bluuebunny/crossref_metadata_2025 huggingface dataset:
An interneurone of unusual morphology is tuned to the female song frequency in the bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae)
Authors: Stumpner Andreas
Published: April 2021

The interneurone AN5-AG7 of the duetting bushcricket Ancistrura nigrovittata has its soma in the seventh (penultimate) abdominal ganglion. Its major postsynaptic arborizations with dense thin branches of smooth appearance are found in the prothoracic ganglion. The branches terminate in the auditory neuropile, predominantly at the same location as those auditory receptors that respond best to the female song frequency. Correspondingly, AN5-AG7 responds preferentially to frequencies between 24 and 28 kHz, thereby matching the carrier frequency of the female response song quite well. At frequencies below 24 kHz, AN5-AG7 receives inhibition, which is sometimes seen as clear inhibitory postsynaptic potentials. At these frequencies, thresholds of excitatory postsynaptic potentials are considerably lower than spike thresholds. In contrast, above 20 kHz, the two thresholds match and they correspond to the behavioural threshold. The AN5-AG7 interneurone is more sensitive to soma-contralateral stimuli and it receives predominantly inhibition, but also some excitation, from the soma-ipsilateral ear. Response strength is not greatly affected by stimulus duration but shows prominent habituation. This habituation depends only weakly on intensity and frequency. Some AN5-AG7 interneurones show very small graded potentials and no spiking responses to any acoustic stimuli.
Muscle growth and development in atlantic cod larvae (Gadus morhua L.) related to different somatic growth rates
Authors: Galloway Trina F. , Kjørsvik Elin , Kryvi Harald
Published: April 2021

The present study describes the development of the axial musculature in first-feeding larvae of Atlantic cod (Gadus morhua L.) with different somatic growth rates achieved by using different nutritional conditions. Muscle growth was assessed by determining the number of muscle fibres (hyperplasia) and the growth of existing fibres (hypertrophy). Larvae were fed rotifers containing a high (1.4; treatment 1) or low (0.2; treatment 2) ratio of docosahexaenoic acid to eicosapentaenoic acid from day 5 after hatching. From day 17, the larvae were fed Artemia nauplii with the same enrichment in both treatments. Treatment 1 gave the highest somatic growth rate and hence the highest dry mass at the end of the experiment, but no difference in larval standard length was found between treatments. In slow-growing larvae, higher priority was thus put into reaching a certain length than into increasing muscle mass.

The largest fibres, which were present from hatching, increased in cross-sectional area during larval development, but no differences were found between treatments in the cross-sectional area of individual fibres or the total cross-sectional area of these fibres at the end of the experiment. The first white recruitment fibres were observed at the dorsal and ventral apices of the myotome at approximately the onset of first feeding (larval length 4.5 mm). In larvae 8.5 mm long, the total cross-sectional area of white muscle fibres in the treatment 2 group was 75 % of that in the treatment 1 group. The highest somatic growth rate was associated with an increased contribution of hyperplasia to axial white muscle growth. In the faster-growing larval group, the relative contribution of hyperplasia to the total white muscle cross-sectional area was 50 %, whereas it was 41 % in the slower-growing larval group. The subsequent growth potential may thus be negatively affected by inadequate larval feeding.
Red muscle activation patterns in yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas during steady swimming
Authors: Knower Torre , Shadwick Robert E. , Katz Stephen L. , Graham Jeffrey B. , Wardle Clement S.
Published: April 2021

To learn about muscle function in two species of tuna (yellowfin Thunnus albacares and skipjack Katsuwonus pelamis), a series of electromyogram (EMG) electrodes was implanted down the length of the body in the internal red (aerobic) muscle. Additionally, a buckle force transducer was fitted around the deep caudal tendons on the same side of the peduncle as the electrodes. Recordings of muscle activity and caudal tendon forces were made while the fish swam over a range of steady, sustainable cruising speeds in a large water tunnel treadmill. In both species, the onset of red muscle activation proceeds sequentially in a rostro-caudal direction, while the offset (or deactivation) is nearly simultaneous at all sites, so that EMG burst duration decreases towards the tail. Muscle duty cycle at each location remains a constant proportion of the tailbeat period (T), independent of swimming speed, and peak force is registered in the tail tendons just as all ipsilateral muscle deactivates. Mean duty cycles in skipjack are longer than those in yellowfin. In yellowfin red muscle, there is complete segregation of contralateral activity, while in skipjack there is slight overlap. In both species, all internal red muscle on one side is active simultaneously for part of each cycle, lasting 0.18T in yellowfin and 0.11T in skipjack. (Across the distance encompassing the majority of the red muscle mass, 0.35–0.65L, where L is fork length, the duration is 0.25T in both species.) When red muscle activation patterns were compared across a variety of fish species, it became apparent that the EMG patterns grade in a progression that parallels the kinematic spectrum of swimming modes from anguilliform to thunniform. The tuna EMG pattern, underlying the thunniform swimming mode, culminates this progression, exhibiting an activation pattern at the extreme opposite end of the spectrum from the anguilliform mode.
Neurochemical control of cricket stridulation revealed by pharmacological microinjections into the brain
Authors: Wenzel B. , Hedwig B.
Published: April 2021

Neuroactive substances were administered into the frontal protocerebrum of tethered male Gryllus bimaculatus by pressure injections from microcapillaries. All three types of species-specific song pattern (calling song, rivalry song and courtship song) could be elicited by injection of acetylcholine and cholinergic agonists. Injection of nicotine led to short bouts of calling song that occurred after a short latency. In contrast, muscarine elicited long-lasting stridulation that took longer to develop. The pharmacologically induced song patterns showed transitions from rivalry song to calling song and from calling song to courtship song, which also occur during natural behaviour. Stridulation induced by a cholinergic agonist could be immediately blocked by microinjection of γ-aminobutyric acid (GABA) into the same neuropile sites. Administration of picrotoxin in resting crickets led to enhanced motor activity that incorporated the three different song patterns. We propose that, in the brain of the cricket, acetylcholine and GABA are putative transmitters involved in the control of stridulation. Histological analysis located the stimulation sites to an area between the pedunculus and the α-lobe of the mushroom body in which the command neurons for calling song have dendritic arborizations.
What determines the bending strength of compact bone?
Authors: Currey John D.
Published: April 2021

The bending strength of a wide variety of bony types is shown to be nearly linearly proportional to Young’s modulus of elasticity/100. A somewhat closer and more satisfactory fit is obtained if account is taken of the variation of yield strain with Young’s modulus. This finding strongly suggests that bending strength is determined by the yield strain. The yield stress in tension, which might be expected to predict the bending strength, underestimates the true bending strength by approximately 40 %. This may be explained by two phenomena. (1) The post-yield deformation of the bone material allows a greater bending moment to be exerted after the yield point has been reached, thereby increasing the strength as calculated from beam formulae. (2) Loading in bending results in a much smaller proportion of the volume of the specimens being raised to high stresses than is the case in tension, and this reduces the likelihood of a weak part of the specimen being loaded to failure.
Effects of sea water and stanniectomy on branchial Ca2+ handling and drinking rate in eel (Anguilla anguilla L.)
Authors: Van Der Heijden A. J. H. , Verbost P. M. , Bijvelds M. J. C. , Atsma W. , Bonga S. E. Wendelaar , Flik G.
Published: April 2021

We examined the effects of seawater adaptation and extirpation of the Stannius corpuscles on branchial Ca2+ flows, gill plasma membrane Ca2+ transporters and drinking rate of European eels, Anguilla anguilla. Transepithelial Ca2+ inflow in the gills increased 2 weeks after transfer of the eels from fresh water to sea water and after stanniectomy. Neither of these treatments changed the membrane density or the affinity of the Ca2+-extrusion mechanisms (Ca2+-ATPase and Na+/Ca2+-exchanger) in the gill cells, as measured in basolateral plasma membrane vesicles. We conclude that the increase in the Ca2+-transporting capacity observed in the gills of fish exposed to the larger transepithelial Ca2+ fluxes, resulting from exposure to sea water or stanniectomy, involves an increase in number and/or size of the Ca2+-transporting cells, but not in the membrane density of Ca2+ transporters. Branchial Ca2+ outflow was higher in stanniectomised than in sham-operated fish. Changes in electrochemical driving forces as well as plasma stanniocalcin or teleocalcin levels may be the basis for the observed differences. Stanniectomy enhanced drinking in stanniectomised eels. Drinking was not further affected by transfer to sea water. These observations suggest that the corpuscles of Stannius are involved in the water balance.
Reflex and muscular adaptations in rat soleus muscle after hindlimb suspension
Authors: Anderson Judith , Almeida-Silveira Maria I. , Pérot Chantal
Published: April 2021

Reflex, mechanical and histochemical adaptations of the soleus muscle following 3 weeks of hindlimb suspension (HS) were measured in the rat. HS transformed the soleus muscle fibre type composition from predominantly slow, type I, to approximately equal proportions of fast, type II and slow fibres. Consistent with this transformation was an increase in the maximum shortening velocity, Vmax, and a decrease in the stiffness of the series elastic component. Disuse also produced muscle atrophy and a resultant decrease in twitch and tetanic force. Reflex responses of the ankle extensors were also obtained at 5 and 9 weeks of age for six control rats (C group) and six rats subjected to HS for 3 weeks (HS group). The soleus reflexes to a mechanical tap applied to the Achilles tendon (T reflex) and to an electrical stimulation of the sciatic nerve (H reflex) were measured. The maximal amplitude of these reflexes (Tmax and Hmax) were normalised to the maximal direct motor response (Mmax) and the Tmax/Hmax ratio was also calculated to give an index of the relative adaptations of the peripheral and central components of the reflex pathway. The HS group showed significantly higher H reflex gains than the C group, possibly due to changes in synaptic efficiency after HS. Conversely, the HS group presented strongly inhibited T reflexes and negative gains for the Tmax/Hmax ratios. This result indicated a reduced spindle solicitation after HS, which may reflect changes in the spindle sensitivity itself, but it could also be due to the decrease in stiffness of the musculo–tendinous elements in series with the muscle spindles. Such mechanical changes may play an important part in the decreased T reflex responses.
The synaptic junctions of LE and RF cluster sensory neurones of Aplysia californica are differentially modulated by serotonin
Authors: Storozhuk Maksim V. , Castellucci Vincent F.
Published: April 2021

The monosynaptic component of withdrawal reflexes in Aplysia californica, from sensory neurones to motor neurones, is a critical site of the synaptic modulation occurring during short-term and long-term behavioural changes. There are four clusters of sensory neurones (LE, rLE, RE, RF) innervating the receptive field for the gill and siphon withdrawal reflex. The receptive fields of these cells are located on the siphon, the mantle, the branchial cavity and the gill itself. In most studies, the synapses made by the sensory neurones of the LE cluster of the abdominal ganglion or the VC cluster of the pleural ganglion have been investigated and shown to be facilitated by the neuromodulator serotonin (5-hydroxytryptamine, 5-HT). In this report, we have examined the effect of 5-HT on the synaptic junctions of the RF cluster neurones. The duration of action potentials in these cells, unlike those of the other clusters, is barely affected by serotonin.

We found that while the LE synapses are facilitated by 5-HT (10 μmol l−1), the RF synapses are not. In fact, the RF–L14 connections are actually depressed by 5-HT; this effect is not due to shunting in the postsynaptic neurone. The RF–L7 connections are also depressed by 5-HT, although the effect is smaller. The RF–L14 connections are blocked by the non-NMDA receptor agonist CNQX (100 μmol l−1), suggesting that the transmitter and the postsynaptic receptors involved are similar to those present on the LE or VC cluster cells. The absence of serotonin-induced facilitation of the RF cluster cells may provide the animal with a means of reducing the nonspecific effects of aversive sensitization and therefore of allowing a greater specificity and more flexibility in plastic behavioural changes.
The self-referencing oxygen-selective microelectrode: detection of transmembrane oxygen flux from single cells
Authors: Land S. C. , Porterfield D. M. , Sanger R. H. , Smith P. J. S.
Published: April 2021

A self-referencing, polarographic, oxygen-selective microelectrode was developed for measuring oxygen fluxes from single cells. This technique is based on the translational movement of the microelectrode at a known frequency through an oxygen gradient, between known points. The differential current of the electrode was converted into a directional measurement of flux using the Fick equation. Operational characteristics of the technique were determined using artificial gradients. Calculated oxygen flux values matched theoretical values derived from static measurements. A test preparation, an isolated neuron, yielded an oxygen flux of 11.46±1.43 pmol cm−2 s−1 (mean ± S.E.M.), a value in agreement with those available in the literature for single cells. Microinjection of metabolic substrates or a metabolic uncoupler increased oxygen flux, whereas microinjection of KCN decreased oxygen flux. In the filamentous alga Spirogyra greveilina, the probe could easily differentiate a 16.6 % difference in oxygen flux with respect to the position of the spiral chloroplast (13.3±0.4 pmol cm−2 s−1 at the chloroplast and 11.4±0.4 pmol cm−2 s−1 between chloroplasts), despite the fact that these positions averaged only 10.6±1.8 μm apart (means ± S.E.M.). A light response experiment showed real-time changes in measured oxygen flux correlated with changes in lighting. Taken together, these results show that the self-referencing oxygen microelectrode technique can be used to detect local oxygen fluxes with a high level of sensitivity and spatial resolution in real time. The oxygen fluxes detected reliably correlated with the metabolic state of the cell.
Colour vision of the foraging swallowtail butterfly Papilio xuthus
Authors: Kinoshita Michiyo , Shimada Naoko , Arikawa Kentaro
Published: April 2021

This paper demonstrates that foraging summer-form females of the Japanese yellow swallowtail butterfly Papilio xuthus have colour vision. The butterflies were trained to feed on sucrose solution placed on a disk of a particular colour in a cage set in the laboratory. After a few such training runs, a butterfly was presented with the training colour randomly positioned within an array of disks of other colours, but with no sucrose solution. The results indicate that the butterflies learn rapidly to select the training colour reliably among different colours. The training colour was also correctly selected when it was covered with neutral density filters to reduce its brightness, or even when the colour was presented together with disks of a variety of shades of grey. These results demonstrate convincingly, for the first time, that a butterfly has true colour vision.
The diving physiology of bottlenose dolphins (Tursiops truncatus): I. Balancing the demands of exercise for energy conservation at depth
Authors: Williams Terrie M. , Haun J. E. , Friedl W. A.
Published: April 2021

During diving, marine mammals must rely on the efficient utilization of a limited oxygen reserve sequestered in the lungs, blood and muscles. To determine the effects of exercise and apnea on the use of these reserves, we examined the physiological responses of adult bottlenose dolphins (Tursiops truncatus) trained to breath-hold on the water surface or to dive to submerged targets at depths between 60 and 210 m. Changes in blood lactate levels, in partial pressures of oxygen and carbon dioxide and in heart rate were assessed while the dolphins performed sedentary breath-holds. The effects of exercise on breath-hold capacity were examined by measuring heart rate and postdive respiration rate and blood lactate concentration for dolphins diving in Kaneohe Bay, Oahu, Hawaii. Ascent and descent rates, stroke frequency and swimming patterns were monitored during the dives. The results showed that lactate concentration was 1.1±0.1 mmol l−1 at rest and increased non-linearly with the duration of the sedentary breath-hold or dive. Lactate concentration was consistently higher for the diving animals at all comparable periods of apnea. Breakpoints in plots of lactate concentration and blood gas levels against breath-hold duration for sedentary breath-holding dolphins occurred between 200 and 240 s. In comparison, the calculated aerobic dive limit for adult dolphins was 268 s. Descent and ascent rates ranged from 1.5 to 2.5 m s−1 during 210 m dives and were often outside the predicted range for swimming at low energetic cost. Rather than constant propulsion, diving dolphins used interrupted modes of swimming, with more than 75 % of the final ascent spent gliding. Physiological and behavioral measurements from this study indicate that superimposing swimming exercise on apnea was energetically costly for the diving dolphin but was circumvented in part by modifying the mode of swimming.
Vocal tract length and acoustics of vocalization in the domestic dog (Canis familiaris)
Authors: Riede Tobias , Fitch Tecumseh
Published: April 2021

The physical nature of the vocal tract results in the production of formants during vocalisation. In some animals (including humans), receivers can derive information (such as body size) about sender characteristics on the basis of formant characteristics. Domestication and selective breeding have resulted in a high variability in head size and shape in the dog (Canis familiaris), suggesting that there might be large differences in the vocal tract length, which could cause formant behaviour to affect interbreed communication.

Lateral radiographs were made of dogs from several breeds ranging in size from a Yorkshire terrier (2.5 kg) to a German shepherd (50 kg) and were used to measure vocal tract length. In addition, we recorded an acoustic signal (growling) from some dogs. Significant correlations were found between vocal tract length, body mass and formant dispersion, suggesting that formant dispersion can deliver information about the body size of the vocalizer. Because of the low correlation between vocal tract length and the first formant, we predict a non-uniform vocal tract shape.
Avoidance reaction of yolk-sac larvae of the inland silverside Menidia beryllina (Atherinidae) to hypoxia
Authors: Weltzien Finn-Arne , Døving Kjell B. , Carr William E. S.
Published: April 2021

Larvae of the inland silverside Menidia beryllina (Atherinidae) were observed in a chamber with two horizontal water layers to study their aversive response to hypoxia. When larvae descended from an upper normoxic layer into a lower hypoxic layer, they displayed a characteristic avoidance reaction consisting of a burst of fast swimming that always ended in an upward direction leading the larva away from the hypoxic region. Each swimming burst lasted for approximately 2–3 s, with a maximum speed of approximately 25 mm s−1, which is approximately four times the maximum swimming speed observed in the normoxic layer. The avoidance reaction was present in larvae from 6 h until 64 h post hatching. At 72 h we observed 50 % mortality as a result of starvation. The avoidance reaction was correlated with the O2concentration but not with the N2 concentration nor with salinity or with salinity gradients. The avoidance response was observed at O2 levels ranging from 4.7 to 0.8 mg O2 l−1. For all concentrations below 3.8 mg O2 l−1, the distribution was significantly different from that observed in normoxic control layers of the same salinity. No avoidance responses were observed at 6.6 mg O2 l−1. We propose that the avoidance reaction of larvae of M. beryllina to hypoxic water is an innate behavioural adaptation to the hypoxic conditions present in the estuaries that are the spawning, hatching and nursery grounds of this species.
Maps of the somata of efferent neurones with axons in the lateral nerves of locust abdominal ganglia
Authors: Bevan S. , Burrows M.
Published: April 2021

We used the cobalt-backfilling method to map the somata of neurones with axons that project in the two paired lateral nerves of the abdominal neuromeres of the locust Schistocerca gregaria with the objective of expanding and bringing together the incomplete and scattered information on these efferent neurones. We compared somata sizes and positions, and the pathways of primary neurites, with information from previous studies on individual, or groups of, abdominal neurones and we identify many of the somata we mapped.

The stained somata belong to paired motor neurones and paired neurosecretory neurones, to unpaired neuromodulatory neurones (dorsal unpaired median, DUM, neurones) and unpaired bilaterally projecting neurones. In different neuromeres, the total number of somata with axons in these lateral nerves ranges from 73 to 106. Within an individual segmental neuromere, approximately 25 % of the somata belong to neurones with axons in nerve 1 (N1) and 35 % to those with axons in nerve 2 (N2) of that segment, while the remaining 40 % belong to neurones with axons in N1 of the next posterior segment. This basic pattern is repeated in all abdominal neuromeres, with differences in the percentages depending on whether the neuromeres are pregenital fused, pregenital unfused or genital.

Nerve 1 contains the axons of 26–37 neurones with central somata in different neuromeres, of which 40 % are in the segmental neuromere and 60 % in the next anterior neuromere. In the segmental neuromere, 15 % of somata are ipsilateral to the nerve, 30 % are at the midline and 55 % are contralateral, whereas in the next anterior neuromere, 70 % are ipsilateral, 10 % are at the midline and 20 % are contralateral.

Nerve 2 contains the axons of 11–28 neurones in different neuromeres, all of which have somata in the same segmental neuromere from which the nerve projects. Of these, approximately 70 % are ipsilateral, 30 % at the midline and none contralateral, except for the first abdominal and eighth male abdominal neuromeres, where one and two somata, respectively, are contralateral.
Egg-laying hormone peptides in the aplysiidae family
Authors: Li Lingjun , Garden Rebecca W. , Floyd Philip D. , Moroz Tatiana P. , Gleeson Juliann M. , Sweedler Jonathan V. , Pasa-Tolic Ljiljana , Smith Richard D.
Published: April 2021

The neuropeptidergic bag cells of the marine mollusc Aplysia californica are involved in the egg-laying behavior of the animal. These neurosecretory cells synthesize an egg-laying hormone (ELH) precursor protein, yielding multiple bioactive peptides, including ELH, several bag cell peptides (BCP) and acidic peptide (AP). While immunohistochemical studies have involved a number of species, homologous peptides have been biochemically characterized in relatively few Aplysiidae species. In this study, a combination of matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MS) and electrospray ionization Fourier transform ion cyclotron resonance MS is used to characterize and compare the ELH peptides from related opisthobranch molluscs including Aplysia vaccaria and Phyllaplysia taylori. The peptide profiles of bag cells from these two Aplysiidae species are similar to that of A. californica bag cells. In an effort to characterize further several of these peptides, peptides from multiple groups of cells of each species were extracted, and microbore liquid chromatography was used to separate and isolate them. Several MS-based sequencing approaches are applied to obtain the primary structures of bag cell peptides and ELH. Our studies reveal that α-BCPs are 100 % conserved across all species studied. In addition, the complete sequences of ε-BCP and ELH of A. vaccaria were determined. They show a high degree of homology to their counterparts in A. californica, with only a few amino acid residue substitutions.
The effects of hypercapnia on force and rate of contraction and intracellular pH of perfused ventricles from the land snail Helix lucorum (L.)
Authors: Michaelidis Basile , Rofalikou Evangelia , Grieshaber Manfred K.
Published: April 2021

The effects of hypercapnia, together with low and high levels of extracellular Ca2+, on heart activity and intracellular pH were examined in isolated perfused hearts from the land snail Helix lucorum. In addition, the intracellular level of Ca2+ was determined in slices of ventricles superfused with both normal and hypercapnic salines, containing low and high concentrations of Ca2+, to investigate whether low extracellular pH affects the entry of Ca2+ into the heart cells. We also examined the effect of a saline that simulated the composition of the haemolymph of snails after estivating for 3 months on the heart activity and intracellular pH. The results showed that hypercapnia causes decreases in the rate and force of heart contraction, and these are more pronounced in the presence of low levels of extracellular Ca2+. Moreover, the present results indicate that Ca2+ maintains the contractility of the heart muscle under acidic conditions and seems to act by competing with protons for the Ca2+ binding sites on sarcolemma. The negative effect of hypercapnia on heart activity appears to be due to a reduction in extracellular pH rather than to changes in intracellular pH.
The relationship between leg stepping pattern and yaw torque oscillations in curve walking of two crayfish species
Authors: Domenici Paolo , Schmitz Josef , Jamon Marc
Published: April 2021

Curve walking in two species of crayfish, Procambarus clarkii and Astacus leptodactylus, was investigated to test whether the mechanism underlying curve walking is the synchronous action of a centrally pre-programmed leg tripod or whether it is the action of one principal leg that produces the main body yaw torque. Curve walking was induced by an optomotor visual stimulus, and the yaw torque produced by the tethered animals was measured in open-loop conditions. Our main results suggest that the yaw torque oscillations in both P. clarkii and A. leptodactylus are related to the movement of outer leg 4 (i.e. leg 4 on the outside of the turn). That is, the peaks in the yaw torque occur, on average, in synchrony with the power stroke of outer leg 4. When comparing the results of this open-loop experiment on P. clarkii with results previously obtained for curve walking in untethered individuals of the same species, we found a much higher variability in leg coordination in the open-loop situation. Similarly, here we did not find the same level of synchrony in the tripod (formed by outer leg 4 and inner legs 2 and 5) observed during untethered free walking. Therefore, we suggest that tethered conditions may diminish the need for stability and thus allow outer leg 4 to produce a body rotation regardless of the leg stepping configuration. The characteristics of leg 4 are in line with its major role in turning. According to previous studies, legs 4 provide the largest force and the largest step amplitude during walking, and their force includes both a pulling and a pushing component which can facilitate the control of turning. Although it is apparent that outer leg 4 is not the only leg that can produce an inward yaw torque, its major role in modulating the yaw torque suggests that there may be a specific, centrally generated control of outer leg 4 during curve walking in crayfish.
Effects of lipid phase transitions on cuticular permeability: model membrane and in situ studies
Authors: Rourke Bryan C. , Gibbs Allen G.
Published: April 2021

The role of lipid physical properties in cuticular water loss was examined in model membranes and intact insects. In model experiments, pure hydrocarbons of known melting point (Tm) were applied to a membrane, and the effects of temperature on permeability were quantified. Arrhenius plots of permeability were biphasic, and transition temperatures for water loss (Tc) were similar to Tm. In grasshoppers Melanoplus sanguinipes, changes in cuticular water loss were measured using flow-through respirometry. Transition temperatures were determined and compared with Tm values of cuticular lipids, determined using Fourier transform infrared spectroscopy, for the same individuals. Individual variation in Tm was highly correlated with Tc, although Tm values were slightly higher than Tc values. Our results show that, in both intact insects and model membranes, lipid melting results in greatly increased cuticular permeability.
Dissecting muscle power output
Authors: Josephson Robert K.
Published: April 2021

The primary determinants of muscle force throughout a shortening–lengthening cycle, and therefore of the net work done during the cycle, are (1) the shortening or lengthening velocity of the muscle and the force–velocity relationship for the muscle, (2) muscle length and the length–tension relationship for the muscle, and (3) the pattern of stimulation and the time course of muscle activation following stimulation. In addition to these primary factors, there are what are termed secondary determinants of force and work output, which arise from interactions between the primary determinants. The secondary determinants are length-dependent changes in the kinetics of muscle activation, and shortening deactivation, the extent of which depends on the work that has been done during the preceding shortening. The primary and secondary determinants of muscle force and work are illustrated with examples drawn from studies of crustacean muscles.
Large-amplitude undulatory fish swimming: fluid mechanics coupled to internal mechanics
Authors: Pedley T. J. , Hill S. J.
Published: April 2021

The load against which the swimming muscles contract, during the undulatory swimming of a fish, is composed principally of hydrodynamic pressure forces and body inertia. In the past this has been analysed, through an equation for bending moments, for small-amplitude swimming, using Lighthill’s elongated-body theory and a ‘vortex-ring panel method’, respectively, to compute the hydrodynamic forces. Those models are outlined in this review, and a summary is given of recent work on large-amplitude swimming that has (a) extended the bending moment equation to large amplitude, which involves the introduction of a new (though probably usually small) term, and (b) developed a large-amplitude vortex-ring panel method. The latter requires computation of the wake, which rolls up into concentrated vortex rings and filaments, and has a significant effect on the pressure on the body. Application is principally made to the saithe (Pollachius virens). The calculations confirm that the wave of muscle activation travels down the fish much more rapidly than the wave of bending.
Functional morphology of undulatory pectoral fin locomotion in the stingray taeniura lymma (Chondrichthyes: dasyatidae)
Authors: Rosenberger Lisa J. , Westneat Mark W.
Published: April 2021

Rajiform locomotion is a unique swimming style found in the batoid fishes (skates and rays) in which thrust is generated by undulatory waves passing down the enlarged pectoral fins. We examined the kinematic patterns of fin motion and the motor patterns of pectoral fin muscles driving the locomotor system in the blue-spot stingray Taeniura lymma. Our goals in this study were to determine overall patterns of fin motion and motor control during undulatory locomotion, to discover how these patterns change with swimming velocity and to correlate muscle function with kinematics and pectoral morphology. Kinematic data were recorded from five individuals over a range of swimming speeds from 22 to 55 cm s−1 (0.9–3.0 DL s−1, where DL is body disc length). Electromyographic (EMG) data were recorded from three individuals over a range of velocities (1.2–3.0 DL s−1) at seven locations (four dorsal, three ventral) along the pectoral fin. As swimming velocity increases, fin-beat frequency, wavespeed and stride length increase, number of waves and reduced frequency decrease and fin amplitude remains constant. There is variability among individuals in frequency and amplitude at a given speed. An inverse relationship was found in which a high fin-beat frequency is associated with a low fin amplitude and a low fin-beat frequency is associated with a high fin amplitude. The motor pattern of undulatory locomotion is alternate firing activity in the dorsal and ventral muscles as the wave moves along the fin from anterior to posterior. Fin muscles are active along the entire length of the fin except at the lowest speeds. As swimming velocity and fin-beat frequency increase, the time of activation of posterior muscles becomes earlier relative to the onset of activity in the anterior dorsal muscles. The duration of muscle activity is longer in the ventral muscles than in the dorsal muscles, indicating that they play a central role in the power stroke of the fin-beat cycle. The anterior muscles (dorsal and ventral) are active for a relatively longer part of the stride cycle than the posterior muscles. Both the anterior position and the large duty factor of the anterior muscles reflect the role of these muscles in initial wave generation. Synchronous recordings of kinematic data with EMG data reveal that the anterior dorsal and middle ventral muscles do mostly positive work, whereas the dorsal and ventral posterior muscles do negative work at most swimming speeds.
Acceleration and balance in trotting dogs
Authors: Lee David V. , Bertram John E. A. , Todhunter Rory J.
Published: April 2021

During quadrupedal trotting, diagonal pairs of limbs are set down in unison and exert forces on the ground simultaneously. Ground-reaction forces on individual limbs of trotting dogs were measured separately using a series of four force platforms. Vertical and fore–aft impulses were determined for each limb from the force/time recordings. When mean fore–aft acceleration of the body was zero in a given trotting step (steady state), the fraction of vertical impulse on the forelimb was equal to the fraction of body weight supported by the forelimbs during standing (approximately 60 %). When dogs accelerated or decelerated during a trotting step, the vertical impulse was redistributed to the hindlimb or forelimb, respectively. This redistribution of the vertical impulse is due to a moment exerted about the pitch axis of the body by fore–aft accelerating and decelerating forces. Vertical forces exerted by the forelimb and hindlimb resist this pitching moment, providing stability during fore–aft acceleration and deceleration.
Characterization of an endothelin ET(B) receptor in the gill of the dogfish shark Squalus acanthias
Authors: Evans David H. , Gunderson Mark P.
Published: April 2021

Endothelins (ETs) are potent vasoconstrictive peptides that are secreted by the vascular endothelium and other tissues in vertebrates. Previous studies have demonstrated that ETs are expressed in a variety of fish tissues and contract various blood vessels. In order to determine if receptors for ET are expressed in fish gill tissue, we examined the binding kinetics of 125 I-labeled, human ET-1 to membrane fragments isolated from the gill of the dogfish shark, Squalus acanthias. 125 I-ET-1 bound at a single site, with a dissociation constant (Kd) and binding site number (Bmax) very similar to those described in a variety of mammalian blood vessels. ET-1 and ET-3 competed equally with 125 I-ET-1, suggesting that the receptor was ETB, which has been shown in mammalian systems to bind to both ligands equally. The ETB-specific agonists sarafotoxin S6c, IRL-1620, and BQ-3020 also competed against 125 I-ET-1 at a single site, supporting this hypothesis. We conclude that the shark gill expresses an ETB receptor with substantial homology to the mammalian receptor and that ET may play an important role in modulating such vital gill functions as gas exchange, ion regulation, acid–base balance, and excretion of nitrogen.
Physiological disturbances at critically high temperatures: a comparison between stenothermal antarctic and eurythermal temperate eelpouts (Zoarcidae)
Authors: Van Dijk P. L. M. , Tesch C. , Hardewig I. , Pörtner H. O.
Published: April 2021

The effect of gradually increased water temperature on the metabolism of temperate eelpout from the North Sea (Zoarces viviparus) and Antarctic eelpout (Pachycara brachycephalum) was investigated. Standard metabolic rate (SMR) was similar in cold-adapted P. brachycephalum and cold-acclimated Z. viviparus in the low temperature range. This indicates that Antarctic eelpout show no metabolic cold adaptation (as originally defined by Wohlschlag); however, they do show a compensatory increase of oxygen consumption compared to warm-acclimated eelpout. SMR increased more strongly with rising temperature in P. brachycephalum than in Z. viviparus, which is reflected in a higher Arrhenius activation energy for oxygen consumption (99±5 kJ mol−1, versus 55±3 kJ mol−1 for cold-acclimated Z. viviparus; means ± S.D.).

The intracellular pH in the white musculature of Z. viviparus follows alphastat regulation over the whole investigated temperature range and dropped at a rate of −0.016 pH units per °C between 3 °C and 24 °C. In Antarctic eelpout white muscle pH declined at a rate of −0.015 pH units per °C between 0 °C and 3 °C, but deviated from alphastat at higher temperatures, indicating that thermal stress leads to acid–base disturbances in this species.

The upper critical temperature limit (TcII; characterised by a transition to anaerobic metabolism) was found to be between 21 °C and 24 °C for Z. viviparus and around 9 °C for P. brachycephalum. In both species a rise of succinate concentration in the liver tissue turned out to be the most useful indicator of TcII. Obviously, liver is more sensitive to heat stress than is white muscle. Accordingly, the energy status of white muscle is not diminished at TcII. Heat-induced hyperglycaemia was observed in Antarctic eelpout (at 9 °C and 10 °C), but not in common eelpout. Based on our results and on literature data, impaired respiration in combination with circulatory failure is suggested as the final cause of heat death. Our data suggest that the southern distribution limit of Zoarces viviparus is correlated with the limit of thermal tolerance. Therefore, it can be anticipated that global warming would cause a shift in the distribution of this species.
Cranial kinesis in gekkonid lizards
Authors: Herrel A. , Vree F. De , Delheusy V. , Gans C.
Published: April 2021

Cranial kinesis was studied in two species of gekkonid lizard, Gekko gecko and Phelsuma madagascariensis, using cineradiography and electromyography. The skull of these geckoes showed the three types of kinesis described by Versluys at the beginning of this century: streptostyly, mesokinesis and metakinesis. In accordance with the later model of Frazzetta, the skull of these animals can be modelled by a quadratic crank system: when the mouth opens during feeding, the quadrate rotates forward, the palato-maxillary unit is lifted and the occipital unit swings forward. During jaw closing, the inverse movements are observed; during crushing, the system is retracted beyond its resting position. The data gathered here indicate that the coupled kinesis (streptostyly + mesokinesis) is most prominently present during the capture and crushing cycles of feeding and is largely absent during late intraoral transport, swallowing, drinking and breathing. The electromyographic data indicate a consistent pattern of muscular activation, with the jaw opener and pterygoid protractor always active during the fast opening phase, and the jaw closers active during closing and crushing. Our data generally support the model of Frazzetta. Although the data gathered here do not allow speculation on the functional significance of the kinesis, they clearly provide some key elements required for a further investigation of the functional and adaptive basis of the system.
Cellular control of renin secretion
Authors: Kurtz Armin , Wagner Charlotte
Published: April 2021

Renin secretion at the level of renal juxtaglomerular cells appears to be controlled mainly by classic second messengers such as Ca2+, cyclic AMP and cyclic GMP, which in turn exert their effects through oppositely acting protein kinases and probably also by affecting the activity of ion channels in the plasma membrane. Thus, protein kinase A stimulates renin secretion, whilst protein kinase C and protein kinase G II inhibit renin secretion. Moreover, Cl− channels could be involved in the mediation of the inhibitory action of Ca2+ on renin secretion. This review summarizes our present knowledge about the possible actions of these kinases in renal juxtaglomerular cells and considers pathways in the organ control of renin secretion.
Exercise and forced submergence in the pond slider (Trachemys scripta) and softshell turtle (Apalone ferox): influence on bimodal gas exchange, diving behaviour and blood acid–base status
Authors: Bagatto B. , Henry R. P.
Published: April 2021

The dynamics of bimodal respiration, diving behaviour and blood acid–base status in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A. ferox and T. scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced submergence, and mean apnoeic time decreased significantly in A. ferox following exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout regardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T. scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induced an acidosis of 0.2 pH units of primarily metabolic origin in both species. Intra-erythrocyte pH was also reduced in both species in response to submergence and exercise. Both intracellular and extracellular acidoses were more severe and longer lasting in A. ferox after each treatment. Plasma [HCO3−] decreased by 25 % in both species following exercise, but only in A. ferox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to resting concentrations sooner in T. scripta than in A. ferox. A. ferox had significantly higher lactate levels than T. scripta following forced submergence as well as a slower recovery time. A. ferox, which is normally a good bimodal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T. scripta, although almost entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both forced submergence and exercise.
Kinematics and muscle dynamics of C- and S-starts of carp (Cyprinus carpio L.)
Authors: Spierts Igor L. Y. , Leeuwen Johan L. Van
Published: April 2021

An analysis is presented of body curvature, acceleration and muscle strain during fast-starts in the common carp (Cyprinus carpio L.). C- and S-starts were filmed at 200 frames s−1 at 23 °C. Curvatures and accelerations of mid-body axes were calculated from digitised outlines. Maximum accelerations at 0.3 FL (fork length) from the snout were 54 m s−2 for C-starts and 40 m s−2 for S-starts. The total turning angle was approximately 150 ° in C-starts. This angle was 70 ° during escape S-starts, significantly larger than for predatory S-starts in other species. Sarcomere strains of axial muscle fibres were calculated at 0.4 and 0.8 FL. During C-starts, white muscle fibres were exposed to maximum sarcomere strains of up to approximately 16 %, and posterior fibres had similar strains to anterior fibres (red 27 %; white 16 %). During S-starts, however, maximum strains in anterior fibres (red 39 %; white 24 %) were more than twice those in posterior fibres (red 17 %; white 10 %). In a C-start, the fish made a large turning angle directed away from the stimulus by bending its tail strongly and thereby producing a large thrust. A larger anterior peak curvature of the fish during S-starts enabled the carp to control the direction of escape better than during C-starts, but with lower accelerations and smaller turning angles. During cyclic and intermittent swimming, red posterior fibres experienced the largest strains. Interestingly, previous studies have shown these fibres to have the lowest passive stiffness and the largest titin isoform, allowing them to attain large strain amplitudes with relatively low passive tensions.
Cyclic AMP Regulates PDGF-stimulated signal transduction and differentiation of an immortalized optic-nerve-derived cell line
Authors: Cohen Rick I. , Mckay Ronald , Almazan Guillermina
Published: April 2021

To facilitate the study of the molecular events underlying the development of optic-nerve-derived oligodendrocytes and their growth-factor-related signal transduction events, we immortalized perinatal rat optic nerve cells with a temperature-sensitive simian virus 40 large T-antigen, carrying the tsA58 and U19 mutations, via a retrovirus vector. The line, tsU19-9, was selected on the basis of the expression of the neural precursor marker nestin. At the permissive temperature, 33 °C, tsU19-9 cells had a flat epithelial morphology. In contrast, following exposure to platelet-derived growth factor (PDGF), a factor important in the lineage progression of oligodendrocytes, or in the presence of dibutyryl cyclic AMP at 39 °C (the non-permissive temperature), the cells underwent morphological and antigenic differentiation to cells characteristic of the oligodendrocyte lineage. We used this cell line to investigate the binding characteristics of PDGF and related signalling cascades. Competition binding, phosphoinositide hydrolysis and intracellular Ca2+ mobilization assays all demonstrated that the three different isoforms of PDGF (AA, AB and BB) bound to and acted on the cell line. Overnight exposure to forskolin, a treatment that initiated morphological and phenotypic progression into an oligodendrocyte lineage, decreased PDGF-BB-induced intracellular Ca2+ mobilization and inhibited basal and PDGF-stimulated [3H]thymidine incorporation. Our results demonstrate that tsU19-9 may serve as a resource to study early optic-nerve oligodendrocyte development.