The dependency of the rat estrous cycle on the daily alternation of light and dark.
D000818:Animals; D003624:Darkness; D004848:Epithelium; D004971:Estrus; D005260:Female; D007962:Leukocytes; D008027:Light; D010060:Ovulation; D011247:Pregnancy; D051381:Rats; D013997:Time Factors; D014626:Vaginal Smears