RADIOIMAGERS AS AN ALTERNATIVE TO FILM AUTORADIOGRAPHY FOR IN-SITU QUANTITATIVE-ANALYSIS OF I-125 LIGAND-RECEPTOR BINDING AND PHARMACOLOGICAL STUDIES

Three radioimagers, the mu-imager, the beta-imager and the phosphorima ger, were tested as alternatives to quantitative autoradiography on fi lm for receptor imaging and pharmacological in situ quantitative analy sis. Two iodinated ligands I-125-interleukin-1 alpha and I-125-gonadot ropin releasing hormone agonist, were used for receptor characterizati on in mouse brain and pituitary sections. Due to the high number of th e agonist receptors in rat pituitary gland, this tissue was used to co mpare measurements obtained from digital autoradiograms with classical gamma detector determination. This permits the evaluation of radioima ger efficiency and absolute quantification. Radioimagers represent an improvement in terms of time of image acquisition. All the radioimager s are more sensitive than film for the detection of low levels of radi oactivity. The spatial resolution provided by the mu-imager compares f avourably with that obtained on film autoradiograms while digital auto radiograms from the phosphorimager and beta-imager did not show precis e definition under our experimental conditions. Superimposition of his tological structures from the stained sections with radiolabelled area s in the autoradiograms remains, at this time, the unique advantage of film. In conclusion, radioimagers represent an alternative to autorad iography on film or emulsion for in situ quantitative studies on tissu e sections. They combine precise imaging for in situ binding studies w ith easy and direct access to counts in cpm. The improvement in radioi maging technology has, therefore, brought in situ analysis of iodinate d ligand binding to the level of accuracy that is obtained with classi cal detectors of radioactivity.