Ultrastructure of palatal epithelium in guinea pigs 5 minutes and 6 hours after excisional wounding

– Standardized excision wounds were made in the palatal mucosa of 21 adult, male guinea pigs in order to study the ultrastructural changes in the epithelium along the wound margins 5 min and 6 h postoperatively. After 5 min the cut cells in the stratum corneum showed neither emptying of the cytoplasm nor any change in the keratin pattern. The cut cells in the stratum granulosum and the stratum spinosum demonstrated little or no change. Cells immediately behind the wound margins appeared normal. After 6 h most of the stratum corneum, cells had retained their cytoplasm with no change in the keratin pattern. A partial or complete loss of the cytoplasm was observed due to cleft formation between the cytoplasm and the electron‐dense zone attached to the inner part of the plasma membrane. In the clefts, bacteria caused destruction of the epithelial cell membranes. The cells of the reactive zone showed characteristic degenerative changes. The cytoplasm was dominated by tonofibrils separated by irregular spaces, making the cytoplasm look “moth‐eaten”. No ribosomes, endoplasmatic reticulum, Golgi‐apparatus, or keratohyalin granules were found. The mitochondria showed changes of the membranes and the matrix with numerous electron‐dense globules. The cytoplasmic changes are discussed in relation to earlier observations by light microscopy, where the changes in the reactive zone have been termed “induced keratinization”. In most cells of the reactive zone different stages of karyolysis were found with distinct changes of the trilaminar outer and inner membranes of the nuclear envelope. In the upper cell layers of the reactive zone the nuclear breakdown comprised pyknosis and karyorrhexis with shrunken nuclei. The chromatin was aggregated into irregular masses inside and outside the ruptured nuclear envelope.