bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Low Ambient Calcium Levels on Whole-Body Ca2+ Flux Rates and Internal Calcium Pools in the Freshwater Cichlid Teleost,Oreochromis Mossambicus
Authors: Flik Gert , Fenwick James C. , Kolar Zvonimir , Mayer-Gostan Nicole , Bonga Sjoerd E. Wendelaar 
Published: April 2021

ABSTRACTCalcium fluxes and internal calcium pools were measured in fed, rapidly growing, male tilapia, Oreochromis mossambicus, acclimated to 0·8 mmol l−1 (FW) and 0-2 mmol l−1 (LFW) Ca2+. Plasma calcium levels were slightly and significantly higher in the LFW tilapia, but muscle calcium concentrations were independent of ambient Ca2+. At the time of the experiments, the LFW fish were growing and accumulated calcium, although the calcium content of their hard tissues was reduced. The LFW fish had higher Ca2+ influx and efflux rates than the FW fish. The increase in the influx of Ca2+ in LFW fish was, however, substantially greater than the increase in the efflux of Ca2+, giving these fish a more than four-fold increase in net Ca2+ influx from the water: for a 20-g tilapia net uptake rates of Ca2+ from the water were 390 and 1620 nmol Ca2+ h−1 for FW-and LFW-adapted fish, respectively. These values were calculated to represent at least 69 % of the total calcium accumulated by these growing fish. This indicates that even in low-calcium water, tilapia absorb a significant amount of their calcium requirement directly from the water.The pool of readily exchangeable calcium in the bone of FW fish was estimated to be about 7 % of the total hard tissue calcium. In the fish acclimated to LFW, this percentage increased to about 15 % as total hard tissue mineralization decreased. This may indicate that tilapia can increase the mobility of their h
A Biological Feedback Control System with Electronic Input: the Artificially Closed Femur-Tibia Control System of Stick Insects
Authors: Weiland G. , Bässler U. , Brunner M. 
Published: April 2021

ABSTRACT
An experimental arrangement was constructed which is based on the open-loop femurtibia control system of two stick insect species (Carausius morosus and Cuniculina impigra). It could be artificially closed in the following way: the position of the tibia was measured by an optical device and this value was used to drive a penmotor which moved the receptor apodeme of the femoral chordotonal organ in the same way as in intact animals. This arrangement allows direct comparison of the behaviour of the open-loop and the closed-loop system as well as introducing an additional delay.
The Carausius system has a phase reserve of only 30° –50° and the factor of feedback control approaches 1 between 1 and 2 Hz. This agrees with the observation that an additional delay of 70–200 ms produces long-lasting oscillations of 1–2 Hz. The Cuniculina system has a larger phase reserve and consequently a delay of 200 ms produced no oscillations. All experiments show that extrapolation from the open-loop system to the closed-loop system is valid, despite the non-linear characteristics of the loop. Consequences for servo-mechanisms during walking and rocking movements are discussed.
Distance and Size Discrimination in a Water Stick Insect, Ranatra Linearis (Heteroptera)
Authors: Cloarec Ann 
Published: April 2021

ABSTRACT
The role of vision in distance, position and size discrimination in prey capture has been investigated in normal adult water stick insects (Ranatra linearis L. : Heteroptera) and in ones with one eye covered.
Both monocular and intact Ranatra were able to discriminate between two targets subtending the same angle but presented at different distances. They usually chose the target nearer to their foreleg claws. Although monocular subjects undershot more often than controls, they could still estimate distance correctly.
When presented with two different-sized targets at the same distance, both monocular and intact subjects usually preferred the larger target within a 1°–10° range, even though monocular animals chose the larger object less consistently. They were able to distinguish between two targets differing in size by only 1 °.
Asymmetrical presentations of two identical targets stressed the importance of the central position. Intact animals always preferred the target nearer their midline.
These data also revealed the unexpected ability of Ranatra to strike accurately at two targets or prey items simultaneously. When two identical targets were presented simultaneously and symmetrically, aims were directed at both targets, and one was grasped by each raptorial foreleg, thus indicating an absence of confusion.
The Physiology of Wandering Behaviour in Manduca Sexta: IV. Hormonal Induction of Wandering Behaviour from the Isolated Nervous System
Authors: Dominick Oliver S. , Truman James W. 
Published: April 2021

ABSTRACT
Prior to exposure to ecdysteroids, the isolated central nervous system (CNS) of the fifth instar Manduca sexta larvae exhibited infrequent motor bursts over a 24-h period of extracellular recording from segmental motor nerves. In contrast, the CNS isolated from wandering larvae was characterized by persistent, frequent spontaneous motor bursts throughout the 24-h incubation. The motor bursts generated by the isolated CNS of wandering larvae were similar to those observed in deafferented segments of partially dissected wandering larvae during locomotion. In both cases bursts in the deafferented ganglia were synchronous and had a lower frequency than in intact animals. Removal of the brain from a CNS isolated prior to ecdysteroid exposure resulted in the appearance of spontaneous bursts, which were abolished by removing the suboesophageal ganglion (SEG). By contrast, when the brain was removed from the isolated CNS of wandering larvae, spontaneous bursts ceased. These results parallel the behavioural effects of the same lesions in intact larvae of the respective stages. The CNS isolated from larvae prior to ecdysteroid exposure initiated sustained frequent bursting after an average latency of 15 h following incubation in haemolymph taken from larvae during the interval of ecdysteroid secretion. Incubations of the CNS with 1μgml−1 20-hydroxyecdysone (20-HE) resulted in the onset of the same pattern of sustained motor activity. In a CNS isolated prior to ecdysone release, it was necessary and sufficient to expose the brain to 20-HE in order to induce the state of persistent motor bursts characteristic of wandering. We conclude that the spontaneous persistent motor bursts observed in the isolated CNS of wandering larvae are directly related to the sustained locomotion seen during the wandering behaviour. 20-HE acts directly on the CNS, specifically the brain, to induce this state of neural activity.
Energy Cost of Contraction in Fast and Slow Muscle Fibres Isolated from an Elasmobranch and an Antarctic Teleost Fish
Authors: Altringham J. D. , Johnston I. A. 
Published: April 2021

Abstract
Single fast and small bundles of slow fibres were isolated from the muscles of an elasmobranch (dogfish, Scyliorhinus canicula) and an Antarctic teleost (Notothenia neglecta). A third fibre type present in the dogfish (superficial fibre) was also isolated. Fibres were chemically skinned with a non-ionic detergent. Tension generation and ATPase activity were measured during isometric activations. ATPase activity was estimated by measuring the release of ADP into the experimental solutions using high performance liquid chromatography. In the dogfish fibre types, both tension and ATPase activity increased in the order superficial &lt; slow &lt; fast, even after corrections were made for differences in myofibrillar density. The economy of isometric contraction (tension/ATPase activity) was 50–60% higher in the slow and superficial fibres than in the fast. In the Antarctic species, both tension and ATPase activity of the fast fibres were higher than those of the slow fibres, and the slow fibres were 30% more economical than fast fibres. After correction for differences in myofibrillar density, tensions were very similar. The results are discussed with reference to the energy supply, recruitment pattern and function of the various fibre types.
Evidence Against Hormonal Control of Integumentary Water Loss in Periplaneta Americana
Authors: Machin J. , O’donnell M. J. , Kestler P. 
Published: April 2021

ABSTRACT
The effect of decapitation on water loss from adult male cockroaches was studied in order to re-examine the possibility of hormonal modulation of integumental permeability. We found no effect of decapitation on the permeability or water content in measurements made on the pronotum. Although overall weight losses of the decapitated animals always exceeded those of intact animals, loss rates and their rate of decline depended on the apparent severity of handling. There was a small but significant difference between the controls and all decapitated and sham-operated animals, and this difference persisted for at least 96 h. We attribute these results principally to the differential effects of cuticle damage, though increased respiratory water loss may also be a factor. Our results draw attention to the complex practical problems involved in obtaining accurate, representative cuticle permeabilities for Periplaneta, and form a basis for questioning the notion of inhibition of cuticular water loss by hormones from the head.
Biophysical Aspects of Directional Hearing in the Tammar Wallaby, Macropus Eugenii
Authors: Coles Roger B. , Guppy Anna 
Published: April 2021

ABSTRACT
The biophysical properties of the external ear of the Tammar wallaby, Macropus eugenii (Desmarest), have been investigated using probe microphones implanted in the ear canal. An acoustic axis of the pinna exists above 2kHz which is located close to the horizonal plane for natural ear positions, whereas azimuthal location of the acoustic axis is determined by pinna orientation on the head. The maximum on-axis acoustic pressure gain of the external ear reaches 25–30 dB for frequencies near 5 kHz. This results from pressure transformation by the horn-like pinna combined with resonance of the auditory meatus. The directionality of the pinna is similar to the sound diffraction properties of a circular aperture with an average radius based on the circumference of the pinna face. These properties determine the acceptance angle of the main lobe containing the acoustic axis and the spatial location of nulls. Large binaural intensity differences, exceeding 30dB, can be produced by the interaction of peaks and nulls between monaural directivity patterns, depending on the relative position of each pinna.
Octopaminergic Modulation of the Membrane Potential of the Schwann Cell of the Squid Giant Nerve Fibre
Authors: Reale Vincenzina , Evans Peter D. , Villegas Jorge 
Published: April 2021

ABSTRACT
The actions of octopamine on the Schwann cells of the giant nerve fibre of the tropical squid are described. The pharmacology of the receptors mediating the actions of octopamine has been investigated in terms of stereospecificity, amine specificity and interactions with a range of agonists and antagonists. The receptors are maximally activated by D(−)-octopamine and share many of the characteristics of OCTOPAMINE2 class receptors in other preparations. The octopamine receptors appear to mediate their actions by increasing the intracellular levels of cyclic AMP in the Schwann cells. Low concentrations of octopamine potentiate the actions of the nicotinic cholinergic activation system of the Schwann cells. The results are discussed in terms of the possible physiological role of octopamine in the modulation of Schwann cell activity during stressful conditions when the giant axon system is likely to be used at a high frequency to facilitate the escape response of the squid.
Responses Of a Stenohaline Freshwater Teleost (Catostomus Commersoni) To Hypersaline Exposure II. Transepithelial Flux of Sodium, Chloride and ‘Acidic Equivalents’
Authors: Wilkes P. R. H. , McMahon B. R. 
Published: April 2021

ABSTRACT
The effects of exposure to 300mosmoll−1 sodium chloride on the transepithelial movement of sodium, chloride and ‘acidic equivalents’ was examined in the stenohaline freshwater teleost Catostomus commersoni (Lacépéde), the white sucker. The transepithelial potential (TEP) was negative in control fish acclimated to soft freshwater ([Ca2+] &lt;0– 1 mmol I−1) but positive in control fish acclimated to hard-water ([Ca2+] &gt; 1–0mmoll−1). Using permeability coefficients calculated from measured unidirectional effluxes of sodium and chloride for both groups above, the Goldman equation predicts the observed change in polarity of the TEP. During saline exposure the ability of external calcium to influence the TEP was greatly attenuated, and the TEP remained positive throughout 96 h exposure to either hard or soft saline water. As a consequence of the reduced (and reversed) chemical potential and of the prevailing TEP, the electrochemical difference for sodium was directed out from the fish while that for chloride was directed inwards. Thus, the passive movement of sodium and chloride in opposite directions could potentially account for the previously reported decrease in plasma strong ion difference (SID), and therefore the prevailing acid-base status. Unfortunately, the existence of possible exchange diffusion processes for sodium and chloride observed in saline-exposed fish prevented a more detailed examination of this hypothesis. Since the change in plasma SID occurred gradually over a 96-h period, there was no measurable change in the net flux of ‘acidic equivalents’ which could have been associated with the active and passive transbranchial movement of sodium and chloride. The significance (or lack of it) of the Na+/H+-NH4+ and C1−/HCO3−-OH− exchange pumps to systemic acid-base balance is discussed.
A New Technique for Measuring Water Transport Across the Seawater Eel Intestine
Authors: Ando Masaaki , Sasaki Hiroshi , Huang Kee C. 
Published: April 2021

ABSTRACT
A new technique was developed for measuring net water flux across the eel intestine in vitro. The new perfusion method was suitable for long duration experiments because of continuous oxygen supply to both the external and the perfusion medium. Net water flux was calculated directly from the difference between the rates of effluent and perfusate flow without measuring the concentration of marker substances. The calculated value of net flux appears to be reliable because: its direction is always from mucosa to serosa in both everted and non-everted intestine; ouabain diminishes it to zero; it is identical with the standard water flux obtained under zero perfusion ; and it is identical with the value obtained by means of [14C]PEG following the previous perfusion method. The net water fluxes obtained by the new method were steadier than those obtained with the previous complicated perfusion method. In this new experimental system, the net water flux and the transepithelial potential difference (PD) decreased gradually with time, and were not restored by application of adrenergic agonists or cortisol. These parameters were stimulated by 5 mmol l−1 L-alanine, but not by D-glucose, L-valine or L-glycine, indicating a specific action of L-alanine.
Peptidergic and Aminergic Modulation of Insect Skeletal Muscle
Authors: Evans Peter D. , Myers Camilla M. 
Published: April 2021

ABSTRACT
Insect skeletal muscles are frequently innervated by small numbers of motor neurones, all of which can be uniquely identified physiologically. They therefore present excellent model systems in which to study the basic principles of neuromuscular transmission and the modulation of these effects by biogenic amines and peptides. The extensor-tibiae muscle of the hind leg of the locust is a much studied, large muscle that is innervated by three identified motor neurones and one identified modulatory neurone. Much attention has recently been focused on the modulation of neuromuscular transmission and muscular contraction in this muscle by biogenic amines and peptides.
One proximal bundle of muscle fibres in the extensor-tibiae muscle exhibits a myogenic rhythm of contraction and relaxation. The rhythm is stimulated by a variety of peptides including proctolin, the AKH-related peptides M1 and M2, and by small cardioactive peptide (SCPB). In addition, it is activated by 5-hydroxy-tryptamine and by one class of adenosine analogues. The rhythm is inhibited by octopamine and by a second class of adenosine analogues. The actions of these various modulatory compounds will be discussed in terms of the likely numbers of pharmacologically distinct receptors in this preparation and their modes of action.
Neuromuscular transmission and muscular contraction in the extensor-tibiae muscle is modulated by the biogenic amine octopamine and by the peptides, proctolin and FMRFamide. The actions of these modulators are discussed in relation to differences in the responsiveness of various regions of the muscle, to the frequency dependence of their effects on motor neurone activity and to their modes of action.
The cellular locations and mode of transmission to the muscle of some of these modulators will be considered. Octopamine and proctolin are contained within neurones which innervate the muscle, whilst FMRFamide-and SCPB-like peptides appear to be released into the locust haemolymph as neurohormones.
Different Types of Calcium Channels
Authors: Mccleskey E. W. , Fox A. P. , Feldman D. , Tsien R. W. 
Published: April 2021

ABSTRACT
Ca2+ channels allow passage of Ca2+ ions into the cytoplasm through a selective pore which is opened in response to depolarization of the cell membrane (for reviews see Hagiwara & Byerly, 1981, 1983; Tsien, 1983; Reuter, 1983). The Ca2+ flux creates a net inward, depolarizing current and the resulting accumulation of Ca2+ in the cytoplasm can act as a chemical trigger for secretion of hormones and neurotransmitters, contraction of muscle and a-variety of other Ca2+-sensitive events. Thus, upon sensing membrane potential changes, Ca2+ channels simultaneously generate an electrical signal while directly creating an intracellular chemical messenger. This dual ability is unique among the family of ion channels and allows the Ca2+ channel to play a variety of roles in excitation-secretion and excitation-contraction coupling.
It has now become clear that versatility of function is reflected by diversity of the types of Ca2+ channels on the membrane of individual cells. This article describes the nature of data which have demonstrated multiple channel types, reviews the literature suggesting that many cells have several kinds of Ca2+ channels, and discusses newer data regarding a neurotoxin that distinguishes among different Ca2+ channels.
Slow Synaptic Transmission in Frog Sympathetic Ganglia
Authors: Adams P. R. , Jones S. W. , Pennefather P. , Brown D. A. , Koch C. , Lancaster B. 
Published: April 2021

ABSTRACT
Bullfrog ganglia contain two classes of neurone, B and C cells, which receive different inputs and exhibit different slow synaptic potentials. B cells, to which most effort has been directed, possess slow and late slow EPSPs. The sEPSP reflects a muscarinic action of acetylcholine released from boutons on B cells, whereas the late sEPSP is caused by a peptide (similar to teleost LHRH) released from boutons on C cells. During either sEPSP there is a selective reduction in two slow potassium conductances, designated ‘M’ and ‘AHP’. The M conductance is voltage dependent and the AHP conductance is calcium dependent. Normally they act synergistically to prevent repetitive firing of action potentials during maintained stimuli. Computer simulation of the interactions of these conductances with the other five voltagedependent conductances present in the membrane allows a complete reconstruction of the effects of slow synaptic transmission on electrical behaviour.
The Size Factor in the Action of Arsenic Upon Silkworm Larvae
Authors: Bliss C. I. 
Published: April 2021

ABSTRACT
The customary method of adjusting dosages of drugs and poisons as simple ratios of the body weight of the individual is questioned. Data recorded by F. L. Campbell on the survival time of silkworm larvae following the ingestion of sodium arsenate were used for analysis. By the method of covariance it is shown that there is a significant residual effect of individual body weight upon the rate of toxic action when the dosage is made proportional to the body weight. By graphic test the rate of toxic action seemed to be a linear function of the log of the dose per larva and the log of the body weight. Accordingly partial regression equations were computed separately for the 2nd to the 5th instars expressing the rate of toxic action in terms of these two dosage characteristics. The adjustment in dosage that was necessary to eliminate the effect upon the rate of toxic action of body size could be expressed as a size factor, where w is the body weight of the individual and h is determined from the partial regression coefficients of each equation. When based upon the reciprocal of the survival time, h increased from 1· 67 to 1· 96 from the 2nd to the 5th instars, but when similar values were computed for the logarithm of the rate, h was the same in all instars and averaged 1· 511 ± 0· 089. Also supporting the theoretical superiority of the log rate as a measure of toxic action was the fact that the data for the separate instars formed parts of a single straight line when log rate was plotted against the log of dose adjusted by the size factor w1’6 and the statistical demonstration that the distribution of rates was significantly skewed and that of log rates symmetrical. If the adjusted dose is considered as a type of con-centration, the final equation for all four instars could be written as C0.49t = 309, a type of formula having wide toxicological applicability. A method is proposed for computing the mean lethal dose from the rate of toxic action.
Metabolic Rates of Trout Fry from Swift and Slow-Running Waters
Authors: Washbourn R. 
Published: April 2021

ABSTRACT
Recent studies on the respiration of fresh-water animals have shown that certain species of ephemerid nymphs and trichopterid larvae inhabiting swift streams have a higher oxygen consumption than other species, comparable in size, which live in still waters, the measurements being made under identical conditions (Fox, Simmonds and Washbourn, 1935). Moreover, within one species of crustacean, Asellus aquaticus, individuals from rapid water have a higher metabolic rate than those from slow water (Fox and Simmonds, 1933). The investigation reported below was undertaken to find out whether trout would show a similar phenomenon.
Studies in Animal Locomotion
Authors: Gray J. 
Published: April 2021

ABSTRACT
In a previous paper (Gray, 1936) it has been shown that the rhythmical movements, characteristic of an eel swimming freely in water, are determined by the spinal cord and not upon impulses reaching the cord from receptors in the skin or muscles. It was also shown that a locomotory rhythm can be elicited from a spinal or decapitate preparation as a response to stimuli applied either to the spinal cord or to exteroceptive sense organs. In all these cases the experimental conditions were such that the muscles of the body were free to contract against the comparatively low resistance of the surrounding water. The present paper deals with the behaviour of the fish when the movements of the muscles are opposed by relatively strong external resistances.