bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of the intensity of stationary flat processes
Authors: Schladitz Katja 
Published: February 2003

The intensity of a stationary process ofk-dimensional affine subspaces (k-flats) of ℝdwith directional distribution from a given familyRis estimated by observing the process in a compact window. To this end we introduce a type of unbiased estimator (theR-estimator) using the available information about the directional distribution.Special cases are estimators for the intensity of stationaryk-flat processes (1) with known directional distribution, (2) with directional distribution invariant with respect to a subgroup of the group of rotations in ℝdand (3) with unknown directional distribution.We give sufficient conditions for theR-estimator to be the uniformly best unbiased estimator for the intensity of stationary Poissonk-flat processes with directional distribution inR. Equivalent statements for certain types of stationary Cox flat processes can be deduced directly from the results in the Poisson case.Moreover, we consider stationary ergodic flat processes with directional distribution inRand general stationary flat processes with unknown directional distribution, all with a non-degeneracy property. In both cases our estimator turns out to be the uniformly best unbiased estimator from a restricted set of estimators. The result for general stationary flat processes is proved with the help of a factorization result for the second factorial moment measure.
Predicting the metabolic energy costs of bipedalism using evolutionary robotics
Authors: Sellers W. I. , Dennis L. A. , Crompton R. H. 
Published: February 2003

SUMMARYTo understand the evolution of bipedalism among the hominoids in an ecological context we need to be able to estimate the energetic cost of locomotion in fossil forms. Ideally such an estimate would be based entirely on morphology since, except for the rare instances where footprints are preserved, this is the only primary source of evidence available. In this paper we use evolutionary robotics techniques (genetic algorithms, pattern generators and mechanical modeling) to produce a biomimetic simulation of bipedalism based on human body dimensions. The mechanical simulation is a seven-segment, two-dimensional model with motive force provided by tension generators representing the major muscle groups acting around the lower-limb joints. Metabolic energy costs are calculated from the muscle model, and bipedal gait is generated using a finite-state pattern generator whose parameters are produced using a genetic algorithm with locomotor economy(maximum distance for a fixed energy cost) as the fitness criterion. The model is validated by comparing the values it generates with those for modern humans. The result (maximum efficiency of 200 J m–1) is within 15% of the experimentally derived value, which is very encouraging and suggests that this is a useful analytic technique for investigating the locomotor behaviour of fossil forms. Initial work suggests that in the future this technique could be used to estimate other locomotor parameters such as top speed. In addition, the animations produced by this technique are qualitatively very convincing, which suggests that this may also be a useful technique for visualizing bipedal locomotion.
Steady swimming muscle dynamics in the leopard sharkTriakis semifasciata
Authors: Donley Jeanine M. , Shadwick Robert E. 
Published: February 2003

SUMMARYPatterns of red muscle strain and activation were examined at three positions along the body (0.42, 0.61 and 0.72 L, where L is total body length) and correlated with simultaneous measurements of midline kinematics during steady swimming (approx. 1.0 Ls–1) in the leopard shark Triakis semifasciata. Analysis of lateral displacement along the body indicates that the leopard shark is a subcarangiform swimmer. Longitudinal variation in red muscle strain was observed with strain amplitudes ranging from ±3.9% in the anterior,±6.6% in the mid, to ±4.8% in the posterior body position. Strain was in-phase with local midline curvature. In addition, strain amplitude calculated from a bending beam model closely matched strain measured using sonomicrometry at all three body positions. There is a high degree of similarity in red muscle activation patterns along the body between the leopard shark and many fish species, in that the onset of activation occurs during muscle lengthening while offset occurs during muscle shortening. However, we found no significant longitudinal variation in the EMG/strain phase relationship and duty cycles, with onset of muscle activation occurring at 51.4–61.8° and offset at 159.7–165.2° (90° is peak length). This consistent pattern of activation suggests that red muscle along the entire length of the body contributes to positive power production. Thus,sharks such as Triakis may have no regional specialization in red muscle function like that seen in many teleosts, which may indicate that the evolution of differential muscle function along the body occurred after the divergence of cartilaginous and bony fishes.
The toxic and lethal effects of the trehalase inhibitor trehazolin in locusts are caused by hypoglycaemia
Authors: Wegener Gerhard , Tschiedel Volker , Schlöder Paul , Ando Osamu 
Published: February 2003

SUMMARY
The main blood sugar of locusts is trehalose, which is hydrolysed to two glucose units by trehalase. Homogenates of locust flight muscles are rich in trehalase activity, which is bound to membranes. A minor fraction of trehalase is in an overt form while the remainder is latent, i.e. active only after impairing membrane integrity. Trehazolin, an antibiotic pseudosaccharide,inhibits locust flight muscle trehalase with apparent Ki-and EC50 values of 10–8 mol l–1and 10–7 mol l–1, respectively. Trehazolin is insecticidal: 50 μg injected into locusts completely and selectively blocked the overt form of muscle trehalase (with little effect on latent activity) and killed 50% of the insects within 24 h. Here, it is demonstrated for the first time that trehazolin causes dramatic hypoglycaemia. Injection of 10 μg trehazolin caused glucose levels to fall by over 90% in 24 h, from 2.8 mmol l–1 to 0.23 mmol l–1, while trehalose increased from 61 mmol l–1 to 111 mmol l–1. Feeding glucose to the locusts fully neutralized the effects of a potentially lethal dose of trehazolin. This indicates that hypertrehalosaemia is not acutely toxic, whereas lack of glucose causes organ failure (presumably of the nervous system), and that sufficient haemolymph glucose can only be generated from trehalose by trehalase. The results also suggest that overt flight muscle trehalase is located in the plasma membrane with the active site accessible to the haemolymph. Trehalase inhibitors are valuable tools for studying the molecular physiology of trehalase function and sugar metabolism in insects.
Photolysis of caged calcium in cilia induces ciliary reversal inParamecium caudatum
Authors: Iwadate Yoshiaki 
Published: February 2003

SUMMARYIntracellular Ca2+ concentration controls both the pattern and frequency of ciliary and flagellar beating in eukaryotes. In Paramecium, it is widely accepted that the reversal of the direction of ciliary beating (ciliary reversal) is induced by an increase in intra-ciliary Ca2+ levels. Despite this, the Ca2+-sensitive region of the cilium that initiates ciliary reversal has not been clearly identified.We injected caged calcium into living P. caudatum cells and applied ultraviolet (UV) light to portions of the injected cells to raise artificially the intracellular Ca2+ level([Ca2+]i). UV application to the upper ciliary region above the basal body induced ciliary reversal in injected cells. Furthermore,UV application to the tips of cilia induced weak ciliary reversal. Larger areas of photolysis in the cilium gave rise to greater angles of ciliary reversal. These results strongly suggest that the Ca2+-sensitive region for ciliary reversal is distributed all over the cilium, above the basal body.
Mitogen-activated protein kinases: new signaling pathways functioning in cellular responses to environmental stress
Authors: Cowan Kyra J. , Storey Kenneth B. 
Published: February 2003

SUMMARYThe mitogen-activated protein kinase (MAPK) superfamily consists of three main protein kinase families: the extracellular signal-regulated protein kinases (ERKs), the c-Jun N-terminal kinases (JNKs) and the p38 family of kinases. Each is proving to have major roles in the regulation of intracellular metabolism and gene expression and integral actions in many areas including growth and development, disease, apoptosis and cellular responses to external stresses. To date, this cellular signal transduction network has received relatively little attention from comparative biochemists,despite the high probability that MAPKs have critical roles in the adaptive responses to thermal, osmotic and oxygen stresses. The present article reviews the current understanding of the roles and regulation of ERKs, JNKs and p38,summarizes what is known to date about MAPK roles in animal models of anoxia tolerance, freeze tolerance and osmoregulation, and highlights the potential that studies of MAPK pathways have for advancing our understanding of the mechanisms of biochemical adaptation.
Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?
Authors: MacArthur Robert A. , Weseen Gillian L. , Campbell Kevin L. 
Published: February 2003

SUMMARYWe tested the hypothesis that the body oxygen stores, aerobic dive limit(ADL) and dive performance of muskrats can be enhanced by dive-conditioning in a laboratory setting. We compared several key variables in 12 muskrats trained to swim a 16 m underwater course to a feeding station (`divers') with those of 12 animals precluded from diving but required to travel identical distances in water to feed (`surface swimmers'). Acclimated muskrats assigned to each group were trained concurrently over a 9–11 week period. We observed significant gains in the haematocrit (P=0.0005) and blood haemoglobin concentration (P=0.015) of `divers', but not `surface swimmers'. The post-training blood O2 store calculated for `divers' (22.9 ml O2 kg–1) was nearly 26% higher than that (18.2 ml O2 kg–1) derived for `surface swimmers'(P=0.03). Dive-conditioning had no apparent effect on lung volume,whole blood and plasma volumes, nor on the glycogen level and buffering capacity of skeletal muscles. Cardiac and skeletal muscle myoglobin levels were also similar in both test groups following training. The mean total body oxygen store of `divers' (37.8ml O2 STPD kg–1) was 13.5% higher (P=0.037) than for `surface swimmers' (33.3 ml O2 STPD kg–1), an increase attributed entirely to the gain in blood O2 storage capacity of the former group. However,owing to a slightly higher estimate of diving metabolic rate in dive-conditioned animals, the calculated ADL for this group (61.3 s) was indistinguishable from that of `surface swimmers' (61.8 s). Few differences were observed in the post-training dive behaviour of `surface swimmers' and`divers', a finding consistent with the strong similarity in their calculated aerobic dive capacities.
The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodileCrocodylus porosus
Authors: Franklin Craig E. , Seebacher Frank 
Published: February 2003

SUMMARYThe effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions;(2) heated via radiant energy while half-submerged in flowing water at 23°C and (3) heated via convective transfer by increasing water temperature from 23°C to 35°C. Cooling was achieved in all treatments by removing the heat source and with C. porosushalf-submerged in flowing water at 23°C. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate (`rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (&lt;0.5°C) resulted in Q10 values greater than 4000, calling into question the usefulness of this measure on heart rate during the initial stages of heating and cooling. In the later phases of heating and cooling, heart rate changed with body temperature, with Q10 values of 2–3. The magnitude of the heart rate response differed between treatments, with radiant heating during submergence eliciting the smallest response. The heart rate of C. porosus outside of the`rapid response' periods was found to be a function of the heat load experienced at the animal surface, as well as on the mode of heat transfer. Heart rate increased or decreased rapidly when C. porosus experienced large positive (above 25 W) or negative (below –15 W) heat loads,respectively, in all treatments. For heat loads between –15 W and 20 W,the increase in heart rate was smaller for the `unnatural' heating by convection in water compared with either treatment using radiant heating. Our data indicate that changes in heart rate constitute a thermoregulatory mechanism that is modulated in response to the thermal environment occupied by the animal, but that heart rate during heating and cooling is, in part,controlled independently of body temperature.
Seasonal acclimatisation of muscle metabolic enzymes in a reptile(Alligator mississippiensis)
Authors: Seebacher Frank , Guderley Helga , Elsey Ruth M. , Trosclair Phillip L. 
Published: February 2003

SUMMARYReptiles living in heterogeneous thermal environments are often thought to show behavioural thermoregulation or to become inactive when environmental conditions prevent the achievement of preferred body temperatures. By contrast, thermally homogeneous environments preclude behavioural thermoregulation, and ectotherms inhabiting these environments (particularly fish in which branchial respiration requires body temperature to follow water temperature) modify their biochemical capacities in response to long-term seasonal temperature fluctuations. Reptiles may also be active at seasonally varying body temperatures and could, therefore, gain selective advantages from regulating biochemical capacities. Hence, we tested the hypothesis that a reptile (the American alligator Alligator mississippiensis) that experiences pronounced seasonal fluctuations in body temperature will show seasonal acclimatisation in the activity of its metabolic enzymes. We measured body temperatures of alligators in the wild in winter and summer (N=7 alligators in each season), and we collected muscle samples from wild alligators (N=31 in each season) for analysis of metabolic enzyme activity (lactate dehydrogenase, citrate synthase and cytochrome coxidase). There were significant differences in mean daily body temperatures between winter (15.66±0.43°C; mean ± S.E.M.) and summer(29.34±0.21°C), and daily body temperatures fluctuated significantly more in winter compared with summer. Alligators compensated for lower winter temperatures by increasing enzyme activities, and the activities of cytochrome c oxidase and lactate dehydrogenase were significantly greater in winter compared with summer at all assay temperatures. The activity of citrate synthase was significantly greater in the winter samples at the winter body temperature (15°C) but not at the summer body temperature(30°C). The thermal sensitivity (Q10) of mitochondrial enzymes decreased significantly in winter compared with in summer. The activity of mitochondrial enzymes was significantly greater in males than in females, but there were no differences between sexes for lactate dehydrogenase activity. The differences between sexes could be the result of the sex-specific seasonal demands for locomotor performance. Our data indicate that biochemical acclimatisation is important in thermoregulation of reptiles and that it is not sufficient to base conclusions about their thermoregulatory ability entirely on behavioural patterns.
N-methyl-D-aspartate receptors mediate chemoreflexes in the shorthorn sculpinMyoxocephalus scorpius
Authors: Turesson J. , Sundin L. 
Published: February 2003

SUMMARYGlutamate microinjected into the vagal sensory area in the medulla produces cardiorespiratory responses mimicking oxygen chemoreflexes in fish. Here we directly investigate whether these reflexes are dependent on the ionotropic N-methyl-D-aspartate (NMDA) glutamate receptor.Fish were equipped with opercular, branchial and snout cannulae for measurements of cardiorespiratory parameters and drug injections. Oxygen chemoreceptor reflexes were evoked by rapid hypoxia, NaCN added into the blood(internal, 0.3 ml, 50 μgml–1) and the mouth (external, 0.5 ml, 1 mg ml–1), before and after systemic administration of the NMDA receptor antagonist MK801 (3 mg kg–1).Hypoxia produced an MK801-sensitive increase in blood pressure and ventilation frequency, whereas the marked bradycardia and the increased ventilation amplitude were NMDA receptor-independent. The fish appeared more responsive to externally applied cyanide, but the injections and MK801 treatment did not distinguish whether external or internal oxygen receptors were differently involved in the hypoxic responses.In addition, using single-labelling immunohistochemistry on sections from the medulla and ganglion nodosum, the presence of glutamate and NMDA receptors in the vagal oxygen chemoreceptor pathway was established.In conclusion, these results suggest that NMDA receptors are putative central control mechanisms that process oxygen chemoreceptor information in fish.
Metabolic enzyme activities across an altitudinal gradient: an examination of pikas (genusOchotona)
Authors: Sheafor Brandon A. 
Published: February 2003

SUMMARYChanges in metabolic enzyme activities were examined in three species of pikas that occur over a range of altitudes. Because these closely related mammals live in comparable ecosystems and face similar environmental factors regardless of altitude, modifications of metabolic machinery are probably due to differences in oxygen availability. Citrate synthase (CS),β-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH)activities were measured in heart, diaphragm, vastus lateralis, gastrocnemius and soleus muscles. Additionally, the activity levels of both M-LDH (skeletal muscle type) and H-LDH (heart type) isozymes were quantified in tissue samples. Pikas from high altitude had greater CS and HOAD activities in heart and diaphragm when compared with pikas from low altitude, while activity levels did not differ in skeletal muscles. The increase in oxidative enzyme activities in tissues with high metabolic demand is thought to enhance oxygen utilization when oxygen availability is low and may reflect greater metabolic demand on heart and diaphragm tissue. Pikas from high altitude were also found to have greater total LDH activities in all tissues examined. High altitude animals had dramatically higher H-LDH activity (2.3–3.8 times greater)while M-LDH activity was more comparable (1.8 times lower to 1.7 times greater) when compared with low altitude animals. High total LDH activity enables pikas to perform short bouts of anaerobic activity, while high levels of H-LDH isozymes may serve to enhance lactate removal and decrease recovery time in animals living at high altitude.
Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat
Authors: Fuller Andrea , Kamerman Peter R. , Maloney Shane K. , Mitchell Graham , Mitchell Duncan 
Published: February 2003

SUMMARYWe used implanted miniature data loggers to measure brain (in or near the hypothalamus) and carotid arterial blood temperatures at 5 min intervals in six free-ranging ostriches Struthio camelus in their natural habitat,for a period of up to 14 days. Carotid blood temperature exhibited a large amplitude (3.0–4.6°C) circadian rhythm, and was positively correlated with air temperature. During the day, brain temperature exceeded carotid blood temperature by approx. 0.4°C, but there were episodes when brain temperature was lowered below blood temperature. Selective brain cooling, however, was not present in all ostriches, and was not tightly coupled to the prevailing body temperature. Brain temperature was maintained within narrow daily limits of approx. 2°C, and varied significantly less than blood temperature at short time scales of 5 to 20 min. At night, brain temperature exceeded blood temperature by as much as 3°C. We attribute the elevated brain temperatures to warming of cerebral arterial blood, by reduced heat exchange in the ophthalmic rete or possibly heat gain from cranial structures, before supplying the hypothalamus. Further studies are necessary to elucidate the significance of such variations in brain temperature and the importance of selective brain cooling in free-living birds.
Growth hormone is a weaker candidate than prolactin for the hormone responsible for the development of a larval-type feature in cultured bullfrog skin
Authors: Takada Makoto , Kasai Miyoko 
Published: February 2003

SUMMARYProlactin (PRL) has, for some years, been considered to be the `juvenile hormone' in amphibians. Recently, growth hormone (GH) has been proposed as another candidate, because in the larval stages the expression of the mRNA GH is high but it is downregulated in the climax stages of metamorphosis or following treatment with thyroid hormone. In the present study, we investigated whether GH promotes the development of one particular larval-type feature of bullfrog tadpole skin in vitro. The amiloride-,acetylcholine- and ATP-stimulated short-circuit current (SCC) is a physiological marker of larval-type bullfrog skin. These types of ligand-stimulated SCC (1) developed when EDTA-treated tadpole skin was cultured with corticoids supplemented with PRL or GH and (2) were not significantly different between skin cultured with PRL and intact tadpole skin. However, the amiloride-induced SCC response in skin cultured with GH differed in its kinetics from that of the intact (control) tadpole. On this basis, PRL seems a better candidate than GH for the juvenile hormone, at least with regard to the development of amiloride-stimulated non-selective cation channels.