bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adaptive Responses to Feeding in Burmese Pythons: Pay Before Pumping
Authors: Secor Stephen M. , Diamond Jared 
Published: April 2021

ABSTRACT
Burmese pythons normally consume large meals after long intervals. We measured gut contents, O2 consumption rates, small intestinal brush-border uptake rates of amino acids and glucose, organ masses and blood chemistry in pythons during the 30 days following ingestion of meals equivalent to 25 % of their body mass. Within 1–3 days after ingestion, O2 consumption rates, intestinal nutrient uptake rates and uptake capacities peaked at 17, 6–26 and 11–24 times fasting levels, respectively. Small intestinal mass doubled, and other organs also increased in mass. Changes in blood chemistry included a 78 % decline in and a large ‘alkaline tide’ associated with gastric acid section (i.e. a rise in blood pH and HCO3-concentrations and a fall in Cl-concentration). All of these values returned to fasting levels by the time of defecation at 8–14 days. The response of O2 consumption (referred to as specific dynamic action, SDA) is the largest, and the up-regulation of intestinal nutrient transporters the second largest, response reported for any vertebrate upon feeding. The SDA is as large as the factorial rise in O2 consumption measured in mammalian sprinters and is sustained for much longer. The extra energy expended for digestion is equivalent to 32 % of the meal’s energy yield, with much of it being measured before the prey energy was absorbed.
Calcium Pump Activities in the Kidneys of Oreochromis Mossambicus
Authors: Bijvelds Marcel J. C. , Heijden Angelique J. H. Van Der , Flik Gert , Verbost Pieter M. , Kolar Zvonimir I. , Bonga Sjoerd E. Wendelaar 
Published: April 2021

ABSTRACT
The mechanism that underlies transcellular Ca2+ reabsorption in the kidney of the euryhaline teleost Oreochromis mossambicus was studied. Preparations of membrane vesicles made from the kidneys of freshwater-and seawater-adapted fish were more than sevenfold enriched in the basolateral plasma membrane marker Na+/K+-ATPase. Significant recovery of NADH– cytochrome c reductase enzyme activity and of oxalate-stimulated Ca2+ pump activities in the membrane preparations indicated that the membrane fraction was of endoplasmic reticular origin. Indeed, thapsigargin specifically inhibited Ca2+ pump activity that could be attributed to oxalate-permeable endoplasmic reticular fragments. Kinetic analysis of thapsigargin-insensitive
Ca2+ pump activity indicated the existence of a homogeneous, high-affinity, ATP-driven Ca2+ pump. No Na+-driven Ca2+ transport mechanism could be demonstrated. Plasma membrane Ca2+ pump activity was 56 % lower in preparations from seawater-adapted fish than in preparations from freshwater-adapted fish, suggesting a physiological role for this Ca2+ pump activity in renal Ca2+ handling by euryhaline species, with an involvement in the regulation of Ca2+ reabsorption.
Ventilatory Responses to Carboxyhaemoglobinaemia and Hypoxic Hypoxia in Bufo Paracnemis
Authors: Branco Luiz G. S. , Glass Mogens L. 
Published: April 2021

ABSTRACT
The modality of the O2 drive to breathe was evaluated in unanaesthetized Bufo paracnemis. Carbon monoxide (CO) hypoxia was applied to reduce (arterial O2 content). Arterial was reduced through inspiration of hypoxic gas mixtures (hypoxic hypoxia). Measurements included pulmonary ventilation, , , pHa, blood pressure and heart rate. Application of fractional concentrations of CO equivalent to 0.001 reduced from 11.6±1.2 to 8.6±0.7 vol% (mean ± S.E.M., N=6) without any effect on heart rate, blood pressure or ventilation. Inspiration of fractionl concentrations of CO equivalent to 0.01 reduced to 5.1±0.7 vol%, which was accompanied by increased ventilation. This response, however, correlated with a decreased arterial pH. The effect of a fractional concentration of CO of 0.01 on ventilation was abolished by compensation of pH through bicarbonate infusion. Consequently, carboxyhaemoglobinaemia per se failed to increase ventilation. By contrast, reductions of clearly stimulated ventilation, which indicates that O2 partial pressure provides the principal O2 stimulus to breathe in Bufo paracnemis.
Modulation Of Crayfish Retinal Function By Red Pigment Concentrating Hormone
Authors: Garfias Alfonso , Rodríguez-Sosa Leonardo , Aréchiga Hugo 
Published: April 2021

ABSTRACT
The role of the crustacean octapeptide red pigment concentrating hormone (RPCH) in the control of crayfish retinal activity was explored. RPCH injection into intact animals resulted, after a latency of 10–30 min, in a dose-dependent enhancement of electroretinogram (ERG) amplitude lasting 60–120 min.
RPCH was able to potentiate ERG amplitude in both light-adapted and dark-adapted animals. Following light-adaptation, responsiveness to RPCH was five times higher than following dark-adaptation.
In conjunction with ERG enhancement, in light-adapted animals, RPCH injection elicited a dose-dependent retraction of distal retinal pigment, but did not affect proximal retinal pigment position.
The effects of RPCH were blocked by a polyclonal antibody raised against a tyrosinated form of RPCH (A-tyr-RPCH). The antibody was also capable of partially blocking the nocturnal phase of the circadian rhythm of ERG amplitude and the darkness-induced retraction of distal retinal pigment.
These results suggest that RPCH acts both on the retinal photoreceptors and on the distal pigment cells, playing a physiological role as a mediator of the effects induced by darkness and by the nocturnal phase of the circadian rhythm.
The Transition To Air Breathing In Fishes : V. Comparative Aspects Of Cardiorespiratory Regulation In Synbranchus Marmoratus And Monopterus Albus (Synbranchidae)
Authors: Graham Jeffrey B. , Lai N. C. , Chiller David , Roberts John L. 
Published: April 2021

ABSTRACT
Extreme heart-rate lability accompanies the air-breathing cycles of Synbranchus marmoratus and Monopterus albus. When air is taken into the buccopharyngeal air-breathing organ of these fishes, heart rate increases sharply above pre-inspiration rates of 3–25 beats min-1 to as high as 40–45 beats min−1. With time, and as O2 is depleted from the air-breathing organ, heart rate gradually declines and drops to its lowest level with, or following, exhalation. Relationships between air breathing and sinus arrhythmia in M. albus were investigated by injecting variable gas volumes and O2 mixtures into the cannulated air-breathing organ. Tests were also carried out on undisturbed fish breathing volitionally in atmospheres containing different O2 levels. Both the volume and O2 content of the inspired gas affect the level and duration of inspiration tachycardia. Additional factors affecting tachycardia are the heart rate prior to inspiration and the time since air was last held. S. marmoratus is a non-obligatory air breather and uses rhythmic branchial aquatic respiration to a greater extent than M. albus, an obligate air breather. While the heart rates of both species are increased during aquatic ventilation, the higher heart rate to ventilation ratio in S. marmoratus (2–3 versus approximately 1 in M. albus) seems attributable to its more proficient aquatic respiratory system. The available cardiorespiratory data for air-breathing fishes indicate that the scope of air-inspiration tachycardia is smaller in lungfishes and other primitive species than in most teleosts. This difference is mainly attributable to the greater chronotropic effect of sympathetic cardiac innervation in teleosts.
Ionic Currents in Identified Swimmeret Motor Neurones of the Crayfish Pacifastacus Leniusculus
Authors: Chrachri Abdesslam 
Published: April 2021

ABSTRACT
Ionic currents from freshly isolated and identified swimmeret motor neurones were characterized using a whole-cell patch-clamp technique. Two outward currents could be distinguished. A transient outward current was elicited by delivering depolarizing voltage steps from a holding potential of -80 mV. This current was inactivated by holding the cells at a potential of -40 mV and was also blocked completely by 4-aminopyridine. A second current had a sustained time course and continued to be activated at a holding potential of -40 mV. This current was partially blocked by tetraethylammonium. These outward currents resembled two previously described potassium currents: the K+ A-current and the delayed K+ rectifier current respectively.
Two inward currents were also detected. A fast transient current was blocked by tetrodotoxin and inactivated at holding potential of -40 mV, suggesting that this is an inward Na+ current. A second inward current had a sustained time course and was affected neither by tetrodotoxin nor by holding the cell at a potential of -40 mV. This current was substantially enhanced by the addition of Ba2+ to the bath or when equimolar Ba2+ replaced Ca2+ as the charge carrier. Furthermore, this current was significantly suppressed by nifedipine. All these points suggest that this is an L-type Ca2+ current.
Bath application of nifedipine into an isolated swimmeret preparation affected both the frequency of the swimmeret rhythm and the duration of power-stroke activity, suggesting an important role for the inward Ca2+ current in maintaining a regular swimmeret rhythmic activity in crayfish.
Role of Adenosine In Nmda Receptor Modulation in the Cerebral Cortex of an Anoxia-Tolerant Turtle (Chrysemys Picta Belli)
Authors: Buck L. T. , Bickler P. E. 
Published: April 2021

ABSTRACT
Accumulation of the neuromodulator adenosine in the anoxia-tolerant turtle brain may play a key role in a protective decrease in excitatory neurotransmission during anoxia. Since excitatory neurotransmission is mediated largely by Ca2+ entry through N-methyl-D-aspartate (NMDA) receptors, we measured the effect of adenosine on NMDA-mediated Ca2+ transients in normoxic and anoxic turtle cerebrocortical sheets. Intracellular [Ca2+] was measured fluorometrically with the Ca2+-sensitive dye Fura-2. Baseline intracellular [Ca2+] and [ATP] were also measured to assess cortical sheet viability and potential toxic effects of NMDA. Baseline [Ca2+] did not change significantly under any condition, ranging from 109±22 to 187±26 nmol l-1. Throughout normoxic and 2 h anoxic protocols, and after single and multiple NMDA exposures, [ATP] did not change significantly, ranging from 16.0±1.9 to 25.3±4.9 nmol ATP mg-1 protein. Adenosine caused a reduction in the normoxic NMDA-mediated increase in [Ca2+] from a control level of 287±35 to 103±22 nmol l-1 (64 %). This effect is mediated by the A1 receptor since 8-phenyltheophylline (a specific A1 antagonist) effectively blocked the adenosine effect and N6-cyclopentyladenosine (a specific A1 agonist) elicited a similar decrease in the NMDA-mediated response. Cortical sheets exposed to anoxia alone exhibited a 52 % decrease in the NMDA-mediated [Ca2+] rise, from 232±30 to 111±9 nmol l-1. The addition of adenosine had no further effect and 8-phenyltheophylline did not antagonize the observed decrease. Therefore, the observed down-regulation of NMDA receptor activity during anoxia must involve additional, as yet unknown, mechanisms.
Application of Putative Neurotransmitters Elicits and Modulates Stridulation in two Species of Acridid Grasshoppers
Authors: Ocker W.-G. , Hedwig B. , Elsner N. 
Published: April 2021

ABSTRACT
The influence of neurotransmitters and neuroactive substances on stridulatory behaviour was analysed in two species of acridid grasshoppers (Omocestus viridulus and Chorthippus mollis). Acetylcholine, octopamine, γ-aminobutyric acid and glutamate were applied by pressure injection (0.5–1.0 nl, 10−3 mol l-1) into the protocerebrum. All except octopamine were also applied to the metathoracic ganglion by pressure injection or superfusion (1 ml).
Injection of acetylcholine into the medial dorsal neuropile of the protocerebrum elicited continuous long-lasting species-specific stridulation in both acridid species. All other substances tested had no effect when injected into the brain. Injection of acetylcholine into the medial dorsal neuropile of the metathoracic ganglion enhanced the amplitude of the stridulatory leg movements elicited by electrical brain stimulation. It did not alter the repetition rate or coordination of the movements in O. viridulus; but it decreased the length of stridulatory cycles in C. mollis.
Injection of γ-aminobutyric acid into the medial dorsal metathoracic neuropile in both species suppressed the stridulatory leg movements ipsilateral to the injection site but did not alter those on the contralateral side. Superfusion of the metathoracic ganglion with -γaminobutyric acid suppressed the movements of both hindlegs.
Pressure injection of glutamate into the metathoracic ganglion had no effect on the stridulatory leg movements, but superfusion enhanced the stridulatory movements.
Chemosensitivity of the Osphradium of the Pond Snail Lymnaea Stagnalis
Authors: Wedemeyer Heiner , Schild Detlev 
Published: April 2021

ABSTRACT
The osphradium of the pond snail Lymnaea stagnalis was studied to determine the stimuli to which this organ responds. The following stimuli were tested: hypoxia, hypercapnia, a mixture of amino acids, a mixture of citralva and amyl acetate and a mixture of lyral, lilial and ethylvanillin.
The mean nerve activity consistently increased with elevated whereas hypoxia produced variable effects. The nerve activity became rhythmic upon application of citralva and amyl acetate, but it increased in a non-rhythmic way upon application of the other two odorant mixtures tested.
Whole-cell patch-clamp recordings were made from a group of 15 neurones that lay next to the issuing osphradial nerve, to determine whether ganglion cells were involved in olfactory signal processing. All neurones tested responded to at least one of the three mixtures of odorants. Both excitatory and inhibitory responses occurred.
Our results indicate that the osphradium of the pond snail Lymnaea stagnalis is sensitive to elevated as well as to three different classes of odorants. In addition, at least some neurones within the osphradium are involved in the processing of olfactory information.
Acid–Base Status and Spiracular Control During Discontinuous Ventilation in Grasshoppers
Authors: Harrison Jon F. , Hadley Neil F. , Quinlan Michael C. 
Published: April 2021

ABSTRACT
Many insects ventilate discontinuously when quiescent, exhibiting prolonged periods during which little or no gas exchange occurs. We investigated the consequences of discontinuous ventilation (DV) on haemolymph acid–base status and tested whether spiracular opening during DV is due to changes in internal gas tensions in the western lubber grasshopper Taeniopoda eques. At 15 °C, resting T. eques exhibited interburst periods of about 40 min. During the interburst period, haemolymph rose from 1.8 to 2.26 kPa, with minimal acidification of haemolymph. Animals in atmospheres in which was 2 kPa or below continued to exhibit DV, while atmospheres in which was 2.9 kPa or above caused cessation of DV. These data indicate that accumulation of internal CO2 to threshold levels between 2 and 2.9 kPa induces spiracular opening in grasshoppers. In contrast to the situation in lepidopteran pupae, variation in atmospheric had no effect on interburst duration. Relative to lepidopteran pupae, the internal of grasshoppers during DV is threefold lower, the required for triggering spiracular opening is also threefold lower, and the open phase spiracular conductance is at least tenfold higher, demonstrating that considerable diversity exists in these aspects of insect respiratory physiology.
Adjustment of K′ to Varying pH and pMg for the Creatine Kinase, Adenylate Kinase and Atp Hydrolysis Equilibria Permitting Quantitative Bioenergetic Assessment
Authors: Golding Elke M. , Teague Walter E. , Dobson Geoffrey P. 
Published: April 2021

ABSTRACT
Physiologists and biochemists frequently ignore the importance of adjusting equilibrium constants to the ionic conditions of the cell prior to calculating a number of bioenergetic and kinetic parameters. The present study examines the effect of pH and free magnesium levels (free [Mg2+]) on the apparent equilibrium constants (K′) of creatine kinase (ATP: creatine N-phosphotransferase; EC 2.7.3.2), adenylate kinase (ATP:AMP phosphotransferase; EC 2.7.4.3) and adenosinetriphosphatase (ATP phosphohydrolase; EC 3.6.1.3) reactions. We show how K′ can be calculated using the equilibrium constant of a specified chemical reaction (Kref) and the appropriate acid-dissociation and Mg2+-binding constants at an ionic strength (I) of 0.25 mol l−1and 38 °C. Substituting the experimentally determined intracellular pH and free [Mg2+] into the equation containing a known Kref and two variables, pH and free [Mg2+], enables K′ to be calculated at the experimental ionic conditions. Knowledge of K′ permits calculation of cytosolic phosphorylation ratio ([ATP]/[ADP][Pi]), cytosolic free [ADP], free [AMP], standard transformed Gibbs energy of formation (ΔfG′ °ATP) and the transformed Gibbs energy of the system (ΔfG′ATP) for the biological system. Such information is vital for the quantification of organ and tissue bioenergetics under physiological and pathophysiological conditions.
Do Fish Acclimated To Low Temperature Improve Microcirculatory Perfusion By Adapting Red Cell Rheology?
Authors: Lecklin Tiina , Nash Gerard B. , Egginton Stuart 
Published: April 2021

ABSTRACT
We have measured the rheological properties of individual red blood cells from fishes inhabiting different thermal environments and have also investigated the effects on red cells of acute in vitro temperature changes. The membrane shear elastic modulus (rigidity) increased markedly with decreasing temperature, and the dependence was similar if temperature was varied acutely in vitro or if cells were measured at normal body temperatures. Red cells from trout and Notothenia coriiceps had almost equal membrane rigidity at comparable temperatures and showed similar temperature-sensitivity in acute experiments. Entry times of trout cells into narrow (approximately 4 μm diameter) micropipettes also increased during in vitro reduction of temperature, and this could be explained largely by the temperature-dependence expected of aqueous solutions. Perhaps surprisingly, entry times did not vary when trout living at different temperatures were tested at these temperatures. Transit times of individual cells through somewhat larger pores (5 μm) in oligopore filters again increased with decreasing temperature in vitro (partly due to increasing fluid viscosity), but such transit times did show a similar temperature-dependence for cells from trout living at different temperatures. Thus, the temperature-dependence of cellular flow resistance appears to arise from variations in membrane rigidity and in the viscosity of fluid components, along with unquantified variations in components such as microtubular structures (which we found did not influence membrane rigidity but did affect pore entry time) and the cell nucleus. Thermal acclimation did not involve adaptation to compensate for increased membrane rigidity or a large pore transit time, with, at most, minor compensation in entry times into smaller pores. We conclude that impaired cellular rheology is not a major factor influencing circulation in fish at low temperature.
In Vivo Muscle Force and Elastic Energy Storage During Steady-Speed Hopping of Tammar Wallabies (Macropus Eugenii)
Authors: Biewener Andrew A. , Baudinette Russell V. 
Published: April 2021

ABSTRACT
In order to evaluate the role of elastic energy recovery in the hopping of macropodids, in vivo measurements of muscle–tendon forces using buckle force transducers attached to the tendons of the gastrocnemius (G), plantaris (PL) and flexor digitorum longus (FDL) of tammar wallabies were made as the animals hopped on a treadmill at speeds ranging from 2.1 to 6.3 m s−1. These muscles and tendons constitute the main structures that are most important in energy storage and recovery. Electromyographic recordings from the lateral gastrocnemius and plantaris muscles, together with high-speed films (200 frames s−1) and video (60 fields s−1), were also used to correlate muscle activation and kinematic patterns of limb movement with force development. On the basis of in situ calibrations of the buckle transducers, we found that muscle forces and elastic energy storage increased with increased hopping speed in all three muscle–tendon units. Elastic energy recovery reached a maximum of 25 % of metabolic energy expenditure at 6.3 m s−1 and is probably greater than this at higher speeds. Force sharing among the three muscles was consistently maintained over this range of speeds in terms of recruitment. Although forces and stresses were generally comparable within the gastrocnemius and plantaris muscles, maximal tendon stresses were considerably greater in the gastrocnemius, because of its smaller cross-sectional area (peak muscle stress: 227 versus 262 kPa; peak tendon stress: 36 versus 32 MPa, G versus PL). As a result, energy storage was greatest in the gastrocnemius tendon despite its much shorter length, which limits its volume and, hence, energy storage capacity, compared with PL and FDL tendons. Forces and stresses (17 MPa maximum) developed within the FDL tendon were consistently much lower than those for the other two tendons. Peak stresses in these three tendons indicated safety factors of 3.0 for G, 3.3 for PL and 6.0 for FDL. The lower stresses developed within the tendons of the plantaris and, especially, the flexor digitorum longus may indicate the need to maintain sufficient stiffness for phalangeal control of foot placement, at the expense of reduced strain energy recovery.
Natriuretic Peptide Receptors in the Kidney and the Ventral and Dorsal Aortae of the Atlantic Hagfish Myxine Glutinosa (Agnatha)
Authors: Toop Tes , Donald John A. , Evans David H. 
Published: April 2021

ABSTRACT
The character of natriuretic peptide receptors (NPRs) in the kidney and aortae of the Atlantic hagfish Myxine glutinosa was determined and compared with that of NPRs in hagfish gills. The relationship of hagfish kidney and aortic NPRs with NPRs from higher vertebrates was also examined. Iodinated atrial and C-type natriuretic peptides (NPs) (125I-ANP, 125I-CNP) were used in tissue section autoradiography, competition studies and guanylate cyclase (GC) assays. Rat atrial and porcine C-type NPs (rANP, pCNP) and rat des[Gln18, Ser19, Gly20, Leu21 Gly22]ANP-(4-23)-NH2 (C-ANF, which binds to the mammalian and teleost ‘clearance’ receptor, NPR-C), were used as competing ligands. 125I-ANP binding sites were observed on both aortae and on the glomeruli, neck segments and archinephric ducts of the kidney. 4.0 nmol l−1 rANP competed for 50 % of 125I-ANP glomerular sites. 125I-CNP did not visibly bind to any of the tissues, but 300 nmol l−1 pCNP competed for 50 % of 125I-ANP glomerular sites. C-ANF failed to compete for 125I-ANP sites. rANP and pCNP stimulated cyclic GMP production in kidney membrane preparations, but C-ANF did not, demonstrating that the hagfish kidney NPR is GC-linked. This study suggests that a predominant population of ANP-like receptors, similar to the mammalian NPR-A, exists in the myxinoid aortae and kidney tissue. However, no detectable population of a receptor that binds all NPs, such as is present in the hagfish gill, nor an NPR similar to the NPR-C of higher vertebrates was discovered.