bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of Thermally Induced Activity In Vivo Upon the Levels of Sodium, Chlorine and Potassium in the Epithelia of the Equine Sweat Gland
Authors: Wilson Stuart M. , Elder Hugh Y. , Jenkinson David Mcewan , Mcwilliams Scott A. 
Published: April 2021

ABSTRACT
Evaporation of moisture from the skin surface is an important means of thermoregulatory heat loss in Equidae, which respond to thermal stress with a smooth increase in the rate of sweat output to a plateau level which may be maintained for several hours (Allen & Bligh, 1969; Robertshaw & Taylor, 1969; Montgomery, Jenkinson & Elder, 1982). This pattern is similar to that which occurs when humans are exposed to a warm environment (Montgomery et al. 1984). The mode of sweat formation in both the horse and man is similar, involving cell death, fluid transport and the loss of vesicles both by exocytosis and microapocrine secretion (Montgomery et al. 1982, 1984). However, the secretions produced by the two glands differ markedly in electrolyte composition. Human sweat is a hypotonic fluid containing sodium chloride as its principal solute (Schulz, 1969; Sato, 1977), whereas equine sweat is hypertonic and contains a high concentration of potassium (Soliman & Nadim, 1967; Kerr & Snow, 1983). This could be a reflection of differences in the underlying mechanism of ionic transport within the gland.
Control of Central Pattern Generators by an Identified Neurone in Crustacea: Activation of the Gastric Mill Motor Pattern by a Neurone Known to Modulate the Pyloric Network
Authors: Dickinson Patsy S. , Nagy Frédéric , Moulins Maurice 
Published: April 2021

ABSTRACT
In the red lobster (Palinurus vulgaris), an identified neurone, the anterior pyloric modulator neurone (APM), which has previously been shown to modulate the output of the pyloric central pattern generator, was shown to modulate the output of the gastric mill central pattern generator. APM activity induced a rhythm when the network was silent and increased rhythmic activity when the network was already active. Rhythmic activity was induced whether APM fired in single bursts, tonically or in repetitive bursts. A single burst in APM induced a rhythm which considerably outlasted the burst, whereas repetitive bursts effectively entrained the gastric oscillator.
These modulations involved two major mechanisms. (1) APM induced or enhanced plateau properties in some of the gastric mill neurones. (2) APM activated the extrinsic inputs to the network, thus increasing the excitatory synaptic drive to most of the neurones of the network. As a result, when APM was active, all the neurones of the pattern generator actively participated in the rhythmic activity. By its actions on two separate but behaviourally related neural networks, the APM neurone may be able to control an entire concert of related types of behaviour.
Negative Geotaxis in Sea Urchin Larvae: a Possible Role of Mechanoreception in the Late Stages of Development
Authors: Mogami Yoshihiro , Oobayashi Chieko , Yamaguchi Tomoko , Ogiso Yumi , Baba Shoji A. 
Published: April 2021

ABSTRACT
Negative geotactic behaviour of sea urchin larvae at various developmental stages from blastula to pluteus was analysed by means of time-exposure dark-field photography of the swimming behaviour of individual larvae. Significant differences in the patterns of behaviour, such as swimming direction and speed, were demonstrated between the early stages (up to the gastrula) and the pluteus, although larvae at any developmental stage showed negative geotactic migration. Larvae in the early stages swam at speeds that varied as a function of the swimming direction with respect to gravity, faster downwards and slower upwards. This might be predicted from the assumption that vertical locomotion is determined by constant propulsion affected passively by gravity. In the pluteus stage, however, larvae swam at a constant speed in any direction, suggesting that the propulsive activity of swimming plutei is actively controlled depending on the swimming direction. This change in the negative geotactic behaviour of sea urchin larvae in the course of embryogenesis indicates development of physiological control systems for propulsive activity at the pluteus stage.
Response of Nautilus to Variation in Ambient Pressure
Authors: Jordan Michael , Chamberlain John A. , Chamberlain Rebecca B. 
Published: April 2021

ABSTRACT
Juvenile Nautilus, tested in a high-pressure animal maintenance apparatus, are sensitive to increases in ambient hydrostatic pressure as small as l × 105Nm−2 (= 1 atm = 100kPa). They respond to such pressure increases in a characteristic ‘depth alarm’ behaviour pattern, which consists primarily of rapid upward swimming. These activity bursts may serve to restore them to their original depth. The animals apparently continue this behaviour until fatigued. Pressure decrease elicits no obvious response. The pressure-sensing mechanism may be located within the statocyst, or possibly in the posterior mantle or siphuncle. The operation of. the latter two mechanisms involves tensional strain induced by the hydrostatic load in the outermost septum and wall of the siphuncular tube.
Flight Performance of a Dragonfly
Authors: Azuma Akira , Watanabe Tadaaki 
Published: April 2021

ABSTRACT
The dragonfly, Anaxparthenope julius (Brauer) was observed in free flight, and a theoretical analysis of flight performance at various speeds was carried out. The variation with time of forces and moments acting on wings and body in steady trimmed flight was calculated by the local circulation method. Measures of flight performance, such as top speed, cruising speed and maximum endurance speed, were estimated from a necessary power curve required in steady flight and from the estimated available power. The results show that without using any novel unsteady aerodynamic force generated by a separated flow over the wings, the dragonfly can make steady trimmed flight at various flight speeds, from hovering to top speed.
The Similarity of Mitochondrial Distribution in Equine Skeletal Muscles of Differing Oxidative Capacity
Authors: Kayar S. R. , Hoppeler H. , Essen-Gustavsson B. , Schwerzmann K. 
Published: April 2021

ABSTRACT
A morphometric analysis was performed on horse muscle tissue to quantify mitochondrial distribution relative to capillaries. Samples of M. vastus medialis, M. semitendinosus, M. masseter and M. cutaneus thoracicus were preserved in a glutaraldehyde fixative for electron microscopy, or frozen for biochemical and histochemical analysis. These four muscles varied from highly oxidative in type, consisting nearly completely of type I fibres, in masseter, to highly glycolytic, primarily type lib fibres, in cutaneus. In all four muscles, mitochondria were found in highest volume density near capillaries at the fibre border, with a sharp, decline in volume density towards the fibre centre. This distribution was independent of myoglobin concentration, muscle fibre type and the activities of three key metabolic enzymes, citrate synthase, 3-OH-acyl-CoA dehydrogenase and lactate dehydrogenase.
Sodium-Independent Proline Transport in the Locust Rectum
Authors: Meredith J. , Phillips J. E. 
Published: April 2021

ABSTRACT
Recta of Schistocerca gregaria possess a high-affinity (Kt = 10 mmol l−1) and high-capacity (Vmax = 4·2 μequiv cm−2h−1) active absorptive mechanism for proline second in magnitude only to stimulated Cl− transport. Transcellular and paracellular pathways have extremely low passive permeability to proline, resulting in very high flux ratios (40:1) compared with those for other.solutes (less than 6:1). Net epithelial transport of proline is largely independent of luminal Na+, K+ and Cl−. Sodium influx does not change when proline net fluxes are varied 14-fold. Therefore Na+ cotransport is not a principal mechanism of proline uptake in this tissue. Prolonged absence of Na+ and K+ from the haemocoel side partially inhibits proline transport, probably indirectly, by affecting the general transport capacity of the rectum. Inhibition is irreversible. A component of the net proline flux (Jpronet) is electrogenic, located in the apical membrane, and may be due to proline/proton cotransport.
Transport Properties of Locust Ileum in vitro: Effects of Cyclic Amp
Authors: Irvine B. , Audsley N. , Lechleitner R. , Meredith J. , Thomson B. , Phillips J. 
Published: April 2021

ABSTRACT
Short-circuited locust ilea exhibited electrical properties remarkably similar to those of recta. The large short-circuit current (Isc) and transepithelial potential, both indicating net active absorption of anions, initially began to decline to zero but could be fully restored by adding cyclic AMP or extracts of corpus cardiacum and ventral abdominal ganglia to the haemocoel side. Ion substitutions and radiotracer flux studies indicated that cyclic AMP-induced ΔISC was due to electrogenic Cl− transport with kinetics identical to those of the rectum. Concurrent decreases in transileal resistance were due to increases in both Cl− and K+ (PK) permeabilities, most evident as a resistance decrease at the apical membrane. The ΔPK was blocked by basolateral addition of Ba2+, as observed for recta. Everted ileal sacs under open-circuit conditions absorbed a slightly hyperosmotic NaCl-rich fluid and the rate of absorption was increased more than twofold by cyclic AMP. This contrasts with stimulated recta which absorb primarily KCl and a hyposmotic absorbate. Flux studies with short-circuited ilea demonstrated active absorption of Na+, which was stimulated twofold by cyclic AMP. Removal of external Na+ had little effect on Isc, suggesting that involves exchange for another cation, e.g. NH4+. Ilea actively secreted acid at lower rates than do recta under open-circuit conditions. Under short-circuit conditions, cyclic AMP addition led to active alkalinization of the ileal lumen at high rates, and the large Isc represented the difference between active secretion of base equivalents and net absorption of Cl−. The transport capacities of locust ilea and recta are compared in relation to their ultrastructure.
The Forces Acting on Swimming Squid
Authors: O’Dor R. K. 
Published: April 2021

ABSTRACT
Analysis of ciné films and intramantle pressure records for squid Loligo opalescens Berry swimming in a tunnel respirometer provided estimates of all the forces acting in the horizontal and vertical planes for swimming speeds from 0·1 to 0·5 ms−1. Different speeds used different gaits; fin thrust was only important below 0·2 ms−1, ‘anaerobic’ circular muscles were recruited only at supracritical speeds, and hyperinflation caused by contraction of the radial muscle was not seen in steady swimming. The extent, rate and frequency of contraction of the obliquely striated circular muscles varied little with speed, and jet thrust was matched to speed primarily by active pressure control through adjustments in the size of the funnel orifice. Hydrodynamic lift production to compensate for negative buoyancy during enforced horizontal swimming in the tunnel required 30–90% of the total force over the speed range studied and appears less efficient than direct use of jet thrust. This suggests a new rationale for ‘climb-and-glide’ swimming which reduces previous estimates of the gross cost of transport for squid under natural conditions by at least 35%, with no loss of speed. The cost of accelerating water into the mantle of a squid moving at high speed appears to have been underestimated in previous studies. A simulation of a series of escape jets predicts a maximum speed of 8 body lengths s−1 (14ms−1), reached after only two jets, because of the high deceleration during refilling.
Acid-Base Regulation in the Freshwater Pearl Mussel Margaritifera Margaritifera: Effects of Emersion and Low Water pH
Authors: Heming T. A. , Vinogradov G. A. , Klerman A. K. , Komov V. T. 
Published: April 2021

ABSTRACT
Freshwater pearl mussels Margaritifera margaritifera L. were exposed to air for 7 days, then immersed in circumneutral water (pH 7·85) or acidified water (pH 5·25) for 5 days. Mantle fluid pH and composition were monitored throughout. The mussels were observed to gape periodically when in air. Periodic gaping permitted aerial gas exchange such that mantle fluid and dissolved oxygen concentration stabilized at levels about twice and half, respectively, those of immersed mussels. During emersion, a dilute carbonate buffer equilibrium was established in the mantle fluid, involving reactions with CaCO3 reserves and, simultaneously, aerial release of CO2. Aerial CO2 release was sufficient to shift the carbonate buffer equilibrium in the alkaline direction, resulting in a significant alkalosis of mantle fluids during air exposure. Mantle fluid characteristics returned to initial (time zero) values within 3 days of immersion in circumneutral water (pH 7·85). When immersed in acid water (pH 5·25), the mussels were able to maintain a sizeable gradient between mantle fluid pH and ambient water pH. Regulation of mantle fluid pH in acid water did not involve any isolation reaction (valve closure), but rather environmental protons were buffered at the expense of CaCO3 reserves. Net calcium transfer, the difference between calcium uptake and loss, was shifted in the negative direction by decreases in water pH.
Ingestive Behaviour and Physiology of the Medicinal Leech
Authors: Lent Charles M. , Fliegner Karsten H. , Freedman Edward , Dickinson Michael H. 
Published: April 2021

ABSTRACT
Ingestion lasts 25 min in Hirudo medicinalis and is characterized by pharyngeal peristalsis which fills the crop. This peristalsis has an initial rate of 2·4 Hz which decays smoothly to 1·2 Hz at termination of ingestion. During ingestion, the leech body wall undergoes peristalsis which appears to aid in filling the crop diverticula. Body peristalsis begins at a rate of 10 min−1 and decreases linearly to 2 min−1 at termination. The body also undergoes dorsoventral flexions when blood flow is occluded. Blood meal size increases slightly with leech size: 8·4 g for 1-g leeches and 9·7 g for 2-g leeches. However, relative meal size decreases markedly with increasing animal size; from 8·15 times body mass for 1-g to 4·80 times for 2-g leeches. When intact leeches were exposed to micromolar concentrations of serotonin, there was an increase in the rate of pharyngeal peristalsis and the size of the blood meals.
Leeches excrete the plasma from their ingested blood meals. Excretion is activated during ingestion, which increases feeding efficiency by increasing the proportion of blood cells in the ingestate. Excretion continues for 4–6 days following ingestion, removing all the remaining plasma from the ingestate. Leech ingestion comprises stereotyped muscular movements, secretion of saliva and excretion of plasma. A strikingly similar feeding physiology is seen in the bloodsucking insect Rhodnius, and we suggest that efficient sanguivory may require the convergent evolution of similar ingestive mechanisms.
Blood Flow Patterns in the Salamander, Ambystoma Tigrinum, Before, During and After Metamorphosis
Authors: Malvin Gary M. , Heisler Norbert 
Published: April 2021

ABSTRACT
The patterns of blood flow through the complex circulation of the tiger salamander, Ambystoma tigrinum, were investigated during aquatic normoxia and hypoxia by application of the microsphere technique. The distribution of differently labelled microspheres injected into the bloodstream towards the left and right atria, respectively, was used to evaluate the role of the ductus arteriosus in lung perfusion before, during and after metamorphosis, as well as the general contribution of right and left atrial outputs to the blood flow in gills and lungs in neotenic and postmetamorphic animals.
The distribution patterns of radioactive microspheres among pulmonary, branchial and systemic tissues indicated that the ductus arteriosus is the major pulmonary perfusion pathway in neotenic and metamorphosing animals, whereas after metamorphosis the main perfusion pathway is down the entire length of the pulmonary artery. In neotenes, the ductus arteriosus becomes even more important during aquatic hypoxia. The anterior branchial arches receive blood richer in pulmonary venous blood than the posterior arches. Approximately 26% of left atrial output and 36% of right atrial output perfuses the branchial respiratory lamellae during normoxia in neotenes. Severe aquatic hypoxia appears to increase the fraction of cardiac output flowing to the lung and decrease the fraction flowing into the first branchial arch in neotenes. This decrease into the first arch may facilitate lung perfusion and also reduce branchial O2 loss. In postmetamorphic animals, approximately 55% of right atrial output and 32% of left atrial output is directed to the lungs. The flow patterns in postmetamorphic animals remain unaffected by aquatic hypoxia.
Hypersensitivity to Light of the Iris (Sphincter Pupillae) of the Albino Axolotl (Ambystoma Mexicanum)
Authors: Barr Lloyd 
Published: April 2021

ABSTRACT
As is common for amphibians, the sphincter pupillae of the axolotl contracts in vitro in response to illumination with visible light.
In a comparison of photomechanical responses of albino and normally pigmented axolotls, similar time courses and maxima of force development were found. The dependence of isometric active force development on the length of the sphincter pupillae is similar to that of other smooth muscles. The action spectrum of the axolotl is similar to the absorption spectrum of frog rhodopsin. At low stimulus strengths, the increase of normalized, isometric, active force with increasing stimulus strength is approximately seven times as great in albino axolotls as in normally pigmented ones. Melanin appears to decrease the light sensitivity of the irises of normally pigmented animals by acting as a simple light shield.
Excitability and Secretory Activity in the Salivary Gland Cells of Jawed Leeches (Hirudinea: Gnathobdellida)
Authors: Marshall Cameron G. , Lent Charles M. 
Published: April 2021

ABSTRACT
Thousands of salivary cells fill the interstices throughout the anterior ends of jawed leeches. The somata are large (30–200 μm in diameter). They project single processes (ductules) into the three jaws, and were found to fire overshooting action potentials of 50–85 mV amplitude and 100–200 ms duration at low spontaneous rates. The action potentials were not detected in the presence of cobalt (10 mmol l−1), but could be recorded when sodium was absent from the Ringer, so they appear to be calcium-dependent.
Salivary material is transported by the long processes of these unicellular glands and secreted into ducts which alternate with paired teeth on the jaws. Secretion is activated reliably by 10−6mol l−1 serotonin, but not by other neurotransmitters found in the leech nervous system. Each jaw secretes at an average rate of 230 nl min−1 in the presence of serotonin, and secretion is completely abolished by cobalt.
Perfusion with serotonin excites the salivary gland cells into impulse activity, and often evokes bursting. Impulse activity of the peripherally projecting, serotonergic Retzius cells evokes both depolarizations and action potentials in the salivary gland cells. In jawed leeches, central neurones appear to control salivation by a peripheral release of serotonin. This neurotransmitter evokes calcium-dependent action potentials and calcium, in turn, stimulates secretion.
Stimulus-Secretion Coupling: a Perspective Highlighting the Contributions of Peter Baker
Authors: Rink T. J. , Knight D. E. 
Published: April 2021

ABSTRACT
Many investigators are using numerous preparations for contributing to our present understanding of stimulus-secretion coupling, by which we mean stimulus-dependent exocytosis, sometimes known as the regulated pathway. However, a few model systems have been particularly illuminating and several of these were exploited by Peter Baker and his close associates: namely, the motor nerve terminal, the adrenal chromaffin cell, the sea urchin egg and the blood platelet. In fact, Peter’s first real contribution in this area came from his seminal studies on calcium transport in his favourite preparation, the squid giant axon, where he investigated Ca2+/Na+ exchange, Ca2+ distribution and voltage-gated Ca2+ entry. More direct investigations into stimulus-secretion coupling came from work on neurone transmitter release in collaboration with Andrew Crawford, and on catecholamine secretion from the adrenal medulla in collaboration (with TJR). His most important generic contribution to this field was in the development (with DEK), of the electropermeabilized cell, which allows control of the low molecular weight components of the cytosol while leaving the exocytotic apparatus and process intact. In the initial experiments on the cells it was finally proved that Ca2+-dependent secretion of catecholamines is indeed from the granules and not from the cytosol. The quantification of the Ca2+ requirement of secretory exocytosis was an important step, as was the investigation of many factors purported to be important in the coupling mechanism or in the exocytotic process itself. Work with the human platelet, using this technique, has proved to be especially valuable in unravelling the complex interactions between different second messengers and has been neatly complemented by work in intact cells containing Ca2+-indicator fluorescent dyes. Peter was also intrigued by post-secretory events both in the early seventies, and at the end of his career when he embarked on analysis of the membrane retrieval process and the associated uptake of extracellular medium.
A Complex Mechanism of Facilitation in Pituitary Acth Cells: Recent Single-Cell Studies
Authors: Leong Denis A. 
Published: April 2021

ABSTRACT
The transfer of information by chemical signals during complex biological processes can, with increasing frequency, be described in terms of interacting signal pairs. External signalling is rarely monolithic; rather, signal pairs are utilized in processes such as hormone secretion, neurotransmission, cell growth and differentiation. The dualism of external signalling often results in the occurrence of synergy. One signal appears to turn the cell on or off, and its synergistic partner increases cell responsiveness, providing gain control of the cellular response. ACTH release provoked by certain stressors arises from a synergistic interaction between two hypothalamic hormones: corticotropin releasing hormone (CRH) and a modulator such as vasopressin (AVP). The pituitary ACTH cell has been used to unravel the intracellular messenger equivalents of an external signal interaction that generates synergy.
Research emphasizes the single cell approach. Direct measurements of intracellular free Ca2+ were performed using the Ca2+-sensitive fluorescent probe fura-2/AM and instrumentation for digital image processing. A reverse haemolytic plaque assay was used to measure cumulative ACTH release from single pituitary cells in culture.
What is the physiological role of intracellular Ca2+ as a messenger? What are the feedforward and feedback relationships between major second messengers [cyclic AMP, diacylglycerol (DAG), inositol 1,4,5-trisphosphate (Ins(l,4,5)P3)] and intracellular Ca2+? That is, how are individual messenger circuits ‘wired’ within ACTH cells. Intracellular Ca2+ may act as a common signal into which interacting second messenger signals [cyclic AMP, Ins(l,4,5)P3, DAG] are transduced and integrated to govern ACTH release. A novel circuit of messenger pathways linked by Ca2+ is proposed as the intracellular basis for the synergistic interaction of CRH- and AVP-regulated ACTH release.