bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Fast Extensor Motor Activity in the Locust Kick Reconsidered
Authors: Heitler W. J. , Bräunig P.
Published: April 2021

Fast extensor tibiae (FETi) activity has been implicated as a crucial element underlying the locust kick motor programme with regard to four circuits, (i) A positive feedback reflex from extensor tibiae (ETi) muscle tension helps maintain FETi spiking during co-contraction. (ii) A central connection from FETi to flexor tibiae (FITi) motor neurones helps initiate FITi spiking at the start of co-contraction. (iii) Reflex feedback from ETi tension to FITi motor neurones helps maintain the latter spiking during co-contraction after the central connection has decremented, (iv) A proprioceptive gate controlled by ETi tension ensures that FITi trigger activity does not occur until sufficient ETi tension has developed to allow an effective kick.

The hypotheses concerning these circuits have been tested in two ways. First, FETi was phasically inhibited for varying periods during co-contraction, abolishing its spikes and hence its central output, and reducing ETi tension. Second, the nerve containing the FETi axon was cut in the femur, thus partially denervating the ETi muscle, and reducing its tension without directly affecting FETi activity. In both cases, kicks were analysed to see whether the motor programme changed in accordance with the circuit model. The overall conclusion is that the model is not correct, since considerable experimentally induced changes in FETi activity and ETi tension had no obvious effects on the motor programme. The circuits may play a supplementary role in generating the programme, but they are not crucial to it.
Quantitative Analysis of Resting Membrane Electrogenesis in Insect (Diptera) Skeletal Muscle : II. Testing of A Model Involving Contributions from Potassium and Sodium Ions, and the Anomalous Effect of Reducing Extracellular Sodium
Authors: Djamgoz M. B. A. , Dawson Jill
Published: April 2021

A model of resting membrane electrogenesis in skeletal muscles of prepupal Calliphora erythrocephala was formulated. From experiments in which reversible effects of changing extracellular K+ and Na+ activities on the membrane potential (EM) were measured, three different values of a (the ratio of the partial permeabilities of the membrane to Na+ and K+) were derived, each from a different range of extracellular Na+ and K+ activities. Two independent tests were carried out to determine the most realistic value of a. Intracellular K+ and Na+ activities and EM values were measured in a population of cells, and the EM values predicted using the Goldman-Hodgkin-Katz equation for different values of a. The best fit for the data was obtained for α= 0·036. In ionic substitution experiments, in which passive movements of Cl− were prevented or minimized, the changes in EM around the resting level could be explained with a high degree of accuracy by assuming again that α = 0·036. However, tests of the model by investigation of direct effects of reducing extracellular Na+ concentration over a wide range of EM values gave an anomalous result. In low-Na+ Ringer, EM values became more positive than the respective resting levels. The anomalous effect of low-Na+ Ringer on EM did not involve a change in the K+ equilibrium potential. Instead, it was probably due to a reduction in the K+ permeability of the membrane. Possible mechanisms underlying this effect are discussed.
Cephalic Neuroendocrine Regulation of Integumentary Water Loss in the Cockroach Periplaneta Americana L
Authors: Noble-Nesbitt John , Al-Shukur Marwan
Published: April 2021

Our experiments show that the brain of cockroaches produces, stores (tempor-arily or otherwise) and releases a water-loss promoting factor (BHP) and a water-loss restricting factor (BHR), depending on the physiological state of the cockroach and environmental conditions.

Fully hydrated cockroaches produce, temporarily store and release the BHP factor, and store but do not release the BHR factor: this leads to high rates of integumentary water loss.

Desiccation arrests the production and storage of BHP factor and stimulates the release of BHR factor, resulting in rapid restriction of integumentary water loss.

Brain homogenates prepared from fully hydrated cockroaches (HBH) contain some BHP factor and much BHR factor, whereas brain homogenates prepared from predesiccated cockroaches (DBH) contain only BHR factor.

Control saline-only injections produce only slight elevations in water loss of either fully hydrated or predesiccated intact cockroaches.

Lowering of integumentary water loss of intact fully hydrated cockroaches (HI) in response to desiccation is little affected by either HBH or DBH injection.

Conversely, injection of HBH into intact predesiccated cockroaches (DI) causes a highly significant increase in water loss during continued desiccation, confirming the presence of BHP factor in HBH.

DBH injection into DI cockroaches has little or no effect, presumably since it adds only BHR factor which is already present and active in the host.

Injected restricting factor (BHR) seems to be more effective than injected promoting factor (BHP) in decapitated cockroaches. Thus, considerably lower losses are found in decapitated fully hydrated cockroaches (HD) following HBH injection (Treherne & Willmer, 1975 and confirmed by us) or DBH injection (present results). Slightly elevated losses are found in decapitated predesiccated cockroaches (DD) following HBH injection, whereas DBH injection has little effect.
The Effects of Thermally Induced Activity In Vivo Upon the Levels of Sodium, Chlorine and Potassium in the Epithelia of the Equine Sweat Gland
Authors: Wilson Stuart M. , Elder Hugh Y. , Jenkinson David Mcewan , Mcwilliams Scott A.
Published: April 2021

Evaporation of moisture from the skin surface is an important means of thermoregulatory heat loss in Equidae, which respond to thermal stress with a smooth increase in the rate of sweat output to a plateau level which may be maintained for several hours (Allen & Bligh, 1969; Robertshaw & Taylor, 1969; Montgomery, Jenkinson & Elder, 1982). This pattern is similar to that which occurs when humans are exposed to a warm environment (Montgomery et al. 1984). The mode of sweat formation in both the horse and man is similar, involving cell death, fluid transport and the loss of vesicles both by exocytosis and microapocrine secretion (Montgomery et al. 1982, 1984). However, the secretions produced by the two glands differ markedly in electrolyte composition. Human sweat is a hypotonic fluid containing sodium chloride as its principal solute (Schulz, 1969; Sato, 1977), whereas equine sweat is hypertonic and contains a high concentration of potassium (Soliman & Nadim, 1967; Kerr & Snow, 1983). This could be a reflection of differences in the underlying mechanism of ionic transport within the gland.
Control of Central Pattern Generators by an Identified Neurone in Crustacea: Activation of the Gastric Mill Motor Pattern by a Neurone Known to Modulate the Pyloric Network
Authors: Dickinson Patsy S. , Nagy Frédéric , Moulins Maurice
Published: April 2021

In the red lobster (Palinurus vulgaris), an identified neurone, the anterior pyloric modulator neurone (APM), which has previously been shown to modulate the output of the pyloric central pattern generator, was shown to modulate the output of the gastric mill central pattern generator. APM activity induced a rhythm when the network was silent and increased rhythmic activity when the network was already active. Rhythmic activity was induced whether APM fired in single bursts, tonically or in repetitive bursts. A single burst in APM induced a rhythm which considerably outlasted the burst, whereas repetitive bursts effectively entrained the gastric oscillator.

These modulations involved two major mechanisms. (1) APM induced or enhanced plateau properties in some of the gastric mill neurones. (2) APM activated the extrinsic inputs to the network, thus increasing the excitatory synaptic drive to most of the neurones of the network. As a result, when APM was active, all the neurones of the pattern generator actively participated in the rhythmic activity. By its actions on two separate but behaviourally related neural networks, the APM neurone may be able to control an entire concert of related types of behaviour.
Negative Geotaxis in Sea Urchin Larvae: a Possible Role of Mechanoreception in the Late Stages of Development
Authors: Mogami Yoshihiro , Oobayashi Chieko , Yamaguchi Tomoko , Ogiso Yumi , Baba Shoji A.
Published: April 2021

Negative geotactic behaviour of sea urchin larvae at various developmental stages from blastula to pluteus was analysed by means of time-exposure dark-field photography of the swimming behaviour of individual larvae. Significant differences in the patterns of behaviour, such as swimming direction and speed, were demonstrated between the early stages (up to the gastrula) and the pluteus, although larvae at any developmental stage showed negative geotactic migration. Larvae in the early stages swam at speeds that varied as a function of the swimming direction with respect to gravity, faster downwards and slower upwards. This might be predicted from the assumption that vertical locomotion is determined by constant propulsion affected passively by gravity. In the pluteus stage, however, larvae swam at a constant speed in any direction, suggesting that the propulsive activity of swimming plutei is actively controlled depending on the swimming direction. This change in the negative geotactic behaviour of sea urchin larvae in the course of embryogenesis indicates development of physiological control systems for propulsive activity at the pluteus stage.
Response of Nautilus to Variation in Ambient Pressure
Authors: Jordan Michael , Chamberlain John A. , Chamberlain Rebecca B.
Published: April 2021

Juvenile Nautilus, tested in a high-pressure animal maintenance apparatus, are sensitive to increases in ambient hydrostatic pressure as small as l × 105Nm−2 (= 1 atm = 100kPa). They respond to such pressure increases in a characteristic ‘depth alarm’ behaviour pattern, which consists primarily of rapid upward swimming. These activity bursts may serve to restore them to their original depth. The animals apparently continue this behaviour until fatigued. Pressure decrease elicits no obvious response. The pressure-sensing mechanism may be located within the statocyst, or possibly in the posterior mantle or siphuncle. The operation of. the latter two mechanisms involves tensional strain induced by the hydrostatic load in the outermost septum and wall of the siphuncular tube.
Flight Performance of a Dragonfly
Authors: Azuma Akira , Watanabe Tadaaki
Published: April 2021

The dragonfly, Anaxparthenope julius (Brauer) was observed in free flight, and a theoretical analysis of flight performance at various speeds was carried out. The variation with time of forces and moments acting on wings and body in steady trimmed flight was calculated by the local circulation method. Measures of flight performance, such as top speed, cruising speed and maximum endurance speed, were estimated from a necessary power curve required in steady flight and from the estimated available power. The results show that without using any novel unsteady aerodynamic force generated by a separated flow over the wings, the dragonfly can make steady trimmed flight at various flight speeds, from hovering to top speed.
The Similarity of Mitochondrial Distribution in Equine Skeletal Muscles of Differing Oxidative Capacity
Authors: Kayar S. R. , Hoppeler H. , Essen-Gustavsson B. , Schwerzmann K.
Published: April 2021

A morphometric analysis was performed on horse muscle tissue to quantify mitochondrial distribution relative to capillaries. Samples of M. vastus medialis, M. semitendinosus, M. masseter and M. cutaneus thoracicus were preserved in a glutaraldehyde fixative for electron microscopy, or frozen for biochemical and histochemical analysis. These four muscles varied from highly oxidative in type, consisting nearly completely of type I fibres, in masseter, to highly glycolytic, primarily type lib fibres, in cutaneus. In all four muscles, mitochondria were found in highest volume density near capillaries at the fibre border, with a sharp, decline in volume density towards the fibre centre. This distribution was independent of myoglobin concentration, muscle fibre type and the activities of three key metabolic enzymes, citrate synthase, 3-OH-acyl-CoA dehydrogenase and lactate dehydrogenase.
Sodium-Independent Proline Transport in the Locust Rectum
Authors: Meredith J. , Phillips J. E.
Published: April 2021

Recta of Schistocerca gregaria possess a high-affinity (Kt = 10 mmol l−1) and high-capacity (Vmax = 4·2 μequiv cm−2h−1) active absorptive mechanism for proline second in magnitude only to stimulated Cl− transport. Transcellular and paracellular pathways have extremely low passive permeability to proline, resulting in very high flux ratios (40:1) compared with those for other.solutes (less than 6:1). Net epithelial transport of proline is largely independent of luminal Na+, K+ and Cl−. Sodium influx does not change when proline net fluxes are varied 14-fold. Therefore Na+ cotransport is not a principal mechanism of proline uptake in this tissue. Prolonged absence of Na+ and K+ from the haemocoel side partially inhibits proline transport, probably indirectly, by affecting the general transport capacity of the rectum. Inhibition is irreversible. A component of the net proline flux (Jpronet) is electrogenic, located in the apical membrane, and may be due to proline/proton cotransport.
Transport Properties of Locust Ileum in vitro: Effects of Cyclic Amp
Authors: Irvine B. , Audsley N. , Lechleitner R. , Meredith J. , Thomson B. , Phillips J.
Published: April 2021

Short-circuited locust ilea exhibited electrical properties remarkably similar to those of recta. The large short-circuit current (Isc) and transepithelial potential, both indicating net active absorption of anions, initially began to decline to zero but could be fully restored by adding cyclic AMP or extracts of corpus cardiacum and ventral abdominal ganglia to the haemocoel side. Ion substitutions and radiotracer flux studies indicated that cyclic AMP-induced ΔISC was due to electrogenic Cl− transport with kinetics identical to those of the rectum. Concurrent decreases in transileal resistance were due to increases in both Cl− and K+ (PK) permeabilities, most evident as a resistance decrease at the apical membrane. The ΔPK was blocked by basolateral addition of Ba2+, as observed for recta. Everted ileal sacs under open-circuit conditions absorbed a slightly hyperosmotic NaCl-rich fluid and the rate of absorption was increased more than twofold by cyclic AMP. This contrasts with stimulated recta which absorb primarily KCl and a hyposmotic absorbate. Flux studies with short-circuited ilea demonstrated active absorption of Na+, which was stimulated twofold by cyclic AMP. Removal of external Na+ had little effect on Isc, suggesting that involves exchange for another cation, e.g. NH4+. Ilea actively secreted acid at lower rates than do recta under open-circuit conditions. Under short-circuit conditions, cyclic AMP addition led to active alkalinization of the ileal lumen at high rates, and the large Isc represented the difference between active secretion of base equivalents and net absorption of Cl−. The transport capacities of locust ilea and recta are compared in relation to their ultrastructure.
The Forces Acting on Swimming Squid
Authors: O’Dor R. K.
Published: April 2021

Analysis of ciné films and intramantle pressure records for squid Loligo opalescens Berry swimming in a tunnel respirometer provided estimates of all the forces acting in the horizontal and vertical planes for swimming speeds from 0·1 to 0·5 ms−1. Different speeds used different gaits; fin thrust was only important below 0·2 ms−1, ‘anaerobic’ circular muscles were recruited only at supracritical speeds, and hyperinflation caused by contraction of the radial muscle was not seen in steady swimming. The extent, rate and frequency of contraction of the obliquely striated circular muscles varied little with speed, and jet thrust was matched to speed primarily by active pressure control through adjustments in the size of the funnel orifice. Hydrodynamic lift production to compensate for negative buoyancy during enforced horizontal swimming in the tunnel required 30–90% of the total force over the speed range studied and appears less efficient than direct use of jet thrust. This suggests a new rationale for ‘climb-and-glide’ swimming which reduces previous estimates of the gross cost of transport for squid under natural conditions by at least 35%, with no loss of speed. The cost of accelerating water into the mantle of a squid moving at high speed appears to have been underestimated in previous studies. A simulation of a series of escape jets predicts a maximum speed of 8 body lengths s−1 (14ms−1), reached after only two jets, because of the high deceleration during refilling.
Acid-Base Regulation in the Freshwater Pearl Mussel Margaritifera Margaritifera: Effects of Emersion and Low Water pH
Authors: Heming T. A. , Vinogradov G. A. , Klerman A. K. , Komov V. T.
Published: April 2021

Freshwater pearl mussels Margaritifera margaritifera L. were exposed to air for 7 days, then immersed in circumneutral water (pH 7·85) or acidified water (pH 5·25) for 5 days. Mantle fluid pH and composition were monitored throughout. The mussels were observed to gape periodically when in air. Periodic gaping permitted aerial gas exchange such that mantle fluid and dissolved oxygen concentration stabilized at levels about twice and half, respectively, those of immersed mussels. During emersion, a dilute carbonate buffer equilibrium was established in the mantle fluid, involving reactions with CaCO3 reserves and, simultaneously, aerial release of CO2. Aerial CO2 release was sufficient to shift the carbonate buffer equilibrium in the alkaline direction, resulting in a significant alkalosis of mantle fluids during air exposure. Mantle fluid characteristics returned to initial (time zero) values within 3 days of immersion in circumneutral water (pH 7·85). When immersed in acid water (pH 5·25), the mussels were able to maintain a sizeable gradient between mantle fluid pH and ambient water pH. Regulation of mantle fluid pH in acid water did not involve any isolation reaction (valve closure), but rather environmental protons were buffered at the expense of CaCO3 reserves. Net calcium transfer, the difference between calcium uptake and loss, was shifted in the negative direction by decreases in water pH.
Ingestive Behaviour and Physiology of the Medicinal Leech
Authors: Lent Charles M. , Fliegner Karsten H. , Freedman Edward , Dickinson Michael H.
Published: April 2021

Ingestion lasts 25 min in Hirudo medicinalis and is characterized by pharyngeal peristalsis which fills the crop. This peristalsis has an initial rate of 2·4 Hz which decays smoothly to 1·2 Hz at termination of ingestion. During ingestion, the leech body wall undergoes peristalsis which appears to aid in filling the crop diverticula. Body peristalsis begins at a rate of 10 min−1 and decreases linearly to 2 min−1 at termination. The body also undergoes dorsoventral flexions when blood flow is occluded. Blood meal size increases slightly with leech size: 8·4 g for 1-g leeches and 9·7 g for 2-g leeches. However, relative meal size decreases markedly with increasing animal size; from 8·15 times body mass for 1-g to 4·80 times for 2-g leeches. When intact leeches were exposed to micromolar concentrations of serotonin, there was an increase in the rate of pharyngeal peristalsis and the size of the blood meals.

Leeches excrete the plasma from their ingested blood meals. Excretion is activated during ingestion, which increases feeding efficiency by increasing the proportion of blood cells in the ingestate. Excretion continues for 4–6 days following ingestion, removing all the remaining plasma from the ingestate. Leech ingestion comprises stereotyped muscular movements, secretion of saliva and excretion of plasma. A strikingly similar feeding physiology is seen in the bloodsucking insect Rhodnius, and we suggest that efficient sanguivory may require the convergent evolution of similar ingestive mechanisms.
Blood Flow Patterns in the Salamander, Ambystoma Tigrinum, Before, During and After Metamorphosis
Authors: Malvin Gary M. , Heisler Norbert
Published: April 2021

The patterns of blood flow through the complex circulation of the tiger salamander, Ambystoma tigrinum, were investigated during aquatic normoxia and hypoxia by application of the microsphere technique. The distribution of differently labelled microspheres injected into the bloodstream towards the left and right atria, respectively, was used to evaluate the role of the ductus arteriosus in lung perfusion before, during and after metamorphosis, as well as the general contribution of right and left atrial outputs to the blood flow in gills and lungs in neotenic and postmetamorphic animals.

The distribution patterns of radioactive microspheres among pulmonary, branchial and systemic tissues indicated that the ductus arteriosus is the major pulmonary perfusion pathway in neotenic and metamorphosing animals, whereas after metamorphosis the main perfusion pathway is down the entire length of the pulmonary artery. In neotenes, the ductus arteriosus becomes even more important during aquatic hypoxia. The anterior branchial arches receive blood richer in pulmonary venous blood than the posterior arches. Approximately 26% of left atrial output and 36% of right atrial output perfuses the branchial respiratory lamellae during normoxia in neotenes. Severe aquatic hypoxia appears to increase the fraction of cardiac output flowing to the lung and decrease the fraction flowing into the first branchial arch in neotenes. This decrease into the first arch may facilitate lung perfusion and also reduce branchial O2 loss. In postmetamorphic animals, approximately 55% of right atrial output and 32% of left atrial output is directed to the lungs. The flow patterns in postmetamorphic animals remain unaffected by aquatic hypoxia.
Hypersensitivity to Light of the Iris (Sphincter Pupillae) of the Albino Axolotl (Ambystoma Mexicanum)
Authors: Barr Lloyd
Published: April 2021

As is common for amphibians, the sphincter pupillae of the axolotl contracts in vitro in response to illumination with visible light.

In a comparison of photomechanical responses of albino and normally pigmented axolotls, similar time courses and maxima of force development were found. The dependence of isometric active force development on the length of the sphincter pupillae is similar to that of other smooth muscles. The action spectrum of the axolotl is similar to the absorption spectrum of frog rhodopsin. At low stimulus strengths, the increase of normalized, isometric, active force with increasing stimulus strength is approximately seven times as great in albino axolotls as in normally pigmented ones. Melanin appears to decrease the light sensitivity of the irises of normally pigmented animals by acting as a simple light shield.
Excitability and Secretory Activity in the Salivary Gland Cells of Jawed Leeches (Hirudinea: Gnathobdellida)
Authors: Marshall Cameron G. , Lent Charles M.
Published: April 2021

Thousands of salivary cells fill the interstices throughout the anterior ends of jawed leeches. The somata are large (30–200 μm in diameter). They project single processes (ductules) into the three jaws, and were found to fire overshooting action potentials of 50–85 mV amplitude and 100–200 ms duration at low spontaneous rates. The action potentials were not detected in the presence of cobalt (10 mmol l−1), but could be recorded when sodium was absent from the Ringer, so they appear to be calcium-dependent.

Salivary material is transported by the long processes of these unicellular glands and secreted into ducts which alternate with paired teeth on the jaws. Secretion is activated reliably by 10−6mol l−1 serotonin, but not by other neurotransmitters found in the leech nervous system. Each jaw secretes at an average rate of 230 nl min−1 in the presence of serotonin, and secretion is completely abolished by cobalt.

Perfusion with serotonin excites the salivary gland cells into impulse activity, and often evokes bursting. Impulse activity of the peripherally projecting, serotonergic Retzius cells evokes both depolarizations and action potentials in the salivary gland cells. In jawed leeches, central neurones appear to control salivation by a peripheral release of serotonin. This neurotransmitter evokes calcium-dependent action potentials and calcium, in turn, stimulates secretion.
Stimulus-Secretion Coupling: a Perspective Highlighting the Contributions of Peter Baker
Authors: Rink T. J. , Knight D. E.
Published: April 2021

Many investigators are using numerous preparations for contributing to our present understanding of stimulus-secretion coupling, by which we mean stimulus-dependent exocytosis, sometimes known as the regulated pathway. However, a few model systems have been particularly illuminating and several of these were exploited by Peter Baker and his close associates: namely, the motor nerve terminal, the adrenal chromaffin cell, the sea urchin egg and the blood platelet. In fact, Peter’s first real contribution in this area came from his seminal studies on calcium transport in his favourite preparation, the squid giant axon, where he investigated Ca2+/Na+ exchange, Ca2+ distribution and voltage-gated Ca2+ entry. More direct investigations into stimulus-secretion coupling came from work on neurone transmitter release in collaboration with Andrew Crawford, and on catecholamine secretion from the adrenal medulla in collaboration (with TJR). His most important generic contribution to this field was in the development (with DEK), of the electropermeabilized cell, which allows control of the low molecular weight components of the cytosol while leaving the exocytotic apparatus and process intact. In the initial experiments on the cells it was finally proved that Ca2+-dependent secretion of catecholamines is indeed from the granules and not from the cytosol. The quantification of the Ca2+ requirement of secretory exocytosis was an important step, as was the investigation of many factors purported to be important in the coupling mechanism or in the exocytotic process itself. Work with the human platelet, using this technique, has proved to be especially valuable in unravelling the complex interactions between different second messengers and has been neatly complemented by work in intact cells containing Ca2+-indicator fluorescent dyes. Peter was also intrigued by post-secretory events both in the early seventies, and at the end of his career when he embarked on analysis of the membrane retrieval process and the associated uptake of extracellular medium.
A Complex Mechanism of Facilitation in Pituitary Acth Cells: Recent Single-Cell Studies
Authors: Leong Denis A.
Published: April 2021

The transfer of information by chemical signals during complex biological processes can, with increasing frequency, be described in terms of interacting signal pairs. External signalling is rarely monolithic; rather, signal pairs are utilized in processes such as hormone secretion, neurotransmission, cell growth and differentiation. The dualism of external signalling often results in the occurrence of synergy. One signal appears to turn the cell on or off, and its synergistic partner increases cell responsiveness, providing gain control of the cellular response. ACTH release provoked by certain stressors arises from a synergistic interaction between two hypothalamic hormones: corticotropin releasing hormone (CRH) and a modulator such as vasopressin (AVP). The pituitary ACTH cell has been used to unravel the intracellular messenger equivalents of an external signal interaction that generates synergy.

Research emphasizes the single cell approach. Direct measurements of intracellular free Ca2+ were performed using the Ca2+-sensitive fluorescent probe fura-2/AM and instrumentation for digital image processing. A reverse haemolytic plaque assay was used to measure cumulative ACTH release from single pituitary cells in culture.

What is the physiological role of intracellular Ca2+ as a messenger? What are the feedforward and feedback relationships between major second messengers [cyclic AMP, diacylglycerol (DAG), inositol 1,4,5-trisphosphate (Ins(l,4,5)P3)] and intracellular Ca2+? That is, how are individual messenger circuits ‘wired’ within ACTH cells. Intracellular Ca2+ may act as a common signal into which interacting second messenger signals [cyclic AMP, Ins(l,4,5)P3, DAG] are transduced and integrated to govern ACTH release. A novel circuit of messenger pathways linked by Ca2+ is proposed as the intracellular basis for the synergistic interaction of CRH- and AVP-regulated ACTH release.
THE Ins(1,4,5)P3-Sensitive Ca2+ Store of Non-Muscle Cells: Endoplasmic Reticulum or Calciosomes?
Authors: Pozzan Tullio , Volpe Pompeo , Zorzato Francesco , Bravin Mariangela , Krause Karl H. , Lew Daniel P. , Hashimoto Sadimatsu , Bruno Bernardino , Meldolesi Jacopo
Published: April 2021

The binding of a number of extracellular ligands (hormones, growth factors, neurotransmitters etc.) to their plasma membrane receptors causes hydrolysis of phosphatidylinositol bisphosphate to initiate the formation of two second messengers, inositol 1,4,5-trisphosphate [Ins(l,4,5)P3] and diacylglycerol, DAG. DAG has been shown to activate protein kinase C, whereas Ins(l,4,5)P3 induces the release of Ca2+ from an intracellular pool. This rapidly mobilizable, Ins(l,4,5)P3-sensitive Ca2+ store has until now been identified as the endoplasmic reticulum, ER. We demonstrate that this is untenable and provide evidence for the existence of an unrecognized organelle, the ‘calciosome’. This conclusion is based on the following experimental evidence. (1) There is no correlation between the abundance of ER and the amount Ins(l,4,5)P3-sensitive Ca2+ release. (2) There is no correlation between ER markers and those for the Ca2+ store [Ins(l,4,5)P3 binding and sensitivity, Ca2+ uptake]. (3) A protein similar to striated muscle calsequestrin, CS, has been identified in microsomal fractions from a number of tissues; it copurifies with markers of the Ca2+ store, but not with those of ER. (4) Subcellular localization of the CS-like protein by electron microscopy reveals that in all cells so far analysed this protein is localized in small, membrane-enclosed structures, calciosomes, which are also stained by an anti-Ca2+-ATPase antibody. Calciosomes appear to be morphologically distinct from any other known cell organelle. (5) Although they stain different portions of the calciosomes (membrane and lumen, respectively), anti-Ca2+-ATPase and anti-CS antibodies do not recognize any antigen in ER cysternae; antibodies directed against known components of ER do not bind to calciosomes.
The Photic Control of Pigmentary Responses in Teleost Fishes
Authors: Wykes Ursula
Published: April 2021

Many shallow-water teleosts, e.g. Gobius paganellus and G. ruthensparri, Ctenolabrus rupestris, Lepadogaster gouani and Phoxinus phoxinus, when blinded, show a pigmentary response to photostimulation. This response was analysed quantitatively in Lepadogaster gouani. The melanophores of the blinded animal contract in darkness and expand when illuminated by a 100-watt lamp. In the normal animal on a light background the latter response is checked by a secondary contraction. The dermal response of these fishes is closely comparable to that of the chameleon and it is possible that it may be similarly controlled. No dermal response was observed in adult Pleuronectes platessa.
The Oxygen Uptake of Suspensions and Cultures of A Free-Living Bacterium
Authors: Meiklejohn Jane
Published: April 2021

The oxygen uptake of pure cultures and suspensions of a free-living bacterial species has been measured at 26° C. At this temperature, liquid cultures reach the maximum stationary phase of growth about 96 hours after inoculation. The greatest total oxygen uptake was observed in samples taken from cultures 72 hours after inoculation, and the greatest uptake per cell at 48 hours after inoculation. The oxygen uptake in cultures which have reached the stationary state falls off rapidly, at each successive sampling, to a very low value. In suspensions deprived of nitrogen, and showing no growth, and in cultures in the stationary phase, oxygen uptake proceeds at a constant rate. In both suspensions and cultures, where active growth is taking place, the rate of oxygen uptake rises continuously; after a preliminary period of adjustment this rise is logarithmic. The rise in oxygen uptake in a growing suspension is proportionately greater than the rise in bacterial numbers. It is suggested that the oxygen uptake of a growing culture can be divided into two parts; “maintenance” respiration and “growth” respiration, and a technique is outlined for estimating the amount of oxygen uptake due to each factor.
Storage of Oxygen in the Bladders of the Seaweed Ascophyllum Nodosum and Their Adaptation to Hydrostatic Pressure
Authors: Damant G. C. C.
Published: April 2021

Ascophyllum nodosum secretes oxygen into its bladders so freely that the total gas pressure within them is usually above atmospheric pressure. The plant draws on this store of oxygen during the night and when shaded; the advantage of storing the gas under pressure is that withdrawals do not diminish the volume or buoyancy of the bladder whose efficiency as a float is of importance to the plant when competing for sunlight. As the bladder walls are somewhat permeable, the contained gas tends to diffuse out into the sea. Disastrous loss of gas may take place if, during an abnormally high tide, hydrostatic pressure overcoming the resistance of the bladder causes it to collapse with formation of a “dimple”. In this event the gas inside takes up the pressure of the water outside and diffuses away more rapidly than before the collapse took place. The bladders lose buoyancy and can no longer support the plant properly ; as a result it is starved of sunlight, fails to replace the lost gas and becomes permanently crippled. Plants growing in situations where they are exposed to severe hydrostatic pressure show an adaptive thickening of the bladder walls which enables them to resist deformation and the sequence of events detailed in (2). This adaptation is so closely fitted to the environment that in a zone of A. nodosum fifteen feet wide the plants of the upper level are unable to withstand the hydrostatic pressure obtaining at the lower and, if transplanted there, lose all their gas and perish.
A Growth Factor Required by Mosquito Larvae
Authors: Trager William
Published: April 2021

A method is presented for the measurement of an accessory factor required by mosquito larvae for their normal growth and development. Various sources of the factor, their relative potency and some of the physical and chemical properties of the material are described.
The Movements of the Proboscis inGlycera DibranchiataEhlers
Authors: Wells G. P.
Published: April 2021

In an earlier paper (Wells, 1937), the writer studied experimentally the movements of the proboscis in Arenicola marina, a worm which lives in a burrow and feeds by taking in the surrounding mud, and in which the brain and sense organs are very much reduced. It was shown that the intact worm, observed in a glass tube, generally exhibits periodic outbursts, either of rhythmic extrusion and withdrawal of the proboscis or, in less vigorous worms, of movements of similar type which do not result in actual extrusion, the activity outbursts alternating in either case with periods of rest. This probably means that the worms, under natural conditions, have a “feeding rhythm”, ingesting mud for a few minutes, then resting, and so on. Moreover, by considering a series of dissected preparations, it was shown that the pacemaker determining this rhythm was situated in the oesophageal wall. Periodic outbursts of excitation originate in the oesophagus and are transmitted forwards along the wall of the proboscis to the central nervous system, calling forth correlated movements of the musculatures of the proboscis itself and of the body wall.
Quantitative Studies on the CiliateGlaucoma
Authors: Harding J. P.
Published: April 2021

Although it is a matter of common observation that ciliates and other Protozoa when starved become smaller in size, and often more slender in shape, very little quantitative work has been done on these changes. It is the purpose of this paper to deal in a quantitative way with the effects of the starvation of Glaucoma; in particular with the changes that result in size and shape. It is hoped that this study may throw some light on the mechanism by which the shape of ciliates is controlled.
The Triple Innervation of Crayfish Muscle and Its Function in Contraction and Inhibition
Authors: Van Harreveld A. , Wiersma C. A. G.
Published: April 2021

The innervation of the muscles of the cheliped of Cambarus clarkü has been investigated both anatomically and physiologically. It is found that at least three of the six principal muscles of the cheliped show a triple innervation. Each of these muscles in the unregenerated claw is innervated by three axons only. Such “completely” innervated muscles are the extensor and flexor of the carpopodite and the flexor of the propodite. The extensor of the propodite and the abductor of the dactylopodite have only a double innervation. Both these muscles together are innervated by three axons; one fibre gives branches to each of the muscles, a second to the abductor only, and a third to the extensor. An extension of the last fibre can, in a number of cases, be seen to join two fibres for the adductor of the dactylopodite, making the innervation of this muscle complete. In other preparations the third fibre for the adductor is very thin.

It is shown for the flexor of the carpopodite that each of the three fibres of this “completely” innervated muscle has a different function. Stimulation of the thickest fibre gives a fast contraction, stimulation of the second in size a slow contraction and stimulation of the third fibre, the smallest, causes inhibition. Both the fast and the slow contraction can be inhibited, but the slow contraction is more sensitive in this respect (see Fig. 4). It is shown that the axon which the abductor and the extensor of the propodite have in common is of the excitatory type. This makes these muscles two parts of one motor unit, each part having its own inhibitory fibre.
Quantitative Studies on the CiliateGlaucoma. Excretion of Ammonia
Authors: Doyle W. L. , Harding J. P.
Published: April 2021

It was at one time generally thought that excretion in the Protozoa was a function of the contractile vacuole. This idea has now been largely discarded (except in relation to the excretion of water) and the authors considered it of interest to correlate the rate and amount of nitrogenous excretion with the activities of other cytoplasmic constituents.
Kinetics of Calcium Fluxes Across The Intestinal Mucosa of the Marine Teleost, Gadus Morhua, Measured Using an in vitro Perfusion Method
Authors: Sundell Kristina , Björnsson Björn thrandur
Published: April 2021

An in vitro technique for perfusion of the intestinal vasculature and lumen was developed and used to measure calcium (Ca2+) fluxes across the intestinal mucosa of the marine teleost, the Atlantic cod (Gadus morhua). Saturable and nonsaturable components of the calcium influx and efflux were determined.

The calcium influx had one passive component and one saturable component, following Michaelis-Menten kinetics with Km = 8·41 mmol l−1 and Vmax = 0·604μmol Ca2+ kg−1 h−1. At physiological Ca2+ concentrations in the vascular ([Ca2+] = 1·9mmoll−1) and luminal ([Ca2+] = 14·9mmoll−1) perfusion fluids, the saturable component amounted to 60% of the Ca2+ influx. The high-affinity Ca2+-ATPase inhibitor chlorpromazine (CP, 10−4moll−1) antagonized 45% of the Ca2+ influx.

The Ca2+ efflux across the intestinal mucosa of the cod was a saturable process, following Michaelis-Menten kinetics with Km = 6·15 mmol l−1 and Vmax = 3·79μnolCa2+ kg−1 h−1, but insensitive to CP (10−5 moll−1). The Ca2+ efflux was l·22μmolCa2+kg−1 h−1, representing about 20% of the total calcium excretion and about 50% of the extrarenal excretion of the Atlantic cod in vivo.
Kangaroo Rat Locomotion: Design for Elastic Energy Storage or Acceleration ?
Authors: Biewener Andrew A. , Blickhan Reinhard
Published: April 2021

Mechanical stresses (force/cross-sectional area) acting in muscles, tendons and bones of the hindlimbs of kangaroo rats (Dipodomys spectabilis) were calculated during steady-speed hops and vertical jumps. Stresses were determined from both high-speed ciné films (light and X-ray) and force plate recordings, as well as from in vivo tendon force recordings. Stresses in each hindlimb support element during hopping (1·6-3·1 m s−1) were generally only 33% of those acting during jumping (3=40cm height): ankle extensor muscles, 80 ±12 (S.D.) versus 297 ±42kPa; ankle extensor tendons, 7·9 ±1·5 versus 32·7 ±4·8 MPa; tibia, −29 ±5 versus – 110 ±25MPa (all values are for hopping versus jumping). The magnitude of stress in each structure during these locomotor activities was similarly matched to the strength of each element, so that a consistent safety factor to failure is achieved for the hindlimb as a whole (1·5–2·0). The large stresses during jumping were correlated with a three-fold increase in ground reaction forces exerted on the ground compared with the fastest steady hopping speeds. We conclude that, for its size, the kangaroo rat has disproportionately large hindlimb muscles, tendons and bones to withstand the large forces associated with rapid acceleration to avoid predation, which limits their ability to store and recover elastic strain energy. Middle ear morphology and behavioural observations of kangaroo rats jumping vertically to avoid predation by owls and rattlesnakes support this view.
Classical Conditioning Alters the Efficacy of Identified Gill Motor Neurones in Producing Gill Withdrawal Movements in Aplysia
Authors: Lukowiak Ken , Colebrook Elaine
Published: April 2021

In a semi-intact preparation of Aplysia californica Cooper, classical conditioning training leads to changes in the synaptic strength at the sensory-motor neurone synapse. However, these changes are neither necessary nor sufficient to bring about the observed behavioural changes of the gill withdrawal reflex. We therefore tested whether the ability of a gill motor neurone to elicit a gill withdrawal response was altered following classical conditioning training of the reflex. We found that following classical conditioning training, the ability of a gill motor neurone to elicit a gill withdrawal response was significantly potentiated. In addition, in control preparations which did not receive classical conditioning training, the ability of a gill motor neurone to elicit a gill response was decreased. Thus, associative learning of this reflex appears to involve alteration in neuronal activity at loci distal to the sensory-motor neurone synapse.
Ultrastructure, Morphology and Organization of Biogenic Magnetite from Sockeye Salmon, Oncorhynchus Nerka: Implications for Magnetoreception
Authors: Mann Stephen , Sparks Nicholas H. C. , Walker Michael M. , Kirschvink Joseph L.
Published: April 2021

Although ferromagnetic material has been detected in the tissues of a variety of animals that are known or suspected to respond to magnetic fields, in only a few cases has the material been identified and its suitability for use in magnetoreception been determined. Using high-resolution transmission electron microscopy (HRTEM), we have studied magnetic particles isolated from ethmoid tissue of the sockeye salmon, Oncorhynchus nerka. Low-magnification electron micrographs showed chains containing up to 58 (median = 21-25) electron-dense particles that were held together by intimately attached organic material. The particle size range was 25-60 nm with a mean of 48 nm and a standard deviation of 8-5 nm. Elemental analysis, by energy-dispersive X-ray analysis (EDXA), electron diffraction patterns and HRTEM lattice images, showed that many of the particles were structurally well-ordered and crystallographically single-domain magnetite. These results imply that the production of the biomineral is under precise biological control. The crystal morphology was cubo-octahedral with the {111} faces of adjacent crystals lying perpendicular to the chain axis. The magnetic moments of the particles will therefore be aligned along the chain axis and will sum to produce a total moment dependent on the number of particles present in each chain. In the presence of the geomagnetic field, the mean moment for the particles will give a magnetic to thermal energy ratio of about 0·2. The corresponding calculations for individual chains gave two clusters of ratios ranging between 2·7 and 5·3 and between 6·6 and 9·5. The implications of these results in the possible use of the particles in magnetoreception are discussed.
Central Synaptic Coupling of Walking Leg Motor Neurones in the Crayfish: Implications for Sensorimotor Integration
Authors: Skorupski Peter , Sillar Keith T.
Published: April 2021

We present electrophysiological evidence for the presence of central output synapses on crayfish walking leg motor neurones. The effect of these central outputs is that a motor neurone can exert tonic graded control over other motor neurones without the requirement for spiking. Excitatory interactions among synergists and inhibitory interactions among antagonists are described. This central coupling among leg motor neurones profoundly affects their responses to afferent input from an identified stretch receptor, the thoracocoxal muscle receptor organ (TCMRO). Injecting current into a motor neurone can change the gain of TCMRO reflexes in other motor neurones. Some motor neurones are also capable of reversing the sign of TCMRO reflexes by inhibiting reflex firing of antagonists and facilitating reflex activity in synergists. The implications of these central interactions of motor neurones in motor control are discussed.
Temperature Effects on Haemolymph Acid-Base Status in vivo and in vitro in the Two-Striped Grasshopper Melanoplus Bivittatus
Authors: Harrison Jon M.
Published: April 2021

In this study, I examine the effect of temperature on haemolymph acid-base status in vivo and in vitro in the two-striped grasshopper Melanoplus bivittatus. Melanoplus bivittatus experience wide (up to 40 °C) diurnal body temperature fluctuations in the field, but maintain body temperature relatively constant during sunny days by behavioural thermoregulation. Haemolymph pH was statistically constant (7·12) between 10 and 25°C, but decreased by –0·017 units °C− 1 from 25 to 40 °C. Relative alkalinity and fractional protein dissociation were conserved only at body temperatures at which feeding and locomotory activity occur, above 20°C. Haemolymph total CO2 (Ctot) increased from 10 to 20°C and decreased from 20 to 40°C. Haemolymph increased from 10 to 20°C and was statistically constant between 20 and 40°C. Carbonic acid pKapp in haemolymph was 6·122 at 35 °C, and decreased with temperature by –0·0081 units °C− 1. Haemolymph buffer value averaged – 35mequivl− 1pHunit− 1. Haemolymph pH changes with temperature were small (less than –0·004 units °C− 1) in vitro at constant . Therefore, passive physicochemical effects cannot account for the pattern of acid-base regulation in vivo. The temperature shift from 10 to 20°C was accompanied by a net addition of 4·2–0·2 mmol I− 1 of bicarbonate equivalents to the haemolymph. The temperature shift from 20 to 40°C was accompanied by a net removal of 10–14 mmol I− 1 of bicarbonate equivalents from the haemolymph. Haemolymph acid-base regulation in vivo during temperature changes is dominated by active variation of bicarbonate equivalents rather than by changes in as observed for most other air-breathers.