bluuebunny/crossref_metadata_2025 huggingface dataset:
‘Paradoxical Driving’ of Walking Activity in Locusts
Authors: Moorhouse J. E. , Fosbrooke I. H. M. , Kennedy J. S.
Published: April 2021

Gregarious fifth-instar larvae of Locusta migratoria migratorioides were placed singly on a counterbalanced, recording treadmill providing precise measurements of (i) walking bout length, (ii) non-walking bout length, (iii) walking speed and (iv) distance walked, over periods of hours.

Under constant conditions in light the walking activity was often inter-rupted but gradually built up to a high intensity which was then sustained for 1−2 h before finally declining; there were orderly relations between the measured behavioural components. In continuous darkness walking activity was less interrupted but less intense and quickly declined; there were less orderly relations between the components.

Under alternating 10 min periods of light and darkness the relations between the behavioural components were again more orderly in the light than the dark. However, walking activity was sharply depressed in these short light periods but was promptly resumed in each subsequent dark period and grew stronger as the fight–dark alternation continued.

These diverse and at first sight paradoxical results are all consistent with the principle of post-inhibitory rebound (‘antagonistic induction’). This type of behavioural after-effect, acting on different time scales, is exemplified by the surge of walking observed in the dark on the release of the experimentally applied inhibition of walking by light, as well as by the build-up and sustained walking in continuous light (‘paradoxical driving’).
Patterns of Water and Solute Regulation in the Muscle Fibres of Osmoconforming Marine Decapod Crustaceans
Authors: Freel Robert W.
Published: April 2021

The patterns of myoplasmic water and solute regulation were examined in several species of marine decapod crustaceans acclimated to various salinities. Three osmoconformers (Callianassa californiensis, Cancer anten-narius, Emerita analoga) and one weak osmoregulator (Pachygrapsus crassipes) were studied. Although haemolymph water and solute activities varied with adaptational salinity in these species, regulation of cell water content was apparent in all but 25 % s.w. acclimated Pachygrapsus. Cell water regulation was correlated with the regulation of ninhydrin-positive solutes. An estimate of the extent of the regulation was achieved by comparing the observed cell hydration changes to that predicted for an ideal osmometer and to that of a perfect volume regulator. It was concluded that the extent of cell volume regulation was variable and incomplete, particularly in dilute salinities. Net losses of myoplasmic sodium, chloride, and ninhydrin-positive nitrogen were observed in animals acclimated to dilute sea water, while net gains of these solutes were noted in crabs acclimated to concentrated sea water. In contrast, the amounts of cell potassium and calcium plus magnesium were relatively constant fractions of the cell dry weight at any salinity. A simple mechanism, based upon Donnan considerations, is sufficient to account for the constancy of myoplasmic potassium and the variability of cell chloride with changing extracellular osmolarity.
Transmembrane Activity Gradients of K and Cl in the Muscle Fibres of Osmoconforming Marine Decapod Crustaceans
Authors: Freel Robert W.
Published: April 2021

The resting membrane potentials (Em) and the transmembrane activity gradients for K and Cl were measured in the muscle fibres of osmoconforming (Callianassa and Cancer) and weakly osmoregulating (Pachygrapsus) marine crustaceans acclimated to various osmotic conditions. The muscle membranes of sea water acclimated crabs behave as good K electrodes. However, a slight contribution of Na to the resting potential was demonstrated in all species. The ratio PNa/PK, was about 0·1 Equilibrium potentials (measured with ion-selective microelectrodes) for Cl were equal to Em, while EK was always more negative than Em as a result of the slight Na contribution. Acclimation to dilute or concentrated sea water had little effect on the K electrode properties or Na permeabilities of these fibres. The muscle fibres were depolarized in crabs acclimated to concentrated sea water and were hyperpolarized in crabs adapted to dilute sea water. These changes resulted solely from alterations in (aK)i/(aK)O which were in turn brought about by changes in cellular and haemolymph hydration. Since the Na contribution to Em was so small in all conditions, it was concluded that the distributions of K and Cl are best considered in terms of Donnan equilibria, and that the cellular K and Cl adjustments observed during salinity adaptation reflect the passive re-establishment of new equilibrium distributions for these ions.
Ventilation in An Aquatic and A Terrestrial Chelonian Reptile
Authors: Glass Imogens , Burggren Warren W. , Johansen Kjell
Published: April 2021

Periods of breath-holding are interrupted by episodes of continuous breathing in the aquatic turtle Pelomedusa subrufa, whereas single breaths and short periods of breath-holding alternate in the terrestrial tortoise Testudo pardalis. This implies that partial pressures of O2 and CO2 in expired air are stable in Testudo in contrast to cyclic fluctuations in Pelo-medusa. In spite of this, air convection requirements (, ml BTPS/ml STPD) are not significantly different for the two species (25·4 in Testudo, 27·3 in Pelomedusa), and differences in weight-specific ventilation between the species can only be ascribed to a difference in mean body weight. The end-tidal in Pelomedusa (mean 15·2 mmHg) is lower than in Testudo (mean 24·7 mmHg), which reflects aquatic CO2 elimination in Pelomedusa. In Testudo, the time course of ventilation correlates with the time course of increase of end-tidal during CO2 breathing, but no simple relationship is evident between ventilation and blood in Pelomedusa. In both species tidal volume as well as respiratory frequency increase approximately in proportion to the end-tidal , although the response to 6% CO2 breathing could be less than expected from extrapolation of the responses to 2 and 4% CO2. Both species also increase ventilation during hypoxia, but hyperoxia depresses ventilation.
Giant Nerve Fibre Activity in Intact, Freely Moving Earthworms
Authors: Drewes C. D. , Landa K. B. , McFall J. L.
Published: April 2021

An approach is described for recording and characterizing giant nerve fibre activity in intact, freely moving earthworms. Medial giant fibre (MGF) spikes were conducted in an anterior-posterior direction at a mean rate of 32·2 m/s; lateral giant fibre (LGF) spikes were conducted in a posterior-anterior direction at a mean rate of 12·6 m/s. Rates of giant fibre spike conduction and maximal frequencies of firing (up to 500/s) in intact animals were higher than values previously reported in isolated preparations. MGF spikes were followed 1:1 by presumed giant motor axon spikes and facilitating muscle potentials. Single MGF or LGF spikes evoked by applying tactile stimulation were not accompanied by longitudinal contraction, but a series of two or more MGF spikes or three or more LGF spikes were accompanied by such contractions. MGF and LGF spikes occurred infrequently during locomotory movements in the absence of any experimenter-applied stimulation, suggesting that sensory inputs associated with normal locomotion over an irregular substrate are sufficient to excite giant fibres.
The Permeability of the Skin of the Aquatic Anuran Xenopus Laevis (Pipidae)
Authors: Yorio T. , Bentley P. J.
Published: April 2021

The undirectional transcutaneous fluxes of Na, Cl, water and urea were measured, in vitro, in the pipoid anuran Xenopus laevis. An active uptake (outside to inside) of Na was observed but Cl movements appeared to be passive. The effluxes of Na and Cl were low compared to those measured in other species of amphibians. The active Na transport was less than that of more terrestrial species and, although it could be stimulated by vasotocin, aldosterone was ineffective. The permeability of the skin to water was also low and although it was increased in the presence of vasotocin the magnitude of the response was much less than seen in more terrestrial anurans. The skin was permeable to urea but the movement of this solute was not remarkable when compared to that in other amphibians. These properties of the skin are discussed in relation to the animal’s aquatic manner of life.
Propagation of Action Potentials Through Electrotonic Junctions in the Salivary Glands of the Pulmonate Mollusc, Helisoma Trivolvis
Authors: Kater S. B. , Rued J. R. , Murphy A. D.
Published: April 2021

The secretory cells of the salivary glands of the snail, Helisoma trivolvis, exhibit regenerative, overshooting action potentials whose amplitude may exceed 100 mV. The salivary glands consist of paired, tubular, epithelial structures with acinar outpocketings. The secretory cells display extensive electrical coupling which allows action potentials to propagate along the glandular epithelium.

Salivary glands from nine genera of gastropod molluscs were examined. The genera comprised one opisthobranch, one prosobranch, two terrestrial pulmonate slugs, one terrestrial pulmonate snail, and four aquatic pulmonate snails. Action potentials were recorded from all of the examined glands, suggesting that the production of action potentials in salivary glands is a general phenomenon among gastropods.
Some Responses of the Electric Ray (Torpedo Marmorata) to Low Ambient Oxygen Tensions
Authors: Hughes G. M. , Johnston I. A.
Published: April 2021

Blood samples were taken during prolonged hypoxia experiments in which the inspired water oxygen tension was less than 10 mmHg. The oxygen tension of the post-branchial blood was about 5 mmHg and its pH shows a significant lowering from normoxic levels. The decrease in blood pH is correlated with increases in levels of lactate and pyruvate. The lactate/pyruvate ratio increases during hypoxia. An increase in blood succinate was also found, and strongly suggests the accumulation of multiple anaerobic end-products within the tissues. Recovery to normoxic levels of succinate takes place almost immediately following the restart of ventilation whereas the decrease in lactate concentration is slower. It is concluded that these adaptations may be related to the habitat of the fish at low tide in pools where the may fall very markedly.
The Distribution of Blood Flow in the Gills of fish: Application of A New Technique to Rainbow Trout (Salmo Gairdneri)
Authors: Booth John H.
Published: April 2021

Injecting vitally stained blood cells into the ventral aorta of unrestrained cannulated fish, and rapid freezing in liquid nitrogen, provided a method of investigating blood flow patterns in the gills. Rainbow trout in air-saturated water perfused an average of 58% of the secondary lamellae of the gills. Perfusion of the filamental central compartment was insignificant indicating that the effects of any non-respiratory shunting would be unimportant. If the functional surface area of the gills is variable, it seems likely that this would be accomplished through lamellar recruitment. There was no evidence that pillar cell contraction affected lamellar perfusion. There was preferential perfusion of lamellae near the base of the filaments, and of filaments near the dorsal end of the gill arches.
Respiratory and Circulatory Changes in the Lobster (Homarus Vulgaris) During Long Term Exposure to Moderate Hypoxia
Authors: Butler P. J. , Taylor E. W. , McMahon B. R.
Published: April 2021

Within a few hours of the lobsters being placed in the experimental chamber in normoxic water (, 130−135 mmHg), their heart rate, oxygen uptake and ventilation volume were relatively high. The scaphog-nathites were simultaneously active on both sides (bilateral ventilation) for 50% of the time, active on one side only (unilateral ventilation) for 32% of the time and simultaneously inactive (respiratory pause) for 18% of the time. Percentage extraction of O2 (% Ext.) was relatively low. 48 h after having been set up, heart rate, and had decreased significantly, % Ext. had increased and bilateral ventilation occupied 25% of the time. Heart rate was low and the beat irregular. Upon subsequent exposure to hypoxia (, 50−55 mmHg), fell, there was initial hyperventilation, bilateral ventilation for 89 % of the time, heart beat was more regular but did not change significantly. An initial increase in pHa caused the O2 affinity of the Hcy to rise. After 72 h exposure to hypoxia and pHa had declined, but was still higher than at the end of the period of normoxia. Blood lactate, and % Ext. were not significantly different from the values recorded after 48 h in normoxic water. Upon return to normoxic water, and the time the animals spent ventilating both branchial chambers fell, but increased. It is concluded that for settled lobsters, could be maintained during moderate hypoxia by increasing , maintaining a regular heart beat, and at least initially by increasing the O2 affinity of the Hcy.
Distributions of Nerve and Muscle Fibre Types in Locust Jumping Muscle
Authors: Hoyle Graham
Published: April 2021

Muscle fibres of the locust extensor tibiae (jumping muscle) were examined by interference microscopy and by electron microscopy. The electrical responses of single fibres and the mechanical responses of bundles or selected regions to the nerve fibres were examined. Four axons innervate the muscle: fast (FETi), slow (SETi), common inhibitor (CI) and dorsal unpaired median (DUMETi). Their distributions were examined by combined electrophysiological tracing and EM sectioning.

The mean diameter of muscle fibres in different regions varies from 40 to 140 μm and is related to the local leg thickness rather than muscle fibre type. The fine structure of a fibre is related to its innervation. Fibres innervated by FETi but not SETi are of fast type ultrastructurally. Fibres innervated by SETi but not by FETi are of slow type ultrastructurally. Fibres innervated by both axons are generally intermediate between the extremes though more nearly of fast type than slow. Distal slow muscle fibres have much slower relaxation rates than do proximal ones. The most proximal bundles are of mixed muscle fibre type. There is an abrupt transition from a mixed population to homogeneous fast type, in the muscle units immediately distal to the most proximal bundles. This transition is associated with the presence of DUMETi terminals on some of the fibres distal to the transition point. There are no SETi endings on these same fibres. Fibres innervated by both SETi and FETi are scattered throughout the leg, but are commonest in the dorsal bundles. The percentage of these increases progressively passing distally. The most distal muscle fibres are innervated by SETi but not by FETi.

It is concluded that different regions of the muscle will play different roles functionally since they are differentially sensitive to the pattern of SETi discharge.
Intersegmental Reflex Coordination by A Single Joint Receptor Organ (Cb) in Rock Lobster Walking Legs
Authors: Clarac F. , Vedel J. P. , Bush B. M. H.
Published: April 2021

In the decapod Crustacea, Palinurus vulgaris and Jasus lalandii, the reflex influences of one particular proprioceptor organ, the coxo-basal chordotonal organ (CB), on all the muscles operating the proximal and distal joints of the same leg, have been analysed. The distal end of CB was clamped in fine forceps mounted on a servo-controlled stretcher, and CB length changes of 2 mm were applied. Motor unit activity of the different muscles was recorded as electromyograms (EMGs).

Two types of proprioceptive reflex evoked by CB length changes have been investigated: (a) resistance reflexes of the two levator and two depressor muscles of the same leg segment, the coxopodite, i.e. ‘intrasegmental reflexes’, (b) ‘intersegmental reflexes’ induced in the muscles operating the proximal (T-C) joint of the same leg, and in all eight muscles of the limb segments distal to CB. Both levator muscles respond reflexly to imposed CB stretch (which normally occurs with limb ‘depression’), while both depressors respond during CB shortening (or passive ‘elevation’ of the leg). Intersegmentally, CB stretch reflexly activates the M-C extensor muscle, and sometimes facilitates the T-C remotor and C-P bender muscles. Shortening of the single CB organ of a leg excites one or two tonic motor units of the T-C promotor and M-C flexor muscles, and also facilitates the remotor, I-M reductor, and the single stretcher-opener excitatory motoneurone. Some of these muscles, particularly the M-C flexor and extensor muscles, are also influenced intersegmentally by the resting length of CB, usually but not invariably in the same direction as for the corresponding dynamic reflexes.

The role of the CB chordotonal organ is discussed, with particular consideration of its intersegmental reflex influence on the posture of the entire leg, and on the more complex motor behaviour of locomotion, where it may be specially significant in coordination of the limb in lateral walking. A complex picture of both tonic and dynamic, intra- and intersegmental reflex regulation of the positions and movements of the limb segments, thus emerges.
Intersegmental Reflex Actions from A Joint Sensory Organ (Cb) to A Muscle Receptor (Mco) In Decapod Crustacean Limbs
Authors: Bush B. M. H. , Vedel J. P. , Clarac F.
Published: April 2021

In the walking legs of decapod crustaceans, intersegmental reflex actions originate from various joint proprioceptors. The activity of the ‘accessory flexor’ (AF) muscle, which with the myochordotonal organ (MCO) constitutes a muscle proprioceptor for the mero-carpopodite (M-C) joint, is modulated by the sensory discharge of a joint receptor (CB chordotonal organ) for the more proximal, coxo-basal (C-B) joint. Selective mechanical stimulation of the CB organ also reflexly modifies the motor activities of the main M-C flexor and extensor muscles (recorded as EMGs).

Dynamic CB stretch (as would occur during a dorso-ventral C-B movement - i.e. ‘depression’ of the limb) stimulates motor discharge to the M-C extensor muscle, while dynamic release of CB (as during a ventrodorsal C-B movement - or leg ‘elevation ‘) excites the accessory flexor as well as the main flexor muscle. Successive M-C muscle responses to repetitive sinusoidal changes of CB length differ quantitatively according to the direction (stretch or release) of the first CB movement, in some cases increasing but more commonly ‘adapting’ with repetition. Reflex discharge frequencies of the extensor, flexor and accessory flexor motoneurones increase with velocity of CB movement. Eye illumination, and spontaneous or other sources of increased central excitability, generally increase the CB reflex drive to the flexor and accessory flexor muscles and, in parallel, decrease the reflex action on the extensor muscle.

The results are discussed in terms of the role of proprioceptive reflexes in intersegmental co-ordination of the leg joints. In particular the significance of the reflex regulation of the myochordotonal receptors, and thereby the gain of the M-C resistance reflexes, is considered in the light of the observed ‘co-activation’ of main flexor and receptor muscle motoneurones.
Heat Transfer in Dragonflies: ‘Fliers’ and ‘Perchers’
Authors: Heinrich Bernd , Casey Timothy M.
Published: April 2021

Both ‘perchers’ (Libellula saturata) and ‘fliers’ (Anax junius and Aeshna multicolor) remained active in the field in sunshine at air temperatures from at least 24 °C to 36 °C. The percher basked at low air temperatures and regulated exogenous heat input by postural adjustments. It markedly reduced flight activity at high air temperatures but flew nearly continuously at intermediate temperatures. In direct sunlight, the abdomen of L. saturata heated faster than the thorax, but this percher exhibited little or no capacity to transfer heat between abdomen and thorax. In contrast, the fliers gave no evidence of behavioural thermoregulation, but both showed impressive capacities for heat transfer from thorax to abdomen. When heated exogenously on the thorax the temperature of the entire abdomen of both fliers increased uniformly, but with endogenous heat production during pre-flight warm-up there was only a slight temperature increase near the anterior portion of the abdomen. Removal of abdominal air sacs or immobilizing the abdomen with wax to prevent all abdominal pumping did not significantly alter the capacity to transfer heat from thorax to abdomen. Ligation of the heart anywhere along the length of the abdomen abolished heat transfer. Given sufficient exogenous heat input, fliers that can regulate their thoracic temperature by transferring the excess heat to the abdomen died in about 2 min due to overheating when the heart was occluded. Under our experimental conditions the fliers appeared to thermoregulate exclusively via a control of blood circulation.
Sources of Variation in the Output of Locust Spiracular Motoneurones Receiving Common Synaptic Driving
Authors: Burrows Malcolm
Published: April 2021

The closer muscles of the left and the right spiracles of a thoracic segment are both innervated by two motoneurones, which spike in a variety of patterns during expiration. This paper seeks to explain the origin of these patterns. No direct coupling between the two motoneurones is revealed. In an isolated thoracic ganglion both motoneurones spike at different frequencies with no tendency for their spikes to become synchronized. The two closer motoneurones in one segment receive common, patterned depolarizing synaptic potentials during expiration caused by interneurones relaying information from the metathoracic ganglion. The closer motoneurones of all the thoracic segments receive the same pattern of synaptic potentials from these interneurones. Despite this, the spiracles of one segment may remain shut while those on other segments continue to open and close rhythmically. The interplay between common synaptic driving, the threshold of the motoneurones for spike initiation, and the tendency for a motoneurone to spike at a particular frequency even in the absence of interneuronal driving, explains the various patterns of spikes during expiration. Common synaptic driving imposes the same basic pattern of commands on all the motoneurones, but the individual motoneurones determine the final pattern of motor spikes. To be effective in producing a patterned output, an input pattern must operate within narrow limits on either side of the threshold of the motoneurone. If the depolarization is too large, a high frequency of unpatterned spikes will result; if too small, then either there will be no output or a low frequency of spikes will result whose patterning will be affected by other inputs.
Fast-Start Performance and Body form In Seven Species of Teleost Fish
Authors: Webb P. W.
Published: April 2021

Fast-start kinematics and performance were determined for Etheostoma caeruleum, Cottus cognatus, Notropis cornutus, Lepomis macrochirus, Perca flavescens, Salmo gairdneri and a hybrid Esox sp. at an acclimation and test temperature of 15 °C. Normal three-stage kinematic patterns were observed for all species. Fast-start movements were similar in all species, except Lepomis, which had slightly higher amplitudes than expected for its length. The duration of kinematic stages was a major variable among the seven species but was a linear function of length. Acceleration rates were not functions of size. Maximum acceleration rates ranged from 22·7 to 39·5 m. s−2 with mean rates from 6·1 to 12·3 m.s−2, averaged to the completion of kinematic stage 2. Maximum velocity and distance covered in each fast-start stage varied among species but were related to length. Fast-start performance depended primarily on compromise between muscle mass as a percentage of body mass, and lateral body and fin profile. Optimal profiles provide large depth distant from the centre of mass to maximize thrust, and anterior depth enhancement to minimize recoil. The body form of Lepomis is considered optimal for multiple swimming modes.
Rebound Resilience of Tendons in the Feet of Sheep (Ovis Aries)
Authors: Cuming W. G. , Alexander R. McN. , Jayes A. S.
Published: April 2021

The interosseous muscle of the fore foot of the sheep is multipennate, with large tendons but extremely short muscle fibres. It is believed to save energy in locomotion by elastic storage in its tendons and its sheath. Its rebound resilience (at 5−7 Hz and 20−37 °C) is about 0·62.
Physiological Discontinuity in An Epithelium with An Apparently Uniform Structure
Authors: Maddrell S. H. P.
Published: April 2021

The lower Malpighian tubule of Rhodnius is made up of cells of apparently uniform structure. Functionally, however, this length of the Malpighian tubule consists of two distinct regions. The upper region is osmotically very permeable and plays no part in reabsorbing KC1 from the primary excretory fluid. By contrast, the lowermost 30% of the length of the lower tubule is osmotically impermeable and when stimulated absorbs KC1 from the lumen at the high rate of about 0·80 μmol cm−2 min−1. In other respects such as permeability to other solutes and the ability to transport alkaloids the two regions scarcely differ.
Depressant Action of Lithium at the Crayfish Neuromuscular Junction: Pre- And Postsynaptic Effects
Authors: Ortiz C. Leo , Junge D.
Published: April 2021

The effects of replacement of external sodium ions with lithium have been studied at the excitatory neuromuscular junction of the crayfish. Intracellularly recorded excitatory junctional potentials fall 45 % in amplitude in the first 10 min after lithium substitution, and fail irreversibly in 48–120 min. The quantal content of extracellularly recorded excitatory junctional potentials declines 25–70% within the first 10 min of Li+ exposure. During the next 40–120 min the nerve terminal potentials and quantal release at individual synapses fail simultaneously and irreversibly. The mean amplitude of the spontaneous miniature excitatory junctional potentials (m.e.j.p.s) is reduced 13 % by Li+ substitution, but recovers upon restoration of sodium. The mean frequency of m.e.j.p.s rises steadily during Li+ exposure, and continues to increase after reintroduction of Na+. The postsynaptic response to iontophoretically applied L-glutamate falls 35–40 % in 10 min, but never falls below 45 % of the control level. The effect on the glutamate response is completely reversible with sodium restoration. The effective resistance of the postsynaptic cells is unaffected or only increased slightly by lithium substitution. Thus, the primary mechanism of transmission block by lithium appears to be decreased transmitter release and inexcitability of presynaptic terminals, probably as a result of intracellular accumulation of lithium.
The Sensitivity and Control of the Scallop Mantle Edge
Authors: Stephens Philip J.
Published: April 2021

Application of mechanical stimulation or crude starfish extracts to the mantle edge of Aequipecten irradians elicited afferent impulse activity in the radial pallial nerves and local movements of the stimulated mantle edge. The evoked afferent spike activity was not recorded from primary receptor cells. The local mantle edge movements were controlled by peripherally located neurones and resembled jet formation on the velum of intact scallops. The central efferent neurones that supply the adductor muscle and much of the mantle edge are situated in the visceroparietal ganglion. Cobaltous chloride back-filling of the radial pallial nerves of the right side revealed the routes of the nerve fibres and the locations of the cell bodies in the visceroparietal ganglion. One group of motor neurones has fibres that are spatio-topically arranged across the visceroparietal ganglion and play a role in jet formation on corresponding portions of the mantle edge on both valves. It is apparent that axons from this group of mantle edge efferents traverse the ganglion without chemical synaptic connection. Two groups of mantle edge efferents that control concerted movements of the mantle edge on both shells appear to have cell bodies in the lateral margins of the dorso-central lobes. One group of motor neurones controls the raising of the velum curtain to an erect position around the shell margin. The output from the second group of efferents can be synchronized with the motor output to the adductor muscle to ensure that the velum folds into the mantle cavity, and thus is protected, as the shells are closed. Fibres in the radial pallial nerves have conduction velocities of up to 2·35 m/s at a temperature of 25 °C.
Evaporative Cooling and Water Balance During Flight In Birds
Authors: Torre-Bueno Jose R.
Published: April 2021

The rate of evaporative cooling was calculated from the rate of mass loss in starlings (Sturnus vulgaris) during 90 min flights in a wind-tunnel. Evaporative heat loss ranged from 5% of the metabolic rate at −5 °C to 19% of the metabolic rate at 29 °C. Radiation and convection accounted for the balance of the heat loss. On average, starlings dehydrated during flights at all temperatures above 7° C. The comparison of these results with data from field studies, which indicate that long-distance migrants do not dehydrate, suggests that migrants may maintain water balance by ascending to colder air in which convection carries off most of the heat produced.
Effects of Osmotic Stress on the Electrical Activities of the Giant Axon of A Marine Osmoconformer, Sabella Penicillus
Authors: Carlson A. D. , Pichon Y. , Treherne J. E.
Published: April 2021

The giant axons of the polychaete, Sabella penicillus, can withstand, in vitro, abrupt changes in osmotic and ionic concentration of the bathing medium in the range measured in the blood of this osmoconformer (543–1236 m-osmol) at different external salinities. Isosmotic dilution of the external ions (i.e. when osmotic concentration was maintained by sucrose) induced a modest hyperpolarization of the axonal membrane and a rapid decline in the overshoot of the action potential. In contrast, abrupt hyposmotic dilution resulted in a relatively slow and complex decline in overshoot in the absence of axonal hyperpolarization. A slow potassium depolarization and rate of decrease in overshoot in sodium-free conditions suggests that there is a reduced intercellular access to the axon surfaces following exposure to hyposmotic media. It is suggested that this restricted access could provide short-term protection from fluctuations in blood osmotic concentration.
Neuronal Control of Swimming in the Medicinal Leech
Authors: Friesen W. Otto , Poon Margaret , Stent Gunther S.
Published: April 2021

Four oscillatory interneurones that appear to be the principal components of the central swim oscillator of Hirudo medicinalis have been identified on each side of the segmental ganglia of the ventral nerve cord. During ‘swimming’ episodes of an isolated nerve cord preparation each interneurone undergoes a polarization rhythm that is phase-locked with the impulse burst rhythm of the motor neurones known to drive the swimming movement. Passage of current into any of the interneurones can shift the phase of the swim rhythm. One of the interneurones projects its axon rearward to posterior ganglia and the other three project their axons frontward to anterior ganglia. The oscillatory interneurones are connected both intra- and interganglionically to form a topologically complex intersegmental network of concatenated ring circuits that possess the feature of recurrent cyclic inhibition. Theoretical analysis and electronic analogue models show that the network is inherently oscillatory and can produce both a cycle period and intra- and intersegmental phase relations of its elements that are appropriate for generating the body wave of the swimming movement.
Long-Term Adaptations of Sabella Giant Axons Tohyposmotic Stress
Authors: Treherne J. E. , Pichon Y.
Published: April 2021

Sabella is a euryhaline osmoconformer which is killed by direct transfer to 50% sea water, but can adapt to this salinity with progressive dilution of the sea water. The giant axons were adapted to progressive dilution of the bathing medium (both in vivo and in vitro) and were able to function at hyposmotic dilutions (down to 50 %) sufficient to induce conduction block in unadapted axons.

Hyposmotic adaptation of the giant axon involves a decrease in intracellular potassium concentration which tends to maintain a relatively constant resting potential during adaptation despite the reduction in external potassium concentration. There is no appreciable change in the intracellular sodium concentration, but the relative sodium permeability of the active membrane increases during hyposmotic adaptation. This increase partially compensates for the reduction in sodium gradient across the axon membrane, during dilution of the bathing media, by increasing the overshoot of the action potentials recorded in hyposmotically adapted axons.
Locusts Use the Same Basic Motor Pattern in Swimming as In Jumping and Kicking
Authors: Pflüger Hans-Joachim , Burrows Malcolm
Published: April 2021

When on the surface of water, locusts (Schistocerca or Locusta) adopt a characteristic posture with the front legs pointing forwards and the middle and hind legs backwards. Swimming is accomplished by the rapid extension of both hind tibiae. The legs move at the same time and not alternately as they do in walking. The swimming strokes are repeated at 2–3 Hz and give the locust a forward velocity of some 13 cm s-1. The motor pattern that brings about the extension of the hind tibiae is described from extracellular recording in the tibial muscles during swimming. The tibia is first flexed and held flexed by spikes of the flexor motoneurones. Then the extensor motoneurones begin to spike so that there is a period when flexor and extensor motoneurones are both spiking. This leads to cocontraction of the muscles. The flexor motoneurones then stop, but the extensors continue, with the result that the tibia extends rapidly. The same basic motor pattern for the movement of the tibia is used by the locust in jumping, kicking and swimming.
Salinity Adaptation in the Salamander Batrachoseps
Authors: Jones Ronald M. , Hillman Stanley S.
Published: April 2021

Batrachoseps attenuatus and B. major were successfully acclimated to 600 m-osmol NaCl and 400 m-osmol sucrose solutions. Accumulation of sodium and an increased rate of synthesis of urea provide substantial increases in plasma concentrations of these solutes. Sodium concentrations in excess of 230 mM and urea concentrations in excess of 200 mm indicate that these are the two major solutes (plus anions) responsible for elevation of osmotic concentration in Batrachoseps. Batrachoseps exhibits a water balance response upon dehydration (greater than twofold increase in cutaneous uptake, 50% reduction in urine production). Urine production, estimated from bladder contents, was significantly reduced in salamanders acclimated to sucrose solutions compared to animals acclimated to tap water or saline of equivalent osmotic concentration. Plasma urea concentration was equivalent to urine urea concentration when Batrachoseps was kept in tap water and during short term saline acclimation. After long term saline acclimation, urine urea concentration was one-fourth the plasma urea concentration.
Oxygen Consumption of Moths During Rest, Pre-Flight Warm-Up, and Flight in Relation to Body Size and Wing Morphology
Authors: Bartholomew George A. , Casey Timothy M.
Published: April 2021

Insect pollinators, such as the tobacco hawkmoth Manduca sexta, are known for locating flowers and learning floral odors by using their antennae. A recent study revealed, however, that the tobacco hawkmoth additionally possesses olfactory sensilla at the tip of its proboscis. Here, we asked whether this second ‘nose’ of the hawkmoth is involved in odor learning, similar to the antennae. We first show that M. sexta foraging efficiency at Nicotiana attenuata flowers increases with experience. This raises the question whether olfactory learning with the proboscis plays a role during flower handling. By rewarding the moths at an artificial flower, we show that, although moths learn an odor easily when they perceive it with their antennae, experiencing the odor just with the proboscis is not sufficient for odor learning. Furthermore, experiencing the odor with the antennae during training does not affect the behavior of the moths when they later detect the learned odor with the proboscis only. Therefore, there seems to be no cross-talk between the antennae and proboscis, and information learnt by the antennae cannot be retrieved by the proboscis.

Morphometries and oxygen consumption were studied in about 35 sphingids, 50 satumiids, and 20 other heterothermic moths belonging to various families. For the pooled data of all species the regression of oxygen consumption on mass in grams is described by the following equations: at rest, cm3/h = 0·402 g0·775 ; during hovering flight, cm3/h = 59·430·818; during warm-up, cm3 = 1·1g0·896. Similar equations are presented for the families Saturniidae and Sphingidae. In sphingids and satuniids thoracic mass, wing length, and wing area increased with body mass, whereas wing loading and aspect ratio were independent of body mass. The sphingids had higher wing loading, aspect ratio, and wing beat frequency during flight than the saturniids. Wing beat frequency was more tightly coupled to morphological parameters in sphingids than in saturniids. The allometry of resting and active aerobic metabolism in heterothermic moths is compared with that of reptiles, mammals and birds. The scaling of oxygen consumption during flight in the moths is almost identical to that of bats and birds.
Patterns of Activity and the Effects of Activation of the Fast Conducting System on the Behaviour of Unrestrained Leeches
Authors: Magni Franco , Pellegrino Mario
Published: April 2021

The neural activity of the nerve cord of Hirudo medicinalis has been recorded in unrestrained animals by means of chronically implanted electrodes. The Fast Conducting System (FCS) is inactive both in motionless animals and during various kinds of active behaviour (creeping, swimming, ventilation). Photic and tactile stimuli applied to a motionless animal elicit a FCS discharge, which may be followed by generalized shortening. Photic and tactile stimuli applied during ventilation are followed by a reversible blockade of the ongoing activity only if they are able to elicit a FCS discharge. No such effect is observed on swimming. An explanation of these findings in terms of the known connexions of leech neurones is offered and a role in the control of reafferent inputs is attributed to the rectifying synapses made by FCS and T cells on the L motor neurones.
Evidence For One-Way Valves in the Water-Flow System of Sponges
Authors: Vogel Steven
Published: April 2021

A water current over a marine sponge can increase flow through the sponge ; even a current below the active pumping rate is effective. To investigate the structural correlates of such flow induction, two series of models were tested in a flow tank. These models were hollow cylinders with either wall perforations serving as ostia or an apical orifice as osculum. They were connected to an external reservoir which acted as a water source with the osculum exposed to flow, or as a sink where ostia were exposed. The reservoir could be raised or lowered to simulate active pumping. The models differed from intact sponges in showing much lower flow induction in general and no induction with ambient currents much below the active pumping rate.

The magnitude of flow induction could be raised to near normal by the addition of one-way valves in the model ostia. These valves prevented backflow out of the ostia lateral and downstream to the current while permitting the positive pressure on the upstream ostia to augment flow. To be effective at low ambient currents, the valves had to be isolated from the active pump ; if the valves were located in the ‘dermis’, the ‘subdermal space’ provided the requisite isolation.

Direct evidence for functional valves was obtained by cannulating freshly collected Haliclona viridis and observing that water could be more easily drawn out of an osculum than forced into it.
Axonal Adaptations to Osmotic and Ionic Stress in an Invertebrate Osmoconformer (Mercierella Enigmatica Fauvel)
Authors: Benson J. A. , Treherne J. E.
Published: April 2021

The giant axon of this extreme euryhaline osmoconformer possess an unusual ability to produce action potentials of large amplitude over a wide range of ionic dilution when constant osmotic concentration is maintained by the addition of mannitol to the bathing medium. Ionic dilution under these circumstances causes a decline in the overshoot of the action potential (resulting largely from reduction in [Na+]0) and an appreciable axonal hyperpolarization (primarily as a result of decrease in [K+]0). This hyperpolarization tends to compensate for the reduction in the extent of the overshoot and so maintains the amplitude of the sodium-mediated action potentials during isosmotic dilution of the bathing medium. The axonal hyperpolarization also appears to reduce sodium inactivation so as to maintain a rapid rate of rise of the action potential despite drastic reduction in the ionic concentration of the bathing medium. Prolonged exposure to reduced ionic concentrations appears to induce a ouabain sensitive reduction in intracellular sodium concentration which increases the sodium gradient across the axon membrane during isosmotic dilution of the external medium.
Axonal Adaptation to Osmotic and Ionic Stress in An Invertebrate Osmoconformer (Mercierella Enigmatica Fauvel)
Authors: Benson J. A. , Treherne J. E.
Published: April 2021

The giant axons of this extreme osmoconformer were adapted, in vitro, to progressive hyposmotic dilution of the bathing medium (from 1024 m-Osmol to concentrations as low as 76·8 m-Osmol). Hyposmotic adaptation is associated with reductions in the intracellular concentrations of both sodium and potassium ions. These reductions do not appear to result from appreciable axonal swelling. The different electrical responses to isosmotic and hyposmotic dilution suggest that reduction in [Na+]1 results from ouabain-dependent sodium extrusion, in response to ionic dilution, and that reduction in [K+]1 is induced by a combination of ionic and osmotic dilution. The reduced level of intracellular potassium achieved during hyposmotic adaptation represents a balance between the necessity to contribute to osmotic equilibration and to maintain a potassium gradient across the axon membrane sufficient to produce appreciable axonal hyperpolarization during dilution of the bathing medium. This hyperpolarization tends to maintain the amplitude of the action potential, by compensating for reduction in overshoot (with decline in ENa), and by reducing sodium inactivation. This, together with the reduction in [Na+]1, enables over shooting action potentials of relatively large amplitude and rapid rise time to be maintained during more than tenfold dilution of the ionic and osmotic concentration of the bathing medium.
Multiple Sites of Spike Initiation in A Bifurcating Locust Neurone
Authors: Heitler W. J. , Goodman Corey S.
Published: April 2021

Recordings were made from the metathoracic dorsal unpaired median neurone to the extensor tibiae muscle (DUMETi) in the locust. This is a bifurcating neurone with axons exiting both sides of the ganglion, whose soma can support a full action potential. Four different spike types were recorded in the soma, each of which we associate with a different region of the neurone. These were (1) a soma (S) spike of 70−90 mV (2) a neurite (N) spike of 20−40 mV, occurring between the axon hillock and axon branch point, (3) and (4) axon (A) spikes of 8−15 mV, occurring distal to the branch point on the left and right axons. Each of these regions must therefore have its own spike initiation site.

At spike frequencies greater than about 10 Hz at room temperature or 1−5 Hz at 32 °C (the preferred environmental temperature of the locust) the S-spike may fail, revealing A-spikes, or more rarely N-spikes. A-spikes usually consist of two more-or-less separate components, Al and Ar, which can be correlated with action potentials in the left and right axon branches by recording spikes extracellularly in the peripheral nerves on each side. Occasionally single component A-spikes occur when an action potential is initiated in only one axon, and fails to propagate across the branch point to the contralateral axon. Thus, action potentials may occur independently in the branches of this bifurcating neurone. After unilateral axotomy only S-spikes and N-spikes are recorded, indicating that action potentials no longer fail to propagate across the branch point. Anatomical asymmetries in the axon branches of DUMETi have been correlated with physiological asymmetries recorded in the soma of the same neurone.
Refinements in the Short-Circuit Technique and Its Application to Active Potassium Transport Across the Cecropia Midgut
Authors: Wood John L. , Moreton Roger B.
Published: April 2021

The conventional, two-electrode method for measuring potential difference across an epithelium is subject to error due to potential gradients caused by current flow in the bathing medium. Mathematical analysis shows that the error in measuring short-circuit current is proportional to the resistivity of the bathing medium and to the separation of the two recording electrodes. It is particularly serious for the insect larval midgut, where the resistivity of the medium is high, and that of the tissue is low. A system has been devised, which uses a third recording electrode to monitor directly the potential gradient in the bathing medium. By suitable electrical connexions, the gradient can be automatically compensated, leaving a residual error which depends on the thickness of the tissue, but not on the electrode separation. Because the thicknesses of most epithelia are smaller than the smallest practical electrode spacing, this error is smaller than that inherent in a two-electrode system. Since voltage-gradients are automatically compensated, it is possible to obtain continuous readings of potential and current. A ‘voltage-clamp’ circuit is described, which allows the time-course of the short-circuit current to be studied. The three-electrode system has been used to study the larval midgut of Hyalophora cecropia. The average results from five experiments were: initial potential difference (open-circuit): 98 ± 11 mV (S.E.M.); short-circuit current at time 60 min: 498 ± 160μA cm−2; ‘steady-state’ resistance at 60 min: 150 ± 26 Ω cm2. The current is equivalent to a net potassium transport of 18μ6 μequiv cm−2 h−1. The electrical parameters of the midgut change rapidly with time. The potential difference decays with a half-time of about 158 min, the resistance increases with a half-time of about 16 min, and the short-circuit current decays as the sum of two exponential terms, with half-times of about 16 and 158 min respectively. In addition, potential and short-circuit current show transient responses to step changes. The properties of the midgut are compared with those of other trans-porting epithelia, and their dependence on the degree of folding of the preparation is discussed. Their time-dependence is discussed in the context of changes in potassium content of the tissue, and the implications for measurements depending on the assumption of a steady state are outlined.