bluuebunny/crossref_metadata_2025_split huggingface dataset:
Refinements in the Short-Circuit Technique and Its Application to Active Potassium Transport Across the Cecropia Midgut
Authors: Wood John L. , Moreton Roger B. 
Published: April 2021

ABSTRACT
The conventional, two-electrode method for measuring potential difference across an epithelium is subject to error due to potential gradients caused by current flow in the bathing medium. Mathematical analysis shows that the error in measuring short-circuit current is proportional to the resistivity of the bathing medium and to the separation of the two recording electrodes. It is particularly serious for the insect larval midgut, where the resistivity of the medium is high, and that of the tissue is low. A system has been devised, which uses a third recording electrode to monitor directly the potential gradient in the bathing medium. By suitable electrical connexions, the gradient can be automatically compensated, leaving a residual error which depends on the thickness of the tissue, but not on the electrode separation. Because the thicknesses of most epithelia are smaller than the smallest practical electrode spacing, this error is smaller than that inherent in a two-electrode system. Since voltage-gradients are automatically compensated, it is possible to obtain continuous readings of potential and current. A ‘voltage-clamp’ circuit is described, which allows the time-course of the short-circuit current to be studied. The three-electrode system has been used to study the larval midgut of Hyalophora cecropia. The average results from five experiments were: initial potential difference (open-circuit): 98 ± 11 mV (S.E.M.); short-circuit current at time 60 min: 498 ± 160μA cm−2; ‘steady-state’ resistance at 60 min: 150 ± 26 Ω cm2. The current is equivalent to a net potassium transport of 18μ6 μequiv cm−2 h−1. The electrical parameters of the midgut change rapidly with time. The potential difference decays with a half-time of about 158 min, the resistance increases with a half-time of about 16 min, and the short-circuit current decays as the sum of two exponential terms, with half-times of about 16 and 158 min respectively. In addition, potential and short-circuit current show transient responses to step changes. The properties of the midgut are compared with those of other trans-porting epithelia, and their dependence on the degree of folding of the preparation is discussed. Their time-dependence is discussed in the context of changes in potassium content of the tissue, and the implications for measurements depending on the assumption of a steady state are outlined.
Non-Release of Lactic Acid From Anaerobic Swimming Muscle of Plaice Pleuronectes Platessa L. : A Stress Reaction
Authors: Wardle C. S. 
Published: April 2021

ABSTRACT
Plaice caught by trawl net and plaice exercised in laboratory tanks all show high levels of lactic acid (33–44 mmol/kg) in the anaerobic swimming muscle. During exhausting exercise 2 moles of lactate are formed from 1 mole of glycogen glucose. After an 8 h rest 50–80% of the muscle glycogen is restored. Blood lactate levels remain low (0·5–2 mmol/1) in the majority of plaice caught by trawl. In a small number of plaice, peak levels over 5 mmol/1 are reached 2–4 h after capture. Low blood lactate levels could be guaranteed in all fish exercised 24 h after the stress of capture and in tank-adapted fish exercised and injected with the β-adrenergic stimulating drug, isoxsuprine hydrochloride. The blood lactate in plaice, tank-adapted for more than 8 days and then exercised, may reach peak levels up to 5 mmol/l 2–4 h later. High blood lactate levels were obtained by injecting the β-adrenergic block propranolol to stressed exercised fish. The a-adrenergic block did not have this effect. All plaice with blood lactate levels reaching 5–12 mmol/1 died. The results indicate that the muscle cells regulate the release or nonrelease of their lactate load to the blood stream and increases in the blood circulating to the muscle do not influence this release. The non-release mechanism may be actived by a catecholamine circulated in the blood stream following a stress.
Reproduction Versus Somatic Growth: Hormonal Control in Octopus Vulgaris
Authors: ’Dor R. K. O , Wells M. J. 
Published: April 2021

ABSTRACT
Octopus vulgaris can be forced into precocious maturity by removal of the subpedunculate lobe from the brain, an operation that releases the optic glands from inhibition, and allows them to secrete a gonadotropin. 14C-leucine was injected into the bloodstream of immature animals and its subsequent incorporation into muscle protein followed by taking successive samples from the arms. The optic glands were then activated, and a further injection of 3H-leucine given and followed by means of further arm samples. Optic gland secretion suppresses protein synthesis in the muscles. This is associated with an increase in the total amino acid pool in the muscles and with a considerable increase in the concentration of free amino acids circulating in the blood. If an ovary is present these events are associated with a rapid growth of the ovary and its ducts, and a loss of weight elsewhere. In ovariectomized animals the ducts grow, but there is no yolk to absorb the large pool of free amino acids, and the animals gain weight by osmotic uptake of water into the muscles. The developing ovary may produce a hormone that increases the release of amino acids from muscle, since the concentration circulating in the blood of intact animals remains at least as high as in ovariectomized octopuses, despite the demands of the developing ovary. These matters are discussed in relation to other evidence for a gonadial hormone and in relation to the ‘self-destruct’ effect of the optic gland secretion in determining the post-reproductive death of octopuses.
Electrophysiological Correlates of Ionic and Osmotic Stress In An Osmoconforming Bivalve (Mytilus Edulis)
Authors: Willmer P. G. 
Published: April 2021

ABSTRACT
Mytilus edulis suffered reductions in trans-membrane sodium concentration gradient during dilute salinity acclimation. Nevertheless the nerves of this osmoconformer had a conventional basis for their excitability, irrespective of the salinity to which they were adapted, and could produce full-sized spikes after acclimation to 25 % media. The connectives showed rapid and predictable responses to sodium and to potassium ions, and the time-courses of these effects were unrelated to the presence or absence of the neural sheath at either of the acclimation salinities tested. Neural adaptation was therefore not a consequence of restricted access after acclimation to dilute media. Classic pharmacological agents (tetrodotoxin, tetra-ethyl ammonium ions, 2,4-dinitrophenol and ouabain) elicited the expected responses, but invariably required rather high concentrations and long exposures for full effect. Acute exposures of the connectives to hyposmotic or isosmotic dilutions resulted in changes in polarization accompanying the decline of the action potential. These were attributed to losses of potassium and of chloride from the axons, with a net loss of anion (and hence depolarization) during naturally occurring hyposmotic stress. Mytilus connectives exhibited a critical salinity, with hyposmotic exposure below this level producing irreversible impairment of function. This salinity occurred at 20 % S.w. for 100 %-adapted tissues, and at 3-25 % s.w. (i.e. 15% initial concentration) for 25%-adapted nerves. Gross isosmotic dilutions produced no permanent decrements in axonal function. The observed patterns of response to chronic and acute osmotic stress in Mytilus are contrasted with those reported in annelid and crustacean conformers, and possible adaptations which might underlie these responses are discussed.
Improved Flame Photometry
Authors: Fletcher C. R. 
Published: April 2021

ABSTRACT
Flame photometry is now the usual means of measuring sodium and potassium, and commercially made flame photometers will measure about 0·2 μmol of either ion in about 2 ml of solution to about 1 %. However, the prior dilution of biological samples is necessary and the minimum quantity for measurement is set by the time constant of the measuring circuit. Specialized flame photometers have been described which extend the detection limit to 10−14 mol (Müller, 1958; Ramsay, Brown & Falloon, 1953), but these are hardly suitable for routine work. This communication describes inexpensive modifications for use with commercial flame photometers which avoid prior dilution of the samples and give a tenfold improvement in the detection limit, defined as the smallest quantity of an ion which may be detected with a 95 % certainty.
A Model for Extracellular Sodium Regulation in the Central Nervous System of An Insect (Periplaneta Americana)
Authors: Treherne J. E. , Schofield P. K. 
Published: April 2021

ABSTRACT
The ionic composition of the immediate fluid environment of insect nerve cells is regulated so as to maintain concentrations which may differ considerably from those of the blood. The regulation of the extracellular sodium in the cockroach central nervous system has been suggested to result from a glial-mediated transport of this cation (cf. Treherne, 1974). We here propose a model system for sodium regulation, incorporating such transport, that accounts for the salient experimental observations (Fig. 1).
Biological and Chemical Studies of Extracts of the Anterior Lobe Pituitary
Authors: Spaul E. A. , Myddleton W. W. 
Published: April 2021

ABSTRACT
A buff-coloured precipitate is obtained by the addition of N/20 iodine solution to dilute acetic acid extracts of fresh anterior lobe substance. The volume of the precipitate depends upon the volume of the iodine solution added. Similar acetic acid extracts of tissues and extracts of the anterior lobes prepared with other extracting media do not give the same precipitate with iodine. The precipitate indicates the presence and, within limits, gives an approximate measure of the metamorphic factor in fresh gland extracts of the anterior lobe. Dilute acetic acid extracts of the precipitates after removal of the iodine by shaking with alcohol are biologically active and characterised by their phosphate content. Similar extracts of the posterior lobe give an iodine precipitate but the phosphate content is much lower than that of the anterior lobe precipitate. The iodine in these precipitates is adsorbed or loosely combined. The adsorbed iodine is chemically more reactive than dissolved iodine or iodine crystals giving rapid evolution of nitrogen from sodium azide compared with the failure of the others. The biological activity of anterior lobe extracts varies with the time of extraction and the concentration of the extracts. There is a maximum for the time of extraction at any particular concentration and acid strength after which a loss of potency occurs. There is a continuous extraction—rapid at first—of the melanophore stimulant. The amount increases with the period of extraction and concentration, but is independent of the strength of the acid used in extraction. The metamorphic factor is slowly destroyed by pepsin but rapidly by trypsin. The biological activity is diminished by boiling, or by boiling with dilute hydrochloric acid, sodium hydroxide, or sodium carbonate.
The Phosphate Content and the Biological Activity of the Anterior Lobe Pituitary
Authors: Spaul E. A. , Myddleton W. W. 
Published: April 2021

ABSTRACT
Qualitative and quantitative studies of the active substance in the anterior lobe of the pituitary gland stimulating amphibian metamorphosis have suffered considerable restriction on account of the limitations of the animal test, in which the specific response—the production or acceleration of metamorphosis— is confined to a small range, and the lack of information upon its chemical nature and relationships (Spaul, 1930). Attempts have been made in recent work to overcome these difficulties by seeking for an interpretation of this biological activity in chemical terms, and so establish a chemical test having wider application. Little progress has been made so far, but a correlation of the biological activity with chemical methods, providing also a means of studying chemically the activity itself, has been discovered (Spaul and Myddleton, 1930).
The Adaptation of Gunda Ulvae to Salinity
Authors: Pantin C. F. A. 
Published: April 2021

ABSTRACT
In previous papers (Pantin, 1931 ; Weil and Pantin, 1931) the environment and water exchange of the estuarine flatworm, Gunda ulvae, have been described. It is found on the sea shore at the mouths of small streams, where it is subject to violent salinity changes.
Detour Experiments With Sticklebacks (Gasterosteus Aculeatus L.)
Authors: Russell E. S. 
Published: April 2021

ABSTRACT
The six individuals of Gasterosteus aculeatus tested learned to find their way into a small jar or bottle for food, and also learned how to come out. One failed in the standard test, with the jar upright. The solution was found at first by chance, but after a few trials the behaviour became definitely directed towards finding the solution. This change was accompanied by a sudden drop in the time taken; the jar also acquired significance, ceasing to be an indifferent object. The mode of solution was retained for over 3 months. The bearing of these results on the theory of learning is briefly discussed.
The flight reaction shown by sticklebacks on sudden illumination is described.
A New Approach to Animal Flight Mechanics
Authors: Rayner J. M. V. 
Published: April 2021

ABSTRACT
The mechanics of lift and thrust generation by flying animals are studied by considering the distribution of vorticity in the wake. As wake generation is not continuous, the momentum jet theory, which has previously been used, is not satisfactory, and the vortex theory is a more realistic model.
The vorticity shed by the wings in the course of each powered stroke deforms into a small-cored vortex ring; the wake is a chain of such rings. The momentum of each ring sustains and propels the animal; induced power is calculated as the rate of increase of wake kinetic energy.
A further advantage of the vortex theory is that lift and induced drag coefficients are not required; estimated instantaneous values of these coefficients are generally too large for steady state aerodynamic theory to be appropriate to natural flapping flight.
The vortex theory is applied to hovering of insects and to avian forward flight. A simple expression for induced power in hovering is found. Induced power is always greater than simple momentum jet estimatés, and the discrepancy becomes substantial as body mass increases.
In hovering the wake is composed of a stack of horizontal, coaxial, circular vortex rings. In forward flight of birds the rings are elliptic; they are neither horizontal nor coaxial because the momentum of each ring balances the vector sum of parasite and profile drag and the bird’s weight. Total power consumption as a function of flight velocity is calculated and compared for several species. Power reduction is one of the major factors influencing the choice of flight style.
A large body of data is used to obtain an approximate scaling between stroke period and the body mass for birds. Together with relations between other morphological parameters, this is used to estimate the variation of flight speed and power with body mass for birds, and on this basis deviations from allometric scaling can be related to flight proficiency and to the use of such strategies as the bounding flight of small passerines.
Thermoregulation of African and European Honeybees during Foraging, Attack, and Hive Exits and Returns
Authors: Heinrich Bernd 
Published: April 2021

ABSTRACT
While foraging, attacking, or leaving or returning to their hives, both the African and European honeybees maintained their thoracic temperature at 30 °C or above, independent of ambient temperature from 7 to 23 °C (in shade). Thoracic temperatures were not significantly different between African and European bees. Thoracic temperatures were significantly different during different activities. Average thoracic temperatures (at ambient temperatures of 8–23 °C) were lowest (30°C) in bees turning to the hive. They were 31–32 °C during foraging, and 36–38 °C in bees leaving the hive, and in those attacking. The bees thus warm up above their temperature in the hive (32 °C) before leaving the colony. In the laboratory the bees (European) did not maintain the minimum thoracic temperature for continuous flight (27 °C) at 10 °C. When forced to remain in continuous flight for at least 2 min, thoracic temperature averaged 15 °C above ambient temperature from 15 to 25 °C, and was regulated only at high ambient temperatures (30–40 °C). At ambient temperatures &gt; 25 °C, the bees heated up during return to the hive, attack and foraging above the thoracic temperatures they regulated at low ambient temperatures to near the temperatures they regulated during continuous flight. In both African and European bees, attack behaviour and high thoracic temperature are correlated. The data suggest that the bees regulate thoracic temperature by both behavioural and physiological means. It can be inferred that the African bees have a higher metabolic rate than the European, but their smaller size, which facilitates more rapid heat loss, results in similar thoracic temperatures.
Classes of Light-Evoked Response in the Retina of Strombus
Authors: Quandt Frederick N. , Gillary Howard L. 
Published: April 2021

ABSTRACT
Two general classes of light-evoked responses were recorded intracellularly from the retina of Strombus luhuanus. In one class, retinal illumination caused depolarization, the amplitude of which was graded with light intensity. In the other, it produced hyperpolarization and concomitant inhibition of repetitive action potentials.
There were two types of depolarizing waveform. Each was associated with a different type of intracellular recording site, characterized on the basis of electrical properties in the dark. In general, the type of response with a more rapid rate of decay was recorded from a site which exhibited a lower resting potential, higher input resistance, and longer ‘membrane charging time. ‘
The two depolarizing responses and the hyperpolarizing response apparently each arose from a different type of neurone. The depolarizing types, at least one of which is a photoreceptor, apparently give rise to the cornea-negativity of the electroretinogram and ‘on’ activity in the optic nerve fibres. The hyperpolarizing type apparently mediates ‘off’ activity in the optic nerve..
An Analysis of the Shape and Propagation of Waves on the Flagellum of Crithidia Oncopelti
Authors: Johnston D. N. , Silvester N. R. , Holwill M. E. J. 
Published: April 2021

ABSTRACT
Ciné micrographs were taken of the flagellated protozoan Crithidia oncopelti under dark-ground illumination. Coordinates of images of the flagella were obtained from the ciné frames by back-projection and automatic data acquisition. The flagellar waveforms of proximally directed waves were characterized using a Fourier-series method and compared by this means with a number of analytical curves. The shape of a wave remained constant as it was propagated and, of the curves suggested, a wave consisting of circular arcs connected by straight lines gave the best fit. The variation of bend curvature as bends moved along the flagellum was also found, for both proximally and distally directed waves. The wavelengths and speeds of proximally directed waves increased linearly with distance as they approached the base of the flagellum, while in distally directed bends the curvature remained constant but the velocity increased as bends moved away from the base. Causes of the above behaviour are discussed and it is concluded from the variation of curvature with time for proximally directed flagellar waves that unbending must be an active process.
On The Endogenous Bursting Properties of ‘Light Yellow’ Neurosecretory Cells in the Freshwater Snail Lymnaea Stagnalis (L.)
Authors: van Swigchem Harm 
Published: April 2021

ABSTRACT
Intracellular microelectrodes were used to study a cluster of neurosecretory ‘Light Yellow’ Cells (LYC) in the central nervous system of Lymnaea stagnalis. LYC usually have a spontaneous firing pattern of bursts, lasting 10-600 s, alternating with periods of silence. Experiments on isolated single cells showed that the bursting activity has an endogenous origin.
Each action potential is followed by a depolarizing afterpotential (DAP), with an amplitude of about 10 mV, lasting several seconds. Bursts end with a subthreshold DAP. It is concluded that two pace-maker mechanisms are responsible for the bursting properties, one initiating and the other (the DAP) maintaining the burst.
The relationship between the electrical and the neurosecretory properties of the cells is discussed.
A Comparative Survey of the Function, Mechanism and Control of Cellular Oscillators
Authors: Berridge M. J. , Rapp P. E. 
Published: April 2021

ABSTRACT
This review attempts to survey in a uniform manner the available evidence concerning the generation and behaviour of several well-investigated cellular oscillators. Members of two broad classifications are contrasted: (i) cytoplasmic oscillations, where the periodic phenomena is generated by an instability in a metabolic pathway and (ii) membrane oscillators in which a membrane potential rhythm is generated at the membrane. Interactions between the cytoplasmic and membrane compartments are considered and the effects of these interactions on oscillatory behaviour is discussed. Because of their biological importance and the greater body of experimental results, particular attention is directed to a study of membrane potential oscillations. These systems can be approximately classified in two groups: (i) systems in which a periodic potential results from oscillatory changes in permeability and (ii) systems in which potential oscillations result from the periodic activity of an electrogenic pump.
The examples considered include the glycolytic oscillator, oscillations in vein contraction in the slime mould Physarum polycephalum, rhythmic aggregation in Dictyostelium discoideum, neural oscillators, the periodic potential in Purkinje fibres and the sino-atrial node and rhythmic behaviour in smooth muscle. Questions considered include the generation of periodic activity, the modulation of the oscillation by drugs and other metabolic and membrane effectors and the question of the functional role of these oscillations.
Oscillations of Cyclic Nucleotide Concentrations in Relation to the Excitability of Dictyostelium Cells
Authors: Gerisch Günther , Malchow Dieter , Roos Werner , Wick Ursula 
Published: April 2021

ABSTRACT
Aggregating cells of Dictyostelium discoideum are able to release cyclic AMP periodically. The oscillations of cAMP generation are associated with changes in adenylate cyclase activity. Cyclic AMP receptors on the cell surface are functionally coupled to the oscillating system as evidenced by phase shifts that are induced by small pulses of extracellular cAMP. An important element of the oscillating system is the signal processing from surface receptors to the adenylate cyclase. This pathway exhibits adaptation resulting in the suppression of responses to constant, elevated concentrations of cAMP. The signal input for adenylate cyclase activation is, therefore, a change in the extracellular cAMP concentration with time.
Oscillations in the absence of detectable changes of intra- or extracellular cAMP concentrations suggest the possibility that there is a metabolic network in D. discoideum cells that undergoes oscillations without coupling to adenylate cyclase. Cyclic GMP concentrations oscillate with a slight phase difference in advance of that of cAMP, suggesting that the two nucleotide cyclases might not be activated by the same mechanism. Elevation of extracellular calcium exerts an inhibitory effect on the accumulation of cAMP and on the second of the two cGMP peaks.