Cellular dynamics of corneal wound re-epithelialization in the rat III. Mitotic activity

The number and distribution of mitotic epithelial cells in the ocular surfa ce during homeostasis and in response to abrasion of the mammalian cornea w ere determined. Normal rats and those receiving a 3 mm diameter centrally l ocated epithelial defect, received an intraperitoneal injection of colchici ne 6 h prior to sacrifice. Mitosis in the basal epithelium during homeostas is was comparable in magnitude across the ocular surface epithelium, with t he exception of a few mitotic figures in the midline. Thirty percent of the mitotic figures were in the basal layer (layer 1), and 70% were in layer 2 ; the cells in layer 2 were often noted to retain connection to the basal l amina by cytoplasmic stalks. Mitosis was rarely noted in the regenerating e pithelium. However, summation of M phase cells in both the basal and suprab asal epithelium adjacent to the wound showed increases of 3- and 5-fold at 30 and 36 h after abrasion, respectively, from levels at homeostasis and th e time of injury. In striking contrast to homeostatic epithelium, 80% of th e mitotic cells were located in layer 1 of the corneal epithelium, with nor mal distribution observed by 72 h. Mitosis in the limbus and conjunctiva wa s increased 3-fold at 30 h and 24 h, respectively, from values at homeostas is and the time of debridement. These results, using rigorous statistical a nalysis and precise topographic assessment, showed that mitosis is not impe ded - but rather often accelerated - following denuding of the corneal epit helium and that the spatial distribution of mitotic cells is correlated wit h wounding. The data revealed that re-epithelialization of the corneal epit helium is not dependent on mitosis in the regenerating epithelium, but rath er in the adjacent unwounded epithelium of the cornea, with most cells bein g located in the basal layer until re-epithelialization is completed. Mitot ic cells in the limbus and conjunctiva may be related to replenishment of o cular surface epithelial cells used in the repair process rather than direc tly supplying the abraded surface. (C) 2000 Elsevier Science B.V. All right s reserved.