bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation of a polygonal cellular pattern during sexual maturation of the avian oviduct epithelium: computer simulation
Authors: Honda Hisao , Yamanaka Hachiro , Eguchi Goro
Published: April 2021

A peculiar cellular pattern resembling a checkerboard has been observed on the luminal surface of the oviduct epithelium of an adult Japanese quail. The epithelium is a monolayer cell sheet and consists of two types of columnar cells, ciliated cells (C-cells) and gland cells (G-cells) assembled in alternating blocks. The pattern develops, during sexual maturation, from a kagome-like pattern (in which large C-cells are surrounded by small G-cells) characteristic of the immature oviduct. In the present paper, computer simulations of the pattern transformation from kagome to checkerboard were performed assuming a few properties of individual cells.

The adult checkerboard-like pattern is not strictly rectangular, but is deformed toward a honeycomb pattern. In theoretical considerations the assumption that adhesion is stronger between unlike cells than between like cells formed an ideal checkerboard pattern, because all cell boundaries in it are edges along which unlike cells meet. On the other hand, a honeycomb pattern formed after assuming that the boundary length of the cellular pattern is minimized (caused by contraction of bundles of microfilaments running along lateral boundaries of the columnar epithelial cell while keeping contact between neighbouring cells). The actual checkerboard-like pattern was considered to be in a balanced state between the effects of (1) the strong adhesion between unlike cells, and (2) the boundary contraction. Using a computational analysis, this consideration enabled us to obtain a quantitative parameter value for the difference between cell adhesions of unlike cells and of like cells.

C-cells divided once during the kagome-checkerboard transformation, while G-cells did not divide. We performed computer simulations starting with the kagome pattern in which all C-cells divided once. The computer program of the boundary shortening procedure we used involved the quantitative parameter value for differential cell adhesion obtained as described above. A checkerboard pattern was successfully generated in the simulation. It is concluded that the strong adhesion between unlike cells and the boundary shortening have important roles in formation and maintenance of the kagome and checkerboard patterns of the avian oviduct epithelium.
Chromosome analysis of single-pronuclear haploid parthenogenetic blastocysts and their inner cell mass derivatives
Authors: Schnebelen M. T. , Kaufman M. H.
Published: April 2021

Single-pronuclear haploid parthenogenetically activated mouse embryos were transferred to the oviducts of suitable recipients. One group of embryos was isolated at the morula stage and subsequently allowed to develop to the expanded blastocyst stage in vitro. Intact embryos were either analysed by the air-drying technique at that stage to determine their total cell number and ploidy, or treated by immunosurgery to isolate their inner cell mass. These were either analysed to establish their total cell number and ploidy, or retained in culture for an additional 24 h or 72 h. The inner cell mass derivatives were then analysed to establish the total cell number and ploidy. A second group of recipients was ovariectomized on the 4th day of pseudopregnancy, treated with Depo-Provera and blastocysts recovered 5 or 6 days later. The ‘delayed’ blastocysts recovered were treated by immunosurgery, and the inner cell masses isolated and either analysed at this time or transferred to culture for 72 h, 96 h or 144h. As in the previous groups, the inner cell mass derivatives were analysed to establish the total cell population present and their ploidy. The analysis of this material was found to be technically particularly difficult, though in general the non-‘delayed’ embryos and their inner cell mass derivatives yielded higher success rates than the ‘delayed’ inner cell mass derivatives. The .‘delayed’ inner cell masses initially contained on average about twice the number of cells compared to the number present in those isolated from the non-‘delayed’ expanded blastocysts. Cellular profiferation occurred in all the groups retained in culture, though only a small proportion of the cells analysed gave ‘scorable’ mitotic cells in which the ploidy could be unequivocally determined. In general, in both the non-‘delayed’ and ‘delayed’ groups, the proportion of diploid mitotic cells observed increased with their duration in culture, though this effect was clearly more marked in the ‘delayed’ series. The present study indicated that the chance of obtaining haploid mouse cell lines in the future might be increased by using inner cell masses derived from non-‘delayed’ rather than ‘delayed’ blastocysts despite their initial reduced cell number at the time of explantation into tissue culture..
The relationship between emerging neural crest cells and basement membranes in the trunk of the mouse embryo: a TEM and immunocytochemical study
Authors: Sternberg J. , Kimber S. J.
Published: April 2021

The earliest stage of neural crest cell (NCC) migration is characterized by an epitheliomesenchymal transformation, as the cells leave the neural tube. There is evidence that in a number of cell systems this transformation is accompanied by alteration or depletion of associated basement membranes. This study examines the ultrastructural relationship between mouse NCCs and adjacent basement membranes during the earliest stages of migration from the neural tube. Basement membranes were identified by transmission electron microscopy (TEM) and immunofluorescence using antibodies to type-IV collagen. The ultrastructural features of NCCs and their relationship with surrounding tissues were also examined using TEM. In the dorsal region of the neural tube, from which NCCs originate, the basement membrane was depleted or absent, and with the immunofluorescence technique it was shown that this pattern was reflected in a deficit of type-IV collagen. TEM observations indicated that ultrastructurally NCCs differ from their neuroepithelial neighbours only in overall cell shape and their relationship to other cells and the extracellular matrix.
Gonadal development of the chick embryo following microsurgically caused agenesis of the mesonephros and using interspecific quail—chick chimaeras
Authors: Rodemer Eva S. , Ihmer Alice , Wartenberg H.
Published: April 2021

Mesonephric agenesis was achieved by microsurgical excision of the left Wolffian duct and the underlying intermediate mesoderm of different regions between somites 16 and 23 in chickens after 50–52 h of incubation (stage 14 HH). Quail-chick chimaeras were produced by transplantation of corresponding quail tissue in the region of somites 18–21.

A morphometrical analysis of the mesonephric and gonadal area in cross sections shows that the intermediate mesoderm from somites 16 to 23 develops into the mesonephros. A partial agenesis of the mesonephros brought about by removal of the intermediate mesoderm at the level of somites 18 to 21 at stage 14 leads to a mean reduction of the gonadal volume of 37·8 % compared to the volume of the untreated side at stage 30. Transplantation of quail intermediate mesoderm in this region of the excision results in development of a hybrid mesonephros. Consequently, the gonads are invaded and colonized by quail cells mobilized from mesonephric corpuscles examined at stage 30, 35 and 36.

These results are discussed in terms of the origin of the gonadal stroma during this developmental period; they show that in the region from the third to the sixth segment the ventromedial part of the differentiating mesonephros participates in the contribution of stromal cells to the gonad.
Axon guidance in the insect periphery
Authors: Palka John
Published: April 2021

The central theme of this essay is the importance of considering neural development, including axonal pathfinding, as but one of a multitude of simultaneously occurring developmental processes. It is very tempting to suppose that the observed regularity of axonal outgrowth is the consequence of mechanisms dedicated to axon guidance, for example, that specific paths are laid down whose exclusive function is to guide axons. I propose to argue from two case studies in insects that regularity does not imply such exclusiveness.
Genes that control dorsoventral polarity affect gene expression along the anteroposterior axis of theDrosophilaembryo
Authors: Carroll Sean B. , Winslow Gary M. , Twombly Vern J. , Scott Matthew P.
Published: April 2021

At least 13 genes control the establishment of dorsoventral polarity in the Drosophila embryo and more than 30 genes control the anteroposterior pattern of body segments. Each group of genes is thought to control pattern formation along one body axis, independently of the other group. We have used the expression of the fushi tarazu {ftz) segmentation gene as a positional marker to investigate the relationship between the dorsoventral and anteroposterior axes. The ftz gene is normally expressed in seven transverse stripes. Changes in the striped pattern in embryos mutant for other genes (or progeny of females homozygous for maternal-effect mutations) can reveal alterations of cell fate resulting from such mutations. We show that in the absence of any of ten maternal-effect dorsoventral polarity gene functions, the characteristic stripes of ftz protein are altered. Normally there is a difference between ftz stripe spacing on the dorsal and ventral sides of the embryo; in dorsalized mutant embryos the ftz stripes appear to be altered so that dorsal-type spacing occurs on all sides of the embryo. These results indicate that cells respond to dorsoventral positional information in establishing early patterns of gene expression along the anteroposterior axis and that there may be more significant interactions between the different axes of positional information than previously determined.
Lithium inhibits morphogenesis of the nervous system but not neuronal differentiation in Xenopus laevis
Authors: Breckenridge Lorna J. , Warren R. L. , Warner Anne E.
Published: April 2021

Xenopus embryos treated with 100 mM-lithium from the 2-to 4-cell stage to the early blastula stage (4h) failed to neurulate and developed without a discernible anteroposterior axis. The internal structure of defective embryos was grossly disorganized, but immunohistochemical staining with cell-type-specific antibodies revealed differentiated nerve and muscle cells. Quantitative assay in tissue cultures from control and acutely abnormal lithium-treated embryos showed that neural differentiation was enhanced and muscle differentiation unaffected. The embryos took up about 0·5 mM-lithium at threshold, maximal effects resulted at 2-3 mM. Most of the lithium was extruded from the cells into the blastocoel fluid, where lithium reached 17 mM. The threshold intracellular concentration was about 150 μM. Lithium uptake rose steeply as the osmotic/ionic strength of the bathing medium increased. Sodium, potassium and lithium were equally able to increase the permeability of the embryo. However, sodium ions enhanced, while potassium ions interfered with, the uptake of lithium. Treatment with lithium at progressively later stages reduced the developmental defects and neural differentiation returned to normal levels. The uptake of lithium did not decline concomitantly. We conclude that lithium does not inhibit neural induction, but interferes with dorsal patterning. The sensitivity of the embryo to lithium is determined by developmental stage. The very low, effective intracellular concentrations may be important in understanding the mechanism of lithium-generated defects.
Complicated colobomatous microphthalmia in the microphthalmic(mi/mi)mouse
Authors: Scholtz C. L. , Chan K. K.
Published: April 2021

A study of the development of the eye in the cinnamon mouse, homozygous for the gene for microphthalmia (mi), has shown that the microphthalmia is due to failure of secondary vitreous formation associated with a coloboma. The retina is dystrophic but there is a residual population of large ganglion cells and the optic nerve also contains ganglion cells. All these ganglion cells have cytoplasm similar to the retinal ganglion cells in the normal controls. It is postulated that they communicate with axons in the optic nerve. In addition, the outer epithelial layer of the eye cup, which normally becomes pigmented, forms retinal tissue in the homozygous mouse and this is also true of the dorsal part of the eyestalk near the eye.
Rescue of the mutant phenotype by reexpression of full-length vinculin in null F9 cells; effects on cell locomotion by domain deleted vinculin
Authors: Xu Weiming , Coll Jean-Luc , Adamson Eileen D.
Published: April 2021

Vinculin plays a role in signaling between integrins and the actin cytoskeleton. We reported earlier that F9-derived cells lacking vinculin are less spread, less adhesive, and move two times faster than wild-type F9 cells. Expression of intact vinculin in null cells restored all wild-type characteristics. In contrast, expression of the head (90 kDa) fragment exaggerated mutant characteristics, especially locomotion, which was double that of vinculin null cells. Expression of the tail domain also had a marked effect on locomotion in the opposite direction, reducing it to very low levels. The expression of the head plus tail domains together (no covalent attachment) effected a partial rescue towards wild-type phenotype, thus indicating that reexpressed polypeptides may be in their correct location and are interacting normally. Therefore, we conclude that: (1) the head domain is part of the locomotory force of the cell, modulated by the tail, and driven by the integrin/matrix connection; (2) intact vinculin is required for normal regulation of cell behavior, suggesting that vinculin head-tail interactions control cell adhesion, spreading, lamellipodia formation and locomotion.
The sparing of extraocular muscle in dystrophinopathy is lost in mice lacking utrophin and dystrophin
Authors: Porter J. D. , Rafael J. A. , Ragusa R. J. , Brueckner J. K. , Trickett J. I. , Davies K. E.
Published: April 2021

The extraocular muscles are one of few skeletal muscles that are structurally and functionally intact in Duchenne muscular dystrophy. Little is known about the mechanisms responsible for differential sparing or targeting of muscle groups in neuromuscular disease. One hypothesis is that constitutive or adaptive properties of the unique extraocular muscle phenotype may underlie their protection in dystrophinopathy. We assessed the status of extraocular muscles in the mdx mouse model of muscular dystrophy. Mice showed mild pathology in accessory extraocular muscles, but no signs of pathology were evident in the principal extraocular muscles at any age. By immunoblotting, the extraocular muscles of mdx mice exhibited increased levels of a dystrophin analog, dystrophin-related protein or utrophin. These data suggest, but do not provide mechanistic evidence, that utrophin mediates eye muscle protection. To examine a potential causal relationship, knockout mouse models were used to determine whether eye muscle sparing could be reversed.

Mice lacking expression of utrophin alone, like the dystrophin-deficient mdx mouse, showed no pathological alterations in extraocular muscle. However, mice deficient in both utrophin and dystrophin exhibited severe changes in both the accessory and principal extraocular muscles, with the eye muscles affected more adversely than other skeletal muscles. Selected extraocular muscle fiber types still remained spared, suggesting the operation of an alternative mechanism for muscle sparing in these fiber types. We propose that an endogenous upregulation of utrophin is mechanistic in protecting extraocular muscle in dystrophinopathy. Moreover, data lend support to the hypothesis that interventions designed to increase utrophin levels may ameliorate the pathology in other skeletal muscles in Duchenne muscular dystrophy.
Interphase-specific association of intrinsic centromere protein CENP-C with HDaxx, a death domain-binding protein implicated in Fas-mediated cell death
Authors: Pluta Ann F. , Earnshaw William C. , Goldberg Ilya G.
Published: April 2021

CENP-C, one of the few known intrinsic proteins of the human centromere, is thought to play structural as well as regulatory roles crucial to proper chromosome segregation and mitotic progression. To further define the functions of CENP-C throughout the cell cycle we have used the yeast interaction trap to identify proteins with which it interacts. One specific CENP-C interactor, which we have named HDaxx, was characterized in detail and found to be homologous to murine Daxx, a protein identified through its ability to bind the death domain of Fas (CD95). The interaction between CENP-C and HDaxx is mediated by the amino-terminal 315 amino acids of CENP-C and the carboxyl-terminal 104 amino acids of HDaxx. This region of Daxx is responsible for binding to death domains of several apoptosis signalling proteins. The biological significance of the interaction between CENP-C and HDaxx was confirmed by immunofluorescence colocalization of these two proteins at discrete spots in the nuclei of some interphase HeLa cells. We discuss the functional implications of the interphase-restricted association of HDaxx with centromeres.
Serotonin and the Control of Salivation in the BlowflyCalliphora
Authors: Trimmer Barry Andrew
Published: April 2021

The possibility that serotonin acts as a neurohormone stimulating salivation in the blowfly Calliphora vicina was studied by investigation of salivation induced by injections of high-potassium saline. Induced salivation is rapid and appears to be mediated by an active factor released into the haemolymph (High Potassium Salivary Gland Factor: HKSGF) since it is antagonized by cadmium (a calcium channel blocker) and by gramine (a serotonin-receptor blocker). The action of HKSGF on salivary glands in vitro is indistinguishable from that of serotonin: (a) it generates serotonin-like transepithelial potential changes, (b) its effect on salivation is antagonized by gramine, (c) it is as heat stable as serotonin, (d) it has the same solubility in a variety of organic solvents, (e) it is unaffected by incubation with leucine aminopeptidase or trypsin and (d) it is inactivated by rat liver monoamine oxidase type A (a serotonin deaminating enzyme).

Radioenzyme assay of haemolymph from high-potassium injected flies shows that the amount of serotonin present could account for all of the retrievable bioactivity.

Significant amounts of serotonin were found in the cerebral ganglion, the thoracic ganglion and nerves attached to the thoracic ganglion. Nerve sectioning experiments demonstrated that the abdominal nerves and the anterior nerves supplying the neck muscles are not involved in the normal salivatory response. However the cerebral-thoracic connective must be intact and it is suggested that release of serotonin is effected close to the main body of the thoracic ganglion. Some of the implications of the neurohormonal role of serotonin are discussed.
Temperature Acclimation of Intestinal Na Transport in the Carp (Cyprinus Carpio L.)
Authors: Gibson J. S. , Ellory J. C. , Cossins A. R.
Published: April 2021

Carp intestine mounted in vitro has a positive serosal potential and a net Na absorption greater than the short-circuit current. At 30°C in vitro, tissues from 10°C-acclimated fish are thought to show heat-damage. When measured at 10°C in vitro, intestine from fish acclimated to 10°C shows a greater rate of sodium transport than that from 30°C-acclimated fish. Mucosal application of amphotericin B, at 10°C in vitro, increases short-circuit current and net Na flux in both 10°C-and 30°C-acclimated fish but does not diminish the difference in Na transport between the two groups, under conditions when the apical membrane permeability is not limiting. It is concluded that the principal acclimatization in carp intestine to low temperature is via an increased basolateral membrane Na pumping capacity.
Cardioactive Peptides From The Cns Of A Caterpillar, The Tobacco Hornworm, Manduca Sexta
Authors: Platt Nicholas , Reynolds Stuart E.
Published: April 2021

A semi-isolated caterpillar heart bioassay was used to detect the presence of endogenous cardioactive material in the CNS of Manduca sexta larvae. Cardioactivity was detected in all nervous tissue examined. Most activity (about 70% of the total in the CNS) was in the ganglia of the abdominal nerve cord (ANC). Cardioactivity was also detected in the abdominal transverse nerves, the proctodeal nerves and the corpora cardiaca/corpora allata. The source with the highest specific activity was the frontal ganglion. Two factors, separable by Sephadex gel filtration, were distinguished in extracts of ANC: CAF 1, which has an estimated relative molecular mass (Mr) of about 4000, and CAF2 for which Mr is probably less than 1000. Both factors are apparently peptides. Neither is similar to any known insect cardioaccelerator. Both CAF 1 and CAF 2 are able to cause cardioacceleration when injected into tetrodotoxin-paralysed caterpillars. CAF 2 is present in both larvae and in adults. CAF 1 is present only in the caterpillar. The larval heart responds to both factors; the adult heart responds only to CAF 2. Partial purification of CAF 1 and CAF 2 by reverse-phase HPLC gives a single peak of bioactivity in each case. The biological activity of CAF 1 is destroyed by a-chymotrypsin, but not by trypsin. CAF 2 is not attacked by trypsin or by a-chymotrypsin. Treatment with performic acid or cyanogen bromide destroys the activity of both CAF 1 and CAF 2.
Respiratory and Cardiovascular Responses of the Exercising Chicken to Spinal Cord Cooling at Different Ambient Temperatures: I. Cardiovascular Responses and Blood Gases
Authors: Barnas G. M. , Gleeson M. , Rautenberg W.
Published: April 2021

We measured oxygen consumption heart rate (HR), stroke volume (SV), cardiac output (CO) and mean arterial blood pressure (MBPa) of chickens during 15 min treadmill exercise at 0·5 ms−1 and 0·8ms−1 at thermoneutral (23°C), low (9°C) and high (34°C) ambient temperature (Ta); the vertebral canal was cooled to 34°C during the middle 5 min of each exercise period. pH and oxygen content of the arterial and mixed venous blood were also measured. during exercise was not significantly affected by Ta. Spinal cord cooling produced definite increases in CO and SV during 0·5ms−1 exercise at 9°C; otherwise, effects of spinal cord cooling were not significant. HR, SV and CO were all linearly related to these relationships were unaffected by spinal cord cooling or Ta. Blood pressure did not increase during exercise. and did not increase significantly during exercise. The arterial-venous difference was increased by exercise only at 34°C. The chickens generally hyperventilated at 34°C Ta compared to the other Ta values. No consistent effect on blood gases or on pH and of the blood could be attributed to spinal cord cooling.
Respiratory and Cardiovascular Responses of the Exercising Chicken to Spinal Cord Cooling at Different Ambient Temperatures: II. Respiratory Responses
Authors: Gleeson M. , Barnas G. M. , Rautenberg W.
Published: April 2021

We measured oxygen consumption , carbon dioxide production , minute volume , respiratory frequency (f) and tidal volume (VT) of chickens during 15 min treadmill exercise at 0·5ms−1 and 0·8 ms−1 at thermoneutral (23°C), low (9°C) and high (34°C) ambient temperature (Ta); the vertebral canal was cooled to 34°C during the middle 5 min of each exercise period. Temperatures of the vertebral canal (Tvc) and rectum (Tre) were also measured. Exercise at 0·5 ms−1 caused increases in O2 consumption, CO2 production, minute volume and tidal volume compared to resting controls at each Ta. Minute volume and respiratory frequency were higher and tidal volume was lower in birds exercising at 34°C than at 23 or 9°C. Spinal cord cooling during exercise (0·5 ms−1) at 9°C caused further increases in O2 consumption, tidal volume and respiratory frequency almost equivalent to those produced by an increase in the running speed to 0·8 m s−1. Spinal cord cooling during exercise (0·5 ms−1) at 23°C did not significantly affect O2 consumption, CO2 production, minute volume, tidal volume or respiratory frequency. Spinal cord cooling during exercise (0·5 ms−1) at 34°C did not affect O2 consumption or CO2 production, but caused decreases in minute volume and respiratory frequency and an increase in tidal volume. We conclude that the domestic fowl exhibits spinal thermosensitivity during exercise, although these responses appear to be smaller than those previously reported for the resting bird. Decreased external temperature potentiates the effects of spinal cord cooling during exercise.
Electrical-Potential Difference and Sodium Ion Fluxes Across the Integument of Corophium Volutator (Crustacea; Amphipoda), A Euryhaline Hyperosmotic Regulator
Authors: Taylor Peter M.
Published: April 2021

Measurements of electrical-potential difference (TEP) and Na+ efflux, across the integument have been made for Corophtum volutator acclimated to 85 or 15%SW. The TEP of acclimated animals in 85 or 15%SW is 1·4 mV or 11·1 mV respectively (haemolymph negative). For acclimated animals, . unidirectional Na+ efflux is 154·3 nmol mg−1 body weight h−1 in 85%SW [efflux rate constant (k) = 0·70 h−1] and approximately 35·5 nmol mg−1 h−1 in 15%SW (k = 0·50h−1 in 10%SW). The results indicate that Na+ and Cl−are passively distributed across the ion-permeable (gill) integument of acclimated animals in 85%SW, but that active uptake of Cl−, and possibly Na+ also, occurs across the gills of acclimated animals in 15%SW. The ion transport mechanisms appear to effect electroneutral transfers across the gill integumental epithelium. Corophium volutator gill integument has a high permeability to ions; permeability to Na+(PNa) is 7·5x 10−8ms−1, and the ratio PCL/PNa is 0·45, for animals acclimated to either salinity. The resistance of the gill thelium of acclimated animals has been calculated to be·3×10−3Ωm2 and 2·0×10−2Ωm2 in 85 and 15%SW respectively.
Mechanical Power Output From Striated Muscle During Cyclic Contraction
Authors: Josephson Robert .K
Published: April 2021

The mechanical power output of a synchronous insect muscle was determined by measuring tension as the muscle was subjected to sinusoidal length change and stimuli which occurred at selected phases of the length cycle. The area of the loop formed by plotting muscle tension against length over a full cycle is the work done on that cycle; the work done times the cycle frequency is the mechanical power output. The muscle was a flight muscle of the tettigoniid Neoconocephalus triops. The measurements were made at the normal wing-stroke frequency for flight (25 Hz) and operating temperature (30°C). The power output with a single stimulus per cycle, optimal excursion amplitude, and optimal stimulus phase was 1·52 J kg−1 cycle−1 or 37Wkg−1. The maximum power output occurs at a phase such that the onset of the twitch coincides with the onset of the shortening half of the length cycle. The optimum excursion amplitude was 5·5% rest length; with greater excursion, work output declined because of decreasing muscle force associated with the more rapid shortening velocity. Multiple stimulation per cycle increases the power output above that available with twitch contractions. In this muscle, the maximum mechanical power output at 25 Hz was 76 Wkg−1 which was achieved with three stimuli per cycle separated by 4-ms intervals and an excursion amplitude of 6·0% rest length. The maximum work output during the shortening of an isotonic twitch contraction was about the same as the work done over a full sinusoidal shortening-lengthening cycle with a single stimulus per cycle and optimum excursion amplitude and phase.
Ventilatory and Acid-Base Responses to Long-Term Hypercapnia in the Freshwater Turtle, Chrysemys Picta Bellii
Authors: Silver Randi B. , Jackson Donald C.
Published: April 2021

The response to hypercapnia was studied in western painted turtles, Chrysemys picta bellii at 20°C. Ventilation, metabolic rate, arterial blood gases, blood pH and blood plasma ions were monitored periodically on individual turtles exposed to 5·7% CO2 for 72 h and then allowed to recover in air.

In response to hypercapnia, there is an immediate 10-to 15-fold increase in ventilation from control levels, which was maintained throughout the entire 5·7% CO2 breathing period. The first hour of CO2 breathing caused an increase in from 24–39 mmHg with a concomitant decrease in pH and rise in [HCO3−]. [HCO3−] rose from 42 to 50 mmol l−1 in the next 24 h of CO2 breathing and remained at this level for the rest of the hypercapnic period. Small, significant increases in total [Ca2+] and total [Mg2+] were found; however, no changes were observed in the plasma Na+, K+ or Cl− concentrations and the overall change in measured ions could not account for the increased [HCO3−]. The maximum change in [HCO3−] attained in Chrysemys exposed to a more severe acidosis (14·3% CO2) for up to 18 h was the same as that seen in the animals breathing 5·7% CO2 (10 mmol l−1) implying that there is an upper limit for the accumulation of [HCO3−] in Chrysemys at 20 °C.

The blood pH of turtles recovering in air returned to the control value (7−56–7’74) within the first hour although did not return to the control value. The HCO3− ion concentration also remained elevated throughout the 48-h recovery period, which suggests that ionic compensation is a slower process.

The freshwater turtle employs two mechanisms to reduce the severity of an imposed respiratory acidosis: increased ventilation and changes in the strong ion difference. In spite of these responses, blood pH is not restored to the control value.
Methods for Producing Disturbances in Pigeon Homing Behaviour by Oscillating Magnetic Fields
Authors: Ioale’ Paolo , Guidarini Dante
Published: April 2021

Experiments were performed with homing pigeons treated before release with oscillating magnetic fields produced by small Helmholtz coils placed around the neck and on the head of the pigeon or by larger Helmholtz coils surrounding the cage of the birds. In both types of treatment, which both used a single frequency of about 0-14 Hz, the pigeons’ initial orientation was strongly affected when the oscillation of the artificial magnetic field was square-shaped, whereas a triangular or sine-shaped variation had no effect.
Mechanical Properties and Factors of Safety of Spider Drag-Lines
Authors: Brandwood A.
Published: April 2021

Experiments were carried out to determine the strain energy capacity and breaking strain of spider drag-line silk. These properties are discussed in terms of a mathematical model of a spider falling on a drag-line. It was found that the strain energy capacity of the drag-line was insufficient to absorb the potential energy lost by a falling spider and that in order to avoid failure of the drag-line the spider dissipates energy by other means, particularly by using its inertia to draw drag-line silk from its spinnerets.
Further Observations on the Regulation of KCl Absorption Across Locust Rectum
Authors: Hanrahan J. W. , Phillips J. E.
Published: April 2021

Electrophysiological and tracer flux techniques were used to study regulation of KCl reabsorption across locust recta. Physiologically high K+ levels (100 mmol 1−1) on the lumen side stimulated net 36C1 flux and reduced the theoretical energy cost of anion transport under open-circuit conductions.

The stimulation of short-circuit current (ISC, i.e. active Cl− absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Isc were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl− absorption and counter-ion (K+) permeability.

High mucosal osmolarity or K+ concentration decreased Isc. and caused a disproportionately large increase in Rt, consistent with a decrease in the shunt (K+) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K+ levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo at the end of resorptive cycles also inhibited Isc, apparently without affecting K+ permeability.
The Effect of Perfusion Flow Rate and Adrenergic Stimulation on Oxygen Transfer in the Isolated, Saline-Perfused Head of Rainbow Trout (Salmo Gairdneri)
Authors: Perry S. F. , Daxboeck C. , Dobson G. P.
Published: April 2021

An isolated, saline-perfused trout head preparation, irrigated with hyperoxic water was used to assess diffusion/perfusion limitations to gill oxygen transfer. In the absence of catecholamines, increasing the perfusion flow rate caused a reduction of the partial pressure of oxygen in the dorsal aortic perfusate, indicating diffusion limitations to oxygen uptake. Physiological concentrations of epinephrine stimulated oxygen uptake in a dose-dependent fashion. Moreover, epinephrine elicited a greater effect during increased perfusion flow rate as a result of larger initial diffusion limitations, caused by the increased flow. By using a variety of adrenergic agonists and antagonists, it was demonstrated that beta-receptor stimulation enhanced oxygen uptake whereas alpha-receptor stimulation had no effect. These results are discussed with reference to changes in gill epithelial permeability to oxygen and/or surface area changes.
The Inherent Walking Direction Differs for The Prothoracic and Metathoracic Legs of Stick Insects
Authors: Bässler Ulrich , Foth Eva , Breutel Gerhard
Published: April 2021

On a slippery surface the forelegs of a decapitated stick insect walk forwards and the hindlegs, backwards. Animals with only forelegs but that are otherwise intact walk forwards, whereas animals with only hindlegs walk mostly backwards. Usually when intact animals start to walk, their hindlegs exert a rearwards thrust on the substrate, but occasionally the starting forces are directed forwards.

A rampwise extension of the femoral chordotonal organ in the fixed foreleg of a walking animal first excites the flexor tibiae muscle (positive feedback). Towards the end of the ramp stimulus the activity of the flexor decreases, and the extensor tibiae motor neurones become strongly active.

All experiments indicated that the inherent direction of movement of the metathorax is rearwards. In intact animals there must be a coordinating pathway from the prothorax to the metathorax that, together with the sub-oesophageal ganglion, induces the hindlegs to walk forwards.
Is the ‘Click’ Mechanism of Dipteran Flight an Artefact of CC14 Anaesthesia?
Authors: Miyan Jaleel A. , Ewing Arthur W.
Published: April 2021

A frame-by-frame analysis of the wing movements of a fly shows characteristics which are incompatible with the accepted model for dipteran flight. Higher amplitude wing beats result in greater velocities on the upstroke. Detailed examination of the wing base articulation has uncovered a wing stop and DVM stretch mechanism. It is argued that there is elastic energy storage during the downstroke which is released on the upstroke. A novel mechanical model for wing movements is proposed which incorporates all the new findings and argues against a ‘click’ mechanism.
Which Parameters Control the Leg Movement of a Walking Insect?: II. The Start of the Swing Phase
Authors: Cruse H.
Published: April 2021

When a stick insect (Carausius morosus) walks on a treadwheel with one leg standing on a platform beside the wheel, this leg can be considered to perform a prolonged stance phase. To elicit a swing phase in this situation, both load and position must decline below definite threshold values.

The swing phase can be elicited when — given a sufficiently posterior leg position - a central temporal signal initiates a small forward movement, and this is followed by a decrease of load.

It is possible for signals from the next posterior leg to change the position threshold at which the swing phase can be started, but these commands do not influence the force values during the stance phase.

Thus position is one parameter used for the decision to end the stance phase. But it does not serve as a signal for a position feedback mechanism controlling leg movement during the stance phase.
Ventilatory Oxygen Extraction During Cold Exposure in the Pigeon (Columba Livia)
Authors: Bech C. , Rautenberg W. , May B.
Published: April 2021

The respiratory responses to cold ambient temperatures in birds have only rarely been described. Bernstein & Schmidt-Nielsen (1974) studied the fish crow (Corvus ossifragus) during moderate cold exposure, while Bouverot, Hildwein & Oulhen (1976) measured ventilatory variables in pigeons (Columba livia) at near thermoneutral (22°C) and at cold (2°C) ambient temperatures. With respect to the amount of oxygen extracted from the ventilated air, both studies did not show any significant alterations correlated with changes in ambient temperature. However, several recent studies have demonstrated an increased oxygen extraction in response to cold exposure in birds [Bucher (1981) in the linneated parakeet (Bolborhynchos lineola), Brent, Rasmussen, Bech & Martini (1983) in the kittiwake (Rissa tridactyla), Brent, Pedersen, Bech & Johansen (1984) in the European coot (Fulica atra) and Bech, Johansen, Brent & Nicol (1984) in the duck (Anas platyrhynchos)). The significance of such an altered is obvious: the resultant decrease in ventilatory requirement will lower the relative loss of heat and water. Thus, together with a low expired air temperature (Schmidt-Nielsen, Hainsworth & Murrish, 1970), the increased oxygen extraction serves to minimize the respiratory heat and water loss in cold environments (Johansen & Bech, 1983).
Fluid Secretion By the Malpighian Tubules of the Dragonfly Libellula Quadrimaculata
Authors: Nicholls S. P.
Published: April 2021

Fluid secretion by the Malpighian tubules of Libellula quadrimaculata is unusual in that it is dependent on sodium and entirely independent of potassium in the external medium. It is suggested that this is due to the primitive, sodium-rich haemolymph of the Odonata. Similarities between these tubules and those of the millipede Glomeris marginata, which has a similar sodium-based haemolymph, support this view. Fluid secretion by the tubules is also dependent on the osmotic pressure of the external medium, declining considerably at higher osmotic pressures. However, there is no difference in the secretory rates of tubules isolated from larvae adapted to tap water, de-ionized water or salt water, even though there are large differences in the haemolymph osmotic pressure under these different conditions. This suggests some form of adaptation of the tubules in larvae from these different conditions. A factor which causes a five-to six-fold increase in the rate of secretion was present in the thoracic ganglia, and a slightly lower increase in secretion rate was recorded in larvae that had been feeding.
Metabolic Activity Related to the Potassium Pump in the Midgut of Bombyx Mori Larvae
Authors: Parenti P. , Giordana B. , Sacchi V. F. , Hanozet G. M. , Guerritore A.
Published: April 2021

The transepithelial electrical potential difference across the isolated midgut of Bombyx mori larvae is dependent on the presence of potassium and is unaffected by the addition of hexoses to perfusion media, whereas it is enhanced by alanine, aspartic acid, glutamic acid and the corresponding 2-oxoacids, glutamine and malate. The midgut enzyme profile indicates that the substrates for the tricarboxylic acid cycle are supplied mainly by amino acid metabolism via transaminases. Accordingly, aminoxyacetate drastically reduces the intestinal transepithelial electrical potential difference stimulated by amino acids. Measurement of the free amino acid concentration in the lumen content, intestinal cells and haemolymph shows that glutamic acid, asparagine and glutamine are accumulated in the cell, whilst the haemolymph is enriched with basic amino acids and with glycine, alanine, serine and tyrosine, the major components of the silk fibroin. Therefore, amino acid metabolism directly related to the tricarboxylic acid cycle seems to be the primary source of energy for the potassium pump activity inB. mori midgut.
Cardiac Performance in Response to Loading Pressures in Busycon Canaliculatum (Gastropoda) and Mercenaria Mercenaria (Bivalvia)
Authors: Smith P. J. S.
Published: April 2021

The performance of the isolated hearts of a gastropod, Busycon canaliculatum (L.), and a bivalve, Mercenaria mercenaria(L.), were examined at different perfusion levels around the expected physiological ranges. Both hearts followed the Frank-Starling relationship with regard to stroke volume versus preload, but the heart-rate response was speciesdependent. The argument is developed that the molluscs might functionally apply Starling’s Law of the heart to accommodate increased output during exercise.

At the expected in vivo filling pressures the power output of the two hearts was the same (15–30 × 10−6Wg−1 ventricular tissue), but the Mercenaria filling levels were considerably lower. This clearly indicates that the cardiac muscle of each of the two species has evolved to operate at specific pressure ranges.

Electrical recordings from the surface of the myocardium in the perfused Busycon hearts confirm that the shape changes reported in the literature, dealing with stretched myocardium, also occur for changes in the whole heart at realistic loading pressures. These results support previous conclusions that the cardiac output is controlled by the duration of the action potential plateau.
Short Communication Prey Capture Hydrodynamics in Fishes: Two Approaches
Authors: Muller M. , Leeuwen J. L. Van , Osse J. W. M. , Drost M. R.
Published: April 2021

Suction feeding is widely used in teleost fish (<20 000 species). It is accomplished by rapid expansion and contraction (<100 ms) of the buccal and opercular cavities and results in movement of both the prey and the fish itself. Suction is often combined with jaw protrusion and swimming. During a single suction movement the volume of water passing through the mouth aperture may exceed, by more than five times, the volume of the fully expanded mouth cavity, since after a given moment water leaves the mouth through the opercular slits. The generated flow is highly unsteady, i.e. large local accelerations (>50m s−2) occur and streamline patterns change rapidly with time.
Evidence From Strandings for Geomagnetic Sensitivity in Cetaceans
Authors: Kirschvink Joseph L. , Dizon Andrew E. , Westphal James A.
Published: April 2021

We tested the hypothesis that cetaceans use weak anomalies in the geomagnetic field as cues for orientation, navigation and/or piloting. Using the positions of 212 stranding events of live animals in the Smithsonian compilation which fall within the boundaries of the USGS East-Coast Aeromagnetic Survey, we found that there are highly significant tendencies for cetaceans to beach themselves near coastal locations with local magnetic minima. Monte-Carlo simulations confirm the significance of these effects. These results suggest that cetaceans have a magnetic sensory system comparable to that in other migratory and homing animals, and predict that the magnetic topography and in particular the marine magnetic lineations may play an important role in guiding long-distance migration. The ‘ map’ sense of migratory animals may therefore be largely based on a simple strategy of following paths of local magnetic minima and avoiding magnetic gradients.
Effects Of Temperature And Thermal Acclimation On Contractile Properties And Metabolism Of Skeletal Muscle In The Flounder (Platichthys Flesus L.)
Authors: Johnston Ian A. , Wokoma Alele
Published: April 2021

Flounder (Platichthys flesus L.) were acclimated in sea water for 1-2 months to either 5°C or 23°C (12h light: 12h dark photoperiod).

Single fast muscle fibres were isolated from anterior ventral myotomes and skinned with detergent (Brij 58). Fibres were maximally activated and force-velocity (P-V) characteristics determined by step tension releases using an isotonic lever. Unloaded shortening speed was independently determined using the slack-test method.

The contractile properties of flounder skinned fibres are not altered by temperature acclimation. Maximum isometric tension development has a low thermal dependence, Q10= 1·2, increasing from 145 kN m−2 at 0°C to 200 kN m−2 at 25 °C. The force-velocity relationship becomes progressively less curved with decreasing temperature (higher values of Hill’s constant a/P0) such that the thermal dependence of contraction velocity is significantly less at loads for optimum power output (Q10= 1·3) than at zero load (Q10= 2·0). Values for a/P0 are 0·27 at 0°C, 0·12 at 10°C and 0·08 at 25°C. Reductions in the curvature of the P-V relationship with decreasing temperature may represent an important mechanism for stabilizing muscle power output at low temperatures.

Longer term metabolic adjustments to temperature were studied by determining maximal enzyme activities in fast and slow muscles (at 15°C). Activities of marker enzymes for mitochondrial metabolism (cytochrome oxidase), aerobic glucose utilization (hexokinase) and fatty acid oxidation (carnitine palmitoyl transferase) are 1·5–2·8 times higher in muscles of cold-acclimated compared to warm-acclimated flounders. Increases in the activities of these enzymes with cold acclimation may serve to offset the effects of low temperature on aerobic ATP supply. Glycolytic enzyme activities (phosphofructokinase, lactate dehydrogenase), however, are similar at both acclimation temperatures.

The results are briefly discussed in relation to the ecology of the flounder and evolutionary strategies of temperature adaptation in teleosts.
Capillarity and Mitochondrial Distribution in Rat Myocardium Following Exercise Training
Authors: Kayar S. R. , Conley K. E. , Claassen H. , Hoppeler H.
Published: April 2021

Rats were subjected to a laddermill running programme either once per week for 6 weeks, or daily for 6 weeks. Heart mass and maximal oxygen consumption rate increased relative to controls and with the frequency of the running programme. Mitochondrial distribution, measured in seven regions within fibres, was similar in all hearts, with a peak volume density of 0·42 ±0·01 occurring 4–5 μm from the centre of a capillary. Capillary density decreased with increasing heart mass, but total capillary length and capillary-to-fibre ratio were constant. Thus the higher metabolic demands of the running programmes did not alter the volume density or distribution of mitochondria, despite significant increases in heart mass and decreases in capillarity.