bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuronal control of catecholamine secretion from chromaffin cells in the rainbow trout (Oncorhynchus mykiss)
Authors: Montpetit Colin J. , Perry Steve F.
Published: April 2021

The goal of the present investigation was to assess the relative involvement of nicotinic and muscarinic cholinergic receptors in the neuronal control of catecholamine secretion from the chromaffin tissue of rainbow trout (Oncorhynchus mykiss). This was accomplished by first developing and validating a nerve-stimulating technique able specifically to activate the nerve fibres innervating the chromaffin cells in order to elicit secretion of catecholamines. Using an in situ saline-perfused posterior cardinal vein preparation, it was demonstrated that whole-body field stimulation caused specific voltage-dependent neuronal stimulation of adrenaline and noradrenaline secretion. The contribution of non-specific depolarization was negligible. Several experimental results confirmed the specificity of the field stimulation technique. First, pre-treatment with neostigmine (an anticholinesterase) prolonged and more than doubled the amount of adrenaline secreted in response to electrical stimulation. Second, pre-treatment with the nicotinic receptor antagonist hexamethonium inhibited the electrically evoked secretion of adrenaline and noradrenaline. Third, perfusion with Na+-free saline or removal of the spinal cord abolished secretion of both catecholamines in response to the electrical stimulus. By using the field stimulation technique, this study is the first to demonstrate conclusively a role for muscarinic receptors in catecholamine secretion from trout chromaffin cells. Specifically, muscarinic cholinergic stimulation enhances nicotinic-evoked secretion of catecholamines and, under intense stimulation, may directly cause secretion. The results of the present study suggest the presence of muscarinic receptors on rainbow trout chromaffin cells with a functional role in the cholinergic control of catecholamine secretion.
Effects of size, motility and paralysation time of prey on the quantity of venom injected by the hunting spider Cupiennius salei
Authors: Malli Heinz , Kuhn-Nentwig Lucia , Imboden Hans , Nentwig Wolfgang
Published: April 2021

Previous experimental studies have shown that neotropical wandering spiders (Cupiennius salei) inject more venom when attacking larger crickets. It has been postulated that this is a consequence of predator–prey interactions during envenomation, which increase in intensity with the size of a given prey species. The present study was designed to test this hypothesis using anaesthetized crickets of different sizes that were moved artificially. Cupiennius salei was found (1) to inject more venom the greater the intensity of the struggling movement of the crickets (prey size kept constant); (2) to inject more venom the longer the duration of the struggling movement of the crickets (prey size and intensity of movement kept constant); and (3) to inject equal amounts into crickets of different size (duration and intensity of movement kept constant). These results indicate that C. salei alters the amount of venom it releases according to the size and motility of its prey. Venom expenditure depends mainly on the extent of the interactions with the prey during the envenomation process, whereas prey size is of minor significance. The regulation of venom injection in concert with behavioural adaptations in response to various types of prey minimizes the energetic cost of venom production, thus increasing the profitability of a given prey item.
NO2− uptake and HCO3− excretion in the intestine of the European flounder (Platichthys flesus)
Authors: Grosell M. , Jensen F. B.
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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.
Effects of incline and speed on the three-dimensional hindlimb kinematics of a generalized iguanian lizard (Dipsosaurus dorsalis)
Authors: Jayne Bruce C. , Irschick Duncan J.
Published: April 2021

Lizards commonly move on steep inclines in nature, but no previous studies have investigated whether the kinematics of the limbs of lizards differ on inclined surfaces compared with level surfaces. Therefore, we examined how the kinematics of the hindlimb were affected by both incline (downhill 30°, level and uphill 30°) and different speeds of steady locomotion (50–250 cm s−1) in the morphologically generalized iguanian lizard Dipsosaurus dorsalis. On the uphill surface, the strides of lizards were shorter and quicker than those at a similar speed on the level and downhill surfaces. A multivariate analysis revealed that the kinematics of locomotion on all three inclines were distinct, but several kinematic features of locomotion on the downhill surface were especially unique.

For example, downhill locomotion had the lowest angular excursions of femur rotation, and the knee and ankle were flexed more at footfall which contributed to a very low hip height. For D. dorsalis, changes in knee and ankle angles on the uphill surface were similar to those described previously for mammals moving up inclines, despite fundamental differences in limb posture between most mammals and lizards. Several features of the kinematics of D. dorsalis suggest that a sprawling limb enhances the ability to move on inclines.
Cholecystokinin affects gastric emptying and stomach motility in the rainbow trout Oncorhynchus mykiss
Authors: Olsson Catharina , Aldman Göran , Larsson Annhild , Holmgren Susanne
Published: April 2021

In this study, we describe new methods for recording gastric emptying and in vivo measurements of intragastric pressure in fish. Using these methods, we investigated the effects of the sulphated octapeptide of cholecystokinin (CCK8) on gastric emptying and on stomach motility in vivo and in vitro. Gastric emptying of 99Tcm-labelled food was measured in swimming fish by using a gamma camera, counting consecutive 2.5 min periods for 18–42 h. After 20 h, 55.3±4.0 % of the labelled food remained in the stomach of the control fish (mean ± S.E.M., N=9). Vascular infusion of CCK8 (25 pmol kg−1 h−1) delayed gastric emptying so that 70.4±4.8 % of the labelled food remained in the stomach after 20 h (N=8). Gastric pressure changes in vivo were measured using a balloon surgically fitted into the cardiac or pyloric part of the stomach. In the cardiac part, intra-arterial infusion of CCK8 at 0.1 nmol kg−1 h−1 resulted in a decrease in the frequency and amplitude of rhythmic contractions, while higher doses started/increased contractions. Atropine blocked much of the basal contractile activity, but did not influence the CCK8-induced inhibition of contractile activity. The pyloric part of the stomach was unaffected by intra-arterial infusion of CCK8 or atropine. In vitro perfusion of the stomach (with a balloon placed in the cardiac part to record motility) with CCK8 at high concentrations (10−7 mol l−1 and above) augmented the spontaneous contractions, while lower concentrations had inconsistent effects. In addition, CCK8 (10−7 to 10−6 mol l−1) decreased the amplitude of spontaneous contractions in longitudinal strip preparations, usually in combination with an increase in the resting tension. The decrease in amplitude was not affected by the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester hydrochloride (L-NAME; 10−4 mol l−1). Depending on the concentration and experimental arrangement, CCK8 had either inhibitory or excitatory effects on the cardiac stomach, suggesting the possible presence of different types of CCK receptor. We conclude that the predominant effect of CCK8 in vivo may be a slowing down of gastric emptying, presumably coinciding with a release of bile into the duodenum.
Control of abdominal extension in the freely moving intact crayfish Cherax destructor: II. Activity of the superficial extensor motor neurones
Authors: McCarthy Bernard J. , Macmillan David L.
Published: April 2021

The activity of the superficial extensor motor neurones was recorded during slow abdominal extension in the crayfish Cherax destructor. Postural extensions were evoked by lowering a platform from beneath the suspended crayfish. During extensions where the abdomen was physically blocked from achieving full extension, the largest superficial extensor motor neurone (SEMN6) fired at a higher rate than during unhindered extensions. Blocking a segment neighbouring that being examined also increased SEMN6 activity, demonstrating an intersegmental spread of the reflex. The increase in SEMN6 firing rate occurred in the absence of activity in the sensory neurone of the tonic muscle receptor organ, demonstrating that the tonic sensory neurone is not necessary for load compensation during these abdominal extensions in C. destructor. The findings support earlier evidence suggesting that other receptor systems can mediate load compensation in the abdomen of the crayfish.
Escape trajectories of the brown shrimp Crangon crangon, and a theoretical consideration of initial escape angles from predators
Authors: Arnott Stephen A. , Neil Douglas M. , Ansell Alan D.
Published: April 2021

Tail-flip escape trajectories of the brown shrimp Crangon crangon have been investigated in response to a natural predator, the cod Gadus morhua, and an artificial stimulus. Shrimps escaped by rolling to their left or right during the initial tail-flip of a response, and thereafter swam on their side. As a result of the laterally directed first tail-flip, initial escape angles always lay between 75° and 156° with respect to the (pre-escape) longitudinal axis (anterior=0°) of the shrimp. Symmetrical attacks from either head-on or tail-on produced escapes to the shrimp’s left or right in equal proportions, although a contralateral bias did occur if the shrimp experienced a looming object from one side before a symmetrical attack was applied. Lateral attacks produced a significantly greater proportion of contralateral responses than ipsilateral ones. Empirical and theoretical analyses indicate that the initial escape direction is influenced by an interaction between the range of first tail-flip escape angles that the shrimp is capable of performing and the risk of being intercepted by a predator during the initial stage of an escape. Thus, the unpredictability (‘protean behaviour’) of the response may be affected by the conditions of the interaction.

Subsequent tail-flips of an escape usually directed the response away from the stimulus, but sometimes escapes were instead steered to the side of the stimulus and then behind it. The probability of each type of escape occurring changed with attack direction.

The elements of protean behaviour that have been identified in both the initial and subsequent stages of the escape may prevent predators from learning a fixed pattern of response, but a trade-off occurs when escape trajectories infringe upon zones of high capture risk.
The development of a biological novelty: a different way to make appendages as revealed in the snout of the star-nosed mole Condylura cristata
Authors: Catania Kenneth C. , Northcutt R. Glenn , Kaas Jon H.
Published: April 2021

The nose of the star-nosed mole Condylura cristata is a complex biological novelty consisting of 22 epidermal appendages. How did this new set of facial appendages arise? Recent studies find remarkable conservation of the genes expressed during appendage formation across phyla, suggesting that the basic mechanisms for appendage development are ancient. In the nose of these moles, however, we find a unique pattern of appendage morphogenesis, showing that evolution is capable of constructing appendages in different ways. During development, the nasal appendages of the mole begin as a series of waves in the epidermis. A second deep layer of epidermis then grows under these superficial epidermal waves to produce 22 separate, elongated epidermal cylinders embedded in the side of the mole’s face. The caudal end of each cylinder later erupts from the face and rotates forward to project rostrally, remaining attached only at the tip of the snout. As a result of this unique ‘unfolding’ formation, the rostral end of each adult appendage is derived from caudal embryonic facial tissue, while the caudal end of each appendage is derived from rostral facial tissue. This developmental process has essentially no outgrowth phase and results in the reversal of the original embryonic orientation of each appendage. This differs from the development of other known appendages, which originate either as outgrowths of the body wall or from subdivisions of outgrowths (e.g. tetrapod digits). Adults of a different mole species (Scapanus townsendii) exhibit a star-like pattern that resembles an embryonic stage of the star-nosed mole, suggesting that the development of the star recapitulates stages of its evolution.
The diving physiology of bottlenose dolphins (Tursiops truncatus): II. Biomechanics and changes in buoyancy at depth
Authors: Skrovan Randolph C. , Williams T. M. , Berry P. S. , Moore P. W. , Davis R. W.
Published: April 2021

During diving, marine mammals must balance the conservation of limited oxygen reserves with the metabolic costs of swimming exercise. As a result, energetically efficient modes of locomotion provide an advantage during periods of submergence and will presumably increase in importance as the animals perform progressively longer dives. To determine the effect of a limited oxygen supply on locomotor performance, we compared the kinematics and behavior of swimming and diving bottlenose dolphins. Adult bottlenose dolphins (Tursiops truncatus) were trained to swim horizontally near the water surface or submerged at 5 m and to dive to depths ranging from 12 to 112 m. Swimming kinematics (preferred swimming mode, stroke frequency and duration of glides) were monitored using submersible video cameras (Sony Hi-8) held by SCUBA divers or attached to a pack on the dorsal fin of the animal. Drag and buoyant forces were calculated from patterns of deceleration for horizontally swimming and vertically diving animals. The results showed that dolphins used a variety of swimming gaits that correlated with acceleration. The percentage of time spent gliding during the descent phase of dives increased with depth. Glide distances ranged from 7.1±1.9 m for 16 m dives to 43.6±7.0 m (means ± S.E.M.) for 100 m dives. These gliding patterns were attributed to changes in buoyancy associated with lung compression at depth. By incorporating prolonged glide periods, the bottlenose dolphin realized a theoretical 10–21 % energetic savings in the cost of a 100 m dive in comparison with dives based on neutral buoyancy models. Thus, modifying locomotor patterns to account for physical changes with depth appears to be one mechanism that enables diving mammals with limited oxygen stores to extend the duration of a dive.
The diving physiology of bottlenose dolphins (Tursiops truncatus): III. Thermoregulation at depth
Authors: Williams Terrie M. , Noren D. , Berry P. , Estes J. A. , Allison C. , Kirtland J.
Published: April 2021

During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5–50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9±7.3 to 126.2±23.1 W m−2 and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0±2.6 beats min−1, N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.
Rhythmic changes in the serotonin content of the brain and eyestalk of crayfish during development
Authors: Castañón-Cervantes Oscar , Battelle Barbara-Anne , Luisa Fanjul-Moles María
Published: April 2021

The present study investigated developmental circadian changes in the content of 5-hydroxytryptamine (5-HT) in two structures proposed to contain pacemakers in crayfish Procambarus clarkii: the cerebral ganglion and the eyestalks. Crayfish (N=260) from three developmental stages were divided into two groups: (1) animals subjected to 12 h:12 h light:dark cycles for 10 days and (2) animals treated as described above, then exposed to 72 h of continuous dim light. Crayfish from both groups were killed at different times of day, and the cerebral ganglion and the eyestalks of each were assayed for 5-HT by reversed-phase HPLC with electrochemical detection. In all stages of development, 5-HT content (expressed asμg g−1 wet mass tissue) showed circadian variations in both structures analyzed; rhythms continued to free-run under constant illumination, and total 5-HT content was higher in the brain (0.581±0.36 μg g−1; mean ± S.E.M.) than in the eyestalks (0.299±0.15 μg g−1). As development advances, the percentage of the rhythm that shows periods of 24 h diminishes, while the percentage of the rhythm that shows periods of 9 to 12 h increases. This seems to indicate that pulsatile variations in 5-HT content are superimposed in a circadian component. The relationship between the 5-HT rhythm and electroretinogram and motor activity rhythms during development is discussed.
Body-building without power training: endogenously regulated pectoral muscle hypertrophy in confined shorebirds
Authors: Dietz Maurine W. , Piersma Theunis , Dekinga Anne
Published: April 2021

Shorebirds such as red knots Calidris canutus routinely make migratory flights of 3000 km or more. Previous studies on this species, based on compositional analyses, suggest extensive pectoral muscle hypertrophy in addition to fat storage before take-off. Such hypertrophy could be due to power training and/or be effected by an endogenous circannual rhythm. Red knots of two subspecies with contrasting migration patterns were placed in a climate-controlled aviary (12 h:12 h L:D photoperiod) where exercise was limited. Using ultrasonography, we measured pectoral muscle size as the birds stored fat in preparation for migration. At capture, there were no differences in body mass and pectoral muscle mass between the two subspecies. As they prepared for southward and northward migration, respectively, the tropically wintering subspecies (C. c. canutus) gained 31 g and the temperate wintering subspecies (C. c. islandica) gained 41 g. During this time, pectoral mass increased by 43–44 % of initial mass, representing 39 % (C. c. canutus) and 29 % (C. c. islandica) of the increase in body mass. The gizzard showed atrophy in conjunction with a diet change from molluscs to food pellets. Although we cannot exclude the possibility that the birds’ limited movement may still be a prerequisite for pectoral muscle hypertrophy, extensive power training is certainly not a requirement. Muscle hypertrophy in the absence of photoperiod cues suggests the involvement of an endogenous circannual process.
Isotope dilution spaces of mice injected simultaneously with deuterium, tritium and oxygen-18
Authors: Król Elzbieta , Speakman John R.
Published: April 2021

The isotope dilution technique for measuring total body water (TBW), and the doubly labelled water (DLW) method for measuring energy expenditure, are both sensitive to small variations in the ratio of the hydrogen to oxygen-18 dilution space. Since the dilution space ratio varies between individuals, there has been much recent debate over what causes this variability (i.e. physiological differences between individuals or analytical error in the isotope determinations), and thus which values (individual or a population mean dilution space ratio) should be employed for TBW and DLW calculations. To distinguish between physiological and analytical variability, we injected 15 non-reproductive and 12 lactating mice (Mus musculus, outbred MF1) simultaneously with deuterium, tritium and oxygen-18. The two hydrogen labels were administered and analysed independently, therefore we expected a strong correlation between dilution space ratios based on deuterium and tritium if most of the variation in dilution spaces was physiological, but only a weak correlation if most of the variation was analytical. Dilution spaces were significantly influenced by reproductive status. Dilution spaces expressed as a percentage of body mass averaged 15.7 % greater in lactating mice than in non-reproductive mice. In addition, the hydrogen tracer employed had a significant effect (deuterium spaces were 2.0 % larger than tritium spaces). Deuterium and tritium dilution spaces, expressed as a percentage of body mass, were highly correlated. Dilution space ratios ranged from 0.952 to 1.146 when using deuterium, and from 0.930 to 1.103 when using tritium. Dilution space ratios based on deuterium and tritium were also highly correlated. Comparison of standard deviations of the dilution space ratio based on deuterium in vivo and in vitro indicated that only 4.5 % of the variation in the dilution space ratios observed in the mice could be accounted for by analytical variation in the deuterium and oxygen-18 analyses. Although our results include data which were outside the limits previously regarded as biologically possible, the correlations that we detected strongly suggest that variation in the observed dilution space ratio was mostly physiological rather than analytical.
Food ingestion and water turnover in hummingbirds: how much dietary water is absorbed?
Authors: McWhorter Todd J. , Martínez del Rio Carlos
Published: April 2021

Hummingbirds are specialized nectarivores that feed on dilute solutions of sugars with trace amounts of amino acids and electrolytes. Their diets contain excess water that, if absorbed, must be eliminated. It has been hypothesized that in hummingbirds only a small fraction of this dietary water may be absorbed in the intestine. Here, we report the results of experiments designed to examine the relationship between nectar intake and water turnover in hummingbirds. Our results also allow the estimation of water absorption across the intestine and therefore test the hypothesis that ingested water in hummingbirds passes largely unabsorbed through the gastrointestinal tract. We found that fractional and total water turnover increased linearly with water ingestion. At low sucrose concentrations, food intake rates between four and five times body mass per 12 h were not unusual. A simple mass-balance model suggested that 78 % of ingested water was absorbed in the gastrointestinal tract and hence must be processed by the kidneys. However, fractional water absorption was variable and did not appear to be correlated with food or water intake parameters. Our results do not lend support to the hypothesis that the bulk of dietary water passes through the intestine unabsorbed. Although hummingbird kidneys appear well suited to excrete large volumes of dilute urine, rates of energy assimilation in hummingbirds may be constrained by excess water elimination when these birds are feeding on nectars with a low sugar concentration.
Genes to remember
Authors: Alberini Cristina M.
Published: April 2021

It has been known for several decades that the formation of long-term memory requires gene expression. In recent years, the use of genetic and molecular approaches has led to the identification and characterization of genes and molecules that play a fundamental role in the biological mechanisms underlying learning and memory. From these studies, it appears that molecules and molecular mechanisms essential for the process of memory have been conserved throughout evolution. The cyclic AMP (cAMP)-dependent activation pathway and a cAMP-dependent cascade of gene expression have been shown to be essential for memory formation in Aplysia californica, Drosophila melanogaster and rodents. Moreover, members of the transcription factor family cAMP response element binding proteins (CREBs) seem to represent key molecules for transforming incoming information into long-term memory. Here, we review the studies showing that conserved molecules and biological mechanisms are engaged in simple and complex forms of memory.