bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Inhibitory Effects Of γ-Aminobutyric Acid (Gaba) On Growth Hormone Secretion in the Goldfish Are Modulated by SEx Steroids
Authors: Trudeau V. L. , Kah O. , Chang J. P. , Sloley B. D. , Dubourg P. , Fraser E. J. , Peter R. E. 
Published: April 2021

ABSTRACT
Double-labelling studies at the electron microscopic level demonstrated that γ-aminobutyric acid (GABA)-immunoreactive nerve endings are associated with growth-hormone-secreting cells in the proximal pars distalis of the goldfish pituitary gland, suggesting that GABA may be important for the control of growth hormone release in this species. An in vitro assay for GABA-transaminase activity demonstrated that the pituitary is a site for the metabolism of GABA to succinic acid. In vitro, GABA or the GABA antagonists bicuculline and saclofen did not affect the rate of growth hormone release from dispersed pituitary cells in static incubation. In contrast, intracerebroventricular injection of GABA reduced serum growth hormone levels within 30 min. During the seasonal gonadal cycle, intraperitoneal injection of GABA was without effect in sexually regressed goldfish, but caused a significant decrease in serum growth hormone levels in sexually recrudescent animals. Intraperitoneal implantation of solid silastic pellets containing oestradiol increased serum GH levels fivefold in sexually regressed and recrudescent goldfish; in both groups, GABA suppressed the oestradiol-stimulated increase in circulating growth hormone levels. The effect of oestradiol on basal serum growth hormone levels was specific since progesterone and testosterone were without effect. However, in recrudescent animals treated with progesterone and testosterone, the inhibitory effects of GABA on serum growth hormone levels were absent, indicating a differential role for these steroids in growth hormone release. Taken together, these results demonstrate that GABA has an inhibitory effect on growth hormone release in goldfish.
Identification of a Sea Urchin Na+ /K+ /2Cl− Cotransporter (Nkcc): Microfilament-Dependent Surface Expression is Mediated by Hypotonic Shock and Cyclic Amp
Authors: D’andrea-Winslow Lisanne , Strohmeier Gregg R. , Rossi Bernard , Hofman Paul 
Published: April 2021

ABSTRACT
We report the identification of an invertebrate Na+/K+/2Cl− cotransporter, NKCC. As a model system, we used the immune cells (coelomocytes) of the Mediterranean sea urchin Paracentrotus lividus. These cells are particularly interesting because they can be activated to undergo a rapid and dynamic change in cell shape. We demonstrate that forskolin, a cyclic AMP agonist known to regulate NKCC, induced coelomocyte transformation at doses of 10 µmol l−1 and greater. Using two distinct monoclonal antibodies (T4 and T9) raised against the human intestinal epithelial NKCC, we have identified a high-molecular-mass (195 kDa) protein in coelomocyte extracts. We propose a novel method for the isolation of NKCC in one step by using bumetanide–Sepharose affinity chromatography under low-[Cl−] conditions. This method was successful in isolating coelomocyte 195 kDa NKCC. The T4 monoclonal antibody was used in immunocytochemical experiments to localize NKCC in resting and activated coelomocytes. In petalloid coelomocytes, a punctate, cytoplasmic distribution was observed in close proximity to actin filament bundles; in transformed coelomocytes, the immunofluorescence was distributed along the length of the filopodia and uniformly throughout the perinuclear region. The change in subcellular distribution of NKCC between the resting and the activated state was further investigated by using cell surface biotinylation followed by immunoprecipitation. These studies revealed an upregulation of NKCC at the plasma membrane upon activation, a process that was blocked by the F-actin-stabilizing drug phalloidin. These studies identify a novel model system in which to investigate a newly identified invertebrate Na+/K+/2Cl− cotransporter.
Oxidative Stress, Dna Damage And P53 Expression In The Larvae Of Atlantic Cod (Gadus Morhua) Exposed To Ultraviolet (290–400 nm) Radiation
Authors: Lesser Michael P. , Farrell Julianne H. , Walker Charles W. 
Published: April 2021

ABSTRACT
Decreases in stratospheric ozone levels from anthropogenic inputs of chlorinated fluorocarbons have resulted in an increased amount of harmful ultraviolet-B (UVB, 290–320 nm) radiation reaching the sea surface in temperate latitudes (30–50°N). In the Gulf of Maine, present-day irradiances of ultraviolet-A (UVA, 320–400 nm) radiation can penetrate to depths of 23 m and UVB radiation can penetrate to depths of 7–12 m, where the rapidly developing embryos and larvae of the Atlantic cod (Gadus morhua) are known to occur. Laboratory exposures of embryos and larvae of Atlantic cod to ultraviolet radiation (UVR) equivalent to a depth of approximately 10 m in the Gulf of Maine resulted in significant mortality of developing embryos and a decrease in standard length at hatching for yolk-sac larvae. Larvae at the end of the experimental period also had lower concentrations of UVR-absorbing compounds and exhibited significantly greater damage to their DNA, measured as cyclobutane pyrimidine dimer formation, after exposure to UVB radiation. Larvae exposed to UVB radiation also exhibited significantly higher activities and protein concentrations of the antioxidant enzyme superoxide dismutase and significantly higher concentrations of the transcriptional activator p53. p53 is expressed in response to DNA damage and can result in cellular growth arrest in the G1-to S-phase of the cell cycle or to programmed cell death (apoptosis). Cellular death caused by apoptosis is the most likely cause of mortality in embryos and larvae in these laboratory experiments, while the smaller size at hatching in those larvae that survived is caused by permanent cellular growth arrest in response to DNA damage. In addition, the sub-lethal energetic costs of repairing DNA damage or responding to oxidative stress may also contribute to poor individual performance in surviving larvae that could also lead to increases in mortality. The irradiances of UVB radiation that elicit these responses in cod larvae can occur in many temperate latitudes, where these ecologically and commercially important fish are known to spawn, and may contribute to the high mortality of cod embryos and larvae in their natural environment.
Acute and Chronic Influence of Temperature on Red Blood Cell Anion Exchange
Authors: Jensen Frank B. , Wang Tobias , Brahm Jesper 
Published: April 2021

ABSTRACT
Unidirectional 36Cl− efflux via the red blood cell anion exchanger was measured under Cl− self-exchange conditions (i.e. no net flow of anions) in rainbow trout Oncorhynchus mykiss and red-eared freshwater turtle Trachemys scripta to examine the effects of acute temperature changes and acclimation temperature on this process. We also evaluated the possible adaptation of anion exchange to different temperature regimes by including our previously published data on other animals. An acute temperature increase caused a significant increase in the rate constant (k) for unidirectional Cl− efflux in rainbow trout and freshwater turtle. After 3 weeks of temperature acclimation, 5 °C-acclimated rainbow trout showed only marginally higher Cl− transport rates than 15 °C-acclimated trout when compared at the same temperature. Apparent activation energies for red blood cell Cl− exchange in trout and turtle were lower than values reported in endothermic animals. The Q10 for red blood cell anion exchange was 2.0 in trout and 2.3 in turtle, values close to those for CO2 excretion, suggesting that, in ectothermic animals, the temperature sensitivity of band-3-mediated anion exchange matches the temperature sensitivity of CO2 transport (where red blood cell Cl−/HCO3− exchange is a rate-limiting step). In endotherms, such as man and chicken, Q10 values for red blood cell anion exchange are considerably higher but are no obstacle to CO2 transport, because body temperature is normally kept constant at values at which anion exchange rates are high. When compared at constant temperature, red blood cell Cl− permeability shows large differences among species (trout, carp, eel, cod, turtle, alligator, chicken and man). Cl− permeabilities are, however, remarkable similar when compared at preferred body temperatures, suggesting an appropriate evolutionary adaptation of red blood cell anion exchange function to the different thermal niches occupied by animals.
Free Vertical Moments and Transverse Forces in Human Walking and Their Role in Relation to Arm-Swing
Authors: Li Yu , Wang Weijie , Crompton Robin H. , Gunther Michael M. 
Published: April 2021

ABSTRACT
We present force plate data on vertical free moments (force couples in the horizontal plane between the foot and the ground) and on transverse force during unloaded walking in different modes and at different speeds (including running) by adults of both sexes and by children, and examine loaded walking by adult males and one boy. Free moments in slow and normal-speed walking are characterised by a lateral peak in the accelerative phase of stance, but the peak during running, and in some cases of fast walking, occurs in the deceleration phase. Free moments are strongly affected by arm fixation in males, but less so in females. The pattern, but not the scale, of free moments is affected by loading position and side, but load magnitude has little effect if the loaded weight is treated as part of the body. Transverse force is more variable than sagittal force. In males, the transverse force curve shows a marked trough at mid-stance, whereas in females this trough is rarely seen. The transverse force of males also differs from that of females in response to arm fixation, showing a local medial inflection at three-quarters of the stance phase that is not present in females. Adults differ from children younger than 9 years in the presence of a very short, medially directed peak following heel-strike. Analysis of the effects of arm fixation and the timing of forces suggests strongly that arm-swing and free moments tend to reinforce each other in balancing trunk torques induced by the lower limbs. Both are of reduced importance in slow walking.
Physical Factors Affecting the Cost and Efficiency of Sound Production in the Treefrog Hyla Versicolor
Authors: Mclister James D. 
Published: April 2021

ABSTRACT
The metabolic cost, energy output and efficiency (i.e. the ratio of energy output to metabolic cost) of sound production were compared among male grey treefrogs (Hyla versicolor) as a function of body size and temperature. The effects of call length (in notes per call) and dominant frequency (in kHz) were also considered. Cost, determined from the amount of oxygen consumed, averaged 12.1 mJ per note and was dependent only upon body mass. Acoustic energy per note, determined from oscillograms of recorded calls, averaged 0.34 mJ and was dependent only upon temperature. Conventional theory suggests that the efficiency of sound production should be a function of the ratio of the linear size of the radiating structures to the wavelength of the sound generated (i.e. efficiency is assumed to be a function of the product of mass0.33 and frequency), but efficiency in H. versicolor was found to be a function of the product of temperature2.1 and mass−1.08. Adjusting for temperature and body mass, the efficiency of sound production in H. versicolor (average 2.4 %) is greater than the efficiency of other frog species for which data are available. Temperature may affect acoustic energy output because trunk muscle contraction speed increases with temperature, which increases the velocity of airflow across the vocal cords.
Transport of Bile Acids in Hepatic and Non-Hepatic Tissues
Authors: St-Pierre Marie V. , Kullak-Ublick Gerd A. , Hagenbuch Bruno , Meier Peter J. 
Published: April 2021

ABSTRACT
Bile acids are steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH and, consequently, require a carrier for transport across the membranes of the enterohepatic tissues. Individual bile acid carriers have now been cloned from several species. Na+-dependent transporters that mediate uptake into hepatocytes and reabsorption from the intestine and biliary epithelium and an ATP-dependent transporter that pumps bile acids into bile comprise the classes of transporter that are specific for bile acids. In addition, at least four human and five rat genes that code for Na+-independent organic anion carriers with broad multi-substrate specificities that include bile acids have been discovered. Studies concerning the regulation of these carriers have permitted identification of molecular signals that dictate eventual changes in the uptake or excretion of bile acids, which in turn have profound physiological implications. This overview summarizes and compares all known bile acid transporters and highlights findings that have identified diseases linked to molecular defects in these carriers. Recent advances that have fostered a more complete appreciation for the elaborate disposition of bile acids in humans are emphasized.
Lift-Based Paddling in Diving Grebe
Authors: Johansson L. Christoffer , Norberg Ulla M. Lindhe 
Published: April 2021

ABSTRACT
To examine the hydrodynamic propulsion mechanism of a diving great crested grebe (Podiceps cristatus), the three-dimensional kinematics was determined by digital analysis of sequential video images of dorsal and lateral views. During the acceleration phase of this foot-propelled bird, the feet move through an arc in a plane nearly normal to the bird’s line of motion through the water, i.e. the toes move dorsally and medially but not caudally relative to the water. The kinematics of the grebe’s lobed feet is different from that in anseriforms, whose feet move in a plane mostly parallel to the bird’s line of progress through the water. Our results suggest that the foot-propelled locomotor mechanism of grebes is based primarily on a lift-producing leg and foot stroke, in contrast to the drag-based locomotion assumed previously. We suggest that the lift-based paddling of grebes considerably increases both maximum swimming speed and energetic efficiency over drag-based propulsion. Furthermore, the results implicate a new interpretation of the functional morphology of these birds, with the toes serving as a self-stabilizing multi-slotted hydrofoil during the power phase.
The Process of Cell Adhesion Among Dissociated Single Cells of Hydra: Morphological Observations
Authors: Takaku Yasuharu , Hariyama Takahiko , Tsukahara Yasuo 
Published: April 2021

ABSTRACT
Ultrastructural observations were made on the initial adhesion process at the adherent region of Hydra endodermal cell pairs brought into contact (following dissociation) using a three-dimensional laser manipulator. Total contact length across the diameter of the adherent region decreased during the period 10–60 min after initial adhesion. However, the mean numbers of closest (&lt;4 nm) and medium (5–25 nm) separation distances between membranes (thought to be important in total cell adhesion) were not significantly different. These data indicate that adherent cell pairs maintain a constant adhesiveness during the first 60 min of the adhesion process, despite membrane rearrangements. The relative length of each separation distance in adherent cell pairs approached that reported previously for intact Hydra. The sums of lengths in both the closest and medium categories (as a proportion of total contact length) increased because the length of cleavages (distances &gt;25 nm) decreased significantly during the same time period. These results suggest that adherent cell pairs undergo rapid, active membrane changes in the adherent region, which might be associated with cell sorting. The possible significance of these changes for active rearrangement are discussed.
Juvenile Coho Salmon Locomotion and Mosaic Muscle are Modified by 3’,3’,5’-Tri-Iodo-L-Thyronine (T3)
Authors: Katzman Shana , Cech Joseph J. 
Published: April 2021

ABSTRACT
Studies of maximum aerobic swimming performance in smolting juvenile salmonids indicate that these animals may be aerobically compromised during downstream migration. To test our hypothesis that hyperthyroid status contributes to decreased swimming performance through modification of muscle contractility in juvenile (112 mm mean total length) coho salmon (Oncorhynchus kisutch), we measured swimming performance and isolated muscle bundle contractility of fish implanted with 3’,3’,5’-tri-iodo-L-thyronine (T3) pellets, of fish implanted with sham pellets and of fish with no pellet implantation (control group). After 3 weeks (N=12–13), critical swimming speeds (maximum aerobic swimming speed or Ucrit) were measured. Muscle bundles (N=15–16) were dissected from the hypaxial musculature and stimulated to measure the force and velocity of an isometric twitch and tetani. T3-treated fish demonstrated visible morphological changes associated with smoltification. Mean values of Ucrit were significantly decreased and the prolonged contraction (tetani) and twitch rates of contraction, relaxation and maximum force were significantly increased by T3 treatment compared with both the sham and control fish. Hematocrit, body mass and body length were not significantly affected by T3 treatment. In conclusion, we suggest that the reported decrease in Ucrit during salmonid smoltification may be mediated by endogenous T3-induced contractile modification of mosaic muscle fibers.
Comparison of the Efficiency of Rat Papillary Muscles During Afterloaded Isotonic Contractions and Contractions With Sinusoidal Length Changes
Authors: Mellors L. J. , Gibbs C. L. , Barclay C. J. 
Published: April 2021

ABSTRACT
The results of previous studies suggest that the maximum mechanical efficiency of rat papillary muscles is lower during a contraction protocol involving sinusoidal length changes than during one involving afterloaded isotonic contractions. The aim of this study was to compare directly the efficiency of isolated rat papillary muscle preparations in isotonic and sinusoidal contraction protocols. Experiments were performed in vitro (27 °C) using left ventricular papillary muscles from adult rats. Each preparation performed three contraction protocols: (i) low-frequency afterloaded isotonic contractions (10 twitches at 0.2 Hz), (ii) sinusoidal length change contractions with phasic stimulation (40 twitches at 2 Hz) and (iii) high-frequency afterloaded isotonic contractions (40 twitches at 2 Hz). The first two protocols resembled those used in previous studies and the third combined the characteristics of the first two. The parameters for each protocol were adjusted to those that gave maximum efficiency. For the afterloaded isotonic protocols, the afterload was set to 0.3 of the maximum developed force. The sinusoidal length change protocol incorporated a cycle amplitude of ±5 % resting length and a stimulus phase of −10 °. Measurements of force output, muscle length change and muscle temperature change were used to calculate the work and heat produced during and after each protocol.
Net mechanical efficiency was defined as the proportion of the energy (enthalpy) liberated by the muscle that appeared as work. The efficiency in the low-frequency, isotonic contraction protocol was 21.1±1.4 % (mean ± S.E.M., N=6) and that in the sinusoidal protocol was 13.2±0.7 %, consistent with previous results. This difference was not due to the higher frequency or greater number of twitches because efficiency in the high-frequency, isotonic protocol was 21.5±1.0 %.
Although these results apparently confirm that efficiency is protocol-dependent, additional experiments designed to measure work output unambiguously indicated that the method used to calculate work output in isotonic contractions overestimated actual work output. When network output, which excludes work done by parallel elastic elements, rather than total work output was used to determine efficiency in afterloaded isotonic contractions, efficiency was similar to that for sinusoidal contractions. The maximum net mechanical efficiency of rat papillary muscles performing afterloaded isotonic or sinusoidal length change contractions was between 10 and 15 %.
A Maxi Cl− Channel in Cultured Pavement Cells From the Gills of the Freshwater Rainbow Trout Oncorhynchus Mykiss
Authors: O’Donnell M. J. , Kelly S. P. , Nurse C. A. , Wood C. M. 
Published: April 2021

ABSTRACT
Primary cultures of pavement cells from the gills of a freshwater fish, the rainbow trout Oncorhynchus mykiss, have been studied for the first time using the patch-clamp technique. Gigaohm seals were obtained in approximately 95 % of cells studied, and channel activity was evident in a high proportion (&gt;90 %). A large-conductance Cl− channel was evident in 6 % of cell-attached and in 31 % of inside-out patches. Single-channel conductance in inside-out patches was 372 pS, and current/voltage relationships were linear over the range −60 to +60 mV. The channel was activated by patch excision, and activation was often associated with polarization of the patch. The mean number of channels per patch was 1.9, and there were several subconductance states. The relationship between channel activity (NPo) and voltage was in the form of an inverted U, and channel activity was highest between 0 and +20 mV. Large-conductance Cl− channels showed a progressive time-dependent reduction in current in response to sustained polarization to voltages outside the range −20 mV to +20 mV. Permeability ratios (P) of Cl− to other anions were and Pisethionate/PCl=0.53. The channel was blocked by Zn2+, SITS, DIDS and diphenylamine carboxylate. This is the first description of a large-conductance Cl− channel in gill cells from freshwater or marine species. Possible functions of the channel are discussed.