Scintillator distribution in high-speed autoradiography.

Durie and Salmon (1) describe the technique of impregnation ofphotographic emulsion with liquid scintillator which allows rapid autoradiographic labeling. In attempting to use this method, we found that freezing the impregnated slides without special conditions led to the formation of large ice crystals and irregularities in the frozen scintillator. They appeared even when the dioxane did not contain either 2,5-diphenyloxazole or I1,4-bis-2-(4-methyl-5-phenyloxazolyl)-benzene. It could be seen clearly with the ultraviolet lamp (UVSL58, Product Inc., San Gabriel, California). Crystalline pictures of the scintillator luminescence show that molecules of the fluorescent substance are distributed nonhomogeneously over the biological sample. Hence, distorted distribution-of silver grains in developed emulsion layers seems to be inevitable. A crystalline structure can also be seen under light microscopy. In order to circumvent these difficulties, we attempted to obtain uniform coating of the slides with the scintillator by quick deep freezing. The slides were dipped in horizontal position into the precooled isopentane so that the surface ofthe slide containing the biological sample and the impregnated emulsion remained free. Isopentane was cooled by liquid nitrogen. Rapid deep freezing of the scintillator can be obtained also by spraying the substance on the previously frozen slides, as above. Examination with an ultraviolet lamp and light microscope of the slices frozen by described techniques shows that crystals are not formed and fluorescent molecules are distributed in a homogeneous way. We think that the suggested system of rapid freezing can contribute to more correct readings of autoradiograms prepared by the high-speed scintillation autoradiography technique. L. GOLDGEFTER, V. TODER Department ofAnatomy and Anthropology and Department of Embryology and Teratology, Tel Aviv University, Tel Aviv, Israel