MESENCHYMAL CELL-ACTIVITY DURING 5-FLUORO-2-DEOXYURIDINE-INDUCED CLEFT-PALATE FORMATION IN THE RAT

Biosynthetic activity of the mesenchymal cells within the palatal shel ves was determined during cleft palate formation induced by 5-fluoro-2 -deoxyuridine (FUDR). The palatal shelves of 30 fetal rat heads with p alatal clefts were surveyed at stages corresponding to normal palatoge nesis, nucleolar organizer region (NOR) staining being employed to det ermine cell activity. Comparing cellular activity during normal and cl eft palatogenesis, significantly lower counts were recorded for most s tages of cleft formation. When anterior or posterior regions were comp ared, significant changes in NOR counts/cell were found at a time corr esponding to the pre-elevation stage of normal palatogenesis. At a tim e equivalent to normal fusion, the shelves in the anterior region show ed signs of recovery, but posteriorly significantly lower activity occ urred throughout all stages of palate dysmorphogenesis. The depressed level of cellular activity found after treatment with FUDR may be dire ctly or indirectly related to the abolition of an intrinsic shelf-elev ation force and, subsequently, cleft palate formation.