Abstract
Early ultrastructural changes in the dorsal skin epidermis of Wistar-derived hypotrichotic WBN/ILA-Ht rats were examined for up to 12 hours after UVB-irradiation (10 kJ/m2) (12 HAI). The first change appeared at 3 HAI as swelling and/or vacuolation of mitochondria in the spinous and basal cells. The number of keratinocytes with such mitochondrial changes decreased thereafter. At 6 HAI, apoptosis of basal cells developed. These cells showed shrinkage of cell bodies with condensed or fragmented nuclei and dark cytoplasm due to densely packed bundles of tonofilaments. At the same time, keratinocytes with prominent nucleoli were also observed in the basal and suprabasal layers. At 12 HAI, the number of keratinocytes with prominent nucleoli increased, and mild and focal intercellular edema developed mainly in the basal layer. In addition, a small number of apoptotic basal cells were still observed. The present ultrastructural findings supported the histopathological findings previously reported by our research group.
