bluuebunny/crossref_metadata_2025 huggingface dataset:
Muscle Power Output During Escape Responses in an Antarctic Fish
Authors: Franklin Craig E. , Johnston Ian A.
Published: April 2021

Escape responses (C-shaped fast-starts) were filmed at 500 frames s−1 in the Antarctic rock cod (Notothenia coriiceps) at 0 °C. The activation and strain patterns of the superficial fast myotomal muscle were measured simultaneously using electromyography and sonomicrometry respectively. In order to bend the body into the initial C-shape, the muscle fibres in the rostral myotomes (at 0.35L, where L is total length) shortened by up to 13 % of their resting length at a maximum velocity of 1.68 fibre lengths s−1. During the contralateral contraction, muscle fibres were stretched (by 5 % and 7 % at 0.35L and 0.65L, respectively) and were activated prior to the end of lengthening, before shortening by up to 12 % of resting fibre length (peak-to-peak strain). Representative strain records were digitised to create cyclical events corresponding to the C-bend and contralateral contraction. Isolated fibres were subjected to the abstracted strain cycles and stimulated at the same point and for the same duration as occurs in vivo. During the early phase of shortening, muscle shortening velocity (V) increased dramatically whilst the load was relatively constant and represented a substantial fraction of the maximum isometric stress. Pre-stretch of active muscle was associated with significant force enhancement. For the contralateral contraction, V exceeded that predicted by the steady-state force–velocity relationship for considerable periods during each tailbeat, contributing to relatively high maximum instantaneous power outputs of up to 290 W kg−1 wet muscle mass. In vitro experiments, involving adjusting strain, cycle duration and stimulation parameters, indicated that in vivo muscle fibres produce close to their maximum power. During escape responses, the maximum velocity and acceleration recorded from the centre of gravity of the fish were 0.71±0.03 m s−1 and 17.1±1.4 m s−2, respectively (mean ± S.E.M., N=7 fish). Muscle performance was sufficient to produce maximum velocities and accelerations that were within the lower end of the range reported for temperate-zone fish.
How Does the Contractile Vacuole of Paramecium Multimicronucleatum Expel Fluid? Modelling The Expulsion Mechanism
Authors: Naitoh Yutaka , Tominaga Takashi , Ishida Masaki , Fok Agnes K. , Aihara Marilynn S. , Allen Richard D.
Published: April 2021

To examine the forces needed for discharge of the fluid contents from the contractile vacuole of Paramecium multimicronucleatum, the time course of the decrease in vacuole diameter during systole (the fluid-discharging period) was compared with that of various vacuole discharge models. The observed time course did not fit that predicted by a model in which contraction of an actin–myosin network surrounding the vacuole caused discharge nor that predicted by a model in which the surface tension of the lipid bilayer of the vacuole caused discharge. Rather, it fitted that predicted by a model in which the cell’s cytosolic pressure was responsible for discharge. Cytochalasin B, an effective inhibitor of actin polymerization, had no effect on the in vivo time course of systole. An injection of a monoclonal antibody raised against the proton pumps of the decorated spongiomes (now known to be the locus of fluid segregation in P. multimicronucleatum) disrupted the decorated spongiomes and reduced the rate of fluid segregation, whereas it did not alter the time course of systole. We conclude that in P. multimicronucleatum the internal pressure of the contractile vacuole is caused predominantly by the cytosolic pressure and that the fluid-segregation mechanism does not directly affect the fluid-discharge mechanism. Elimination of this cytosolic pressure by rupturing the cell revealed the presence of a novel fluid-discharge mechanism, apparently centered in the vacuole membrane. The involvement of tubulation of the vacuole membrane as the force-generating mechanism for fluid discharge in disrupted cells is discussed.
Increased Concentrations of Haemolymph Mg2+ Protect Intracellular Ph and Atp Levels During Temperature Stress and Anoxia in the Common Shrimp Crangon Crangon
Authors: Sartoris F. J. , Pörtner H. O.
Published: April 2021

The effects of temperature (0, 5, 10, 15 and 20 °C) and of anoxia (at 5 °C) on extracellular Mg2+ concentration ([Mg2+]e), intracellular pH (pHi) and ATP and lactate levels were investigated in intermoult adults of the common shrimp Crangon crangon. All animals caught in summer (summer animals) showed a slight but significant increase in [Mg2+]e at low temperatures. In contrast, at every temperature tested, a few of the animals caught in winter (winter animals) showed elevated [Mg2+]e during shortterm (4 h) but not during long-term (6 days) incubations. The reasons for the overshoot in Mg2+ concentrations in individual animals remain unexplained, but a protective effect of extracellular Mg2+ on intracellular pH and on ATP concentrations was visible at haemolymph Mg2+ concentrations above 15 mmol l−1. The influence of high extracellular [Mg2+] on pHi and intracellular ATP and lactate levels under normoxic and anoxic conditions was tested using an incubation medium containing 150–250 mmol l−1 Mg2+. When haemolymph Mg2+ levels were manipulated by exposure of the animal to high levels of Mg2+ in the external medium, animals with a haemolymph [Mg2+] below the threshold concentration of 15 mmol l−1 had significantly lower values of intracellular pH than animals with haemolymph [Mg2+] above 15 mmol l−1. In addition, the elevation of haemolymph [Mg2+] by incubation in high-[Mg2+] water prevented the drop in pHi and the rise in lactate levels induced by anoxia. The protective effect of high levels of extracellular Mg2+ did not depend upon the [Ca2+]/[Mg2+] ratio but only on [Mg2+]e. However, experiments with isolated muscle tissues showed no dependence of muscle intracellular pH on [Mg2+]e under both normoxic and anoxic conditions, leading to the conclusion that the protective effect is evoked via a central, possibly anaesthetising, effect of high [Mg2+]e. The dependence of pHi and muscle [ATP] on extracellular [Mg2+] resembles the protective effect of high Mg2+ levels on the post-ischaemic mammalian heart.
The Sub-Pulmonary Conus and the Arterial Anastomosis as Important Sites of Cardiovascular Regulation in the Crocodile Crocodylus Porosus
Authors: Axelsson Michael , Franklin Craig E. , Fritsche Regina , Grigg Gordon C. , Nilsson Stefan
Published: April 2021

We present evidence to support the hypothesis that the arterial anastomosis and the cogteeth-like valves located in the sub-pulmonary conus in the right ventricle are important sites of cardiovascular regulation in the crocodile Crocodylus porosus. The influence of the arterial anastomosis on the development of the ‘foramen spike’ in the left aortic pressure trace, which occurs at the onset of diastole when the pressures in the right and left aortas become equal, and on gastrointestinal blood flow was examined in unanaesthetised C. porosus using blood vessel occluders. Measurements of blood flow in the arterial anastomosis showed that, during non-shunting conditions, there was a substantial systolic blood flow from the right aorta into the coeliac artery. The total coeliac artery blood flow was the sum of the anastomosis flow from the right aorta plus the left aortic flow originating from the right aorta via the foramen of Panizza during diastole. During mechanically induced pulmonary-to-systemic shunting, the anastomosis blood flow was reversed, with blood flowing from the left to the right aorta. The magnitude of the ‘foramen spike’ was directly related to the vascular resistance in the anastomosis. When vascular resistance in the anastomosis was high, such as during mechanical occlusion, there was an increase in the right aortic to left aortic pressure gradient during systole which resulted in an increase the foramen spike amplitude. Recordings of right intraventricular pressure in unanaesthetised C. porosus showed spontaneous changes in right intracardiac systolic pressure. The pressure recordings were biphasic, with the second contraction (isometric) being highly variable in size, indicating the control of pulmonary outflow resistance, possibly via the ‘cogteeth valves’ located in the sub-pulmonary conus in the right ventricle.
Temperature and Developmental Plasticity of Muscle Phenotype in Herring Larvae
Authors: Johnston Ian A. , Cole Nicholas J. , Vieira Vera L. A. , Davidson Irvine
Published: April 2021

Myogenesis, the expression of myofibrillar protein isoforms and the development of muscle innervation were investigated in Clyde herring (Clupea harengus L.) in two successive spawning seasons at temperatures ranging from 5 °C to 15 °C. Myotube formation occurred in a rostral to caudal progression at similar somite stages at all temperatures. Superficial mononuclear muscle pioneer fibres were present at the horizontal septum. Myofibrillogenesis was retarded with respect to somite stage at low temperatures; for example, by the 50-somite stage, myofibrils were observed in the muscle pioneers of the first 31 somites at 12 °C, but only the first 20 somites at 5 °C. In the electron microscope, the earliest stages of myofibril assembly were observed in the muscle pioneer cells and in a proportion of the multinucleated myotubes within the same somite. By the end of somitogenesis, the density of myofibrils in the rostral myotomes was much higher at 15 °C than at 5 °C. Embryonic isoforms of myosin light chain 2 (LC2), troponin I and troponin T were identified in the presumptive white muscle using two-dimensional gel electrophoresis. Expression of the embryonic isoforms was gradually switched off during the larval stages. The size range over which embryonic isoforms were present was inversely related to rearing temperature. For example, the adult pattern of myosin LC2 expression was established at 11 mm total length (TL) at 15 °C, but not until 15 mm TL at 5 °C. Acetylcholinesterase staining was apparent at the myosepta in 31-somite stage embryos at 15 °C, but not until approximately the 40-somite stage at 5 °C. The red muscle fibres of larvae were initially innervated only at their myoseptal ends. The temperature at which the red muscle fibres became multiply innervated was inversely related to body size, occurring at 12–14 mm at 12 °C, but not until 16–19 mm at 5 °C. We conclude that the temperature during early development determines the relative timing and degree of expression of the myogenic programme, resulting in significant phenotypic variation in the swimming muscles of the larval stages. Our results highlight a potential mechanism whereby early thermal experience could influence survival and hence the strength of particular year classes of fish.
Control of Insect Ecdysis by a Positive-Feedback Endocrine System: Roles of Eclosion Hormone and Ecdysis Triggering Hormone
Authors: Ewer John , Gammie Stephen C. , Truman James W.
Published: April 2021

A successful ecdysis in insects requires the precise coordination of behaviour with the developmental changes that occur late in a moult. This coordination involves two sets of endocrine cells: the peripherally located Inka cells, which release ecdysis triggering hormone (ETH), and the centrally located neurosecretory neurones, the VM neurones, which release eclosion hormone (EH). These two sets of endocrine cells mutally excite one another: EH acts on the Inka cells to cause the release of ETH. ETH, in turn, acts on the VM neurones to cause the release of EH. This positive-feedback relationship allows the Inka cells and the VM neurones to be the peripheral and central halves, respectively, of a decision-making circuit. Once conditions for both halves have been satisfied, their reciprocal excitation results in a massive EH/ETH surge in the blood as well as a release of EH within the central nervous system. This phasic signal then causes the tonic activation of a distributed network of peptidergic neurones that contain crustacean cardioactive peptide. The relationship of the latter cells to the subsequent maintenance of the ecdysis motor programme is discussed.
Energetic Consequences of Coordinating Wingbeat and Respiratory Rhythms in Birds
Authors: Funk Gregory D. , Valenzuela Ignacio J. , Milsom William K.
Published: April 2021

The coordination of ventilatory and locomotor rhythms has been documented in many birds and mammals. It has been suggested that the physiological significance of such coordination is a reduction in the cost of ventilation which confers an energetic advantage to the animal. We tested this hypothesis by measuring the external work required to ventilate birds mechanically during simulated flight. Patterns of wing motion and breathing were produced in which the relationship between wing motion and breathing was in phase and out of phase with the relationship seen during normal flight. Differences between the energetic costs of in-phase versus out-of-phase synchronization were particularly large (26 %) in instances where locomotion and respiration frequency were synchronized at one breath per wingbeat. The saving (9 %) obtained from in-phase versus out-of-phase coordination at the 3:1 coordination ratio seen normally in free-flying Canada geese was smaller but still supported the hypothesis that there is a significant net saving obtained from reducing the mechanical interference between locomotion and ventilation by locomotor–respiratory coupling.
Adrenergic Stimulation of Sea Bream (Sparus Aurata) Red Blood Cells in Normoxia and Anoxia: Effects on Metabolism and on The Oxygen Affinity of Haemoglobin
Authors: Roig Teresa , Sánchez Josep , Tort Lluís , Altimiras Jordi , Bermúdez Jordi
Published: April 2021

The metabolic response of sea bream (Sparus aurata) red blood cells to adrenergic stimulation was determined in normoxia and anoxia. In the presence of oxygen, red blood cells swelled and then recovered their resting volume. Continuous monitoring of oxygen uptake displayed the kinetics of the increase in the oxygen affinity of haemoglobin. Cell volume recovery correlated with an activation of ATP consumption, and the energy equilibrium was restored by increasing the rates of respiration and glycolysis. When the respiratory chain was blocked, adrenergic stimulation increased the rates of ATP consumption and glycolysis of red blood cells. Moreover, adrenergic stimulation of deoxygenated erythrocytes also increased cell volume but did not enhance glycolysis or ATP consumption, and the cells remained swollen. Our results suggest that there is an oxygen-linked signal transducer that activates ATP-consuming processes, provided that the adrenergic stimulation occurs in the presence of oxygen.
Cultured Branchial Epithelia From Freshwater Fish Gills
Authors: Wood Chris M. , Pärt Peter
Published: April 2021

We have developed a method for the primary culture of gill epithelial cells from freshwater rainbow trout on permeable supports, polyethylene terephthalate membranes (‘filter inserts’). Primary cultures of gill cells (6–9 days in Leibowitz L-15 culture medium plus foetal bovine serum and glutamine) are trypsinized and the cells seeded onto the inserts. After 6 days of growth with L-15 medium on both surfaces (approximately isotonic to trout plasma), the cells form a tight epithelium as judged from a progressive rise in transepithelial resistance which reaches a stable plateau for a further 6 days, as long as L-15 exposure is continued on both surfaces. The cultured epithelium (approximately 8 μm thick) typically consists of 2–4 overlapping cell layers organized as in the lamellae in vivo, with large intercellular spaces, multiple desmosomes and putative tight junctions. The cells appear to be exclusively pavement-type cells with an apical surface glycocalyx, an abundance of rough endoplasmic reticulum, no selective DASPEI staining and relatively few mitochondria. Transepithelial resistance (approximately 3.5 kΩ cm2), permeability to a paracellular marker (polyethylene glycol-4000; 0.17×10−6 cm s−1) and unidirectional flux of Na+ and Cl− (approximately 300 nmol cm−2 h−1) all appear realistic because they compare well with in vivo values; net fluxes of Na+ and Cl− are zero. The preparation acidifies the apical medium, which accumulates a greater concentration of ammonia. Upon exposure to apical freshwater, resistance increases six-to elevenfold and a basolateral-negative transepithelial potential (TEP) develops as in vivo. These responses occur even when mannitol is used to prevent changes in apical osmotic pressure. Net Na+ and Cl− loss rates are low over the first 12 h (−125 nmol cm−2 h−1) but increase substantially by 48 h. The elevated resistance and negative TEP gradually attenuate but remain significantly higher than pre-exposure values after 48 h of apical freshwater exposure. The preparation may provide a valuable new tool for characterizing some of the mechanisms of active and passive ion transport in the pavement cells of the freshwater gill.
Reaction–Diffusion Analysis Of The Effects Of Temperature On High-Energy Phosphate Dynamics In Goldfish Skeletal Muscle
Authors: Hubley Mark J. , Locke Bruce R. , Moerland Timothy S.
Published: April 2021

Thermal acclimation results in dramatic changes in the fractional volume of mitochondria within skeletal muscle of teleost fish. We investigated the hypothesis that changes in mitochondrial volume represent a compensatory response to temperature-induced changes in intracellular diffusion coefficients (D) of the high-energy phosphate compounds ATP and creatine phosphate (PCr). Using 31P nuclear magnetic resonance spectroscopy, we determined DPCr and DATP in goldfish (Carassius auratus) skeletal muscle at 25 °C and 5 °C: DPCr was 3.28±0.18×10−6 cm2 s−1 at 25 °C and 2.00±0.09×10−6 cm2 s−1 at 5 °C; DATP was 2.13±0.16×10−6 cm2 s−1 at 25 °C and was estimated to be 1.30×10−6 cm2 s−1 at 5 °C. There was no evidence for an effect of acclimation temperature or fiber type on DATP or DPCr. A mathematical reaction–diffusion model was used to calculate profiles of [ATP], [PCr] and the free energy of ATP hydrolysis (ΔGATP) in activated goldfish muscle fibers at 5 °C and 25 °C. The results showed spatial and temporal constancy of [ATP], [PCr] and ΔGATP in red fibers at both temperatures, regardless of changes in acclimation temperature or mitochondrial density. The model also showed spatial and temporal constancy of [ATP] in white fibers at 5 °C and 25 °C, but gradients in [PCr] and ΔGATP developed in white fibers under all conditions of temperature and acclimation temperature. These gradients were attenuated in cold-acclimated animals by cold-induced increases in mitochondrial density. However, the model shows that the proximal stimulus for temperature-induced changes in mitochondrial volume density in muscle is not a disruption in intracellular diffusion of high-energy phosphates.
Insect Tolerance to A Neurotoxic Polypeptide: Pharmacokinetic and Pharmacodynamic Aspects
Authors: Fishman Lena , Herrmann Rafael , Gordon Dalia , Zlotkin Eliahu
Published: April 2021

Androctonus australis insect toxin (AaIT) is an insect-selective neurotoxic polypeptide from scorpion venom used to probe insect Na+ channels and to design insecticidal recombinant baculoviruses. When injected into susceptible insects (such as flies or cockroaches), nanogram doses of the toxin induce a rapid paralysis within seconds. More tolerant insects respond to microgram doses by developing either a slow progressive paralysis, as in lepidopterous larvae, or a rapid but reversible paralysis, as in Trachyderma philistina, a tenebrionid beetle. Using toxicity and binding assays, microscopy and chromatography, we show that the tolerance of insects to AaIT occurs at both the pharmacokinetic and pharmacodynamic levels. Pharmacokinetic effects occur in Trachyderma philistina in which the toxin undergoes a progressive process of degradation and elimination from the hemolymph, resulting in the loss of 95–97 % of toxin activity 6 h after injection. The pharmacodynamic aspect was demonstrated in studies of the kinetics of binding dissociation of [125I]AaIT from neuronal membranes of susceptible and tolerant insects. Stable binding is shown in susceptible insects such as cockroaches and locusts, which have a dissociation half-time of approximately 9 and 5 min, respectively. This contrasts strongly with the fast half-time of dissociation of 7 s for Spodoptera littoralis larvae and 9 s for Trachyderma philistina, which are both relatively tolerant to AaIT. These differences in binding kinetics may reflect a structural and functional diversity of Na+ channels in different insects that is responsible for their diverse susceptibility to neurotoxic polypeptides.
Polarization Pattern of Freshwater Habitats Recorded by Video Polarimetry in Red, Green and Blue Spectral Ranges and its Relevance for Water Detection by Aquatic Insects
Authors: Horváth Gábor , Varjú Dezsö
Published: April 2021

The reflection-polarization patterns of small freshwater habitats under clear skies can be recorded by video polarimetry in the red, green and blue ranges of the spectrum. In this paper, the simple technique of rotating-analyzer video polarimetry is described and its advantages and disadvantages are discussed. It is shown that the polarization patterns of small water bodies are very variable in the different spectral ranges depending on the illumination conditions. Under clear skies and in the visible range of the spectrum, flat water surfaces reflecting light from the sky are most strongly polarized in the blue range. Under an overcast sky radiating diffuse white light, small freshwater habitats are characterized by a high level of horizontal polarization at or near the Brewster angle in all spectral ranges except that in which the contribution of subsurface reflection is large. In a given spectral range and at a given angle of view, the direction of polarization is horizontal if the light mirrored from the surface dominates and vertical if the light returning from the subsurface regions dominates. The greater the degree of dominance, the higher the net degree of polarization, the theoretical maximum value being 100 % at the Brewster angle for the horizontal E-vector component and approximately 30 % at flat viewing angles for the vertical E-vector component. We have made video polarimetric measurements of differently coloured fruits and vegetables to demonstrate that polarized light in nature follows this general rule. The consequences of the reflection-polarization patterns of small bodies of water for water detection by polarization-sensitive aquatic insects are discussed.
The Kinematics and Performance of Fish Fast-Start Swimming
Authors: Domenici Paolo , Blake Robert W.
Published: April 2021

Fast-starts are brief, sudden accelerations used by fish during predator–prey encounters. The kinematics and performance of fish during fast-start manoeuvres have received a lot of attention since they may determine the outcome of predator–prey interactions in terms of feeding success or survival. We will discuss recent progress on (1) the kinematics of escape responses and feeding strikes, (2) the fast-start performance of species with different body morphologies and from different habitats, and (3) the functional significance of fast-start kinematics and performance within the context of predator–prey interactions.
Opercular Jetting During Fast-Starts by Flatfishes
Authors: Brainerd Elizabeth L. , Page Benjamin N. , Fish Frank E.
Published: April 2021

When attacked by predators, flatfishes perform fast-starts that result in a rapid take-off from the ocean bottom on which they lie. High-speed video recordings of the blind side of flatfishes indicate that they expel a coherent jet of water from the blind-side opercular valve during take-off. Buccal pressure recordings in winter flounder (Pseudopleuronectes americanus) show that a buccal pressure pulse begins 0–20 ms before the beginning of the fast-start and has a range of mean magnitudes for three individuals of 1.6–10.7 kPa. We hypothesize that one function of the opercular jet in flatfishes may be to reduce the effects of Stefan adhesion. Stefan adhesion occurs as the fish lifts its head up rapidly from the ocean bottom, when water must flow into the space forming beneath the fish. Water viscosity opposes this rapid shear, and a suction pressure develops under the fish, making it more difficult for the fish to escape from the bottom. To estimate the magnitude of Stefan adhesion, we simulated fast-starts using a physical model in which a dead flounder was pulled upwards with an acceleration of 95 m s−2. Results from the physical model indicate that up to 35 % of the total force required to lift the head at 20 ms into the start can be attributed to Stefan adhesion. Despite this large adhesion force, previous work has shown that live flatfish do not show improved fast-start performance when Stefan adhesion has been eliminated by starting the fish from an open wire grid. Thus, live fishes are likely to be using behavioral mechanisms to reduce the adhesion force. Both the timing and location along the body of the opercular jet indicate that it is ideally suited to attenuate the effects of Stefan adhesion. Propping the body up on the median fins may also reduce adhesion by increasing the initial distance between the fish and the ocean floor.
Postnatal Development of Body Architecture and Gait in Several Rodent Species
Authors: Eilam David
Published: April 2021

Observations on five species of rodents, vole (Microtus socialis), gerbil (Gerbillus dasyurus), jird (Meriones tristrami), dormouse (Eliomys melanurus) and jerboa (Jaculus orientalis), revealed that, during the period when their neonates share a matching morphology, they also share the same forms of quadruped locomotion (gaits). The order in which the different gaits develop is similar in all species, beginning with the basic gaits of lateral walk and trot. Gaits and body morphology do not undergo further changes in voles, whereas the other species incorporate more specialized gaits later in ontogeny, when the adult body morphology has been attained. Gerbils and jirds incorporate a bounding gait, dormice incorporate galloping and jerboas incorporate bipedal running. Species with more specialized locomotion thus undergo more developmental stages than those with less specialized locomotion. Except for the jerboa, the nesting period was roughly the same for all species, but those with more specialized locomotion exhibited earlier onset of the basic gaits as if condensing their development in order to reach the adult gait within the same nesting period. Consequently, the adult gait emerges approximately 10 days before the end of nesting, regardless of nesting duration. Since growth rate does not seem to account for the differences in morphology and onset of gaits, the heterochrony in the observed species probably stems from differences in the duration of growth, which seems to be the key factor in the diversion from the basic common morphology. The present results reconfirm the traditional generalities of functional morphology derived from cross-species comparisons. In addition, they provide another perspective by comparing form and function within the same individuals in the course of ontogeny.
Interneuronal and Motor Patterns During Crawling Behavior of Semi-Intact Leeches
Authors: Baader A. P.
Published: April 2021

Semi-intact tethered preparations were used to characterize neuronal activity patterns in midbody ganglia of the medicinal leech during crawling. Extra- and intracellular recordings were obtained from identified interneurons and from motor neurons of the longitudinal and circular muscles during crawling episodes. Coordinated activities of nine excitatory and inhibitory motor neurons of the longitudinal and circular muscles were recorded during the appropriate phases of crawling. Thus, during crawling, the leech uses motor output components known to contribute to other types of behavior, such as swimming or the shortening/local bending reflex. Interneurons with identified functions in these other types of behavior exhibit membrane potential oscillations that are in phase with the behavior pattern. Therefore, the recruitment of neuronal network elements during several types of behavior occurs not only at the motor neuron level but also involves interneurons. This applies even to some interneurons that were previously thought to have dedicated functions (such as cells 204 and 208 and the S cell). The function of neuronal circuitries in producing different types of behavior with a limited number of neurons is discussed.
Neural Mechanisms of Adaptive Gain Control in a Joint Control Loop: Muscle Force and Motoneuronal Activity
Authors: Kittmann Rolf
Published: April 2021

An adaptive gain control system of a proprioceptive feedback system, the femur–tibia control loop, is investigated. It enables the joint control loop to work with a high gain but it prevents instability oscillations. In the inactive stick insect, the realisation of specific changes in gain is described for tibial torque, for extensor tibiae muscle force and for motoneuronal activity. In open-loop experiments, sinusoidal stimuli are applied to the femoral chordotonal organ (fCO). Changes in gain that depend on fCO stimulus parameters (such as amplitude, frequency and repetition rate), are investigated. Furthermore, spontaneous and touch-induced changes in gain that resemble the behavioural state of the animal are described.

Changes in gain in motoneurones are always realised as changes in the amplitude of modulation of their discharge frequency. Nevertheless, depending on the stimulus situation, two different mechanisms underlie gain changes in motoneurones. (i) Changes in gain can be based on changes in the strength of the sensorimotor pathways that transmit stimulus-modulated information from the fCO to the motoneurones. (ii) Changes in gain can be based on changes in the mean activity of a motoneurone by means of its spike threshold: when, during the modulation, the discharge of a motoneurone is inhibited for part of the stimulus cycle, then a change in mean activity subsequently causes a change in modulation amplitude and gain.

A new neuronal mechanism is described that helps to compensate the low-pass filter characteristics of the muscles by an increased activation, especially by a sharper distribution of spikes in the stimulus cycle at high fCO stimulus frequencies.
Peripheral Encoding of Moving Sources by the Lateral Line System of a Sit-and-Wait Predator
Authors: Montgomery J. C. , Coombs S.
Published: April 2021

Video-tape recordings of prey-capture behaviour were made to demonstrate that stargazers can detect and capture prey in the dark and to determine the range of prey movement velocities that resulted in prey capture. Electrophysiological recording techniques were then used to determine how an artificial source (a sphere), moving at speeds within the range of recorded prey movement velocities, was encoded by anterior lateral line nerve fibres innervating the preopercular-mandibular canals on the head. A vibrating sphere was also used to measure frequency–response characteristics to determine the bandwidth of response and fibre origin (type of neuromast and location). In order to measure the relevant stimulus parameters likely to govern neural responses, the pressure-gradient pattern produced by the moving sphere was characterised with a pair of miniature hydrophones separated by approximately the same distance as head lateral line canal pores on stargazers. At least four different features of neural response patterns, including direction-dependent changes in the overall envelope of the firing rate pattern, could be predicted on the basis of measured pressure-gradient patterns. The dominant features of both the pressure-gradient and neural response patterns were produced by the wake behind the moving sphere, but behavioural observations indicated that stargazers were responding to the bow of an approaching prey, rather than its wake. Although the form of the wake behind the moving sphere is unlikely to be a good match for the stimulus mediating prey detection, these results clearly establish that pressure-gradient patterns are good predictors of neural response patterns. Thus, similar measurements of pressure-gradient patterns produced by more biologically relevant sources can be used to predict peripheral lateral line responses and stimulus features likely to be of key importance.
Reactivation of Sea-Urchin Sperm Flagella Induced by Rapid Photolysis of Caged ATP
Authors: Tani Tomomi , Kamimura Shinji
Published: April 2021

Sea-urchin sperm flagella in a state of rigor were reactivated by rapid photolysis of caged ATP. After a time lag of 11−17 ms, all bends in the axonemes present during rigor began to be propagated towards the tip as if their propagation had not been interrupted. This result suggests that the site-specific activity of dyneins along the length of the axoneme is preserved even during rigor states when ATP is absent and that regulation of the activity can be restarted immediately with a new cycle of ATP turnover. During the starting transient, pre-existing rigor waves in the distal region were propagated without a change in the maximal shear angle until they disappeared at the tip. This was more evident when the rapid reactivation was triggered in high-viscosity solution, in which only the form of new bends was greatly affected by viscous load. After reactivation, the velocity of microtubule sliding increased and reached a plateau within 28 ms. This time course reflects the rate of force generation by dynein in situ.
5´-Nucleotidase and Alkaline Phosphodiesterase Activities in Trout Gill Localize to Endothelial (Pillar) Cells
Authors: Robertson John C. , Hazel Jeffrey R.
Published: April 2021

Tissue homogenates from rainbow trout gill had three-to fivefold higher specific activity for 5´-nucleotidase (5´NT) and more than twofold greater alkaline phosphodiesterase (APD) activity than liver or kidney homogenates. In isolated plasma membranes, gill 5´NT activity was 3–5 times greater than that of the kidney or liver; gill and kidney plasma membranes had similar APD specific activities, both more than five times that of liver. 5´NT and APD activities were localized by histochemistry to the endothelial (pillar) cells of trout gill secondary lamellae. Staining was consistent with the concentration of both activities at the apical plasma membranes of pillar cells (i.e. at the lamellar microvascular surfaces). This localization may reflect a capacity for processing nucleotide metabolites circulating in the blood, perhaps relating to purinergic regulation of local lamellar hemodynamics. There was no histochemical evidence of either 5´NT or APD activity in the gill epithelial (pavement) cells that interface directly with the environment. In contrast, in trout kidney, both enzyme activities localized to the apical region of tubule epithelial cells. The absence of 5´NT and APD activity in pavement cells reinforces the unique structural and functional character of the gill–environment epithelial barrier. The results indicate that 5´NT and APD activities have particular potential application as markers in efforts to isolate and characterize specific gill plasma membrane fractions.
Contralateral Coordination and Retargeting of Limb Movements During Scratching in the Locust
Authors: Matheson T.
Published: April 2021

Locusts, Schistocerca gregaria, in common with many limbed vertebrates, can make directed scratching movements in response to tactile stimulation. For instance, stimulation of different sites on a wing elicits different movements that are accurately targeted so that the hindleg tarsus passes across the stimulus site. I have analysed these limb movements to define the ability of a locust to target stimulus sites correctly under a range of experimental conditions. In particular, I describe aspects of the behaviour that reveal possible neuronal pathways underlying the responses. These neuronal pathways will be the subject of further physiological analyses.

Limb targeting during scratching is continuously graded in form; different patterns of movement are not separated by sharp transitions. The computation of limb trajectory takes into account the starting posture of the hindleg, so that different trajectories can be used to reach a common stimulus site from different starting postures. Moreover, the trajectories of the two hindlegs moving simultaneously from different starting postures in response to a single stimulus can be different, so that their tarsi converge onto the common stimulus site. Different trajectories can be used to reach a common stimulus site from the same start posture. Targeting information from a forewing is passed not only down the nerve cord to the ipsilateral hindleg but also across the nerve cord, so that the contralateral hindleg can also make directed movements. This contralateral transmission does not rely on peripheral sensory feedback. When the stimulus site moves during a rhythmical scratch, the targeting of subsequent cycles reflects this change. Both ipsilateral and contralateral hindlegs can retarget their movements. The trajectory of a single cycle of scratching directed towards a particular stimulus site can be modified after it has begun, so that the tarsus is redirected towards a new stimulus site.
Why are there no insects in the open sea?
Authors: Maddrell SH
Published: April 2021

The air-filled tracheal respiratory system of insects prevents them from diving deeply in water. It is argued that this is the major factor in preventing insects from colonizing the open sea: they cannot descend sufficiently deeply in the daytime to escape being eaten by fish.
Modelling Of The Dynamic Relationship Between Arterial Pressure, Renal Sympathetic Nerve Activity And Renal Blood Flow In Conscious Rabbits
Authors: Berger Clive S. , Malpas Simon C.
Published: April 2021

A linear autoregressive/moving-average model was developed to describe the dynamic relationship between mean arterial pressure (MAP), renal sympathetic nerve activity (SNA) and renal blood flow (RBF) in conscious rabbits. The RBF and SNA to the same kidney were measured under resting conditions in a group of eight rabbits. Spectral analysis of the data sampled at 0.4 Hz showed that the low-pass bandwidth of the signal power for RBF was approximately 0.05 Hz. An autoregressive/moving-average model with an exogenous input (ARMAX) was then derived (using the iterative Gauss–Newton algorithm provided by the MATLAB identification Toolbox), with MAP and SNA as inputs and RBF as output, to model the low-frequency fluctuations. The model step responses of RBF to changes in SNA and arterial pressure indicated an overdamped response with a settling time that was usually less than 2 s. Calculated residuals from the model indicated that 79±5 % (mean ± S.D., averaged over eight independent experiments) of the variation in RBF could be accounted for by the variations in arterial pressure and SNA. Two additional single-input models for each of the inputs were similarly obtained and showed conclusively that changes in RBF, in the conscious resting rabbit, are a function of both SNA and MAP and that the SNA signal has the predominant effect. These results indicate a strong reliance on SNA for the dynamic regulation of RBF. Such information is likely to be important in understanding the diminished renal function that occurs in a variety of disease conditions in which overactivity of the sympathetic nervous system occurs.
A Gregarizing Factor Present In The Egg Pod Foam Of The Desert Locust Schistocerca Gregaria
Authors: Mccaffery Alan R. , Simpson Stephen J. , Islam M. Saiful , Roessingh Peter
Published: April 2021

The behavioural phase state and coloration of hatchling Schistocerca gregaria were examined in a series of experiments to determine the means by which phase characteristics are passed between generations. Both crowding of solitary-reared females at the time of oviposition and high egg pod densities promoted behavioural gregarization, although the former appeared to be a rather more potent factor. In contrast, egg pod density alone appeared to promote the development of hatchlings with dark patterns characteristic of the gregarious phase. The phase characteristics of hatchlings were unaffected when sand previously used for oviposition was used to collect further egg pods. Early separation of presumptive gregarious eggs from egg pods laid by crowd-reared females led to solitarization of the hatchlings, indicating that a factor, either in or around the eggs, removed by early separation promoted gregarization. Both the eggs and foam plugs of egg pods from crowd-reared, gregarious females appeared to be a source of this gregarizing factor. In contrast, there was no evidence for a solitarization factor in egg pods from solitary-reared S. gregaria. Saline extracts of egg pod foam plugs produced an active factor which promoted gregarization both in eggs from solitary-reared females and in eggs from gregarious females which were separated and washed to removed the factor. Solitary eggs were influenced by the gregarizing factor in foam plug extracts for up to 1 day after oviposition. Saline extracts of foam plug retained their activity for up to 1 day. Initial studies on the properties of this factor were made. We conclude that the foam plugs of egg pods from crowd-reared, gregarious locusts contain a small (<3 kDa), hydrophilic gregarizing factor which is produced at the time of oviposition and which predisposes hatchlings to attain characteristics of the gregarious phase.
A Protein Titration Hypothesis for the Temperature-Dependence of Tissue CO2 Content in Reptiles and Amphibians
Authors: Stinner J. N. , Hartzler L. K. , Grguric M. R. , Newlon D. L.
Published: April 2021

Whole-body CO2 stores are known to increase with cooling in reptiles and amphibians (−Δ[CO2]/ΔT ). The aim of this study was to determine the mechanism(s) producing this inverse relationship. The Δ[CO2]/ΔT coefficients were determined for eight reptilian and one amphibian species and were found to differ by a factor of approximately 10, from −0.21 mmol kg−1 °C−1 in the Mediterranean spur-thighed tortoise Testudo graeca to −0.02 mmol kg−1 °C−1 in the bullfrog Rana catesbeiana. The Δ[CO2]/ΔT coefficients were correlated with values in the literature for in vivo plasma ΔpH/ΔT coefficients (Δ[CO2]/ΔT=−0.18–8.24ΔpH/ΔT; r2=0.87). Plasma electrolyte concentrations (Na+, K+, Ca2+, Mg2+, Cl−, inorganic phosphate, SO42−; and lactate), [protein], [CO2], PCO2 and pH were measured in chronically cannulated resting black racer snakes Coluber constrictor. When the temperature was reduced from 30 to 10 °C, pH increased slightly (by −0.0028 pH units °C−1), decreased by 7 mmHg, [CO2] increased by 3.2 mmol l−1 and [HPO42−+H2PO4−] increased by 0.7 mmol l−1. Concentrations of protein and of the remaining electrolytes were not significantly different (P>0.05) at 30 and 10 °C. Net plasma protein charge, calculated from the principle of electroneutrality (the sum of the cations in mequiv = the sum of anions in mequiv), was −0.48 mequiv g−1 protein at 30 °C and −0.38 mequiv g−1 protein at 10 °C. This 21 % decrease was attributed to the increases in [CO2] (i.e. carbonic acid) and inorganic phosphate concentration. Between 30 and 10 °C, skeletal muscle pH and [CO2] in C. constrictor increased (by −0.009 units °C−1 and −0.125 mmol kg−1 °C−1, respectively), [Na+] and [Cl−] each decreased by approximately 12 mequiv l−1, and [K+] and the percentage of water did not change significantly. It is concluded that the increase in whole-body CO2 stores with cooling in reptiles and amphibians results from the passive effects of temperature changes upon the ionization constants of proteins and the active adjustment of (ventilatory regulation), so that −ΔpK is greater than −ΔpH. Active transmembrane ion-exchange processes do not appear to be involved.
Processing Of Defensive Pigment in Aplysia Californica: Acquisition, Modification And Mobilization Of The Red Algal Pigment R-Phycoerythrin By The Digestive Gland
Authors: Coelho L. , Prince J. , Nolen T. G.
Published: April 2021

The marine snail Aplysia californica obtains its purple defensive ink exclusively from the accessory photosynthetic pigment r-phycoerythrin, which is found in the red seaweeds of its diet. The rhodoplast digestive cell, one of three types of cell lining the tubules of the digestive gland, appears to be the site of catabolism of red algal chloroplasts (rhodoplasts) since thylakoid membranes, including phycobilisome-sized membrane-associated particles, were found within the large digestive vacuoles of this cell. Immunogold localization showed that there was a statistically significant occurrence of the red algal phycobilisome pigment r-phycoerythrin within these rhodoplast digestive vacuoles, but not in other compartments of this cell type (endoplasmic reticulum, mitochondria, nucleus) or in other tissues (abdominal ganglion).

Immunogold analysis also suggested that the rhodoplast vacuole is the site for additional modification of r-phycoerythrin, which makes it non-antigenic: the chromophore is either cleaved from its biliprotein or the biliprotein is otherwise modified. The hemolymph had spectrographic absorption maxima typical of the protein-free chromophore (phycoerythrobilin) and/or r-phycoerythrin, but only when the animal had been feeding on red algae. Rhodoplast digestive cells and their vacuoles were not induced by the type of food in the diet: snails fed green seaweed and animals fed lettuce had characteristic rhodoplast cells but without the large membranous inclusions (rhodoplasts) or phycobilisome-like granules found in animals fed red seaweed.

Two additional cell types lining the tubules of the digestive gland were characterized ultrastructurally: (1) a club-shaped digestive cell filled with electron-dense material, and (2) a triangular ‘secretory’ cell devoid of storage material and calcium carbonate.

The following model is consistent with our observations: red algal rhodoplasts are freed from algal cells in the foregut and then engulfed by rhodoplast digestive cells in the tubules of the digestive diverticula, where they are digested in membrane-bound vacuoles; r-phycoerythrin is released from phycobilisomes on the rhodoplast thylakoids and chemically modified before leaving the digestive vacuole and accumulating in the hemolymph; the pigment then circulates throughout the body and is concentrated in specialized cells and vesicles of the ink gland, where it is stored until secreted in response to certain predators.
Ontogeny Of Hemocyanin Function In The Dungeness Crab Cancer Magister: Hemolymph Modulation Of Hemocyanin Oxygen-Binding
Authors: Brown A. Christine , Terwilliger Nora B.
Published: April 2021

The in vivo oxygen-binding characteristics of Cancer magister whole hemolymph were compared across developmental stages with those of purified hemocyanin. When the 25S hemocyanins from first-instar juvenile and adult C. magister were dialyzed against first-instar juvenile saline, the P50 values at pH 7.8 differed by 54 %: 2.16 kPa for the adult and 4.68 kPa for the first-instar juvenile. Since both purified proteins were examined under identical conditions, this represents an intrinsic stage-specific difference in hemocyanin O2-affinity. When the two types of hemocyanin were dialyzed against their respective stage-specific salines, the oxygen affinities differed by only 28 %: 3.39 kPa for the adult and still 4.68 kPa for the first-instar juvenile. Thus, the intrinsic difference in hemocyanin O2-affinity was reduced by the stage-specific differences in hemolymph ion concentrations. Even more significant is the fact that the whole-hemolymph P50 values of the juvenile and adult were indistinguishable at in vivo pH and divalent cation levels specific for each stage. Thus, despite significant differences in the intrinsic oxygen affinity of the purified 25S hemocyanin during development, the whole-hemolymph oxygen-binding properties are conserved. In the juvenile crab, it appears that the low-affinity hemocyanin serves to modulate the effects of a weak renal regulation of [Mg2+]. As ion regulation is enhanced during development and divalent cation levels decrease, the crab synthesizes higher-affinity hemocyanin.