bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the Responses to Hypoxia, Ischaemia and Ischaemic Preconditioning in Wild Marmot and Laboratory Rabbit Hearts
Authors: Mckean Tom , Mendenhall Wade 
Published: April 2021

ABSTRACT
Marmots (Marmota flaviventris) are burrowing mammals that may be subjected to low levels of oxygen and high levels of carbon dioxide in their underground environment. Since marmots successfully deal with this physiological challenge, we hypothesized that the isolated perfused marmot heart would be damaged less and recover better from a bout of induced hypoxia or ischaemia than would the heart of a comparison animal, the New Zealand laboratory rabbit (Oryctolagus cuniculus).
Isolated marmot and rabbit hearts were made hypoxic by a 30 min perfusion with an oxygen-deficient buffer. The hearts were then perfused with an oxygen-replete buffer and measurements of heart rate, left ventricular pressure and lactate dehydrogenase (LDH) release (an indicator of cell damage) were made over 5 or 10 min intervals for 30 min of hypoxia and 30 min of recovery. There were no species differences in the responses, except that the heart rate in marmots was about 50 % of the rate in rabbits during the hypoxia part of the experiment. There was no evidence that the marmot hearts were damaged less or recovered better from hypoxia and reoxgenation than the rabbit hearts. Marmot and rabbit hearts were also subjected to 30 min of total ischaemia; measurements of heart rate, left ventricular pressure and LDH release were obtained during 30 min of reperfusion and compared with the pre-ischaemia values for these variables. There were no significant species differences. When the 30 min ischaemic period was preceded by a 5 min period of ischaemia and a 10 min reperfusion period (preconditioning), the rabbit hearts were protected by this brief ischaemic insult and recovered better than the hearts that had not been subjected to the preconditioning ischaemia. This was not true in the marmot hearts, however, as the preconditioning ischaemia did not promote a greater recovery over that in its absence. When preconditioned marmots hearts were compared with preconditioned rabbit hearts, there were no statistical differences in the responses.
The hypothesis that marmot hearts would be damaged less and recover better from hypoxia and ischaemia was not supported by the experimental data.
Why the Urchin Lost Its Spines: Hydrodynamic Forces and Survivorship in Three Echinoids
Authors: Denny Mark , Gaylord Brian 
Published: April 2021

ABSTRACT
Two species of sea urchins (Colobocentrotus atratus and Echinometra mathaei) commonly co-occur on wave-swept intertidal shores in the Indo West Pacific. E. mathaei is a typical spiny urchin and is confined to cavities in the rock. In contrast, C. atratus has an unusual morphology, in which the spines are much reduced, and is found on substrata fully exposed to wave-induced velocities and accelerations. Previous researchers have suggested that spine reduction may therefore be a morphological adaptation to hydrodynamic forces. However, measurement of the drag, lift and accelerational forces on sea urchins show that the adaptive significance of spine reduction is less straightforward than it initially appears. The reduction in drag in C. atratus as compared with that in E. mathaei is to a large extent offset by an increase in lift. Instead, the ‘streamlined’ morphology of C. atratus seems best adapted to provide a reduction in the force imposed by water acceleration, thereby making it feasible for C. atratus to venture safely into the tumultuous flows of the surf zone.
Targetting and Visuomotor Space in the Leaf-Hopper Empoasca Vitis (Gothe) (Hemiptera: Cicadellidae)
Authors: Brackenbury John 
Published: April 2021

ABSTRACT
The accuracy with which the visuomotor system of Empoasca vitis can prescribe a jump trajectory towards a bright, uniformly illuminated target shape was investigated. The targets consisted of discs, rings or bars cut out of black card and mounted in front of a source of stroboscopic light diffused through translucent paper. The targets varied in size, subtending angles of 7–110 ° to the insect’s eye. Target resolution was measured independently along the horizontal and vertical axes and was defined in terms of the standard deviation of the horizontal (S.D.x) or vertical (S.D.y) angular coordinates of the take-off paths measured with respect to the geometric centre of the target. In all cases involving single connected images, the point towards which jumping was directed coincided with the geometric centre of the image area (the light centroid). This meant, for example, that the insects specifically targetted the dark core of a ring of light. No formal features of the target shapes, such as light–dark boundaries, were targetted. Vertical axial resolution was independent of image size (mean S.D.y for all image sizes 6.9 °), but horizontal axial resolution only achieved this minimal value at intermediate image sizes (approximately 30–60 °). When two separate but identical target shapes (vertical bars) were presented at different horizontal separations, the dark area between them was accurately targetted up to target separations of approximately 30–50 °. At greater separations, there was an increasing tendency to target one or other of the two shapes. From these experiments it is concluded that, in the frontal visual field, spatial integration can be performed to an accuracy (as defined in these experiments) of 7 °X7 °. Performance deteriorates outside an optimal range of image sizes, and this is faithfully reflected in the decline in horizontal axial resolution when jumping. However, this decline in visual performance is not reflected in target resolution along the vertical axis because it is masked by a biomechanical constraint, i.e. the inability of the legs to set take-off angles outside a narrow range of 30–60 ° to the horizontal.
Novel dual innervation of a larval proleg muscle by two similar motoneurons in the tobacco hornworm Manduca sexta
Authors: Sandstrom David J. , Weeks Janis C. 
Published: April 2021

ABSTRACT
In Manduca sexta, the accessory planta retractor muscle (APRM), which retracts the larval proleg, is innervated by two excitatory motoneurons, the accessory planta retractor motoneurons (APRs). These muscles and motoneurons have been the focus of a number of developmental and behavioral studies. The present study investigated properties of the pair of APRs that innervate each APRM and determined their pattern of innervation of APRM fibers. Members of APR pairs could not be distinguished by their anatomical or electrical properties (resting membrane potential, input resistance and spike threshold). Spontaneous synaptic inputs to members of APR pairs were highly correlated, whereas spontaneous synaptic inputs to APRs and functionally dissimilar motoneurons were not well correlated. Synaptic inputs from identified mechanosensory neurons and interneurons to the two APRs were qualitatively similar, but the magnitude of the response to sensory stimulation sometimes differed within a pair. Both APRs produced large, rapidly rising excitatory junction potentials in APRM fibers. Within the APRM, some fibers were singly innervated by one or the other APR while the remaining fibers were dually innervated by both APRs. In dually innervated fibers, the motor terminals of the two APRs were spatially segregated. This innervation pattern appears to be unique among insects and shares some properties with the innervation of vertebrate muscle.
Mechanical power and work of cat soleus, gastrocnemius and plantaris muscles during locomotion: possible functional significance of muscle design and force patterns.
Authors: Prilutsky B. I. , Herzog W. , Allinger T. L. 
Published: April 2021

ABSTRACT
Electrical activity, forces, power and work of the soleus (SO), the gastrocnemius (GA) and the plantaris (PL) muscles were measured during locomotion in the cat in order to study the functional role of these ankle extensor muscles. Forces and electrical activity (EMG) of the three muscles were measured using home-made force transducers and bipolar, indwelling wire electrodes, respectively, for walking and trotting at speeds of 0.4 to 1.8 m s−1 on a motor-driven treadmill. Video records and a geometrical model of the cat hindlimb were used for calculating the rates of change in lengths of the SO, GA and PL muscles. The instantaneous maximum possible force that can be produced by a muscle at a given fibre length and the rate of change in fibre length (termed contractile abilities) were estimated for each muscle throughout the step cycle. Fibre lengths of the SO, GA and PL were calculated using a planar, geometrical muscle model, measured muscle forces and kinematics, and morphological measurements from the animal after it had been killed. Mechanical power and work of SO, GA and PL were calculated for 144 step cycles. The contribution of the positive work done by the ankle extensor muscles of one hindlimb to the increase of the total mechanical energy of the body (estimated from values in the literature) increased from 4–11 % at speeds of locomotion of 0.4 and 0.8 m s-1 to 7–16 % at speeds of 1.2 m s−1 and above. The relative contributions of the negative and positive work to the total negative and positive work done by the three ankle extensor muscles increased for GA, decreased for SO and remained about the same for PL, with increasing speeds of locomotion. At speeds of 0.4–0.8 m s−1, the positive work normalized to muscle mass was 7.5–11.0 J kg−1, 1.9–3.0 J kg−1 and 5.3–8.4 J kg−1 for SO, GA and PL, respectively. At speeds of 1.2–1.8 m s−1, the corresponding values were 9.8–16.7 J kg−1, 6.0–10.7 J kg−1 and 13.4–25.0 J kg−1. Peak forces of GA and PL increased and peak forces of SO did not change substantially with increasing speeds of locomotion. The time of decrease of force and the time of decrease of power after peak values had been achieved were much shorter for SO than the corresponding times for GA and PL at fast speeds of locomotion. The faster decrease in the force and power of SO compared with GA and PL was caused by the fast decrease of the contractile abilities and the activation of SO. The results of this study suggest that the ankle extensor muscles play a significant role in the generation of mechanical energy for locomotion.
Ventilatory and Blood Acid–Base Adjustments to a Decrease in Body Temperature From 30 To 10 °C In Black Racer Snakes Coluber Constrictor
Authors: Stinner J. N. , Grguric M. R. , Beaty S. L. 
Published: April 2021

ABSTRACT
There is increasing evidence that many amphibian and reptilian species use relatively slow ion-exchange mechanisms in addition to ventilation to adjust pH as body temperature changes. Large changes in blood bicarbonate concentration with changes in temperature have previously been reported for the snake Coluber constrictor. The purpose of the present study was to determine the ventilatory and pH adjustments associated with the increase in CO2 stores when the snakes are cooled. Body temperature was lowered from 30 to 10 °C within 4 h, at which time measurements of inspired minute ventilation , O2 consumption and CO2 production were started and continued for 56 h. The decrease in temperature produced a transient fall in the respiratory exchange ratio to 0.2–0.3 and a steady-state value of 0.65±0.14 (mean ± S.D., N=7) was not achieved until about 35 h. There were concomitant transient reductions in and . However, initially increased, with a corresponding reduction in arterial and increase in arterial pH. By 35 h, had decreased and had increased to steady-state levels, but pH decreased very little because of a gradual increase in bicarbonate concentration. We conclude that the drop in temperature imposed a metabolic acidosis for approximately 35 h because of the time required to increase bicarbonate concentration, and that the acidosis was compensated for by an elevated . Steady-state breathing and acid–base status were not achieved until the relatively slow increase in CO2 stores had been completed.
Hindbrain Signal Processing in the Lateral line System of the Dwarf Scorpionfish Scopeana Papillosus
Authors: Montgomery John , Bodznick David , Halstead Matthew 
Published: April 2021

ABSTRACT
Recordings were made from primary afferent fibres and secondary projection neurones (crest cells) in the mechanosensory lateral line system of the dwarf scorpionfish. Crest cells were identified by antidromic stimulation from the contralateral midbrain. Differences between primary afferent fibre and crest cell response characteristics are indicative of signal processing by the neuronal circuitry of the medial octavolateralis nucleus. There are a number of differences between primary afferent fibres and crest cells. Primary afferents have relatively high levels of spontaneous activity (mean close to 40 impulses s−1) and many of them are strongly modulated by ventilation. By contrast, crest cells have a much lower rate of spontaneous activity that is not obviously modulated by ventilation. Primary afferents show a simple tonic response to a maintained stimulus, whereas crest cells show a variety of temporal response properties, but in general show a phasic/tonic response to the same prolonged stimulus. Afferents are most sensitive to frequencies of stimulation around 100 Hz; in contrast, crest cells show a strong suppression of activity at this frequency. Crest cells are most responsive around 50 Hz. These afferent/secondary comparisons show similarities with those reported for allied electrosensory and auditory pathways.
Amino-Acid-Dependent Modulation of Amino Acid Transport in Xenopus Laevis Oocytes
Authors: Taylor Peter M. , Kaur Surinder , Mackenzie Bryan , Peter George J. 
Published: April 2021

ABSTRACT
We have measured rates of uptake of arginine, glutamine, glutamate, serine, phenylalanine and glycine in Xenopus laevis oocytes cultured for periods of up to 24 h in saline in the presence or absence of a mixture of 20 amino acids at concentrations approximating those in Xenopus plasma. Amino acid supplementation increased the total intracellular amino acid concentration from 8.2 to 18.4 nmol per oocyte. Specific Na+-dependent amino acid transporters (systems B0,+, Xāg) exhibit ‘adaptive regulation’ (up-regulation during amino acid deprivation and down-regulation during amino acid supplementation). Na+-independent transporters of glutamate, glutamine and glycine (including system asc) display an opposite modulation in activity, which may help to combat amino-acid-induced oxidative stress by increasing the supply of glutathione precursors. Single amino acids at physiological plasma concentrations (0.47 mmol l−1 L-alanine, 0.08 mmol l−1 L-glutamate) mimicked at least some effects of the amino acid mixture. The mechanisms of transport modulation do not appear to include trans-amino acid or membrane potential effects and, in the case of Na+-independent transport, are independent of protein or mRNA synthesis. Furthermore, activation of protein kinase C by phorbol 12-myristate 13-acetate did not significantly affect endogenous glutamine and glutamate transport. The Xenopus oocyte appears to possess endogenous signalling mechanisms for selectively modulating the activity of amino acid transport proteins expressed in its surface membranes, a factor for consideration when using oocytes as an expression system for structure–function studies of cloned amino acid transporters.
Relative Effects of Carbonic Anhydrase Infusion or Inhibition on Carbon Dioxide Transport and Acid–Base Status in the Sea Lamprey Petromyzon Marinus Following Exercise
Authors: Tufts B. L. , Currie S. , Kieffer J. D. 
Published: April 2021

ABSTRACT
In vivo experiments were carried out to determine the relative effects of carbonic anhydrase (CA) infusion or inhibition on carbon dioxide (CO2) transport and acid–base status in the arterial and venous blood of sea lampreys recovering from exhaustive exercise. Infusion of CA into the extracellular fluid did not significantly affect CO2 transport or acid–base status in exercised lampreys. In contrast, infusion of the CA inhibitor acetazolamide resulted in a respiratory acidosis in the blood of recovering lampreys. In acetazolamide-treated lampreys, the post-exercise extracellular pH (pHe) of arterial blood was significantly lower than that in the saline-infused (control) lampreys. The calculated arterial and venous partial pressure of carbon dioxide and the total CO2 concentration in whole blood and red blood cells during recovery in the acetazolamide-infused lampreys were also significantly greater than those values in the saline-infused control lampreys. These results suggest that the CO2 reactions in the extracellular compartment of lampreys may already be in equilibrium and that the access of plasma bicarbonate to CA is probably not the sole factor limiting CO2 transport in these animals. Furthermore, endogenous red blood cell CA clearly has an important role in CO2 transport in exercising lampreys.
Cephalopod Sucker Design and the Physical Limits to Negative Pressure
Authors: Smith Andrew M. 
Published: April 2021

ABSTRACT
Two factors determine the strength of pressure-based adhesive mechanisms such as suction: the magnitude of the pressure differential that their musculature and mechanics can produce and the pressure differential that water can sustain. This paper compares the adhesive strength of the primary cephalopod sucker types: the stalked suckers of decapods (cuttlefish and squid) and the unstalked suckers of octopods. These results are compared with the physical limits imposed by cavitation, the failure of water under negative pressure.
The maximum pressure differentials that suckers can produce were measured using a wettable pressure transducer or by measuring their force of attachment on a wettable surface and dividing by the area exposed to reduced pressure. The maximum pressure differentials that water can sustain on a typical marine surface were measured in a Z-tube. Fifteen cephalopod species representing three orders were studied. At sea level, cavitation limits all suckers to the same range of pressure differentials (100–200 kPa), regardless of their morphology. As ambient pressure increases with depth, cavitation ceases to be limiting. In this case, stalked decapod suckers produce greater pressure differentials than unstalked octopod suckers. In addition, small suckers produce greater pressure differentials than large suckers. Suckers larger than 7.5 mm2, both decapod and octopod, typically achieve pressure differentials of 100 kPa. As their size decreases below 7.5 mm2, octopod suckers get slightly stronger, sometimes producing pressure differentials of 250–300 kPa, while decapod suckers get exponentially stronger, sometimes producing pressure differentials near 800 kPa. There were no differences in sucker strength among the four octopod species, but seven of the ten decapod species differed from the overall decapod regression curve. The strongest suckers belonged to the fast-swimming, open-water species in the decapod sub-order Oegopsida.
Validation of the Doubly Labelled Water Technique for Bumblebees Bombus Terrestris (L.)
Authors: Wolf Thomas J. , Ellington Charles P. , Davis Simon , Feltham Mark J. 
Published: April 2021

ABSTRACT
The doubly labelled water (DLW) technique was validated for the bumblebee Bombus terrestris (L.) using respirometry (RESP) from tethered roundabout flights. We injected small volumes (1 μl) of a mixture containing low concentrations of deuterium and 18O and withdrew 1–2 μl of haemolymph to determine initial 18O concentration. The injected isotopes were equilibrated with the body water pool after 10 min, and high material turnover allowed the analysis of final blood isotope concentrations after 5–7 h. On average (n=16), values measured using the DLW technique exceeded values measured using RESP by 3.1±9.9 %, a difference that was not statistically significant at the 99 % confidence level.
The absolute error was 7.4±7.1 % (mean ± S.D.). Isotope dilution spaces of both deuterium and 18O were almost identical with the body water pool. We corrected for isotope fractionation, using a slightly higher value than usual for one of the fractionation factors. The single most important variable to influence DLW results, which could not be measured with the desired accuracy, was the volume of the final body water pool N. An overestimate of final N possibly resulted in the DLW overestimate.
Diving Energetics in King Penguins (Aptenodytes Patagonicus)
Authors: Culik B. M. , Pütz K. , Wilson R. P. , Allers D. , Lage J. , Bost C. A. , Maho Y. Le 
Published: April 2021

ABSTRACT
Dive duration in wild king penguins and the energetic cost of swimming in a 30 m long swim channel were determined at Ile de la Possession, Crozet Archipelago, using external data loggers and respirometry, respectively. Calibrated electronic data loggers equipped with a pressure sensor were used to determine dive durations: 95 % of dives were less than 6 min long and 66 % of dives were less than 4 min long. Dive patterns show that king penguins may intersperse long dive durations (4–6.3 min) with short ones (1.5–3 min) and make surface pauses of variable duration between them (0.5–3.5 min), or dive regularly (for up to 5 h) with long dive durations (5 min) and constant interdive surface intervals (1.5 min). The latter indicates that the aerobic dive limits (ADL) of this species could be higher and oxygen consumption lower than previously reported. Assuming that king penguins dive within their aerobic limit, different approaches to the analysis of the data obtained in the swim channel are discussed to derive the ADL. Swimming speeds observed in the channel ranged from 0.9 to 3.4 m s−1. Transport costs were lowest between 1.8 and 2.2 m s−1. Although at 2.2 m s−1 king penguins used only 10.3 W kg-1 over a dive + surface cycle (minimal transport costs of 4.7J kg−1 m−1), we speculate that tissue oxygen consumption during submergence may be as low as 0.23 ml O2 kg−1 s−1 (2.1 times standard metabolic rate, SMR) or perhaps lower (which gives an ADL of 4.2 min). During surface phases, oxygen uptake would be increased to at least 1 ml O2 kg−1 s−1 (9.3 times SMR). This implies that at least 70 % of all dives are aerobic. Potential physiological mechanisms allowing king penguins to partition O2 consumption between submergence and surface periods remain, however, unclear.
Polarization Contrast Vision in Octopus
Authors: Shashar Nadav , Cronin Thomas W. 
Published: April 2021

ABSTRACT
While the ability to analyze polarized light is widespread among animals, its contribution to form vision has not yet been documented. We tested the hypothesis that polarization vision can be used for object discrimination, by training octopuses to distinguish between targets on the basis of the presence or absence of a pattern produced by a 90 ° polarization contrast within the target. Octopuses recognized a 90 ° contrast pattern within a single target, when presented either on a horizontal/vertical axis or on a 45 °/135 ° axis. They were able to transfer their learning to new situations and to detect a polarization contrast when the orientations of the e-vector of light passing through the target center and background differed by as little as 20 °. Polarization vision may provide information similar to that available from color vision and thus serve to enhance the detection and recognition of objects.