bluuebunny/crossref_metadata_2025 huggingface dataset:
How predictable are aphid population responses to elevated CO2?
Authors: Newman J. A. , Gibson D. J. , Parsons A. J. , Thornley J. H. M.
Published: July 2003

Experiments investigating the population responses of aphids to CO2 enrichment have yielded results suggesting that aphid populations will be both larger under elevated CO2 and that they will be smaller under elevated CO2. Most studies have failed to reject the null hypothesis of no difference in population sizes due to atmospheric CO2 concentration. This diversity of results has led some investigators to conclude that aphid responses are not general, and that every aphid–plant interaction may be unique and unpredictable a priori. We use a single, general, mathematical model to consider the population responses of cereal aphids to grass grown under different CO2 concentrations.

The model shows that it is possible to explain any of the three observed results: larger populations, smaller populations, or no difference, and that which of these three outcomes arises may depend critically on the interaction between aphid nitrogen requirements and the nitrogen fertility of the soil. The model also shows that the qualitative results will depend on how sensitive the aphid species is to increases in its own density. Past studies have shown that aphids increase their production of winged offspring in response to increasing aphid density. The model predicts that, in general, aphid species that have lower nitrogen requirements and that are less sensitive to their own density will be more likely to have larger populations in elevated CO2 compared to ambient CO2.

Differences between aphid species (and clones) in their nitrogen requirements and the strength of their density‐dependent response have not been widely reported in the literature. Also, the nitrogen fertility of the soil has rarely been manipulated in experiments on aphid responses to rising CO2 levels. The model suggests that the diversity of population responses of aphids may be both understandable and predictable in the context of such an interaction.
Transience, dispersal and survival rates in newt patchy populations
Authors: Perret Nadège , Pradel Roger , Miaud Claude , Grolet Odile , Joly Pierre
Published: July 2003

This work aims to illustrating how it is possible to measure different modalities of adult dispersal in two subdivided populations of the alpine newt (Triturus alpestris). Recent developments in capture–mark–recapture methods make it possible to estimate transience rates from individuals captured only once. In the context of subdivided newt populations, transience is assumed to express nomadic behaviour that contribute to breeding dispersal. Skeletochronology and recaptures within each pond system also made it possible to estimate emigration rates and local dispersal.

Two subdivided populations of alpine newts were monitored over 4 and 5 years, respectively. Whereas population A is suspected to have been established for more than 100 years, population B was monitored when colonizing a newly created archipelago of ponds.

Transience was detected in each population at similar rates (37% in population A and 35% in the population B). Annual apparent survival rates were estimated as 82% in population A vs. 33% in population B. Similarity of age structures between populations leads us to consider such low survival rates in population B as resulting from emigration. Emigration was thus negligible in population A and was estimated to reach 57·3% in population B. Conversely, high local dispersal (movements within a pond system) was detected in population A, but not in population B.

Even though the causation of dispersal in newts (genetic polymorphism vs. phenotypic plasticity) remains unexplored, our study succeeded in identifying several dispersal components that could result from different selective pressures (habitat heterogeneity at different temporal scales). Experimental approaches are needed to investigate the causative bases of these traits.
Effects of climate variability on the temporal population dynamics of southern fulmars
Authors: Jenouvrier Stephanie , Barbraud Christophe , Weimerskirch Henri
Published: July 2003

Ecological and population processes are affected by large‐scale climatic fluctuations, and top predators such as seabirds can provide an integrative view on the consequences of environmental variability on ecosystems. Here, we examine the dynamics of a southern fulmar population in Antarctica over a 39‐year period and evaluate the impact of environmental variability on the life history traits of this top predator species.

Between 1963 and 2002, the number of breeding pairs fluctuated between seven and 53 in relation to variations in sea ice concentration, and increased overall (annual growth rate: 1·0035). Breeding performance tended to be lower in years with low sea ice concentration. The proportion of birds attempting to breed varied strongly from one year to the next despite the birds were alive, indicating strong environmental forcing on the decision to breed. The number of new local recruits and immigrants was correlated highly with the number of local breeders, and capture probabilities were positively related to the breeding population size. Local recruitment, number of local breeders and proportion of birds attempting to breed were lower when sea ice concentration during summer was low.

Adult survival between 1964 and 2002 was on average 0·923 ± 0·006, and decreased during years with high sea surface temperature and low sea ice concentration.

Modelled population growth rate, estimated using matrix models, of the population was 0·9728, a difference of 3·6% compared to the observed rate of increase. This discrepancy is due probably to the immigration rate (3 ± 3%).

Demographic parameters were affected by sea ice concentration and sea surface temperature anomalies, probably through an impact on krill availability, the main prey of southern fulmars. During warm anomalies, birds skip breeding probably because the food availability was low and limiting for the highly energy demanding reproductive activities.

We also emphasize that demographic parameters were very low during the period 1975–80 and showed a higher variability after 1980, which could be interpreted in the context of a regime shift. Our study indicates that the southern fulmar population dynamics may be very susceptible to environmental variability. Further long‐lasting warm anomalies are likely to affect negatively their populations.
Population regulation in group‐living birds: predictive models of the Seychelles warbler
Authors: Ridley Jo , Komdeur Jan , Sutherland William J.
Published: July 2003

A major challenge for population ecology is to predict population responses to novel conditions, such as habitat loss. This frequently involves understanding dispersal decisions, in terms of their consequences for fitness. However, this approach requires detailed data, and is thus often inappropriate for urgent problems on poorly known species. This may be resolved by developing a predictive framework based on well‐studied species, for applying to those that are less well understood.

Population size, group sizes and habitat occupancy of the Seychelles warbler (Acrocephalus sechellensis) can be predicted by determining the evolutionary stable dispersal strategy. For densities near to demographic equilibrium, regulation results from the combined effects of non‐breeding and use of sink habitats.

In the Seychelles warbler, resident male non‐breeders compete for breeding vacancies on neighbouring territories. The resulting kin competition is a key process for predicting the observed balance between regulation by non‐breeding and regulation by sink use. Family groups, in which offspring delay dispersal, hoping to fill a vacancy on a local territory, are common among group‐living species. This suggests that kin competition may frequently play a central role in the population regulation of socially complex species.

Although all the model variants considered are complex, predictions are shown to be insensitive to a range of simplifications, illustrating that, despite significant evolutionary import at the individual level, some behaviour can be unimportant when considering population level questions. Identifying which behavioural strategies have significant demographic consequences is key to the further development of population models based on fitness maximizing behaviour.
Why do shore crabs not prefer the most profitable mussels?
Authors: Smallegange Isabel M. , Van Der Meer Jaap
Published: July 2003

We examined the link between handling time (Th), adopted feeding techniques, profitability curves and prey size selection to further understand the constraints that influence bivalve prey selection in shore crabs (Carcinus maenas L.).

Blue mussels (Mytilus edulis L.) of different sizes were used as prey. Prey size was generalized to the ratio between mussel width and major chela length (MW : MCL) and prey profitability standardized to the ratio between prey mass eaten per unit breaking time and predator mass (1/h Tb).

Crabs either crushed the mussel with their claws or opened the mussel using the more time‐consuming cutter technique. The latter technique was employed above a critical MW : MCL ratio (0·24). This threshold appeared to coincide with the ratio where prey profitability is maximal.

When a range of prey sizes were offered simultaneously, an observed MW : MCL ratio (0·14–0·16) turned out to be lower than the predicted optimal MW : MCL ratio (0·16–0·22) and lower than the MW : MCL ratio where the first crab switched feeding techniques (0·16). Crabs preferred a MW : MCL ratio of 0·16 over the optimal ratio of 0·24 when given dichotomous choices between different MW : MCL ratios.

Although larger and more profitable mussels can be crushed, we suggest that crabs select small crushable mussels to prevent claw wear and tear. Claw damage has a considerable effect on mating success and hence on an individual's fitness. Risk of claw damage may thus be of greater importance to a foraging shore crab than energy maximization.
Isotope trophic‐step fractionation: a dynamic equilibrium model
Authors: Olive Peter J. W. , Pinnegar John K. , Polunin Nicholas V. C. , Richards Gareth , Welch Rachel
Published: July 2003

Trophic position is a fundamental feature of food‐web structure, knowledge of which is being improved by stable isotope approaches which assume a constant enrichment in heavier isotopes in consumers relative to their diet.

We argue that the typical enrichment reflects a dynamic equilibrium between fractionation vectors associated with assimilation and excretion.

We develop a linear model to characterize the relationship between the equilibrium isotopic signature and the feeding rate influenced by isotopic discrimination during assimilation and excretion.

We present new data for both diet switching and starvation experiments using a marine worm Nereis virens and use this, and previously published data for a fish, bird and mammal to calculate controlling parameters from observations of the isotopic signature following diet‐switching and the onset of starvation.

We show that the observed variance in isotopic signatures at each trophic step carries substantially more information than has been used hitherto and is influenced by feeding rate in addition to the isotopic signature of the food source.

Using the linear model as a tool we predict that parasitic organisms may be depleted relative to the tissues of their host.
A comparative analysis of patch‐leaving decision rules in a parasitoid family
Authors: Wajnberg Eric , Gonsard Pierre‐Alexis , Tabone Elisabeth , Curty Christine , Lezcano Nathalie , Colazza Stefano
Published: July 2003

The proximate behavioural rules adopted by parasitoid females to manage their foraging time on patches of hosts were studied, under standardized laboratory conditions, in different species (and populations) of the Trichogrammatidae (Hymenoptera) family.

Seventeen species/populations were compared and the behavioural mechanisms adopted by the females were identified by means of a Cox's proportional hazards model.

On average, females increased their patch‐leaving tendency each time a healthy host was attacked and each time a parasitized host was rejected.

Strong variation was observed in these patch‐leaving mechanisms among the different species.

Moreover, the interspecific variation in these two behavioural mechanisms showed a significant positive correlation, and this correlation remained significant when the phylogenetic relationship between the strains was controlled with the use of phylogenetic comparative methods.

The adaptive and evolutionary meanings of these results are probably related to the ecological features and distribution patterns of the hosts attacked by the species/populations compared.
The relationship between the floristic composition of rain forests and the abundance of folivorous marsupials in north‐east Queensland
Authors: Kanowski J. , Irvine A. K. , Winter J. W.
Published: July 2003

Three species of folivorous ringtail possums (Marsupialia: Pseudocheiridae) inhabit higher elevation rain forests on the Atherton Tablelands, north‐east Queensland, Australia. Each possum is thought to specialize on a restricted suite of host plants. It has been hypothesized that the absence of the possums from lowland forests may reflect the absence or ‘inappropriate combination’ of their host plants in lowland forests.

We test this ‘floristics hypothesis’ using data from published dietary studies, herbarium records and field surveys. Studies of the possums’ diets show that each possum eats a wide variety of plant species. However, the majority of each possum's diet comes from a few genera or families of plants and there is considerable dietary partitioning between the possums. These data are consistent with the hypothesis that the possums are specialists on a restricted suite of plant taxa.

The altitudinal ranges of plants known to be important in the diets of the ringtail possums were compiled from herbarium records. Several plant species eaten by the possums are absent from lowland forests, but all genera and families of plants important in the possums’ diets occur in lowland forests.

The relationship between the floristic composition of forests and the abundance of the ringtail possums was examined at 16 sites on the Atherton Tablelands. The floristic composition of forests varied primarily with geology and secondarily with altitude. This was true whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet. Possum abundance varied primarily with altitude and secondarily, for two species, with geology. There was no correlation between the abundance of ringtail possums and the floristic composition of forests, whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet.

Altitudinal variation in the abundance of ringtail possums in north Queensland does not appear to be a response to variation in the floristic composition of those forests.
Parasitism and developmental plasticity in Alpine swift nestlings
Authors: Bize Pierre , Roulin Alexandre , Bersier Louis‐Felix , Pfluger Dominik , Richner Heinz
Published: July 2003

Development plasticity is a common evolutionary and phenotypic response to poor growth condition, in particular in organisms with determinate growth such as most birds and mammals. Because various body structures can contribute differently to overall fitness, natural selection will adjust the degree of plasticity of each structure to its proportionate contribution to fitness at a given life stage.

Two non‐mutually exclusive mechanisms can account for plasticity in the growth of offspring to compensate for the effect of parasites. First, if parasite infestation levels fluctuate over the nestling period, parasitized young may show reduced growth until peak parasite infestation, and accelerated growth once the conditions improve (the accelerated growth hypothesis). Secondly, if the period of tissue maturation is not fixed in time, hosts may grow slower than parasite‐free hosts but for a longer period of time (the delayed maturation hypothesis).

To test whether hosts compensate for the effects of parasites on their development, the load of the blood‐sucking louse‐flyCrataerina melbaeRondani in the nests of Alpine swifts,Apus melbaLinnaeus, was increased or decreased experimentally. Parasite prevalence was 100% in both treatments, but intensity (no. of parasites per nestling) was significantly lower for deparasitized nestlings. In both treatments, parasite intensity increased up to halfway through the rearing period (i.e. 30 days of age) and decreased afterwards.

In line with the accelerated growth hypothesis, wings of parasitized nestlings grew at a lower rate than those of deparasitized ones before the peak of parasite infestation, but at a greater rate after the peak. Louse‐flies had no significant effect on the growth of body mass. In agreement with the delayed‐maturation hypothesis, wings of parasitized nestlings grew for 3 additional days and were of similar size at fledging as in deparasitized birds.

In summary, the present study shows in a wild bird population that nestling hosts can compensate for the effect of parasitism on their phenotype. It emphasizes the need to take the dynamics of parasite populations into account in studies of host–parasite relationships, and to investigate the effect of parasites on host development over the entire growing period rather than only at fledging, as employed traditionally.
Variable age structure and apparent density dependence in survival of adult ungulates
Authors: Festa‐Bianchet Marco , Gaillard Jean‐Michel , Côté Steeve D.
Published: July 2003

Large herbivores have strongly age‐structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density‐dependent changes in age structure could lead to apparent density‐dependence in adult survival.

To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1 year at Chizé, France, ranged from 157 to 569.

We used recent developments of capture–mark–recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account.

Survival rates were 10–15% higher during the prime‐age stage than during the senescent stage for all sex‐species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account.

In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure.
Determinants of colobine monkey abundance: the importance of food energy, protein and fibre content
Authors: Wasserman Michael D. , Chapman Colin A.
Published: July 2003

A fundamental ecological question is what determines the abundance of animals? Answering this question is vital in the formulation of effective management plans for endangered or threatened species. However, there are few general hypotheses proposed to account for variation in animal abundance. Studies of folivorous primates are a notable exception. In this group, the protein to fibre ratio of mature leaves is a significant predictor of biomass. However, Dasilva (1992) suggested that the availability of energy may play a critical role in colobine behaviour and ecology.

Here we evaluate the importance of food energy content for the red colobus (Procolobus badius) and black‐and‐white colobus (Colobus guereza) monkeys of Kibale National Park, Uganda.

Energy was found to be of little importance. None of the eight groups studied selected high‐energy foods: there was no correlation between food energy content and foraging effort. For all groups, estimates of energy expenditure [daily energy expenditure (DEE) and average daily metabolic needs (ADMN)] were less than estimates of energy consumption. Finally, the average energy content of mature leaves from the 20 most abundant tree species at four sites was not related to colobine biomass.

In contrast, the protein and fibre content of foods was important to both colobine species. Seven of the eight groups selected foods with a high‐protein, low‐fibre content. The average protein to fibre ratio of mature leaves from the 20 most abundant tree species at four sites was correlated positively with colobine biomass.

This study provides further validation of the protein to fibre model, suggesting the importance of this model for conservation and management of colobus monkeys, with the potential application to other small mammalian herbivores.
Seasonal range size in relation to reproductive strategies in brown bears Ursus arctos
Authors: Dahle Bjørn , Swenson Jon E.
Published: July 2003

Data on seasonal ranges of 93 radio‐collared adult brown bears (Ursus arctos) were used to test hypotheses explaining variation in range size in relation to male and female reproductive strategies.

Both males and oestrous females used large ranges in the mating season, but decreased their ranges after the mating season. These results suggested that both sexes in this species roam to mate, because the results could not be explained by a seasonal change in food availability nor by increased foraging movements of oestrous females to replenish body reserves after previous cub raising.

Females with cubs‐of‐the‐year (cubs) restricted their range size in the mating season and increased their ranges in the post‐mating season. This finding suggests that females with cubs restricted their ranges to avoid contact with infanticidal males, an important cause of cub mortality, because the proposed alternative explanation − limited mobility of small cubs − was unable to explain the small size of mating season ranges.

Our results suggest that range size in females is influenced by sexually selected infanticide, selecting for large mating season ranges and multiple mating in oestrous females to hide paternity and for restricted mating season ranges in females with cubs to avoid infanticidal males.

To our knowledge, we are the first to report a significant relationship between seasonal range size and reproductive status in female brown bears and the first to report an effect of oestrus on seasonal range size in female carnivores.
Population‐level mechanisms for reddened spectra in ecological time series
Authors: Akçakaya H. Resit , Halley John M. , Inchausti Pablo
Published: July 2003

The temporal variability of many animal populations increases with the length of census period. This pattern is associated with the reddened spectral colour, quantified by the spectral exponent, which is typically around + 1.

We used simulation models to explore the effects of various population‐level processes on the spectral colour of the simulated time series of abundances.

Our results showed that the observed spectral exponents could be explained as the effect of a combination of measurement error and natural variability (in the form of white environmental noise).

Thus, it may not be necessary to invoke complex varieties of environmental noise to explain the observed spectral exponents.
Variability in marine resources affects arctic fox population dynamics
Authors: Roth James D.
Published: July 2003

Terrestrial predators in coastal areas are often subsidized by marine foods. In order to determine the potential impact on terrestrial prey, the numerical response of predators to each food source must be determined.

In winter, arctic foxes (Alopex lagopus) may forage on the frozen Arctic ocean and scavenge carcasses of seals killed by polar bears (Ursus maritimus), but the importance of this food source and its effect on the population cycles of arctic foxes and lemmings (their primary prey) are unclear.

I estimated the marine component of the late winter diet of arctic foxes near Churchill, Manitoba, using stable‐carbon isotope analysis, and compared these estimates to abundance of arctic foxes and collared lemmings (Dicrostonyx richardsoni).

From 1994 to 1997, fox density varied with lemming abundance, but following a decline, fox abundance began increasing before lemmings. During this increase marine foods were consumed more than in other years, with over two‐thirds of food intake from marine sources.

Arctic and red fox (Vulpes vulpes) harvests in the 1980s to 1990s were correlated with published estimates of polar bear body mass, which varies with seal productivity. However, this relationship disappeared during high lemming years.

Thus, variation in marine productivity affects arctic fox abundance, especially when their primary prey are scarce, and this numerical response of arctic foxes to marine resources and lemmings suggests that increased predation by arctic foxes subsidized by seal carrion may delay the recovery of low lemming populations.
Energy dynamics in a parasitoid foraging in the wild
Authors: Casas Jerome , Driessen Gerard , Mandon Nicole , Wielaard Sebastiaan , Desouhant Emmanuel , Van Alphen Jacques , Lapchin Laurent , Rivero Ana , Christides Jean Philippe , Bernstein Carlos
Published: July 2003

Although parasitoids are used widely as a biological models for understanding the evolution of animal behaviour, most studies have been constrained to the laboratory. The dearth of field studies has been compounded by the almost complete ignorance of the physiological parameters involved in foraging and dispersal, in particular of the energetic constraints imposed by resource limitation.

We estimated the dynamics of carbohydrates and lipids reserves ofVenturia canescens (Gravenhorst) females by releasing individuals of known nutritional status in a natural environment and recapturing them using host‐containing traps. The recapture rate was around 30%. These results were compared with the reserves of caged animals kept under different experimental conditions (freshly emerged, starved to death, fedad libitumand partially starved). Wild animals were also sampled in order to estimate the resource levels of the local population.

The results show that: (i) wasps are able to maintain a nearly constant level of energy over an extended foraging period; (ii)V. canescenstakes sugars in the field; and (iii) the lipid reserves accumulated during the larval life may be limiting as lipogenesis does not take place in adults even under conditions of high sugar availability.

These results demonstrate that wasps can forage for hosts and food and disperse in this habitat for hours and days without running into a severe risk of energy limitation.
Mid‐domain models of species richness gradients: assumptions, methods and evidence
Authors: Zapata F. A. , Gaston K. J. , Chown S. L.
Published: July 2003

Patterns of species richness along latitudinal, elevational and depth gradients often exhibit a mid‐gradient peak. Similar patterns with a mid‐domain peak in richness are produced, as a result of geometric constraints on species distributions, by models that randomize species range size and placement over a bounded gradient.

Proponents of these so‐called mid‐domain models argue that they provide an appropriate null hypothesis for examining species richness patterns along spatial gradients. Furthermore, some claim that because these models seem to explain a large proportion of the large‐scale spatial variation in richness, geometric constraints on species distribution are in fact the cause of these patterns.

A critical examination of model assumptions reveals that some are unrealistic, conceptually flawed or internally inconsistent. Additionally, tests of mid‐domain models have suffered from methodological deficiencies derived from arbitrariness and circularity in the definition of domain boundaries, collapsing two‐dimensional (2‐D) patterns into a single dimension (1‐D), and the use of interpolated ranges, all of which can bias test results in favour of the models. Tests have also been statistically naive by using fairly insensitive measures of deviation between observed and predicted patterns and ignoring the increased probability of Type I error that can result in analyses of spatially autocorrelated data.

In spite of this, a review of the empirical evidence indicates that most studies do not show a high degree of concordance between observed and predicted species richness patterns, particularly in 2‐D. Additionally, spatial patterns of variation in range size and species turnover do not unequivocally support mid‐domain models. Thus, the models do not adequately describe observed species richness gradients and thus fail to explain them.

Although mid‐domain models have served a useful purpose in drawing attention to the need to clarify the null expectation in the study of species richness gradients, their use appears to be severely limited by difficulties associated with the treatment of ranges, boundary definitions and a lack of clarity regarding the extent to which the observed data should be used to generate the null patterns.
Characterization of the intrinsic and extrinsic innervation of the gall bladder epithelium in the Australian Brush‐tailed possum (Trichosurus vulpecula)
Authors: Meedeniya A. C. B. , Schloithe A. C. , Toouli J. , Saccone G. T. P.
Published: July 2003

Abstract Intrinsic neurones of the gall bladder modulate its function. Nitric oxide synthase (NOS) and vasoactive intestinal polypeptide (VIP) are present in gall bladder neurones and nitric oxide and VIP modulate its epithelial functions. As an extensive extrinsic innervation of the gall bladder is also present, the source of the epithelial innervation is unclear. In this study the source of the gall bladder epithelial innervation is defined. Immunoreactivity for VIP, NOS, substance P (SP), calcitonin gene related peptide (CGRP) and tyrosine hydroxylase (TH) in organotypic cultured and freshly fixed gall bladder were compared. Retrograde tracing in vitro from the epithelium was used to identify putative intrinsic secretomotor neurones, which were then characterized by immunohistochemistry. Abundant spinal afferent and sympathetic innervation of the gall bladder epithelium was demonstrated by CGRP/SP and TH immunohistochemistry, respectively. The intrinsic secretomotor innervation of the epithelium is derived exclusively from neurones of the subepithelial plexus. A majority of these neurones were immunoreactive for NOS. Some of the NOS‐immunoreactive neurones of the subepithelial plexus also contained VIP and/or SP. Gall bladder subepithelial plexus neurones, containing NOS and/or VIP/SP, innervate the epithelium, as do extrinsic neurones.
A model for chronic quantitative studies of colorectal sensitivity using balloon distension in conscious mice – effects of opioid receptor agonists
Authors: Larsson M. , Arvidsson S. , Ekman C. , Bayati A.
Published: July 2003

Abstract In the current study, colorectal distension (CRD) was performed in conscious mice, in order to study visceral (colon) sensitivity. Electrodes were chronically implanted into the external oblique muscle to obtain the electromyographic (EMG) response to CRD. CRD was performed using a computerized system, which inflated the balloon with air to the desired pressures. An increasing (10–80 mmHg) and a repeated (12 × 55 mmHg) phasic paradigm with distensions lasting 10 s and with 5‐min intervals were used. The EMG recordings were linearly correlated to intracolonic pressures between 10 and 80 mmHg, which are characteristic of the visceromotor response (VMR). Repeated phasic distensions at 55 mmHg resulted in a stable VMR in female mice, but an increasing VMR in male mice. Interestingly, the duration of the VMR was about 5 s, which is shorter than the actual duration of the distension. U‐69593 and fentanyl (selective κ and μ opioid receptor agonists) significantly reduced the VMR at subcutaneous doses of 0.5 and 0.05 mg kg−1, respectively. In conclusion, a CRD model for repetitive quantitative studies of colorectal sensitivity and evaluation of pharmacological modulation of visceral sensitivity in conscious mice is presented.
Intestinal anti‐nociceptive behaviour of NK3 receptor antagonism in conscious rats: evidence to support a peripheral mechanism of action
Authors: Fioramonti J. , Gaultier E. , Toulouse M. , Sanger G. J. , Bueno L.
Published: July 2003

Abstract The involvement of neurokinin receptors in visceral nociception is well documented. However, the role and localization of NK3 receptors is not clearly established. This study was designed to determine whether NK3 receptor antagonists crossing (talnetant) or not (SB‐235375) the blood–brain barrier reduce the nociceptive response to colo‐rectal distension (CRD) and whether NK3 antagonism reduces inflammation‐ or stress‐induced hypersensitivity to rectal distension. Isobaric CRD and isovolumic rectal distensions were performed in rats equipped with intramuscular electrodes to record abdominal muscle contractions. In controls, CRD induced a pressure‐related (15–60 mmHg) increase in the number of abdominal contractions. Both talnetant and SB‐235375 [50 mg kg−1, per oral (p.o.)], which had no effect on colo‐rectal tone, reduced the number of contractions associated with CRDs from 30 to 60 mmHg. Three days after rectal instillation of TNBS, abdominal contractions were increased for rectal distension volume of 0.4 mL. This effect was not modified by talnetant (30 mg kg−1, p.o.). Partial restraint stress increased abdominal contractions at all distension volumes (0–1.2 mL). Talnetant (10 mg kg−1, p.o.) abolished the increase observed for 0.8 and 1.2 mL. These results indicate that peripheral NK3 receptor antagonism reduced nociception associated with CRD and hypersensitivity induced by stress but not inflammation.
Release of nitric oxide in the central nervous system mediates tonic and phasic contraction of the cat lower oesophageal sphincter
Authors: Beyak M. J. , Collman P. I. , Xue S. , Valdez D. T. , Diamant N. E.
Published: July 2003

Abstract Nitric oxide (NO) in the brainstem is implicated in the control of swallowing and oesophageal peristalsis. This study examines the role of brainstem NO in the maintenance of lower oesophageal sphincter (LOS) tone, relaxation and contraction. In urethane‐anaesthetized cats, oesophageal peristalsis and sphincter pressures were continuously monitored. Drugs were administered into the fourth ventricle. Oesophageal peristalsis and sphincter relaxation and contraction were induced by superior laryngeal nerve stimulation or intra‐oesophageal balloon distention. Basal sphincter pressure was significantly reduced after the i.c.v. administration of the nitric oxide synthase (NOS) inhibitor, l‐Ng‐monomethyl arginine. The inhibitor's d‐isomer had no significant effect on basal sphincter pressure, while l‐arginine partially reversed the effect. The NOS inhibitor had no effect on sphincter relaxation, whereas the contraction of the sphincter following relaxation was significantly inhibited. Central nitric oxide synthase inhibition reduces basal LOS tone and contraction amplitude but has no effect on swallow or balloon distention induced sphincter relaxation. Therefore, central release of NO acts in the pathway to stimulate dorsal motor nucleus of the vagus neurones projecting to excitatory neurones in the sphincter. Inhibition of nitric oxide synthase in the CNS does not prevent relaxation of the LOS, suggesting that other pathways that do not utilize NO are important in the induction of LOS relaxation.
Effects of glucagon‐like peptide‐1 and feeding on gastric volumes in diabetes mellitus with cardio‐vagal dysfunction
Authors: Delgado‐Aros S. , Vella A. , Camilleri M. , Low P. A. , Burton D. D. , Thomforde G. M. , Stephens D.
Published: July 2003

Abstract Glucagon‐like peptide‐1 (GLP‐1) increases gastric volume in humans possibly through the vagus nerve. Gastric volume response to feeding is preserved after vagal denervation in animals. We evaluated gastric volume responses to GLP‐1 and placebo in seven diabetic patients with vagal neuropathy in a crossover study. We also compared gastric volume response to feeding in diabetes with that in healthy controls. We measured gastric volume using SPECT imaging. Data are median (interquartile range). In diabetic patients, GLP‐1 did not increase gastric volume during fasting [5 mL (−3; 30)] relative to placebo [4 mL (−14; 50) P = 0.5], or postprandially [Δ postprandial minus fasting volume 469 mL (383; 563) with GLP‐1 and 452 mL (400; 493) with placebo P = 0.3]. Change in gastric volume over fasting in diabetic patients on placebo was comparable to that of healthy controls [452 mL (400; 493)], P = 0.5. In contrast to effects in health, GLP‐1 did not increase gastric volume in diabetics with vagal neuropathy, suggesting GLP‐1's effects on stomach volume are vagally mediated. Normal gastric volume response to feeding in diabetics with vagal neuropathy suggests that other mechanisms compensate for vagal denervation.
Analysis of factors that determine the compliance of rat jejunum to distension in vivo
Authors: Bogeski G. , Lean N. P. , Kitchener P. D. , Timar‐Peregrin A. , Sanger G. J. , Shafton A. D. , Furness J. B.
Published: July 2003

Abstract Distension of the intestine is commonly used to elicit reflex responses at other sites in the gastrointestinal tract, and also to evaluate pain of intestinal origin. The sensory neurones, that initiate the reflexes or pain responses, react to the forces generated in the wall of the intestine. Thus, the responses of the intestine at the site of distension, particularly changes in contractile activity, influence the signals from the gut. In the present work we have analysed the relationship between distension and pressure changes in the jejunum of the rat, in vivo. Isovolumic distension for 5 min caused an initial pressure increase which declined quickly in the first 30 s, and then declined more slowly. Phasic pressure increases were superimposed on the baseline pressure change. Hexamethonium blocked the phasic pressure increases, whereas the initial rapid and subsequent slower pressure decline during distension persisted. Inhibition of nitric oxide synthase (NOS) increased intraluminal pressure and caused increased frequency and irregularity of phasic pressure increases. However, the decline in jejunal pressure during distension was not changed by inhibition of NOS. The pressure decline during isovolumic distension was similar whether saline or paraffin oil were used to distend the intestine, indicating that the decline was not due to increased hydrostatic pressure causing water and electrolyte to cross the mucosal epithelium from the lumen to the intestinal interstitium. Hyoscine had no significant effect on the pressure profile when the intestine was distended. However, when the systemic or the local circulation of the jejunum was infused with nicardipine, the pressure that was achieved during isovolumic distension was less, although the rate of change in pressure during the slow decline was similar. It is concluded that distension evokes phasic pressure increases in the jejunum, that are nerve‐mediated, and increases the tension in the wall through a stretch‐activated increase in contractile force generated by the circular muscle. The decline in pressure during maintained distension is primarily a consequence of visco‐elastic properties of the wall of the intestine.
Endothelin‐1 stimulates sphincter of Oddi motility and decreases trans‐sphincteric flow: a possible mechanism contributes to cholestasis in disease states
Authors: Chen J. W. C. , Schloithe A. C. , Toouli J. , Saccone G. T. P.
Published: July 2003

Abstract Endothelin‐1 (ET‐1) is a potent stimulator of gallbladder contractility. Its role in modulation of sphincter of Oddi (SO) motility and trans‐sphincteric flow (TSF) has not been evaluated. To characterize the effects of ET‐1 on SO motility and TSF, 10 anaesthetized Australian possums (in vivo, n = 6) were given graded doses of ET‐1 (5–200 pmol kg−1) via closed intra‐arterial injection. Blood pressure, TSF and SO motility (basal pressure, phasic amplitude, contraction frequency) were analysed. For in vitro studies, eight SO rings were subjected to 10−12–10−7 mol L−1 cumulative concentrations of ET‐1 in organ bath and SO motility was measured. Data are expressed as mean ± SEM. Statistical analysis used anova. ET‐1 induced a dose‐related increase in blood pressure with a maximal increase of 37.5 ± 2.5 mmHg at 200 pmol kg−1, (P < 0.001). ET‐1 also increases SO basal pressure (P < 0.001) and contraction frequency (P < 0.0001). However, the contraction amplitude was not significantly affected. ET‐1 decreased TSF in a dose‐related manner (P < 0.001) with cessation of TSF at the highest dose (P < 0.001). In vitro studies showed a significant increase in mean SO motility index, and frequency of contractions at higher ET‐1 concentrations (10−9–10−7 mol L−1). ET‐1 is a potent stimulator of SO motility resulting in a reduction in TSF.
Effects of gastric electrical field stimulation with long pulses on gastric emptying in dogs
Authors: Ouyang H. , Yin J. , Zhu H. , Xu X. , Chen J. D. Z.
Published: July 2003

Abstract The aim was to investigate the effects of electrical field stimulation (EFS) with long and short pulses on gastric emptying, gastric contractility and vagal activity in dogs. Sixteen dogs were equipped with a duodenal cannula, electrodes and strain gauges (10 dogs) in the stomach. Each dog was fed with Ensure and gastric effluent was collected from the cannula. Electrical stimulation was applied via two electrodes (about 12 cm apart, one in the corpus and the other in the antrum) with long pulses (a frequency of 6 cycles min−1, pulse amplitude of 6 mA and width of 100 ms) in 10 dogs and with short pulses (frequency of 30 Hz and pulse width of 300 μs) in six dogs. The electrocardiogram was also recorded and heart rate variability was derived to assess the vagal activity. It was found that: (i) EFS with long pulses did not alter gastric emptying during stimulation but increased gastric emptying during the 45 min immediately after stimulation; (ii) EFS with long pulses increased gastric contractility in both proximal and distal antrum during and after the stimulation; (iii) EFS with long pulses resulted in an increase in vagal tone during the 45 min immediately after stimulation. However, there is no difference during the 45 min period of stimulation; (iv) EFS with short pulses had no effect on gastric emptying. We concluded that long pulse gastric electrical field stimulation with one electrode in the corpus and the other electrode in the antrum has postponed effects on gastric emptying of liquid, gastric contractility and vagal activity.
Abdominal distension after colonic lactulose fermentation recorded by a new extensometer
Authors: Basilisco G. , Marino B. , Passerini L. , Ogliari C.
Published: July 2003

Abstract Colonic lactulose fermentation induces bloating, but whether it also causes abdominal distension is not known. The aim of this study was to assess the effect of colonic lactulose fermentation on abdominal girth using a new extensometer. We recorded abdominal girth in 24 healthy subjects by means of an extensometer that measures the phase shift of an ultrasound wave propagating in a tube encircling the abdomen. The recordings were continuously made for 3 h after the ingestion of 100 mL of tap water with (16 subjects) or without (eight subjects) 10 g of lactulose. Every 10 min, H2 in the breath was analysed and the intensity of bloating was recorded. Bloating was never reported after water ingestion, whereas it was reported by 10 subjects after lactulose ingestion (P = 0.002). The mean ± SD changes in abdominal girth in comparison with resting conditions were statistically significant after lactulose ingestion (3 ± 2.9 mm; P = 0.002) but not after water ingestion (−0.2 ± 2.7 mm; P = 0.82). The area under the curve of the changes in abdominal girth after lactulose were significantly greater than after water ingestion (P = 0.03). In conclusion, colonic lactulose fermentation induces bloating and abdominal distension. The new extensometer is useful for continuously recording changes in abdominal girth.
Nerve growth factor and gastric hyperalgesia in the rat
Authors: Lamb K. , Kang Y. M. , Gebhart G. F. , Bielefeldt K.
Published: July 2003

Abstract We recently demonstrated an association between the development of hyperalgesia and an increase in nerve growth factor (NGF) during gastric inflammation. We hypothesized that block of NGF signalling will blunt injury‐induced hyperalgesia. Male Sprague–Dawley rats (300–400 g) were anaesthetized, the stomach was exposed and placed in a circular clamp. Acetic acid (60%) or saline (control) was injected into this area and aspirated 45 s later, resulting in kissing ulcers. A balloon was surgically placed into the stomach and electromyographic responses to gastric distension (GD) were recorded from the acromiotrapezius muscle. Animals received a daily injection of neutralizing NGF antibody or control serum for 5 days. NGF in the stomach wall was measured with an ELISA. The severity of gastric injury was assessed macroscopically and by determination of myeloperoxidase (MPO) activity. Gastric injury enhanced the visceromotor response to GD and increased NGF content. Anti‐NGF significantly blunted the development of hyperalgesia and led to a decrease in gastric wall thickness and MPO activity. Increases in NGF contribute to the development of hyperalgesia after gastric injury. This may be partly mediated by direct effects on afferent nerves and indirectly by modulatory effects on the inflammatory response.
Fidelity of hepatitis B virus polymerase
Authors: Park Sung Gyoo , Kim Younhee , Park Esther , Ryu Hyun Mi , Jung Guhung
Published: July 2003

Although efficient vaccines are available, chronic hepatitis B (HBV) infection poses a major health problem worldwide, and prolonged treatment of chronically infected HBV patients with nucleoside analogs often results in drug‐resistant HBV variants. Therefore, it is critical to evaluate the contribution of the HBV polymerase to mutations. FLAG‐tagged wild‐type (FPolE) and mutant (FPolE/D551A) HBV polymerases have been expressed in insect cells and purified. The purified FPolE showed DNA polymerase activity, but FPolE/D551A did not, implying that the activity was derived from FPolE. No 3′→5′exonuclease activity was detected in FPolE. The fidelity of FPolE was investigated and compared with that of HIV‐1 RT, which is highly error‐prone. The fidelity of HBV polymerase seems to be achieved by increasing the Km for the dNTP being misinserted. The nucleotide misinsertion efficiency of FPolE and HIV‐1 RT ranged from 3.59 × 10−4 (C : T) to 1.51 × 10−3 (G : T) and from 1.75 × 10−4 (C : T) to 1.62 × 10−3 (G : T), respectively, and the overall misinsertion efficiency of HIV‐1 RT was just 1.04‐fold higher than that of FPolE, implying that HBV polymerase is fairly error‐prone. Though HBV genetic mutation rate in replication is thought to be between those in RNA and DNA viruses, our data shows that the rate of mutation by HBV polymerase is higher than the rate of genetic mutation in vivo. This may be a result from more overlapping HBV genes in the HBV genome than that of other retroviruses.