bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlations of the Position of Center of Body Mass With Butterfly Escape Tactics
Authors: Srygley Robert B. , Dudley Robert
Published: April 2021

Using the evolution of neotropical butterflies as a natural experiment, we examine Ellington’s biomechanical hypothesis that the position of center of body mass affects insect maneuverability. We find that the position of center of body mass is correlated with the butterflies’ palatability, natural flight speeds and their ability to evade predators in a small cage. Relative to distasteful species, palatable butterflies fly faster and maneuver more successfully to evade attacks from aerial predators. The large thorax and short abdomen of palatable species position the center of body mass near to the wing base, whereas the mass allocation and body shape of distasteful butterflies position center of body mass further posteriorly. The position of center of body mass is an important indicator of flight performance, including both aerial maneuverability and flight speed, that warrants incorporation into future studies of invertebrate and vertebrate flight.
Body Size, Muscle Power Output and Limitations on Burst Locomotor Performance in the Lizard Dipsosaurus Dorsalis
Authors: Johnson Timothy P. , Swoap Steven J. , Bennett Albert F. , Josephson Robert K.
Published: April 2021

The power output of fast-glycolytic (FG) muscle fibres isolated from the iliofibularis (IF) muscle of desert iguanas (Dipsosaurus dorsalis) was measured at 35°C using the oscillatory work-loop technique. To simulate cyclical muscle length changes during running, isolated fibre bundles were subjected to sinusoidal length changes and phasic stimulation during the strain cycle. At constant strain (12%), the duration and timing (phase) of stimulation were adjusted to maximise power output. Using both hatchlings (4–8g) and adults of varying sizes (15–70g), the intraspecific allometries of IF length and contractile properties were described by regression analysis. The muscle length at which isometric force was maximum ( L0, mm) increased geometrically with body mass (M, g) (L0=5.7M0.33). Maximum power output and the force produced during shortening showed no significant relationship to body size; work output per cycle (Wopt, Jkg−1) under conditions required to maximise power did increase with body size (Wopt=3.7M0.24). Twitch duration (Td, ms), measured from the onset of force generation to 50% relaxation, increased allometrically with body mass (Td=12.4M0.18). Limb cycling frequency during burst running (f, reported in the literature) and the frequency required to maximise power output in vitro (fopt) decreased with body size, both being proportional to body mass raised to the power 0.24. These findings suggest that limb cycling frequency may be limited by twitch contraction kinetics. However, despite corresponding proportionality to body size, limb cycling frequencies during burst running are about 20% lower than the cycling frequencies required to maximise power output. Differences in the contractile performance of the IF in vitro and in vivo are discussed in relation to constraints imposed by gravitational forces and the design of muscular, nervous and skeletal systems.
Odor Sensitivity of Cultured Lobster Olfactory Receptor Neurons is Not Dependent on Process Formation
Authors: Fadool D. A. , Michel W. C. , Ache B. W.
Published: April 2021

Cultured lobster olfactory receptor neurons (ORNs) were surveyed for their odor sensitivity with whole-cell, voltage-clamp recording. The nature of the adequate stimuli, the degree of tuning (response spectra) of the cells, the threshold of sensitivity and the dual polarity of the odor-evoked currents are consistent with chemosensitivity in the cultured ORNs being olfactory. The ability of odors to evoke currents in cultured ORNs that lack processes suggests that lobster ORNs can be induced in vitro to insert all the elements of the transduction cascade in the soma, including those that might normally be confined to processes. This should greatly facilitate analysis of olfactory transduction in these cells.
The Modulatory Effects of Serotonin, Neuropeptide F1 and Proctolin on the Receptor Muscles of the Lobster Abdominal Stretch Receptor and Their Exoskeletal Muscle Homologues
Authors: Pasztor Valerie M. , Golas Lillian B.
Published: April 2021

The muscle receptor organ (MRO) of the lobster is a complex proprioceptive system lying in parallel with the axial extensor musculature. Two peripherally located sensory neurones extend stretch-sensitive dendrites into individual receptor muscle strands one tonic (RM1) and one phasic (RM2). Previous studies have shown that the sensitivity of the sensory neurones to passive stretch could be enhanced by serotonin and proctolin. Here we show that the receptor muscles and their exoskeletal muscle homologues are also responsive to serotonin, proctolin and, in addition, to neuropeptide F1 (TNRNFLRF-NH2).

Two measures of motor performance were enhanced by all three neurohormones: EJP amplitude and nerve-evoked tension development. Serotonin was the most effective modulator of both tonic and phasic muscles. F1 had powerful effects on the phasic extensor muscle. A low incidence of tonic muscle fibres with synapses responding to the neurohormones suggests that there are distinct populations of synapses: those sensitive to specific modulators and others that are insensitive. These findings, taken together with the enhancing effects of modulation on the primary sensory afferents, suggest that circulating neurohormones may act at multiple loci in the MRO system in a concerted and hormone-specific manner to alter the flow of proprioceptive feedback.
The Role of the Spleen During Exercise in the Antarctic Teleost, Pagothenia Borchgrevinki
Authors: Franklin Craig E. , Davison William , Mckenzie Jan C.
Published: April 2021

Physiological changes in fish associated with swimming are highly dependent on the intensity of exercise performed (Wood, 1991). Swimming at high speed requires large increases in the delivery of oxygen to the tissues and the circulatory system must be able to meet this demand. Exercise at a speed great enough to cause exhaustion results in an elevation in haematocrit (Hct), which can increase the oxygen content of the blood. The magnitude of the Hct increase varies among different species of fish, although generally the increase is about 50% (Milligan and Wood, 1987; Wells and Weber, 1990; Yamamoto et al. 1980; Yamamoto and Itazawa, 1989). The antarctic cryopelagic teleost Pagothenia borchgrevinki (Boulenger, 1902, see also Notothenia hodgsoni) appears to be an exception as exercise produces an increase in Hct of more than 110% (Davison et al. 1988), an increase approximately 2–4 times greater than that in other species of fish studied.
A Novel Pattern of Embryonic Nutrition in a Viviparous Reptile
Authors: Stewart James R. , Thompson Michael B.
Published: April 2021

Vitellogenesis and placental transfer both contribute substantially to embryonic nutrition in the viviparous scincid lizard Pseudemoiaentrecasteauxii. Neonatal wet mass was 396% greater than egg wet mass and neonatal dry mass was 168% greater than egg dry mass. We estimate that 49% of the organic molecules for embryonic growth and metabolism were provided by placental nourishment. This pattern of embryonic nutrition, in which ovarian and uterine contributions are approximately equivalent, has not been reported previously for reptiles. Female Bassiana duperreyi, a closely related oviparous species, produced larger clutches of larger eggs. Although there was a great disparity in egg mass between these two species, differences in newborn composition were less pronounced. Mean dry mass, adjusted for female size, of B. duperreyi eggs was 135% greater than mean dry mass of P. entrecasteauxii eggs, yet mean dry mass of B. duperreyi offspring was only 21% greater than that of P. entrecasteauxii offspring. Embryonic gains in water and inorganic salts during gestation in P. entrecasteauxii were substantial and resulted in the production of neonates that contained greater quantities of these variables compared to offspring of B. duperreyi. These data confirm Weekes’ hypothesis that P. entrecasteauxii is matrotrophic and support her hypothesis that this species has undergone evolutionary reduction in yolk quantity.
Propranolol Impairs the Hyperventilatory Response to Acute Hypercapnia in Rainbow Trout
Authors: Kinkead R. , Aota S. , Perry S. F. , Randall D. J.
Published: April 2021

This study investigated the possible role of catecholamines in the ventilatory response of rainbow trout (Oncorhynchus mykiss) to acute external hypercapnia. The ventilatory response to hypercapnia [partial pressure of CO2 in water of fish pre-treated with the selective β-adrenoceptor antagonist, D,L-propranolol, was compared with that of D-propranolol (an isomer with minimal β-antagonistic activity) and saline pre-treated fish (sham). A sustained 3.6-fold increase in gill ventilation volume was observed in the sham and D-propranolol-treated groups during the 30min interval of hypercapnia. Fish pre-treated with D,L-propranolol displayed a blunted hyperventilatory response to hypercapnia (1.9-fold increase at 30min). These results indicate that the β-component of an adrenergic response is involved in the usual hyperventilatory response to external hypercapnia. It is suggested that the impaired hyperventilatory response of the D,L-propranolol-treated group reflects an inhibition of central adrenergic mechanism(s) involved in the hyperventilatory reflex to respiratory acidosis.
Osmoregulation in the Parasitic Nematode Pseudoterranova Decipiens
Authors: Fusé M. , Davey K. G. , Sommerville R. I.
Published: April 2021

When subjected to hyper-or hypo-osmotic stress at 5°C for 24h, third-stage larvae of the parasitic nematode Pseudoterranova decipiens do not exhibit changes in mass or in the osmotic pressure of the pseudocoelomic fluid. Immersion in solutions containing 3H2O demonstrates that exchange with the water in the pseudocoelomic fluid is substantially complete within 24h. Sacs composed of cylinders of body wall without the intestine and pseudocoelomic fluid do not gain weight when immersed for 24h in hypotonic medium. Metabolic poisons abolish the ability of whole worms and sacs to maintain their weight when immersed in hypotonic media. These observations support the conclusion that the nematode is capable of at least short-term osmoregulation and that the site of osmoregulation is the body wall. The observations that more fluid is passed from the anus in some hypo-osmotically stressed worms and that worms ligatured at the tail exhibit a small increase in mass when exposed to hypo-osmotic conditions may indicate that the intestine plays a minor and subsidiary role in osmoregulation.
Allosteric Control of Oxygen Binding by Haemoglobin During Embryonic Development in the Crocodile Crocodylus Porosus: The Role of Red Cell Organic Phosphates and Carbon Dioxide
Authors: Grigg G. C. , Wells R. M. G. , Beard L. A.
Published: April 2021

The P50 of whole blood [30°C, (15.6mmHg)] decreases during embryonic development from approximately 6.7kPa (50mmHg) at 15 days to about half this value at hatching (86 days), paralleling a decrease in ATP from 100 to 5–10 μmol g−1 Hb. There is also a progressive changeover from embryonic to adult haemoglobin (HbA). A pulse of 2,3-diphosphoglycerate (2,3-DPG) (18μmol g−1 Hb) occurs late in embryonic life. It has no effect on whole-blood oxygen-affinity and falls rapidly at hatching to values typical of post-hatchling crocodilians in general (<1.0 μmol g−1 Hb). ATP has a marked effect on the oxygen affinity of embryonic haemoglobin (HbE) but not on HbA. 2,3-DPG has only very small effects on the oxygen affinities of HbE and HbA. CO2 has a small effect on the oxygen affinity of HbE but a marked effect on that of HbA. Values of measured in the chorio-allantoic artery [2.9kPa (22mmHg)] and vein [5.9kPa (52mmHg)] imply an increase in saturation from approximately 30% to more than 80%. Neither whole-blood oxygen-affinity nor ATP level was altered in response to an experimental 7-day exposure to low ambient oxygen levels [10.7kPa (80mmHg)]. The results do not lend themselves easily to the pan-selectionist paradigm in which all physiological traits are viewed as being adaptive.
The Effect of Thermal Acclimation And Exercise Upon The Binding of Glycolytic Enzymes in Muscle of the Goldfish Carassius Auratus
Authors: Huber Maria , Guderley Helga
Published: April 2021

To examine whether the changes in metabolic organization induced by thermal acclimation modify glycolytic enzyme-binding, we acclimated goldfish, Carassius auratus, to 8 and 25 °C and measured the binding of phosphofructokinase (PFK), aldolase, pyruvate kinase and lactate dehydrogenase to subcellular particles in red and white muscle. When fish were sampled at rest at their acclimation temperature, only the percentage binding of PFK in red muscle was altered by thermal acclimation. By contrast, exhausting exercise at 15 °C led to markedly higher levels of binding of PFK in muscle of warm-than of cold-acclimated fish. This pattern was apparent in both red and white muscle. The specific activity of PFK in red muscle declined with exhausting exercise in warm-but not in cold-acclimated fish. In contrast, the units of PFK bound per gram of muscle did not differ in exhausted warm- and cold-acclimated fish. Cold-and warm-acclimated fish did not differ in their accumulation of lactate in white muscle at exhaustion. Furthermore, the PFK from white muscle of warm- and cold-acclimated fish did not differ in the pH dependence of binding to subcellular particles. These changes in the dynamics of PFK binding with temperature acclimation suggest that soluble PFK may be more susceptible to exercise-induced inhibition in warm- than in cold-acclimated goldfish. While the percentage binding and the specific activity of the other glycolytic enzymes were little affected by exhausting exercise, the units of aldolase bound per gram of white muscle decreased with exercise in warm-acclimated fish.
Fluid Uptake And The Maintenance of Blood Volume in Octopus
Authors: Wells M. J. , Wells J.
Published: April 2021

The replacement of fluid following withdrawal of up to 40% of the blood from Octopus vulgaris can be tracked over a period of days by measuring the dilution of haemocyanin, which is not simultaneously replaced. Haemocyanin concentration was measured from the copper content or the oxygen-carrying capacity of further small blood samples. Fluid lost was replaced within 1–2h, provided that the digestive gland ducts were left intact. If these were ligated, the haemocyanin concentration remained the same as before withdrawal of the initial large blood sample and the animals died within a few hours. Evidence presented elsewhere has indicated that the site of the fluid uptake is the digestive gland appendages. Urine production would be continued or increased during the restoration of blood volume. When urine volume is added to the volume of fluid replaced, it appears that this fluid transport system must be capable of moving at least its own volume of fluid from the gut into the blood every 5min. An immediate consequence of blood withdrawal is a fall in blood pressure and pulse amplitude, followed within minutes by a transient rise to high blood pressures, apparently as a result of an increase in peripheral resistance as circulation to the arms is restricted, conserving the blood for vital central organs. Following these transient swings, the diastolic blood pressure returns to normal values despite blood loss; pulse amplitude returns as blood volume is replaced. Duct-ligated animals continue to show a reduced pulse.
Beating of Cilia of Sea Urchin Embryos: A Critical Comparison of the Normal and Reversed Beating of Cilia of Isolated Cells
Authors: Mogami Yoshihiro , Sekiguchi Shima , Baba Shoji A.
Published: April 2021

Two different types of ciliary beating, normal and reversed, were analyzed on the same cilia on cells isolated from echinoplutei. Bends on the cilium in reversed beating were observed to increase in curvature during propagation in the effective stroke of the beat, whereas in normal beating, bends propagate with a constant curvature in both effective and recovery strokes. The proximal region of the cilium showed an almost identical oscillation of shear angle in both normal and reversed beating with respect to the time normalized to the average beat period, which was determined by the rotational movement of the cell body. In reversed beating, a common temporal profile generated at the proximal region was preserved in the oscillation over the length of the cilium. The local oscillations in normal beating, however, changed in temporal profile as seen from base to tip. The conversion of the temporal oscillatory profile from normal to reversed beating occurred in association with changes in the centre of the oscillation (static bias), whose difference increased with the distance from the base. The data indicate that the changes in bending pattern between normal and reversed beating of sea urchin embryo cilia are not due to changes in the initiation of the oscillation at the base, but largely to temporal and static changes in the pattern of propagation of the oscillatory activity.
Characterization of insect sense organs and optical clearing of whole-mount preparations using diI in fixed tissues
Authors: Zill Sasha N. , Frazier S. Faith , Macfarland Dawn L. , Fish Stephen E.
Published: April 2021

Studies of invertebrate sensory receptors have been greatly aided by the use of compounds, such as cobalt salts, which can diffuse or be transported in peripheral nerves, to characterize morphologically and to label identified exteroceptive and proprioceptive sense organs (Bräunig, et al. 1981). However, most of these methods require the maintenance of live preparations, which can be difficult when attempting to fill axons over long distances. We have mapped sense organs of the cockroach leg using the carbocyanine dye, diI. This lipid-soluble dye, recently developed for use in vertebrates (Honig and Hume, 1989), diffuses passively in neuronal membranes and can be used in fixed tissues. However, because of its lipid solubility, it has the disadvantage that it dissolves in standard organic clearing agents. We have developed methods of applying diI and clearing cockroach preparations that permit the visualization of both sensory neuron somata under fluorescent illumination and their associated cuticular specializations by conventional light microscopy. These experiments have confirmed the location of many receptors previously identified by serial sectioning and light microscopy (Dresden and Nijenhuis, 1958; Nijenhuis and Dresden, 1952, 1956). We have also mapped sense organs on the distal leg segments and demonstrated the widespread presence of multiply innervated, chemoreceptor-like sense organs on all segments of the cockroach mesothoracic and metathoracic legs.
The In Vitro Effect of Hypoxia on the Trout Erythrocyte β-Adrenergic Signal Transduction System
Authors: Reid Scott D. , Lebras Y. , Perry S. F.
Published: April 2021

We have investigated the effects of acute in vitro hypoxia on trout (Oncorhynchus mykiss) erythrocytes in order to elucidate the mechanism(s) by which increased catecholamine responsiveness of the Na+/H+ antiporter is achieved. Blood was withdrawn from cannulated trout and maintained in vitro under normoxic or hypoxic conditions for 30min prior to exposure to concentrations of noradrenaline, forskolin or 8-bromo-cyclic AMP ranging from 0 to 10−6 mol l−1, 10−7 to 10−5 mol l−1 or 10−4 to 10−2 mol l−1, respectively. Na+/H+ exchange activity was quantified as the maximal reduction in whole-blood pH (pHe) after addition of the various Na+/H+ antiporter activators. Erythrocyte intracellular cyclic AMP contents were also determined after addition of noradrenaline or forskolin. To complete the investigation, radioreceptor binding assays were conducted on separate blood samples to characterize the numbers and affinities of the surface population of β-adrenoceptors of erythrocytes maintained under normoxic or hypoxic conditions.

Exposure of erythrocytes to noradrenaline, forskolin or 8-bromo-cyclic AMP resulted in dose-dependent reductions in pHe as a result of Na+/H+ antiporter activation. In all cases, the effects were significantly more pronounced under hypoxic than normoxic conditions. Hypoxia significantly increased the production of cyclic AMP in the presence of noradrenaline but did not affect the forskolin-induced production of cyclic AMP. Blood oxygen status also affected the number of β-adrenoceptors expressed at the erythrocyte surface; hypoxic erythrocytes possessed 880.7±28.6 (N=6) receptors per cell whereas normoxic erythrocytes possessed 532.6±43.2 (N=6) receptors per cell.

These results suggest that in vitro exposure of trout erythrocytes to hypoxic conditions results in at least two significant alterations in the catecholamine signal transduction system: (1) an enhancement in erythrocyte cyclic AMP production, in part by virtue of an increase in the number of surface β-adrenoceptors, and (2) a hypoxia-induced increase in the cyclic AMP sensitivity of one or more of the steps culminating in Na+/H+ antiporter activation. These events ultimately increase the responsiveness of the erythrocyte Na+/H+ antiporter to catecholamines during hypoxia.
Glycogen Loss in Rat Muscles During Locomotion on Different Inclines
Authors: Armstrong R. B. , Taylor C. R.
Published: April 2021

Running downhill causes structural damage in deep slow-twitch extensor muscles of the limbs. Both mechanical and metabolic hypotheses have been proposed to explain the damage. The purpose of this study was to use measurements of glycogen loss in the muscles and metabolic rates of rats running on the level and up and down 16° inclines at 26 m min−1 to try to distinguish between these hypotheses. Glycogen loss in the soleus and medial head to the triceps brachii muscles during running on the three inclines was proportional to whole-animal oxygen consumption, indicating that there were no unusual metabolic demands on these muscles during the downhill exercise. The minimum area of these muscles showing glycogen loss was smaller during downhill than during uphill running. Average forces in the muscles are similar during locomotion on different inclines at the same speed, suggesting that stresses in the active motor units were greater during downhill running. Thus, the results are more consistent with a mechanical than with a metabolic etiology for the muscle injury resulting from downhill running.
Mitochondrial Activity in Rainbow Trout Red Muscle: the Effect of Temperature on the Adp-Dependence of Atp Synthesis
Authors: Blier Pierre U. , Guderley Helga E.
Published: April 2021

By coupling mitochondrial ATP production to an enzymatic NADPH-producing reaction, we monitored the rates of ATP production spectrophotometrically. ATP production was coupled to the oxidation of malate and pyruvate. Interference by adenylate kinase was eliminated by using P1,P5-di(adenosine-5′)pentaphosphate and we found no interference by NADPH oxidase. We studied the kinetics of ATP synthesis by mitochondria from rainbow trout red muscle at three temperatures (8, 15 and 22°C) and under two pH regimes (a constant pH of 7.4 and temperature-dependent pH). The mitochondria oxidized pyruvate and malate. The apparent Michaelis constant (Km,app) for ADP as well as the maximal velocity (Vmax) for ADP phosphorylation are markedly affected by temperature but not by pH. The Km,app for ADP decreases with increasing temperature while the Vmax increases. These data suggest that reduced temperatures decrease mitochondrial sensitivity to control by ADP availability.
Influence of Dietary Sodium and Other Factors on Plasma Aldosterone Concentrations and in Vitro Properties of the Lower Intestine in House Sparrows (Passer Domesticus)
Authors: Goldstein David L.
Published: April 2021

House sparrows ( Passer domesticus) had plasma aldosterone concentrations of about 180pgml−1 while maintained on a low-sodium diet (LS, 0.1mequiv Na+ ingested per day), 135pgml−1 on a sodium intake of 0.9mequivday−1 (high-salt diet, HS) and 45pgml−1 on a Na+ intake of 3.8mequivday−1 (high-salt diet with saline drinking water, HSS). The plasma concentration of aldosterone changed to the LS or the HS level within 1 day of switching from the HS or the LS diet, respectively. Neither dehydration (22h, 14.5% loss in body mass) nor brief periods of stress (1–5min of handling) caused a change in circulating levels of aldosterone. The electrical properties of the lower intestine acclimated to the different sodium intakes with a time course similar to that of the changes in aldosterone levels. On the LS diet, the lower intestine generated an electrical potential difference (PD) of 5mV (lumen negative) and a short-circuit current (Isc) of about 50 μA cm−2; these were consistently inhibited by amiloride (resulting in a lumen-positive PD) and were stimulated by glucose or amino acids (leucine and lysine) in about half of the tissues. In HS birds, the PD and Isc were abolished and the effects of glucose and amino acids were reduced, but amiloride still caused a significant change in transmural PD (to a mucosa-positive value). These properties resemble those of the chicken coprodeum more than they do those of chicken colon, although the tissues tested were from the mid-region of the large intestine and their histology resembled that of colon. Sparrows tested immediately upon capture from the wild had plasma aldosterone levels not significantly different from those of birds on the LS diet, which is consistent with the known diet of this species. However, Isc was higher and tissue resistance was lower in wild birds compared with low-salt birds in the laboratory, perhaps indicating the influence of other hormones in addition to aldosterone.
Contractile Properties of the Striated Adductor Muscle in the Bay Scallop Argopecten Irradians At Several Temperatures
Authors: Olson John M. , Marsh Richard L.
Published: April 2021

The isometric and isotonic contractile properties of the cross-striated adductor muscle of the bay scallop (Argopecten irradians) were measured in vitro at 10, 15 and 20°C. The length at which twitch force was maximal as a function of the closed length in situ (L0/Lcl) averaged 1.38±0.01 (mean ± S.E.M.) at 10°C. This length is very close to the typical length at maximum gape during natural swimming at this temperature. Passive force was very low over the range of lengths measured here; at L0, passive force averaged approximately 0.08 N cm−2, or only 0.5% of the corresponding peak twitch force. The mean peak isometric twitch force (Ptw,max) at 10°C was 21.43±0.68 N cm−2 (S.E.M.), and the ratio of peak twitch force to tetanic force (Ptw,max/P0) averaged 0.89±0.01. Temperature did not affect either twitch force (Ptw), once fatigue was taken into account, or Ptw,max/P0. In contrast, the time-related properties of twitch contractions (latent period, tL; time to peak tension, tPtw; and time from peak tension to half-relaxation, t50%R) were positively modified by temperature at all temperatures measured (Q10>1.8). All three properties were more temperature-sensitive over the range 10–15°C than over the range 15–20°C.

The force–velocity relationships of the striated adductor muscle were fitted to the hyperbolic-linear (HYP-LIN) equation. The force–velocity curves of the striated adductor muscle of the scallop were strongly influenced by temperature. Maximal velocity at zero force (Vmax), and therefore maximal power output, increased significantly with temperature. The Q10 over the temperature range 10–15°C (1.42) was significantly lower than that over the range 15–20°C (2.41). The shape of the force–velocity relationship, assessed through comparisons of the power ratio (Ẇmax/VmaxP0), was not influenced by temperature.
The Physiology of the Alligator Heart: Left Aortic Flow Patterns and Right-To-Left Shunts
Authors: Jones David R. , Shelton Graham
Published: April 2021

Blood pressures have been recorded in the heart along with pressures and flow in the aortic arches of anaesthetized and awake alligators. Systemic blood pressures were significantly lower [5.22±0.57kPa (N=3) versus 9.85±0.46kPa (N=5)] and cardiac outputs higher [51.6±3.5mlmin−1 kg-1 (N=3) versus 25.5±8.2mlmin−1 kg-1 (N=5)] in awake compared with anaesthetized animals. Using pharmacological interventions, two types of right-to-left shunt could be induced in all alligators. In one, established after acetylcholine (ACh) injection into the right side of the circulation, left aortic flow was an anterograde monophasic pulse which occurred when pulmonary pressure exceeded systemic blood pressure. Hence, this left aortic flow pattern could also be induced by mechanical occlusion of both pulmonary arteries. About one-quarter of cardiac output could bypass the lungs during this shunt. However, this left aortic flow pattern was never seen under any conditions other than pharmacological intervention. In the other type of shunt, induced pharmacologically by ACh injection into the left side of the circulation, left aortic flow was biphasic with a period of backflow, initiated during systole, being progressively shortened by the onset of forward flow from the right ventricle. Establishment of this type of shunt depended on the magnitude of both the systemic pressure and the pressure generated by right ventricular contraction after closure of the pulmonary outflow tract. The amount of blood bypassing the lungs during this shunt was small (13.7±5% of cardiac output) but, at maximum, could be almost 25% of cardiac output. This shunt occurred naturally in resting animals and could be maintained for substantial periods (13.2min). The present observations confirm those made previously on anaesthetized alligators and extend previous work by showing two potential types of shunt. Finally, we suggest that right-to-left blood shunting in crocodilians may be related to the ‘alkaline tide’ that occurs after feeding, so the unique design of the central cardiovascular system in crocodilians could relate to both gastrointestinal and cardiorespiratory physiology.
Plateau Potentials in an Insect Motoneurone can be Driven by Synaptic Stimulation
Authors: Hancox Jules C. , Pitman Robert M.
Published: April 2021

Cyclical patterns of behaviour such as respiration and locomotion are generated by groups of neurones whose output depends not only upon their synaptic interconnections but also on the intrinsic membrane properties of individual cells. For example, the ionic conductances of some neurones in rhythm-generating circuits allow these cells to respond to non-patterned excitatory synaptic drive with ‘plateau’ or ‘driver’ potentials: prolonged, regenerative depolarizations which can drive bursts of impulses and, thereby, contribute to characteristics of the motor rhythm (Russell and Hartline, 1978, 1982; Tazaki and Cooke, 1979a–c, 1983a–c, 1986, 1990). Plateau potentials are not restricted to interneurones of the central pattern generator; they may also be recorded from motoneurones, which form the final output to muscles. Thus, plateau potentials have been recorded from locomotor motoneurones from the crayfish (Sillar and Elson, 1986), lamprey (Wallén and Grillner, 1987), cat (Hounsgaard et al. 1988) and turtle (Hounsgaard and Kiehn, 1989) (see also review by Kiehn, 1991).
Roles of Buffering Capacity and Pentose Phosphate Pathway Activity in the Gas Gland of the Gulf Toadfish Opsanus Beta
Authors: Walsh Patrick J. , Milligan C. Louise
Published: April 2021

The teleost gas gland is truly remarkable in its abilities to secrete gases into the swim bladder of physoclistous fish. The physiological and metabolic adaptations of this tissue have been elegantly summarized in a recent review article by Pelster and Scheid (1992). There are two key contributors to the function of the gland. First, a specialized metabolism of the swim bladder, involving copious and simultaneous production of lactate and CO2 from anaerobic glycolysis and the pentose phosphate pathway (also known as the hexose monophosphate shunt), respectively, contributes to gas exchange through pH and salting-out effects on the oxygen-carrying capacity of the blood. Second, a countercurrent multiplier system (i.e. a rete mirabile) enables gas tensions to be elevated further by back diffusion. Several features of metabolism and acid–base physiology remain unclear. First, despite the remarkable ability of this tissue to produce acid, it is not clear if or how intracellular pH (pHi) is regulated. Since ultimately the blood must be acidified, one would predict that the pHi of the tissue would be well regulated via high rates of membrane exchange of protons and/or high tissue buffering capacity. Second, although the functioning of the pentose phosphate pathway has been strongly inferred from measurements of enzyme activities (Boström et al. 1972; Pelster and Scheid, 1991), and from measurements of enhanced rates of CO2 excretion relative to the rates of oxygen uptake (Pelster et al. 1989), direct evidence for the existence of the shunt is lacking. Lastly, although the pentose phosphate pathway is expected to produce CO2, and thus contribute to the acidification of blood entering the gland, the pathway may have a different primary, or perhaps a dual, role, namely to maintain high tissue levels of NADPH for protection against oxygen radical damage to cells (Pelster and Scheid, 1992). The composition of the gas stored in the swim bladder can approach pure oxygen in some species, so it is not surprising that the teleost gas gland contains substantial levels of the enzymes catalase, superoxide dismutase and glutathione peroxidase, which scavenge deleterious radicals of oxygen and related harmful compounds (Morris and Albright, 1984). Noteworthy is glutathione peroxidase, which requires a constant supply of NADPH (presumably from the shunt) to maintain glutathione in a reduced state. Reduced glutathione is then used in a variety of oxygen radical detoxification mechanisms. If the pentose phosphate pathway has a role in oxygen detoxification, one would predict that flux rates through the pathway would increase with increased oxygen levels.
Calcium Channel Currents In Neurones From Locust (Schistocerca Gregaria) Thoracic Ganglia
Authors: Pearson H. A. , Lees G. , Wray D.
Published: April 2021

Using the patch-clamp technique, Ca2+ channel currents were recorded from neurones freshly isolated from the thoracic ganglia of the desert locust Schistocerca gregaria. In solutions containing 10mmol l−1Ba2+ we observed high-voltage-activated whole-cell inward currents with sustained and transient components, both of which had similar steady-state inactivation properties. Substitution of Ca2+ for Ba2+ was found to reduce whole-cell currents, whereas removal of monovalent cations had no effect. Cd2+ (1mmol l−1) completely blocked the whole-cell current, but at 10 μmol l−1 preferentially inhibited the sustained component without affecting the transient component. Verapamil (1 μmol l−1) inhibited both current components but appeared to be more selective for the sustained component, whereas nitrendipine (1 μmol l−1) had no effect on either component. A single-channel recording suggested that the transient component was carried by a low-conductance channel. Certain compounds with insecticidal action (ryanodine, S-bioallethrin, deltamethrin and avermectin) did not affect calcium channel currents in these cells. These data suggest that there are two types of Ca2+ channels present in locust neurones. These channel types have properties differing from the T-, L- and N-type channels found in vertebrates and, furthermore, were not targets for the insecticides we tested.
The Regulation of Haemolymph Potassium Activity During Initiation and Maintenance of Diuresis in Fed Rhodnius Prolixus
Authors: Maddrell S. H. P. , O’donnell M. J. , Caffrey R.
Published: April 2021

The blood-sucking insect Rhodnius prolixus rapidly eliminates a Na+-rich K+-poor urine after its large meals. K+-rich fluid is first secreted by the upper Malpighian tubules and passes to the lower tubules where most of the potassium is reabsorbed.

During the initial stimulation of the tubules, the lower tubules must be activated first to avoid loss of potassium. The major element in this is that they respond more rapidly than do the upper tubules to particular hormonal concentrations rather than that they react to lower hormonal concentrations than do the upper tubules.

During subsequent diuresis, regulation of the haemolymph potassium concentration depends on three cooperative homoeostatic mechanisms in the tubules. A fall in potassium concentration of the medium bathing the tubules causes (i) a decrease in the rate of fluid secretion by the upper tubules, (ii) a decrease in potassium concentration in the fluid secreted by the upper tubules and (iii) an increase in the rate of potassium absorption by the lower tubules. The tubules respond in the opposite direction to an increase in potassium concentration of the medium. As a result, the potassium concentration of the urine can be adjusted to match the potassium concentration of the fluids absorbed from the gut, so that the potassium concentration of the insect’s haemolymph remains unaltered.
in vivo Utilization of Glucose by Heart and Locomotory Muscles of Exercising Rainbow Trout (Oncorhynchus Mykiss)
Authors: West Timothy G. , Arthur Peter G. , Suarez Raul K. , Doll Christopher J. , Hochachka Peter W.
Published: April 2021

In vivo rates of glucose utilization were estimated in red muscle and heart of rainbow trout using the radiolabeled glucose analogue, [14C]-2-deoxyglucose ([14C]-2-DG). The 2-DG ‘lumped constant’ (LC), representing the uptake ratio between 2-DG and glucose for each tissue, was determined in vitro using tissue slices. For both red muscle and heart, the LC was approximately 0.40. In addition, changes in circulatory glucose utilization induced in an isolated trout heart preparation had no effect on the LC. The LC was applied to calculations of in vivo rates of circulatory glucose disposal in muscle tissue of resting and swimming trout. Utilization was estimated at 0.87±0.15 and 5.31±1.04nmol g−1 min−1 in red muscle and heart of resting fish, respectively. In trout swimming at 80 % Ucrit, glucose utilization in heart was unchanged compared to resting controls, while red muscle utilization increased by 28-fold. Estimates of the oxidative demand of heart and locomotory muscle of swimming trout indicate that glucose utilization accounted for less than 10% of the energy production in both tissues. In trout heart, in vitro measures of glucose flux suggest an apparent excess capacity to use circulatory glucose. Preference for other intra-and extramuscular fuels may partially explain limited glucose utilization, but it remains unclear to what degree, and under what conditions, glucose utilization may be increased in vivo.
Intracellular-Messenger-Mediated Cation Channels in Cultured Olfactory Receptor Neurons
Authors: Stengl Monika
Published: April 2021

After 2–3 weeks in culture, pupal olfactory receptor neurons from the antennae of male Manduca sexta respond to their species-specific sex pheromone by opening cation channels. These pheromone-dependent cation channels are the only channels previously found in cultured olfactory neurons that promote inward currents at membrane potentials more negative than the resting potential. The pheromone-dependent currents depend on external Ca2+ concentration. They are inwardly rectified with 10−7 mol l−1 external Ca2+ and linear with 6mmol l−1 Ca2+. This paper shows that perfusion of cultured olfactory receptor neurons with GTPγS, ATP, inositol 1,4,5,-trisphosphate or 10−6moll−1 Ca2+ elicits cation currents resembling the pheromone-dependent cation currents in expressing inward rectification with 10−7 mol l−1 external Ca2+ and being linear at external Ca2+ concentrations of 2 μmol l−1 or more. Stimulation with protein kinase C also elicits cation currents that share properties with the pheromone-dependent cation currents. All agent-induced cation currents appear to depend either directly or indirectly on Ca2+concentration.
Metabolic Heat Production by Artemia Embryos Under Anoxic Conditions
Authors: Hontoria Francisco , Crowe John H. , Crowe Lois M. , Amat Francisco
Published: April 2021

The metabolic status of encysted Artemia embryos under anoxic conditions has been studied by calorimetry. Previous work demonstrated a very low, but still measurable, source of metabolic heat (31nWmg-1 drymass) after 6 days of anoxia, attributed to the catabolism of small amounts of carbohydrate storage compounds and the unusual nucleotide diguanosine tetraphosphate. Our results indicate that the heat measured drops below the detection limits of our calorimeter (11nWmg-1 drymass) after 1.5h of anoxia, in sharp contrast with previously published results. The possible sources of error that could explain this difference, and a re-evaluation of the metabolic status of cysts during anoxia, are discussed. We conclude that if the cysts are carefully protected from oxygen they become essentially ametabolic.
Membrane Permeability and Utilization of L-Lactate and Pyruvate in Carp Red Blood Cells
Authors: Tiihonen Kirsti , Nikinmaa Mikko
Published: April 2021

L-Lactate and pyruvate permeability and utilization in carp (Cyprinus carpio) red blood cells was studied in vitro with tracer methods. Transport of lactate and pyruvate across the carp red blood cell membrane is rapid. At low plasma concentrations, lactate and pyruvate are transported into carp red blood cells mainly via a specific monocarboxylate carrier. This is shown by a study of the saturation kinetics and by inhibition using α-cyano-4-hydroxycinnamic acid and, more powerfully, p-chloromercuriphenylsulphonic acid. At higher plasma concentrations both simple diffusion and, apparently, the band 3 anion exchange system become increasingly important transport pathways. Carbon dioxide production rates from lactate and pyruvate as a function of their extracellular concentrations showed saturation kinetics. The transport rates of lactate and pyruvate are considerably higher than those required for their maximal rate of oxidation. The rapid transport of lactate and pyruvate into carp red blood cells thus guarantees that substrate availability is not the rate-limiting factor for the oxidation of these substrates.
Serotonin-Mediated Release of Catecholamines in the Rainbow Trout Oncorhynchus Mykiss
Authors: Fritsche Regina , Reid Steve G. , Thomas Serge , Perry Steve F.
Published: April 2021

The effects of serotonin (5-hydroxytryptamine; 5-HT) on catecholamine release from chromaffin tissue were investigated in the rainbow trout (Oncorhynchus mykiss) in vivo and in situ. Intra-arterial injections of serotonin in vivo caused dose-dependent (50–250nmolkg−1) increases in both plasma noradrenaline and adrenaline levels. Pre-treatment of fish with the serotonergic receptor antagonist methysergide did not abolish these increases.

An in situ saline-perfused head kidney preparation was developed and validated to study the potential direct effect of serotonin on catecholamine release. The chromaffin cells in the preparation showed a dose-dependent release of catecholamines in response to bolus injections of the cholinergic receptor agonist carbachol (10−7–10−4 molkg-1). The carbachol-induced release of noradrenaline, but not of adrenaline, was reduced significantly when the nicotinic receptor antagonist hexamethonium (10−4 mol l−1) was present in the perfusion fluid. The removal of calcium from the perfusion fluid prevented the usual release of catecholamines evoked by carbachol.

Bolus injections of serotonin (250nmolkg−1) into the inflowing perfusion fluid resulted in significantly increased levels of adrenaline and noradrenaline in the outflowing perfusate. Addition of hexamethonium to the perfusion fluid did not abolish this serotonin-induced release of catecholamines. The serotonin-induced release of adrenaline, however, was abolished totally by the addition of methysergide. Serotonin is present in high concentrations (44.61±5.96 μgg−1 tissue) in the anterior region of the posterior cardinal vein within the head kidney. Carbachol (10−5 molkg−1) did not elicit release of the stored serotonin from the perfused head kidney preparation.

We conclude that the chromaffin cells in the perfused trout head kidney preparation display characteristics similar to those of other vertebrates and that this preparation is a useful tool for studying the control of catecholamine release in fish. The results demonstrate that serotonin has a direct impact on the chromaffin cells by interacting with methysergide-sensitive receptors to initiate the release of adrenaline. The potential physiological role of serotonin on catecholamine release in trout is discussed.
The Effects of Manduca Sexta Diuretic Hormone on Fluid Transport by the Malpighian Tubules and Cryptonephric Complex of Manduca Sexta
Authors: Audsley Neil , Coast Geoffrey M. , Schooley David A.
Published: April 2021

Manduca sexta diuretic hormone (Mas-DH) stimulates fluid secretion by adult Malpighian tubules of M. sexta, demonstrating its site of diuretic action in M. sexta for the first time. It was not possible to develop a suitable bioassay to measure fluid secretion in larval proximal tubules. Mas-DH has an antidiuretic action on the cryptonephric complex of larval M. sexta because it increases fluid absorption from the rectum. It appears that in this complex Mas-DH is acting on a Na+/K+/2Cl− co-transporter, presumably on the basal membrane of the cryptonephric Malpighian tubules, because Mas-DH-stimulated fluid absorption by the cryptonephric complex is inhibited by bumetanide or the removal of Cl-, Na+ or K+ from the haemolymph side of the tissue. This is the first demonstration of hormonal control of fluid absorption by the cryptonephric complex. Concomitant with the stimulation of fluid transport, Mas-DH increases the amount of cyclic AMP secreted by adult Malpighian tubules and the cryptonephric complex. In addition, Mas-DH promotes cyclic AMP production by the larval proximal tubules.
A Comparison of Avian and Reptilian Chorioallantoic Vascular Density
Authors: Birchard Geoffrey F. , Reiber Carl L.
Published: April 2021

Oviparous amniotes exchange respiratory gases across a specialized vascular membrane, the chorioallantois. Although many investigations into the physiology of amniote eggs, particularly those of the chicken, have been carried out, there is no comparative information about the chorioallantoic membrane. Given the differences in size and phylogeny, it might be expected that significant morphological differences exist in this gas-exchange organ.
Ecological Correlates of Hovering Flight of Hummingbirds
Authors: Wells Dominic J.
Published: April 2021

Simultaneous recordings of oxygen consumption and wing kinematics were collected from hummingbirds hovering at artificial flowers of different dimensions or when loaded by the addition of small weights to simulate increased fat stores. Hovering at wide-diameter flowers required increased wingbeat frequencies to compensate for decreased wingbeat amplitude, and it was 5% more metabolically expensive than at narrow flowers. Loaded birds increased their wingbeat amplitude to support the extra load whilst maintaining a nearly constant wingbeat frequency. A 10% increase in load required a 5.7% increase in mass-specific oxygen consumption. Although the variation in wing kinematics was associated with an increased metabolic cost, there was very little effect on flight efficiency. This ability to vary wing kinematics allows hummingbirds to exploit a wide range of flower types and to accommodate increased energy stores for seasonal migration.