Archived 2hr Survival Images
This page links you to all the tritiated-thymidine injection groups that survived 2hrs after the injection. These images are best to examine the mitotic activity in germinal zones of the developing brain and (in younger specimens) spinal cord.
Methods: Several pregnant female rats were injected once between 8 and 9 a.m. with tritiated-thymidine beginning on E12, another on E13, and so on, until the last group was injected on E20. The females were killed 2 hours later with an overdose of pentobarbital, the embryos were removed, and either the whole body (E12-E17) or the heads (E18-E20) were immersed in Bouin’s fixative for 24 hours, then transferred to 10% neutral formalin. E12-E14 embryos were embedded in methacrylate, from E15 on, they were embedded in paraffin. Some embryos were cut coronally, while others were cut sagittally. One E15 embryo was cut in the horizontal plane. Serial 6µm slices were placed on microscopic slides. The deparaffinized slices were coated with liquid Kodak NTB3 photographic emulsion in a humid darkroom. The slides were placed in light-tight boxes and stored in a refrigerated room for a 3-month exposure period. Then the slides were developed in Kodak D-19 and the tissue was post-stained with hematoxylin alone or with hematoxylin and eosin. Methacrylate-embedded embryos were stained with toluidine blue. The E12, E13, and E14 embryos are only shown in the sagittal plane. Unfortunately, methacrylate interacts with the photographic emulsion to create excess reduced silver grains. Because of the excess noise in methacrylate specimens, we only show those in the sagittal plane. The heavily labeled cells can still be easily seen in spite of the background noise.
Links to each set of archived images–ALL IMAGES HAVE BEEN UPLOADED: