Blocking of the cell division by stress-inducing electrical stimulation. A study in rat oral epithelium.

The purpose of the present study was to localize in the cell cycle, the site of the stress-induced blockage of cells entering the mitotic phase, and to estimate the length of time this block is effective. A total of 140 rats were subjected to electrical stimulation applied by a live metal grill in the bottom of their cages. Forty animals left undisturbed in the cages were used as controls. At various intervals after the start of electrical stimulation, groups of animals were killed and histologic sections were prepared of the palatal mucosa. The number of prophases, metaphases, and ana/telophases was counted in the epithelium in three sections of each animal. Electrical stimulation for 1 min resulted in a blocking of the entrance of cells into mitosis, followed by a transient increase in the number of mitotic figures to a level much higher than that of the controls. Electrical stimulation for 10 min resulted in the maintenance of the blocking effect for approximately 45 min. By renewed electrical stimulation the period of blockage was extended for a further 35 min. In each experiment the number of prophases decreased immediately after the start of electrical stimulation, indicating that the site of the blockage of the entrance of cells into mitosis is located near the G2/M transition.