bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Length Trajectory on the Mechanical Power Output of Mouse Skeletal Muscles
Authors: Askew Graham N. , Marsh Richard L.
Published: April 2021

The effects of length trajectory on the mechanical power output of mouse soleus and extensor digitorum longus (EDL) muscles were investigated using the work loop technique in vitro at 37 °C. Muscles were subjected to sinusoidal and sawtooth cycles of lengthening and shortening; for the sawtooth cycles, the proportion of the cycle spent shortening was varied. For each cycle frequency examined, the timing and duration of stimulation and the strain amplitude were optimized to yield the maximum power output. During sawtooth length trajectories, power increased as the proportion of the cycle spent shortening increased. The increase in power was attributable to more complete activation of the muscle due to the longer stimulation duration, to a more rapid rise in force resulting from increased stretch velocity and to an increase in the optimal strain amplitude. The power produced during symmetrical sawtooth cycles was 5–10 % higher than during sinusoidal work loops. Maximum power outputs of 92W kg−1 (soleus) and 247 W kg−1 (EDL) were obtained by manipulating the length trajectory. For each muscle, this was approximately 70 % of the maximum power output estimated from the isotonic force–velocity relationship.

We have found a number of examples suggesting that animals exploit prolonging the shortening phase during activities requiring a high power output, such as flying, jet-propulsion swimming and vocalization. In an evolutionary context, increasing the relative shortening duration provides an alternative to increasing the maximum shortening velocity (Vmax) as a way to increase power output.
The Effects of Walls, Paternity and Ageing on Sperm Motility
Authors: Gee Christopher C. , Zimmer-Faust Richard K.
Published: April 2021

The measurement of sperm motility is critical when studying fertilization kinetics and chemotaxis. Analysis of motility has traditionally been carried out on cells in small fluid volumes on microscope slides. Several theoretical treatments suggest that drag forces significantly affect flagellar motion within 10 sperm body lengths of the slide surface. Understanding how sperm move in the absence of surface drag is crucial when considering natural locomotory patterns. To examine the effects of solid surfaces, motile sperm from sea urchins (Arbacia punctulata) were placed in a Plexiglas chamber (69 mm×45 mm×15.5 mm; length × width × height). A system was constructed to minimize convective flow by limiting temperature differences within the chamber to less than 0.1 °C. The movement of sperm was video-recorded at two levels:⩽100 μm (3 body lengths) and 5 mm (150 body lengths) below the chamber lid. When swimming speeds were measured using a computerized video motion-analysis system, a highly significant difference (P<0.0001) between cells at the two depths was found. Cells nearest the lid swam at 174.6±5.9 μm s−1 (mean ± S.E.M.), whereas those farther away slowed to only 111.1±9.9 μm s−1 (mean ± S.E.M.). Swimming speed was also found to be significantly (P<0.01) affected by paternity, but not by sperm age. We conclude that viscous wall effects must be carefully considered in studies of sperm motility and chemotaxis. The analysis of sperm on a microscope slide may substantially exaggerate swimming speed.
The Effect of Reduced Gravity on the Kinematics of Human Walking: A Test of the Dynamic Similarity Hypothesis for Locomotion
Authors: Donelan J. Maxwell , Kram Rodger
Published: April 2021

To gain insight into the basic principles that govern the biomechanics of locomotion, we investigated the effect of reduced gravity on walking kinematics. We hypothesized that humans walk in a dynamically similar fashion at combinations of speed and simulated gravity that provide equal values of the Froude number, v2/gLleg, where v is forward speed, g is gravitational acceleration and Lleg is leg length. The Froude number has been used to predict the kinematics and kinetics of legged locomotion over a wide range of animal sizes and speeds, and thus provides a potentially unifying theory for the combined effects of speed, size and gravity on locomotion biomechanics. The occurrence of dynamic similarity at equal Froude numbers has been attributed previously to the importance of gravitational forces in determining locomotion mechanics. We simulated reduced gravity using a device that applies a nearly constant upward force to the torso while subjects walked on a treadmill. We found that at equal Froude numbers, under different levels of gravity (0.25g–1.0g), the subjects walked with nearly the same duty factor (ratio of contact time to stride time), but with relative stride lengths (Ls/Lleg, where Ls is stride length) that differed by as much as 67 %, resulting in the rejection of our hypothesis. To understand the separate effects of speed and gravity further, we compared the mechanics of walking at the same absolute speed at different levels of gravity (0.25g–1.0g). In lower gravity, subjects walked with lower duty factors (10 %) and shorter relative stride lengths (16 %). These modest changes in response to the fourfold change in gravity indicate that factors other than gravitational forces are the primary determinants of walking biomechanics.
Comparison of Ca2+ Currents of Peptidergic Neurons Developing Differing Morphology with Time in Culture
Authors: Meyers Donald E. R. , Cooke Ian M.
Published: April 2021

The whole-cell patch-clamp technique was used to examine Ca2+ currents (ICa) in mature neurons cultured in defined medium and derived from the principal neurosecretory system of decapod crustaceans, the X-organ–sinus gland. After 1 day in culture, X-organ neurons of the crab Cardisoma carnifex showed vigorous outgrowth characterized either by the production of broad lamellipodia (veils) or, from smaller somata, a branching morphology. The neurons developing veils (veilers) had a large ICa (approximately 650 pA) and ICa current density (approximately 5 μA cm−2) while other types of neuron had little or no ICa. This distinction between the two types was still present after 5–6 days in culture. However, morphologies observed after additional outgrowth, when correlated with the ICa responses, allowed four groups to be distinguished: (1) veilers and (2) branching veilers, which developed from veilers and had a similar ICa density (approximately 3 μA cm−2); and, developing from the 1 day branchers, (3) spiny branchers or (4) small cells (ICa density approximately 0.8 μA cm−2). Immunoreactivity indicative of the presence of crustacean hyperglycemic hormone was found in all veilers and branching veilers tested, while molt-inhibiting hormone reactivity, when observed, was seen in cells having a robust ICa density (≥:1.2 μA cm−2). Normalized average current–voltage curves for each morphological group were examined for changes with increasing time in culture. The curves were consistent with the ICa being produced by a population of high-voltage-activated Ca2+ channels whose properties are biophysically indistinguishable and unaffected by time in culture. The averaged peak current did not change, despite an increase in neuronal surface area as outgrowth proceeded, and this resulted in a reduction of ICa density. This indicated that net addition of Ca2+ channels did not match the addition of new membrane under our culturing conditions.
The Kinematics of Swallowing In The Buccal Mass of Aplysia Californica
Authors: Drushel Richard F. , Neustadter David M. , Shallenberger Lori Lyn , Crago Patrick E. , Chiel Hillel J.
Published: April 2021

Changes in the positions, shapes and movements of the feeding apparatus (buccal mass) of the marine mollusc Aplysia californica were studied in intact, transilluminated juveniles. The buccal mass assumes characteristic shapes as its internal structure, the radula/odontophore, moves anteriorly (protracts) or posteriorly (retracts). These shapes are especially distinctive when the radula/odontophore has protracted forwards fully, is close to its resting or neutral position, or has retracted backwards fully. We refer to the shapes that occur at full protraction, transition and full retraction as shape 1 (spherical), shape 2 (ovoid) and shape 3 (Γ-shaped), respectively. We introduce this shape nomenclature in order to avoid confusion with the existing terms protraction and retraction, which we reserve exclusively to describe the direction of movement of the radula/odontophore.

The observed shape changes do not agree with those predicted on the basis of in vitro observations of a feeding head preparation, but are similar to shapes observed in vitro in the snail Lymnaea stagnalis. The buccal mass also rotates approximately 10 ° dorsally during retraction, pivoting on the attachment to the mouth, before the subsequent protraction and return of the buccal mass to the transition shape. This rotation may be due to activation of the extrinsic muscles of the buccal mass.

Plots of the buccal mass shape parameters eccentricity versus ellipticity create a two-dimensional shape space, which accurately quantifies the subtle transitions of shape between the different phases of the feeding cycle. Quantitative differences are observed between pure swallows and swallows with tearing behavior, but the qualitative shapes are similar. Hysteresis in the shape space plots of most swallows provides evidence for the hypothesis that protraction and retraction each have distinct ‘active’ and ‘return’ phases.

The observed kinematic pattern imposes constraints on the internal structures of the buccal mass and may be used to infer the shape and positions of the radula and odontophore.
Sprawling Locomotion in the Lizard Sceloporus Clarkii: Quantitative Kinematics of a Walking Trot
Authors: Reilly Stephen M. , Delancey Michael J.
Published: April 2021

Although the hindlimb is widely considered to provide the propulsive force in lizard locomotion, no study to date has investigated the kinematic patterns of the lizard hindlimb during running for more than one stride for a single individual. The quantitative kinematics of the hindlimb, pelvis and backbone are described here for two individuals of the lizard Sceloporus clarkii using a fast walking trot on a treadmill moving at a constant speed of 0.833 m s−1. Pelvic rotation, femoral retraction, knee flexion and posterior movement of the foot all begin before the foot hits the substratum and, thus, there is a terminal portion of the swing phase during which the limb is retracting. Pelvic rotation (to the opposite side), femoral protraction and knee flexion all begin before the foot leaves the substratum. The foot, however, continues to move posteriorly into the early swing phase. Thus, limb retraction and protraction movements do not directly correlate with footfall phases. Axial bending involves a rough standing wave with two nodes, one centered on each limb girdle. In Sceloporus clarkii, the foot clearly remains lateral to the knee and, thus, has a more sprawling posture than that of any other vertebrate studied to date. Therefore, the generalization that the ‘lacertilian’ foot passes under the knee joint is no longer supported. The kinematics of sprawling locomotion in Sceloporus clarkii are compared and contrasted with the general understanding of lizard locomotion based on qualitative work to date. Comparisons with other tetrapods reveal a fundamental functional dichotomy in hindlimb retraction mechanics in salamanders and mammals versus lizards that may be related to a key morphological difference in the saurian caudifemoralis muscle.
Effect of Reduced Gravity on The Preferred Walk–Run Transition Speed
Authors: Kram Rodger , Domingo Antoinette , Ferriss Daniel P.
Published: April 2021

We investigated the effect of reduced gravity on the human walk–run gait transition speed and interpreted the results using an inverted-pendulum mechanical model. We simulated reduced gravity using an apparatus that applied a nearly constant upward force at the center of mass, and the subjects walked and ran on a motorized treadmill. In the inverted pendulum model for walking, gravity provides the centripetal force needed to keep the pendulum in contact with the ground. The ratio of the centripetal and gravitational forces (mv2/L)/(mg) reduces to the dimensionless Froude number (v2/gL). Applying this model to a walking human, m is body mass, v is forward velocity, L is leg length and g is gravity. In normal gravity, humans and other bipeds with different leg lengths all choose to switch from a walk to a run at different absolute speeds but at approximately the same Froude number (0.5). We found that, at lower levels of gravity, the walk–run transition occurred at progressively slower absolute speeds but at approximately the same Froude number. This supports the hypothesis that the walk–run transition is triggered by the dynamics of an inverted-pendulum system.
The Anaerobic Endproduct Lactate Has a Behavioural and Metabolic Signalling Function in the Shore Crab Carcinus Maenas
Authors: Wachter Bart De , Sartoris Franz-Jozef , Pörtner Hans-Otto
Published: April 2021

This study presents the first evidence that, in invertebrates, the anaerobic endproduct lactate has an alarm signal function and induces metabolic and behavioural responses as in the anuran Bufo marinus. In support of this function, behavioural hypothermia was demonstrated in the shore crab Carcinus maenas. The animals moved to a cooler environment when exposed to hypoxic conditions. A decrease in preferred temperature of the same magnitude was also found when normoxic animals were injected with an iso-osmotic lactate solution resulting in a haemolymph concentration of approximately 12 mmol l−1. Under normoxic and moderately hypoxic conditions , injection of this lactate solution also caused a significant increase in the rate of oxygen consumption (100 and 50 % respectively). The increase in the rate of oxygen consumption was smaller and delayed, but lasted longer, under hypoxic conditions compared with normoxic conditions. Low but significant correlations between levels of lactate and levels of adrenaline, octopamine and tryptophan suggest the involvement of biogenic amines in the mediation of the signal.
Pulsatile Urea Excretion in the Toadfish (Opsanus Beta) is Due to A Pulsatile Excretion Mechanism, not a Pulsatile Production Mechanism
Authors: Wood Chris M. , Hopkins Todd E. , Walsh Patrick J.
Published: April 2021

When subjected to a crowding/confinement protocol in the laboratory, toadfish become facultatively ureotelic, excreting approximately 90 % of their nitrogenous waste as urea-nitrogen (urea-N). The great majority of this excretion occurs via large, irregular pulses from the head region which occur on average once per day, with a duration of 3 h or less. Pulses measured chemically by the appearance of urea-N in the external water were identical to those measured by assaying [14C]urea appearance in the water from the blood plasma. Individual toadfish maintained plasma urea concentrations over widely differing ranges (6600–39 890 μmol-N l−1). However, independent of absolute levels, both [14C]urea and total urea were distributed at ratios close to unity between the blood plasma and the water compartments of liver and white muscle. At times of pulsatile excretion, plasma urea concentration fell sharply. These decreases, distributed throughout the tissues of the whole body, closely matched the sizes of the measured excretion pulses. Between pulses, plasma urea concentration increased steadily at a much slower rate; the rate of rise, when distributed throughout the tissues of the whole body, corresponded to the time-averaged excretion rate over the whole day. Infusion of a typical pulse amount of urea immediately after the end of a natural pulse event raised plasma urea concentration slightly above the pre-pulse level, but did not induce another pulse event. Plasma cortisol levels declined by approximately 60 % over the 4 h period prior to a natural pulse event and then rose quickly again once the pulse had occurred. These results indicate that urea pulses are due to activation of an excretion mechanism that rapidly clears urea from the blood plasma, thereby lowering stores throughout the whole body. Metabolic production of urea is continuous and is not responsible for pulsatile excretion. The pulse event is not triggered by a specific plasma urea threshold, but may involve the hypothalamo–interrenal axis.
Maintenance of Motor Pattern Phase Relationships in the Ventilatory System of the Crab
Authors: Dicaprio R. A. , Jordan G. , Hampton T.
Published: April 2021

The central pattern generator responsible for the gill ventilation rhythm in the shore crab Carcinus maenas can produce a functional motor pattern over a large (eightfold) range of cycle frequencies. One way to continue to generate a functional motor pattern over such a large frequency range would be to maintain the relative timing (phase) of the motor pattern as cycle frequency changes. This hypothesis was tested by measuring the phase of eight events in the motor pattern from extracellular recordings at different rhythm frequencies. The motor pattern was found to maintain relatively constant phase relationships among the various motor bursts in this rhythm over a large (sevenfold) range of cycle frequencies, although two phase-maintaining subgroups could be distinguished. Underlying this phase maintenance is a corresponding change in the time delay between events in the motor pattern ranging from 470 to 1800 ms over a sevenfold (300–2100 ms) change in cycle period. Intracellular recordings from ventilatory neurons indicate that there is very little change in the membrane potential oscillation in the motor neurons with changes in cycle frequency. However, recordings from nonspiking interneurons in the ventilatory central pattern generator reveal that the rate of change of the membrane potential oscillation of these neurons varies in proportion to changes in cycle frequency. The strict biomechanical requirements for efficient pumping by the gill bailer, and the fact that work is performed in all phases of the motor pattern, may require that this motor pattern maintain phase at all rhythm frequencies.
Cardiovascular Functions in Two Macruran Decapod Crustaceans (Procambarus Clarkii and Homarus Americanus) During Periods of Inactivity, Tail Flexion and Cardiorespiratory Pauses
Authors: Reiber Carl L. , Mcmahon Brian R. , Burggren Warren W.
Published: April 2021

Arterial hemolymph flow was measured in restrained crayfish (Procambarus clarkii) and lobsters (Homarus americanus). Implanted pulsed Doppler flow transducers were used to measure arterial flows in the anterior aorta, posterior aorta, sternal artery, lateral artery, ventral thoracic artery and ventral abdominal artery, allowing determination of flow simultaneously in several arteries over a period of 4 days. Calculated Doppler hemolymph flow showed a strong correlation (P<0.05) with ‘pumped’ hemolymph flow as determined by in situ calibration.

Arterial flow patterns remained constant during quiet conditions. In crayfish, cardiac output was 7.5±1.1 ml min−1 (252 ml kg−1 min−1), of which the anterior aorta received 1.3±0.15 ml min−1 (20.1±4.0 %), the posterior aorta received 0.8±0.1 ml min−1 (12.3±2.7 %) and the sternal artery received 5.2±1.4 ml min−1 (67.5±37.0 %). Mean heart frequency at rest was 125.6±5.2 beats min−1 and stroke volume was 0.06±0.01 ml beat−1 (1.98 ml kg−1 beat−1). In lobsters, cardiac output was 60.8±4.4 ml min−1 (93.6±6.8 ml kg−1 min−1), with the anterior aorta receiving 7.8±0.8 ml min−1 (12.8±2.7 %), the lateral arteries receiving 0.6±0.2 ml min−1 (1.0±0.5 %), the posterior aorta receiving 12.6±1.0 ml min−1 (20.7±3.3 %) and the sternal artery receiving 38.9±4.1 ml min−1 (64.0±13.4 %). Flows in the branches of the sternal artery were 0.3±0.05 ml min−1 (0.5±2 %) in the ventral abdominal artery and 4.0±0.1 ml min−1 (6.5±0.3 %) in the ventral thoracic artery. Lobster heart rate was 82.5±2.9 beats min−1 and stroke volume was 0.7±0.05 ml beat−1.

Periods of constant hemolymph flow were interrupted by tail flexions (abdominal flexion) and, in lobsters, periods of cardiac/respiratory pause. Tail movement increased flow (peak height and minimum flow values) in both crayfish and lobsters, although the general wave form of hemolymph flow and pressure did not change. In lobsters, periodic respiratory pauses were observed during which all arteries received hemolymph, despite the low heart rate.
Quantitative Modelling of the Effects of Selected Intracellular Metabolites on pH in Fish White Muscle
Authors: Arthur Peter G. , West Timothy G. , Hochachka Peter W.
Published: April 2021

A model is presented that provides guidelines to the identification of key experimental variables influencing proton balance and intracellular pH in vertebrate white muscle. We have drawn on data from the literature on rainbow trout (Oncorhynchus mykiss) in an attempt to quantify the influence of metabolic, ionic and transport components of proton generation and proton consumption after exercise. Only minor changes in proton balance and in calculated intracellular pH were caused by considering changes in the concentration of bicarbonate or including the acid–base characteristics of purine nucleotides. Intracellular pH, as estimated by the model, was more acidic at some time points in recovery compared with in vivo measurements, and this would appear to result mainly from inaccuracies in quantifying the phosphate component of proton buffering. Nevertheless, the model was able to simulate the typical pattern of muscle acidosis and recovery observed for trout, including the transient post-exercise acidification and the slow recovery rate. As with previous pHi models, comparison of model estimates with experimental observations is essential in this approach in order to identify whether all of the relevant metabolic processes have been considered for accurate quantification of proton balance within the white muscle compartment.
Feeding Kinematics of Juvenile Swellsharks, Cephaloscyllium Ventriosum
Authors: Ferry-Graham Lara A.
Published: April 2021

To investigate how feeding behaviors change with prey size, high-speed video recording was used to examine the kinematics of prey capture and transport in 1-year-old swellsharks Cephaloscyllium ventriosum (Scyliorhinidae: Carchariniformes) feeding on two differently sized prey items. Prey capture in these sharks generally consisted of an initially ram-dominated capture bite, one or more manipulation bites, a holding phase during which the food was held in the teeth of the shark, and then suction-dominated prey transport. During initial capture and transport, most of the water taken in is forced back out of the mouth anteriorly rather than continuing posteriorly out through the gill openings. Dye experiments in which dye-perfused prey items were ingested by the sharks confirm this observation; distinct jets of colored water were video-taped as they were ejected from the mouth. Very late in prey transport, a bolus of water is ejected through the gill slits; however, by this time, the majority of water appears already to have exited the buccal cavity through the mouth. Such patterns were observed for sharks feeding on both small and large prey items. Although a basic pattern of prey capture and transport was regularly repeated among strikes, kinematic patterns during prey capture and transport were variable both within and among individuals, indicating that prey acquisition is not tightly controlled. However, the amount of variability was similar among prey sizes. In addition, there were no detectable changes in behavior due to prey item size. Ram-suction index values confirmed that similar capture modes were being utilized for both prey sizes.
Honeybee Vision: Analysis of Orientation and Colour in the Lateral, Dorsal and Ventral Fields of View
Authors: Giger A. D. , Srinivasan M. V.
Published: April 2021

The ability of honeybees (Apis mellifera) to learn and recognise peripherally presented patterns was investigated by training bees in a Y-maze which presented patterns on the side walls, the ceiling or the floor. We found that pattern orientation is learnt and recognised in the lateral and frontal visual field, but not in the dorsal or ventral fields. Colour information, in contrast, is used in the lateral and frontal as well as the ventral visual field, but not in the dorsal field. If pattern orientation is different on opposite sides of the visual field during training, both patterns are learned, but each on its own is sufficient for the bees to recognise the learnt stimulus. However, unilaterally learnt pattern information, be it orientation or colour, cannot be accessed when the test pattern is viewed on the other side. That is, interocular transfer of such information does not occur.
Processing of Artificial Visual Feedback in the Walking Fruit Fly Drosophila Melanogaster
Authors: Strauss Roland , Schuster Stefan , Götz Karl Georg
Published: April 2021

A computerized 360 ° panorama allowed us to suppress most of the locomotion-induced visual feedback of a freely walking fly without neutralizing its mechanosensory system (‘virtual open-loop’ conditions). This novel paradigm achieves control over the fly’s visual input by continuously evaluating its actual position and orientation.

In experiments with natural visual feedback (closed-loop conditions), the optomotor turning induced by horizontal pattern motion in freely walking Drosophila melanogaster increased with the contrast and brightness of the stimulus. Conspicuously striped patterns were followed with variable speed but often without significant overall slippage.

Using standard open-loop conditions in stationarily walking flies and virtual open-loop or closed-loop conditions in freely walking flies, we compared horizontal turning induced by either horizontal or vertical motion of appropriately oriented rhombic figures. We found (i) that horizontal displacements and the horizontal-motion illusion induced by vertical displacements of the oblique edges of the rhombic figures elicited equivalent open-loop turning responses; (ii) that locomotion-induced visual feedback from the vertical edges of the rhombic figures in a stationary horizontal position diminished the closed-loop turning elicited by vertical displacements to only one-fifth of the response to horizontal displacements; and (iii) that virtual open-loop responses of mobile flies and open-loop responses of immobilized flies were equivalent in spite of delays of up to 0.1 s in the generation of the virtual stimulus.

Horizontal compensatory turning upon vertical displacements of oblique edges is quantitatively consistent with the direction-selective summation of signals from an array of elementary motion detectors for the horizontal stimulus components within their narrow receptive fields. A compensation of the aperture-induced ambiguity can be excluded under these conditions. However, locomotion-induced visual feedback greatly diminished the horizontal-motion illusion in a freely walking fly. The illusion was used to assay the quality of open-loop simulation in the new paradigm.
Octopamine Modulates the Responses and Presynaptic Inhibition of Proprioceptive Sensory Neurones in the Locust Schistocerca Gregaria
Authors: Matheson Thomas
Published: April 2021

A multineuronal proprioceptor, the femoral chordotonal organ (feCO), monitors the position and movements of the tibia of an insect leg. Superfusing the locust metathoracic feCO with the neuromodulator octopamine, or the octopamine agonist synephrine, affects the position (tonic) component of the organ’s response, but not the movement (phasic) component. Both octopamine and synephrine act with the same threshold (10−6 mol l−1).

Individual sensory neurones that respond tonically at flexed tibial angles show increased tonic spike activity following application of octopamine, but those that respond at extended angles do not. Tonic spiking of phaso-tonic flexion-sensitive neurones is enhanced but their phasic spiking is unaffected.

Bath application of octopamine to the feCO increases the tonic component of presynaptic inhibition recorded in the sensory terminals, but not the phasic component. This inhibition should at least partially counteract the increased sensory spiking and reduce its effect on postsynaptic targets such as motor neurones. Furthermore, some phasic sensory neurones whose spiking is not affected by octopamine nevertheless show enhanced tonic synaptic inputs.

The chordotonal organ is not known to be under direct efferent control, but its output is modified by octopamine acting on its sensory neurones to alter their responsiveness to mechanical stimuli and by presynaptic inhibition acting on their central branches. The effects of this neuromodulator acting peripherally on sensory neurones are therefore further complicated by indirect interactions between the sensory neurones within the central nervous system. Increases of sensory neurone spiking caused by neuromodulators may not necessarily lead to parallel increases in the responses of postsynaptic target neurones.
Cholinergic Activation of Stridulatory Behaviour in the Grasshopper Omocestus Viridulus (L.)
Authors: Heinrich Ralf , Hedwig Berthold , Elsner Norbert
Published: April 2021

When acetylcholine (ACh) and its agonists are injected into neuropile regions of the protocerebrum and the suboesophageal ganglion of male and female grasshoppers of the species Omocestus viridulus (L.), they elicit stridulation in a pattern no different from that of natural song. Stridulation can even be evoked in mated females which normally do not sing. By choosing suitable ACh agonists, nicotinic and muscarinic ACh receptors can be activated selectively. Activation of nicotinic ACh receptors produces individual song sequences with rapid onset; the stridulation induced by activation of the muscarinic ACh receptors begins after a longer latency, increases slowly in intensity and is maintained for many minutes. The sites within the cephalic ganglia where song can be initiated pharmacologically coincide with regions in which descending stridulatory command neurones arborize.
The Effects of the Wingbeat Cycle on Respiration in Black-Billed Magpies (Pica Pica)
Authors: Boggs Dona F. , Jenkins Farish A. , Dial Kenneth P.
Published: April 2021

Interclavicular and posterior thoracic airsac pressures, tracheal airflows and pectoralis muscle activity were recorded simultaneously to determine the effect of the wingbeat cycle upon the function of the respiratory system. The effects of the wingbeat cycle on the relative positions of thoraco-abdominal skeletal structures were also assessed using high-speed X-ray cinematography of magpies Pica pica flying in a windtunnel.

We found that the furcula bends laterally on the downstroke and recoils medially on the upstroke, as previously described for starlings, and that the coraco-sternal joint (the most consistently visible point on the sternum for digitization) is displaced dorsally during the downstroke and ventrally, with respect to the vertebral column, during the upstroke. In magpies, there are generally three wingbeat cycles during a respiratory cycle. When downstroke occurs during inspiration, its compressive effect reduces the inspiratory subatmospheric airsac pressure by an average of 92 % (0.35 kPa), whereas when upstroke occurs during expiration its expansive effect can reduce the expiratory supra-atmospheric airsac pressure by 63 % (0.23 kPa). Corresponding changes occur in tracheal airflow. Changes in respiratory parameters during short flights with respect to resting values include a doubling of tidal volume and a tripling of respiratory frequency.

We conclude that the wingbeat cycle can have a substantial impact on respiratory system function in the flying magpie, and that this represents a mechanical basis for breathing patterns and patterns of phasic coordination between wingbeat and respiratory cycles that may result in minimal interference and maximal assistance from the wingbeat upon the respiratory cycle.
Hearing and Hunting in red Bats (Lasiurus Borealis, Vespertilionidae): Audiogram and ear Properties
Authors: Obrist Martin K. , Wenstrup Jeffrey J.
Published: April 2021

We examined aspects of hearing in the red bat (Lasiurus borealis) related to its use of biosonar. Evoked potential audiograms, obtained from volume-conducted auditory brainstem responses, were obtained in two bats, and the sound pressure transformation of the pinna was measured in three specimens. Field-recorded echolocation signals were analysed for comparison. The fundamental sonar search calls sweep from 45 to 30 kHz (peak energy at 35 kHz), approach-phase calls sweep from 65 to 35 kHz (peak 40 kHz) and terminal calls sweep from 70 to 30 kHz (peak 45 kHz). The most sensitive region of the audiogram extended from 10 kHz to 45–55 kHz, with maximum sensitivity as low as 20 dB SPL occurring between 25 and 30 kHz. A relative threshold minimum occurred between 40 and 50 kHz. With increasing frequency, the acoustic axis of the pinna moves upwards and medially. The sound pressure transformation was noteworthy near 40–45 kHz; the acoustic axis was closest to the midline, the −3 dB acceptance angles showed local minima, and the pinna gain and interaural intensity difference were maximal. These results are related to the known echolocation and foraging behavior of this species and match the spectral components of approach- and final-phase calls. We conclude that co-evolution with hearing prey has put a higher selective pressure on optimizing localization and tracking of prey than on improving detection performance.
Alterations of Ionic Membrane Permeabilities in Multidrug-Resistant Neuroblastoma × Glioma Hybrid Cells
Authors: Gérard Valerie , Rouzaire-Dubois Beatrice , Dilda Pierre , Dubois Jean-Marc
Published: April 2021

A population of NG108-15 neuroblastoma cells resistant to doxorubicin (NG/DOXR) was established. The cells exhibited a multidrug resistance phenotype with cross-resistance to vinblastin and colchicine, overexpression of a 170 kDa membrane protein identified as P-glycoprotein and reversal of resistance by verapamil and quinine. Compared with NG108-15 cells, NG/DOXR cells showed an increase in Na+ current density and a decrease in cyclic-AMP-activated Cl− current density with no change in K+- and volume-sensitive Cl− current densities. As previously observed in NG108-15 cells, the vacuolar-type H+-ATPase inhibitors bafilomycin A1 and nitrate induced membrane depolarizations in NG/DOXR cells. The resting potentials of sensitive and resistant cells were not significantly different, but the depolarizations evoked by these agents were significantly larger in NG/DOXR than in NG108-15 cells. The resting membrane potential of NG/DOXR cells, but not that of NG108-15 cells, was depolarized by verapamil, and this effect was abolished by bafilomycin. The volume-sensitive Cl− currents of drug-sensitive and drug-resistant cells were inhibited by a decrease in intracellular pH from 7.3 to 6.8. Whereas bafilomycin prevents activation of Cl− currents in both drug-sensitive and drug-resistant cells, verapamil inhibited the Cl− current only in NG/DOXR cells. The results are discussed in terms of the roles of cytoplasmic pH and membrane potential in multidrug resistance.
Muscle Power Output Limits Fast-Start Performance in Fish
Authors: Wakeling James M. , Johnston Ian A.
Published: April 2021

Fast-starts associated with escape responses were filmed at the median habitat temperatures of six teleost fish: Notothenia coriiceps and Notothenia rossii (Antarctica), Myoxocephalus scorpius (North Sea), Scorpaena notata and Serranus cabrilla (Mediterranean) and Paracirrhites forsteri (Indo-West-Pacific Ocean). Methods are presented for estimating the spine positions for silhouettes of swimming fish. These methods were used to validate techniques for calculating kinematics and muscle dynamics during fast-starts. The starts from all species show common patterns, with waves of body curvature travelling from head to tail and increasing in amplitude. Cross-validation with sonomicrometry studies allowed gearing ratios between the red and white muscle to be calculated. Gearing ratios must decrease towards the tail with a corresponding change in muscle geometry, resulting in similar white muscle fibre strains in all the myotomes during the start. A work-loop technique was used to measure mean muscle power output at similar strain and shortening durations to those found in vivo. The fast Sc. notata myotomal fibres produced a mean muscle-mass-specific power of 142.7 W kg−1 at 20 °C. Velocity, acceleration and hydrodynamic power output increased both with the travelling rate of the wave of body curvature and with the habitat temperature. At all temperatures, the predicted mean muscle-mass-specific power outputs, as calculated from swimming sequences, were similar to the muscle power outputs measured from work-loop experiments.
Morphometric and Biochemical Characteristics of Ventricular Hypertrophy in Male Rainbow Trout (Oncorhynchus Mykiss)
Authors: Clark Raymond J. , Rodnick Kenneth J.
Published: April 2021

We examined the morphometric and biochemical effects of ventricular hypertrophy in male rainbow trout (Oncorhynchus mykiss) during sexual maturation. Our investigation focused on characterizing the growth of ventricular layers, on cardiomyocyte dimensions (length, cross-sectional area and cell volume) and on the activities of enzymes involved in intermediary metabolism.

Relative ventricle mass (100×ventricle mass/body mass) increased by as much as 2.4-fold during sexual maturation [as defined by an increasing gonadosomatic index (100×gonad mass/body mass)], and this resulted in an increased proportion of epicardium relative to endocardium. Ventricular enlargement was associated with increased length (+31 %) and transverse cross-sectional area (+83 %) of cardiomyocytes, which resulted in an expansion of up to 2.2-fold in mean myocyte volume (from 1233 to 2751 μm3). These results indicate that sexual maturation induces ventricular enlargement through myocyte hypertrophy. Cell length and cross-sectional area were similar in both myocardial layers, and myocytes were elliptical rather than circular in transverse cross section. Ventricular hypertrophy did not alter transverse cell shape, perhaps reflecting the maintenance of short diffusion distances for small molecules as cells hypertrophy. Myocyte hypertrophy could not account entirely for the sevenfold range of ventricle masses from different-sized fish, indicating that myocyte hyperplasia contributes substantially to ventricular growth as trout grow.

Measurements of the maximal activities of metabolic enzymes demonstrated that ventricular hypertrophy was associated with (1) higher epicardial but not endocardial activities of citrate synthase (by 23 %) and β-hydroxyacyl-CoA dehydrogenase (by 20 %); (2) lower activities of hexokinase (by 50 %) in both layers, and (3) no change in lactate dehydrogenase or pyruvate kinase activities, which were also similar between layers. These results suggest that the energetic needs of the hypertrophied trout ventricle may be met through increased reliance on fatty acid oxidation, particularly by the endocardium, but decreased reliance on glucose as a metabolic fuel in both layers.
Ontogenetic Scaling Of Hydrostatic Skeletons: Geometric, Static Stress And Dynamic Stress Scaling Of The Earthworm Lumbricus Terrestris
Authors: Quillin Kim J.
Published: April 2021

Soft-bodied organisms with hydrostatic skeletons range enormously in body size, both during the growth of individuals and in the comparison of species. Therefore, body size is an important consideration in an examination of the mechanical function of hydrostatic skeletons. The scaling of hydrostatic skeletons cannot be inferred from existing studies of the lever-like skeletons of vertebrates and arthropods because the two skeleton types function by different mechanisms. Hydrostats are constructed of an extensible body wall in tension surrounding a fluid or deformable tissue under compression. It is the pressurized internal fluid (rather than the rigid levers of vertebrates and arthropods) that enables the maintenance of posture, antagonism of muscles and transfer of muscle forces to the environment. The objectives of the present study were (1) to define the geometric, static stress and dynamic stress similarity scaling hypotheses for hydrostatic skeletons on the basis of their generalized form and function, and (2) to apply these similarity hypotheses in a study of the ontogenetic scaling of earthworms, Lumbricus terrestris, to determine which parameters of skeletal function are conserved or changed as a function of body mass during growth (from 0.01 to 8 g). Morphometric measurements on anesthetized earthworms revealed that the earthworms grew isometrically; the external proportions and number of segments were constant as a function of body size. Calculations of static stresses (forces per cross-sectional area in the body wall) during rest and dynamic stresses during peristaltic crawling (calculated from measurements of internal pressure and body wall geometry) revealed that the earthworms also maintained static and dynamic stress similarity, despite a slight increase in body wall thickness in segment 50 (but not in segment 15). In summary, the hydrostatic skeletons of earthworms differ fundamentally from the rigid, lever-like skeletons of their terrestrial counterparts in their ability to grow isometrically while maintaining similarity in both static and dynamic stresses.
Long-Lasting Depolarization Of Leech Neurons Mediated By Receptors With A Nicotinic Binding Site
Authors: Szczupak Lidia , Edgar Julia , Peralta Maria Luisa , Kristan William B.
Published: April 2021

The serotonergic Retzius neurons of the leech midbody ganglia respond in a complex manner to pressure pulses of acetylcholine (ACh) applied onto their soma with a fast depolarization followed by a slower hyperpolarization and an additional delayed long-lasting depolarization. The delayed depolarization is the subject of the present study. The delayed depolarization could be elicited by long (>1 s) ACh pressure pulses or by short pulses (10 ms) of carbachol, nicotine and DMPP, but not by muscarinic agonists. It was inhibited by bath application of nicotine (10–100 μmol l−1), strychnine (100 μmol l−1) and atropine (10–100 μmol l−1). Nicotinic antagonists that blocked the fast depolarization and the slow hyperpolarization (100 μmol l−1 mecamylamine and d-tubocurarine) did not affect the delayed depolarization induced by carbachol. Partial replacement of the extracellular Na+ by glucamine caused a decrease in the amplitude of the response and a shift of its reversal potential to more negative values. Carbachol pulses applied to Retzius neurons of the ganglia innervating the reproductive segments elicited delayed depolarizations of much smaller amplitude than the ones recorded in Retzius neurons from standard segments. The delayed depolarization could be elicited by the application of short agonist pulses onto different loci over the surface of the ganglion, at a distance from the soma. Isolated cultured Retzius neurons did not exhibit the delayed depolarization although they readily expressed the earlier phases of the complex cholinergic response. Carbachol pulses applied to the soma of other neurons in the leech ganglion produced a variety of specific responses.

The results suggest that the delayed depolarization was produced by the activation of a cationic conductance mediated by receptors with a pharmacological profile similar to that of the α9 nicotinic receptors and was not a byproduct of the early phases of the cholinergic response. The response seemed to be initiated in the extensive neuropilar processes of the Retzius cell, enabling a persistent excitatory signal.
Basal Acetylcholine Release In Leech Ganglia Depolarizes Neurons Through Receptors With A Nicotinic Binding Site
Authors: Burgin Antonia Marín , Szczupak Lidia
Published: April 2021

The response of Retzius neurons, the main neuronal source of serotonin in the leech nervous system, to cholinergic agonists has been extensively investigated. In this study, we analyzed the effects of inhibiting the acetylcholinesterase (AChE) activity in the leech midbody ganglion on the electrophysiological activity of the Retzius neurons. Bath application of neostigmine and physostigmine (0.1–100 μmol l−1) produced, after a delay, a strong depolarization of the Retzius neurons with a dose-dependent amplitude and latency. The amplitude of this depolarization increased as the extracellular level of Ca2+ increased and decreased as the extracellular level of Ca2+ decreased. The response to neostigmine and physostigmine was inhibited by curare (100 μmol l−1), nicotine (10 μmol l−1), atropine (100 μmol l−1) and strychnine (100 μmol l−1), but was not affected by mecamylamine (100 μmol l−1) or hexamethonium (100 μmol l−1). Superfusion with solutions containing 100 μmol l−1 strychnine or atropine produced a progressive hyperpolarization of the Retzius neurons, while superfusion with 100 μmol l−1 curare did not. The hyperpolarization induced by atropine was inhibited in the presence of curare. Other neurons in the ganglion showed distinctive responses to the AChE inhibitors that were coincident with their responses to cholinergic agonists.

The results suggest the existence of a basal level of acetylcholine (ACh) release in the leech ganglion that is powerfully counteracted by endogenous AChE activity. Under control conditions, this basal release appears to be sufficient to generate an ACh tonus that regulates the membrane potential of Retzius neurons. Since these neurons can support a sustained firing rate, which is dependent on the membrane potential, the results presented in this report suggest that the basal ACh tonus regulates the output of these neuromodulatory serotonergic neurons.
Regulation of Ion Transport Across Lamprey (Lampetra Fluviatilis) Erythrocyte Membrane by Oxygen Tension
Authors: Virkki Leila V. , Salama Annika , Nikinmaa Mikko
Published: April 2021

We have measured the effects of oxygen tension on the transport of Na+, K+ and Cl− across the erythrocyte membrane of the lamprey Lampetra fluviatilis. The transport of each ion was affected by the oxygen tension of the medium. Hypoxic conditions (2 kPa) caused an increase in the acidification-induced influx of Na+via Na+/H+ exchange. The influx of K+ was only slightly affected by the oxygenation of the medium. In contrast, the basal K+ efflux, measured using the radioactive isotope 43K, was markedly reduced by decreasing the oxygen tension of the medium, whereas the K+ flux in hypotonic medium was not affected. Only minor effects of hypoxic conditions on the influx of Cl−were observed in either isotonic or hypotonic conditions (there was a tendency for the isotonic influx to increase) or on the efflux in isotonic conditions. However, deoxygenation caused a marked reduction in the Cl− efflux in hypotonic conditions. The results show that oxygen tension has a marked effect on the pH and volume regulatory transport pathways of lamprey erythrocytes. For K+ and Cl−, the regulation appears to be asymmetric, i.e. influx and efflux are affected differently.