bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Mechanical Work on Electrolyte and Water Distribution in Amphibian Skeletal Muscle
Authors: Boutilier R. G. , Emilio M. G. , Shelton G.
Published: April 2021

The present experiments were undertaken to confirm whether the increase in haematocrit that consistently accompanies the build-up of lactate in amphibian muscle cells during exercise can be explained in terms of a movement of water from the blood into the active muscles.

Electrically stimulated sartorius and gastrocnemius muscles isolated from Rana ridibunda and Xenopus laevis had consistently higher total water contents than their paired control muscles. In both instances, it was the intracellular water volume which gave rise to the increase in total muscle water. These results were corroborated in vivo by sampling gastrocnemius muscles from exercising and resting Xenopus laevis. Analyses of tissue electrolyte levels in the working muscles of each experimental series showed an increase in intracellular [lactate−] and [Na+]. A corresponding decline in cellular [K+] occurred in concert with increases in extracellular [K+],

In saline-perfused gastrocnemii of Xenopus, the uptake of vascular water was proportional to the total mechanical work performed. Saline leaving the femoral vein of isotonically contracting gastrocnemius muscles had a greater osmotic pressure than that of the arterial perfusate, whereas arterio-venous osmolality differences of control muscles were negligible. Calculations show that the haemoconcentration during exercise in vivo can be attributed at least in part to a net flow of plasma water to osmotically enriched muscle cells.
Phorbol Esters, Protein Phosphorylation and the Regulation of Neuronal Ion Channels
Authors: Kaczmarek L. K.
Published: April 2021

Protein kinase C is an enzyme whose activity is modulated by its lipid environment and which is fully activated by diacylglycerol in the presence of phosphatidyl serine and calcium ions. This kinase is highly enriched in the nervous systems of both vertebrates and invertebrates. The activity of protein kinase C can be stimulated in intact cells by certain synthetic diacylglycerols as well as by phorbol esters which substitute for endogenous diacylglycerol. The effects of such activators on the endogenous electrical properties of neurones, as well as on synaptic transmission, have recently been investigated in several vertebrate and invertebrate preparations of neurones. One example is that of the bag cell neurones of Aplysia which, in response to brief stimulation, generate a prolonged discharge during which the height of their action potentials is increased. Exposure of isolated bag cell neurones to activators of protein kinase C results in the enhancement of their action potentials through an increase in the amplitude of their voltage-dependent calcium current. This is caused by the unmasking of a previously inactive species of calcium channel in the plasma membrane.
Physiological Modulation of Gap Junction Permeability
Authors: Neyton Jacques , Trautmann Alain
Published: April 2021

In many tissues cells communicate directly through arrays of intercellular channels which are organized to form gap junctions. These channels are permeant to inorganic ions as well as to small hydrophilic molecules up to Mr2000. The electrical and chemical coupling provided by such junctions is under the control of intracellular and, in many cases, extracellular substances. The latter (hormones or neurotransmitters) function via the activation of intracellular second messengers. These can rapidly affect the state of opening of the junctions, or induce long-term modulation of the coupling. What are the second messengers and how do they control the functional state of the junctions? These questions′ remain largely unanswered, although several internal molecules are thought to be involved in these modulations (e.g. Ca2+, H+ or cyclic AMP). The double patch-clamp technique which enables control of both the intracellular milieu and high resolution measurement of transjunctional currents, has recently been applied to study these problems. In particular, it is now possible to examine at the single channel level how junctional conductance is modulated in terms, for example, of the number of open channels or channel elementary properties.
Physics of the Hen’s Egg
Authors: Moran T. , Hale H. P.
Published: April 2021

This paper is an account of observations made on the composition and behaviour of certain of the membranes in the hen’s egg. The composition is based on the examination of stained sections; the results should, however, give pointers in a purely chemical survey. Needham (1) has reviewed the work—chemical and histological—that has been carried out on the nature of the yolk and shell membranes. The common constituent appears to be keratin, but as he points out, this protein can exist in different forms with somewhat different properties.
Physics of the Hen’s Egg
Authors: Moran T.
Published: April 2021

The strength of this membrane is an important factor in the commercial storage of eggs, but it is also of fundamental interest as an index to the complex changes, chemical, physical and bacteriological, taking place in the egg. This paper describes a method for measuring the bursting strength together with a number of observations on the effects of different storage conditions.
The Excretion of Ammonia and Uric Acid During The Larval Life of Certain Muscoid Flies
Authors: Brown A. W. A.
Published: April 2021

In the early years of this century Weinland (1906) conclusively showed that ammonia constitutes the bulk of the nitrogenous excreta of larvae of the blow-fly, Calliphora vomitoria. This was a remarkable observation in a subphylum that was, and still is, considered essentially uricotelic. Pupae and imagines of this species excrete uric acid; Weinland was therefore led to postulate that pupation was basically a physiological change, the change from ammonia to uric acid as the protein catabolite. Twenty-five years later Delaunay (1931), reviewing protein catabolism in invertebrates, quotes Weinland’s work and states that “les larves de Calliphora…n’excrètent pas d’acide urique”.
Studies on the Growth of Tissues in Vitro
Authors: Willmer E. N. , Jacoby F.
Published: April 2021

In a previous number of this Journal (8) a method was described for measuring the growth rates of tissues in vitro. The colonies of fibroblasts were grown in modified Carrel flasks and photographed from below at regular intervals, so that a continuous record was obtained of the behaviour of the more peripheral cells of the colony over long periods of time. Mitoses could be easily observed, and the total number of cells on the field fairly accurately estimated. In this way the percentage of cells dividing per hour, or “mitotic index “, was calculated, and thereby a measure obtained of one of the more important factors concerned in the growth of tissues. By the use of this method it is possible to investigate the reaction of tissues to various growth-promoting or growth-inhibiting media, and to gain some insight into the general behaviour of growing tissues.
Apparatus for Investigating the Reactions of Land Arthropods to Humidity
Authors: Gunn Donald L. , Kennedy John S.
Published: April 2021

Apparatus for the investigation of the reactions of land arthropods to air humidity is described.

A(1). A straight line gradient of humidity is obtained with a long closed channel, into which water vapour is diffusing at one end, while being absorbed from it at the other end.

The undesirable ends present in the above apparatus are eliminated by constructing the channel in the form of a ring.

A (2). Any two humidities may be presented to an animal as alternatives in a simple chamber which has the advantage of providing space in which the animal can manœuvre, as well as being very cheap and easy to make. The exact form of the gradient is not, however, known in this chamber.

B (1). The effect of different air humidities on the general state of activity of an insect may be investigated in an “Aktograph” consisting of a delicately balanced box; the movements of an insect inside the box cause it to tip to one side or the other, and this tipping is recorded by a lever writing on a drum.

B (2). The existence of an avoiding reaction to humidity may be determined in the apparatus described under A (2), arranged so as to provide a wall of suddenly rising humidity across the centre of the dish.

B (3). A straight line gradient, which for convenience must be shorter than A (1), may be obtained across a wide area, suitable for the study of directed reactions.
The Role of the Fins in the Equilibrium of the Swimming Fish
Authors: Harris J. E.
Published: April 2021

An attempt was made to determine the relationship of the fins to the equilibrium of the swimming dogfish. Two factors at least are involved in this equilibrium; passive mechanical forces and reflex motions of the fins themselves. The part played by the automatic (passive) components was estimated by experimenting on a model of Mustelus canis mounted in a wind tunnel tested at a suitable air speed. The equilibrium in the horizontal plane (yawing equilibrium--for turning movements) is unstable without fins, completely stable only in the absence of the first dorsal fin, and is neutral when all fins are present. In the vertical plane (pitching equilibrium--for rising and diving turns) the equilibrium is unstable without fins, and this instability is greatly increased by the presence of the pectorals. The pelvics have little or no effect. Stability and controllability are inversely related. The fish is comparatively stable in the horizontal plane, extremely controllable in the vertical plane. This fact is closely related to the flexibility of the body for lateral movements. The results obtained in the wind tunnel were confirmed by amputation of the fins of the living dogfish. The normal equilibrium of the swimming dogfish in the vertical plane is determined largely by the pectoral fins and the heterocercal tail. The relationship of these facts to the problem of the evolution of the swimming chordates is considered.
Distribution of Na+ and K+ Currents in Soma, Axons and Growth Cones of Leech Retzius Neurones in Culture
Authors: García U. , Grumbacher-Reinert S. , Bookman R. , Reuter H.
Published: April 2021

Leech Retzius neurones were isolated by a new technique which allowed investigation of macroscopic currents over the surface of the cell body and the axons using loose patch-clamp. The distribution of ion current densities was measured for neurones that had just been removed from the CNS, and for cultured cells in which neurite outgrowth had begun. To standardize the mapping procedure, the same patch electrode was used at various sites along the neurone. Immediately after isolation of the cell, rapidly activating and inactivating Na+ currents were recorded from distal segments of the axons, but not from the soma or the proximal segment. Na+ currents were isolated by using patch electrodes containing tetraethylammonium (TEA+) and 4-aminopyridine (4-AP) to block K+ channels and Cd2+ to block calcium channels. Na+ currents in all regions of the neurone where they could be recorded were similar in their voltage dependence and kinetics. The Na+ current density was highest at the broken tips of the axon stumps. Neurites began to extend from the broken axon tips approximately 30 min after isolation. Newly grown processes showed a high density of Na+ currents at their growth cones. After 2 days in culture the current densities became more uniformly distributed and Na+ currents could then be recorded in the soma and proximal axon segments. In agreement with earlier studies made with conventional two-electrode voltage-clamp, three principal K+ currents were detected in Retzius cells: a rapidly activating and inactivating A-type current blocked by 4-AP (IA); a more slowly activating and inactivating delayed K+ current blocked by TEA+ (IK1) ; and a Ca2+-activated K+ current (Ic). Immediately after isolation of the Retzius cell, both rapid A-type and slow delayed K+ currents were distributed more uniformly than Na+ currents over the soma and axons. In their voltage sensitivities and kinetics, these two K+ currents were markedly different from each other; their characteristics were, however, constant in different regions of the cell. Ca2+ currents were too small to be measured directly during depolarizing pulses. However, tail currents were large enough to demonstrate the presence of Ca2+ channels in the proximal segment of the axon and in the soma; the currents were not sufficiently large to resolve their spatial distribution. It is concluded that ion channels are present in newly grown membranes and that the density of Na+ channels is highest in the tips of distal axon stumps from which outgrowth begins. By contrast, K+ currents are distributed more uniformly along the neurone.
Biomechanics of Flight in Neotropical Butterflies: Morphometries and Kinematics
Authors: Dudley Robert
Published: April 2021

Wing and body kinematics of free cruising flight are described for 37 species of Panamanian butterflies ranging over two orders of magnitude in body mass. Butterflies exhibit considerable diversity in body and wing shape, but morphological design is, in general, isometric. Wing loading and mean body diameter show positive allometry. The cruising flight of butterflies is characterized by low wingbeat frequencies (here averaging 11 Hz), stroke amplitudes averaging 103°, and forward speeds in excess of 1ms−1. Body angles during flight are close to horizontal, and stroke plane angles are correspondingly high. Advance ratios are typically greater than 0.9, indicating that the forward and flapping velocity vectors are of comparable magnitude. Flight speed scales with morphological parameters in general accordance with predictions based on isometric design. Interspecifically, no consistent correlation exists between wing kinematics and absolute flight speed. However, maximum positional angle and stroke amplitude tend to increase while body angle decreases with increased relative flight speed.
Taurine accumulation by the heart of embryonic skates,Raja eglanteria
Authors: Goldstein L , Luer CA , Blum PC
Published: April 2021

The hearts of elasmobranchs, like those of other vertebrates, contain high concentrations of the β-amino acid taurine, which is thought to play an osmoregulatory role in cardiac tissue. Although mammals and certain invertebrates can synthesize taurine from sulfur-containing precursors, e.g. cysteine, fish are unable to do so since they lack at least one enzyme involved in taurine biosynthesis: cysteine sulfinate decarboxylase (Jacobsen and Smith, 1968). Therefore, taurine must be acquired by fish via their diet (King et al. 1986). This poses a problem for the embryos of those fish that lay eggs and, for the early period of development at least, have no direct contact with amino acids in the external environment. Although solutes in the egg-case fluids can exchange with the sea water (Evans, 1981), the taurine concentration gradient between the egg case and the environment actually favors outward movement of taurine rather than uptake (L. Golstein, unpublished results). Therefore, we chose to study the mechanism by which the embryonic skate heart accumulates and maintains elevated trations of taurine in its heart. Concentrations of about 50 mmol l−1 taurine are typically found in cardiac muscle of adult specimens of the little skate Raja erinacea (Boyd et al. 1977).
Short Communication: Proline Transport by Brush-Border Membrane Vesicles of Starfish Pyloric Caeca
Authors: Ahearn Gregory A.
Published: April 2021

Starfish, unlike other echinoderms such as sea cucumbers and sea urchins, lack an effective intestine for nutrient absorption. Instead, they possess digestive diverticula called pyloric caeca which extend from the stomach wall into each arm and branch laterally into numerous blind-ended, epithelial-lined tubules. These tubules exhibit a number of physiological activities including the secretion of extracellular proteolytic enzymes (Lawrence, 1982), the storage of carbohydrates and lipids as energy reservoirs (Lawrence and Lane, 1982) and the absorption of low molecular weight organic solutes resulting from digestive activities in the diverticulum lumen (Ferguson, 1979, 1982; Jangoux, 1982; Lawrence, 1982). While it is clear from these studies that starfish pyloric caeca participate in nutrient absorption, there has been no direct physiological characterization of a transapical or transcellular transport process for amino acids or sugars by the epithelial cells of this organ. The present investigation is the first to show, using purified brushborder membrane vesicles from asteroid pyloric caeca, that amino acids can be transported across this membrane by at least one carrier-mediated process that displays properties in common with gastrointestinal absorptive organs of animals from a variety of phyla.
On the Function of a Locust Flight Steering Muscle and its Inhibitory Innervation
Authors: Wolf Harald
Published: April 2021

In tethered flying locusts, the pleuroalar (or pleuroaxillary) muscle of the forewing (M85) was stimulated via its efferent nerve. The effect on the angular setting of the wing was observed using photogrammetry. Maximal tetanic contraction of the muscle reduced downstroke pronation and upstroke supination by more than 25°. A more physiological stimulus regime resulted in angular changes of about 7°, which is near the range observed during steering manoeuvres. This confirms that the pleuroalar muscle plays an important role in adjusting the wing’s aerodynamic angle of attack, as proposed in anatomical studies by Pfau (1978). Unit a of the pleuroalar muscle was found to be innervated by the common inhibitor neurone 1 (CI) of the segmental ganglion. IJPs with amplitudes between 2 and 10mV were elicited by action potentials in CI. A basic tonus was observed in the pleuroalar muscle in the absence of activity in excitatory motoneurones. CI input reduced this basic contracture but did not affect EJPs or muscle twitches elicited by excitatory input. Activity of the common inhibitor was recorded intracellularly and with nerve electrodes in tethered flying locusts. Tonic discharges were observed with spike frequencies ranging from 5 to 35 Hz, 25 Hz being a typical value. EMG recordings from the two units of the pleuroalar muscle showed that only unit a was active during most horizontal flight sequences. While its discharge was modulated in response to imposed roll movements, unit b was recruited primarily during ipsilateral roll.

These results indicate functional specialization between pleuroalar muscle units a and b and suggest that the inhibitory innervation of unit a functions in the fine adjustment of wing pronation.
A Comparison of the Respiratory Function of the Haemocyanins of Vertically Migrating and Non-Migrating Pelagic, Deep-Sea Oplophorid Shrimps
Authors: Sanders N. K. , Childress J. J.
Published: April 2021

The effects of temperature and pH on haemocyanin oxygen-binding were compared for three species of diurnally vertically migrating and two species of non-migrating, pelagic oplophorid shrimps from the deep sea off the Hawaiian island of Oahu. The effects of L-lactate were also measured for three of these species. Haemocyanin concentrations were higher in the haemolymphs of oplophorids that migrate vertically (39.4, 46.8 and 57.6 mg ml−1) than in those of non-migrators (26.0 and 36.4 mg ml−1). Moderately high Bohr effects were found for vertically migrating and non-migrating oplophorids at all temperatures examined (5−25°C, ϕ= −0.46 to −0.80, and −0.55 to −0.88, respectively). The vertically migrating species had temperature-sensitive haemocyanins (ΔH=−23.1 to −41.2 kJ mol−1) across the normal temperature range (5–25 °C) encountered during diurnal vertical migration. This results in haemocyanins that have relatively high affinities (P50=0.80–1.06 kPa at pH 7.8,5 °C) at the low temperatures and low O2 partial pressures (approximately 2.66kPa O2 at 5°C) found at depth, and low affinities (P50=4.00–4.66kPa at pH 7.5, 25°C) at the higher temperatures and higher O2 partial pressures (approximately 13.33–17.50 kPa at 25°C) found in the near-surface waters. In contrast, the non-migrating species, which live within a narrower temperature range (3–6°C) and at a constant, low partial pressure of O2 (2.66–4.00 kPa), have haemocyanins with a high affinity for oxygen (P50=0.67–0.93 kPa at pH 7.8, 5°C) and lower sensitivity to temperature (ΔH−4.2 to −21.6kJ mol−1). The effects of temperature on the haemocyanin oxygen-affinities of the vertical migrators appear to be highly adaptive, enabling these haemocyanins to be functional across the entire depth (and thus, temperature and oxygen partial pressure) range encountered.
Autonomic regulation of cutaneous vascular resistance in the bullfrogRana catesbeiana
Authors: Malvin G. M. , Riedel C.
Published: April 2021

To gain a better understanding of the regulation of cutaneous blood flow in the bullfrog, the vascular innervation, vasoactivity and adrenoceptor types of the cutaneous vasculature were investigated using a pump-perfused skin preparation. Stimulation of cranial nerve I, the vagal ganglion, sympathetic ganglion 1 and sometimes sympathetic ganglion 2 caused cutaneous vascular resistance (CVR) to increase. Stimulation of cranial nerve IX and spinal nerves 1 and 2 had no effect on CVR. The response to stimulation of sympathetic ganglion 1 was antagonized by phentolamine but not by atropine. Phentolamine, atropine and α, β-methylene ATP had no effect on the response to vagal stimulation. Both epinephrine (EPI) and norepinephrine (NE) increased CVR, with EPI being more potent than NE. The minimum concentrations of EPI and NE required for a significant change in CVR were much higher than plasma catecholamine levels reported for resting bullfrogs. Phentolamine antagonized, but propranolol had no effect on, the responses to the catecholamines. Isoproterenol caused small decreases in CVR which were abolished by propranolol. Acetylcholine was a weak vasodilator. The results indicate that the cutaneous vasculature has two types of vasomotor nerves: sympathetic nerves that are probably adrenergic, and other nerves that are non-adrenergic/non-cholinergic and which do not use ATP as a transmitter. Although catecholamines are vasoactive, the sensitivity of the cutaneous vasculature to EPI and NE is probably too low to allow a direct regulatory role of these hormones on CVR. There is no evidence for cholinergic regulation of CVR. Both α- and β- adrenoceptors are present in the cutaneous vasculature, α-Adrenoceptors mediate the constrictor responses to sympathetic nerve stimulation and catecholamine administration. It is unlikely that β-adrenoceptors play a significant role in regulating CVR.
The Importance of Vascular Elasticity in the Circulatory System of the CephalopodOctopus Vulgaris
Authors: Shadwick R. E. , Nilsson E. K.
Published: April 2021

The passive mechanical properties of the dorsal aorta and the vena cava of Octopus vulgaris were investigated in vitro. Both vessels are highly distensible structures that exhibit non-linear elasticity, but have substantially different material properties. The volume compliance of each vessel is maximal within the resting physiological pressure range (2–3 kPa in the aorta and 0–0.5 kPa in the vena cava) but is five times greater in the vena cava than in the aorta. The aorta is mechanically suited to function as an elastic storage reservoir in the arterial circulation, while the vena cava is appropriately designed to be a low-pressure capacitance element.

Pressure wave velocity in the aorta was calculated from the elastic modulus to be 1.8ms−1 under resting conditions. Therefore, pressure changes will occur almost simultaneously throughout the arterial tree and pressure wave transmission properties can be described by a two-element Windkessel model. Predictions of vascular impedance amplitude made from this model are presented.

The effectiveness of the aorta as an elastic reservoir appears to be severely reduced during exercise in Octopus. Because blood pressure increases while heart rate does not, the efficiency of the Windkessel will be diminished as the time constant of the system decreases and the pulsatile work of the heart subsequently increases.
The Actions of Proctolin, Octopamine and Serotonin on Crustacean Proprioceptors Show Species and Neurone Specificity
Authors: Pasztor Valerie M. , Macmillan David L.
Published: April 2021

A comparative survey is presented of the responsiveness of crustacean mechanoreceptors to the neurohormones proctolin, octopamine and serotonin. Seven identifiable primary afferents were examined in the crayfish Cherax destructor and the lobster Homarus americanus: three from the oval organ (OO) of the second maxilla, two from the non-spiking stretch receptor (NSSR) of the swimmeret and two from the muscle receptor organ (MRO) of the abdomen. Proctolin modulation was observed in 10 of the 14 fibres tested and was invariably potentiating, resulting in enhanced receptor potential amplitudes and increased firing. Octopamine and serotonin each modulated 8 of the 14 fibres and their effects were excitatory or depressive depending upon the target fibre. In the latter case the receptor potentials became attenuated, often to subthreshold levels, with loss of spiking.

A comparison of results from Cherax with those of Homarus shows that there is species specificity in the responses of homologous neurones. Neurohormones that are excitatory in one species may be ineffective or depressive in the other.

The broad distribution of modulatory effects observed here suggests that sensitivity to biogenic amines and peptides is a general property of proprioceptors.
Substratum Slope and the Alignment of Acute Zones in Semi-Terrestrial Crabs (Ocypode Ceratophthalmus)
Authors: Zeil Jochen
Published: April 2021

The organisation of the visual system in semi-terrestrial crabs is related to the three-dimensional structure of the environment (Zeil et al. 1986; Nalbach and Nalbach, 1987; Nalbach et al. 1989a,b;Zeil et al. 1989). In species that Eve in flat habitats - like sandy ocean beaches or mudflats - we find: (1) long, vertically oriented eye stalks; (2) a small separation between the eyes; (3) an acute zone for vertical resolving power with its maximum along the eye equator; and (4) a specific gradient of vertical resolution towards more dorsal and more ventral directions of view. Species that live in three-dimensionally more complex worlds - like rocky shorelines and within mangrove forests - have short eye stalks far apart at the lateral corners of the carapace and lack prominent acute zones.
Modulation of Heart Activity in the Terrestrial SlugLimax Maximusby the Feeding Motor Program, Small Cardioactive Peptides and Stimulation of Buccal Neuron B1
Authors: Welsford Ian G. , Prior David J.
Published: April 2021

Activation of the feeding motor program (FMP) increases the force of ventricular contractions in heart/central nervous system (CNS) preparations of the terrestrial slug Limax maximus (Linnaeus). The FMP-induced increase in ventricular activity requires innervation of the heart by abdominal ganglion nerves N9 and Nil. Application of the small cardioactive peptides SCPA and SCPB to isolated preparations of the heart causes dose-dependent increases in the force of ventricular contractions. In addition, the SCPs induce rhythmic contractions in quiescent heart preparations. The effects of the SCPs appear to be specific in that the neuropeptide FMRFamide has an inhibitory effect on ventricular activity. SCP-like and FMRFamide-like immunoreactive material is found in the heart, kidney and pericardium and in the nerves that innervate these organs. Unilateral intracellular stimulation of buccal neuron Bl, which contains SCP-like and FMRFamide-like immunoreactive material, mimics the FMP-and SCP-induced increases in ventricular activity. The effect of B1 on ventricular activity is frequency dependent and requires innervation of the heart by Nil. These results are consistent with the hypothesis that the SCPs are involved in feeding-related alterations in heart activity in Limax and that the control of this effect involves neuron Bl.
Actions Of Putative Amino Acid Neurotransmitters On The Neuropile Arborizations Of Locust Flight Motoneurones
Authors: Dubas F.
Published: April 2021

To characterize the receptors for putative amino acid neurotransmitters present on the dendritic arborizations of flight motoneurones in Locusta migratoria, the effects of pressure applications of glutamate, γ-aminobutyric acid (GABA), aspartate, taurine, glycine and cysteine were studied using an animal preparation in which neuropile intracellular recordings could be made during expression of the flight motor output. A majority of cells responded to glutamate, GABA, aspartate and taurine. At resting potential, glutamate and GABA caused, in different cells, a depolarization, a hyperpolarization or, in a few cells, a biphasic response, all accompanied by a decrease in the size of the evoked and spontaneous postsynaptic potentials (PSPs). At spiking threshold, the responses were always hyperpolarizing. Activation of a chloride conductance mediated the effects of both glutamate and GABA. In some cells, the response to glutamate or GABA desensitized during long-lasting applications, but in most cells the amplitude of the response did not decrease during applications lasting several minutes. Responses to aspartate and glutamate had identical reversal potentials and cross-desensitized. Responses to GABA and taurine had more negative reversal potentials and did not cross-desensitize with those elicited by glutamate or aspartate. Only a few neurones responded to applications of glycine or cysteine at resting potential; they responded with an inhibition of spiking at depolarized potentials. These data suggest that a variety of amino acid receptors are present on the neuropile arborizations of flight motoneurones.
The Function of the Urinary BladderIn Vivoin the Freshwater Rainbow Trout
Authors: Curtis B. James , Wood Chris M.
Published: April 2021

Two different approaches were employed to examine the possible urine storage and ionoregulatory functions of the urinary bladder in vivo in the freshwater trout. An indirect approach, using non-catheterized fish, involved ‘spot sampling’ from the bladder to determine urine composition and measurement of PEG-4000 release into surrounding water to quantify urination events. The direct approach employed a new external catheterization technique to collect naturally discharged urine. Both methods demonstrated that trout urinate in intermittent bursts at 20–30 min intervals, and that natural urine flow rate is at least 20% lower and urinary Na+ and Cl− excretion rates at least 40 % lower than those determined by the traditional internal bladder catheter technique. The urine is stored for approximately 25 min prior to discharge, and significant ionic reabsorption via the bladder epithelium occurs during this period; a small residual volume is always likely to be retained. We conclude that previous studies using internal bladder catheterization have underestimated the ionoregulatory effectiveness of the entire renal system by preventing the function of the urinary bladder.
Olfactory Cues Perceived at the Home Loft are not Essential for the Formation of a Navigational Map in Pigeons
Authors: Waldvogel Jerry A. , Phillips John B.
Published: April 2021

Deflector lofts consist of a ‘pinwheel’ arrangement of four stationary deflector panels attached to the sides of a cube-shaped cage. These panels are made of wood and Plexiglas and rotate incoming winds in either a clockwise or counterclockwise direction. When released at a distant site, homing pigeons (Columba livia) raised in deflector lofts exhibit a shift in orientation relative to controls which corresponds to the clockwise or counterclockwise rotation of winds in their loft, suggesting the involvement of wind-borne olfactory cues in pigeon navigation. As part of a long-term study designed to test whether orientation cues other than odors might also be involved in creating the deflector-loft effect, we carried out experiments in upstate New York, USA, in which deflector lofts were modified to reverse the direction of light reflected from the Plexiglas panels while leaving the rotation of winds unchanged. The results indicate that the orientation of pigeons raised as permanent residents of these altered deflector lofts is not influenced by reflected light cues; i.e. they exhibit the same orientation bias as birds raised in the lofts with normal panels. This is in direct contrast to our previous findings that non-resident pigeons kept in the altered lofts for short periods exhibit a reversal of initial orientation compared to birds from the lofts with normal panels. However, when permanent-resident birds are prevented from having a direct view of the horizon sky by the addition of ‘anti-cheating’ slats (which prevent the birds from seeing beyond the end of each panel), the deflections are either greatly reduced or eliminated entirely, contrary to the predictions of olfactory navigation models. This disappearance of the deflector-loft effect in the presence of anti-cheating slats suggests that the positions of the deflector panels in the two experimental lofts must be differentially influencing important visual orientation cues reaching the birds housed inside. We believe that these cues are probably derived from polarized skylight emanating from the horizon, and that the obstruction of specific regions of horizon skylight by the deflector panels in the two experimental lofts is responsible for a miscalibration of the pigeon’s sun compass. This miscalibration, in turn, generates the orientation bias observed for deflector-loft birds. Our findings force us to conclude that, at least for pigeons raised in New York (and perhaps those from other geographical locations as well), olfactory cues perceived at the home loft do not contribute to the formation of the navigational map.
Studies on the Fauna of an Algerian Hot Spring
Authors: Mason I. L.
Published: April 2021

Many exaggerated statements have been made, and too often uncritically repeated, concerning the temperatures at which animals and plants have been found in hot springs. To throw light on this subject, the author undertook two expeditions—in the summer of 1937 and the winter of 1938–9—to study the hot springs at Hammam Meskoutine, Algeria.
The Evolution of Activity Capacity
Authors: Bennett Albert F.
Published: April 2021

The capacities of animals for activity (burst speed, maximal exertion, endurance) are examined in relation to their selective importance in extant populations and the pattern of their evolution in major animal taxa.

Activity capacities have been demonstrated to be both heritable and highly variable in natural populations and hence susceptible to natural selection. Some field studies have demonstrated significant positive associations between activity capacities, particularly burst speed, and survivorship; other studies have not. The potential for such selection therefore clearly exists, although it may not operate in all populations.

Comparative studies of major taxa have linked endurance capacities to maximal rates of oxygen consumption; speed and exertion are correlated with capacities for anaerobic metabolism, either the catabolism of phosphagens or the production of lactic acid or octopine, depending on taxon. In vertebrates, the primitive metabolic pattern involved the use of aerobic metabolism to support moderate swimming performance, supplemented by bursts of activity fuelled through lactic acid production. Because of much greater locomotor costs, the transition of vertebrates onto land entailed a decrease in endurance, which was greatly expanded again only after the evolution of the higher rates of aerobic metabolism characteristic of the birds and mammals. These greater aerobic capacities may have been selected for thermoregulatory reasons and/or for increased activity capacity itself.
Effect of Exercise on Amino Acid Concentrations in Skeletal Muscle and Plasma
Authors: Henriksson Jan
Published: April 2021

Protein is not normally an important energy fuel for exercising muscle. In spite of this, there is a significant increase in the rate of amino acid catabolism during exercise. This is secondary to the exercise-induced increase in several metabolic processes, such as hepatic gluconeogenesis and the citric acid cycle, where amino acid carbon is utilized. The suppression of protein synthesis during an exercise bout leaves amino acids available for catabolism. There is some evidence that basal amino acid concentrations in plasma and muscle may be higher in trained than in untrained individuals. In the rat, the concentration of free amino acids is higher in slow-twitch than in fast-twitch muscles. With short-term exercise, the transamination of glutamate by alanine aminotransferase leads to increased levels of alanine in muscle and plasma, and an increased release of alanine from the muscle. At the same time, the muscle and plasma glutamate concentrations are markedly decreased. The plasma glutamine level is elevated with short-term exercise, but changes in muscle glutamine concentration are more variable. With prolonged exercise, there is a depletion of the plasma amino acid pool, which may be explained by an increased consumption in organs other than muscle. With the exception of alanine, we found, however, that the muscle levels of free amino acids are kept stable throughout a 3.5-h exercise period. There is a significant activation of branched-chain amino acid metabolism with prolonged exercise, and the current data indicate that this is more pronounced in endurance-trained subjects than in untrained controls.
Patterns of Metabolic Recovery from Exercise in Amphibians and Reptiles
Authors: Gleeson Todd T.
Published: April 2021

The physiological responses of amphibians and reptiles undergoing vigorous exercise are qualitatively similar to those of other vertebrates. Oxygen consumption increases rapidly to rates that are three-to 10-fold the rates at rest. The aerobic response to graded exercise in locomoting reptiles and amphibians is for the most part linear. Oxygen transport by the cardiovascular system during exercise is accomplished by factorial increases in heart rate and oxygen extraction from arterial blood in a fashion similar to that in mammals. Increments in stroke volume during exercise are small or in some cases negative. The influence of temperature or of intracardiac shunting on the cardiovascular function of active amphibians and reptiles is poorly understood. These aerobic responses to exercise are accompanied by robust anaerobic contributions to energy metabolism, resulting in significant lactate accumulation and glycogen depletion. The rate of lactate accumulation during exercise is generally greater in reptiles than in amphibians, but in all cases is so rapid that the only significant substrate source to support anaerobic energy production is muscle glycogen. Vigorous behavior in these animals is therefore limited to some degree by the maintenance and replenishment of muscle glycogen stores. Whereas data from rats and dogs suggest that most lactate is oxidized to CO2 following exercise, amphibians and reptiles appear to use lactate as a substrate for immediate muscle glycogen replenishment. Data from a variety of amphibians and lizards demonstrate that lactate removal following activity and glycogen replenishment are stoichiometrically and temporally related. Studies employing isotopically labelled compounds in intact frogs and lizards indicate that most lactate is resynthesized to glycogen during recovery. In vivo studies suggest skeletal muscle as the site for glycogenesis from lactate, and in vitro studies from many laboratories demonstrate a gluconeogenic capacity in skeletal muscle of lizards, frogs and salamanders. The liver appears to play no significant role in recovery metabolism in any of these classes. Data from lizard muscle suggest that oxidative fiber types have the most significant gluconeogenic capacity, and that the process may be stimulated by the hormonal milieu that exists following exercise. Whereas the recovery metabolism of many mammals seems to facilitate the rapid return of acid-base balance via lactate oxidation, the strategy of lactate removal employed by amphibians and reptiles provides for a mechanism of immediate muscle glycogen replenishment and consequently a reestablished capacity for subsequent activity.
Cardiovascular and Respiratory Control Mechanisms During Exercise: an Integrated View
Authors: Turner Duncan L.
Published: April 2021

Exercise can impose an immense stress upon many physiological systems throughout the body. In order that exercise performance may be optimally maintained, it is essential that a profound and complex series of responses is coordinated and controlled. The primary site for coordination is the central nervous system, whereas control mechanisms (both feedback loops and feedforward activation) involve complex sensory information, often in the form of neural coding but also in the form of blood-borne chemical signals, a number of levels of peripheral and central integration and, finally, the efferent branches of the nervous system coursing via sympathetic and parasympathetic nerves to target sites of action.

The neurohumoral control of the cardiorespiratory responses to exercise has received intense attention for over two decades and some particularly important steps forward in its understanding have occurred within the last 10 years. The initial fast increase (phase 1) in cardiovascular and ventilatory flow parameters are brought about by neurally mediated muscle mechanoreceptor feedback reflexes and a feedforward ‘central motor command’. The blood pressure operating point is also raised by a combination of these two neural mechanisms. Fine control of the matching of cardiac output to ventilation may occur by means of a feedforward ventilatory control of cardiac origin. During the slower phase of adjustment (phase 2), the neurally mediated mechanisms are augmented by a cohort of humorally mediated feedback reflexes involving muscle and vascular chemoreceptors as well as being supported by central neural reverberation. A steady state of cardiorespiratory responses is achieved (phase 3) by an amalgamation of neural and humoral, i.e. ‘neurohumoral’, control mechanisms, which then must further modulate the cardiorespiratory responses to exercise in the face of increasing competition from other basic physiological requirements, such as thermoregulation and fluid homeostasis.

The myriad of subtle modifications in the basic blueprint found throughout the vertebrates illustrates the flexibility of the principal design and also how it can be applied to an extraordinary number of specific ecophysiological niches.
The Ionic Basis of the Hypo-Osmotic Depolarization in Neurons From the Opisthobranch Mollusc Elysia Chlorotica
Authors: Quinn R. H. , Pierce S. K.
Published: April 2021

The resting potential of identified cells (Parker cells) in the abdominal ganglion of Elysia chlorotica (Gould) depolarizes by about 30 mV in response to a 50% reduction in osmolality and returns to the original potential in 20 min. Cell volume recovery requires approximately 2 h. Thus, recovery of the resting potential is not dependent on recovery of cell volume. The hypo-osmotic depolarization persists following inhibition of the electrogenic Na+/K+-ATPase with ouabain, and the levels of extracellular K+ and Cl− have little effect on the magnitude of the depolarization, while decreasing extracellular Na+ concentration produces a depolarization of only 10 mV. This suggests that the hypo-osmotic depolarization in Parker cells results mostly from increased relative permeability to Na+. Following transfer from 920 to 460mosmolkg−1, Na+, Cl− and proline betaine leave the cells while intracellular K+ is conserved. Loss of intracellular Na+ and conservation of intracellular K+ are dependent on active transport by the Na+/K+-ATPase. Na+ and proline betaine leave the cells with a time course that is much longer than that of the hypo-osmotic depolarization. Unlike the other solutes, most of the reduction in intracellular Cl− concentration occurs coincidentally with the hypo-osmotic depolarization. However, unlike the hypo-osmotic depolarization, bulk loss of Cl− does not require the reduction in osmolality, only the reduction in extracellular ion concentrations. There is no apparent relationship between membrane depolarization and the regulation of intracellular osmolytes in Elysia neurons following hypo-osmotic stress.
Wing Movements Associated With Collision-Avoidance Manoeuvres During Flight in the Locust Locusta Migratoria
Authors: Robertson R. Meldrum , Reye David N.
Published: April 2021

Flying locusts will try to avoid colliding with objects directly in their flight path. This study investigated the wing movements and behaviour patterns associated with collision avoidance. Tethered locusts were flown in a wind tunnel. Targets were transported at different speeds either directly towards the head of the animal or to one side of the midline but parallel to it. Changes in the form of the wingbeat for each of the wings were monitored using either a video camera or a high-speed ciné camera. Animals attempted to avoid an impending collision by making movements interpreted here as (a) increasing lift to fly over the object, (b) gliding and extending the forelegs to land on the object, and (c) steering to one side of the object. Steering was monitored by observation of abdominal movements. Steering to one side of an approaching target was reliably associated with an earlier and more pronounced pronation of the wings on the inside of the turn. Also, in the middle of the downstroke, the forewings were markedly asymmetrical. On the outside of the turn, the forewing was more elevated and separate from the hindwing. On the inside of the turn, the forewing was more depressed and often came down in conjunction with, or in advance of, the hindwing on that side. The forewing asymmetry correlated with the position of the target such that most attempted turns were in the direction that would take the animal around the closest edge. High-speed cinematography showed that the asymmetry was caused both by changes in the timing of the two wings and by changes in the angular ranges of the wingbeats. We propose that these changes in the form and timing of the wingbeats are likely to have swung the flight force vector around the long axis of the body to produce a banked turn around the closest edge of the object.
A Paradoxical Problem in Insect Communication: Can Bush Crickets Discriminate Frequency?
Authors: Hartley J. C. , Stephen R. O.
Published: April 2021

Many bush crickets (Tettigoniidae) produce calls that consist of trains of transient high-frequency pulses (Fig. 1). Each pulse is generated by a file tooth on one wing being struck by a plectrum on the other, causing the wing resonator to produce harmonic transients each composed of only two or three cycles of oscillation. In animals, high-frequency sound can only be detected by means of some form of auditory filter, since the refractory period of the nervous system restricts direct measurement using periodicity to frequencies below 1 kHz. The necessity of using a filter produces a paradoxical situation with these brief transients. If the bandwidth of a tuned filter is such that frequency can be accurately discriminated, the response time may exceed the duration of the signal and then there would be no output. To respond to such a signal, the filter bandwidth must be increased but then frequency information is lost.