Membrane specializations in the form of regular membrane-to-membrane attachment sites in Paramecium. A correlated freeze-etching and ultrathin-sectioning analysis.
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Cell Membrane↗
Biomedical subjects
L Bachmann
Publications and source records attributed to L Bachmann.
Freeze etching of cells without cryoprotectants.
The technique of spray-freeze etching was applied to unicellular organisms. The superior freezing rates obtainable with this method gave excellent cryofixation on Chlorella, Euglena, and spermatozoa without the use of antifreeze agents, and cell damage due to ice crystal formation was never observed. In many instances the resultant morphology differed significantly from that obtained from glycerol-treated, freeze-etched cells. Furthermore, viability studies of spray-frozen Chlorella compared favorably with cells frozen by other methods.
Animals↗
Improved cryofixation applicable to freeze etching.
Freeze etching of solute model systems (e.g., glycerol or ferritin solutions) demonstrates that cryofixation can introduce serious artifacts due to the segregation of the dissolved or dispersed material from the solvent. Since, in principle, this problem can be reduced by increasing the cooling rate, a new technique has been developed which combines spray freezing with freeze etching. This spray-freeze-etching is applied by first spraying the specimen into a liquid cryomedium. The frozen droplets are then "glued" together with butylbenzene to form a regular freeze-etch specimen, while the temperature of the sample is kept at -85 degrees C. The results obtained by spray-freeze-etching are far superior to those obtained by standard freezing. Our results, using 5% glycerol as a test specimen, are equivalent to those obtained by the high-pressure method (1). The reduction of segregation during freezing makes freeze etching a method applicable for the investigation of solute systems. Furthermore, the study of unicellular organisms or cellular fractions by freeze etching without the use of antifreeze is made possible.
Freeze Etching↗
[Improved resolution in freeze-etching].
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Chemical Phenomena↗
Resolution in electron microscope radioautography.
An analysis of grain distributions around a radioactive line source (consisting of polystyrene-(3)H) showed that the shape of the distribution was independent of the factors that influence resolution, i.e. section and emulsion thickness, silver halide crystal, and developed grain size. These factors did effect the spread of the distribution, however, and thus the distance from the line source within which 50% of the total developed grains fell. We called this distance "half distance" (HD) and determined it for a variety of specimens. When grain distributions were normalized in units of HD, one could plot universal grain distributions for specimens with radioactive sources of various shapes. The use of HD and the universal curves in interpreting radioautograms is discussed.
Autoradiography↗
[Resolving power of electron microscope autoradiography].
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Autoradiography↗
Absolute sensitivity of electron microscope radioautography.
A calibration method is described for measuring absolute radioautographic sensitivities under various experimental conditions. Sensitivities to (3)H and (35)S radiation, i.e. ratio of developed grains to radioactive decays in the specimen, were determined with Ilford L4 and Kodak NTE emulsions. The highest values obtained in monolayers of emulsion were (1/8) for (3)H and 1/21 for (35)S. The influence of various experimental parameters on sensitivity is described, and the possibilities for quantitative electron microscope radioautography are discussed.
Autoradiography↗
Feasibility of obtaining sexual risk and STD history in the context of a drinking drivers' program.
OBJECTIVES: This study was designed (a) to assess the feasibility of obtaining data about sexually transmitted diseases and sexual risk behavior in an alternative-to-incarceration program for convicted drinking drivers and (b) to determine whether asking health history and sexual risk questions using an anonymous questionnaire, anonymous interviews, or confidential interviews affected the willingness of people to participate. METHODS: The same survey instrument was used across three data collection modes to collect information on sexually transmitted diseases and sexual risk behavior. RESULTS: Overall, there were no differences across modes in self-reports of STDs and details of sexual history. Although the difference in refusal rates between the anonymous questionnaire and the anonymous interview was not significant, the refusal rate for the anonymous questionnaire was significantly higher than the rate for the confidential interview. Those answering the self-administered questionnaire were more likely than those receiving face-to-face interviews to refuse to answer questions about having sex while high and condom use. CONCLUSIONS: A drinking driver intervention program may be an appropriate site for health screenings and prevention activities for an at-risk population.
Adult↗