A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer-algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.

Aluminium-free glass polyalkenoate cements: ion release and in vitro antibacterial efficacy

Glass polyalkenoate cements (GPCs) have exhibited potential as bone cements. This study investigates the effect of substituting TiO₂ for SiO₂ in the glass phase and the subsequent effect on cement rheology, mechanical properties, ion release and antibacterial properties. Glass characterization revealed a reduction in glass transition temperature (T(g)) from 685 to 669 °C with the addition of 6 mol % TiO₂ (AT-2). Magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed a shift from -81 ppm to -76 pmm when comparing a Control glass to AT-2, indicating de-polymerization of the Si network. The incorporation of TiO₂ also increased the working time (T(w)) from 19 to 61 s and setting time (T(s)) from 70 to 427 s. The maximum compressive strength (σ(c)) increased from 64 to 85 MPa. Ion release studies determined that the addition of Ti to the glass reduced the release of zinc, calcium and strontium ions, with low concentrations of titanium being released. Antibacterial testing in E. coli resulted in greater bactericidal effects when tested in aqueous broth for both titanium containing cements.

Phase separation in mixtures of ionized iron in a hydrogen plasma

The accuracy of the hypernetted chain theory for mixtures of iron nuclei and protons in a charge-neutralizing background is demonstrated by comparison with molecular dynamics calculations. Near critical conditions the Debye-Hückel approximation fails to converge, even with second-order concentration corrections. The critical conditions, determined by assuming a uniform electron gas background, have a critical temperature more than a factor of 2 lower than present estimates of interior solar conditions. Qualitative arguments are made that including the polarization of the electron gas background would not change this result significantly and thus phase separation of iron in the interior of the sun is unlikely.

Quantum control of coupled two-electron dynamics in quantum dots

We investigate optimal control strategies for state to state transitions in a model of a quantum dot molecule containing two active strongly interacting electrons. The Schrödinger equation is solved nonperturbatively in conjunction with several quantum control strategies. This results in optimized electric pulses in the terahertz regime which can populate combinations of states with very short transition times. The speed-up compared to intuitively constructed pulses is an order of magnitude. We furthermore make use of optimized pulse control in the simulation of an experimental preparation of the molecular quantum dot system. It is shown that exclusive population of certain excited states leads to a complete suppression of spin dephasing, as was indicated in Nepstad et al (2008 Phys. Rev. B 77 125315).

A critical GxxxA motif in the gamma6 calcium channel subunit mediates its inhibitory effect on Cav3.1 calcium current

The eight members of the calcium channel gamma subunit family are integral membrane proteins that regulate the expression and behaviour of voltage and ligand gated ion channels. While a subgroup consisting of gamma(2), gamma(3), gamma(4) and gamma(8) (the TARPs) modulate AMPA receptor localization and function, the gamma(1) and gamma(6) subunits conform to the original description of these proteins as regulators of voltage gated calcium channels. We have previously shown that the gamma(6) subunit is highly expressed in atrial myocytes and that it is capable of acting as a negative modulator of low voltage activated calcium current. In this study we extend our understanding of gamma(6) subunit modulation of low voltage activated calcium current. Using engineered chimeric constructs, we demonstrate that the first transmembrane domain (TM1) of gamma(6) is necessary for its inhibitory effect on Cav3.1 current. Mutational analysis is then used to identify a unique GxxxA motif within TM1 that is required for the function of the subunit strongly suggesting the involvement of helix-helix interactions in its effects. Results from co-immunoprecipitation experiments confirm a physical association of gamma(6) with the Cav3.1 channel in both HEK cells and atrial myocytes. Single channel analysis reveals that binding of gamma(6) reduces channel availability for activation. Taken together, the results of this study provide both a molecular and a mechanistic framework for understanding the unique ability of the gamma(6) calcium channel subunit to modulate low voltage activated (Cav3.1) calcium current density.

Optical control in coupled two-electron quantum dots

The dynamics of two electrons in a 2-dimensional quantum dot molecule in the presence of a time-dependent electromagnetic field is calculated from first principles. We show that carefully selected microwave pulses can exclusively populate a single state of the first excitation band and that the transition time can be further decreased by optimal pulse control. Finally we demonstrate that an oscillating charge localized state may be created by multiple transitions using a sequence of pulses.

Nondipole ionization dynamics of atoms in superintense high-frequency attosecond pulses

The ionization of H(1s) in superintense, high-frequency, attosecond pulses is studied beyond the dipole approximation. We identify a unique nondipole 3rd lobe in the angular distribution of the ejected electron and show that this lobe has a well-defined classical counterpart. The ionization is likely to occur in the direction opposite to the laser propagation direction, which is fully understood from an analysis of the classical dynamics.

Strong orientation effects in ionization of H+2 by short, intense, high-frequency light pulses

We present three-dimensional time-dependent calculations of ionization of arbitrarily spatially oriented H+2 by attosecond, intense, high-frequency laser fields. The ionization probability shows a strong dependence on both the internuclear distance and the relative orientation between the laser field and the internuclear axis. The physical features are explained in terms of two-center interference effects.

Exact nondipole Kramers-Henneberger form of the light-atom hamiltonian: an application to atomic stabilization and photoelectron energy spectra

The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three-dimensional nondipole ab initio wave packet calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization effect in the photoelectron spectrum.

Density-functional study of interfacial properties of colloid-polymer mixtures

Interfacial properties of colloid-polymer mixtures are examined within an effective one-component representation, where the polymer degrees of freedom are traced out, leaving a fluid of colloidal particles interacting via polymer-induced depletion forces. Restriction is made to zero-, one-, and two-body effective potentials, and a free energy functional is used that treats colloid excluded volume correlations within Rosenfeld's fundamental measure theory, and depletion-induced attraction within first-order perturbation theory. This functional allows a consistent treatment of both ideal and interacting polymers. The theory is applied to surface properties near a hard wall, to the depletion interaction between two walls, and to the fluid-fluid interface of demixed colloid-polymer mixtures. The results of the present theory compare well with predictions of a fully two-component representation of mixtures of colloids and ideal polymers (the Asakura-Oosawa model) and allow a systematic investigation of the effects of polymer-polymer interactions on interfacial properties. In particular, the wall surface tension is found to be significantly larger for interacting than for ideal polymers, whereas the opposite trend is predicted for the fluid-fluid interfacial tension.

Calcium channel ? subunits are unique modulators of low voltage-activated (Cav3.1) calcium current

The calcium channel gamma (gamma) subunit family consists of eight members whose functions include modulation of high voltage-activated (HVA) calcium currents in skeletal muscle and neurons, and regulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propanoic acid (AMPA) receptor targeting. Cardiac myocytes express at least three gamma subunits, gamma(4), gamma(6) and gamma(7), whose function(s) in the heart are unknown. Here we compare the effects of the previously uncharacterized gamma(6) subunit with that of gamma(4) and gamma(7) on a low voltage-activated calcium channel (Cav3.1) that is expressed in cardiac myocytes. Co-expression of both the long and short gamma(6) subunit isoforms, gamma(6L) and gamma(6S), with Cav3.1 in HEK-293 cells significantly decreases current density by 49% and 69%, respectively. Two other gamma subunits expressed in cardiac myocytes, gamma(4) and gamma(7), have no significant effect on Cav3.1 current. Neither gamma(6L), gamma(6S), gamma(4) nor gamma(7) significantly affect the voltage dependency of activation or inactivation or the kinetics of Cav3.1 current. Transient expression of gamma(6L) in an immortalized atrial cell line (HL-1) significantly reduces the endogenous low voltage-activated current in these cells by 63%. Green fluorescent protein tagged gamma(6L) is localized primarily in HEK-293 cell surface membranes where it is evenly distributed. Expression of gamma(6L) does not affect the level of Cav3.1 mRNA or the amount of total Cav3.1 protein in transfected HEK-293 cells. These results demonstrate that the gamma(6) subunit has a unique ability to inhibit Cav3.1 dependent calcium current that is not shared with the gamma(4) and gamma(7) isoforms and is thus a potential regulator of cardiac low voltage-activated calcium current.

Influence of solvent quality on polymer solutions: A Monte Carlo study of bulk and interfacial properties

The effect of solvent quality on dilute and semidilute regimes of polymers in solution is studied by means of Monte Carlo simulations. The equation of state, adsorption near a hard wall, wall-polymer surface tension, and effective depletion potential are all calculated as a function of concentration and solvent quality. We find important differences between polymers in good and theta solvents. In the dilute regime, the physical properties for polymers in a theta solvent closely resemble those of ideal polymers. In the semidilute regime, however, significant differences are found.

Coulomb bicrystals of species with identical charge-to-mass ratios

Structures of cold bicomponent Coulomb systems of particles with identical charge-to-mass ratios and common oscillation frequency in a spherical harmonic potential are studied by molecular dynamics simulations with up to 10(6) particles. For most initial conditions and cooling rates, the final state becomes a completely mixed core surrounded by a set of nearly degenerated double shells of separate species. For an equal amount of the two species, it is found that the ground state for larger systems consists of a simple cubic structured core surrounded by outer double-shell structures.

Nonmonotonic variation with salt concentration of the second virial coefficient in protein solutions

The osmotic virial coefficient B2 of globular protein solutions is calculated as a function of added salt concentration at fixed pH by computer simulations of the "primitive model." The salt and counterions as well as a discrete charge pattern on the protein surface are explicitly incorporated. For parameters roughly corresponding to lysozyme, we find that B2 first decreases with added salt concentration up to a threshold concentration, then increases to a maximum, and then decreases again upon further raising the ionic strength. Our studies demonstrate that the existence of a discrete charge pattern on the protein surface profoundly influences the effective interactions and that linear and nonlinear Poisson Boltzmann theories fail for large ionic strength. The observed nonmonotonicity of B2 is compared with experiments. Implications for protein crystallization are discussed.

Excitation in ion-atom collisions inside subfemtosecond laser pulses

We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions.

[Relatives' attitude towards death in hospital]

INTRODUCTION

A survey was conducted over 13 months to measure the satisfaction level of relatives to patients, who had died in hospital.

METHODS

The survey contained a questionnaire of 75 questions measuring satisfaction in different areas: the amount and quality of information given to the relatives by doctors, the support and care provided by the staff, and the quality of the physical environment.

RESULTS

Out of 619 questionnaires posted, 462 were returned (74.6% response rate). Only half the relatives were satisfied with the level of information given by doctors to themselves and the one dying. Twenty-four per cent of the respondents were dissatisfied by the length of time taken by doctors to inform them about the situation. A broad majority of respondents (85%) were very satisfied with the care and support provided by the nursing staff. Sixty-six per cent of the patients died in private wards. Fifty-five per cent of the relatives were satisfied with the quality of the patient's room, but only 37% were satisfied with the environment offered to them. One in five was especially dissatisfied by the lack of a special room, which would permit enabling private conversations in an undisturbed environment.

DISCUSSION

Our survey shows that doctors' communication with the relatives of dying patients needs to be improved. There also seems to be a need for providing a better environment for the relatives of dying patients by reserving separate rooms for rest and conversation.

Numerical solution of the Smoluchowski equation for a vibrofluidized granular bed

A stochastic approach, similar to that used to describe Brownian motion, was used to model the displacement probability of grains in a three-dimensional vibrofluidized granular bed. As neither an analytical description nor measurements of the diffusion coefficients were available, the governing partial differential equation, namely, the Smoluchowski equation, was solved numerically using an iterative procedure, modifying the granular temperature profile at each step. The results of this stochastic model were compared to experimental measurements of the displacement probability density made using positron emission particle tracking. The results indicate that methods based on hard elastic systems such as the Smoluchowski equation are appropriate to granular systems, particularly over timescales greater than the mean collision time.

Treatment of Helicobacter pylori in children with recurrent abdominal pain

BACKGROUND

The role of Helicobacter pylori remains unclear in children with recurrent abdominal pain (RAP). In this study children with RAP were included in a double blind treatment study to elucidate whether symptoms disappear in children with a H. pylori infection and RAP, if the bacteria are eradicated.

METHODS

Thirty-seven H. pylori-infected children aged 4.9-14.5 years (median 9.8 years) with RAP were included. H. pylori was identified by histology and culture. The children were treated with amoxicillin and metronidazole for 14 days. A re-endoscopy including biopsies for histology and culture was done at least one month after the end of treatment. Simple questions for symptoms were asked and blood for serology was repeated 3 and 6 months after the end of treatment. During the observation period the results of the re-endoscopy and the serology 3 and 6 months after the re-endoscopy were blinded for 23 patients and opened to 14 of the patients according to the choice of the families.

RESULTS

The eradication rates were 81% (30/37) in the total group and 74% (17/23) in the blinded group. The IgG antibodies to H. pylori decreased significantly 3 (p =.03) as well as 6 months after end of treatment (p <.001) in children with successful eradication. The number of children with RAP decreased after examination and treatment and the well-being improved after 6 months in almost 95% of the children. However, no correlation was seen between eradication of H. pylori and disappearance of RAP, neither after 3 nor after 6 months' observation in the total group of patients (p =.94 and p =.90) or in the blinded group (p =.42 and p =.65).

CONCLUSIONS

These results do not provide evidence for a causal relationship between RAP and H. pylori.

Many-body interactions and correlations in coarse-grained descriptions of polymer solutions

We calculate the two-, three-, four-, and five-body (state-independent) effective potentials between the centers of mass (c.m.'s) of self-avoiding walk polymers by Monte Carlo simulations. For full overlap, these coarse-grained n-body interactions oscillate in sign as (-1)(n), and decrease in absolute magnitude with increasing n. We find semiquantitative agreement with a scaling theory, and use this to discuss how the coarse-grained free energy converges when expanded to arbitrary order in the many-body potentials. We also derive effective density dependent two-body potentials that exactly reproduce the pair-correlations between the c.m. of the self avoiding walk polymers. The density dependence of these pair potentials can be largely understood from the effects of the density independent three-body potential. Triplet correlations between the c.m. of the polymers are surprisingly well, but not exactly, described by our coarse-grained effective pair potential picture. In fact, we demonstrate that a pair potential cannot simultaneously reproduce the two- and three-body correlations in a system with many-body interactions. However, the deviations that do occur in our system are very small, and can be explained by the direct influence of three-body potentials.

Mean-field fluid behavior of the gaussian core model

We show that the Gaussian core model of particles interacting via a penetrable repulsive Gaussian potential, first considered by Stillinger [J. Chem. Phys. 65, 3968 (1976)], behaves as a weakly correlated "mean-field fluid" over a surprisingly wide density and temperature range. In the bulk, the structure of the fluid phase is accurately described by the random phase approximation for the direct correlation function, and by the more sophisticated hypernetted chain integral equation. The resulting pressure deviates very little from a simple mean-field-like quadratic form in the density, while the low density virial expansion turns out to have an extremely small radius of convergence. Density profiles near a hard wall are also very accurately described by the corresponding mean-field free-energy functional. The binary version of the model exhibits a spinodal instability against demixing at high densities. Possible implications for semidilute polymer solutions are discussed.

Effective interactions between electric double layers

This review summarizes and assesses recent theoretical and experimental advances, with special emphasis on the effective interaction between charge-stabilized colloids, in the bulk or in confined geometries, and on the ambiguities of defining an effective charge of the colloidal particles. Some consideration is given to the often neglected discrete solvent effects.

Can polymer coils Be modeled as "Soft colloids"?

We map dilute or semidilute solutions of nonintersecting polymer chains onto a fluid of "soft" particles interacting via a concentration dependent effective pair potential, by inverting the pair distribution function of the centers of mass of the initial polymer chains. A similar inversion is used to derive an effective wall-polymer potential; these potentials are combined to successfully reproduce the calculated exact depletion interaction induced by nonintersecting polymers between two walls. The mapping opens up the possibility of large-scale simulations of polymer solutions in complex geometries.

Single-particle motion in three-dimensional vibrofluidized granular beds

A technique to probe the interior of three-dimensional dynamic granular systems is presented. Positron emission particle tracking (PEPT) allows a single tracer particle to be followed around a three dimensional vibrofluidized granular bed for periods up to six hours. At present the technique is able to resolve the position of the grains to +/-4 mm, with an average temporal resolution of about 7 ms. Packing fraction profiles are calculated by making use of the ergodicity of the system, and granular temperature profiles are obtained, in the dilute case, from the short time behavior of the mean squared displacement. At longer times, the mean squared displacement shows a range of behavior which can be explained by the presence of strong gradients in the packing fraction. Convection currents were observed, but were sufficiently small in magnitude to be ignored during the analysis of grain motion. The system was modeled using the Smoluchowski equation, which was solved numerically, and the results compared with the experimentally determined displacement probability density functions. Good agreement between experiment and numerical results was achieved using Brownian motion relationships modified to accommodate differences between granular systems and thermal systems.

Spin anisotropy for excitation in collisions between two one-electron atoms

The singlet and triplet contributions of excitation cross sections are studied theoretically for collisions between various two one-electron atoms. The spin anisotropy is shown to have a general behavior in the important impact energy range. At low energies triplet cross sections dominate completely over the singlet ones while the opposite is true when the active electron and projectile velocities are comparable. Beyond the matching velocity regime singlet and triplet contributions become identical. We propose a general dynamical interpretation based on the analysis of the time dependency of the electron probability density and probability current density.

Size selectivity of narrow pores

The selectivity of micropores and ion channels is examined for simple pore topologies within the framework of density functional theory of highly confined fluids. In an infinite cylindrical pore purely steric (excluded volume) effects are shown to lead to strong, nontrivial size selectivity, which is highly sensitive to the pore radius. A crude modeling of electrostatic effects does not alter the relative absorbance of Na+ and K+ ions in a significant way.

Interobserver variation in diagnosing coeliac disease. A joint study by Danish and Swedish pathologists

There is an almost 40-fold difference in incidence rates of symptomatic coeliac disease between Denmark and Sweden. In an attempt to explain this difference, the present study focused on the interobserver agreement when pathologists were assessing small intestinal biopsy specimens from children suspected of suffering from coeliac disease. The study was performed on 90 biopsy specimens from 73 children. Most of the biopsies came from children who turned out not to suffer from coeliac disease after a clinical evaluation including small intestinal biopsy. Using the kappa methodology, the interobserver agreement between two Danish pathologists and one Swedish pathologist, all of whom were experienced, was "moderate" to "substantial" or 0.57-0.75. Kappa indices when the pathologists evaluated selected histological elements were in the interval from 0.24 to 0.67. A comparison of a previous routine diagnostic assessment of the 90 biopsies (14 pathologists) with the results of the experienced pathologists in the present study gave kappa indices of from 0.53 to 0.57. The study could prove no major differences in the histopathological assessment of small intestinal biopsy specimens made by Danish and Swedish pathologists. The difference in clinical presentation of coeliac disease in Denmark and Sweden does not relate to differences in the histopathological assessment of small intestinal biopsies.

Crystallization and phase separation in nonadditive binary hard-sphere mixtures

We calculate for the first time the full phase diagram of an asymmetric nonadditivehard-sphere mixture. The nonadditivity strongly affects the crystallization and the fluid-fluid phase separation. The global topology of the phase diagram is controlled by an effective size ratio y(eff), while the fluid-solid coexistence scales with the depth of the effective potential well.

Self-diffusion of grains in a two-dimensional vibrofluidized bed

The analogy of vibrofluidized granular beds with a thermal gas of hard discs has been tested. Analysis of the mean squared displacement behavior of the grains allowed comparison of the measured diffusion with the predicted value at a particular combination of granular temperature and packing fraction. High speed photography, image analysis, and particle tracking software enabled accurate location of the grains. Appropriate analysis of the three mean squared displacement regimes, ballistic, diffusive, and crossover between the two extremes, allowed both the diffusion coefficient and the granular temperature to be measured at the same packing fraction. Broad agreement between Chapman-Enskog theory relating temperature to self-diffusion and observation was observed up to packing fractions of eta approximately equal to 0.7. At higher packing fractions the grains showed evidence of caging and jump diffusion, with the observed diffusion rapidly diverging from that predicted by theory. Measurement of self-diffusion coefficients and subsequent use of kinetic theory was found to be an accurate method to determine the granular temperature for intermediate packing fractions (eta=0.4-0.6), and would be particularly suitable for those situations where the time resolution of the experimental facility is insufficient to resolve the speed of the grain between collisions.

Plasma-insulator transition of spin-polarized hydrogen

A mixed classical-quantum density functional theory is used to calculate pair correlations and the free energy of a spin-polarized hydrogen plasma. A transition to an atomic insulator phase is estimated to occur around r(s)=2.5 at T=10(4) K, and a pressure P is approximately equal to 0.5 Mbar. Spin polarization is imposed to prevent the formation of H2 molecules.

Chiropractic services in a staff model HMO: utilization and satisfaction

Utilization of chiropractic services was assessed in the continuously enrolled, non-Medicaid membership of Group Health Cooperative of South Central Wisconsin in 1993 and 1994. In addition, a random sample of 500 members using chiropractic services in the last quarter of 1994 was surveyed about satisfaction with the services. A total of 5.1% and 5.3% of members used the services in 1993 and 1994, respectively. Highest utilization occurred among women aged 35 to 49, with rates of 9.5% and 9.9%. Satisfaction levels were high in all areas; 95.8% indicated overall satisfaction with chiropractic care and services.

Observer variation in histological classification of cutaneous malignant melanoma

To evaluate the variations within and between observers in the interpretation of important histological prognostic factors, a series of 96 melanoma patients was randomly selected from a database of 1691 patients with cutaneous malignant melanoma. The stained sections were examined on two occasions by four experienced pathologists. Analysis by observed agreement and kappa statistics showed maximal tumour thickness to be the best reproducible variable, with ulceration the second best. Regression was the least reproducible, with level of invasion and type of melanoma in the mid range. Intra-observer variation was uniformly less than inter-observer variation for each variable. For tumour thickness a variance component analysis was done to quantify the variability further. The clinician should not base his choice of treatment entirely on the microscopic classification but take into consideration the clinical course and appearance of the tumour.

[Alcohol, drugs and narcotics in suicides in the Aarhus police district]

For a period of one year all suicides in Aarhus police district were investigated with a view to identifying the presence of alcohol or drugs in the body of the deceased. Fifty-one suicides occurred, 46 of which were examined. One third of the suicides were due to poisoning and one fourth to hanging. Alcohol was detected in 20% and drugs or narcotics were found in approximately 60%. The most frequent findings were benzodiazepines, analgetics, antidepressants and carbon monoxide. Approximately 40% of the deceased had received psychiatric treatment.

Helicobacter pylori infection in children with recurrent abdominal pain

Helicobacter pylori was cultured and Helicobacter-like organisms (HLO) were seen in 6 (16%) of 37 children with recurrent abdominal pain. Five children had concomitant histological inflammation, but none had endoscopic changes. All 6 children demonstrated positive serology. Compared with the total group, they were more often from developing countries, larger families and lower social groups. Treatment with phenoxymethyl penicillin and colloidal bismuth subcitrate did not result in side effects or elevated serum levels of serum bismuth. Three children demonstrated metronidazole-resistant strains and the treatment of these children remained an unsolved problem. Among the 31 H. pylori/HLO negative children 8 (26%) demonstrated histological changes, 5 (16%) endoscopic changes and 11 (35%) had positive serology. In conclusion, pathological findings at upper gastrointestinal endoscopy are common in children with recurrent abdominal pain. Because of disconcordance between endoscopy, histology and culture, we recommend that biopsies should always be taken to clarify the diagnosis.

The humoral immune response to Helicobacter pylori infection in children with recurrent abdominal pain

The systemic humoral immune response to Helicobacter pylori antigens was investigated in 36 children with recurrent abdominal pain (RAP). H. pylori was cultured and Helicobacter-like organisms (HLO) were seen in six children, three of whom had active and two inactive chronic gastritis. None of these children had endoscopic abnormalities. All sex children had increased IgG antibodies to heat-stable H. pylori antigens which were of the IgG1 and IgG3 subclasses. Using six other IgG tests, four of which were commercially available, two to five H. pylori-positive children were found seropositive. Five of six H. pylori-negative children with inactive chronic gastritis and no endoscopic abnormalities had increased IgM antibody levels in addition to increased or borderline increased IgG antibody levels to H. pylori, indicating activity in a chronic H. pylori infection. Five children without H. pylori and with no morphological changes, but with gastritis or duodenitis by endoscopy, had significantly lower IgG and IgA antibody levels compared to other groups. Six of nineteen children without H. pylori, and with no morphological or endoscopic changes had increased IgG and IgM antibody levels to H. pylori. All H. pylori-negative children were seronegative by the four commercial kits. Overall, 12 (33%) of 36 children with RAP were either H. pylori positive by culture and microscopy or had increased IgG antibody levels to H. pylori, which is significantly different from the 10-14% seropositive rate of asymptomatic children. H. pylori may therefore be a cause of RAP in one quarter to one third of the children with RAP in whom other etiologies of RAP are excluded. Further studies on a large number of children are needed for an extended evaluation of the humoral immune response to H. pylori and for further examination of commercial kits which seem to give a high number of false-negative results.