bluuebunny/crossref_metadata_2025 huggingface dataset:
Power Output of Fish Muscle Fibres Performing Oscillatory Work: Effects of Acute and Seasonal Temperature Change
Authors: Johnson Timothy P. , Johnston Ian A.
Published: April 2021

Fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin Myoxocephalus scorpius L. Sinusoidal length changes were imposed about resting muscle length and fibres were stimulated at a selected phase during the strain cycle. The work output per cycle was calculated from the area of the resulting force-position loops. The strain amplitude required for maximum work per cycle had a distinct optimum at ±5 % of resting length, which was independent of temperature. Maximum positive work loops were obtained by retarding the stimulus relative to the start of the length-change cycle by 30° (full cycle=360°). The maximum negative work output was obtained with a 210° stimulus phase shift. At intermediate stimulus phase shifts, work loops became complex with both positive (anticlockwise) and negative (clockwise) components. The number and timing of stimuli were adjusted, at constant strain amplitude (±5 % of resting muscle length), to optimize net positive work output over a range of cycle frequencies. The cycle frequency required for maximum power output (work per cycle times cycle frequency) increased from around 5-7 Hz at 4°C to 9-13 Hz at 15°C. The maximum tension generated per cycle at 15 °C was around two times higher at all cycle frequencies in summer-relative to winter-acclimatized fish. Fast muscle fibres from summer fish produced consistently higher tensions at 4°C, but the differences were only significant at 15 Hz. Acclimatization also modified the relationship between peak length and peak force at 4 °C and 15 °C. The maximum power output of muscle fibres showed little seasonal variation at 4°C and was in the range 20-25Wkg-1. In contrast, at 15°C, maximum muscle power output increased from 9 Wkg-1 in the winter-to 30 Wkg-1 in the summer-acclimatized fish.
Routes of Transpiratory Water Loss in a Dry-Habitat Tenebrionid Beetle
Authors: Zachariassen Karl Erik
Published: April 2021

Routes of evaporative water loss in the tenebrionid beetle Phrynocolus petrosus Gerstaecker from dry savanna in East Africa were investigated. The humidity of the air surrounding the abdomen, the air surrounding the head and pronotum and the air inside the subelytral cavity was varied independently, and the effects on organismal rate of water loss were observed.

The rate of organismal water loss dropped when the humidity around the head and pronotum and inside the subelytral cavity increased. Saturation of these air compartments, which both exchange respiratory gases with the tracheae through the spiracles, reduced the organismal rate of water loss by more than 80 %, even when the large abdominal surface was surrounded by dry air. The results indicate that the transcuticular water loss makes up only about 20% of the total transpiratory water loss in these beetles, i.e. transcuticular water permeability is very low.

The results also indicate that the average air humidity inside the subelytral cavity of normal intact beetles is close to saturation. Water loss from the subelytral chamber is reduced accordingly, and appears to make up less than 10% of the total transpiratory water loss. The water loss over the pronotal spiracles amounts to about 70 %, and is thus the dominant component of transpiratory water loss in these beetles.
The Fate of Calcium in The Diet of Rhodnius Prolixus: Storage in Concretion Bodies in the Malpighian Tubules
Authors: Maddrell S. H. P. , Whittembury G. , Mooney R. L. , Harrison J. B. , Overton J. A. , Rodriguez B.
Published: April 2021

We have investigated the fate of the large amounts of calcium ingested by Rhodnius prolixus in its meals of blood. 45Ca2+ injected into the haemolymph or fed to fifth-stage Rhodnius reared on rabbits is accumulated at high concentrations in the cells of the upper Malpighian tubules; very little is excreted from the body. This 45Ca2+ accumulation goes on continuously for at least 12 days and the rate of uptake is increased several-fold within 3–4 days of a meal. The extent of calcium accumulation in tubule cells is correlated with the presence of intracellular membrane-bound concretion bodies, which are therefore likely sites of calcium deposition. X-ray diffraction showed that the calcium deposits are non-crystalline. Tubules from rabbit-fed fifth-stage Rhodnius contain 410 mmol l −1 calcium; in those from chicken-fed insects the calcium concentration is over Imoll−1; and in those fed in vitro on heparinised low-K+ sheep blood the calcium concentration is only 21 mmol l−1. The concentration of calcium in the haemolymph in all these insects was 8 mmol I−1 and its activity determined by an ion-selective electrode was 2.5 mmol l−1. 45Ca2+ deposited in the tubules is readily exchangeable, but the efflux preferentially passes to the haemolymph side of the tubule epithelium. The ability to sequester calcium in the Malpighian tubules may prevent calcium from interfering with reabsorptive processes in the rectum.
Oxygen Supply and In Vitro Performance of the Systemic Heart of Octopus Vulgaris: Effects of Haemocyanin
Authors: Agnisola C. , Houlihan D. F.
Published: April 2021

The effect of increasing oxygen supply on the perfused systemic heart of Octopus vulgaris (Lam.) by using oxygenated or haemocyanin-containing perfusates was investigated. Providing aerated blood or seawater solutions of haemocyanin that were comparable with blood in oxygen-carrying capacity improved the performance of the isolated heart compared with that of hearts perfused with aerated sea water. Aortic outputs were similar to in vivo values (44 ml min-1 g-1) at close to in vivo values of preload and afterload owing to an increase in both heart rate (from 24.0 to 38.4 beats min-1) and stroke volume (from 0.69 to 1.10ml g-1). Coronary flow fell in these conditions, becoming 2.5 % of the aortic output (against 24% with aerated sea water). A parallel increase in coronary resistance was found. Oxygenated sea water also improved the performance of the heart, mainly by improving the stroke volume. Both with haemocyanin solutions or blood and with oxygenated sea water, the isolated heart was able to do more work at lower preloads compared with the hearts perfused with aerated sea water. Power output was linearly related to total oxygen consumption and carbon dioxide production. The major site of oxygen consumption was the coronary bed. Haemocyanin released about 70 % of the bound oxygen as it passed through the ventricular wall.
Sulphide Silver Staining for Endogenous Heavy Metals Reveals Subsets of Dorsal Unpaired Median (Dum) Neurones In Insects
Authors: Siegler Melody V. S. , Manley Philip E. , Thompson Karen J.
Published: April 2021

The central nervous systems of many insects contain segmentally arranged groups of unpaired midline neurones. These have been called DUM (dorsal unpaired median) neurones because of the position of their cell bodies. The larger DUM neurones, with bilaterally symmetrical peripheral axons, have been most extensively studied in grasshoppers and locusts. DUM cells in the metathoracic ganglion modulate tension of skeletal muscle, potentiate synaptic transmission at neuromuscular junctions and slow a myogenic rhythm (Evans and O’Shea, 1977, 1978; Whim and Evans, 1989), whereas those in the abdominal ganglia alter tension in visceral muscle (Lange and Orchard, 1984). In fireflies, DUM neurones of the terminal abdominal ganglia control flashing by activating the photocytes of the lantern (Christensen and Carlson, 1981). The effects are mediated by the biogenic amine octopamine (Carlson and Jalenak, 1986; Evans and O’Shea, 1977, 1978; Morton and Evans, 1984; Orchard and Lange, 1985), which is also implicated in other modulatory actions (see Ramirez and Orchard, 1990, for references). In grasshoppers, in addition to the octopamine-containing efferent DUM neurones, there are a substantial number of local and intersegmental DUM interneurones with small cell bodies (Thompson and Siegler, 1989, 1991).
The Influence of Hypoxia on the Preferred Temperature of Rainbow Trout Oncorhynchus Mykiss
Authors: Schurmann H. , Steffensen J. F. , Lomholt J. P.
Published: April 2021

The behavioural thermoregulation of rainbow trout Oncorhynchus mykiss was investigated in a shuttlebox at normoxia and at three levels of hypoxia: 13.3, 9.3 and 5.3 kPa. The final preferred temperatures at normoxia, and at 13.3, 9.3 and 5.3 kPa, were 16.1, 14.9, 15.0 and 12.7°C, respectively. A decreased rate of metabolism and an increased blood oxygen-affinity are among the physiological advantages of selecting a lower temperature during hypoxia. It is suggested that catecholamines may play a part in controlling temperature selection during hypoxia. In natural environments, this behaviour may result in habitat shifts of fish living in heterothermal environments with changing oxygen tensions.
Sailing Downwind: Aerodynamic Performance of the Velella Sail
Authors: Francis Lisbeth
Published: April 2021

Using a wind tunnel built over a shallow pool and methods devised for measuring the performance of yacht sails, I describe aerodynamic performance in situ for the sailor-by-the-wind, Velella velella. By contrast with designers of the modern yacht mainsail, natural selection has apparently favored stability and seaworthiness over performance to windward. The Velella sail is a low aspect ratio airfoil with an unusually flat polar plot. Primarily a drag-based locomotory structure, this thin, leaf-like sail generates maximum force when oriented at attack angles between 50° and 90°. In the wind tunnel, free-sailing animals spontaneously assumed stable orientations at attack angles ranging from 28° to 87° and sailed with their hulls approximately broadside to the apparent flow of oncoming water. At these angles, aerodynamic force on the sail is asymmetrical, with the center of pressure upwind of the sail midline. Since aerodynamic force on the sail is balanced at equilibrium by hydrodynamic force on the hull, this orientation must be caused by asymmetrical forces acting on surface and underwater parts as the wind drags the animal along the surface of the water.
Consequences of a Gait Change During Locomotion in Toads (Bufo Woodhousii Fowleri)
Authors: Anderson Bruce D. , Feder Martin E. , Full Robert J.
Published: April 2021

Most animals cannot sustain speeds above that at which the rate of oxygen consumption reaches a maximum Fowler’s toad (Bufo woodhousii fowler), by contrast, has a maximum aerobic speed (MAS, the speed at ) of 0.27 km h−1 but can sustain speeds as high as 0.45 km h−1 without increasing the , above the . The present study investigates the discrepancy between MAS and the maximum sustainable speed (MSS). Toads switched from walking to hopping as their speed increased. The cost of a hop (4.1×10−4ml O2g−1 hop−1) was greater than the cost of a walking stride (2.5×10−4ml O2g−1 stride−1) and was independent of speed for both hopping and walking. However, individual hops were much longer than walking strides, which more than offset the greater cost of a hop. The calculated cost to traverse a given distance was approximately 1.9 times as much for walking as for hopping. During natural locomotion animals used combined walking and hopping. Individual toads that favored walking had higher locomotor costs than those that favored hopping. The estimated cost of exclusive hopping was less than the cost of natural locomotion at all but the highest speeds. This discrepancy may reflect the fact that the natural gait is a combinastion of both the less economical walking gait and the more economical hopping gait. To achieve speeds above the MAS toads walked less and used the more economical hopping gait more, and thus did not increase energy cost above that of . The speed at which the estimated cost of exclusive hopping exceeded the cost of a natural gait and approached the was close to the MSS. Creatine phosphate and lactate concentrations in the muscles of the thigh and calf did not change from resting levels at sustainable speeds greater than the MAS.
Insect-Like Characteristics of the Malpighian Tubules of a Non-Insect: Fluid Secretion in the Centipede Lithobius Forficatus (Myriapoda: Chilopoda)
Authors: Wenning Angela , Greisinger U. T. E. , Proux Jacques P.
Published: April 2021

Fluid secretion by isolated upper and lower portions of Malpighian tubules in the centipede Lithobius forficatus L. was studied. Ion requirements, cellular and transepithelial potentials, dependence on external osmolality and the effects of an insect diuretic factor and transport-active drugs were investigated. Unlike many insects, L. forficatus exhibited strongly Na+-dependent, K+-independent urine formation. However, as in many insects, upper and lower tubule portions from L. forficatus produced a K+-enriched, hypertonic fluid, and the transepithelial potential was positive with respect to the haemolymph. Furthermore, furosemide (5×10−4mol l−1) reversibly inhibited urine formation. Ouabain, even at 10−3mol l−1, had little effect on urine flow rate in upper tubules but inhibited secretion in lower tubules, albeit not completely. Locust diuretic hormone (at 10−7mol l−1) enhanced fluid secretion in L. forficatus, but its action was not mimicked by dibutyryl cyclic AMP. The results suggest that some characteristics attributed exclusively to insects are common to non-insect arthropods.
Effects of Exercise, Hypoxia and Feeding on the Gastrointestinal Blood flow in the Atlantic Cod Gadus Morhua
Authors: Axelsson Michael , Fritsche Regina
Published: April 2021

Cardiac output, ventral and dorsal aortic blood pressure, heart rate, and coeliac and mesenteric artery blood flow were recorded simultaneously in the Atlantic cod, Gadus morhua L., at rest, during exercise, during hypoxia and after feeding.

In the resting unfed animals, coeliac artery blood flow was 4.1±0.8mI min−1 kg−1 and mesenteric artery blood flow was 3.5±1.1 ml min−1 kg−1 (mean± S.E.M., N=10); together, these flows represent approximately 40% of the cardiac output.

Exercise or exposure to hypoxia resulted in increased visceral vascular resistance, leading to reductions in the coeliac and mesenteric artery blood flows.

Coeliac and mesenteric blood flows were increased 24 h after feeding and the coeliac and systemic vascular resistances decreased in comparison with the prefeeding values. Phentolamine did not affect the gastrointestinal artery blood flow, but produced a significant decrease in the mesenteric and systemic vascular resistance.

Treatment with bretylium and phentolamine revealed differences between the coeliac and the mesenteric vasculature regarding the control mechanisms during hypoxia and during exercise and feeding. During hypoxia, an adrenergic control of the gastrointestinal vasculature with both nervous and humoral components was found, whereas during exercise and after feeding an additional non-adrenergic mechanism controlling gut blood flow was demonstrated.
Moments of Inertia of Bat Wings and Body
Authors: Thollesson Mikael , Norberg Ulla M.
Published: April 2021

The moments of inertia of the wings about the shoulder joint and about the roll axis were estimated in eight species of bats, using strip analysis. The moment of inertia of the bat’s trunk about the roll axis was estimated by assuming the body and head to be ellipsoids. The slopes of the regressions of moment of inertia of one wing about the shoulder joint (Jw) versus body mass (mtot), wing span (b) and wing area (S) were as expected for geometrically similar animals of different size. The exponent for Jwversus body mass in bats deviates from that found for birds, while the exponent for Jwversus wing span does not. A multiple regression was used to show that Jw may be estimated by:

The mean value of the moment of inertia originating from the trunk is 7% of the bat’s total moment of inertia (of wings and body combined) about the roll axis. The mass of one wing (mw) was plotted against body mass for the eight bat species, which gives:

The slope for our bats, 1.11, is similar to that obtained for birds, 1.10. Adaptations to reduce the moments of inertia may be more important for increasing a bat’s flight agility (roll acceleration) than for decreasing the total mechanical power required to fly. The influences of wing moment of inertia and wing shape on manoeuvrability and agility are discussed.
Swimming Energetics and Performance of Instrumented Adélie Penguins (Pygoscelis Adeliae)
Authors: Culik Boris , Wilson Rory P.
Published: April 2021

The effects of implanted and of externally attached instruments (1.8% of body cross-sectional area) were studied on Adélie penguins (Pygoscelis adeliae) using a 21 m long canal in conjunction with respirometry at Esperanza Bay, Antarctica. Penguins in both groups covered the same mean distance (173 m in 5 min) as controls. Implanted birds preferred to swim at slower speeds (1.3–1.7 m s−1) than did the controls (1.9–2.1 m s−1), whereas penguins with external instruments had a bimodal speed distribution with maxima at 1.7–1.9 and 2.3-2.5ms−1. Power input during swimming averaged 20% less in implanted penguins (12.7 W kg−1) and 42% more in penguins fitted with external instruments (22.5Wkg−1) compared with controls (15.8 W kg− x). Similarly, cost of transport was 23% lower in implanted penguins (7.0 J kg−1 m−1) and 25% higher in externally instrumented birds (11.3 Jkg−1 m−1) compared with controls (9.0 Jkg−1m−1). Possible reasons for the effects caused by the devices are discussed and the advantages and disadvantages of implanted and externally fitted devices are compared.
Coordination of Locomotor and Cardiorespiratory Networks of Lymnaea Stagnalis by A Pair of Identified Interneurones
Authors: Syed N. I. , Winlow W.
Published: April 2021

The morphology and electrophysiology of a newly identified bilateral pair of interneurones in the central nervous system of the pulmonate pond snail Lymnaea stagnalis is described. These interneurones, identified as left and right pedal dorsal 11 (L/RPeDll), are electrically coupled to each other as well as to a large number of foot and body wall motoneurones, forming a fast-acting neural network which coordinates the activities of foot and body wall muscles. The left and right sides of the body wall of Lymnaea are innervated by left and right cerebral A cluster neurones. Although these motoneurones have only ipsilateral projections, they are indirectly electrically coupled to their contralateral homologues via their connections with L/RPeDll. Similarly, the activities of left and right pedal G cluster neurones, which are known to be involved in locomotion, are also coordinated by L/RPeDll. Selective ablation of both neurones PeDll results in the loss of coordination between the bilateral cerebral A clusters. Interneurones L/RPeDll are multifunctional. In addition to coordinating motoneuronal activity, they make chemical excitatory connections with heart motoneurones. They also synapse upon respiratory motoneurones, hyperpolarizing those involved in pneumostome opening (expiration) and depolarizing those involved in pneumostome closure (inspiration). An identified respiratory interneurone involved in pneumostome closure (visceral dorsal 4) inhibits L/RPeDll together with all their electrically coupled follower cells. Both L/RPeDll have strong excitatory effects on another pair of electrically coupled neurones, visceral dorsal 1 and right parietal dorsal 2, which have previously been shown to be sensitive to changes in the partial pressure of environmental oxygen . Although L/RPeDll participate in whole-body withdrawal responses, electrical stimulation applied directly to these neurones was not sufficient to induce this behaviour.
Auditory Interneurones in the Metathoracic Ganglion of the Grasshopper Chorthippus Biguttulus: II.Processing of Temporal Patterns of the Song of the Male
Authors: Stumpner Andreas , Ronacher Bernhard , von Helversen Otto
Published: April 2021

Auditory interneurones originating in the metathoracic ganglion of females of the grasshopper Chorthippus biguttulus were investigated with respect to their processing of models of the male’s song. In these models two temporal configurations were varied: (i) the song pattern, consisting of ‘syllables’ and ‘pauses’, and (ii) the duration of short gaps within syllables. A precise encoding of the song pattern is found only among receptors and ‘thoracic’ neurones (SN1, TNI), but not among ascending neurones. The only ascending neurone that reacts tonically at all intensities (AN6) encodes the song pattern much less precisely than do receptors. Other ascending neurones (AN3, AN11) encode the gross pattern of model songs, but only at low intensities. One spontaneously active ‘local’ neurone (SN6) is tonically inhibited and encodes the pauses of a model song. A similar response, however, is not found in three ascending neurones (AN13, AN14, AN15), which are merely inhibited. Among ascending neurones, AN12 is the most reliably influenced by the syllable-pause structure of the songs. Its phasic burst marks the onset of every syllable in a behaviourally attractive song. Its activity could account for the rising part of the corresponding behavioural response curve. However, no ascending neurone shows activity corresponding to the falling part of the behavioural response. Among local neurones, the phasic BSN1 neurones are most clearly influenced by varying syllable-pause combinations. Gaps within the song syllables cause a complete inhibition of the activity of AN4. The response of AN4 to syllables with and without gaps is strikingly similar to the behavioural response and is maintained over the whole intensity range tested. Several local neurones, especially SN6, are strongly influenced by gaps within model songs - though only in certain intensity ranges. In accordance with behavioural results, the pathways for information on song pattern and sound direction appear to be separated among ascending neurones. Among local interneurones, however, this separation does not appear to take place, since the most directional local neurone, BSN1, might also be suited for pattern-filtering tasks.
Effect of Endurance Swimming on the Lactate Kinetics of Rainbow Trout
Authors: Weber Jean-Michel
Published: April 2021

The lactate turnover rate of rainbow trout (Oncorhynchus mykiss) was measured by bolus injection of [U-14C]lactate at rest and during prolonged swimming at 85% Ucrit to determine the importance of this metabolic fuel for endurance locomotion in fish, to assess whether lactate exchange between white and red muscle could be a possible mechanism for supplying oxidizable fuel to their lateral red muscle, and to compare the contribution of lactate to total energy provision between teleost and mammalian species. Turnover rate only increased from 4.41±0.33 to 9.71±1.69 μmolkg−1min−1 between rest and prolonged swimming, and the contribution of lactate oxidation to total metabolism declined during exercise. Lactate exchange between white and red muscle is, therefore, not a significant mechanism to fuel the active lateral red musculature during prolonged swimming. The lactate turnover rate of teleosts is one or two orders of magnitude lower than in mammals of equivalent size, but lactate has the same importance as a fuel in both vertebrate groups. However, lactate turnover rate and oxidation rate do not scale with body mass in the same fashion as does metabolic rate. The slope of the mammalian relationship for whole-body lactate turnover and oxidation is much lower (0.58) than the slope of the classic relationship for metabolic rate (0.75), indicating that lactate is a much more important oxidative substrate for small than for large animals.
L-Proline Transport Systems of Starfish Pyloric Caeca
Authors: Ahearn Gregory A. , Behnke Rachel D.
Published: April 2021

Purified brush-border membrane vesicles (BBMV) of starfish [Pycnopodia helianthoides (Brandt)] pyloric caecal epithelium were prepared by magnesium precipitation in order to characterize the possible role of this organ in amino acid transport. L-[3H]proline uptake by these vesicles was Na+-dependent and greater at pH7.5 than at pH5.5. L-Pipecolate was a competitive inhibitor of L-proline influx into these BBMV, exhibiting a Ki value of 0.02 mmol l−1. The amino acid inhibitors, L-pipecolate, L-alanine and L-leucine were used as test substrates to block L-proline influx by the IMINO, NBB and L transport systems, respectively, in order to estimate the contribution of each process to total L-proline entry into pyloric caecal cells. The carrier-mediated transport constants for L-proline transfer by these three systems were: Kt=0.18mmoll−1 (IMINO), 0.13mmoll−1 (NBB) and 0.21 mmol T1 (L); Jmax= 1310 pmol mg−1 protein 30 s −1 (IMINO), 360 pmol mg−1 protein 30 s−1 (NBB) and 470pmolmg−1protein30s−1 (L). L-Proline influxes through both the IMINO and NBB systems were sigmoidal functions of the external [Na+], while transfer by the L system was Na+-independent. Multiple sodium ions (e.g. 2 or 3 Na+/L-proline) appear to be associated with L-proline transport by both Na+-dependent transport systems, but the nature of this association (i.e. activation or energization) is unclear. Results suggest that starfish pyloric caecal epithelium possesses a similar array of L-proline transport proteins to those found in similar cell types of mammalian intestine or kidney, providing tentative support for an absorptive function for this organ.
Electrogenic 2Na+/H+ Antiport in Echinoderm Gastrointestinal Epithelium
Authors: Ahearn Gregory A. , Franco Pierette
Published: April 2021

Purified brush-border membrane vesicles (BBMV) of starfish (Pycnopodia helianthoides) pyloric caecal epithelium were prepared by a magnesium precipitation technique in order to compare the properties of Na+/H+ exchange in this invertebrate tissue with those of an apparently unique recently described crustacean electrogenic antiporter. In starfish BBMV 22Na uptake was markedly enhanced by an outwardly directed pH gradient and membrane potential (inside negative) compared to control short-circuited vesicles. External amiloride abolished the stimulatory capacity of the proton gradient and membrane potential as driving forces for sodium transport. Sodium influx, in the presence of an outwardly directed proton gradient, was a sigmoidal function of [Na+]o and yielded a Hill coefficient of 2.6, suggesting that more than one sodium ion was exchanged with each internal proton during the exchange event. Two additional findings were used to establish the number of external Na+ binding sites and the transport stoichiometry of the starfish antiporter. First, amiloride acted as a competitive inhibitor of Na+ binding to two external sites with markedly dissimilar apparent amiloride affinities (Kil=28μmoll−1; Ki2= I650μmol F1). Second, a static head flux ratio analysis resulted in a 2Na+/H+ exchange stoichiometry where a balance of driving forces (e.g. no net Na+ flux) was attained with a combination of a 10:1 Na+ gradient and a 100:1 H+ gradient. Results suggest that the electrogenic 2Na+/H+ exchanger previously characterized for crustacean epithelia also occurs in echinoderm cells and may be a widely distributed invertebrate antiporter.
Distribution of Carbonic Anhydrase in the Uterus of Late-Term Pregnant Spiny Dogfish (Squalus Acanthias)
Authors: Flügel Cassandra , Lütjen-Drecoll Elke
Published: April 2021

Carbonic anhydrase (CA) activity was localized in the late-term pregnant spiny dogfish uterus using the modified histochemical staining method of Hansson. Staining was found in the cytoplasm of red blood cells and in the membranes of the endometrial epithelial cells. Under the electron microscope, reaction products were seen in the basolateral membranes of the superficial cells, whereas the apical membranes were unstained. The cells of the underlying layer contacting the stromal capillaries showed staining in all their membranes. This staining pattern is similar to that found in other epithelia noted for active ion transport.
Noninvasive Detection of Electrical Events During the Startle Response in Larval Medaka
Authors: Featherstone Dave , Drewes Charles D. , Coats Joel R.
Published: April 2021

In teleosts, a startle response occurs when one of a pair of Mauthner cells (M-cells) originating in the fish hindbrain is excited by sensory afferents and fires a single action potential. This action potential propagates caudally along the M-axon, which crosses the midline and continues tailward within the spinal cord. In passage, the M-spike excites (via collaterals) primary motor neurons within the spinal cord which, in turn, activate nearby axial musculature. The most obvious behavioral result of this highly conserved (at least in teleosts) and stereotypic sequence is a fast body bend toward the side of the active M-axon such that the fish forms the shape of the letter C. This is stage 1 of the teleost ‘C-start’, also previously called the M-reflex (for reviews, see Nissanov and Eaton, 1989; Eaton and DiDomenico, 1986; Eaton and Nissanov, 1985; Eaton and Hackett, 1984; Eaton and Bombardieri, 1978; Diamond, 1971).
Waveform Discrimination in the Electric Fish Eigenmannia: Sensitivity for the Phase Differences Between the Spectral Components of a Stimulus Wave
Authors: KRAMER BERND , OTTO BRUNHILDE
Published: April 2021

Eigenmannia lineata is a tropical South American gymnotiform fish that is both electrogenic and electroreceptive. Its electric organ generates a constant-frequency wave discharge (EOD) that is sexually dimorphic in waveform and harmonic content. Eigenmannia discriminates digitally synthesized, natural male and female EOD waveforms of identical frequency and amplitude. Experiments were devised to investigate behaviourally the sensory mechanism of this discrimination.

Both the content in higher harmonics (as seen in an amplitude spectrum) and the waveform (phase spectrum) could provide the cues Eigenmannia uses for discrimination. Five Eigenmannia were trained to discriminate artificially generated stimuli composed of the fundamental frequency, f1, and its harmonic, f2, of a frequency twice that of f1 and of weaker intensity (−13 to −3dB re f1; a similar variation is found among the EODs of different Eigenmannia individuals). The rewarded stimulus, S+ (with a strong f2 intensity of −3dB re f1), remained constant throughout the experiments. The family of negative (S-) stimuli all had a phase difference of 0°, that is, no phase difference, between their harmonics, while the S+ stimulus had a phase difference of 90°. Therefore, all S- stimuli differed from the S+ stimulus in waveform, while one S- stimulus had an amplitude spectrum identical to that of the S+ stimulus.

All fish discriminated any S- signal tested from the S+ stimulus, including the S- stimulus with an identical amplitude spectrum, both when the test signals had identical energy contents (that is, slightly different peak-to-peak amplitudes) and when they had identical peak-to-peak amplitudes (hence, slightly different energy contents).

These results arc evidence for a true waveform (time domain) sensitivity of Eigenmannia. A sensory mechanism is proposed that enables Eigenmannia to assess the P/N ratio of a wave signal, that is, the duration ratio of positive (P) and negative (N) half-waves between zero-crossings of a stimulus cycle (the S+ and all S- stimuli, as well as female and male EODs, differ in this regard).
Mechanical Properties of Demembranated Flight Muscle Fibres from a Dragonfly
Authors: PECKHAM M. , WHITE D.C. S.
Published: April 2021

The mechanical properties of demembranated muscle fibres of synchronous flight muscle from a dragonfly Libellula quadrimaculata, asynchronous flight muscle from the giant waterbug Lethocerus indicus and synchronous psoas muscle from rabbit were compared in relaxed, active and rigor conditions. The properties were compared to the known structure and protein compositions of these muscles. We found that active tension of L. indicus flight muscles was stretch-activated (tension was low and was significantly increased following a rapid stretch of 1 % of muscle length), whereas both dragonfly flight muscle and rabbit psoas muscle were not (active tension was high and did not significantly increase following a rapid stretch of 1%). Three different properties have been suggested to give rise to stretch activation in asynchronous muscles: (1) a matching of the helix periodicities of actin target sites to myosin crossbridge heads, (2) a special form of troponin subunit called troponin-H, and (3) the high resting stiffness of these muscles inducing strain in the thick filaments. Rabbit psoas muscle has none of these properties. Dragonfly flight muscles do not have the helix matching, but they do have a form of troponin-H and a high resting stiffness. It seems most likely that dragonfly flight muscles are not stretch-activated because they do not have the helix matching.

Note:

Present address: Department of Biophysics, King's College London, 26–29 Drury Lane, London, WC2B 5RL, UK.
Antagonist properties of arylaminopyridazine GABA derivatives at the Ascaris muscle GABA receptor
Authors: Duittoz A. H. , Martin R. J.
Published: April 2021

1. In a previous study, it was shown that the potency order for two arylamino-pyridazine derivatives, SR95531 and SR95103, was different in Ascaris suum when compared to vertebrate preparations. SR95531, the most potent analogue at the vertebrate GABAA receptor, was found to be very weak at antagonizing GABA responses in Ascaris, but SR95103, approximately 20 times less potent than SR95531 in vertebrate preparations, was more potent than SR95531 in Ascaris. These results suggested the existence of different accessory binding sites at the Ascaris GABA receptor. 2. To test this hypothesis, the effects of a series of arylaminopyridazine derivatives of GABA on the GABA response in Ascaris suum muscle were investigated using a two-microelectrode current-clamp technique. 3. The results showed that SR42627, a potent antagonist at the GABAA receptor, was one of the weakest analogues in Ascaris muscle. In contrast, SR95132, virtually inactive in vertebrate preparations, was equipotent to SR95103, the most potent analogue of the series in Ascaris muscle. 4. The three most potent analogues in Ascaris, SR95103, SR95132 and SR42666, displace GABA dose-response curves to the right without decreasing the maximal response. The modified Schild plots for these compounds are consistent with a competitive mechanism involving two molecules of GABA and only one molecule of antagonist interacting with the receptor. The estimated dissociation constants for SR95103, SR95132 and SR42666 are, respectively, 64, 65 and 105 mumol l-1. 5. Structure-activity relationships for this series of compounds were examined in Ascaris and compared to those in vertebrates. Substitution on the pyridazine ring in the 4-position, while detrimental for the antagonist potency at the vertebrate GABAA receptor, appears to be a prerequisite for antagonistic activity on the Ascaris muscle GABA receptor. These results are interpreted in terms of the accessory binding site theory of Ariens, and suggest the existence of different accessory binding sites on the Ascaris GABA receptor.
The Effects of Hydrostatic Pressure on A1 Adenosine Receptor Signal Transduction in Brain Membranes of Two Congeneric Marine Fishes
Authors: SIEBENALLER JOSEPH F. , HAGAR ARTHUR F. , MURRAY THOMAS F.
Published: April 2021

To investigate the effects of deep-sea temperatures and hydrostatic pressures on transmembrane signal transduction, the A1 adenosine receptor/inhibitory G protein/adenylyl cyclase complex was studied in brain membranes from two congeneric marine fishes that live at different depths. These scorpaenid species, Sebastolobus alascanus and S. altivelis, have been used as a model system to study adaptations to the deep sea. At 5°C and atmospheric pressure the basal adenylyl cyclase activities of the two species are similar. The inhibition of adenylyl cyclase by the A1 adenosine receptor-specific agonist, N6-cyclopentyladenosine (CPA), was dependent on GTP. The IC50 values for inhibition of adenylyl cyclase by CPA were 2.0±1.14μmoll−1 and 1.6±1.06 for S. alascanus and S. altivelis, respectively. The A1 adenosine receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine reversed the CPA-induced inhibition of adenylyl cyclase in a concentration-dependent manner. Brain membranes prepared from the Sebastolobus species incubated at 48.1 MPa (0.1 MPa = l atmosphere) and 5°C for 2.5 h did not lose basal adenylyl cyclase activity or sensitivity to inhibition by CPA when assayed at atmospheric pressure. In contrast, rat brain membranes lost 59% of their activity under these conditions. At atmospheric pressure, the Km values of 2-deoxy-ATP were identical for the Sebastolobus species adenylyl cyclases. Increased pressure increased the Km values in both species. However, the Km of 2-deoxy-ATP was less sensitive to pressure for the enzyme from the deeper-living S. altivelis. Basal adenylyl cyclase activity and the inhibitory effect of 100μmoll−1 CPA were assayed at 0.1, 13.7 and 41.2MPa. Increased pressure inhibited basal adenylyl
The effect of N-ethylmaleimide on K+ and Cl- transport pathways in the lamprey erythrocyte membrane: activation of K+/Cl- cotransport
Authors: Kirk K.
Published: April 2021

The effect of the sulphydryl reagent N-ethylmaleimide on the K+ and Cl- transport pathways of the lamprey erythrocyte membrane was found to be quite complex. N-Ethylmaleimide inhibited the Ba(2+)-sensitive pathway that mediates most of the ouabain-resistant influx of K+ into the cell under physiological conditions but stimulated a Cl(−)-dependent, B(2+)-resistant K+ transport pathway that was inhibited by compounds that inhibit Cl(−)-dependent K+ transport in the human erythrocyte. N-Ethylmaleimide (in most cases) reduced the total influx of Cl- into the lamprey erythrocyte but (in all cases) introduced a K(+)-dependent component into the measured Cl- uptake; this was explained in terms of N-ethylmaleimide having inhibited the pathway primarily responsible for Cl- influx under physiological conditions but having stimulated a second, K(+)-dependent Cl- transport pathway. Although the magnitude of the K+ and Cl- fluxes stimulated by N-ethylmaleimide varied widely between cells from different lampreys, there was, in each individual case, a close similarity between the magnitude of the Cl(−)-dependent K+ influx (calculated from the 86Rb+ uptake) and the K(+)-dependent Cl- influx; the mean value for the ratio of the former to the latter was 1.01 +/− 0.03 (N = 5). The results are therefore consistent with the sulphydryl reagent having activated a K+/Cl- cotransport system similar to that present in erythrocytes from many mammalian species. This raises the possibility that the lamprey red cell may be a uniquely suitable system in which to study the characteristics of Cl- transport by this pathway.
Acid-base regulation and blood gas transport following exhaustive exercise in an agnathan, the sea lamprey Petromyzon marinus
Authors: Tufts B. L.
Published: April 2021

Exhaustive exercise in cannulated sea lampreys, Petromyzon marinus, resulted in a marked extracellular acidosis in the arterial blood which had both a respiratory and a metabolic component. Blood CO2 tension (PCO2) returned to control levels within an hour after exercise, but the metabolic acidosis had a somewhat longer time course and the extracellular pH (pHe) did not fully recover until the 4 h recovery sample. The magnitude and duration of the changes in both the plasma lactate concentration and the concentration of metabolic protons were very similar and the maximal proton deficit after exercise was, therefore, only 1.5 mequiv l-1. In contrast to the changes in pHe, there were no significant changes in the erythrocyte pH (pHi) following the exercise period. The regulation of pHi was apparently not adrenergically mediated, however, since addition of catecholamines to lamprey blood in vitro had no significant effect on pHi. In addition, the period of exhaustive exercise in vivo was not associated with any significant changes in the mean cellular hemoglobin concentration. The total carbon dioxide concentration in the arterial whole blood and true plasma were both significantly reduced after exercise, but the total carbon dioxide concentration within the erythrocytes was transiently increased. Finally, there was a marked decrease in the arterial PO2 immediately after exercise, which was associated with a significant reduction in the amount of oxygen bound to hemoglobin; however, within 30 min, these values had both returned to normal. The maintenance of pHi presumably contributes to the regulation of oxygen transport in lampreys and it may be particularly important during the brief period immediately after exercise when oxygen transport is clearly compromised. Although several studies have provided evidence that chloride/bicarbonate exchange limitations may exist in agnathan blood in vitro, the present results demonstrate that the characteristics of carbon dioxide transport and acid-base regulation after exercise in P. marinus are not markedly different from those in other lower vertebrates.
Neural Control of Fibrillar Muscles in Bees During Shivering and Flight
Authors: ESCH HARALD , GOLLER FRANZ
Published: April 2021

The big indirect flight muscles in the thorax of honeybees and bumblebees show two modes of action: they contract with ‘conventional’ twitches in response to slowly repeated muscle potentials and go into tetanus at higher muscle potential frequencies. They can also contract much faster when quickly stretched (stretch activation).

We observed contractions of DV (dorsoventral) and DL (dorsal longitudinal) muscles optically with the help of a tiny mirror glued to the scutellum. We noticed that DL muscles contracted much more than DV muscles during pre-flight warmup. During warm-up, muscle potential frequencies in DL muscles were higher than in DV muscles (DL frequency/DV frequency =1.3), whereas during flight the ratio reversed (DL/DV=0.8). The scutal fissure was completely closed during shivering warm-up, apparently because the DL muscles shortened as much as they could. As a consequence, fast antagonistic stretching was not possible. However, the scutal fissure oscillated between wide open and closed during flight, and antagonists could stretch each other quickly. Flight was started by highly synchronized ‘conventional’ contractions of many muscle elements in DV muscles. Antagonistic stretch-activation during flight led to faster shortening than during shivering warm-up and synchronized all activated muscle elements to produce maximal contractions.

The indirect flight muscles of bumblebees were in tetanic contractions during shivering warm-up over the whole range of temperatures between 8 and 36°C. These tetanic contractions probably prevented other researchers from observing mechanical muscle activity. Our results, which for the first time allow us to detect tetanic contractions directly, make it very improbable that non-shivering thermogenesis occurs in bumblebees, as has been proposed previously.
Acid-Base Variables in Malpighian Tubule Secretion and Response to Acidosis
Authors: STAGG ANDREW P. , HARRISON JON F. , PHILLIPS JOHN E.
Published: April 2021

1. Malpighian tubule fluid from Schistocerca gregaria adults, starved for 1 day, was collected in situ by cannulation of the gut, both before and after injecting 10 μmol of HCl or NaCl into the haemocoel. 2. Haemolymph pH at the neck remained depressed by 0.3 units for at least 6 h in HCl- as compared to NaCl-injected locusts. A lower haemolymph pH persisted near the acid injection site for several hours. 3. The pH of tubule fluid remained about 0.5 units more acid than haemolymph under all conditions. Thus, net tubular acid secretion was proportional to haemolymph acid-base status. 4. The greater acidity of tubular fluid after acid injection was associated with lower estimated bicarbonate concentrations and higher Pcoco2 without any change in total CO2 when compared to controls. 5. The combined contribution of bicarbonate, phosphate and urate to total buffering capacity of tubular fluid was estimated to be 75°, with bicarbonate responsible for 55° of the total. 6. The maximum rate of acid removal by all Malpighian tubules of starved locusts, including H+ trapped in ammonium ions, was calculated to be very small in relation to the acid load injected into the haemocoel

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Pressure and Temperature Adaptation of Cytosolic Malate Dehydrogenases of Shallowand Deep-Living Marine Invertebrates: Evidence for High Body Temperatures in Hydrothermal Vent Animals
Authors: DAHLHOFF ELIZABETH , SOMERO GEORGE N.
Published: April 2021

Effects of temperature and hydrostatic pressure were measured on cytosolic malate dehydrogenases (cMDHs) from muscle tissue of a variety of shallow- and deep-living benthic marine invertebrates, including seven species endemic to the deep-sea hydrothermal vents. The apparent Michaelis-Menten constant (Km) of coenzyme (nicotinamide adenine dinucleotide, NADH), used to index temperature and pressure effects, was conserved within a narrow range (approximately 15–25 μmoll−1) at physiological temperatures and pressures for all species. However, at elevated pressures, the Km of NADH rose sharply for cMDHs of shallow species (depths of occurrence >Approximately 500 m), but not for the cMDHs of deep-sea species. Cytosolic MDHs of invertebrates from the deep-sea hydrothermal vents generally were not perturbed by elevated temperatures (15–25°C) at in situ pressures, but cMDHs of cold-adapted deep-sea species were. At a single measurement temperature, the Km of NADH for cMDHs from invertebrates from habitats with well-characterized temperatures was inversely related to maximal sustained body temperature. This correlation was used to predict the maximal sustained body temperatures of vent invertebrates for which maximal habitat and body temperatures are difficult to estimate. Species occurring on the ‘smoker chimneys’, which emit waters with temperatures up to 380°C, are predicted to have sustained body temperatures that are approximately 20–25°C higher than vent species living in cooler vent microhabitats. We conclude that, just as adaptation of enzymes to elevated pressures is important in establishing species’ depth distribution patterns, adaptation of pressure-adapted enzymes to temperature is critical in enabling certain vent species to exploit warm-water microhabitats in the vent environment.
Habituation of the ultrasound-induced acoustic startle response in flying crickets
Authors: May M. L. , Hoy R. R.
Published: April 2021

The ultrasound-induced negative phonotactic response of tethered, flying Australian field crickets habituates to repeated stimuli. Using the magnitude of the metathoracic leg's swing during a series of ultrasonic stimuli as a measure of habituation, we show that: (1) the response declines exponentially; (2) the response recovers spontaneously; (3) repeated trials produce more rapid and stronger habituation; (4) successive stimuli presented more rapidly produce more rapid and stronger habituation; (5) a weaker stimulus intensity produces more rapid and stronger habituation; (6) the habituation shows stimulus generalization (i.e. the response is similar for different ultrasonic frequencies); (7) a novel stimulus produces dishabituation; and (8) the effect of the dishabituating stimulus habituates after repeated trials. These findings place habituation of cricket negative phonotaxis in the context described for habituation in mammals.
Acceleration of Haemolysis in Relation to Chemical Structure
Authors: Ponder Eric
Published: April 2021

Since methods for measuring acceleration and inhibition of haemolysis were first described (Ponder, 1926), very little attention has been paid to the way in which accelerators and inhibitors act. The effects of only a few chemical substances have been studied, and detailed investigations on the accelerating and inhibiting effects of various ions, etc., have certainly not tended to simplify the situation (Yeager, 1929, 1931; Gordon, 1933 a,b); recently, however, the problem has become of interest from quite a different point of view.