bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Pharmacology of γ-Aminobutyric Acid and Acetylcholine Receptors at the Echinoderm Neuromuscular Junction
Authors: Devlin C. Leah 
Published: April 2021

ABSTRACT
This review describes the various subtypes of γ-aminobutyric acid (GABA) receptors found at the echinoderm neuromuscular junction (NMJ), based on pharmacological and physiological studies. The review focuses mainly on holothurian GABA receptors at the NMJ located between the radial nerve and longitudinal muscle of the body wall (LMBW) and compares them to GABA receptors described at other echinoderm NMJs. Since a primary action of GABA on the holothurian LMBW is to modulate contractile responses to the excitatory neurotransmitter, acetylcholine (ACh), the pharmacology of echinoderm nicotinic ACh receptors (nAChRs) and muscarinic ACh receptors (mAChRs) is also addressed.
GABA responses have been described in the asteroids, echinoids and holothuroids but not in the other echinoderm classes. Some actions of GABA on echinoderm muscle include regulation of basal tone and spontaneous rhythmic contractions and modulation of cholinergic responses. Both GABA A and B receptor subtypes are present at the echinoderm NMJ, a feature also common to the arthropods, molluscs and chordates. Echinoderm GABA A receptors may mediate the excitatory responses to GABA. The GABA A receptor antagonist bicuculline has a paradoxical effect on contractility, stimulating large protracted contractions of the LMBW. The GABA A agonist muscimol potentiates cholinergic contractions of the holothurian LMBW. Another population of GABA receptors is inhibitory and is sensitive to the GABA B agonist baclofen and GABA B antagonists phaclofen and 2-OH-saclofen. The pre- and/or postsynaptic location of the GABA A and B receptors is not currently known. The folded GABA analogue 4-cis-aminocrotonic acid has no effect on the contractility of the holothurian LMBW so GABA C receptors are probably lacking in this preparation.
Pharmacological studies have shown that distinct nAChRs and mAChRs are colocalized in numerous echinoderm muscle preparations. Most recently, nAChR agonists were used to characterize pharmacologically receptors at the holothurian LMBW that bind ACh. Nicotinic AChRs with unique pharmacological profiles are localized both pre- and postsynaptically at this NMJ, where their physiological action is to enhance muscle tone. Muscarinic agonists also have excitatory actions on the LMBW but their action is to stimulate phasic, rhythmic contractions of the muscle. The location of mAChRs at the echinoderm NMJ, however, is unknown.
Since most of the studies described in the present review have used whole-mount preparations consisting largely of a combination of muscle fibers, neurons and connective tissue, it is extremely difficult to determine pharmacologically the exact location of the various receptor subtypes. Additional electrophysiological studies on isolated neurons and muscle fibers are therefore required to clearly define extra-, pre- and/or postsynaptic sites for the receptor subtypes at the echinoderm NMJ.
Ca2+ Transport by the Sarcoplasmic Reticulum Ca2+-ATPase in sea Cucumber (Ludwigothurea Grisea) Muscle
Authors: Landeira-Fernandez Ana Maria 
Published: April 2021

ABSTRACT
In muscle cells, the excitation–contraction cycle is triggered by an increase in the concentration of free cytoplasmic Ca2+. The Ca2+-ATPase present in the membrane of the sarcoplasmic reticulum (SR) pumps Ca2+ from the cytosol into this intracellular compartment, thus promoting muscle relaxation. The microsomal fraction derived from the longitudinal smooth muscle of the body wall from the sea cucumber Ludwigothurea grisea retains a membrane-bound Ca2+-ATPase that is able to transport Ca2+ mediated by ATP hydrolysis. Immunological analyses reveal that monoclonal antibodies against sarco-endoplasmic reticulum Ca2+-ATPase (SERCA1 and SERCA2a) cross-react with a 110 kDa band, indicating that the sea cucumber Ca2+-ATPase is a SERCA-type ATPase. Like the mammalian Ca2+-ATPase isoforms so far described, the enzyme also shows a high affinity for Ca2+ and ATP, has an optimum pH of approximately 7.0 and is sensitive to thapsigargin and cyclopiazonic acid, specific inhibitors of the SERCA pumps. However, unlike the mammalian SERCA isoforms, concentrations of ATP above 2 mmol l−1 inhibit Ca2+ transport, but not ATP hydrolysis, in sea cucumber vesicles, suggesting that high ATP concentrations uncouple the Ca2+-ATPase. Another unique feature observed with the sea cucumber Ca2+-ATPase is the high dependence of maximal activity on K+ or Na+. Similar activation promoted by these cations was observed with various mammalian Ca2+-ATPase preparations when they were incubated in the presence of low concentrations of sulphated polysaccharides. In control experiments, K+ and Na+ have almost no effect on Ca2+ transport, but in the presence of heparin or fucosylated chondroitin sulphate, the activity of the different mammalian Ca2+-ATPases is inhibited and they are activated by either K+ or Na+ in a manner similar to the native sea cucumber ATPase. These results led us to investigate the possible occurrence of a highly sulphated polysaccharide on vesicles from the SR of sea cucumber smooth muscle that could act as an ‘endogenous’ Ca2+-ATPase inhibitor. In fact, SR vesicles derived from the sea cucumber, but not from rabbit muscle, contain a highly sulphated polysaccharide. After extraction and purification of these polysaccharide molecules, their effect was tested on vesicles obtained from rabbit muscle. This compound inhibited Ca2+ uptake in rabbit SR vesicles, at concentrations lower than heparin, and restored the dependence on monovalent cations. These results strongly suggest that the sea cucumber Ca2+-ATPase is activated by monovalent cations because of the presence of endogenous sulphated polysaccharides.
Control of Cardiovascular Function and its Evolution in Crustacea
Authors: Mcmahon Brian R. 
Published: April 2021

ABSTRACT
Work in the last decade has shown that crustacean open circulatory systems are highly efficient and controlled in a complex manner. Control occurs at several levels. Myocardial contraction is initiated in the cardiac ganglion but constantly modulated by the central nervous system, both directly via the cardioregulatory nerves and indirectly via the neurohormonal system. Heart rate and stroke volume can be controlled independently and measurements of both are needed to assess cardiac output accurately. Haemolymph outflow from many arthropod hearts is via a complex multiarterial distribution system, and the regional distribution of cardiac output is tightly controlled via cardioarterial valves at the base of each artery. These valves contain innervated muscle, and differential contraction serves to regulate the efflux of oxygenated haemolymph into a particular system. The major influence on both the evolution and control of arthropod open blood vascular systems is efficiency of oxygen uptake and delivery. This influence is illustrated by reference to a variety of crustacean and other arthropod types.
Lactate Sequestration in the Carapace of the Crayfish Austropotamobius Pallipes During Exposure in air
Authors: Jackson D. C. , Wang T. , Koldkjaer P. , Taylor E. W. 
Published: April 2021

ABSTRACT
When held in air for up to 24 h, crayfish accumulated Ca2+ and Mg2+ in their haemolymph in direct proportion to raised levels of lactate. K+ levels were highly variable, with elevated levels associated with morbidity. Lactate accumulation in the haemolymph was reflected in proportional increases in lactate levels in the carapace and muscle. Pieces of carapace incubated in saline containing elevated levels of lactate accumulated lactate to up to half the dissolved concentration. Measured levels in the carapace, relative to its water content, implied that lactate accumulated in the carapace in a combined form, possibly complexed to calcium. The exoskeleton seems to provide a reserve of buffering capacity and a sink for lactate during anaerobic metabolism. A similar mechanism has been identified in pond turtles.
Novel Subcellular and Molecular Tools to Study Ca2+ Transport Mechanisms During the Elusive Moulting Stages of Crustaceans: Flow Cytometry and Polyclonal Antibodies
Authors: Wheatly Michele G. , Zhang Zhiping , Weil Jennifer R. , Rogers James V. , Stiner La’tonia M. 
Published: April 2021

ABSTRACT
Our understanding of calcium homeostasis during the crustacean moulting cycle derives from research on intermoult animals that has been extrapolated to other stages. In terms of transepithelial Ca2+ flux, the more interesting stages are those surrounding ecdysis since crustaceans experience a sizeable negative calcium balance in immediate premoult and a significant positive calcium balance in immediate postmoult. These stages are elusive in the sense that larger species such as lobsters are rarely captured at this time, and smaller species such as blue crabs and crayfish are seldom synchronized in their moulting cycle. The reductionist approaches employed in cellular physiology, such as vesicle techniques, employ pooling of fresh tissues from many organisms. Examination of the elusive moulting stages requires more sensitive approaches that can utilize tissue from an individual crustacean to characterize Ca2+ pumps (Sarco/Endoplasmic Reticulum Ca2+-ATPase, SERCA; Plasma Membrane Ca2+-ATPase, PMCA) and the Na+/Ca2+ eXchanger (NCX). An emerging subcellular approach described in this paper is to use flow cytometry as a technique to monitor Ca2+ uptake into Fluo-3-loaded membrane vesicles. This paper illustrates the utility of this technique for measuring ATP-dependent Ca2+ uptake into hepatopancreatic basolateral membrane vesicles. Obstacles to progress in molecular studies have not been limited by synchronization of moulting since tissue can be snap-frozen and collected from many animals over time. Here, the problem has been the lack of specific antibodies that hybridize with the Ca2+ transporters of interest so that they can be localized within epithelia. In this paper, we introduce polyclonal antibodies raised in rabbits against crayfish SERCA, PMCA and NCX. Immunocytochemistry of SERCA in muscle, PMCA in antennal gland and NCX in heart confirms the specificity of the antibodies.
Neuroendocrine Regulation of Osmoregulation and the Evolution of Air-Breathing in Decapod Crustaceans
Authors: Morris Stephen 
Published: April 2021

ABSTRACT
Gills are the primary organ for salt transport, but in land crabs they are removed from water and thus ion exchanges, as well as CO2 and ammonia excretion, are compromised. Urinary salt loss is minimised in land crabs by redirecting the urine across the gills where salt reabsorption occurs. Euryhaline marine crabs utilise apical membrane branchial Na+/H+ and Cl−/HCO3− exchange powered by a basal membrane Na+/K+-ATPase, but in freshwater crustaceans an apical V-ATPase provides for electrogenic uptake of Cl− in exchange for HCO3−. The HCO3− is provided by carbonic anhydrase facilitating CO2 excretion while NH4+ can substitute for K+ in the basal ATPase and for H+ in the apical exchange. Gecarcinid land crabs and the terrestrial anomuran Birgus latro can lower the NaCl concentration of the urine to 5 % of that of the haemolymph as it passes across the gills. This provides a filtration–reabsorption system analogous to the vertebrate kidney.
Crabs exercise hormonal control over branchial transport processes. Aquatic hyper-regulators release neuroamines from the pericardial organs, including dopamine and 5-hydroxytryptamine (5-HT), which via a cAMP-mediated phosphorylation stimulate Na+/K+-ATPase activity and NaCl uptake. Freshwater species utilise a V-ATPase, and additional mechanisms of control have been suggested. Crustacean hyperglycaemic hormone (CHH) has now also been confirmed to have effects on hydromineral regulation, and a putative role for neuropeptides in salt and water balance suggests that current models for salt regulation are probably incomplete. In a terrestrial crabs there may be controls on both active uptake and diffusive loss. The land crab Gecarcoidea natalis drinking saline water for 3 weeks reduced net branchial Na+ uptake but not Na+/K+-ATPase activity, thus implying a reduction in diffusive Na+ loss. Further, in G. natalis Na+ uptake and Na+/K+-ATPase were stimulated by 5-HT independently of cAMP. Conversely, in the anomuran B. latro, branchial Na+ and Cl− uptake and Na+/K+-ATPase are inhibited by dopamine, mediated by cAMP. There has been a multiple evolution of a kidney-type system in terrestrial crabs capable of managing salt, CO2 and NH3 movements.
A shot in the dark: the silent quest of a free-flying phonotactic fly
Authors: Müller Pie , Robert Daniel 
Published: April 2021

ABSTRACT
To reproduce, females of the parasitoid fly Ormia ochracea detect and localise a calling male cricket upon which they deposit their endoparasitic larvae. Calling male crickets are therefore subject to both sexual and natural selection by simultaneously attracting mates and phonotactic parasitoids. The possible strategy of song interruption employed by the cricket host to reduce his attractiveness to acoustic parasitoids was tested in the laboratory by examining the fly’s phonotactic quest in response to synthetic cricket songs. Phonotactic flight trajectories were recorded in three dimensions with a stereo infrared video tracking system while the sound stimulus was controlled on-line as a function of the fly’s position in space. Within a single flight, three distinct phases could be observed: a take-off phase, a cruising phase, during which course and altitude were rather constant, and a landing phase characterised by a spiralling descent towards the sound source. The flies showed remarkable phonotactic accuracy in darkness; they landed at a mean distance of 8.2 cm from the centre of the loudspeaker after a flight distance of approximately 4 m. The present data illustrate the fly’s surprising ability to gauge the direction and distance of a sound source in three dimensions and, subsequently, to find it in darkness and silence.
ATP-regenerating system in the cilia of Paramecium caudatum
Authors: Noguchi Munenori , Sawadah Taketoshi , Akazawa Toshikazu 
Published: April 2021

ABSTRACT
The energy supply for eukaryotic ciliary and flagellar movement is thought to be maintained by ATP-regenerating enzymes such as adenylate kinase, creatine kinase and arginine kinase. In this study, the energy-supplying system for the ciliary movement of Paramecium caudatum was examined. Arginine kinase and adenylate kinase activities were detected in the cilia. To demonstrate that phosphoarginine satisfactorily supplies high-energy phosphate compounds into the narrow ciliary space, we prepared an intact ciliated cortical sheet from live Paramecium caudatum. These cortical sheets, with an intact ciliary membrane, produced a half-closed system in which each cilium was covered with a ciliary membrane with an opening to the cell body. Ciliary beating on the intact cortical sheets was induced by perfusing not only ATP but also ADP. Addition of phosphoarginine (0.2 mmol l−1 ) increased the beat frequency. A further increase in beat frequency was observed in 0.4 mmol l−1 phosphoarginine, and this was enhanced when the cilia were reactivated with relatively low concentrations of ATP. We have demonstrated that phosphoarginine supplies energy as a ‘phosphagen’ for ciliary beating in Paramecium caudatum, suggesting that phosphoarginine functions not only as a reservoir of energy but also as a transporter of energy in these continuously energy-consuming circumstances.
Movies available on-line: http://www.biologists.com/JEB/movies/jeb3123.html
Mechanics of limb bone loading during terrestrial locomotion in the green iguana (Iguana iguana) and American alligator (Alligator mississippiensis)
Authors: Blob Richard W. , Biewener Andrew A. 
Published: April 2021

ABSTRACT
In vivo measurements of strain in the femur and tibia of Iguana iguana (Linnaeus) and Alligator mississippiensis (Daudin) have indicated three ways in which limb bone loading in these species differs from patterns observed in most birds and mammals: (i) the limb bones of I. iguana and A. mississippiensis experience substantial torsion, (ii) the limb bones of I. iguana and A. mississippiensis have higher safety factors than those of birds or mammals, and (iii) load magnitudes in the limb bones of A. mississippiensis do not decrease uniformly with the use of a more upright posture. To verify these patterns, and to evaluate the ground and muscle forces that produce them, we collected three-dimensional kinematic and ground reaction force data from subadult I. iguana and A. mississippiensis using a force platform and high-speed video. The results of these force/kinematic studies generally confirm the loading regimes inferred from in vivo strain measurements. The ground reaction force applies a torsional moment to the femur and tibia in both species; for the femur, this moment augments the moment applied by the caudofemoralis muscle, suggesting large torsional stresses. In most cases, safety factors in bending calculated from force/video data are lower than those determined from strain data, but are as high or higher than the safety factors of bird and mammal limb bones in bending. Finally, correlations between limb posture and calculated stress magnitudes in the femur of I. iguana confirm patterns observed during direct bone strain recordings from A. mississippiensis: in more upright steps, tensile stresses on the anterior cortex decrease, but peak compressive stresses on the dorsal cortex increase. Equilibrium analyses indicate that bone stress increases as posture becomes more upright in saurians because the ankle and knee extensor muscles exert greater forces during upright locomotion. If this pattern of increased bone stress with the use of a more upright posture is typical of taxa using non-parasagittal kinematics, then similar increases in load magnitudes were probably experienced by lineages that underwent evolutionary shifts to a non-sprawling posture. High limb bone safety factors and small body size in these lineages could have helped to accommodate such increases in limb bone stress.
Reproductive behaviour in the male cricket Gryllus bimaculatus DeGeer. I. Structure and function of the genitalia
Authors: Kumashiro Mikihiko , Sakai Masaki 
Published: April 2021

ABSTRACT
We have investigated the morphology and physiology of the genitalia of the male cricket to establish a basis for neuroethological study of its reproductive behaviour. First, the structure of the phallic complex, including the dorsal pouch, guiding rod, epiphallus, ventral lobes and median pouch, are described, as are the muscles, cuticle, membranes and biomechanics of copulation. The innervation and sensory receptors have also been examined. Second, the functional role of the muscle in each genital organ has been determined by direct observation of muscle contraction during spontaneous or evoked movements and by analysis of the changes in movements after the ablation of the muscle. Third, for the flexible membranous organs, the ventral lobes and median pouch, the passages for haemolymph and their dynamic properties have been examined using petroleum jelly. Fourth, the sequence of coordinated motor actions performed by the internal and external genital organs, which were induced in both restrained and dissected males using newly developed techniques, has been analyzed during tethered copulation and spermatophore formation. As a result, the mechanisms of copulation and spermatophore formation are now more fully understood.
Gliding flight in a jackdaw: a wind tunnel study
Authors: Rosén Mikael , Hedenström Anders 
Published: April 2021

ABSTRACT
We examined the gliding flight performance of a jackdaw Corvus monedula in a wind tunnel. The jackdaw was able to glide steadily at speeds between 6 and 11 m s−1. The bird changed its wingspan and wing area over this speed range, and we measured the so-called glide super-polar, which is the envelope of fixed-wing glide polars over a range of forward speeds and sinking speeds.
The glide super-polar was an inverted U-shape with a minimum sinking speed (Vms) at 7.4 m s−1 and a speed for best glide (Vbg) at 8.3 m s−1. At the minimum sinking speed, the associated vertical sinking speed was 0.62 m s−1. The relationship between the ratio of lift to drag (L:D) and airspeed showed an inverted U-shape with a maximum of 12.6 at 8.5 m s−1. Wingspan decreased linearly with speed over the whole speed range investigated. The tail was spread extensively at low and moderate speeds; at speeds between 6 and 9 m s−1, the tail area decreased linearly with speed, and at speeds above 9 m s−1 the tail was fully furled. Reynolds number calculated with the mean chord as the reference length ranged from 38 000 to 76 000 over the speed range 6–11 m s−1.
Comparisons of the jackdaw flight performance were made with existing theory of gliding flight. We also re-analysed data on span ratios with respect to speed in two other bird species previously studied in wind tunnels. These data indicate that an equation for calculating the span ratio, which minimises the sum of induced and profile drag, does not predict the actual span ratios observed in these birds. We derive an alternative equation on the basis of the observed span ratios for calculating wingspan and wing area with respect to forward speed in gliding birds from information about body mass, maximum wingspan, maximum wing area and maximum coefficient of lift. These alternative equations can be used in combination with any model of gliding flight where wing area and wingspan are considered to calculate sinking rate with respect to forward speed.
Field estimates of body drag coefficient on the basis of dives in passerine birds
Authors: Hedenström Anders , Liechti Felix 
Published: April 2021

ABSTRACT
During forward flight, a bird’s body generates drag that tends to decelerate its speed. By flapping its wings, or by converting potential energy into work if gliding, the bird produces both lift and thrust to balance the pull of gravity and drag. In flight mechanics, a dimensionless number, the body drag coefficient (CD,par), describes the magnitude of the drag caused by the body. The drag coefficient depends on the shape (or streamlining), the surface texture of the body and the Reynolds number. It is an important variable when using flight mechanical models to estimate the potential migratory flight range and characteristic flight speeds of birds. Previous wind tunnel measurements on dead, frozen bird bodies indicated that CD,par is 0.4 for small birds, while large birds should have lower values of approximately 0.2. More recent studies of a few birds flying in a wind tunnel suggested that previous values probably overestimated CD,par.
We measured maximum dive speeds of passerine birds during the spring migration across the western Mediterranean. When the birds reach their top speed, the pull of gravity should balance the drag of the body (and wings), giving us an opportunity to estimate CD,par. Our results indicate that CD,par decreases with increasing Reynolds number within the range 0.17–0.77, with a mean CD,par of 0.37 for small passerines. A somewhat lower mean value could not be excluded because diving birds may control their speed below the theoretical maximum. Our measurements therefore support the notion that 0.4 (the ‘old’ default value) is a realistic value of CD,par for small passerines.