Effects of pinealectomy and constant light on the estrous cycles of female rats

Adult Charles River female rats were pinealectomized, sham-operated or left intact, and half of each group was placed in 12L:12D while the other half we exposed to constant light (LL). Daily vaginal smears permitted the calculation, at weekly intervals, of the percent of rats in each group in LL showing 5 or more consecutive days of vaginal cornification. After 11 weeks in LL, those rats were returned to LD for 6 weeks and then put back into LL until the termination of the experiment 3 weeks later.