bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Structure and Hydromechanics of the Musculo-epithelium in Metridium
Authors: Robson Elaine A. 
Published: April 2021

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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 (&lt;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

ABSTRACT
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

ABSTRACT
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.