Anencephaly and spina bifida are the two most common neural tube defects (NTDs) that occur in humans. They cause considerable fetal wastage and neonatal morbidity and mortality. Numerous animal models have been discovered and have been used to study these malformations. We used the scanning electron microscope (SEM) to compare the development of embryonic stages of spina bifida and anencephaly. Pregnant 180 g Sprague-Dawley rats were given either a 1 ml subcutaneous injection of 1% trypan blue on gestational days 7-8 or an intragastric administration of 75,000 units of vitamin A on gestational days 8-10 to produce embryos with spina bifida or anencephaly. Controls were given vehicle only. The SEM examination of day 9 and 10 embryos revealed no morphologic differences between controls and subjects. Subsequent gestational days showed closure of neural tubes in controls but progressive opening of neural tubes (in the rostral and caudal regions) in experimental subjects. Growth of the dysmorphic neural tube region with subsequent sponteneous necrosis late in gestation resulted in the mature malformations of anencephaly and spina bifida. This study emphasizes the similarities in the developmental stages of spina bifida and anencephaly. We also surveyed a large series of human anencephalic autopsy specimens and noted striking similarities to the animal model.
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