Silver grains

Reflection contrast Reflection-imaging microscopy Field ion microscopy Quantification in gap between light and em microscopies Useful for imaging highly reflective particles such as silver grains in autoradiographs Atomic structure of crystals Immunoelectron Localization of cellular antigens... 

Table 5 illustrates the effects of emulsion thickness on resolution as indicated by HD (distance from the line within which 50% of all the silver grains from it lie). The data indicate that resolution is improved as emulsion thickness is decreased. If the emulsion thickness exceeds 2 pm, an insignificant quantity of (3-particles (see radioisotopes) will reach the emulsion from most biological specimens. Some factors which influence emulsion thickness include dilution of the emulsion, temperature of the emulsion, temperature and wetness of the slide as well as the temperature and humidity during drying. The reader is referred to Rogers (7) for thorough discussions of each. 

Stemam U. Loss of silver grains from radioautographs stained by gallocyanin-chrome alum. Stain Technol 1962 37 231-234. 

Robertson GB, Rogers AW. Loss of silver grains from completed autoradiographs. JMicrosc 1979 117 301-303. 

The reader is referred to Evans and Callow (3) for a discussion of efficiency, i.e., the number of silver grains in the developed emulsion relative to the number of disintegrations occurring in the specimen during exposure. These authors present data representing estimates of efficiency values for tritium in EM autoradiographs. 

EM radioautography possesses certain limitations. For example, the observation that silver grains representing decay of a [3H] -labeled compound over an organelle may or may not mean that the compound was incorporated intact. Concomitant biochemistry is required to determine... 

Cellular autoradiography techniques using radioactive nucleic acid probes have several features in common with nucleic acid immunocytochemistry. The method is based on the hybridization of radioactive probes to cellular targets and the subsequent exposure of photographic emulsion, which, when developed, reveals blackened (exposed) silver grains close to the site of hybridiza-hon. Hence, cellular autoradiography techniques permit excellent specihcity and localizahon of the hybridized probe—to 1 qm when tritium is the label used in the autoradiography-based method (9). 

Mammalian cells in culture are exposed to the test substance. Established cell lines are treated both with and without metabolic activation. Cells are incubated for an appropriate length of time, then rinsed, fixed, and dried. Slides are developed, stained, and exposed silver grains are counted. The endpoint of UDS is measured by determining the uptake of labeled nucleosides in cells that are not undergoing scheduled (S-phase) DNA synthesis. The most widely used technique is the determination of the uptake of H-TdR by autoradiography. Primary cultures (e.g., rat hepatocytes), human lymphocytes, or established cell lines (e.g., human diploid fibroblasts) may be used in the assay. Multiple concentrations of the test substance over a range adequate to define the response, should be used. 

Fig. 5. Electron micrograph of two silver grains obtained by developing silver bromide grains in a distortionless hydroquinone developer.

Figure 6. Incorporation of tritiated phenylalanine into the compound middle lamella lignin and the secondary wall lignin determined by counting the silver grains. Symbols are as follows 0, compound middle lamella 0> secondary wall.

Figure 4. Distribution of silver grains in microautoradiograms of differentiating xylem of pine administered with precursors of lignin and hemicellu-lose.

Figure 5. Carbonyl group labeling. Application of the TAg sequence. 5A Control = TAg on sound wood. 5B silver grain deposits correspond to the carbonyl groups created by the fungus. (ML + PW = middle lamella + primary wall Si and S2 = outer and middle layers of the secondary wall, respectively.)...

Person 1 Calcnlate the self-diffusivity in polycrystalline silver (grain boundary diffusion), Dgb, at 500°C in m /s. What is the activation energy for this process in kJ/mol ... 

In cultured mammalian cells, acrylonitrile induced DNA strand breakage, gene mutation, sister chromatid exchanges and chromosomal aberrations, but not aneuploidy or unscheduled DNA synthesis in rat hepatocytes, at least if the silver grain counting method was used. [Studies using the less reliable scintillation counting method have not been summarized.] Cell transformation was induced in several test systems and gap-junctional intercellular communication was inhibited in one study with Chinese hamster V79 cells. 

To allow a clear-cut distinction between the two labeled antigens after silver enhancement, the final size of the developed silver grains should be rather homogeneous and accurately predictable. The following parameters influence size, variation in size, and shape of the final gram-... 

Place a few drops of the silver solution on each slide, and monitor under light microscope. Silver grains take 5-10 min to develop. 

Suissa M. 1983. Spectrophotometric quantitation of silver grains eluted from autoradiograms. Anal Biochem 133 511-514. 

The color development of silver grains in IGSS has been used to convert the black silver signal to red, yellow, or blue-green (38). The method is a histochemical application of the chemical reactions more traditionally used in color photography. 

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