Biomedical subjects
Publications and source records attributed to K Bergman.
The effect of motility on the competitive success of Rhizobium meliloti in nodule production was investigated. A motile strain formed more nodules than expected when mixed at various unfavorable ratios with either flagellated or nonflagellated nonmotile derivatives. We conclude that motility confers a selective advantage on rhizobia when competing with nonmotile strains.
Rhizobium meliloti exhibited behavior resembling that of other chemotactic bacteria. Nonflagellated, nonmotile but flagellated, and nonchemotactic mutants were isolated, and genetic mapping placed all three types of lesions within a small region of the R. Meliloti chromosome. Results from nodulation experiments performed with these mutants indicate that members of the three classes (Fla-, Mot-, and Che-) infect and produce as many nodules on alfalfa plants as does the wild-type strain.
Chemotaxis of the bacterium Escherichia coli and the planarian Dugesia dorotocephala toward a variety of substances impregnated in sustained-release polymers has been demonstrated. Tests were carried out in soft agar and in aqueous medium with highly consistent results. The simplicity of this method may make it particularly useful for rapid qualitative screening of new wild-type and mutant strains of bacteria for chemotaxis toward nonmetabolites. The cost, ease of fabrication, and the facility with which they can be utilized in test systems suggest that these sustained-release vehicles will provide a new and general method of creating concentration gradients to study chemotaxis.
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Whole-body autoradiography has been used to study the distribution and fate of 14C-labeled benzene, toluene, xylene, styrene, methylene chloride, chloroform, carbon tetrachloride and trichloroethylene in mice after inhalational exposure. Total radioactivity, including the volatile part of the solvents were registered by autoradiography of dried, evaporated tape-fastened sections. In addition, dried, evaporated tape-fastened sections were extracted with water, trichloroacetic acid and a series of organic solvents and autoradiographed to register organs where metabolites were firmly bound. In another facet of the study, the quantitative elimination of the solvents and their metabolites via various routes was investigated. The expiration of unchanged solvents was subject to mathematical and computerized compartmental pharmacokinetic analysis. All solvents were rapidly taken up in fatty and nervous tissues where they were retained for different periods of time largely dependent on their fat solubility. Unexpectedly long retention times were noted for the chlorinated solvents, particularly for chloroforn, which showed a specific long-term retention in the cerebellum, meninges and spinal nerves, indicating interactions with specific nervous tissue receptors. Solvent metabolites appeared rapidly in several organs, mainly the liver and kidney, and were excreted both via urine and bile. Toluene and xylene metabolites were completely extractable whereas firmly bound metabolites were registered after inhalation of benzene, styrene and all chlorinated solvents, notably in the liver and kidney but also in the bronchi of the lung. Three-compartment pharmacokinetics were observed for the majority of the solvents selected for study although a two-compartment model was found to fit the elimination rate curves for styrene, methylene chloride and chloroform in the exhaled air. The fat solubility of the solvents was found to influence their pharmacokinetics since lower rate constants were generally obtained for the expiration of more fat soluble solvents.
Results are reported of measurements around 1974 on a thousand patient at 13 Swedish hospitals, and additionally at several photofluorographic and dental installations. Energy imparted as well as doses to the thyroid, breast, lung, bone marrow, ovary and testis have been calculated for many types of examination. Collective doses have been calculated and risk estimates made. The energy imparted corresponds to an annual mean body dose to the Swedish population of about 1 mGy (100 mrad), and the genetically significant dose was about the same as the 1955 total of 0.4 mGy; in both cases the uncertainty of the estimate is about +/- 50%. The possibility of dose reduction by a factor of 2 or more using available techniques is demonstrated. The risk of future serious injury is estimated to 0.0002 cases per joule of energy imparted to the patient.
A structural and biochemical study is presented concerning the agglutination of gametic flagella, the initial step in the mating reaction of Chlamydomonas reinhardtii. An alteration in the distribution of the intramembranous particles revealed by freeze-fracturing of flagella membranes is shown to accompany gametic differentiation in both mating types. The isolation and electrophoretic analysis of flagellar membranes and mastigonemes are reported; no electrophoretic differences can be detected when the membrane or mastigoneme glycoproteins from vegative and gametic cells are compared, nor when glycoproteins from the two mating types are compared, and no novel polypeptides are present in gametic preparations. The membrane vesicles, after they are freed of mastigonemes by sedimentation through a discontinuous sucrose gradient, are extremely active as an isoagglutinin, indicating a direct involvement of the membrane in the mating reaction.
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This extension study was conducted to (1) identify which characteristics of the effective clinical teacher are deemed most important by nursing students and faculty; (2) determine whether previous findings remain valid (are transferable); and (3) investigate whether the perception of effective teaching behavior shifts as students advance toward graduation. The research tool, a two-part questionnaire developed by Brown, was circulated among students and instructors at a university college of nursing in southwestern Ohio. The first section listed 20 characteristics of teachers to be rated, using a Likert-type scale, from "of most importance" to "of no importance." The second section required subjects to select and rank in order the five most important characteristics from the list of 20. Descriptive analysis was applied to the data, and findings were compared with those of Brown. The study suggests that both faculty and students favor articulate, knowledgeable clinical instructors who are "objective and fair" in student evaluation. There is a high degree of similarity between the responses of faculty and students, but differences emerge. Both value skills involving the student-faculty relationship over skills centering on the professional or personal attributes of the instructor. However, faculty respondents appear to place a higher value on instructor interest in patients, and students are more concerned with communication-related attributes. Faculty members place a greater value on showing interest in patients than do students. The results, when compared with Brown's findings, appear largely transferable, but significant differences appear. For example, faculty members ranked characteristics dealing with the clinical instructor's relationship with students to be more important than those dealing with professional competence--the opposite of Brown's results. This study shows the need for nursing institutions to implement programs to foster and to promote uniformly identified effective clinical teaching characteristics. Given the special challenges of clinical nursing education, graduate programs should also seek to teach the skills identified as most effective, and persons with the skills perceived as effective should be urged to enter clinical instruction and should be rewarded for success in this important area.
The embryotoxic and teratogenic potential of monomethylhydrazine (MMH), a toxic component of the widely consumed false morel (Gyromitra esculenta), was studied in rat. Groups of pregnant Sprague-Dawley rats received MMH as a constant i.v. infusion via implanted osmotic minipumps (1.2, 3.0, 4.2, 6.0, 9.0 or 13.2 mg MMH/kg bw/day) on days 6-13 of pregnancy, or as a single intragastric bolus (1 mg MMH/kg/bw or 5 mg MMH/kg/bw) on day 6 of pregnancy. Controls received corresponding amounts of saline. The average maternal serum concentrations, measured during the infusion treatment with a sensitive HPLC method, ranged from 0.072 micrograms MMH/ml (lowest dose) to 0.60 microgram MMH/ml (highest dose). The average serum levels measured 45 min after the intragastric application (peak levels) were 0.28 microgram MMH/ml and 1.6 microgram MMH/ml, respectively. Serum concentrations of MMH corresponding to those measured in the lower dose groups in this study were seen in pilot studies after a single mushroom meal in human volunteers. A dose-dependent, statistically significant increase in the number of resorptions was seen in all but the lowest dose group after the infusion of MMH. In addition, except for the two lowest doses, there was a dramatic, dose-dependent decrease in the pregnancy rate as compared to controls, with no pregnancies occurring at the two highest dose level groups. The decreased pregnancy rate was probably due to preimplantation loss which was shown to occur after a single intragastric bolus dose of MMH (5 mg/kg bw).(ABSTRACT TRUNCATED AT 250 WORDS)
Female C3H mice were fed a standard pellet diet (containing 0.2 ppm Se and 30 ppm vit. E) or the same diet supplemented with 0.8 ppm (low dose) or 3.4 ppm (high dose) of selenomethionine for 10 weeks. After mating with males receiving the standard diet the mice were subjected, on the 9th day of pregnancy, to whole body roentgen irradiation of 1.75 Gy. On day 18 of gestation the frequency of resorptions, mortality and the incidence of fetal malformations were studied. Supplementation with Se-methionine resulted in a significant but dose-independent decrease (p less than 0.005) of the number of malformed fetuses from 62 per cent in the irradiated controls to 47 per cent in the low Se-group and high Se-group, respectively. In addition, the number of total malformations as well as fetal resorptions were significantly decreased in a dose-independent manner in the supplemented groups. The decrease in fetal malformations occurred proportionally for all the major malformations observed, i.e. short or kinked tail, rib and vertebral malformations, coloboma and deformation of retina and iris. Glutathione peroxidase activity in whole blood of Se-methionine fed mice was significantly increased. Thus, Se-rich diet may result in scavenaging of radiation-induced hydroperoxides.
Selenium (Se) compounds have shown an inhibitory effect on chemically induced tumours in several laboratory models and there is an inverse epidemiological relationship between Se status and certain types of cancer. Little is known about the influence of Se on the development of stomach cancer. Three different forms of dietary Se, selenomethionine, sodium selenite, and high-selenium yeast were investigated as possible inhibitors of benzo(a)pyrene-induced forestomach tumours in mice. The effects of sodium selenite in combination with vitamin E, and of Se-deficiency were also studied. None of the dietary modifications had any effect on tumour incidence or number. Marked elevations of whole-blood glutathione peroxidase (GSH-Px) activities were observed in animals supplemented with all Se-compounds. High-selenium yeast caused the largest increase of GSH-Px activity followed by sodium selenite and selenomethionine. The results indicate that the inhibitory effect of Se on carcinogenesis may be specific with respect to organ site or tumour cell examined.