bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon dioxide and pH affect sperm motility of white sturgeon(Acipenser transmontanus)
Authors: Ingermann R. L. , Holcomb M. , Robinson M. L. , Cloud J. G. 
Published: April 2021

SUMMARYMaintenance of sperm at pH values less than approximately 7.5 inhibited the onset of motility when sperm were subsequently diluted with water; maintenance at pH values above approximately 8.2 was associated with maximal motility upon dilution with water. Within 5∼min of exposure to low pH buffer (pH 6.9),there was a 50% decline in sperm motility upon dilution with water suggesting that exposure to low pH interferes with motility within a time frame that may affect fertilization. In most instances, maintenance of sperm under CO2 at a pressure of 4-5 kPa almost completely blocked their capacity for motility. Furthermore, exposing semen to increasing partial pressures of CO2 up to about 1 kPa resulted in a marked decrease in semen pH. These observations are consistent with the findings that the buffering capacity of semen is particularly low at physiological pH, and that this low buffering capacity corresponds to the highest pH sensitivity of the capacity for sperm motility. The low seminal buffering capacity may represent a physiological adaptation in the control of sperm function. It may also represent a vulnerability to environmental hypercapnia or metabolic acidosis.
Hearing asymmetry and auditory acuity in the Australian bushcricketRequena verticalis(Listroscelidinae; Tettigoniidae;Orthoptera)
Authors: Bailey Winston J. , Yang Suanne 
Published: April 2021

SUMMARYFluctuating asymmetry in bilaterally placed sensory structures of insects may be considered maladaptive; natural selection should favour a symmetrical system. Among bushcrickets or katydids, threshold hearing sensitivity is, in part, dependent on the size of the auditory spiracle in the prothorax. We tested the degree of natural asymmetry in the hearing system of the ensiferan orthopteran Requena verticalis by measuring the size of the auditory spiracle of females. Naturally occurring asymmetry approached 8%, which translates to a hearing bias at a threshold of only 0.8 dB. Auditory asymmetry of females was experimentally exaggerated by packing cotton wool into either the right or left auditory spiracle. We made neurophysiological recordings from the ascending auditory T-fibre in the neck connective and found that the left—right bias created by this operation approximated 5 dB; this is greater than that found in nature. For these experiments, sound was delivered to the operated side of the insect from a speaker placed at either 90° or 30° to the long-body axis. To test the influence of this induced auditory bias, free-moving females were allowed to orient towards a speaker emitting male calls at near-natural call intensities of 51 and 82 dB (SPL), 80 cm from the speaker on a flat arena. There was no variation in angle or vector between experimental and control insects, and there was no difference in acuity between intensity. We discuss the relevance of threshold measurements of bushcricket hearing systems in regard to sound localisation and, from these experiments question any role of asymmetry.
Mechanisms of acid secretion in pseudobranch cells of rainbow trout(Oncorhynchus mykiss)
Authors: Kern G. , Bösch S. T. , Unterhuber E. , Pelster B. 
Published: April 2021

SUMMARYCell suspensions of rainbow trout Oncorhynchus mykisspseudobranch, prepared by Ca2+ depletion and mechanical maceration,contained a distinct population of cells that always kept their relatively cuboidal shape and did not round up in suspension or proliferate after adhering to the surface of cell culture dishes. Phasecontrast microscopy revealed an extensive system of basal membrane invaginations, and Na+-K+-ATPase- and anionexchanger-like immunoreactivity could be localized in cell membranes. The cells were characterized by a high mitochondrial density. Using specific antibodies, V-ATPase subunit B was localized in the plasma membrane. Using a cytosensor microphysiometer, the rate of acid secretion of these cells was measured and compared with the activity of a gill cell preparation. Incubation of pseudobranch cells with bafilomycin A1 (10-6 moll-1), a specific inhibitor of V-ATPase, reduced the rate of acid secretion by about 10% under control conditions, while no effect of bafilomycin on the rate of acid secretion of gill cells was observed. Application of amiloride (5×10-5moll-1) reduced the rate of acid secretion in cells of both organs,pseudobranch and gills. Incubation of pseudobranch cells with DIDS(10-3 moll-1) resulted in a minor increase in the rate of proton secretion, but in cells prepared from the gills of rainbow trout acid secretion was reduced by about 30-40%. It is concluded that pseudobranch cells are equipped with various pathways to secrete protons, and that the anion exchange activity especially of pseudobranch cells appears to be different from that in gills.
Amino acid composition and nutritional quality of potato leaf phloem sap for aphids
Authors: Karley A. J. , Douglas A. E. , Parker W. E. 
Published: April 2021

SUMMARYTo define plant `nutritional quality' for aphids, the causal basis of the variation in aphid performance between host plants of different developmental ages was explored using the aphids Myzus persicae and Macrosiphum euphorbiae on potato plants (Solanum tuberosum). Both aphid species performed better on developmentally young (`pre-tuber-filling') plants than on mature (`tuber-filling') plants. Aphid performance did not vary with leaf phloem sucrose:amino acid ratio but could be related to changes in the amino acid composition of the phloem, which included a developmental shift from high glutamine levels in pre-tuber-filling plants to low glutamine levels in tuber-filling plants. Aphid performance on chemically defined `young' and`old' diets, with amino acid composition corresponding to that of phloem amino acid composition in pre-tuber-filling and tuber-filling plants, respectively,confirmed that phloem amino acid composition contributed to low aphid performance on tuber-filling plants. The relatively poor performance on `old'diets could be accounted for, at least in part, by depressed feeding rates. These data suggest that amino acid composition of the phloem is one factor shaping the nutritional quality of plants for aphids.
Osmoregulation in the terrestrial Christmas Island red crabGecarcoidea natalis(Brachyura: Gecarcinidae): modulation of branchial chloride uptake from the urine
Authors: Taylor H. H. , Greenaway P. 
Published: April 2021

SUMMARYCrabs generally produce urine iso-osmotic to their haemolymph, but terrestrial crabs are able to vary the composition of their final excretory fluid (termed P) postrenally, in the branchial chambers. Regulatory aspects of branchial urine processing were investigated in the Christmas Island red crab Gecarcoidea natalis acclimated to drinking either freshwater (FW crabs) or 70% seawater (SW crabs). FW crabs released dilute P (mean[Cl-] 8.8 mmol l-1). Drinking 70% seawater caused the mean [Cl-] of the P to rise to 376 mmol l-1 over 5 days,approaching the haemolymph [Cl-]. FW crabs with saline-perfused branchial chambers absorbed chloride at a high rate (10 mmol kg-1h-1), and haemolymph [Cl-] increased at approximately 20 mmol l-1 h-1. SW crabs exhibited elevated haemolymph osmolalities and ion concentrations and zero branchial chloride uptake. FW crabs that were salt-loaded by branchial chamber perfusion over several hours downregulated, and eventually ceased, chloride uptake. The rate of downregulation, but not the initial chloride flux, was dependent on initial haemolymph [Cl-]. Intravascular infusion of NaCl caused immediate reduction in branchial [Cl-] of 80%. Crabs ingested and regurgitated the perfusion saline, supporting suggestions that reingestion of urine could conserve water and ions. Dopamine upregulated branchial chloride transport in G. natalis. This is consistent with the ion-regulatory effects of dopamine in euryhaline marine brachyurans but contrasts with its inhibitory effects in the terrestrial anomuran Birgus latro. Dopamine increased the rate of urine release in FW crabs. Urine composition appears to be unimportant in ionic regulation, except in the case of magnesium, levels of which were elevated in the urine of SW crabs.
Adrenergic control of the cardiovascular system in the turtleTrachemys scripta
Authors: Overgaard Johannes , Stecyk Jonathan A. W. , Farrell Anthony P. , Wang Tobias 
Published: April 2021

SUMMARYFreshwater turtles, Trachemys scripta, like all non-crocodilian reptiles, are able to shunt blood between the pulmonary and systemic circulations owing to their undivided ventricle. The prevailing hypothesis is that the ratio of pulmonary and systemic resistances is the primary determinant of cardiac shunting in turtles. In the present study, we have examined the adrenergic influences on vascular resistances in the pulmonary and systemic circulations and the associated effects on cardiac shunts in turtles. To achieve this objective, systemic blood flow and pressures and pulmonary blood flow and pressures were measured simultaneously in anaesthetised turtles during bolus injections of α- andβ-adrenergic agonists and antagonists. Total cardiac output, systemic vascular resistance, pulmonary vascular resistance, heart rate and cardiac stroke volume were derived from these measurements. Anaesthetised turtles showed cardiovascular characteristics that were similar to those of non-apnoeic non-anaesthetised turtles, because anaesthesia blocked the cholinergically mediated constriction of the pulmonary artery that is normally associated with apnoea. As a result, the anaesthetised turtles exhibited a large net left-to-right shunt, and the adrenergic responses could be observed without confounding changes resulting from apnoea. Potent α-adrenergic vasoconstriction and weaker β-adrenergic vasodilation were discovered in the systemic circulation. Modest β-adrenergic vasodilation and possible weak α-adrenergic vasodilation were discovered in the pulmonary circulation. This adrenergically mediated vasoactivity produced the largest range of cardiac shunts observed so far in turtles. Regression analysis revealed that 97% of the variability in the cardiac shunts could be accounted for by the ratio of the pulmonary and systemic resistances. Thus, we conclude that, independent of whether the pulmonary vascular resistance is modulated(as during apnoea) or the systemic resistance is modulated with adrenergic mechanisms (as shown here), the consequences on the cardiac shunt patterns are the same because they are determined primarily by the ratios of the pulmonary and systemic resistance.
Cardiorespiratory adjustments during hypercarbia in rainbow troutOncorhynchus mykissare initiated by external CO2receptors on the first gill arch
Authors: Perry Steve F. , Reid Stephen G. 
Published: April 2021

SUMMARYExperiments were performed to test the hypothesis that the marked ventilatory and cardiovascular responses to hypercarbia in rainbow trout Oncorhynchus mykiss arise from specific stimulation of chemoreceptors localised to the first gill arch. This was accomplished by measuring cardiorespiratory variables during acute hypercarbia (20 min at PCO2=8 mmHg; 1 mmHg=0.133 kPa) in fish subjected to selective bilateral extirpation of the first gill arch. The cardiovascular responses to hypercarbia in the intact fish included a significant bradycardia (from 75.0±1.6 to 69.0±2.0 beats min-1; means ± S.E.M.; N=16), an increase in dorsal aortic blood pressure (from 30.8±1.5 to 41.9±2.5 mmHg; N=16) and a rise in systemic vascular resistance (from 1.1±0.1 to 1.4±0.1 mmHg ml-1 kg-1 min-1; N=16). Removal of the first gill arch or pre-treatment with the muscarinic receptor antagonist atropine prevented the hypercarbic bradycardia without affecting the pressure or resistance responses. Correlation analysis,however, revealed shallow but significant inverse relationships between water PCO2 and cardiac frequency in both atropinised(r2=0.75) and gill-extirpated(r2=0.90) fish, suggesting a direct mild effect of CO2 on cardiac function. The ventilatory response to hypercarbia in the intact fish consisted of an increase in ventilation amplitude (from 0.62±0.06 to 1.0±0.13 cm; N=16) with no change in breathing frequency. Removal of the first gill arch lowered resting breathing frequency and prevented the statistically significant elevation of breathing amplitude. Gill extirpation, however, did not totally abolish the positive correlation between water PCO2 and ventilation amplitude (r2=0.84), suggesting the presence of additional(although less important) chemoreceptive sites that are not confined to the first gill arch. Plasma catecholamine levels were elevated during hypercarbia,and this response was unaffected by prior gill extirpation.To assess whether the CO2 chemoreceptors of the first gill arch were sensing water and/or blood PCO2, bolus injections of CO2-enriched water or saline were made into the buccal cavity or caudal vein, respectively. Injections of CO2-enriched water to preferentially stimulate external receptors evoked catecholamine release and cardiorespiratory responses that closely resembled the responses to hypercarbia. As in hypercarbia, extirpation of the first gill arch prevented the bradycardia and the increase in ventilation amplitude associated with externally injected CO2-enriched water. Except for a slight decrease in cardiac frequency (from 73.0±2.8 to 70.3±3.5 beats min-1; N=11), injection of CO2-enriched saline to preferentially stimulate internal chemoreceptors did not affect any measured variable. Taken together, these data indicate that, in rainbow trout, the bradycardia and hyperventilation associated with hypercarbia are triggered largely by external CO2chemoreceptors confined to the first gill arch.
Discrete electrolytic lesion of the preoptic area prevents LPS-induced behavioral fever in toads
Authors: Bicego Kenia C. , Branco Luiz G. S. 
Published: April 2021

SUMMARYThe preoptic area (POA) plays an important role in fever in mammals, but the role of this region in fever in ectothermic vertebrates has never been assessed. Toads, like all ectotherms, regulate their body temperature(Tb) primarily by behavior and develop behavioral fever when injected with lipopolysaccharide (LPS). Therefore, we tested the hypothesis that the POA plays a role in the behavioral fever induced by LPS in the toad Bufo paracnemis. We made electrolytic lesions in the POA of toads (0.3 mA, 8 s) and measured preferred Tb using a thermal gradient. After a period of 24h inside the gradient chamber, control,sham-operated and lesioned toads were systemically injected with LPS (200μg kg-1) or pyrogen-free saline. There was no significant effect of POA lesion in animals at their normal preferred Tb. LPS caused a significant increase in preferred Tb of control and sham-operated toads, but lesions in the POA abolished this response. These results indicate that the POA is an important site in the central nervous system of toads, and perhaps of all vertebrates, involved in the development of fever.
Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfishEptatretus burgeriGirard
Authors: Inoue Isao , Tsutsui Izuo , Bone Quentin 
Published: April 2021

SUMMARYHagfishes are regarded as the most primitive living craniates. Excitation—contraction (E—C) coupling mechanisms were studied in skeletal and caudal heart muscle fibres of the hagfish Eptatretus burgeri. In white (fast) skeletal muscle fibres from the musculus tubulatus, force generation in response to electrical stimulation was maintained in nominally Ca2+ free artificial seawater (ASW)(0Ca2+-ASW) containing 10 mmol l-1 Co2+ (a blocker of Ca2+ currents). Similarly, in red (slow) fibres from parietal muscle bathed in 0Ca2+-ASW containing 10 mmol l-1 Co2+, force generation occurred in association with K+ depolarisation when the external K+ concentration was increased to 100 mmol l-1. Therefore, external Ca2+ is not required for muscle contraction. Hence, both white and red fibres possess the function of depolarisation-induced Ca2+-release from intracellular Ca2+ stores. This function is the same as in the skeletal muscle of all other vertebrates. In caudal heart muscle fibres,twitches in response to electrical stimuli were maintained in 0Ca2+-ASW containing 30 mmol l-1 Co2+. In fibres loaded with fluo-3 bathed in 0Ca2+-ASW containing 30 mmol l-1 Co2+, an increase in the intracellular free Ca2+ level associated with K+ depolarisation was observed after the external K+ concentration was increased to 100 mmol l-1. Thus E—C coupling in the caudal heart muscle is also of the vertebrate skeletal muscle type.
Effects of temperature on intracellular [Ca2+] in trout atrial myocytes
Authors: Shiels Holly A. , Vornanen Matti , Farrell Anthony P. 
Published: April 2021

SUMMARYAcute temperature change can be cardioplegic to mammals, yet certain ectotherms maintain their cardiac scope over a wide temperature range. To better understand the acute effects of temperature on the ectothermic heart,we investigated the stimulus-induced change in intracellular Ca2+concentration ([Ca2+]i; cytosolic Ca2+transient) in isolated rainbow trout myocytes at 7°C, 14°C and 21°C. Myocytes were voltage-clamped and loaded with Fura-2 to measure the L-type Ca2+ channel current (ICa) and[Ca2+]i during physiological action potential (AP)pulses at frequencies that correspond to trout heart rates in vivo at 7°C, 14°C and 21°C. Additionally, [Ca2+]iand ICa were examined with square (SQ) pulses at slow (0.2 Hz) and physiologically relevant contraction frequencies. The amplitude of[Ca2+]i decreased with increasing temperature for both SQ and AP pulses, which may contribute to the well-known negative inotropic effect of warm temperature on contractile strength in trout hearts. With SQ pulses, [Ca2+]i decreased from 474±53 nmol l-1 at 7°C to 198±21 nmol l-1 at 21°C,while the decrease in [Ca2+]i with AP pulses was from 234±49 nmol l-1 to 79±12 nmol l-1,respectively. Sarcolemmal Ca2+ influx was increased slightly at cold temperatures with AP pulses (charge transfer was 0.27±0.04 pC pF-1, 0.19±0.03 pC pF-1 and 0.13±0.03 pC pF-1 at 7°C, 14°C and 21°C, respectively). At all temperatures, cells were better able to maintain diastolic Ca2+levels at physiological frequencies with AP pulses compared with 500 ms SQ pulses. We suggest that temperature-dependent modulation of the AP is important for cellular Ca2+ regulation during temperature and frequency change in rainbow trout heart.
Developmental changes in the cone visual pigments of black breamAcanthopagrus butcheri
Authors: Shand Julia , Hart Nathan S. , Thomas Nicole , Partridge Julian C. 
Published: April 2021

SUMMARYThe spectral absorption characteristics of the visual pigments in the photoreceptors of the black bream Acanthopagrus butcheri Munro(Sparidae, Teleostei), were measured using microspectrophotometry. A single cohort of fish aged 5-172 days post-hatch (dph), aquarium-reared adults and wild-caught juveniles were investigated. During the larval stage and in juveniles younger than 100 dph, two classes of visual pigment were found, with wavelengths of maximum absorbance (λmax) at approximately 425 nm and 535 nm. Following double cone formation, from 40 dph onwards, the short wavelength-sensitive pigment was recorded in single cones and the longer wavelength-sensitive pigment in double cones. From 100 dph, a gradual shift in the λmax towards longer wavelengths was observed in both cone types. By 160 dph, and in adults, all single cones had aλ max at approximately 475 nm while theλ max in double cones ranged from 545 to 575 nm. The relationships between the λmax and the ratio of bandwidth:λmax, for changes in either chromophore or opsin,were modelled mathematically for the long-wavelength-sensitive visual pigments. Comparing our data with the models indicated that changes inλ max were not mediated by a switch from an A1 to A2 chromophore, rather a change in opsin expression was most likely. The shifts in the λmax of the visual pigments occur at a stage when the juvenile fish begin feeding in deeper, tanninstained estuarine waters, which transmit predominantly longer wavelengths, so the spectral sensitivity changes may represent an adaptation by the fish to the changing light environment.
Hovering flight mechanics of neotropical flower bats (Phyllostomidae:Glossophaginae) in normodense and hypodense gas mixtures
Authors: Dudley Robert , Winter York 
Published: April 2021

SUMMARYExisting estimates of flight energetics in glossophagine flower bats, the heaviest hovering vertebrate taxon, suggest disproportionately high expenditure of mechanical power. We determined wingbeat kinematics and mechanical power expenditure for one of the largest flower bats(Leptonycteris curasoae Martinez and Villa) during hovering flight in normodense and hypodense gas mixtures. Additional experiments examined the effects of supplemental oxygen availability on maximum flight performance. Bats failed to sustain hovering flight at normoxic air densities averaging 63%that of normodense air. Kinematic responses to hypodense aerodynamic challenge involved increases in wing positional angles and in total stroke amplitude;wingbeat frequency was unchanged. At near-failure air densities, total power expenditure assuming perfect elastic energy storage was 17-42% greater than that for hovering in normodense air, depending on the assumed value for the profile drag coefficient. Assuming a flight muscle ratio of 26%, the associated muscle-mass-specific power output at the point of near-failure varied between 90.8 W kg-1 (profile drag coefficient of 0.02) to 175.6 W kg-1 (profile drag coefficient of 0.2). Hyperoxia did not enhance hovering performance in hypodense air, and, with the exception of a small increase (10%) in stroke plane angle, yielded no significant change in any of the kinematic parameters studied. Revised energetic estimates suggest that mechanical power expenditure of hovering glossophagines is comparable with that in slow forward flight.