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Study of the Normal Development of Rat Palatal Rugae and the Role of Collagen Fibers in Rugae Development

=Abstract=Sprague-Dawley rat fetuses ranging from 15- to 19-day of gestational age, were studied with their rugae morphogenesis at the light microscopic level. The distribution of collagen fibers in the palatal mesenchyme was analyzed. In addition, an attempt to evaluate the role of collagen fibers in rugae development was made. The specimens were H-E stained and collagen fiber stained according to the Gorden and Sweet method. To evaluate the role of collagen fibers in rugae formation, P-aminopropionitrile (BAPN), a well-known lathyrogen, was orally administered to the pregnant rats. Concurrently, an organ culture of the fetal palate was taken with and without BAPN in the culture media. Rugae in the palate had maturated anteroposteriorly in general. Individual ruga development was accompanied by local epithelial cell proliferation, changes in the position of the basement membrane, and crowding and rearrangement of the mesenchymal cells. Collagen fibers were also accumulated beneath the basement membrane of the rugae with changes of their arrangement pattern from reticular to concentric form. The palatal processes of a 15-day-old fetuses cultured with BAPN showed some mesenchymal invasion by proliferating epithelial cells of rugae. In contrast, the cultured palate of the 17-day-old fetus with BAPN showed an exaggerated protruding of rugae above the epithelial surface. Following the above procedures, some descriptions of rugae development in rat fetuses were obtained. With these results, it was suggested that mesenchymal cells and collagen fibers may play important roles in rugae formation, and the contrasting results of the organ culture experiment with 15- and 17-day-old fetuses might mean that collagen fibers have the possibility of not inducing but counterbalancing normal development of rugae in rat fetuses.