bluuebunny/crossref_metadata_2025_split huggingface dataset:
Respiratory and Cardiovascular Responses of the Exercising Chicken to Spinal Cord Cooling at Different Ambient Temperatures: II. Respiratory Responses
Authors: Gleeson M. , Barnas G. M. , Rautenberg W. 
Published: April 2021

ABSTRACT
We measured oxygen consumption , carbon dioxide production , minute volume , respiratory frequency (f) and tidal volume (VT) of chickens during 15 min treadmill exercise at 0·5ms−1 and 0·8 ms−1 at thermoneutral (23°C), low (9°C) and high (34°C) ambient temperature (Ta); the vertebral canal was cooled to 34°C during the middle 5 min of each exercise period. Temperatures of the vertebral canal (Tvc) and rectum (Tre) were also measured. Exercise at 0·5 ms−1 caused increases in O2 consumption, CO2 production, minute volume and tidal volume compared to resting controls at each Ta. Minute volume and respiratory frequency were higher and tidal volume was lower in birds exercising at 34°C than at 23 or 9°C. Spinal cord cooling during exercise (0·5 ms−1) at 9°C caused further increases in O2 consumption, tidal volume and respiratory frequency almost equivalent to those produced by an increase in the running speed to 0·8 m s−1. Spinal cord cooling during exercise (0·5 ms−1) at 23°C did not significantly affect O2 consumption, CO2 production, minute volume, tidal volume or respiratory frequency. Spinal cord cooling during exercise (0·5 ms−1) at 34°C did not affect O2 consumption or CO2 production, but caused decreases in minute volume and respiratory frequency and an increase in tidal volume. We conclude that the domestic fowl exhibits spinal thermosensitivity during exercise, although these responses appear to be smaller than those previously reported for the resting bird. Decreased external temperature potentiates the effects of spinal cord cooling during exercise.
Electrical-Potential Difference and Sodium Ion Fluxes Across the Integument of Corophium Volutator (Crustacea; Amphipoda), A Euryhaline Hyperosmotic Regulator
Authors: Taylor Peter M. 
Published: April 2021

ABSTRACT
Measurements of electrical-potential difference (TEP) and Na+ efflux, across the integument have been made for Corophtum volutator acclimated to 85 or 15%SW. The TEP of acclimated animals in 85 or 15%SW is 1·4 mV or 11·1 mV respectively (haemolymph negative). For acclimated animals, . unidirectional Na+ efflux is 154·3 nmol mg−1 body weight h−1 in 85%SW [efflux rate constant (k) = 0·70 h−1] and approximately 35·5 nmol mg−1 h−1 in 15%SW (k = 0·50h−1 in 10%SW). The results indicate that Na+ and Cl−are passively distributed across the ion-permeable (gill) integument of acclimated animals in 85%SW, but that active uptake of Cl−, and possibly Na+ also, occurs across the gills of acclimated animals in 15%SW. The ion transport mechanisms appear to effect electroneutral transfers across the gill integumental epithelium. Corophium volutator gill integument has a high permeability to ions; permeability to Na+(PNa) is 7·5x 10−8ms−1, and the ratio PCL/PNa is 0·45, for animals acclimated to either salinity. The resistance of the gill thelium of acclimated animals has been calculated to be·3×10−3Ωm2 and 2·0×10−2Ωm2 in 85 and 15%SW respectively.
Mechanical Power Output From Striated Muscle During Cyclic Contraction
Authors: Josephson Robert .K 
Published: April 2021

ABSTRACT
The mechanical power output of a synchronous insect muscle was determined by measuring tension as the muscle was subjected to sinusoidal length change and stimuli which occurred at selected phases of the length cycle. The area of the loop formed by plotting muscle tension against length over a full cycle is the work done on that cycle; the work done times the cycle frequency is the mechanical power output. The muscle was a flight muscle of the tettigoniid Neoconocephalus triops. The measurements were made at the normal wing-stroke frequency for flight (25 Hz) and operating temperature (30°C). The power output with a single stimulus per cycle, optimal excursion amplitude, and optimal stimulus phase was 1·52 J kg−1 cycle−1 or 37Wkg−1. The maximum power output occurs at a phase such that the onset of the twitch coincides with the onset of the shortening half of the length cycle. The optimum excursion amplitude was 5·5% rest length; with greater excursion, work output declined because of decreasing muscle force associated with the more rapid shortening velocity. Multiple stimulation per cycle increases the power output above that available with twitch contractions. In this muscle, the maximum mechanical power output at 25 Hz was 76 Wkg−1 which was achieved with three stimuli per cycle separated by 4-ms intervals and an excursion amplitude of 6·0% rest length. The maximum work output during the shortening of an isotonic twitch contraction was about the same as the work done over a full sinusoidal shortening-lengthening cycle with a single stimulus per cycle and optimum excursion amplitude and phase.
Ventilatory and Acid-Base Responses to Long-Term Hypercapnia in the Freshwater Turtle, Chrysemys Picta Bellii
Authors: Silver Randi B. , Jackson Donald C. 
Published: April 2021

ABSTRACT
The response to hypercapnia was studied in western painted turtles, Chrysemys picta bellii at 20°C. Ventilation, metabolic rate, arterial blood gases, blood pH and blood plasma ions were monitored periodically on individual turtles exposed to 5·7% CO2 for 72 h and then allowed to recover in air.
In response to hypercapnia, there is an immediate 10-to 15-fold increase in ventilation from control levels, which was maintained throughout the entire 5·7% CO2 breathing period. The first hour of CO2 breathing caused an increase in from 24–39 mmHg with a concomitant decrease in pH and rise in [HCO3−]. [HCO3−] rose from 42 to 50 mmol l−1 in the next 24 h of CO2 breathing and remained at this level for the rest of the hypercapnic period. Small, significant increases in total [Ca2+] and total [Mg2+] were found; however, no changes were observed in the plasma Na+, K+ or Cl− concentrations and the overall change in measured ions could not account for the increased [HCO3−]. The maximum change in [HCO3−] attained in Chrysemys exposed to a more severe acidosis (14·3% CO2) for up to 18 h was the same as that seen in the animals breathing 5·7% CO2 (10 mmol l−1) implying that there is an upper limit for the accumulation of [HCO3−] in Chrysemys at 20 °C.
The blood pH of turtles recovering in air returned to the control value (7−56–7’74) within the first hour although did not return to the control value. The HCO3− ion concentration also remained elevated throughout the 48-h recovery period, which suggests that ionic compensation is a slower process.
The freshwater turtle employs two mechanisms to reduce the severity of an imposed respiratory acidosis: increased ventilation and changes in the strong ion difference. In spite of these responses, blood pH is not restored to the control value.
Methods for Producing Disturbances in Pigeon Homing Behaviour by Oscillating Magnetic Fields
Authors: Ioale’ Paolo , Guidarini Dante 
Published: April 2021

ABSTRACT
Experiments were performed with homing pigeons treated before release with oscillating magnetic fields produced by small Helmholtz coils placed around the neck and on the head of the pigeon or by larger Helmholtz coils surrounding the cage of the birds. In both types of treatment, which both used a single frequency of about 0-14 Hz, the pigeons’ initial orientation was strongly affected when the oscillation of the artificial magnetic field was square-shaped, whereas a triangular or sine-shaped variation had no effect.
Mechanical Properties and Factors of Safety of Spider Drag-Lines
Authors: Brandwood A. 
Published: April 2021

ABSTRACT
Experiments were carried out to determine the strain energy capacity and breaking strain of spider drag-line silk. These properties are discussed in terms of a mathematical model of a spider falling on a drag-line. It was found that the strain energy capacity of the drag-line was insufficient to absorb the potential energy lost by a falling spider and that in order to avoid failure of the drag-line the spider dissipates energy by other means, particularly by using its inertia to draw drag-line silk from its spinnerets.
Further Observations on the Regulation of KCl Absorption Across Locust Rectum
Authors: Hanrahan J. W. , Phillips J. E. 
Published: April 2021

ABSTRACT
Electrophysiological and tracer flux techniques were used to study regulation of KCl reabsorption across locust recta. Physiologically high K+ levels (100 mmol 1−1) on the lumen side stimulated net 36C1 flux and reduced the theoretical energy cost of anion transport under open-circuit conductions.
The stimulation of short-circuit current (ISC, i.e. active Cl− absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Isc were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl− absorption and counter-ion (K+) permeability.
High mucosal osmolarity or K+ concentration decreased Isc. and caused a disproportionately large increase in Rt, consistent with a decrease in the shunt (K+) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K+ levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo at the end of resorptive cycles also inhibited Isc, apparently without affecting K+ permeability.
The Effect of Perfusion Flow Rate and Adrenergic Stimulation on Oxygen Transfer in the Isolated, Saline-Perfused Head of Rainbow Trout (Salmo Gairdneri)
Authors: Perry S. F. , Daxboeck C. , Dobson G. P. 
Published: April 2021

ABSTRACT
An isolated, saline-perfused trout head preparation, irrigated with hyperoxic water was used to assess diffusion/perfusion limitations to gill oxygen transfer. In the absence of catecholamines, increasing the perfusion flow rate caused a reduction of the partial pressure of oxygen in the dorsal aortic perfusate, indicating diffusion limitations to oxygen uptake. Physiological concentrations of epinephrine stimulated oxygen uptake in a dose-dependent fashion. Moreover, epinephrine elicited a greater effect during increased perfusion flow rate as a result of larger initial diffusion limitations, caused by the increased flow. By using a variety of adrenergic agonists and antagonists, it was demonstrated that beta-receptor stimulation enhanced oxygen uptake whereas alpha-receptor stimulation had no effect. These results are discussed with reference to changes in gill epithelial permeability to oxygen and/or surface area changes.
The Inherent Walking Direction Differs for The Prothoracic and Metathoracic Legs of Stick Insects
Authors: Bässler Ulrich , Foth Eva , Breutel Gerhard 
Published: April 2021

ABSTRACT
On a slippery surface the forelegs of a decapitated stick insect walk forwards and the hindlegs, backwards. Animals with only forelegs but that are otherwise intact walk forwards, whereas animals with only hindlegs walk mostly backwards. Usually when intact animals start to walk, their hindlegs exert a rearwards thrust on the substrate, but occasionally the starting forces are directed forwards.
A rampwise extension of the femoral chordotonal organ in the fixed foreleg of a walking animal first excites the flexor tibiae muscle (positive feedback). Towards the end of the ramp stimulus the activity of the flexor decreases, and the extensor tibiae motor neurones become strongly active.
All experiments indicated that the inherent direction of movement of the metathorax is rearwards. In intact animals there must be a coordinating pathway from the prothorax to the metathorax that, together with the sub-oesophageal ganglion, induces the hindlegs to walk forwards.
Is the ‘Click’ Mechanism of Dipteran Flight an Artefact of CC14 Anaesthesia?
Authors: Miyan Jaleel A. , Ewing Arthur W. 
Published: April 2021

ABSTRACT
A frame-by-frame analysis of the wing movements of a fly shows characteristics which are incompatible with the accepted model for dipteran flight. Higher amplitude wing beats result in greater velocities on the upstroke. Detailed examination of the wing base articulation has uncovered a wing stop and DVM stretch mechanism. It is argued that there is elastic energy storage during the downstroke which is released on the upstroke. A novel mechanical model for wing movements is proposed which incorporates all the new findings and argues against a ‘click’ mechanism.
Which Parameters Control the Leg Movement of a Walking Insect?: II. The Start of the Swing Phase
Authors: Cruse H. 
Published: April 2021

ABSTRACT
When a stick insect (Carausius morosus) walks on a treadwheel with one leg standing on a platform beside the wheel, this leg can be considered to perform a prolonged stance phase. To elicit a swing phase in this situation, both load and position must decline below definite threshold values.
The swing phase can be elicited when — given a sufficiently posterior leg position - a central temporal signal initiates a small forward movement, and this is followed by a decrease of load.
It is possible for signals from the next posterior leg to change the position threshold at which the swing phase can be started, but these commands do not influence the force values during the stance phase.
Thus position is one parameter used for the decision to end the stance phase. But it does not serve as a signal for a position feedback mechanism controlling leg movement during the stance phase.
Ventilatory Oxygen Extraction During Cold Exposure in the Pigeon (Columba Livia)
Authors: Bech C. , Rautenberg W. , May B. 
Published: April 2021

ABSTRACT
The respiratory responses to cold ambient temperatures in birds have only rarely been described. Bernstein & Schmidt-Nielsen (1974) studied the fish crow (Corvus ossifragus) during moderate cold exposure, while Bouverot, Hildwein & Oulhen (1976) measured ventilatory variables in pigeons (Columba livia) at near thermoneutral (22°C) and at cold (2°C) ambient temperatures. With respect to the amount of oxygen extracted from the ventilated air, both studies did not show any significant alterations correlated with changes in ambient temperature. However, several recent studies have demonstrated an increased oxygen extraction in response to cold exposure in birds [Bucher (1981) in the linneated parakeet (Bolborhynchos lineola), Brent, Rasmussen, Bech & Martini (1983) in the kittiwake (Rissa tridactyla), Brent, Pedersen, Bech & Johansen (1984) in the European coot (Fulica atra) and Bech, Johansen, Brent & Nicol (1984) in the duck (Anas platyrhynchos)). The significance of such an altered is obvious: the resultant decrease in ventilatory requirement will lower the relative loss of heat and water. Thus, together with a low expired air temperature (Schmidt-Nielsen, Hainsworth & Murrish, 1970), the increased oxygen extraction serves to minimize the respiratory heat and water loss in cold environments (Johansen & Bech, 1983).
Fluid Secretion By the Malpighian Tubules of the Dragonfly Libellula Quadrimaculata
Authors: Nicholls S. P. 
Published: April 2021

ABSTRACT
Fluid secretion by the Malpighian tubules of Libellula quadrimaculata is unusual in that it is dependent on sodium and entirely independent of potassium in the external medium. It is suggested that this is due to the primitive, sodium-rich haemolymph of the Odonata. Similarities between these tubules and those of the millipede Glomeris marginata, which has a similar sodium-based haemolymph, support this view. Fluid secretion by the tubules is also dependent on the osmotic pressure of the external medium, declining considerably at higher osmotic pressures. However, there is no difference in the secretory rates of tubules isolated from larvae adapted to tap water, de-ionized water or salt water, even though there are large differences in the haemolymph osmotic pressure under these different conditions. This suggests some form of adaptation of the tubules in larvae from these different conditions. A factor which causes a five-to six-fold increase in the rate of secretion was present in the thoracic ganglia, and a slightly lower increase in secretion rate was recorded in larvae that had been feeding.
Metabolic Activity Related to the Potassium Pump in the Midgut of Bombyx Mori Larvae
Authors: Parenti P. , Giordana B. , Sacchi V. F. , Hanozet G. M. , Guerritore A. 
Published: April 2021

ABSTRACT
The transepithelial electrical potential difference across the isolated midgut of Bombyx mori larvae is dependent on the presence of potassium and is unaffected by the addition of hexoses to perfusion media, whereas it is enhanced by alanine, aspartic acid, glutamic acid and the corresponding 2-oxoacids, glutamine and malate. The midgut enzyme profile indicates that the substrates for the tricarboxylic acid cycle are supplied mainly by amino acid metabolism via transaminases. Accordingly, aminoxyacetate drastically reduces the intestinal transepithelial electrical potential difference stimulated by amino acids. Measurement of the free amino acid concentration in the lumen content, intestinal cells and haemolymph shows that glutamic acid, asparagine and glutamine are accumulated in the cell, whilst the haemolymph is enriched with basic amino acids and with glycine, alanine, serine and tyrosine, the major components of the silk fibroin. Therefore, amino acid metabolism directly related to the tricarboxylic acid cycle seems to be the primary source of energy for the potassium pump activity inB. mori midgut.
Cardiac Performance in Response to Loading Pressures in Busycon Canaliculatum (Gastropoda) and Mercenaria Mercenaria (Bivalvia)
Authors: Smith P. J. S. 
Published: April 2021

ABSTRACT
The performance of the isolated hearts of a gastropod, Busycon canaliculatum (L.), and a bivalve, Mercenaria mercenaria(L.), were examined at different perfusion levels around the expected physiological ranges. Both hearts followed the Frank-Starling relationship with regard to stroke volume versus preload, but the heart-rate response was speciesdependent. The argument is developed that the molluscs might functionally apply Starling’s Law of the heart to accommodate increased output during exercise.
At the expected in vivo filling pressures the power output of the two hearts was the same (15–30 × 10−6Wg−1 ventricular tissue), but the Mercenaria filling levels were considerably lower. This clearly indicates that the cardiac muscle of each of the two species has evolved to operate at specific pressure ranges.
Electrical recordings from the surface of the myocardium in the perfused Busycon hearts confirm that the shape changes reported in the literature, dealing with stretched myocardium, also occur for changes in the whole heart at realistic loading pressures. These results support previous conclusions that the cardiac output is controlled by the duration of the action potential plateau.
Short Communication Prey Capture Hydrodynamics in Fishes: Two Approaches
Authors: Muller M. , Leeuwen J. L. Van , Osse J. W. M. , Drost M. R. 
Published: April 2021

ABSTRACT
Suction feeding is widely used in teleost fish (&lt;20 000 species). It is accomplished by rapid expansion and contraction (&lt;100 ms) of the buccal and opercular cavities and results in movement of both the prey and the fish itself. Suction is often combined with jaw protrusion and swimming. During a single suction movement the volume of water passing through the mouth aperture may exceed, by more than five times, the volume of the fully expanded mouth cavity, since after a given moment water leaves the mouth through the opercular slits. The generated flow is highly unsteady, i.e. large local accelerations (&gt;50m s−2) occur and streamline patterns change rapidly with time.
Evidence From Strandings for Geomagnetic Sensitivity in Cetaceans
Authors: Kirschvink Joseph L. , Dizon Andrew E. , Westphal James A. 
Published: April 2021

ABSTRACTWe tested the hypothesis that cetaceans use weak anomalies in the geomagnetic field as cues for orientation, navigation and/or piloting. Using the positions of 212 stranding events of live animals in the Smithsonian compilation which fall within the boundaries of the USGS East-Coast Aeromagnetic Survey, we found that there are highly significant tendencies for cetaceans to beach themselves near coastal locations with local magnetic minima. Monte-Carlo simulations confirm the significance of these effects. These results suggest that cetaceans have a magnetic sensory system comparable to that in other migratory and homing animals, and predict that the magnetic topography and in particular the marine magnetic lineations may play an important role in guiding long-distance migration. The ‘ map’ sense of migratory animals may therefore be largely based on a simple strategy of following paths of local magnetic minima and avoiding magnetic gradients.
Effects Of Temperature And Thermal Acclimation On Contractile Properties And Metabolism Of Skeletal Muscle In The Flounder (Platichthys Flesus L.)
Authors: Johnston Ian A. , Wokoma Alele 
Published: April 2021

ABSTRACT
Flounder (Platichthys flesus L.) were acclimated in sea water for 1-2 months to either 5°C or 23°C (12h light: 12h dark photoperiod).
Single fast muscle fibres were isolated from anterior ventral myotomes and skinned with detergent (Brij 58). Fibres were maximally activated and force-velocity (P-V) characteristics determined by step tension releases using an isotonic lever. Unloaded shortening speed was independently determined using the slack-test method.
The contractile properties of flounder skinned fibres are not altered by temperature acclimation. Maximum isometric tension development has a low thermal dependence, Q10= 1·2, increasing from 145 kN m−2 at 0°C to 200 kN m−2 at 25 °C. The force-velocity relationship becomes progressively less curved with decreasing temperature (higher values of Hill’s constant a/P0) such that the thermal dependence of contraction velocity is significantly less at loads for optimum power output (Q10= 1·3) than at zero load (Q10= 2·0). Values for a/P0 are 0·27 at 0°C, 0·12 at 10°C and 0·08 at 25°C. Reductions in the curvature of the P-V relationship with decreasing temperature may represent an important mechanism for stabilizing muscle power output at low temperatures.
Longer term metabolic adjustments to temperature were studied by determining maximal enzyme activities in fast and slow muscles (at 15°C). Activities of marker enzymes for mitochondrial metabolism (cytochrome oxidase), aerobic glucose utilization (hexokinase) and fatty acid oxidation (carnitine palmitoyl transferase) are 1·5–2·8 times higher in muscles of cold-acclimated compared to warm-acclimated flounders. Increases in the activities of these enzymes with cold acclimation may serve to offset the effects of low temperature on aerobic ATP supply. Glycolytic enzyme activities (phosphofructokinase, lactate dehydrogenase), however, are similar at both acclimation temperatures.
The results are briefly discussed in relation to the ecology of the flounder and evolutionary strategies of temperature adaptation in teleosts.
Capillarity and Mitochondrial Distribution in Rat Myocardium Following Exercise Training
Authors: Kayar S. R. , Conley K. E. , Claassen H. , Hoppeler H. 
Published: April 2021

ABSTRACT
Rats were subjected to a laddermill running programme either once per week for 6 weeks, or daily for 6 weeks. Heart mass and maximal oxygen consumption rate increased relative to controls and with the frequency of the running programme. Mitochondrial distribution, measured in seven regions within fibres, was similar in all hearts, with a peak volume density of 0·42 ±0·01 occurring 4–5 μm from the centre of a capillary. Capillary density decreased with increasing heart mass, but total capillary length and capillary-to-fibre ratio were constant. Thus the higher metabolic demands of the running programmes did not alter the volume density or distribution of mitochondria, despite significant increases in heart mass and decreases in capillarity.