bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature and the Force-Velocity Relationship of Live Muscle Fibres from the Teleost Myoxocephalus Scorpius
Authors: Langfeld Karen S. , Altringham John D. , Johnston Ian A. 
Published: April 2021

ABSTRACT
Small bundles of fast fibres were isolated from the myotomal muscle of the teleost Myoxocephalus scorpius. The temperature-dependence of isometric contractile properties and the force-velocity (P-V) relationship were studied. Fibres were found to deteriorate above 18 °C, and the force plateau during tetanic stimulation was not maintained above 15°C. Twitch and tetanic tension (Po) showed optima at around 8 °C. Force-velocity curves were fitted using either Hill’s hyperbolic equation or a hyperbolic-linear equation (hyp-lin). The best fit to the data was provided by the hyp-lin equation, which gave consistently higher values for unloaded contraction velocity (Vmax): 4·3, 8·1 and 9·5 muscle lengths s-1 at 1,8 and 12 °C, respectively. The P-V relationship was found to become progressively more curved at higher temperatures. Muscle power output calculated from the hyp-fin equation was 123 W kg-1 at 1°C and 256 W kg-1 at 8 °C. Curves normalized for Po and Vmax at each temperature show that the change in curvature is sufficient to increase the relative power output of the muscle by around 15 % on decreasing the temperature from 8 to 1 °C.
Ionic Species Involved in the Electrical Activity of Single Adult Aminergic Neurones Isolated from the Sixth Abdominal Ganglion of the Cockroach Periplaneta Americana
Authors: Lapied Bruno , Malécot Claire O. , Pelhate Marcel 
Published: April 2021

ABSTRACT
Adult neurones were obtained by dissociation of the dorsal area of the sixth abdominal (A6) ganglion of the cockroach, and electrical properties were studied with the patch-clamp technique. The neurones showed spontaneous fast action potentials, similar to those recorded with microelectrodes in neurones in situ along the dorsal median line of the A6 ganglion. Synthetic saxitoxin (sSTX) at concentrations of 10 × 10−8 to 1·0×10−7moll−1 suppressed the action potential (AP) and induced a dose-dependent hyperpolarization of the resting potential, suggesting that two types of sSTX-sensitive Na+ channels are present. The resting potential was dependent on the external concentration of both Na+ and K+, with a similar sensitivity to each, yielding a slope of about 43 mV per 10-fold change in concentration. The delayed outward rectification present under control conditions was reduced by tetraethylammonium chloride (TEA-CI, 1·0×10−2moll−1). TEA-CI or Ca2+-free saline abolished the afterhyperpolarization and increased the overshoot and duration of triggered APs, indicating that a calcium-activated potassium conductance contributes to the falling phase of the AP. At 3·0×10−3moll−1, the Ca2+ channel blockers MnCl2, CoCl2 and NiCl2 lengthened the AP. A blocker-dependent increase in the overshoot and threshold of the AP and reduction of the afterhyperpolarization were observed, probably reflecting the relative potencies of these ions in blocking Ca2+ channels and thus the Ca2+-activated K+ conductance. Increasing MgCl2 concentration by 3·0 ×10−3moll−1 had no effect on the AP, indicating that the positive shift of the threshold is due to the blockade of Ca2+ channels present at this potential. The results suggest that these isolated neurones are dorsal unpaired median neurones previously studied in a number of insect species.
The Movement of Cadmium Through Freshwater Trout Branchial Epithelium and its Interference with Calcium Transport
Authors: Verbost P. M. , Van Rooij J. , Flik G. , Lock R. A. C. , Bonga S. E. Wendelaar 
Published: April 2021

ABSTRACT
Exposure of freshwater trout (Salmo gairdneri) to waterborne Cd2+ results in accumulation of the metal in the branchial epithelial cells and its appearance in the blood. Cd2+ apparently enters the cells via Ca2+ channels in the apical membrane. Transfer of Cd2+ through the basolateral membrane is probably by diffusion. Inhibition by Cd2+ of transepithelial Ca2+ influx is time-and Cd2+-concentration-dependent. The inhibition of transepithelial Ca2+ influx is accompanied by blockage of apical Ca2+ channels. In line with the assumption that cytosolic Cd2+ inhibits Ca2+ uptake by inhibiting the basolateral Ca2+ pump, we hypothesize that the blockage of Ca2+ channels is an indirect effect of Cd2+ and results from a rise in cytosolic Ca2+ level caused by inhibition of the basolateral membrane Ca2+ pump.
Motile Characteristics of 9+2 and 9+1 Flagellar Axonemes of Crithidia Oncopelti
Authors: Marchese-Ragona S. P. , Glazzard A. N. , Holwili M. E. J. 
Published: April 2021

ABSTRACT
Crithidia oncopelti flagella were progressively solubilized by exposure to solutions containing the detergent Nonidet P42. During the course of the exposure, demembranated flagella were obtained that first had 9+2 axonemes, then 9+1, followed by 9+0. Finally, cylinders of A microtubules were obtained. The 9+2 and 9+1 flagella could be reactivated, indicating that the central complex does not have to be intact to allow wave propagation in this preparation. 9+0 axonemes could not be reactivated. Fourier analysis showed that the waveforms of the 9+2 and 9+1 axonemes were essentially the same, conforming to a meander shape. This shape is significantly different from the arc-line waves seen on in vivo flagella and indicates that (a) the membrane plays a significant role in the regulation of this parameter and (b) the passive elastic resistance of the microtubules in demembranated flagella has an important influence on bend patterns. The responses of 9+2 and 9+1 demembranated flagella to ATP were essentially the same, demonstrating that the extraction process had not affected the dynein-tubulin interaction. The central complex in Crithidia may be responsible for controlling the direction of wave propagation.
Effect of Low Extracellular Calcium Concentration on Photosensitivity of Isolated Rods From Frog Retina
Authors: Azuma Katsu 
Published: April 2021

ABSTRACT
The effects of extracellular calcium concentration ([Ca2+]o) on the light sensitivity of isolated single rods from the retina of the frog (Rana catesbeiana) were investigated by sucking the rod inner segments into tightly fitting pipettes.
Light flashes (500nm, 1 s duration) evoked transient outward changes of membrane current (photoresponses). The peak amplitude of maximal photoresponses in normal physiological solution varied between 6 and 12 pA. Reducing [Ca2+]o from 0·9 mmol l−1 (normal Ca2+) to 90 μmol l−1 (low Ca2+) increased the peak amplitude of photoresponses and shortened the recovery phase of the responses.
The effects of larger changes in light intensity were also investigated. After light-on there was a steady outward change of membrane current, and after light-off the current recovered to the initial dark level. With a low external Ca2+ concentration, light-off induced a large inward change of membrane current which transiently overshot the initial dark level. During the overshoot stage, light flashes evoked photoresponses which were larger than those in the initial dark period.
In Situ Dye-Visualization and Photoinactivation Using an Epifluorescent Compound Microscope
Authors: Heitler W. J. , Fraser K. 
Published: April 2021

ABSTRACT
A very useful technique to emerge in recent years in the field of neural circuit analysis is in situ dye-visualization and photoinactivation using Lucifer Yellow (Stewart, 1978). This allows direct anatomical identification of neurones during an experiment, and greatly facilitates placing several microelectrodes within a single neurone (Reichert & Krenz, 1986). If the visualization is kept brief, the neurone is not damaged, but with continued exposure the neurone is specifically killed (Miller & Selverston, 1979). This enables neurones to be selectively deleted from a circuit.
“Tho’ she kneel’d in that place where they grew…” The uses and origins of primate colour vision
Authors: Mollon J. D. 
Published: April 2021

ABSTRACT
The disabilities experienced by colour-blind people show us the biological advantages of colour vision in detecting targets, in segregating the visual field and in identifying particular objects or states. Human dichromats have especial difficulty in detecting coloured fruit against dappled foliage that varies randomly in luminosity; it is suggested that yellow and orange tropical fruits have co-evolved with the trichromatic colour vision of Old World monkeys. It is argued that the colour vision of man and of the Old World monkeys depends on two subsystems that remain parallel and independent at early stages of the visual pathway. The primordial subsystem, which is shared with most mammals, depends on a comparison of the rates of quantum catch in the short-and middle-wave cones; this system exists almost exclusively for colour vision, although the chromatic signals carry with them a local sign that allows them to sustain several of the functions of spatiochromatic vision. The second subsystem arose from the phylogenetically recent duplication of a gene on the X-chromosome, and depends on a comparison of the rates of quantum catch in the long-and middle-wave receptors. At the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast. The New World monkeys have taken a different route to trichromacy: in species that are basically dichromatic, heterozygous females gain trichromacy as a result of X-chromosome inactivation, which ensures that different photopigments are expressed in two subsets of retinal photoreceptor.
Sensory coding and corollary discharge effects in mormyrid electric fish
Authors: Bell C. C. 
Published: April 2021

ABSTRACT
Weakly electric fish use their electrosensory systems for electrocommunication, active electrolocation and low-frequency passive electrolocation. In electric fish of the family Mormyridae, these three purposes are mediated by separate classes of electro receptors: electrocommunication by Knollenorgan electroreceptors, active electrolocation by Mormyromast electroreceptors and low-frequency passive electrolocation by ampullary electroreceptors. The primary afferent fibres from each class of electroreceptors terminate in a separate central region. Thus, the mormyrid electrosensory system has three anatomically and functionally distinct subsystems.
This review describes the sensory coding and initial processing in each of the three subsystems, with an emphasis on the Knollenorgan and Mormyromast subsystems. The Knollenorgan subsystem is specialized for the measurement of temporal information but appears to ignore both intensity and spatial information. In contrast, the Mormyromast subsystem is specialized for the measurement of both intensity and spatial information. The morphological and physiological characteristics of the primary afferents and their central projection regions are quite different for the two subsystems and reflect the type of information which the subsystems preserve.
This review also describes the electric organ corollary discharge (EOCD) effects which are present in the central projection regions of each of the three electrosensory subsystems. These EOCD effects are driven by the motor command that drives the electric organ to discharge. The EOCD effects are different in each of the three subsystems and these differences reflect differences in both the pattern and significance of the sensory information that is evoked by the fish’s own electric organ discharge. Some of the EOCD effects are invariant, whereas others are plastic and depend on previous afferent input.
The mormyrid work is placed within two general contexts: (a) the measurement of time and intensity in sensory systems, and (b) the various roles of motor command (efferent) signals and self-induced sensory (reafferent) signals in sensorimotor systems.
On the So-called Constant-lift Reaction of Migratory Locusts
Authors: Zarnack Wolfram , Wortmann Michael 
Published: April 2021

ABSTRACT
Locusts were fastened to a force transducer in front of a wind tunnel to measure their lift and thrust during tethered flight heading into the wind. The thrust measurement was used to adapt the wind speed to the flight speed of the animals. Thus, the locusts could choose their flight speed freely in the range 0.5– 7ms− 1. At light intensities of about 0.02 lx (twilight), the locusts generally produced a maximum lift greater than 100% of their body weight. A miniature motor mounted on the force transducer could alter the body angle of the locusts without further interference. Lift was found to be influenced by body angle. No ‘constant-lift reaction’ evoked by exteroceptive information of the aerodynamic flow was found. Flight speed was almost independent of the imposed body angle. Generally, a flight speed of about 3 m s− 1 was necessary for level flight. There was no further correlation between lift and flight speed.
Modulation of Haemocyanin Oxygen-Affinity by L-Lactate and Urate in the PrawnPenaeus Japonicus
Authors: Lallier F. , Truchot J. P. 
Published: April 2021

ABSTRACTThe addition of either L-lactate or urate to dialysed haemolymph from the prawn Penaeus japonicus (Bate) increased the in vitro haemocyanin oxygen affinity. The quantitative values of these two effects, expressed as ΔlogP50/ Δlog[effector], were found to be −0·077 for L-lactate and −0. ·032 for urate, at pH7·6 and 25°C. The normal, significant Bohr effect (ΔlogP50/ΔpH approx. −1·5 at pH 7·.6, 25°C) was not modified by the two effectors tested, nor was the cooperativity of haemocyanin oxygen-binding (n50 approx. 4).Hypoxic exposure of the prawns to or 4·4 kPa(1 kPa=7·5 mmHg) for up to 48 h at 25°C induced only a small, less than 2·5-fold, elevation of L-lactate concentration in the haemolymph, all values remaining below 0·5 mmol 1−1, but urate concentration increased to a greater extent (12-fold maximum increase from 0·01 to 0·12 mmol 1−1). Haemocyanin oxygen-affinity, measured in vitro on haemolymph samples drawn from hypoxic prawns, increased slightly during the first 3h of hypoxia acclimation (ΔP50=0·8–0·9kPa at pH7·6), returning to near normoxic control values after a 48 h hypoxic exposure.The respective roles of L-lactate and urate in enhancing oxygen transport during hypoxia are discussed on the basis of their in vitro effects on haemocyanin oxygen affinity and their in vivo concentration variations in haemolymph.
Regulation of Hepatic Gluconeogenesis and Glycogenolysis By Catecholamines in Rainbow Trout During Environmental Hypoxia
Authors: Wright Patricia A. , Perry Steve F. , Moon Thomas W. 
Published: April 2021

ABSTRACT
This study tests the hypothesis that catecholamines regulate glucose availability during hypoxia in the rainbow trout by activating glycogen phosphorylase (GPase) while inhibiting pyruvate kinase (PK) in the liver. The net result would be an increase in liver glycogenolysis and a reduction of glycolysis and/or enhancement of gluconeogenesis. We used the criteria of Stalmans & Hers (1975) and report much lower resting percent GPase a (active) values (20–30%) than those previously published. Dorsal aortic injections of epinephrine or norepinephrine increased plasma glucose (16–46%), had no effect on liver or muscle glycogen levels, decreased the activity of PK, and increased total and percent GPase a activities. Pre-treatment with the β-adrenoreceptor antagonist propranolol eliminated these effects. During moderate hypoxia, plasma glucose remained unchanged, while lactate levels increased fourfold. When fish were pre-treated with propranolol, hypoxia depressed plasma glucose levels (−26%), total and percent GPase a, and increased PK activity, suggesting that hypoxia mediated the dephosphorylation of these enzymes. We conclude that catecholamines stimulate hepatic β-adrenoreceptors during hypoxia and sustain plasma glucose levels by nullifying the deleterious effects of hypoxia on metabolic function. The specific metabolic consequences of these catecholamine-mediated effects are an increase in the activity of the active form of GPase and a reduction in PK activity, which suggests an activation of glycogenolysis and an inhibition of glycolysis and/or activation of gluconeogenesis, respectively.
Control of metabolism and growth in embryonic turtles: a test of the urea hypothesis
Authors: Packard G. C. , Packard M. J. 
Published: April 2021

ABSTRACTWe performed two experiments to determine (1) whether the metabolism and growth of embryonic snapping turtles (Chelydra serpentina) incubating in wet and dry environments are correlated inversely with the concentration of urea inside their eggs, and (2) whether urea accumulating inside eggs might be the cause of reductions in metabolism and growth by embryos. Eggs in the first experiment were incubated in different hydric environments to induce different patterns of net water exchange between the eggs and their surroundings. Turtles hatching from eggs that were in positive water balance had larger carcasses, smaller residual yolks and lower concentrations of urea in their blood than animals emerging from eggs that were in negative water balance. Thus, we confirmed the existence of correlations among water exchange by eggs, concentrations of urea in fluid compartments inside eggs, and metabolism and growth of embryos. In the second experiment, eggs were injected with solutions of urea at the mid-point of incubation to induce different levels of uremia in developing embryos. The injection protocol induced variation in the concentration of urea in blood of hatchlings similar to that observed in the first experiment for turtles hatching in wet and dry environments. However, the injection protocol did not induce variation in size of hatchlings or in mass of their residual yolk. Thus, the reduction in metabolism and growth of chelonian embryos developing in dry environments does not result from an inhibition of intermediary metabolism caused by urea, and the ‘urea hypothesis’ for control of metabolism cannot be accepted in its present form.
Tracheal Hypertrophy in Mealworms: Design and Plasticity in Oxygen Supply Systems
Authors: Loudon Catherine 
Published: April 2021

ABSTRACTLarval Tenebrio molitor L. (Insecta) were reared in three different levels of oxygen: 21 % (normal), 15 % and 10.5 %, all at 101.3kPa (=1atm) total pressure (remainder nitrogen). Some larvae were transferred from one oxygen level to another during development.The main tracheae (branching off from the spiracular tracheae) were of greater cross-sectional area in lower ambient oxygen. Compared to larvae of the same body mass reared in 21 % oxygen, larvae reared in 15 % oxygen had main tracheae 40% larger in cross-sectional area on average, and larvae in 10.5% oxygen had main tracheae 120% larger. This hypertrophy is not consistent with the widely accepted hypothesis that tracheae contribute an insignificant resistance to the net movement of oxygen in insect tracheal systems.The magnitude of the hypertrophy is consistent with predictions from Fick’s law of diffusion and with the hypothesis that diffusion is the primary mechanism for oxygen movement in the larval tracheal system of holometabolous insects.
A rapid cold-hardening response protecting against cold shock injury in Drosophila melanogaster
Authors: Czajka Maureen C. , Lee Richard E. 
Published: April 2021

ABSTRACT
In studies of insect cold-hardiness, the supercooling point (SCP) is defined as the temperature at which spontaneous nucleation of body fluids occurs. Despite having an SCP of − 20°C, adults of Drosophila melanogaster did not survive exposure to −5°C, which suggests that cold shock causes lethal injury that is not associated with freezing. If, however, flies were chilled at 5 °C, for as little as 30min, approximately 50% of the flies survived exposure to −5°C for 2h. This capacity to cold-harden rapidly was greatest in 3-and 5-day-old adults. The rapid cold-hardening response was also observed in larvae and pupae: no larvae survived 2 h of exposure to − 5 °C, whereas 63 % pupariated if chilled at 5 °C before subzero exposure. Similarly, although exposure of pupae to −8°C was lethal, if pre-chilled at 5°C 22% eclosed. This extremely rapid cold-hardening response may function to allow insects to enhance cold-tolerance in response to diurnal or unexpected seasonal decreases in environmental temperature.
Compensation of progressive hypercapnia in the toad (Bufo marinus) and the bullfrog (Rana catesbeiana)
Authors: Toews D. P. , Stiffler D. F. 
Published: April 2021

ABSTRACT
Toads (Bufo marinus L.) and bullfrogs (Rana catesbeiana Shaw) were subjected to a series of 24 h step increases in aerial CO2 (2, 4, 6 and 8%) to assess the degree of extracellular pH compensation at each CO2 level and to ascertain the importance of cutaneous ion transport in this process. Elevation of plasma [HCO3−] occurs during the 24 h period, with the bullfrogs showing a greater ability to compensate at each step. There was no indication that a [HCO3−] threshold of 30 mmol l−1 existed in either species, although bullfrogs appeared to have a greater compensatory potential when exposed to the higher levels of CO2. The results of the ion flux experiments suggest that neither the terrestrial Bufo nor the semi-aquatic Rana use their skin to any great extent for acid-base balance during hypercapnia.
Interactions of light and gravity reception with magnetic fields in Xenopus laevis
Authors: Leucht T. 
Published: April 2021

ABSTRACT
Tadpoles of Xenopus laevis are shown to respond to magnetic fields using a gravity-related test paradigm. They exhibit a directional selectivity with respect to angular variations of the inclination of low-intensity magnetic fields. This response is abolished when the optic nerves of the tadpole are transected, indicating that the peripheral optical system is involved in the detection of magnetic fields.
Oscillations of Glial Membrane Potential in a Localized Region of the Blood-Brain Barrier of an Insect
Authors: Schofield P. K. 
Published: April 2021

ABSTRACT
In an abdominal ganglion of the American cockroach, Periplaneta americana, electrophysiological characteristics of the perineurium, the glial layer that forms the insect blood-brain barrier, were investigated by microelectrode recording. The potential across the barrier was positive relative to the bathing medium. Its value increased when the external K concentration was raised, as to be expected from a depolarization of the perineurial cell membrane facing the saline, the basolateral membrane. A negative ‘all-or-nothing’ transient, having an amplitude of some 30mV and a half-amplitude duration of about 1·5 min, was also induced, either during the K elevation or after. Given sufficient K exposure, a series of these transients occurred, with a periodicity of 3–15 min, indicating that a cellular oscillator had been activated. The delay between application of high K and the appearance of the first transient was variable, and could be as long as 60 min for a threefold increase in K level. The transients could persist upon return of normal saline, for at least 85min, with little change in amplitude. By recording transperineurial potential simultaneously with recording from superficial cells, one of which was identified as a perineurial cell by peroxidase injection, the transients were found to be generated by a depolarization of the membrane adjacent to the underlying nerve cells, the adglial membrane. Analysis using a simple electrical model yielded values for the resting electromotive force (e.m.f.) generated by the membranes, – 50mV for the basolateral, –71 mV for the adglial, and indicated that the paracellular pathway had a resistance 4·3 times larger than the transcellular resistance. These results reveal a cellular oscillator, apparently of cytosolic type, in the perineurial glia of an insect ganglion, and demonstrate physiological differences between the perineurium of the ganglion and that of other regions of the insect nervous system.