bluuebunny/crossref_metadata_2025 huggingface dataset:
Stanniectomy Increases Renal Magnesium and Calcium Excretion in Freshwater North American Eels (Anguilla Rostrata)
Authors: Butler David G.
Published: April 2021

The corpuscles of Stannius are linked to the renal transport of magnesium in freshwater North American eels. The urinary magnesium concentration and rate of magnesium excretion increased 3 days after the corpuscles had been removed, a trend which continued throughout a 14 day observation period. There was no overall change in urine flow rates except for a brief 50% reduction 2 days after stanniectomy. Plasma magnesium concentrations drifted downward after stanniectomy. In contrast, plasma calcium concentrations increased significantly within 2 days following stanniectomy and they continued to increase thereafter. Urinary calcium concentrations and the rate of urinary calcium excretion increased 7 days after stanniectomy, implying that the renal response was subject to the increase in plasma calcium concentration: the urine/plasma calcium ratio remained constant. Even though the urinary calcium concentration increased after stanniectomy, the increase in urinary magnesium concentration was proportionally greater.
Hormonal Control of Transmitter Plasticity in Insect Peptidergic Neurons: I. Steroid Regulation of the Decline in Cardioacceleratory Peptide 2 (Cap2) Expression
Authors: Loi P. K. , Tublitz N. J.
Published: April 2021

Transmitter plasticity, the ability to alter transmitter expression, has been documented in several different preparations both in vivo and in vitro. One of these is the tobacco hawkmoth, Manduca sexta, whose central nervous system contains four individually identified lateral neurosecretory cells (LNCs) that undergo a postembryonic transmitter switch in vivo. In larvae, the LNCs express high levels of a myoregulatory peptide, cardioacceleratory peptide 2 (CAP2). In contrast, the predominant LNC transmitter in adult moths is bursicon, a classic insect peptide hormone responsible for cuticular tanning. Here we show that the CAP2-to-bursicon conversion by the LNCs is a multi-step process beginning with a decline in CAP2 levels midway through the final larval stage. We provide several lines of evidence that this CAP2 drop is regulated by the insect steroid hormone 20-hydroxyecdysone (20-HE). The LNCs exhibit a fall in CAP2 levels at the beginning of metamorphosis, immediately after the commitment pulse of 20-HE when steroid levels are elevated. LNCs not exposed to this 20-HE rise do not exhibit a decline in CAP2 level. The transmitter switch can also be prevented by using an analog of juvenile hormone to create a larval hormonal environment during the commitment pulse of 20-HE. The CAP2 decline in the LNCs could be directly induced by exogenous steroid application, but only under conditions where the LNCs remained connected to the brain. Thus, the first step in the transmitter switch by the LNCs, the decline in CAP2 levels, is triggered by the commitment pulse of 20-HE, which may act indirectly through a set of steroid-sensitive cells in the brain.
Effects of Feeding and Food Deprivation on Oxygen Consumption, Muscle Protein Concentration and Activities of Energy Metabolism Enzymes in Muscle and Brain of Shallow-Living (Scorpaena Guttata) and Deep-Living (Sebastolobus Alascanus) Scorpaenid Fishes
Authors: Yang Tzung-Horng , Somero George N.
Published: April 2021

The effects of feeding and fasting were examined on the deep-living short-spine thornyhead (Sebastolobus alascanus) and the confamilial shallow-living spotted scorpionfish (Scorpaena guttata) to determine whether the low metabolic rate of the deeper-living species was in part a consequence of food deprivation in its habitat. Laboratory acclimation for periods of 90–115 days under either ad libitum feeding or complete fasting did not lead to similar rates of respiration in individuals of the two species held under identical conditions. Respiration of fish fed ad libitum was 52 % (S. guttata) or 68% (S. alascanus) higher than for fasted fish of the same species. Furthermore, the metabolic rates of freshly collected specimens of S. alascanus resembled those of laboratory-fasted fish. In white skeletal muscle, both total protein concentration and the activities of four enzymes of ATP metabolism, lactate dehydrogenase (LDH) and pyruvate kinase (PK) of glycolysis, malate dehydrogenase (MDH) and citrate synthase (CS, a citric acid cycle indicator), were lower in S. alascanus than in S. guttata. Within a species, protein concentration and activities of the four enzymes in white muscle, but not in brain, were higher in fed than in starved fish, although these differences were greater in S. alascanus than in S. guttata. During fasting, LDH and PK activity in white muscle of S. alascanus decreased much more than MDH and CS activity; decreases in enzyme activities in red muscle were smaller than those in white muscle. Activities of enzymes in white skeletal muscle of field-collected S. alascanus generally resembled those of the fasted specimens. In contrast, red muscle of field-collected S. alascanus, compared with that of either fed or starved laboratory-held specimens, had a highly glycolytic poise (high LDH and PK activities relative to MDH and CS activities), which may suggest that muscle enzyme activities in the field-collected fish reflect adaptation to the low oxygen level in its adult habitat, the oxygen minimum layer. The strong correlations found between tissue biochemical properties and respiration rate allow us to develop a predictive index for metabolic rate from simple biochemical analyses, e.g. white muscle protein content or CS activity. We conclude that the low metabolic rate of S. alascanus is due to at least four depth-related factors: reduced abundance of food, low temperature, low ambient oxygen concentration and darkness, which may select for reduced locomotory activity.
Pharmacological and Electrophysiological Characterization of a Postsynaptic Muscarinic Receptor in the Central Nervous System of the Cockroach
Authors: Corronc H. Le , Hue B.
Published: April 2021

The properties of the postsynaptic muscarinic receptors of a ventral giant interneurone in the sixth abdominal ganglion of the cockroach were studied using the single-fibre oil-gap technique.

Pressure-ejections of 10−4 mol l−1 arecoline (ARE) and muscarine evoked a small (approximately 1mV), prolonged slow depolarization whereas the muscarinic agonist McN-A-343 (10−3 mol l−1) elicited only a fast transient depolarization. At a higher concentration, ARE (10−3 mol l−1) produced a biphasic depolarization composed of a fast depolarization followed by the slow depolarization. The fast depolarization was specifically inhibited by the nicotinic antagonist d-tubocurarine (dTC; 5×10−5 mol l−1) and the slow depolarization was blocked by muscarinic antagonists such as atropine (ATR; 10−5 mol l−1), scopolamine (10−6 mol l−1) and quinuclidinyl benzilate (10−6 mol l−1). The ARE-induced slow depolarization was reduced by 10−5 mol l−1 pirenzepine, but neither methoctramine (10−5 mol l−1) nor 4-DAMP (10−5 mol l−1) modified the slow depolarization. The McN-A-343-induced depolarization was fully blocked by dTC. The slow depolarization was tetrodotoxin-insensitive and was unchanged when the external Na+ concentration was reduced by half. Tetraethylammonium (5×10−3 moll−1) and Ba2+ (5.4×10−3 moll−1) inhibited the slow depolarization. The inward K+ current induced by pressure-ejections of high-K+ saline was reduced by ARE but no increase of the membrane resistance was observed. The calcium channel blockers Co2+ (2×10−3 mol l−1), Cd2+ (10−3 moll−1) and La3+ (10−3 moll−1) did not modify the muscarinic response. The threshold of action potentials triggered by presynaptic stimulation was reduced by ARE and increased by ATR.

These results suggest that muscarinic receptors are present on cockroach ventral giant interneurones and that they can reduce a K+ conductance and increase an unknown conductance. The physiological role of these receptors might be to reduce the spike threshold and consequently to modify the integrative properties of giant interneurones.
Thermal Acclimation Alters Both Adrenergic Sensitivity and Adrenoceptor Density in Cardiac Tissue of Rainbow Trout
Authors: Keen John E. , Vianzon Daisy-Mae , Farrell Anthony P. , Tibbits Glen F.
Published: April 2021

We examined the effect of temperature acclimation on the sensitivity of the rainbow trout heart to adrenaline and on the density of β-adrenoceptors. The sensitivity of the heart was assessed using in situ working perfused heart and in vitro isometric ventricular strip preparations. When tested in situ and at acclimation temperature, hearts from fish acclimated to 8°C were approximately 10-fold more sensitive to adrenaline-supplemented perfusate than were hearts from fish acclimated to 18°C. The concentrations required for half-maximal stimulation (EC50) of myocardial power output were 1.9×10-8 mol l-1 adrenaline and 1.7×10-7 mol l-1 adrenaline for hearts acclimated to 8°C and 18°C, respectively. In vitro, isometric ventricular strip preparations demonstrated a similar increase in adrenergic sensitivity with cold-acclimation. The EC50 values for maximal tension development were 2.7×10-7 mol l-1 adrenaline (8°C-acclimated) and 1.1×10-6 mol l-1 adrenaline (18°C-acclimated) when tested at acclimation temperature. This shift in adrenergic sensitivity was a function of the temperature acclimation because changes in bath temperature per se, either from 8°C to 18°C for 8°C-acclimated hearts or from 18°C to 8°C for 18°C-acclimated hearts, had no significant effect on the concentration–response curve for adrenaline.

We conducted radioligand binding studies with [125I]iodocyanopindolol and propranolol to quantify the β-adrenoceptor density (Bmax) of both homogenates and isolated sarcolemmal fractions of ventricles from rainbow trout acclimated to either 8°C or 18°C. The Bmax for isolated sarcolemmal fractions was significantly higher in the 8°C-acclimated group, but the Bmax of ventricular homogenates was not significantly different in the two acclimation groups. No significant differences in dissociation constant (Kd) were apparent in either the homogenates or sarcolemmal fractions. These results suggest that cardiac tissue from rainbow trout acclimated to 8°C has a greater cell surface adrenoceptor population available for -antagonist binding. This might explain the heightened cardiac sensitivity to adrenaline observed in situ and in vitro in 8°C-acclimated fish.
Extracellular Atp Selectively Modulates a High-Voltage-Activated Calcium Conductance in Salivary Gland Cells of the Leech Haementeria Ghilianii
Authors: Wuttke Werner A. , Berry Michael S.
Published: April 2021

Extracellular ATP appears to have a widespread role as a neurotransmitter or neuromodulator in mammals (Gordon, 1986; Burnstock, 1990), but little is known about any similar functions in invertebrates. During studies of the effects of cyclic nucleotides on electrically excitable salivary cells of the leech, we found that cyclic GMP produced a rapid (less than 1min) reduction of spike duration, suggesting an extracellular effect (Wuttke and Berry, 1991). We now show that micromolar concentrations of ATP (and higher doses of other nucleotides) also reduce spike duration, and that this is caused by depression of a specific voltage-dependent Ca2+ conductance. Selective modulation of Ca2+ current by external ATP has rarely been found, and the effect is also unusual because it changes the kinetics of inactivation rather than those of activation.
CYCLIC-AMP-MEDIATED EXCITATORY RESPONSES TO LEUCINE ENKEPHALIN IN APLYSIA NEURONES
Authors: Kemenes G. , Rozsa K. S. , Carpenter D. O.
Published: April 2021

Although there are several different types of opiate receptors in mammals (Goldstein and James, 1984) and a variety of different ionic responses can be elicited by each of the receptor types on different neurones (Crain and Shen, 1990), relatively little attention has been given to the role of opiate receptors in invertebrates. We have previously demonstrated that the nervous system of the marine mollusc Aplysia californica contains both leucine-enkephalin-like and methionine-enkephalin- like opiate peptides (Leung et al. 1986) and that receptors for these substances exist on many neurones (Carpenter and Hall, 1986; S.-Rozsa et al. 1991; Kemenes et al. 1992). Although these responses are not identical to those observed in mammalian neurones, there are several common features.
Vortex Formation During Tethered Flight of Functionally and Morphologically Two-Winged Insects, Including Evolutionary Considerations on Insect Flight
Authors: Grodnitsky Dmitry L. , Morozov Pahvel P.
Published: April 2021

Tethered flight of six insect species (two pentatomid bugs, a moth, a butterfly, a muscid fly and a crane fly) was studied using several modifications of a dust flow visualization procedure. The spatial structure of the near vortex wake of flying specimens was reconstructed on the basis of two-dimensional flow pictures. The dynamics of the wake was followed during a stroke cycle, revealing interspecific differences in vortex formation.

It is suggested that insects create a single vortex ring during each stroke. Therefore, the hypothesis of double vortex chains advanced by Brodsky is not verified. The same is true of the jet hypothesis of Bocharova-Messner. While pronating at the top of their trajectory, the flapping wings throw air masses off their lower surfaces, but there is not a jet from between their upper sides. Flow separation from leading edges was found to be a rare phenomenon, taking place irregularly during the stroke cycle. That is why, contrary to widespread theoretical expectations, the Weis-Fogh fling mechanism is not likely to contain a leading edge separation bubble, which must follow stalling at the front part of the wings.

It is suggested that flying animals possess special mechanisms for extracting energy back from the near vortex wake. Some hypothetical adaptations for such an extraction in insects are put forward. Possible pathways for the evolution of insect flight are described.
Ion Channel Activity in Lobster Skeletal Muscle Membrane
Authors: Worden Mary Kate , Rahamimoff Rami , Kravitz Edward A.
Published: April 2021

Ion channel activity in the sarcolemmal membrane of muscle fibers is critical for regulating the excitability, and therefore the contractility, of muscle. To begin the characterization of the biophysical properties of the sarcolemmal membrane of lobster exoskeletal muscle fibers, recordings were made from excised patches of membrane from enzymatically induced muscle fiber blebs. Blebs formed as evaginations of the muscle sarcolemmal membrane and were sufficiently free of extracellular debris to allow the formation of gigaohm seals. Under simple experimental conditions using bi-ionic symmetrical recording solutions and maintained holding potentials, a variety of single channel types with conductances in the range 32–380pS were detected. Two of these ion channel species are described in detail, both are cation channels selective for potassium. They can be distinguished from each other on the basis of their single-channel conductance and gating properties. The results suggest that current flows through a large number of ion channels that open spontaneously in bleb membranes in the absence of exogenous metabolites or hormones.
The Behavioural State of Satiation in the Leech is Regulated by Body Distension and Mimicked by Serotonin Depletion
Authors: Groome James R. , Clark Madeline , Lent Charles M.
Published: April 2021

The behavioural state of an organism consists of an array of constituent behaviours or responses which may be altered differentially as the behavioural state of an animal changes (Kupferman et al. 1991). The medicinal leech, Hirudo medicinalis, exhibits a long cycle in feeding behaviour (Dickinson and Lent, 1984). When they have not fed for some months, Hirudo exhibit an array of appetitive behaviours that are associated with the state of hunger. These leeches rest near the water surface and spontaneously initiate swimming bouts. Shadows, mechanical shocks or surface ripples alert hungry Hirudo, after which they swim towards a point source of water waves. Upon contacting a surface, leeches cease to swim and will explore the surface by crawling. If warmth is encountered at this time, hungry leeches will bite; biting is typically localized in or near surface folds.
Maximum Metabolism and the Aerobic Factorial Scope of Endotherms
Authors: Hinds David S. , Baudinette R. V. , Macmillen Richard E. , Halpern E. Annette
Published: April 2021

Minimum and maximum metabolism in response to cold were measured in 30 species of Australian monotremes, marsupials, eutherians and birds. In marsupials and the echidna, maximum metabolism was also determined during treadmill locomotion. These data were used to determine, for the first time, the relationships between maximum metabolism and body mass in the four endothermic groups and to compare aerobic factorial scopes (the ratio of maximum to minimum metabolism) elicited by cold and locomotion. The effect of body mass on maximum metabolism is the same in marsupials and eutherians (the therians) but is significantly less in birds. At the same body mass, there is no difference between the two therian groups for either minimum or maximum metabolism induced by either cold or locomotion. Aerobic scope during cold is significantly higher in marsupials (8.3) than in eutherians (5.1), birds (5.4) and monotremes (5.4). Aerobic scope during locomotion in all groups is almost twice that observed in cold conditions.
Wing Movements and Lift Regulation in the Flight of Desert Locusts
Authors: Wortmann Michael , Zarnack Wolfram
Published: April 2021

We simultaneously recorded lift/body weight, flight speed, body angle and 12 variables of wing movement for locusts performing tethered long-term flight with low movement scatter. The movements of the forewings and hindwings were recorded in three dimensions by means of miniature induction coils. By adjusting the body angle, we could reproducibly manipulate lift generation as a consequence of induced changes in the wings’ movement patterns. We were therefore able to analyse various relationships between the movement patterns and lift. The most prominent variations of kinematic variables were observed for the forewing movements. The relative lift and the steady angle of pitch were positively correlated but there was a negative correlation between relative lift and pitching amplitude. We found no correlation between relative lift and flapping amplitude. Our results seem to correspond to a new theory about unsteady aerodynamics of oscillating aerofoils. We sometimes observed variations in lagging. The forewing downstroke was delayed by 0–8ms following the hindwing downstroke. Relative lift was positively correlated to this delay.
Detection of Intense Ultrasound by the Cod Gadus Morhua
Authors: Astrup Jens , Møhl Bertel
Published: April 2021

The ability of cod to detect intense 38kHz pulses was studied in an anechoic tank, using a classical cardiac conditioning method. All 15 cod studied reacted to 3ms pulses. The average threshold was 194.4dB re 1μPa (S.D. 5.4dB, S.E.M. 0.3dB). The data do not reveal the sensory modality involved. A number of additional experiments indicate that the ultrasonic energy per se is the effective stimulus. The threshold is too high for most sources of marine ultrasound to be detected, but is low enough to allow the cod to detect echolocating odontocetes at a range of 10–30m. The results also indicate that cod can detect echo-sounders of the fishing fleet at similar ranges.
Sensory and Neurosecretory Innervation of Leech Nephridia is Accomplished by a Single Neurone Containing FMRFamide
Authors: Wenning A. , Cahill M. A. , Hoeger U. , Calabrese R. L.
Published: April 2021

The neural control of the excretory system of the medicinal leech Hirudo medicinalis has been characterized morphologically and chemically using light and electron microscopy, immunocytochemistry and biochemistry. Immunoreactivity against RFamide-like peptides revealed elaborate neuronal aborizations of a neurone in the nephridium, around the urinary bladder sphincter and in the central nervous system. The processes arose from the nephridial nerve cell (NNC), a previously identified receptor neurone. Using a combination of reverse-phase high pressure liquid chromatography, radioimmunoassay and subsequent Edman degradation and mass spectrometry, authentic FMRFamide has been identified as the major peptide of the NNC. Sensory and neurosecretory innervation of the nephridia is thus accomplished by a single neurone, which is thought to modulate nephridial performance.
Ventricular and Arterial Dynamics of Anaesthetised and Swimming Tuna
Authors: Jones David R. , Brill Richard W. , Bushnell Peter G.
Published: April 2021

Cardiovascular dynamics of tuna have been investigated by recording blood pressures and flows in the central circulation of both anaesthetised and swimming individuals. In anaesthetised fish (N=5), heart rate averaged 112±21 beatsmin−1 (mean ± S.E.) and stroke volume was 0.67±0.24 mlkg−1 when normoxic water flowed over the gills. Ventricular diastolic pressure was zero until atrial contraction filled the ventricle. Ventral aortic pressures were high (mean 12.08±1.15kPa), and blood flow was continuous in the ventral aorta throughout diastole. Dorsal aortic pressure (mean 6.3±1.28kPa; N=4) and flow were both pulsatile. Pressure pulsatility (pulse pressure as a proportion of mean pressure) was about one-quarter of flow pulsatility, indicating considerable compliance in the dorsal aortic circulation. Total peripheral resistance averaged 0.17±0.4 kPaml−1 kg−1 min−1 of which gill resistance averaged 48±15% (N=4). For the ventral aorta, impedance modulus fell markedly from the mean value and then declined more gradually towards zero with increasing harmonic frequencies. Impedance phase was negative (−0.8 to −1.1rad) meaning that flow leads pressure at all harmonics. In swimming yellowfin tuna (N=5), heart rate averaged 108.8±12.1 beatsmin−1 and mean ventral and dorsal aortic pressures were 11.6±0.5 and 6.8±1.2kPa, respectively, so gill resistance was 42% of total peripheral resistance. Average stroke volume in three swimming kawakawa was 0.54±0.2mlkg−1 at a mean heart rate of 128±48 beatsmin−1. Data from swimming fish were within the range obtained from anaesthetised tuna. A simple model of the fish circulation consisting of two sets of compliant and resistive elements coupled in series (a second-order RC network) gave reasonable predictions of arterial pressure–flow relationships. Hence, we conclude that a ‘Windkessel’ dominates central cardiovascular dynamics of tuna despite heart rates and blood pressures that fall in the mammalian range.
Ontogeny of Hemocyanin Function in the Dungeness Crab Cancer Magister: The Interactive Effects of Developmental Stage and Divalent Cations on Hemocyanin Oxygenation Properties
Authors: Terwilliger Nora B. , Brown A. Christine
Published: April 2021

Calcium and magnesium ions raise the oxygen affinities of 25S hemocyanins of both first-instar juvenile and adult Cancer magister. A physiologically relevant change in magnesium concentration from 16 to 32mmol l−1 changes first-instar juvenile hemocyanin affinity by 5.6mmHg (0.7kPa) but adult affinity by only 1.1mmHg (0.15kPa). In early juvenile crabs, the higher magnesium sensitivity of the hemocyanin may be compensated for by the lower oxygen affinity, which has been shown previously to be 50% lower than that of the adult under identical experimental conditions. Furthermore, ontogeny of ionic and osmotic regulation occurs during the development of C. magister, with especially high concentrations of magnesium being found in the hemolymph of early juveniles. Intermediate-stage juveniles (fifth to eighth instars) have hemocyanins with subunit stoichiometries and P50 values approaching those of the adult. These findings are significant because they indicate that modulation of C. magister hemocyanin oxygen-affinity during development incorporates differences in intrinsic affinity and differences in divalent cation sensitivity of the stage-specific hemocyanins.
in vivo Muscle Length Changes in Bumblebees and the in vitro Effects on Work and Power
Authors: Gilmour K. M. , Ellington C. P.
Published: April 2021

The amplitude and time course of muscle length changes were examined in vivo in tethered, flying bumblebees Bombus lucorum. A ‘window’ was cut in the dorsal cuticle and aluminium particles were placed on the exposed dorsal longitudinal muscle fibres. Muscle oscillations were recorded using high-speed video and a high-magnification lens. The amplitude of muscle length changes was 1.9% (S.D.=0.5%, N=7), corresponding to the commonly quoted strain of 1–3% for asynchronous muscle. Higher harmonics, particularly the second, were found in the muscle oscillations and in the wing movements. The second harmonic for wing movements was damped in comparison to that for muscle length changes, probably as a result of compliance in the thoracic linkage. Inclusion of the second harmonic in the driving signal for in vitro experiments on glycerinated fibres generally resulted in a decrease in the work and power, but a substantial increase was found for some fibres.
Efficiency of Energy Conversion During Sinusoidal Movement of White Muscle Fibres from the Dogfish Scyliorhinus Canicula
Authors: Curtin N. A. , Woledge R. C.
Published: April 2021

Net work output and heat production of white myotomal muscle fibres from the dogfish were measured during complete cycles of sinusoidal movement at 12°C. The peak-to-peak movement was about 9% of the muscle fibre length; three stimuli at 32ms intervals were given in each mechanical cycle. The frequency of movement and the timing of the stimulation were varied for each preparation to find the optimal conditions for power output and those optimal for efficiency (the ratio of net work output to total energy output as heat+work). To achieve either maximum power or maximum efficiency, the tetanus must start while the muscle fibres are being stretched, before the beginning of the shortening part of the mechanical cycle. The highest power output, averaged over one cycle, was 0.23±0.014 Wg−1 drymass (±S.E.M., N=9, 46.9±2.8mWg−1 wetmass) and was produced during movement at 3.5Hz. The highest efficiency, 0.41±0.02 (±S.E.M., N=13), occurred during movements at 2.0–2.5Hz. This value is higher than the efficiency previously measured during isovelocity shortening of these fibres. The implications of the high efficiency for crossbridge models of muscle contraction are discussed.
Myofibrillar Protein Composition Correlates with Histochemistry in Fibres of the Abdominal Flexor Muscles of the Norway Lobster Nephrops Norvegicus
Authors: Neil Douglas M. , Fowler William S. , Tobasnick Graham
Published: April 2021

The myofibrillar proteins in fibres from the abdominal flexor muscles of the Norway lobster, Nephrops norvegicus, have been identified using SDS–PAGE gel electrophoresis. Several contractile and regulatory proteins are expressed as multiple isoforms in single fibres and, according to these, one fast fibre phenotype (F) can be identified in the deep flexor muscles and two slow fibre phenotypes (S1 and S2) can be distinguished in the superficial flexor muscles. The two slow fibre phenotypes are distributed non-uniformly across the superficial flexor muscle, and in the lateral bundle there is a heterogeneous mixture of both S1 and S2 fibres. Using histochemical procedures applied to intact or freeze-dried fibres in conjunction with measurements of fibre sarcomere length and gel electrophoresis, an exact correspondence can be demonstrated between the morphological properties, enzymatic content and myofibrillar protein composition of individual fibres from the deep and superficial flexor muscles. In the superficial flexor muscle, fibres of the S1 phenotype have a mean sarcomere length of <8 μm, a low oxidative capacity and an acid-labile isoform of myosin ATPase, while fibres of the S2 phenotypes have a longer sarcomere length (mean >9 μm), a higher oxidative capacity and an acid-stable isoform of myosin ATPase. These results are discussed in terms of the relationships between the different muscle fibre properties and the usefulness of procedures applied to single fibres for determining them.
Fundamental Analysis of Three-Dimensional ‘Near Fling’
Authors: Sunada Shigeru , Kawachi Keiji , Watanabe Isao , Azuma Akira
Published: April 2021

A series of experiments on three-dimensional ‘near fling’ was carried out. Two pairs of plates, rectangular and triangular, were selected, and the distance between the rotation axes of the two plates of each pair was varied. The motion of the plates as well as the forces and the moment were measured, and the interference between the two plates of a pair was studied. In addition, a method of numerical calculation was developed to aid in the understanding of the experimental results.

The interference between the two plates of a pair, which acted to increase both the added mass of each plate and the hydrodynamic force due to dynamic pressure, was noted only when the opening angle between the plates was small. The hydrodynamic forces were strongly influenced by separated vortices that occurred during the rotation. A method of numerical calculation, which took into account the effect both of interference between the plates and of separated vortices, was developed to give adequate accuracy in analyzing beating wings in ‘near fling’.
Mechanisms of Intracellular Calcium Release During Hormone and Neurotransmitter Action Investigated with Flash Photolysis
Authors: Ogden D. C. , Khodakhah K. , Carter T. D. , Gray P. T. A. , Capiod T.
Published: April 2021

To understand the complex time course of cytosolic Ca2+ signalling evoked by hormones and neurotransmitters, it is necessary to know the kinetics of steps in the second-messenger cascade, particularly cooperative and inhibitory interactions between components that might give rise to periodic fluctuations. In the case of inositol trisphosphate (InsP3)-evoked Ca2+ release, fast perfusion studies with subcellular fractions or permeabilised cells can be made if sufficient homogeneous tissue is available. Single-cell studies can be made by combining whole-cell patch-clamp techniques and microspectrofluorimetry with flash photolytic release of InsP3 to give quantitative, time-resolved data of Ca2+ release from stores. A technical description is given here of flash photolysis of caged InsP3, and the results of fast perfusion and flash photolytic experiments are reviewed. Studies of kinetics of Ca2+ release have shown that the InsP3 receptor/channel is regulated first by positive and then by negative feedback by free cytosolic Ca2+ concentration, producing a pulse of Ca2+ release having properties that may be important in the spatial propagation of Ca2+ signals within and between cells. The properties of InsP3-evoked Ca2+ release in single cells differ between peripheral tissues, such as the liver, and Purkinje neurones of the cerebellum. Purkinje neurones need 20–50 times higher InsP3 concentrations and release Ca2+ to change the free cytosolic concentration 30 times faster and to higher peak concentrations than in liver. The Ins P3 receptors in the two cell types appear to differ in apparent affinity, and the greater Ca2+ efflux from stores in Purkinje cells is probably due to a high receptor density.
Calcium Transport in Fish Gills and Intestine
Authors: Flik G. , Verbost P. M.
Published: April 2021

In calcium-transporting epithelia, calcium can move transcellularly (when it passes inwards, from mucosa to serosa) and paracellularly (when it moves in both an inward and outward direction). An epithelium is considered to be ‘tight’ when the transcellular route dominates and leaky when there is additional significant paracellular transport. The branchial epithelium of the gills of freshwater fish is a good model for tight epithelia, whereas the gills of seawater fish and the intestine present a model for leaky epithelia. Generally, the regulation of transcellular inward calcium transport determines whether net absorption occurs and the regulation of paracellular calcium transport is pivotal to secretion in calcium-transporting epithelia. In its simplest form, transcellular transport requires movement of Ca2+ across the apical membrane, through the cytosol and across the basolateral membrane. At the same time, cellular calcium homeostasis must be maintained and, to this end, calcium is buffered in the cytosol by calcium-binding proteins and sequestered in the endoplasmic reticulum and mitochondria. Movement of calcium from the exterior of the cell to the cytosol is passive, down an electrochemical gradient, and appears to be regulated through channel or carrier proteins. The apical membrane contains a hormone-regulated carrier mechanism for Ca2+ entry. Movement from the cytosol to the exterior requires energy-consuming extrusion mechanisms, involving Ca2+-ATPase and/or Na+/Ca2+ exchange. The roles of such mechanisms in calcium transport phenomena in fish gills and intestine will be addressed.
Role of Prolactin and Somatolactin in Calcium Regulation in Fish
Authors: Kaneko Toyoji , Hirano Tetsuya
Published: April 2021

The endocrine control of calcium metabolism in fish is performed by hyper-and hypocalcaemic hormones as in terrestrial vertebrates. However, the hormones involved in calcium regulation in fish, which lack parathyroid glands, differ from those in terrestrial vertebrates. The pituitary is important in hypercalcaemic regulation in fish; prolactin exerts a hypercalcaemic action in addition to its well-established hypernatraemic effect. However, alternation of plasma calcium concentration may not be the primary factor influencing prolactin secretion; changes in osmolality or sodium levels seem to be more critical for the regulation of prolactin release. Somatolactin, a putative pituitary hormone related structurally to both growth hormone and prolactin, is another possible factor responsible for hypercalcaemic regulation in fish. Exposure of rainbow trout to high-calcium environments reduces the activity of somatolactin-producing cells located in the hypophysial pars intermedia. Conversely, an increased activity of somatolactin cells is observed in low-calcium environments. Somatolactin has also been implicated in fat metabolism from comparisons of normal rainbow trout with a blue-coloured variant, which lacks most of the somatolactin cells normally present in the pituitary. Diverse functions for somatolactin, in maturation, in the stress response, in acid–base regulation and in background adaptation, have also been proposed. More detailed studies are needed to define the function of somatolactin.
Amphibian Calcium Metabolism
Authors: Stiffler Daniel F.
Published: April 2021

Calcium is present in amphibian blood at a concentration similar to that in other vertebrates, about 1–2mmol l−1. The fraction of free calcium in amphibians is lower than that in other tetrapod vertebrates because about 50% of the plasma Ca2+ is bound to plasma proteins and perhaps other molecules. Plasma [Ca2+] varies seasonally, increasing in spring and summer and decreasing in winter. Changes in plasma [Ca2+] also occur during larval development, as the concentration of this ion increases in larval forms as they approach metamorphosis. Calcium is exchanged at a variety of sites in animals. There is evidence for Ca2+ uptake across the skin and gills of larval anurans. It is also transported into the blood from the small intestine (especially the duodenum) and reabsorbed in renal tubules from the glomerular filtrate. The possibility of Ca2+ absorption from urine stored in the urinary bladder has not been confirmed, however. Calcium is stored in bone and in specialized endolymphatic sacs. This Ca2+ can be mobilized when the need arises. There are a number of endocrine and other humoral factors that appear to be involved in amphibian calcium metabolism. These include parathyroid hormone, calcitonin, vitamin D and prolactin.
Homologous Recombinant Growth Hormone and Calcium Metabolism in the Tilapia, Oreochromis Mossambicus, Adapted to Fresh Water
Authors: Flik G. , Atsma W. , Fenwick J. C. , Rentier-Delrue F. , Smal J. , Bonga S. E. Wendelaar
Published: April 2021

Homologous recombinant tilapia growth hormone (rtGH) was tested for its effects on calcium metabolism in freshwater tilapia Oreochromis mossambicus. Fish were fed an optimal ration of 5% of their body mass per day. A positive correlation was found between the amount of food given and the branchial calcium influx. In male tilapia, the mean calcium influxes were 5.80 and 11.71 μmol h−1 100 g−1 when they were fed 2 % and 5% food, respectively. In female fish fed 5% food, the calcium influx was 6.20 μmol h−1 100 g−1. Calcium influx via the gills was not affected by rtGH. However, in rtGH-treated fish, the net efflux of calcium was lower than in the controls. Apparently, the calcium taken up from the water was more efficiently stored in the body. GH increased the hepatosomatic index and had mild growth-promoting effects (mass and length increases); it increased the total body calcium pool without affecting bone or scale calcium density. The chloride cell density in the opercular epithelium almost doubled after GH treatment. GH did not influence plasma ion composition. Plasma cortisol levels were lower in rtGH-treated fish. A comparison of the roles of GH and prolactin (the products of the prolactin gene family) in calcium regulation of the tilapia led us to conclude that GH has specific calcitropic effects on freshwater tilapia that differ from those of prolactin.
Glucose Metabolism of the Swimbladder Tissue of the European Eel Anguilla Anguilla
Authors: Pelster Bernd , Scheid Peter
Published: April 2021

Glucose uptake from, and lactate release into, the blood have been analysed in the active gas-depositing swimbladder of the immobilized European eel Anguilla anguilla. Under normoxic conditions, 0.72 μmolmin−1 glucose was removed from the blood supply, while lactate was released into it at a rate of 1.16 μmolmin−1. The rate of gas deposition into the swimbladder was significantly correlated with the rate of lactate production. Under hypoxic conditions, glucose consumption by, and lactate production of, the swimbladder tissue were reduced, as was the rate of gas deposition. Compared with normoxic conditions, lactate concentration in the swimbladder tissue was elevated after 1h of hypoxia, indicating a decrease in lactate release. No difference in the osmolality of arterial and venous blood could be detected in these experiments.

Combining the data for glucose uptake and lactate release measured under normoxic conditions with the values for O2 uptake and CO2 production of the swimbladder tissue measured under similar conditions in a previous study, a quantitative evaluation of glucose catabolism was performed. According to the O2 uptake of the tissue, only about 1 % of the glucose was oxidized, while about 80% was fermented to lactic acid. The remaining 0.14 μmolmin−1 glucose was presumably catabolized through the pentose phosphate shunt, as indicated by the CO2 production of 0.16 μmolmin−1 that cannot be explained by aerobic metabolism.
Dynamic Mechanical Properties of Passive Single Cardiac Fibers From the Crab Cancer Magister
Authors: Meyhöfer Edgar
Published: April 2021

I determined the dynamic mechanical properties of single relaxed cardiac fibers from the Dungeness crab Cancer magister. Single fibers were mechanically isolated, chemically skinned and subjected to small-amplitude sinusoidal length perturbations over a wide range of strain rates and sarcomere lengths to characterize their viscoelastic behavior. The observed mechanical properties, together with transcardiac pressure recordings and ultrastructural measurements, were related to the overall function of the heart.

Single fibers, often longer than 1mm, could be mechanically dissected from the heart of Cancer magister. They typically ranged from 20 to 100 μm in diameter and were surrounded by a 100–400nm thick extracellular matrix. In situ, under normal physiological loads, the heart of Cancer magister generated transcardiac pressures of about 1000Pa and beat at 1Hz, while the sarcomere lengths of fibers changed by 10 % from about 4.0 to 4.4 μm during contractions. The total stiffness of all fibers increased from approximately 0.01MPa to 1MPa in the sarcomere length range from 3.8 to 6.0 μm and increased two-to threefold with a rise in strain rate from 0.01 to 5rad s−1. In the physiological range of sarcomere length (4.0–4.4 μm) and strain rate (0.5–1.2rad s−1), single cardiac fibers behaved viscoelastically, with average values for the relative energy dissipation ranging from 0.5 to 0.7. The volume fraction of the extracellular matrix correlated positively with the stiffness of single cardiac fibers.

On the basis of these results, I propose a dual role for the viscoelastic behavior of Cancer magister cardiac fibers: (1) the viscous energy dissipation confers dynamic mechanical stability at the level of the single fiber, and (2) the storage and return of elastic strain energy saves energy at the level of the whole heart.
Recruitment Patterns and Contractile Properties of Fast Muscle Fibres Isolated From Rostral and Caudal Myotomes of the Short-Horned Sculpin
Authors: Johnston Ian A. , Franklin Craig E. , Johnson Timothy P.
Published: April 2021

Muscle action during swimming and the contractile properties of isolated muscle fibres were studied in the short-horned sculpin Myoxocephalus scorpius at 5 ° C. Semi-steady swimming, startle responses and prey-capture events were filmed with a high-speed video at 200frames s−1, using fish 22–26cm in total length (L). Electromyographical (EMG) recordings, synchronised with the video, were made from fast muscle in rostral and caudal myotomes at points 0.40L and 0.80L along the body. Fast muscle fibres were first recruited at tail-beat frequencies of 3.7–4.2Hz, corresponding to a swimming speed of 1.7 L s−1. Electrical activity in the muscles occurred during 16–38% of each tail-beat cycle regardless of frequency. Muscle fibres were activated during the lengthening phase of the cycle. In caudal myotomes, the onset of the muscle activity occurred at a phase of 75–105 ° at 3.7Hz, decreasing to approximately 50 ° at frequencies greater than 4.5Hz (0 ° phase was defined as the point at which muscle fibres passed through their resting lengths in the stretch phase of the cycle; a full cycle is 360 °). Prey capture was a stereotyped behaviour consisting of a preparatory movement, a powerstroke at 7–9Hz and a glide of variable duration. The delay between the activation of muscle fibres in rostral and caudal myotomes during prey capture and startle responses was approximately 10ms.

Fast muscle fibres isolated from rostral and caudal myotomes were found to have similar isometric contractile properties. Maximum tetanic stress was 220kN m−2, and half-times for force development and relaxation were approximately 50ms and 135ms respectively. Power output was measured by the ‘work loop’ technique in muscle fibres subjected to sinusoidal length changes at the range of frequencies found during swimming. Under optimal conditions of strain and stimulation, muscle fibres from rostral and caudal myotomes produced similar levels of work (3.5 J kg−1) and generated their maximum power output of 25–30 W kg−1 at the tail-beat frequencies used in swimming (4–8Hz). Progressively delaying the onset of stimulation relative to the start of the strain cycle resulted in an initial modest increase, followed by a decline, in the work per cycle. Maximum positive work and net negative work were done at stimulus phase values of 20–50° and 120–140° respectively. The EMG and swimming studies suggest that fast muscle fibres in both rostral and caudal myotomes do net positive work under most conditions.
The Activity Pattern of Identified Neurosecretory Cells During Feeding Behaviour in the Locust
Authors: Schachtner Joachim , Bräunig Peter
Published: April 2021

In the locust, Locusta migratoria, the activity of identified efferent neurones of the suboesophageal ganglion was recorded extracellularly for long periods (hours or days). During recording, the animals were free to move in their enclosures. Activity of the cells appears to accompany feeding behaviour: they become active shortly before feeding starts and their activity persists during feeding. The cells have previously been shown to be serotonin-immunoreactive and to have a dense network of neurohaemal terminals on the sheath of the peripheral nerves supplying the mouthparts. The role of serotonin as a neuromediator involved in feeding activities is discussed for insects and other organisms.
The Multisegmental Motor Supply to Transverse Muscles Differs in a Cricket and a Bushcricket
Authors: Consoulas Christos , Hustert Reinhold , Theophilidis George
Published: April 2021

Most abdominal sternites of the cricket Gryllus bimaculatus and the bushcricket Decticus albifrons are bridged by a transverse muscle (TM) which supports expiratory movements. In the cricket, ventilatory contractions are controlled both within each segment, by a bilateral pair of excitatory motoneurones in the abdominal ganglion supplying the left and right halves of the TM independently, and intersegmentally, by peripheral collaterals of homologous motoneurones from adjacent segments. The axons of these motoneurones run in the ipsilateral paramedian nerve. This unique divergence of excitatory motoneurones to different muscles also results in massive convergence of excitatory inputs from different ganglia, especially on the TMs of the middle abdominal segments. TM contraction rates are increased by this intersegmentally divergent and convergent motor supply, especially in the middle abdominal segments.

In bushcrickets, each transverse muscle in segments 3–7 is innervated bilaterally by four pairs of neurones: (i) two pairs of contralateral excitatory motoneurones with axons that diverge, supplying two adacent muscles; (ii) one pair of contralateral excitatory neurones found in the second anterior ganglion and (iii) a pair of median inhibitory neurones in the segmental ganglion. Transverse muscles 2 and 8 receive reduced innervation. The excitatory motoneurones generate slow excitatory postsynaptic potentials (EPSPs), which must sum to cause muscle contractions. During ventilation, contralateral paired transverse motoneurones fire at similar frequencies, thus sychronizing the contractions of the left and right halves of the muscle so that the whole muscle acts as a single unit.
Wireless Transmission of Muscle Potentials During Free Flight of a Locust
Authors: Kutsch W. , Schwarz G. , Fischer H. , Kautz H.
Published: April 2021

Scientists have long been interested in recording data from freely moving animals. For larger animals, several telemetric techniques are available not only for following the movement of unrestrained animals in the wild (White and Garrott, 1990) but also for transmitting measures of heartbeat, body temperature, wingbeat, respiration, etc. (e.g. Lord et al. 1962; Butler and Woakes, 1980; Funk et al. 1993; for an overview, see Amlaner and Macdonald, 1980). Because of the size of such transmission devices, however, data acquisition has been restricted to larger animals. The development of lightweight batteries and microchips has only recently facilitated efforts to transmit data from smaller animals such as insects. Such data should greatly enhance our understanding of the processes involved in the neuronal control of unrestricted behaviour. Eventually it should be possible to monitor the activity of individual units (neurones, muscles) under closed-loop conditions, which closely resemble free movement. It is to be expected that this new approach will surpass previous studies involving intact but surface-bound animals implanted with long flexible electrodes (for crickets, see Kutsch, 1969) or animals tethered in a windstream (for improvement of the flight balance device, compare Weis-Fogh, 1956, with Dombrowsky, 1991). Increased freedom has been achieved in experiments on ‘free flight’ of large insects (Möhl, 1988; Stolley, 1990), although even these animals were restricted to a short or stationary flight handicapped by several implanted flexible electrodes.