bluuebunny/crossref_metadata_2025_split huggingface dataset:
Initiation of locomotion by lateral line photoreceptors in lamprey: behavioural and neurophysiological studies
Authors: Deliagina T. G. , Ullén F. , Gonzalez M.-J. , Ehrsson H. , Orlovsky G. N. , Grillner S. 
Published: April 2021

ABSTRACT
The lateral line system of lampreys includes photoreceptors distributed in the skin of the tail region. These are innervated by the trunk lateral line nerves, and the afferents terminate bilaterally in the medial octavolateral nucleus, crossing the midline through the cerebellar commissure. Stimulation of the dermal photoreceptors by tail illumination initiates locomotion. The present study was performed to characterize the response to illumination in larval and adult lampreys in detail and to elucidate the neuronal pathways responsible for the activation of locomotion. In both larval and adult quiescent lampreys, the response to unilateral illumination of the tail was found to consist of an initial turn followed by rectilinear swimming. The sign and magnitude of the turning angle were not correlated with the laterality of the optic stimulus. In mechanically restrained lampreys, spinalized at the level of segments 15–20, tail illumination evoked a complex motor response in the rostral part of the body, with switches between different patterns of coordination (turns in different directions, locomotion, and turns combined with locomotion). Thus, the response to tail illumination is not a simple reflex, but includes a behavioural choice.
Reticulospinal neurones play a crucial role in the initiation of locomotion in lampreys. The response to unilateral tail illumination in rhombencephalic reticular cells was studied with extracellular single-unit recordings. It was found that neurones in the middle and posterior rhombencephalic reticular nuclei were activated bilaterally. Tonic activity or slow bursts (&lt;0.5 Hz) were evoked, in some cases lasting up to 60 s after the stimulation. The response remained bilateral after transection of one lateral line nerve and the cerebellar commissure. Afferents from one side can thus activate reticulospinal cells on both sides through a pathway outside the cerebellar commissure. This bilateral activation of reticulospinal neurones is presumably responsible for the activation of spinal locomotor networks, without any directional bias to the left or the right side, and for the rectilinear swimming observed in behavioural experiments.
In the caudal part of the termination area of the lateral line nerve afferents, neurones with contralateral projections were retrogradely stained with horseradish peroxidase. These neurones appear to be likely candidates for mediating the contralateral effects of the lateral line fibres.
The Force–velocity Relationship of the Atp-Dependent Actin–Myosin Sliding Causing Cytoplasmic Streaming in Algal Cells, Studied Using a Centrifuge Microscope
Authors: Chaen S. , Inoue J. , Sugi H. 
Published: April 2021

ABSTRACT
When uncoated polystyrene beads suspended in Mg-ATP solution were introduced into the internodal cell of an alga Chara corallina, the beads moved along the actin cables with directions and velocities (30–62 µm s−1) similar to those of native cytoplasmic streaming. Bead movement was inhibited both in the absence of ATP and in the presence of Ca2+, as with native cytoplasmic streaming. These results indicate that bead movement is caused by cytoplasmic myosin molecules attached to the bead surface interacting with actin cables. The steady-state force–velocity relationship of the actin–myosin sliding that produces cytoplasmic streaming was determined by applying constant centrifugal forces to the beads moving on the actin cables. The force–velocity curve in the positive load region was nearly straight, and the implications of this shape are discussed in connection with the kinetic properties of the actin–myosin interaction in cytoplasmic streaming. It is suggested that the time for which a cytoplasmic myosin head is detached from actin in one cycle of actin–myosin interaction is very short. The Ca2+-induced actin–myosin linkages, responsible for the Ca2+-induced stoppage of cytoplasmic streaming, were shown to be much stronger than the rigor actin–myosin linkages.
The Role of l-Dopa in the Nervous System of Sea Anemones: A Putative Inhibitory Transmitter in Tentacles
Authors: Hudman Diane , McFARLANE Ian D. 
Published: April 2021

ABSTRACT
L-Dopa evokes transitory inhibition of spontaneous contractions of tentacle longitudinal muscles in sea anemones. It also modulates spontaneous contractions of the sphincter muscle in isolated preparations and whole animals. Extracellular recordings from the tentacles of Calliactis parasitica show that L-Dopa evokes bursts of electrical events apparently associated with a local nerve net. We propose that L-Dopa be added to the growing list of putative transmitter substances in sea anemones, its action being to coordinate local inhibition of spontaneous tentacle contractions.
Serotonergic Modulation of Swimming Speed in the Pteropod Mollusc Clione Limacina: III. Cerebral Neurons
Authors: Satterlie Richard A. , Norekian Tigran P. 
Published: April 2021

ABSTRACT
Swim acceleration in Clione limacina can occur via central inputs to pattern generator interneurons and motor neurons and through peripheral inputs to the swim musculature. In the previous paper, peripheral modulation of the swim muscles was shown to increase wing contractility. In the present paper, central inputs are described that trigger an increase in swim frequency and an increase in motor neuron activity. In dissected preparations, spontaneous acceleration from slow to fast swimming included an increase in the cycle frequency, a baseline depolarization in the swim interneurons and an increase in the intensity of motoneuron firing. Similar effects could be elicited by bath application of 10−5 mol l−1 serotonin. Two clusters of cerebral serotonin-immunoreactive interneurons were found to produce acceleration of swimming accompanied by changes in neuronal activity. Posterior cluster neurons triggered an increase in swim frequency, depolarization of the swim interneurons, an increase in general excitor motoneuron activity and activation of type 12 interneurons and pedal peripheral modulatory neurons. Cells from the anterior cerebral cluster also increased swim frequency, increased activity in the swim motoneurons and activated type 12 interneurons, pedal peripheral modulatory neurons and the heart excitor neuron. The time course of action of the anterior cluster neurons did not greatly outlast the duration of spike activity, while that of the posterior cluster neurons typically outlasted burst duration. It appears that the two discrete clusters of serotonin-immunoreactive neurons have similar, but not identical, effects on swim neurons, raising the possibility that the two serotonergic cell groups modulate the same target cells through different cellular mechanisms.
Functional Characterization of Leucine Transport Induced in Xenopus Laevis Oocytes Injected With mRNA Isolated From Midguts of Lepidopteran Larvae (Philosamia Cynthia)
Authors: Sacchi V. Franca , Perego Carla , Magagnin Simona 
Published: April 2021

ABSTRACT
The injection of poly(A)+ mRNA prepared from Philosamia cynthia midgut caused time-and dose-dependent increases of leucine transport in Xenopus laevis oocytes, with an increase in leucine uptake 1.5–3 times that of oocytes injected with water. When the NaCl concentration was reduced from 100 to 5 mmol l−1, the difference between mRNA-and water-injected oocytes was greater and a fourfold increase of L-leucine uptake was measured. D-Leucine (10 mmol l−1) completely inhibited the induced uptake of 0.1 mmol l−1 L-leucine. The newly expressed component of L-leucine uptake increased at alkaline pH and was abolished by incubation for 15 min with 15 mmol l−1 phenylglyoxal. The mean Km values, calculated using Na+ activation curves of leucine uptake, were 23.3±6.1 mmol l−1 in water-injected oocytes and 0.4±0.2 mmol l−1 for the newly expressed component of leucine uptake in mRNA-injected oocytes. On the basis of these results, we conclude that the increase of L-leucine uptake in mRNA-injected oocytes was due to the expression of a new transport system, which differs from the endogenous ones and shares many features with that found previously in Philosamia cynthia midgut.
The Emg–Force Relationship of the Cat Soleus Muscle and its Association with Contractile Conditions During Locomotion
Authors: Guimaraes A. C. , Herzog W. , Allinger T. L. , Zhang Y. T. 
Published: April 2021

ABSTRACT
The relationship between force and electromyographic (EMG) signals of the cat soleus muscle was obtained for three animals during locomotion at five different speeds (154 steps), using implanted EMG electrodes and a force transducer. Experimentally obtained force–IEMG (=integrated EMG) relationships were compared with theoretically predicted instantaneous activation levels calculated by dividing the measured force by the predicted maximal force that the muscle could possibly generate as a function of its instantaneous contractile conditions. In addition, muscular forces were estimated from the corresponding EMG records exclusively using an adaptive filtering approach. Mean force–IEMG relationships were highly non-linear but similar in shape for different cats and different speeds of locomotion. The theoretically predicted activation–time plots typically showed two peaks, as did the IEMG–time plots. The first IEMG peak tended to be higher than the second one and it appeared to be associated with the initial priming of the muscle for force production at paw contact and the peak force observed early during the stance phase. The second IEMG peak appeared to be a burst of high muscle activation, which might have compensated for the levels of muscle length and shortening velocity that were suboptimal during the latter part of the stance phase. Although it was difficult to explain the soleus forces on the basis of the theoretically predicted instantaneous activation levels, it was straightforward to approximate these forces accurately from EMG data using an adaptive filtering approach.
Ca2+ and Zn2+ Are Transported by the Electrogenic 2Na+/1H+ Antiporter in Echinoderm Gastrointestinal Epithelium
Authors: Zhuang Zhenpeng , Duerr Jeffrey M. , Ahearn Gregory A. 
Published: April 2021

ABSTRACT
45Ca2+ uptake by purified brush-border membrane vesicles of starfish (Pycnopodia helianthoides) pyloric ceca was stimulated by an outwardly directed H+ gradient and this stimulation was enhanced by the simultaneous presence of an induced membrane potential (inside negative; K+/valinomycin). External amiloride (competitive inhibitor; Ki=660 μmol l−1) and a monoclonal antibody raised against proteins associated with the lobster (Homarus americanus) electrogenic 2Na+/1H+ antiporter both inhibited approximately half of the proton-gradient-stimulated 45Ca2+ uptake. These results suggested that Ca2+ might be transported by the electrogenic antiporter and that the crustacean antibody was inhibitory to the exchange function in echinoderms, as was recently shown in crustacean epithelial brush-border membrane vesicles. Carrier-mediated 45Ca2+ influx by amiloride-sensitive and amiloride-insensitive systems displayed the following kinetic constants: (amiloride-sensitive) Kt=66±2 μmol l−1; Jmax=0.173±0.002 pmol μg−1 protein 8 s−1; (amiloride-insensitive) Kt=18±0.3 μmol l−1; Jmax=0.100±0.001 pmol μg−1 protein 8 s−1. Zn2+ was a mixed inhibitor of 45Ca2+ influx by carrier-mediated transport, displaying a Ki of 920 μmol l−1. Mn2+, Cu2+, Fe2+ and Mg2+ also inhibited 45Ca2+ uptake, but the mechanism(s) of inhibition by these other cations was not disclosed. An equilibrium shift experiment showed that both Na+ and Zn2+ were able to exchange with equilibrated 45Ca2+ in these vesicles, suggesting that both monovalent and divalent cations were able to enter pyloric cecal cells through a common carrier-mediated transport system. In addition, the echinoderm electrogenic system appeared to exhibit a molecular component recognized by the crustacean antibody that may imply a similar epitope in the two animals.
On The Mechanism of Isomerization of Ocular Retinoids by the Crayfish Procambarus Clarkii
Authors: Srivastava Ranjana , Goldsmith Timothy H. 
Published: April 2021

ABSTRACT
The eyes of some crustaceans store substantial amounts of retinyl esters, with most of the retinol in the 11-cis configuration. Earlier work in this laboratory suggested that in lobster and crayfish the mechanism of isomerization of retinol to the 11-cis form involves the hydrolysis of all-trans retinyl esters. Although this is the same process as that occurring in the vertebrate eye, it is different from the retinal photoisomerase reaction known in other arthropods, specifically diurnal insects (Hymenoptera and probably Diptera). Using homogenates of crayfish, we have tested this proposed mechanism by inhibiting retinyl ester synthetase activity in the presence of exogenous all-trans retinol. Inhibition of lecithin:retinol acyl transferase with 5 μmol l-1 retinyl bromoacetate or 2 mmol l-1 phenylmethylsulfonyl fluoride blocks the formation of both all-trans and 11-cis retinyl esters as well as 11-cis retinol, as shown by direct assay and by the decrease in counts derived from tritiated all-trans retinol. The similarity of this isomerization to the mechanism in vertebrate pigment epithelium is thus an interesting example of convergent evolution in the biochemistry of visual pigments, in which the pigments themselves (the opsins) are largely conserved across phyla.
In Vivo Muscle Force–Length Behavior During Steady-Speed Hopping in Tammar Wallabies
Authors: Biewener Andrew A. , Konieczynski David D. , Baudinette Russell V. 
Published: April 2021

ABSTRACT
Moderate to large macropodids can increase their speed while hopping with little or no increase in energy expenditure. This has been interpreted by some workers as resulting from elastic energy savings in their hindlimb tendons. For this to occur, the muscle fibers must transmit force to their tendons with little or no length change. To test whether this is the case, we made in vivo measurements of muscle fiber length change and tendon force in the lateral gastrocnemius (LG) and plantaris (PL) muscles of tammar wallabies Macropus eugenii as they hopped at different speeds on a treadmill. Muscle fiber length changes were less than ±0.5 mm in the plantaris and ±2.2 mm in the lateral gastrocnemius, representing less than 2 % of total fiber length in the plantaris and less than 6 % in the lateral gastrocnemius, with respect to resting length. The length changes of the plantaris fibers suggest that this occurred by means of elastic extension of attached cross-bridges. Much of the length change in the lateral gastrocnemius fibers occurred at low force early in the stance phase, with generally isometric behavior at higher forces. Fiber length changes did not vary significantly with increased hopping speed in either muscle (P&gt;0.05), despite a 1.6-fold increase in muscle–tendon force between speeds of 2.5 and 6.0 m s−1. Length changes of the PL fibers were only 7±4 % and of the LG fibers 34±12 % (mean ± S.D., N=170) of the stretch calculated for their tendons, resulting in little net work by either muscle (plantaris 0.01±0.03 J; gastrocnemius −0.04±0.30 J; mean ± S.D.). In contrast, elastic strain energy stored in the tendons increased with increasing speed and averaged 20-fold greater than the shortening work performed by the two muscles. These results show that an increasing amount of strain energy stored within the hindlimb tendons is usefully recovered at faster steady hopping speeds, without being dissipated by increased stretch of the muscles’ fibers. This finding supports the view that tendon elastic saving of energy is an important mechanism by which this species is able to hop at faster speeds with little or no increase in metabolic energy expenditure.
Partitioning of Oxygen Uptake between the Gills and Skin in Fish Larvae: A Novel Method for Estimating Cutaneous Oxygen Uptake
Authors: Rombough Peter J. 
Published: April 2021

ABSTRACT
The goal of this study was to develop an alternative to the traditional rubber dam method for measuring cutaneous oxygen uptake in bimodally respiring (skin + gills) fish larvae. The method tested involved using microelectrodes to measure the gradient in the diffusive boundary layer adjacent to seven positions on the skin surface (one on the head, two on the yolk sac, two on the trunk, one at the base of the dorsal fin-fold and one on the proximal portion of the caudal fin-fold) of rainbow trout (Oncorhynchus mykiss) larvae in still water. The gradient , where x is the distance from the skin surface) wa.s then used to calculate area-specific rate of O2 uptake according to the Fick equation, , where A is the cross-sectional area of the boundary layer, D is the diffusion coefficient and β is the capacitance coefficient for O2 in water. The accuracy of the method was assessed by comparing it with the rubber dam method. After correcting for differences in body mass, the two methods gave essentially identical results. According to the boundary layer method, the mean (±95 % CI) rate of O2 uptake across the skin of newly hatched rainbow trout at 10 °C is 3.13±0.18 μg O2 cm−2 h−1 (N=265).
The corresponding value obtained using the rubber dam method was 3.36±0.35 μg O2 cm−2 h−1 (N=27). The advantages of the boundary layer method are that it can be used with smaller, more delicate larvae and that variables, such as flow rate, that can affect the efficiency of gas exchange can be regulated more precisely. The boundary layer method also permits examination of regional differences in exchange efficiency, although in still water such differences do not appear to be significant in trout larvae. The mean steepness of the gradient in the boundary layer and, hence, the mean rate of area-specific O2 uptake were essentially the same (P&gt;0.05) at all seven locations tested in this study. The boundary layer method can potentially be used to study the transcutaneous flux, not only of O2 but of virtually any diffusible substance that can be measured with microelectrodes and that is consumed (e.g. Na+, Ca2+) or excreted (e.g. CO2, NH3) by fish larvae or other small organisms.
Burrow Ventilation in the Tube-Dwelling Shrimp Callianassa Subterranea (Decapoda: Thalassinidea): III. Hydrodynamic Modelling and the Energetics of Pleopod Pumping
Authors: Stamhuis Eize J. , Videler John J. 
Published: April 2021

ABSTRACT
The process of flow generation with metachronally beating pleopods in a tubiform burrow was studied by designing a hydrodynamic model based on a thrust–drag force balance. The drag of the tube (including the shrimp) comprises components for accelerating the water into the tube entrance, for adjusting a parabolic velocity profile, for accelerating the flow into a constriction due to the shrimp’s body and another constriction due to the extended tail-fan, for shear due to separation and for the viscous resistance of all tube parts. The thrust produced by the beating pleopods comprises components for the drag-based thrust and for the added-mass-based thrust. The beating pleopods are approximated by oscillating flat plates with a different area and camber during the power stroke and the recovery stroke and with a phase shift between adjacent pleopod pairs. The added mass is shed during the second half of the power stroke and is minimized during the recovery stroke. A force balance between the pleopod thrust and the tube drag is effected by calculating the mean thrust during one beat cycle at a certain flow velocity in the tube and comparing it with the drag of the tube at that flow velocity.
The energetics of the tube and the pump are derived from the forces, and the mechanical efficiency of the system is the ratio of these two. Adjusted to standard Callianassa subterranea values, the model predicts a mean flow velocity in the tube of 1.8 mm s−1. The mean thrust force, equalling the drag, is 36.8 μN, the work done by the pleopod pump per beat cycle is 0.91 μJ and the energy dissipated by the tube system is 0.066 μJ per cycle. The mechanical efficiency is therefore 7.3 %. Pump characteristics that may be varied by the shrimp are the beat frequency, the phase shift, the amplitude and the difference in pleopod area between the power and recovery strokes. These parameters are varied in the model to evaluate their effects. Furthermore, the moment of added mass shedding, the distance between adjacent pleopods, the number of pleopods and the total tube drag were also varied to evaluate their effects.
Stress/Strain Behaviour of the Equine Laminar Junction
Authors: Douglas J. E. , Biddick T. L. , Thomason J. J. , Jofriet J. C. 
Published: April 2021

ABSTRACT
The equine laminar junction plays a vital role in transferring the forces of weight-bearing between the epidermal hoof wall and the bone of the third phalanx, but the way in which it performs this function is poorly understood. Using samples from sites varying proximodistally and circumferentially around the hoof, the stress/strain behaviour of this tissue was characterised in three directions: radial tension and proximodistal and mediolateral shear. The influences of toe angle and length were also examined.
For all three test directions, the modulus of elasticity increased with increasing strain magnitude. The mean modulus of elasticity in tension was 18.25±5.38 MPa (mean ±1 S.D., N=116; mean strain 0.25). In proximodistal shear, the mean shear modulus was 5.38±1.49 MPa (N=76; mean shear strain 0.48) and in mediolateral shear 2.57±0.91 MPa (N=66; mean shear strain 0.81). In many cases, the individual hoof or horse from which the samples were taken significantly affected the value of the modulus, suggesting that mechanical history may affect the material properties of this tissue. Few biologically significant variations with location, toe length or toe angle were unambiguously demonstrated, suggesting that the material properties of the laminar junction are independent of position, despite apparent regional variations in function, and that foot shape is not a major determinant of material properties.