Showing papers by "University of Bergen published in 1990"

High diversity in DNA of soil bacteria.

Abstract: Soil bacterium DNA was isolated by minor modifications of previously described methods. After purification on hydroxyapatite and precipitation with cetylpyridinium bromide, the DNA was sheared in a French press to give fragments with an average molecular mass of 420,000 daltons. After repeated hydroxyapatite purification and precipitation with cetylpyridinium bromide, high-pressure liquid chromatography analysis showed the presence of 2.1% RNA or less, whereas 5-methylcytosine made up 2.9% of the total deoxycytidine content. No other unusual bases could be detected. The hyperchromicity was 31 to 36%, and the melting curve in 1 X SSC (0.15 M NaCl plus 0.015 M sodium citrate) corresponded to 58.3 mol% G+C. High-pressure liquid chromatography analysis of two DNA samples gave 58.6 and 60.8 mol% G+C. The heterogeneity of the DNA was determined by reassociation of single-stranded DNA, measured spectrophotometrically. Owing to the high complexity of the DNA, the reassociation had to be carried out in 6 X SSC with 30% dimethyl sulfoxide added. Cuvettes with a 1-mm light path were used, and the A275 was read. DNA concentrations as high as 950 micrograms ml-1 could be used, and the reassociation rate of Escherichia coli DNA was increased about 4.3-fold compared with standard conditions. C0t1/2 values were determined relative to that for E. coli DNA, whereas calf thymus DNA was reassociated for comparison. Our results show that the major part of DNA isolated from the bacterial fraction of soil is very heterogeneous, with a C0t1/2 about 4,600, corresponding to about 4,000 completely different genomes of standard soil bacteria.(ABSTRACT TRUNCATED AT 250 WORDS) Images

Diatoms and pH Reconstruction

Abstract: Palaeolimnological diatom data comprise counts of many species expressed as percentages for each sample. Reconstruction of past lake-water pH from such data involves two steps; (i) regression, where responses of modern diatom abundances to pH are modelled and (ii) calibration where the modelled responses are used to infer pH from diatom assemblages preserved in lake sediments. In view of the highly multivariate nature of diatom data, the strongly nonlinear response of diatoms to pH, and the abundance of zero values in the data, a compromise between ecological realism and computational feasability is essential. The two numerical approaches used are (i) the computationally demanding but formal statistical approach of maximum likelihood (ML) Gaussian logit regression and calibration and (ii) the computationally straightforward but heuristic approach of weighted averaging (WA) regression and calibration. When the Surface Water Acidification Project (SWAP) modern training set of 178 lakes is reduced by data-screening to 167 lakes, WA gives superior results in terms of lowest root mean squared errors of prediction in cross-validation. Bootstrapping is also used to derive prediction errors, not only for the training set as a whole but also for individual pH reconstructions by WA for stratigraphic samples from Round Loch of Glenhead, southwest Scotland covering the last 10 000 years. These reconstructions are evaluated in terms of lack-of-fit to pH and analogue measures and are interpreted in terms of rate of change by using bootstrapping of the reconstructed pH time-series.

A review of the palaeohydrological interpretation of carbon and oxygen isotopic ratios in primary lacustrine carbonates

Abstract: Primary carbonates are a common feature of many modern and ancient lacustrine deposits. Carbonates from hydrologically open lakes show little or no correlation between δ13C and δ18O. In short-residence-time open lakes, carbonate oxygen isotopic composition is relatively invariant and typically is closely related to the bulk isotopic composition of inflow waters to the lake. Suites of carbonates which display covarying 13C and 18O compositions precipitate from waterbodies having relatively long residence times. Where the correlation between carbon and oxygen isotopic variations is high (r⪖ 0.7 ), the carbonates have normally precipitated from a closed lake. In addition, because of large changes in water balance, the δ18O of closed-lake carbonates usually varies over a range of several %o. Therefore, the combination of degree of covariance and spread of δ18O-values can be used to discriminate between carbonates produced in hydrologically open and closed basins. Within individual basins, covariant trends may have remarkable long-term persistence despite major environmental changes, indicating considerable stability in basin hydrology. Each closed lake has a unique isotopic identity defined by its covariant trend, which is a function of the basin's geographical and climatic setting, its hydrology, and the history of the waterbody. Any major interruption or realignment of this trend reflects a fundamental change in basin hydrology. Isotopic trends based upon the carbon and oxygen isotopic composition of primary lacustrine carbonates have several applications in palaeolimnology. The oxygen isotopic composition of open-lake carbonates may, with caution, be used as a proxy indicator of the composition of regional rainfall. Covariant trends can be used to trace the hydrological history of a basin, the evolution of individual water masses, and to correlate carbonate-bearing sediments from different parts of a basin.

The formalin test in mice: effect of formalin concentration.

Abstract: The effect of different formalin concentrations on the nociceptive response in the formalin test was examined in mice. Subcutaneous formalin injection induces 2 distinct periods of high licking activity: an early phase lasting the first 5 min, and a late phase lasting 20-30 min after the injection. Formalin concentrations of 0.02-0.2% induced only the early phase, while concentrations of 1% or more induced both the early phase and the late phase. The ability of the test to show the antinociceptive effect of morphine and acetylsalicylic acid was similar for high and low formalin concentrations. For both these analgesics, a lower dose was needed to induce antinociception in the late phase than in the early phase using the same formalin concentration. Indomethacin had no effect in the early phase. In the late phase indomethacin induced antinociception when 1% formalin was used, while no significant effect was observed using 5% formalin. Clear histological changes in the paw were demonstrated after formalin concentrations that induced both phases. Lower formalin concentrations induced only very small changes. Using a low formalin concentration (0.2%), repeated testing using the same paw could be performed at intervals of 1 week without any significant change in the response. It was concluded that the formalin concentration should be kept as low as possible to minimize the suffering of the animal. Formalin concentrations of 0.05-0.2% are recommended for studying the early phase. Formalin concentrations of 1% or higher have to be used when studying the nociceptive response in the late phase.

Viruses as partners in spring bloom microbial trophodynamics.

Abstract: Population sizes of algae, bacteria, heterotrophic flagellates, and viruses were observed through the 1989 spring diatom bloom in Raunefjorden in western Norway. The culmination of the diatom bloom was followed by a peak in the concentration of bacteria and an increase in the concentration of heterotrophic flagellates, a pattern consistent with the concept of a food chain from photosynthetically produced organic material, through bacteria, to bacterivorous flagellates. The concentration of viruses varied through the spring bloom from 5 x 10 in the prebloom situation to a maximum of 1.3 x 10 viruses ml 1 week after the peak of the diatom bloom. Coinciding with the collapse in the diatom bloom, a succession of bacteria and viruses was observed in the mucous layer surrounding dead or senescent diatoms, with an estimated maximum of 23% of the total virus population attached to the diatoms. The dynamic behavior observed for the virus population rules out the possibility that it is dominated by inactive species, and the viruses are suggested to be active members of the microbial food web as agents causing lysis in parts of the bacterial population, diverting part of the bacterial production from the predatory food chain.

Enumeration and biomass estimation of planktonic bacteria and viruses by transmission electron microscopy.

Abstract: Bacteria and virus particles were harvested from water samples by ultracentrifugation directly onto Formvar-coated electron microscopy grids and counted in a transmission electron microscope. With this technique, we have counted and sized bacteria and viruses in marine water samples and during laboratory incubations. By X-ray microanalysis, we could determine the elemental composition and dry-matter content of individual bacteria. The dry weight/volume ratio for the bacteria was 600 fg of dry weight microns-3. The potassium content of the bacteria was normal compared with previous estimates from other bacterial assemblages; thus, this harvesting procedure did not disrupt the bacterial cells. Virus particles were, by an order of magnitude, more abundant than bacteria in marine coastal waters. During the first 5 to 7 days of incubation, the total number of viruses increased exponentially at a rate of 0.4 day-1 and thereafter declined. The high proliferation rate suggests that viral parasitism may affect mortality of bacteria in aquatic environments.

Comparison of phenotypic diversity and DNA heterogeneity in a population of soil bacteria.

Abstract: The phenotypic diversity of about 200 bacterial strains isolated from soil was compared with the genotypic diversity of the same population. The strains were phenotypically characterized by the API 20B test system. The results of these tests were subjected to cluster analysis, which revealed 41 biotypes at 80% similarity. The five dominating biotypes contained 43% of the strains. The phenotypic diversity as determined by the Shannon index, equitability, rarefaction, and cumulative differences was high, but indicated some dominant biotypes. The genetic diversity was measured by reassociation of mixtures of denatured DNA isolated from the bacterial strains (C0t plots). The observed genetic diversity was high. Reassociation of DNA from all bacterial strains together revealed that the population contained heterologous DNA equivalent to 20 totally different bacterial genomes (i.e., genomes that have no homology). This study showed that reassociation of DNA isolated from a collection of bacteria gave a good estimate of the diversity of the collection and that there was good agreement with different phenotypic diversity measures. The Shannon index in particular has features in common with the genetic diversity measure presented here.

Age at first birth, parity and risk of breast cancer: a meta-analysis of 8 studies from the Nordic countries.

Abstract: Several large epidemiological studies in the Nordic countries have failed to confirm an association between age at first birth and breast cancer independent of parity. To assess whether lack of power or heterogeneity between the countries could explain this, a meta-analysis was performed of 8 population-based studies (3 cohort and 5 case-control) of breast cancer and reproductive variables in the Nordic countries, including a total of 5,568 cases. It confirmed that low parity and late age at first birth are significant and independent determinants of breast-cancer risk. Nulliparity was assoclated with a 30% increase in risk compared with parous women, and for every 2 births, the risk was reduced by about 16%. There was a significant trend of increasing risk with increasing age at first birth, women giving first birth after the age of 35 years having a 40% increased risk compared to those with a first birth before the age of 20 years. Tests for heterogeneity between studies were not significant for any of the examined variables. In the absence of bias, this suggests that several individual Nordic studies may have had too little power to detect the weak effect of age at first birth observed in the meta-analysis.

Sex Determination in Daphnia Magna

Abstract: The factors inducing male offspring and the mechanism of sex-ratio adjust- ment were investigated in Daphnia magna, a cyclically parthenogenetic cladoceran (Crus- tacea). Laboratory experiments were conducted on individual animals living in flow-through chambers, to separate the effects of various density-dependent factors. Fluctuating food levels had no effects on offspring sex when starvation was not severe. Water from crowded populations of different Daphnia species contained substances that induced up to 43% male broods. The chemically mediated crowding effect was detectable under conditions repre- senting a low population density, implying that animals responded to their own metabolites. Daphnia species differed in their inducing effects, and in one case (water from D. pulex) strong male offspring induction was associated with growth inhibition. A short daylength was also demonstrated to induce male offspring effectively. Evidence was found to support a mechanism of sex-ratio regulation that implies a regular alternation of brood sex, resulting in a sex ratio close to 1/2, the expected optimum ratio. Even individual mothers adjusted the sex ratio of their offspring within a sequence of seven broods. No resting eggs were formed in the experiments, indicating that formation of male offspring and resting eggs are independently controlled, possibly by distinct sets of environmental cues.

Effect of Epidermal Growth Factor on Glioma Cell Growth, Migration, and Invasion in Vitro

Abstract: Effects of epidermal growth factor (EGF) and an antibody (Ab-528) reactive against the binding site for EGF on human EGF receptors were studied on multicellular tumor spheroids obtained from three human glioma cell lines with high (D-37 MG), medium (D-247 MG), and low (D-263 MG) levels of EGF receptor expression. The D-247 MG and D-263 MG spheroids grew slowly or not at all in the absence of EGF, while in the presence of EGF they were growth stimulated. Tumor cell migration, as measured by the spread of cells from spheroids on a plastic substratum, was increased by the addition of EGF for all three cell lines. Stimulation of migration could be blocked by a subsequent addition of Ab-528 to the medium at a concentration of 50 micrograms/ml. Invasiveness of glioma cell spheroids into fetal rat brain aggregates was related to EGF receptor expression; the two lines with medium to high receptor expression (D-247 MG and D-37 MG) were invasive, while the line with low EGF receptor expression (D-263 MG) was noninvasive, as assessed by an in vitro coculture assay. In the D-247 MG cell line, morphometry revealed EGF-enhanced invasiveness of the tumor cells. The addition of the Ab-528 to EGF-treated cocultures reduced invasion in both D-247 MG and D-37 MG cell lines. Antibody Ab-528 alone did not affect glioma cell growth or migration but did inhibit invasiveness. The present study suggests that, in brain tumors with an increased number of normal-sized Mr 170,000 EGF receptors, EGF or an EGF-like ligand such as transforming growth factor-alpha may selectively facilitate expansive tumor growth and tumor cell invasion. This effect may in part be blocked or retarded by specific antibodies to the EGF receptor.

Clonazepam and imipramine in the treatment of panic attacks: a double-blind comparison of efficacy and side effects.

Abstract: Data from 12 patients (in two control study groups) provide preliminary results of an ongoing double-blind comparison of clonazepam and imipramine in the treatment of panic disorder. In both treatment groups, the patients' global improvement was substantial over the first few weeks and persisted over the 6-month treatment period based on assessments by the therapist and the patient; side effects were mild. Faintness was slightly more prevalent among patients on clonazepam treatment but disappeared after the first few weeks. Mild, persistent tachycardia was reported among patients receiving imipramine. No tolerance emerged, and discontinuation was successful in 2 patients from each group after 6 months of treatment. Eight patients needed continued medication (25-50 mg/day of imipramine, 0.5-2.0 mg/day of clonazepam) to maintain substantial improvement. Findings confirm earlier reports from open studies that low doses of both drugs eliminate panic attacks (about 50 mg/day for imipramine and 1.5 mg/day for clonazepam).

A prospective, randomized study of three surgical techniques for treatment of acute ruptures of the anterior cruciate ligament

Abstract: Treatment of ACL tears is controversial. Recent reports on nonoperative treatment have shown poor results. Results after primary repair have deteriorated with time, leading to augmentation procedures that seem to have improved the results. However, there have been few prospective, randomized studies in this field. Our goal was to compare primary repair with a bone-patellar tendon-bone augmentation method and with a new method using the Kennedy Ligament Augmentation Device. One hundred fifty patients aged 16 to 50, all of whom had acute ACL tears, were randomized with the closed envelope method to one of three groups treated with open surgical methods. Fifty patients were treated with primary repair, 50 patients with patellar tendon augmentation, and 50 patients were augmented with the Kennedy Ligament Augmentation Device. All patients were operated on within 10 days of injury. The rehabilitation protocol was identical, consisting of a long leg cast for 2 weeks, followed by a brace with no weight-bearing and limited motion for 6 weeks. The patients were followed prospectively by one surgeon (LE) using the Lysholm functional score, Tegner activity level score, clinical evaluation and KT-1000 arthrometer at 6 months, 1, and 2 years. Three patients were lost to followup. There was no age or activity level difference between the groups. Sport activities led to 85% of the injuries, with skiing, soccer, and European handball representing 80% of injuries. All three groups reduced their activity level the 1st year. The repair group remained at the same level after 2 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Multicellular tumor spheroids from human gliomas maintained in organ culture.

Abstract: Tumor tissue from seven human gliomas was maintained in long-term agar overlay culture as multicellular organotypic spheroids Light microscopic and ultrastructural observation of the spheroids displayed morphological features similar to those of the original tumor tissue in vivo; in this respect they were different from spheroids obtained from permanent cell lines The spheroids contained preserved vessels, connective tissue, and macrophages, revealing a close resemblance to the conditions in the original tumor Flow cytometric deoxyribonucleic acid measurements of cells from the tumor spheroids and from biopsy material obtained directly from the operation revealed the same ploidy and the same amount of proliferating cells in the spheroids as in the original tumor Fluorescence microscopy using bromodeoxyuridine (BUdR) incorporation and anti-BUdR monoclonal antibody confirmed the proliferative potential of tumor cells in the spheroids Diameter measurements showed that the size of the spheroids from two of the tumors increased over time while in three other cases it decreased Spheroids from the remaining two tumors showed no change in size, even after 80 days in culture These growth data and the relatively high number of proliferating cells, as measured by flow cytometry, indicate that the degree of cell proliferation and cell loss from the spheroids are closely linked, as is the case for tumors in vivo The culture system presented provides a valuable alternative to propagation of human tumors in animals

Identification of nonlinear time series: First order characterization and order determination

Abstract: SUMMARY We study the possibility of identifying nonlinear time series using nonparametric estimates of the conditional mean and conditional variance. It is shown that most nonlinear models satisfy the assumptions needed to apply nonparametric asymptotic theory. Sampling variations of the conditional quantities are studied by simulation and explained by asymptotic arguments for a number of first-order nonlinear autoregressive processes. The conditional mean and variance can be used for identification purposes, but one must be aware of bias and misspecification effects. We also propose a criterion for determining the order of a general nonlinear model. The criterion is justified in parts by heuristics, but encouraging results are obtained from a limited set of simulation experiments. Several

Assessment of four ambulatory blood pressure monitors and measurements by clinicians versus intraarterial blood pressure at rest and during exercise

Abstract: The accuracy of 4 different ambulatory blood pressure (BP) monitors was assessed by comparing them to simultaneous intraarterial BP (contralateral brachial artery) during rest, isometric and dynamic (bicycle) exercise in 48 hypertensive patients undergoing invasive hemodynamic evaluation. The differences between the intraarterially determined BP and values obtained by the various monitors were then compared to differences between BP measured directly and by 2 clinicians using a standard mercury column in 10 additional hypertensive patients. The monitors studied were the Accutracker II (auscultatory with mandatory electrocardiographic gating), Colin ABPM 630 (auscultatory or oscillometric), Del Mar Pressurometer IV (auscultatory with optional electrocardiographic gating) and SpaceLabs 90202 (oscillometric). During rest, the differences between intraarterially and clinician-determined systolic and diastotic BP were 4 ± 8 and −4 ± 6 mm Hg, respectively. The Accutracker II and Colin ABPM 630 using the auscultatory method showed less disparity and closer limits of agreement (2 standard deviations of the mean difference) with intraarterial BP than the clinicians' measurements, whereas the other units showed similar or greater limits of agreement. During both isometric and dynamic exercise, mean BP differences between intraarterial and clinician determinations were similar to those at rest but the limits of agreement increased. The limits of agreement between intraarterial and monitor-derived BP also increased during exercise compared to differences observed at rest. The Accutracker II and Colin ABPM 630 using the auscultatory method had limits of agreement with intraarterial BP that were either similar to or less than the clinicians', whereas the Colin monitor using the oscillometric method and the Del Mar Pressurometer IV showed greater disparity. The SpaceLabs unit produced only error codes in 8 of 10 subjects during dynamic exercise. Thus, these data show that at rest, noninvasive ambulatory BP monitors are similar in accuracy to clinicians in BP determination but during exercise there are differences among the monitors that make some of them unsuitable for measurements while in motion.

Evidence for two-step deglaciation and its impact on North Atlantic deep-water circulation

Abstract: Oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35,000 years in the northeastern Atlantic. The results support the idea that the last deglaci­ation took place in two major steps1–4, and conflict with theories calling for a strong reduction in North Atlantic deep-water formation to explain the abrupt cooling of the Younger Dryas cold period5–7.

Vertical distribution and trophic interactions of zooplankton and fish in Masfjorden, Norway

Abstract: The distribution, biomass, and predator-prey relationships of the pelagic assemblage in Masfjorden, western Norway, was studied in January 1989. The pelagic biomass was dominated by particulate organic matter. Biomasses of copepods, macroplankton, and mesopelagic fishes were of the same order of magnitude, while the biomass of larger pelagic fishes were one order less. Predator-prey relationships seemed most important at intermediate and higher trophic levels. Two sound-scattering layers, consisting of adult Maurolicus muelleri (lower layer) and juvenile M. muelleri (upper layer) performed instantaneous lightdependent vertical migration. Vertical distributions are explained in terms of balancing food demands against predation risk.

Scanning Electron Microscopic Observations of Cell Population and Bacterial Contamination of Membranes Used for Guided Periodontal Tissue Regeneration in Humans

Abstract: Fourteen intrabony periodontal defects and six furcation defects (Class II) were treated by a flap procedure which included the use of a polytetrafluoroethylene membrane to allow guided tissue regeneration. After 4 to 6 weeks of healing, the membranes were retrieved and examined by scanning electron microscopy for the presence of adherent cells and other tissue elements. The cervical open pore-structured collar of the membrane, which in most cases had become partially exposed to the oral cavity, had a deposit of bacterial plaque. Bacterial Bacterial colonies and a scatter of single cells in some instances extended into the mid-third of the membrane. Fibroblast-like cells and, in some specimens, blood vessels and fibrous structures were seen in the mid-third and deep parts of the membrane. Generally, however, the occlusive portion of the membrane was characterized by a sparseness of adherent tissue elements. There did not seem to be a systematic difference in the nature and distribution of the adherent structures on the inner and outer surfaces of the membrane. The findings suggest that, in addition to preventing flap tissues from contacting the root surface, an important function of the membrane is to protect the integrity of the underlying blood clot by diverting mechanical stress acting on the flap during early stages of healing.

Postal survey on airborne occupational exposure and respiratory disorders in Norway: causes and consequences of non-response.

Abstract: STUDY OBJECTIVE--The aim was to examine causes for non-response in a community survey, and how non-response influences prevalence estimates of some exposure and disease variables, and associations between the variables. DESIGN--This was a cross sectional questionnaire study with two reminder letters. The questionnaire asked for information on smoking habits, occupational airborne exposure and respiratory disorders. SETTING--A random sample of 4992 subjects from the general population aged 15-70 years of Hordaland County, Norway. MAIN RESULTS--The overall response rate was 90%, with a 63% response to the initial letter. The response rates to the first and second reminder letters were 56% and 36% respectively. In 20% of the non-respondents an uncompleted questionnaire was returned with cause for non-response; in two thirds of these the cause for non-response was that the subject was not resident at the mailing address. A home visit to a random sample of 50 urban non-respondents provided further information on 29 subjects. A wrong address at the Central Population Registry and the subject9s feeling of lack of personal benefit from a postal survey were the major reasons for non-response. Smokers were late respondents and subjects with respiratory disorders tended to be early respondents. CONCLUSION--The main reasons for non-response were a wrong mailing address and a feeling of lack of personal benefit from responding. Using only the initial letter would have changed the estimated prevalence of smokers from 39% to 35%. Otherwise, the estimated prevalence of the exposure and disease variables as well as the associations between them were only slightly changed after including the respondents to the first and second reminder letters.

Morphological and behavioural development of halibut, Hippoglossus hippoglossus (L.) larvae

Abstract: Live yolk-sac halibut, Hippoglossus hippoglossus (L.) larvae from rearing experiments at Austevoll Aquaculture Station, Norway, were examined from hatching to past first feeding for developmental morphology and behaviour. The findings include development of the respiratory and circulatory organs, eye pigmentation, mouth formation, organs of the digestive system and the process of yolk absorption, as well as swimming speed and activity levels. A stomodeum is not present at hatching although drinking is possible through a pair of branchial pits which gradually develop into the operculum and gill basket. The mouth normally opens slowly, the gape being restricted by a transverse septum until bones are formed. The amount of time spent swimming varies from less than 15% of the observation period during the first 2 weeks after hatching to between 70 and 100% around the seventh week after hatching, when individual differences become more apparent. Larvae generally react with a burst of swimming when two come into contact. Speed and duration of swimming seems to be correlated with development of eye pigment, heart size and fin formation. The yolk-sac period is divided into four stages.

Extensional and compressional zones in slumps and slides in the Namurian of County Clare, Ireland

Abstract: Extensional and compressional zones in slumps and slides have been studied in a well-exposed Namurian (Carboniferous) base-of-slope and delta slope sedimentary succession in County Clare, Ireland. Extensional zones are in slumps dominantly characterized by single, downslope-dipping normal faults, while in slides they are characterized by normal, listric fault families. These faults sometimes show minor growth. Compressional zones in slumps are dominated by a single reverse fault with upslope-dip. They are only rarely characterized by imbricate fault fans. Compres­sional zones in slides fall into a tri-partite division of thick packages, thin packages and basal zones. Thick packages compare with tectonic imbricate zones, while thin packages are simpler and characterized by very shallow synthetic thrusts. Basal zones compare with blind imbricate fans. Lateral margins of both extensional and compressional zones in slumps and slides show transfer faults with transtensional, transpressional or purely strike-slip motion, depending on the width variability of the slide and slump scars. The similarity in structural style between soft-sediment deformational structures and deformation structures in lithified rocks shows that, on the basis of structural style alone, it is problematical to differentiate between these two groups of structures.

On the limited ability of superoxide to release iron from ferritin

Abstract: Reductive release of iron from ferritin may catalyze cytotoxic radical reactions like the Haber-Weiss reaction. The ability of ·O−2 to mobilize Fe(II) from ferritin was studied by using the xanthine/xanthine oxidase reaction, with and without superoxide dismutase, and with bathophenanthroline sulphonate as the chelator. Not more than one or two Fe(II)/ferritin molecules could be released by an ·O−2-dependent mechanism, even after repeated exposures of ferritin to bursts of ·O−2. The amount of releaseable iron depended on the size and the age of the iron core, but not on the iron content of the protein shell of ferritin which was manipulated by chelators and addition of FeCl3. The kinetic characteristics of the ·O−2 mediated iron release indicated the presence of a small pool of readily available iron at the surface of the core. The very limited ·O−2 dependent release of iron from ferritin is compatible with a protective role of ferritin against toxic iron-catalyzed reactions.

Postglacial history of alder (Alnus glutinosa (L.) Gaertn.) in the British Isles

Abstract: Data from 92 postglacial pollen sequences are used to map the spread and increase of alder (Alnus glutinosa) across the British Isles between 9000 and 5000 years ago. The spread is found to be patchy and erratic in space and time. Consideration of the habitat requirements and reproductive ecology of alder suggest that it spread within Britain and Ireland after about 10 000 yr BP, when suitable habitat for it was scarce. Alder spread across most of Britain and Ireland early in the postglacial but only increased in abundance as (i) suitable habitat became available through changing sea levels, hydroseral successions, and floodplain development, and as (ii) rare weather events produced the necessary conditions for reproduction. Alder is unique among British and Irish trees in its requirement for a suitable habitat isolated among expanses of unsuitable habitats. Because of this, maps of its postglacial population spread and increase do not show the spatial coherence of maps for other forest tree taxa.

Milk consumption and cancer incidence: a Norwegian prospective study.

Abstract: Relationships between milk intake and cancer incidence were investigated after 11 1/2 years of follow-up of 15,914 individuals. A diagnosis of cancer was made in a total of 1,422 individuals. No association was established with total cancer incidence, in analyses adjusted for sex, age and residential characteristics. However, a strong positive association with milk consumption was observed for cancers of the lymphatic organs (odds ratio 3.4 for greater than or equal to 2 glasses per day vs less than 1; 95% confidence interval 1.4-8.2). An inverse association was found for cancer of the bladder. Kidney cancer and cancers of the female reproductive organs (except the uterine cervix) showed weak positive associations with milk intake.