An experimental study on the morphogenesis of spina bifida

This investigation was performed to study the morphogenesis of caudal meningomyeloschisis or spina bifida aperta during neurulation. Pregnant rats were treated wih trypan blue to induce these defects in the closure of the neural walls. Maternal serum was studied to determine trypan blue levels. Both control and treated embryos were examined grossly, at cellular and subcellular level on days 10 through 13 of gestation. Trypan blue was distributed throughout the maternal tissues. There existed a maternal blood-brain barrier and a barrier at the level of the visceral yolk sac and embryonic gut preventing passage of the dye through these entodermal structures. The interstitial space in the paraxial mesenchyme was considerably increased in day 10 treated embryos (6--7 somites) but cellular and ultrastructural changes were not seen. This accumulation of intercellular fluid was only seen in the restricted area of the mesoderm above the invaginating intra-embryonic entoderm. On day 11 the closure of the neural walls was completed in control embryos. In the treated embryos of the similar stages a blister which contained embryonic blood cells had replaced the interstitial mesenchymal fluid. This structural disturbance in the non-segmented mesenchyme interfered primarily with the neurulation and resulted in caudal meningomyeloschisis (spina bifida aperta). Trypan blue was thought to interfere with the function of the extra-embryonic membranes and the primitive gut. The results of this study supported the hypothesis of indirect teratogenic effect upon the embryo.