Influence of the light and dark phase of the cycle on the cellular proliferation in the pineal gland of the adult rat: a bromodeoxyuridine immunohistochemical study.

The cellular proliferative activity in the adult rat pineal gland was studied using bromodeoxyuridine immunohistochemistry during the light and dark phases of an artificial 12L:12D photoperiod. The results showed statistically significant differences in the number of labeled cells between the light and dark phases, with the labeled cells being almost threefold more abundant in the light period. Minor changes were also found in the pineal gland volume between both periods. The decrease in the number of labeled cells in the dark phase of the cycle could be related to the well-documented antimitotic action of melatonin.