Evaluation of prenatal androgen and ovarian secretions on receptivity in female and male rats.

A total of 102 male and 146 female offspring of Sprague-Dawley rats injected daily from Day 16 through Day 20 of gestation with either 2 mg of testosterone propionate (TP) in .1 ml of sesame oil or oil alone were tested for sexual receptivity following injections of 3.3 μg of estradiol benzoate (EB) and .5 mg of progesterone (P) beginning at 40, 80, or 120 days of age. At each age, neonatally gonadectomized males and females from TP-injected litters exhibited less receptivity than corresponding oil-injected controls. Prenatally androgenized females were similar to neonatally castrated oil-injected males at all ages. Ovarian implants from birth to 35 days of age significantly increased receptivity in neonatally castrated males and androgenized females. Increasing the age at which testing was initiated systematically reduced receptivity in all groups. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in sensitivity of food intake, body weight, and running-wheel activity to ovarian steroids in rats

The effects of sex and experimental androgenization on the responsiveness of food intake and running-wheel activity to exogenously administered ovarian hormones were investigated in adult, gonadectomized rats. Food intake was found to be analogous to lordotic behavior in that males and neonatally androgenized females were relatively insensitive to the influences of either estradiol benzoate (EB) or progesterone (P). Running-wheel activity, however, could be differentiated from food intake in that males responded the same as females to the effects of EB and P. Androgenized females (500-mug testosterone propionate on the third day of life) showed a response to EB quantitatively equivalent to that of nonandrogenized females, but they had a longer latency to respond. The estrogen-antagonistic effects of P were confirmed for both of these behaviors, and there was a positive correlation between the magnitude of the responses to EB and P.     

Responses to copulatory stimulation in neonatally androgenized female rats.

Five experiments evaluated the extent to which copulatory stimulation could ameliorate the anestrus and sterility exhibited by neonatally androgenized female Long-Evans rats (N?=?102). The age at which Ss began to exhibit persistent vaginal estrus and the degree of sexual receptivity exhibited under several testing paradigms were found to be inversely related to the dose of testosterone propionate (TP) injected neonatally. With increasing numbers of mounts received, both the number of androgenized Ss exhibiting sexual receptivity and the quality of the estrous behavior exhibited tended to increase. Ss injected with high doses of TP (500 μg) usually showed little or no receptive behavior even in the most extensive behavioral tests. However, under some testing conditions Ss receiving 50 μg of TP neonatally, while showing little or no receptivity during initial mounts, showed increased receptivity as behavioral tests were extended. Following matings that included 1–5 ejaculations, only control Ss were observed to become pregnant. However, when androgenized females cohabited with males for an extended period, Ss that had neonatally received .5 μg of TP, but not higher doses, did become pregnant. It is concluded that (1) the capacity of systems mediating reproductive physiology and behavior is facilitated by stimuli associated with males; and (2) mating is a characteristic of the female rat, which can be manipulated by injection of hormones during the neonatal period. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of proceptive without receptive defeminization in male ferrets.

The latencies of 71 gonadectomized male and female ferrets to approach and interact with a sexually active stimulus male were measured after subcutaneous (sc) administration of estradiol benzoate ([EB] 0, 5, 10, or 15 μg/kg) in adulthood. Receptive responsiveness to stud males was also assessed during additional tests. Control females gonadectomized on Postnatal Day 35 displayed a dose-dependent reduction in approach latencies to the stud male that did not occur in control males castrated on Day 35. The approach latencies of males castrated on Day 20 or Day 5 were intermediate between these 2 extremes. Equivalent dose-dependent reductions in approach latencies were observed in Ss ovariectomized on Day 5 and implanted sc with silastic capsules containing either no hormone or different doses of testosterone over Days 5–20 or 20–35. Equivalent dose-dependent increments in acceptance quotients were obtained in all groups following EB treatment. Results suggest that the capacity to display the proceptive, or appetitive, components of feminine sexual behavior is normally reduced in male ferrets as a consequence of the perinatal action of testicular hormones, whereas receptive behavioral capacity is retained in males of this species. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence that physiologic levels of circulating estrogens and neonatal sex-imprinting modify postpubertal hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity

Intact, but sham-operated female rats had 2- to 3-fold higher levels of hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity than their male counterparts (15--21.5 vs. 6.7--8.7 nmol mevalonate/mg protein per h). The activity of the hepatic enzyme declined to about the same relative degree (40--60%) in male and female rats that were gonadectomized after puberty (53 days of age) and killed 5 weeks later. Implantation of silastic capsules containing 17 beta-estradiol increased the level of hepatic 3-hydroxy-3-methylglutaryl CoA reductase to levels found in sham-operated controls. In rats that were gonadectomized in infancy (12 h old) and killed 7--8 weeks later, the level of enzyme activity was not altered in females, but it was increased from 60--240% in males. Consequently, following neonatal gonadectomy, male-female differences in enzyme activity were no longer apparent. Implantation of silastic capsules containing estradiol in neonatally gonadectomized rats resulted in a doubling of enzyme activity in both males and females. Ovariectomy reduced plasma estrogen levels, but implantation of estradiol in gonadectomized males and females increased the hormone level to that found in sham-operated females. Thus, the results strongly suggest a role for physiologic levels of estrogen as a positive effector of 3-hydroxy-3-methylglutaryl CoA reductase activity. Neonatal sex imprinting also appears to modulate the enzyme activity since sex-mediated differences are effaced by gonadectomy in infancy, but not by gonadectomy following puberty.     

Sex differentiation of t-e circadian system in the golden hamster

The effect of estradiol benzoate (EB) on free-running circadian activity rhythms was studied in gonadectomized hamsters maintained in constant dim illumination. EB shortened the period (tau) of the female, but not of the male circadian activity rhythm. Responsiveness of the circadian system to EB was subject to sexual differentiation. The circadian period of wheel running by female hamsters given a single injection of testosterone propionate on the day of birth did not shorten in response to EB in adulthood. This failure to respond to EB also was observed in normal male hamsters, and was different from the response shown by normal females. Preliminary data suggest that tau of the activity rhythm of males castrated on the day of birth is shortened during EB treatment in adulthood. The differential effects of estradiol on tau are related to anatomic differences between the sexes in neural connections of the substrate for circadian rhythms.     

Differences among ovariectomized female rhesus macaques in the display of sexual behavior without and with estradiol treatment.

Ovariectomized, estrogen-primed, adult female rhesus macaques were preselected for the display of high (HLP) and low (LLP) levels of sexual performance. Eight sexually vigorous adult males were selected as partners. For 13 consecutive days each month, females received 0, 2.5, 5.0, and 10.0 μg of estradiol benzoate (EB) and were tested on Days 12 and 13 of injection. Blood samples were taken before and on the last day of each of the four injection series, and serum levels of estradiol, progesterone, and testosterone were determined with a radioimmunoassay. The HLP females (n?=?5) displayed higher levels of receptivity and proceptivity and received more mounts, intromissions, and ejaculations when tested without EB treatment than LLP females (n?=?5) did when they were tested with 10.0 μg of EB. Female receptivity, proceptivity, and attractiveness cannot be explained by estrogen action alone. The effectiveness of estrogen is limited by the somatic characteristics of the individual on which it acts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual behavior in adult gonadectomized female pseudohermaphrodite, female, and male rhesus macaques (Macaca mulatta) treated with estradiol benzoate and testosterone propionate.

Studied the sexual behavior of gonadectomized adult rhesus macaques given no hormonal treatment, treated with estradiol benzoate (EB; 20 μg/day), or treated with testosterone propionate (TP; 10 mg/day). Six experimentally produced female pseudohermaphrodites, 9 long-term castrated males, and 7 ovariectomized females were given 36 pair tests of 10-min duration with 6 ovariectomized, estrogen-primed female partners. 12 tests were given under each treatment condition. Yawning was the only behavior that showed a significant effect across treatments for hermaphrodites and females; the yawning rate was greater with TP treatment. The number of tests during which hermaphrodites showed erections increased significantly under TP treatment. Only one hermaphrodite mounted, but none achieved intromission or ejaculated. Males displayed several significant treatment effects, including increased mounting, intromitting, and ejaculating frequencies under TP treatment. EB had little effect on any of the behaviors in any group. Rates of aggression and grimacing were greater among hermaphrodites than among males and females. Males displayed significantly greater rates of sexual behavior than hermaphrodites or females. As infants and juveniles, these hermaphrodites had displayed social and sexual behaviors characteristic of males; however, as mature adults, their behavior and responsiveness to TP at a dose capable of activating a high level of sexual behavior in castrated males gave little evidence of masculinization. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of receptivity in estrogen-primed rats during successive mating tests with progestins and methysergide.

Evaluated the role of hormonal and experiential variables in mediating the gradual increase of receptivity occurring during weekly tests in 142 Sprague-Dawley adult ovariectomized females. Hormone treatment consisted of estradiol benzoate (EB) injection followed by progesterone, 20alpha-hydroxyprogesterone, methysergide maleate, or oil during weekly mating tests. The experiential conditions were vaginal stimulation, mounts only, or no interaction with males. There was a gradual increase in receptivity in all groups even in the one receiving oil. Progressive facilitation occurred even when no interaction with the male was permitted. Interchanging the synergists on the 6th and 7th tests was not detrimental to the display of receptivity attained with synergists given previously. Thus, it is concluded that successive injections of EB rather than synergists or experience mediate this increase in receptivity. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hormonal modulation of genital reflexes in male and masculinized female dogs.

When testosterone propionate (TP) is administered to adult, neonatally castrated male dogs and to adult females with masculinized genitalia produced by prenatal and neonatal exposure to androgen, both types of animals are unsuccessful in their attempts to copulate with receptive females. In the present experiment, 6 neonatally castrated male and 10 genitally masculinized female beagles were tested before and after TP treatment for responses to manual stimulation of the genitalia. An additional experimental group consisted of 6 males castrated as adults, and there was a control group of 5 normal males. After a series of TP injections (5 mg/kg), neonatally castrated males, adult castrates, and genitally masculinized females exhibited complete and strong erectile and ejaculatory reflexes. Erect penis lengths of neonatally castrated males and masculinized females were significantly shorter than those of normal males or of males castrated as adults. It is suggested that the failure of males castrated at birth, and of genitally masculinized females, to insert and lock when mounting receptive females is due to incomplete penile development and not to incomplete "organization" of spinal reflex mechanisms. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual differentiation of play behavior in the ferret.

Three experiments examined the endocrine mechanisms responsible for sex differences in prepubertal play behavior of ferrets. In Exp I, 6 gonadally intact adolescent males exhibited higher levels of "stand-over" behavior than 6 females did in tests between 63 and 123 days of age with gonadally intact female partners of the same age. In Exp II, with 69 Ss, those Ss exposed to androgen or to ovarian steroids over Days 5–20 of postnatal life subsequently exhibited significantly higher levels of stand-over behavior in tests with females than did control females gonadectomized on Day 5 and not given steroids. None of the Ss in Exp II exhibited levels of stand-over behavior comparable to those of the gonadally intact males in Exp I. In Exp III, with 36 Ss, males gonadectomized and implanted subcutaneously with testosterone capsules on Day 70 and tested with females at 84–96 days of age exhibited levels of stand-over behavior comparable to those observed in Exp I in gonadally intact males of the same age (Weeks 12–24). Males gonadectomized on Day 70 and given no hormone at testing exhibited significantly lower levels of this behavior. Significantly lower levels were also exhibited by males gonadectomized on Day 35 and females gonadectomized on Day 70, regardless of whether they were tested with testosterone present after Day 70. Sex differences in the expression of prepubertal play behavior of ferrets apparently result from differential exposure of males and females to androgen over an extended postnatal period. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of perinatal gonadal secretions on parameters of receptivity and weight gain in hamsters.

Examined the influence of ovarian and testicular secretions on lordosis in 64 female golden hamsters (Mesocricetus auratus) ovariectomized when 1 or 43 days old and in 80 males castrated when 1, 3, 5, or 43 days old. The 1st of 8 weekly 10-min mating tests was initiated at 57 or 113 days. Receptivity was not different among female groups except for higher initial scores for those with ovaries through puberty. Initial and maximum receptivity in males was inversely proportional to castration age. Rate of decrease from maximum appeared higher in males castrated at Days 3 and 5 than at Day 1. Age of initial test was significant for males; older Ss had lower initial and maximum receptivity scores. Gonadal secretions decreased weights in both sexes. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of testosterone propionate administered perinatally on sexual behavior of female ferrets.

Conducted an experiment with 25 female and 8 male albino ferrets ( Mustela furo ). Females that received injections of testosterone propionate (TP) early in postnatal life displayed significantly more masculine behavior than did control females when gonadectomized and administered either TP or estradiol benzoate in adulthood. This increased masculine response potential was not correlated with the effects of early TP treatment on phallic development. In contrast to results obtained in most other species, perinatal administration of TP to females failed to disrupt their ability to display the behavior that is characteristic of the sexually receptive animal in estrus. When estrogenic stimulation was provided in adulthood, the receptive behavior of 3 groups of perinatally androgenized females was indistinguishable from that of both male and female controls. However, after gonadectomy and administration of TP, control males and females that had received TP prenatally plus on Day 3 were significantly more receptive than were control females. The induction of receptivity by TP was significantly inhibited by simultaneous administration of the antiestrogen MER-25. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hypophysectomy facilitates sexual behavior in female rats

Lordosis was elecited in 49% of 87 hormonally untreated, hypophysectomized-ovariectomized (hypox-ovx) female rats in response to palpation of the flanks and perineum (vaginal stimulation was not applied). By contrast, only 12% of 113 hormonally untreated ovariectomized (ovx) rats showed lordosis in response to such stimulation. Subsequently, hypox-ovx and ovx-only rats were given daily injections of 1 mug/kg estradiol benzoate (EB) and tested for sexual receptivity with males. Teh estrogen-treated hypox-ovx females became sexually receptive significantly earlier, and exhibited higher lordosis quotients and more soliciting behavior, than the estrogen-treated ovx-only rats. The increased sexual responsiveness in the hypox-ovx rats could be due to increased LRH activity. To test this, we treated hypox-ovx rats with dihydrotestosterone propionate (DHT-P), which suppresses plasma LH levels but is relatively ineffective in inducing sexual receptivity, and found a significant depression of lordosis responsiveness. These experiments suggest that hypox-ovx females show a heightened responsiveness to hormonal and/or sensory factors that induce a lordosis response, possibly because of increased LRH activity.     

Polyandrous females discriminate against previous mates

In most animal species, particularly those in which females engage in polyandry, mate choice is a sequential process in which a female must choose to mate or not to mate with each male encountered. Although a number of theoretical and empirical investigations have examined the effects of sequential mate choice on the operation of sexual selection, how females respond to solicitation by previous mates has received little attention. Here, we report the results of a study carried out on the polyandrous pseudoscorpion, Cordylochernes scorpioides, that assessed the sexual receptivity of once-mated females presented after a lapse of 1.5 hr or 48 hr with either their first mate or a different male. Females exhibited a high level of receptivity to new males, irrespective of intermating interval. By contrast, time between matings exerted a strong effect on female receptivity to previous mates. After a lapse of 48 hr, females did not differ significantly in their receptivity toward previous mates and different males, whereas at 1.5 hr after first mating, females were almost invariably unreceptive to males from whom they had previously accepted sperm. This result could not be attributed to male size or mating experience or to male sexual receptivity. Indeed, males were as willing to transfer sperm to a previous mate as they were to a new female. This difference between males and females in their propensity to remate with the same individual may reflect a conflict between the sexes, with males seeking to minimize postcopulatory sexual selection and females actively keeping open the opportunity for sperm competition and female choice of sperm by discriminating against previous mates.     

Hormonal control of behavior in the Japanese quail.

Adult male and female Japanese quail were functionally castrated by exposure to a short photoperiod and then injected with either estradiole benzoate (EB) or testosterone propionate (TP). Females injected with EB (n = 24) exhibited normal sexual receptivity again but displayed no male courtship behavior. Males injected with EB (n = 10) showed both male and female copulatory patterns. Females injected with TP (n = 14) showed little sexual behavior of any sort, while males injected with TP (n = 10) displayed male sexual behavior. The male quail is thus more bisexual than the female. In contrast with mammalian species, the female is more bisexual. The difference is discussed in relation to the differences in the embryology and cytogenetics of birds and mammals. (29 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal androstenedione and adult sexual behavior in golden hamsters.

Notes that male rats castrated and given androstenedione neonatally can show high levels of both masculine and feminine copulatory behavior in adulthood. In the present study, 24 intact female and 30 intact male hamsters castrated at birth were treated for their 1st 20 days with oil, free testosterone, or androstenedione. All neonatal androgen treatments mimicked the naturally occurring developmental process of the male in that all androgenized groups were capable of high levels of male behavior (males but not females showing ejaculation patterns) as well as moderate levels of lordotic receptivity. There were no significant differences in effect among neonatal androgen treatments. Results are discussed as they relate to species differences, sex differences, hamster "bisexuality," and posthormone copulatory performance. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex-related differences in spatial divided attention and motor impulsivity in rats.

The acquisition and performance of a self-paced test of spatial divided attention linked with frontal cortex function were assessed in postpubertal (> 60 days) normal or gonadectomized male and female rats. Males were more accurate at detecting relatively brief visual stimuli than females, but this difference was eliminated by increasing the target stimulus duration, indicating an attentional basis for this effect. Premature errors were, however, greater in males than in females, suggesting greater impulsivity in males. Subsequent experiments in gonadectomized rats suggest that circulating hormones influence attention and impulsivity, but not necessarily sex differences. These results demonstrate a double dissociation between components of impulse control and divided attention in male and female rats and may have implications for sex differences in disorders of attention and cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual dimorphism in ultrasonic vocalizations of mice (Mus musculus): Gonadal hormone regulation.

Male mice, during courtship and sexual behavior, vocalize substantially more 70-kHz ultrasounds than do females. Four experiments conducted with 109 male and female DBA/2J and ADK2F? mice demonstrated that testosterone propionate (TP) substantially increased ultrasonic emissions and mounting by ovariectomized females and that long-term gonadectomized males and females increased their amount of ultrasound production in response to TP to approximately the same levels. From these results it is suggested that the sexual dimorphism normally seen in ultrasonic vocalizations can be accounted for by the activational effects of androgen in adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social play soliciting by male and female juvenile rats: Effects of neonatal androgenization and sex of cagemates.

Investigated the behavior of male and female Long-Evans hooded rats during individual exposure to nonplayful juvenile social stimuli in a novel test of play-soliciting behavior in 2 experiments examining hormonal and experiential determinants of sex differences. In Exp I, using 36 female and 18 male Ss, neonatally androgenized females engaged in play soliciting at a level equal to that of male controls and greater than that of nonandrogenized female controls. In Exp II, 52 males and 32 females were reared in unisexual and bisexual groups in order to compare long-term sex-related social experience effects on juvenile play soliciting. Males exposed only to other young males engaged in greater play soliciting than males exposed to both sexes; females, in contrast, were unaffected by sex of cagemates. Within rearing conditions, however, males engaged in greater play soliciting than females. The combined results suggest that perinatal gonadal androgen exposure effects on social play are prepotent and contribute essentially to sex differences in the initiation of social play behavior. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)