bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the Reproductive System of the Snail Helix Aspersa Caused by Mucus From the Love Dart
Authors: Koene Joris M. , Chase Ronald
Published: April 2021

The function of the love dart in certain species of terrestrial snails is unknown. In Helix aspersa, the dart is a sharp calcareous structure that is used to pierce the partner’s skin during courtship. When expelled, the dart is covered with a thick mucus. The hypothesis tested here is that the mucus contains a biologically active substance. Extracts of the digitiform glands that produce this mucus were applied to parts of the reproductive system in vitro. The extracts triggered an initial reconfiguration of the copulatory canal that caused the bursa tract diverticulum to become more accessible to the spermatophore. The reconfiguration of the copulatory canal also closed off the tract leading to the bursa copulatrix, a sperm-digesting organ. A few minutes after the initial contraction, the peristaltic contractions in the diverticulum became significantly more frequent. This latter effect continued for at least 1 h, provided that the mucus extract remained in the saline bath. The minimum effective dosage was less than the 2.2 mg of mucus transferred with the dart.

Sperm competition is expected in Helix aspersa since multiple matings occur before eggs are laid. By influencing the female organs involved in the processing of foreign sperm, the dart shooter may increase the chance that his sperm will fertilise eggs.
Utilisation of Substrates During Tethered Flight with and without Lift Generation in the African Fruit Beetle Pachnoda Sinuata (Cetoniinae)
Authors: Auerswald Lutz , Schneider Peter , Gäde Gerd
Published: April 2021

We have investigated the pattern of metabolic changes during tethered flight with and without lift generation in the African fruit beetle Pachnoda sinuata.

Two distinct metabolic phases occur during lift-generating flight. The first phase is characterised by a high rate of oxygen consumption and a rapid change in proline and alanine levels in the haemolymph and flight muscles and in glycogen level in the flight muscles. Carbohydrates are released from the fat body into the haemolymph. These carbohydrates are oxidised during the second phase. Changes in proline and alanine levels in the haemolymph and flight muscles and in glycogen level in the flight muscles are minor during the second phase and the rate of oxygen consumption is reduced.

During lift-generating flight, metabolic changes are rapid. Proline concentrations in the haemolymph and flight muscles fall dramatically during the first 30 s of flight, while alanine concentrations rise concomitantly. While haemolymph concentrations of proline and alanine remain virtually unchanged thereafter, further changes in the levels of these amino acids occur in the flight muscles during 5 min of flight. The initial levels of the two amino acids in the flight muscles are re-established over 1 h of rest following a 5 min flight, while this process takes longer in the haemolymph. The concentration of haemolymph carbohydrates increases during the first 30 s of flight and declines thereafter during 5 min of flight. The pre-flight levels are restored after 1 h of subsequent rest. The stores of glycogen in the flight muscles are rapidly diminished during the first 10 s of flight and decrease at a lower rate during further flight lasting up to 5 min. A subsequent 1 h of rest is sufficient almost to restore pre-flight levels. Haemolymph lipid levels are slightly but significantly increased during 11 min of flight and after 1 h of subsequent rest.

During flight without lift production, the metabolic changes are considerably slower and beetles fly approximately seven times longer than during lift-generating flight.

Resting basalar (BM), dorso-ventral (DVM) and dorso-longitudinal (DLM) flight muscles show no differences in levels of proline, alanine and glycogen. After different periods of flight, during which lift and wing loading were minimised, the DVM was found to have the highest level of proline after 5 min of flight. Levels of alanine in the DVM were lower than in the DLM. There was no evidence to suggest that different flight muscles are specialised for either proline or carbohydrate utilisation.

Proline and carbohydrates participate equally in supplying energy to the flight muscles during lift-generating flight. The contribution to the energy supply by the flight muscles is 54 %, while that of the haemolymph is 46 %.
Nitrogen Recycling or Nitrogen Conservation in an Alga–Invertebrate Symbiosis?
Authors: Wang J.-T. , Douglas A. E.
Published: April 2021

When corals and allied animals are deprived of their symbiotic algae, the ammonium content in their tissues rises. This is commonly interpreted as evidence for nitrogen recycling (i.e. algal assimilation of animal waste ammonium into amino acids that are released back to the animal), but it can also be explained as nitrogen conservation by the animal (i.e. reduced net ammonium production in response to the receipt of algal photosynthetic carbon). This study discriminated between these interpretations in two ways. First, the increased ammonium concentration in the sea anemone Aiptasia pulchella, caused by darkness or depletion of the alga Symbiodinium, was partially or completely reversed by supplementing the medium with organic carbon compounds (e.g. α-ketoglutarate). Second, the activity of the ammonium-assimilating enzyme glutamine synthetase and the concentration of protein amino acids in the free amino acid pool of the animal, which were depressed by darkness and algal depletion, were restored by exogenous carbon compounds. It is concluded that organic carbon, whether derived from algal photosynthate or exogenously, promotes the animal’s capacity for ammonium assimilation and reduces ammonium production from amino acid degradation. These processes contribute to nitrogen conservation in the animal, but they confound the interpretation of various studies on nitrogen recycling by symbiotic algae.
Localizing transepithelial conductive pathways using a vibrating voltage probe
Authors: Somieski Petra , Nagel Wolfram
Published: April 2021

A model simulation of the electrical field distribution for the voltage-activated Cl− current across amphibian skin has been carried out for two potential pathways, i.e. transcellularly, through the mitochondria-rich cells (MRCs), or paracellularly, across the tight junctions (TJs) between the outermost living cell layer. The calculations are based on the mean density of MRCs and the typical dimensions of stratum granulosum cells of amphibian skin. It is demonstrated that current flow across MRCs would be detectable by scanning with the vibrating voltage probe in the extracellular space above the epithelium, whereas accurate representation of current flow through the TJs cannot be obtained using a probe of the present design. The experimental data indicate that field patterns corresponding to an MRC origin for the Cl− current are never observed. It is concluded that the voltage-activated Cl− conductance is localized to ion-selective structures in the paracellular pathway which may be regulated by the TJs.
The effects of walking on heart rate, ventilation rate and acid–base status in the lobster Homarus americanus
Authors: Rose R. A. , Wilkens J. L. , Walker R. L.
Published: April 2021

American lobsters Homarus americanus were exercised on an underwater treadmill at speeds from 1.7 to 8 m min−1 to determine the effects of exercise on heart rate, ventilation rate and acid–base status. Heart and ventilation rates showed almost instantaneous increases at the start of exercise, but the magnitude of the increase was not related to speed. Maximum heart rate was approximately 80–90 beats min−1 and maximum ventilation rate was 175–180 beats min−1 at all speeds tested.

Exercise at all speeds caused a decrease in haemolymph pH, with the acidosis after exercise at 8 m min−1 being significantly greater than at the other three speeds. Concomitant with this acidosis was a large increase in partial pressure of carbon dioxide, with the largest increase occurring after exercise at 8 m min−1. The concentration of lactate in the haemolymph increased to similar levels at all speeds of walking. Davenport analysis indicates that the acidosis was predominantly respiratory in nature.

Although it was anticipated that heart and ventilation rates would show increases proportional to the speed of exercise, this was not the case. Rather, the responses were fixed regardless of walking speed. The reason for this phenomenon remains unexplained.
Energetics of Bipedal Running: I. Metabolic Cost of Generating Force
Authors: Roberts Thomas J. , Kram Rodger , Weyand Peter G. , Taylor C. Richard
Published: April 2021

Similarly sized bipeds and quadrupeds use nearly the same amount of metabolic energy to run, despite dramatic differences in morphology and running mechanics. It has been shown that the rate of metabolic energy use in quadrupedal runners and bipedal hoppers can be predicted from just body weight and the time available to generate force as indicated by the duration of foot–ground contact. We tested whether this link between running mechanics and energetics also applies to running bipeds. We measured rates of energy consumption and times of foot contact for humans (mean body mass 78.88 kg) and five species of birds (mean body mass range 0.13–40.1 kg). We find that most (70–90 %) of the increase in metabolic rate with speed in running bipeds can be explained by changes in the time available to generate force. The rate of force generation also explains differences in metabolic rate over the size range of birds measured. However, for a given rate of force generation, birds use on average 1.7 times more metabolic energy than quadrupeds. The rate of energy consumption for a given rate of force generation for humans is intermediate between that of birds and quadrupeds. These results support the idea that the cost of muscular force production determines the energy cost of running and suggest that bipedal runners use more energy for a given rate of force production because they require a greater volume of muscle to support their body weight.
Differential Effects of Temperature on Specific and Nonspecific Immune Defences in Fish
Authors: Morvan Caroline Le , Troutaud Danielle , Deschaux Pierre
Published: April 2021

The susceptibility of fish to disease is partly dependent on their environment, in particular on water temperature. It is generally accepted that lower temperatures adversely affect specific immune responses mediated by T helper cells. The probable mechanisms involved in such suppression in teleost fish are reviewed. Furthermore, the effects of temperature on nonspecific defences, such as phagocytosis and cytotoxicity, are described and total immune competence in teleosts at low environmental temperatures is discussed.
Energized Ca2+ Transport by Hepatopancreatic Basolateral Plasma Membranes of Homarus Americanus
Authors: Zhuang Zhenpeng , Ahearn Gregory A.
Published: April 2021

Ca2+ transport by hepatopancreatic basolateral mem-brane vesicles of Atlantic lobster (Homarus americanus) occurred by at least two independent processes: (1) an ATP-dependent carrier transport system, and (2) a Na+-gradient-dependent carrier mechanism. The sensitivity of ATP-dependent Ca2+ transport to vanadate indicated that it was probably due to a P-type ATPase. This system exhibited an extremely high apparent affinity for Ca2+ (Kt=65.28±14.39 nmol l−1; Jmax=1.07±0.06 pmol µg−1 pro-tein 8 s−1). The Na+-gradient-dependent carrier transport system exhibited the properties of a Ca2+/Na+ antiporter capable of exchanging external Ca2+ with intravesicular Na+ or Li+. Kinetic analysis of the Na+-dependence of the antiport indicated that at least three Na+ were exchanged with each Ca2+ (n=2.91±0.22). When Li+ replaced Na+ in exchange for 45Ca2+, the apparent affinity for Ca2+ influx was not significantly affected (with Na+, Kt=14.57±5.02 µmol l−1; with Li+, Kt=20.17±6.99 µmol l−1), but the maximal Ca2+ transport velocity was reduced by a factor of three (with Na+, Jmax=2.72±0.23 pmol µg−1 pro-tein 8 s−1; with Li+, Jmax=1.03±0.10 pmol µg−1 protein 8 s−1). It is concluded that Ca2+ leaves hepatopancreatic epithelial cells across the basolateral membrane by way of a high-affinity, vanadate-sensitive Ca2+-ATPase and by way of a low-affinity Ca2+/Na+ antiporter with an apparent 3:1 exchange stoichiometry. The roles of these transporters in Ca2+ balance during the molt cycle are discussed.
Gas Exchange During Hovering Flight in a Nectar-Feeding Bat Glossophaga Soricina
Authors: Winter York , Voigt Christian , Helversen Otto Von
Published: April 2021

Glossophagine nectar-feeding bats exploit flowers while hovering in front of them. Aerodynamic theory predicts that power output for hovering flight in Glossophaga soricina is 2.6 times higher than during horizontal flight. We tested this prediction by measuring rates of gas exchange during hover-feeding. Five individuals of Glossophaga soricina (mean mass 11.7 g) were trained to feed from a nectar dispenser designed as a flow-through respirometry mask. Single hover-feeding events lasted for up to 4.5 s. Measured rates of gas exchange varied as a function of hovering duration. and during short hovering events (up to 1 s) were 20.5±6.7 ml g−1 h−1 (N=55) and 21.6±5.6 ml g−1 h−1 (N=39) (means ± S.D.), respectively. These values are in the range of a previous estimate of the metabolic power input for level forward flight (23.8 ml O2 g−1 h−1). However, during hovering events lasting longer than 3 s, oxygen uptake was only 16.7±3.5 ml g−1 h−1 (N=73), which is only 70 % of the value expected for forward flight. Thus, bats reduced their rate of oxygen uptake during longer periods of hovering compared with level forward flight. This result is in contrast to the predicted hovering cost derived from aerodynamic theory. The exact metabolic power input during hovering remains uncertain. During longer hovering events, bats were probably not in respiratory steady state, as indicated by the deviation of the respiratory exchange ratio from the expected value of 1 (oxidization of nectar sugar) to the measured value of 0.8.
Persistent Desensitisation of the β2 Adrenoceptors Expressed by Cultured Equine Sweat Gland Epithelial Cells
Authors: Rakhit Soma , Murdoch Ruth , Wilson Stuart M.
Published: April 2021

Adrenaline, forskolin and ATP all evoked accumulation of cyclic AMP in equine sweat gland epithelial cells, although the response to adrenaline was more transient than that to forskolin and ATP. Cells preincubated in adrenaline (10 µmol l−1, 32 min) showed essentially complete, homologous desensitisation, and this phenomenon reversed slowly (half-time 6.3±0.9 h). After 10 min of recovery from preincubation in adrenaline, isobutylmethylxanthine (IBMX, 5 mmol l−1) had no effect upon the desensitisation and the cells showed no loss of sensitivity to ATP and forskolin. After 10 h, however, the persistent desensitisation was partially reversed by IBMX and the cells showed reduced responses to ATP and forskolin. Increased phosphodiesterase activity may thus contribute to the persistent desensitisation. Experiments using forskolin-preincubated (100 µmol l−1, 32 min) cells suggested that increased cytosolic cyclic AMP levels did not underlie the initial loss of sensitivity to adrenaline but that this second messenger may initiate the series of events leading to the generalised loss of sensitivity seen after 10 h.
Cardiovascular Responses In Vivo to Angiotensin II and the Peptide Antagonist Saralasin in Rainbow Trout Oncorhynchus Mykiss
Authors: Fuentes Juan , Eddy F. Brian
Published: April 2021

The effects of [Asn1,Val5 ]-angiotensin II (AngII) and [Sar1,Val5,Ala8 ]-angiotensin II (saralasin) on dorsal aortic blood pressure, pulse pressure and heart rate were examined in rainbow trout in vivo. AngII when administered as a single dose of 25 µg kg−1 induced a biphasic response in blood pressure, with a significant hypertensive response during the initial 10 min, followed by a significant hypotension of 70–75% compared with the initial blood pressure after 50 min and continuing until approximately 80 min post-injection. The co-administration of AngII (25 µg kg−1 ) and saralasin (50 µg kg−1 ) resulted in the same hypertensive response during the initial phase, but abolished the hypotensive effect of AngII. Heart rate was significantly increased in response to AngII, but the administration of AngII and saralasin together attenuated the increase by approximately 44%. Stimulation of the endogenous renin–angiotensin system using a vasodilator, sodium nitroprusside, significantly increased drinking rate in rainbow trout fry, a response inhibited by saralasin, indicating a role for AngII-induced hypotension in drinking. For the first time, a decrease in blood pressure in response to AngII in vivo has been demonstrated in fish, and this is discussed in relation to homeostasis of blood pressure and a possible role in the control of drinking.
Effects Of Incline On Speed, Acceleration, Body Posture And Hindlimb Kinematics In Two Species Of Lizard Callisaurus Draconoides And Uma Scoparia
Authors: Irschick Duncan J. , Jayne Bruce C.
Published: April 2021

We examined the effects of incline on locomotor performance and kinematics in two closely related species of iguanian lizards that co-occur in sandy desert habitats. Callisaurus draconoides differs from Uma scoparia of equal snout–vent length by being less massive and having greater limb and tail lengths. We analyzed high-speed video tapes of lizards sprinting from a standstill on a sand-covered racetrack which was level or inclined 30° uphill. C. draconoides sprinted significantly faster than U. scoparia on both level and uphill sand surfaces, although U. scoparia is considered to be more specialized for sandy habitats. Initial accelerations (over the first 50 ms) did not differ significantly either between species or between inclines within species. Overall, the effects of incline were more pronounced for C. draconoides than for U. scoparia. For example, the incline caused a significant decrease in the maximum stride length of C. draconoides but not in that of U. scoparia. For C. draconoides, uphill stride durations were significantly shorter than on the level surface, and this partially compensated for the effects of shorter uphill stride lengths on velocity. C. draconoides ran bipedally more often than did U. scoparia on both the level and uphill surfaces.
Evolutionary Link Between Prokaryotic and Eukaryotic K+ Channels
Authors: Derst Christian , Karschin Andreas
Published: April 2021

Considering the importance of K+ channels in controlling the crucial K+ gradient across the plasma membranes of all living cells, it comes as no surprise that, besides being present in every eukaryotic cell, these integral membrane proteins have recently also been identified in prokaryotes. Today, approximately a dozen successfully completed and many more ongoing sequencing projects permit a search for genes related to K+ channels in the genomes of both eubacteria and archaea. The coding regions of homologues show a remarkable variety in primary structure. They predict membrane proteins with one, two, three and six hydrophobic segments surrounding a putative K+-selective pore (H5) and the presence or absence of a cytosolic putative NAD+-binding domain (PNBD) that probably senses the reducing power of the cell. The analysis of kinships on the basis of phylogenetic algorithms identifies sequences closely related to eukaryotic voltage-dependent Kv channels, but also defines members of a primordial class of prokaryotic K+ channel (containing the 2TMS/PNBD motif). Considering the unique mechanisms that may account for the assembly of modern proteins from different ancestral genes, and with more primary sequence data soon to appear, a scheme for the evolutionary origin of K+ channels comes within reach.
Molecular Cloning and Developmental Expression Patterns of the Myod and Mef2 Families of Muscle Transcription Factors in the Carp
Authors: Kobiyama Atsushi , Nihei Yoshiaki , Hirayama Yasushi , Kikuchi Kiyoshi , Suetake Hiroaki , Johnston Ian A. , Watabe Shugo
Published: April 2021

cDNA clones encoding the myogenic regulatory factors (MRFs) myogenin, MyoD and myf-5 were isolated by reverse-transcription polymerase chain reaction from larvae and embryos of the common carp (Cyprinus carpio L.). Myocyte-specific enhancer factor 2 (MEF2) cDNAs were identified from a cDNA library from adult carp. Northern blot analysis showed that MyoD, myf-5 and MEF2C transcripts were present in three-somite embryos, whereas myogenin and MEF2A transcripts were not detected until the 15-somite stage. Intense signals of myogenin and MyoD transcripts were observed even in 1-month-old juveniles. Levels of MyoD, myogenin and MEF2A transcripts declined between 1 and 7 months after hatching, and myf-5 gave only a weak signal in the oldest fish. In contrast, levels of MEF2C transcripts were considerably higher in 7-month-old juveniles than in 1-month-old larvae. mRNAs encoding carp myosin heavy chain and α-actin were first detected at approximately the time of the first heartbeat, and levels were maximal in juveniles 1 month post-hatching. The relatively high levels of MRF mRNA in juvenile fish probably reflect the recruitment of new muscle fibres from the satellite cell population. It was concluded that the relative importance of the different members of the MyoD and MEF2 families of transcription factors for muscle differentiation changes during ontogeny in the carp.
Migrating young pied flycatchers Ficedula hypoleuca do not compensate for geographical displacements
Authors: Mouritsen Henrik , Næsbye Larsen Ole
Published: April 2021

The present study tested whether young Scandinavian pied flycatchers, Ficedula hypoleuca, would direct their orientation back towards their southwest-directed migratory route in autumn if displaced by the maximal biologically realistic distance due south or due west. The aim was to clarify the nature of their inherited spatiotemporal orientation programme. Forty-eight young pied flycatchers were caught and tested at Christiansø, Denmark. They were then divided into three groups of equal size and orientation, of which one group was displaced due south and another due west, while the third remained as a control at Christiansø. Three different experimenters then simultaneously tested their orientation. The birds oriented in the same direction at all localities, showing no signs of compensatory orientation. This result suggests that young pied flycatchers on their first autumn migration use a simple clock-and-compass strategy to reach their wintering area. If this suggestion holds, then all the prerequisites (a compass and an internal clock) for orientation during the autumn migration seem to be known at present, at least at the behavioural level. In addition, the present study provides further evidence supporting the assumption that observations in an orientation funnel reflect the orientation of actual migration.
Evolution of Osmotic Stress Signaling Via Map Kinase Cascades
Authors: Kültz Dietmar , Burg Maurice
Published: April 2021

Cells respond to changes in osmotic pressure with compensatory molecular adaptations that allow them to re-establish homeostasis of osmotically disturbed aspects of cell structure and function. In addition, some cell types respond to osmotic stress by changing their phenotype or, if their tolerance threshold is exceeded, by initiating programmed cell death. To understand how cells achieve these different types of adaptive response to osmotic stress, it is necessary to identify the key elements of osmosensory signal transduction and to analyze the complex networks that process osmotic stimuli imposed upon cells by their environment. This review highlights mitogen-activated protein kinase (MAPK) cascades as important intracellular signal-transduction pathways activated in response to changes in osmolality. A unifying theme of osmotic stress signaling via MAPKs seems to be regulation of the cell cycle as part of the cellular stress response. This very important physiological capacity may have been conserved throughout evolution as a major function of MAPKs from many different subfamilies. The evidence for this conjecture is discussed, and our current knowledge about osmotic stress signaling pathways in yeast, animals and plants is briefly reviewed.
Ambient Temperature Does not Affect the Tactile Sensitivity of Mystacial Vibrissae in Harbour Seals
Authors: Dehnhardt G. , Mauck B. , Hyvärinen H.
Published: April 2021

Vibrissae provide pinnipeds with tactile information primarily in the aquatic environment, which is characterized by its high thermal conductivity and large potential cooling power. Since studies of thermal effects on human tactile sensitivity have revealed that cooling below normal skin temperature impairs sensitivity, the present study investigates the tactile sensitivity of the vibrissal system of harbour seals at varying ambient temperatures. Using plates bearing gratings of alternating grooves and ridges, the texture difference thresholds of two adult seals were determined under water. We took advantage of the natural difference in ambient temperature between summer and winter. Mean water temperature was 1.2 °C during the winter and 22 °C during the summer. During the cold season, the thermal status of both seals was examined using an infrared-sensitive camera system. The texture difference threshold of both seals remained the same (0.18 mm groove width difference) under both test conditions. The thermographic examination revealed that the skin areas of the head where the mystacial and supraorbital vibrissae are located show a substantially higher degree of thermal emission than do adjacent skin areas. This suggests that, in the vibrissal follicles of harbour seals, no vasoconstriction occurs during cold acclimation, so that the appropriate operating temperature for the mechanoreceptors is maintained.
In vivo strains in pigeon flight feather shafts: implications for structural design
Authors: Corning WR , Biewener AA
Published: April 2021

To evaluate the safety factor for flight feather shafts, in vivo strains were recorded during free flight from the dorsal surface of a variety of flight feathers of captive pigeons (Columba livia) using metal foil strain gauges. Strains recorded while the birds flew at a slow speed (approximately 5-6 m s-1) were used to calculate functional stresses on the basis of published values for the elastic modulus of feather keratin. These stresses were then compared with measurements of the failure stress obtained from four-point bending tests of whole sections of the rachis at a similar location. Recorded strains followed an oscillatory pattern, changing from tensile strain during the upstroke to compressive strain during the downstroke. Peak compressive strains were 2.2+/-0. 9 times (mean +/- s.d.) greater than peak tensile strains. Tensile strain peaks were generally not as large in more proximal flight feathers. Maximal compressive strains averaged -0.0033+/-0.0012 and occurred late in the downstroke. Bending tests demonstrated that feather shafts are most likely to fail through local buckling of their compact keratin cortex. A comparison of the mean (8.3 MPa) and maximum (15.7 MPa) peak stresses calculated from the in vivo strain recordings with the mean failure stress measured in four-point bending (137 MPa) yields a safety factor of between 9 and 17. Under more strenuous flight conditions, feather stresses are estimated to be 1.4-fold higher, reducing their safety factor to the range 6-12. These values seem high, considering that the safety factor of the humerus of pigeons has been estimated to be between 1.9 and 3.5. Several hypotheses explaining this difference in safety factor are considered, but the most reasonable explanation appears to be that flexural stiffness is more critical than strength to feather shaft performance.
Analysis of Fluid Dynamics in Perfused Glomeruli of the Hagfish Eptatretus Stouti (Lockington)
Authors: Riegel J. A.
Published: April 2021

The capillary tuft of glomeruli of the hagfish mesonephros contains both ‘low’-pressure and ‘high’-pressure glomerular vessels (LPGVs and HPGVs). The existence of the HPGV raised the possibility that pressure filtration could occur in the hagfish kidney when the blood pressure was sufficiently high. Therefore, measurements of glomerular capillary pressure were made in HPGVs and LPGVs whilst single glomeruli were perfused with hagfish Ringer’s solution that contained the colloid Ficoll 70. Calculations of the effective colloid osmotic pressure in perfused capillaries were made; these showed that hydrostatic pressures within the HPGV were inadequate to effect pressure filtration except at high rates of perfusion. However, high rates of perfusion provoked perfusion pressures that exceeded the highest values measured in the renal blood supply of lightly anaesthetised hagfish. It was concluded that some process other than pressure filtration must account for formation of the primary urine by hagfish glomeruli.

The proportion of the perfusate that became urine, the single glomerulus filtration fraction (SGFF), bore a strong positive relationship to the vascular resistance of perfused glomeruli. Both the SGFF and the vascular resistance were inversely related to the rate of perfusion except when that rate was very high. From these two observations it was concluded that at least two flow pathways exist in hagfish glomeruli: one that has a high vascular resistance and that contributes to the elaboration of the urine, and one that has a low vascular resistance and does not contribute to urine formation. The possible anatomical location of the various flow pathways through hagfish glomeruli and how they may function are discussed.
Feeding mechanism of the atlantic guitarfish rhinobatos lentiginosus: modulation of kinematic and motor activity
Authors: Wilga Cheryl D. , Motta Philip J.
Published: April 2021

The kinematics and muscle activity pattern of the head and jaws during feeding in the Atlantic guitarfish Rhinobatos lentiginosus are described and quantified using high-speed video and electromyography to test hypotheses regarding the conservation and modulation of the feeding mechanism. Prey is captured by the guitarfish using suction. Suction capture, bite manipulation and suction transport behaviors in the guitarfish are similar to one another in the relative sequence of kinematic and motor activity, but can be distinguished from one another by variation in absolute muscle activation time, in the presence or absence of muscle activity and in the duration of muscle activity. A novel compression transport behavior was observed that is strikingly different from the other feeding behaviors and has not been described previously in elasmobranchs. The mechanism of upper jaw protrusion in the guitarfish differs from that described in other elasmobranchs. Muscle function and motor pattern during feeding are similar in the plesiomorphic cranial muscles in the guitarfish and the spiny dogfish probably because of their shared ancestral morphology. Modulation in recruitment of jaw and hyoid depressor muscles among feeding behaviors in the guitarfish may be a consequence of duplication of muscles and decoupling of the jaws and hyoid apparatus in batoids.
Neuromuscular control of anguilliform locomotion: patterns of red and white muscle activity during swimming in the american eel anguilla rostrata
Authors: Gillis Gary B.
Published: April 2021

Two areas that have received substantial attention in investigations of muscle activity during fish swimming are (1) patterns of fiber type recruitment with swimming speed and (2) the timing of muscle activation in relation to muscle strain. Currently, very little is known about either of these areas in eels, which represent an extreme body form among fishes and utilize a mode of locomotion found at one end of the undulatory spectrum (anguilliform locomotion). To assess how this swimming mode and body form influence the neuromuscular control of swimming, I recorded electromyographic data from red and white muscle at four positions, 0.3L, 0.45L, 0.6L and 0.75L, where L is body length, in eels (Anguilla rostrata) simultaneously video- taped (250 fields s−1 ) swimming at three speeds, 0.5, 0.75 and 1.0 L s−1. As in other fish, exclusively red muscle is used at slow swimming speeds and white muscle is additionally recruited at higher swimming speeds. However, this study also revealed a novel posterior-to-anterior pattern of muscle recruitment with increasing swimming speed. At slow speeds, anteriorly located muscles are never active, muscle strain is negligible and forward thrust must be generated by posterior muscles. As speed increases, more anterior muscles are additionally recruited. Electromyogram (EMG) burst durations typically occupy between 0.2 and 0.3 undulatory cycles, irrespective of speed or position. EMG burst intensity increases significantly with swimming speed. The onset of EMG activity typically occurred near the end of muscle lengthening, whereas the offset of EMG activity occurred during shortening (typically before the muscle’s return to resting length). There was a significant shift in red muscle onset times such that anterior muscles were typically active later in their strain cycle than posterior muscles. When red muscle activity patterns across various fish taxa are compared, differences in propulsive wavelength among species are related to differences in muscle activity, providing insight into the underlying neuromuscular bases of differences among undulatory swimming modes.
Transport and metabolism of glucose in isolated enterocytes of the black bullhead ictalurus melas: effects of diet and hormones
Authors: Soengas José L. , Moon Thomas W.
Published: April 2021

The uptake and metabolism of glucose were assessed in enterocytes isolated from black bullhead Ictalurus melas. The objective of this study was to examine the effects of diet and hormone treatment on glucose transport and metabolism, so the enterocyte was the most appropriate preparation. Glucose transport was estimated using specific inhibitors: glucose uptake measured in the presence of phlorizin presumably represents transport at the basolateral membrane, whereas glucose uptake in the presence of cytochalasin B presumably represents transport at the brush border. Feeding bullheads a standard diet resulted in maximum enterocyte rates of glucose uptake of 438.2±35.5 nmol mg−1 cells h−1 for transport in the presence of cytochalasin B and 427.0±49.7 nmol mg−1 cells h−1 (means ± S.E.M., N=12) for transport in the presence of phlorizin. These values represent 50 % of the total 3-O-methylglucose transported. The rate of transport in the presence of cytochalasin B was increased in bullheads fed a high-carbohydrate diet. Incubating bullhead enterocytes with glucagon or glucagon-like peptide-1 (GLP) at 10−8 mol l−1 and with dexamethasone or isoproterenol at 10−6 mol l−1 significantly increased the rate of brush-border transport, but not the apparent affinity constant (Kt). Activation was dependent on hormone concentration. In contrast, insulin was without effect on transport rates, nor did it counteract activation by glucagon-family peptides. CO2 production rates from D- [14 C]glucose indicated that glucose metabolism was not limited by transport rates in the enterocytes. Glucagon and GLP decreased maximal oxidation rates, whereas dexamethasone, isoproterenol and insulin did not alter these rates. The activities of enterocyte hexokinase exceeded the rate of glucose oxidation but not the rate of transport of glucose, at least at maximum activities, implicating this enzyme as one component of the strategy to ensure that glucose is maximally available to the blood of this species.
CHANGES IN H+-TRANSLOCATING VACUOLAR-TYPE ATPase IN THE ANTERIOR SILK GLAND CELL OF BOMBYX MORI DURING METAMORPHOSIS
Authors: Azuma Masaaki , Ohta Yasuhiko
Published: April 2021

A proton-translocating vacuolar-type ATPase (V-ATPase) was identified and characterized in the anterior silk gland of Bombyx mori. By incubating the intact tissue with the fluorescent dye Acridine Orange, the acidified compartment was detected at the apical pole of the epithelial cells. This was observed throughout the feeding period of the fifth-instar larva until the onset of spinning. Acidification was prevented completely and reversibly by 0.8 μmol l−1 bafilomycin A1, a specific inhibitor of V-ATPase. The presence of V-ATPase in a microsomal fraction was verified by immunoblots using an antiserum to the V-ATPase holoenzyme from Manduca sexta midgut. The antiserum localized the V-ATPase to the apical plasma membrane of the anterior silk gland cells, suggesting that the enzyme is functionally active in pumping protons out of the cell towards the glandular lumen of feeding silkworm larvae. In spinning larvae, the acidification produced by the V-ATPase appears to cease, because acidic compartments were seen rarely and only in the periphery of basal cytoplasm, and because immunocytochemical staining for the V-ATPase was greatly reduced at the apical surface. The metamorphic changes in relation to the occurrence of V-ATPase corresponded well with the ultrastructural changes in the anterior silk gland cell of Bombyx mori larvae.
Gating of Sensory Responses of Descending Brain Neurones During Walking in Crickets
Authors: Staudacher Erich , Schildberger Klaus
Published: April 2021

Single descending brain neurones were recorded and stained intracellularly in the neck connectives of crickets while they walked upon a styrofoam ball under open-loop conditions. The animal’s translational and rotational velocities were measured simultaneously, and various stimuli were used to investigate the neuronal response characteristics. Stimulation with a moving grating or an artificial calling song of 5 kHz induced optomotor behaviour and positive phonotaxis. An acoustic stimulus of 20 kHz elicited negative phonotaxis.

We report the first clear evidence for behaviourally dependent gating of sensory responses of identified descending brain neurones. Most descending cells only responded to visual stimuli or to an artificial calling song of 5 kHz while the animal was walking, indicating that the responses to these stimuli were gated by the walking activity of the animal. In contrast to this, responses to stimuli that elicit negative phonotaxis, such as acoustic stimuli of 20 kHz, were not gated. This indicates that the gating of sensory responses in these cells depends on the behavioural context of the stimulus.

From these findings, we conclude that significant information about the properties of sensory processing in higher-order neurones can only be gained from tests in behaviourally relevant paradigms. Important characteristics might otherwise be missed, thus leading to misinterpretations regarding their function.
Effects Of Speed on the Hindlimb Kinematics of the Lizard Dipsosaurus Dorsalis
Authors: Fieler Carrie L. , Jayne Bruce C.
Published: April 2021

Lizards are the most diverse extant lineage of vertebrates believed to have retained the sprawling limb posture of ancestral tetrapods and, although the sprinting speeds of lizards are well documented, quantitative analyses of limb movements are lacking. We therefore examined a wide range of steady running speeds to quantify variation in the kinematics of a morphologically generalized hindlimb in the lizard Dipsosaurus dorsalis. From speeds of 50 to 350cm s−1, stride length, step length and stride frequency all had significant curvilinear increases from 13.3 to 39.4cm, from 8.9 to 12.8cm and from 3.9 to 8.6Hz, respectively, whereas duty factor (percentage of cycle when foot is on ground) decreased from 63 to 34% with increased speed. For five standardized speeds ranging from 50 to 250cm s−1, analyses of variance detected highly significant (P<0.001) effects of speed on 27 out of a total of 46 kinematic variables. The height of the hip at the time of footfall increased significantly with increased speed, whereas the amount of pelvic rotation in the horizontal plane (mean 36°) per stride was unaffected by speed. The orientation of the long axis of the foot changed by nearly 50° with increased speed such that the foot was nearly straight forward at 250cm s−1, and at high speeds the heel often did not touch the ground. The effective length of the limb at footfall nearly doubled with increased speed as a combined result of increased plantar flexion and knee extension and a more erect femur. The pervasive effects of speed on hindlimb kinematics observed for this species do not conform simply with previous generalizations of lizards as having plantigrade foot posture and sprawling limbs.
Blood Volume, Plasma Volume and Circulation Time in a High-Energy-Demand Teleost, the Yellowfin Tuna (Thunnus Albacares)
Authors: Brill Richard W. , Cousins Katherine L. , Jones David R. , Bushnell Peter G. , Steffensen John F.
Published: April 2021

We measured red cell space with 51Cr-labeled red blood cells, and dextran space with 500 kDa fluorescein-isothiocyanate-labeled dextran (FITC-dextran), in two groups of yellowfin tuna (Thunnus albacares). Red cell space was 13.8±0.7 ml kg−1 (mean ± S.E.M.) Assuming a whole-body hematocrit equal to the hematocrit measured at the ventral aortic sampling site and no significant sequestering of 51Cr-labeled red blood cells by the spleen, blood volume was 46.7±2.2 ml kg−1. This is within the range reported for most other teleosts (30–70 ml kg−1), but well below that previously reported for albacore (Thunnus alalunga, 82–197 ml kg−1). Plasma volume within the primary circulatory system (calculated from the 51Cr-labeled red blood cell data) was 32.9±2.3 ml kg−1. Dextran space was 37.0±3.7 ml kg−1. Because 500 kDa FITC-dextran appeared to remain within the vascular space, these data imply that the volume of the secondary circulatory system of yellowfin tuna is small, and its exact volume is not measurable by our methods. Although blood volume is not exceptional, circulation time (blood volume/cardiac output) is clearly shorter in yellowfin tuna than in other active teleosts. In a 1 kg yellowfin tuna, circulation time is approximately 0.4 min (47 ml kg−1/115 ml min−1 kg−1) compared with 1.3 min (46 ml kg−1/35 ml min−1 kg−1) in yellowtail (Seriola quinqueradiata) and 1.9 min (35 ml kg−1/18 ml min−1 kg−1) in rainbow trout (Oncorhynchus mykiss). In air-breathing vertebrates, high metabolic rates are necessarily correlated with short circulation times. Our data are the first to imply that a similar relationship occurs in fishes.
Mechanics of Lung Ventilation in a Large Aquatic Salamander, Siren Lacertina
Authors: Brainerd Elizabeth L. , Monroy Jenna A.
Published: April 2021

Lung ventilation in Siren lacertina was studied using X-ray video, measurements of body cavity pressure and electromyography of hypaxial muscles. S. lacertina utilizes a two-stroke buccal pump in which mixing of expired and inspired gas is minimized by partial expansion of the buccal cavity during exhalation and then full expansion after exhalation is complete. Mixing is further reduced by the use of one or two accessory inspirations after the first, mixed-gas cycle. Exhalation occurs in two phases: a passive phase in which hydrostatic pressure and possibly lung elasticity force air out of the lungs, and an active phase in which contraction of the transverse abdominis (TA) muscle increases body cavity pressure and forces most of the remaining air out. In electromyograms of the lateral hypaxial musculature, the TA became active 200–400 ms before the rise in body cavity pressure, and activity ceased at peak pressure. The TA was not active during inspiration, and no consistent activity during breathing was noted in the external oblique, internal oblique and rectus abdominis muscles. The finding that the TA is the primary expiratory muscle in S. lacertina agrees with findings in a previous study of another salamander, Necturus maculosus. Together, these results indicate that the use of the TA for exhalation is a primitive character for salamanders and support the hypothesis that the breathing mechanism of salamanders represents an intermediate step in evolution between a buccal pump, in which only head muscles are used for ventilation, and an aspiration pump, in which axial muscles are used for both exhalation and inhalation.
Chloride Transport in Red Blood Cells of Lamprey Lampetra Fluviatilis: Evidence for a Novel Anion-Exchange System
Authors: Bogdanova Anna Yu. , Sherstobitov Alexander O. , Gusev Gennadii P.
Published: April 2021

The existence of a furosemide-sensitive Cl− transport pathway activated by external Ca2+ and Mg2+ has been demonstrated previously in studies of Cl− influx across the lamprey erythrocyte membrane. The aim of the present study was to characterize further specific Cl− transport pathways, especially those involved in Cl− efflux, in the red blood cell membrane of Lampetra fluviatilis. Cl− efflux was inhibited by 0.05 mmol l−1 dihydroindenyloxyalkanoic acid (DIOA) (81 %), 1 mmol l−1 furosemide (76 %) and 0.1 mmol l−1 niflumic acid (54 %). Bumetanide (100 μmol l−1) and DIDS (100 μmol l−1) had no effect effect on Cl− efflux. Substitution of external Cl− by gluconate, but not by NO3−, led to a gradual decline of Cl− efflux. In addition, the removal of external Ca2+ resulted in a significant reduction in the rate of Cl− efflux. Membrane depolarization caused by increasing external K+ concentration or by inhibiting K+ channels with 1 mmol l−1 Ba2+ did not affect Cl− efflux. The furosemide-sensitive component of Cl− influx was a saturable function of external [Cl−] with an apparent Km of approximately 92 mmol l−1 and Vmax of approximately 17.8 mmol l−1 cells−1 h−1. Furosemide did not affect intracellular Cl− concentration (57.6±5.2 mmol l−1 cell water), measured using an ion-selective Cl− electrode, showing that a furosemide-sensitive pathway is not involved in net Cl− movement. A gradual fall (from 28.1±1.4 to 15.0±1.3 mmol l−1 cells−1 h−1) in unidirectional Cl− influx with time was observed within 3 h of cell preincubation in the standard physiological medium. These data provide evidence for the existence for an electroneutral furosemide-sensitive anion-exchange pathway in the lamprey erythrocyte membrane that accepts chloride and nitrate, but not bicarbonate or bromide.