The Archived E21 Survival Series
This page links you to all the tritiated-thymidine injection groups that survived to Embryonic day (E) 21. 11 to 14 different levels were chosen from the left half of one coronally-sliced brain in each injection group, beginning with the olfactory bulb as Level 1. The remaining Levels are from progressively more posterior parts of the brain. The last Level is from the medulla or cervical spinal cord. 5 different levels of a sagittally-sliced brain in each injection group are also presented. There are 2 images shown for each Level, one of the brain in the head and another of the brain only. All images are presented without any labels to identify structures–we are working on adding that information at a later date.
With the exception of the forebrain and cerebellum, E21 brain structures have a very similar appearance to the mature brain. The E21 survival series is excellent for examining the time of origin of most of the neuronal populations in the midbrain tegmentum, pons, and medulla. This group is the only one that includes injections on E11+12, which makes it excellent to view the heavy label in some of the earliest generated neurons in the brain. This particular set of brains was never used by us in a publication–so we are sharing it with everybody who may wish to use it in the future. There is a wealth of information in these images for those who are willing to spend some time on analysis.
Methods: Several pregnant female rats were injected on 2 consecutive days with tritiated-thymidine beginning on E11+12, another on E13+14, and so on, until the last one was injected on E17+18. The females were killed on the morning of E21 with an overdose of pentobarbital, the embryos were removed, decapitated, and the heads were immersed in Bouin’s fixative for 24 hours, then transferred to 10% neutral formalin. Before embedding in paraffin, the heads were cut lengthwise in the midline sagittal plane. The left half of each head was sectioned coronally, while the remaining half was sectioned sagittally. 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.
Links to each set of archived images–ALL IMAGES HAVE BEEN UPLOADED: