bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of Lampbrush Chromosomes in the formation of Nucleoli in Amphibian Oocytes
Authors: MACGREGOR H. C.
Published: April 2021

Theories concerning the mode of origin of peripheral nucleoli in amphibian oocytes have been examined and tested.

In Triturus cristatus the giant fusing loops of the 3 shortest lampbrush bivalents resemble nucleoli when viewed in phase contrast and may be considered as possible sites of production of nucleoli. Giant fusing loops, however, differ from peripheral nucleoli in certain important respects, and animals lacking giant fusing loops on their lampbrush chromosomes nevertheless have normal peripheral nucleoli. Therefore, similarity in appearance between objects attached to lampbrush chromosomes and free peripheral nucleoli may not be significant.

In oocytes of T. c. carnifex, T. c. karelinii, and T. c. danubialis, peripheral nucleoli do not increase in number during the lampbrush phase of oogenesis, except by division of pre-existing nucleoli towards the end of oogenesis. There are about 1,000 nucleoli per oocyte nucleus in each of these sub-species.

In T. c. cristatus there are more nucleoli in large oocytes than in small ones, and it seems likely that in this sub-species the giant fusing loops add to the existing population of nucleoli in an oocyte by successively growing and shedding new nucleoli. A similar situation probably holds in Plethodon cinereus.

Hexaploid oocytes from triploid females of Ambystoma jeffersonianum have 3 times as many nucleoli as diploid oocytes from diploid females of the same species. The number of nucleoli in an amphibian oocyte nucleus is therefore related to the number of sets of chromosomes in the cell.

In yolky oocytes from hypophysectomized newts most peripheral nucleoli are firmly attached to the inner surface of the nuclear membrane; whereas in similar oocytes from unoperated or gonadotrophin-treated animals none of the nucleoli is so attached.

On the basis of these observations 2 mechanisms are suggested for the formation of amphibian oocyte nucleoli. The first of these mechanisms probably operates in T. c. carnifex, where all peripheral nucleoli are formed before or soon after the chromosomes assume the lampbrush form, and no part of a lampbrush chromosome is involved in a process which adds to the existing population of nucleoli. The second mechanism probably operates in T. c. cristatus, where most of the peripheral nucleoli are formed before the lampbrush phase of oogenesis but a nucleolar organizer on the lampbrush chromosomes continues to grow and detach nucleoli throughout oogenesis. Both these mechanisms are discussed in terms of what is known of the chemical composition and function of peripheral nucleoli.
The Structure of the Cornea as Revealed by Polarized Light
Authors: Naylor E. J.
Published: April 2021

Studies of corneal sections in polarized light indicate that there are about too lamellae in the cat cornea; the coefficient of fibre birefringence is 0·0030.

No evidence was found of preferential orientation of fibre directions. Corneal disks examined by an immersion technique show that the cornea exhibits both form and intrinsic birefringence of positive sign with a micellar refractive index of 1·50-1·52. The values of both form and intrinsic birefringence in various fixatives can be explained on the basis of swelling, which is both inter- and intra-micellar. The micellar volume according to the Wiener relationships does not exceed 3 per cent.; possible causes of this are discussed.

MEASUREMENTS of the retardation of the cat cornea as a whole (Stan-worth and Naylor, 1950) can be analysed mathematically (Stanworth and Naylor, 1952) and indicate that the coefficient of birefringence of the constituent fibres of the cornea is about 0·0028. In order to investigate this value experimentally, antero-posterior sections 15 μ thick were prepared from fresh cat corneae by freezing methods or from formalin-fixed corneae by prior embedding in paraffin wax. When these were examined under the polarizing microscope it was found that the retardation varied considerably according to the method of preparation and the mounting medium employed, indicating that the corneal birefringence is in great part due to the form or textural variety. The investigation was therefore extended and approached from two aspects, the microscopic and the sub-microscopic structure.
The Sarcosomes of Heart Muscle
Authors: CLELAND K. W. , SLATER E. C.
Published: April 2021

1. A study of the distribution of the granules in rat heart-muscle fibres confirmed the early morphological findings. We prefer to describe these granules under the name of sarcosomes, first introduced by Retzius.

2. In sections, heart sarcosomes are seen as rods in close association with the anisotropic disks of the myofibrils. The rod-shape is believed to be due to compression of the sarcosomes between adjacent myofibrils. Isolated sarcosomes which retain the elasticity of those in the living state would be expected to be spherical.

3. Preparations of sarcosomes isolated with hypertonic sucrose contained many rods. Spheres were obtained with isotonic saline or sucrose. Water, ethylene glycol, or glycerol gave greatly swollen and otherwise altered sarcosomes.

4. In hypotonic media, sarcosomes underwent a series of partially reversible morphological changes termed ‘transformation’. These changes, which are caused by penetration of water into the sarcosomes, are described in detail.

5. Studies of ‘transformation’ gave clear evidence that the intact sarcosome is composed of a central body in the form of a gel surrounded by a membrane. As the tonicity of the medium was decreased, the body progressively disappeared, leaving eventually a large vesicle surrounded by the membrane. In this condition the membrane readily breaks up into particles which contain all the enzymes which constitute the respiratory chain, but is devoid of most dehydrogenases and phosphorylating enzymes.

6. On standing in isotonic media the membrane is rapidly damaged, causing penetration of solutes so that the sarcosomes transform in much the same way as in hypotonic media. This ‘spontaneous transformation’ was greatly delayed by the calcium-chelating agents versene or citrate and by adenosine diphosphate or triphos-phate, and was accelerated by calcium.
The Fine Structure of the Scales and Teeth of Raia Clavata
Authors: POOLE D. F. G.
Published: April 2021

The fine structure of the scales of Raia clavata has been determined by means of the polarizing microscope and X-ray analysis. Each scale consists of a cone of dentine covered by an enamel-like layer and both of these tissues contain crystallites of the mineral hydroxyapatite. In each case the crystallite size is similar to that of mammalian dentine possessing the same mineral. However, whereas the dentine of Raia contains both collagen fibres and mineral crystallites arranged parallel with the surface of the scale, the enamel-like layer has a low organic content and its crystallites lie with their optic axes at right angles to the surface. These differences in crystallite arrangement and organic content result in different optical properties in the two tissues. Nevertheless, both tissues are produced by the mesoderm cells of the dentine papilla, and in this respect the enamel-like tissue differs fundamentally from the ectodermal enamel of mammalian teeth.
The Supposed Pre-pupa in Cyclorrhaphous Diptera
Authors: Whitten Joan M.
Published: April 2021

The pre-pupal cuticle generally described for Diptera Cyclorrhapha is here considered to be an inner layer of larval endocuticle rather than the cuticle of a distinct prepupal instar. Chemical and microscopical evidence is given. The mechanism of rupture of the operculum is also discussed in connexion with endocuticle secretion, sclerotization, and subsequent water loss.
The Structure and Hydromechanics of the Musculo-epithelium in Metridium
Authors: Robson Elaine A.
Published: April 2021

Musculo-epithelial cells have been isolated from mesenteries of the sea-anemone Metridium senile, and the descriptions of earlier workers confirmed. The cells contribute both to the muscle-field above the mesogloea and to its overlying epithelium. In sections or whole mounts it is possible to see numerous vertical strands passing from the epithelial elements to their muscle-fibres. The protoplasmic strands are separate from one another and are thus surrounded by fluid which forms a continuous thin layer between the epithelium and muscle-field. It is proposed to call this the subepithelial fluid.

Epithelial elements from contracted mesenteries are much taller than those from stretched tissue. As the area of the mesentery decreases during contraction a reversible change from pavement to columnar epithelium takes place. The epithelium is able to follow rapid contractions without delay, owing to the hydrostatic action of the subepithelial fluid in thrusting it outward. There is as yet no evidence that the epithelial protoplasm moves by its own activity during contraction or relaxation. It may be moved passively and has considerable elasticity. Modifications of the musculo-epithelium in certain anatomical regions are discussed.

Although true musculo-epithelium characterizes only the coelenterates, analogous systems occur in the tissues of several higher animals, and it is suggested that intercellular fluid may have a hydrostatic function in these situations also. The possible metabolic role of subepithelial fluid in Metridium is discussed, and it is suggested that it and the mesogloeal fluid together form an ‘internal medium’ which may provide some degree of biochemical co-ordination in this animal.
The use of Cholinesterase Techniques for the Demonstration of Peripheral Nervous Structures
Authors: Coupland R. E. , Holmes R. L.
Published: April 2021

An account is given of a modification of the method of Koelle and Friedenwald for the demonstration of cholinesterase activity. When this method is employed, diffusion artifacts are minimal, and good histological pictures of central and peripheral nervous structures can be obtained. Certain advantages of this method over metallic impregnation and methylene blue techniques for demonstration of nervous elements are discussed, and its application to a variety of tissues described.
The Physical Nature of the Lipid Globules in the Living Neurones of Helix aspersa as indicated by Measurements of Refractive Index
Authors: Ross K. F. A. , Chou J. T. Y.
Published: April 2021

The lipid globules in the neurones of Helix aspersa have been found by Chou in 1957 to be of three distinct kinds that differ from each other in chemical composition. In the present investigation, the refractive indices of these three kinds of globule were measured by the technique for measuring the refractive indices of cytoplasmic inclusions in living cells developed by Ross in 1954, which is here described in detail.

It was found that the refractive indices of the globules containing mixed lipids and proteins and those that probably contained triglycerides alone, all had relatively high refractive indices of about 1-47-1-50. These values are comparable with the known refractive indices of many pure lipids.

The refractive indices of the globules containing phospholipid were much lower, being about 1-41-1-42, which is lower than that of any pure lipid. This indicates that these globules probably also contain appreciable amounts of water associated with the phospholipid molecules, as was suggested by Schmidt in 1939.

The results also show that refractive index measurement made in conjunction with histochemical investigations may, in some cases, provide useful additional information about the physico-chemical nature of cell constituents.
The Structure of Insect Tracheae
Authors: Locke M.
Published: April 2021

Tracheae of Rhodnius prolixus StÅhl have been studied with the light and electron microscopes. The tracheae have three cuticular components: a two-layered membrane lining the tube and the taenidia between it and the epithelium. The layer upon the lumen face is similar in appearance and properties to the cuticulin layer over the abdomen. The other layer is of chitin with the micelles axially oriented and protein with a stability suggesting tanning. A comparable but slightly thicker layer not penetrated by pore canals exists over the abdomen where it is sclerotized and lipid impregnated. The taenidia also contain chitin and protein but the micelles are arranged tangentially. A tube constructed in this way is well adapted to resist lateral compression while allowing changes in length.
The Cuticular Stress Detector (Csd2) of the Crayfish II. Activity During Walking and Influences on Leg Coordination
Authors: Klärner Diemut , Barnes W. Jon P.
Published: April 2021

When a crayfish walks forward, its legs are not loaded equally. The third pair is the one exerting the largest vertically directed force, and the fourth legs produce the major part of the propulsive force. Chronic recordings from a CSD2 nerve were made in crayfish walking on a treadmill. The activity of CSD2 rises during the stance phase. The activity peak at the beginning of the power stroke is especially pronounced in leg 4, which was studied in detail. The average spike frequency of CSD2 recordings during the first part of the power stroke is positively correlated with the initial increase in force produced by the leg. This suggests that CSD2 responds especially well to rapid load changes. When a wire was fixed around a fourth leg such that it depressed the patch of compliant cuticle associated with CSD2, the activity of the sense organ was elevated throughout the entire step cycle, and the time between leg 4 touching the ground and leg 3 lifting off was more variable than in normal walking. Thus, CSD2 seems to be involved in the coordination of the walking legs. Depressing the compliant cuticle of CSD2 elicits reflexes in the flexor muscle and the anterior levator in tethered crayfish. Interleg reflexes were not found.
Mechanisms of Ph Regulation in Lamprey (Lampetra Fluviatilis) Red Blood Cells
Authors: Nikinmaa Mikko , Kunnamo-Ojala Tuna , Railo Eira
Published: April 2021

Mechanisms regulating the red cell pH in lamprey (Lampetra fluviatilis) were studied using the ammonium chloride prepulse technique. The cells were initially incubated in a physiological saline containing 20 mmol l−1 ammonium chloride, and intracellular pH measured with the DMO technique. Ammonium chloride was then rapidly removed by centrifugation, and the changes in the intracellular pH followed.

The intraerythrocytic pH is primarily regulated by an amiloride-sensitive sodium/ proton exchange. When sodium is present in the incubation medium, the intracellular pH rapidly recovers from the acidification associated with the removal of ammonium chloride from the incubation. When sodium is removed from the incubation medium, intracellular pH does not recover, and when the cells are treated with 10−3mol l−1 amiloride in the presence of sodium, carbon dioxide and bicarbonate, the intracellular pH recovery is drastically reduced.

The movements of carbon dioxide, its consecutive catalysed hydration and dissociation to protons and bicarbonate and, possibly, movements of bicarbonate out of the cell acidify the cell contents. This is shown by the observation that the steady-state intracellular pH is higher in a HEPES-buffered medium than in a CO2/HCO3− -buffered medium at the same extracellular pH. The acidification is dependent on cellular carbonic anhydrase activity, present in lamprey red cells, which speeds up the hydration reaction. When the action of carbonic anhydrase is inhibited by acetazolamide, removal of ammonium chloride from the incubation medium does not cause intracellular acidification.
Oviposition Digging in the Grasshopper: I. Functional Anatomy and the Motor Programme
Authors: Thompson Karen J.
Published: April 2021

The ovipositor appendages of acridid insects (grasshoppers and locusts) consist of two pairs of shovel-shaped valves that are used to dig a deep chamber in the ground for egg burial, to manipulate the eggs, and to assist in capping the egg-pod with froth. During oviposition the valves undergo cyclical opening, closing, retraction and protraction movements. These movements are produced by the contractions of ten pairs of muscles. The eighth and ninth segmental nerves of the terminal abdominal ganglion supply the ovipositor muscles. Rhythmical ovipositor movements are produced by the severed abdomen of sexually mature female grasshoppers. By comparing this activity to the activity underlying the natural behaviour, it was determined that the isolated abdomen produced the digging portion of the oviposition motor programme. Electrical recordings from the ovipositor nerves in the isolated nervous system showed spontaneous rhythmical bursting activity. This activity corresponds to the neural correlate of digging behaviour and indicates the presence of a central pattern generator for oviposition digging in the terminal abdominal ganglion of females.
Intestinal Blood Flow in Swimming Chinook Salmon Oncorhynchus Tshawytscha and the Effects of Haematocrit On Blood Flow Distribution
Authors: Thorarensen H. , Gallaugher P. E. , Kiessling A. K. , Farrell A. P.
Published: April 2021

Blood flow in the intestinal artery (qIA), the rate of oxygen consumption and a number of haematological variables were measured in chinook salmon, Oncorhynchus tshawytscha, while they swam up to the critical swimming velocity (Ucrit). The fish used in this study had previously been exposed to one of two different exercise-training regimes, swimming for 8 months at either 1.5bl s−1 (HS) or 0.5bl s−1 (LS) (where bl is body length). During this period, growth rate was the same in both groups.

At rest, qIA was approximately 36% of cardiac output. qIA was inversely related to , indicating that blood flow was gradually redistributed from the viscera as the oxygen demands of the locomotory muscles increased. Both and qIA were relatively constant at swimming velocities less than 50% Ucrit, but at Ucrit, qIA had decreased by 60–70% as reached a maximum. Blood flow redistribution away from the intestine contributed significantly to the oxygen supply for locomotory muscles, since it was estimated that the oxygen-transporting capacity of this redistributed blood flow was enough to support 12–18% of the maximum internal oxygen consumption (total – gill ).

Following exercise training, haematocrit (Hct) in the HS group (27.1%) was significantly higher than in the LS group (23.3%). However, neither the maximum nor Ucrit was significantly different in the two groups. qIA was inversely related to Hct but, in spite of lower qIA at rest, oxygen transport to the intestines was greater at all swimming speeds in the HS than in the LS training group. In addition, blood flow in the HS group was better maintained as the swimming speed was increased. As a result of the higher Hct in the HS-trained group, oxygen transport to the intestines was similar in both groups at their respective training velocities. Therefore, we suggest that, by increasing Hct and thereby maintaining oxygen delivery to the intestines, the HS group maintained normal intestinal function while swimming at the higher velocity, enabling overall growth rate to be the same as in the LS group.
Time Course of Changes in Brain Serotonergic Activity and Brain Tryptophan Levels in Dominant and Subordinate Juvenile Arctic Charr
Authors: Winberg Svante , Nilsson Göran E.
Published: April 2021

Concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan (TRP, the amino acid precursor of 5-HT) were measured, and 5-HIAA/5-HT ratios calculated, in the telencephalon, hypothalamus and brain stem of Arctic charr (Salvelinus alpinus) with 1–21 days experience of a dominant or subordinate position in a pair. Brain 5-HIAA levels and 5-HIAA/5-HT ratios (an index of serotonergic activity) increased rapidly in all three areas of the brain in subordinate fish and remained high for up to 21 days. The brain stem 5-HIAA concentration in dominant fish showed a temporary increase after 1 day of social interaction, but returned to the control level 2 days later. The social interactions did not affect 5-HT concentrations in any of the brain regions. An initial, but temporary, increase in brain TRP concentration was seen in both subordinate and dominant fish. After 1–3 days of social interaction, brain TRP levels declined. This decline was most pronounced in subordinate individuals which, after 7 and 21 days, had hypothalamic TRP concentrations significantly lower than those of controls. Moreover, TRP levels in the telencephalon after 21 days, and in the hypothalamus after 7 days, were significantly lower in subordinate individuals than in dominant fish. These results show that subordinate experience rapidly causes a sustained increase in brain 5-HT metabolism which does not correlate with changes in brain TRP levels. Thus, the increases in brain 5-HIAA concentration and in brain 5-HIAA/5-HT ratios probably reflect an increase in functional 5-HT release, a phenomenon that appears to have a wide distribution in the brain.
Spiracular Control of Respiratory Water Loss in Female Alates of the Harvester Ant Pogonomyrmex Rugosus
Authors: Lighton John R. B. , Garrigan Dana A. , Duncan Frances D. , Johnson Robert A.
Published: April 2021

It has been suggested that the discontinuous ventilation cycle (DVC) observed in many insects, including all ants described to date, is an adaptation to reduce respiratory water loss. To test this hypothesis, it is necessary to measure respiratory water loss as a percentage of total water loss and to estimate what sustained rates of water loss would be in the absence of spiracular control. We used two independent techniques to measure real-time water loss rates in female alates of Pogonomyrmex rugosus. The first measured water vapor emission and CO2 production simultaneously using dual-wavelength infrared absorbance analysis (DWIRAA). The second measured water loss gravimetrically. Real-time measurement allowed the separation of cuticular water loss rates (interburst) from water loss rates during the ventilation phase (burst) of the DVC. Cuticular permeability of P. rugosus female alates was only 27ng h−1 cm−2 Pa−1, one-third of that reported for workers of the same species and the lowest yet reported for ants. Partly because of this low cuticular permeability, respiratory water loss represented a greater percentage of overall water loss (13%) than has generally been reported for other insects. The DWIRAA and gravimetric techniques gave equivalent results. Peak rates of water loss during the burst phase were 2.8-fold higher than cuticular water loss rates alone (7.68mg g−1 h−1versus 2.77mg g−1 h−1 at 25°C). This is a conservative estimate of water loss rates in the absence of spiracular control. Contrary to findings in certain other insects that suggest a negligible role for respiratory water loss, we find that, in an insect that employs the DVC and has low cuticular permeability, overall water loss rates rise several-fold in the absence of direct spiracular control. Our findings lend strong support to the water conservation hypothesis for the role of the DVC. In at least some insects, respiratory water loss rates can reach magnitudes significant enough, relative to other routes of water loss, for strong selective pressure to act on them.
Response Properties of Lateral Line and Auditory Units in the Medulla Oblongata of the Rainbow Trout (Oncorhynchus Mykiss)
Authors: Wubbels R. J. , Kroese A. B. A. , Schellart N. A. M.
Published: April 2021

The objective of this study was to investigate the response properties of second-order lateral line and auditory neurones in the medulla oblongata of the rainbow trout. The frequency response of 20 medullary units was measured by recording single-unit spike activity in response to a mechanical stimulus provided by an oscillating membrane or by a small vibrating sphere.

These 20 units were categorized, according to their frequency response properties, into two classes. Ten units responded to relatively low frequencies (<50Hz) and showed a maximum in the frequency response between 70 and 120Hz. The other units responded to higher frequencies, showing a maximum in the frequency response above 150Hz. Significant differences between these two classes were also observed with respect to recording site, latency and sensitivity. It is concluded that these two classes of medullary units are lateral line units and auditory units, respectively. In the medulla, the input from the two mechanosensory systems appears to be mainly processed separately.

The majority of mechanically sensitive units (95%) showed a sustained, phase-locked response; 25% displayed a transient response component, mostly in addition to a sustained response component. All units were spontaneously active, with a mean firing rate of 27spikes s−1. Two units responded to a visual stimulus. No topographical representation of lateral line receptive fields was found in the caudal part of the medulla.

The response characteristics of primary afferents reported in the literature differ from those of the medullary units of this study, so we conclude that the latter are higher-order units.

Medullary lateral line units stimulated by the vibrating sphere appeared to be less sensitive than units stimulated by the vibrating membrane. The sensitivity of the units and the size of their receptive fields indicate that lateral line input converges in the medial nucleus.
Dynamics And Energetics Of Scallop Locomotion
Authors: Cheng J.-Y. , Davison I. G. , Demont M. E.
Published: April 2021

A dynamic model for a swimming scallop was developed which integrates the mechanical properties of the hinge ligaments, valve inertia, the external fluid-flow reaction, the fluid pressure in the mantle cavity and the muscle contraction. Kinematic data were recorded for a swimming Placopecten magellanicus from high-speed film analysis. Dynamic loading experiments were performed to provide the required mechanical properties of the hinge for the same species. The swimming dynamics and energetics based on data from a 0.065 m long Placopecten magellanicus at 10 °C were analyzed. The main conclusions are as follows. The mean period of a clapping cycle during swimming is about 0.28 s, which can be roughly divided into three equal intervals: closing, gliding and opening. The maximum angular velocity and acceleration of the valve movements are about 182 degrees s−1 and 1370 degrees s−2, respectively.The hysteresis loop of the hinge was found to be close to an ellipse. This may be represented as a simple Voigt body consisting of a spring and dashpot in parallel, with a rotational stiffness of 0.0497 N m and viscosity coefficient of 0.00109 kg m2 s−1 for the 0.065 m long Placopecten magellanicus.The external fluid reaction has three components, of which the added mass is about 10 times higher than the mass of a single valve, and the flow-induced pseudo-viscosity compensates for nearly half of the hinge viscosity for the 0.065 m long Placopecten magellanicus.The locomotor system powered by the muscle can be divided into two subsystems: a pressure pump for jet production and a shell-hinge/outer-fluid oscillator which drives the pumping cycle. The dynamics of the oscillator is determined predominantly by the interaction of the external fluid reaction and the hinge properties, and its resonant frequency was found to be close to the swimming frequencies.The momentum and energy required to run the oscillator are negligibly small (about 1 % for the 0.065 m long Placopecten magellanicus) compared with that for the jet. Almost all the mechanical energy from muscle contraction is used to perform hydrodynamic work for jet production. Thus, the Froude efficiency of propulsion in scallops is nearly the same as the entire mechanical efficiency of the locomotor system. This could be a fundamental advantage of jet propulsion, at least for a scallop.The estimated maximum muscle stress is about 1.06×105 N m−2, the cyclic work is 0.065 J and power output is 1.3 W. Using an estimate of the mass of an adductor muscle, the work done by the muscle per unit mass is 9.0J kg−1 and the peak power per unit mass is 185 W kg−1.The time course of the force generation of the contracting adductor muscle is basically the same as that of the hydrodynamic propulsive force.
Characterization of the Ca2+ Current in Isolated Terminals of Crustacean Peptidergic Neurons
Authors: Richmond J. E. , Penner R. , Keller R. , Cooke I. M.
Published: April 2021

Ca2+ currents (ICa) were recorded from the neurosecretory terminals of the crab X-organ–sinus gland under voltage-clamp conditions. ICa was detectable at command potentials above −40 mV, with maximum currents at approximately +20 mV. No differences were observed between current–voltage (I/V) relationships from holding potentials of −50 or −90 mV, indicating that there were no low-voltage-activated Ca2+ channels present in the terminals. The decay of ICa was best fitted with a single exponential, the extent of inactivation over 50 ms averaging 53 %. The rate of decay of ICa was reduced by the substitution of Ca2+ with Sr2+ in the external solution and was eliminated by substitution with Ba2+.

The effect of varying prepulse potential on the amplitude of ICa at +20 mV was tested. ICa declined with increasing prepulse depolarization up to +20 mV and then showed partial recovery at more depolarized prepulse potentials. Inactivation curves in solutions containing Sr2+ and Ba2+ showed much less current-dependent inactivation. Removing Ca2+ chelators from the internal solution significantly increased ICa decay. ICa was insensitive to nifedipine at a concentration of 1 μmol l−1. Pretreatment of the isolated sinus gland containing the intact terminals with a combination of ω-conotoxin (ω-Ctx) GVIA, ω-Ctx MVIIC and ω-agatoxin IVA had no effect on the levels of K+-induced peptide release.
The Wake Dynamics and Flight Forces of the Fruit Fly Drosophila Melanogaster
Authors: Dickinson Michael H. , Götz Karl G.
Published: April 2021

We have used flow visualizations and instantaneous force measurements of tethered fruit flies (Drosophila melanogaster) to study the dynamics of force generation during flight. During each complete stroke cycle, the flies generate one single vortex loop consisting of vorticity shed during the downstroke and ventral flip. This gross pattern of wake structure in Drosophila is similar to those described for hovering birds and some other insects. The wake structure differed from those previously described, however, in that the vortex filaments shed during ventral stroke reversal did not fuse to complete a circular ring, but rather attached temporarily to the body to complete an inverted heart-shaped vortex loop. The attached ventral filaments of the loop subsequently slide along the length of the body and eventually fuse at the tip of the abdomen. We found no evidence for the shedding of wing-tip vorticity during the upstroke, and argue that this is due to an extreme form of the Wagner effect acting at that time.

The flow visualizations predicted that maximum flight forces would be generated during the downstroke and ventral reversal, with little or no force generated during the upstroke. The instantaneous force measurements using laser-interferometry verified the periodic nature of force generation. Within each stroke cycle, there was one plateau of high force generation followed by a period of low force, which roughly correlated with the upstroke and downstroke periods. However, the fluctuations in force lagged behind their expected occurrence within the wing-stroke cycle by approximately 1 ms or one-fifth of the complete stroke cycle. This temporal discrepancy exceeds the range of expected inaccuracies and artifacts in the measurements, and we tentatively discuss the potential retarding effects within the underlying fluid mechanics.
3-Hydroxybutyrate Co-Infused With Noradrenaline Decreases Resulting Plasma Levels Of Noradrenaline In Wistar Rats
Authors: Cañas X. , Sanchis D. , Gómez G. , Casanovas J. M. , Artigas F. , Fernández-lópez J. A. , Remesar X. , Alemany M.
Published: April 2021

Pentobarbital-anaesthetized male Wistar rats were infused with 6 μg kg−1 min−1 of noradrenaline. The infusion was supplemented with 8.5 mg kg−1 min−1 of D-3-hydroxybutyrate (3-OHB) for 15 min in order to determine its effect on the adrenergic response of the rat. Plasma levels of noradrenaline rose to a plateau of approximately 50 nmol l−1 with infusion. In the group infused with noradrenaline alone, noradrenaline levels were maintained for 1 h. Supplementation with 3-OHB induced a decrease in plasma noradrenaline level that was inversely correlated with 3-OHB level. Aortic and interscapular brown adipose tissue temperatures increased with noradrenaline infusion, but the rise was arrested by 3-OHB; replacing 3-OHB with glucose had no effect. Infusion of saline, glucose or 3-OHB in the absence of noradrenaline did not induce a rise in temperature in either tissue. Blood 3-OHB concentration increased to 1.2 mmol l−1 during 3-OHB infusion, decreasing rapidly at the end of infusion. Blood glucose levels increased with noradrenaline infusion; the presence of high 3-OHB levels decreased glucose concentration. The effects observed were transient and dependent on 3-OHB concentration; these effects may help explain most of the other effects of noradrenaline described here. The role of 3-OHB as a regulator of adrenergic responses seems to be part of a complex fail-safe mechanism which prevents wasting.
Hyperosmoregulation in the red freshwater crab Dilocarcinus pagei (Brachyura, Trichodactylidae): structural and functional asymmetries of the posterior gills
Authors: Onken Horst , McNamara John Campbell
Published: April 2021

The osmotic and ionic status of the haemolymph and the structural and ion-transport characteristics of the posterior gills of Dilocarcinus pagei, a hololimnetic crab, were investigated. Haemolymph osmolality was 386±18 mosmol kg–1, while [Na+] and [Cl–] were 190±13 and 206±12 mmol l–1, respectively; [K+], [Ca2+] and [Mg2+] were 9.7±0.7, 10.2±0.5 and 2.8±0.4 mmol l–1, respectively (means ± s.e.m., N=12–17). The gill lamellae possess a central, osmiophilic area, which exhibits a marked structural asymmetry. The thick (18–20 μm) proximal epithelium is characterised by basal invaginations and a few apical vesicles, while the thin (3–10 μm) distal epithelium consists of apical pillar cell flanges populated by vesicles and membrane invaginations. Isolated gills, bathed and perfused with NaCl saline, spontaneously generate a negative transbranchial potential difference (Vte), which stabilises at positive or negative values. Ouabain shifts Vte to more positive values. When mounted in an Ussing chamber, distal split lamellae generate a negative, Cl–-dependent short-circuit current (Isc). Na+ substitution leads to more negative values of Isc. Internal ouabain is without effect, while diphenylamine-2-carboxylate and acetazolamide abolish Isc. Proximal split lamellae show a positive, Na+-dependent Isc, which decreases after internal application of ouabain. These data suggest that the thin epithelium actively absorbs Cl–, while the thick epithelium actively absorbs Na+.
The under-appreciated fats of life: the two types of polyunsaturated fats
Authors: Hulbert A. J.
Published: April 2021

There are two types of polyunsaturated fatty acids (i.e. fats that contain multiple carbon-carbon double bonds) – omega-6 and omega-3. They are not interconvertible, and they contribute ‘double-bonded carbons’ to different depths in bilayer membranes, with different effects on membrane processes. This Commentary emphasises the importance of these fats for biological membrane function and examines their evolution and biochemistry. Omega-6 and omega-3 fatty acids are separately essential in the diet of animals, and they pass up the food chain largely from plants, with ‘seeds’ being a prevalent source of omega-6, and ‘leaves’ a prevalent source of omega-3. The dietary balance between these fatty acids has a strong influence on membrane composition. Although this aspect of diet has been little investigated outside of the biomedical field, emerging evidence shows it can alter important physiological capacities of animals (e.g. exercise endurance and adiposity), which has implications for activities such as avian migration and hibernation and torpor, as well as significant implications for human health. This Commentary will focus on the separate effects of omega-3 and omega-6 on membrane properties and will emphasise the importance of the balance between these two fatty acids in determining the function of biological membranes; I hope to convince the reader that fats should be considered first and foremost as the basic unit of biological membranes, and secondarily as a means of energy storage.
The Spectral Sensitivity of the Echinoid Diadema Antillarum Philippi
Authors: Millott N. , Yoshida M.
Published: April 2021

Several species of sea urchin show sensitivity to light, by the reactions of the whole animal or those of effectors such as the spines, podia, pedicellariae and chromatophores. The reactions have recently been reviewed by Millott (1954, 1956, 1957a).
Co-Ordinating Systems and Behaviour in Hydra
Authors: Passano L. M. , McCullough C. B.
Published: April 2021

In the first paper of this series (Passano & McCullough, 1964) we described the system concerned with the periodic bursts of impulses arising from the subhypostome and conducted throughout the column of several species of the genus Hydra, the familiar freshwater polyp (hydrozoan coelenterate). Each of these bursts of impulses is followed by a co-ordinated contraction of the epidermal, longitudinally arranged muscles, so that the total burst of this contraction-burst system results, in reducing the animal to a stubby ball. Periodic contraction bursts (CB) are the most important overt behaviour of Hydra.
The Relation Between Age and Flight Activity in the Milkweed Bug, Oncopeltus
Authors: Dingle Hugh
Published: April 2021

The mean flight-duration, in tethered flight, of the ‘large milkweed bug’, Oncopeltus fasciatus (Dallas), was measured as a function of age in days after the final moult. In both sexes a peak of flight occurs at 8-10 days. In males there is a second flight peak at 30-35 days, whereas there is no second peak in females. Virgin males tested at 20 days, a time when mated males were short-flying, flew longer than bugs at any other age. Thirty-day-old virgin females were not significantly different from mated females of the same age. When long flights occurred in males they were in general preceded by one or more flights of less than 1 min. This was not true for females, and the difference between the sexes was statistically significant. The results in 2, 3 and 4, above indicate two, and possibly three, differences between the sexes. Males and females should thus be studied separately with respect to flight activity. Some individuals never flew. These were as long-lived and as "productively active as those which did, indicating the possibility of a behavioural polymorphism. The initial peak of mean flight-duration for both sexes occurs when the daily deposition of paired cuticular growth rings ceases. Maximum flight thus seems to occur at the end of the teneral period. The threshold for flight declines with age. There are thus three types of flight : long-duration, high-threshold; short-duration, low-threshold; and (in males only) long-duration, low-threshold. The initial flight peak is pre-reproductive and occurs at a time when reproductive value, a measure of the expected contribution of an individual to future population growth and hence of sensitivity to selection, is high. Long-flying bugs are evidently colonizers, and a migration is an evolved adaptation, not a response to current adversity. It is concluded that the long-duration, high-threshold flights represent migration and the short-duration, low-threshold flights represent non-migratory ‘flits’.
Proprioception by the Coxo-Basal Chordotonal Organ, Cb, in Legs of the Crab, Carcinus Maenas
Authors: Bush B. M. H.
Published: April 2021

The chordotonal organ, CB, spanning the coxo-basal joint in walking legs of the crab, not being attached to a muscle tendon like the receptors of the more distal joints, is stretched during extension of the joint (i.e. limb depression) and relaxes during flexion (elevation). Afferent impulses have been recorded extracellularly from whole sensory nerves of CB, and from fibres isolated from it: (a) during passive movement of the coxo-basal joint, with CB in situ in a preparation containing no other joints, and (b) during stretching and releasing of the excised receptor strand. Unidirectional movement fibres and unidirectional position fibres for both directions were recorded. Thus, of the afferents responding primarily during movement, with a constant frequency for steady movement over the whole joint arc, some responded only during extension (or stretch of receptor), others only during flexion (release). Similarly, distinct fibres responded tonically in the extended positions of the joint (stretched), and others in the flexed (relaxed) positions. Fibres intermediate between true movement and true position fibres, and phasic movement—or ‘acceleration’— fibres, were also observed. Since the scolopidia of CB are isodynal, with only ciliary-type distal processes (Whitear, 1962), the simple hypothesis that the ciliary cell responds solely to relaxation of the receptor strand—and the paraciliary cell to stretch—is now untenable. Alternative hypotheses on the mechanism of activation of crab chordotonal organs, and on the function of CB in the intact animal, are discussed.
Structural Limitations on the Power Output of the Pigeon’s Flight Muscles
Authors: Pennycuick C. J. , Parker G. A.
Published: April 2021

The tensile strength of the flight-muscle tendons, the distances through which they move and the wingbeat frequency set a maximum of 48 W on the power which could conceivably be transmitted to the pigeon’s wings. A minimum of 0·1 W is required to account for observed climbing performance. The safety factor on tension of the muscle insertions cannot exceed 5·2 and is probably substantially less than this. The maximum possible average specific power over one complete cycle is 0·58 W/g.wt. for the pectoralis and 0·28 W/g.wt. for the supracoracoideus. The maximum possible peak specific power during shortening is 0·86 W/g.wt. for both muscles. The minimum average specific power for the flight muscles as a whole is 0·10 W/g.wt. (from rate of climb measurements). These figures do not imply any unusual mechanical properties in the muscles, as compared to other vertebrate muscles. The coracoid can bear a compressive load of over 40 kg. wt., which appears to be about 3·7 times as much as could ever be applied to it in life. The greatest bending moment (about the centre of rotation of the head of the humerus) which the pectoralis could apply to the humerus is 10·2 kg. wt. cm. The supracoracoideus could apply a maximum of 0·88 kg. wt. cm. The tensile strength of supracoracoideus tendon is about 250 kg. wt./cm.2. The compressive strength of coracoid bone is about 1140 kg. wt./cm.2.
Reflexes Mediated by Non-Impulsive Afferent Neurones of Thoracic-Coxal Muscle Receptor Organs in the Crab, Carcinus Maenas
Authors: Cannone A. J. , Bush B. M. H.
Published: April 2021

Injection of depolarizing and hyperpolarizing currents into the non-impulsive S and T sensory fibres has allowed a quantitative analysis of the input-output relationships of this sensory-reflex system. Graded depolarization of the T fibre typically results in sigmoid voltagefrequency relationships for motoneurones Pm 1–3, the maximum ‘slopes’ in the most sensitive preparation being 31, 47·5 and 33 Hz/mV respectively, without taking into account further afferent attenuation within the thoracic ganglion. Graded depolarizations of the S fibre recruit four motoneurones (Pm 1–4) common to the T fibre reflex pathway, although activation thresholds are much higher and the maximum slope or ‘gain’ of the voltagefrequency relationships is much reduced compared to that of the T fibre reflex pathways. Thus, although the S fibre synapses either directly or indirectly with promotor motoneurones, typical 5–10 mV stretch-induced receptor potentials remain sub-threshold for a contribution to the reflex output, albeit under experimental conditions and at all but the most extended receptor muscle lengths. Differentiating between motor impulse amplitudes, and using simultaneously recorded promotor muscle junction potentials as a further aid, establishes at least nine motoneurones as being reflexly recruited by the S and T fibres: Pm 1–8 by the T fibre and Pm 1–4 and Pmq by the S fibre. Hyperpolarization of the T and S fibres confirms that ongoing tonic motor activity is peripherally determined by receptor length proscribed T fibre ‘resting’ potentials, rather than by the more linearly related S fibre ‘resting’ potentials at different receptor muscle lengths. Moreover, suppression of the reflex response by sensory fibre hyperpolarizations coincident with stretch stimuli leaves little doubt that it is the T rather than the S fibre that provides the sensory drive for the stretch reflex in vitro. By using long duration, constant value T fibre depolarizing potentials, the postsynaptic component of adaptation for Pm 1–3 has been found to be slight, in contrast to the more rapid adaptation of the higher threshold P1T15–8 motoneurones. Moreover, adaptation rates for Pm 1–3 discharges are lower the smaller the afferent drive. It is suggested therefore that reflexly activated promotor MNs can be differentiated into ‘tonic’ and ‘phasic’ categories. Motoneurone Pm2 sometimes discharges in the form of ‘rigid’ (7–8 ms intervals) impulse couplets. At low mean reflex frequencies all Pm2 impulses are locked into couplets (‘complete’ patterning). While both ‘rigid’ and ‘complete’ patterning break down abruptly as mean frequencies increase, re-establishment is more gradual (hysteretic) with decreasing mean frequencies. Patterning, albeit a particularly labile phenomenon, is almost certainly an intrinsic, if unknown, property of the motoneurone itself.
Movement Parallax and Distance Perception in the Grasshopper (Phaulacridium Vittatum (Sjöstedt))
Authors: Eriksson E. S.
Published: April 2021

It has sometimes been argued that insects use binocular vision to obtain correct perception of sizes and distances in their visual world (cf. Wigglesworth, 1972). In the praying mantids it has also been claimed that monocular animals essentially lack depth perception (Maldonado, Benko & Isern, 1970).
Energetic Cost of Generating Muscular Force During Running
Authors: Taylor C. Richard , Heglund Norman C. , McMahon Thomas A. , Looney Todd R.
Published: April 2021

The energetic cost of generating muscular force was studied by measuring the energetic cost of carrying loads in rats, dogs, humans, and horses for loads ranging between 7 and 27 % of body mass.

Oxygen consumption increased in direct proportion to mass supported by the muscles, i.e. where is the oxygen consumption of the animal running with a load, is the oxygen consumption at the same speed without a load, mL is the mass of the animal plus the load, and m is the mass of the animal.

Stride frequency, average number of feet on the ground over an integral number of strides, the time of contact of each foot relative to the other feet, and the average vertical acceleration during the contact phase were not measurably changed by the loads used in our experiments. From these observations we conclude that the average accelerations of the centre of mass of the animal are not changed by carrying the loads, and that muscular force developed by the animal increases in direct proportion to the load.

It follows that the rate of energy utilization by muscles of an animal as it runs along the ground at any particular speed is nearly directly proportional to the force exerted by its muscles.

The energetic cost of generating force over an interval of time (∫Fdt) increases markedly with running speed.

An important consequence of the direct proportionality between increased oxygen consumption and mass of the load is that small animals expend much more energy to generate a given force at a given speed than large animals.