bluuebunny/crossref_metadata_2025 huggingface dataset:
Feedback from Motor Neurones to Pacemaker Neurones in Lobster Cardiac Ganglion Contributes to Regulation of Burst Frequency
Authors: Berlind A.
Published: April 2021

The crustacean cardiac ganglion has traditionally been viewed as a two-layered system in which pacemaking is a function of the four small cells which trigger the five follower motor neurones via chemical and electrotonic synaptic excitation. The work reported here shows that there is strong feedback from motor neurones to small cells, by which endogenous burst-organizing potentials (driver potentials or DPs) and their hyperpolarizing afterpotentials contribute to regulation of bursting frequency. Isolated cardiac ganglia were placed in a two-chamber perfusion system which allowed independent treatment of small cells and motor neurones. When the motor neurones were silenced with tetrodotoxin (TTX), the small cells continued organizing bursts of activity which recurred at an average frequency 41 % higher than bursting by normal ganglia in saline. The average burst duration was not altered. Driver potentials were evoked in TTX-treated motor neurones by electrical stimulation, by ionic alteration of the medium, or by treatment with the cardioexcitor peptide proctolin. DPs which occurred synchronously with small-cell bursts prolonged and intensified the bursts (more spikes per burst). When DPs were evoked in motor neurones during the interburst interval, they triggered small-cell bursts even at very short intervals after a spontaneous burst had occurred. All small-cell bursts which were associated with motor neurone DPs were followed by interburst intervals of longer than normal duration. The decrease in instantaneous burst frequency (increase in total burst cycle duration) caused by motor neurone DPs whs similar in magnitude to the drop in burst frequency observed when the ganglion recovered normal activity after T1X washout.
Physiological Bases of Feeding Behaviour in Salamanders: Do Motor Patterns Vary With Prey Type?
Authors: Reilly S. M. , Lauder G. V.
Published: April 2021

Muscle activity patterns (motor patterns) of the jaw musculature of all vertebrates studied to date (primarily fishes and amniotes) vary considerably when they feed on different types of prey. Previous data on buccal pressure patterns suggested that feeding in the aquatic salamander, Ambystoma mexicanum (Shaw), is highly stereotyped. This hypothesis was tested by quantifying the motor pattern used during feeding on two prey types: earthworms and guppies. Twenty-nine variables were measured from the activity pattern of six cranial muscles in the feeding mechanism of Ambystoma mexicanum. These variables included the area under the electromyogram of each muscle, relative muscle onset times, and the amplitudes and durations of muscle bursts. Univariate and multivariate statistical analyses demonstrate that the feeding motor pattern of Ambystoma mexicanum is stereotyped and does not change with prey type, in contrast to motor patterns of other vertebrates studied to date. Individual salamanders use significantly different motor patterns from one another during feeding, but do not alter their motor pattern during feeding on different prey.
Prey Processing in Haemulid Fishes: Patterns of Variation in Pharyngeal Jaw Muscle Activity
Authors: Wainwright Peter C.
Published: April 2021

This study examines patterns of variation in 15 electromyographic (EMG) variables measured from recordings of pharyngeal jaw muscle activity during prey processing in four species of the perciform fish family Haemulidae. Two questions were of primary interest. (1) Are motor patterns conserved across the four species? (2) Do the fishes alter (modulate) muscle activity patterns when feeding on different prey types? The experimental design used allowed the partitioning of variance in EMG variables among species, among individuals within species, among days within individuals, among feedings within days, and among prey types. Only one variable exhibited a significant species effect, indicating that the four species used virtually the same motor pattern during prey processing. In response to three prey types differing in hardness, all four species demonstrated an ability to modulate several EMG variables that characterized the intensity of electrical activity. However, variables characterizing the relative timing of muscle activities were not influenced by prey type. A significant variance component was found among recording days and, together with the possibility of variation among experimental preparations, this raises questions about the extent of previously reported inter-individual variation in EMGs. These results support a growing data base on aquatic feeding in lower vertebrates which finds that: (1) motor patterns tend to be highly conserved among closely related taxa; (2) the ability to modulate motor patterns in response to different prey types appears to be a general property of teleost fish feeding mechanisms; and (3) variation in experimental EMG data is ubiquitous and, when unaccounted for, confounds comparisons among treatment groups.
Effects of Anoxia on Serotonin Metabolism in Crucian Carp Brain
Authors: Göran E. Nilsson
Published: April 2021

In the brain, oxygen is required for both the synthesis and the degradation of monoamine transmitters, so monoaminergic systems can be expected to be strongly affected by anoxia. However, crucian carp (Carassius carassius L.) may survive anoxia for many days or even weeks. In the present study, crucian carp were exposed to anoxia for 22, 76, and 160 h at 8°C. All survived and were found to excrete ethanol at a constant rate. The brain concentrations of serotonin and its two main metabolites, 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophol, were analysed after each experiment. In a preliminary experiment, it was found that the brain of the crucian carp contained about the same amount of serotonin and 5-HIAA as two species less tolerant to anoxia - the common carp and the rainbow trout. The levels of the serotonin metabolites decreased drastically (by 80–90%) during anoxia, whereas serotonin levels were only slightly reduced (by 15 % or less). These results suggest a complete or nearly complete stop in serotonin metabolism during anoxia.
Attached Magnets Impair Magnetic Field Discrimination by Honeybees
Authors: Walker Michael M. , Bitterman M. E.
Published: April 2021

Evidence that honeybees respond to magnetic fields comes from both orientation (Lindauer & Martin, 1968, 1972; Towne & Gould, 1985) and conditioning experiments (Walker & Bitterman, 1985; Walker et al. 1988a). Perhaps because suitable behavioural methods have not yet been developed, the effects obtained are not very large. They are, however, reliable enough to permit evaluation of the ferromagnetic transduction hypothesis (Ising, 1945; Lowenstam, 1962; Gould et al. 1978; Kirschvink & Walker, 1985), to which the discovery of large numbers of single-domain particles of magnetite in the anterodorsal abdominal region of honeybees lends credence (Gould et al. 1978), and which alone among the various transduction hypotheses that have been proposed (Kirschvink & Gould, 1981; Kirschvink & Walker, 1985; Yorke, 1981; Kalmijn, 1974; Jungerman & Rosenblum, 1980; Leask, 1977; Korall & Martin, 1987) predicts that discrimination can be abolished by magnets attached in the vicinity of those particles (Jungerman & Rosenblum, 1980; Kirschvink & Walker, 1985). Free-flying honeybees were trained in two experiments to discriminate a local anomaly in the ambient magnetic field. Animals carrying small pieces of magnetized steel wire glued to the anterodorsal abdomen failed in the task, but untreated animals and control animals carrying small pieces of nonmagnetic wire succeeded. The results imply that the magnetite crystals in the anterodorsal abdomen play a critical role in magnetoreception by honeybees.
κ-Bungarotoxin Blocks Nicotinic Transmission at an Identified Invertebrate Central Synapse
Authors: Chiappinelli V. A. , Hue B. , Mony L. , Sattelle D. B.
Published: April 2021

A comparison was made between the effects of κ-bungarotoxin and κ-bungarotoxin upon nicotinic cholinergic transmission at an identified synapse (the cereal afferent, giant interneurone 2 synapse) in the central nervous system of the cockroach (Periplaneta americana), κ-Bungarotoxin, a snake venom x-neurotoxin, completely blocked nicotinic unitary excitatory postsynaptic potentials (EPSPs) and evoked composite EPSPs when applied at a concentration of l·0×10−7mol l−1. No recovery was observed after a 2h wash in normal saline. κ-Bungarotoxin produced a decrease in acetylcholine-induced nicotinic responses which paralleled decreases in nicotinic synaptic potentials and currents, indicating that κ-bungarotoxin blocked postsynaptic nicotinic receptors. This blockade appeared to be specific as resting membrane potential, input resistance and the ability to elicit an action potential in response to direct stimulation of giant interneurone 2 were unchanged following prolonged toxin exposures. Samples of α-bungarotoxin which were free from κ-neurotoxin contamination were also found to be potent antagonists of cockroach neuronal nicotinic receptors. It is concluded that the cockroach receptor is the first reported example of a neuronal nicotinic receptor which is sensitive to blockade by both α-neurotoxins and α-neurotoxins.
No Relationship Between Progressive Muscle Hyperaemia and Temperature in Exercising Rats
Authors: Delp M. D. , Laughlin M. H. , Armstrong R. B.
Published: April 2021

During prolonged submaximal exercise muscle blood flow has been shown to increase progressively in rats and miniature swine. This study was designed to test the hypothesis that the increases in muscle blood flow are associated with progressive elevations in body temperature in rats. Colonic temperature and muscle blood flow (determined using radioactive microspheres) were measured after 15, 30 and 45 min of exercise in rats exercising on a treadmill at 15 m min−1 on a 0·) incline. Total hindlimb muscle blood flow increased from 79 ± 8 ml min−1100 g−1 at 15 min to 95 ± 10 ml min−1100 g−1 at 30 min (P< 0·05). The greatest increases in blood flow occurred in the deep extensor muscles of the hindlimb. For example, in the red portion of the gastrocnemius muscle, blood flow increased from 197 ± 15 ml min−1100 g−1 at 15 min to 285 ± 17 ml min−1100 g−1 at 30min (P<0·05). Colonic temperature, however, remained stable at 38·5°C over this period. These data indicate that the progressive hyperaemia in muscle was unrelated to body temperature.
Span-Ratio Analysis Used to Estimate Effective Lift: Drag Ratio in the Double-Crested Cormorant Phalacrocorax Auritus From Field Observations
Authors: Pennycuick C. J.
Published: April 2021

A method is described for measuring the effective lift: drag ratio of a bird in flapping flight from the bird’s span ratio; that is, the ratio of the wing span in the upstroke to that in the downstroke. The method depends on the assumptions that the circulation on the wing is constant, and that the lift varies in proportion to the span. With some simplifications, it can be applied in the field to birds that cruise in steady, continuous flapping flight. Double-crested cormorants, observed on foraging flights, flew at a mean airspeed of 14·7ms−1, with a span ratio of 0·70. The effective lift: drag ratio, taking account of mechanical components of power only, was estimated to be 14·8. A much lower estimate (8·96) was obtained from a power curve program (Pennycuick, 1989). The discrepancy could be due (at least partly) to bias in the observations, but it is also suggested that one or more of the default values, used in the program for calculating induced, profile and parasite power, may be in need of downward revision.
Blood Acid-Base Balance in the Lugworm Arenicola Marina Ventilating in Hypo-or Hyperoxic Sea Water
Authors: Toulmond André , Tchernigovtzeff Catherine
Published: April 2021

The time course of variation in blood acid-base balance was examined in lugworms, Arenicola marina (L.), experimentally acclimated for up to 72 h in hypoxic (1 mmHg = 133-3 Pa), normoxic ) or hyperoxic sea water. In hyperoxic animals, a blood acidosis is entirely compensated 12 h after the beginning of the acclimation. In hypoxic animals, a blood alkalosis develops very quickly, persists and increases, reaching a maximum 72h after the beginning of the acclimation. In both cases, variation in blood acid-base balance is mainly of respiratory origin. These data are consistent with previous results showing that the lugworm hypoventilates in hyperoxic sea water and hyperventilates in hypoxic sea water.
Climbing Performance of Harris’ Hawks (Parabuteo Unicinctus) With Added Load: Implications for Muscle Mechanics and for Radiotracking
Authors: Pennycuick C. J. , Fuller M. R. , McALLISTER Lynne
Published: April 2021

Two Harris’ hawks were trained to fly along horizontal and climbing flight paths, while carrying loads of various masses, to provide data for estimating available muscle power during short flights. The body mass of both hawks was about 920g, and they were able to carry loads up to 630 g in horizontal flight. The rate of climb decreased with increasing all-up mass, as also did the climbing power (product of weight and rate of climb). Various assumptions about the aerodynamic power in low-speed climbs led to estimates of the maximum power output of the flight muscles ranging from 41 to 46 W. This, in turn, would imply a stress during shortening of around 210 kPa. The effects of a radio package on a bird that is raising young should be considered in relation to the food load that the forager can normally carry, rather than in relation to its body mass.
Voltage-Independent Block of a Neuronal Nicotinic Acetylcholine Receptor by N-Methyl Lycaconitine
Authors: Sattelle David B. , Pinnock Robert D. , Lummis Sarah C. R.
Published: April 2021

N-Methyl lycaconitine is the most effective low molecular weight antagonist reported for an insect neuronal nicotinic receptor. In the present study, the citrate salt of this neurotoxin from the plant Delphinium brownii was found to inhibit [3H]-a-bungarotoxin binding to nerve cord extracts of the cockroach Periplaneta americana with a K, of 1·4 × 10−9moll−1. At a concentration of 1·0×10−7moll−1, V-methyl lycaconitine completely blocked the response to ionophoretically applied acetylcholine recorded from the cell body membrane of the fast coxal depressor motor neurone (Df) in the desheathed metathoracic ganglion of the cockroach. The block was voltage-independent over the range of membrane potential –100 to –30 mV. The effectiveness of N-methyl lycaconitine on the nicotinic receptor, which is present in very high concentrations in the insect nervous system, suggests that this alkaloid is a natural plant protection agent.
Time Course of Failure and Resumption of Excitatory and Inhibitory Transmission in the Denervated Muscle Fibres of the Cockroach
Authors: Washio Hiroshi
Published: April 2021

Functional changes in neuromuscular transmission following denervation of the coxal depressor muscle of the cockroach Periplaneta americana have been studied by intracellular recording. Miniature postsynaptic potentials, both excitatory (MEPSPs) and inhibitory (MIPSPs), disappeared by about 24 h following nerve section or crush when animals were maintained at 26°C. Generally this was accompanied by the disappearance of excitatory and inhibitory junctional potentials. When animals were kept at 15°C, the onset of failure was delayed markedly, and excitatory transmission ceased a few days before inhibitory transmission, as found previously. Excitatory transmission resumed before inhibitory transmission: in animals maintained at 26°C after nerve crush, MEPSPs reappeared at 11 days and MIPSPs at 28 days. The resumption of transmission was accompanied by the reappearance of junctional potentials. It appears likely that the differences between excitatory and inhibitory transmission, in the timing of failure and of resumption of potentials, are related to the sizes of the axons innervating the coxal muscle of the insect leg.
Seasonal Adjustment of Solar Heat Gain in A Desert Mammal By Altering Coat Properties Independently of Surface Coloration
Authors: Walsberg Glenn E. , Schmidt Catherine A.
Published: April 2021

Physical theory predicts that animals with fur or feather coats can adjust solar heat gain independently of surface coloration or environmental factors by altering coat structure or hair optical properties. This hypothesis is tested by examining seasonal changes in the solar heat load transferred to the skin by the pelage of a desert-dwelling mammal, the rock squirrel (Spermophilus variegatus). Although coat colour remains constant, solar heat gain at low wind speeds is about 20% greater in winter coats than in summer coats. This change is in an apparently adaptive direction and is predicted to have a major effect on the animal’s heat balance in nature. The determinants of these alterations in solar heat gain are explored using an empirically validated biophysical model and are found to result from changes in hair optics and coat structure. These results suggest the existence of a previously unknown mode of long-term thermoregulation that allows adjustment of solar heat gain without affecting the animal’s external appearance.
Rainbow Trout Hypocalcin Stimulates Bone Resorption in Embryonic Mouse Calvaria in Vitro in A Pth-Like Fashion
Authors: Lafeber Floris P. J. G. , Herrmann-Erlee M. P. M. , Flik G. , Bonga S. E. Wendelaar
Published: April 2021

Hypocalcin, the major hormone with hypocalcaemic action in fish, was isolated from trout corpuscles of Stannius (SCs). The bioactivity of hypocalcin was assessed in a parathyroid hormone (PTH) bioassay involving bone resorption in embryonic mouse calvaria. Calcium and phosphate release and lactate production were stimulated in a dose-dependent manner by hypocalcin. On a molar basis about equal amounts of hypocalcin and PTH were required to obtain similar effects in this assay. Hypocalcin did not stimulate cyclic AMP production either in mouse calvaria or in cultured osteoblasts. In this respect hypocalcin resembles shortened or N-terminus-modified PTH molecules that induce bone resorption without increasing cyclic AMP levels. Since hypocalcin and PTH have comparable bioactivity in this mammalian bioassay (as well as in fish bioassays), we tentatively suggest that both hormones are structurally similar and that both hormones may act via the same receptors. The two hormones show no resemblance to one another in primary structure, so we suggest that they have similarities in tertiary structure.
Kinematics of Labriform and Subcarangiform Swimming in the Antarctic Fish Notothenia Neglecta
Authors: Archer Stephen D. , Johnston Ian A.
Published: April 2021

The kinematics of labriform and subcarangiform swimming have been investigated for juvenile (7–8 cm) and adult (27–30 cm) stages of the antarctic teleost Notothenia neglecta Nybelin at 1–2 °C. Upper threshold speeds using the pectoral fins alone (labriform swimming) were 0·8Ls−1 in adult fish and l·4Ls−1 in juveniles, where L is body length. In adult fish, steady subcarangiform swimming is only used at speeds of 3·6–5·4Ls−1 (tail-beat frequencies of 5·0–8·3Hz). Intermediate speeds involve unsteady swimming. In contrast, juvenile fish employ subcarangiform swimming at a range of intermediate velocities between the maximum labriform and burst speeds (2·3–8·4Ls−1 at tail-beat frequencies of 4·0–12·5 Hz). These differences in swimming behaviour are discussed in relation to changes in life-style and muscle fibre type composition between juvenile and adult fish. Burst swimming speeds in N. neglecta have been compared with equivalent data from temperate species. It seems likely that low temperature limits swimming performance in antarctic fish. This is more noticeable in juvenile stages, which normally have much higher tail-beat frequencies than adult fish.
Adaptations to A Terrestrial Existence by the Robber Crab, Birgus Latro L. III. Nitrogenous Excretion
Authors: Greenaway P. , Morris S.
Published: April 2021

Nitrogenous excretion by the terrestrial anomuran crab Birgus latro L. was examined. The main excretory product was uric acid, representing 79·5 % of total excretory nitrogen. It was eliminated as white faeces separate from undigested food material and made up 82·6% of excretory faecal nitrogen. The faeces were the principal route of nitrogenous excretion, accounting for 96·2 % of total excretion. Loss of nitrogen in the urine and as gaseous ammonia was negligible. The midgut gland had substantial activity of xanthine oxidase and was considered to be the site of production of uric acid and its point of entry into the gut.
Metabolic Control of Luminescence in the Luminous Organs of the Teleost Porichthys: Effects of the Metabolic Inhibitors Iodoacetic Acid and Potassium Cyanide
Authors: Rees J. F. , Baguet F.
Published: April 2021

The treatment of isolated photophores of the epipelagic luminescent fish Porichthys notatus Girard with the glycolytic inhibitor iodoacetic acid (IAA) induces light production. This luminescence is not significantly affected by the adrenergic antagonists phentolamine and propranolol. The addition of pyruvate, phosphoenolpyruvate or glyceraldehyde 3-phos-phate in saline suppresses the light response to IAA. D-Glucose, D-glyceraldehyde, and 2-and 3-phosphoglycerate have no inhibitory effects. The luminescence of the photophores induced by KCN is inhibited by D-glucose, D-glyceraldehyde 3-phosphate and 3-phosphoglycerate. In contrast, 2-deoxy-D-glucose, pyruvate, phosphoenolpyruvate, D-glyceraldehyde and 2-phosphoglycerate do not affect this light production. These results confirm the view that glycolysis and oxidative phosphorylation are essential metabolic pathways in the photogenic cells. They further indicate that common products of these tightly associated metabolic pathways may regulate the activity of the luminous system in these cells.
Extraglandular Innervation of the Salivary Cells of the Leech Haementeria Ghilianii: Neuronal Stimulation Elicits Gland-Cell Action Potentials and Secretion
Authors: Wuttke Werner A. , Sawyer Roy T. , Berry Michael S.
Published: April 2021

Each salivary gland cell of Haementeria extends a single process, or ductule, anteriorly into the proboscis; secretory products are released at the ductule ending. Some ductules secrete into the lumen of the proboscis and others at the outer surface of its tip, more than 5 cm from the gland in large leeches. Depolarization of a gland-cell body elicits action potentials which appear to be conducted along the ductule to its ending. Electrical stimulation of the proboscis tip elicits action potentials in those ductules which end there, and the impulses are propagated to the cell body (approx. 5cms−1). Bathing the salivary glands in calcium-free saline causes spontaneous repetitive firing in the cell bodies and also elicits secretion at the proboscis tip (bathed in normal saline); the action potential thus appears to be a stimulus for secretion. A paired stomatogastric nerve, from the brain, enters the proboscis near its base. Cobalt-filling of the nerve shows numerous cell bodies in the brain and first body ganglion, and an intricate network of fibres and a cluster of stained cell bodies near its entry point in the proboscis. Repetitive stimulation of the stomatogastric nerve produces action potentials in certain gland cells, after a delay of at least 15 s, and also elicits secretion. The action potentials are initiated near the ductule tip, and are conducted to the cell body. The salivary glands themselves do not appear to be innervated. Application of acetylcholine (ACh), dopamine or octopamine (10−4mol 1−1) does not initiate secretion. Neither dopamine nor octopamine excites the gland cells but ACh produces a transient suprathreshold depolarization of the cell body and occasionally elicits 1–3 ductule spikes when applied to the proboscis tip. 5-Hydroxytryptamine (5-HT) produces secretion when applied to the proboscis but not when applied to the glands alone; it does not excite the cells, indicating that the action potential is not the only stimulus for secretion. 5-HT produces a depolarization, and increase in membrane resistance, in the cell body, and prevents the rapid adaptation of action potentials which occurs during maintained depolarization.

7.Electrophoretic analysis shows that the protein compositions of secretions at the proboscis tip and in the lumen are completely different, with the tip apparently secreting only two major proteins. These same two protein bands occur in the cytoplasm of certain gland-cell bodies which can be distinguished in living glands on the basis of size and degree of staining with Methylene Blue.

8.Following stimulation of the stomatogastric nerve, secretory products at the proboscis tip can be seen to emerge from discrete points which appear to be single ductule endings. This presents the possibility of studying excitation-secretion coupling in single cells.
Pressure Adaptation of Na+/K+-ATPase in Gills of Marine Teleosts
Authors: Gibbs Allen , Somero George N.
Published: April 2021

The effects of pressure and temperature on an integral membrane protein, Na+/K+-adenosine triphosphatase (Na+/K+-ATPase), were studied in fish gill membrane preparations from shallow- and deep-living marine teleosts. The inhibition by pressure of maximal velocity of the enzyme is nonlinear, increasing at higher pressures. Na+/K+-ATPases from deep-sea fish were less inhibited by pressure than those of shallow-living species. Habitat temperature also affected the pressure response of the enzyme. As a function of physiological pressure and temperature, the order of increasing pressure-sensitivity was cold, deep-sea < warm, deep-sea (hydrothermal vents) < polar = shallow and mid-depth, cold< shallow, warm. Activation volumes in all species were conserved at 30–60ml mol−1 at physiological pressures, which may reflect a similar membrane physical state at the actual pressure the animal experiences. Arrhenius plots [in(Na+/K+-ATPase activity) vs 1/T] were steeper for warm-water and shallow living species than for deep-sea species. The depth at which adaptation was first observed was about 2000m (≈200atm; 1 atm = 101·3kPa). The data are consistent with a model of increased membrane fluidity resulting in reduced pressure sensitivity of Na+/K+-ATPase from deep-sea species.
Physiological Responses of the Crayfish Pacifastacus Leniusculus to Environmental Hyperoxia : II. Role of the Antennal Gland in Acid–Base and Ion Regulation
Authors: Wheatly Michèle G. , Toop Tes
Published: April 2021

Handling of electrolytes and acidic equivalents by the antennal gland was monitored in freshwater crayfish (Pacifastacus leniusculus) during control normoxia (; 1 mmHg = 133·3 Pa), 72h of hyperoxia () and 24 h of recovery. A preparation was developed for direct collection of urinary flow (UFR) which was confirmed using inulin clearance (ĊIN)-Renal effluxes of Na+, Cl−, Mg2+, K+, Ca2+, sulphate, phosphate, titratable and nontitratable acidity and CO2 were monitored. These were used in conjunction with filtration rates to calculate net rates of reabsorption.

UFR was elevated by around 50 % during hyperoxia. Contributing to this were an increase in ĊIN and a reduction in [IN]u: [IN]e. Excretion of Na+ (ĖNa) tended to increase initially whereas ĖCl tended to decrease after 36h. ĖK and ĖMg showed a similar profile to that of ĖNa with increases averaging 60 %. The increases in excretion of Ca2+, phosphate and sulphate were more pronounced (threefold). In control crayfish, 65–95 % of filtered electrolytes were reabsorbed at the antennal gland except for ammonia which was secreted. Electrolyte reabsorption increased during hyperoxia; percentage increases varied from 70% (Na+, Cl−) to 150% (sulphate, phosphate) with HCO3− showing a fourfold increase above control values. Ammonia secretion correspondingly increased. Control urine was acid with respect to the haemolymph and became increasingly acidified during initial hyperoxic exposure. Net renal proton excretion largely reflected (90%) ammonia excretion; both were approximately doubled during hyperoxia. Unlike the situation in mammals, ammonia appears to be more important than phosphate in buffering urine pH. Urinary parameters generally required 24 h for complete recovery when normoxia was reinstated.

Renal net efflux and reabsorption rates were compared with branchial net and unidirectional influx rates from an earlier part of this study. Branchial and renal net effluxes of Na+ and Cl− had similar vectors and magnitudes during the control period but tended to counter each other during hyperoxia. Renal reabsorption rates of these ions were threefold greater than branchial influx rates, confirming increased transporting capability. Both epithelia exhibited a net H+ efflux during hyperoxia; the kidney contributed only 10% of the whole-animal response. Possible mechanisms of renal postfiltrational electrolyte and acidic equivalent processing are discussed.
Kinematic Analysis of Symmetrical Flight Manoeuvres of Odonata
Authors: Rüppell G.
Published: April 2021

By analysis of slow-motion films of dragonflies and damselflies in free flight, released in front of a backdrop or startled during flight, the following flight parameters have been quantified for symmetrical manoeuvres: wingbeat frequency, relative durations of up-and downstroke, phase relationships of the beats of fore-and hindwings, stroke amplitude, mean stroke velocity, flight velocity, nondimensional flight velocity, advance ratio, acceleration, angle of attack and stroke plane.

The wingbeat frequencies are higher in the smaller species and in those with relatively large wing loading. As a rule, Zygoptera have a wingbeat frequency only half that of Anisoptera. The stroke amplitude is almost always much larger in Zygoptera than in Anisoptera, which have a greater range of variation in this respect. Stroke velocity is higher in Anisoptera than in Zygoptera; it is also higher in the more elaborate flight manoeuvres than in others. The calculated stroke velocities resemble those actually measured.

Anisoptera fly more rapidly than Zygoptera. With respect to the nondimensional flight velocities, it is notable that although the values for Anisoptera are higher than those for Zygoptera, they are exceeded by the Calopterygidae; the latter can fold their wings back during rapid forward flight and shoot away, as in the ‘ballistic’ flight of small songbirds. However, the advance ratio is higher in Anisoptera than in Calopterygidae.

Anisoptera also perform better than Zygoptera with respect to acceleration. Three categories of phase relationships between the beats of the fore-and hindwings are established: counterstroking, phase-shifted stroking and parallel stroking. Counterstroking produces uniform flight, whereas the flight produced by phase-shifted and, in particular, parallel stroking is irregular. The angles of attack of the wings are shown to be associated with particular flight manoeuvres, as are the stroke planes. Flight manoeuvres are discussed without drawing detailed aerodynamic conclusions. The flight of Anisoptera is compared with that of Zygoptera.
More Than One Type of Conductance is Activated During Responses of Blowfly Monopolar Neurones
Authors: Weckström M. , Kouvalainen E. , Djupsund K. , Järvilehto M.
Published: April 2021

The principal second-order neurones in the blowfly compound eye, the large monopolar neurones (LMCs), were studied using intracellular recording and discontinuous current-clamp techniques, in combination with measurement of dynamic input resistance. The LMCs had resting potentials of –35 to –45 mV and showed a linear current-voltage relationship in the lamina in the physiological voltage range. The hyperpolarizing light-on transient was associated with a drop in input resistance from 17 ± 5 to 3 ± 1MΩ, and had a reversal potential between –60 and –90 mV. The dynamic input resistance of saturated responses and the properties of reversed responses suggested that more than one conductance was activated during the response of the LMCs. In lamina recordings, the input resistance increased beyond the resting level during repolarization, which can be interpreted in terms of a continuous release of transmitter by the photoreceptor terminals, even in darkness. The input resistance of LMCs in axon recordings in darkness and during the light-on response was generally higher than in the lamina recordings. The responses to light in axons also differed from those recorded in lamina by showing regenerative properties.
Salt Gland Function in the Green Sea Turtle Chelonia Mydas
Authors: Nicolson Sarah W. , Lutz Peter L.
Published: April 2021

When salt-gland-cannulated green sea turtles were stimulated by the intravenous injection of various salt loads the secretion osmolality rose quickly from a basal value of 300–400 mosmol kg-1 to a plateau of 1680–2000. The height of the plateau and the duration of the response were dependent on the amount of salt given. An increase in flow rate accompanied the initial rise in concentration, but the flow rate thereafter declined while the plateau concentration was held. The fluid was protein-free, and was mainly composed of Na+ and Cl-, in similar relative concentrations to those in sea water, but had substantial amounts of K+, Mg2+ and HCO3- and negligible amounts of glucose. Urea concentrations did not change with osmolarity, and were similar to that of plasma, suggesting that the walls of the salt gland ducts are permeable to urea. The composition of the tears was uninfluenced by the concentration of the injected solutions, and its ionic content did not directly depend upon the identity of the added salts. The two eyes of individual turtles frequently did not function in synchrony. The average amount of the salt load remaining in a turtle at the end of salt gland activity, 4·5 mmol ion kg body mass-1, was very similar to the median load required to stimulate the salt gland (4·0mmolion kg body mass-1). This suggests that there is a threshold salt load level of around 4·5 mmol ion kg body mass-1 that determines salt gland on/off activity.

The flow/concentration relationships of the salt gland fluid are consistent with water reabsorption from a primary isosmotic secretion being the major mechanism for concentrating the tears. A high maximal secretory rate is indicated for the primary fluid, 0·32 ml g salt gland-1 min-1, equivalent to that of the mammalian kidney. Calculations suggest that 83% of the initial fluid is recovered, Na+ is passively concentrated, Cl- and Mg2+ concentrations are enhanced, and that the duct walls are either impermeable to glucose or that glucose is actively taken up.
Are the Hindwing Chordotonal Organs Elements of the Locust Flight Pattern Generator?
Authors: Pearson K. G. , Hedwig B. , Wolf H.
Published: April 2021

Anatomical and electrophysiological techniques were used to examine the structure, central nervous connections and discharge patterns of afferents arising from the hindwing chordotonal organs in the locust, Locusta migratoria. The hindwing chordotonal organ afferents were found to be sensitive to low-frequency sounds (approx. 3 kHz) and to vibrations of the supporting surface. During flight in tethered animals these afferents were strongly activated. This flight-related activity was weakly modulated and the maximum occurred between depressor bursts. Low-frequency sound pulses were used to activate selectively the hindwing chordotonal organ afferents during rhythmic flight activity in deefferented preparations (all motor nerves cut). Phasic stimulation of the chordotonal organs, time-locked to every cycle, had no effect on the frequency of the centrally generated rhythm as recorded from proximal nerve stumps. Staining of single afferents from the hindwing chordotonal organ showed that they bifurcate in the metathoracic ganglion, with one branch terminating in the ring tract and the other branch projecting to the mesothoracic ganglion via the ipsilateral connective. None of the terminal processes of chordotonal afferents was observed to be located in dorsal neuropile regions containing the processes of flight neurones. Consistent with this finding, the chordotonal afferents were not observed to make synaptic connections to flight interneurones or motoneurones. The main conclusion of this investigation is that the hindwing chordotonal organs do not contribute to the patterning of motor activity for flight. The hindwing chordotonal organs probably function as detectors of vibration and perhaps low-frequency sound.
Sensory Systems in the Swimmerets of the Crayfish Cherax Destructor and their Effectiveness in Entraining the Swimmeret Rhythm
Authors: Macmillan David L. , Deller Simon R. T.
Published: April 2021

The branching patterns and profiles of the main sensory nerves of the swimmerets of Cher ax destructor are described. The innervation is generally similar to that in Pacifastacus but there are important differences that may be due to species variation or that may explain apparent differences in the physiology of the two species. The two large axons from the long strand of the stretch-receptor complex in Cherax give rise to non-spiking signals whereas those from the short strand are not active during passive protraction and retraction of the swimmeret.

The rhythmic movements of one swimmeret are sufficient to entrain the fictive swimmeret rhythm of an otherwise deafferented ventral nerve cord. The parameters of this entrainment match those of the known reflexes associated with swimmeret movement. Ablation experiments show that the stretch-receptor complex is necessary and sufficient for this entrainment and that input from the pleural plate hairs and swimmeret hairs is not required. Sinusoidal current injection into the non-spiking stretch receptors can also entrain the fictive rhythm of the deafferented cord.

From these results it is argued that the non-spiking stretch receptors play an important part in stabilizing and adjusting the frequency of the swimmeret rhythm. The swimmeret system is therefore another example of patterned motor output generated by a distributed, multicomponent network and this may be a general feature of cyclically rhythmic systems.
Response Features of Visual Units in the Lower Midbrain of the Rainbow Trout
Authors: Schellart Nico A. M. , Rikkert Walther E. I.
Published: April 2021

In the mesencephalic torus semicircularis of fish, visual processing is carried out in addition to acousticolateral processing, and takes place in unimodal and bimodal units. To study the encoding of visual stimuli in the torus of the rainbow trout, unit recordings made in the torus were compared with recordings made in the tectum.

The receptive fields (RFs) of the torus units in the rainbow trout (Salmo gairdneri) mostly measured more than 80°, generally had no well-defined borders and showed non-X type behavior. As in the tectum, the majority of the units showed On-responses and the RFs of On units were smaller than those of On/Off and Off units. From single unit and evoked potential data, obtained up to an eccentricity of 45°, it appears that the rostral visual field projects to the rostral and central part of the torus. In contrast to the features of tectal units, the RFs lacked spatial antagonism, wavelength coding was practically absent and directional selectivity rare. The responses, generally with latencies between 40 and 160ms, were often erratic. The most striking neurophysiological feature of the torus units was habituation to repetition of the stimulus, e.g. to an on-off flashing spot. The visuo-auditory interaction of most bimodal units showed algebraic summation, but for about 20% the visual modality enhanced the sensitivity to auditory stimulation.

The data from the trout confirm that the tectum plays an important role in visual functions such as acuity, pattern vision and vision of movement. The common feature of habituation in the torus suggests that the torus may be involved in the signalling of sudden changes in the visual scenery.
Lactate and Glycogen Metabolism in the Lizard Dipsosaurus Dorsalis following Exhaustive Exercise
Authors: Gleeson Todd T. , Dalessio Paula M.
Published: April 2021

We evaluated the metabolic mechanisms by which the iguanid lizard Dipsosaurus dorsalis deals with the lactate which accumulates during vigorous exercise. Fasted, cannulated lizards were run for 5 min on a treadmill at 40°C, which elevated whole-body lactate to 24 mmol l-1 and depleted hindlimb glycogen to 70% of resting levels. Oxygen consumption increased fivefold and respiratory exchange ratios approached 2·0. Exhausted animals were then injected intravenously with either [U-14C]lactate or [U-14C]glucose, and allowed to recover quietly on the treadmill at 40°C. After 2h, 79% of the accumulated lactate had been removed and hindlimb muscle glycogen stores had returned to pre-exercise levels. Although blood glucose remained unchanged at 8·6 ± 0·27 mmol l-1 throughout the recovery period, whole-body glucose increased significantly from 1·6 ±0·23 to 5·5 ± 0·38mmoll-1 (P<0·05). Based on isotope distribution, 50% of the lactate removed was used to synthesize glucose and glycogen, but only 16 % of the lactate was oxidized. Lactate oxidation accounted for about 40% of the post-exercise oxygen consumption. Lactate rather than glucose appeared to be the prevalent substrate for muscle glycogen synthesis under these conditions. These animals appear to employ a strategy of lactate removal which is different from that in mammals; favoring lactate-supported gluco-and glyconeogenesis and rapid muscle glycogen replenishment instead of rapid lactate removal via oxidative pathways.
Temperature and the Force-Velocity Relationship of Live Muscle Fibres from the Teleost Myoxocephalus Scorpius
Authors: Langfeld Karen S. , Altringham John D. , Johnston Ian A.
Published: April 2021

Small bundles of fast fibres were isolated from the myotomal muscle of the teleost Myoxocephalus scorpius. The temperature-dependence of isometric contractile properties and the force-velocity (P-V) relationship were studied. Fibres were found to deteriorate above 18 °C, and the force plateau during tetanic stimulation was not maintained above 15°C. Twitch and tetanic tension (Po) showed optima at around 8 °C. Force-velocity curves were fitted using either Hill’s hyperbolic equation or a hyperbolic-linear equation (hyp-lin). The best fit to the data was provided by the hyp-lin equation, which gave consistently higher values for unloaded contraction velocity (Vmax): 4·3, 8·1 and 9·5 muscle lengths s-1 at 1,8 and 12 °C, respectively. The P-V relationship was found to become progressively more curved at higher temperatures. Muscle power output calculated from the hyp-fin equation was 123 W kg-1 at 1°C and 256 W kg-1 at 8 °C. Curves normalized for Po and Vmax at each temperature show that the change in curvature is sufficient to increase the relative power output of the muscle by around 15 % on decreasing the temperature from 8 to 1 °C.
Ionic Species Involved in the Electrical Activity of Single Adult Aminergic Neurones Isolated from the Sixth Abdominal Ganglion of the Cockroach Periplaneta Americana
Authors: Lapied Bruno , Malécot Claire O. , Pelhate Marcel
Published: April 2021

Adult neurones were obtained by dissociation of the dorsal area of the sixth abdominal (A6) ganglion of the cockroach, and electrical properties were studied with the patch-clamp technique. The neurones showed spontaneous fast action potentials, similar to those recorded with microelectrodes in neurones in situ along the dorsal median line of the A6 ganglion. Synthetic saxitoxin (sSTX) at concentrations of 10 × 10−8 to 1·0×10−7moll−1 suppressed the action potential (AP) and induced a dose-dependent hyperpolarization of the resting potential, suggesting that two types of sSTX-sensitive Na+ channels are present. The resting potential was dependent on the external concentration of both Na+ and K+, with a similar sensitivity to each, yielding a slope of about 43 mV per 10-fold change in concentration. The delayed outward rectification present under control conditions was reduced by tetraethylammonium chloride (TEA-CI, 1·0×10−2moll−1). TEA-CI or Ca2+-free saline abolished the afterhyperpolarization and increased the overshoot and duration of triggered APs, indicating that a calcium-activated potassium conductance contributes to the falling phase of the AP. At 3·0×10−3moll−1, the Ca2+ channel blockers MnCl2, CoCl2 and NiCl2 lengthened the AP. A blocker-dependent increase in the overshoot and threshold of the AP and reduction of the afterhyperpolarization were observed, probably reflecting the relative potencies of these ions in blocking Ca2+ channels and thus the Ca2+-activated K+ conductance. Increasing MgCl2 concentration by 3·0 ×10−3moll−1 had no effect on the AP, indicating that the positive shift of the threshold is due to the blockade of Ca2+ channels present at this potential. The results suggest that these isolated neurones are dorsal unpaired median neurones previously studied in a number of insect species.
The Movement of Cadmium Through Freshwater Trout Branchial Epithelium and its Interference with Calcium Transport
Authors: Verbost P. M. , Van Rooij J. , Flik G. , Lock R. A. C. , Bonga S. E. Wendelaar
Published: April 2021

Exposure of freshwater trout (Salmo gairdneri) to waterborne Cd2+ results in accumulation of the metal in the branchial epithelial cells and its appearance in the blood. Cd2+ apparently enters the cells via Ca2+ channels in the apical membrane. Transfer of Cd2+ through the basolateral membrane is probably by diffusion. Inhibition by Cd2+ of transepithelial Ca2+ influx is time-and Cd2+-concentration-dependent. The inhibition of transepithelial Ca2+ influx is accompanied by blockage of apical Ca2+ channels. In line with the assumption that cytosolic Cd2+ inhibits Ca2+ uptake by inhibiting the basolateral Ca2+ pump, we hypothesize that the blockage of Ca2+ channels is an indirect effect of Cd2+ and results from a rise in cytosolic Ca2+ level caused by inhibition of the basolateral membrane Ca2+ pump.
Motile Characteristics of 9+2 and 9+1 Flagellar Axonemes of Crithidia Oncopelti
Authors: Marchese-Ragona S. P. , Glazzard A. N. , Holwili M. E. J.
Published: April 2021

Crithidia oncopelti flagella were progressively solubilized by exposure to solutions containing the detergent Nonidet P42. During the course of the exposure, demembranated flagella were obtained that first had 9+2 axonemes, then 9+1, followed by 9+0. Finally, cylinders of A microtubules were obtained. The 9+2 and 9+1 flagella could be reactivated, indicating that the central complex does not have to be intact to allow wave propagation in this preparation. 9+0 axonemes could not be reactivated. Fourier analysis showed that the waveforms of the 9+2 and 9+1 axonemes were essentially the same, conforming to a meander shape. This shape is significantly different from the arc-line waves seen on in vivo flagella and indicates that (a) the membrane plays a significant role in the regulation of this parameter and (b) the passive elastic resistance of the microtubules in demembranated flagella has an important influence on bend patterns. The responses of 9+2 and 9+1 demembranated flagella to ATP were essentially the same, demonstrating that the extraction process had not affected the dynein-tubulin interaction. The central complex in Crithidia may be responsible for controlling the direction of wave propagation.