[Epidermal keratinocyte proliferation, differentiation and apoptosis in rats in postnatal ontogeny]

Quantitative ratios between reproduction of the keratinocytes and their apoptotic death vary in different periods of postnatal ontogenesis. During the first month of life of the rats the mitotic activity of keratinocytes and thickness of the epidermis gradually decrease. The epidermis undergoes further development, which terminates by the 30th day after birth. The number of apoptotic cells in the epidermis increases from the 1st until 16th day and that of intraepidermal lymphocytes from the 1st until 30th day. In 3-month old animals the peak of mitotic activity coincided with the enhanced apoptotic death of the keratinocytes. The anagen signs were noted in such animals. In the old rats the mitotic activity of the epidermal cells was markedly reduced with the increased rate of apoptosis of the keratinocytes and the decreased thickness of epidermis. Single Merkel cells were visualized in the epidermis using the silver plating technique. Hence, their role in apoptosis of the keratinocytes cannot be significant. The possibility of lymphocyte-associated apoptosis of the keratinocytes in the early postnatal ontogenesis of rats is assumed.