bluuebunny/crossref_metadata_2025 huggingface dataset:
Myotomal Muscle Function at Different Locations in the Body of a Swimming Fish
Authors: Altringham J. D. , Wardle C. S. , Smith C. I.
Published: April 2021

We describe experiments on isolated, live muscle fibres which simulate their in vivo activity in a swimming saithe (Pollachius virens). Superficial fast muscle fibres isolated from points 0.35, 0.5 and 0.65bodylengths (BL) from the anterior tip had different contractile properties. Twitch contraction time increased from rostral to caudal myotomes and power output (measured by the work loop technique) decreased. Power versus cycle frequency curves of rostral fibres were shifted to higher frequencies relative to those of caudal fibres. In the fish, phase differences between caudally travelling waves of muscle activation and fish bending suggest a change in muscle function along the body. In vitro experiments indicate that in vivo superficial fast fibres of rostral myotomes are operating under conditions that yield maximum power output. Caudal myotomes are active as they are lengthened in vivo and initially operate under conditions which maximise their stiffness, before entering a positive power-generating phase. A description is presented for the generation of thrust at the tail blade by the superficial, fast, lateral muscle. Power generated rostrally is transmitted to the tail by stiffened muscle placed more caudally. A transition zone between power generation and stiffening travels caudally, and all but the most caudal myotomes generate power at some phase of the tailbeat. Rostral power output, caudal force, bending moment and force at the tail blade are all maximal at essentially the same moment in the tailbeat cycle, as the tail blade crosses the swimming track.
Regulation of Body Fluid Compartments During Dehydration of the Tenebrionid Beetle Rhytinota Praelonga
Authors: Zachariassen Karl Erik , Einarson Sigrun
Published: April 2021

Tenebrionid beetles are an important element of the fauna on the African dry savanna. In contrast to the majority of savanna insect groups, which spend the dry season as larvae, the tenebrionids pass the dry season as adults. The adult tenebrionids probably feed on dry plant material and detritus (Louw and Seely, 1982), and they may undergo severe dehydration during the dry season (authors’ observation), probably because of their limited access to water.
Taurine Transport Characteristics of the Embryonic Skate (Raja Eglanteria) Heart
Authors: Goldstein Leon , Luer Carl A. , Blum Patricia C.
Published: April 2021

The hearts of elasmobranchs, like those of other vertebrates, accumulate high concentrations of the amino acid taurine (Boyd et al. 1977), which is used to maintain osmotic equilibrium with the extracellular fluid. We recently demonstrated that embryonic hearts of the clearnose skate (Raja eglanteria Bosc) were able to accumulate taurine equally as well as hearts of adult skates and, as in adults, the accumulation was the result of transport from extracellular taurine across the cell membrane against a steep concentration gradient (Goldstein et al. 1990). In adult skate hearts, the uptake of taurine is Na+-dependent and competitively inhibited by β-alanine (Forster and Hannafin, 1980a), indicating that transport occurs by the β-amino acid system found in many vertebrate hearts (Huxtable, 1992). During hypotonic stress, adult skate hearts release taurine and other amino acids. The Na+/taurine cotransport system permits the skate heart to maintain high concentrations of intracellular taurine, while the hypotonicity-activated taurine release aids in cell volume regulation following dilution of the extracellular fluid. The aims of the present study were to determine whether taurine uptake in the embryonic skate heart is Na+-dependent as in the adult and whether the skate heart has the capability of cell volume regulation (during hypotonic stress) before hatching.
Water Propulsion Speeds and Power Output by Comb Plates of the Ctenophore Pleurobrachia Pileus Under Different Conditions
Authors: Barlow David , Sleigh Michael A.
Published: April 2021

Parameters of ciliary beating and water propulsion can be studied in a unique fashion in ctenophores because the beat frequency can be controlled. Pleurobrachia pileus comb plates were driven at frequencies between 2 and 25Hz and at temperatures between 10 and 25°C. As frequency is increased from 5 to 25Hz, the rest period between beats is first shortened and then disappears: the duration of the effective stroke is reduced because the angular velocity (which is directly proportional to the sliding velocity of the microtubules) and the tip speed of each plate increase whilst the amplitude of the beat remains unchanged. The recovery stroke is shortened because the recovery bend is propagated more quickly to the tip of the plate. The phase difference between adjacent plates in the metachronal wave (expressed as a percentage of the cycle) is increased in spite of a sharp decrease in the time delay between adjacent plates, a reduction in the number of plates per wave and an increase in the metachronal wave velocity. The water flow speed becomes more continuous and increases in approximate proportion to the tip speed whilst the estimated power output of a metachronal wave increases exponentially, from 10−10W at a tip speed of about 20 mm s−1 to 10−8 W at a tip speed of about 75 mms−1. When comb plates are driven to beat at 10 Hz and the temperature is raised from 10°C towards 20°C, the duration of the effective stroke is reduced and the comb plates have a somewhat higher angular velocity and tip speed; the duration of the recovery stroke is reduced with a faster propagation of the recovery bend; a rest phase first appears between successive beats and then becomes longer. The phase difference between adjacent plates in a metachronal wave (expressed as a percentage of the cycle time) is decreased, as is the time delay between successive plates in a metachronal wave, so that the number of plates per wave and the wave velocity are increased. The water flow speed and power output are increased by a modest amount (a rise in temperature from 10 to 20°C produces changes equivalent to those produced by a 5Hz increase in frequency at 20°C). The cooperation between adjacent plates in the antiplectic metachronal wave makes a major contribution to the dramatic increase in power output of each metachronal wave that is seen as the beat frequency is increased.
Load-Compensating Reactions in the Proximal Leg Joints of Stick Insects During Standing and Walking
Authors: Schmitz Josef
Published: April 2021

The responses of retractor coxae and protractor coxae motoneurones and of the retractor coxae muscle to cuticular stress applied to the leg were investigated in standing and walking stick insects, Carausius morosus. The coxa of a middle or hind leg was restrained and the trochanterofemur was bent by moving the distal tip of the femur anteriorly or posteriorly, i.e. perpendicular to its normal plane of movement. The maximum amplitude used was 200 μm, which corresponds to a deflection of 0.95°, and the forces necessary to bend the trochanterofemur were between 0.29 and 2.91mN. Thus, cuticular stress could be applied in particular directions and with controlled amplitudes within the physiological range. This cuticular stress induced direction- and amplitude-dependent reflex responses in excitatory retractor coxae and protractor coxae motoneurones. The reflexes clearly constitute a negative feedback system which continuously compensates cuticular stress in the legs of standing and walking animals. Two groups of trochanteral campaniform sensilla, the posterior group and the anterior ventral group, were shown to underlie this feedback loop. These results prove directly for the first time the important function of single groups of trochanteral campaniform sensilla in the control of posture and locomotion in stick insects. I discuss the importance of these results for the interpretation of previous findings on stick insects subjected to increased load during walking.
Hindbrain Circuitry Mediating Common Mode Suppression of Ventilatory Reafference in the Electrosensory System of the Little Skate Raja Erinacea
Authors: Montgomery John C. , Bodznick David
Published: April 2021

Elasmobranch fish have an electrosensory system which they use for prey detection and for orientation. Sensory inputs to this system are corrupted by a form of reafference generated by the animal’s own ventilation, but this noise is reduced by sensory processing within the medullary nucleus of the electrosensory system. This noise cancellation is achieved, at least in part, by a common mode rejection mechanism. In this study we have examined characteristics of neurones within the medullary nucleus in an attempt to understand the neural circuitry responsible for common mode suppression. Our results are in accord with previous indications that ascending efferent neurones of the medullary nucleus are monosynaptically activated from the ipsilateral electrosensory nerves and project to the midbrain. We demonstrate that in Raja erinacea, as has been previously shown in one other species (Cephaloscyllium isabella), ascending efferent neurones typically have a discrete focal excitatory receptive field and an inhibitory receptive field which may be discrete or diffuse and which often includes a contralateral component. We identify a group of interneurones within the medullary nucleus which are driven monosynaptically from the electrosensory nerves, have simple discrete excitatory receptive fields and respond vigorously to imposed common mode signals. The simplest model of the circuitry underlying common mode rejection that is consistent with the evidence is that direct afferent input impinges onto the basal dendrites of the ascending efferent neurones and onto interneurones within the nucleus, and the interneurones in turn inhibit the ascending efferents. The pattern of this projection, including commissural inputs, determines the nature and extent of ascending efferents’ inhibitory surrounds and mediates the suppression of common mode signals.
Investigation of Stimulus–Secretion Coupling in Equine Sweat Gland Epithelia Using Cell Culture Techniques
Authors: Wilson Stuart M. , Pediani John D. , Ko Wing Hung , Bovell Douglas L. , Kitson Susan , Montgomery Ian , Brown Ursilla M. O. , Smith Godfrey L. , Elder Hugh Y. , Jenkinson David McEwan
Published: April 2021

When sweat glands isolated from samples of horse skin were explanted and cultured under favourable conditions, they could exhibit cellular outgrowth. This growth could be maintained for 2–4 weeks and these primary cultures were then disaggregated and the resultant cell suspensions used to initiate epithelial cell lines. Secretion from intact equine sweat glands is regulated by β 2-adrenoceptors and appears to be mediated by cyclic AMP, but there is evidence that calcium may also play a role. Adrenaline could increase the cyclic AMP content of the cultured cells and this response was mediated by 2-adrenoceptors. Adrenaline was also able to evoke a small increase in intracellular free calcium ([Ca2+]i) but the pharmacology of this response remains obscure. Adrenaline thus activates at least two potentially important second-messenger signalling pathways which have the capacity to interact, because adrenaline-evoked cyclic AMP formation was inhibited if [Ca2+]i was raised with ionomycin. The chloride permeability of mammalian epithelial cells characteristically rises during secretion, and adrenaline could increase chloride permeability in the cultured epithelia but the cells did not contain cyclic-AMP-dependent chloride channels and so this response was mediated by [Ca2+]i.
Locust Medial Neurosecretory Cells in vitro: Morphology, Electrophysiological Properties and Effects of Temperature
Authors: Rössler Wolfgang , Bickmeyer Ulf
Published: April 2021

The medial neurosecretory cells of the pars intercerebralis in the protocerebrum of larval and adult locusts (Locusta migratoria) were cultured in a chemically defined serum-free culture medium. The morphology of the cells was investigated by light microscopy and the electrophysiological properties were studied using the patch-clamp technique in the whole-cell configuration. The dissociated neurosecretory cells grew new processes under these conditions and were maintained in culture for up to 2 months. The percentage of cells showing outgrowth was significantly higher in third-instar larvae than in instars 4 and 5 and adults. A primary axonal stump promoted a unipolar cell morphology; in other cases, most neurosecretory cells became multipolar. The presence of glial cells in undissociated groups of neurosecretory cells improved outgrowth and the formation of neurite bundles. A considerable number of the recorded cells showed spiking activity in response to depolarization. The influences of temperature on spike frequency, duration and amplitude as well as on membrane potential and ionic currents were investigated. The results suggest that temperature may directly affect the function of neurosecretory cells.
Toads Taste Sodium With Their Skin: Sensory Function in a Transporting Epithelium
Authors: Hoff Karin Von Seckendorff , Hillyard Stanley D.
Published: April 2021

Amphibians do not normally ingest water orally. Rather, they obtain water by osmotic flow across their skin (Bentley and Yorio, 1979). Previous studies of the desert toad, Bufo punctatus, showed that dehydrated animals placed on a surface moistened with pure water adopted a particular type of behavior, termed the water absorption response (WR), in which toads splayed their hindlimbs and oscillated their body to maximize the area of skin in contact with the surface (Brekke et al. 1991). If the surface was moistened with a hyperosmotic urea solution, the animals moved over the surface as if to search for osmotically available water and soon jumped off the surface without initiating WR behavior. Since the skin was the only part of the animal in contact with the surface, it was concluded that receptors in the skin enabled the animals to avoid WR behavior on surfaces where water was not osmotically available. Similarly, toads did not initiate WR behavior when NaCl was used as the solute. These observations suggested that toads have either cutaneous receptors for detecting osmolality, per se, or cutaneous receptors for specific solutes.
HIGH pH IN THE ECTOPERITROPHIC SPACE OF THE LARVAL LEPIDOPTERAN MIDGUT
Authors: Gringorten J. L. , Crawford D. N. , Harvey W. R.
Published: April 2021

The midgut lumen of lepidopteran larvae is highly alkaline (Waterhouse, 1949; Berenbaum, 1980), a condition maintained in the presence of a large and opposing transapical H + gradient from the midgut epithelial cells. Lumen pH values of approximately 11 may be common (Dow, 1984), whereas the cell cytoplasm itself is maintained at approximately neutral pH (Dow and O’Donnell, 1990; Chao et al. 1991), giving rise to cell/lumen H + concentration ratios of 10 4 or more. Dow (1984) reported a mean pH of 12.0 in the midgut of a sphingid larva, Acherontia atropos, and Schultz and Lechowicz (1986) recorded a maximum reading of pH12.4 in the European gypsy moth, Lymantria dispar. These values are among the highest recorded in any biological system.
Male Accessory Gland Factors Elicit Change From ‘Virgin’ to ‘Mated’ Behaviour in the Female Corn Earworm Moth Helicoverpa Zea
Authors: Kingan Timothy G. , Thomas-Laemont Patricia A. , Raina Ashok K.
Published: April 2021

After mating, the females of many species of moths become depleted of sex pheromone, calling behaviour is terminated, and they become transiently or permanently unreceptive to additional matings. In the corn earworm moth, Helicoverpa zea, we have found that the male accessory gland/duplex is required for evoking the post-mating depletion of sex pheromone but apparently not for the cessation of calling. The latter change requires the receipt of a spermatophore or a chemical messenger derived from non-accessory gland/duplex sources. Desalted extracts of combined accessory glands and duplexes caused a depletion of pheromone in injected females. Proteinaceous components in extracts purified by fractionation in cation-exchange cartridges and by reverse-phase high-performance liquid chromotography retain their pheromonostatic activity. In addition, this fractionated material shuts off calling behaviour and prevents mating in injected females, raising the possibility that redundant mechanisms exist in eliciting the different components of ‘mated’ behaviour.
Stimulus–Secretion Coupling In Excitable Cells: A Central Role For Calcium
Authors: Cheek Timothy R. , Barry Victoria A.
Published: April 2021

Secretion of vesicular contents by exocytosis is a common feature of neuroendocrine secretory cells such as adrenal chromaffin cells and PC12 cells. Although it is clear that in these cells an elevation in intracellular calcium concentration, [Ca2+]i, is the triggering event that induces secretion, recent studies using video-imaging, patch-clamp and flash photolysis techniques have all indicated that the Ca2+ signal that triggers secretion is in fact very complex, with the subcellular distribution of Ca2+ being of particular importance along with the magnitude of the rise.

It has become evident that Ca2+ signals with different spatial profiles can be triggered in the same cell by a given stimulus, depending upon the nature of the Ca2+ signalling pathway activated, and that this ability to be able to vary the method of delivery of Ca2+ into the cell is important physiologically, because it provides a means of obtaining differential activation of Ca2+-dependent processes.
Imaging Calcium Waves in Eggs and Embryos
Authors: Gillot Isabelle , Whitaker Michael
Published: April 2021

Sea urchin eggs and those of most other deuterostomes are activated at fertilization by an increase in cytoplasmic free calcium concentration ([Ca2+]i) that triggers the onset of the embryonic cell division cycles. We can image the calcium wave using fluorescent calcium indicator dyes and confocal microscopy. There are two components to the [Ca2+]i increase at fertilization. The first is due to a rapid calcium influx caused by a calcium action potential; this leads to a small increase in [Ca2+]i just beneath the plasma membrane with spherical symmetry. After a latent period of some 15s, there is a second large and rapid increase in [Ca2+]i localized to the region of sperm–egg contact: during the latent period [Ca2+]i does not change but within 1s of the end of the latent period [Ca2+]i reaches 2 μmol l-1. The calcium wave then spreads across the egg with a velocity of 5 μms-1. Behind the advancing wavefront, the calcium concentration is uniformly high, even within the egg nucleus, though there are no indications that intranuclear calcium concentration differs from [Ca2+]i. [Ca2+]i falls uniformly towards resting levels over the next 500s. In cases where there is an apparent inhomogeneity in [Ca2+]i in either the cortex or the nucleus, we find that the calcium indicator dye is inhomogeneously distributed. This appears to be due to uptake of the indicator dye (Fluo-3), probably into mitochondria. The artefact can be avoided by using a dextran-conjugated dye.
The Effect of Graded Methaemoglobin Levels on the Swimming Performance of Chinook Salmon (Oncorhynchus Tshawytscha)
Authors: Brauner C. J. , Val A. L. , Randall D. J.
Published: April 2021

Nitrite oxidizes haemoglobin (Hb) to methaemoglobin (MetHb), which is unable to bind oxygen. Nitrite exposure can therefore be used as a tool to manipulate the oxygen-carrying capacity of the blood without changing haematocrit. The objective of this study is to examine the relationship between the critical swimming velocity (Ucrit) and the functional haemoglobin concentration ([Hb]) of the blood in adult chinook salmon. Functional [Hb] was reduced by increasing MetHb levels through intraperitoneal administration of a mass-dependent volume of sodium nitrite. In resting fish, MetHb levels were found to stabilize at 25% of total [Hb] 3h after the injection of 30mgkg−1 sodium nitrite. Methaemoglobin levels increased in proportion to the amount of sodium nitrite injected and reached a maximum (following the injection of 90mgkg−1 sodium nitrite) of 51.8% in resting fish and 72% in fish forced to swim to Ucrit. At 60 and 90mgkg−1 sodium nitrite, MetHb formation was greater in exercised than in resting fish. A second-order regression revealed that Ucrit was virtually independent of functional [Hb] between 51 and 100% of control functional [Hb], but was positively correlated with functional [Hb] below 51% of total [Hb] (4.5 g dl−1). The insensitivity of Ucrit to a functional [Hb] greater than 51% may be partly due to the exponential increase in aerobic metabolism required to provide the power to overcome hydrodynamic drag at higher water velocities. There were no significant changes in intraerythrocytic organic phosphate (adenylates and guanylates) concentrations standardized to [Hb] in swimming or resting fish over the range of MetHb levels induced in this study. Fish may encounter nitrite naturally; if MetHb levels become severely elevated as a result, swimming ability will be significantly impaired.
Effects of Temperature on Mitochondria From Abalone (Genus Haliotis): Adaptive Plasticity and its Limits
Authors: Dahlhoff Elizabeth , Somero George N.
Published: April 2021

The effects of temperature on mitochondrial oxygen consumption, membrane fluidity and cytochrome c oxidase activity were measured for five species of eastern Pacific abalone (genus Haliotis) found at different latitudes and tidal heights. Mitochondria were isolated from freshly collected individuals and from specimens that had been acclimated in the laboratory to temperatures spanning the extremes of each species’ known habitat temperature range. The temperatures at which Arrhenius plots of respiration rate of mitochondria from freshly collected abalone exhibited sharp breaks in slope were found to correlate with the habitat temperature at the time of capture of each species. Membranes isolated from freshly collected abalone living at warm temperatures (Haliotis cracherodii and H. corregata) were significantly less fluid (as determined by the fluorescence polarization of the probe 1,6-diphenyl 1,3,5-hexatriene) than were membranes from species captured at cooler temperatures (H. rufesens and H. kamtschatkana kamtschatkana). Laboratory acclimation significantly shifted the temperature of mitochondrial thermal inactivation in an adaptive manner in the eurythermal species, H. fulgens, H. corregata and H. rufesens, but did not alter this property significantly for mitochondria from the stenothermal species, H. k. kamtschatkana. Laboratory acclimation resulted in temperature-compensatory changes in membrane fluidity in all species except H. rufesens. The temperatures at which cytochrome c oxidase activity was inactivated also shifted in an adaptive manner in some species. Acclimation of mitochondrial respiration, membrane fluidity and cytochrome c oxidase activity occurred only over the ranges of temperature at which each species is common, suggesting that there is a relationship between acclimatory ability and the biogeographical distribution of congeneric species.
Differential Effects of Acetylcholine on Coronary Flow in Isolated Hypothermic Hearts From Rats and Ground Squirrels
Authors: Burlington Roy F. , Milsom William K.
Published: April 2021

This study was designed to determine whether cholinergic receptors are operative in the coronary vessels of a hibernating species (golden mantled ground squirrel, Spermophilus lateralis) and a nonhibernating species (rat, Rattus norvegicus) under normothermic and hypothermic conditions. Coronary flow and left ventricular systolic pressure were measured in isolated perfused hearts from squirrels at 37, 20 or 7°C and from rats at 37 and 20°C. During cooling, rat hearts became arrhythmic and failed between 15 and 12°C. Squirrel hearts remained functional at 7°C. Bolus injections of acetylcholine (>1.0 μg) caused significant coronary vasoconstriction in rat hearts at 37 and 20°C. Similar treatment caused mild coronary vasodilation in squirrel hearts at both temperatures. Squirrel hearts did not respond to acetylcholine at 7°C. The responses in both species were blocked by atropine. Rat coronary vessels appear to contain muscarinic constrictor receptors similar to those described in humans, sheep, cattle and pigs. The coronary vessels of squirrels, by contrast, do not. In this latter species there appears to be a preponderance of muscarinic (possibly endothelial-relaxing-factor-linked) dilator receptors. Given that acetylcholine acts only as a mild vasodilator at higher temperatures in squirrels, parasympathetic regulation of coronary flow in the squirrel heart is unlikely, especially during hibernation.
Efficiency of Energy Conversion During Sinusoidal Movement of Red Muscle Fibres from the Dogfish Scyliorhinus Canicula
Authors: Curtin N. A. , Woledge R. C.
Published: April 2021

Bundles of red myotomal muscle fibres isolated from dogfish were electrically stimulated at 12°C. Peak twitch force was 54% of that produced by a brief isometric tetanus. Relaxation was slower than in white fibres, but much faster than would be expected for the tonic fibres found in amphibian muscle. These two results indicate that the red fibres in dogfish are slow, but not tonic, in their behaviour.

Net work output and heat production were measured during complete cycles of sinusoidal movement. The following variables were kept constant: peak-to-peak movement, about 7% of the muscle fibre length; tetanus duration, 33% of the mechanical cycle time; stimulus frequency, 40Hz. The frequency of movement and the timing of the stimulation were varied for each preparation to find the conditions optimal for power output and those optimal for efficiency (the ratio of net work output to total energy output as heat+work). To achieve either maximum power or maximum efficiency, the tetanus must start while the muscle fibres are being stretched, before the beginning of the shortening part of the mechanical cycle. The highest power output was produced during movement at 1.02Hz. The highest efficiency, 0.507±0.045 (±S.E.M., N=9), was at 0.61–0.95Hz. The efficiency is higher than that previously measured during sinusoidal movement of white fibres; the difference, 0.095±0.045 (±S.E.M. of the difference, d.f. 20), is statistically significant at the 5% level.
Vagal Influence on Heart Rate in Hibernating Ground Squirrels
Authors: Milsom William K. , Burlington Roy F. , Burleson Mark L.
Published: April 2021

The heart rate of anesthetized golden mantled ground squirrels (Spermophilus lateralis) falls from 372±20 to 37±9beatsmin−1 during hibernation at 7°C body temperature. Heart rate in the hibernating animals often waxed and waned in a fashion that was not clearly linked to the breathing pattern. Similar observations have been made on unanesthetized ground squirrels. Under anesthesia, the effects of vagotomy were small in both euthermic and hibernating animals and led to a 6–8% increase in heart rate. Vagotomy also eliminated the cyclic fluctuations of heart rate in hibernating animals exhibiting this phenomenon. The post-vagotomy heart rate exhibited by these individuals suggested that both sympathetic excitation and parasympathetic depression were involved in producing these cyclic changes. Vagal stimulation reduced mean heart rate by at most 60–80% in euthermic and hibernating animals. The strength of the stimulus required to elicit a maximal response in the hibernating animals was 35–45% greater than that required in euthermic animals. Comparisons of mean heart rates obtained from euthermic and hibernating animals which were vagotomized, intact or stimulated to produce a maximum bradycardia produced temperature quotients of 2.21, 2.15 and 2.31, respectively. In this species, both resting vagal tone and the effects of vagal stimulation decrease in parallel with decreasing temperature over the range studied.
A Method For Long-Term Multiple-Channel Recording of Oxygen Consumption in Aquatic Animals
Authors: Nordtug Trond , Olsen Anders Johny
Published: April 2021

The objective of the present work has been to develop a method for measuring the rate of oxygen consumption on a routine basis during toxicity testing and environmental monitoring. This requires a method that is reliable over long periods and can be used with a minimum of maintenance work in a variable environment. The system should consist of a compact unit easily transported and available at a reasonable cost. Visual updated records of the oxygen consumption should be available at all times.
Running Springs: Speed and Animal Size
Authors: Farley Claire T. , Glasheen James , Mcmahon Thomas A.
Published: April 2021

Trotting and hopping animals use muscles, tendons and ligaments to store and return elastic energy as they bounce along the ground. We examine how the musculoskeletal spring system operates at different speeds and in animals of different sizes. We model trotting and hopping as a simple spring-mass system which consists of a leg spring and a mass. We find that the stiffness of the leg spring (kleg) is nearly independent of speed in dogs, goats, horses and red kangaroos. As these animals trot or hop faster, the leg spring sweeps a greater angle during the stance phase, and the vertical excursion of the center of mass during the ground contact phase decreases. The combination of these changes to the spring system causes animals to bounce off the ground more quickly at higher speeds.

Analysis of a wide size range of animals (0.1–140kg) at equivalent speeds reveals that larger animals have stiffer leg springs (kleg∝M0.67, where M is body mass), but that the angle swept by the leg spring is nearly independent of body mass. As a result, the resonant period of vertical vibration of the spring-mass system is longer in larger animals. The length of time that the feet are in contact with the ground increases with body mass in nearly the same way as the resonant period of vertical vibration.
Switching in the activity state of an interneuron that controls coordination of the hearts in the medicinal leech (Hirudo medicinalis)
Authors: Gramoll S. , Schmidt J. , Calabrese R. L.
Published: April 2021

The rhythmically active heart interneuron HN(5) in the medicinal leech exhibits two distinct activity states, which have been associated with different coordination states of the two hearts. During the active state, it discharges high-frequency bursts of action potentials interrupted by rhythmic inhibitory input from other interneurons. In the inactive state, the same cell receives rhythmic inhibition but the membrane potential remains subthreshold between these volleys, producing few or no action potentials. We investigated differences in the membrane properties of the cell during the active and inactive states. The membrane potential in the active state oscillates on average between about -56±6 mV (S.D.) and -45±7 mV; the mean oscillation amplitude is 11±4 mV. In the inactive state, the membrane potential oscillates on average between -58±6 mV and -55±6 mV with a mean amplitude of 3±1 mV. The overall conductance of an HN(5) interneuron during the active state is approximately 10 nS lower than that during the inactive state, indicating that an outward current is turned off during the active state or turned on during the inactive state. This outward current is not voltage-dependent in the range -80 mV to -10 mV, as shown in voltage-clamp experiments by a linear current–voltage relationship. The reversal potential of this current is approximately -60 mV, indicating that chloride or potassium ions underlie the current. Using dynamic-clamp, we show that by adding an artificial current with a linear voltage-dependence (leak conductance) to an HN(5) interneuron (conductance 15 nS, reversal potential -60 mV), the cell can be transferred from its active to its inactive state.
Ultraviolet photoreception contributes to prey search behaviour in two species of zooplanktivorous fishes
Authors: Browman Howard I. , Novales-Flamarique Iñigo , Hawryshyn Craig W.
Published: April 2021

We tested the hypothesis that ultraviolet photoreception contributes to prey search in small juvenile rainbow trout (Oncorhynchus mykiss) and pumpkinseed sunfish (Lepomis gibbosus) while foraging on Daphnia pulex. Small individuals of these species are ultraviolet-photosensitive zooplanktivores. For both species, prey pursuit distances and angles were larger under full-spectrum illumination than under ultraviolet-absent illumination. The same was true for the distances and angles associated with repositioning movements (i.e. those not leading to the location of a prey item). Thus, ultraviolet photoreception contributes to prey search and detection in these fishes. We argue that the most likely mechanism underlying this enhancement of prey search abilities is improved target contrast.
Down-regulation of red blood cell β-adrenoreceptors in response to chronic elevation of plasma catecholamine levels in the rainbow trout
Authors: Gilmour Kathleen M. , Didyk Nicole E. , Reid Steve G. , Perry Steve F.
Published: April 2021

In many teleost fish, including the rainbow trout, Oncorhynchus mykiss, catecholamines are mobilized into the blood in situations when enhanced oxygen transport is necessary, such as hypoxia, anaemia, hypercapnia and strenuous exercise (see review by Thomas and Perry, 1992). These hormones initiate a series of integrated physiological responses that optimize cardiovascular and respiratory functions (see reviews by Perry and Wood, 1989; Randall and Perry, 1992; Thomas and Perry, 1992). Stimulation of red blood cell β-adrenoreceptors leads to the activation of a red blood cell membrane Na+/H+ antiporter which extrudes protons in exchange for plasma Na+, thereby elevating intracellular pH (pHi) (Baroin et al. 1984; Cossins and Richardson, 1985; see review by Nikinmaa, 1992). The binding of catecholamines to - βadrenoreceptors, which are coupled to adenylate cyclase, engenders the formation of cyclic AMP. This second messenger, in turn, presumably initiates a phosphorylation cascade which ultimately activates the Na+/H+ antiporter. Erythrocyte alkalization can increase haemoglobin oxygen-binding affinity and capacity via the Bohr and Root effects, thus increasing the ability of the blood to transport oxygen (Tufts and Randall, 1989; see also reviews by Nikinmaa and Tufts, 1989; Perry and Wood, 1989; Randall and Perry, 1992; Thomas and Perry, 1992).
Two distinct receptors are activated by arecoline on cockroach sixth abdominal ganglion DUM neurones
Authors: Tribut F. , Duval A. , Lapied B.
Published: April 2021

During the last decade, extensive biochemical and electrophysiological studies have been performed to characterize the pharmacological properties of cholinergic receptors of insect neurone somata (Sattelle, 1985; Breer and Sattelle, 1987; Benson, 1992). Although most of these studies have been focused on the pharmacological characterization of the cell body nicotinic receptors (Lane et al. 1982; Harrow and Sattelle, 1983; David and Sattelle, 1984; Benson, 1992), evidence for a population of acetylcholine (ACh) receptors exhibiting muscarinic and ‘mixed’ (nicotinic/muscarinic) properties has been reported on insect neurone somata (Benson and Neumann, 1987; Knipper and Breer, 1988; Benson, 1989, 1992, 1993; Trimmer and Weeks, 1989; David and Pitman, 1990, 1992, 1993). One group of insect neurones, called dorsal unpaired median (DUM) neurones, expresses functional cholinergic receptors that differ from the classic vertebrate ACh receptors in that, although DUM neurones were sensitive to ACh, the nicotinic and/or muscarinic nature of these receptors has not been resolved since the cholinergic antagonists α-bungarotoxin and atropine were relatively ineffective in blocking the ACh response (Goodman and Spitzer, 1980; Lane et al. 1982; Lapied et al. 1990). However, using a range of cholinergic antagonists known to be selective for vertebrate ACh receptors, it has recently been possible to demonstrate the diversity of functional ACh receptors; these include nicotinic, ‘mixed’ and muscarinic receptors mediating specific responses elicited by different cholinergic agonists, such as nicotine, muscarine, oxotremorine and McN-A-343, on both isolated and in situ DUM neurones (Lapied et al. 1990, 1992; Bai et al. 1992). Extending these studies, we report in this paper that another cholinergic ligand, arecoline, which is known to act preferentially as a muscarinic agonist in vertebrate preparations (Wess et al. 1990), induced a complex response mediated by both nicotinic and muscarinic receptors on DUM neurones.
Effects of zinc on the kinetics of branchial calcium uptake in freshwater rainbow trout during adaptation to waterborne zinc
Authors: Hogstrand C. , Wilson R. W. , Polgar D. , Wood C. M.
Published: April 2021

The effects of sublethal waterborne Zn2+ (150 µg l-1=2.3 µmol l-1) on the kinetics of unidirectional Ca2+ influx were studied in juvenile freshwater rainbow trout during chronic exposure (60 days) at a water [Ca2+] of 1.0 mmol l-1. An unexposed group held under identical conditions served as control. The presence of Zn2+ in the water increased the apparent Km for Ca2+ influx by up to 300 % with only a small inhibitory effect (35 % at most) on the maximum rate of uptake (Jmax). These results, in combination with earlier data showing that Ca2+ competitively inhibits Zn2+ uptake, suggest that Zn2+ and Ca2+ compete for the same uptake sites. Acute withdrawal of Zn2+ after 3 h of exposure resulted in a 23-fold reduction in Km for Ca2+, but a persistent small depression of Jmax. During prolonged exposure to Zn2+, the apparent Km for Ca2+ remained greatly elevated and Jmax remained slightly depressed. The actual Ca2+ influx in hard water ([Ca2+]=1.0 mmol l-1) decreased marginally and paralleled the small changes in Jmax. The increases in apparent Km had a negligible influence on the actual Ca2+ influx because Km values (38–230 µmol l-1), even when elevated by Zn2+, remained below the water [Ca2+] (1000 µmol l-1). Rainbow trout exposed to Zn2+ exhibited a slower rate of protein synthesis in the gills (measured on day 23) and an increased tolerance to Zn2+ challenge (measured on both days 27 and 50). Unidirectional Zn2+ influx, measured at the end of the exposure period, was significantly reduced in the Zn2+-exposed fish. There were no changes in hepatic or branchial Zn2+, Cu2+ or metallothionein concentrations. We hypothesize that, during exposure to sublethal [Zn2+] in hard water, the fish may change the Km for a mutual Ca2+/Zn2+ carrier so as to reduce markedly Zn2+ influx without greatly altering Ca2+ influx. This reduced Zn2+ influx, rather than metallothionein induction, may be the basis of adaptation to elevated concentrations of waterborne Zn2+.
Kinetics of ATP- and Na+-gradient driven Ca2+ transport in basolateral membranes from gills of freshwater- and seawater-adapted tilapia
Authors: Verbost P. M. , Schoenmakers T. J. , Flik G. , Wendelaar Bonga S. E.
Published: April 2021

Plasma membranes of the gills of freshwater- and seawater-adapted tilapia were analyzed for Ca2+-ATPase and Na+/Ca2+ exchange activity. The relative importance of ATP-driven and Na+-gradient-driven Ca2+ transport in Ca2+ extrusion was evaluated on the basis of kinetic analyses in vitro. The Na+/Ca2+ exchangers in branchial membranes from freshwater or seawater fish displayed similar kinetics. The ATP-driven Ca2+ pump, however, showed a somewhat lower affinity for Ca2+ in membranes isolated from seawater gills than in membranes from freshwater gills; no difference in Vmax was found. The activity of the exchanger was estimated to be 50 % of that of the ATP-driven pump at prevailing cytosolic Ca2+ concentrations (10−7 mol l-1).

Opercular ionocyte densities and branchial Na+/K+-ATPase content were not significantly different in fish residing in fresh water or sea water. We conclude that the gills of tilapia living for prolonged periods in fresh water or sea water do not differ in the make-up of their basolateral membrane with regard to Ca2+-ATPase, Na+/Ca2+ exchange and Na+/K+-ATPase activity. Apparently, the densities of these carriers suffice for calcium and sodium homeostasis under these vastly different ambient conditions.
Neuromuscular control and kinematics of intermittent flight in budgerigars (Melopsittacus undulatus)
Authors: Tobalske Bret W. , Dial Kenneth P.
Published: April 2021

Kinematic and electromyographic data were collected from budgerigars (parakeets), Melopsittacus undulatus, flying at different speeds in a variable-speed wind tunnel. Birds exhibited flap-gliding at low speeds and flap-bounding at high speeds. The percentage of time spent flapping generally decreased at intermediate speeds. These behavior patterns are consistent with minimizing energy expenditure according to aerodynamic theory. During intermittent glides, the pectoralis exhibited an isometric contraction while the supracoracoideus was inactive. During bounds, both muscles were inactive.

Contrary to earlier work, our studies indicate that budgerigars do not exhibit simultaneous twitch contractions of the pectoralis during each wingbeat, but rather generate typical multiple-spike electromyographic bursts that represent motor unit action potential trains or asynchronous twitch contractions from different motor units. The relative intensity of electromyographic bursts from the primary flight muscles increased with flight speed. This may indicate an increase in force production.

Our observations of isometric contractions during glides, along with patterns of variation in muscle activity and wingbeat frequency, do not support the hypothesis that small birds such as the budgerigar use flap-bounding as their only means of reducing power output during flight.
Directional sensitivity of hair cell afferents in the Octopus statocyst
Authors: Budelmann Bernd U. , Williamson Roddy
Published: April 2021

Changes in threshold sensitivity of hair cell afferents of the macula and crista of the Octopus statocyst were analyzed when the hair cells were stimulated with sinusoidal water movements from different directions. The experiments indicate that cephalopod statocyst hair cells are directionally sensitive in a way that is similar to the responses of the hair cells of the vertebrate vestibular and lateral line systems, with the amplitude of the response changing according to the cosine of the angle by which the direction of the stimulus (the deflection of the ciliary bundle) deviates from the direction of the hair cell’s morphological polarization.
Contractile properties of a high-frequency muscle from a crustacean: I. Activation patterns in vivo
Authors: Josephson Robert K. , Stokes Darrell R.
Published: April 2021

The flagella of crustaceans are small appendages, borne on the maxillipeds, which beat repetitively when active. Flagellar movement is brought about by contraction of a single muscle, the flagellum abductor (FA). The stroke frequency of the flagella of the green crab, Carcinus maenas, was about 11 Hz at 15 °C and was relatively independent of animal size [frequency is proportional to (animal mass)−0.07], even though scaling considerations suggest that, for constant muscle stress, frequency should be proportional to mass−0.33. The coefficient of variation for intervals between successive strokes of a flagellum was about 4 %. The FA is innervated by two excitatory motoneurones. Each of the neurones fired 0–5 times during a stroke. The interspike interval when a neurone fired more than once during a stroke was 3–4 ms.
Integration of positive and negative feedback loops in a crayfish muscle
Authors: Skorupski Peter , Vescovi Paul J. , Bush Brian M. H.
Published: April 2021

It is now well established that in arthropods movement-related feedback may produce positive, as well as negative, feedback reflexes (Bässler, 1976; DiCaprio and Clarac, 1981; Skorupski and Sillar, 1986; Skorupski et al. 1992; Vedel, 1980; Zill, 1985). Usually the same motor neurones are involved in both negative feedback (resistance) reflex responses and positive feedback reflexes. Reflex reversal involves a shift in the pattern of central inputs to a motor neurone, for example from excitation to inhibition.
Function of the tensor muscle in the cicada Tibicen linnei
Authors: Hennig R. M. , Weber T. , Moore T. E. , Huber F. , Kleindienst H.-U. , Popov A. V.
Published: April 2021

The calling song and the disturbance squawk of the cicada Tibicen linnei (Insecta: Homoptera) are described in terms of their physical parameters. The calling song is composed of quiet parts, which are very similar to the disturbance squawk, and loud parts, which are amplitude-and rate-modulated. The role of the tensor muscle acting on the tymbal frame in modulating the sound pulse amplitude was investigated. We demonstrate by tensor nerve recordings, by mechanical mimicking of the tensor muscle action and by electrical stimulation of the tensor nerve, that the contraction of the tensor muscle is responsible for (a) initiating sound production and (b) modulating the sound pulse amplitude. These results allow us to construct a model which suggests that the tensor shifts the tymbal into a mechanical working range that enables sound production and modulation of the sound pulse amplitude.
Oxygen transport in marine green turtle (Chelonia Mydas) hatchlings: blood viscosity and control of hemoglobin oxygen-affinity
Authors: Wells R. M. G. , Baldwin J.
Published: April 2021

Erythrocytes from green turtle hatchlings contain a single embryonic component, unlike those from other cleidoic eggs, in which adult hemoglobin (Hb) constitutes a significant fraction of total Hb at hatching. The functional properties of the isolated and purified green turtle hatchling Hb that distinguish it from adult Hb are a high affinity for oxygen and marked sensitivity to organic phosphate modulators. Hatchling erythrocytes also contain higher concentrations of ATP and 2,3-diphosphoglyceric acid, but their oxygen affinity is indistinguishable from that of adult erythrocytes. Hatchling erythrocyte mean cell volume is approximately half of the adult value, but hematocrit, blood hemoglobin concentration and blood viscosity of hatchlings and adults are similar. Oxygen-carrying capacity in green turtles, unlike that of other diving vertebrates, corresponds with a theoretically derived optimum. The possibility of allosteric control of Hb oxygen-binding in hatchlings may relate not to the challenge of exercise during the dispersal phase but to conditions in the late embryo in the nest.
Cyclic amp stimulation of electrogenic uptake of Na+ and Cl− Across the gill epithelium of the chinese crab Eriocheir Sinensis
Authors: Riestenpatt S. , Zeiske W. , Onken H.
Published: April 2021

Split gill lamellae (epithelium plus cuticle) of hyperregulating Chinese crabs acclimated to fresh water were mounted in a modified Ussing chamber. Active and electrogenic absorption of sodium and chloride were measured as positive amiloride-sensitive and negative Cl−-dependent short-circuit currents (INa, ICl), respectively. Both currents were characterized before and after treatment of the tissue with theophylline or dibutyryl cyclic AMP. Both drugs increased INa and ICl. A simple circuit analysis showed that INa stimulation reflected a marked increase in the transcellular Na+ conductance, whereas the respective electromotive force was unchanged. The Michaelis constant (KNa) for Na+ current saturation was decreased after INa stimulation, indicating an increased affinity of the transport mechanism for its substrate. Consequently, the affinity for the Na+ channel blocker amiloride decreased as expected for a competitive interaction between substrate and inhibitor. Analysis of the amiloride-induced current-noise revealed a marked increase in the number of apical Na+ channels after INa stimulation with theophylline, whereas there was little change in the single-channel current. Stimulation of Cl− absorption was accompanied by a substantial increase in both transcellular conductance and electromotive force, indicating an activation of the apical H+ pump that provides the driving force for active Cl− uptake via apical Cl−/HCO3− exchange and basolateral Cl− channels.