bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physiological disturbances at critically high temperatures: a comparison between stenothermal antarctic and eurythermal temperate eelpouts (Zoarcidae)
Authors: Van Dijk P. L. M. , Tesch C. , Hardewig I. , Pörtner H. O. 
Published: April 2021

ABSTRACT
The effect of gradually increased water temperature on the metabolism of temperate eelpout from the North Sea (Zoarces viviparus) and Antarctic eelpout (Pachycara brachycephalum) was investigated. Standard metabolic rate (SMR) was similar in cold-adapted P. brachycephalum and cold-acclimated Z. viviparus in the low temperature range. This indicates that Antarctic eelpout show no metabolic cold adaptation (as originally defined by Wohlschlag); however, they do show a compensatory increase of oxygen consumption compared to warm-acclimated eelpout. SMR increased more strongly with rising temperature in P. brachycephalum than in Z. viviparus, which is reflected in a higher Arrhenius activation energy for oxygen consumption (99±5 kJ mol−1, versus 55±3 kJ mol−1 for cold-acclimated Z. viviparus; means ± S.D.).
The intracellular pH in the white musculature of Z. viviparus follows alphastat regulation over the whole investigated temperature range and dropped at a rate of −0.016 pH units per °C between 3 °C and 24 °C. In Antarctic eelpout white muscle pH declined at a rate of −0.015 pH units per °C between 0 °C and 3 °C, but deviated from alphastat at higher temperatures, indicating that thermal stress leads to acid–base disturbances in this species.
The upper critical temperature limit (TcII; characterised by a transition to anaerobic metabolism) was found to be between 21 °C and 24 °C for Z. viviparus and around 9 °C for P. brachycephalum. In both species a rise of succinate concentration in the liver tissue turned out to be the most useful indicator of TcII. Obviously, liver is more sensitive to heat stress than is white muscle. Accordingly, the energy status of white muscle is not diminished at TcII. Heat-induced hyperglycaemia was observed in Antarctic eelpout (at 9 °C and 10 °C), but not in common eelpout. Based on our results and on literature data, impaired respiration in combination with circulatory failure is suggested as the final cause of heat death. Our data suggest that the southern distribution limit of Zoarces viviparus is correlated with the limit of thermal tolerance. Therefore, it can be anticipated that global warming would cause a shift in the distribution of this species.
Cranial kinesis in gekkonid lizards
Authors: Herrel A. , Vree F. De , Delheusy V. , Gans C. 
Published: April 2021

ABSTRACT
Cranial kinesis was studied in two species of gekkonid lizard, Gekko gecko and Phelsuma madagascariensis, using cineradiography and electromyography. The skull of these geckoes showed the three types of kinesis described by Versluys at the beginning of this century: streptostyly, mesokinesis and metakinesis. In accordance with the later model of Frazzetta, the skull of these animals can be modelled by a quadratic crank system: when the mouth opens during feeding, the quadrate rotates forward, the palato-maxillary unit is lifted and the occipital unit swings forward. During jaw closing, the inverse movements are observed; during crushing, the system is retracted beyond its resting position. The data gathered here indicate that the coupled kinesis (streptostyly + mesokinesis) is most prominently present during the capture and crushing cycles of feeding and is largely absent during late intraoral transport, swallowing, drinking and breathing. The electromyographic data indicate a consistent pattern of muscular activation, with the jaw opener and pterygoid protractor always active during the fast opening phase, and the jaw closers active during closing and crushing. Our data generally support the model of Frazzetta. Although the data gathered here do not allow speculation on the functional significance of the kinesis, they clearly provide some key elements required for a further investigation of the functional and adaptive basis of the system.
Cellular control of renin secretion
Authors: Kurtz Armin , Wagner Charlotte 
Published: April 2021

ABSTRACT
Renin secretion at the level of renal juxtaglomerular cells appears to be controlled mainly by classic second messengers such as Ca2+, cyclic AMP and cyclic GMP, which in turn exert their effects through oppositely acting protein kinases and probably also by affecting the activity of ion channels in the plasma membrane. Thus, protein kinase A stimulates renin secretion, whilst protein kinase C and protein kinase G II inhibit renin secretion. Moreover, Cl− channels could be involved in the mediation of the inhibitory action of Ca2+ on renin secretion. This review summarizes our present knowledge about the possible actions of these kinases in renal juxtaglomerular cells and considers pathways in the organ control of renin secretion.
Exercise and forced submergence in the pond slider (Trachemys scripta) and softshell turtle (Apalone ferox): influence on bimodal gas exchange, diving behaviour and blood acid–base status
Authors: Bagatto B. , Henry R. P. 
Published: April 2021

ABSTRACT
The dynamics of bimodal respiration, diving behaviour and blood acid–base status in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A. ferox and T. scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced submergence, and mean apnoeic time decreased significantly in A. ferox following exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout regardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T. scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induced an acidosis of 0.2 pH units of primarily metabolic origin in both species. Intra-erythrocyte pH was also reduced in both species in response to submergence and exercise. Both intracellular and extracellular acidoses were more severe and longer lasting in A. ferox after each treatment. Plasma [HCO3−] decreased by 25 % in both species following exercise, but only in A. ferox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to resting concentrations sooner in T. scripta than in A. ferox. A. ferox had significantly higher lactate levels than T. scripta following forced submergence as well as a slower recovery time. A. ferox, which is normally a good bimodal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T. scripta, although almost entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both forced submergence and exercise.
Kinematics and muscle dynamics of C- and S-starts of carp (Cyprinus carpio L.)
Authors: Spierts Igor L. Y. , Leeuwen Johan L. Van 
Published: April 2021

ABSTRACT
An analysis is presented of body curvature, acceleration and muscle strain during fast-starts in the common carp (Cyprinus carpio L.). C- and S-starts were filmed at 200 frames s−1 at 23 °C. Curvatures and accelerations of mid-body axes were calculated from digitised outlines. Maximum accelerations at 0.3 FL (fork length) from the snout were 54 m s−2 for C-starts and 40 m s−2 for S-starts. The total turning angle was approximately 150 ° in C-starts. This angle was 70 ° during escape S-starts, significantly larger than for predatory S-starts in other species. Sarcomere strains of axial muscle fibres were calculated at 0.4 and 0.8 FL. During C-starts, white muscle fibres were exposed to maximum sarcomere strains of up to approximately 16 %, and posterior fibres had similar strains to anterior fibres (red 27 %; white 16 %). During S-starts, however, maximum strains in anterior fibres (red 39 %; white 24 %) were more than twice those in posterior fibres (red 17 %; white 10 %). In a C-start, the fish made a large turning angle directed away from the stimulus by bending its tail strongly and thereby producing a large thrust. A larger anterior peak curvature of the fish during S-starts enabled the carp to control the direction of escape better than during C-starts, but with lower accelerations and smaller turning angles. During cyclic and intermittent swimming, red posterior fibres experienced the largest strains. Interestingly, previous studies have shown these fibres to have the lowest passive stiffness and the largest titin isoform, allowing them to attain large strain amplitudes with relatively low passive tensions.
Cyclic AMP Regulates PDGF-stimulated signal transduction and differentiation of an immortalized optic-nerve-derived cell line
Authors: Cohen Rick I. , Mckay Ronald , Almazan Guillermina 
Published: April 2021

ABSTRACT
To facilitate the study of the molecular events underlying the development of optic-nerve-derived oligodendrocytes and their growth-factor-related signal transduction events, we immortalized perinatal rat optic nerve cells with a temperature-sensitive simian virus 40 large T-antigen, carrying the tsA58 and U19 mutations, via a retrovirus vector. The line, tsU19-9, was selected on the basis of the expression of the neural precursor marker nestin. At the permissive temperature, 33 °C, tsU19-9 cells had a flat epithelial morphology. In contrast, following exposure to platelet-derived growth factor (PDGF), a factor important in the lineage progression of oligodendrocytes, or in the presence of dibutyryl cyclic AMP at 39 °C (the non-permissive temperature), the cells underwent morphological and antigenic differentiation to cells characteristic of the oligodendrocyte lineage. We used this cell line to investigate the binding characteristics of PDGF and related signalling cascades. Competition binding, phosphoinositide hydrolysis and intracellular Ca2+ mobilization assays all demonstrated that the three different isoforms of PDGF (AA, AB and BB) bound to and acted on the cell line. Overnight exposure to forskolin, a treatment that initiated morphological and phenotypic progression into an oligodendrocyte lineage, decreased PDGF-BB-induced intracellular Ca2+ mobilization and inhibited basal and PDGF-stimulated [3H]thymidine incorporation. Our results demonstrate that tsU19-9 may serve as a resource to study early optic-nerve oligodendrocyte development.
Physiological optics in the hummingbird hawkmoth: a compound eye without ommatidia
Authors: Warrant Eric , Bartsch Klaus , Günther Claudia 
Published: April 2021

ABSTRACT
The fast-flying day-active hawkmoth Macroglossum stellatarum (Lepidoptera: Sphingidae) has a remarkable refracting superposition eye that departs radically from the classical principles of Exnerian superposition optics. Unlike its classical counterparts, this superposition eye is highly aspherical and contains extensive gradients of resolution and sensitivity. While such features are well known in apposition eyes, they were thought to be impossible in superposition eyes because of the imaging principle inherent in this design. We provide the first account of a superposition eye where these gradients are not only possible, but also produce superposition eyes of unsurpassed quality. Using goniometry and ophthalmoscopy, we find that superposition images formed in the eye are close to the diffraction limit. Moreover, the photoreceptors of the superposition eyes of M. stellatarum are organised to form local acute zones, one of which is frontal and slightly ventral, and another of which provides improved resolution along the equator of the eye. This angular packing of rhabdoms bears no resemblance to the angular packing of the overlying corneal facets. In fact, this eye has many more rhabdoms than facets, with up to four rhabdoms per facet in the frontal eye, a situation which means that M. stellatarum does not possess ommatidia in the accepted sense. The size of the facets and the area of the superposition aperture are both maximal at the frontal retinal acute zone. By having larger facets, a wider aperture and denser rhabdom packing, the frontal acute zone of M. stellatarum provides the eye with its sharpest and brightest image and samples the image with the densest photoreceptor matrix. It is this eye region that M. stellatarum uses to fixate flower entrances during hovering and feeding. This radical departure from classical Exnerian principles has resulted in a superposition eye which has not only high sensitivity but also outstanding spatial resolution.
White muscle strain in the common carp and red to white muscle gearing ratios in fish
Authors: Wakeling James M. , Johnston Ian A. 
Published: April 2021

ABSTRACT
White muscle strains were recorded using sonomicrometry techniques for 70 fast-starts in the common carp Cyprinus carpio L. High-speed ciné images were recorded simultaneously for 54 of these starts, and muscle strain was calculated independently from the digitized outlines of the fish. Sonomicrometry measurements of superficial muscle strain were not significantly different from the strain as calculated from the theory of simple bending of a homogeneous material: superficial muscle strain thus varied with chordwise distance from the spine. However, white muscle strain across a transverse section of the myotome shows less variation with chordwise position than would be expected from simple bending theory. Muscle strains measured using sonomicrometry thus do not necessarily represent the more uniform strain predicted for the whole section of the fish. White muscle strain can be accurately predicted from the spine curvatures as measured from the ciné images if the gearing ratio between the red and white muscle fibres is known. A model for calculating the gearing ratio from the helical muscle fibre geometry was re-evaluated using current data for the kinematics of fast-starting C. carpio. This model predicted a mean gearing ratio of 2.8 for these fast-starts. A quicker, alternative approach to estimating gearing ratio from the position of the centroid of white fibre area is proposed and results in ratios similar to those calculated from the model of helical geometry. White muscle strains in fish can thus be estimated from measurements of spine curvature and muscle distribution alone.
The development of microcracking and failure in bone depends on the loading mode to which it is adapted
Authors: Reilly Gwendolen C. , Currey John D. 
Published: April 2021

ABSTRACT
During locomotion, the anterior cortex of the equine radius is loaded predominantly in tension, the posterior predominantly in compression. The anterior cortex is relatively strong in tension, the posterior in compression. We investigated the pattern of failure of specimens from the two cortices using laser scanning confocal microscopy.
All specimens were loaded in four-point bending to increasingly higher loads. We quantified the amount of diffuse microcracking on the tensile side of these specimens by observing the amount of light emitted under laser illumination. The amount of light emitted agreed well with subjective estimates of the amount of microcracking. Tensile microcracks first appeared at a strain of approximately 0.004, and all specimens showed considerable growth in microcrack density once the tensile strain had passed approximately 0.008.
In specimens from the posterior cortex, there was little compressive microcracking, and such cracks as were present were small and diffuse. These specimens failed on the tensile side first. In specimens from the anterior cortex, compression cracks were more numerous, longer and less diffuse, and specimens failed initially in compression.
The patterns of failure in the bone tissues of the two cortices are what would be expected assuming they were adapted to the mode of loading to which they are usually subjected.
Immune-mediated alterations in nociceptive sensory function in Aplysia californica
Authors: Clatworthy Andrea L. , Grose Eric 
Published: April 2021

ABSTRACT
Nerve injury in Aplysia californica is accompanied by a profound long-lasting enhancement of the excitability of nociceptive sensory neurons that have axons in injured nerves. It is likely that a variety of signals are involved in triggering this injury-induced sensory plasticity. The objective of the present study was to determine whether cells of the cellular defense system (hemocytes) play a role in the modulation of sensory excitability following injury. In support of such an idea, we have shown previously that the induction of a cellular defense reaction close to sensory axons is accompanied by an increase in the excitability of sensory neurons with axons close to responding hemocytes. Furthermore, in the present study, we verified that, following axonal crush, numerous hemocytes accumulate at the injured site on the nerve. Using a hemocyte/nervous system co-culture preparation, we found that there were no significant differences in the expression of injury-induced sensory plasticity between sensory neurons incubated in the presence or absence of hemocytes. To overcome some potential limitations of our co-culture preparation, we used the endotoxin lipopolysaccharide (LPS) as a tool to activate the hemocytes. Sensory cells incubated in the presence of LPS and hemocytes were significantly more excitable than sensory cells incubated in the presence of LPS alone. We speculate that the addition of LPS to the incubation medium containing hemocytes enhanced the release of hemocyte-derived cytokine-like factors such as interleukin-1 and tumor necrosis factor. These cytokine-like factors may act as signals to modulate the expression of injury-induced sensory hyperexcitability.
Inducible NO synthase: role in cellular signalling
Authors: Beck Karl-Friedrich , Eberhardt Wolfgang , Frank Stefan , Huwiler Andrea , Meßmer Udo K. , Mühl Heiko , Pfeilschifter Josef 
Published: April 2021

ABSTRACT
The discovery of endothelium-derived relaxing factor and its identification as nitric oxide (NO) was one of the most exciting discoveries of biomedical research in the 1980s. Besides its potent vasodilatory effects, NO was found under certain circumstances to be responsible for the killing of microorganisms and tumour cells by activated macrophages and to act as a novel, unconventional type of neurotransmitter. In 1992, Science picked NO as the ‘Molecule of the Year’, and over the past years NO has become established as a universal intercellular messenger that acutely affects important signalling pathways and, on a more long-term scale, modulates gene expression in target cells. These actions will form the focus of the present review.
Development of diving capacity in emperor penguins
Authors: Ponganis P. J. , Starke L. N. , Horning M. , Kooyman G. L. 
Published: April 2021

ABSTRACT
To compare the diving capacities of juvenile and adult emperor penguins Aptenodytes forsteri, and to determine the physiological variables underlying the diving ability of juveniles, we monitored diving activity in juvenile penguins fitted with satellite-linked time/depth recorders and examined developmental changes in body mass (Mb), hemoglobin concentration, myoglobin (Mb) content and muscle citrate synthase and lactate dehydrogenase activities. Diving depth, diving duration and time-at-depth histograms were obtained from two fledged juveniles during the first 2.5 months after their depature from the Cape Washingon colony in the Ross Sea, Antarctica. During this period, values of all three diving variables increased progressively. After 8–10 weeks at sea, 24–41 % of transmitted maximum diving depths were between 80 and 200 m. Although most dives lasted less than 2 min during the 2 month period, 8–25 % of transmitted dives in the last 2 weeks lasted 2–4 min. These values are lower than those previously recorded in adults during foraging trips. Of the physiological variables examined during chick and juvenile development, only Mb and Mb content did not approach adult values. In both near-fledge chicks and juveniles, Mb was 50–60 % of adult values and Mb content was 24–31 % of adult values. This suggests that the increase in diving capacity of juveniles at sea will be most dependent on changes in these factors.
Brain blood flow and blood pressure during hypoxia in the epaulette shark Hemiscyllium ocellatum, a hypoxia-tolerant elasmobranch
Authors: Söderström Veronica , Renshaw Gillian M. C. , Nilsson Göran E. 
Published: April 2021

ABSTRACT
The key to surviving hypoxia is to protect the brain from energy depletion. The epaulette shark (Hemiscyllium ocellatum) is an elasmobranch able to resist energy depletion and to survive hypoxia. Using epi-illumination microscopy in vivo to observe cerebral blood flow velocity on the brain surface, we show that cerebral blood flow in the epaulette shark is unaffected by 2 h of severe hypoxia (0.35 mg O2 l−1 in the respiratory water, 24 °C). Thus, the epaulette shark differs from other hypoxia- and anoxia-tolerant species studied: there is no adenosine-mediated increase in cerebral blood flow such as that occurring in freshwater turtles and cyprinid fish. However, blood pressure showed a 50 % decrease in the epaulette shark during hypoxia, indicating that a compensatory cerebral vasodilatation occurs to maintain cerebral blood flow. We observed an increase in cerebral blood flow velocity when superfusing the normoxic brain with adenosine (making sharks the oldest vertebrate group in which this mechanism has been found). The adenosine-induced increase in cerebral blood flow velocity was reduced by the adenosine receptor antagonist aminophylline. Aminophylline had no effect upon the maintenance of cerebral blood flow during hypoxia, however, indicating that adenosine is not involved in maintaining cerebral blood flow in the epaulette shark during hypoxic hypotension.
Water skating in the larvae of Dixella aestivalis (Diptera) and Hydrobius fuscipes (Coleoptera)
Authors: Brackenbury John 
Published: April 2021

ABSTRACT
The kinematics of locomotion was investigated in the aquatic larvae of Dixella aestivalis and Hydrobius fuscipes with the aid of high-speed video recordings. Both insects are able to skate on the surface of the water using the dorso-apical tracheal gill as an adhesive organ or ‘foot’. Progress relies on the variable adhesion of the foot between ‘slide’ and ‘hold’ periods of the locomotory cycle. The flexural body movements underlying skating in D. aestivalis can be derived directly from the figure-of-eight swimming mechanism used in underwater swimming. The latter is shown to be similar to figure-of-eight swimming in chironomid larvae. This study shows how the deployment of a ‘foot’ enables simple side-to-side flexural movements of the body to be converted into effective locomotion at the air–water interface.