bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synergism of Hormones Controlling Epithelial Fluid Transport in an Insect
Authors: Maddrell S. H. P. , Herman W. S. , Farndale R. W. , Riegel J. A. 
Published: April 2021

ABSTRACT
Forskolin stimulates rapid fluid secretion by the Malpighian tubules of Rhodnius prolixus at concentrations above 5X10−6 mol l−1. In the presence of a threshold concentration of forskolin, the tubules are 30–50 times more sensitive to 5-hydroxytryptamine (5-HT) than in its absence. Similar synergism is seen between 5-HT and extracts of the mesothoracic ganglionic mass (which is rich in the peptide diuretic hormone, DH) and between 5-HT and samples of haemolymph, also rich in peptide DH, from fed insects 1–2h after feeding. The dose–response curves for mixtures of forskolin and 5-HT and of peptide DH and 5-HT are all very steep, approximately five times steeper than for any one stimulant alone.
Forskolin, 5-HT and extracts of the ganglionic mass all stimulated adenylate cyclase from broken membrane preparations from the Malpighian tubules in a dose-dependent manner and at doses similar to those required to stimulate fluid secretion by intact tubules. Mixtures of ganglionic extract and 5-HT stimulated adenylate cyclase activity in a synergistic fashion.
Injections into fifth-instar Rhodnius, 24h before feeding, of 5,7-dihydroxytryptamine, which is known to block or reduce 5-HT release, caused delays in the onset of the consequent diuresis or prevented it altogether. This is consistent with the proposal that the rapid onset of diuresis after feeding is caused by the simultaneous release of 5-HT and peptide DH acting synergistically.
A Comparison of the Effects of two Putative Diuretic Hormones from Locusta Migratoria On Isolated Locust Malpighian Tubules
Authors: Coast G. M. , Rayne R. C. , Hayes T. K. , Mallet A. I. , Thompson K. S. J. , Bacon J. P. 
Published: April 2021

ABSTRACT
Previous work has shown that a peptide related to arginine vasopressin is present in the suboesophageal ganglion of the locust, Locusta migratoria. This peptide was determined to be an anti-parallel dimer of the nonapeptide Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly-NH2 and was reported to stimulate cyclic AMP production and fluid secretion in a combined Malpighian tubules and midgut preparation from locusts. For these reasons the peptide has been called the arginine-vasopressin-like insect diuretic hormone (AVP-like IDH). Recently, a second diuretic peptide (Locusta-DP), which is related to corticotropin releasing factor, has been identified: this is a potent stimulant of fluid secretion and cyclic AMP production by isolated locust tubules. Because water balance in insects is likely to be controlled by a cocktail of hormones acting on both Malpighian tubules and hindgut, this study directly compares the activity of these two peptides in fluid secretion and cyclic AMP production bioassays on one target organ, the isolated Malpighian tubule of Locusta migratoria. Locusta-DP was synthesised directly, whereas the dimeric AVP-like IDH was obtained by oxidation of a synthetic nonapeptide monomer. Products were separated by RP-HPLC and their structures unequivocally confirmed by enzymatic digestion, sequence analysis and electrospray mass spectrometry. We show that Locusta-DP causes strong stimulation of fluid secretion and cyclic AMP production, whereas the AVP-like IDH has no effect in either assay. These findings are discussed in the light of recent work on the anatomy and physiology of the vasopressin-like immunoreactive (VPLI) neurones in the suboesophageal ganglion of Locusta migratoria, the proposed source of the AVP-like peptide.
Water Compartments and Osmoregulation in the Parasitic Nematode Pseudoterranova Decipiens
Authors: Fusé M. , Davey K. G. , Sommerville R. I. 
Published: April 2021

ABSTRACT
A study of the time course of penetration of 3H2O into whole worms suggests that worms immersed in a hypo-osmotic environment (15% artificial sea water) reach full exchange equilibrium more slowly than worms in an iso-osmotic environment (40 % artificial sea water). The apparent water content, determined by dry mass, matches that determined by 3H2O exchange when worms are immersed for 24h in 40% artificial sea water (ASW), but the water content measured by 3H2O exchange is lower when worms are kept in a hypo-osmotic environment for 24h. These differences disappear after 48h. No such differences are apparent when sacs, consisting of cylinders of body wall lacking their intestines and pseudocoelomic fluid and closed at both ends by ligatures, are immersed in either 40% or 15% ASW for 24h. The placing of ligatures at the head, but not at the tail, results in a failure of worms immersed in 40% ASW or 15% ASW containing 3H2O to achieve full exchange equilibrium within 24h. These results suggest that although worms immersed in an iso-osmotic environment drink, those immersed in a hypo-osmotic environment do not, a conclusion supported by studies involving the addition of [14C]inulin to the medium. The application of ligatures to the head and tail of worms immersed in 40% ASW results in a slower penetration of 3H2O into the pseudocoelomic fluid, whereas similar ligatures do not further retard the penetration in worms exposed to 15% ASW. The results are consistent with a model which sees the pseudocoelomic fluid as consisting of two compartments containing water, one of which exchanges more slowly than the other.
Ammonia and urea excretion in Lahontan cutthroat trout (Oncorhynchus clarki henshawi) adapted to the highly alkaline Pyramid Lake (pH 9.4)
Authors: Wright Patricia A. , Iwama George K. , Wood Chris M. 
Published: April 2021

ABSTRACT
Earlier studies have reported that acute exposure to alkaline pH strongly inhibits ammonia excretion in freshwater rainbow trout, but the Lahontan cutthroat trout thrives in Pyramid Lake, Nevada, at pH9.4. We investigated the rates and mechanisms of ammonia and urea excretion in this species in Pyramid Lake water to determine whether special strategies are employed to excrete nitrogenous wastes in an environment unfavourable for ammonia excretion. The majority of nitrogen wastes (N-wastes) were excreted as ammonia (56% through the gills, 10% through the kidney), while urea excretion accounted for 34% (32% gills, 2% kidney). Ammonia excretion was dependent on the NH3 partial pressure gradient across the gills and independent of Na+ influx and acidification of the gill water boundary layer. Acute exposure to more alkaline water (pH10) decreased ammonia excretion by 52%, while exposure to neutral water (pH7.6) increased ammonia excretion by 200%. When fish were held in a ‘closed system’ for 8h, ammonia excretion decreased as water ammonia levels increased over the first 6h. However, after 6h a marked increase in ammonia excretion occurred which may have been associated with an increase in the gradient and/or activation of a carrier-mediated transporter. We conclude that Lahontan cutthroat trout, adapted to pH9.4 water, maintain N-waste excretion by modifying mechanisms common to other teleosts. These modifications include lower rates of ammonia excretion, a higher ratio of urea excretion to ammonia excretion, a higher rate of renal ammonia excretion, greater plasma pH and greater total ammonia level (increased plasma ), which facilitate the diffusive excretion of NH3 across the gills, and a lack of dependence of ammonia excretion on Na+ influx.
The physiological responses of the Lahontan cutthroat trout (Oncorhynchus clarki henshawi), a resident of highly alkaline Pyramid Lake (pH 9.4), to challenge at pH 10
Authors: Wilkie Michael P. , Wright Patricia A. , Iwama George K. , Wood Chris M. 
Published: April 2021

ABSTRACT
Desiccation of Pyramid Lake, Nevada, has led to continued increases in the lake’s alkalinity (currently pH9.4) that may threaten the resident Lahontan cutthroat trout population. In this study, Lahontan cutthroat trout were challenged with more alkaline water (pH10). The objectives were to describe physiological responses which may permit survival or lead to death in future potential environmental conditions and to cast further light on the mechanisms of nitrogenous waste excretion, acid–base regulation and ionoregulation in this unusual salmonid. Ammonia excretion (Jamm) was reduced by 50 % in the first few hours, but had fully recovered by 24h and exceeded control values by 36–48h. A sustained, twofold elevation of plasma ammonia concentration may have facilitated the recovery of Jamm by increasing the blood-to-water ammonia partial pressure diffusion gradient and NH4+ electrochemical gradient. Urea excretion (Jurea) almost doubled at 24–48h of pH10 exposure. Activities of ornithine–urea cycle enzymes in the liver were very low and there was no induction at pH10. However, all three enzymes of the uricolytic pathway were present, and allantoicase activity increased significantly at pH10, a possible explanation for the elevated Jurea. Increased liver glutamine synthetase activity at pH10 is consistent with a possible ammonia detoxification mechanism. A combined respiratory (decreased ) and metabolic (gain of basic equivalents) alkalosis developed at pH10 and resulted in a 0.25 unit increase in arterial blood pH. Electrochemical gradients for CO32- and OH− entry and H+ efflux all increased, but the gradient for HCO3− entry decreased to zero. Blood lactate level increased without marked changes in arterial O2 tension, suggesting that increased lactic acid production contributed to acid–base control. Plasma Na+ and Cl− levels decreased and K+ level increased during pH10 exposure. Survival at pH10 was relatively poor: more than 50% of the fish died after 72h exposure. Greatly elevated plasma and depressed plasma Na+ and Cl− levels in non-surviving trout suggest that a combination of ammonia toxicity and ionoregulatory failure led to death in susceptible cutthroat trout.
Motor Neuron M3 Controls Pharyngeal Muscle Relaxation Timing in Caenorhabditis Elegans
Authors: Avery Leon 
Published: April 2021

ABSTRACT
Previous work has shown that 12 of the 14 types of neurons in the Caenorhabditis elegans pharyngeal nervous system are collectively but not individually necessary for the trapping and transport of bacteria. The aim of these experiments was to determine the functions of individual neuron types by laser−killing combinations of neurons and looking at the effects on behavior.
The motor neuron M3 and the sensory neuron I5 are important in trapping bacteria, as shown by two observations. First, when M3 and I5 are both killed, trapping is inefficient in the isthmus (the middle section of the pharynx). Second, M3 is sufficient in the absence of the other 11 neuron types for normal trapping in the corpus (anterior pharynx).
M3 and I5 influence the timing of pharyngeal muscle motions. When M3 is killed, pump duration (the interval from the beginning of pharyngeal contraction to the end of relaxation) increases from 170to 196ms. This increase is at least partially due to a slower relaxation. Thus, M3 speeds up relaxation. Pump duration decreases to 159ms when I5 is killed. When I5 and M3 are both killed, pump durations are long (192ms), just as when M3 alone is killed. These observations, together with previous electron microscopic work showing synapses from I5 to M3, suggest that I5 slows down relaxation by inhibiting M3.
To explain these results, I propose that M3 and I5 promote bacterial trapping by regulating the relative timing of muscle relaxation in different regions of the pharynx.
Damping in the Hinge of the Scallop Placopecten Magellanicus
Authors: Bowie Michael A. , Layes Jonathan D. , Demont M. Edwin 
Published: April 2021

ABSTRACT
The family Pectinaceae are the only bivalves that have been well documented as swimmers (DeMont, 1992), although Ensis minor has been observed to swim (McMahon and McMahon, 1983). The behaviour was once regarded only as an escape response (Gäde, 1981; McMahon and McMahon, 1983), but some studies suggest seasonal migrations are involved (Gruffydd, 1976; DeMont, 1990). DeMont (1990) suggests that they swim at the natural frequency of the shell-hinge system for more efficient use of energy.
Augmentation Of Bursting Pacemaker Activity By Serotonin In An Identified Achatina Fulica Neurone: An Increase In Sodium- And Calcium-Activated Negative Slope Resistance Via Cyclic-Amp-Dependent Protein Phosphorylation
Authors: Funase Kozo , Watanabe Kazuko , Onozuka Minoru 
Published: April 2021

ABSTRACT
The mechanism of serotonin (5-HT) action on bursting activity was examined in a bursting pacemaker neurone of the snail Achatina fulica. 5-HT augmented both the depolarizing and post-burst-hyperpolarizing phases of the bursting cycle in a dose-dependent manner. This biogenic amine also enhanced the negative slope resistance (NSR), which was normally detectable at membrane potentials between -40 and -20mV, and produced another NSR at voltages between -20 and 0mV. The former NSR disappeared in Na+-free saline and the latter was abolished by replacement with Co2+-substituted Ca2+-free saline. Both isobutylmethylxanthine, extracellularly applied, and intracellularly applied cyclic AMP simulated a 5-HT effect on the current–voltage relationships. In contrast, the 5-HT effect was suppressed in a dose-dependent manner by prior treatment with a cyclic-AMP-dependent protein kinase inhibitor, isoquinoline sulphonamide. Similar suppression was observed after intracellular injection of a cyclic-AMP-dependent protein kinase inhibitor isolated from bovine muscle. These results suggest that 5-HT may augment the bursting pacemaker activity by its stimulatory effect on both the slow Na+ channels and the Ca2+ channels through cyclic-AMP-dependent protein phosphorylation.
Convergence in the Feeding Mechanics of Ecomorphologically Similar Species in the Centrarchidae and Cichlidae
Authors: Norton Stephen F. , Brainerd Elizabeth L. 
Published: April 2021

ABSTRACT
We examined the hypothesis that fish species with similar ecomorphological patterns, but from different taxonomic groups, would use similar feeding modes. We contrasted the feeding behavior of Micropterus salmoides (Lacépède) (Centrarchidae) and Cichla ocellaris (Block and Schneider) (Cichlidae), both large-mouthed piscivores with a locomotor morphology designed for fast acceleration, with Lepomis spp. (Centrarchidae) and Cichlosoma severum (Heckel) (Cichlidae), both small-mouthed predators on benthic invertebrates with a locomotor morphology designed for maneuverability. Pressure profiles in the buccal and opercular cavities were more similar for species that shared ecomorphological patterns than for species that shared phylogenetic histories. For smallmouthed predators, minimum buccal pressures were significantly greater and occurred earlier than the corresponding opercular pressures. For both large-mouthed predators, minimum buccal and opercular pressures were similar in magnitude and in timing. We developed the ram–suction index (RSI) to identify the relative contributions of ram feeding (i.e. predator movement) and of suction feeding (i.e. prey movement) to shortening the predator–prey distance during the strike. The RSI values for smallmouthed predators fell closer to the suction end of the ram–suction continuum than did strikes by the large-mouthed predators. The RSI provides a bench mark for evaluating the hydrodynamic consequences of intraspecific, interspecific and interprey variation in strike mechanics.
Re-Evaluation of the Stretch Sensitivity Hypothesis of Crustacean Hearts: Hypoxia, not Lack of Stretch, Causes Reduction in Heart Rate of Isolated Hearts
Authors: Wilkens J. L. 
Published: April 2021

ABSTRACT
Decapod crustacean hearts are suspended by a three-dimensional array of alary ligaments. These ligaments are stretched during systole; diastolic filling via the ostia occurs as the ventricle is stretched by ligamental elastic recoil. There is no direct venous return to the hearts in these animals. In the present study, an isolated heart preparation with intact ligaments, hereafter called in situ, was used to evaluate the effects of artificially induced stretch on heart rate. Strongly beating in situ neurogenic hearts of the crab Carcinus maenas responded to direct perfusion of the ventricle with oxygenated saline and the attendant augmentation of natural stretch with a small increase in heart rate (fH); however, fH was well maintained for up to 15min after eliminating stretch by cutting the alary ligaments. In contrast to crabs, high rates of artificial perfusion usually depressed fH in crayfish hearts. Crab heart rate falls during hypoxia and this is readily reversed by even low rates of perfusion with oxygenated saline. It is concluded that the gradual decline in fH of totally isolated in vitro hearts arises from the deepening intraventricular hypoxia experienced by the cardiac ganglion.
Total Ammonia Concentration and PH of Haemolymph, Pleon Fluid and Maxillary Urine in Porcellio Scaber Lattreille (Isopoda, Oniscidea): Relationships to Ambient Humidity and Water Vapour Uptake
Authors: Wright Jonathan C. , O’Donnell Michael J. 
Published: April 2021

ABSTRACT
Ammonia levels and pH were studied in body fluids of Porcellio scaber with special reference to ambient humidity and the timing of pleon fluid secretion and pleopodal ventilation. In high humidity (approximately 96.7%), concentrations of total ammonia (NH3+NH4+) in haemolymph display pronounced episodic changes, ranging from less than 1mmol l−1 to more than 50mmol l−1. Elevated concentrations (&gt;5mmol l−1) occur in discrete bouts lasting from 40min to more than 2h. Concomitant changes in total ammonia levels are seen in pleon fluid and maxillary urine. Overall, mean ammonia concentrations in pleon fluid, but not maxillary urine, are significantly higher than in the haemolymph, which may indicate active secretion of NH4+ in the pleon. Elevated ammonia concentrations are not observed in reduced ambient humidities (85% and 30%). Evidence supports a physiological coupling between pleon NH3 volatilization and active water vapour absorption. Pleon fluid and haemolymph pH values are similar, discounting a role of alkalization in NH3 volatilization. Published rates of ammonia excretion are compatible with intermittent volatilization from pleon fluid and with measured NH3 levels during elevations in ammonia concentration.
The Relationship Between Intracellular pH and Swimming Performance of Brown Trout Exposed to Neutral and Sublethal pH
Authors: Butler P. J. , Day N. 
Published: April 2021

ABSTRACT
Adult brown trout were acclimated for 2–4 weeks to artificial soft water ([Ca2+] 25 μmol l−1) at neutral pH and at summer (15°C) temperature. During this period they swam against a current of approximately 0.25 ms −1. They then had their dorsal aorta cannulated and were exposed to neutral or sublethal pH (4.5) for 4 days in still water.
After 4 days of exposure to sublethal pH, critical swimming speed (Ucrit) was 35% lower than that for fish at neutral pH. There were significant increases in arterial and in blood lactate concentrations at Ucrit compared with the values in resting fish at neutral pH and these led to significant reductions in plasma pH. There were no such changes in fish at sublethal pH. There were no significant changes in intracellular pH (pHi) of red blood cells at Ucrit, probably as a result of increases in the levels of plasma catecholamines. There were significant reductions in pHi of red and white muscle fibres at Ucrit. It is argued that these values were not as low in the white fibres as those seen in previous studies after fish have been chased to exhaustion and, therefore, that the fish in the present study were not completely exhausted, although they would no longer swim at a steady speed. As pHi of the red muscle was the same at Ucrit for fish at neutral and at sublethal pH, it is suggested that Ucrit (fatigue) coincides with a particular pHi of the red muscles and possible mechanisms are discussed.
Pectoralis Muscle Force and Power Output During Different Modes of Flight in Pigeons (Columba Livia)
Authors: Dial Kenneth P. , Biewener Andrew A. 
Published: April 2021

ABSTRACT
In vivo measurements of pectoralis muscle force during different modes of free flight (takeoff, level flapping, landing, vertical ascending and near vertical descending flight) were obtained using a strain gauge attached to the dorsal surface of the delto-pectoral crest (DPC) of the humerus in four trained pigeons (Columbalivia). In one bird, a rosette strain gauge was attached to the DPC to determine the principal axis of strain produced by tension of the pectoralis. Strain signals recorded during flight were calibrated to force based on in situ measurements of tetanic force and on direct tension applied to the muscle’s insertion at the DPC. Rosette strain recordings showed that at maximal force the orientation of tensile principal strain was −15° (proximo-anterior) to the perpendicular axis of the DPC (or +75° to the longitudinal axis of the humerus), ranging from +15 to −25° to the DPC axis during the downstroke. The consistency of tensile principal strain orientation in the DPC confirms the more general use of single-element strain gauges as being a reliable method for determining in vivo pectoralis force generation. Our strain recordings show that the pectoralis begins to develop force as it is being lengthened, during the final one-third of the upstroke, and attains maximum force output while shortening during the first one-third of the downstroke. Force is sustained throughout the entire downstroke, even after the onset of the upstroke for certain flight conditions. Mean peak forces developed by the pectoralis based on measurements from 40 wingbeats for each bird (160 total) were: 24.9±3.1N during takeoff, 19.7±2.0N during level flight (at speeds of about 6–9 ms−1 and a wingbeat frequency of 8.6±0.3Hz), 18.7±2.5N during landing, 23.7±2.7N during near-vertical descent, and 26.0±1.8N during vertical ascending flight. These forces are considerably lower than the maximum isometric force (67N, P0) of the muscle, ranging from 28% (landing) to 39% (vertical ascending) of P0. Based on estimates of muscle fiber length change determined from high-speed (200frames s−1) light ciné films taken of the animals, we calculate the mass-specific power output of the pigeon pectoralis to be 51 W kg−1 during level flight (approximately 8ms−1), and 119W kg−1 during takeoff from the ground. When the birds were harnessed with weighted backpacks (50% and 100% of body weight), the forces generated by the pectoralis did not significantly exceed those observed in unloaded birds executing vertical ascending flight. These data suggest that the range of force production by the pectoralis under these differing conditions is constrained by the force–velocity properties of the muscle operating at fairly rapid rates of shortening (4.4 fiberlengths s−1 during level flight and 6.7fiberlengths s−1 during takeoff).