bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acid–Base Regulation in Tadpoles of Rana Catesbeiana Exposed to Environmental Hypercapnia
Authors: Busk Morten , Larsen Erik Hviid , Jensen Frank B. 
Published: April 2021

ABSTRACT
Tadpoles of Rana catesbeiana were exposed to different levels of environmental hypercapnia. The acid–base regulatory response differed from that in adult amphibians in showing a high degree of pH compensation in the extracellular fluid (65–85 %) and complete compensation in the intracellular fluid (tail muscle and liver) within 24 h. Hypercapnia induced a massive transfer of HCO3− equivalents and Ca2+ from the tadpoles to the environment, which lasted some 4–6 h. Bicarbonate accumulated in the body fluids came mainly from internal buffer sources (probably CaCO3 in lime sacs and/or skin deposits). It is suggested that the large bicarbonate efflux from the animal is a consequence of the dissolution of CaCO3 stores and the delayed adjustment of bicarbonate-retaining mechanisms. Re-exposure of tadpoles to hypercapnia after 1–3 weeks of normocapnic recovery only affected transepithelial fluxes of acid–base equivalents marginally, suggesting that mobilisable CaCO3 stores were depleted during the first exposure to hypercapnia and that they were not refilled. The CaCO3 stores may normally be mobilised during the slowly developing internal hypercapnia that occurs during metamorphosis.
Visually Mediated Odometry in Honeybees
Authors: Srinivasan M. V. , Zhang S. W. , Bidwell N. J. 
Published: April 2021

ABSTRACT
The ability of honeybees to gauge the distances of short flights was investigated under controlled laboratory conditions where a variety of potential odometric cues such as flight duration, energy consumption, image motion, airspeed, inertial navigation and landmarks were manipulated. Our findings indicate that honeybees can indeed measure short distances travelled and that they do so solely by analysis of image motion. Visual odometry seems to rely primarily on the motion that is sensed by the lateral regions of the visual field. Computation of distance flown is re-commenced whenever a prominent landmark is encountered en route. ‘Re-setting’ the odometer (or starting a new one) at each landmark facilitates accurate long-range navigation by preventing excessive accumulation of odometric errors. Distance appears to be learnt on the way to the food source and not on the way back.
Regulation Analysis Of Energy Metabolism
Authors: Brand Martin D. 
Published: April 2021

ABSTRACT
This paper reviews top-down regulation analysis, a part of metabolic control analysis, and shows how it can be used to analyse steady states, regulation and homeostasis in complex systems such as energy metabolism in mitochondria, cells and tissues. A steady state is maintained by the variables in a system; regulation is the way the steady state is changed by external effectors. We can exploit the properties of the steady state to measure the kinetic responses (elasticities) of reactions to the concentrations of intermediates and effectors. We can reduce the complexity of the system under investigation by grouping reactions into large blocks connected by a small number of explicit intermediates – this is the top-down approach to control analysis. Simple titrations then yield all the values of elasticities and control coefficients within the system. We can use these values to quantify the relative strengths of different internal pathways that act to keep an intermediate or a rate constant in the steady state. We can also use them to quantify the relative strengths of different primary actions of an external effector and the different internal pathways that transmit its effects through the system, to describe regulation and homeostasis. This top-down regulation analysis has been used to analyse steady states of energy metabolism in mitochondria, cells and tissues, and to analyse regulation of energy metabolism by cadmium, an external effector, in mitochondria. The combination of relatively simple experiments and new theoretical structures for presenting and interpreting the results means that top-down regulation analysis provides a novel and effective way to analyse steady states, regulation and homeostasis in intricate metabolic systems.
Volume-Sensitive Transport Systems and Volume Homeostasis in Vertebrate Red Blood Cells
Authors: Cossins Andrew R. , Gibson John S. 
Published: April 2021

ABSTRACT
Animal cells regulate their volume in the short term by controlling solute movements into and out of the cell. A suite of dissipative transport systems are involved which allow either regulatory volume increase (RVI) or decrease (RVD) responses depending upon the direction of the electrochemical gradients of the solutes. Many of these transporters have been identified at the molecular level and structure–function studies have identified transmembrane transport domains and cytoplasmic regulatory domains. In vertebrate red blood cells, protein phosphorylation appears to be central to the coordinated regulation of transporter activity. Inhibitors of protein phosphatases (PPs) cause inhibition of the K+/Cl− cotransporter (a transporter mediating RVD), whilst some inhibitors of protein kinases (PKs) cause activation. A sequence of potential phosphorylation sites appears to constitute a cascade of reactions leading to transporter regulation. PP and PK inhibitors have opposite effects on transporters mediating RVI responses, which is consistent with the coordinated but reciprocal regulation of transporters activated during both RVI and RVD using some common phosphorylation reactions. The transporters are sensitive to other stimuli including, in red blood cells, changes in and pH. These responses are also sensitive to PK/PP inhibitors and may involve elements of the volume-sensitive transduction pathway.
Imidacloprid actions on insect neuronal acetylcholine receptors
Authors: Buckingham S. D. , Lapied B. , Le Corronc H. , Grolleau F. , Sattelle D. B. 
Published: April 2021

ABSTRACT
The neonicotinoid insecticide Imidacloprid acts at three pharmacologically distinct acetylcholine receptor (AChR) subtypes in the cockroach (Periplaneta americana) nervous system, but is ineffective on muscarinic receptors. Imidacloprid (3–100 μmol l−1) induced dose-dependent depolarizations at cockroach cercal afferent/giant interneurone synapses. These responses were insensitive to 20 μmol l−1 atropine but were completely blocked by the nicotinic antagonist mecamylamine (50 μmol l−1). Similarly, Imidacloprid-induced depolarizations of cultured cockroach dorsal unpaired median (DUM) neurones dissociated from the same (terminal abdominal) ganglion were also completely blocked by 100 μmol l−1 mecamylamine. However, two components of the response could be distinguished on the basis of their differential sensitivities to 0.1 μmol l−1 α-bungarotoxin (α-BTX), which selectively blocks AChRs with ‘mixed’ nicotinic/muscarinic pharmacology in this preparation. This indicates that Imidacloprid affects both AChRs sensitive to α-BTX and α-BTX-insensitive nicotinic acetylcholine receptors (nAChRs). Thus, in the cockroach, Imidacloprid activates α-BTX-sensitive synaptic nAChRs in giant interneurones, α-BTX-insensitive extrasynaptic nAChRs in DUM neurones, and a recently characterized DUM neurone ‘mixed’ AChR that is sensitive to both nicotinic and muscarinic ligands. Imidacloprid does not act on muscarinic acetylcholine receptors (mAChRs) present on DUM neurone cell bodies and at the cercal afferent/giant interneurone synapses. This study shows that Imidacloprid can act on pharmacologically diverse nAChR subtypes.
Measuring the angle of attack of beating insect wings: robust three-dimensional reconstruction from two-dimensional images
Authors: Willmott Alexander P. , Ellington Charles P. 
Published: April 2021

ABSTRACT
A robust technique for determining the angle of attack of insect wings from film of free flight has to date proved elusive. This report describes the development of two new methods – the Strips and Planes techniques – which were designed to overcome some of the limitations experienced in previous studies. The accuracy and robustness of these novel methods were tested extensively using simulated hawkmoth wing outlines generated for a realistic range of wing positions and torsion. The results were compared with those from two existing methods – the Symmetry and Landmarks procedures. The performance of the latter technique will be strongly species-dependent; it could not be successfully applied to hawkmoth flight because of practical difficulties in obtaining suitable landmarks.
The Planes method was the least successful of the remaining techniques, especially during those phases of the wingbeat when the orientations of the two wings relative to the camera viewpoint were similar. The Symmetry and Strips methods were tested further to investigate the effects on their performance of introducing additional camber or wing motion asymmetry. The results showed clearly that the Strips method should be the technique of choice wherever the axis of wing torsion is close to the longitudinal axis of the wing. The procedure involves the experimenter matching a model wing divided into chordwise strips to the true wing outline digitized from high-speed film. The use of strips rather than the points digitized in previous studies meant that the analysis required only one wing outline to be digitized. Symmetry of motion between the left and right wings is not assumed.
The implications of requiring human input to the Strips method, as opposed to the strictly numerical algorithms of the alternative techniques, are discussed. It is argued that the added flexibility that this provides in dealing with images which have typically been recorded in suboptimal conditions outweighs the introduction of an element of subjectivity. Additional observations arising from the use of the Strips analysis with high-speed video sequences of hawkmoth flight are given.
The mechanics of flight in the hawkmoth Manduca sexta II. Aerodynamic consequences of kinematic and morphological variation
Authors: Willmott Alexander P. , Ellington Charles P. 
Published: April 2021

ABSTRACT
Mean lift coefficients have been calculated for hawkmoth flight at a range of speeds in order to investigate the aerodynamic significance of the kinematic variation which accompanies changes in forward velocity. The coefficients exceed the maximum steady-state value of 0.71 at all except the very fastest speeds, peaking at 2.0 or greater between 1 and 2 m s−1. Unsteady high-lift mechanisms are therefore most important during hovering and slow forward flight. In combination with the wingtip paths relative to the surrounding air, the calculated mean lift coefficients illustrate how the relative contributions of the two halfstrokes to the force balance change with increasing forward speed. Angle of incidence data for fast forward flight suggest that the sense of the circulation is not reversed between the down- and upstrokes, indicating a flight mode qualitatively different from that proposed for lower-speed flight in the hawkmoth and other insects. The mid-downstroke angle of incidence is constant at 30–40 ° across the speed range. The relationship between power requirements and flight speed is explored; above 5 m s−1, further increases in forward velocity are likely to be constrained by available mechanical power, although problems with thrust generation and flight stability may also be involved.
Hawkmoth wing and body morphology, and the differences between males and females, are evaluated in aerodynamic terms. Steady-state force measurements show that the hawkmoth body is amongst the most streamlined for any insect.
Different Excitation–Contraction Coupling Mechanisms Exist in Squid, Cuttlefish and Octopod Mantle Muscle
Authors: Rogers C. M. , Nelson L. , Milligan B. J. , Brown E. R. 
Published: April 2021

ABSTRACT
Excitation–contraction (EC) coupling was studied in central zone mantle muscle fibres of a squid (Alloteuthis subulata), a cuttlefish (Sepia officinalis) and an octopod (Eledone cirrhosa). Thin slices of muscle were used for twitch experiments and enzymatic isolation of single fibres for whole-cell patch-clamp studies. The current required for a supramaximal twitch response during direct stimulation of muscle slices was lower for squid than for cuttlefish. In squid, but not in cuttlefish, the current–response relationship was independent of slice thickness (range 0.1–0.5 mm). Twitches of squid and cuttlefish slices were reversibly abolished by removal of extracellular Ca2+. In squid, but not in cuttlefish, the current–response relationship was Na+-dependent, and in the absence of Na+ higher current strengths were required to generate a supramaximal response. In whole-cell voltage-clamp experiments on isolated muscle fibres from squid, cuttlefish and Eledone cirrhosa, a sustained inward current was recorded upon depolarisation. This current was blocked by 5 mmol l−1 Co2+ and suppressed by 10 μmol l−1 nifedipine. In squid, an additional inward fast-activating transient current was seen which was blocked by 2 μmol l−1 tetrodotoxin and depolarised holding potentials. The fast current represents a voltage-activated Na+ channel, and the slow currents represent L-type Ca2+ channels. We conclude that squid possess a specialised rapid EC coupling mechanism in central zone fibres that is absent in cuttlefish and Eledone cirrhosa.
Diving and Swimming Performance of White Whales, Delphinapterus Leucas: an Assessment of Plasma Lactate and Blood Gas Levels and Respiratory Rates
Authors: Shaffer S. A. , Costa D. P. , Williams T. M. , Ridgway S. H. 
Published: April 2021

ABSTRACT
The white whale Delphinapterus leucas is an exceptional diver, yet we know little about the physiology that enables this species to make prolonged dives. We studied trained white whales with the specific goal of assessing their diving and swimming performance. Two adult whales performed dives to a test platform suspended at depths of 5–300 m. Behavior was monitored for 457 dives with durations of 2.2–13.3 min. Descent rates were generally less than 2 m s−1 and ascent rates averaged 2.2–3 m s−1. Post-dive plasma lactate concentration increased to as much as 3.4 mmol l−1 (4–5 times the resting level) after dives of 11 min. Mixed venous measured during voluntary breath-holds decreased from 79 to 20 mmHg within 10 min; however, maximum breath-hold duration was 17 min. Swimming performance was examined by training the whales to follow a boat at speeds of 1.4–4.2 m s−1. Respiratory rates ranged from 1.6 breaths min−1 at rest to 5.5 breaths min−1 during exercise and decreased with increasing swim speed. Post-exercise plasma lactate level increased to 1.8 mmol l−1 (2–3 times the resting level) following 10 min exercise sessions at swimming speeds of 2.5–2.8 m s−1. The results of this study are consistent with the calculated aerobic dive limit (O2 store/metabolic rate) of 9–10 min. In addition, white whales are not well adapted for high-speed swimming compared with other small cetaceans.
Endocardial Endothelium in the Avascular Heart of the Frog: Morphology and Role of Nitric Oxide
Authors: Sys Stanislas U. , Pellegrino Daniela , Mazza Rosa , Gattuso Alfonsina , Andries Luc J. , Tota Bruno 
Published: April 2021

ABSTRACT
Endocardial endothelial morphology and the physiological modulatory role of nitric oxide (NO) were studied in an in vitro preparation of the working intact heart of the frog Rana esculenta, which lacks coronary vasculature and is thus devoid of a coronary vascular endothelium. En face confocal scanning laser microscopy of samples of perfused fixed hearts demonstrated the presence of NO synthase as a cytoplasmic constituent of the endocardial endothelial cells. Stroke volume (as a measure of performance in paced frog hearts) and stroke work (as an index of systolic function) increased by approximately 5 % after inhibition of the NO–cGMP pathway with 10−4 mol l−1NG-nitro-L-arginine methyl ester and by approximately 8 % after inhibition with 10−6 mol l−1 Methylene Blue. In contrast, stroke volume and stroke work decreased by approximately 22 % after activation of the NO–cGMP pathway with sodium nitroprusside (10−4 mol l−1), while 3-morpholinosydnonimine (5×10−8 to 10−5 mol l−1) caused a decrease of between 15 and 30 % and 8-bromo-cGMP (10−6 mol l−1) a decrease of approximately 8 %. These responses were significantly attenuated after exposure of the ventricular luminal to Triton X-100 (0.05 %, 0.1 ml), which itself increased performance (by over 10 %) without detectable morphological changes. These results show that the endocardial endothelium of Rana esculenta produces amounts of NO sufficient to modulate ventricular performance.
Differential Physiology and Morphology of Phasic and Tonic Motor Axons in a Crayfish Limb Extensor Muscle
Authors: Bradacs H. , Cooper R. L. , Msghina M. , Atwood H. L. 
Published: April 2021

ABSTRACT
The main leg extensor muscle of the crayfish Procambarus clarkii is innervated by two excitatory motor axons (phasic and tonic) and by the common inhibitory axon. The axons and their terminals were investigated using vital fluorescent dyes, antibodies and electron microscopy. Correlative physiological observations were made using intracellular microelectrodes and focal ‘macro-patch’ electrodes. The excitatory axons innervate the muscle fibres more extensively than does the inhibitory axon. Striking morphological and physiological differences between the two excitatory axons were discerned. The tonic motor axon contains many mitochondria and has varicose junctional terminals; the phasic axon has fewer mitochondria and thin terminals. In freely moving animals, the tonic axon is very active, whereas the phasic axon is inactive but fires in brief bursts during walking. Throughout the muscle, tonic excitatory postsynaptic potentials (EPSPs) are very small at low frequencies and facilitate greatly at higher frequencies. The EPSPs of the phasic axon are larger at low frequencies and depress with maintained stimulation. At identified tonic terminals, quantal content at 1–10 Hz is very low, whereas at identified phasic terminals, quantal content is 50-to 200-fold greater. The results indicate that transmitter release is regulated differently at the synapses of the two axons.
Anguilliform Locomotion in an Elongate Salamander (Siren Intermedia): Effects of Speed on Axial Undulatory Movements
Authors: Gillis Gary B. 
Published: April 2021

ABSTRACT
Many workers interested in the mechanics and kinematics of undulatory aquatic locomotion have examined swimming in fishes that use a carangiform or subcarangiform mode. Few empirical data exist describing and quantifying the movements of elongate animals using an anguilliform mode of swimming. Using high-speed video, I examine the axial undulatory kinematics of an elongate salamander, Siren intermedia, in order to provide data on how patterns of movement during swimming vary with body position and swimming speed. In addition, swimming kinematics are compared with those of other elongate vertebrates to assess the similarity of undulatory movements within the anguilliform locomotor mode. In Siren, most kinematic patterns vary with longitudinal position. Tailbeat period and frequency, stride length, Froude efficiency and the lateral velocity and angle of attack of tail segments all vary significantly with swimming speed. Although swimming speed does not show a statistically significant effect on kinematic variables such as maximum undulatory amplitude (which increases non-linearly along the body), intervertebral flexion and path angle, examination of the data suggests that speed probably has subtle and site-specific effects on these variables which are not detected here owing to the small sample size. Maximum lateral displacement and flexion do not coincide in time within a given tailbeat cycle. Furthermore, the maximum orientation (angle with respect to the animal’s direction of forward movement) and lateral velocity of tail segments also do not coincide in time. Comparison of undulatory movements among diverse anguilliform swimmers suggests substantial variation across taxa in parameters such as tailbeat amplitude and in the relationship between tailbeat frequency and swimming speed. This variation is probably due, in part, to external morphological differences in the shape of the trunk and tail among these taxa.
Digging in Sand Crabs (Decapoda, Anomura, Hippoidea): Interleg Coordination
Authors: Faulkes Zen , Paul Dorothy H. 
Published: April 2021

ABSTRACT
Sand crabs (Decapoda, Anomura, Hippoidea) are highly specialised for digging into sand using their thoracic legs. Using video-recording and electromyography, we examined the digging leg movements of three species of sand crabs belonging to two families: Blepharipoda occidentalis (Albuneidae), Lepidopa californica (Albuneidae) and Emerita analoga (Hippidae). The digging patterns of all three species are similar. The ipsilateral legs 2 and 3 are tightly coupled and shovel sand forward from underneath the animal, whereas the movements of leg 4 are more variable, apparently stirring up sand and providing the purchase for rearward descent into the sand. The digging patterns of B. occidentalis and L. californica resemble each other more than either resembles that of E. analoga. In the albuneids, leg 4 cycles at the same frequency as legs 2 and 3, and both albuneid species switch gait from bilateral alternation to synchrony midway through digging. In E. analoga, right and left legs 2 and 3 always alternate. Legs 4 can cycle at about twice the frequency of legs 2 and 3, and they tend to move in bilateral synchrony during high-frequency leg movements (e.g. at the start of digging); their bilateral coupling becomes variable during low-frequency movements. Sand crab digging may have originated as a modified form of walking, but this behavioural innovation subsequently diverged in the sand crab superfamily.
Effects of Inhibition of Nitric Oxide Synthesis and Of Hypercapnia on Blood Pressure and Brain Blood Flow in The Turtle
Authors: Söderström Veronica , Nilsson Göran E. , Lutz Peter L. 
Published: April 2021

ABSTRACT
In the mammalian brain, nitric oxide (NO) is responsible for a vasodilatory tonus as well as the elevation of cerebral blood flow (CBF) induced by hypercapnia. There have been few comparative studies of cerebral vasoregulation in lower vertebrates. Using epi-illumination microscopy in vivo to observe CBF velocity on the brain surface (cerebral cortex), we show that turtles (Trachemys scripta) exposed to hypercapnia (inspired ) displayed a 62 % increase in CBF velocity, while systemic blood pressure remains constant. Exposing turtles to a of 14.9 kPa caused an additional increase in CBF velocity, to 104 % above control values, as well as a 30 % increase in systemic blood pressure. The elevated CBF velocity during hypercapnia could not be blocked by a systemic injection of the NO synthase (NOS) inhibitor NG-nitro-L-arginine (L-NA). However, L-NA injection caused a temporary stop in CBF as well as a persistent increase in systemic blood pressure, suggesting that there is a NO tonus that is attenuated by the NOS inhibitor and that CBF is strongly dependent on this tonus, although compensatory mechanisms exist. Thus, although the cerebrovascular reaction to hypercapnia appeared to be NO-independent, the results suggest that there is a NO-dependent vasodilatory tonus affecting both cerebral and systemic blood circulation in this species