Comparison between brain paste and polymer [125I]standards for quantitative receptor autoradiography.

[125I]standards prepared from grey and white matter from rat brain have been compared to commercially available polymer-based standards using two types of radiation-sensitive film for use in quantitative receptor autoradiography. There was a linear relationship between the natural log of optical density and radioactivity (dpm/mm2) for both types of tissue standard exposed to Hyperfilm [3H] or betamax from 1-14 days. No difference between either the slopes or intercepts of these lines for each period of exposure was identified. There was also no significant difference between the slopes and intercepts of tissue-based standards and the lowest 5 activity levels of polymer standards. Over the complete range of ten radioactivity levels of polymer standards, the linear relationship was lost and a quadratic function was the best model for describing the relationship between 1n optical density and radioactivity. Moreover, a linear relationship between section thickness over the range frequently used in receptor studies (5-20 microns) was observed. These results suggest that the lower activity levels of polymer standards are comparable to tissue standards and can be used for quantitative receptor autoradiography.