bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Studies of the Secretory Event at Vertebrate Nerve Terminals
Authors: Salzberg Brian M. , Obaid Ana Lia
Published: April 2021

Potentiometric probes are small (300–500 Mr) amphipathic molecules that bind to, but do not cross, cell membranes and behave as fast linear transducers of membrane voltage. Their optical properties, particularly absorbance and fluorescence, respond to changes in potential in less than 2μs, and they may be used to follow electrical events in membranes which are inaccessible to microelectrodes. We have used these dyes to study the properties of the action potential in the neurosecretory terminals of vertebrate neurohypophyses and, in particular, to investigate the behaviour of the local population of calcium channels. These channels are sensitive to the peptide toxin ω-conotoxin GV1A, derived from the venom of the marine snail Conus geographicus, but insensitive to dihydropyridine channel modulators. In the neurohypophysis of the mouse, it is possible to demonstrate that the calcium channels that are blocked by ω-conotoxin are those that are required for secretion of peptide hormones.

In the terminals of the neurohypophysis, excitation is coupled to secretion, and the secretory event is accompanied by large and rapid changes in light scattering. These intrinsic optical signals provide a millisecond time-resolved monitor of events in the terminal that follow the entry of calcium, and may precede the release of hormones. We will consider how the changes in light scattering can be related to secretion, and how the extrinsic (absorption) and intrinsic optical signals may provide complementary information about excitation-secretion coupling.
A Molecular Basis for Synexin-Driven, Calcium-Dependent Membrane Fusion
Authors: Pollard Harvey B. , Burns A. Lee , Rojas Eduardo
Published: April 2021

Membranes of secretory vesicles fuse with each other and with plasma membranes during exocytosis in many different cell types. The probable role of calcium in the process is now widely accepted, and it is possible that at least one cytosolic mediator of calcium action is synexin. Synexin is a 47 000 Mr calcium-binding protein, initially discovered in the bovine adrenal medulla, which binds to granule membranes and to inner aspects of chromaffin cell plasma membranes. Synexin causes chromaffin granules to aggregate, and such aggregates can be caused to fuse in the additional presence of arachidonic acid. Synexin also mediates the direct fusion of liposomes and chromaffin granule ghosts. To understand better the mechanisms of membrane fusion promoted by synexin we have attempted to define the primary sequence of the protein. Our initial efforts were directed towards purification of bovine synexin in sufficient amounts to allow us to sequence tryptic peptides. However, as the project progressed we also directed our attention to human synexin, preparing peptides from this protein as well. From analysis of bovine peptides we learned that the synexin molecule might be closely related to a class of proteins including lipocortin I, calpactin (p36), endonexin II, protein II and calelectrin 67K. Complete analysis of a human synexin cDNA clone revealed strong homology with bovine synexin. The analysis also showed that synexin contained a unique, long, highly hydrophobic N-terminal leader sequence followed by a characteristic four-fold repeat homologous with those found in other members of the synexin gene family. The highly hydrophobic character of synexin seems consistent with information previously obtained that synexin is able to insert directly into the interior of bilayers prepared not only from purified phosphatidylserine but also from biological membranes. The evidence for such insertions is a dramatic increase in the capacitance of the membrane, formed at the tip of a patch pipette, when calcium-activated synexin is applied to the bilayer. Additional evidence is the fact that synexin also forms calcium-selective channels when the protein is applied to the cytosolic aspect of the plasmalemma when that side is also exposed to calcium at sub-millimolar concentrations. Thus, the synexin molecule not only enters the membrane, but also spans it. From these and other data we have developed the concept that the fusion process may involve synexin forming a ‘hydrophobic bridge’ between two fusing membranes. Lipid movement across this bridge may then be the material basis for final fusion. We have termed this concept the ‘hydrophobic bridge hypothesis’, and have developed the predictive properties of this hypothesis in considerable detail.
The Mechanism of Urine Formation in Invertebrates
Authors: Picken L. E. R.
Published: April 2021

In Anodonta cygnea: The blood has a vapour pressure equivalent to that of a solution of ca. 0.10 per cent sodium chloride. The pericardial fluid is isotonic with the blood. The urine has a vapour pressure equivalent to that of a solution of ca. 0.06 per cent sodium chloride. The hydrostatic pressure of the blood is ca. 6 cm. of water. The calculated colloid osmotic pressure is ca. 3.8 mm. of water. The average rate of filtration of fluid into the pericardium is ca. 250 c.c. in 24 hours. The salt uptake from ingested phytoplankton is estimated as equivalent to 0.012. g. sodium chloride in 24 hours. The loss of osmotically active substance in the urine is estimated as equivalent to 0.15 g. sodium chloride in 24 hours. In Limnaea peregra the vapour pressure of the blood is equivalent to that of a solution of ca. 0.43 per cent sodium chloride. The pericardial fluid is isotonic with the blood, and the urine has a concentration equivalent to ca. 0.30 per cent sodium chloride. In Limnaea stagnalis the hydrostatic pressure of the blood is ca. 8 cm. of water. The colloid osmotic pressure of the blood is ca. 2.5 cm. of water (calculated); that of the pericardial fluid is ca. 0.7 cm. of water.
The Oxygen Consumption of Ephemerid Nymphs From Flowing and From Still Waters in Relation to the Concentra-Tion of Oxygen in the Water
Authors: Fox H. Munro , Wingfield C. A. , Simmonds B. G.
Published: April 2021

Fox & Simmonds (1933) and Fox et al. (1935) have shown that certain may-fly nymphs, a caddis larva and an isopod from swift streams have a higher oxygen consumption than nearly related forms from still waters or slow-flowing streams. Their results were summarized in Table IV1 of Fox et al. (1935). It has since been shown by Washbourn (1936) that the oxygen consumption of trout fry reared in swiftly flowing water is greater than that of fry reared in slow water.

Wolsky & Holmes (1933) found the oxygen consumptions of four individuals of the crayfish Astacus leptodactylus Eschscholtz, from Lake Balaton, to be 90, 103, 104 and 105 mg. of oxygen per kg. of animal per hour at 19–21° C., the animals weighing 16, 22, 36 and 64 g. respectively. The mean of these values for oxygen consumption is 101. Without studying the problem we are now considering, Wolsky (1934) later found that the oxygen consumptions of seven individuals of A. torren-tium (Schrank), living in a swift stream in Hungary, were 160, 188, 157, 157, 170, 102 and 137 mg. oxygen per kg. of animal per hour at 19–21° C., the animals weighing 8, 8, 15, 17, 17, 21 and 32 g. respectively. The mean of these values for oxygen consumption is 153. The oxygen consumption of A. torrentium is thus 50 per cent greater than that of A. leptodactylus, and the relation between oxygen consumption and weight suggests that habitat, not size, was responsible for this difference.
The Absorption of Water and the Associated Volume Changes Occurring in the Eggs ofNotostira ErraticaL. (Hemiptera, Capsidae) During Embryonic Development Under Experimental Conditions
Authors: Johnson C. G.
Published: April 2021

The eggs of Notostira erratica L. (Hemiptera) swell during embryonic development. Increase in wet weight accompanies swelling.

Under the conditions of the experiments described in this paper the gross increase in wet weight of the eggs from oviposition till hatching is due entirely to the increase in amount of water. The weight of water per egg is, however, slightly greater than the increase in wet weight of the same egg, since the amount of dry matter per egg decreases slightly during development.

The increased amount of water must be largely due to absorption from the external environment: a certain amount, however, is probably metabolic water, which if due to oxidation of fat in the yolk would result in an increase in wet weight of the egg. This increase due to metabolic water will tend to be balanced by the decrease in dry matter during embryonic development.

The increase in volume of an egg during embryonic development is directly proportional to its increase in wet weight during the same period. Theoretically it would be more accurate to correlate volume change with the amount of water in the egg; this cannot be done accurately enough, however, with the present methods.

The embryonic development and the extrusion of the subopercular yolk-plug in relation to water absorption are briefly described. The work of other authors concerned with water-absorbing insect eggs is discussed.

The method used for finding the volume of the eggs (which does not involve their death) is described in detail.
Quantitative Studies on the CiliateGlaucoma
Authors: Harding J. P.
Published: April 2021

Glaucoma was cultured in various concentrations of bacteria which were kept as constant as possible. The rate of disappearance of the bacteria was a function of the concentration of the Glaucoma. In low concentrations of bacteria the rate of feeding of the Glaucoma was a function of the concentration of bacteria. In high concentrations of bacteria the Glaucoma were able to find almost as much food as they could take in; so that the rate of feeding tended to become independent of the concentration of bacteria. Counts of food vacuoles showed that the rate of feeding never became quite independent of the concentration of bacteria. For every increase in the concentration, up to at least 8,000,000 bacteria per cu. mm., there was an increase in the rate of formation of food vacuoles. High concentrations of bacteria did not inhibit the growth or the reproduction of the Glaucoma. When the concentration of bacteria was less than 600,000 per cu. mm. the Glaucoma were semi-starved and both their size and their rate of fission was dependent on the concentration. Between concentrations of 600,000 and 7,000,000 bacteria per cu. mm. the rate of growth in size, but not the rate of fission of Glaucoma, was influenced by the concentration. The generation-time was constant throughout this range at between 2-3 and 2-4 hours.
The Tonic Function of the Horizontal Semicircular Canals in Fishes
Authors: Löwenstein Otto
Published: April 2021

An operative technique is described, which makes possible the elimination of a single horizontal semicircular canal in the pike (Esox lucius). Such an operation, carried out unilaterally, leads to a lasting tonic asymmetry of the eye muscle apparatus. Hence a tonic function of the horizontal semicircular canals must be assumed. The eye reactions of the pike during and after rotation in a horizontal plane are in complete agreement with the properties of the ampullary sense organ of the dogfish described by Löwenstein & Sand (1936). It is demonstrated that a single horizontal semicircular canal can give rise to reflex responses of the eyes on both clockwise and anti-clockwise rotation of the fish in the horizontal plane.
Preservation of Glucose Transport and Enzyme Activity in Fish Intestinal Brush-Border and Basolateral Membrane Vesicles
Authors: Reshkin Stephan J. , Cassano Giuseppe , Womersley Christopher , Ahearn Gregory A.
Published: April 2021

The preservation of glucose transport and membrane-bound enzyme activity in intestinal brush-border and basolateral membrane vesicles from the euryhaline teleost, Oreochromis mossambicus, was examined. Transport was well-preserved when the vesicles were either frozen in liquid nitrogen or lyophilized and stored in the presence of trehalose. Transport activity was not well-maintained when vesicles were lyophilized with mannitol as the protective carbohydrate. Enzyme activities were reduced by liquid nitrogen storage or by lyophilization with mannitol. However, enzyme enrichments of all treatments remained fairly constant over storage time, suggesting similar functional and perhaps structural changes in the different membrane fractions in response to preservation. These techniques provide a simple way to obtain functionally similar vesicles over a relatively long period of storage, permitting improved comparisons of transport properties. These results extend for the first time to vertebrate epithelial membranes the finding that trehalose preserves transport activity during lyophilization, storage and rehydration.
The Importance of Torsion in the Design of Insect Wings
Authors: Ennos A. Roland
Published: April 2021

A model insect wing is described in which spars of corrugated membrane which incorporate stiffening veins branch serially from a V-section leading edge spar. The mechanical behaviour of this model is analysed.

The open, corrugated spars possess great resistance to bending, but are compliant in torsion. Torsion of the leading edge spar will result in torsion and relative movement of the rear spars. As a result camber will automatically be set up in the wing as it twists.

Aerodynamic forces produced during the wing strokes will result in torsion and camber of the wing which should improve its aerodynamic efficiency.

The effects of varying parameters of the wing model are examined. For given wing torsion, higher camber is given by spars branching from the leading edge at a lower angle, by spars which curve posteriorly, and by spars which diverge from each other.

Wings of three species of flies were each subjected to two series of mechanical tests. Application of a force behind the torsional axis caused the wings to twist and to develop camber. Immobilizing basal regions of the leading edge greatly reduced compliance to torsion and camber, as predicted by the theoretical model. Aerodynamic forces produced during a half-stroke are sufficient to produce observed values of torsion and camber, and to maintain changes in pitch caused by inertial effects at stroke reversal.
The Inertial Cause of Wing Rotation in Diptera
Authors: Ennos A. Roland
Published: April 2021

The cause of the changes in wing pitch at stroke reversal in Diptera has been investigated. The high compliance of the wing base makes it seem unlikely that pitch changes are caused by active torsion at the wing articulation.

The centre of mass of insect wings tends to be behind the centre of torsion of the wing, and it is proposed that wing inertia about the torsional axis alone is responsible for pitch changes as the wing is accelerated at stroke reversal. A simplified inertial model is developed to calculate the angular velocity about the torsional axis that would be caused by wing inertia.

The mass distribution and the torsional axis of the wings of two species of flies was found and it was shown that in these animals inertial causes alone could develop the angular velocity in the pitching plane that is observed at stroke reversal.

Analysis of the movement of individual regions of the wing shows further that inertial effects will produce the tip to base ‘torsion wave’ seen in the wing at stroke reversal.
Parallel Inhibition of the Motor Giant, Segmental Giant and Fast Flexor Neurones of the Hermit Crab
Authors: Fraser K. , Heitler W. J.
Published: April 2021

Previous work has shown that the giant fibres (GFs) of the hermit crab make excitatory electrical connections with the motor giant (MoG) and segmental giant (SG) neurones, and that the SGs in turn make connections to fast flexor (FF) motor neurones. In this paper we show that synchronous or almost-synchronous IPSPs can be elicited in all three classes of neurone by electrical stimulation of the connectives or roots. These IPSPs are depolarizing in the MoG and SG, and hyperpolarizing in the FFs. The IPSPs can functionally disconnect the MoG, SG and FF neurones from the GF command. Several interneurones have been found which initiate the IPSPs when driven with injected current. These are referred to collectively as inhibitory driver neurones (IDNs). In some cases IPSPs follow IDN spikes 1:1; in others more than one IDN spike is required to produce a single IPSP.
The Mechanical Power Output of a Crab Respiratory Muscle
Authors: Stokes Darrell R. , Josephson Robert K.
Published: April 2021

The mechanical power output was measured from scaphognathite (SG = gill bailer) muscle L2B of the crab Carcinus maenas (L.). The work was determined from the area of the loop formed by plotting muscle length against force when the muscle was subjected to sinusoidal length change (strain) and phasic stimulation in the length cycle. The stimulation pattern (10 stimuli per burst, burst length = 20% of cycle length) mimicked that which has been recorded from muscle L2B in intact animals. Work output was measured at cycle frequencies ranging from 0·5 to 5 Hz. The work output at optimum strain and stimulus phase increased with increasing cycle frequency to a maximum at 2-3 Hz and declined thereafter. The maximum work per cycle was 2·7 J kg−1 (15 °C). The power output reached a maximum (8·8 W kg−1) at 4 Hz. Both optimum strain and optimum stimulus phase were relatively constant over the range of burst frequencies examined.

Based on the fraction of the total SG musculature represented by muscle L2B (18%) and literature values for the oxygen consumption associated with ventilation in C. maenas and for the hydraulic power output from an SG, we estimate that at a beat frequency of 2 Hz the SG muscle is about 10% efficient in converting metabolic energy to muscle power, and about 19% efficient in converting muscle power to hydraulic power.
Gliding Birds: Descending Flight Of The White-Backed Vulture, Gyps Africanus
Authors: Tucker Vance A.
Published: April 2021

The air speeds and sinking speeds of birds gliding at equilibrium fall in a performance area when these quantities are plotted against one another. Three curves bound the performance area: (i) a curve for minimum sinking speed at each air speed, (ii) a curve for maximum sinking speed at each air speed, and (iii) a curve dependent on the maximum lift coefficient of the wings. I have discussed curve i in a previous paper. This paper discusses the theory of curves ii and iii, which describe rapid descent in gliding birds. I used an optical tracking device (an ornithodolite) to measure air speeds and sinking speeds of 16 African white-backed vultures (Gyps africanus Salvadori) descending rapidly from altitudes 200–500 m above the ground. The ornithodolite measured the polar coordinates of a bird’s position in space (relative to the ground) and recorded them on magnetic tape. The vultures had air speeds between 5·4 and 39·1 ms−1, and sinking speeds between 0·2 and 8·3 ms−1. Most of the observations fell within the theoretical boundaries of the performance area. These data are consistent with a maximum lift coefficient of 2·2 for the wings of white-backed vultures.
Predominance of Vagal Bradycardia Mechanism in the Brain Stem of Turtles
Authors: Hsieh J. H. , Pan C. M. , Kuo J. S. , Chai C. Y.
Published: April 2021

Cardiovascular parameters of spontaneously breathing pond turtles (Cyclemys flavomarginata) anaesthetized with chloralose (4 mg 100 g−1) and urethane (40 mg 100 g−1), were examined during exploratory electrical stimulation of the brain stem. Turtles exhibited a low mean systemic arterial blood pressure (MSAP, average 25 mmHg) and slow heart rate (average 24 beats min−1). Upon stimulation, pressor (sympathetic), depressor (sympathetic inhibition), bradycardia and hypotensive (vagal) responses were elicited from regions of the brain stem extending from the hypothalamus to the medulla, principally in the medial region. The pressor response appeared after a longer latency than did the bradycardia and hypotensive responses. It developed rather slowly, and rarely attained a magnitude double its resting value. In contrast, stimulation of many points in the brain stem produced marked slowing or even cessation of the heart beat, and thus resulted in an immediate fall of the blood pressure even to zero. This cardio-inhibitory response depended on the integrity of the vagus nerves and was particularly marked upon stimulation in the caudal medulla, the areas of the ambiguus, solitary and dorsomotor nuclei of the vagus and the midline structures. When such an area was stimulated continuously the heart stopped beating throughout the stimulation. The longest period of cardiac arrest before the appearance of escape was 35 min. With continuous stimulation of the peripheral end of the cut vagus, the earliest escape beat occurred even later (65min). Epinephrine given intravenously produced an increase of MSAP and force of cardiac contraction, although the slope of pressor rise was shallow. Reflex bradycardia, however, was not observed. These experiments show that a very prominent vagal bradycardia can be evoked from the turtle brain stem, which may contribute to its well-known capacity for tolerating anoxia.
Motor Activity in the Stump of an Amputated Leg During Free Walking in Cockroaches
Authors: Delcomyn Fred
Published: April 2021

A rhythmic pattern of motor activity was recorded in the stump of an amputated leg during free walking in cockroaches. During relatively rapid walking, extensor (depressor) and flexor (elevator) muscles in the intact coxa of the amputated leg showed one burst of activity during each cycle of bursting in an adjacent, intact leg. However, during slower walking these muscles could show two or three bursts of activity during each cycle of bursting in an intact leg. Motor bursts in the stump of an amputated leg showed features similar to those of bursts recorded from intact legs. Burst duration increased with an increase in period, and the bursts generally showed consistent timing (phase) relative to bursts in most of the intact legs. The motor pattern recorded in a stump was very like that recorded in an intact leg during walking, and unlike that recorded during searching for a foothold (defined in the text). It is concluded that after the amputation of most of a leg, motor neurones innervating muscles in the stump of the amputated leg continue to be driven by the interneurones that normally drive the intact leg during walking. Analysis of the motor pattern in the stump may therefore reveal important features of the locomotor control system.
The Pars Intercerebralis Neurone PI(2)5 of Locusts: Convergent Processing of Inputs Reporting Head Movements and Deviations from Straight Flight
Authors: Hensler Klaus
Published: April 2021

The pars intercerebralis neurone PI(2)5 of Locusta migratoria is a descending large-field deviation detector (DN), projecting from the brain to the fused abdominal ganglia. It responds with bursts of action potentials (1) to specific movements of an artificial horizon, simulating deviations from course (preferred deviations are roll and yaw to the side of the axon, and pitch-up), and (2) to proprioceptive input from neck receptors signalling head movements in either direction. During compensatory head movements both inputs act together so that the deficit in visual information is balanced by proprioceptive input.

The number of spikes elicited by roll deviations depends on the sector of the visual vield initially covered by the horizon (sector specificity), increasing the more the horizon is oriented in the visually preferred direction. Hence, sector specificity involves information about the absolute orientation with respect to the horizon. The number of spikes depends further on the roll position of the head with respect to the prothorax. The response is amplified when the head is oriented in the visually preferred direction, and is attenuated when the head is oriented in the visually antipreferred direction. Visual and proprioceptive modulatory effects balance each other so that sector specificity relates to the body (i.e. the aerodynamic organs) even when head and body are rotated against each other.

During flight, the excitability of PI(2)5 is further influenced by tonic inhibition from frontal wind (no directionality), which is overriden by tonic excitation of central origin.
Na+, K+ and Ca2+ Currents in Identified Leech Neurones in Culture
Authors: Stewart R. R. , Nicholls J. G. , Adams W. B.
Published: April 2021

Na+, K+ and Ca2+ currents have been measured by voltage-clamp in Retzius (R), anterior pagoda (AP) and sensory (pressure, touch and nociceptive) cells dissected from the central nervous system (CNS) of the leech. These cells maintain their distinctive membrane properties and action potential configurations in culture. Currents carried by the individual ions were analysed by the use of channel blockers and by their kinetics. Since the cells are isopotential they can be voltage-clamped effectively. Depolarization, as expected, gave rise to an early inward Na+ current followed by a delayed outward K+ current. In Na+-free medium containing tetraethylammonium (TEA+), and in the presence of 4-aminopyridine (4-AP), inward Ca2+ currents were revealed that inactivated slowly and were blocked by Cd2+ and Mn2+. Na+ and Ca2+ currents were similar in their characteristics in R, AP and sensory neurones. In contrast, K+ currents showed marked differences. Three principal K+ currents were identified. These differed in their time courses of activation and inactivation and in their responses to Ca2+ channel blockers. K+ currents of the A-type (IA) activated and inactivated rapidly, were not affected by Ca2+ channel blockers and were eliminated by steady-state inactivation at holding potentials of −30 mV. A-type K+ currents were found in AP cells and as a minor component of the outward current in R cells. A Ca2+-activated K+ current (IC), that inactivated more slowly and was reduced by Ca2+ channel blockers, constituted the major outward current in R cells. The third K+ current resembled the delayed rectifier currents (IK1 and IK2) of squid axons with slow activation and inactivation kinetics. Such currents were found in R cells and in the sensory neurones (T, P and N). The principal differences in membrane properties of identified leech neurones can be explained in terms of the numbers of Na+ channels and the distinctive kinetics of K+ channels in each type of cell.
Distribution of Intersegmental Interneurones That can Reset the Respiratory Rhythm of the Locust
Authors: Ramirez J. M. , Pearson K. G.
Published: April 2021

Interneurones in the respiratory rhythm generator of the locust were identified by means of intracellular recording and staining techniques. A description is made of the properties and structures of nine intersegmental neurones which reset the respiratory rhythm when injected with current pulses. All but one of these neurones discharged in phase with expiration. The injection of constant depolarizing current into these interneurones altered the respiratory rate (increase for six, decrease for three). The respiratory rhythm generator extends more posteriorly within the ventral nerve cord than the metathoracic ganglion. In the first fused abdominal ganglion, four individual interneurones were identified descending into the unfused abdominal ganglia. In the first unfused abdominal ganglion an intemeurone which reset the respiratory rhythm was found ascending into the metathoracic ganglion. The respiratory rhythm generator also extends more anteriorly within the ventral nerve cord than the metathoracic ganglion. Two interneurones influencing the respiratory rhythm send their axons from the first fused abdominal ganglion into the meta- and mesothoracic ganglia. One of these directly excited a mesothoracic intemeurone which also influenced the respiratory rhythm when injected with current. In the suboesophageal ganglion another intemeurone was found which, although capable of resetting the respiratory rhythm, was not alway active during respiration. We conclude that the respiratory rhythm generator is distributed over abdominal, thoracic and suboesophageal ganglia. At least one part of the respiratory rhythm generator (in the suboesophageal ganglion) is not always active and can be recruited during vigorous respiration. Thus the number of active components in the respiratory rhythm generator is variable and additional elements can be recruited depending on the behavioural situation.
Strontium is Required for Statolith Development and Thus Normal Swimming Behaviour of Hatchling Cephalopods
Authors: Hanlon Roger T. , Bidwell Joseph P. , Tait Richard
Published: April 2021

When cephalopod eggs were incubated in artificial sea water it was found that they sometimes resulted in hatchlings with defects of the statocyst suprastructure, leading to the severe behavioural defect of uncontrolled swimming. Experiments in defined media (seven basic salts mixed in deionized water) with seven species of cephalopods demonstrated clearly that there is 100 % normal development of the aragonite statoliths when strontium levels were 8 mg l−1. Conversely, statoliths did not develop when strontium was absent. In cuttlefish, the growth of the cuttlebone was also affected adversely when strontium was absent. In mariculture production tanks, supplementing commercial artificial sea water with strontium to normal levels of 8 mg l−1 almost eliminated the occurrence of abnormal hatchlings. Circumstantial evidence indicates that there is a critical window in development during which strontium is required for normal development. The role of strontium in biomineralization during embryogenesis is unknown, but it appears to be important in the Mollusca.
Regional Differences in Cuticular Permeability in the Desert Cicada Diceroprocta Apache: Implications for Evaporative Cooling
Authors: Hadley Neil F. , Toolson Eric C. , Quinlan Michael C.
Published: April 2021

The cuticular permeability of the desert cicada Diceroprocta apache was measured in vivo from three regions of the dorsal surface: (1) the midline of the thorax (= dorsal thorax), a region that contains large pores (7–8 μm in diameter) located in a central tract; (2) the lateral thorax, a region in which large pores are absent, and (3) the midline of the abdomen, a region in which large pores are uniformly distributed over the surface. Transcuticular water flux rates were similar for all three areas at 27·0°C; however, at 41·5°C rates increased sharply for the dorsal thorax and abdomen, with tracings showing numerous irregular peaks that represent cycles of water extrusion. Transcuticular water flux for the lateral thorax, in contrast, was relatively unaffected by the temperature increase and the tracings remained relatively flat. Death of the animal at the higher temperature resulted in a significant decrease in water loss rates and a loss of the cycling pattern in both the dorsal thorax and abdomen, whereas water loss through the lateral thorax did not change. The active extrusion of water begins at 39·2–39·3°C in both male and female cicadas. Our findings confirm that the large pores are the routes by which water reaches the surface and that the temperature at which this active extrusion of water begins corresponds to the point where cicadas must seek milder microclimates to prevent body temperature from reaching lethal levels.
The Relationship Between Diving Activity and Oxygen Storage Capacity in the Tufted Duck (Aythya Fuligula)
Authors: Stephenson R. , Turner D. L. , Butler P. J.
Published: April 2021

For a period of 6 months, a group of eight tufted ducks (‘control’ ducks) were kept on a shallow outdoor pond and performed short dives to obtain food (maximum depth, 0·;65 m; observed mean duration, 10·9 ± 0·54 s). At the same time, a group of seven tufted ducks (‘dive-trained’ ducks) were kept on an adjacent deeper and partly covered pond, and performed ‘extended’ dives under the surface mesh in order to feed (maximum distance to food, 10m; observed mean dive distance, 6·0 ± 0·25 m; observed mean duration, 24·8 ± 0·58 s). At the end of this time, the calculated total usable oxygen store was approximately the same in control and dive-trained ducks (44 and 42 mlO2STPD kg−1, respectively), although the relative quantities of usable oxygen in each of the three main storage sites (respiratory system, blood and skeletal muscle) differed between groups.

The end-expiratory lung/air sac volume was found to be significantly smaller (P<0·01) in the dive-trained ducks (165 ml BTPs kg−1) than in the control ducks (232 ml BTPs kg−1). The dive-trained ducks, however, had a significantly greater (P<0·01) blood volume (141 ml kg−1) than the control ducks (107ml kg−1), although the blood oxygen capacity and several haematological indices (measured haemoglobin content, red blood cell count and haematocrit, and calculated mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration) were statistically the same in both groups. Mean corpuscular volume was significantly greater (P<0·05) in the dive-trained ducks. The myoglobin content of the myocardium was the same in both groups. The pectoralis muscle and the locomotory leg muscles, however, contained significantly higher concentrations of myoglobin in the dive-trained ducks than in the control ducks (pectoralis, P<0·05; lateral gastrocnemius and semitendinosus, P<0·01).

It is suggested that the anatomical adaptations which occur in response to chronic increases in diving activity may increase the aerobic diving capacity of the tufted duck by effecting a decrease in buoyancy (reduced end-expiratory lung/air sac volume) and an increase in blood oxygen storage capacity (hypervolaemia). Locomotory muscle function may be maintained in the face of decreasing oxygen delivery during extended dives by means of increased myoglobin content after dive-training.
Efficiency of Rat Medial Gastrocnemius Muscle in Contractions with and Without an Active Prestretch
Authors: Haan A. De , Van Ingen Schenau G. J. , Ettema G. J. , Huijing P. A. , Lodder M. A.
Published: April 2021

The efficiency of positive work was measured for rat medial gastrocnemius muscle at 25°C during repeated contractions. Six muscles were stimulated to perform concentric contractions preceded by an active prestretch (PS contractions) and six muscles made to give concentric contractions from an isometric state (PI contractions). Both lengthening and shortening of the muscles (distance: 6 mm) occurred at a constant velocity of 20 mms−1 (1·5 fibre lengths s−1). Stimulation was started 150 ms prior to the onset of concentric contraction for both types of contraction. For the PS contractions this meant that the active state was developed during the last 2·4 mm of the lengthening.

Energy consumption (calculated from high-energy phosphate consumption) appeared to be equal for both types of contraction, although positive work output was 39·4% higher in the PS contractions than in the PI contractions. The efficiency of positive work was 36·8 ± 3·5 % in the PS contractions and 26 ± 2·0 % in the PI contractions. In contrast to results of previous studies, the positive work done by the muscle in the PS contractions was much larger than the negative work done on the muscle during stretch owing to the applied stimulation protocol which was intended to simulate in vivo conditions during running. The efficiency of positive work in the PS contractions is too low to explain the efficiencies of 40–70 % reported for human and animal running.
A Reappraisal of the Oil-Gap Technique for the Measurement of Transtubular Potentials in Insect Epithelia
Authors: Isaacson Leon , Nicolson Sue
Published: April 2021

Transtubular potentials of insect Malpighian tubules and salivary glands are commonly measured in unperfused tubules in which the two ends are separated by means of an insulating oil gap. The validity of this method has been examined, using Malpighian tubules of a tenebrionid beetle, Onymacris plana. The measured interelectrode potential was found to depend not only on the transtubular potential but also on potentials within the oil gap and at the open end of the tubule, and upon the core resistance, the length constant and a small but finite electrical leak beneath the insulating oil. In perfused tubules of O. plana, the apparent transtubular potential recorded at the collecting end (analogous to the oil gap) was indistinguishable from that previously measured with the oil-gap technique. However, it was invariably lower than that recorded by an intraluminal pipette. The results demonstrate that the interelectrode potential observed with the oil-gap technique is a poor measure of the true transtubular potential.
Peripheral Neurosecretory Cells of Insects Contain a Neuropeptide with Bursicon-Like Activity
Authors: Garcia-Scheible Isabel , Honegger Hans-Willi
Published: April 2021

In insects, neurosecretory cells have been found not only within ganglia of the central and stomatogastric nervous system, but also in the peripheral nerves (Fifield & Finlayson, 1978; Wasserman, 1985; Baudry-Partiaoglou, 1987). These peripheral neurones and their processes along peripheral nerves contain electron-dense granules and stain with various dyes for neurosecretory cells, suggesting that they produce, store and probably release neurosecretory material. The nature of this material, however, is unknown. Only the results of Raabe (1986), showing that some abdominal peripheral neurosecretory cells of three insects are glucagonimmunoreactive, have suggested that such cells are peptidergic. We demonstrate in this study that a group of peripheral neurosecretory cells in crickets contains such a peptide. Moreover, we are able to suggest a function for this peptide and thus for an identified set of peripheral neurosecretory neurones.
A Simple and Low-Cost Illumination System for in vivo Fluorescent Visualization of Neurones
Authors: Büschges A. , Koch U. T. , Breutel G.
Published: April 2021

The use of fluorescent dyes for staining neurones has become very common since the introduction of Lucifer Yellow (Stewart, 1978) because it permits high-luminance stainings, for detailed structural analysis, with a minimum of filling time. Lucifer Yellow has been used in a variety of techniques in neurophysiology: in vitro visualization (Stewart, 1978); killing of neurones or parts of neurones (e.g. Miller & Selverston, 1979; Miller & Jacobs, 1984); and in vivo visualization (e.g. Reichert & Krenz, 1986; Kater & Hadley, 1982). We describe a new system for in vivo and in vitro visualization. It can be used with a standard dissecting microscope, features a very simple optical design and costs much less than other systems used previously.
Effects of Octopamine on Calcium Action Potentials in Insect Oocytes
Authors: O’donnell M. J. , Singh B.
Published: April 2021

Our experiments show that octopamine receptors are present on the developing follicles of an insect, Rhodniusprolixus. Application of D,L-octopamine decreased the duration and overshoot of calcium-dependent action potentials (APs), and increased the intrafollicular concentration of cyclic AMP. The threshold concentration of D,L-octopamine for the reduction in electrical excitability was between 1 and 5×10−7moll−1, and maximal effects of a 40–50% reduction in AP overshoot and duration were apparent at 10−4moll−1. At concentrations above 10−5moll−1, a small (<10%) hyperpolarization of the resting potential was also apparent. Effects of D,L-octopamine on oocyte excitability were independent of these small shifts in resting potential.

Current injection experiments, in which calcium entry was blocked by cobalt, demonstrated that D,L-octopamine reduced membrane resistance at both hyperpolarizing and depolarizing potentials. Octopamine did not affect the maximum rate of rise of the AP, dV/dtmax, which is an indicator of inward calcium current. It is suggested that octopamine may mediate its effects on excitability through an increase in a voltage-dependent potassium conductance.

Application of other phenolamines indicated a rank order of potency of D,L-octopamine > D,L-synephrine > tyramine. The α-adrenergic agonists clonidine, naphazoline and tolazoline were without significant effect at 10−5–10−3moll−1. Reduction of excitability by D,L-octopamine was effectively blocked by phentol-amine and metoclopramide. Yohimbine and gramine were less effective as antagonists. Possible functions of octopamine receptors in insect follicles are discussed.
Renal Responses to Continuous and Short-Pulse Infusion of Arginine Vasotocin in the Toad Bufo Marinus
Authors: Toews Daniel P. , Mallet Maryse , Maclatchy Laura
Published: April 2021

Chronically catheterized specimens of the toad Bufo marinus (L.) were given single bolus injections, periodic bolus injections, and continuous infusions (via peristaltic pump) of the neuropeptide arginine vasotocin (AVT). Urine flow and glomerular filtration rates (GFR) were monitored to quantify the antidiuretic response of the toad to AVT under these conditions. The response to single bolus injections was dissipated after 1 h, despite the continued presence of AVT, whereas continuous infusion of AVT at levels as high as 100 ng kg−1 was ineffective in lowering flow rates, suggesting that pulsatile increases in the hormone might be required to effect a more prolonged response. In toads which were ‘primed’ with AVT via continuous infusion with the pump, additional pulses of AVT were able to lower flow rates for 1 h, with sensitivity to the hormone decreasing with an increase in primed concentration of AVT. Pulses of AVT given to unprimed toads significantly lowered flow for over 2h. This study is the first to show that phasic bursts of AVT are more effective in regulating the renal response of the toad than are continuous, nonpulsatile infusions.
Selective Utilization of Serum Vitamin A for Visual Pigment Synthesis
Authors: Tsin Andrew T. C. , Gentles Suzanne N. , Castillo Elizabeth A.
Published: April 2021

Two groups of goldfish (Carassius auratus) were subjected to light and temperature conditions known to promote a contrast in their scotopic visual pigment compositions. After 3 weeks, the porphyropsin/rhodopsin ratio in the neuroretina of these goldfish ranged from 99% porphyropsin in one group to 59% in the other. Samples of blood, liver and retinal pigment epithelium (RPE) were also removed from these animals and analysed by high-performance liquid chromatography (HPLC) for vitamin A composition. There was consistently more vitamin A2 than vitamin Aj (over 50% vitamin A2) in both vitamin A alcohol and vitamin A esters extracted from the liver and the RPE. In contrast, only 30% of all vitamin A extracted from the blood was vitamin A2. These observations suggest that it is mainly vitamin A1 that is transported in the blood, whereas vitamin A2 is selectively retained in the liver and in the RPE and used to form porphyropsin in the eye.
Aminergic and Peptidergic Modulation of Motor Function at an Identified Neuromuscular Junction in Helisoma
Authors: Zoran Mark J. , Haydon Philip G. , Matthews Paul J.
Published: April 2021

Electrophysiological studies suggest that motoneurone B19 in the buccal ganglia of Helisoma makes monosynaptic, cholinergic connections with the supralateral radular tensor (SLT) muscle of the buccal mass. Serotonin (5-HT) and small cardioactive peptide B (SCPB) were found to have peripheral modulatory effects on this motor pathway that are consistent with their previously described central facilita tory effects. Both neurotransmitters, when applied exogenously (10−6moll−1) to isolated buccal ganglion-buccal muscle preparations, potentiated the magnitude of motoneurone B19-evoked muscle contractions (6·3 and 2·7 times, respectively) without affecting excitatory junctional potential (EJP) amplitudes. When applied to single dissociated SLT muscle fibres in cell culture, these modulators had similar effects on acetylcholine (ACh)-evoked muscle fibre shortening, demonstrating that these neuromodulators exert direct actions on the muscle cells.

The cardioactive peptide FMRFamide (10−6moll−1), although slightly potentiating muscle contractions in reduced neuromuscular preparations, significantly decreased both ACh-evoked muscle fibre shortening and depolarizing potentials in cultured SLTmuscle cells. The differential effects of FMRFamide may, in part, be due to the elimination of interactive effects between multiple neurotransmitters that might exist in semi-intact preparations and in vivo.

These results demonstrate that 5-HT, SCPB and FMRFamide in Helisoma can directly modulate the peripheral muscle targets of buccal motoneurones involved in the generation of cyclical feeding behaviour.
Desiccation Tolerance and Water-Retentive Mechanisms in Tardigrades
Authors: Wright Jonathan C.
Published: April 2021

Tardigrades entering a state of anhydrobiosis (cryptobiosis) show considerable interspecific variation in desiccation tolerance, lower lethal humidities for initial desiccation ranging from 78 to 53%. Species most tolerant of rapid initial drying also show the most rapid acquisition of tolerance to low humidities (25–31% ) following drying in high humidity.

Surface area reduction during tun formation shows a significant positive regression against desiccation tolerance in the Eutardigrada. The most desiccation-tolerant species thus infold the largest areas of cuticle. By comparison, the heterotardigrade Echiniscus testudo shows a very poor capacity for surface area reduction. The thick dorsal plates may restrict cuticle intucking in this species.

When hydrated tardigrades are desiccated in 80% relative humidity they show a characteristic profile of mass loss, dehydrating rapidly in the first few minutes and then showing an abrupt reduction in transpiration (the ‘permeability slump’). This applies to living animals, which form tuns when desiccated, and to dead animals remaining extended. The permeability slump is not, therefore, a metabolic phenomenon and is not related to tun formation. Subsequent transpiration rates are very low and decline exponentially. The permeability slump allows animals to retain considerable amounts of internal water when desiccated, although less water is retained if the desiccation rate is increased. This may determine upper tolerable desiccation rates if a certain minimum quantity of water is required for the metabolic synthesis of membrane protectants. A significant positive regression between water retention and desiccation tolerance supports this hypothesis.
Acetylcholine-Activated Ion Channels In Embryonic Cockroach Neurones Growing In Culture
Authors: Beadle David J. , Horseman G. , Pichon Y. , Amar M. , Shimahara T.
Published: April 2021

Application of acetylcholine and carbamylcholine to cultured cockroach neurones held under whole-cell voltage-clamp conditions evoked an inward current that was accompanied by an increase in current noise. Fluctuation analysis of the noise revealed the existence of two Lorentzian components in acetylcholine, of comer frequencies 10 ± 0·6 Hz and 116 ± 9 Hz, and one Lorentzian component in carbamylcholine, of corner frequency 35 ± 13 Hz. Single-channel analysis of the unitary currents evoked by acetylcholine or carbamylcholine in neurones held in the cell-attached mode of the patch-clamp technique revealed the presence of two categories of channel events. The large events had mean currents of 4·77 pA with acetylcholine and 5·09 pA with carbamylcholine, and the small events 1·92 pA (acetylcholine) and l·72pA (carbamylcholine) for a hyperpolarization of 60 mV. The reversal potentials for these currents relative to the resting potential were estimated to be −70 mV for acetylcholine and −68 mV for carbamylcholine, and the conductance values calculated from the l/V curves were 37 pS (large) and 19 pS (small) for acetylcholine and 52 pS (large) and 15 pS (small) for carbamylcholine. It is concluded that embryonic cockroach neurones growing in vitro possess two populations of acetylcholine-activated ion channels, and the possibility that one of these represents an embryonic receptor and the other an adult receptor is discussed.