bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Low-Turbulence Wind Tunnel for Bird Flight Experiments at Lund University, Sweden
Authors: Pennycuick C. J. , Alerstam Thomas , Hedenström Anders 
Published: April 2021

ABSTRACT
A new wind tunnel for experiments on bird flight was completed at Lund University, Sweden, in September 1994. It is a closed-circuit design, with a settling section containing five screens and a contraction ratio of 12.25. The test section is octagonal, 1.20 m wide by 1.08 m high. The first 1.2 m of its length is enclosed by acrylic walls, and the last 0.5 m is open, giving unrestricted access. Experiments can be carried out in both the open and closed parts, and comparison between them can potentially be used to measure the lift effect correction. The fan is driven by an a.c. motor with a variable-frequency power supply, allowing the wind speed to be varied continuously from 0 to 38 m s−1. The whole machine can be tilted to give up to 8 ° descent and 6 ° climb. A pitot-static survey in the test section showed that the air speed was within ±1.3 % of the mean at 116 out of 119 sample points, exceeding this deviation at only three points at the edges. A hot-wire anemometer survey showed that the turbulence level in the closed part of the test section was below 0.04 % of the wind speed throughout most of the closed part of the test section, rising to approximately 0.06 % in the middle of the open part. No residual rotation from the fan could be detected in the test section. No decrease in wind speed was detectable beyond 3 cm from the side walls of the closed part, and turbulence was minimal beyond 10 cm from the walls. The installation of a safety net at the entrance to the test section increased the turbulence level by a factor of at least 30, to 1.2 % longitudinally and 1.0 % transversely.
Na+ and Ca2+ Homeostatic Mechanisms in Isolated Chloride Cells of the Teleost Oreochromis Mossambicus Analysed by Confocal Laser Scanning Microscopy
Authors: Li Jie , Eygensteyn Jelle , Lock Robert A. C. , Wendelaar Bonga Sjoerd E. , Flik Gert 
Published: April 2021

ABSTRACT
Chloride cells (CCs; recognised by the vital mitochondrial stain DASPEI) and pavement cells (PCs) isolated from tilapia opercular epithelium were adhered to Cell-Tak-coated glass coverslips and loaded with fluorescent probes for the measurement of intracellular concentrations of Na+ or Ca2+. Basal levels of cytosolic Na+ and Ca2+ ranged from 6.4 to 16.5 mmol l−1 and from 76 to 110 nmol l−1, respectively, and did not differ between CCs and PCs. In CCs, inhibition of Na+/K+-ATPase by ouabain or Cu2+ increased intracellular [Na+]. Replacing extracellular Na+ with N-methyl-D-glucamine+ led to a rise in cytosolic [Ca2+] that was dependent on the extracellular [Ca2+], indicating that a Na+/Ca2+ exchanger was operating in reverse mode (importing Ca2+). The forward mode of this exchanger could be demonstrated by inhibition with bepridil. The CC has various pathways for passive Na+ influx: a tetrodotoxin-sensitive pathway, an amiloride-sensitive pathway and other as yet unidentified pathways.
Labriform Propulsion in Fishes: Kinematics of Flapping Aquatic Flight in the Bird Wrasse Gomphosus Varius (Labridae)
Authors: Walker Jeffrey A. , Westneat Mark W. 
Published: April 2021

ABSTRACT
Labriform, or pectoral fin, propulsion is the primary swimming mode for many fishes, even at high relative speeds. Although kinematic data are critical for evaluating hydrodynamic models of propulsion, these data are largely lacking for labriform swimmers, especially for species that employ an exclusively labriform mode across a broad range of speeds. We present data on pectoral fin locomotion in Gomphosus varius (Labridae), a tropical coral reef fish that uses a lift-based mechanism to fly under water at sustained speeds of 1–6 total body lengths s−1 (TL s−1). Lateral- and dorsal-view video images of three fish swimming in a flow tank at 1–4 TL s−1 were recorded at 60 Hz. From the two views, we reconstructed the three-dimensional motion of the center of mass, the fin tip and two fin chords for multiple fin beats of each fish at each of four speeds. In G. varius, the fin oscillates largely up and down: the stroke plane is tilted by approximately 20 ° from the vertical. Both frequency and the area swept by the pectoral fins increase with swimming speed. Interestingly, there are individual differences in how this area increases. Relative to the fish, the fin tip in lateral view moves along the path of a thin, inclined figure-of-eight. Relative to a stationary observer, the fin tip traces a sawtooth pattern, but the teeth are recumbent (indicating net backwards movement) only at the slowest speeds. Distal fin chords pitch nose downward during the downstroke and nose upward during the upstroke. Hydrodynamic angles of attack are largely positive during the downstroke and negative during the upstroke. The geometry of the fin and incident flow suggests that the fin is generating lift with large upward and small forward components during the downstroke. The negative incident angles during the upstroke suggest that the fin is generating largely thrust during the upstroke. In general, the large thrust is combined with a downward force during the upstroke, but the net backwards motion of the fin at slow speeds generates a small upward component during slow swimming. Both the alternating sign of the hydrodynamic angle of attack and the observed reduced frequencies suggest that unsteady effects are important in G. varius aquatic flight, especially at low speeds. This study provides a framework for the comparison of aquatic flight by fishes with aerial flight by birds, bats and insects.
The Contractile Vacuole Fluid Discharge Rate is Determined by the Vacuole Size Immediately Before the Start of Discharge in Paramecium Multimicronucleatum
Authors: Naitoh Yutaka , Tominaga Takashi , Allen Richard D. 
Published: April 2021

ABSTRACT
The precise relationship between the rate of contractile vacuole fluid discharge and the vacuole diameter at the start of systole was determined in cells of Paramecium multimicronucleatum subjected to various external conditions. The rate of discharge was higher when the diameter was larger. When the rate of discharge was plotted against the diameter, the points fell around a single parabolic line passing through the origin and were independent of the external conditions employed. This implies that the rate of discharge is proportional to the square of the vacuole diameter. We have previously proposed a hypothesis in which membrane tension in the contractile vacuole is altered as its planar membrane becomes tubular or as tubules become planar membrane (termed the membrane area-proportional tension hypothesis). We propose here that it is this change in membrane tension which determines the vacuole pore shape and sets the subsequent rate of fluid discharge.
Evidence for a Persistent Na+ Conductance In Neurons of the Gastric Mill Rhythm Generator of Spiny Lobsters
Authors: Elson Robert C. , Selverston Allen I. 
Published: April 2021

ABSTRACT
Evidence for a persistent Na+ conductance was obtained in identified motor neurons of the gastric mill network in the stomatogastric ganglion of the spiny lobster Panulirus interruptus. The cells studied were the lateral gastric and lateral posterior gastric motor neurons, which in vivo control chewing movements of the lateral teeth of the gastric mill. We examined basic cellular properties in the quiescent network of the isolated stomatogastric ganglion. In current-clamp recordings, we found two types of evidence for a persistent Na+ conductance. First, tetrodotoxin-sensitive inward rectification occurred during depolarization from rest to spike threshold. Second, 5 mmol l−1 tetraethylammonium (a K+ channel blocker) induced plateau potentials that persisted in the presence of Mn2+ or a low [Ca2+]o but were blocked by a low [Na+]o or 100 nmol l−1 tetrodotoxin. The plateau potentials could drive trains of fast spikes in the motor axon and strong transmitter release at central output synapses within the ganglion.
This conductance probably corresponds to the persistent Na+ current, INaP, described in cultured stomatogastric neurons and in neurons from several other preparations. During normal neuronal activity, it may contribute to the prolonged plateau depolarizations and long spike trains typical of motor neuronal activity during gastric rhythm generation. Persistent inward currents of this type are likely to be important in neurons that must fire prolonged bursts in cycle after cycle of rhythmical activity.
Temporal Resolution of General Odor Pulses by Olfactory Sensory Neurons in American Cockroaches
Authors: Lemon William C. , Getz Wayne M. 
Published: April 2021

ABSTRACT
Behavioral and physiological evidence indicates that insect pheromone sensory neurons are able to resolve pulses of pheromone concentration as they occur downwind from a point source, but the abilities of insect sensory neurons that are sensitive to general odors to respond to pulsatile stimuli are unknown. The temporal response characteristics of olfactory sensory neurons of female American cockroaches Periplaneta americana in response to general odors were measured using a series of short odor pulses (20–400 ms). Odor pulses were delivered to olfactory sensilla in a moving airstream controlled by electromagnetic valves. The responses of sensory neurons were recorded using a tungsten electrode placed at the base of the sensillum. The temporal responses of sensory neurons followed the temporal changes in stimulus concentration, which were estimated by replacing the odorant with oil smoke and measuring the concentration of smoke passing through a light beam. Spike frequency varied with odorant concentration with surprisingly fine temporal resolution. Cockroach olfactory sensory neurons were able reliably to follow 25 ms pulses of the pure odorant 1-hexanol and 50 ms pulses of the complex odor blend coconut oil. Lower concentrations of odorants elicited responses with lower peak spike frequencies that still retained the temporal resolution of the stimulus pulses. Thus, responses of olfactory sensory neurons can reflect the fine structures of non-uniform distributions of general odorants in a turbulent odor plume as well as the average odorant concentration.
Role of Serotonin In Fish Immunomodulation
Authors: Khan Naim A. , Deschaux Pierre 
Published: April 2021

ABSTRACT
In the recent past, the importance of the fish brain monoaminergic system in aggression, mating and feeding has been documented. There are several apparent similarities between the functioning of the fish and mammalian monoaminergic systems. In fish, the hypermetabolism of catecholamines (norepinephrine and dopamine) and indoleamine (serotonin, 5-hydroxytryptamine, 5-HT) has been found to be associated with stressful conditions. In contrast to the situation in mammals, these monoamines can pass through the blood–brain barrier in teleost fishes, contributing to the high levels of biogenic amines in the periphery. Hence, high levels of serotonin in the peripheral circulation, during different stressful conditions, may influence the functioning of other physiological systems, notably the immune system. Serotonin is also stored in considerable amounts by mast cells and platelets, and can be synthetized by chromaffin cells. In mammals, it has been established that 5-HT modulates immune function at a variety of levels. However, little is known about the role of serotonin in the functioning of the immune system in fish. In this perspective article, we will discuss our results and the findings of other laboratories, although meagre on this subject, on the possible role of serotonin in the functioning of immunocompetent cells in fish.
Kinematics and Efficiency of Steady Swimming in Adult Axolotls (Ambystoma Mexicanum)
Authors: D’août Kristiaan , Aerts Peter 
Published: April 2021

ABSTRACT
The kinematics of steady swimming at a wide range of velocities was analysed using high-speed video recordings (500 frames s−1) of eight individuals of Ambystoma mexicanum swimming through a tunnel containing stationary water. Animals in the observed size range (0.135–0.238 m total body length) prefer to swim at similar absolute speeds, irrespective of their body size. The swimming mechanism is of the anguilliform type. The measured kinematic variables – the speed, length, frequency and amplitude (along the entire body) of the propulsive wave – are more similar to those of anguilliform swimming fish than to those of tadpoles, in spite of common morphological features with the latter, such as limbs, external gills and a tapering tail. The swimming speed for a given animal size correlates linearly with the tailbeat frequency (r2=0.71), whereas the wavelength and tail-tip amplitude do not correlate with this variable. The shape of the amplitude profile along the body, however, is very variable between the different swimming bouts, even at similar speeds. It is suggested that, for a given frequency, the amplitude profile along the body is adjusted in a variable way to yield the resulting swimming speed rather than maintaining a fixed-amplitude profile. The swimming efficiency was estimated by calculating two kinematic variables (the stride length and the propeller efficiency) and by applying two hydrodynamic theories, the elongated-body theory and an extension of this theory accounting for the slope at the tail tip. The latter theory was found to be the most appropriate for the axolotl’s swimming mode and yields a hydromechanical efficiency of 0.75±0.04 (mean ± S.D.), indicating that Ambystoma mexicanum swims less efficiently than do anuran tadpoles and most fishes. This can be understood given its natural habitat in vegetation at the bottom of lakes, which would favour manoeuvrability and fast escape.
Ionic Composition of Endolymph in Teleosts: Origin and Importance of Endolymph Alkalinity
Authors: Payan P. , Kossmann H. , Watrin A. , Mayer-Gostan N. , Boeuf G. 
Published: April 2021

ABSTRACT
Ionic (Na+, K+, Cl−, PO43−, pH), total CO2, total calcium and protein concentrations in the plasma and endolymph of the inner ear were compared in trout Oncorhynchus mykiss and turbot Scophthalmus maximus. In both species, saccular endolymph was characterized by high levels of K+ and total CO2 and in trout by an alkaline pH. The kinetic characteristics of proton secretion across the saccular epithelium of trout were investigated using a titration technique in which isolated saccules were mounted as closed sacs. The rate of proton secretion depends strongly on the pH of the Ringer’s solution and secretion stops at a pH below 7.2. Proton secretion is driven by an energy-dependent mechanism involving basolateral ouabain-sensitive Na+/K+ exchangers. Proton secretion was partially inhibited by acetazolamide and completely inhibited in Na+-free Ringer or in the presence of 1 mmol l−1 amiloride. A cellular model stressing the importance of proton exchange through the saccular epithelium is proposed to explain the regulation of endolymph pH, a crucial factor for the deposition of otolith calcium.
Role for Adenosine in Channel Arrest in the Anoxic Turtle Brain
Authors: Pék Marta , Lutz Peter L. 
Published: April 2021

ABSTRACT
The remarkable ability of the turtle brain to survive anoxia is based on its ability to match energy demand flexibly to energy production. Earlier studies indicate that reduced ion leakage is an important mechanism for energy conservation during anoxia. We tested the hypothesis that extracellular adenosine plays a role in the reduction of K+ flux (channel arrest) that occurs in the anoxic turtle brain. Changes in extracellular K+ concentration ([K+]o) in the in situ brain of the turtle Trachemys scripta were monitored following inhibition of Na+/K+-ATPase with ouabain. The time to reach full depolarization ([K+]o plateau) was three times longer in the anoxic brain than in normoxic controls, and the initial rate of K+ leakage was reduced by approximately 70 %. Superfusing the brain before and during anoxia with the general adenosine receptor blocker theophylline, or the specific adenosine A1 receptor blocker 8-cyclopentyltheophylline, significantly shortened the time to full depolarization in the ouabain-challenged anoxic brain and increased the rate of K+ efflux. The results suggest that adenosine A1 receptors are involved in the expression of anoxia-induced ion channel arrest in the turtle brain.
Three-Dimensional Kinematics and Limb Kinetic Energy of Running Cockroaches
Authors: Kram R. , Wong B. , Full R. J. 
Published: April 2021

ABSTRACT
We tested the hypothesis that fast-running hexapeds must generate high levels of kinetic energy to cycle their limbs rapidly compared with bipeds and quadrupeds. We used high-speed video analysis to determine the three-dimensional movements of the limbs and bodies of cockroaches (Blaberus discoidalis) running on a motorized treadmill at 21 cm s−1 using an alternating tripod gait. We combined these kinematic data with morphological data to calculate the mechanical energy produced to move the limbs relative to the overall center of mass and the mechanical energy generated to rotate the body (head + thorax + abdomen) about the overall center of mass. The kinetic energy involved in moving the limbs was 8 μJ stride−1 (a power output of 21 mW kg−1), which was only approximately 13 % of the external mechanical energy generated to lift and accelerate the overall center of mass at this speed. Pitch, yaw and roll rotational movements of the body were modest (less than ±7 °), and the mechanical energy required for these rotations was surprisingly small (1.7 μJ stride−1 for pitch, 0.5 μJ stride−1 for yaw and 0.4 μJ stride−1 for roll) as was the power (4.2, 1.2 and 1.1 mW kg−1, respectively). Compared at the same absolute forward speed, the mass-specific kinetic energy generated by the trotting hexaped to swing its limbs was approximately half of that predicted from data on much larger two- and four-legged animals. Compared at an equivalent speed (mid-trotting speed), limb kinetic energy was sa smaller fraction of total mechanical energy for cockroaches than for large bipedal runners and hoppers and for quadrupedal trotters. Cockroaches operate at relatively high stride frequencies, but distribute ground reaction forces over a greater number of relatively small legs. The relatively small leg mass and inertia of hexapeds may allow relatively high leg cycling frequencies without exceptionally high internal mechanical energy generation.
Effects of Anoxia, Acidosis and Temperature on the Contractile Properties of Turtle Cardiac Muscle Strips
Authors: Shi Hongyu , Jackson Donald C. 
Published: April 2021

ABSTRACT
The responses to anoxia and acidosis of cardiac ventricular muscle strips from the anoxia-tolerant turtle Chrysemys picta bellii were investigated at 10 °C and 20 °C. Force–velocity curves were determined by quick isotonic releases at 85 % of the time to peak isometric force under control, anoxia, lactate acidosis and anoxic lactate acidosis conditions. The isotonic forces during quick releases spanned 5–95 % of the measured isometric force at each condition. Superfusion solution pH was 7.8 and 7.95 for non-acidosis experiments, and 7.0 and 7.15 for acidosis experiments, at 20 °C and 10 °C, respectively. After normalizing force data to control isometric force, the values of maximum isometric force (P0), maximum velocity of shortening (Vmax) and maximal power output (Powermax) were evaluated by fitting the curves using the hyperbolic Hill equation. The maximum rate of force development (dF/dtmax), time-to-peak force (TPF) and half-relaxation time (T1/2) were also determined. At 20 °C, during acidosis, anoxia and anoxic acidosis, P0 decreased significantly to 81 %, 40 % and 24 % of control values, dF/dtmax decreased significantly to 67 %, 53 % and 23 % of control values, and Powermax decreased significantly to 75 %, 40 % and 14 % of control values, respectively. Vmax, however, was not significantly affected by acidosis, anoxia or even anoxic acidosis. TPF was significantly shortened by anoxia, but prolonged by acidosis. The effects were similar at 10 °C. Temperature did not affect P0, but Vmax decreased by a factor of 1.6–1.8 at all corresponding conditions when temperature was reduced from 20 °C to 10 °C. We conclude that acidosis and anoxia inhibit isometric force production and Powermax of turtle cardiac muscle, but have no effect on Vmax, and the insensitivity of Vmax indicates that the rate of cross-bridge cycling is not affected by these conditions. Our observations indicate that the reduced power outputs of the hearts of submerged anoxic turtles at low temperature are due in part to inhibition of force production by anoxia and acidosis, and to a reduction of contraction velocity at low temperature.
Spatial Acuity of Ultrasound Hearing in Flying Crickets
Authors: Wyttenbach Robert A. , Hoy Ronald R. 
Published: April 2021

ABSTRACT
The minimum audible angle is the smallest angular separation at which two sounds are perceived as coming from distinct sources. To determine the spatial acuity of hearing in crickets, we measured minimum audible angles at various locations in azimuth and elevation. Crickets (Teleogryllus oceanicus) were able to discriminate between sources separated by 11.25 ° (1/32 of a circle) in azimuth directly ahead of them; acuity declined to 45 ° in azimuth for sound sources 90 ° to the side and then improved to 33.75 ° at the rear. Crickets were also able to discriminate between sources separated in elevation, although acuity was much poorer, ranging from 45 ° at the front and rear of the animal to 90 ° below the animal.
A habituation–dishabituation test was used to test discrimination. This involved presenting a train of ultrasound pulses from one location, habituating the cricket’s escape response. This train was followed by a test pulse of ultrasound from another location, after which a final pulse was presented from the original source. If the test pulse was discriminated from the habituating pulses, then the response to the final pulse was dishabituated. To determine the minimum audible angle, we repeated such tests while moving the two sound sources closer together until dishabituation no longer occurred.
Tissue-Specific Variation In Hsp70 Expression and Thermal Damage in Drosophila Melanogaster Larvae
Authors: Krebs Robert A. , Feder Martin E. 
Published: April 2021

ABSTRACT
All tissues of larval Drosophila melanogaster express Hsp70, the major heat-shock protein of this species, after both mild (36 °C) and severe (38.5 °C) heat shock. We used Hsp70-specific immunofluorescence to compare the rate and intensity of Hsp70 expression in various tissues after these two heat-shock treatments, and to compare this with related differences in the intensity of Trypan Blue staining shown by the tissues. Trypan Blue is a marker of tissue damage. Hsp70 was rarely detectable before heat shock. Brain, salivary glands, imaginal disks and hindgut expressed Hsp70 within the first hour of heat shock, whereas gut tissues, fat body and Malpighian tubules did not express Hsp70 until 4–21 h after heat shock. Differences in Hsp70 expression between tissues were more pronounced at the higher heat-shock temperature. Tissues that expressed Hsp70 slowly stained most intensely with Trypan Blue. Gut stained especially intensely, which suggests that its sensitivity to heat shock may limit larval thermotolerance. These patterns further suggest that some cells respond primarily to damage caused by heat shock rather than to elevated temperature per se and/or that Hsp70 expression is itself damaged by heat and requires time for recovery in some tissues.