An experimental study of the influence of sensory nerve fibers on Merkel cell differentiation in the labial mucosa of the rabbits.

The influence of the sensory nerve fibers on the differentiation of the Merkel cell was examined in the denervated labial mucosa of adult rabbits. Part of the lower labial mucosa was excised following mental nerve resection. Twenty-one and 50 days later, the regenerated mucosa was examined by electron microscopy with special reference to the distribution and maturation of Merkel cells, and compared with the normal and the denervated intact mucosa. A number of immature Merkel cells appeared in the denervated and regenerated epithelium by 21st day after the operation. The distribution density of the Merkel cells in a unit area of the mucosa did not change much but the percentage of the mature Merkel cells increased significantly until 50 days after the operation. The mature Merkel cells in the denervated and regenerated mucosa showed a normal ultrastructure, though their orientation and location were not uniform, shifting more superficially than the cells in the normal mucosa. In the controlateral intact epithelium of the denervated labial mucosa, no substantial decrease in the population density of Merkel cells was recognized, though the desquamation of Merkel cells was observed. It was conspicuous that the percentage of immature Merkel cells to the total number of the Merkel cells was significantly increased after the denervation in the intact labial mucosa. This study suggests that Merkel cells differentiate independently of sensory nerve fibers, but the latter are requisite to maintain the former in a uniform, basal disposition in the epithelium.