bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Preload and Afterload on the Performance of the In Situ Perfused Portal Heart of the New Zealand Hagfish Eptatretus Cirrhatus
Authors: Johnsson Marianne , Axelsson Michael , Davison William , Forster Malcolm E. , Nilsson Stefan
Published: April 2021

The portal heart of the New Zealand hagfish (Eptatretus cirrhatus) was perfused in situ. Stroke volume, cardiac output and power output increased in response to increased preload, in accordance with Starling’s law of the heart. A positive chronotropic effect was found when the input pressure increased from 0.05 to 0.1 kPa. Increased afterload decreased stroke volume and cardiac output. Power output peaked at an output pressure of 0.22 kPa, after which it decreased. There was no change in heart rate in response to increased afterload. In unanaesthetized resting animals, the pressure in the supraintestinal vein, which supplies the portal heart, ranged from 0.025 to 0.07 kPa (mean 0.040±0.005 kPa).

The β-adrenoceptor antagonist sotalol did not affect the response to different input and output pressures. Sotalol produced a significant decrease in heart rate and abolished the pressure-sensitive increase in heart rate. Bolus injections of adrenaline produced a transient increase in portal heart rate. The negative chronotropic response to sotalol and the response to adrenaline indicate the presence of an endogenous β-adrenergic tonus on the portal heart.
The Contribution of Nitrate Respiration to the Energy Budget of the Symbiont-Containing Clam Lucinoma Aequizonata:A Calorimetric Study
Authors: Hentschel U. , Hand S. C. , Felbeck H.
Published: April 2021

Heat production and nitrate respiration rates were measured simultaneously in the gill tissue of Lucinoma aequizonata. This marine bivalve contains chemoautotrophic, intracellular, bacterial symbionts in its gill tissue. The symbionts show constitutive anaerobic respiration, using nitrate instead of oxygen as a terminal electron acceptor. An immediate increase in heat production was observed after the addition of nitrate to the perfusion medium of the calorimeter and this was accompanied by the appearance of nitrite in the effluent sea water. The nitrate-stimulated heat output was similar under aerobic and anaerobic conditions, which is consistent with the constitutive nature of nitrate respiration. The amount of heat released was dependent on the concentration of nitrate in the perfusion medium. At nitrate concentrations between 0.5 and 5 mmol l-1, the total heat production was increased over twofold relative to unstimulated baseline values. A mean (±S.E.M.) experimental enthalpy of -130±22.6 kJ mol−1 nitrite (N=13) was measured for this concentration range.
Two Opsins From the Compound Eye of the Crab Hemigrapsus Sanguineus
Authors: Sakamoto Katsuhiko , Hisatomi Osamu , Tokunaga Fumio , Eguchi Eisuke
Published: April 2021

The primary structures of two opsins from the brachyuran crab Hemigrapsus sanguineus were deduced from the cDNA nucleotide sequences. Both deduced proteins were composed of 377 amino acid residues and included residues highly conserved in visual pigments of other species, and the proteins were 75 % identical to each other. The distribution of opsin transcripts in the compound eye, determined by in situ hybridization, suggested that the mRNAs of the two opsins were expressed simultaneously in all of the seven retinular cells (R1–R7) forming the main rhabdom in each ommatidium. Two different visual pigments may be present in one

photoreceptor cell in this brachyuran crab. The spectral sensitivity of the compound eye was also determined by recording the electroretinogram. The compound eye was maximally sensitive at about 480 nm. These and previous findings suggest that both opsins of this brachyuran crab produce visual pigments with maximal absorption in the blue-green region of the spectrum. Evidence is presented that crustaceans possess multiple pigment systems for vision.
Response of Cell Volume in Mytilus Gill to Acute Salinity Change
Authors: Neufeld Douglas S. , Wright Stephen H.
Published: April 2021

The response of gill cell volume in Mytilus californianus and Mytilus trossolus (=edulis) to acute changes in salinity was assessed using three independent indicators: optical measurement of lateral cell height, measurement of intracellular water content using radiolabeled tracers and measurement of the contents of the major osmolytes of the gills. Optical measurements indicated significant variation in the response of individual lateral cells of M. californianus to acute low-salinity shock. Lateral cell height increased by approximately 20 % shortly after abrupt exposure to 60 % artificial sea water (ASW). Following this initial swelling, we estimate that a substantial regulatory volume decrease (RVD) was present in 25 % of the trials. More commonly, however, an RVD was either absent or minimal: cell height remained elevated for at least 1 h, then returned to the control height when gills were re-exposed to 100 % ASW. Changes in the combined water space of all cells in the gill, measured as the difference between total water space and extracellular space ([14 C]polyethylene glycol space), indicated that cell volume regulation in the gill as an organ was also absent or minimal. Cell water space was 2.16 ml g−1 dry mass in isolated gills of M. californianus acclimated to 100 % sea water in the laboratory and increased to 2.83 ml g−1 dry mass after a 6 min exposure to 60 % ASW. Cell water space was still 2.81 ml g−1 dry mass after 1 h in 60 % ASW and returned to 2.06 ml g−1 dry mass upon re-exposure to 100 % ASW. Consistent with these observations, the gill contents of the principal cytoplasmic osmolytes (taurine, betaine and K+ ) were unchanged (approximately 450, 250 and 230 μmol g−1 dry mass, respectively) following exposure of gills from 100 % ASW-acclimated mussels to 60 % ASW. A decrease in cell water space to 2.66 ml g−1 dry mass after 4 weeks of acclimation to 60 % ASW corresponded with a 37 % decrease in betaine content; taurine and K+ contents were unchanged. The changes in water space and solute content of gills from freshly collected M. californianus and M. trossolus were also consistent with the absence of volume regulation; cell water space remained elevated for at least 1 h after low-salinity exposure, and solute contents were unchanged after this period. We calculated the potential energetic cost of cell volume regulation for mussels exposed to 12 h of sinusoidal fluctuations between 100 % and 50 % sea water; solute uptake for full volume regulation in all tissues would cost a minimum of approximately 30 % of the standard metabolic rate during the period of salinity increase. The routine absence of substantial cell volume regulation in Mytilus gill may reflect the potentially high energetic cost of volume regulation in the face of the large and frequent salinity fluctuations that are regularly encountered by estuarine bivalves.
Adenosine Receptor Blockade and Hypoxia-Tolerance in Rainbow Trout and Pacific Hagfish: I. Effects on Anaerobic Metabolism
Authors: Bernier Nicholas J. , Harris Joelle , Lessard Joanne , Randall David J.
Published: April 2021

The physiological properties of adenosine may be essential in the control of energy metabolism for the survival of animals exposed to oxygen shortages. Accordingly, we tested the hypothesis that adenosine modulates metabolic regulation in rainbow trout and Pacific hagfish exposed to acute hypoxia. Treatment of hypoxic rainbow trout (=3.33 or 4.00 kPa) with the adenosine receptor (AR) blocker theophylline was associated with greater increases in plasma [lactate], more rapid and pronounced metabolic acidosis, higher tissue [lactate], and lower heart creatine charge and glycogen content than in the hypoxic controls. The recruitment of anaerobic metabolism in hypoxic trout treated with enprofylline, an AR blocker with very weak affinity, was intermediate to that of the hypoxic theophylline-injected and control groups. In hagfish, plasma [lactate] increased following exposure to a of 1.33 kPa but did not increase following exposure to 3.33 kPa and, like plasma acidosis, it was greatest in the animals treated with theophylline. These findings indicate that AR blockade results in a more rapid and pronounced recruitment of anaerobic metabolism following acute hypoxic exposure, and while rainbow trout and Pacific hagfish show marked differences in their responses to hypoxia, adenosine appears to play an important protective role in both species.
Producing Directed Behaviour: Muscle Activity Patterns of the Cockroach Escape Response
Authors: Levi Rafael , Camhi Jeffrey M.
Published: April 2021

The cockroach responds to wind from the front left by making an escape turn to the right, and vice versa. So far, no interneurones in the escape system are known that respond only to wind from the left or only to wind from the right. In this study, we used electromyographic recordings to determine whether motor neurones respond in this direction-selective manner during escape behaviour.

In the mesothoracic coxal–femoral joint, whose movement direction is diagnostic for escape direction, the fast motor neurones of one muscle respond selectively to one wind direction, and those of the antagonistic muscle respond selectively to wind from the other direction, resulting in an appropriate turning response. This rules out an alternative hypothesis, a co-activation mechanism of specifying turn direction. These results suggest that it would be fruitful to search among the interneurones of the escape system for additional cells and circuit properties that could give rise to this sharp directional discrimination.
Brain and Body Oxygen Requirements of Gnathonemus Petersii, a Fish with an Exceptionally Large Brain
Authors: Nilsson Göran E.
Published: April 2021

Vertebrates have repeatedly been noted for having remarkably constant ratios of brain to body O2 consumption, the brain using 2–8 % of resting body O2 consumption, suggesting that evolution has put strict limits on the energetic cost of brain function. Only man, with a value of 20 %, is an exception to this rule. However, the results presented here suggest that, in the electric fish Gnathonemus petersii, the brain is responsible for approximately 60 % of body O2 consumption, a figure three times higher than that for any other vertebrate studied, including man. The exceptionally high energetic cost of the G. petersii brain appears to be a consequence both of the brain being very large and of the fish being ectothermic.

It was also found that G. petersii has a high ability to utilise O2 at low levels. Thus, during falling [O2], this species was found to maintain both its O2 uptake and its electric discharge rate down to an ambient O2 level of 0.8 mg l-1 (at 26 °C), although it was unable to tolerate an [O2] below 0.3 mg l-1. During severe hypoxia (<0.8 mg l-1), G. petersii attempted to gulp air from the water surface. These results establish a new record for the energetic cost of a vertebrate brain and they show that the species possessing such a brain has a high capacity for utilising O2 at very low ambient concentrations.
Inexpensive Load Carrying by Rhinoceros Beetles
Authors: Kram Rodger
Published: April 2021

These experiments determined the magnitude of loads that rhinoceros beetles (Scarabaeidae) can carry and also the metabolic energy required for carrying loads. I hypothesized that, like many other animals, these beetles would have metabolic rates in direct proportion to the total load (body mass plus added mass). Eight beetles (Xylorctes thestalus) walked at 1 cm s-1 on a motorized treadmill enclosed in a respirometer. The beetles could sustain this speed with loads of more than 30 times their body mass. In addition to being strong, these beetles carry loads with remarkable economy. The metabolic cost of moving a gram of additional load was more than five times cheaper than that of moving a gram of body mass. This phenomenon cannot be explained by conventional models that link the biomechanics and metabolic energy cost of locomotion.
Haemolymph Flow Distribution, Cardiac Performance and Ventilation During Moderate Walking Activity in Cancer Magister (Dana) (Decapoda, Crustacea)
Authors: Wachter Bart De , McMahon Brian R.
Published: April 2021

Adult male Cancer magister (Dana) were equipped with pulsed-Doppler flowmeters and pressure transducers for simultaneous measurement of heart and ventilation frequencies, haemolymph flow through each of the major arterial systems and cardiac output and for calculation of stroke volume. Each variable was measured at rest and during two consecutive periods of moderate treadmill walking activity and recovery. During activity, haemolymph flow through the sternal and anterolateral arteries increased, while flow through the hepatic arterial system decreased. This resulted in a redistribution of haemolymph flow in which a proportion of cardiac output was shifted from the anterior, posterior and hepatic arterial systems to the sternal arterial system. The relative proportion of the cardiac output flowing through the anterolateral artery remained constant. This indicated that oxygen supply was shifted away from the digestive system to the muscles of the walking legs and the respiratory system. Cardiac output, heart rate and stroke volume all increased in response to activity. The increase in cardiac output is the result of a large increase in stroke volume and a small increase in heart rate. A doubling of ventilation rate also occurred during activity. Both the circulatory and ventilatory systems were restored to pre-activity values by 60 min of recovery.
Motor Corollary Discharge Activity and Sensory Responses Related to Ventilation in the Skate Vestibulolateral Cerebellum: Implications for Electrosensory Processing
Authors: Hjelmstad Gregory O. , Parks Geoffrey , Bodznick David
Published: April 2021

The dorsal granular ridge (DGR) of the elasmobranch vestibulolateral cerebellum is the source of a parallel fiber projection to the electrosensory dorsal nucleus. We report that the DGR in Raja erinacea contains a large percentage of units with activity modulated by the animal’s own ventilation. These include propriosensory and electrosensory units, responding to either ventilatory movements or the resulting electroreceptive reafference, and an additional population of units in which activity is phase-locked to the ventilatory motor commands even in animals paralyzed to block all ventilatory movements. A principal function of processing in the dorsal nucleus is the elimination of ventilatory noise in second-order electrosensory neurons. The existence of these ventilatory motor corollary discharge units, along with other DGR units responsive to ventilatory movements, suggests that the parallel fiber projection is involved in the noise cancellation mechanisms.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
A Compartmental Approach to the Mechanism of Calcification in Hermatypic Corals
Authors: Tambutté Éric , Allemand Denis , Mueller Erich , Jaubert Jean
Published: April 2021

Ca2+ compartments, Ca2+ transport and the calcification process were studied by using 45Ca as a tracer. The biological model used was clones of Stylophora pistillata developed into microcolonies whose skeleton is entirely covered by tissues, thus avoiding direct radioisotope exchange between the sea water and the skeleton. The study of Ca2+ compartments was performed by measuring two complementary parameters: Ca2+ influx and Ca2+ efflux kinetics. Kinetic analysis of 45Ca uptake revealed three exchangeable and one non-exchangeable Ca2+ compartments in these microcolonies. The first compartment was saturable with a short half-time (4 min), correlated to external Ca2+ concentration and insensitive to metabolic or ion transport inhibitors. This compartment (72.88 nmol Ca2+ mg-1 protein) has been previously attributed to sea water present in the coelenteron. The second Ca2+ compartment (7.12 nmol Ca2+ mg-1 protein) was soluble in NaOH, saturable with a half-time of 20 min and displayed a combination of Michaelis–Menten kinetics and diffusional entry. It was insensitive to a variety of inhibitors but its loading was stimulated by Ca2+ channel inhibitors. On the basis of uptake experiments, the existence of a third compartment with a rapid turnover rate (about 2 min) and a very small size is predicted. It is suggested that this compartment corresponds to the calicoblastic epithelium. Ca2+ flux through this compartment was facilitated by voltage-dependent Ca2+ channels (with L-type characteristics) and Ca2+-ATPase and was coupled to an anion carrier. Transcellular Ca2+ movement was dependent on the cytoskeleton. The rate of Ca2+ flux across this epithelium was about 975 pmol mg-1 protein min-1. The fourth calcium compartment, corresponding to the skeleton, was soluble in HCl and non-exchangeable. After a short lag phase (about 2 min), the rate of Ca2+ deposition was linear over a period of at least 5 h. The calcification rate was 975 pmol mg-1 protein h-1 at an irradiance of 175 μmol photons m-2 s-1. It followed Michaelis–Menten kinetics and saturated at levels (9 mmol l-1) close to the Ca2+ concentration of sea water. Wash-out (efflux) experiments employing several different protocols allowed identification of six compartments. The first two compartments were extracellular (bulk extracolonial water and coelenteron). The third compartment may be part of the second Ca2+ compartment identified by influx experiments. A fourth compartment was sensitive to the Ca2+ channel inhibitor D600 and appeared to be associated with the NaOH-soluble (tissue) Ca2+ pool. Two compartments were identified during skeletal efflux, the first being small and due to either tissue carry-over or a labile skeletal compartment. The second compartment corresponded to bulk skeletal deposition. The various efflux protocols produced varying estimates of tissue Ca2+ levels and calcification rates and, thus, coral post-incubation processing has a profound impact on experimental interpretation.
Nadph Diaphorase Activity In The Antennae Of The Hawkmoth Manduca Sexta
Authors: Stengl Monika , Zintl Rita
Published: April 2021

Biochemical and physiological studies suggested that increases in the levels of cyclic GMP in insect antennal receptor cells play a role in olfactory adaptation. As inositol-trisphosphate-dependent Ca2+ influx appears to precede the increase in intracellular cyclic GMP levels, it was hypothesized that a Ca2+-dependent mechanism might stimulate the guanylyl cyclase. The present study used histochemical staining for NADPH diaphorase to examine whether antennal receptor neurones of male Manduca sexta could contain nitric oxide synthase. This Ca2+/calmodulin-dependent enzyme is a prerequisite for nitric-oxide-dependent stimulation of guanylyl cyclase and possesses NADPH diaphorase activity. It was found that a subpopulation of olfactory receptor neurones as well as mechano-, thermo- and hygroreceptors on the moth antenna are NADPH-diaphorase-positive. Staining was also seen in non-neuronal cells. In the developing antenna, the NADPH-diaphorase-dependent staining was first observed at pupal stage 13–14, at approximately the same time as the antennal receptor neurones became physiologically active. The number and location of stained receptor cells was highly variable, and significantly more pheromone-sensitive sensilla were NADPH-diaphorase-positive in pheromone-stimulated antennae. This suggests that the enzyme is transiently activated by pheromone rather than being continuously active.
Strain-Rate-Dependent Mechanical Properties of the Equine Hoof Wall
Authors: Kasapi Mario A. , Gosline John M.
Published: April 2021

The mechanical properties of fully hydrated equine hoof wall were examined at various loading rates in compact tension (CT) fracture, tensile and three-point bending dynamic tests to determine possible effects of hoof wall viscoelasticity on fracture toughness and tensile parameters. Four cross-head rates were used in CT tests: 1.7 × 10−5, 1.7 × 10−3, 1.7× 10−2 and 2.5 m s-1; four strain rates were used in tensile tests: 1.6 × 10−3, 3.2× 10−2, 0.33 and 70 s-1. Speeds for the highest test rates were achieved using a large, custom-built impact pendulum. Bending test frequencies ranged from 0.04 to 200 Hz.

In CT tests, both the initial modulus Ei and the stress intensity factor K rose with increasing strain rate (from 0.38 to 0.76 GPa for Ei and from 0.71 to 1.4 MN m-3/2 for K), whereas the fracture toughness parameter J remained constant at 12 kJ m-2. All tensile parameters except ultimate strain were sensitive to strain rate. Ei, total energy to breakage and maximum stress rose with increasing strain rate from 0.28 to 0.85 GPa, from 5.4 to 9.7 MJ m-3 and from 17 to 31 MPa, respectively. Data from low-amplitude dynamic tests agreed well with Ei trends from CT and tensile tests.

Direction of crack growth differed through the thickness of the wall, the pattern of which resembled a trilaminar ply. Although scanning electron microscopic examination of fracture surfaces revealed a decreasing pseudo-ductile behaviour with increasing strain rate, and ultimate tensile parameters are positively affected, equine hoof wall viscoelasticity does not appear to compromise fracture toughness at high strain rates.
Separate Control Of Anion And Cation Transport In Malpighian Tubules Of Drosophila Melanogaster
Authors: O’Donnell M. J. , Dow J. A. T. , Huesmann G. R. , Tublitz N. J. , Maddrell S. H. P.
Published: April 2021

Microelectrode measurements of basal, apical and transepithelial potentials in the Malpighian tubules of Drosophila melanogaster were obtained under a range of conditions in order to investigate whether each of the three main second messenger systems known to act in the tubules (cyclic AMP, cyclic GMP and Ca2+) acted specifically on either cation or anion transport, or whether they activated both systems.

Ion-selective microelectrode determinations of K+ concentration and pH of secreted fluid allowed the role of each signalling system to be analysed further.

Stimulation with cyclic nucleotides markedly alters the potential profile across principal cells through the selective activation of an apical electrogenic V-ATPase. By contrast, manipulation of extracellular chloride levels, combined with stimulation with leucokinin, does not affect the potential profile across the principal cells, showing that chloride must pass through another route.

The cell-permeant Ca2+ chelator BAPTA-AM was shown to suppress the action of leucokinins (insect peptides that induce rapid fluid secretion), but not those of cyclic AMP, the neuronally derived insect peptide cardioacceleratory peptide 2b (CAP2b) or its intracellular messenger cyclic GMP. This shows that leucokinins act through Ca2+ and not through cyclic nucleotides and that the cyclic nucleotide pathways do not co-activate the intracellular Ca2+ pathway to exert their effects.

Taken together, these results show that leucokinin acts through intracellular Ca2+, independently of cyclic AMP or cyclic GMP, to raise the chloride permeability of the epithelium. By contrast, either cyclic AMP or cyclic GMP (upon CAP2b stimulation) acts on the electrogenic cation-transporting apical V-ATPase, with only a negligible effect on anion conductance and without perturbing intracellular [Ca2+].

There is thus a clear functional separation between the control pathways acting on cation and anion transport in the tubules. Given the evidence from D. melanogaster and other species that chloride does not pass through the principal cells, we speculate that these two pathways may also be physically separated within cell subtypes of the tubules.
Seasonal Variations of Pineal Involvement in the Circadian Organization of the Ruin Lizard Podarcis Sicula
Authors: Innocenti A. , Bertolucci C. , Minutini L. , Foà A.
Published: April 2021

To establish whether the effects of pinealectomy on circadian locomotor rhythmicity vary with season, we examined, in constant temperature and darkness, the locomotor behaviour of ruin lizards Podarcis sicula collected and subjected to pinealectomy at different times of the year. Changes in the freerunning period in response to pinealectomy were found to be significantly greater in summer than in winter, spring and autumn. Circadian activity time changed significantly in response to pinealectomy only in spring and summer. Furthermore, while pinealectomy was effective in altering the locomotor rhythms of all individual lizards tested in summer, the same surgery was found to leave locomotor rhythmicity of many lizards tested in autumn and winter completely undisturbed. These results demonstrate for the first time in a non-mammalian vertebrate that the pineal gland is centrally involved in determining circadian organization in some seasons and is only marginally involved in others.