Induction of sexual receptivity in the female lizard, Anolis carolinensis: Effects of estrogen and the antiestrogen CI-628

Daily behavioral testing revealed that there is a latency period of at least 48 hr from the administration of a single injection of estradiol benzoate (EB) to the first significant increase in female sexual receptivity in the ovariectomized female lizard, Anolis carolinensis. This latency period did not vary with dosage of EB used in these experiments (i.e., 0.8, 1.4, and 4.0 μg) nor with method of injection (subcutaneous vs intraperitoneal for dose of 1.4 μg EB). Following a single EB injection, female sexual receptivity increased after the 48-hr latency period, reached an observed peak from Day 3 to Day 6, and thereafter declined to pretreatment levels by Day 19. Although both 1.4 and 4.0 μg of EB produced higher levels of female sexual receptivity than did treatment with 0.8 μg of EB, results obtained with 4.0 μg EB did not differ from those obtained with 1.4 μg EB. Administration of the nonsteroidal antiestrogen CI-628 (80 μg) at either 4 or 24 hr following a single subcutaneous injection of 1.4 μg EB significantly reduced subsequent female sexual receptivity. These results suggest that there is a critical length of time during which estrogen must act on the brain and support the concept of an estrogen “maintenance” effect during this priming period.