Effects of Light Deprivation on the Rat Estrous Cycle

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Abstract
Intact or blinded Wistar female rats were exposed to 0, 14, or 24 hr. of light/24 hr. Some animals were exposed to 14 hr. of light/day but with day and night reversed. Estrous cycles were followed by means of vaginal lavage. Blinded animals did not respond to changes in external lighting they did not reverse the time of beginning of vaginal cornification in reversed light, nor did they show persistent vaginal estrus in response to constant light. Animals blinded or placed in constant dark at the age of 21 days showed normal vaginal cycles for up to 8 months, with normal uterine weight but reduced ovarian and pituitary weights at autopsy. Animals blinded or placed in the dark at 90 days of age began showing prolonged cycles after 2 to 3 months and 11 out of 41 animals stopped cycling completely. At autopsy at 6 to 7 months of age, uterine, ovarian, adrenal and pituitary weights of these anestrous animals were significantly lower than in the controls.