Combined Autoradiography and Electron Microscopy of Thin Sections of Intestinal Epithelial Cells of the Mouse Labeled with H3-thymidine

Recent developments in au toradiography leading to the use of tr i t iated compounds in the study of biosynthetic processes have provided a basic method for accurate intracel lular localization of such labeled substances (1). The high resolution obta ined by using such compounds is a t t r ibuted to the short pa th of the beta rays emit ted by tr i t ium, 50 per cent of which are stopped in less than 1 # of tissue. Pa th distances of such magnitude could probably be obta ined with higher energy particles in thin sections covered with thin emulsion. Hence, technics of au torad iography should be seriously considered for more general appl icat ion in electron microscopy. Limitat ions in resolution imposed by the emulsion thickness and by the relatively large size of silver grains preclude the possibility of localization of labeled compounds at the molecular or even macromolecular level. But the possibility of observing differences in fine structure between cells or cell components which were, and were not, incorporating labeled compounds at the t ime of fixation is real and is the main justification for the application of the technics reported here. Autoradiographs of whole liver cell nuclei (2) labeled with cobalt-60, of radioact ive dust particles (3), and of sections of t r i t ium-labeled tissues (4) have been studied in the electron microscope. This report presents addi t ional evidence tha t au toradiographic technics employing H3-thymidine can be appl ied to thin sections for study in the electron microscope.