bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in Force-Frequency Relationships and Calcium Dependency between Elasmobranch and Teleost Hearts
Authors: Driedzic William R. , Gesser Hans
Published: April 2021

Ventricle strips from little skate (Raja erinacea), spiny dogfish (Squalus acanthias), black dogfish (Etmopterus spinax), sea raven (Hemitripterus americanas), cod (Gadus morhua), hagfish (Myxine glutinosa) and white sturgeon (Acipenser transmontanus) were mounted for isometric force recording. Force development was assessed as a function of external calcium concentration and frequency of contraction. Post-rest potentiation was determined in skate and the teleost species to assess indirectly calcium storage capacities. Sea raven and cod preparations were also treated with ryanodine to assess the importance of calcium release from the sarcoplasmic reticulum.

Ventricle strips from skate and black dogfish showed a five-fold increase in force development when external calcium was raised from a physiological to a saturating level. Force development by ventricle strips from other species tested increased by only about 50% over the same range of calcium concentration.

For all elasmobranchs tested, an elevation in frequency of contraction of ventricle strips resulted first in an increase and subsequently in a decrease in force development. The apices of the curves were well within the physiological range of heart rates exhibited by these species. Preparations from teleosts showed only a decrease in force development when contraction frequency was elevated.

Skate ventricle strips exhibited a very marked post-rest potentiation at 3 mmol 1−1 external calcium. This protocol is considered to reflect the importance of intracellular calcium stores in the beat-to-beat maintenance of contractility. Sea raven and cod ventricle strips did not show any major post-rest potentiation, suggesting that calcium storage in hearts of these species is minimal. Ryanodine treatment had no effect upon sea raven and cod heart preparations. This approach further implies that calcium release from sarcoplasmic reticulum is not critical in these species.
In Vivo Cardiac Pressure and Heart Rate, and Heart Mass, of Busycon Canaliculatum (L.)
Authors: Jones H. D.
Published: April 2021

In vivo cardiac pressure and heart rate, and relative heart mass, have been measured in Busycon canaliculatum. Base pressure was about l·3cmH2O above ambient and effectively the same in the ventricle, atrium, pericardium and veins. Ventricular systolic pressures were very variable. Highest pressure was over 80cmH2O, but sustained levels were lower, up to about 40cmH2O. Heart rate was also very variable, 5-15 beats min−1. Heart mass was about 0·19% of body mass. Cardiac refilling, control and power output are discussed.
Visual Discrimination of Distance by Octopuses
Authors: Muntz W. R. A. , Gwyther J.
Published: April 2021

If two stimuli are presented to an octopus simultaneously, but at different distances from the animal, the nearer of the two is usually attacked. This preference was used to test the ability of octopuses to discriminate distance. White discs, 37 mm in diameter, were used as stimuli, and two parameters were varied: the distance of the farther stimulus from the animal (D), and the difference between the distances of the farther and nearer stimulus (d). Animals chose the nearer stimulus on 70% of occasions under the most difficult conditions used, where D was 370 mm and d was 50 mm. This percentage increased as D decreased or d increased. Further tests showed that varying the size of the discs, or using white vertical or horizontal rectangles instead of discs as stimuli, did not affect performance.

The most likely cue being used by the animals to discriminate distances is accommodation. If this is the case octopuses can detect blurring of points on the retinal image comparable in size to a single retinal receptor, and lens displacements of around 10 μm.
The Functions of Eye and Body Movements in Labidocera and Other Copepods
Authors: Land Michael F.
Published: April 2021

Male Labidocera have three eyes derived from the nauplius eye. The dorsal pair have large lenses and are fused to give a single mobile eyecup containing a transverse row of 10 rhabdoms. This rhabdom row scans across 35° of the dorsal visual field at rates of up to 3 Hz, and it is suggested that the scanning movements are concerned with the detection of conspecifics. In addition there are movements which enable the eyecups to track a source of light, and these are mediated by three other receptors in each eyecup. The tracking movements are closely linked to tail movements which tend to keep the animal’s back directed towards the light. The total effect is to stabilize both body and eye direction against involuntary disturbance. Other pontellid copepods show similar visually controlled tail movements, but without the eye movements.
Adaptations to a Terrestrial Existence by the Robber Crab Birgus Latro: I. An in vitro Investigation of Blood Gas Transport
Authors: Morris S. , Greenaway P. , Mcmahon B. R.
Published: April 2021

The gas-transporting properties of the haemolymph of Birgus latro L. were investigated in vitro. This terrestrial anomuran is restricted in distribution to the tropics, and on Christmas Island inhabits a highly stenothermal environment.

The effect of temperature on haemocyanin oxygen-affinity was pronounced (ΔH = –39 kJ mol−1) and was considered to represent the absence of any specific adaptation to environmental temperature. The Bohr effect was large for a terrestrial decapod (ϕ = –0·60), although reduced at low pH. Changes in [Ca] had a significant effect on oxygen affinity of dialysed haemolymph (ΔlogP50/ Δlog[Ca] = –0·39) whereas [Mg] had no effect. Increasing, [L-lactate] had a small effect on the oxygen affinity of dialysed haemolymph (ΔlogP50/ Δlog[lactate] =–0·013) but not whole haemolymph. Dialysis increased oxygen affinity, suggesting the presence of a dialysable component that suppresses affinity. The effect of L-lactate was inhibited in whole haemolymph.

The oxygen affinity of Birgus haemolymph was largely insensitive to effector substances, with the possible exception of Ca. In the case of lactate, at least, this was not due to a reduced sensitivity of the haemocyanin, a situation different from that in closely related species.

Carbon dioxide transport was also affected by temperature. Birgus haemolymph showed a high nonbicarbonate buffer capacity which could be correlated with a high haemocyanin concentration. It is concluded that terrestrial anomuran decapods depend on mechanical adjustments of ventilation and perfusion, rather than employing direct modulation of haemocyanin function, to optimize oxygen delivery.
Adaptations to a Terrestrial Existence by the Robber Crab Birgus Latro: II. in vivo Respiratory Gas Exchange and TRANSPORT
Authors: Greenaway P. , Morris S. , Mcmahon B. R.
Published: April 2021

The lungs are responsible for essentially all uptake of oxygen in Birgus latro. Elimination of CO2 in resting crabs appears to occur largely across the gills but during exercise approximately half the output of CO2 is pulmonary. was high in resting crabs (43·8 mmHg; 1 mmHg = 133·3 Pa) but fell during exercise (to 27 mmHg). remained constant at 10–12 mmHg. rose substantially during exercise (from 7·1 to 14·6mmHg).

Haemocyanin delivered 90% of oxygen in resting crabs rising to 97% following exercise. Oxygen delivery at rest was 0·46 mmol l−1 haemolymph rising to 0·72 mmol l−1 following exercise. Pigment-bound oxygen capacity was 1·1 mmol l−1. Oxygen delivery to the tissues was diffusion-limited during exercise.

Anaerobic metabolism during exercise raised the concentration of L-lactate in the haemolymph 100-fold (from 0·25 to 25 mmol l−1) and concomitantly caused a fall in pH of 0·7 units. This acidosis was partially compensated by the end of the 30-min exercise period.
Ammonia and Acid-Base Balance During High Ammonia Exposure in a Marine Teleost (Myoxocephalus Octodecimspinosus)
Authors: Claiborne James B. , Evans David H.
Published: April 2021

For the first time in a marine teleost (the long-horned sculpin; Myoxocephalus octodecimspinosus), the maintenance of blood pH, , [HCO3−] and the net movements of NH4+, HCO3− and H+ between the fish and the water have been studied during exposure to ammonia stress induced either by infusion (NH4C1 or NH4HCO3; 5 mmol kg−1) or by external application (NH4C1; approx. 1 mmol I−1).

Following NH4C1 infusion, a rapid decrease in blood pH (0·36units) and [HCO3−] (2·38 mmol I−1) was observed, and within 1h about 40% of the ammonia load had been excreted to the water. Analysis of NH4+ and HCO3− transfers revealed that the total ammonia (TAmm) efflux was due to a loss of NH3 and NH4+ in approximately equal proportions when an outwardly directed NH3 diffusion gradient was established.

Infusion of NH4HCO3 induced only small changes in plasma pH, and the rate of net HCO3− excretion was some 90% higher than that of NH4+ over 20 h. These data indicate a predominance of NH3 as the form of ammonia lost. In both infusion experiments, a presumed intracellular buffering of a majority of the ammonia load was noted.

High external TAmm induced an initial uptake of NH4+, but after 4 h of exposure ammonia efflux resumed even though NH3 diffusion gradients were negligible. Thus, in this seawater teleost, a role for the excretion of ammonia in the form of NH4+ is also likely.
Relative Importance of Song Parameters During Flight Phonotaxis and Courtship in the Bladder Cicada Cystosoma Saundersii
Authors: Doolan Jane M. , Young David
Published: April 2021

Parameters of the calling song that were necessary to evoke phonotaxis in female bladder cicadas (Cystosoma saundersii) were determined for both long-range and short-range communication between the sexes.

Females flew to loudspeakers that were broadcasting model calling songs that resembled the natural calling song of the males. They also initiated courtship in response to the model calling songs. When flying females were offered a choice between a model resembling the natural song in all parameters (the control model) and a model in which one of the temporal parameters had been changed (the experimental model), they were attracted equally to the control and experimental models. When the carrier frequency of the experimental model was changed, the females were attracted exclusively to the control model. When the same model calling songs were presented to tethered, flying females in the laboratory, they turned only towards models with a carrier frequency close to that found in the natural song. Changing the temporal parameters of the model did not affect either the turning preferences of the females or their reaction times. When the same series of control and experimental models were played, one at a time, to caged females in the laboratory, courtship responses were elicited only by models with temporal parameters similar to those of the natural song. In contrast, a wide range of carrier frequencies was found to elicit courtship, provided that the temporal parameters were similar to those of the control. It is concluded that, in C. saundersii, identification of conspecific males by females is a two-stage process, with the carrier frequency of the male calling song being more important in long-range communication (flight) and the temporal parameters of the calling song being more important in short-range communication (courtship).
The Use of Alpha-Methyl-p-Tyroslne to Control Circulating Catecholamines in the Dogfish Scyliorhinus Canicula: the Effects on Gas Exchange in Normoxia and Hypoxia
Authors: Metcalfe J. D. , Butler P. J.
Published: April 2021

We assessed the effectiveness of alpha-methyl-p-tyrosine in inhibiting catecholamine synthesis in the dogfish and examined the effects of catecholamine depletion on the cardiovascular system in normoxia and in response to hypoxia.

Although alpha-methyl-p-tyrosine (50 mg day−1 intraperitoneally for 5 days) substantially reduced the dogfish’s ability to increase the level of circulating catecholamines in response to hypoxia, it also substantially reduced normoxic oxygen consumption in the whole animal, an observation not previously reported. Metabolic studies on isolated dogfish hepatocytes indicate that this is a direct effect on oxidative metabolism at the cellular level rather than any effect on the oxygen delivery function of the fish’s cardiovascular system. Despite the effects of alpha-methyl tyrosine on normoxic oxygen consumption, the present results indicate that the lack of any large increase in the circulating levels of catecholamines in response to hypoxia in fish treated with alpha-methyl tyrosine does not compromise their gas exchange ability.
Metabolic Stimulation of Transepithelial Potential Difference Across the Midgut of the Tobacco Hornworm (Manduca Sexta)
Authors: Chamberlin M. E.
Published: April 2021

The maintenance of in vitro transepithelial potential difference (PD) across the larval midgut of Manduca sexta is dependent upon the presence of metabolic substrates. Deletion of exogenous substrates from the bathing saline results in a rapid decline in PD. The PD can be restored by the bilateral addition of a saline containing physiological levels of amino acids and sugars. This stimulation is largely dependent upon the presence of potassium. The following substrates stimulate the PD more than twofold: citrate, succinate, malate, fructose, sucrose, trehalose, glucose, hexanoate and octanoate. Acetate and some amino acids stimulate the PD, but to a lesser extent. Of the substrates tested, only proline, glycine and 3-methyl-O-glucose fail to stimulate the PD. To determine if the observed stimulation of PD is due to absorption of anions, negatively charged substrates were added to either the haemolymph or luminal side of the tissue and the PD was monitored. The results indicate that diffusion of anions cannot account for the stimulation of PD. These results are discussed with regard to midgut oxidative metabolism and the metabolic support of active potassium secretion.
The Structural Basis for Iridescent Colour Changes in Dermal and Corneal Iridophores In Fish
Authors: Lythgoe J. N. , Shand Julia
Published: April 2021

The reflectance from the iridophores in the skin of the neon tetra Paracheirodon innesi (Myers) and the iridophores in the cornea of the sand goby Pomatoschistus minutus (Pallas) changes in response to light. In both cases the reflectance comes from the constructive interference of alternating plates of material of high and low refractive index. In the neon tetra the high refractive index plates are mainly guanine, and the low refractive index plates are cytoplasm. In the goby cornea the plates are made of intercellular matrix and cytoplasm, but it is not known which has the higher refractive index. In neon tetra dermal iridophores, the response to light is a shift to longer wavelength reflection without an accompanying increase in the amplitude of reflectance. In goby cornea, light can induce an increase in the amplitude of reflectance without a shift in wavelength. It is suggested that the wavelength shift is produced by an inflow of material into the iridophore and that the change in amplitude, without a shift in wavelength, is produced by a transfer of material, such as water, between the high and low refractive index layers of the multilayer stack.
Enhancement of Desensitization of Quisqualate-Type Glutamate Receptor by the Dissociative Anaesthetic Ketamine
Authors: Ashford M. L. J. , Boden P. , Ramsey R. L. , Usherwood P. N.
Published: April 2021

Application of ketamine (10−4–10−3mol l−1) to locust retractor unguis muscle produced a reversible, dose-dependent reduction in neurally evoked twitches, and blocked agonist-induced contractions. With increasing ketamine concentration (5×10−5–10−3mol l−1), the amplitude of glutamate potentials was reduced and dose-response curves for ionophoresis of L-glutamate were shifted to the right, particularly after concanavalin A treatment. Ketamine (10−4mol l−1) enhanced the rate of desensitization to consecutive pulses of L-glutamate and this action was eliminated by concanavalin A. The amplitude of the excitatory postsynaptic current (EPSC) was reduced by ketamine (10−5×5×10−4mol l−1) in a dosedependent manner but without a concomitant reduction in EPSC rise time. The decay phase of the EPSC was usually biphasic in the presence of ketamine (>5×10−5mol l−1) but did not exhibit any voltage dependence. It is concluded that ketamine enhances desensitization and blocks the channel, particularly the closed form.
Hypoxic Responses in a Fish From a Stable Environment: Blood Oxygen Transport in the Antarctic Fish Pagothenia Borchgrevinki
Authors: Wells R. M. G. , Grigg G. C. , Beard L. A. , Summers G.
Published: April 2021

The effects of hypoxic exposure on whole-blood oxygen-affinity were examined in the antarctic fish Pagothenia borchgrevinki. Fish exposed to for 11–14 days at −1·5°C had a P50 value of 20·6 ± 4·8 mmHg (S.D., N =13) at pH8-16, compared with 31·1 ± 4·3mmHg (N = 10) at pH8-00 for normoxic fish. Exposure to low oxygen levels resulted in a significant (66 %) rise in haemoglobin concentration, and erythrocyte [ATP] decreased by approximately 27%. There was no evidence for erythrocyte swelling. An aberrant gill morphology was observed in six fish and these showed unexpectedly high erythrocyte ATP levels. Oxygen-carrying capacity increased by approximately 40% in hypoxic fish and was correlated with a 34 % decrease in spleen mass. Despite the fact that antarctic fish have exceptionally low demands for oxygen and are unlikely ever to encounter environmental hypoxia, this antarctic fish has the necessary machinery to respond to hypoxia in a way that is typical of teleosts that naturally inhabit oxylabile environments. The ability to make short-term adaptive changes in the O2 delivery system in response to hypoxic exposure may be typical for vertebrates in general, rather than a feature seen only in those organisms which encounter environmental hypoxia on a regular basis.
The Insecticide Avermectin Bla Activates A Chloride Channel In Crayfish Muscle Membrane
Authors: Zufall F. , Franke CH. , Hatt H.
Published: April 2021

Effects of avermectin Bla (AVM) have been tested on excised outside-out or inside-out patches of crayfish stomach muscle membrane. Continuous superfusion of AVM (0·1–1 pmoll−1) to the outside-out patches induced openings of channels (22 pS) which were similar in conductance and kinetics to the chloride channels activated by glutamate, quisqualic acid, ibotenic acid and nicotinic agonists, whereas GABA mainly activated a second, larger conductance state (44pS). This effect was reversible. AVM did not activate the excitatory, glutamate-activated cation channel. Upon raising the AVM-concentration to 10 pmol I−1 and above, an enormous increase in the rate of openings of channels (22 pS) occurred. This effect could not be washed out during the lifetime of the patch. Using inside-out patches, it was shown that the single-channel current amplitude, for both the reversible and irreversible drug actions, strongly depended on intracellular chloride concentration. Applied to the sarcoplasmic side of inside-out patches, AVM did not activate any channel. The distribution of open times for 0·1 pmoll−1 AVM could be fitted by a single exponential (τ =3·3ms). For a higher AVM concentration (1 pmol I−1) two exponentials (τ1 = 0·5 ms, τ2 = 2·4ms) were needed to fit the distribution. A similar effect was elicited by decreasing the extracellular Ca2+ concentration from 13-5 to 1 mmol I−1 during the application of 0·1 pmol I−1 AVM. Picrotoxin blocked the activation of chloride channels for both the reversible and irreversible effects of AVM. It is suggested that AVM activates the multitransmitter-gated chloride channel in this preparation. Binding sites for the drug are discussed.
Visual Function in Four Antarctic Nototheniid Fishes
Authors: Pankhurst N. W. , Montgomery J. C.
Published: April 2021

Visual function was investigated in the antarctic fish Pagothenia borchgrevinki (Boulenger), Trematomus bernacchii Boulenger, T. centronotus Regan and T. hansoni Boulenger. All Trematomus species have large anterior aphakic spaces (indicating a forward feeding vector), whereas Pagothenia does not. Pagothenia and T. hansoni, which both feed in the water column, lack the corneal iridescence displayed by T. bernacchii and T. centronotus. This is thought to relate to the importance of downwelling light for image formation in Pagothenia and T. hansoni. Absolute sensitivity thresholds to white and monochromatic light were measured using electroretinogram (ERG) responses in light- and dark-adapted Pagothenia and dark-adapted Trematomus species. Dark-adapted fish (retinal screening pigment withdrawn from rod outer segments) had thresholds of l–3×10−3μEm_2s−1 to a 200ms pulse of white light, whereas that of light-adapted Pagothenia (rod outer segments covered by the retinal screening pigment) was l·9×10−2μE m−2s−1. We suggest that the thresholds approximate threshold stimuli for rods and cones, respectively. Measurement of thresholds of light-adapted Pagothenia made using a behavioural measure (feeding responses) gave a threshold of 5×10−3μEm−2s−1. Limits for photopic and scotopic vision are predicted to be reached at depths of 20–40 and 30–60 m, respectively, under snow and ice conditions typically encountered at this time of year. ERG-determined spectral sensitivity curves peaked around 500 nm in all four species and matched the spectral irradiance under the ice. Shifts to longer wavelengths in spectral irradiance caused by sub-ice phytoplankton growth may degrade visual ability. Flicker fusion frequencies (FFFs) reached a maximum value of 15 Hz in Pagothenia at the maximum stimulus intensity used, but at environmentally realistic light intensities they were less than 8 Hz. FFFs were lower in all Trematomus species than in Pagothenia.
Simultaneous Direct and Indirect Calorimetry on Normoxic and Anoxic Goldfish
Authors: Waversveld J. Van , Addink A. D. F. , Thillart G. Van Den
Published: April 2021

Simultaneous direct and indirect calorimetry together with biochemical determinations of metabolite concentrations were used to compare the normoxic and anoxic energy metabolism of goldfish at 20°C. The normoxic and anoxic heat production levels determined by direct calorimetry were in agreement with previous results: 700 and 200Jh−1MW−1, respectively (where MW is metabolic weight, kg0 85). Metabolite determinations during normoxia and after 3 and 8 h of anoxia showed that during anoxia a thermodynamic steady state is reached. By simultaneous calorimetry the amounts of oxidized substrates during normoxia and anoxia and the amount of excreted ethanol, the end product of incomplete anaerobic oxidation, as well as normoxic and anoxic carbon dioxide production were determined. During normoxia and anoxia the same substrates for oxidation are used (carbohydrate and protein) by small starving goldfish, but the end products are different. During normoxia oxidation is complete (to CO2 and H2O; protein oxidation also has ammonia as an end product, but this is considered physiologically as complete oxidation), whereas during anoxia oxidation is incomplete, with ethanol, which is excreted, and CO2 as end products. From the indirect calorimetric calculations it appeared that anoxic goldfish also produce fat. Glycogen storage appears to be crucial in the anoxia survival strategy.
Thermal Sensitivity of Swimming Performance and Muscle Contraction in Northern and Southern Populations of Tree Frogs (Hyla Crucifer)
Authors: John-Alder Henry B. , Barnhart M. Christopher , Bennett Albert F.
Published: April 2021

The effects of temperature on sprint swimming ability and muscle contractile properties were examined in northern and southern populations of the holarctic tree frog, Hyla crucifer Wied-Neuwied, acclimated to 20–23°C. Maximal swimming velocities of 29 (southern) and 32 (northern) cm s−1 and stroke frequencies of 4·1 (southern) and 5·5 (northern) strokes s−1 were attained at 30°C, and maximal stroke lengths (i.e. distance moved per stroke) of 8·0 (southern) and 7·4 (northern) cm at 20°C. The thermal dependence of swimming velocity decreases with increasing temperature (e.g. Q10 = 4·0 from 6 to 10°C, 1·2 from 20 to 30°C), as reported for locomotion in other ectothermic vertebrates. Over a temperature range of l·5–30°C, velocity increases by a factor of 5·5, frequency by a factor of 4, and length by a factor of 1·7. Thus, increased velocity at higher temperatures can be attributed mostly to increased stroke frequency; increments in stroke length contribute less. Muscle contractile properties have similar thermal dependencies to those of other vertebrates: rate processes [including twitch time-to-peak tension (TPT), twitch half-relaxation time (RT1/2), maximal rate of tetanic tension development and isotonic shortening velocity] are much more sensitive to temperature than is force generation (twitch and tetanic tension). Below 8°C, stroke frequency is limited by twitch contraction time (TPT + RT[/2), and leg extension in a swimming stroke by TPT. At higher temperatures, the thermal dependence of stroke time is lower than that of contraction time. Neither locomotor nor muscle contractile properties are different between the two populations (except for twitch tension at low temperatures). Inflexibility in the thermal dependence of muscle contraction and locomotion in this species may help to explain differences in breeding phenologies between northern and southern populations.
Gas Exchange and Air-Sac Composition in the Unanaesthetized, Spontaneously Breathing Goose
Authors: Scheid Peter , Fedde M. Roger , Piiper Johannes
Published: April 2021

Gas exchange variables were measured in unanaesthetized domestic geese fitted with rubber facemasks and indwelling air-sac and arterial catheters. The results were analysed on the basis of functional models.

Ventilation was characterized by low frequency (8·4 min−1) and high tidal volume (29·3 ml kg−1). Average values (± S.E.) of arterial blood variables were as follows: kPa, pH = 7·52 ± 0·01. Body temperature was 41·4 ± 0·2°C. The gas exchange ratio (calculated with reference to inspired gas) of caudal air sacs (average 1·09) was higher, and that of cranial air sacs (0·73) lower, than that of mixed-expired (0·82) or end-expired gas (0·78). This pattern can be explained by a higher effective ventilation/perfusion ratio in the neopulmo than in the paleopulmo. During inspiration, the neopulmo was estimated to contribute about 7% to the overall inspiratory O2 uptake, and about 18% to the CO2 output. Total inspiratory gas exchange was twice that during expiration. Arterial , was close to, but lower than, the partial pressure in cranial air sacs and in end-expired gas. This can be explained on the basis of a crosscurrent gas exchange system with unequal distribution of ventilation to perfusion between functional compartments.
Do Presynaptic Muscarinic Receptors Regulate Acetylcholine Release in the Central Nervous System of the Cockroach Periplaneta Americana?
Authors: Hue Bernard , Lapied Bruno , Malecot Claire O.
Published: April 2021

Although insects have proved to be suitable subjects for neuropharmacological investigations, the role of muscarinic acetylcholine (ACh) receptors remains unresolved. Up to now, this problem has mainly been investigated by studying the characteristics of ACh release from insect synaptosomes (Breer & Knipper, 1984) and by characterizing the binding to central nervous system (CNS) extracts from the cockroach of two muscarinic receptor-blocking drugs, L-[benzilic-4,4′-3H] quinuclidinyl benzilate (Meyer & Edwards, 1980; Lummis & Sattelle, 1985) and [N-methyl-3H]scopolamine (Lummis & Sattelle, 1986). These parallel approaches have shown that muscarinic receptors exist in the insect CNS. The functional role of these receptors is investigated in the present study by electrophysiological experiments on a synaptic preparation from the CNS of the cockroach, Periplaneta americana.
The Kinematics and Aerodynamics of the Free Flight of Some Diptera
Authors: Ennos A. Roland
Published: April 2021

Seven representative species of the order Diptera were filmed in free flight using high-speed cinematography. Insects were killed after filming, and morphological measurements were made in the manner of Ellington (1984b).

The detailed kinematics of selected sequences were then found using frame-by-frame digitization, followed by computer reconstruction of the third dimension. Kinematics were qualitatively similar to those observed by Ellington (1984c), though in three species the wings often underwent ventral flexion near the base at the end of the downstroke.

For aerodynamic analysis of hovering flight, modified forms of the equations of Ellington (1984e,f) were used. Forward flight was analysed by a novel method, which assumes that an equal but opposite circulation is built up for each half-stroke and allows linear equations to be used.

The lift coefficients calculated for hovering were commonly well above those possible by quasi-steady mechanisms, but rotational coefficients were within those that could be achieved by the unsteady lift mechanisms: clap-and-fling (Weis-Fogh, 1973) and flex (Ellington, 1984d). The lift and rotational coefficients of the two half-strokes were often unequal.

In forward flight, the equal circulation assumption often led to an incorrect estimation of the aerodynamic force vector, showing that the circulations during the two half-strokes were unequal.

It is suggested that flies manoeuvre largely by altering the unsteady circulations produced at stroke reversal via alterations in the speed and timing of wing rotation. The differences in the mechanisms used by different fly species are related to their flight behaviour in the field.
Physiological Responses of the Crayfish Pacifastacus Leniusculus to Environmental Hyperoxia: I. Extracellular Acid-Base and Electrolyte Status and Transbranchial Exchange
Authors: Wheatly Michèle G.
Published: April 2021

Extracellular acid-base and ionic status, and transbranchial exchange of acidic equivalents and electrolytes, were monitored in freshwater crayfish (Pacifastacus leniusculus’) during control normoxia ( = 148 mmHg; 1 mmHg = 133·3 Pa), 72 h of hyperoxia ( and 24 h of recovery. An initial (3 h) respiratory acidosis of 0·2 pH units was completely compensated within 48 h by a 50% increase in metabolic [HCO3−+CO32−] accompanied by a significant reduction in circulating [Cl−]. In addition, the original increase in was partially accommo dated. The time course of transbranchial acidic equivalent exchange paralleled the change in extracellular metabolic base load with a significant branchial output of H+ during the first 48 h of hyperoxia. This was associated with net branchial effluxes of Cl− and Mg2+. Unidirectional flux analysis revealed parallel reductions in Na+ influx and efflux during initial hyperoxic exposure, reflecting an alteration in exchange diffusion. The net Cl− efflux was due to an initial increase in efflux followed by a reduction in influx. The reverse sequence of events occurred more rapidly when normoxia was reinstated: metabolic base was removed from the haemolymph and control haemolymph acid-base and ion levels were re-established within 24 h. Transbranchial fluxes of acidic equivalents similarly recovered within 24 h although net Na+ output and Cl− uptake persisted.

The study attempted to identify relationships between branchial net H+ exchange and components of Na+ and Cl− exchange and quantitatively to correlate changes in the acidic equivalent and electrolyte concentrations in the extracellular fluid compartment with those in the external water.
Natural Dehydration Regimes as A Prerequisite for the Successful Induction of Anhydrobiosis in the Nematode Rotylenchulus Reniformis
Authors: Womersley Christopher , Ching Cherie
Published: April 2021

Induction of anhydrobiosis in the nematode Rotylenchulus reniformis (Linford & Oliveira) was studied using direct exposure to elevated relative humidities and conditions resembling natural dehydration regimes. All larvae and preadults were unable to survive direct short-term exposure to 97 % relative humidity. However, dehydration of larvae on model substrates (0·5 % agar: 1·0 % agarose) that mimic the natural rate of soil moisture loss induced coiling and successful entry into anhydrobiosis. Coiling was maximized at 10–12 days and only coiled larvae survived dehydration, emerging as the preadult form. Larvae could withstand severe dehydration at 80 and 40 % relative humidity after the induction of coiling, but were unable to withstand direct exposure to 0 % relative humidity.

The levels of adaptation utilized by anhydrobiotes to ensure slow dehydration and the adaptive significance of this are discussed in relation to the different environments in which these organisms are found. The results suggest that R. reniformis is well-adapted to its environment and emphasize the importance of natural dehydration regimes for assessing anhydrobiotic potential.
The Treading-on-Tarsus Reflex in Stick Insects: Phase-Dependence and Modifications of the Motor Output During Walking
Authors: Schmitz J. , Haβfeld G.
Published: April 2021

In stick insects walking forwards or backwards, a treading-on-tarsus (TOT) reflex of the middle leg could be elicited by mechanical stimulation of the ipsilateral front leg tarsus. The probability of eliciting a TOT reflex in the middle leg depended on the phase of the stimulus within the middle leg’s step cycle and on the position of the middle leg relative to its normal anterior and posterior extreme positions. During a TOT reflex the functional swing muscle (protractor coxae in forward walks and retractor coxae in backward walks) was inhibited while the functional stance muscle was activated. This suggests that the step generator of the middle leg contains two hierarchical levels: the higher level would determine the timing of swing and stance independent of walking direction; the lower one would drive the appropriate muscle groups for swing and stance depending on which programme -forward or backward walking -was running. The stimulus information from the front leg necessary to elicit a TOT reflex was observed only in the ipsilateral connective. In terms of the model, this information would have to be processed according to the actual state of the higher level of the step generator. Movement and position of the front leg and tarsal contact of the middle leg were not relevant for the TOT reflex of the middle leg. Steps with a TOT reflex were significantly prolonged, and compensation for this disturbance of walking coordination was made within the next step.
An Acoustic Telemetry System for Monitoring The Heart Rate of Pike, Esox Lucius L., and Other Fish In Their Natural Environment
Authors: Armstrong J. D. , Lucas M. C. , Priede I. G. , Vera L. De
Published: April 2021

Heart rate can be telemetered from fish using FM radio transmitters (Nomura & Ibaraki, 1969), FM acoustic transmitters (Wardle & Kanwisher, 1974), acoustic pulsed transmitters (Priede & Young, 1977), electromagnetic transmitters (Priede et al. 1985) and acoustic transponders (Storeton-West et al. 1978). Most of these systems transmit only over short distances or cannot be used with the standard equipment used in animal-tracking studies. This paper describes an acoustic transmitter which emits a high-power pulse triggered by the R wave of the electrocardiogram (ECG) and is compatible with normal field equipment for tracking fish.
Modes of Ammonia Transport Across the Gill Epithelium of the Marine Teleost Fish Opsanus Beta
Authors: Evans David H. , More Kane J. , Robbins Steven L.
Published: April 2021

The modes of ammonia transport across the gill epithelium of the marine teleost Opsanus beta were investigated using an isolated, perfused head preparation. During perfusion for approximately 2h there was no macro- or microscopic damage to the exterior surface of the gill filaments or lamellae, no swelling of lamellae, the structural leak was only 0·3%, the afferent perfusion pressure was constant, and the transepithelial electrical potential (TEP) approximated that measured in vivo. The rate of ammonia efflux was similar to that measured in vivo, was constant for at least 80 min, and approached zero when the perfusate was nominally ammonia-free. Addition of ouabain or bumetanide to the perfusate indicated that basolateral Na+/NH4+ exchange, but not Na+/NH4+/2C1− cotransport, was important in transbranchial ammonia transport. No evidence was found for apical Na+/ NH4+exchange. Specific increases in perfusate NH3 were nearly 100 times as effective as increases in NH4+ concentrations in stimulating ammonia efflux. Alteration of TEPs could not account for any of these effects. Calculated relative permeabilities to NH3 and NH4+indicate that the toadfish gill is relatively permeable to NH4+ compared to the shark gill and other ‘tight’ epithelia, consistent with the general conclusion that marine teleost gills are relatively cation-’leaky’. Computation of the relative roles of the three delimited pathways for ammonia efflux indicate that 22% is via basolateral Na+/ NH4+exchange, 57% via non-ionic diffusion of NH3 and 21% via ionic diffusion of NH4+. Comparison with other published data suggests that the relative roles of non-ionic and ionic diffusion of ammonia across epithelia may be correlated with relative ionic permeabilities.
The Seasonal Modulation of Na+/H+ Exchanger Activity in Trout Erythrocytes
Authors: Cossins Andrew R. , Kilbey Robert V.
Published: April 2021

A pH-stat method is described for determining the initial rate of efflux of H+ equivalents from trout erythrocytes after stimulation with catecholamines. This measure of transport capacity of the Na+/H+ exchanger was sensitive to medium pH with a peak at 7·24 ± 0·09 pH units. After washing blood into a trout saline the exchange capacity recovered to a maximal value after 2 h and remained stable for at least 24 h at 5 °C. Internal Na+ concentration reached a low, stable value also within 2–3 h of washing. The antiporter was comparatively unstable when incubated at room temperature. The concentrations for half-maximal responses to the agonists adrenaline, noradrenaline and isoproterenol were 3·0 ± 1·1 × 10−7, 2·5 ± 3·0 × 10−8 and 1·5 ± 0·6× 10−8moll-1, respectively.

The variation of antiporter capacity with time of the year was followed over a 24month period. Capacity was highest during early summer at 200–250 mmol h-1 I-packed cell volume (pcv), but declined from November to March to a low of approximately 100mmolh-11-1 pcv. Exchange capacity increased rapidly during the early spring back to values characteristic of early summer. It appears that both temperature and photoperiod are involved in regulating the spring increase.
Metabolism of the Perfused Swtmbladder of the European EEL: Oxygen, Carbon Dioxide, Glucose and Lactate Balance
Authors: Pelster B. , Kobayashi H. , Scheid P.
Published: April 2021

We have measured the metabolic activity in the vascularly isolated, salineperfused swimbladder of the eel (Anguilla anguilla) in order to investigate the pathways for CO2 formation in the gas gland tissue. Concentrations of O2, CO2, glucose and lactate were measured in the arterial inflow and venous outflow of the swimbladder, and metabolic rates were calculated by the direct Fick principle.

Total CO2 production, averaging 55·8 nmol min−1, was about 4·6 times the O2 consumption (mean 12·0 nmol min−1). This suggests that only about 22% of the CO2 is formed by aerobic glucose metabolism. CO2 formation from HCO3− or CO2 washout does not appear to be significant in our experiments with steady perfusion of a saline containing a low level of HCO3−. The ratio of lactate production to glucose uptake averaged 1·2, indicating that only 60% of the glucose is converted to lactate. Since only 1–2% of the glucose was found to be oxidized (2 nmol min−1), the extra glucose appears to be anoxidatively metabolized to CO2. The anoxidative CO2 formation appears to be of functional importance for producing the high gas partial pressures of both CO2 and O2 which are required for secretion of these gases into the swimbladder.
Metabolism of isolated fish gill cells: contribution of epithelial chloride cells
Authors: Perry S. F. , Walsh P. J.
Published: April 2021

Gill cell suspensions from freshwater (FW)- and seawater (SW)-adapted teleosts were obtained by density gradient centrifugation. The proportion of chloride cells (CCs) in the mixed cell suspensions was estimated using the fluorescent mitochondrial stain, DASPMEI, and ranged from less than 1 % (FW-adapted tilapia) to approximately 13% (SW-adapted toadfish). The gill cells displayed relatively high viability based on Trypan Blue exclusion (>75%), lactate dehydrogenase leakage (<6·5% h−1), oxygen consumption rates (5–15μmolg−1 cell wet mass h−1) and ATP levels (1–3μmol g−1 cell wet mass). There were no obvious differences between the viability of CCs and the other cell types present.

An initial comparison of gill oxidative metabolism in SW-adapted tilapia (Oreochromis mossambicus) and toadfish (Opsanus beta) demonstrated that both species oxidized glucose and lactate at substantially greater rates than alanine or oleate. Metabolic rates were significantly higher in toadfish cell suspensions. Kinetic experiments revealed that toadfish gill cells displayed lower values of Km and higher values of Vm for both lactate and glucose, in comparison to tilapia. The elevated metabolism in toadfish gill cells was correlated with increased activities of the oxidative enzyme citrate synthase and Na+/K+-ATPase. The toadfish cell suspensions had a greater proportion of CCs and it is likely that the difference in CC numbers between the two species is the basis for the observed differences in enzyme activities and rates of oxidative metabolism. This idea is supported by the highly significant correlation between Na+/K+-ATPase activity (or CC numbers) and rates of lactate oxidation in gill cell suspensions from FW-and SW-adapted tilapia and toadfish, as well as SW-adapted tilapia chronically treated with cortisol to elevate CC numbers.

Although it has been assumed widely that the high metabolic rate of gill tissue reflects, in part, the oxidative demands of the chloride cell, the results of this study provide the first experimental, albeit indirect, evidence for differential rates of metabolism in the various cell types that comprise the gill.
Temperature Effects on Membrane Chloride Conductance and Electrical Excitability of Lizard Skeletal Muscle Fibres
Authors: Adams Brett A.
Published: April 2021

Intracellular recording techniques were used to study the effects of temperature on resting membrane conductances, electrical excitability and synaptic efficacy in fast-glycolytic (FG) skeletal muscle fibres from the lizard Dipsosaurus dorsalis. The conductance of the resting muscle membrane to chloride ions (gci) increased from 488 μS cm−2 at 15°C (pH7-8) to 730 μS cm−2 at 45°C (pH7·4), yielding a temperature coefficient (thermal ratio, Rio) of 1·14. Resting potassium conductance (gK) increased from 84μS cm−2 at 15 °C to 236 μS cm−2 at 45 °C (R10=1·41). Fibres bathed in Cl−-free Ringer’s solution were hyperexcitable, and produced repetitive action potentials both during and following intracellular current injection. At the preferred body temperature of Dipsosaurus (near 40°C) the fibres also fired repetitively in response to single nerve shock. The electrical excitability of Dipsosaurus fibres decreased with increasing temperature. Threshold current, measured at endplate regions of fibres bathed in normal Ringer’s solution, was 146 nA at 15°C and 353 nA at 45°C (R10= 1·34). Despite the temperature-dependent change in threshold current, at both 15 and 45 °C all fibres examined had suprathreshold neuromuscular transmission in response to single nerve shock. The relative thermal independence of gCl in Dipsosaurus fibres may be an adaptation that contributes to a large safety factor for neuromuscular transmission at the high body temperatures preferred by this lizard species.
High Concentrations of Zinc in the Fangs and Manganese in the Teeth of Spiders
Authors: Schofield Robert , Lefevre Harlan
Published: April 2021

Various organisms have recently been shown to contain significant amounts of zinc and manganese in mechanical structures such as mandibular teeth. These accumulations are different from those in the bones and teeth of vertebrates and the shells and teeth of some mollusks in that the elements are both less common and are not obviously incorporated in biominerals. High concentrations of zinc (about 1 % of dry mass) were reported in the jaws of polychaete worms by Bryan & Gibbs (1979), using wet-ash analysis. These authors suggested that the zinc influences the mechanical properties of the jaw in a fashion analogous to the role of biominerals in the teeth of many organisms. Hillerton & Vincent (1982) detected zinc and manganese in the cutting edge of the mandibles of herbivorous insects from several orders using an electron microprobe. They determined the zinc concentration, averaged over the whole mandible, with wet chemical analysis, finding about 0·5% in a locust species. Hillerton et al. (1984) found either manganese or zinc in large quantities in the mandibles of separate species of beetles. Hillerton & Vincent (1982) went on to suggest that zinc may increase the density and fracture toughness of the mandibular teeth by increasing the number of secondary bonds in the cuticle. The hardening hypothesis has been accepted by Bone et al. (1983), who studied zinc in chaetognath teeth and spines, and by Perry et al. (1988), who studied zinc in copepod mandibles.
Nitrogen Budget in Developing Embryos of the Spiny Dogfish Squalus Acanthias
Authors: Kormanik Gregg A.
Published: April 2021

Embryos of the dogfish Squalus acanthias (L.) complete their development in a uterine environment that is quite unusual. During the latter portion of a gestation period which lasts nearly 2 years (Hisaw & Albert, 1947), the embryos are bathed by a uterine solution that resembles sea water with respect to the major ions, but the ammonia concentration may approach 22 mmol l−1 and the pH is about 6 (Kormanik & Evans, 1986).
The Effects of Morphology and Perch Diameter on Sprint Performance of Anolis Lizards
Authors: Losos Jonathan B. , Sinervo Barry
Published: April 2021

We investigated the mechanistic basis for the observed correlation between leg length and perch size among West Indian Anolis lizards by testing the hypothesis that species use those perches upon which they can move most effectively. We used four Anolis species which differed in leg length and perch use in nature. We measured maximum sprint speed on rods of several sizes. Longer-legged species ran faster on thick rods. The speed of all species declined on thinner rods, but long-legged species were affected to a greater extent in that all species ran at approximately the same speed on the smallest rod. The short-legged A. valen-cienni experienced much less difficulty moving on thin rods than did the other species. Variation in leg length among Anolis might thus represent an evolutionary trade-off between maximizing sprint speed and maximizing stability on thin perches.