Abstract
The purpose of this study was to examine the developmental morphology of the mandible in fetal mice using pregnant females with retinoic acid (RA) excess. RA solutions with various concentrations and administration times injected into the abdominal cavity of mice between 7 and 14 days of pregnancy. Fetuses were removed on day 18 of the pregnancy from the mother animals under anesthesia.
The mandibles were then extirpated, stained with a mixture of alizarin red and alcianblue solution, and mounted as transparent preparations by clearing to study the bone and cartilage architecture.
In addition, some of the mandibles were cut into serial sections and processed for examination by the light microscopy. The following results were obtained.
1) The fetuses from the maternal group that received RA before day 10 of the pregnancy showed maxillo-facial abnormality at a higher frequency than those from mothers given RA later in the pregnancy.
2) The fetuses in the group administrated RA at 5-50μg/g weight on day 7 of the pregnancy exhibited malformation in the maxillo-facial region, the frequency being particularly high in the mandibles.
3) Almost all of the mandubular abnormalities involved hypoplasia, in which the mandibular ramus was extremly thin or the coronoid process was lacking, accompanied by exencephaly.
4) The mandibular ramus with hypoplasia showed underdevelopment of bone and cartilage tissue. The articular disc and fibrous covering were also underdeveloped.
5) Compared with severe abnormality of the mandibular ramus shape and tissue formation, that of the mandibular body was slight.
