Changes in rat palatal epithelium during neonatal growth.

The epithelium of rat palatal mucosa was examined from 2 to 30 days after birth and changes in epithelial thickness, cellularity, average cell volume, mitotic activity and the turnover time of the nucleated cell layer were determined from histological sections. The mean epithelial thickness, which was 35.3 +/- 1.5 micron at 2 days, remained constant for the first 9 days and then progressively increased, reaching 91.7 +/- 1.7 micron by 30 days. This change in thickness was partly bought about by a doubling of the number of nucleated cells per mm2 of the surface, from 90.4 +/- 2.81 X 10(3) to 187.63 X 5.65 X 10(3), and partly due to a change in the ratio of cells in the progenitor and maturing cell compartments, as assessed by the change in volume of an "average" epithelial cell. Mitotic activity also remained constant for the first 9 days and then increased, reaching levels five times greater than initial levels by 30 days. It is suggested that these changes are brought about by frictional stimulation associated with the initial intake of solid food as well as systemic influences related to general growth mechanisms.