Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

The role of sex steroids in courtship, pairing and pairing behaviors in the socially monogamous zebra finch

The purpose of this study was to test whether sex steroid actions are necessary for courtship and pairing in socially monogamous birds. We examined the effects of an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), combined with an anti-androgen, flutamide (F), on the behavior and pairing status of initially unpaired male and female zebra finches (Taeniopygia guttata). In the first experiment, 24 adult males were implanted with either a combination of ATD and flutamide or empty implants. Two weeks after implantation, birds were housed in aviaries containing 3 ATD + F males, 3 control males, and 3 females and allowed 2 weeks to pair, with observations 7 times during the 2-week period. A second experiment tested the effects of these same treatments in females. During the first 4 days of testing, ATD + F males were less likely to attack conspecifics than were control males. ATD + F males were also less likely to "greet," or approach, females than were control males, but other courtship behaviors, including directed singing, were unaffected. ATD + F females did not differ from control females on any courtship behavior measured. Furthermore, these treatments did not affect pairing behaviors (time spent clumping or in a nest box together) or the likelihood of pairing with a partner of the opposite sex. ATD + F treatments in females did, however, increase the likelihood of same-sex pairing. This suggests that, although sex steroids may regulate some courtship behaviors in males, they do not regulate pairing behaviors and have little effect on the likelihood that a male or female will be chosen as a mate by a bird of the opposite sex.     

The postnatal demasculinization of sexual behavior in the Japanese quail (Coturnix coturnix japonica)

Three experiments were performed to analyze the time course of demasculinization in the Japanese quail and to test the activating and organizing effects of estradiol (E2) in adult sexually active birds. In Experiment 1, males and females were castrated at the age of 1 day or 1, 2, 4, and 6 weeks and treated as adults with testosterone (T). The age of castration had no effect on behavior and morphology in males. Plasma gonadotrophins (LH and FSH) were, however, higher in males castrated at or before than in those castrated after 2 weeks of age. This suggests that postnatal testicular secretions have organizing effects on the pituitary activity. Females which were castrated before 1 week of age were less sensitive to the activating effects of T than males, but were not fully demasculinized. The demasculinization of different reproductive characteristics such as male sexual behavior, cloacal gland size, and weight of the syringeal muscles is achieved in females at different times posthatching. In Experiment 2, castration of male and female quail at the ages of 4 days or 4 weeks confirmed that postnatal ovarian secretions contribute to the full behavioral and morphological demasculinization of females. It is easier to elicit mounting in T-treated females when they are tested in their home cage instead of a test arena. This difference was not observed in males. During Experiment 3, it was impossible to demasculinize sexually active adult males or females by treatment with Silastic implants of E2. E2 did not maintain sexual behavior in ovariectomized females showing male sexual behavior when treated with T but maintained the behavior in males.     

Aromatization: Important for sexual differentiation of the neonatal rat brain

This paper examines the hypothesis that testosterone (T) produces its differ-entiative effect on the neonatal rat brain after undergoing conversion in situ to estradiol-17β (E₂). We examined the abilities of an aromatizing enzyme inhibitor, (1,4,6-androstatriene-3,17-dione) (ATD), and an anti-estrogen, CI628, to inhibit sexual differentiation. Male and female rats were treated during the first few days of postnatal life with ATD or CI628, and females were treated on the following day with T in Silastic capsules or its propionate (TP) in oil. ATD and ATD+T females were normal with respect to time of vaginal opening, ovarian weight, ability to demonstrate an LH surge, and lordosis behavior. T and TP females were masculinized with respect to all these measures. CI628 and CI628+TP females had impaired ovarian function and intermediate lordosis quotients (LQs) compared to controls, though they were higher in both measures than T females. ATD males demonstrated high LQs in response to estradiol benzoate (EB) + progesterone, comparable to those of control females. CI628 males had intermediate LQs, which were significantly higher than those of control males. These results indicate that ATD can substantially protect the neonatal rat brain from the differentiative effects of exogenous or endogenous T, probably by blocking aromatization. CI628 affords only partial protection against T and produces a weak differentiative effect due to its own weak estrogenicity. Thus, aromatization of T in newborn rat brains appears to be essential if sexual differentiation is to occur.     

Neonatal hormonal influences on the development of proceptive and receptive feminine sexual behavior in rats

The objective of this study was to examine the influence of androgen and of the inhibiting of aromatization of androgen to estrogen during the early neonatal period on the development of receptive (lordosis and acceptance of stimulus male mounting attempts) and proceptive (affiliation with and solicitation of stimulus males) feminine sexual behavior. Within 8 hr of birth, male rats were castrated or received subcutaneous implants of the aromatase inhibitor androst-1,4,6-triene-3, 17-dione (ATD) while females received injections of testosterone propionate (TP). At 90 days of age all treated animals and controls were tested for receptive and proceptive feminine sexual behavior. It was found that androgen present neonatally blocked proceptive as well as receptive behavior patterns in adult rats. The proceptive and receptive feminine sexual behavior patterns displayed by adult males deprived of the effects of androgen neonatally either by castration or by treatment with ATD were comparable to those of normal females.     

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.     

Sexual differentiation of behavior in the zebra finch: effect of early gonadectomy or androgen treatment

Treatment of nestling zebra finches with estradiol benzoate (EB) has been shown to masculinize singing in females and demasculinize copulatory behavior in males, suggesting that sexual differentiation of these behaviors is under hormonal control such that testicular hormones induce the capacity for song and ovarian hormones suppress the capacity for mounting. Two experiments were carried out to obtain a more complete picture of sexual differentiation in this species. In Experiment 1, nestlings were injected daily for the first 2 weeks after hatching with testosterone propionate (TP), dihydrotestosterone propionate (DHTP), or a combination of DHTP and EB. As adults, birds were gonadectomized and implanted with TP prior to testing, then tested again after implantation with EB. Singing was not increased in females by any of the treatments. The only effect of either TP or DHTP given alone was defeminization of female proceptive behavior by DHTP. Thus androgens appear to have less influence than estrogens on sexual differentiation of behavior in this species. The combination of DHTP and EB demasculinized mounting in males. In Experiment 2, nestlings were gonadectomized at 7-9 days of age and implanted with TP prior to testing in adulthood. Early gonadectomy had little effect on later behavior; early castrated males sang, danced, and copulated normally and early ovariectomized females neither sang nor mounted.     

Activation of sexual behavior by implantation of testosterone propionate and estradiol benzoate into the preoptic area of the male Japanese quail (Coturnix japonica)

Intracranial implantation of minute pellets of gonadal steroids was performed to determine neuroanatomical loci at which steroids activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, systemic treatment of castrated males with either testosterone propionate (TP) or estradiol benzoate (EB) restores male-typical copulatory behavior (head grabbing, mounting, and cloacal contact movements). In addition, EB activates female-typical receptive behavior (crouching). Adult male castrated quail were implanted intracranially with 300-micrograms pellets containing TP, EB, or cholesterol (CHOL) and behavior was tested with intact males and females. Either TP or EB pellets in the preoptic area (POA) activated male-typical copulatory behavior. Mounting was specifically activated without concomitant activation of other steroid-sensitive sexual and courtship behaviors. TP and EB implants in adjacent nuclei containing receptors for these steroids and CHOL implants in POA had no effect on male-typical copulatory behavior. Eighteen percent of all males tested for female-typical receptivity crouched, but no specific effect of EB was seen at any site. The similarity of the POA sites for activation of mounting by TP and EB is consistent with the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to behavioral activation.     

Influence of androgen in the neonatal period on ejaculatory and postejaculatory behavior in the rat

The objective of the present report was to investigate the influence of androgen in the neonatal period on the development of ejaculatory and postejaculatory behavior. At birth, male rats were either castrated (neonatally castrated males), implanted with a Silastic tube of the aromatase inhibitor androsta-1,4,6-triene-3,17-dione for the first 10 days (ATD males), or left untreated (normal males). Female rats were either injected with 0.5 mg testosterone propionate (TP) on Days 1 (day of birth) and 2 (androgenized females) or left untreated (normal females). All gonadally intact animals were castrated at 60 days of age. Following TP administration, all animals were tested for ejaculatory and postejaculatory behavior under both shock and nonshock conditions. All animals were capable of showing the intromission pattern; however, the ejaculatory pattern was exhibited regularly only by those animals exposed to androgen at birth (normal males, androgenized females, and ATD males). The normal males required fewer intromissions to achieve ejaculation than the other two groups exhibiting this reflex. This result is discussed in terms of peripheral genital stimulation deficits and the differentiation of neural tissue responsible for masculine copulatory behavior. Androgenized females and ATD males displayed a refractory period, characterized by 22-kHz vocalizations, equal to or longer than that found in normal males. These results indicate that defeminization is not necessary for the display of normal ejaculatory and postejaculatory behavior.     

Evidence for androgen independence of male mounting behavior in white-crowned sparrows (Zonotrichia leucophrys gambelii)

Previous experiments have shown that expression of mounting behavior in sexually inexperienced, adult male white-crowned sparrows does not require elevated plasma levels of androgen; adult males maintained on nonstimulatory short days mount sexually receptive females. The experiments reported here demonstrate that (1) sexually inexperienced, prepubertal males maintained on nonstimulatory short days show very low mounting rates in response to female sexual displays; (2) these males exhibit high mounting rates when exposed to stimulatory long days but androgen treatment on short days is ineffective in stimulating high mounting rates; and (3) prepubertal castration has no effect on the expression of mounting behavior by photostimulated adult males. Thus, there is no evidence that mounting behavior of adult male white-crowned sparrows depends on androgen.     

Adult partner preference and sexual behavior of male rats affected by perinatal endocrine manipulations

Intact adult male rats, in which aromatization of testosterone to estradiol was prevented pre- and/or neonatally by ATD (1,4,6-androstatriene-3,17-dione), were repeatedly tested for partner preference behavior (choice: estrous female vs active male). In consecutive tests increasing preference scores for the female were found. Neonatal ATD males showed significantly lower preference scores for an estrous female than controls or prenatal ATD males. Prenatal ATD caused preference scores only slightly lower than those of controls. Ejaculation frequencies were markedly reduced or even absent in neonatal ATD males. Prenatal ATD treatment only had no or a moderately lowering effect on ejaculation frequency. Lordosis behavior of adult intact males was more facilitated following neonatal ATD treatment than following prenatal ATD treatment. In a number of tests the serotonergic drug 8-OH-DPAT was injected prior to testing for sexual partner preference and copulatory behavior. DPAT significantly increased preference for an estrous female in all groups of males when interaction was possible, but had no effect when sexual interaction was prevented by wire mesh. DPAT was able to increase the number of ejaculators in nonejaculating groups (i.e., perinatally ATD-treated males). "Premature ejaculations," i.e., ejaculations with the first intromission, were frequently observed with DPAT treatment in all groups of males. In conclusion, the availability of neonatal estrogen (derived from testosterone) organizes, at least partially, the preference for an estrous female normally shown by adult male rats. The lack of neonatal estrogen causes males to be less masculinized, both in partner preference behavior and ejaculatory behavior, and less defeminized in lordosis behavior.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadal hormones and sexual behavior in groups of adult talapoin monkeys (Miopithecus talapoin).

Three heterosexual groups of six to eight monkeys were studied; all females were ovariectomized, whereas males were either intact or castrated. Aggressive hierarchies were evident in all groups, with females generally outranking males. When females were treated with estradiol, all males looked more frequently at the latters' sexual skin swellings, but only one male who was both dominant and intact copulated with them. Thus, either castration or low rank resulted in decreased levels of sexual behavior in male talapoins. The sexual behavior of dominant castrated males was restored by testosterone therapy, whereas subordinate castrates never copulated, even after large doses of testosterone, though penile erections and ejaculatory reflex (during masturbation) were restored. Following removal of a dominant male, the sexual behavior of the next male in rank was restored, provided he was not castrated and untreated. In contrast to males, female talapoins showed no consistent correlation between their rank and sexual activity. Estradiol therapy was without overall effect upon the frequency of female mounting behavior, though some females mounted and presented to one another more often. Estradiol treatment also caused females to present to males more frequently, but only to those that were sexually active (i.e., who mounted females).     

Masculine sexual behavior in male and female rats following perinatal manipulation of androgen: Effects of genital anesthetization and sexual experience

Androgenized females, Day 1 male castrates, normal males, and normal females were tested for mounting behavior as adults following TP administration (1 mg/day). Genital anesthetization was used to eliminate all intromission and ejaculation behavior. Results showed that sexually-naive normal males and androgenized females mounted significantly more then Day 1 male castrates, while the Day 1 male castrates mounted significantly more than normal females. Sexually-experienced normal males and androgenized females displayed a significant facilitation of mounting behavior as compared to the sexually-naive animals. Tests of masculine copulatory behavior without genital anesthetization also were conducted with androgenized females and normal males. In these tests, androgenized females were indistinguishable from normal males in all aspects of the complete masculine pattern. The present results provide evidence that during perinatal development androgen acts directly on neural systems which will later regulate adult masculine sexual behavior.     

Female-female mounting among goats stimulates sexual performance in males

The hypothesis that female-female mounting is proceptivity in goats, in that male goats are aroused by the visual cues of this mounting behavior, was tested. Once a week, male goats were randomly selected and placed in a test pen in which they were allowed to observe one of six selected social or sexual stimulus conditions. The stimulus conditions were one familiar male with two estrous females (MEE); three estrous females that displayed female-female mounting (E(m)); three estrous females that did not mount (E(nm)); three non-estrous females (N(E)); three familiar males (M); and no animals in the pen (Empty). After 10 min, the stimulus animals were removed, and an estrous female was placed in the test pen with the male for a 20-min sexual performance test. During sexual performance tests, the frequencies and latencies of all sexual behaviors were recorded. This procedure was repeated so all males (n = 6) were tested once each test day, and all the stimulus conditions were presented each test day. This was repeated weekly until all males had been exposed to each stimulus condition. Viewing mounting behavior, whether male-female or female-female, increased the total number of sexual behaviors displayed, increased ejaculation frequency, and decreased latency to first mount and ejaculation, post-ejaculatory interval, and the interval between ejaculations. We conclude that male goats are aroused by the visual cues of mounting behavior, and that female-female mounting is proceptivity in goats.     

Experimental evidence that ovary and oviducal gland extracts influence male agonistic behavior in squids

Recent investigations of sensory and behavioral cues that initiate sexual selection processes in the squid Loligo pealeii have determined that egg capsules deposited on the substrate provide a strong visual and chemotactile stimulus to males, even in the absence of females (1, 2, 3). The visual stimulus of egg capsules attracts males to the eggs, and when the males touch the eggs, they encounter a chemical stimulus that leads to highly aggressive fighting behavior. We have recently demonstrated that egg capsule extracts implanted in artificial egg capsules elicit this aggressive behavior (4). In this communication, we present evidence that the salient chemical factor originates in the ovary and perhaps the oviducal gland of the female reproductive tract.     

Role of aromatization in sexual differentiation: Effects of prenatal ATD treatment and neonatal castration

Pregnant female rats were administered either the aromatization inhibitor ATD (1,4,6-androstatriene-3,17-dione) or propylene glycol from Days 10 to 21 of gestation. On the day of birth one-half of the offspring from each group were gonadectomized. The remaining offspring were gonadectomized 35 days after birth. When adult the animals were given eight weekly mating tests following treatment with 2 or 8 μg of estradiol benzoate (EB) and 25 or 200 μg of progesterone (P). The probability of lordotic behavior as well as the frequency of ear-wiggle and hop and dart responses was measured. Prenatal ATD treatment resulted in a slight increase in lordotic behavior in the males. Lordotic potential was greatly facilitated by castration at birth. ATD treatment also increased the frequency of proceptive behaviors in males and combined ATD treatment and neonatal castration produced a dramatic increase in these behaviors. Prenatal ATD treatment and neonatal ovariectomy had only modest effects on the display of receptive and proceptive behaviors in females. Two weeks after the last test for female mating behaviors, the animals received daily injections of 200 μg of testosterone propionate. Four weekly tests for male-typical responses were given starting 1 week after the first injection. Prenatal ATD treatment did not markedly affect masculine behavior in the males. Castration at birth eliminated the ejaculatory response and reduced the frequency of mounting and intromission behavior. Prenatal ATD treatment and ovariectomy at birth had no appreciable effects on the display of male-typical behaviors in the females. Testosterone-stimulated masculine behavior of the female was similar to that of the male castrated at birth.     

Sex differences and effects of neonatal aromatase inhibition on masculine and feminine copulatory potentials in prairie voles

Copulatory behaviors in most rodents are highly sexually dimorphic, even when circulating hormones are equated between the sexes. Prairie voles (Microtus ochrogaster) are monomorphic in their display of some social behaviors, including partner preferences and parenting, but differences between the sexes in their masculine and feminine copulatory behavior potentials have not been studied in detail. Furthermore, the role of neonatal aromatization of testosterone to estradiol on the development of prairie vole sexual behavior potentials or their brain is unknown. To address these issues, prairie vole pups were injected daily for the first week after birth with 0.5 mg of the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) or oil. Masculine and feminine copulatory behaviors in response to testosterone or estradiol were later examined in both sexes. Males and females showed high mounting and thrusting in response to testosterone, but only males reliably showed ejaculatory behavior. Conversely, males never showed feminine copulatory behaviors in response to estradiol. Sex differences in these behaviors were not affected by neonatal ATD, but ATD-treated females received fewer mounts and thrusts than controls, possibly indicating reduced attractiveness to males. In other groups of subjects, neonatal ATD demasculinized males' tyrosine hydroxylase expression in the anteroventral periventricular preoptic area, and estrogen receptor alpha expression in the medial preoptic area. Thus, although sexual behavior in both sexes of prairie voles is highly masculinized, aromatase during neonatal life is necessary only for females' femininity. Furthermore, copulatory behavior potentials and at least some aspects of brain development in male prairie voles are dissociable by their requirement for neonatal aromatase.     

Effect of forebrain implants of testosterone or estradiol on scent-marking and sexual behavior in male and female rabbits

Chinning consists of rubbing the chin against an object, thereby depositing secretions from the submandibular glands. As mating, chinning is stimulated in male and female rabbits by testosterone and estradiol, respectively. To investigate the brain sites where steroids act to stimulate chinning and mating we implanted into the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of gonadectomized male and female rabbits testosterone propionate (TP; males) or estradiol benzoate (EB; females) and quantified chinning and sexual behavior. EB implants into the VMH or MPOA reliably stimulated chinning in females. Most of those implanted into the VMH and around half of the ones receiving EB into MPOA or diagonal band of Broca (DBB) showed lordosis. Chinning, but not sexual behavior, was stimulated in males by TP implants into the MPOA or DBB. Neither chinning nor mounting were reliably displayed by males following TP implants into the VMH. Results indicate that, in females, the VMH is an estrogen-sensitive brain area that stimulates both chinning and lordosis while the MPOA seems to contain subpopulations of neurons involved in either behavior. In males, androgen-sensitive neurons of the MPOA, but not the VMH, are involved in chinning stimulation but it is unclear if these areas also participate in the regulation of copulatory behavior.     

Effect of forebrain implants of testosterone or estradiol on scent-marking and sexual behavior in male and female rabbits

Chinning consists of rubbing the chin against an object, thereby depositing secretions from the submandibular glands. As mating, chinning is stimulated in male and female rabbits by testosterone and estradiol, respectively. To investigate the brain sites where steroids act to stimulate chinning and mating we implanted into the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of gonadectomized male and female rabbits testosterone propionate (TP; males) or estradiol benzoate (EB; females) and quantified chinning and sexual behavior. EB implants into the VMH or MPOA reliably stimulated chinning in females. Most of those implanted into the VMH and around half of the ones receiving EB into MPOA or diagonal band of Broca (DBB) showed lordosis. Chinning, but not sexual behavior, was stimulated in males by TP implants into the MPOA or DBB. Neither chinning nor mounting were reliably displayed by males following TP implants into the VMH. Results indicate that, in females, the VMH is an estrogen-sensitive brain area that stimulates both chinning and lordosis while the MPOA seems to contain subpopulations of neurons involved in either behavior. In males, androgen-sensitive neurons of the MPOA, but not the VMH, are involved in chinning stimulation but it is unclear if these areas also participate in the regulation of copulatory behavior.     

Behavioral action of estrogen in male hamsters: effect of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD)

This study examines three independent behavioral variables known to be activated by testosterone in the male hamster; namely, the tendency to approach the female, the tendency to leave the female, and the amount of sniffing directed to her. Both intact and testosterone-maintained castrated male hamsters were given the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) in subcutaneous, Silastic capsules. In intact males, there was an ATD dose-dependent increase in the tendency to leave the female and a decrease in the amount of olfactory investigation. The tendency of the male to approach the female was unaffected. The higher doses of ATD also abolished the ability of males to discriminate between females using vaginal odor cues. These results were confirmed in castrated males whose behavior was maintained at the intact level by testosterone implants. In addition, in both intact and castrated males, estradiol or diethylstilbestrol was able to reverse the behavioral changes induced by ATD. Our results indicate that estrogen produced by aromatization of testosterone activates behavior. We conclude that estrogen, by influencing some, but not all, components of masculine behavior, has a specific role in modulating male-female interactions.