bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relative roles of external and internal CO2versusH+ in eliciting the cardiorespiratory responses ofSalmo salarandSqualus acanthiasto hypercarbia
Authors: Perry S. F. , McKendry J. E. 
Published: April 2021

SUMMARYFish breathing hypercarbic water encounter externally elevated PCO2 and proton levels ([H+]) and experience an associated internal respiratory acidosis, an elevation of blood PCO2 and [H+]. The objective of the present study was to assess the potential relative contributions of CO2versus H+ in promoting the cardiorespiratory responses of dogfish (Squalus acanthias) and Atlantic salmon (Salmo salar) to hypercarbia and to evaluate the relative contributions of externally versus internally oriented receptors in dogfish.In dogfish, the preferential stimulation of externally oriented branchial chemoreceptors using bolus injections (50 ml kg–1) of CO2-enriched (4 % CO2) sea water into the buccal cavity caused marked cardiorespiratory responses including bradycardia (–4.1±0.9 min–1), a reduction in cardiac output (–3.2±0.6 ml min–1 kg–1), an increase in systemic vascular resistance (+0.3±0.2 mmHg ml min–1 kg–1), arterial hypotension (–1.6±0.2 mmHg) and an increase in breathing amplitude (+0.3±0.09 mmHg) (means ± s.e.m., N=9–11). Similar injections of CO2-free sea water acidified to the corresponding pH of the hypercarbic water (pH 6.3) did not significantly affect any of the measured cardiorespiratory variables (when compared with control injections). To preferentially stimulate putative internal CO2/H+ chemoreceptors, hypercarbic saline (4 % CO2) was injected (2 ml kg–1) into the caudal vein. Apart from an increase in arterial blood pressure caused by volume loading, internally injected CO2 was without effect on any measured variable.In salmon, injection of hypercarbic water into the buccal cavity caused a bradycardia (–13.9±3.8 min–1), a decrease in cardiac output (–5.3±1.2 ml min–1 kg–1), an increase in systemic resistance (0.33±0.08 mmHg ml min–1 kg–1) and increases in breathing frequency (9.7±2.2 min–1) and amplitude (1.2±0.2 mmHg) (means ± s.e.m., N=8–12). Apart from a small increase in breathing amplitude (0.4±0.1 mmHg), these cardiorespiratory responses were not observed after injection of acidified water.These results demonstrate that, in dogfish and salmon, the external chemoreceptors linked to the initiation of cardiorespiratory responses during hypercarbia are predominantly stimulated by the increase in water PCO2 rather than by the accompanying decrease in water pH. Furthermore, in dogfish, the cardiorespiratory responses to hypercarbia are probably exclusively derived from the stimulation of external CO2 chemoreceptors, with no apparent contribution from internally oriented receptors.
Carbonic anhydrase activity in tissues of the icefish Chionodraco hamatus and of the red-blooded teleosts Trematomus bernacchii and Anguilla anguilla
Authors: Maffia M. , Rizzello A. , Acierno R. , Rollo M. , Chiloiro R. , Storelli C. 
Published: April 2021

SUMMARY
Carbonic anhydrase (CA) activity was measured in blood, intestine, kidney and gill of two Antarctic teleosts, the haemoglobinless Chionodraco hamatus and the red-blooded Trematomus bernacchii, and of the temperate teleost Anguilla anguilla. In all species, the highest CA activity was in the gills, with the greatest activity in C. hamatus. CA activity in the blood was highest in A. anguilla, but none was detected in the blood of C. hamatus despite the presence of plasma CA inhibitors. The enzyme was present but its activity was low in the intestine and kidney of all three species.
The existence of very high CA activity in C. hamatus gills compared with the red-blooded species was investigated further by isolating and characterising the branchial cytosolic CA isoforms. The turnover rate of the C. hamatus isoform was significantly higher than that of T. bernacchii and A. anguilla. The isoforms from both the Antarctic species exhibited lower apparent Km (Km,app) and heat stability than those from A. anguilla. Sensitivity to sulphonamides was similar in all species and was within the range of the mammalian CA II isoform. The branchial CA isoforms of C. hamatus, T. bernacchii and A. anguilla displayed relative molecular masses of 28.9, 29.9 and 31.2 kDa, respectively.
The results suggest that the hemoglobinless teleost possesses a different branchial cytosolic CA isoform from that of red-blooded teleosts.
Modelling the biomechanics and control of sphincters
Authors: Heldoorn Marcel , Van Leeuwen Johan L. , Vanderschoot Jan 
Published: April 2021

SUMMARY
This paper reviews current mathematical models of sphincters and compares them with a new spatial neuromuscular control model based on known physiological properties. Almost all the sphincter models reviewed were constructed as a component of a more extensive model designed to mirror the overall behaviour of a larger system such as the lower urinary tract. This implied less detailed modelling of the sphincter component. It is concluded that current sphincter models are not suitable for mimicking detailed interactions between a neural controller and a sphincter. We therefore outline a new integrated model of the biomechanics and neural control of a sphincter. The muscle is represented as a lumped-mass model, providing the possibility of applying two- or three-dimensional modelling strategies. The neural network is a multi-compartment model that provides neural control signals at the level of action potentials.The integrated model was used to simulate a uniformly activated sphincter and a partially deficient innervation of the sphincter, resulting in a non-uniformly activated sphincter muscle. During the simulation, the pressure in the sphincter lumen was prescribed to increase sinusoidally to a value of 60 kPa. In the uniformly activated situation, the sphincter muscle remains closed, whereas the partially denervated sphincter is stretched open, although the muscle is intact.
Water-tunnel studies of heat balance in swimming mako sharks
Authors: Bernal Diego , Sepulveda Chugey , Graham Jeffrey B. 
Published: April 2021

SUMMARYThe mako shark (Isurus oxyrinchus) has specialized vascular networks (retia mirabilia) forming counter-current heat exchangers that allow metabolic heat retention in certain regions of the body, including the aerobic, locomotor red muscle and the viscera. Red muscle, white muscle and stomach temperatures were measured in juvenile (5–13.6 kg) makos swimming steadily in a water tunnel and exposed to stepwise square-wave changes in ambient temperature (Ta) to estimate the rates of heat transfer and to determine their capacity for the activity-independent control of heat balance. The rates of heat gain of red muscle during warming were significantly higher than the rates of heat loss during cooling, and neither the magnitude of the change in Ta nor the direction of change in Ta had a significant effect on red muscle latency time. Our findings for mako red muscle are similar to those recorded for tunas and suggest modulation of retial heat-exchange efficiency as the underlying mechanism controlling heat balance. However, the red muscle temperatures measured in swimming makos (0.3–3°C above Ta) are cooler than those measured previously in larger decked makos. Also, the finding of non-stable stomach temperatures contrasts with the predicted independence from Ta recorded in telemetry studies of mako and white sharks. Our studies on live makos provide new evidence that, in addition to the unique convergent morphological properties between makos and tunas, there is a strong functional similarity in the mechanisms used to regulate heat transfer.
Scavenger-receptor-mediated endocytosis of lipopolysaccharide in Atlantic cod (Gadus morhuaL.)
Authors: Seternes Tore , Dalmo Roy A. , Hoffman James , Bøgwald Jarl , Zykova Svetlana , Smedsrød Bård 
Published: April 2021

SUMMARYThe mechanism of elimination of blood-borne Vibrio salmonicida lipopolysaccharide (LPS) from Atlantic cod (Gadus morhua L.) was studied. The anatomical distribution of LPS was determined using both morphological and radiotracing methods. Immunohistochemistry performed on tissue specimens after injection of LPS disclosed that the endocardial endothelial cells (EECs) represented the cellular site of uptake in heart. Co-injection of trace amounts of [125I]LPS together with excess amounts of formaldehyde-treated albumin (FSA), a ligand for the scavenger receptor, significantly inhibited the accumulation of the radiotracer in heart only. Studies on purified monolayer cultures of atrial EECs showed that fluorescein-labelled LPS was taken up in structures reminiscent of endosomal/lysosomal vesicles. Incubation of cultures with [125I]LPS together with excess amounts of FSA, fucoidan and dextran sulphate, molecules known to compete for endocytosis via the scavenger receptor, reduced uptake of the probe by 80 %. Mannan, a ligand for the mannose receptor, did not compete for uptake. Kinetic studies on the uptake and degradation of [125I]LPS in cultured atrial endocardial cells revealed no degradation after 48 h of culture. In conclusion, we have shown that the EECs of cod remove V. salmonicida LPS from the circulation by scavenger-receptor-mediated endocytosis.
The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution
Authors: Hays G. C. , Åkesson S. , Broderick A. C. , Glen F. , Godley B. J. , Luschi P. , Martin C. , Metcalfe J. D. , Papi F. 
Published: April 2021

SUMMARY
Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (&lt;5 min) but that some submergences were longer (&gt;20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (2–4 min), shallow (approximately 0.9–1.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 20–30 min), deep (typically 10–20 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks.
Simulated weightlessness alters the nycthemeral distribution of energy expenditure in rats
Authors: Blanc Stéphane , Géloën Alain , Normand Sylvie , Gharib Claude , Somody Laurence 
Published: April 2021

SUMMARYThe energy metabolism adaptations to simulated weightlessness in rats by hindlimb tail suspension are unknown. 12 male rats were assigned to 7 days of isolation, 7 days of habituation to the suspension device, 10 days of simulated weightlessness, and 3 days of recovery. The 24-hour energy expenditure was measured by continuous indirect calorimetry. We calculated the 12-hour energy expenditure during the active (night) and inactive (day) periods, the minimal observed metabolic rates with the day values taken as an index of the basal metabolic rate, and the non-basal energy expenditure representing the cost of physical activity plus the diet-induced thermogenesis. Suspension did not change the mean 24-hour energy expenditure (360.8±15.3 J min–1 kg–0.67), but reduced the night/day difference by 64 % (P&lt;0.05) through a concomitant drop in night-energy expenditure and increase in day values. The difference between night and day minimal metabolic rates was reduced by 81 % (P&lt;0.05), and the transient rise in day values suggests an early and moderate basal metabolic rate increase (9 %). An overall 19 % reduction in non-basal energy expenditure was observed during simulated weightlessness (P&lt;0.05), which was mainly attributable to a reduction in the cost of physical activity. 3 days of recovery restored the night/day differences but increased the 24-hour energy expenditure by 10 % (P&lt;0.05). In conclusion, hindlimb tail suspension in rats did not alter the 24-hour energy expenditure, but it transiently increased the basal metabolic rate, and altered both the energy expended on physical activity and the nycthemeral distribution of motor activity. These data suggest that the circadian rhythms of energy expenditure are affected during simulated weightlessness.
The cultured branchial epithelium of the rainbow trout as a model for diffusive fluxes of ammonia across the fish gill
Authors: Kelly Scott P. , Wood Chris M. 
Published: April 2021

SUMMARYA novel branchial epithelial preparation grown in L-15 medium in culture was used as a model system for understanding the diffusion of ammonia across the gills of the rainbow trout Oncorhynchus mykiss. The epithelium is known to contain both respiratory and mitochondria-rich cells in the approximate proportion in which they occur in vivo and to exhibit diffusive fluxes of Na+ and Cl– similar to in vivo values, but does not exhibit active apical-to-basolateral transport of Na+. Transepithelial resistance and paracellular permeability are also known to increase when the apical medium is changed from L-15 medium (symmetrical conditions) to fresh water (asymmetrical conditions). In the present study, net basolateral-to-apical ammonia fluxes increased as basolateral total ammonia concentration, basolateral-to-apical pH gradients and basolateral-to-apical PNH3 gradients were experimentally increased and were greater under asymmetrical than under symmetrical conditions. The slope of the relationship between ammonia flux and PNH3 gradient (i.e. NH3 permeability) was the same under both conditions and similar to values for other epithelia. The higher fluxes under asymmetrical conditions were explained by an apparent diffusive flux of NH4+ that was linearly correlated with transepithelial conductance and was probably explained by the higher electrochemical gradient and higher paracellular permeability when fresh water was present on the apical surface. In this situation, NH4+ diffusion was greater than NH3 diffusion under conditions representative of in vivo values, but overall fluxes amounted to only approximately 20 % of those in vivo. These results suggest that branchial ammonia excretion in the intact animal is unlikely to be explained by diffusion alone and, therefore, that carrier-mediated transport may play an important role.
The efficiency of an asynchronous flight muscle from a beetle
Authors: Josephson Robert K. , Malamud Jean G. , Stokes Darrell R. 
Published: April 2021

SUMMARYMechanical power output and metabolic power input were measured from an asynchronous flight muscle, the basalar muscle of the beetle Cotinus mutabilis. Mechanical power output was determined using the work loop technique and metabolic power input by monitoring CO2 production or both CO2 production and O2 consumption. At 35°C, and with conditions that maximized power output (60 Hz sinusoidal strain, optimal muscle length and strain amplitude, 60 Hz stimulation frequency), the peak mechanical power output during a 10 s burst was approximately 140 W kg–1, the respiratory coefficient 0.83 and the muscle efficiency 14–16 %. The stimulus intensity used was the minimal required to achieve a maximal isometric tetanus. Increasing or decreasing the stimulus intensity from this level changed mechanical power output but not efficiency, indicating that the efficiency measurements were not contaminated by excitation of muscles adjacent to that from which the mechanical recordings were made. The CO2 produced during an isometric tetanus was approximately half that during a bout of similar stimulation but with imposed sinusoidal strain and work output, suggesting that up to 50 % of the energy input may go to muscle activation costs. Reducing the stimulus frequency to 30 Hz from its usual value of 60 Hz reduced mechanical power output but had no significant effect on efficiency. Increasing the frequency of the sinusoidal strain from 60 to 90 Hz reduced power output but not CO2 consumption; hence, there was a decline in efficiency. The respiratory coefficient was the same for 10 s and 30 s bursts of activity, suggesting that there was no major change in the fuel used over this time range.The mass-specific mechanical power output and the efficiency of the beetle muscle were each 2–3 times greater than values measured in previous studies, using similar techniques, from locust flight muscles, which are synchronous muscles. These results support the hypothesis that asynchronous flight muscles have evolved in several major insect taxa because they can provide greater power output and are more efficient than are synchronous muscles for operation at the high frequencies of insect flight.
Patch-clamp analysis of voltage-activated and chemically activated currents in the vomeronasal organ of Sternotherus odoratus (stinkpot/musk turtle)
Authors: Fadool D. A. , Wachowiak M. , Brann J. H. 
Published: April 2021

SUMMARY
The electrophysiological basis of chemical communication in the specialized olfactory division of the vomeronasal (VN) organ is poorly understood. In total, 198 patch-clamp recordings were made from 42 animals (Sternotherus odoratus, the stinkpot/musk turtle) to study the electrically and chemically activated properties of VN neurons. The introduction of tetramethylrhodamine-conjugated dextran into the VN orifice permitted good visualization of the vomeronasal neural epithelium prior to dissociating it into single neurons. Basic electrical properties of the neurons were measured (resting potential, –54.5±2.7 mV, N=11; input resistance, 6.7±1.4 GΩ, N=25; capacitance, 4.2±0.3 pF, N=22; means ± s.e.m.). The voltage-gated K+ current inactivation rate was significantly slower in VN neurons from males than in those from females, and K+ currents in males were less sensitive (greater Ki) to tetraethylammonium. Vomeronasal neurons were held at a holding potential of –60 mV and tested for their response to five natural chemicals, female urine, male urine, female musk, male musk and catfish extract. Of the 90 VN neurons tested, 33 (34 %) responded to at least one of the five compounds. The peak amplitude of chemically evoked currents ranged from 4 to 180 pA, with two-thirds of responses less than 25 pA. Urine-evoked currents were of either polarity, whereas musk and catfish extract always elicited only inward currents. Urine applied to neurons harvested from female animals evoked currents that were 2–3 times larger than those elicited from male neurons. Musk-evoked inward currents were three times the magnitude of urine- or catfish-extract-evoked inward currents. The calculated breadth of responsiveness for neurons presented with this array of five chemicals indicated that the mean response spectrum of the VN neurons is narrow (H metric 0.11). This patch-clamp study indicates that VN neurons exhibit sexual dimorphism in function and specificity in response to complex natural chemicals.
Juvenile sturgeon exhibit reduced physiological responses to exercise
Authors: Kieffer James D. , Wakefield Andrea M. , Litvak Matthew K. 
Published: April 2021

SUMMARYExperiments were conducted to determine the physiological responses to exercise of Atlantic sturgeon (Acipenser oxyrhynchus) and shortnose sturgeon (A. brevirostrum). We measured the rates of oxygen consumption and ammonia excretion in both species and a variety of physiological parameters in both muscle (e.g. lactate, glycogen, pyruvate, glucose and phosphocreatine concentrations) and blood (e.g. osmolality and lactate concentration) in juvenile shortnose sturgeon following 5 min of exhaustive exercise.In both species, oxygen consumption and ammonia excretion rates increased approximately twofold following exhaustive exercise. Post-exercise oxygen consumption rates decreased to control levels within 30 min in both sturgeon species, but post-exercise ammonia excretion rates remained high in Atlantic sturgeon throughout the 4 h experiment. Resting muscle energy metabolite levels in shortnose sturgeon were similar to those of other fish species, but the levels decreased only slightly following the exercise period and recovery occurred within an hour. Under resting conditions, muscle lactate levels were low (&lt;1 μmol g–1) but they increased to approximately 6 μmol g–1 after exercise, returning to control levels within 6 h. Unlike similarly stressed teleost fish, such as the rainbow trout, plasma lactate levels did not increase substantially and returned to resting levels within 2 h. Plasma osmolality was not significantly affected by exercise in shortnose sturgeon.Taken together, these results suggest that shortnose and Atlantic sturgeon do not exhibit the physiological responses to exhaustive exercise typical of other fish species. They may possess behavioural or endocrinological mechanisms that differ from those of other fishes and that lead to a reduced ability to respond physiologically to exhaustive exercise.
Peripheral representation of antennal orientation by the scapal hair plate of the cockroach Periplaneta americana
Authors: Okada J. , Toh Y. 
Published: April 2021

SUMMARY
Arthropods have hair plates that are clusters of mechanosensitive hairs, usually positioned close to joints, which function as proprioceptors for joint movement. We investigated how angular movements of the antenna of the cockroach (Periplaneta americana) are coded by antennal hair plates. A particular hair plate on the basal segment of the antenna, the scapal hair plate, can be divided into three subgroups: dorsal, lateral and medial. The dorsal group is adapted to encode the vertical component of antennal direction, while the lateral and medial groups are specialized for encoding the horizontal component. Of the three subgroups of hair sensilla, those of the lateral scapal hair plate may provide the most reliable information about the horizontal position of the antenna, irrespective of its vertical position. Extracellular recordings from representative sensilla of each scapal hair plate subgroup revealed the form of the single-unit impulses in response to hair deflection. The mechanoreceptors were characterized as typically phasic-tonic. The tonic discharge was sustained indefinitely (&gt;20 min) as long as the hair was kept deflected. The spike frequency in the transient (dynamic) phase was both velocity- and displacement-dependent, while that in the sustained (steady) phase was displacement-dependent.
Venom flow in rattlesnakes: mechanics and metering
Authors: Young Bruce A. , Zahn Krista 
Published: April 2021

SUMMARY
The functional morphology of venom injection in Crotalus atrox was explored using high-speed digital videography combined with direct recording of venom flow using perivascular flow probes. Although venom flow was variable, in most strikes the onset of venom flow was coincidental with fang penetration, and retrograde flow (venom suction) was observed prior to fang withdrawal. The duration of venom flow was consistently less than the duration of fang penetration. The occurrence of retrograde flow, ‘dry bites’ (which accounted for 35 % of the strikes) and unilateral strikes all support a hypothesis for venom pooling in the distal portion of the venom-delivery system. No significant difference in temporal or volumetric aspects of venom flow were found between defensive strikes directed at small and large rodents. With the species and size of target held constant, the duration of venom flow, maximum venom flow rate and total venom volume were all significantly lower in predatory than in defensive strikes.