Long-Term Estrogen and Progesterone and Mating Stimuli As Regulators of Female Sexual Receptivity in the Mongolian Gerbil
In ovariectomized female Mongolian gerbils (Meriones unguiculatus) estradiol benzoate (6.6 ?g/day) injections elicited high levels of lordosis. Lordosis was first observed after 7 days of estrogen treatment and lordosis quotients of greater than 100 occurred after 10 continuous days of estrogen treatment. In females primed with estrogen for 13 days a further facilitation of lordosis frequency was observed 4–6 hr after progesterone injection. In estrogen-primed females, lordosis quotients of over 100 were still possible even after 9 consecutive days of progesterone treatment, although prolonged progesterone exposure (0.4 mg/day for 24 hr or more) may have depressed lordosis. Mating stimuli also interact with hormonal treatments to depress receptivity in this species. Previously tested females showed lower levels of responding than females first tested after 21 consecutive days of estrogen and 9 days of progesterone. Males often footstomped in tests in which females showed lordosis, while pairs fought and males scent marked most often in tests with nonreceptive females.