bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of the Systemic Heart and the Portal Heart of Myxine Glutinosa
Authors: Johnsson Marianne , Axelsson Michael 
Published: April 2021

ABSTRACT
The effects of preload and afterload on the performance of the systemic heart of the hagfish Myxine glutinosa were investigated before and during sotalol treatment using an in situ perfusion technique. Elevation of input pressure (preload) increased flow by means of increased stroke volume and heart rate in accordance with Starling’s law of the heart, while increased output pressure (afterload) decreased flow mainly because of decreased stroke volume. Treatment with the β-adrenoceptor antagonist sotalol did not change the quality of the responses to increased preload or afterload, although power output decreased by 40 % and flow rate was reduced by 35 % mainly due to a decrease in heart rate.
Isolated preparations of the systemic heart and the portal heart provided information on the chronotrop effects of different agonists and antagonists. Both the systemic heart and the portal heart were insensitive to adrenergic and cholinergic agonists, adrenocorticotropic hormone and the cholinoceptor antagonist atropine. Sotalol treatment lowered the rate of spontaneous contractions by 30 % in the systemic heart preparation and by 21 % in the portal heart preparation.
This study has given further evidence for the existence of a tonic β-adrenoceptor stimulation of the hagfish systemic heart and portal heart, and demonstrated the importance of that stimulation in maintaining systemic heart performance.
Active Absorption Of Na+ and CL− Across the Gill Epithelium of the Shore Crab Carcinus Maenas: Voltage-Clamp and Ion-Flux Studies
Authors: Riestenpatt Sven , Onken Horst , Siebers Dietrich 
Published: April 2021

ABSTRACT
Mechanisms of active NaCl uptake across the posterior gills of the shore crab Carcinus maenas were examined using radiochemical and electrophysiological techniques. In order to measure short-circuit current (Isc), transepithelial conductance (Gte) and area-related unidirectional fluxes of Na+ and Cl−, single split gill lamellae (epithelium plus cuticle) of hyperregulating shore crabs were mounted in a modified Ussing chamber. The negative short-circuit current measured with haemolymph-like NaCl saline on both sides of the epithelium could be inhibited by application of basolateral ouabain (ouabain inhibitor constant KOua=56±10 μmol l−1), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB; KNPPB=7.5±2.5 μmol l−1) or Cs+ (10 mmol l−1). From the apical side, Isc was nearly completely blocked by Cs+ (10 mmol l−1) or Ba2+ (15 mmol l−1), whereas apical addition of furosemide (1 mmol l−1) resulted in only a small current decrease. Cl− influxes were linearly related to negative Isc.
The ratio between net influxes of Cl− and Na+ was found to be approximately 2:1. With a single membrane preparation, achieved by permeabilizing the basolateral membrane with amphotericin B, Cl− influxes which were driven by a concentration gradient were shown to depend on the presence of apical Na+ and K+. On the basis of these observations, we propose that active and electrogenic absorption of NaCl across the gill epithelium of hyperregulating shore crabs proceeds as in the thick ascending limb of Henle’s loop in the mammalian nephron. Accordingly, branchial NaCl transport is mediated by apical K+ channels in cooperation with apical Na+/K+?2Cl− cotransporters and by the basolateral Na+/K+-ATPase and basolateral Cl− channels.
Autonomic Nervous Control of Heart Rate in Muskrats During Exercise in Air and Under Water
Authors: Signore Pierre E. , Jones David R. 
Published: April 2021

ABSTRACT
Neural control of the cardiac responses to exercise in air (running) and under water (diving) was studied in the muskrat (Ondatra zibethicus) by means of acute pharmacological blockade with the muscarinic blocker atropine and the β-adrenergic blocker nadolol. Saline injection was used as a control. Controls running on a treadmill showed a marked increase in heart rate with exercise. Atropine-treated animals had a higher resting heart rate than controls, but heart rate still increased with running. Nadolol-treated animals had a lower resting heart rate than controls and displayed a less pronounced increase in heart rate with running than controls. Animals treated with a combination of atropine and nadolol had a resting heart rate similar to that of controls but their heart rate was unaffected by running. Thus, exercise tachycardia in muskrats is due to activation of the sympathetic system and also to a reduction in parasympathetic tone. Heart rate decreased markedly during voluntary submergence in controls but rose as muskrats swam submerged against increasing water flows. Nevertheless, diving bradycardia was still present. Free-diving bradycardia and the relative increase in heart rate with underwater exercise were abolished by atropine and unaffected by nadolol. Hence, unlike the cardiac response to exercise in air, the cardiac response to underwater exercise is due only to a reduction in parasympathetic tone. Injection of the β-adrenergic agonist isoproterenol markedly increased heart rate in air but had little effect during voluntary and forced dives, indicating a marked decrease in the sensitivity of cardiac cells to adrenergic stimulation during submergence. These results strongly suggest that accentuated antagonism between the two branches of the autonomic nervous system occurs during diving so that parasympathetic influences on the heart predominate and inhibit any chronotropic response to adrenergic stimulation.
Seasonal-, Tidal-Cycle- and Microhabitat-Related Variation in Membrane Order of Phospholipid Vesicles from Gills of the Intertidal Mussel Mytilus Californianus
Authors: Williams E. Eugene , Somero George N. 
Published: April 2021

ABSTRACT
Alterations in the order, or fluidity, of cellular membranes in response to variations in environmental temperature are well known. The mussel Mytilus californianus, a common inhabitant of mid-intertidal regions along the Pacific coast of North America, can experience large (20 °C or more) and cyclic (every 6 h) changes in body temperature (Tb ) during tidal cycles. In the present study, we explore membrane order during seasonal and tidal temperature cycles and find that vesicles prepared from gill phospholipids exhibit significant seasonal differences in order that are consistent with homeoviscous adaptation and suggest winter-acclimatization to mean Tb values and summer-acclimatization to upper extreme Tb values or to large cyclic thermal fluctuations, despite repeated resubmergence in sea water at 10 °C during both seasons. Phospholipid vesicles prepared from the gills of mussels acclimated for 6 weeks to constant high or low temperatures in the laboratory fail to exhibit temperature-compensatory differences in order. In addition, during the summer, mussels inhabiting high intertidal sites, but not those from low sites, possess the ability to alter membrane order rapidly (within hours). This alteration of order appears to represent a mechanism designed to offset the thermal variations encountered during the tidal cycle. Thus, M. californianus have the ability to adjust membrane order on seasonal as well as hourly time scales and do so on the basis of their height in the intertidal region.
Design of the Oxygen and Substrate Pathways: II. Defining the Upper Limits of Carbohydrate and Fat Oxidation
Authors: Roberts Thomas J. , Weber Jean-Michel , Hoppeler Hans , Weibel Ewald R. , Taylor C. Richard 
Published: April 2021

ABSTRACT
This paper quantifies maximal flows of carbohydrates and lipids through the pathways supplying the mitochondria. Maximal flow rates are the main functional parameter used in testing the principle of symmorphosis, which states that structural capacities are quantitatively matched to functional demand. Only under rate-limiting conditions will all of the structural capacity be used. Dogs and goats were compared to obtain large differences in absolute rates. We exercised the animals for long enough to reach steady-state O2 and CO2 exchange rates at intensities eliciting 40 %, 60 %. and 85 % of the maximal rate of oxygen consumption (). We then calculated rates of fat and carbohydrate oxidation from the ratio of CO2 produced to O2 consumed (the respiratory exchange ratio). The dog’s was more than twice that of the goat (6517 versus 3026 μmol O2 kg−1 min−1). We found the same pattern of fuel selection as a function of exercise intensity in both species, and it appears to be general to mammals. Maximal rates of fat oxidation were reached at 40 % exercise intensity, where 77 % of the energy was supplied by fat. As exercise intensity increased, all additional energy was supplied by carbohydrates. We conclude that the partitioning of fuel supply to the fat and carbohydrate pathways follows the same pattern in both dogs and goats.
Design of the Oxygen and Substrate Pathways: III. Partitioning Energy Provision from Carbohydrates
Authors: Weber Jean-Michel , Roberts Thomas J. , Vock Ruth , Weibel Ewald R. , Taylor C. Richard 
Published: April 2021

ABSTRACT
This paper quantifies maximal fluxes through the pathway supplying carbohydrates to the mitochondria of muscle cells. Continuous infusions of D-[3-3H]glucose together with indirect calorimetry were used to investigate the partitioning of the supply of carbohydrates through the two branches of the pathway: from circulating glucose and from glycogen stores within the muscle cells to the mitochondria. The relative contribution of circulating glucose to total carbohydrate oxidation was small, accounting for only 13 % and 23 % of the carbohydrate oxidized at exercise intensities approaching in dogs and goats, respectively. Unexpectedly, maximal rates of circulating glucose oxidation were nearly the same in the two species (when expressed in absolute terms; dog:goat ratio = 1.2), despite the 2.2-fold difference in aerobic capacity. We conclude that the glycogen stores in the muscle cells are the major source of substrates at maximal rates of oxidation, supplying 60–70 % of the total energy. Furthermore, it is this branch of the carbohydrate pathway that is adapted to the large difference in aerobic capacity between dogs and goats.
Temporal Resolution in Olfaction: Stimulus Integration Time of Lobster Chemoreceptor Cells
Authors: Gomez George , Atema Jelle 
Published: April 2021

ABSTRACT
The stimulus integration time of lobster olfactory receptor cells in situ was determined using extracellularly recorded spiking responses from receptor cells and on-line high-resolution measurement of odor square pulses. At a fixed odor concentration, odor steps of 200 ms duration elicited maximum responses; shorter odor steps did not drive the cells to their maximum response and longer odor steps added spikes but did not result in higher firing rates. Excitatory processes peaked within 220 ms of stimulus onset. At 160–300 ms, stimulus intensity discrimination was most evident. Adaptation processes reduced response magnitude to near-zero levels within 1000 ms of stimulus onset. Olfactory receptor cells thus resolve odor peak onsets within the first few hundred milliseconds: this time window corresponds to the 4–5 Hz frequency of olfactory sampling (i.e. ‘sniffing’) as well as the rapid fluctuations in odor concentration that are common in natural odor plumes. The stimulus integration time of 200 ms may play a role in the filtering of information used by lobsters to orient to distant odor sources.
Do Australian Desert Frogs Co-Accumulate Counteracting Solutes with Urea During Aestivation?
Authors: Withers Philip C. , Guppy Michael 
Published: April 2021

ABSTRACT
Australian desert frogs of the genera Neobatrachus, Cyclorana and Heleioporus experience significant dehydration, and iono- and osmoconcentration, during aestivation in the laboratory and accumulate substantial amounts of urea (100–200 mmol l−1). We expected a priori that aestivating frogs probably would not need to accumulate balancing osmolytes but would accumulate trimethylamine oxide (TMAO) or betaine as counteracting solutes to urea. These aestivating frogs did not co-accumulate a substantial quantity of any particular balancing osmolyte or counteracting solute, such as a methylamine [TMAO, trimethylamine amine (TMA), betaine, sarcosine, glycerophosphorylcholine (GPC)] or polyol (inositol, mannitol, sorbitol) in plasma or muscle relative to urea accumulation. However, for aestivating frogs, the total concentration of all measured methylamines and polyols (TMAO + TMA + betaine + sarcosine + GPC + inositol) in muscle was approximately 35–45 mmol kg−1, and so it is possible that all of these solutes have a combined counteracting osmolyte role in aestivating frogs at a ratio to urea of approximately 1:2.5, as has been described for elasmobranch fishes. Alternatively, the absence of substantial co-accumulation with urea of any particular solute suggests that aestivating frogs might not require any major extracellular or intracellular counteracting solutes (TMAO, betaine, GPC). The enzyme systems of these aestivating frogs may be insensitive to the perturbing effects of urea, or the perturbing effects of accumulated urea may be a mechanism for metabolic depression, during aestivation.
The Modulus of Elasticity of Equine Hoof Wall: Implications for the Mechanical Function of the Hoof
Authors: Douglas J. E. , Mittal C. , Thomason J. J. , Jofriet J. C. 
Published: April 2021

ABSTRACT
During normal weight-bearing and locomotion, the equine hoof wall deforms in a consistent pattern: the proximal dorsal wall rotates caudo-ventrally about the distal dorsal border and there is latero-medial flaring posteriorly. The aim of this study is to examine whether there are regional differences in the modulus of elasticity of hoof wall material and whether such differences correlate with the pattern of deformation which occurs in vivo.
The modulus of elasticity of equine hoof wall was determined in tension and compression for samples from six forefeet. Samples were tested at the mid-point of the inner and outer halves of the wall thickness at two positions along the proximo-distal axis of the dorsal wall, and from the mid-point of its thickness at the lateral and medial quarters. Test samples were oriented both parallel and perpendicular to the tubules that characterise the microstructure of the wall. The colour of each sample was noted, and the moisture content measured.
The range in the mean modulus of elasticity for all samples and tests was 460–1049 MPa, the dorsal outer wall having the highest values, the dorsal inner wall the lowest, and the quarters having intermediate values. The mean value obtained for the quarters was similar to the average of the values for the dorsal inner and outer walls. At all sites, the modulus of elasticity was marginally higher in compression than in tension, possibly owing to microstructural defects. The difference in stiffness between the outer wall and the inner wall was inversely related to moisture content.
The difference in stiffness between the dorsal outer and inner walls demonstrates that the equine hoof wall has a comparatively rigid external capsule with a lining of lower stiffness. This arrangement presumably provides some stress protection to the internally adjacent living tissues. The similarity in stiffness between the samples from the quarters and the mean of the two dorsal wall sites suggests that the wall at the quarters has a similar change in stiffness across its thickness as the dorsal wall. However, the reduced thickness of the wall at the quarters compared with the dorsal wall means that, functionally, the quarters are more flexible than the dorsal wall. This will facilitate the flaring of the lateral and medial walls which occurs during weight-bearing. Anisotropy was evident only in tensile tests of the dorsal wall samples. Contrary to popular assertions that white hooves are mechanically inferior, horn pigmentation had no detectable effect on stiffness.
A Preliminary Note on the Pollen Development of Lathyrus Odoratus
Authors: Latter Joan 
Published: April 2021

ABSTRACT
In this paper the main points in the pollen development of Lathyrus odoratus are briefly described. At the beginning of the meiotic phase the reticulum contracts from the nuclear membrane and exhibits an entirely granular appearance. During thread formation, occasional amœboid nucleoli are observed. Nucleolar “budding” is also seen. Connecting strands are constantly found between the synizetic knot and the nucleolus. The thread at all stages appears usually to be a continuous structure. The synizetic knot is followed by a stage in which the thread is thrown into seven definite loops which radiate out from the centre of the nucleus. For this stage, which has frequently been called the second contraction stage in cytological literature, the name broxonema is proposed. The haploid number of chromosomes in Lathyrus odoratus is seven. Each loop represents one pair of homologous chromosomes joined distally end to end. The arms of each loop are twisted round one another at one period. This affords opportunity for exchange of segments of chromosomes, and gives a possible physical basis for crossing over in a telosynaptic form. These stages are followed by typical diakinesis and heterotypic divisions. During homotypic telophase evanescent cell plates occur between the daughter nuclei. Later, the cell walls are formed by furrowing. The tapetum remains uninucleate throughout.
Birds Without Gonads: Their Origin, Behaviour, and Bearing On the Theory of the Internal Secretion of the Testis
Authors: Riddle Oscar 
Published: April 2021

ABSTRACT
Sixteen cases of pigeons without a discoverable trace of gonadal tissue have been found and described. Supplementary groups, one of fifteen birds in which one gonad only was abnormally absent, and still another of seventeen cases of nearly suppressed gonads, comprise the principal material obtained and examined.
It is practically certain that this absence of gonads was complete and persistent—not a temporary condition nor one attained shortly before examination of the birds.
Previous observations on the “no gonad” and “one gonad” condition in birds and in other animals are reviewed.
The basis of the gonadless condition is a purely developmental one, in which it is probable that physiological rather than cytological or genetic disturbance is chiefly concerned.
An attempt is made to identify the type of disturbance involved in this developmental anomaly. It is concluded that such failures of gonad development are a consequence of the failure of all “primordial germ cells” to reach or enter the anlage of the germinal ridge.
Some data are available for a test of this view ; they are found to be in conformity with it.
Despite the complete and persistent absence of testicular tissue, some of these birds developed complete and emphatic masculine behaviour ; some additional secondary sex characters observable in these forms were likewise developed to one or another degree.
Since such birds were, according to all the evidence, entirely without interstitial or spermatogenic tissues, it is clear that the thing which is normally accomplished with the aid of the testis incretion may also be accomplished without it. In such cases it is considered that the effective impulse in the determination of the individual’s sex, is capable of effecting the development of at least certain of these “secondary “sex characters. This material offered no opportunity to examine the effects of loss of gonad incretions on plumage characters.
These results, like those of other parts of our studies, lead to the view that the gonad incretions are “controlled” as well as controlling factors in sex development. That they, like the chromosomal or genetic sex factors, rest upon the more basic condition which we elsewhere identify as metabolic level or rate.
On Sex-Intergrade Pigs: Their Anatomy, Genetics, and Developmental Physiology
Authors: Baker John R. 
Published: April 2021

ABSTRACT
Sex-intergrade pigs show all variations between complete and abortive development of the derivatives of the Müllerian and Wolffian ducts. The external genitalia are, however, always essentially female in type. The seminiferous tubules are degenerate even when the testes are descended. In the two true hermaphrodites described the ovary is on the left and the ovo-testis is on the right ; and in each case the ovarian part of the ovo-testis is anterior. It is not improbable that all sex-intergrades were true hermaphrodites in embryonic or early post-natal stages. A tendency to sexual abnormality in pigs is inherited. The ratio of normals to sex-intergrades among the offspring of intergrade - producing parents is 8: 1 or &gt; 8: 1.
The abnormality does not appear to be associated with abnormality of any other ductless gland.
Sex-intergrades often have male sexual instincts.
Sex Differences in the Requirements of Certain Food Factors
Authors: Hartwell Gladys Annie 
Published: April 2021

ABSTRACT
On certain diets quoted in this paper, the male rat grows at about the same rate as the female, and does not show the more rapid growth which is usually exhibited by the male of the species. Finally the male becomes distinctly the heavier, but his growth is slow during the first weeks of life. It is suggested that the growing male requires more vitamin B than the growing female, and also that he is more susceptible to the quality of the protein in the diet. The expenses of this research were defrayed by a grant from the Medical Research Council.
Some Protein Properties of Plant Protoplasm
Authors: Pearsall W. H. , Ewing James 
Published: April 2021

ABSTRACT
In attempting to explain the reactions and behaviour of living organisms, the experimental biologist is often tempted to fall back on the causal consideration of the observed phenomena in terms of the single living cell. While it is true that our physiological knowledge of this unit is almost negligible, there is at any rate a widely accepted belief that its properties may often be expressed in terms of two of its most important chemically active substances, the various proteins and their derivatives or the fatty bodies. So far as proteins are concerned, this assumption is justified by the classical analyses of Reinke and Rodewald,12’ which show that in the plasmodium of Fuligo varians, about 60 per cent, of the dry weight of protoplasm is composed of protein. It is therefore legitimate to consider the hypothesis that certain properties of normal plant cells appear to be most simply expressed in terms of their protein reactions.