Mesenchymal cell activity during 5-fluoro-2-deoxyuridine-induced cleft palate formation in the rat.

Biosynthetic activity of the mesenchymal cells within the palatal shelves was determined during cleft palate formation induced by 5-fluoro-2-deoxyuridine (FUDR). The palatal shelves of 30 fetal rat heads with palatal clefts were surveyed at stages corresponding to normal palatogenesis, nucleolar organizer region (NOR) staining being employed to determine cell activity. Comparing cellular activity during normal and cleft palatogenesis, significantly lower counts were recorded for most stages of cleft formation. When anterior or posterior regions were compared, significant changes in NOR counts cell were found at a time corresponding to the pre-elevation stage of normal palatogenesis. At a time equivalent to normal fusion, the shelves in the anterior region showed signs of recovery, but posteriorly significantly lower activity occurred throughout all stages of palate dysmorphogenesis. The depressed level of cellular activity found after treatment with FUDR may be directly or indirectly related to the abolition of an intrinsic shelf-elevation force and, subsequently, cleft palate formation.