Influence of age on the morphology and transit time of murine stratified squamous epithelia.

To determine whether stratified squamous epithelia from aged animals differ from those of young animals, specimens of skin from the pinna of the ear, the back and footpad and mucosa from the palate, cheek and ventral surface of the tongue were excised from 10 young (3-4 month-old) and 10 old (23-24 month-old) C57B1/6NNia mice and prepared for light microscopy. Tracings were prepared of the nucleated cell compartment and epithelial thickness, the number of nucleated cells/mm2 surface, the basement membrane: surface ratio, cell density and the number of basal cells/mm basement membrane were determined. To evaluate the epithelial labelling index and tissue renewal, a further group of young and old mice were injected with 1 microCi/g [3H]-thymidine and killed after 1 h or 2, 4, 5, 6 or 8 days and sections were prepared for autoradiography. Whereas the epidermis from the ear and footpad showed a statistically-significant increase in thickness, the epithelium from the palate was thinner in the old animals. The other tissues examined showed no change. Cell density decreased with age in the palate; cell size increased with age in the ear and footpad. No statistically-significant differences in labelling index or minimum transit time were observed between young and old animals in any of the tissues. Thus, there is no single age-associated change in epithelial structure or renewal common to all epithelia.