bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the Rhesus Monkey Ghrelin Gene and Factors Influencing Ghrelin Gene Expression and Fasting Plasma Levels
Authors: Angeloni Stephen V. , Glynn Nicole , Ambrosini Grazia , Garant Michael J. , Dee Higley J. , Suomi Stephen , Hansen Barbara C. 
Published: January 2004

AbstractGhrelin stimulates release of GH from the pituitary, stimulates appetite, and may influence metabolic processes in other tissues expressing the GH secretagogue receptor. Ghrelin can thus influence behaviors and endocrine pathways contributing to weight gain. In this study we characterized the ghrelin gene from the rhesus monkey and analyzed the association of plasma ghrelin levels with metabolic and endocrine markers. Rhesus ghrelin is 97, 91, and 96% homologous to the human cDNA, gene, and peptide, respectively. Ghrelin expression was highest in the stomach with lower levels found in muscle and duodenum. In these tissues, ghrelin expression in calorie-restricted and obese animals was about 40–99% lower than in lean animals. In addition, ghrelin expression in muscle was fairly high and may allow this tissue to contribute significantly to plasma levels. Fasting plasma ghrelin concentrations were also inversely correlated with body mass index and exhibited a nonlinear association with age with increased levels in younger and older monkeys and lower levels in middle-aged monkeys. Although a significant inverse correlation between fasting plasma ghrelin and fasting insulin levels were found, iv glucose and insulin administration did not significantly alter ghrelin levels. These studies demonstrate that ghrelin levels are influenced by age-related factors and adiposity in the rhesus monkey. These similarities between the rhesus monkey and human ghrelin genes and plasma ghrelin responses suggest a unique opportunity to study the mechanisms regulating ghrelin secretion and gene expression in different tissues in normal and disease states using this model system.
Regulation of the Aldo-Keto Reductase Gene akr1b7 by the Nuclear Oxysterol Receptor LXRα (Liver X Receptor-α) in the Mouse Intestine: Putative Role of LXRs in Lipid Detoxification Processes
Authors: Volle David H. , Repa Joyce J. , Mazur Andrzej , Cummins Carolyn L. , Val Pierre , Henry-Berger Joelle , Caira Francoise , Veyssiere Georges , Mangelsdorf David J. , Lobaccaro Jean-Marc A. 
Published: January 2004

AbstractLiver X receptors (LXRs) regulate the expression of a number of genes involved in cholesterol and lipid metabolism after activation by their cognate oxysterol ligands. AKR1-B7 (aldo-keto reductase 1-B7) is expressed in LXR target tissues such as intestine, and because of its known role in detoxifying lipid peroxides, we investigated whether the AKR1-B7 detoxification pathway was regulated by LXRs. Here we show that synthetic LXR agonists increase the accumulation of AKR1-B7 mRNA and protein levels in mouse intestine in wild-type but not lxr−/− mice. Regulation of akr1b7 by retinoic X receptor/LXR heterodimers is dependent on three response elements in the proximal murine akr1b7 promoter. Two of these cis-acting elements are specific for regulation by the LXRα isoform. In addition, in duodenum of wild-type mice fed a synthetic LXR agonist, we observed an LXR-dependent decrease in lipid peroxidation. Our results demonstrate that akr1b7 is a direct target of LXRs throughout the small intestine, and that LXR activation plays a protective role by decreasing the deleterious effects of lipid peroxides in duodenum. Taken together, these data suggest a new role for LXRs in lipid detoxification.
The giant mudskipperPeriophthalmodon schlosserifacilitates active NH4+ excretion by increasing acid excretion and decreasing NH3 permeability in the skin
Authors: Ip Yuen K. , Randall David J. , Kok Timothy K. T. , Barzaghi Cristiana , Wright Patricia A. , Ballantyne James S. , Wilson Jonathan M. , Chew Shit F. 
Published: January 2004

SUMMARYPeriophthalmodon schlosseri is an amphibious and obligatory air-breathing teleost, which is extremely tolerant to environmental ammonia. It actively excretes NH4+ in ammonia loading conditions. For such a mechanism to operate efficaciously the fish must be able to prevent back flux of NH3. P. schlosseri could lower the pH of 50 volumes (w/v) of 50% seawater in an artificial burrow from pH 8.2 to pH 7.4 in 1 day, and established an ambient ammonia concentration of 10 mmol l-1 in 8 days. It could alter the rate of titratable acid efflux in response to ambient pH. The rate of net acid efflux (H+ excretion)in P. schlosseri was pH-dependent, increasing in the order pH 6.0&lt;7.0&lt;8.0&lt;8.5. Net acid flux in neutral or alkaline pH conditions was partially inhibited by bafilomycin, indicating the possible involvement of a V-type H+-ATPase. P. schlosseri could also increase the rate of H+ excretion in response to the presence of ammonia in a neutral (pH 7.0) external medium. Increased H+ excretion in P. schlosseri occurred in the head region where active excretion of NH4+ took place. This would result in high concentrations of H+ in the boundary water layer and prevent the dissociation of NH4+, thus preventing a back flux of NH3 through the branchial epithelia. P. schlosseriprobably developed such an `environmental ammonia detoxification' capability because of its unique behavior of burrow building in the mudflats and living therein in a limited volume of water. In addition, the skin of P. schlosseri had low permeability to NH3. Using an Ussing-type apparatus with 10 mmol l-1 NH4Cl and a 1 unit pH gradient (pH 8.0 to 7.0), the skin supported only a very small flux of NH3 (0.0095 μmol cm-2 min-1). Cholesterol content (4.5 μmol g-1) in the skin was high, which suggests low membrane fluidity. Phosphatidylcholine, which has a stabilizing effect on membranes, constituted almost 50% of the skin phospholipids, with phosphatidyleserine and phsophatidylethanolamine contributing only 13% and 15%, respectively. More importantly, P. schlosseri increased the cholesterol level (to 5.5 μmol g-1) and altered the fatty acid composition (increased total saturated fatty acid content) in its skin lipid after exposure to ammonia (30 mmol l-1 at pH 7.0) for 6 days. These changes might lead to an even lower permeability to NH3 in the skin, and reduced back diffusion of the actively excreted NH4+ as NH3 or the net influx of exogenous NH3, under such conditions.
Temperature regulation in burying beetles (Nicrophorusspp.:Coleoptera: Silphidae): effects of body size, morphology and environmental temperature
Authors: Merrick Melissa J. , Smith Rosemary J. 
Published: January 2004

SUMMARYThis study compares the thermoregulatory ability of three species of burying beetle (Coleoptera: Silphidae: Nicrophorus hybridus, Nicrophorus guttula and Nicrophorus investigator) that vary significantly in body size. It also explores possible mechanisms for temperature regulation in burying beetles, including physiological and behavioral thermoregulatory strategies, and the influence of environmental temperatures on body temperature and activity times. We measured beetle thoracic and abdominal temperatures before and after short (&lt;5 s) flights, and thoracic temperature during sustained, tethered flights and following flight in the field. We calculated two measures of thermoregulatory ability: the slope of post-flight thoracic temperature against ambient air temperature and the slope of post-flight thoracic temperature against operative flight temperature. Thoracic temperatures following flight were significantly higher than abdominal temperatures, and the largest species, N. hybridus, was determined to be the better thermoregulator, with regression slopes closer to zero (0.315–0.370) than N. guttula (0.636–0.771) or N. investigator (0.575–0.610). We also examined the roles that insulation, wing loading, physiological heat transfer, basking and perceived environmental temperature play on temperature regulation and activity times in Nicrophorus. This study shows that body size, morphological features,such as wing loading and insulation, and perceived environmental temperatures affect thermoregulation and activity times in burying beetles.
Calcium responses of chicken trigeminal ganglion neurons to methyl anthranilate and capsaicin
Authors: Kirifides Michael L. , Kurnellas Michael P. , Clark Larry , Bryant Bruce P. 
Published: January 2004

SUMMARYUsing digital fluorescence imaging, we determined the effects of methyl anthranilate (MA), an avian irritant, and capsaicin (CAP), a mammalian irritant, on intracellular calcium ([Ca2+]i) in chicken trigeminal neurons. Concentration–response functions indicated that the threshold for inducing increases in [Ca2+]i was higher for CAP (30 μmol l–1) than for MA (10 μmol l–1). The maximum magnitudes of [Ca2+]iin response to MA and CAP were compared after normalization to 40 mmol l–1 KCl. At equal concentrations (300 μmol l–1), trigeminal neurons responded with a greater change in[Ca2+]i to MA (78% of KCl) than to CAP (43% of KCl). Furthermore, at 300 μmol l–1, 48% of neurons responded to MA whereas only 16% responded to CAP. The increases in[Ca2+]i induced by both MA and CAP were dependent upon extracellular calcium. While the calcium responses to MA were also dependent on extracellular sodium, responses to CAP were not. There were separate but overlapping populations of neurons sensitive to MA and CAP. Taken together,the higher threshold concentration of CAP, the higher response magnitude to MA than CAP and the greater number of neurons sensitive to MA than CAP provide a rationale for the observed behavioral differences of birds to these two compounds. Finally, the findings that the calcium responses to MA and CAP have different ion dependencies and that there are separate populations sensitive to these compounds suggest different transduction mechanisms mediating chicken trigeminal responses to MA and CAP.
Why is it worth flying at dusk for aquatic insects? Polarotactic water detection is easiest at low solar elevations
Authors: Bernáth Balázs , Gál József , Horváth Gábor 
Published: January 2004

SUMMARY
Using 180° field-of-view imaging polarimetry, we measured the reflection-polarization patterns of two artificial surfaces (water-dummies) in the red, green and blue spectral ranges under clear and partly cloudy skies at different solar elevations. The dummies consisted of a horizontal glass pane with a matt black or matt light grey cloth underneath, imitating a dark or bright water body, respectively. Assuming that polarotactic water insects interpret a surface as representing water if the degree of linear polarization of reflected light is higher than a threshold and the deviation of the direction of polarization from the horizontal is lower than a threshold, we calculated the proportion, P, of the artificial surfaces detected polarotactically as water. We found that at sunrise and sunset P is maximal for both water-dummies and their reflection-polarizational characteristics are most similar. From this, we conclude that polarotactic water detection is easiest at low solar elevations, because the risk that a polarotactic insect will be unable to recognize the surface of a dark or bright water body is minimal. This partly explains why many aquatic insect species usually fly en masse at dusk. The daily change in the reflection-polarization pattern of water surfaces is an important visual ecological factor that may contribute to the preference of the twilight period for habitat searching by polarotactic water insects. Air temperature at sunrise is generally low, so dusk is the optimal period for polarotactic aquatic insects to seek new habitats.
Nitrogen metabolism in the African lungfish (Protopterus dolloi)aestivating in a mucus cocoon on land
Authors: Chew Shit F. , Chan Noelle K. Y. , Loong Ai M. , Hiong Kum C. , Tam Wai L. , Ip Yuen K. 
Published: January 2004

SUMMARYThis study aimed to elucidate the strategies adopted by the African slender lungfish, Protopterus dolloi, to ameliorate the toxicity of ammonia during short (6 days) or long (40 days) periods of aestivation in a layer of dried mucus in open air in the laboratory. Despite decreases in rates of ammonia and urea excretion, the ammonia content in the muscle, liver, brain and gut of P. dolloi remained unchanged after 6 days of aestivation compared with the control fasted for 6 days. For specimens aestivated for 40 days, the ammonia contents in the muscle, liver and gut were significantly lower than those of the control fasted for 40 days, which suggests a decrease in the rate of ammonia production. In addition, there were significant increases in contents of alanine, aspartate and glutamate in the muscle, which suggests decreases in their catabolism. During the first 6 days and the last 34 days of aestivation, the rate of ammonia production was reduced to 26% and 28%, respectively, of the control rate (6.83 μmol day–1g–1 on day 0). During the first 6 days and the next 34 days of aestivation, the averaged urea synthesis rate was 2.39-fold and 3.8-fold,respectively, greater than the value of 0.25 μmol day–1g–1 for the day 0 control kept in water. No induction of activities of the ornithine-urea cycle (OUC) enzymes was observed in specimens aestivated for 6 days, because the suppression of ammonia production led to a light demand on the OUC capacity. For specimens aestivated for 40 days, the activities of carbamoyl phosphate synthetase, ornithine transcarbamylase and argininosuccinate synthetase + lyase were significantly greater than those of the control fasted for 40 days. This is in agreement with the observation that the rate of urea synthesis in the last 34 days was greater than that in the first 6 days of aestivation. P. dolloi aestivated in a thin layer of dried mucus in open air with high O2 tension throughout the 40 days of aestivation, which could be the reason why it was able to sustain a high rate of urea synthesis despite this being an energy-intensive process. Our results indicate that a reduction in ammonia production and decreases in hepatic arginine and cranial tryptophan contents are important facets of aestivation in P. dolloi.
The fracture properties and mechanical design of human fingernails
Authors: Farren L. , Shayler S. , Ennos A. R. 
Published: January 2004

SUMMARYFingernails are a characteristic feature of primates, and are composed of three layers of the fibrous composite keratin. This study examined the structure and fracture properties of human fingernails to determine how they resist bending forces while preventing fractures running longitudinally into the nail bed. Nail clippings were first torn manually to examine the preferred crack direction. Next, scissor cutting tests were carried out to compare the fracture toughness of central and outer areas in both the transverse and longitudinal direction. The fracture toughness of each of the three isolated layers was also measured in this way to determine their relative contributions to the toughness. Finally, the structure was examined by carrying out scanning electron microscopy of free fracture surfaces and polarized light microscopy of nail sections.When nails were torn, cracks were always diverted transversely, parallel to the free edge of the nail. Cutting tests showed that this occurred because the energy to cut nails transversely, at approximately 3 kJ m–2,was about half that needed (approx. 6 kJ m–2) to cut them longitudinally. This anisotropy was imparted by the thick intermediate layer,which comprises long, narrow cells that are oriented transversely; the energy needed to cut this layer transversely was only a quarter of that needed to cut it longitudinally. In contrast the tile-like cells in the thinner dorsal and ventral layers showed isotropic behaviour. They probably act to increase the nail's bending strength, and as they wrap around the edge of the nail, they also help prevent cracks from forming. These results cast light on the mechanical behaviour and care of fingernails.
A hierarchical analysis of the scaling of force and power production by dragonfly flight motors
Authors: Schilder Rudolf J. , Marden James H. 
Published: January 2004

SUMMARYMaximum isometric force output by single muscles has long been known to be proportional to muscle mass0.67, i.e to muscle cross-sectional area. However, locomotion often requires a different muscle contraction regime than that used under isometric conditions. Moreover, lever mechanisms generally affect the force outputs of muscle–limb linkages, which is one reason why the scaling of net force output by intact musculoskeletal systems can differ from mass0.67. Indeed, several studies have demonstrated that force output by intact musculoskeletal systems and non-biological systems is proportional to motor mass1.0. Here we trace the mechanisms that cause dragonflies to achieve a change from muscle mass0.67 scaling of maximum force output by single flight muscles to mass1.0 scaling of dynamic force output by the intact dragonfly flight motor. In eight species of dragonflies, tetanic force output by the basalar muscle during isometric contraction scaled as muscle mass0.67. Mean force output by the basalar muscle under dynamic conditions (workloops) that simulated in vivo maximum musculoskeletal performance was proportional to muscle mass0.83, a significant increase in the scaling exponent over that of maximum isometric force output. The dynamic performance of the basalar muscle and the anatomy of its lever, consisting of the second moment of area of the forewing (d2) and the distance between the muscle apodeme and the wing fulcrum (d1), were used to analyze net force output by the integrated muscle-lever system(Find). The scaling of d2 conformed closely to the expected value from geometic similarity (proportional to muscle mass0.31), whereas d1 scaled as muscle mass0.54, a significant increase over the expected value from geometric similarity. Find scaled as muscle mass1.036, and this scaling exponent was not significantly different from unity or from the scaling exponent relating maximum load-lifting by flying dragonflies to their thorax mass. Thus, the combined effect of a change in the scaling of force output by the muscle during dynamic contraction compared to that during isometric contraction and the departure from geometric similarity of one of the two lever arm lengths provides an explanation for how mass1.0 scaling of force output by the intact musculoskeletal system is accomplished. We also show that maximum muscle mass-specific net work and power output available scale as mass0.43 and mass0.24, respectively.
Drosophila CG8422encodes a functional diuretic hormone receptor
Authors: Johnson Erik C. , Bohn Laura M. , Taghert Paul H. 
Published: January 2004

SUMMARYDiuretic hormone 44 (DH) is a bioactive neuropeptide that mediates osmotic balance in a wide variety of insects through increases in cAMP. It is structurally similar to mammalian corticotrophin releasing factor (CRF)peptides. In the moth Manduca and the cricket Acheta,functional studies have shown that its cognate receptor (DH-R) is related to the mammalian CRF receptor. The Drosophila genome contains two genes(CG8422 and CG12370) orthologous to Manduca and Acheta DH-Rs. Here, we present multiple lines of evidence to support the hypothesis that the orphan CG8422 G-protein-coupled receptor is a functional DH-R. When expressed in mammalian cells, CG8422 conferred selective sensitivity to DH, as indicated by translocation of aβ-arrestin-2-GFP reporter from the cytoplasm to the cell membrane. Consistent with its in vivo activities in other insects, DH activation of CG8422 elicited increases in a cAMP reporter system(CRE-luciferase), with an EC50 of 1.7 nmol l-1. CG8422 activation by DH also led to increases in intracellular calcium but at substantially higher doses (EC50 ∼300 nmol l-1). By microarray analysis, the CG8422 transcript was detectable in Drosophila head mRNA of different genotypes and under different environmental conditions. The identification of a Drosophila receptor for the DH neuropeptide provides a basis for genetic analysis of this critical factor's roles in maintaining physiological homeostasis.
A three-dimensional kinematic analysis of tongue flicking inPython molurus
Authors: de Groot Jurriaan H. , van der Sluijs Inke , Snelderwaard Peter Ch. , van Leeuwen Johan L. 
Published: January 2004

SUMMARYThe forked snake tongue is a muscular organ without hard skeletal support. A functional interpretation of the variable arrangement of the intrinsic muscles along the tongue requires a quantitative analysis of the motion performance during tongue protrusion and flicking. Therefore, high-speed fluoroscopy and high-speed stereo photogrammetry were used to analyse the three-dimensional shape changes of the tongue in Python molurus bivittatus (Boidae). The posterior protruding part of the tongue elongated up to 130% while the flicking anterior portion elongated maximally 60%. The differences in tongue strains relate to the absence or presence,respectively, of longitudinal muscle fibres in the peripheral tongue. Maximum overall protrusion velocity (4.3 m s–1) occurred initially when the tongue tip left the mouth. Maximum tongue length of ∼0.01 body length (20 mm) was reached during the first tongue flick. These observations are discussed within the scope of the biomechanical constraints of hydrostatic tongue protrusion: a negative forward pressure gradient, longitudinal tongue compliance and axial tongue stiffness. The three-dimensional deformation varied along the tongue with a mean curvature of 0.06 mm–1and a maximum value of 0.5 mm–1. At the basis of the anterior forked portion of the tongue tips, extreme curvatures up to 2.0 mm–1 were observed. These quantitative results support previously proposed inferences about a hydrostatic elongation mechanism and may serve to evaluate future dynamic models of tongue flicking.
In situcardiac performance of Pacific bluefin tuna hearts in response to acute temperature change
Authors: Blank Jason M. , Morrissette Jeffery M. , Landeira-Fernandez Ana M. , Blackwell Susanna B. , Williams Thomas D. , Block Barbara A. 
Published: January 2004

SUMMARYThis study reports the cardiovascular physiology of the Pacific bluefin tuna (Thunnus orientalis) in an in situ heart preparation. The performance of the Pacific bluefin tuna heart was examined at temperatures from 30°C down to 2°C. Heart rates ranged from 156 beats min–1 at 30°C to 13 beats min–1 at 2°C. Maximal stroke volumes were 1.1 ml kg–1 at 25°C and 1.3 ml kg–1 at 2°C. Maximal cardiac outputs were 18.1 ml kg–1 min–1 at 2°C and 106 ml kg–1 min–1 at 25°C. These data indicate that cardiovascular function in the Pacific bluefin tuna exhibits a strong temperature dependence, but cardiac function is retained at temperatures colder than those tolerated by tropical tunas. The Pacific bluefin tuna's cardiac performance in the cold may be a key adaptation supporting the broad thermal niche of the bluefin tuna group in the wild. In situ data from Pacific bluefin are compared to in situ measurements of cardiac performance in yellowfin tuna and preliminary results from albacore tuna.