Immunocytochemical identification of chromaffin cells. A. Fluorescence image of cells labeled with anti-TH antibodies (total population); B. Immunostaining with anti-PNMT antibodies (adrenergic cells); C. Pseudocolor image of PNMT/TH immunofluorescence ratio (labeling index) and corresponding scale (right). Yellow corresponds to an index of ~98, the center of the mis-identification region (84–112) indicated by the black box on the scale; D. Frequency distribution histogram for all cells analyzed in this study (number of cells vs. labeling index, measured as the averaged index over the region covered by the cell). Cells with a labeling index above the upper threshold (toward red) were considered PNMT+ (adrenergic) cells. Conversely, cells with an index below the lower threshold were considered TH+/PNMT- (noradrenergic) cells. Controls without primary antibodies showed a very faint, almost indiscernible fluorescence, in photographs taken using the same exposure times. Scale bar = 50 μm.