Correlative light and electron microscopy on the same cells of the adrenal gland of the frog, Rana nigromaculata, fixed in glutaraldehyde followed by osmium tetroxide, was done using the adjacent Epon embedded sections.
Electron microscope observation revealed three different types of granule-filled secretory cells; the noradrenaline-storing cells (NA cells) filled with intensely dense and varying shaped granules, the adrenaline-storing cells (A cells) filled with relatively less dense granules and the summer cells (STILLING, 1898) containing very large, round or polygonal granules (0.2-1.3μ in diameter).
Light microscopically, an essential difference could be observed in the affinity to ammoniacal silver solution between NA and A cells. It was clarified that the granules of NA cells stained in black and were clearly distinguishable from the yellow- or brown-stained granules in both A cells and summer cells. This silver method can be applied for the light microscopic identification of the NA cells in the Epon-embedded sections. Furthermore, after immersing the thick sections in toluidine blue or methylene blue, the granules of NA cells showed much stronger affinity to both dyes than those of A cells and became dark blue and occasionally stained greenish blue in methylene blue, while the summer cells became blue and the granules of the A cells stained light blue.