglia and ordinarily provide unpatterned synaptic inputs to all efferent unpaired median neurons, become rhythmically active during fictive crawling in response to ascending information from the segmental pattern-generating network.