bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in Motoneuron Membrane Potential and Reflex Activity Induced by Sudden Cooling of Isolated Spinal Cords: Differences Among Cold-Sensitive, Cold-Resistant and Freeze-Tolerant Amphibian Species
Authors: Daló Nelson L. , Hackman John C. , Storey Kenneth , Davidoff Robert A.
Published: April 2021

The effects of sudden cooling of the spinal cord were studied in three species of amphibians – a cold-sensitive tropical toad (Bufo marinus), a cold-resistant, aquatic, hibernating frog (Rana pipiens, northern leopard frog) and a freeze-tolerant frog (Rana sylvatica, wood frog). Ventral root (motoneuron) potentials were recorded from isolated, hemisected spinal cords of each species mounted in a sucrose-gap recording apparatus and superfused with HCO3--buffered Ringer’s solution at room temperature (21 °C).

In the toad, sudden cooling to 6–8 °C produced large, sustained motoneuron depolarizations that returned slowly to baseline levels and were accompanied by extensive paroxysmal activity. Larger, but shorter-lasting, motoneuron depolarizations associated with only a limited amount of paroxysmal activity were generated by rapid cooling of the leopard frog spinal cord. Small, brief motoneuron depolarizations followed by a hyperpolarization, or hyperpolarizations not preceded by depolarizations, were seen in cooled wood frog spinal cords. The wood frog displayed a large amount of spontaneous motoneuron activity, but little paroxysmal activity in response to sudden cooling. Following prolonged cooling, rewarming the spinal cords of all three species resulted in motoneuron hyperpolarizations that slowly decayed towards the baseline value. The amplitude of the rewarming-induced response was larger and longer in toad motoneurons than in leopard frog and wood frog motoneurons. At room temperature, a single supramaximal dorsal root stimulus evoked a depolarizing ventral root potential in toad and leopard frog motoneurons that was decreased in amplitude and prolonged when the spinal cords were cooled to 8 °C or below. In contrast, at room temperature, the ventral root reflex in the wood frog was followed by a distinct hyperpolarization. Cooling the wood frog spinal cord only slightly reduced the amplitude of the ventral root potential. In contrast, the evoked hyperpolarization was blocked by sudden cooling and also by the addition of dihydro-ouabain to the Ringer’s solution. The motoneuron hyperpolarizations induced by sudden cooling in the wood frog were converted to depolarizations when Cl- in the superfusate was replaced with isethionate. The depolarizations elicited by sudden cooling were reduced by the addition of kynurenate in all three species. A dose–response curve generated by short applications of L-glutamate demonstrated that wood frog motoneurons were less sensitive than leopard frog motoneurons to L-glutamate.

In summary, three species of amphibians, differing in their adaptations to the temperature of their environments, vary in their responses to sudden reductions in temperature. The relationship of these responses to their environmental adaptations remains to be determined.
The Mode Of ATP-Dependent Microtubule–Kinesin Sliding In The Auxotonic Condition
Authors: Shirakawa I. , Oiwa K. , Chaen S. , Shimizu T. , Tanaka H. , Sugi H.
Published: April 2021

Kinesin is a motor protein that converts chemical energy derived from ATP hydrolysis into mechanical work to transport cellular components along microtubules. We studied the properties of ATP-dependent microtubule– kinesin sliding with two different in vitro assay systems. In one assay system, a kinesin-coated glass microneedle (elastic coefficient, 1–2.5 pN μm−1) was made to slide along an axoneme. Using this system, we obtained the relationship between the force (=load) on the microneedle and the velocity of microneedle–kinesin sliding in the auxotonic condition, in which the load on the microtubule–kinesin contacts increased as sliding progressed. The force–velocity curve was upwardly convex (maximum velocity Vmax, 0.58±0.15 μm s−1; maximum isometric force P0, 5.0±1.6 pN) and was similar to that of in vitro actin–myosin sliding in the auxotonic condition, suggesting that the two motor protein systems have fundamental kinetic properties in common. In the other assay system, an axoneme attached to a glass microneedle (elastic coefficient, 4–5 pN μm−1) was made to slide on a kinesin-coated glass surface (Vmax, 0.68±0.17 μm s−1; P0, 46.1±18.6 pN). The change in shape of the axoneme indicated an enormous flexibility of randomly oriented kinesin molecules.
The Wind-Evoked Escape Behavior of the Cricket Gryllus Bimaculatus: Integration of Behavioral Elements
Authors: Tauber Eran , Camhi Jeffrey M.
Published: April 2021

The wind-evoked escape behavior of freely ranging crickets (Gryllus bimaculatus) was studied using high-speed video and film analysis. The escape response can be of three types: a turn, a jump or a turn + jump. Any of these can be followed by running.

The turn is similar to that of the cockroach, in terms of the details of body and leg movements. A jump occurs only when the cricket has its back to the wind, either because the stimulus came approximately from behind or because the cricket had first turned away from the wind and then jumped.

The jump, like that of locust, requires some form of energy storage and quick release to obtain the necessary power. Locusts use long-term co-activation of antagonistic leg motor neurons to produce mechanical energy storage. By contrast, crickets do not appear to co-activate antagonistic leg motor neurons. Possible alternative energy storage and release mechanisms are discussed.
Dynamic Properties of Orientation to Turbulent air Current by Walking Carrion Beetles
Authors: Böhm Hartmut
Published: April 2021

A beetle orients its walk with respect to the direction of even a brief air current lasting only a few seconds. In a discontinuous current, the degree of orientation increases with the proportion of time during which the air flows. In the absence of wind, a walking beetle generates its own opposing airstream, the velocity of which is rhythmically modulated.

Sinusoidal modulation of the wind direction elicits approximately sinusoidal changes in walking direction. The amplitude of the following response at frequencies below 0.1 s−1 is almost as large as the amplitude of the change in wind direction. As the stimulus frequency increases, the response amplitude decreases. The Bode plot shows that at frequencies above 1 s−1 the phase of the following response lags by almost 360°.

The dynamic temporal behaviour of the wind-orientation system is comparable with that of a control mechanism having low-pass characteristics of at least second order. It follows that rapid changes in wind direction do not immediately affect orientation behaviour. The wind-orientation system is thus well adapted to the air currents recorded in nature which, at the level of a walking beetle, can change very quickly and erratically in both direction and velocity.
Visual Navigation in Insects: Coupling of Egocentric and Geocentric Information
Authors: Wehner Rüdiger , Michel Barbara , Antonsen Per
Published: April 2021

Social hymenopterans such as bees and ants are central-place foragers; they regularly depart from and return to fixed positions in their environment. In returning to the starting point of their foraging excursion or to any other point, they could resort to two fundamentally different ways of navigation by using either egocentric or geocentric systems of reference. In the first case, they would rely on information continuously collected en route (path integration, dead reckoning), i.e. integrate all angles steered and all distances covered into a mean home vector. In the second case, they are expected, at least by some authors, to use a map-based system of navigation, i.e. to obtain positional information by virtue of the spatial position they occupy within a larger environmental framework.

In bees and ants, path integration employing a skylight compass is the predominant mechanism of navigation, but geocentred landmark-based information is used as well. This information is obtained while the animal is dead-reckoning and, hence, added to the vector course. For example, the image of the horizon skyline surrounding the nest entrance is retinotopically stored while the animal approaches the goal along its vector course. As shown in desert ants (genus Cataglyphis), there is neither interocular nor intraocular transfer of landmark information. Furthermore, this retinotopically fixed, and hence egocentred, neural snapshot is linked to an external (geocentred) system of reference.

In this way, geocentred information might more and more complement and potentially even supersede the egocentred information provided by the path-integration system. In competition experiments, however, Cataglyphis never frees itself of its homeward-bound vector – its safety-line, so to speak – by which it is always linked to home. Vector information can also be transferred to a longer-lasting (higher-order) memory. There is no need to invoke the concept of the mental analogue of a topographic map – a metric map – assembled by the insect navigator. The flexible use of vectors, snapshots and landmark-based routes suffices to interpret the insect’s behaviour.

The cognitive-map approach in particular, and the representational paradigm in general, are discussed.
Distance Estimation by Foraging Honeybees
Authors: Esch Harald E. , Burns John E.
Published: April 2021

Honeybees are widely believed to assess feeder distances by the energy spent on foraging flights. However, a critical review of this ‘energy hypothesis’ reveals many inconsistencies in the experiments from which it was derived. In fact, new evidence shows that the energy hypothesis cannot be correct. Foragers loaded with weights do not overestimate distance, as indicated by their waggle dances performed upon return to the hive. Bees that climb to a feeder on top of a high building (50 m) signal the same distance as hive mates that visit an equidistant feeder at ground level. Foragers visiting a feeder suspended from a balloon at 70 m from their hive underestimate the distance flown dramatically when the balloon lifts the feeder from ground level to 90 m, even though the energy required to reach the feeder increases considerably. Foragers from a hive situated on a high building (50 m) that fly to a feeder on the roof of another high building (34 m) signal a much shorter distance than the actual distance flown. We propose instead an ‘optical flow hypothesis’: bees use the speed of retinal image motion perceived from the ground to estimate the distance flown. Flight altitude is important for distance estimation by retinal image flow, because objects move faster and farther across the retina when the bee flies closer to the ground. When the forager’s flight behavior is considered, the optical flow hypothesis does not conflict with previous findings.
Landmark Stability: Studies Exploring Whether the Perceived Stability of the Environment Influences Spatial Representation
Authors: Biegler Robert , Morris Richard G. M.
Published: April 2021

To investigate whether spatial learning complies with associative learning theories or with theories of cognitive mapping, rats were trained in three experiments exploring the effect of variations in spatial predictive relationships.

In experiment 1, it was found that making one of two landmarks the sole spatial predictor of reward, by varying the spatial relationship between reward and other cues, reduced the control over search exerted by that landmark compared with that observed when the landmark and context cues were both reliable predictors of reward location. This requirement for landmark stability rather than predictive power appears to contradict results obtained in conventional conditioning paradigms. Discrimination learning was unaffected, suggesting a dissociation between discrimination and spatial learning with respect to the influence of geometric stability. Further experiments used arrays of both single and multiple landmarks. Experiment 2 revealed that the stability of a single landmark improved accuracy of search, but also showed that local stability between a pair of landmarks that moved around the arena together was sufficient to support spatial learning. Experiment 3 examined landmark stability using fixed directional cues in the absence of vestibular disorientation. This also revealed a relative advantage of stable landmarks, but animals presented with a landmark that moved from trial to trial did show some evidence of learning.

Parametric manipulation of landmark stability offers an intriguing way of influencing the process of spatial representation and thus understanding better the processes through which egocentric representations of perceived space are transformed into allocentric representations of the real world.
Short-Range Navigation: Does it Contribute to Understanding Navigation Over Longer Distances?
Authors: Collett T. S.
Published: April 2021

A major reason for analysing short-range navigation is that it is relatively easy to record on video tape the details of an animal’s behaviour over an area of about a square metre. Frequently, the orientation of the animal’s body is revealed in addition to its trajectory through space. This is particularly useful in the study of insect navigation, the subject of the four contributions to this section. An insect’s eyes are fixed in its head, and there are often no significant head movements during flight. Consequently, reasonable assumptions can be made about where the insect looks while it navigates and how the image of its surroundings moves over its retina. All four contributions depend to a large degree upon being able to freeze behaviour on video tape and to infer what the animal sees. To what extent do the conclusions using the abundant information that can be collected in this way extrapolate to navigation on a larger scale? Clearly, the coded information that instructs the monarch butterfly on its migrations from wide areas of North America to northern Michoacan in Mexico contains elements unique to long-distance travel. But there may be many similarities in the mechanisms available to an orchid bee as it travels over its 20 km foraging route from orchid to orchid and a wasp negotiating the last few metres through a complex environment to reach its nest.
Insect Navigation En Route to the Goal: Multiple Strategies for the Use of Landmarks
Authors: Collett T. S.
Published: April 2021

There are at least four distinct ways in which familiar landmarks aid an insect on its trips between nest and foraging site. Recognising scenes: when bees are displaced unexpectedly from their hive to one of several familiar locations, they are able to head in the direction of home as though they had previously linked an appropriate directional vector to a view of the scene at the release site. Biased detours: ants recognise familiar landmarks en route and will correct their path by steering consistently to the left or to the right around them. Aiming at beacons: bees and ants also guide their path by approaching familiar landmarks lying on or close to the direct line between start and finish. Simulations suggest that such mechanisms acting together may suffice to account for the routes taken by desert ants through a landmark-strewn environment: the stereotyped trajectories of individual ants can be modelled by a weighted combination of dead reckoning, biased detours and beacon-aiming. These mechanisms guide an insect sufficiently close to an inconspicuous goal for image matching to be successfully employed to locate it. Insects then move until their current retinal image matches a stored view of the surrounding panorama seen from a vantage point close to the goal.

Bees and wasps perform learning flights on their first departure from a site to which they will return. These flights seem to be designed to pick up the information needed for several navigational strategies. Thus, a large portion of the learning flight of a bee leaving a feeder tends to be spent close to the feeder so aiding the acquisition of a view from that vantage point, as is needed for image matching. Bees and social wasps also tend to inspect their surroundings while facing along preferred directions and to adopt similar bearings before landing, thereby making it easy to employ retinotopically stored patterns in image matching. Aiming at beacons, in contrast, requires a landmark to be familiar to the frontal retina. Objects tend to be viewed frontally while the insect circles through arcs centred on the goal. This procedure may help insects to pick out those objects close to the goal that are best suited for guiding later returns.
Magnetic Orientation in Birds
Authors: Wiltschko Wolfgang , Wiltschko Roswitha
Published: April 2021

The magnetic field of the earth is an omnipresent, reliable source of orientational information. A magnetic compass has been demonstrated in 18 species of migrating birds. In all species studied with regard to its functional properties, it was found to be an ‘inclination compass’, i.e. the birds derive directional information from the inclination of the field lines, and thus distinguish between ‘poleward’ and ‘equatorward’ rather than ‘north’ and ‘south’. Such a mechanism means that birds from the northern and southern hemisphere may rely on the same migratory programme. Long-distance migrants, however, face the problem that their magnetic compass gives bimodal information at the magnetic equator. Transfers of information between the magnetic field and celestial sources of directional information have been demonstrated; the two systems interact in a complex way. The data on the use of magnetic parameters for position finding are less clear. The experiments involve releases of homing pigeons; correlations of their orientation with natural variations in the magnetic field and the effects of magnetic manipulation reveal an enormous variability. The role of magnetic parameters in the multifactorial navigational system is poorly understood.
Orientation and Open-Sea Navigation in Sea Turtles
Authors: Lohmann Kenneth J. , Lohmann Catherine M. F.
Published: April 2021

Loggerhead sea turtle hatchlings (Caretta caretta L.) emerge from underground nests, scramble to the sea and begin a transoceanic migration by swimming away from their natal beach and into the open ocean. Evidence suggests that hatchlings sequentially use three different sets of cues to maintain orientation during their initial migration offshore. While on the beach, hatchlings find the ocean by crawling towards the lower, brighter seaward horizon and away from the dark, elevated silhouettes of vegetation and dunes. Upon entering the ocean, turtles initially orient seawards by swimming into waves, which can be detected as orbital movements from under water.

Laboratory experiments have demonstrated that turtles can transfer a course initiated on the basis of waves or visual cues to a course mediated by a magnetic compass. Thus, by setting a magnetic course on the basis of nearshore cues that indicate the seaward direction, hatchlings may continue on offshore headings after entering deep water beyond sight of land.

Sea turtles may use the earth’s magnetic field not only as a cue for compass orientation but also as a source of world-wide positional information. Recent experiments have demonstrated that loggerheads can detect subtle differences in magnetic field inclination and intensity, two geomagnetic features that vary across the surface of the earth. Because most nesting beaches and oceanic regions are marked by a unique combination of these features, these findings raise the possibility that adult sea turtles navigate using a bicoordinate magnetic map.
Monarch Butterfly Orientation: Missing Pieces of a Magnificent Puzzle
Authors: Brower Lincoln P.
Published: April 2021

From late August to early September, millions of adult monarch butterflies of the eastern North American population cease reproducing, become highly gregarious and begin migrating southwards. By mid-October, they migrate through central Texas into Mexico where they follow the Sierra Madre Oriental across the Tropic of Cancer. They then shift direction westwards towards the Transverse Neovolcanic Belt of mountains where they overwinter without breeding. A rapid exodus northwards occurs at the spring equinox, and by early April both sexes reach the Gulf Coast states where the females lay eggs on the resurgent spring milkweed (Asclepias) flora and die. Adults of the new generation continue the migration to the northernmost breeding range, arriving by early June. Two or more short-lived breeding generations are produced over the summer, spread eastwards across the Appalachian Mountains and, by September, the autumn migration is again under way. This paper presents a new hypothesis that the orientation of adult monarchs undergoes a continual clockwise shifting throughout the 3–5 generations, rotating by 360 ° in the course of the year. This hypothesis is consistent with the timing of arrivals and the relative abundances of the successive generations of monarchs throughout eastern North America, with the directions of movement of their spring, summer and autumn generations, and with the timing of their arrival at the overwintering area in central Mexico.
The Interaction of Pulmonary Ventilation and the Right–Left Shunt on Arterial Oxygen Levels
Authors: Wang Tobias , Hicks James W.
Published: April 2021

In adult mammals, arterial blood gases closely reflect lung gas composition, and arterial blood gases can, therefore, be effectively regulated through changes in ventilation. This is not the case among most ectothermic vertebrates, where the systemic and pulmonary circulations are not completely separated, resulting in central vascular shunts. In the presence of a right-to-left shunt (R–L shunt), the O2 levels ( and haemoglobin O2-saturation) of systemic arterial blood are depressed relative to those of the blood returning from the lungs. Arterial blood gas composition is, accordingly, not determined only by ventilation, but also by the magnitude of admixture as well as the blood gas composition of systemic venous blood. Changes in the central shunt patterns, therefore, represent an alternative mechanism by which to control arterial blood gas levels. The primary aim of this report is to evaluate the relative importance of the R–L shunt and ventilation in determining arterial blood gas levels.

Using standard equations for gas exchange and the two-compartment model, we predicted arterial O2 levels at physiologically relevant levels of ventilation, R–L shunt and blood flows. The analyses show that the effects of changing ventilation and the size of the R–L shunt on arterial O2 levels vary with parameters such as the rate of O2 uptake, the blood O2-carrying capacity and the level of hypoxia. The relative importance of ventilation and the R–L shunt in determining arterial values is largely explained by the sigmoidal shape of the O2 dissociation curve. Thus, if lung is high relative to blood O2 affinity, a large change in ventilation may have little effect on pulmonary venous O2 content, although may have changed considerably. If an R–L shunt is taking place, this, in turn, implies that arterial O2 content is affected only marginally, with a correspondingly small effect on . These predictions are discussed in the light of the limited existing experimental data on cardiac shunts in lower vertebrates; we propose that, in future experiments, the measurement of both ventilatory and cardiovascular parameters must be combined if we aim to understand the regulation of arterial blood gas levels in lower vertebrates.
Functions of Fish Skin: Flexural Stiffness and Steady Swimming of Longnose Gar Lepisosteus Osseus
Authors: Long John H. , Hale Melina E. , Mchenry Matt J. , Westneat Mark W.
Published: April 2021

The functions of fish skin during swimming remain enigmatic. Does skin stiffen the body and alter the propagation of the axial undulatory wave? To address this question, we measured the skin’s in situ flexural stiffness and in vivo mechanical role in the longnose gar Lepisosteus osseus. To measure flexural stiffness, dead gar were gripped and bent in a device that measured applied bending moment (N m) and the resulting midline curvature (m−1). From these values, the flexural stiffness of the body (EI in N m2) was calculated before and after sequential alterations of skin structure. Cutting of the dermis between two caudal scale rows significantly reduced the flexural stiffness of the body and increased the neutral zone of curvature, a region of bending without detectable stiffness. Neither bending property was significantly altered by the removal of a caudal scale row. These alterations in skin structure were also made in live gar and the kinematics of steady swimming was measured before and after each treatment. Cutting of the dermis between two caudal scale rows, performed under anesthesia, changed the swimming kinematics of the fish: tailbeat frequency (Hz) and propulsive wave speed (body lengths per second, L s−1) decreased, while the depth (in L) of the trailing edge of the tail increased. The decreases in tailbeat frequency and wave speed are consistent with predictions of the theory of forced, harmonic vibrations; wave speed, if equated with resonance frequency, is proportional to the square root of a structure’s stiffness. While it did not significantly reduce the body’s flexural stiffness, surgical removal of a caudal scale row resulted in increased tailbeat amplitude and the relative total hydrodynamic power. In an attempt to understand the specific function of the scale row, we propose a model in which a scale row resists medio-lateral force applied by a single myomere, thus functioning to enhance mechanical advantage for bending. Finally, surgical removal of a precaudal scale row did not significantly alter any of the kinematic variables. This lack of effect is associated with a lower midline curvature of the precaudal region during swimming compared with that of the caudal region. Overall, these results demonstrate a causal relationship between skin, the passive flexural stiffness it imparts to the body and the influence of body stiffness on the undulatory wave speed and cycle frequency at which gar choose to swim.
Contributions of Structure and Innervation Pattern of the Stick Insect Extensor Tibiae Muscle to the Filter Characteristics of the Muscle–Joint System
Authors: Bässler Ulrich , Stein Wolfgang
Published: April 2021

It is shown that the low-pass filter characteristics of the muscle–joint system of the femur–tibia joint of the stick insect Cuniculina impigra result from co-contraction of the extensor and flexor tibiae muscles. The most distal region of the extensor muscle, which contains a high percentage of slow muscle fibres, is involved in this co-contraction. This conclusion results from the following evidence. (1) Inertial and friction forces do not affect the characteristics of the low-pass filter of the muscle–joint system. (2) There is some co-contraction of the extensor and flexor muscles during sinusoidal stimulation of the femoral chordotonal organ at high stimulus frequencies. Both muscles generate tonic forces that increase with increasing stimulus frequency and also increase with time from the beginning of stimulation until a plateau is reached. (3) For the extensor muscle, this tonic force is produced by its most distal portion only. (4) Electrical stimulation of the common inhibitory motoneurone (CI1) reduces the tonic force generated in this most distal portion of the extensor muscle. Therefore, CI1 stimulation reduces the amplitude of tibial movement in response to sinusoidal stimulation of the femoral chordotonal organ at stimulus frequencies below 0.5 Hz (over this frequency range, the tibial movement amplitude is a function of the force amplitude produced by the whole extensor muscle and there is no co-contraction), but at chordotonal organ stimulus frequencies of 1 Hz and above, CI1 stimulation increases the tibial movement amplitude (in this case, movement amplitude is limited by the degree of co-contraction of the extensor and flexor muscles).

With repeated chordotonal organ stimulation at higher stimulus frequencies, the tibial movement amplitude steadily decreases. This must be a consequence of increasing levels of co-contraction of the extensor and flexor muscles, since at low stimulus frequencies (no co-contraction) there is no reduction in movement amplitude during repeated stimulations.

It is concluded that co-contraction of the extensor and flexor tibiae muscles prevents instability in the reflex loop in spite of the high gain necessary for the generation of catalepsy. Therefore, the mechanism described can be considered to be an adaptation to the ecological niche occupied by this animal. The contribution of the distal part of the extensor muscle to this system can be switched off by the CI1 during active movements.
Heterocercal Tail Function in Leopard Sharks: A Three-Dimensional Kinematic Analysis of Two Models
Authors: Ferry Lara A. , Lauder George V.
Published: April 2021

Two different models have been proposed to explain the function of the heterocercal tail in shark locomotion. The classical model proposes that, as a result of lift generated by the tail as it beats, the net force acting on the tail is directed dorsally and anteriorly. In contrast, Thomson’s model suggests that the tail generates a net force directed through the shark’s center of gravity, i.e. ventrally and anteriorly. In this study, we evaluate these two models by describing the three-dimensional kinematics of the heterocercal tail in the leopard shark Triakis semifasciata during swimming. Lateral and posterior views of the tail were examined from four individuals swimming in a flow tank at 1.2 L s−1 (where L is total length) using two high-speed video cameras filming simultaneously at 250 fields s−1. These two simultaneous views allowed eight landmarks on the tail to be followed in three dimensions through time. These landmarks allowed the tail to be divided into separate surfaces whose orientation over time was calculated. Points located anteriorly on the tail go through significantly smaller excursions and reach their maximum lateral excursion significantly earlier in the beat cycle than points on the trailing edge of the tail. Three-dimensional angle calculations show that the terminal lobe leads the ventral lobe through a beat, as predicted by the classical model. Dye-stream visualizations confirmed that this pattern of movement deflects water ventrally and posteriorly to the moving tail, providing strong support for the classical model. Additionally, our results show that a three-dimensional analysis is critical to understanding the function of the heterocercal tail.
Electrophysiological and Endocrinological Evidence That F-Series Prostaglandins Function as Priming Pheromones in Mature Male Atlantic Salmon (Salmo Salar) Parr
Authors: Moore Andrew , Waring Colin P.
Published: April 2021

Previous work has demonstrated that the urine from mature female salmonids contains a priming pheromone that significantly enhances the reproductive physiology of receiving males. The chemical identity of the pheromone(s) has not yet been identified. The present study investigated the possibility that F-type prostaglandins (PGFs) may have a pheromonal role in Atlantic salmon by measuring the olfactory sensitivity of male salmon to PGFs, the effect of waterborne PGFs on male reproductive physiology and the PGF content of mature female urine. Electrophysiological studies demonstrated that the olfactory epithelium of mature male salmon parr was acutely sensitive to PGF1α and PGF2α, with detection threshold concentrations of 10−11 mol l−1. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF2α (threshold 10−8 mol l−1), but did not detect a further metabolite, 13,14-dihydro-15-ketoPGF2α. Sensitivity to both PGF1α and PGF2α increased as the reproductive season progressed. Exposure of mature male parr to waterborne PGF1α and PGF2α (10−8 mol l−1) resulted in significant increases in levels of expressible milt and in the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. Urine from ovulated female salmon also contained large quantities (18 ng ml−1) of immunoreactive PGFs, whereas urine from mature males and non-ovulated mature females contained significantly smaller amounts (<1 ng ml−1). The results support the theory that PGFs function as priming pheromones in Atlantic salmon and are released in the urine of ovulated female salmon. The involvement of these pheromones in synchronising male–female salmon spawning is discussed.
Mitochondria-Rich, Proton-Secreting Epithelial Cells
Authors: Brown Dennis , Breton Sylvie
Published: April 2021

Several transporting epithelia in vertebrates and invertebrates contain cells that are specialized for proton or bicarbonate secretion. These characteristic ‘mitochondria-rich’ (MR) cells have several typical features, the most important of which is an extremely high expression of a vacuolar-type proton-pumping ATPase (H+V-ATPase) both on intracellular vesicles and on specific domains of their plasma membrane. Physiological modulation of proton secretion is achieved by recycling the H+V-ATPase between the plasma membrane and the cytoplasm in a novel type of nonclathrin-coated vesicle. In the kidney, these cells are involved in urinary acidification, while in the epididymis and vas deferens they acidify the luminal environment to allow normal sperm development. Osteoclasts are non-epithelial MR cells that use H+V-ATPase activity for bone remodeling. In some insects, similar cells in the midgut energize K+ secretion by means of a plasma membrane H+V-ATPase. This review emphasizes important structural and functional features of proton-secreting cells, describes the tissue distribution of these cells and discusses the known functions of these cells in their respective epithelia.
New Features of the Locust Optic Lobe: Evidence of a Role for Nitric Oxide in Insect Vision
Authors: Elphick Maurice R. , Williams Les , O’shea Michael
Published: April 2021

The enzyme nitric oxide synthase can be localised by NADPH-diaphorase histochemistry. Here we have applied this technique to the optic lobe of the locust Schistocerca gregaria and revealed new features of the insect visual system. Extensive but locally intense staining is associated with identified tracts, distinct neuropiles and cell body groups, and a detailed analysis of stained elements is provided here. The most striking staining occurs in the anterior lo Nbe of the lobula complex and its connection with the medulla by means of the dorsal uncrossed bundle. Eleven groups of cell bodies are identified and their contribution to fibre tracts and neuropile areas is described. Diaphorase-positive fibre tracts pass between all major subdivisions of the optic lobe, but there are no conspicuous fibre connections from the optic lobe to the brain. The widespread distribution of NADPH-diaphorase staining in the optic lobe suggests that nitric oxide is likely to play an important role in information processing in insect vision.
Gain Changes in Sensorimotor Pathways of the Locust Leg
Authors: Büschges Ansgar , Wolf Harald
Published: April 2021

Feedback systems that control the leg joints of animals must be highly flexible in adapting to different behavioural tasks. One manifestation of such flexibility is changes in the gain of joint control networks. The femur–tibia (FT) control network of the locust leg is one of the feedback systems most thoroughly studied with regard to its neural circuitry. Despite excellent information concerning network topology, however, actual gain changes and their underlying mechanisms have not yet been examined because of the marked spontaneous variations in the action of the control network for this joint. We describe a behavioural situation and a preparation in which the locust (Locusta migratoria L.) FT control network exhibits reproducible changes in gain, allowing investigation of the neuronal basis of gain control. After (‘fictive’) flight motor activity, the gain of resistance reflexes in the FT joint of the locust middle leg is significantly decreased, with the flexor tibiae muscles being affected more strongly than the extensor muscles. Immediately after flight motor activity, the gain may be as low as 30 % of pre-flight levels. It returns to pre-flight values in under 150 s.

The decrease in gain following flight motor activity is due to a decrease in motoneurone recruitment in the resistance reflex elicited by stimulation of the appropriate mechanoreceptor, the femoral chordotonal organ. Motoneurone recruitment is changed as a result of a drastic decline in the stimulus-related synaptic input to the motoneurones, which appears to be produced exclusively at the level of the pre-motor network. Two factors led to this conclusion: first, we found no indication of changes in membrane potential or membrane conductance of the tibia flexor and extensor motoneurones; second, recording from identified pre-motor nonspiking interneurones demonstrated that these may be involved in the observed gain changes. The putative behavioural relevance is discussed.
Mechanism and Possible Behavioural Relevance of Retinal Movements in the Ctenid Spider Cupiennius Salei
Authors: Kaps Florian , Schmid Axel
Published: April 2021

Like most spiders, the nocturnal hunting spider Cupiennius salei is able to move the retinae of its antero-median (AM) eyes. In the present study, the morphological and physiological properties of the eye muscles and the mechanism and behavioural relevance of retinal movements are investigated.

The retinal movements are brought about by two forces: (i) contractions of the dorsal and ventral eye muscles, and (ii) the passive elastic restoring force of the eye tube and eye muscles (the presumed counteracting force). The dorsal eye muscle consists of 15–18 striated fibres and is 600 µm long. The ventral eye muscle is longer (650 µm) and consists of 20–22 striated fibres.

The direction of the gaze of the retinae brought about by the eye muscles (active retinal movements) depends on the contraction states of the two eye muscles. The medially directed action of both eye muscles does not allow active movements of the eye tube in any lateral direction. Thus, the direction of gaze cannot actively be shifted medially. After active displacement of the retina, the elasticity of the eye tube and eye muscles passively moves the eye tube back to its resting position.

There are two types of retinal movements. (i) Spontaneous microsaccades (duration 80ms; excursion 3 °) are caused by the spontaneous contraction of only the dorsal eye muscle. They are ideally suited for preventing the adaptation of the sensory cells since their mean excursion (3°) perfectly fits the inter-receptor angle (2.9°) in the AM eye of Cupiennius salei. (ii) Induced movements (duration 100–500ms; excursions 4–15°) are caused by the contraction of both eye muscles and occur only after mechanical stimulation. Induced movements were elicited by stimulating the mechanosensory organs (trichobothria and slit sense organs) of the spider’s legs. A stimulus on one side of the spider induces movements of the ipsilateral retina only. We therefore suggest that induced retinal movements are saccades shifting the gaze of the spider laterally towards the site of mechanical stimulation.

According to behavioural experiments, the ability of a spider to locate an immobile target is highly impaired after blinding its AM eyes. We suggest that the motility of the AM eyes is required to locate stationary objects.
Food-Deprivation Affects Seawater Acclimation in Tilapia: Hormonal and Metabolic Changes
Authors: Vijayan Mathilakath M. , Morgan John D. , Sakamoto Tatsuya , Grau E. Gordon , Iwama George K.
Published: April 2021

We tested the hypothesis that nutritional state affects seawater acclimation by transferring either fed or food-deprived (2 weeks) male tilapia (Oreochromis mossambicus) from fresh water to full-strength sea water. Food-deprivation resulted in a significant increase in plasma concentrations of Na+, Cl−, cortisol, glucose, total amino acid, glutamate, serine and alanine, and in hepatic pyruvate kinase (PK) and lactate dehydrogenase (LDH) activities, whereas the prolactin-188 to prolactin-177 ratio (tPRL188:tPRL177) and plasma prolactin-188 (tPRL188), lactate, arginine and hepatic glycogen content and hepatic alanine aminotransferase (AlaAT) and 3-hydroxyacyl-Coenzyme A dehydrogenase (HOAD) activities were lower than in the fed group. Seawater transfer significantly increased the tPRL188:tPRL177 ratio and plasma concentrations of Na+, Cl−, K+, growth hormone (GH), glucose, aspartate, tyrosine, alanine, methionine, phenylalanine, leucine, isoleucine and valine levels as well as gill Na+/K+-ATPase activity and hepatic PK and LDH activities, whereas plasma tPRL177, tPRL188, glycine and lysine concentrations were significantly lower than in fish retained in fresh water. There was a significant interaction between nutritional state and salinity that affected the tPRL188:tPRL177 ratio and plasma concentrations of Cl−, GH, glucose, aspartate, tyrosine, serine, alanine, glycine, arginine and hepatic PK, LDH, AlaAT, aspartate aminotransferase, glutamate dehydrogenase and HOAD activities. These results, taken together, indicate that food-deprived fish did not regulate their plasma Cl− levels, despite an enhancement of plasma hormonal and metabolic responses in sea water. Our study also suggests the possibility that plasma prolactin and essential amino acids may be playing an important role in the seawater acclimation process in tilapia.
Axial Muscle Function During Lizard Locomotion
Authors: Ritter Dale
Published: April 2021

It was recently reported that the epaxial muscles of a lizard, Varanus salvator, function to stabilize the trunk during locomotion, and it was suggested that this stabilizing role may be a shared derived feature of amniotes. This result was unexpected because it had previously been assumed that the epaxial muscles of lizards function to produce lateral bending during locomotion and that only in mammals and birds were the epaxial muscles active in stabilizing the trunk. These results and the inferences made from them lead to two questions. (1) Is the pattern of epaxial muscle activity observed in V. salvator representative of a basal lizard condition or is it a derived condition that evolved within lizards? (2) If the epaxial muscles do not produce lateral bending, which muscles do carry out this function? These questions were addressed by collecting synchronous electromyographic (EMG) and kinematic data from two lizard species during walking and running. EMG data were collected from the epaxial muscles of a lizard species from a basal clade, Iguana iguana, in order to address the first question. EMG data were collected from the hypaxial muscles of both Iguana iguana and Varanus salvator to address the second question. The timing of epaxial muscle activity in Iguana iguana relative to the kinematics of limb support and lateral trunk bending is similar to that observed in Varanus salvator, a finding that supports the hypothesis that the epaxial muscles stabilize the trunk during locomotion in lizards and that this stabilizing role is a basal feature of lizards. Therefore, a stabilizing function of the epaxial muscles is most parsimoniously interpreted as a basal amniote feature. In both Iguana iguana and Varanus salvator, the activity of two of the hypaxial muscles, the external oblique and rectus abdominis, is appropriately timed for the production of lateral bending. This indicates that elements of the hypaxial musculature, not the epaxial musculature, are the primary lateral bending muscles of lizards.
Prolactin Antagonizes the Corticoid-Promoted Development of Adult-Type Epidermis in Cultured Larval Bullfrog Skin
Authors: Takada Makoto , Yai Hideko , Komazaki Shinji , Takayama-Arita Kazue
Published: April 2021

EDTA-treated larval bullfrog skin, in which apical and skein cells had been removed and only basal cells remained, was cultured in one of four media. These contained either aldosterone (Aldo) or a mixture of Aldo, hydrocortisone (HC) and corticosterone (C), each either supplemented with prolactin (PRL) or lacking PRL. Skin cultured with Aldo alone or with the corticoid mixture (Aldo+HC+C) developed an adult-type epidermis: (i) both types of skin reacted to human blood group antigen A, a marker for the adult-type epidermis of bullfrog skin; (ii) amiloride decreased the short-circuit current Isc in these skin preparations, but acetylcholine (ACh) had no effect on the Isc. It seemed to make little difference to the results whether the skin was cultured with Aldo or with the corticoid mixture. PRL antagonized the action of Aldo and induced the development of a larval-type epidermis in both skin preparations: (i) the skin preparations did not react to human blood group antigen A; (ii) acetylcholine and amiloride each stimulated Isc in these preparations. Since ACh and amiloride each stimulated the Isc in skin with apical cells, ACh/amiloride-stimulated channels may be located on these cells.
Comparison Of The Fast-Start Performances Of Closely Related, Morphologically Distinct Threespine Sticklebacks (Gasterosteus Spp.)
Authors: Law T. C. , Blake R. W.
Published: April 2021

Fast-start escape performances for two species of threespine stickleback, Gasterosteus spp., were investigated using high-speed cinematography (400 Hz). The two fishes (not yet formally described, referred to here as benthic and limnetic) inhabit different niches within Paxton Lake, British Columbia, Canada, and are recent, morphologically distinct species. All escape responses observed for both species were double-bend C-type fast-starts. There were no significant differences between the species for any linear or angular parameter (pooled averages, both species: duration 0.048 s, distance 0.033 m, maximum velocity 1.10 m s−1, maximum acceleration 137m s−2, maximum horizontal angular velocity 473.6 rad s−1 and maximum overall angular velocity 511.1 rad s−1). Benthics and limnetics have the greatest added mass (Ma) at 0.3 and 0.6 body lengths, respectively. The maximum Ma does not include the fins for benthics, but for limnetics the dorsal and anal fins contribute greatly to the maximum Ma. The deep, posteriorly placed fins of limnetics enable them to have a fast-start performance equivalent to that of the deeper-bodied benthics.

Both the limnetic and benthic fishes have significantly higher escape fast-start velocities than their ancestral form, the anadromous threespine stickleback Gasterosteus aculeatus, suggesting that the high performance of the Paxton Lake sticklebacks is an evolutionarily derived trait. In this biomechanical study of functional morphology, we demonstrate that similar high fast-start performance can be achieved by different suites of morphological characteristics and suggest that predation might be the selective force for the high escape performance in these two fishes.