Estrogen plus androgen induced mounting in adult female hamsters

This study demonstrated that the combined administration of estrogens and androgens activates the display of mounting by female hamsters. Forty-nine ovariectomized hamsters were injected daily with either estradiol benzoate (EB, N = 8); dihydrotestosterone propionate (DHTP, N = 7); testosterone propionate (TP, N = 6); androstenedione (AD, N = 9); EB plus DHTP (N = 10); or estrone plus DHTP (E₁ + DHTP, N = 9). All androgens were administered at a dose of 1 mg per day for the first 24 days and at a dose of 2 mg per day for the last 14 days. The EB dose was 6 μg per day and the E₁ dose was 100 μg per day. Females were tested for male behavior once a week starting on Day 10 of injections and for female behavior on Day 39.One hundred percent of EB + DHTP treated females; 67% of the E₁ + DHTP treated females; 55% of the AD treated females; 33% of the TP treated females; 29% of the DHTP treated females; and none of the EB treated females mounted during at least one test. Only one of the E₁ + DHTP treated females showed the intromission pattern; otherwise most females which mounted displayed the intromission pattern. The median number of days preceding the onset of mounting ranged from 21 to 31 days and did not differ among treatment groups.     

Neonatal androgen and mounting behaviour in female house mice

Strains of intact, mature female mice were found to differ appreciably in their levels of performance of masculine copulatory patterns when presented with a stimulus oestrous female. Balb/c and DBA/2 strains, which showed few responses to stimulus females, were still unresponsive when given exogenous androgen, whereas the C57BL/6Fa strain and its F₁ hybrids with the DBA/2 strain, showed more pre-injection masculine responses which increased to consistent and very high levels following androgen treatment. In a second study, injection of Balb/c females with testosterone propionate on the day of birth did not increase the number of masculine responses displayed, even after androgen treatment at maturity.     

Early androgen treatment and male and female sexual behavior in mice

To investigate the role of neonatal androgen stimulation in the development of the potential for masculine and feminine sexual behavior in the mouse, different groups of mice were hormonally manipulated early in life. One group of female mice was administered testosterone propionate (TP) within 24 hr of birth; a second group of females was given a control injection of oil on the day of birth; a third group of females received an injection of TP on the 10th day after birth. A group of males received a control injection of oil on the day of birth. All mice were gonadectomized at about 30 days of age. At 60 days of age, mice were injected with estrogen and progesterone and tested for sexual receptivity; several weeks later all mice were injected with TP and tested for male sexual behavior. Female behavior: Females given oil at birth and females given TP on the 10th day after birth showed high levels of sexual receptivity as adults following estrogen-progesterone treatment. Females given TP on the day of birth, and male mice, rarely exhibited lordosis following estrogen-progesterone treatment. Male behavior: Most mice, regardless of genetic sex or neonatal treatment, mounted in adulthood following administration of exogenous androgen. There was little difference in mounting frequency between groups, suggesting that exogenous or endogenous androgen stimulation of the neonatal mouse does not facilitate adult mounting behavior. These data for the mouse are in essential agreement with existing data for the rat, and indicate that sexual behavioral differentiation induced by androgen stimulation in infancy is best characterized as an inhibition of the potential to display feminine sexual behavior in adulthood.     

Differential hormonal control of aggression and sexual behavior in female Syrian hamsters

These experiments were designed to test the effects of chronic estradiol treatment on aggression and sexual behavior in female hamsters. Isolated female hamsters were ovariectomized and tested for their behavioral responses to a group-housed, ovariectomized female hamster (aggression test) and a group-housed, intact male hamster (sexual behavior test). Following these baseline tests, the experimental females were implanted sc with Silastic capsules containing different concentrations of estradiol (100, 25, 10, or 0%) diluted with cholesterol and retested 3, 7, 10, and 14 days after implantation. High levels of aggression were observed on the baseline test, with no changes in aggression toward an intruder female observed for any implant group on subsequent tests. Despite these high levels of aggression toward another female, most of the estradiol-treated females (80% at 14 days) were sexually responsive in the presence of a male. There was no effect of Silastic estradiol concentration on sexual behavior, even though a range of serum estradiol levels (39–105 pg/ml) resulted. Lordosis latencies decreased and lordosis durations increased over the extent of estradiol treatment. Seventeen days after Silastic implantation, all females were injected with progesterone and retested. Estradiol-treated females showed an extreme reduction in aggression toward a stimulus female, as well as a further stimulation of sexual behavior after progesterone treatment. High levels of aggression in cholesterol-treated females (0% estradiol) were maintained even after progesterone injection, and these females never displayed any sexual responsivity. These results suggest that sexual behavior in the female hamster is sensitive to estradiol alone, whereas the inhibition of aggression requires the combination of estradiol plus progesterone.     

Inhibition of lordosis behavior in male and female rats by androgens and progesterone.

Several studies suggest that when manipulated experimentally in adulthood, the lordosis response to estrogen can be increased dramatically in male rats. Because adult-gonadectomized (Gx) animals were used in these studies, the lack of testicular hormones in adulthood may have been a factor. To examine this possibility, adult-Gx rats were implanted with blank (Bk)-, testosterone (T)-, 5alpha-dihydrotestosterone (DHT)-, or progesterone (P)-filled capsules, alone or in combination. We report a new finding, that a combined treatment of T plus P (T+P) at physiological doses for the male, but not T or P alone, reduced lordosis significantly in males, with and without estrogen priming. T+P did not inhibit lordosis in females, nor did this specific treatment affect open field, aggressive, and male copulatory behaviors. In confirming studies done with much higher doses, DHT reduced lordosis in both sexes. DHT and T+P also reduced lordosis in adrenalectomized/Gx males. Mechanisms responsible for the T+P inhibition of lordosis in males are not known, but they may include an upregulation of androgen receptors by P, and this possibility is discussed.     

Conditioned defeat in male and female Syrian hamsters

A brief exposure to social defeat in male Syrian hamsters (Mesocricetus auratus) leads to profound changes in the subsequent agonistic behavior exhibited by the defeated animals. Following defeat in the home cage of an aggressive conspecific, male hamsters will subsequently fail to defend their home territory even if the intruder is a smaller, nonaggressive male. This phenomenon has been called conditioned defeat. In Experiment 1, we examined the duration of conditioned defeat by repeatedly testing (every 3-5 days) defeated hamsters with a nonaggressive intruder. We found that conditioned defeat occurs in all defeated male hamsters and persists for a prolonged period of time (at least 33 days) in the majority of male hamsters tested despite the fact that these animals are never attacked by the nonaggressive intruders. In Experiment 2, we examined whether conditioned defeat could be induced in female Syrian hamsters. While conditioned defeat occurred in some females, they displayed only low levels of submissive/defensive behavior and, in contrast to males, the conditioned defeat response did not persist beyond the first test. These results suggest that in male hamsters conditioned defeat is a profound, persistent behavioral change characterized by a total absence of territorial aggression and by the frequent display of submissive and defensive behaviors. Conversely, social defeat in female hamsters does not appear to induce long-term behavioral changes. Finally, in Experiment 3, we determined that plasma adrenocorticotropin-like immunoreactivity increases in females following social defeat in a manner similar to that seen in males, suggesting that the disparate behavioral reactions of males and females are not due to sex differences in the release of, or response to, plasma adrenocorticotropin.     

Compensatory adrenal growth in aldosterone-treated male and female hamsters

The aim of the study was to investigate the compensatory adrenal growth in aldosterone-treated male and female hamsters. Hemiadrenalectomised and sham-operated animals were treated for 5 days with a daily d-aldosterone dose of 25 micrograms/animal. In both male and female aldosterone-treated hamsters monoadrenalectomy did not change the relative adrenal weight if compared with sham-operated groups. The fasciculata zonae of monoadrenalectomised aldosterone-treated males was larger and contained more parenchymal cells than in appropriate control group. There was no difference in the volume of adrenocortical zones, average cell volume and in cell number between sham-operated and unilaterally adrenalectomised females. In vitro 3H-thymidine incorporation per adrenal was markedly higher in monoadrenalectomised than in sham-operated aldosterone-treated males while the opposite was true for female hamsters. Thus, the action of aldosterone on CAG in the hamster seems to depend on sex, with no effect in males and inhibitory action in females.     

Aromatization and the induction of male sexual behavior in male, female, and androgenized female hamsters

Eight weeks after gonadectomy male, female, and androgenized [10 μg testosterone propionate (TP), 24 hr after birth] female hamsters were given daily treatment with: 150 μg dihydrotestosterone (DHT), 5 μg estradiol benzoate (EB), 150 μg DHT + 5 μg EB, 150 μg DHT + 1 μg EB, 30 μg DHT + 5 μg EB, 30 μg DHT + 1 μg EB, or the oil vehicle. Treatment of castrated male hamsters with 5 μg EB fully restored mounting but relatively few of these animals intromitted and none ejaculated. Treatment with 150 μg DHT restored all components of male sexual behavior but only in a small proportion of the males. Combined treatment with EB and DHT restored mounts, intromissions, and ejaculations in the majority of the males. Although as little as 30 μg DHT + 1 μg EB restored the full complement of male behavior, the males which received 150 μg DHT + 5 μg EB or 150 μg DHT + 1 μg EB required fewer intromissions to achieve ejaculation than the males which received 30 μg DHT + either dose of EB. The response of the androgenized females was similar to that of the males except that the androgenized females had lower intromission rates and none ejaculated. Relatively few of the nonandrogenized females responded to EB and DHT treatment and those that did mounted only a few times each test. These results demonstrate that both EB and DHT can stimulate male sexual behavior in the hamster and that the sensitivity to EB and DHT for copulatory behavior is determined by early postnatal androgen exposure.     

Androgenic regulation of chemoinvestigatory behaviors in male and female hamsters

In male hamsters, chemosensory responsiveness to sexually relevant female odors is facilitated by testosterone (T). Some evidence suggests that this is not a sexually dimorphic response in that adult females can respond similarly to males following administration of T. This was evaluated and additionally, the hypothesis that facilitation of chemosensory responsiveness by T might be mediated by the conversion of T to aromatized or 5 alpha-reduced metabolites was tested. In 2-min tests, we measured the time adult males or females investigated female hamster vaginal secretion (FHVS). These animals were gonadectomized and administered T, 5 alpha-dihydrotestosterone (DHT), estradiol (E2), or a combination of DHT and E2, by subcutaneous implantation of Silastic capsules. FHVS tests were conducted either 2 and 4 weeks, or 4 and 6 weeks subsequent to gonadectomy and hormone treatment. Comparisons among groups receiving different hormone doses indicated that (1) males and females are not equally responsive to the attractant properties of FHVS, and that (2) neither DHT, E2, nor their combination, can duplicate the effects of T in facilitating responsiveness to FHVS in either sex. The copulatory behavior of males under the hormone conditions described was also tested and it was found that variations in the rate at which the test males sniffed or licked the receptive female's anogenital region correlated with variations in measures of the males' sexual performance.     

Hormonal and experiential control of female-male mounting in the female rat

Mounting behavior in the female rat has been studied extensively in same-sex interactions, but not in the heterosexual dyad. The present study examined the display of female mounting of castrated noncopulating male rats (FMM). Ovariectomized (OVX) sexually naive female rats (N = 80) were given either estrogen (E) + progesterone (P), E + oil (O), P + O, or O + O treatment for five tests with castrated male rats. FMMs were observed in both the E + P and E + O females. The influence of the ovarian cycle on FMM was also investigated. Vaginal smears from sexually naive females (N = 16) were taken daily for 12 days immediately after testing with castrated males. FMM frequency was greatest during Proestrus. Finally, OVX females (N = 30) treated with E + P were given either 0, 1, 10 multi-ejaculatory heterosexual experiences with intact, sexually experienced males, prior to tests with intact, copulating or castrated, noncopulating males for five tests. Sexually naive females displayed a greater number of mounts relative to the sexually experienced females when tested with castrated, noncopulating males. In contrast, very few FMMs were observed in females of any group tested with intact, copulating males. These data suggest that FMM occurs naturally in rats as a "super-solicitational" behavior that is modified by hormone treatment and prior heterosexual experience.     

Differential effects of the anti-estrogen MER-25 and of three 5alpha-reduced androgens on mounting and lordosis behavior in the rat.

Four experiments were performed in order to evaluate further the hypothesis that androgen must be aromatized to estrogen for the activation of masculine sexual behavior in the male rat. In Experiment 1 it was found that the anti-estrogen MER-25 failed to disrupt mounting behavior in castrated males which simultaneously received testosterone propionate (TP). However, in Experiment 2 it was found that MER-25 as weil as 3β-androstanediol effectively activated masculine behavior in castrated males treated simultaneously with dihydrotestosterone propionate. Both MER-25 and 3β-androstanediol had previously been shown to display an affinity for cytoplasmic estradiol-17β receptors present in male rat anterior hypothalamus. In Experiments 3 and 4, performed with ovariectomized females, it was found that whereas MER-25 antagonized the stimulatory effect of estradiol benzoate (EB) on lordosis behavior, 3β-androstanediol did not. In addition, 5α-dihydrotestosterone and 3α-androstanediol, two compounds which had previously been shown to have almost no affinity for estradiol-17β receptors in the hypothalamus, both inhibited the stimulatory effect of EB on lordosis. It is concluded that the fact that anti-estrogens suppress lordosis induced in females with either EB or TP, but fail to disrupt TP-induced mounting behavior in male rats does not argue against the aromatization hypothesis for masculine sexual behavior.     

Cortisol and androgen concentrations in female and male elite endurance athletes in relation to physical activity.

To evaluate the effect of variations in physical activity on selected hormone concentrations in male versus female athletes, fasting serum concentrations of cortisol (C), total-testosterone, free-testosterone, non sex hormone binding globulin (SHBG) bound testosterone, dehydroepiandrosterone, 4-androstene-3,17-dione and SHBG were studied. The tests were performed in nine male and seven female elite endurance athletes during the off-season (test 1), early in the competition season (test 2) and at the end of the competition season (test 3). The C concentration increased significantly during the competition season in women but not in men. Further, the mean C concentrations at test 3 as well as the mean level during the whole observation period (tests 1, 2, 3) were significantly higher in women than in men. No significant changes were found in androgen concentrations or androgen:cortisol ratios within the two groups. The differences between the sexes in C response may indicate different adaptive mechanisms to similar physical stress.     

Effects of estrone, estradiol and estriol combined with dihydrotestosterone on mounting and lordosis behavior in castrated male rats

Prepuberally castrated male rats were injected with estrone (1 or 5 μg), estradiol (1 or 5 μg) or estriol (1, 5, or 25 μg) either alone or in combination with dihydrotestosterone, (0.5 mg). Each of these steroids, when given alone, had no or only weak stimulatory effects on male sexual behavior. When combined with dihydrotestosterone all estrogens stimulated full copulatory behavior, the order of potency being estradiol, estrone, and estriol. Lordosis behavior in response to male mounting or manual stimulation was facilitated by all estrogens. All estrogens caused a slight weight increase of the seminal vesicles, ventral prostate and glans penis.     

Effects of an estrogen antagonist,MER-25, on mounting behavior and lordosis behavior in the female rat

Four daily injections of 20 mg ethamoxytriphetol, MER-25, to intact female rats with regular 4-day estrous cycles inhibited lordosis behavior, but had no inhibitory effect on mounting behavior. Ten mg/day of MER-25 for 9 days partially antagonized the stimulatory effect of 2 μg/day of estradiol benzoate on lordosis behavior in ovariectomized female rats, but had no inhibitory effect upon mounting behavior. MER-25 (10 mg/day for 9 days) stimulated the display of mounting behavior in ovariectomized female rats. No effects of MER-25 treatment (10 mg for 10 days) comparable to those of testosterone propionate (10, 50, or 250 μg for 10 days) on testicular, seminal vesicle, or ventral prostate weights of intact male rats or on seminal vesicle or ventral prostate weights of castrated male rats were observed. The results show that MER-25 acts differently upon various estrogen sensitive behaviors in the female rat.