bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pore Properties of Lymnaea Stagnalis Neuron Stretch-Activated K+ Channels
Authors: Small Daniel L. , Morris Catherine E. 
Published: April 2021

ABSTRACT
In many neurons, variations in membrane excitability are determined by a resting K+ conductance whose magnitude is modulated via neurotransmitters. The S-channel in Aplysia californica mechanosensory neurons is such a conductance, but it has also been shown to be a stretch-activated K+ channel. In this, it resembles stretch-activated K+ channels common to all molluscan neurons. Comparable channels are widespread, having been reported in molluscan and insect muscle and various vertebrate cells. The pore properties of the S-channel and similar stretch-activated K+ channels have received only sporadic attention. Here we examine, at the single-channel level, the permeation characteristics of a stretch-activated K+ channel from neurons of the mollusc Lymnaea stagnalis.
Michaelis–Menten constants (Km) for the conductance, obtained separately for inward (28 mmol l−1) and outward (91 mmol l−1) K+ currents, suggest that the channel presents to the external medium, where [K+] is lower, a higher-affinity site than it presents to the cytoplasmic medium. This may help to ensure that influx is not diffusion-limited at potentials near the resting potential, i.e. near the K+ equilibrium constant. Anomalous mole fraction behavior, observed when the ratio of permeant ion (K+ and Rb+) was varied, indicated that the stretch-activated K+ channel is a multi-ion pore. The ion selectivity sequence determined using reversal potentials under bi-ionic conditions was Cs+&gt;K+&gt;Rb+&gt;NH4+&gt;Na+&gt;Li+, and using relative conductance in symmetrical solutions, the sequence was Tl+=K+&gt;Rb+&gt;NH4+⪢Na+=Li+=Cs+. Extreme variations in extracellular pH from 4.7 to 11.4 had no effect on stretch-activated K+ channel conductance, whereas normal concentrations of extracellular Mg2+ reduced inward K+ current. Intracellular, but not extracellular, Ba2+ produced a slow, open channel block with an IC50 of 140±80 μmol l−1.
These pore properties are compared with those of other stretch-activated K+ channels and of K+ channels in general. In spite of a greater than half order of magnitude difference in the cytoplasmic [K+] in marine (Aplysia californica) and freshwater (Lymnaea stagnalis) molluscs, the conductances of stretch-activated K+ channels from the two groups are very similar.
Ballistics and Visual Targeting in Flea-Beetles (Alticinae)
Authors: Brackenbury John , Wang Richard 
Published: April 2021

ABSTRACT
The kinematics of jumping was measured in seven species of flea-beetle (Alticinae). The accuracy of two species during targeted jumping was also investigated. Take-off accelerations ranged from 15 to 270 times gravity. Rotational energy accounted for 4–21 % of the total translational energy. Two species were able to control jump direction and landing. When presented with a high-contrast optical grid, Chalcoides aurata exhibited two alternative jump modes. In mode 1 or wingless jumping, the body rotated continuously, the insect rarely landed on its feet and no discrimination was shown between landing on the black or white stripes of the grid. In mode 2 jumping, recruitment of the wings eliminated rotation and virtually ensured a feet-first landing; there was also a significant preference for jumping towards the black stripes. Aphthona atrocaerulea could alter take-off angle in order to strike targets at inclinations of 0–90° to the horizontal. Targets consisting of a white illuminated cross on a black background were struck with equal accuracy, regardless of distance (within the normal jumping range). The beetle aimed specifically for the centre of the target and not for the high-contrast boundary. The distribution of hits about the target centre was radially symmetrical. Although take-off was wingless, rotation could be abolished in mid jump, within 10 ms, by extending the wings. This virtually guaranteed a feet-first landing. Targeting accuracy is discussed in the context of biomechanical steering mechanisms and visual control.
Distribution of 2-[125I]Iodomelatonin Binding Sites in the Brain of the Pied Flycatcher (Ficedula Hypoleuca) and the Zebra Finch (Taeniopygia Guttata)
Authors: Schneider Thomas 
Published: April 2021

ABSTRACT
Using in vitro autoradiography, the distribution of 2-[125I]iodomelatonin (IMEL) binding sites in the brain of the pied flycatcher and the zebra finch was examined. The results show IMEL binding in retinofugal, tectofugal and thalamofugal brain areas of the visual system. Additionally, IMEL binding sites were detected in the ectostriatum, the thalamus, the mesencephalon and the limbic system. No IMEL binding could be demonstrated in the pineal gland, the hippocampus, the nucleus suprachiasmaticus, the visual wulst or the pituitary.
Motor Patterns for Horizontal and Upside-Down Walking and Vertical Climbing in the Locust
Authors: Duch C. , Pflüger H. J. 
Published: April 2021

ABSTRACT
The motor patterns of the locust’s flexor tibiae and metathoracic subcoxal joint muscles were compared during unrestrained horizontal walking, vertical climbing and walking upside-down hanging from a branch. Combining anatomical and structural data with the results from myographic recordings revealed the role of these muscles during walking and their functional adjustments to different loads and gravity effects caused by changes in walking conditions. Motor patterns are remarkably constant during a given walking situation even at quite different walking speeds. In all walking situations, changes in step duration correlate strongly with changes in the duration of retraction but only weakly with the duration of protraction. Different motor units of one muscle can be distinguished by their spike amplitude. They may be active simultaneously or they may alternate and then fire in different phases of the step cycle. For example, during horizontal walking, the small unit of the first abductor (M125) is active during protraction and the large one during retraction. During retraction, the coxal muscles serve two functions: (1) the joint has to be brought back to the posterior extreme position by retractor muscles; (2) the joint has to be stabilized, that is held ‘stiffly’, by co-activity of functional antagonists. During protraction, it is moved to the anterior extreme position by powerful contractions of protractor muscles. The muscular activity patterns show marked differences depending on the walking situation. Some large motor units spike only sporadically during horizontal walking but burst during vertical climbing and upside-down walking (muscle M121p, the large units of muscles M126 and M120). During upside-down walking, muscles M120 and M121 and the large unit of muscle M125 are active during opposite phases of the step cycle when compared with horizontal walking and vertical climbing (for example, during walking and climbing, muscle M120 is active at the transition between retraction and protraction, whereas during upside-down walking, activity occurs during late protraction and early retraction). The results describe how motor patterns are adjusted to the different requirements of various walking situations.
Functional Organisation of the Metathoracic Femoral Chordotonal Organ in the Cricket Acheta Domesticus
Authors: Nowel M. S. , Shelton P. M. J. , Stephen R. O. 
Published: April 2021

ABSTRACT
The metathoracic chordotonal organ of the cricket Acheta domesticus (Gryllidae) consists of two closely associated scoloparia situated proximally within the femur with their distal ends connected by a pair of ligaments to an apodeme arising from the tibia. The smaller scoloparium is associated with the dorsal ligament, which arises from the dorsal surface of the apodeme 150 µm from its proximal end. The larger scoloparium is attached directly to the proximal end of the apodeme by a larger ventral ligament. Both ligaments are composed of bundles of attachment cells containing densely packed microtubules. Longitudinally orientated, Acid-Fuchsin-staining fibrils are found in an extracellular matrix surrounding the individual attachment cells. Similar fibrils occur in the sheath surrounding each ligament. The fibrils are thickest and most densely packed in the sheath surrounding the ventral ligament. They are thinner and more sparsely distributed in the sheath of the dorsal ligament. The finest fibrils are found in the extracellular matrix surrounding individual attachment cells. Staining with phosphotungstic acid provides the first evidence that they are elastic. The ventral ligament also contains a spring-like cuticular core arising as a proximal extension of the apodeme. As femoro-tibial angle changes, the cuticular core changes in length, shortening with tibial extension and lengthening with flexion. Ventral ligament attachment cells terminate at different levels along the cuticular core. This arrangement provides a new possible mechanism for differential sensitivity of the sensory neurones associated with the attachment cells.
Sound Pressure Transformation at the Pinna of Mus Domesticus
Authors: Chen Qi-Cai , Cain David , Jen Philip H.-S. 
Published: April 2021

ABSTRACT
Sound pressure transformation properties at the pinna of laboratory mice Mus domesticus were studied by measuring the sound pressure level of a continuous tone at a series of frequencies at the tympanic membrane as a function of the position of a sound source under free-field stimulation conditions. The spectral transformation, the interaural spectral difference, the isopressure contours and the interaural pressure difference contours were plotted. Sound pressure transformation functions showed some prominent spectral notches throughout the frequency range tested (10–80 kHz). However, the notch frequency did not appear to be systematically related to sound direction. The study of interaural pressure difference demonstrated that, when delivered from some angles within the ipsilateral frontal hemisphere, the sound pressure at the tympanic membrane of certain frequencies may be lower than that determined at the corresponding contralateral angles. For each sound frequency tested, there was an angle (the acoustic axis) within the ipsilateral frontal hemisphere from which the delivered sound reached a maximal pressure level at the tympanic membrane. However, the acoustic axis often changed to a new angle after removal of the ipsilateral pinna. In addition, sound delivered from the acoustic axis did not always generate a maximal pressure transformation. The isopressure contours determined within 2–5 dB of the maximal pressure were circumscribed, and their contained angular areas were found to decrease with increasing sound frequency. The 2 dB maximal pressure area may appear at more than one angular area for some test frequencies. Removal of the ipsilateral pinna or modification of pinna posture expanded isopressure contours irregularly and split the 2 dB maximal pressure area into several parts. The sound pressure difference determined between the angles of maximal and minimal sound pressure (the maximal directionality) increased with sound frequency regardless of pinna posture. Acoustic gain of the pinna at the acoustic axis reached 6–12 dB, depending upon sound frequency. However, the pinna gain was not always maximal at the acoustic axis for a given frequency.
The Knowledge Base of Bee Navigation
Authors: Menzel Randolf , Geiger Karl , Chittka Lars , Joerges Jasdan , Kunze Jan , Müller Uli 
Published: April 2021

ABSTRACT
Navigation in honeybees is discussed against the background of the types of memories employed in the navigational task. Two questions are addressed. Do bees have goal-specific expectations, and when are novel routes travelled? Expectations are deduced from (1) context stimuli as determinants for local cue memories, (2) landmark-dependent path integration, (3) sequential learning of landmarks, and (4) motivation-and context-dependent memory retrieval. Novel routes are travelled under two conditions: (1) goal-cue-based piloting and (2) integration of simultaneously activated vector memories. Our data do not support the conclusion that memory integration in bees is organised by a cognitive map. The assumption of purely separate memories that are only retrieved according to the chain of events during navigational performance also appears to be inadequate. We favour the view that multiple memories are integrated using external and internal sources of information. Such configural memories lead to both specific expectations and novel routes.
Honeybee Navigation En Route to the Goal: Visual Flight Control and Odometry
Authors: Srinivasan M. V. , Zhang S. W. , Lehrer M. , Collett T. S. 
Published: April 2021

ABSTRACT
Recent research has uncovered a number of different ways in which bees use cues derived from optic flow for navigational purposes. The distance flown to a food source is gauged by integrating the apparent motion of the visual world that is experienced en route. In other words, bees possess a visually driven ‘odometer’ that is robust to variations in wind load and energy expenditure. Bees flying through a tunnel maintain equidistance to the flanking walls by balancing the apparent speeds of the images of the walls. This strategy enables them to negotiate narrow passages or to fly between obstacles. The speed of flight in a tunnel is controlled by holding constant the average image velocity as seen by the two eyes. This avoids potential collisions by ensuring that the bee slows down when flying through narrow passages. Bees landing on a horizontal surface hold constant the image velocity of the surface as they approach it. This automatically ensures that flight speed decreases with altitude and is close to zero at touchdown. The movement-sensitive mechanisms underlying these various behaviours seem to be different, qualitatively as well as quantitatively, from those mediating the well-investigated optomotor response.
Visualization of Cement Exocytosis in the Cypris Cement Gland of the Barnacle Megabalanus Rosa
Authors: Okano Keiju , Shimizu Katsuhiko , Satuito Cyril Glenn , Fusetani Nobuhiro 
Published: April 2021

ABSTRACT
Cementation to substrata during permanent attachment concludes the planktonic larval phase in many sessile marine invertebrates, including barnacles. However, the neural control and the mechanism of cement secretion from cement organs are poorly understood. In the present study, using isolated cement glands from cyprids of Megabalanus rosa, we have visualized cement secretion and demonstrated the stimulatory effect of dopamine and noradrenaline on such secretion. The abrupt disappearance of secretory granules and subsequent omega-figure formation indicated that exocytosis was the major mode of cement secretion. Exocytosis was localized at the apical surface of cement-secreting cells and lasted for over 30 min. Dopamine and noradrenaline also activated the directional transport of secretory granules to the sites of exocytosis. Glyoxylic acid staining provided histochemical evidence for catecholaminergic innervation to the cement glands. These results suggest that gradual, localized exocytotic secretion of cement triggered by catecholaminergic neurones is a key mechanism during permanent attachment by barnacle cyprids.
Activation of Apical P2U Purine Receptors Permits Inhibition of Adrenaline-Evoked Cyclic Amp Accumulation in Cultured Equine Sweat Gland Epithelial Cells
Authors: Wilson S. M. , Rakhit S. , Murdoch R. , Pediani J. D. , Elder H. Y. , Baines D. L. , Ko W. H. , Wong P. Y. D. 
Published: April 2021

ABSTRACT
Experiments were undertaken using cultured equine sweat gland epithelial cells that express purine receptors belonging to the P2U subclass which allow the selective agonist uridine triphosphate (UTP) to increase the concentration of intracellular free Ca2+ ([Ca2+]i). Experiments using pertussis toxin (Ptx), which inactivates certain guanine-nucleotide-binding proteins (G-proteins), showed that this response consisted of Ptx-sensitive and Ptx-resistant components, and immunochemical analyses of the G-protein α subunits present in the cells showed that both Ptx-sensitive (αi1–3) and Ptx-resistant (αq/11) G-proteins were expressed. P2U receptors may, therefore, normally activate both of these G-protein families. Ptx-sensitive, αi2/3 subunits permit inhibitory control of adenylate cyclase, and UTP was shown to cause Ptx-sensitive inhibition of adrenaline-evoked cyclic AMP accumulation, suggesting that the receptors activate Gi2/3. Experiments using cells grown on permeable supports suggested that P2U receptors became essentially confined to the apical membrane in post-confluent cultures. Polarised epithelia may, therefore, express apical P2U receptors which influence two centrally important signal transduction pathways. It is highly improbable that these receptors could be activated by nucleotides released from purinergic nerves, but they may be involved in the autocrine regulation of epithelial function.
Graviresponses in Paramecium Biaurelia Under Different Accelerations: Studies on the Ground and In Space
Authors: Hemmersbach Ruth , Voormanns Regine , Häder Donat-P. 
Published: April 2021

ABSTRACT
Behavioural responses to different accelerations below 1 g and up to 5 g were investigated in Paramecium biaurelia by using a centrifuge microscope on Earth and in space during a recent space flight. Increased stimulation (hypergravity) enhanced the negative gravitactic and the gravikinetic responses in Paramecium biaurelia within seconds. Cells did not adapt to altered gravitational conditions. Repetitive stimulation did not change the graviresponses. The minimum acceleration found to induce gravitaxis was between 0.16 and 0.3 g.
The Effect of Altering Pulmonary Blood Flow on Pulmonary Gas Exchange in the Turtle Trachemys (Pseudemys) Scripta
Authors: Hopkins Susan R. , Wang Tobias , Hicks James W. 
Published: April 2021

ABSTRACT
In resting reptiles, the of pulmonary venous return (; left atrial blood) may be 20 mmHg (1 mmHg=0.1333 kPa) lower than the of gas in the lung. This level of is considerably higher than that observed in resting mammals and birds and results from ventilation–perfusion heterogeneity, pulmonary diffusion limitation and intrapulmonary shunting. However, the relative contribution of each of these factors is unknown. Many reptiles, particularly chelonians, exhibit an intermittent ventilation pattern where pulmonary blood flow (Q̇l) increases during the ventilatory periods and, therefore, we hypothesized that matching would improve with increasing Q̇l. We applied the multiple inert gas elimination technique in anaesthetized turtles at 22 °C. Turtles were continuously ventilated at a rate of 140 ml kg−1 min−1, equivalent to the rate of ventilation within a ventilatory period. Trace amounts of six inert gases were infused through the jugular vein. Blood samples from the pulmonary artery and the left atrium and mixed expired gases were collected for analysis. Q̇l was reduced by a factor of six (low flow) using a vascular occluder placed around the common pulmonary artery or increased by a factor of two (high flow) through bolus injection of adrenaline. heterogeneity was significantly reduced with increasing pulmonary blood flow (P&lt;0.05). Consistent with these changes, the effective lung–pulmonary artery difference was reduced (P&lt;0.05) from 58±16 mmHg to 29±5 mmHg (means ± S.E.M.) and increased significantly (P&lt;0.05) from 88±17 mmHg (low flow) to 120±14 mmHg (high flow). There was evidence of pulmonary diffusion limitation under all conditions, which was unchanged with increasing blood flow. These findings suggest that increased pulmonary blood flow during a ventilatory period results in both temporal and spatial matching of ventilation and perfusion, without altering pulmonary diffusion limitation.
1H- and 31P-Nuclear Magnetic Resonance Studies of L-Lactate Transport in Isolated Muscle Fibers from the Spiny Lobster Panulirus Argus
Authors: Kinsey Stephen T. , Ellington W. Ross 
Published: April 2021

ABSTRACT
Proton (1H) and phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy were used to investigate the mode of transport of L-lactate across the plasma membranes of the abdominal extensor muscles of the spiny lobster Panulirus argus. Individual fibers or bundles of 2–3 fibers were superfused in a dual-tuned (1H, 31P) microsolenoid NMR probe. 1H-NMR spectra were diffusion-weighted, which eliminated the signal contribution of the fast-flowing extracellular lactate but retained that of intracellular lactate. Well-resolved intracellular lactate signals could be acquired at 15 s intervals, permitting estimation of initial velocities (Vi) of influx and efflux during loading/unloading of muscle fibers. 31P-NMR spectra were acquired to assess cellular energy status and intracellular pH. Transport results showed that Vi values for influx and efflux were a linear function of total lactate concentration, displaying no saturation effects. The rate of lactate influx was enhanced by increasing the concentration of the free acid by altering the superfusate pH. Vi values for influx and efflux of D- and L-lactate were identical. Finally, traditional inhibitors of monocarboxylate and/or anion transport had no effect on influx/efflux of lactate from these cells. The above results strongly suggest that the primary mode of lactate transport is by passive diffusion. These cells appear to lack a monocarboxylate transporter, which may be related to the apparent absence of organ-specific compartmentation of lactate metabolism in crustaceans.
Pectoral Fin Locomotion in the Striped Surfperch: I. Kinematic Effects of Swimming Speed and Body Size
Authors: Drucker Eliot G. , Jensen Jeffrey S. 
Published: April 2021

ABSTRACT
Swimming trials at increasing velocity were used to determine the effects of steady swimming speed on pectoral fin kinematics for an ontogenetic series of striped surfperch Embiotoca lateralis, ranging from 6 to 23 cm in standard length (SL). The fin stroke cycle consisted of a propulsive period, the duration of fin abduction and adduction, and a ‘refractory’ period, during which the fin remained adducted against the body. Pectoral fin-beat frequency (fp) measured as the inverse of the entire stride period, as in past studies, increased curvilinearly with speed. Frequency, calculated as the reciprocal of the propulsive period alone, increased linearly with speed, as shown previously for tail-beat frequency of fishes employing axial undulation. Fin-beat amplitude, measured as the vertical excursion of the pectoral fin tip during abduction, increased over a limited range of low speeds before reaching a plateau at 0.35–0.40 SL. Pectoral fin locomotion was supplemented by intermittent caudal fin undulation as swimming speed increased. At the pectoral–caudal gait transition speed (Up−c), frequency and amplitude attained maxima, suggesting that the fin musculature reached a physiological limit. The effects of body size on swimming kinematics differed according to the method used for expressing speed. At a given absolute speed, small fish used higher stride frequencies and increased frequency at a faster rate than large fish. In contrast, the relationship between fp and length-specific speed (SL s−1) had a greater slope for large fish and crossed that for small fish at high speeds. We recommend that comparisons across size be made using speeds expressed as a percentage of Up−c, at which kinematic variables influencing thrust are size-independent.