SENSITIVITY IN ELECTRON MICROSCOPE AUTORADIOGRAPHY FOR ¹²⁵I

Abstract

Sensitivity in electron microscope autoradiography was determined for 125!. Values are given using Ilford L4 and Kodak NTE emulsions combined with different developers. The extent of self-absorption as a function of section thickness and heavy metal staining and the effect of radiation dose (dose dependence) were assessed. It was found that the overall efficiency for 125! was better than that for tritium and that, as is the case with tritium, there is a distinct "dose dependence" especially when Microdol X is the developer. Selfabsorption studies indicate that self-absorption is increased by about 15% when the specimen thickness is increased from 300 to 1000 A. An increase of under 15% is also introduced by heavy metal staining of sections in this thickness range.

Resolution in electron microscope autoradiography. III. Iodine-125, the effect of heavy metal staining, and a reassessment of critical parameters.

“…Doing so entails a loss in grain yield and no significant gain in resolution. A fine-grained emulsion like Kodak NTE2 gains 38% in resolution and is recommended since specific activities with 1251 are high as is sensitivity (6). As shown in this study, resolution of ~500 A is thereby attainable-the best yet for EM autoradiography.…”

“…The albumin was applied with a medicine dropper onto a slide held horizontally and was then drained vertically. This procedure was similar to that used for making the sensitivity specimen described previously (6). Then, to render the film insoluble in water, it was exposed to paraformaldehyde vapor for 10 min.…”

“…We therefore call this specimen the "plastic resolution specimen." RESOLUTION IN FIXED AND STAINED TIS-SUE: The calibration specimen to test the effect of heavy metal staining on resolution was a modification of the one devised to test its effect on sensitivity (6,17). Dorsal root ganglia from the newt were fixed in OsO4 (1% in phosphate buffer for 1 h) and block-stained with uranium at 600C (12).…”

“…This was early recognized by Kayes et al (11) in 1962. However, although some calibration studies for both sensitivity and resolution have been performed using this isotope (6,10), the resolution attainable with this isotope under varying experimental conditions has not yet been systematically assessed. In the present study we have adapted previous calibration procedures used for tritium and ~4C (2,7,20,22) to obtain resolution values for mzsI as a function of section thickness, photographic emulsions, developing procedures, and heayy metal staining as employed in Em autoradiography.…”

Density and distribution of α-bungarotoxin-binding sites in postsynaptic structures of regenerated rat skeletal muscle

“…The determination of grain density (grains/micrometer2) and of the length of primary and secondary clefts and the thickened postsynaptic membrane were determined by previously published morphometric procedures (15,16). Histograms of the grain distribution in motor endplates were constructed for the various control and experimental groups.…”