Fine structural and morphometric studies of the Merkel cell during fetal and postnatal development.

The morphological and morphometric changes of the Merkel cells during fetal and postnatal development were studied in the glabrous digital pads of rats. In 20-day-old fetus rats, the Merkel cells we observed were present in the lower spinous and basal layers, and not associated with axon terminals. The Merkel cell granules were few and sparse. The Merkel cell had clumps of fibrils and formed many desmosomes with surrounding keratinocytes. In postnatal rats, innervation was followed by an increase in the number of Merkel cell granules, and their specific accumulation. The fibrils of the Merkel cells were not prominent. It was found by t-test that the numerical density of the Merkel cell granules significantly increased from the fetal stage to 4-day-old postnatal rats. These results suggest that the Merkel cells are present in the epidermis without nerve contact in 20-day-old fetus rats, and that innervation is necessary for the increase of cellular activity in Merkel cells.