Abstract
1. Wistar rats were treated with a single intraperitoneal injection of trypan blue solution on day 8 of pregnancy. Embryos and fetuses were removed surgically from mothers on days 10, 11, 12, 13, 14, 15, 17, and 20. After gross observations, fetuses were fixed with Bouin's solution for microscopic observations. 2. Embryonic mortality increased from day 10 to 13, and frequency of myeloschisis manifested declined gradually from day 10 to 13. Thereafter, both mortality and frequency of myeloschisis showed no difference among groups examined from days 13 to 20, respectively. 3. Cystic myeloschisis observed in the day 10-embryo appeared to be myelocystocele, and the cyst was filled with blood or fluid. This blood or fluid was gradually resorbed as the developmental stage advanced. Meanwhile, degenerative changes on the surface of the exposed neural tissue gradually exceeded both the development and differentiation of the involved region. Finally, on day 20, cystic myeloschisis was observed as spina bifida aperta. 4. Non-cystic myeloschisis was found in the embryos on day 11 and 12. Morphogenetic process of this type was different from that described above in the early stages of development. After day 13, there was no difference between the two types of myeloschisis in their external appearance. 5. The morphogenetic process of myeloschisis in the rat fetus due to trypan blue is not simple. Although the morphological features seemed to be similar when obseved in the later stages, two different processes were found in the earlier stages of development.
