bluuebunny/crossref_metadata_2025 huggingface dataset:
Vagal Regulation of Intracardiac Shunting in the Turtle Pseudemys Scripta
Authors: Hicks James W. , Comeau Stephen G.
Published: April 2021

Two principal hypotheses account for intracardiac shunting in reptiles. The ‘pressure shunting’ hypothesis proposes that there is no fuctional separation between the ventricular cava during systole. The ‘washout shunting’ hypothesis suggests that the cavum pulmonale is functionally separated from the rest of the ventricle during systole. The purpose of this study was to test the two principal hypotheses in a turtle, Pseudemys scripta, after inducing a right-to-left shunt by electrical stimulation of the vagus nerve. Animals were anaesthetized with sodium pentobarbital (30–40 mg kg-1), tracheotomized and mechanically ventilated. Two experimental groups were used. Both groups had the right and left cervical vagi exposed and sectioned and silver bipolar electrodes were attached for electrical stimulation. In addition, cardiac function was evaluated by determining the pulmonary blood flow, pulmonary arterial pressure, peak systolic pressure in the cavum pulmonale, central arterial pressure, pulmonary vascular resistance and heart rate. In group I, hydrogen electrodes were inserted into the right aorta, the left aorta and the pulmonary artery. Hydrogen, dissolved in saline, was infused into the left atrium, jugular vein and cavum pulmonale. Blood flow from these sites was deduced from detection of a H2 signal in the right and left aortae and the pulmonary artery. In group II, catheters were inserted in the left and right atria and aortae for the measurement of blood gases. For both groups, the protocol consisted of control periods and periods of electrical stimulation of the efferent and afferent ends of the vagus nerve. During the control periods, infusion of a H2 solution into either the left atrium or the jugular vein resulted in the detection of H2 in the right and left aortae and the pulmonary artery. This suggested that both right-to-left and left-to-right intracardiac shunts were present. H2 infused into the cavum pulmonale was always detected in the pulmonary artery but never in the left or right aortae. During stimulation of the right vagal efferents, a bradycardia developed (heart rate declined by 65 %), pulmonary blood flow was reduced by 73 % and pulmonary vascular resistance increased by 158 %. This was accompanied by a reduction in the of both the right and left aortae, although the of the left and right atria remained constant. Under these conditions, H2 infused into the jugular vein and the left atrium was detected in the right and left aortae and the pulmonary artery of all animals studied. Infusion of H2 into the cavum pulmonale was detected in the right and left aortae in only two animals. The results supported the washout mechanism for right-to-left intracardiac shunting.
Effect of coronary ablation and adrenergic stimulation on in vivo cardiac performance in trout (Oncorhynchus Mykiss)
Authors: Gamperl A. K. , Pinder A. W. , Boutilier R. G.
Published: April 2021

In fish, catecholamine-induced changes in cardiac performance in vivo are the result of complex interactions between the direct adrenergic effects on the heart and peripheral circulation and the reflex responses to increased blood pressure. In addition, coronary artery transport of catecholamines and oxygen to the compact myocardium may be essential for maximal in vivo cardiac performance during adrenergic stimulation. Cardiac output (Q̇), heart rate (fH), stroke volume (Vs) and dorsal aortic pressure (PDA) were measured in trout with intact or ablated coronary arteries at rest and following intra-arterial administration of 0.2, 0.5, 1.0 and 2.0 µg kg−1 adrenaline. Resting Q̇, fH, Vs and PDA were the same in fish with intact and ablated coronaries at 48 h post-surgery, averaging approximately 18 ml min−1 kg−1, 42 beats min−1, 0.42 ml kg−1 and 2.2 kPa, respectively. All cardiovascular variables showed a strong relationship between response magnitude and adrenaline dose. However, our results indicate that adrenaline doses above 0.5 µg kg−1 may have a limited ability to increase Q̇ (ED50 0.22 µg kg−1). Coronary artery ablation had little effect on post-injection Q̇, Vs, PDA or fH at any dose of adrenaline. In both intact and ablated groups, two types of responses in Q̇ were observed following adrenaline injection. In the ‘type 1’ response, Q̇ increased shortly (15–30 s) after adrenaline administration, as increases in Vs more than compensated for a pressor-stimulated reflex bradycardia. In the ‘type 2’ response, alterations in Q̇ were biphasic. In the initial minutes post-injection, Q̇ fell and reached a minimum level at 1–2 min, the result of an immediate drop in fH and a delayed post-injection increase in Vs. Thereafter, Q̇ gradually increased as a result of concordant increases in fH and Vs. Although time to maximum Q̇ was 5–6 min longer for fish exhibiting type 2 responses, there was no difference in maximum Q̇ increase or in the time courses for changes in fH and PDA between response types. Our results suggest (1) that during normoxic conditions, cardiac performance does not depend highly on coronary blood flow; (2) that the capacity of adrenaline to increase Q̇ may be limited by elevations in output pressure and/or by the low dose (concentration) of adrenaline required to achieve near maximal adrenergic stimulation of the heart; and (3) that fish exhibiting type 2 responses have an increased barostatic gain (% fH per unit PDA) compared with those with type 1 responses.
Effects of diluted natural water and altered ionic environments on gustatory responses in rainbow trout (Oncorhynchus mykiss)
Authors: Kitada Y. , Hara T. J.
Published: April 2021

The effects of adaptation to diluted natural water (NW) and various salt solutions on the gustatory responses recorded from the palatine nerve in rainbow trout (Oncorhynchus mykiss) were studied. The magnitude of the response to 1 mmol l−1 L-proline (L-Pro) decreased when the perfusing NW was diluted with artificial fresh water (AFW) that maintained concentrations of major cations. AFW suppressed the responses to L-Pro by about 70 %. The responses to 1 mmol l−1 L-Pro, 0.1 mmol l−1 quinine–HCl (Q-HCl) and 10 nmol l−1 taurolithocholic acid (TLCA) were eliminated or reduced (to <10 %) by adapting the palate to distilled water (DW). The addition of 0.1–100 mmol l−1 salts (NaCl, KCl, CaCl2, MgCl2) and choline chloride restored the gustatory responses to about 50 % of those in NW. The addition of salts to NW had no effect on the gustatory responses. The gustatory responses to 5 % CO2 were similarly reduced when the palate was adapted to solutions that contained no NW (DW, AFW, 10 mmol l−1 NaCl in DW). However, the reduction was independent of salt concentration, suggesting a different transduction mechanism for CO2. Tetrodotoxin (1 µmol l−1) had no effect on the gustatory responses to L-Pro.

We conclude that NW is required and that cations alone are not sufficient to support maximal gustatory responses. The results suggest that an unknown substance(s) contained in NW plays an essential role in gustatory reception and that permeation of cations through the apical membrane of gustatory cells is not involved in gustatory transduction in rainbow trout.
Concealed transepithelial potentials and current rectification in tsetse fly malpighian tubules
Authors: Isaacson L. C. , Nicolson S. W.
Published: April 2021

Electrophysiological techniques have been applied to tsetse fly Malpighian tubules for the first time. In either Cl− or SO42− Ringer, both non-perfused and perfused tubules displayed transtubular potentials (Vt) at or close to 0 mV. Exposure to cyclic AMP elicited a marked secretory response and, in SO42− Ringer, a sharp (lumen-positive) increase in Vt. In Cl− Ringer, despite more than double the secretory response, there was little or no change in Vt. Replacing Cl− with SO42− Ringer, in the presence of cyclic AMP, promptly increased Vt. In perfused tubules, this occurred irrespective of the Cl− or SO42− composition of the perfusate. In Cl− Ringer, the transepithelial resistance (Rtrans) was less than half that previously reported in Malpighian tubules of other species. Cyclic AMP reduced Rtrans still further, whether tubules were bathed in Cl− or SO42− Ringer. Current–voltage (I/V) plots often displayed current rectification, both before and more frequently after exposure to cyclic AMP, thus permitting estimation of both the electromotive force of the Na+ transport mechanism (ENa) and of the shunt resistance (Rshunt). Both ENa and Rshunt were markedly lower in tubules bathed in Cl− than in SO42− Ringer. Cyclic AMP was without effect on ENa and Rshunt, in either Cl− or SO42− Ringer. In terms of the equivalent electrical circuit, the secretory response to cyclic AMP was due solely to a fall in resistance of the active transport pathway (Rseries). The absence of an appreciable Vt, in Cl− Ringer, is consistent with an apical Cl− shunt.
Molecules that become redistributed during regeneration of the leech central nervous system
Authors: Lüthi T. E.
Published: April 2021

A search has been made for molecules other than laminin that change their distribution during axonal regrowth after injury. Two monoclonal antibodies, generated against a protein extract of leech central nervous system (CNS), stain distinct regions of leech CNS and, following lesions, show changes in distribution with time.

Monoclonal antibody NP17 stained two bands of Mr 80×103 and 60×103 on Western blots of protein extracted from whole CNS. On cryosections of leech CNS, staining was predominantly within the neuropile. A second antibody, mAb CT16, stained a collagen-associated molecule of the extracellular matrix. It labelled the outer capsule, which surrounds the neuronal cell packets, and the inner capsule, which envelops the neuropile. In the connectives, CT16 immunoreactivity was restricted to the connective capsule and was not associated with nerve fibres or glia. When the connectives were crushed, immunocytochemical studies revealed changes in distribution of both mAb NP17 and mAb CT16. After 3 days, a time when fibres begin to sprout and form connections, an increase in NP17 immunoreactivity appeared at the site of the lesion. Staining levels remained elevated for several weeks. In contrast, CT16 immunoreactivity did not change for several days after damage. After 10 days, fibre-like staining appeared at the site of the crush; for several weeks it continued to spread throughout the connective. These results show that regeneration of the leech CNS involves the redistribution of at least two molecules. Using monoclonal antibodies, these two molecules, which are situated in distinct regions of the CNS, have been visualized at different stages of the repair process. It has been shown that they alter their distribution at distinct times during regeneration.
EMG–force relationship of the cat soleus muscle studied with distributed and non-periodic stimulation of ventral root filaments
Authors: Guimaraes A. C. , Herzog W. , Hulliger M. , Zhang Y. T. , Day S.
Published: April 2021

Distributed stimulation of ventral root (VR) filaments and pseudo-random interpulse intervals (based on a Gaussian distribution with a coefficient of variation of 12.5 %) were used to modulate electromyographic activity (EMG) and force of the cat soleus muscle to assess the EMG–force relationship. A protocol consisting of addition and rate modulation of ten VR filaments that contain alpha motoneurones to the soleus muscle was adopted. EMG was measured using indwelling electrodes and forces were measured at the distal tendon using a strain transducer. EMG records obtained using this approach were similar in the time and frequency domains to those obtained during voluntary contractions. Force records obtained from stimulation of single VR filaments showed summation effects typical of irregular interpulse intervals. The overall relationship between integrated rectified EMG (IEMG) and mean force was found to be non-linear. At low and high stimulation levels, IEMG tended to increase proportionally more than mean force. In the intermediate stimulation region (i.e. producing forces between approximately 5 % and 88 % of the maximal tetanic force), the IEMG–mean force relationship was virtually linear. Muscles with a homogeneous fibre type composition, such as the cat soleus muscle, have been reported to have a linear EMG–force relationship.
Sound production and hearing in the pyralid mothSymmoracma minoralis
Authors: Heller Klaus-Gerhard , Krahe Rüdiger
Published: April 2021

Males of the moth Symmoracma minoralis (Snellen) (Lepidoptera: Pyralidae, Nymphulinae) were observed producing a high-intensity calling song (95 dB SPL at a distance of 10 cm) with a complex amplitude and frequency modulation (peaks of carrier frequency at 60 and 120 kHz). This sound is produced by a hitherto unknown type of sound organ located in the last abdominal (genital) segment, which may act as a tymbal. The observed directionality of sound output is probably achieved by means of a hollow cone surrounding the sound organ. Electrophysiological recordings revealed that the tympanal organs of S. minoralis are most sensitive in the frequency range from 50 to at least 100 kHz, which is distinctly higher than the minimum threshold levels in most other moths yet examined. The origin of genital sound production is discussed with respect to abdominal pheromone glands and pheromone-releasing movements.
Gas exchange through the lungs and gills in air-breathing crabs
Authors: Farrelly Caroline A. , Greenaway Peter
Published: April 2021

Lung and gill performance in gas exchange have been evaluated in eight species of air-breathing crabs with two different lung circulatory designs, those with portal systems and smooth lung linings, and those without portal systems and with invaginated and evaginated lung linings. In all species, the lungs were extremely effective in oxygen uptake whilst the performance of the gills was inferior. An exception to this was Gecarcoidea natalis, which has gills highly modified for aerial gas exchange; its gills and lungs were equally efficient in O2 uptake. The relative efficiencies of the lungs and gills in CO2 excretion differed between species, with the gills being the major site of CO2 loss in the more amphibious species and the lungs having an increasingly important role in the more terrestrial crabs. The presence or absence of lung portal systems was not found to correlate with either saturation rates or efferent oxygen concentrations, with both lung types being extremely efficient in O2 uptake. The lungs with portal systems showed a large increase in oxygen content in the first lacunar bed and progressively smaller increases in the next two; these lungs may, therefore, have some reserve for exercise.
Thermal acclimation, neuromuscular synaptic delay and miniature end-plate current decay in the frog rana temporaria
Authors: Tiiska A. J. , Lagerspetz K. Y. H.
Published: April 2021

The effects of 1 or 2–3 weeks of acclimation to 4 °C and 24 °C of overwintering grass frogs (Rana temporaria) on the synaptic delay and on the time constant of the decay phase (τ) of miniature end-plate currents (MEPCs) in the neuromuscular junction of sartorius muscle were studied. In order to equalize the possible effects of differential starvation, the animals were usually cross-acclimated to the two temperatures. Synaptic delay was not affected by temperature acclimation but was slightly prolonged by the more profound starvation at the higher temperature when the cross-acclimation procedure was not used. The average Q10 of synaptic delay between 4 and 24 °C was 2.60 and of minimum synaptic delays, 2.64. The corresponding values for apparent activation energy (Ea) were 65.79 and 66.48 kJ mol−1. The time constant of the decay phase of MEPCs was not affected by temperature acclimation. The average Q10 between 4 and 24 °C was 2.27. The corresponding Ea value was 56.02 kJ mol−1. The function of peripheral neuromuscular synapses is well regulated and changes in its time relationships do not appear to be involved in the thermal acclimation of frogs.
Partial purification, tissue distribution and modulatory activity of a crustacean cholecystokinin-like peptide
Authors: Turrigiano G. G. , Van Wormhoudt A. , Ogden L. , Selverston A. I.
Published: April 2021

Reversed-phase chromatography was used to separate several forms of cholecystokinin-like peptides (CCKLP) from the pericardial organs (PCOs) of the spiny lobster Panulirus interruptus. Fast protein liquid chromatography of PCOs, stomatogastric ganglia (STGs) and eyestalks revealed five peaks of CCKLP (peaks A–E) that were common to all three tissues, as well as two additional peaks (peaks F and G) in the STG. Peaks A–E were present in the hemolymph of fed, but not starved, lobsters. The bioactivity of peaks A–E was tested on the gastric mill rhythm of the isolated STG. Only peak E elicited activity. The effects of peak E included activating the gastric mill rhythm in quiescent preparations and strengthening existing rhythms in a dose-dependent manner. Further purification of peak E by high performance liquid chromatography resolved this peak into two immunoreactive peaks, one of which retained its bioactivity. The effects of peak E were blocked by the CCK antagonist proglumide. These results are consistent with a role for peak E in the feeding-induced activation of the gastric mill.
Scaling modulus as a degree of freedom in the design of locust legs
Authors: Katz Stephen L. , Gosline John M.
Published: April 2021

Previous work has shown that the scaling of mechanical behaviour in bending of the metathoracic tibiae of the African desert locust (Schistocerca gregaria) is not predicted by the scaling of external dimensions. The flexural stiffness of the tibia scales to (body mass)1.53, which is similar to the predictions of the elastic similarity model of scaling. The external dimensions, however, scale in a manner that produces relatively more elongate limb segments – an observation that differs from the predictions of any existing scaling model. In this paper, we examined two alternative hypotheses to explain this uncoupling of morphology and mechanics: (1) that the load-bearing cuticular material is distributed in the legs in a manner that is not indicated by changes in external dimensions, or (2) that the stiffness of the cuticular material is altered to produce the observed scaling of flexural stiffness.

The second moment of area (I) scaled to (body mass)1.19, which was similar to scaling I to (tibial radius)4. This indicates that the relationship between the external dimensions of the tibiae and the specific distribution of load-bearing material is conserved independently of scale. Therefore, the locust achieves the observed scaling of flexural stiffness by altering the modulus of the load-bearing cuticular material. In fact, the time-dependent modulus (E′) scales to (body mass)0.311. In essence, the scaled material stiffness provides a degree of freedom in design in addition to external morphological dimensions in accommodating the changing demands placed on a skeletal structure with increases in body size.
Contractile properties of a high-frequency muscle from a crustacean: II. Contraction kinetics
Authors: Stokes Darrell R. , Josephson Robert K.
Published: April 2021

The flagella (small appendages on the maxillipeds) of the crab Carcinus maenas beat regularly when active at about 10 Hz (15 °C). The beat of a flagellum is due to contraction of a single small muscle, the flagellum abductor (FA). The optimal stimulus frequency for tetanic contraction of the FA was about 200 Hz. When the muscle was stimulated at 10 Hz with paired stimuli per cycle, the interstimulus interval that maximized peak force was 2–4 ms, which corresponded well to the interspike intervals within bursts recorded from motor axons during normal beating. Contraction of the isolated FA showed pronounced neuromuscular facilitation and many stimuli were needed to activate the muscle fully. The dependence on facilitation in isolated muscles appeared to be greater than that in vivo. It is suggested that neuromodulators in the blood of the crab enhance neuromuscular transmission and reduce the dependency on facilitation in intact animals. The FA had a narrow length–tension curve. Tetanic tension became vanishingly small at muscle lengths less than about 90 % of the maximum in vivo length. The maximum length change of the muscle during in vivo contraction was about 5 %. The maximum isometric force of the FA was low (about 6 N cm-2) but its shortening velocity was high. Vm, the maximum shortening velocity determined from isotonic shortening, was 4.0 muscle lengths s−1; V0, the maximum shortening velocity from slack test measurements, was about 8 lengths s−1. The structure and physiology of the FA are compared with those of locust flight muscle, chosen because it too is a muscle capable of long-duration, high-frequency performance.
Contractile properties of a high-frequency muscle from a crustacean: III. Mechanical power output
Authors: Josephson Robert K. , Stokes Darrell R.
Published: April 2021

The mechanical power output during oscillatory contraction was determined for the flagellum abductor muscle of the crab Carcinus maenas using the work loop technique. Measurements were made at 10 Hz, which is the normal operating frequency of the muscle. The temperature was 15 °C. Increasing the number of stimuli per cycle (given at an interstimulus interval of 3.3 ms) decreased the number of cycles required to reach a work plateau and increased the work per cycle at the plateau to a maximum at 4–5 stimuli per cycle. The maximum mechanical power output was 9.7 W kg−1 muscle (about 26 W kg−1 myofibril). The optimum strain for work output (5.7 %) was close to the estimated muscle strain in vivo (5.2 %).
Auditory threshold change in singing cicadas
Authors: Hennig R. M. , Weber T. , Huber F. , Kleindienst H.-U. , Moore T. E. , Popov A. V.
Published: April 2021

The hearing sensitivity in singing cicadas is reduced during sound production by a folding of the tympanal membranes. Using electrophysiological recording and nerve stimulation techniques, we have shown an effect of the folded tympanum on the auditory threshold of two species of cicadas, Tibicen linnei and Okanagana rimosa. Auditory thresholds of both species increased by about 20 dB when the tympana folded during singing. In T. linnei the increase in threshold affected the whole frequency range, from 1 to 16 kHz, in a similar way. Electrical stimulation of one or both auditory nerves resulted in a folding of both tympanal membranes in a way very similar to that seen in singing animals. We have demonstrated that a cicada male is able to adjust its auditory threshold within a range of about 20 dB by the tympanal folding mechanism.
Antagonistic frequency tuning of hair bundles by different chemoreceptors regulates nematocyst discharge
Authors: Watson Glen M. , Hessinger David A.
Published: April 2021

Sea anemones capture prey by discharging nematocysts into them. Chemical and mechanical cues identify suitable prey to sensory receptor systems on the anemone. Conjugated N-acetylated sugars from prey bind to chemoreceptors on cnidocyte/supporting cell complexes to tune hair bundles on the complexes to lower frequencies matching prey movements. The hair bundles regulate discharge of microbasic p-mastigophore nematocysts into vibrating targets. Provided that proline receptors are activated after those for N-acetylated sugars, nematocyst discharge is tuned to much higher frequencies. Thus, anemone hair bundles are tuned to either higher or lower frequencies by antagonistic chemoreceptors. Chemoreceptors for proline can adapt to 10−8 mol l−1 proline and yet respond to increases in proline concentration of less than 10−15 mol l−1. Under these conditions, too few molecules of proline are added to activate chemoreceptors on all responding cnidocyte/supporting cell complexes. Evidence indicates that the extreme sensitivity of anemones to proline may be attributed, in part, to intercellular communication.
The swimming of unipolar cells of Spirillum volutans: Theory and observations
Authors: Ramia M. , Swan M. A.
Published: April 2021

Bright-field high-speed cinemicrography was employed to record the swimming of six unipolar cells of Spirillum volutans. A complete set of geometrical parameters for each of these six cells, which are of typical but varying dimensions, was measured experimentally. For each cell, the mean swimming linear and angular speeds were measured for a period representing an exact number of flagellar cycles (at least four and up to 12 cycles). Two independent sets of measurements were carried out for each cell, one relating to the trailing and the other to the leading configuration of the flagellar bundle. The geometry of these cells was numerically modelled with curved isoparametric boundary elements (from the measured geometrical parameters), and an existing boundary element method (BEM) program was applied to predict the mean swimming linear and angular speeds. A direct comparison between the experimentally observed swimming speeds and those of the BEM predictions is made. For a typical cell, a direct comparison of the swimming trajectory, in each of the trailing and the leading flagellar configurations, was also included. Previous resistive force theory (RFT) as well as slender body theory (SBT) models are both restricted to somewhat non-realistic ‘slender body’ geometries, and they both fail to consider swimming kinematics. The present BEM model, however, is applicable to organisms with arbitrary geometry and correctly accounts for swimming kinematics; hence, it agrees better with experimental observations than do the previous models.
Mechanism of the net uptake of water in moulting blue crabs (Callinectes Sapidus) acclimated to high and low salinities
Authors: Neufeld Douglas S. , Cameron James N.
Published: April 2021

Blue crabs (Callinectes sapidus Rathbun) acclimated to a salinity of 2 ‰ approximately doubled in wet mass (excluding carapace) during the period from 10 h before moult to 2 h after moult. Both in blue crabs acclimated to 2 ‰ salinity and in crabs acclimated to 28 ‰ salinity, the drinking rate increased from approximately 0.4 ml 100 g−1 h−1 at 1 day prior to moult to approximately 8 ml 100 g−1 h−1 during the first hour after moult. The drinking rate had decreased 1 day after moult in both salinities, but was significantly higher in crabs acclimated to high salinity (1.84±0.16 ml 100 g−1 h−1) than in crabs acclimated to low salinity (0.26±0.04 ml 100 g−1 h−1). Drinking accounted for two-thirds of the weight gain during the first hour after moult at both acclimation salinities, indicating that water enters the body at moult primarily through the gut rather than through the gills. [14C]polyethylene glycol, added as a tracer in the bath water, was concentrated in the midgut gland rather than in the stomach, implicating the midgut gland as the primary site of water absorption. The rate of water efflux was significantly greater in crabs acclimated to 30 ‰ salinity (66.4±9.0 ml 100 g−1 h−1) than in crabs acclimated to 2 ‰ salinity (34.0±4.7 ml 100 g−1 h−1). The osmotic uptake of water is equal at both salinities as a result of the decreased water permeability at low salinity. The rate of urine formation was estimated to be between 0.5 and 1 ml 100 g−1 h−1 during the first hour after moult in crabs acclimated to both low and high salinities, suggesting that the antennal gland plays a relatively small role in water regulation during this period.
Exercise in the terrestrial christmas island red crab Gecarcoidea Natalis: I. Blood gas transport
Authors: Adamczewska Agnieszka M. , Morris Stephen
Published: April 2021

The respiratory and circulatory physiology of the terrestrial Christmas Island red crab Gecarcoidea natalis was investigated with respect to exercise in the context of its annual breeding migration. Red crabs were allowed to walk for predetermined periods of up to 45 min. During this exercise period, blood gas measurements were made on venous, pulmonary and arterial samples to assess the function of the lungs in gas exchange and the performance of the circulatory system in gas transport and to determine the role and importance of the haemocyanin.

The lungs of G. natalis were very efficient at O2 uptake, pulmonary blood being 80–90 % saturated throughout the 45 min exercise period. The maximum O2-carrying capacity was 1.1 mmol l−1, and haemocyanin (Hc) delivered 86 % of oxygen in resting crabs and 97 % during exercise. Oxygen delivery to the tissues was diffusion-limited during exercise. Indirect evidence, from the changes in haemolymph pH during transit through the lungs, suggested that the lung is the site of CO2 excretion. The Bohr shift was high at high pH (pH 7.8–7.5, φ.=-1.23) but decreased at low pH (pH 7.1–6.8, φ.=-0.48). The decreased Hc affinity for O2 during the exercise period facilitated O2 delivery to the tissues without impairing O2 loading at the lungs. The decrease in pH was sufficient to explain the change of affinity of Hc for O2 during the exercise period. The marked acidosis (0.8 pH unit decrease) was largely metabolic in origin, especially during sustained locomotion, but less than could be predicted from concomitant lactate production.
Exercise in the terrestrial christmas island red crab Gecarcoidea Natalis: II. Energetics of locomotion
Authors: Adamczewska Agnieszka M. , Morris Stephen
Published: April 2021

The respiratory and circulatory physiology of exercising Christmas Island red crabs Gecarcoidea natalis were investigated with respect to their annual breeding migration. Red crabs were allowed to walk for up to 45 min. During this exercise period, the functioning of the circulatory system in gas transport and the energy status of the red crabs were quantified.

Energy production during exercise required both aerobic and anaerobic contributions. The aerobic scope of G. natalis was low, with only a doubling of the resting rate of oxygen consumption . Maximal O2 consumption was attained within the first 5 min of exercise and the level remained stable thereafter.

The anaerobic contribution to energy production was directly related to the speed of locomotion. L-lactate levels in blood and leg muscle were similar throughout the exercise period; blood lactate concentration was 33.39±2.29 mmol l−1 after 45 min of exercise. Heart rate in resting animals was 56±7 beats min−1. At the onset of exercise, heart rate also doubled, but without a significant increase in cardiac output. Increased O2 delivery was facilitated by increased extraction from the blood.

During the 45 min of exercise, glucose levels increased rapidly in the muscle tissue (from 2.30±0.54 to 8.78±1.20 mmol l−1) and subsequently in the blood (from 1.22±0.26 to 2.12±0.17 mmol l−1), fuelling increased glycolysis during locomotion. The energy production from stored glucose/glycogen was sufficient to support the energetic needs of locomotion, since the energy charge remained stable at 0.82.

Haemolymph L-lactate levels in crabs sampled in the field after migration were high compared with levels in many crustacean species but equivalent to L-lactate levels in laboratory animals exercised for less than 10 min. During their migration, therefore, the red crabs avoid exceptional L-lactate build-up in the blood by either walking very slowly or intermittently. However, G. natalis are exceptionally well adapted to cope with exhaustive locomotion and the resultant severe metabolic acidosis.
Use of a specialized magnetoreception system for homing by the eastern red-spotted newt Notophthalmus Viridescens
Authors: Phillips John B. , Borland S. Chris
Published: April 2021

Laboratory experiments were carried out to investigate the effects of varying the wavelength of light on the use of an earth-strength magnetic field for shoreward orientation and for the compass component of homing. In the earlier shoreward orientation experiments, newts tested under full-spectrum and short-wavelength (i.e. 400 and 450 nm) light exhibited shoreward magnetic compass orientation. Under long-wavelength (i.e. 550 and 600 nm) light, newts exhibited magnetic compass orientation that was rotated 90 ° counterclockwise to the shoreward direction. This wavelength-dependent shift in magnetic compass orientation was shown to be due to a direct effect of light on the underlying magnetoreception mechanism. In homing experiments, newts tested under full-spectrum and short-wavelength light exhibited homeward magnetic compass orientation. Under long-wavelength light, newts were randomly distributed with respect to the magnetic field. The different effects of long-wavelength light on shoreward orientation and homing confirmed earlier evidence that different magnetoreception systems mediate these two forms of orientation behaviour. The properties of the newt’s homing response are consistent with the use of a hybrid magnetoreception system receiving inputs from the light-dependent magnetic compass and from a non-light-dependent intensity (or inclination) detector which, unlike the compass, is sensitive to the polarity of the magnetic field.
Acclimation of the threshold induction temperatures for 70-kDa and 90-kDa heat shock proteins in the fish Gillichthys mirabilis
Authors: Dietz Thomas J.
Published: April 2021

The characteristic heat shock or stress response is induced upon exposure of an organism (cell) to a number of environmental stressors, e.g. heat, anoxia and heavy metals (reviewed in Morimoto et al. 1990; Ellis and van der Vies, 1991). The heat shock or stress proteins are the most broadly distributed class of proteins known and amongst the most highly conserved. These stress proteins and their cognates (non-stress-inducible forms of the proteins) play key roles in the proper folding, oligomerization, compartmentalization, translocation and activation of other cellular proteins. They have additionally been implicated in the process of acquired thermotolerance (Bosch et al. 1988; Mosser and Bols, 1988; McLennan and Miller, 1990; Sanchez and Lindquist, 1990) and in restoring aberrant proteins to their native state subsequent to thermal denaturation (Morimoto et al. 1990).
Allatotropin is a cardioacceleratory peptide in Manduca sexta
Authors: Veenstra Jan A. , Lehman Herman K. , Davis Norman T.
Published: April 2021

Allatotropin is a neuropeptide that was originally isolated from the sphinx moth Manduca sexta, in which it stimulates the synthesis of juvenile hormone in adults (Kataoka et al. 1989). An antiserum raised against this peptide was characterized, shown to be specific for allatotropin and used in a competitive enzyme-linked immunosorbent assay (ELISA) to demonstrate that allatotropin is present not only in the brain and retrocerebral complex but also in the ventral nerve cord of Manduca sexta (Veenstra and Hagedorn, 1993). In the present study, allatotropin-immunoreactive neurons were located using the allatotropin antiserum in a whole-mount immunofluorescence method adapted from Davis et al. (1989). Several cell types were found to be immunoreactive, including three pairs of intensely staining median neurons in abdominal ganglia 3–6 of the pharate adult. The location of these median pairs of cells in each ganglion is anterior, mid-dorsal and posterio-ventral (Fig. 1A). The cells project bilaterally via the ventral nerves of each ganglion to the next transverse nerve (Fig. 2), where their axons terminate in numerous superficial varicosities (Fig. 1D). It is well established that the transverse nerve is a neurohemal organ in Lepidoptera (Provansal, 1972; Taghert and Truman, 1982; Tublitz and Truman, 1985a–d). The location and projection pattern of these three pairs of median neurons indicate that they belong to a group of abdominal median neurosecretory cells identified previously (Taghert and Truman, 1982; Tublitz and Truman, 1985a). Using the nomenclature of Davis et al. (1993), these are the M1, M2 and M5 neurosecretory cells. The M1 and M2 cells mature during adult development, but the M5 cells are already differentiated in the larval stages (Taghert and Truman, 1982; Tublitz and Truman, 1985a). The M5 cells of larvae were not stained by the allatotropin antiserum and only became immunoreactive, along with the M1 and M2 cells, during adult metamorphosis. Two pairs of the abdominal median neurosecretory cells were not allatotropin-immunoreactive: (1) the M3 cells, which are ventral and mature during adult metamorphosis (Taghert and Truman, 1982); and (2) the M4 cells, which are already differentiated in the larval stages (Tublitz and Truman, 1985a).
The position-dependent nature of postural resistance reflexes in the locust
Authors: Field L. H. , Coles M. M. L.
Published: April 2021

The resistance reflexes of tibial extensor and flexor muscles, of all six legs in the locust, show changes in gain at different femur–tibia angles (FTA). In all muscles the gain is high for small angles (near full flexion) and low for large angles (near full extension, approximately 160 °). An exception occurs in the mesothoracic flexor muscle, which shows two modes: one as above and another in which maximum gain occurs at 100–120 ° FTA.

The position-dependent character is evident at each stage of the reflex pathway: motor neurone, non-spiking interneurone and femoral chordotonal organ (the afferent source of the reflex). We conclude that position-dependency originates from a decrease in the number of phasic femoral chordotonal organ neurones sensitive to joint movement as larger FTAs are approached.

Position-dependency is only roughly correlated with the postural FTAs most commonly observed in the meso- and metathoracic legs of unrestrained resting locusts; no such correlation was evident for prothoracic legs. We propose that the major role of position-dependency is to allow resistance reflexes efficiently to counter torque introduced onto the femur–tibia joint by perturbations in the horizontal plane when the insect rests on a horizontal substratum and in the vertical plane when it rests on a vertical substratum.
The use of stomach temperature records for the calculation of daily food intake in cormorants
Authors: Grémillet David J. H. , Plös Andrea L.
Published: April 2021

We present a new method of measuring the food intake in cormorants based on stomach temperature recordings. Stomach temperature loggers were deployed both in captive and in free-living birds. We examine the accuracy of this method and compare it with the standard methods of evaluating food intake by pellet or stomach content analysis.
Comparison between thermoreceptor and mechanoreceptor currents in Paramecium caudatum
Authors: Tominaga Takashi , Naitoh Yutaka
Published: April 2021

A voltage-clamped Paramecium produced an inward membrane current upon thermal or mechanical stimulation of its anterior region, whereas it produced an outward membrane current upon similar stimulation of its posterior region. Anterior thermo- and mechanoreceptor currents decreased when the membrane potential was shifted in a positive direction, showing sign reversal at a positive membrane potential, whereas posterior thermo- and mechanoreceptor currents decreased when the membrane potential was shifted in a negative direction, showing sign reversal at a membrane potential more negative than the resting potential. The reversal potential for both anterior receptor currents shifted in a positive direction when external [Ca2+] was increased, whereas those for both posterior receptor currents shifted in a positive direction when external [K+] was increased. External [Mg2+], [Mn2+], [Na+], [Rb+] and [TEA+] had similar effects on the thermo- and mechanoreceptor currents. Thermoreceptor currents decreased whereas mechanoreceptor currents increased as the ambient temperature was raised. When a mechanical stimulus was applied to the membrane where a thermoreceptor current was being produced, an algebraic summation of these receptor currents occurred. It is concluded that thermoreceptor currents are dependent on ion channels different from those responsible for the mechanoreceptor currents, although the ionic pores for the channels are similar to each other in various respects. A possibility that a thermoreceptor mechanism exclusively shares a Ca2+ pore in the anterior membrane, or a K+ pore in the posterior membrane, with a mechanoreceptor mechanism is discussed.
Urea production, acid–base regulation and their interactions in the lake magadi tilapia, a unique teleost adapted to a highly alkaline environment
Authors: Wood Chris M. , Bergman Harold L. , Laurent Pierre , Maina J. N. , Narahara Annie , Walsh Patrick J.
Published: April 2021

The Lake Magadi tilapia, Oreochromis alcalicus grahami, thrives in highly alkaline geothermal springs and pools surrounding Lake Magadi, Kenya (control ), has a functional hepatic ornithine–urea cycle (OUC) and excretes all nitrogenous waste as urea-N at variable rates (JUrea) related to O2 consumption . The mean value of was high for fish but below the theoretical maximum (approximately 0.27) for 100 % aerobic respiration of protein, so an exogenous source of substrates is not required to explain the observed JUrea. JUrea was insensitive to thiourea. Urea excretion occurred largely (80 %) through the gills, but urea-N was also present in bile and urine. Control blood pHe, pHi and [HCO3−] (approximately 8.1, 7.6 and 15 mmol l−1, respectively, at approximately 32 °C) were extremely high. When fish were exposed to lake water titrated with HCl and aerated to remove CO2, N/O2 progressively declined. At a lake water pH of 7.05 and of 0 mmol l−1, N/O2 was reduced by 80 % and an intense metabolic acidosis occurred (pHe=7.04, [HCO3−]=1.5 mmol l−1). Restoration of control water pH 9.9 at a of 0 mmol l−1 resulted in intermediate levels of N/O2 and internal acid–base status. Additional experiments confirmed that urea production was inhibited by low pHe, was dependent on blood [HCO3−] with a Km of 3.06 mmol l−1 and was insensitive to acetazolamide. While metabolic acidosis clearly inhibited OUC ureagenesis, the system appeared to be saturated with HCO3− under control conditions so that additional basic equivalent loading would not stimulate ureagenesis. Urea production in the Lake Magadi tilapia does not appear to remove exogenous HCO3− or to play a role in normal acid–base regulation.
Kinematics of pectoral fin locomotion in the bluegill sunfish Lepomis macrochirus
Authors: Gibb Alice C. , Jayne Bruce C. , Lauder George V.
Published: April 2021

The pectoral fins of ray-finned fishes are flexible and capable of complex movements, and yet little is known about the pattern of fin deformation during locomotion. For the most part, pectoral fins have been modeled as rigid plates. In order to examine the movements of different portions of pectoral fins, we quantified the kinematics of pectoral fin locomotion in the bluegill sunfish Lepomis macrochirus using several points on the distal fin edge and examined the effects of swimming speed on fin movements. We simultaneously videotaped the ventral and lateral views of pectoral fins of four fish swimming in a flow tank at five speeds ranging from 0.3 to 1.1 total lengths s−1. Four markers, placed on the distal edge of the fin, facilitated field-by-field analysis of kinematics. We used analyses of variance to test for significant variation with speed and among the different marker positions. Fin beat frequency increased significantly from 1.2 to 2.1 Hz as swimming speed increased from 0.3 to 1.0 total lengths s−1. Maximal velocities of movement for the tip of the fin during abduction and adduction generally increased significantly with increased swimming speed. The ratio of maximal speed of fin retraction to swimming speed declined steadily from 2.75 to 1.00 as swimming speed increased. Rather than the entire distal edge of the fin always moving synchronously, markers had phase lags as large as 32 °with respect to the dorsal edge of the fin. The more ventral and proximal portions of the fin edge usually had smaller amplitudes of movement than did the more dorsal and distal locations. With increased swimming speed, the amplitudes of the lateral and longitudinal fin movements generally decreased. We used two distal markers and one basal reference point to determine the orientation of various planar fin elements. During early adduction and most of abduction, these planar fin elements usually had positive angles of attack. Because of fin rotation, angles of attack calculated from three-dimensional data differed considerably from those estimated from a simple lateral projection. As swimming speed increased, the angles of attack of the planar fin elements with respect to the overall direction of swimming approached zero. The oscillatory movements of the pectoral fins of bluegill suggest that both lift- and drag-based propulsive mechanisms are used to generate forward thrust. In addition, the reduced frequency parameter calculated for the pectoral fin of Lepomis (<Y=0.85) and the Reynolds number of 5×103 indicate that acceleration reaction forces may contribute significantly to thrust production and to the total force balance on the fin.
Control of cellular contraction by calcium in Vorticella
Authors: Katoh Kaoru , Naitoh Yutaka
Published: April 2021

Vorticella extracted with Triton X-100 contracted (i.e. the cell body shrank and the stalk coiled) when the external Ca2+ concentration was raised. The degree of contraction increased with increasing Ca2+ concentration. The threshold Ca2+ concentration for shrinkage of the cell body was identical with that for coiling of the stalk in Vorticella extracted with Triton X-100. Living Vorticella showed a graded shrinkage of the cell body when Ca2+ buffer was injected into the cell body, while the stalk showed coiling of an all-or-nothing type. The degree of shrinkage of the cell body increased with increasing free Ca2+ concentration of the buffer. Living Vorticella showed a sustained contraction in response to external application or intracellular injection of caffeine. The effect of caffeine was inhibited by intracellular injection of procaine or Ruthenium Red. Vorticella injected with Ruthenium Red showed graded shrinkage of the cell body as well as graded coiling of the stalk when Ca2+ buffer was injected into the cell body. Caffeine, procaine and Ruthenium Red had no measurable effect on Ca2+-activated contraction in Vorticella extracted with Triton X-100. It is assumed that regenerative liberation of Ca2+ from the endoplasmic reticulum and/or membranous tubules in the contractile system (Ca2+-induced Ca2+ release) is responsible for evoking contraction of an all-or-nothing type following stimulation in living Vorticella.
The influence of hematocrit, temperature and shear rate on the viscosity of blood from a high-energy-demand teleost, the yellowfin tuna Thunnus albacares
Authors: Brill Richard W. , Jones David R.
Published: April 2021

The high cardiac output, arterial blood pressure and cardiac energy demand of tuna make it likely that blood viscosity has an important influence on cardiovascular function. Furthermore, tuna regularly subject themselves to ambient temperature changes of 10 °C or more during their daily vertical migrations. They can also maintain muscle temperatures several degrees Celsius above ambient and reach maximum muscle temperatures of approximately 15 °C above ambient. The blood of tuna is, therefore, subjected to more frequent and rapid temperature changes than those that occur in other teleosts. Nothing is known, however, about the effects of temperature, shear rate or hematocrit on the viscosity of tuna blood.

Viscosity of yellowfin tuna blood (hematocrits of 0–55 %) was measured at 15, 25 and 35 °C and at shear rates of 45, 90, 225 and 450 s−1 using a cone-plate viscometer. As found for the blood of other vertebrates, viscosity increased with increasing hematocrit. Viscosity also increased nonlinearly with decreasing shear rate, until a shear rate of 90 s−1 was reached. There was no significant increase in viscosity when shear rate was decreased further, to 45 s−1. Because of the relatively flat hematocrit–viscosity curves, predicted optimal hematocrit curves were nearly flat above a hematocrit of approximately 30 %.