bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Acid–Base Regulation in Migrant Sea Lampreys (Petromyzon Marinus) Following Exhaustive Exercise
Authors: Wilkie Michael P. , Couturier Jennifer , Tufts Bruce L.
Published: April 2021

The life cycle of the sea lamprey (Petromyzon marinus) is characterized by a terminal upstream spawning migration that may be associated with brief bursts of high-intensity swimming. Such activity usually leads to pronounced blood acid–base disturbances in fishes, but lampreys rapidly correct these perturbations within 1 h. In the present study, patterns of post-exercise H+ excretion and ion movements were followed in sea lampreys to test the hypothesis that dynamic manipulation of Na+versus Cl− movements across the animal’s body surface, presumably at the gills, accounted for the rapid restoration of blood pH following exercise. The first hour of post-exercise recovery in sea lampreys was associated with marked stimulation of (equivalent to base uptake), which approached −500 μmol kg−1 h−1. After 1 h, patterns had returned to resting rates. Analyses of net Na+ and Cl− movements suggested that elevated net Cl− losses, which greatly exceeded net Na+ losses, accounted for most of the . Subsequent experiments, using radiotracers (22Na+, 36Cl−), indicated that differential increases in Cl−versus Na+ permeability accounted for the greater post-exercise Cl− losses and the corresponding stimulation of net proton excretion. Finally, metabolic acid budget analyses confirmed our hypothesis that rapid excretion of metabolic protons was the primary means used by sea lampreys to correct post-exercise extracellular acidosis.
The electric organ discharge of pulse gymnotiforms: the transformation of a simple impulse into a complex spatio-temporal electromotor pattern
Authors: Caputi Angel Ariel
Published: April 2021

An understanding of how the nervous system processes an impulse-like input to yield a stereotyped, species-specific electromotor output is relevant for electric fish physiology, but also for understanding the general mechanisms of coordination of effector patterns. In pulse gymnotids, the electromotor system is repetitively activated by impulse-like signals generated by a pacemaker nucleus in the medulla. This nucleus activates a set of relay cells whose axons descend along the spinal cord and project to electromotor neurones which, in turn, project to electrocytes. Relay neurones, electromotor neurones and electrocytes may be considered as layers of a network arranged with a lattice hierarchy. This network is able to coordinate a spatio-temporal pattern of postsynaptic and action currents generated by the electrocyte membranes. Electrocytes may be innervated at their rostral face, at their caudal face or at both faces, depending on the site of the organ and the species. Thus, the species-specific electric organ discharge patterns depend on the electric organ innervation pattern and on the coordinated activation of the electrocyte faces. The activity of equally oriented faces is synchronised by a synergistic combination of delay lines. The activation of oppositely oriented faces is coordinated in a precise sequence resulting from the orderly recruitment of subsets of electromotor neurones according to the ‘size principle’ and to their position along the spinal cord. The body of the animal filters the electric organ output electrically, and the whole fish is transformed into a distributed electric source.
Plasticity of feedback inputs in the apteronotid electrosensory system
Authors: Bastian Joseph
Published: April 2021

Weakly electric fish generate an electric field surrounding their body by means of an electric organ typically located within the trunk and tail. Electroreceptors scattered over the surface of the body encode the amplitude and timing of the electric organ discharge (EOD), and central components of the electrosensory system analyze the information provided by the electroreceptor afferents. The electrosensory system is used for electrolocation, for the detection and analysis of objects near the fish which distort the EOD and for electrocommunication. Since the electric organ is typically located in the tail, any movement of this structure relative to the rest of the body alters the EOD field, resulting in large changes in receptor afferent activity. The amplitude of these reafferent stimuli can exceed the amplitudes of near-threshold electrolocation signals by several orders of magnitude. This review summarizes recent studies of the South American weakly electric fish Apteronotus leptorhynchus aimed at determining how the animals differentiate self-generated or reafferent electrosensory stimuli from those that are more behaviorally relevant. Cells within the earliest stages of central electrosensory processing utilize an adaptive filtering technique which allows the system preferentially to attenuate reafferent as well as other predictable patterns of sensory input without degrading responses to more novel stimuli. Synaptic plasticity within the system underlies the adaptive component of the filter and enables the system to learn to reject new stimulus patterns if these become predictable. A Ca2+-mediated form of postsynaptic depression contributes to this synaptic plasticity. The filter mechanism seen in A. leptorhynchus is surprisingly similar to adaptive filters described previously in mormyrid weakly electric fish and in elasmobranchs, suggesting that this mechanism may be a common feature of sensory processing systems.
Plasticity of the electric organ discharge: implications for the regulation of ionic currents
Authors: Zakon Harold , McAnelly Lynne , Smith G. Troy , Dunlap Kent , Lopreato Gregory , Oestreich Joerg , Few W. Preston
Published: April 2021

Weakly electric fish emit electric organ discharges (EODs) to locate objects around themselves and for communication. The EOD is generated by a simple hierarchically organized, neurophysiologically accessible circuit, the electromotor system. A number of forms of plasticity of the EOD waveform are initiated by social or environmental factors and mediated by hormones or neurotransmitters. Because the behavior itself is in the form of electric discharges, behavioral observations easily lead to testable hypotheses about the biophysical bases of these plasticities. This allows us to study ionic channels in their native cellular environments, where the regulation of various parameters of these currents have obvious functional consequences. In this review, we discuss three types of plasticity: a rapidly occurring, long-lasting, N-methyl-D-aspartate (NMDA)-receptor-dependent increase in baseline firing frequency of neurons in the pacemaker nucleus that underlies a readjustment of the baseline EOD frequency after long bouts of the jamming avoidance response; a rapidly occurring diurnal change in amplitude and duration of the EOD pulse that depends in part on modulation of the magnitude of the electrocyte Na+ current by a protein kinase; and a slowly occurring, hormonally modulated tandem change in pacemaker firing frequency and in the duration of the EOD pulse in which changes in EOD pulse duration are mediated by coordinated shifts in the activation and inactivation kinetics of the electrocyte Na+ and K+ currents.
Development and regeneration of the electric organ
Authors: Zakon Harold H. , Unguez Graciela A.
Published: April 2021

The electric organ has evolved independently from muscle in at least six lineages of fish. How does a differentiated muscle cell change its fate to become an electrocyte? Is the process by which this occurs similar in different lineages? We have begun to answer these questions by studying the formation and maintenance of electrocytes in the genus Sternopygus, a weakly electric teleost. Electrocytes arise from the fusion of fully differentiated muscle fibers, mainly those expressing fast isoforms of myosin. Electrocytes briefly co-express sarcomeric proteins, such as myosin and tropomyosin, and keratin, a protein not found in mature muscle. The sarcomeric proteins are subsequently down-regulated, but keratin expression persists. We investigated whether the maintenance of the electrocyte phenotype depends on innervation. We found that, after spinal cord transection, which silences the electromotor neurons that innervate the electrocytes, or destruction of the spinal cord, which denervates the electrocytes, mature electrocytes re-express sarcomeric myosin and tropomyosin, although keratin expression persists. Ultrastructural examination of denervated electrocytes revealed nascent sarcomeres. Thus, the maintenance of the electrocyte phenotype depends on neural activity.
A kinematic comparison of forward and backward swimming in the eel Anguilla anguilla
Authors: D’Août Kristiaan , Aerts Peter
Published: April 2021

In addition to forward undulatory swimming, eels (and some other elongated swimmers) can swim backwards in a similar way. We compared the kinematics (wave speed, cycle frequency, amplitude, local bending and estimated muscle strain) of forward and backward swimming in the European eel Anguilla anguilla.

Both swimming modes are characterised by a wave of undulation that travels over the body in the direction opposite to that of swimming. We observe two major kinematic differences. First, the slope of wave frequency against swimming speed is significantly higher for backward than for forward swimming. Second, the amplitude profile along the body of the propulsive wave differs greatly. During forward swimming, the yaw at the head is minimal and the amplitude of the propulsive wave increases to approximately 15 % (left-to-right) of total body length towards the tail tip. During backward swimming, the amplitude profile is rather uniform along the body (with values similar to the tail-tip amplitude during forward swimming), resulting in considerable lateral head oscillation. Strikingly, the head remains approximately parallel to the swimming direction, which presumably enhances visual and acoustico-lateral perception. Furthermore, muscle strain is much higher in the rostral part of the body during backward swimming than during forward swimming. Values for stride length and propeller efficiency suggest that backward undulatory swimming is mechanically less efficient than forward swimming.

We suggest that the typical anguilliform body shape is an important feature that allows these animals to swim backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. Most other fishes, if able to swim backwards at all, do so using fin oscillations or undulations.
Auditory sensory cells in hawkmoths: identification, physiology and structure
Authors: Göpfert Martin C. , Wasserthal Lutz T.
Published: April 2021

The labral pilifers are thought to contain auditory sensory cells in hawkmoths of two distantly related subtribes, the Choerocampina and the Acherontiina. We identified and analysed these cells using neurophysiological and neuroanatomical techniques. In the death’s head hawkmoth Acherontia atropos, we found that the labral nerve carries the auditory afferent responses of a single auditory unit. This unit responds to ultrasonic stimulation with minimum thresholds of 49–57 dB SPL around 25 kHz. Ablation experiments and analyses of the neuronal activity in different regions of the pilifer revealed that the auditory afferent response originates in the basal pilifer region. The sensory organ was identified as a chordotonal organ that attaches to the base of the pilifer. This organ is the only sensory structure in the basal pilifer region and consists of a single mononematic scolopidium and a single sensory cell. In Choerocampina, a homologous scolopidium was also found and is probably the only sensory structure of the pilifer that might serve an auditory function. Since a pilifer chordotonal organ with only a single scolopidium has also been detected in a non-hearing hawkmoth species, hearing in the distantly related choerocampine and acherontiine hawkmoths presumably evolved from a single proprioceptive mechanoreceptor cell that is present in all hawkmoths.
Many-legged maneuverability: dynamics of turning in hexapods
Authors: Jindrich Devin L. , Full Robert J.
Published: April 2021

Remarkable similarities in the vertical plane of forward motion exist among diverse legged runners. The effect of differences in posture may be reflected instead in maneuverability occurring in the horizontal plane. The maneuver we selected was turning during rapid running by the cockroach Blaberus discoidalis, a sprawled-postured arthropod. Executing a turn successfully involves at least two requirements. The animal’s mean heading (the direction of the mean velocity vector of the center of mass) must be deflected, and the animal’s body must rotate to keep the body axis aligned with the heading. We used two-dimensional kinematics to estimate net forces and rotational torques, and a photoelastic technique to estimate single-leg ground-reaction forces during turning. Stride frequencies and duty factors did not differ among legs during turning. The inside legs ended their steps closer to the body than during straight-ahead running, suggesting that they contributed to turning the body. However, the inside legs did not contribute forces or torques to turning the body, but actively pushed against the turn. Legs farther from the center of rotation on the outside of the turn contributed the majority of force and torque impulse which caused the body to turn. The dynamics of turning could not be predicted from kinematic measurements alone. To interpret the single-leg forces observed during turning, we have developed a general model that relates leg force production and leg position to turning performance. The model predicts that all legs could turn the body. Front legs can contribute most effectively to turning by producing forces nearly perpendicular to the heading, whereas middle and hind legs must produce additional force parallel to the heading. The force production necessary to turn required only minor alterations in the force hexapods generate during dynamically stable, straight-ahead locomotion. A consideration of maneuverability in the horizontal plane revealed that a sprawled-postured, hexapodal body design may provide exceptional performance with simplified control.
Modulatory effects of some amino acids and neuropeptides on luminescence in the brittlestar Amphipholis squamata
Authors: De Bremaeker N. , Baguet F. , Thorndyke M. C. , Mallefet J.
Published: April 2021

Amphipholis squamata is a polychromatic luminescent ophiuroid. The effects of amino acids ( γ-aminobutyric acid, GABA, taurine, glycine and glutamate), N-methyl-D-aspartate (NMDA) and the invertebrate neuropeptides Antho-RFamide, FMRFamide and SALMFamides S1 and S2 were tested on acetylcholine-induced luminescence from isolated arms of clear and black specimens of Amphipholis squamata. The results showed that GABA, glycine and Antho-RFamide inhibited ACh-induced luminescence of clear specimens and had no significant effect on black specimens. Glutamic acid had no significant effect on ACh-induced luminescence, but triggered luminescence in the absence of ACh in both types of specimen. Taurine, NMDA and FMRFamide showed no significant effects on either clear or black specimens. S1 potentiated ACh-induced luminescence of clear and black specimens, while S2 had no clear modulatory effect on luminescence. These results suggest that, in addition to the previously described cholinergic system in Amphipholis squamata, there is also a modulatory component to luminescence control. Moreover, we observed a difference in modulation of luminescence between clear and black specimens.
Developmental analysis of Ganaspis xanthopoda, a larval parasitoid of Drosophila melanogaster
Authors: Melk Jonathan P. , Govind Shubha
Published: April 2021

Ganaspis xanthopoda is a solitary larval parasitoid wasp of the fruit fly Drosophila melanogaster. The life cycle of Ganaspis xanthopoda in the wild-type and developmental mutant ecdysoneless strains of Drosophila melanogaster is described. The female infects a second-instar host larva. The parasitoid embryo hatches into a mobile first-instar (L1) larva. The L1 parasitoid has fleshy appendages and, while mobile, it remains confined within the wandering larval host. The second-instar larva (L2) is an endoparasite within the host prepupa and lacks appendages. The L2-to-L3 molt is dependent on pupation and marks the transition of the endoparasite into an ectoparasite. The third-instar larva (L3) is a sessile ectoparasite, develops an extensive tracheal system and consumes the host as it progresses through its prepupal and pupal stages. A single adult male or female emerges from the host puparium. The developmental analysis of Ganaspis xanthopoda reveals a tight synchrony between host and parasitoid development which is, at least in part, dependent on the ecdysone levels of the host.
The relationship of central and peripheral organ masses to aerobic performance variation in house sparrows
Authors: Chappell Mark A. , Bech Claus , Buttemer William A.
Published: April 2021

We evaluated the relationship between organ mass and the limits to aerobic metabolism in house sparrows Passer domesticus. The results were used to test three models of performance limitation (the central limitation, peripheral limitation and symmorphosis concepts). Basal metabolic rate (BMR) was determined during the rest phase. The maximum rate of oxygen consumption during exercise was measured in an enclosed wheel that allowed limited hovering flight. Neither BMR nor was affected by gender, but adults had significantly higher and lower BMR than juveniles. The masses of most central organs (gut, gizzard, liver, heart, kidney and reproductive organs) differed significantly between ages. There were no gender differences in organ mass among juveniles, but liver mass differed between male and female adults. In the pooled data, BMR was positively correlated with the mass of three central organs (gut, liver and kidney) and with one peripheral effector (breast muscle); together, these explained more than half the variance in BMR (r2=0.57). In adults, BMR was positively correlated with the mass of reproductive tissue. The masses of one peripheral effector (breast muscle) and one central organ (the heart) were positively correlated with (r2=0.17 for the pooled data set). These results are consistent with a symmorphosis model of aerobic capacity. We found a significant positive relationship between BMR and in juveniles, but not in adults. Taken together, our data indicate that house sparrows can achieve elevated without paying a ‘penalty’ (fitness trade-off) in the form of an increased BMR.
Near-body flow dynamics in swimming fish
Authors: Wolfgang M. J. , Anderson J. M. , Grosenbaugh M. A. , Yue D. K. P. , Triantafyllou M. S.
Published: April 2021

We consider the motions and associated flow patterns of a swimming giant danio (Danio malabaricus). Experimental flow-visualization techniques have been employed to obtain the unsteady two-dimensional velocity fields around the straight-line swimming motions and a 60 ° turn of the fish in the centerline plane of the fish depth. A three-dimensional numerical method is also employed to predict the total velocity field through simulation. Comparison of the experimental and numerical velocity and vorticity fields shows good agreement. The fish morphology, with its narrow peduncle region, allows for smooth flow into the articulated tail, which is able to sustain a large load for thrust generation. Streamlines of the flow detail complex processes that enhance the efficiency of flow actuation by the tail. The fish benefits from smooth near-body flow patterns and the generation of controlled body-bound vorticity, which is propagated towards the tail, shed prior to the peduncle region and then manipulated by the caudal fin to form large-scale vortical structures with minimum wasted energy. This manipulation of body-generated vorticity and its interaction with the vorticity generated by the oscillating caudal fin are fundamental to the propulsion and maneuvering capabilities of fish.
Isolation of magnetic nanoparticles from Pachycondyla marginata ants
Authors: Acosta-Avalos Daniel , Wajnberg Eliane , Oliveira Paulo S. , Leal Inara , Farina Marcos , Esquivel Darci M. S.
Published: April 2021

We report on the presence of magnetic iron oxides in the migratory ant Pachycondyla marginata. Magnetic particles were extracted from different parts of the ant (head, thorax and abdomen) using magnetic precipitation methods. Electron spectroscopic images for iron and oxygen were obtained from the extracted particles, and, by using the corresponding electron micrographs, histograms of size distribution were constructed. Selected area diffraction patterns were also obtained from the particles, and analysis of these showed the presence of a mixture of different iron oxides, including the magnetic oxides, magnetite and maghemite. The size distribution of the particles in the abdomen is different from that in the thorax and the head. In accordance with the hypothesis of magnetic orientation based on the presence of magnetic material within the body, two regions of the ant, the head and the abdomen, could be implicated in the detection of the geomagnetic field.
Directional hearing in grasshoppers: neurophysiological testing of a bioacoustic model
Authors: Schul Johannes , Holderied Marc , Helversen Dagmar Von , Helversen Otto Von
Published: April 2021

A recently proposed biophysical model for directional hearing in grasshoppers was tested using complex stimulus situations, with two loudspeakers, one on either side of the animal, synchronously emitting sinusoids with defined phase and amplitude relationships. Hearing responses were determined from whole nerve recordings and compared with the predictions of the model. In Schistocerca gregaria, there were only minor differences between the predictions of the model and measurements and, by reducing the value of the gain of the internal sound path measured previously, a close agreement was achieved between model and measured hearing responses. In Chorthippus biguttulus, larger discrepancies between model calculations using the values measured previously and neuronal response functions were found in both shape and amplitude. A better fit between measurements and model predictions was achieved by increasing the values of the internal delay over those measured previously. The measurements presented here indicate high inter-individual variability of the parameters of the internal pathway, with a range of 60° for the internal phase delay. Calculating the directional characteristics using this range of values for the internal delay indicated that sufficient directional information was available down to 5 kHz. Increasing the value of the internal delay over that measured in an earlier study therefore provides an explanation for the discrepancy between the poor directional information attributed to C. biguttulus in that study and the excellent lateralization ability of males of this species at 5 kHz.
Control of abdominal extension in the freely moving intact crayfish Cherax destructor:: I. Activity of the tonic stretch receptor
Authors: McCarthy Bernard J. , Macmillan David L.
Published: April 2021

Electrical recordings were made from the sensory neurone of the tonic muscle receptor organ in the abdomen of the intact, freely behaving crayfish Cherax destructor. Slow extensions of the abdomen were evoked by lowering a platform from beneath the suspended crayfish, and the movements and tonic sensory neurone activity were video-recorded simultaneously. The recordings showed that the tonic sensory neurone was active when the abdomen was fully flexed prior to the extension. When the extension began, however, the sensory neurone ceased firing shortly after movement was detected, irrespective of the load applied to the abdomen. When the abdomen was physically blocked from extending fully, the sensory neurone did not fire. The tonic muscle receptor organ is considered to be the length-detecting sensor for a load-compensating servo-loop, but the results demonstrate that its activity pattern during extensions evoked by a platform-drop in C. destructor are not consistent with that role.
The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine
Authors: Clark Thomas M. , Koch Alan , Moffett David F.
Published: April 2021

The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.
Glycerol and fatty acid kinetics in rainbow trout: effects of endurance swimming
Authors: Bernard S. F. , Reidy S. P. , Zwingelstein G. , Weber J.-M.
Published: April 2021

Continuous infusions of 2-[3H]glycerol and 1-[14C]palmitate were performed in vivo in rainbow trout to measure the effects of prolonged swimming on (1) the rate of appearance of glycerol (Ra glycerol or lipolytic rate), (2) the rate of appearance of non-esterified fatty acids (Ra NEFA) and (3) the rate of triacylglycerol:fatty acid cycling (TAG:FA cycling or re-esterification). Our goals were to test the hypothesis that sustained exercise for up to 4 days causes the progressive mobilization of triacylglycerol reserves to supply fuel to contracting muscles, and to assess whether TAG:FA cycling plays a role in the regulation of NEFA availability in teleosts. Contrary to expectation, the rates of lipolysis and fatty acid release in resting trout are not affected by endurance exercise. Unlike mammals, which increase the rate of lipolysis by two-to fourfold during submaximal exercise, these active teleosts do not mobilize triacylglycerol reserves beyond resting levels to supply more NEFAs to working muscles. Furthermore, they maintain Ra glycerol and Ra NEFA well in excess of oxidative fuel requirements even at rest. More than two-thirds of the NEFAs produced are re-esterified, but the results show that TAG:FA cycling is not involved in the regulation of NEFA availability during or after swimming. We propose that the observed high rates of re-esterification represent an important feature of ectothermic metabolism that allows the restructuring of membrane phospholipids to be synchronized with frequent changes in body temperature.
Single-cell analyses of nitrergic neurons in simple nervous systems
Authors: Moroz Leonid L. , Gillette Rhanor , Sweedler Jonathan V.
Published: April 2021

Understanding the role of the gaseous messenger nitric oxide (NO) in the nervous system is complicated by the heterogeneity of its nerve cells; analyses carried out at the single cell level are therefore important, if not critical. Some invertebrate preparations, most especially those from the gastropod molluscs, provide large, hardy and identified neurons that are useful both for the development of analytical methodologies and for cellular analyses of NO metabolism and its actions. Recent modifications of capillary electrophoresis (CE) allow the use of a small fraction of an individual neuron to perform direct, quantitative and simultaneous assays of the major metabolites of the NO–citrulline cycle and associated biochemical pathways. These chemical species include the products of NO oxidation (NO2−/NO3−), L-arginine, L-citrulline, L-ornithine, L-argininosuccinate, as well as selected NO synthase inhibitors and cofactors such as NADPH, biopterin, FMN and FAD. Diverse cotransmitters can also be identified in the same nitrergic neuron. The sensitivity of CE methods is in the femtomole to attomole range, depending on the species analysed and on the specific detector used. CE analysis can be combined with prior in vivo electrophysiological and pharmacological manipulations and measurements to yield multiple physiological and biochemical values from single cells. The methodologies and instrumentation developed and tested using the convenient molluscan cell model can be adapted to the smaller and more delicate neurons of other invertebrates and chordates.
P-type Ca2+ current in crayfish peptidergic neurones
Authors: García-Colunga Jesús , Valdiosera René , García Ubaldo
Published: April 2021

Inward Ca2+ current through voltage-gated Ca2+ channels was recorded from freshly dissociated crayfish X-organ (XO) neurones using the whole-cell voltage-clamp technique. Changing the holding potential from —50 to —90 mV had little effect on the characteristics of the current–voltage relationship: neither the time course nor the amplitude of the Ca2+ current was affected. Inactivation of the Ca2+ current was observed over a small voltage range, between —35 and —10 mV, with half-inactivation at —20 mV. The activation of the Ca2+ current was modelled using Hodgkin–Huxley kinetics. The time constant of activation, τm, was 568±66 μs at —20 mV and decreased gradually to 171±23 μs at 40 mV (means ± S.E.M., N=5). The steady-state activation, m∞, was fitted with a Boltzmann function, with a half-activation voltage of —7.45 mV and an apparent threshold at —40 mV. The instantaneous current–voltage relationship was adjusted using the Goldman–Hodgkin–Katz constant-field equation, giving a permeation of 4.95×10−5 cm s−1. The inactivation of the Ca2+ current in XO neurones was dependent on previous entry of Ca2+. Using a double-pulse protocol, the inactivation was fitted to a U-shaped curve with a maximal inactivation of 35 % at 30 mV. The time course of the recovery from inactivation was fitted with an exponential function. The time constants were 17±2.6 ms for a prepulse of 10 ms and 31±3.2 ms for a prepulse of 20 ms. The permeability sequence of the Ca2+ channels was as follows: Ba2+>Sr2+≈Ca2+Mg2+. Other divalent cations blocked the Ca2+ current, and their effects were voltage-dependent; the potency of blockage was Cd2+≈Zn2+Co2+≈Ni2+. The peptide ω-agatoxin-IVA, a selective toxin for P-type Ca2+ channels, blocked 85 % of the Ca2+ current in XO neurones at 200 nmol l−1, but the current was insensitive to dihydropyridines, phenylalkylamines, ω-conotoxin-GVIA and ω-conotoxin-MVIIC, which are blockers of L-, N- and Q-type Ca2+ channels, respectively. From the voltage- and Ca2+-dependent kinetics, the higher permeability to Ba2+ than to Ca2+ and the higher sensitivity of the current to Cd2+ than to Ni2+, we conclude that the Ca2+ current in XO neurones is generated by high-voltage-activated (HVA) channels. Furthermore, its blockage by ω-agatoxin-IVA suggests that it is mainly generated through P-type Ca2+ channels.
Lactate metabolism and glucose turnover in the subterranean crustacean Niphargus virei during post-hypoxic recovery
Authors: Hervant F. , Garin D. , Mathieu J. , Freminet A.
Published: April 2021

Glucose and lactate metabolism were studied in a hypoxia-resistant subterranean crustacean, Niphargus virei, using an injection of L-[U-14C]lactate and tracer D-[6-3H]glucose either in normoxic conditions or after a 24 h exposure to severe hypoxic. Post-hypoxic animals (H animals) were compared with two treatment groups of normoxic animals. In the first normoxic group (NLL animals), animals were simultaneously injected with labelled and unlabelled lactate to obtain a lactate load similar to that of H animals. In the second normoxic group (N, control animals), animals were only injected with labelled lactate. During a 24 h recovery period, the incorporation of 14C and 3H into glycogen, lactate, glucose, amino acids, lipids and CO2 was measured.

During recovery, glucose turnover rate was enhanced in H and depressed in NLL compared with N animals. However, when energy expenditure was taken into account, the changes were due only to a reduction of glucose turnover rate by lactate load. It was concluded that gluconeogenesis was not the main source of glyconeogenesis.

Equivalent lactate loading in NLL and H animals resulted in an equivalent enhancement (fivefold) of lactate utilization in both groups when energy expenditure was taken into account. Lactate label incorporation appeared later in glycogen than in glucose, but remained high 24 h after the injection. Since glucose is mainly an extracellular metabolite, this observation may be consistent with the hypothesis of two distinct sites for glycogen restoration in hypogean crustaceans: a gluconeogenic organ (a liver equivalent) and a glyconeogenic organ (a muscle equivalent).

The oxidative pathways of glucose and lactate were depressed in post-hypoxic N. virei and to a lesser extent in the NLL group. Since there is no evidence of marked protein utilization, it is postulated that, during recovery, repayment of the O2 debt relies on an increase in lipid utilization.

During recovery from severe hypoxia or after a lactate load, the subterranean N. virei appeared to implement a strategy of lactate removal quite different from that observed in epigean crustaceans, favouring lactate-supported gluco- and glyconeogenesis and rapid glycogen replenishment instead of rapid lactate removal via oxidative pathways.
High-frequency steering maneuvers mediated by tactile cues: antennal wall-following in the cockroach
Authors: Camhi J. M. , Johnson E. N.
Published: April 2021

Cockroaches (Periplaneta americana) use their antennae to detect a wall and to maintain a constant distance from it as they walk or run along it. The faster they run, the closer they position themselves to the wall. They also use their antennae to detect and follow multiple accordion-like projections in the wall. They can make up to 25 body turns s−1 for short periods during rapid running to follow such wall projections. Each turn apparently involves a change in stepping direction. These turns help to avoid collisions with the outward projections, while keeping the body close to the wall.

Sensory inputs from the flagellum of the antenna, and not from its base, appear to evoke the turns in response to wall projections. These flagellar inputs appear to report the position along the antenna of its contact with the wall and/or the position of the consequent antennal bend. This flagellar information constitutes a one-dimensional sensory map, with location along the map indicating the distance to the wall.
Structure and mechanics of the squid mantle
Authors: MacGillivray Patrick S. , Anderson Erik J. , Wright Glenda M. , Demont M. Edwin
Published: April 2021

The goal of this study was to obtain a complete description of the elastic modulus and hysteresis of the mantle tissue of the squid Loligo pealei over the entire functional region of the mantle. In addition, in vivo strains were measured to allow calculations of the amount of energy stored and returned in each region of the mantle studied, and microscopic analysis of the tissue was carried out with the aim of correlating macroscopic properties with microscopic structure. The results of dynamic tissue tests indicate that mean elastic moduli for each of the 35 mantle positions tested ranged from 5.0×105 to 1.2×106 N m−2. The elastic modulus varied within a narrow range, in no predictable manner. Mean hysteresis values for each position varied from 19.7 % to 27.3 % with no discernible patterns found either around or along the mantle. In vivo mantle strains peaked in the middle (lengthwise) of the mantle and declined towards both ends, and the absolute strains increased with increasing swimming velocity. Energy storage calculations showed that most energy was stored in the middle of the mantle, with an increase in storage with increased swimming velocity. Microscopic tissue analysis found direct correlations between macroscopic properties and microscopic characteristics, and electron microscopical analysis of all three types of intramuscular fibre revealed that all three types are collagenous in nature.
Excretion of thiosulphate, the main detoxification product of sulphide, by the lugworm Arenicola marina L.
Authors: Hauschild Kerstin , Weber Wolf-Michael , Clauss Wolfgang , Grieshaber Manfred K.
Published: April 2021

Thiosulphate, the main sulphide detoxification product, is accumulated in the body fluids of the lugworm Arenicola marina. The aim of this study was to elucidate the fate of thiosulphate. Electrophysiological measurements revealed that the transepithelial resistance of body wall sections was 76±34 Ω cm2 (mean ± S.D., N=14), indicating that the body wall of the lugworm is a leaky tissue in which mainly paracellular transport along cell junctions takes place. The body wall was equally permeable from both sides to thiosulphate, the permeability coefficient of which was 1.31×10−3±0.37×10−3 cm h−1 (mean ± S.D., N=30). No evidence was found for a significant contribution of the gills or the nephridia to thiosulphate permeation. Thiosulphate flux followed the concentration gradient, showing a linear correlation (r=0.997) between permeated and supplied (10–100 mmol l−1) thiosulphate. The permeability of thiosulphate was not sensitive to the presence of various metabolic inhibitors, implicating a permeation process independent of membrane proteins and showing that the lugworm does not need to use energy to dispose of the sulphide detoxification product. The present data suggest a passive permeation of thiosulphate across the body wall of A. marina. In live lugworms, thiosulphate levels in the coelomic fluid and body wall tissue decreased slowly and at similar rates during recovery from sulphide exposure. The decline in thiosulphate levels followed a decreasing double-exponential function. Thiosulphate was not further oxidized to sulphite or sulphate but was excreted into the sea water.
The sarcoplasmic reticulum plays a major role in isometric contraction in atrial muscle of yellowfin tuna
Authors: Shiels H. A. , Freund E. V. , Farrell A. P. , Block B. A.
Published: April 2021

We used an isometric muscle preparation to test the hypothesis that yellowfin tuna Thunnus albacares utilize the intracellular Ca2+ storage sites of the sarcoplasmic reticulum (SR) during routine contractions. Ryanodine (a blocker of SR Ca2+ release) reduced the force of contraction by approximately 50 % and the rates of contraction and relaxation by 60 % in yellowfin tuna atrium. High levels of adrenaline were unable to ameliorate the effects of ryanodine. We conclude that the SR is active in contributing Ca2+ to force development at physiological contraction frequencies. Further, we suggest that, by using intracellular Ca2+ cycling, the yellowfin tuna is able to increase the maximum contraction frequency of its cardiac muscle beyond that of most other fishes.
Structure, fluorescent properties and proposed function in phototaxis of the stigma apparatus in the ciliate Chlamydodon mnemosyne
Authors: Selbach Matthias , Kuhlmann Hans-Werner
Published: April 2021

Chlamydodon mnemosyne, a brackish-water ciliate which feeds on cyanobacteria, is capable of sensing the direction of light. Cells are negatively phototactic in the well-fed state and tend to swim towards the light source when mildly starved. Severely starved cells normally fail to show phototactic responses. An autofluorescent substance, which is present in all life cycle stages, occurs in, or immediately beneath, the plasma membrane of this ciliate. It is located in the anterior left side of a cell, in the same region where mildly starved cells accumulate small orange globules that form a structure known as the stigma. The diameter of the whole area where the autofluorescent substance is located appears to be smaller than the stigma; typically, it consists of two rows of blue-green fluorescence, each row subdivided into 5–10 squares. Since the blue-green autofluorescence is excited by both blue (450–490 nm) and near-ultraviolet (340–380 nm) light, it possibly originates from flavin- and/or pterin-like molecules. We suggest that the autofluorescent substance located in or beneath the plasma membrane of Chlamydodon mnemosyne acts as a photoreceptor pigment in phototaxis and that photo-orientation of this ciliate is triggered by a combined mechanism involving the photoreceptor and either the stigma or a number of light-absorbing food vacuoles as a shading device.
Differential expression of mitochondrial genes between queens and workers during caste determination in the honeybee Apis mellifera
Authors: Corona Miguel , Estrada Enrique , Zurita Mario
Published: April 2021

The nourishment received by female honeybee larvae determines their differentiation into queens or workers. In this study, we report the first molecular analysis of differences that occur between queens and workers during the caste-determination process. RNA-differential display experiments identified a clone that encodes for a gene that is homologous to the nuclear-encoded mitochondrial translation initiation factor (AmIF-2mt). Semi-quantitative analysis by reverse transcriptase/polymerase chain reaction (RT-PCR) throughout honeybee development detected a higher level of expression of this gene in queen larvae than in worker larvae. Analysis of two other genes encoding mitochondrial proteins, cytochrome oxidase subunit 1 (COX-1; mitochondrial-encoded) and cytochrome c (cyt c; nuclear-encoded) also showed differential expression of these two genes between queens and workers. In particular, the cyt c transcript is more abundant in queen larvae and throughout the metamorphosis of the queen. These results indicate that the higher respiratory rate previously documented in queen larvae is accomplished through a higher level of expression of both nuclear- and mitochondrial-encoded genes for mitochondrial proteins.
Evidence for orientation using the e-vector direction of polarised light in the sleepy lizard Tiliqua rugosa
Authors: Freake Michael J.
Published: April 2021

Adult sleepy lizards (Tiliqua rugosa) were trained to orient in a predictable direction under natural sky light in outdoor pens. When tested under clear skies in the late afternoon, without a view of the sun, the lizards exhibited a symmetrical bimodal pattern of orientation with respect to the trained axis. Since the e-vector of polarised light provides an axial rather than a polar cue, the bimodal orientation exhibited by the lizards is consistent with the use of a celestial compass based on sky polarisation patterns. To confirm that the lizards could orient with respect to a polarisation pattern, lizards were trained in indoor pens to orient in a predictable direction under a linearly polarised light source. When tested in a circular arena illuminated by another polarised light source, the lizards used the e-vector direction of the polarised light source to orient along the trained axis. There was no evidence that the lizards were using any room-specific cues or brightness patterns to orient in the training direction. These results support the hypothesis that the lizards can use the e-vector direction of polarised light in the form of a sky polarisation compass.
PELVIC ASPIRATION IN THE AMERICAN ALLIGATOR (ALLIGATOR MISSISSIPPIENSIS)
Authors: Farmer Colleen G. , Carrier David R.
Published: April 2021

The pelvis of crocodilians is highly derived in that the pubic bones are isolated from the acetabulum and are attached to the ischia via moveable joints. We examined the possible role of this unusual morphology in lung ventilation by measuring ventilation, abdominal pressure and the electrical activity of several abdominal and pelvic muscles in the American alligator (Alligator mississippiensis). We found that the activity of two pelvic muscles, the ischiopubis and ischiotruncus muscles, was correlated with inspiration; these muscles rotate the pubes ventrally and thereby increase abdominal volume. During expiration, contraction of the rectus abdominis and transversus abdominis rotates the pubes dorsally. We suggest that this mechanism facilitates diaphragmatic breathing by creating space for caudal displacement of the viscera during inspiration. Because birds also use a dorso-ventral movement of the pelvis to effect ventilation, some form of pelvic aspiration may be plesiomorphic for archosaurs.
Permeation Through the Cftr Chloride Channel
Authors: Mccarty Nael A.
Published: April 2021

The cystic fibrosis transmembrane conductance regulator (CFTR) protein forms a Cl− channel found in the plasma membranes of many epithelial cells, including those of the kidney, gut and conducting airways. Mutation of the gene encoding CFTR is the primary defect in cystic fibrosis, a disease that affects approximately 30 000 individuals in the United States alone. Alteration of CFTR function also plays an important role in the pathophysiology of secretory diarrhea and polycystic kidney disease. The basic mechanisms of permeation in this channel are not well understood. It is not known which portions of the protein contribute to forming the pore or which amino acid residues in those domains are involved in the biophysical processes of ion permeation. In this review, I will discuss (i) the present understanding of ion transport processes in the wild-type CFTR channel, (ii) the experimental approaches currently being applied to investigate the pore, and (iii) a proposed structure that takes into account the present data on mechanisms of ion selectivity in the CFTR channel and on blockade of the pore by open-channel blockers.
Sensory Habituation of Auditory Receptor Neurons: Implications for Sound Localization
Authors: Givois V. , Pollack G. S.
Published: April 2021

Auditory receptor neurons exhibit sensory habituation; their responses decline with repeated stimulation. We studied the effects of sensory habituation on the neural encoding of sound localization cues using crickets as a model system. In crickets, Teleogryllus oceanicus, sound localization is based on binaural comparison of stimulus intensity. There are two potential codes at the receptor-neuron level for interaural intensity difference: interaural difference in response strength, i.e. spike rate and/or count, and interaural difference in response latency. These are affected differently by sensory habituation. When crickets are stimulated with cricket-song-like trains of sound pulses, response strength declines for successive pulses in the train, and the decrease becomes more pronounced as the stimulus intensity increases. Response decrement is thus greater for receptors serving the ear ipsilateral to the sound source, where intensity is higher, resulting in a decrease in the interaural difference in response strength. Sensory habituation also affects response latency, which increases for responses to successive sound pulses in the stimulus train. The change in latency is independent of intensity, and thus is similar for receptors serving both ears. As a result, interaural latency difference is unaffected by sensory habituation and may be a more reliable cue for sound localization.