Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate.

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8 mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p < 0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.