bluuebunny/crossref_metadata_2025 huggingface dataset:
The Biological Action of Ions and the Concentration of Ions at Surfaces
Authors: Danielli J. F.
Published: April 2021

It is pointed out that at the surface of a cell the absolute concentration of ions, and the ratios of the concentrations of the individual ions, are usually different from the corresponding quantities in the environmental fluid. It is suggested that the necessity for a Na : Ca ratio of the order of 50:1 in a physiologically balanced fluid is found because such a ratio in the environmental fluid produces a Na : Ca ratio of the order of unity at the cell surface. The concentrations of calcium and sodium ions at the surface of ovalbumin molecules are calculated. It is shown that calcium is bound (a) by electrostatic forces, (b) by formation of apparently unionized complexes with carboxyl groups. The complex formation obeys the law of mass action. The ratio, total Na:total Ca at the surface of various cells in physiological media is calculated from the electrokinetic potentials of the cells. The calculated ratio is of the order of unity. In two cases calculation of the maximum possible total Ca at the cell surface by two other independent methods gives values of the same order of magnitude as the calculation from electrokinetic potentials. It is shown that, where the toxic action of ions is due to complex formation with anions present at a surface, the logarithms of the equitoxic concentrations of the metals should be a linear function of the standard electrode potentials of the metals. Calculations show that the concentration of colloidal Fe at the surface of organisms in sea-water should be far greater than the concentration in the environment: it is suggested that marine plants derive their iron from this layer of adsorbed colloidal iron. A mechanism is suggested which provides for intense adsorption of drugs at specific surfaces.
Bafilomycins and concanamycins as inhibitors of V-ATPases and P-ATPases
Authors: Dröse Stefan , Altendorf Karlheinz
Published: April 2021

Bafilomycins and concanamycins, two groups of the plecomacrolide-defined class of macrolide antibiotics, have recently been recognized as important tools for studying the physiological role of vacuolar-type, proton-translocating ATPases (V-ATPases) and ATPases with phosphorylated states (P-ATPases) in animal and plant cells as well as in yeast, fungi and bacteria. The following review will give an account of the classification and function of these antibiotics.
Characterisation of the Binding of Leukotriene B4 To Macrophages of the Rainbow Trout Oncorhynchus Mykiss
Authors: Bowden Linda A. , Fiore Stefano , Restall Colin J. , Serhan Charles N. , Rowley Andrew F.
Published: April 2021

The binding of leukotriene B4 (LTB4) to macrophages from the head kidney of the rainbow trout Oncorhynchus mykiss was measured. Binding of [3H]LTB4 achieved a steady state after approximately 30 min of incubation and was 30 % reversible in the presence of a minimum of 1000-fold excess of LTB4. Scatchard analysis of the kinetics of LTB4 binding over a range of [3H]LTB4 concentrations indicated the existence of only a single class of receptor with a dissociation constant, KD, of 0.14 nmol l−1 and a maximum receptor density, Bmax, of approximately 17 800 sites per macrophage. The LTB4 receptor antagonist LY223982 was ineffective in inhibiting the binding of [3H]LTB4 to trout macrophages, although another receptor antagonist, LTB4-dimethylamide, displaced a maximum of 25 % of the total binding. LTB5 was equally effective as LTB4 at displacing [3H]LTB4, while other eicosanoids tested were without significant effect. It is suggested that the putative receptors for LTB4 on trout macrophages are similar to the high-affinity receptors for this compound reported to occur on mammalian granulocytes, although any structural similarities of the binding sites await further investigation.
Dynamic Imaging of Functional Nerve Terminals and Schwann Cells in Presynaptic ‘Nerve Plates’ Isolated From the Skate Electric Organ
Authors: Dowdall Michael J. , Green A. Chris , Richardson C. Mark
Published: April 2021

The cholinergic innervation and its glial support were isolated in a functional state from the electric organ of the skate (Raja species) using a combined enzymatic and mechanical dissociation technique. Examination using light and electron microscopy showed that this ‘nerve plate’ is a disc-shaped structure several hundred micrometres in diameter consisting of a dense plexus of nerve terminals attached to branching nerve fibrils with numerous associated myelinating and perisynaptic Schwann cells. In unfixed nerve plates, depolarisation and Ca2+-dependent staining of the nerve terminals was seen with RH-414, a fluorescent marker for functional motor terminals. The components of the nerve plate could be loaded with the Ca2+-sensitive dyes Fluo-3 and Fura-2. Depolarisation of nerve plates loaded with either dye leads to an immediate increase of intracellular Ca2+ levels ([Ca2+]i) in the nerve terminals. This response was blocked by certain Ca2+ channel antagonists from the ω-conotoxin family. Glial cell responses to depolarisation were in general minimal. However, increases of [Ca2+]i were seen in these cells, but not in nerve terminals, during applications of ATP and acetylcholine. These results show that both nerve terminal and glial elements in this ‘nerve plate’ preparation are functional. The ease of this preparation and its functional reliability give it considerable potential as a useful model for elucidating presynaptic mechanisms.
An All-or-Nothing Rise in Cytosolic [Ca2+] in Vorticella SP.
Authors: Katoh Kaoru , Kikuyama Munehiro
Published: April 2021

The peritrich ciliate Vorticella sp. exhibits cellular contraction of an all-or-nothing type in response to a mechanical stimulus. Many authors have suggested that the contraction may be controlled by the cytosolic level of Ca2+, since glycerol-extracted Vorticella contracts when Ca2+ is added to the external solution. However, no direct evidence for the increase in cytosolic [Ca2+] has yet been obtained in living Vorticella.

In the present study, by injecting a fluorescent Ca2+ indicator into living Vorticella and monitoring the cytosolic [Ca2+] with a confocal microscope, we have demonstrated that a mechanical stimulus evoked an all-or-nothing rise in cytosolic [Ca2+] (Ca2+ ‘spike’). The onset of the Ca2+ spike was similar in its time course to that of cellular contraction. Since the Ca2+ spike was recorded in a Ca2+-deprived solution containing 1 mmol l−1 EGTA, we concluded that release of Ca2+ from intracellular Ca2+ storage site(s) is responsible for the Ca2+ spike.
Modification of Ciliary Beating in Sea Urchin Larvae Induced by Neurotransmitters: Beat-Plane Rotation and Control of Frequency Fluctuation
Authors: Wada Yuuko , Mogami Yoshihiro , Baba Shoji A.
Published: April 2021

The modification of ciliary beating by neurotransmitters in sea urchin larvae at the four-armed pluteus stage was analyzed in terms of the direction of beating and fluctuation in the beat period. Application of dopamine to Pseudocentrotus depressus causes the cilia to turn their beat plane but retain its characteristic planar feature up to the complete ‘reversal’ of the beat direction. This new type of response was termed the ‘beat-plane turning response’.

It was also found that neurotransmitters, especially dopamine and serotonin, can modify the length of the beating cycle in P. depressus and Hemicentrotus pulcherrimus. Dopamine decreased and serotonin increased the beat frequency averaged over the ciliated epithelium with the standard deviation from the mean increasing in the presence of dopamine and decreasing with serotonin. The beat-period fluctuation and its modification suggested by this observation was confirmed from measurements of the beating of individual cilia in the presence or absence of these neurotransmitters. Further analysis of the correlation between angular velocity and beat period indicates that variation in the beat period is not controlled by the same processes as those that modulate angular velocity.

These findings in sea urchin larvae suggest that both the stability and the direction of ciliary beating is under nervous control.
Hindleg Targeting During Scratching in the Locust
Authors: Matheson T.
Published: April 2021

Intact locusts (Schistocerca gregaria) respond to tactile stimulation of their folded wings with rhythmic scratching movements of the ipsilateral hindleg that are directed towards the site of stimulation. For example, sites near the base of a wing elicit anteriorly directed scratches, whereas sites near the distal end of a wing elicit posteriorly directed scratches.

Locusts also scratch in response to tactile stimulation of a wing that is held outstretched in a posture similar to that normally adopted during flight, but they fail to alter their leg targeting to compensate for this changed position of the stimulus site. Instead, they scratch at an empty point in space near the abdomen, where the stimulus site would have been if the wing was folded in the resting posture. This inappropriate scratching does not result from mechanical constraints on the hindleg’s movement, from stimulation of abdominal sensory receptors, or from an absence of sensory information from the outstretched wing. It also persists when the metathoracic ganglion that controls movements of the hindlegs is isolated from the remainder of the central nervous system (CNS).

Targeted scratching of sites on the wings of locusts therefore appears to be fixed relative to body coordinates and does not take into account alterations of the target wing’s position.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
A Putative Cortisol Receptor in The Rainbow Trout Erythrocyte: Stress Prevents Starvation-Induced Increases in Specific Binding of Cortisol
Authors: Pottinger T. G. , Brierley I.
Published: April 2021

Binding sites for the steroid hormone cortisol, with characteristics typical of a steroid receptor, were detected in the rainbow trout (Oncorhynchus mykiss) erythrocyte. Binding of [3H]cortisol to a washed and purified erythrocyte suspension was saturable (Bmax=0.33±0.06 fmol per 2×106 cells; approximately 100±18 sites per cell; mean ± S.E.M., N=6), of high affinity (Kd=4.7±0.4 nmol l−1) and reversible in the presence of an excess of unlabelled ligand. Maximum levels of specific binding were observed within 60 min of the addition of [3H]cortisol at 4 °C and were stable for 2–3 h. Within 20 min of the addition of excess unlabelled ligand, 60 % of specifically bound [3H]cortisol had dissociated. Both dexamethasone and cortisol completely displaced specifically bound [3H]cortisol at 100-fold excess, whereas a 1000-fold excess of unlabelled cortisone, 11-ketotestosterone, oestradiol-17β, testosterone and 17α,20β-dihydroxy-4-pregnen-3-one failed to displace specifically bound [3H]cortisol completely. Specific binding sites for [3H]cortisol were located predominantly (92 %) within the cytosolic fraction of the erythrocyte, with a trace amount of specific binding (8 %) detectable in the membrane fraction. No specific binding of [3H]cortisol was apparent in the erythrocyte nuclear fraction. A 7 day period of confinement stress resulted in no significant change in the number of erythrocyte cortisol-binding sites in rainbow trout, although plasma cortisol levels were significantly elevated in the stressed fish. However, in control unconfined fish, there was a progressive and significant increase in the amount of specifically bound cortisol per cell during the course of the experiment (from 0.097±0.030 to 0.260±0.070 fmol per 2×106 cells). A similar result was obtained when the experiment was repeated for confirmation. In both experiments, food was withheld from control and confined fish because of the negative impact of stress on appetite. The possibility that the increase in the number of erythrocyte cortisol-binding sites was related to the withdrawal of food was tested by quantifying the amount of specifically bound cortisol in erythrocytes over a 14 day period in unstressed rainbow trout maintained on normal rations and in unstressed fish from which food was withheld. A significant increase in the amount of specifically bound cortisol was observed with time in the fasted fish (from 0.33±0.07 to 0.53±0.03 fmol per 2×106 cells). These data suggest that the abundance of erythrocyte cortisol-binding sites in trout is a function of nutritional status and that stress opposes a fasting-induced increase in the number of binding sites.
The Olfactory Memory of The Honeybee Apis Mellifera: III. Bilateral Sensory Input is Necessary for Induction and Expression of Olfactory Blocking
Authors: Thorn Robert S. , Smith Brian H.
Published: April 2021

The associative learning phenomenon termed ‘blocking’ demonstrates that animals do not necessarily associate a conditioned stimulus (e.g. X) with reinforcement if X is coincident with a second conditioned stimulus (e.g. A) that had already been associated with the same reinforcement. Blocking therefore represents a tactic that animals can use to modulate associative learning in order to focus on the most predictive stimuli at the expense of novel ones. Using an olfactory blocking paradigm in the honeybee, we investigated the mechanistic basis for olfactory blocking. We show that removing input from one antenna eliminates the blocking of one odor by another. Since antennal sensory neurons only project to the ipsilateral antennal lobe in the honeybee, more central processing regions of the brain than the antennae must be crucial for establishing blocking. Further experiments show that this bilateral interaction between brain hemispheres is crucial during both the induction and the expression of blocking. This result implies that blocking involves an active inhibition of odor association and recall, and that this inhibition is mediated by a structure that spans both brain hemispheres. This interpretation is consistent with a role for identified bilateral modulatory neurons in the production of blocking.
Trafficking of Adoptively Transferred B Lymphocytes in B-Lymphocyte-Deficient Mice
Authors: Roth Rita , Mamula Mark J.
Published: April 2021

Many studies have investigated the fate of adoptively transferred lymphocytes in recipient mice, although little is known of the sites where these transferred cells reside at particular time points. Using flow cytometry, we analyzed the trafficking pattern of adoptively transferred naive B cells into the lymphoid organs of syngeneic B-cell-deficient (μMT) mice. Within the first 24 h of transfer, the location of B cells was highly dependent on the mode of B-cell transfer. When B cells were injected subcutaneously into μMT mice, they showed a different trafficking pattern from cells administered into the peritoneal cavity or injected intravenously. After subcutaneous transfer into the thigh, the greatest number of B cells was detected in the popliteal lymph node nearest to the injection site, whereas the lowest number was detected in the axillary lymph node opposite to the injection side. Within the first 24 h of either intraperitoneal and intravenous injection, B cells were found in approximately equal numbers in the lymph nodes and the spleen. Two days later, the B-cell distribution in the lymphoid organs appeared to be independent of the mode of B-cell transfer. A transient decrease in the numbers of splenic and lymph node B cells occurred 9 days after B-cell transfer (a decrease from 70 to 87 %) prior to the outgrowth of B cells that occurs 21 days after transfer. These studies are useful for understanding the numbers of B cells that may be required in adoptive transfer studies and their potential cellular interactions at particular physiological sites based on the route of cell transfer.
Perireception in Olfaction: Molecular Mass Sieving by Aesthetasc Sensillar Cuticle Determines Odorant Access to Receptor Sites in the Caribbean Spiny Lobster Panulirus Argus
Authors: Derby Charles D. , Cate Holly S. , Gentilcore Lisa R.
Published: April 2021

The responsiveness of chemoreceptor neurons depends on a combination of perireceptor and receptor events. Olfactory neurons of crustaceans are packaged into distinctive cuticular sensilla called aesthetascs. The cuticle of aesthetascs is thin and permeable, even though it does not contain any obvious surface pores or pore tubules. This suggests that this ‘spongy’ aesthetasc cuticle may act as a molecular sieve that restricts large odorant molecules from entering the sensilla and binding to the olfactory neurons. We examined whether this is so for the aesthetasc cuticle of the Caribbean spiny lobster Panulirus argus. We used a chromatographic column packed with aesthetasc cuticle and connected to a flow-through ultraviolet spectrophotometer to measure the elution times of ultraviolet-absorbent molecular mass markers between 165 and 2×106 Da. Molecules larger than approximately 8.5 kDa had similar elution times, indicating that they did not penetrate the cuticle. Molecules smaller than 8.5 kDa had longer elution times that were directly and inversely proportional to their molecular mass. These results suggest that aesthetasc cuticle excludes molecules larger than 8.5 kDa from having access to the olfactory receptor neurons. We conclude that the molecular sieving capacity of the aesthetasc cuticle of P. argus is a perireceptor mechanism that is a critical determinant of the types of molecules capable of stimulating its olfactory receptors.
Heart Rates of Northern Elephant Seals Diving at Sea and Resting on the Beach
Authors: Andrews R. D. , Jones D. R. , Williams J. D. , Thorson P. H. , Oliver G. W. , Costa D. P. , Boeuf B. J. Le
Published: April 2021

Heart rates of northern elephant seals diving at sea and during apnoea on land were monitored to test whether a cardiac response to submergence is an important factor in their ability to make repetitive, long-duration dives. Seven juvenile northern elephant seals were captured at Año Nuevo, CA, instrumented and translocated to release sites around Monterey Bay. Heart rate and dive depth were recorded using custom-designed data loggers and analogue tape monitors during the seals’ return to Año Nuevo. Heart rates during apnoea and eupnoea were recorded from four of the seals after they hauled out on the beach. Diving patterns were very similar to those of naturally migrating juveniles. The heart rate response to apnoea at sea and on land was a prompt bradycardia, but only at sea was there an anticipatory tachycardia before breathing commenced. Heart rate at sea declined by 64 % from the surface rate of 107±3 beats min−1 (mean ± S.D.), while heart rate on land declined by 31 % from the eupnoeic rate of 65±8 beats min−1. Diving heart rate was inversely related to dive duration in a non-linear fashion best described by a continuous, curvilinear model, while heart rate during apnoea on land was independent of the duration of apnoea. Occasionally, instantaneous heart rate fell as low as 3 beats min−1 during diving. Although bradycardia occurs in response to apnoea both at sea and on land, only at sea is heart rate apparently regulated to minimise eupnoeic time and to ration oxygen stores to ensure adequate supplies for the heart and brain not only as the dive progresses normally but also when a dive is abnormally extended.
The Direction of Celestial Rotation Influences the Development of Stellar Orientation in Young Garden Warblers (Sylvia Borin)
Authors: Weindler Peter , Baumetz Mathias , Wiltschko Wolfgang
Published: April 2021

The study presented here was conducted in order to analyze the role of the direction of celestial rotation in the development of stellar orientation in young migratory birds. The test birds were garden warblers, Sylvla borin, which leave their breeding ground on a southwesterly compass course. The birds were hand-raised and, during the premigratory period, exposed to an artificial ‘sky’ in the local geomagnetic field. For the control group C, the star pattern was rotating in the natural direction, with the centre of rotation and magnetic North coinciding. For the three experimental groups, the star pattern was rotating in the opposite direction; for group E1, the centre of rotation coincided with magnetic North, for group E2 the centre of rotation was at magnetic West and for group E3 it was at magnetic East. During autumn migration, the birds were tested without magnetic information under the same, now stationary, sky. All four groups were able to use stellar information for orientation, but only the control group preferred the normal southwesterly course. The three experimental groups, in contrast, all oriented towards a significantly different direction, preferring due south. The results for group E1 showed less scatter than those for the other two experimental groups.

These results indicate that the direction of celestial rotation is crucial for the development of the normal migratory course with respect to the stars in young garden warblers. Establishing the species-specific southwesterly migratory course requires an interaction between celestial rotation and magnetic cues; this interaction appears to depend on the natural direction of celestial rotation. Rotation in the reverse direction allowed the birds to respond only in a manner that oriented them away from the centre of rotation.
Do Metabolic Responses to Solar Radiation Scale Directly with Intensity of Irradiance?
Authors: Walsberg Glenn E. , Tracy Randall L. , Hoffman Ty C. M.
Published: April 2021

Endotherms exposed to air temperatures below thermal neutrality reduce their metabolic heat production when exposed to sunlight. The physiological effects of this additional source of heat gain from the environment usually are assumed to be proportional to the intensity of irradiance if other factors are held constant. We test this assumption by measuring changes in metabolic heat production produced by exposing a small mammal, the Siberian hamster (Phodopus sungorus) to four intensities of simulated solar radiation (0 W m−2, 317 W m−2, 634 W m−2 and 950 W m−2).

In the absence of solar radiation, metabolic heat production is inversely correlated with air temperature over the measured range of 3–27 °C. The respiratory quotient varies significantly with ambient temperature, indicating that the catabolic substrate and the thermal equivalent of oxygen consumed or carbon dioxide produced also vary with temperature. The depression of metabolic heat production resulting from exposure to simulated solar radiation is not simply a multiple of the intensity of irradiance. Rather, metabolic responses to higher levels of irradiance are blunted by 14–29 % compared with those expected on the basis of the response to less intense irradiance. Because changes in irradiance levels do not have simple linear effects upon the animal’s metabolic heat production, even in a simplified situation, significant errors may accumulate in biophysical analyses in which an animal’s responses to a restricted set of radiative conditions are measured and the results are extrapolated to a wider range observed in nature.
Honeydew Sugars and Osmoregulation in the Pea Aphid Acyrthosiphon Pisum
Authors: Wilkinson T. L. , Ashford D. A. , Pritchard J. , Douglas A. E.
Published: April 2021

Pea aphids, Acyrthosiphon pisum, containing their symbiotic bacteria (untreated aphids) and experimentally deprived of their bacteria by treatment with the antibiotic rifampicin (antibiotic-treated aphids) were reared on the plant Vicia faba. The sugars in the honeydew produced by untreated aphids comprised predominantly the monosaccharides glucose and fructose, while the honeydew of antibiotic-treated aphids contained considerable amounts of oligosaccharides of up to 16 hexose units. The honeydew and haemolymph of the aphids were iso-osmotic, and their osmotic pressure was significantly lower in untreated aphids (0.91–0.95 MPa) than in antibiotic-treated aphids (1.01–1.05 MPa) (P<0.05). For insects reared on chemically defined diets containing 0.15–1.0 mol l−1 sucrose (osmotic pressure 1.1–4.0 MPa), the osmotic pressure of the aphid haemolymph did not vary with dietary osmotic pressure, but was regulated to approximately 1.0 MPa in untreated and 1.3 MPa in antibiotic-treated aphids. The sugars in the aphid honeydew varied with dietary sucrose concentration; with monosaccharides dominant at low concentrations and oligosaccharides dominant at high concentrations of dietary sucrose. The lowest dietary sucrose concentration at which honeydew oligosaccharides were detected was 0.2 mol l−1 for the antibiotic-treated aphids and 0.3 mol l−1 for untreated aphids. These data indicate that the aphid, and not its associated microbiota, mediates the synthesis of oligosaccharides when the osmotic pressure of the ingesta is high.