Hormonal regulation of female proceptivity and its influence on male sexual preference in rats

Two experiments were conducted that assessed the effect of varying levels of female proceptive/attractive behaviors on male sexual preferences in sexually experineced rats. In Experiment I, adult ovariectomized Sprague-Dawley rats were brought into behavioral estrus by a combination of estradiol-17β-benzoate (EB) (4 μg) and progesterone (500 μg). In addition, females received an injection of either the anti-estrogen Cl-628 (1 mg) or the control vehicle (10% ethanol) only. In tests for sexual responsiveness. CI-628 caused a 3 to 4 fold decline in proceptive behavior along with a small but significant decline in receptivity. When individual males were placed in a testing arena with a pair of receptive females, only one of which received CI-628, males displayéd a preference for the control-group females, as measured by overall copulatory rate. However, males did not display a consistent preference towards females of either treatment, as measured by choice of female for ejaculation. Similarly, there were no significant correlations between female proceptive behaviors and either overall copulatory rate or ejaculation. In Experiment 2, females came into behavioral estrus after being given four daily injections of EB followed by either a single injection of progesterone or just the oil vehicle. The absence of progesterone caused a significant decline in receptivity and almost entirely eliminated proceptive behaviors. When males were tested with a pair of females, only one of which received progesterone, males preferred the progesterone-injected female as measured by overall copulatory rate. However, similar to Experiment I, no consistent preferences were evident when measured by using choice of female for ejaculation. There were again no significant correlations between proceptivity and either measure of male sexual behavior. Together, the results of the two experiments suggest that differences in proceptive behavior among female rats that are at least minimally receptive may not have a great effect on male sexual preferences when sexually experienced males are observed in a small testing arena.