Methacrylate Brain Map Sets
QUICK LINKS TO ARCHIVED FILES
Because we do not want to delay worldwide access, we are setting up various ARCHIVED FOLDERS of our histological library. The images are high resolution jpeg files that can be downloaded and opened with a variety of image viewers. Zooming up to the 100% magnification level will reveal cellular details. Because methacrylate embedding preserves superior histological detail, viewing these images shows amazing clarity of histological structure. All images are presented without any labels to identify structures. We will select images from each specimen at a later time and label them. Please go to the NAVIGATION PAGE to view the image set of a selected specimen.
THE METHACRYLATE EMBEDDING TECHNIQUE
Beginning in the mid-1970s, the Laboratory of Developmental Neurobiology searched for a method to improve the histological preservation of developing brains in embryonic rats. We wanted a method that would enable us to see entire rat embryos in a single tissue block. About that same time, methyl-methacrylate embedding was being developed for histological use. The two major advantages of methacrylate embedding are (1) soft tissue is preserved with excellent detail, and (2) there is little shrinkage. Velde et al., (Histopathology, 1977, 1:319-330) estimates that shrinkage is around 2%, compared to the 10-40% shrinkage in paraffin. The chief disadvantage of methacrylate embedding is the heat generated during polymerization can cause histological distortions. To combat the heat generation problems, we carried out the final embedding step in a refrigerated room and used thick aluminum molds to surround the blocks of polymerizing methacrylate.
The embryos were embedded lying with their left sides down. They could be seen inside the translucent blocks. We sanded and polished the blocks in different orientations so that the embryos could be cut in the three histological planes: SAGITTAL (longitudinal slices parallel to the midline), CORONAL (vertical slices perpendicular to the midline from front to back), and HORIZONTAL (crosswise slices perpendicular to the midline from top to bottom). E11 through E22 embryos were embedded and cut in the three planes. The very young specimens (E10 and E10.5) were embedded in situ in the uterine enlargement. These were cut longitudinally and transversely.
The blocks were cut in 3µm sections on an ultramicrotome with steel knives. One of the tricks we found most helpful was the face of the block had to be briefly touched with a very slightly moist cloth before each section was cut. That procedure helped to eliminate chatter of thick and thin ridges in slices of blocks that had become too dry. On the other hand, too much moisture could cause problems of uneven slicing. After much practice, we had histologists who were able to find the happy medium. Libby Craft, Sarah Frasier, Kim Sandefur, Gene Eastland, and Yung Sook-Yu all participated in preparing the best specimens.
It took many, many years to get good specimens for each age in the three planes. The final result is a complete set of methacrylate embedded embryos with excellent preservation of the delicate histological features that exist during development. The Aperio Scanscope allows these fine details to be presented in all their spectacular beauty. We are happy to share them with you.