Effects of progesterone and estradiol on sexual attractivity of female rhesus monkeys

Does scent attractiveness reveal women's ovulatory timing? Evidence from signal detection analyses and endocrine predictors of odour attractiveness

Odour cues associated with shifts in ovarian hormones indicate ovulatory timing in females of many nonhuman species. Although prior evidence supports women's body odours smelling more attractive on days when conception is possible, that research has left ambiguous how diagnostic of ovulatory timing odour cues are, as well as whether shifts in odour attractiveness are correlated with shifts in ovarian hormones. Here, 46 women each provided six overnight scent and corresponding day saliva samples spaced five days apart, and completed luteinizing hormone tests to determine ovulatory timing. Scent samples collected near ovulation were rated more attractive, on average, relative to samples from the same women collected on other days. Importantly, however, signal detection analyses showed that rater discrimination of fertile window timing from odour attractiveness ratings was very poor. Within-women shifts in salivary oestradiol and progesterone were not significantly associated with within-women shifts in odour attractiveness. Between-women, mean oestradiol was positively associated with mean odour attractiveness. Our findings suggest that raters cannot reliably detect women's ovulatory timing from their scent attractiveness. The between-women effect of oestradiol raises the possibility that women's scents provide information about overall cycle fecundity, though further research is necessary to rigorously investigate this possibility.

Neural and Hormonal Control of Sexual Behavior

Gonadal hormones contribute to the sexual differentiation of brain and behavior throughout the lifespan, from initial neural patterning to "activation" of adult circuits. Sexual behavior is an ideal system in which to investigate the mechanisms underlying hormonal activation of neural circuits. Sexual behavior is a hormonally regulated, innate social behavior found across species. Although both sexes seek out and engage in sexual behavior, the specific actions involved in mating are sexually dimorphic. Thus, the neural circuits mediating sexual motivation and behavior in males and females are overlapping yet distinct. Furthermore, sexual behavior is strongly dependent on circulating gonadal hormones in both sexes. There has been significant recent progress on elucidating how gonadal hormones modulate physiological properties within sexual behavior circuits with consequences for behavior. Therefore, in this mini-review we review the neural circuits of male and female sexual motivation and behavior, from initial sensory detection of pheromones to the extended amygdala and on to medial hypothalamic nuclei and reward systems. We also discuss how gonadal hormones impact the physiology and functioning of each node within these circuits. By better understanding the myriad of ways in which gonadal hormones impact sexual behavior circuits, we can gain a richer and more complete appreciation for the neural substrates of complex behavior.

The neuroendocrinology of sexual attraction

Sexual attraction has two components: Emission of sexually attractive stimuli and responsiveness to these stimuli. In rodents, olfactory stimuli are necessary but not sufficient for attraction. We argue that body odors are far superior to odors from excreta (urine, feces) as sexual attractants. Body odors are produced by sebaceous glands all over the body surface and in specialized glands. In primates, visual stimuli, for example the sexual skin, are more important than olfactory. The role of gonadal hormones for the production of and responsiveness to odorants is well established. Both the androgen and the estrogen receptor α are important in male as well as in female rodents. Also in primates, gonadal hormones are necessary for the responsiveness to sexual attractants. In males, the androgen receptor is sufficient for sustaining responsiveness. In female non-human primates, estrogens are needed, whereas androgens seem to contribute to responsiveness in women.

Processing by the main olfactory system of chemosignals that facilitate mammalian reproduction

This article is part of a Special Issue "Chemosignals and Reproduction". Most mammalian species possess two parallel circuits that process olfactory information. One of these circuits, the accessory system, originates with sensory neurons in the vomeronasal organ (VNO). This system has long been known to detect non-volatile pheromonal odorants from conspecifics that influence numerous aspects of social communication, including sexual attraction and mating as well as the release of luteinizing hormone from the pituitary gland. A second circuit, the main olfactory system, originates with sensory neurons in the main olfactory epithelium (MOE). This system detects a wide range of non-pheromonal odors relevant to survival (e.g., food and predator odors). Over the past decade evidence has accrued showing that the main olfactory system also detects a range of volatile odorants that function as pheromones to facilitate mate recognition and activate the hypothalamic-pituitary-gonadal neuroendocrine axis. We review early studies as well as the new literature supporting the view that the main olfactory system processes a variety of different pheromonal cues that facilitate mammalian reproduction.

Psychobehavioral effects of hormonal contraceptive use

Although female use of hormonal contraceptives (HCs) has been associated with a variety of physical side effects, the psychological and behavioral side effects have received comparatively little attention until recently. Indeed, the long-term impact of HC use on human psychology has been vastly under-researched and has only recently become a focus for mainstream scholars. Women who use HCs report higher rates of depression, reduced sexual functioning, and higher interest in short-term sexual relationships compared to their naturally-cycling counterparts. Also, HC use may alter women's ability to attract a mate, as well as the mate retention behaviors in both users and their romantic partners. Some evidence even suggests that HC use alters mate choice and may negatively affect sexual satisfaction in parous women, with potential effects on future offspring. Interestingly, HCs have become a standard method of population control for captive nonhuman primates, opening up exciting avenues for potential comparative research. Here, the existing literature on the psychobehavioral effects of HCs in humans and nonhuman primates is reviewed and discussed. The potential resulting downstream consequences for the path of human evolution and recommendations for how future research could tease apart the underlying causes of these psychobehavioral effects of HC use are discussed, including suggestions for research involving nonhuman primates.

Contribution of pheromones processed by the main olfactory system to mate recognition in female mammals

Until recently it was widely believed that the ability of female mammals (with the likely exception of women) to identify and seek out a male breeding partner relied on the detection of non-volatile male pheromones by the female's vomeronasal organ (VNO) and their subsequent processing by a neural circuit that includes the accessory olfactory bulb (AOB), vomeronasal amygdala, and hypothalamus. Emperical data are reviewed in this paper that demonstrate the detection of volatile pheromones by the main olfactory epithelium (MOE) of female mice which, in turn, leads to the activation of a population of glomeruli and abutting mitral cells in the main olfactory bulb (MOB). Anatomical results along with functional neuroanatomical data demonstrate that some of these MOB mitral cells project to the vomeronasal amygdala. These particular MOB mitral cells were selectively activated (i.e., expressed Fos protein) by exposure to male as opposed to female urinary volatiles. A similar selectivity to opposite sex urinary volatiles was also seen in mitral cells of the AOB of female mice. Behavioral data from female mouse, ferret, and human are reviewed that implicate the main olfactory system, in some cases interacting with the accessory olfactory system, in mate recognition.

Activation of progestin receptors in female reproductive behavior: Interactions with neurotransmitters

The steroid hormone, progesterone (P), modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and reproductive behavior in female mammals. A wide body of evidence indicates that these neural effects of P are predominantly mediated via their intracellular progestin receptors (PRs) functioning as "ligand-dependent" transcription factors in the steroid-sensitive neurons regulating genes and genomic networks. In addition to P, intracellular PRs can be activated by neurotransmitters, growth factors and cyclic nucleotides in a ligand-independent manner via crosstalk and convergence of pathways. Furthermore, recent studies indicate that rapid signaling events associated with membrane PRs and/or extra-nuclear, cytoplasmic PRs converge with classical PR activated pathways in neuroendocrine regulation of female reproductive behavior. The molecular mechanisms, by which multiple signaling pathways converge on PRs to modulate PR-dependent female reproductive behavior, are discussed in this review.

The inhibition of female rabbit sexual behavior by progesterone: progesterone receptor-dependent and-independent effects

In the pregnant domestic rabbit, scent marking ("chinning") and sexual behavior are inhibited by ovarian-derived progesterone (P). In order to distinguish behavioral effects of P that are PR-dependent from those mediated by its ring A reduced metabolites, we administered P, P+RU486 (PR antagonist), chlormadinone acetate (CA, synthetic progestin that does not form ring A reduced metabolites), or vehicle to ovariectomized (ovx) estradiol-benzoate (EB)-treated female rabbits, via sc injection, on experimental day 0. Chinning was quantified daily, and mating tests were done on days -1, 1, 3, 5, and 7. On day 1, chinning was significantly decreased, and the latency to be mounted by the male was significantly increased (indicating decreased sexual attractivity of the female) in P-treated females. The effect of P on chinning, but not its effect on sexual attractivity, was completely blocked by RU486 and replicated by CA. Although CA had no effect on attractivity on day 1, it decreased both sexual receptivity and attractivity on day 3. In a preference test in which the male could interact with either an ovx EB-treated female or an ovx female that had received one of the above hormone treatments 24 h earlier, P decreased sexual attractivity and increased aggression. The effect of P on aggression, but not its effect on attractivity, was blocked by RU486 and replicated by CA. These results indicate that both PR-dependent and PR-independent mechanisms decrease sexual attractivity, whereas PR activation is necessary for the inhibition of chinning and sexual receptivity, and for the stimulation of aggression.

Progesterone receptor activation signals behavioral transitions across the reproductive cycle of the female rabbit

The female rabbit is an exceptional experimental model to define mechanisms by which progesterone (P) controls the expression of reproductive behaviors. In the rabbit, the rise in P levels during pregnancy inhibits estrous scent marking ("chinning"), stimulates the excavation of a nest burrow ("digging"), and primes behaviors later used for nest construction. The pre-parturient fall of P triggers the construction of a straw nest ("straw carrying") that is lined with hair that she pulls from her own body ("hair pulling"). These behaviors can be replicated in ovariectomized (ovx) females given a schedule of estradiol (E) and P that mimics hormone levels during pregnancy (E from days 0 to 4, E + P from days 5 to 17, E from days 18 to 27). We administered PR antagonists RU486 or CDB(VA)2914 to ovx female rabbits during either the initial (days 5-11) or late (days 12-17) phases of P treatment, to determine the role of PR activation in coordinating the expression of these behaviors. Both antiprogestins attenuated the P-mediated decline in chinning and increase in digging when administered during days 5-11. When given across days 12-17, both antiprogestins triggered an early decline in digging, the onset of nest building in some Ss, and the reinstatement of chinning. These results point to a central role of PR activation for establishing and maintaining the behavioral phenotype of pregnancy, and for the behavioral transition from pregnancy to estrus.

Medroxyprogesterone acetate acutely facilitates and sequentially inhibits sexual behavior in female rats

Medroxyprogesterone acetate (MPA), a synthetic progestin commonly used in contraception and hormone replacement therapy, appears to inhibit libido in women, but little is known about the mechanisms through which it may exert this effect. We compared the acute and sequential actions of MPA and natural progesterone (P4) on sexual behavior in female rats to test the hypothesis that MPA inhibits sexual behavior, at least in part, by acting as a potent progesterone receptor (PR) agonist. Ovariectomized females were placed in one of three dose groups (high, mid, or low), and each subject was tested under three different conditions (MPA, P4, and vehicle). The order of progestin treatment was balanced among subjects, and within each dose group equimolar quantities of MPA and P4 were administered. During each trial, females were injected with estradiol benzoate (EB, 4 mug) followed by one of three progestin treatments (MPA, P4, or vehicle) at +44 h, and behavioral testing at +48 h. On the next day, all females were given a standard 500-microg injection of P4 at +68 h and were tested again for sexual behavior at +72 h. On the first day of behavioral testing, both MPA and P4 induced a pronounced rise in receptive and proceptive behavior at the mid and high doses, but at the lowest dose MPA had a much greater effect in comparison to P4. On the second day of behavioral testing, MPA attenuated the expression of proceptive and receptive behavior at both the mid and high doses, whereas P4 only attenuated the expression of lordosis and only did so at the highest dose. These findings illustrate that MPA and P4 have a similar impact on sexual behavior in female rats and suggest that the inhibitory effects of MPA may be attributable, at least in part, to its potent effects at the progesterone receptor.

Relationship between ovarian cycle phase and sexual behavior in female Japanese macaques (Macaca fuscata)

We conducted behavioral observations simultaneously with fecal sample collection on eight nonlactating females 2-3 times per week, October 1997-March 1998, to examine the relationship between ovarian hormones and the sexual behavior of female Japanese macaques (Macaca fuscata) during the mating season. We analyzed samples by enzyme immunoassay for fecal hormone levels. Hormone profiles of estrone-glucuronide (E1) and pregnanediol-glucuronide (PdG) were used to separate ovarian cycles into three phases (follicular, periovulatory, and luteal). Hormonal profiles indicate average cycle lengths of 27.6 +/- 4.2 days (+/- SD; n = 26). Average lengths of the luteal and follicular phases were 12.3 +/- 3.8 days (+/- SD) and 8.3 +/- 3.4 days (+/- SD), respectively. We observed female Japanese macaques engaging in sexual activity throughout the ovarian cycle, with the highest rates occurring during the follicular and periovulatory phases as compared to the luteal phase. The attractivity of female Japanese macaques increased significantly during the follicular and periovulatory phases of the ovarian cycle, when E1 levels are peaking and PdG levels drop to baseline. In addition, females displayed a significant increase in proceptive behavior during the follicular and periovulatory phases. Grooming bouts, as well as proximity between female and male macaques, also increased significantly during the follicular and periovulatory phases. We conclude that fluctuating levels of ovarian hormones in different phases of the cycle are significantly associated with variable rates of copulatory and pericopulatory behaviors in these Japanese macaque females.

Unconditioned sexual incentive motivation in the male Norway rat (Rattus norvegicus)

Sexual incentive motivation was evaluated in a procedure consisting of a large open field where incentive animals were confined behind wire mesh openings. When sexually inexperienced male rats (Rattus norvegicus) were exposed to the receptive female-male incentives, they spent more time close to the female. If the incentives were receptive female-nonreceptive female, the receptive female was preferred. However, when the alternatives were nonreceptive female-male, no preference was obtained. Castration abolished preference for the receptive female, and treatment with testosterone propionate restored it. Estradiol plus oil is as efficient as estradiol plus progesterone for giving the ovariectomized female incentive properties. The living female can be replaced with female odor. Sexual experience did not have any long-term effects on the female's incentive value, but immediately preceding limited sexual activity enhanced it

Neuroendocrine regulation of GnRH release in induced ovulators

GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic (MBH) release of GnRH leading to the preovulatory secretion of LH by the anterior pituitary gland. In females of spontaneously ovulating species, including rats, mice, guinea pigs, sheep, monkeys, and women, ovarian steroids secreted by maturing ovarian follicles induce a pulsatile pattern of GnRH release in the median eminence that, in turn, stimulates a preovulatory LH surge. In females of induced ovulating species, including rabbits, ferrets, cats, and camels, the preovulatory release of GnRH, and the resultant preovulatory LH surge, is induced by the receipt of genital somatosensory stimuli during mating. Induced ovulators generally do not show "spontaneous" steroid-induced LH surges during their reproductive cycles, suggesting that the positive feedback actions of steroid hormones on GnRH release are reduced or absent in these species. By contrast, mating-induced preovulatory surges occasionally occur in some spontaneously ovulating species. Most research in the field of GnRH neurobiology has been performed using spontaneous ovulators including rat, guinea pig, sheep, and rhesus monkey. This review summarizes the literature concerning the neuroendocrine mechanisms controlling GnRH biosynthesis and release in females of several induced ovulating species, and whenever possible it contrasts the results with those obtained for spontaneously ovulating species. It also considers the adaptive, evolutionary benefits and disadvantages of each type of ovulatory control mechanism. In females of induced ovulating species estradiol acts in the brain to induce aspects of proceptive and receptive sexual behavior. The primary mechanism involved in the preovulatory release of GnRH among induced ovulators involves the activation of midbrain and brainstem noradrenergic neurons in response to genital-somatosensory signals generated by receipt of an intromission from a male during mating. These noradrenergic neurons project to the MBH and, when activated, promote the release of GnRH from nerve terminals in the median eminence. In contrast to spontaneous ovulators, there is little evidence that endogenous opioid peptides normally inhibit MBH GnRH release among induced ovulators. Instead, the neural signals that induce a preovulatory LH surge in these species seem to be primarily excitatory. A complete understanding of the neuroendocrine control of ovulation will only be achieved in the future by comparative studies of several animal model systems in which mating-induced as well as spontaneous, hormonally stimulated activation of GnRH neurons drives the preovulatory LH surge.

Estradiol increases female sexual initiation independent of male responsiveness in rhesus monkeys

Copulation and female initiation of sexual behavior vary across the ovarian cycle, suggesting that female hormonal condition influences female sexual motivation in rhesus monkeys. However, the effects of hormones on female sexual motivation are difficult to identify because male behavior also varies with female hormonal condition. During the nonbreeding season, male rhesus monkeys are sexually unresponsive to females; thus the effects of estradiol treatment on female sexual motivation can be examined independent of male behavior. This study administered estradiol to five ovariectomized females living in a large age-graded social group during the nonbreeding season. The behavior of these females with and without estradiol treatment was compared. Data were collected concurrently on five intact, noncycling, nonpregnant females. Estradiol treatment significantly increased sexual initiation by ovariectomized females toward males without any significant changes in male behavior. Estradiol-treated females also displayed greater sexual initiation than nonpregnant, intact females. Both estrogen and progesterone were important predictors of sexual initiation in females, with progesterone having an inhibitory effect. Endogenous progesterone levels in females were negatively correlated with male contact behavior, suggesting that female attractiveness is reduced by progesterone. This study provides further support for estrogen as the critical steroid increasing female sexual motivation in primates.

Effects of an oral contraceptive on sexual behavior of chimpanzees (Pan troglodytes)

Behavioral and physiological effects of a combined oral contraceptive (OC) were studied in chimpanzees for comparative purposes related to (i) the ambiguity surrounding the effects of OCs on the sexuality of humans, (ii) the close biological relationship between chimpanzees and humans, especially with respect to endogenous sex hormones and sexual behavior, and (iii) the relatively greater behavioral sensitivity of the chimpanzee to changes in sex hormone levels such as those that accompany the use of OCs. Two different types of pair tests and detailed behavioral assessments were used to differentiate the hormonal effects of female behavior from social effects imposed by the male. Anogenital swelling and copulation were reduced during OC cycles, but the effect of the OC on copulation was directly related to the social and sexual relationship of the pair during natural cycles. The more compatible and more frequently copulating pairs in the natural cycles continued to copulate during the OC cycles, albeit at reduced rates, whereas the less compatible and less frequently copulating pairs ceased copulating altogether when the female received the OC. There was no independent effect of the OC on ejaculation per se. Both male and female sexual initiative were reduced in the OC cycles, but female responsiveness to male sexual solicitations and direct copulatory attempts were not affected. Data indicate that despite generally adverse effects of the OC on certain physiological and behavioral dimensions of sexuality, social factors ultimately determined the degree of response to the OC.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of depo-medroxyprogesterone acetate (DMPA) on copulation-related and agonistic behaviors in an island colony of stumptail macaques (Macaca arctoides)

This study examined the effects on copulation-related and agonistic behaviors of repeated DMPA (depo-Provera) treatment of adult females in a heterosexual island colony of stumptail macaques (Macaca arctoides). Comparison of mean rates revealed a decrease in male approach to females and dominant male following of females after they were treated with DMPA. As treatment did not affect female genital present, female approach or follow of males, we conclude, consistent with earlier results, that DMPA primarily reduced female sexual attractiveness. DMPA treatment was also consistently associated with increased female agonistic behavior (i.e., low-level threat, bite, and fear grimace), with aggression directed primarily at subadults, juveniles, and infants. Treatment did not alter dominance relationships. These data suggest that DMPA treatment is associated with increased low-key contact aggression.

Biochemical and radioautographic analysis of estrogen-inducible progestin receptors in female ferret brain and pituitary: correlations with effects of progesterone on sexual behavior and gonadotropin-releasing hormone-stimulated secretion of luteinizing hormone

Cytosolic binding molecules for the synthetic progestin [3H]R5020, were isolated in vitro from several brain regions including preoptic area/anterior hypothalamus, mediobasal hypothalamus, medial amygdala and parietal cortex as well as the pituitary gland of ovohysterectomized female ferrets. Binding of [3H]R5020 to cortical cytosols was saturable, of high affinity (apparent dissociation constant of 2.0 nM), and was steroid specific. Pretreatment of ferrets with a Silastic capsule containing estradiol caused significant increments in the concentration of cytosolic R5020 binding sites in hypothalamus and pituitary gland, but not in the other brain regions studied. Brains of additional ovohysterectomized ferrets, which had been primed with estradiol prior to receiving an i.v. injection of [3H]R5020, were processed radioautographically. Intense labeling of cells was seen in the medial and lateral preoptic area, in the lateral hypothalamus, and in the ventromedial and arcuate nuclei of the hypothalamus. Radioautograms from the brains of additional ovohysterectomized ferrets given an i.v. injection of [3H]estradiol revealed labeled cells in all of the above regions, in addition to the basolateral portion of the septum, the bed nucleus of the stria terminalis, and in the anterior amygdaloid area as well as the medial and cortical nuclei of the amygdala. This distribution of neural progestin and estrogen binding sites resembles those previously reported for these steroids in the rat, guinea pig, hamster and macaque. Functional studies showed that acute s.c. implantation of a Silastic capsule containing progesterone to ovohysterectomized ferrets, which had been primed with a low dosage of estradiol, failed to augment their sexual receptivity in limited tests with stimulus males given 4 and 8 h after progesterone treatment. This result contrasts with the well-established facilitatory effect of progesterone on sexual receptivity in rat and guinea pig. Chronic exposure to a progesterone capsule caused significant reductions in sexual receptivity in ovohysterectomized ferrets which were implanted concurrently with a second Silastic capsule containing a high dosage of estradiol. Similar effects of progesterone have been reported in rat and guinea pig, but not in the rhesus monkey. Thus species differences in the ability of progesterone to facilitate or inhibit sexual receptivity are not readily explained by species differences in the neural distribution of estrogen-induced progestin receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of the synthetic progestin 3H-ORG 2058 in neurons of the primate brain: evidence for the site of action of progestins on behavior

The location of neurons that concentrate progestin in the brains of female cynomolgus monkeys was mapped by autoradiography using the specific synthetic progestin receptor ligand 3H-ORG 2058. Three females were ovariectomized and treated with estrogen (20 micrograms estradiol benzoate daily for 7 days), and one of them was also pretreated with progesterone. Each received an i.v. injection of 1 mCi 3H-ORG 2058 and was killed 1 hour later. Thaw-mount autoradiograms revealed intense accumulation of radioactivity in the nuclei of many neurons in the mediobasal hypothalamus, particularly in the ventromedial nucleus (n.), arcuate n., and premammillary n. Neuronal labeling was also observed frequently in the medial preoptic n., and occasionally in the anterior hypothalamic area, paraventricular n., and organum vasculosum of the lamina terminalis. In the pituitary gland, about 5% of cells in the pars distalis were intensely labeled. In the female pretreated with progesterone, however, labeling was almost completely blocked. Analysis of samples by high-performance liquid chromatography demonstrated that the radioactivity extracted from brain and pituitary gland cell nuclei was almost entirely unmetabolized 3H-ORG 2058. The nuclear concentration of progestin was much greater in the pituitary gland than in the brain, and was greater in the hypothalamus than in any other brain area. These results revealed well-localized groups of progestin-concentrating neurons in the primate brain which presumably mediate the effects of progesterone on both gonadotropin secretion and female sexual behavior.

The effect of estradiol and progesterone on the sexual behavior of ovariectomized mares

Daily treatment (5 days) with estradiol resulted in increased levels (p less than 0.05) of proceptive behavior in ovariectomized as compared to control mares (N = 8 per treatment) within 4 hr of injection and for the 4 subsequent days. Ejaculations occurred more often (p less than 0.05) in estrogen-treated mares on days 2-5, but the number of precopulatory investigations by the stallions was not altered. Progesterone treatment resulted in an absence of sexual behavior except in one mare on Day 1. Control mares exhibited varying levels of sexual interest. The concurrent administration of estradiol and progesterone produced a biphasic effect on proximity-related behaviors. Proximity behaviors were initially (Day 1) greater and subsequently less in the group treated with both hormones than in the group treated with estradiol alone. Injections of free estradiol resulted in a shorter latency to effect for two measures of proceptivity than did injections of estradiol benzoate. A dose response test for progesterone showed no effect with 0, 1, or 10 mg, but 100 mg was inhibitory (p less than 0.05). These results demonstrated that within 4 hr estradiol stimulated, while progesterone inhibited estrous behavior in ovariectomized mares and that concurrent administration of estradiol and progesterone produced a biphasic effect, first enhancing, then suppressing some aspects of the estrous response. The relatively short latency to action of all treatments and the biphasic effect of concurrent estradiol and progesterone may be attributable to low level, endogenous hormones.

Differentiation of coital behavior in mammals: a comparative analysis

The evidence reviewed suggests that in all mammalian species the adult male's ability to display masculine coital behavior depends in part on exposure of the developing brain to testicular testosterone or its metabolites. In many mammals, particularly rodents, ruminants, and some carnivores, perinatal exposure to androgen also causes behavioral defeminization, i.e., reduced capacity to display typically feminine coital behavior in response to gonadal hormones in adulthood. The data reviewed suggest that no such process occurs in certain other mammalian species, including ferret, rhesus monkey, marmoset, and man. Testicular androgen may cause behavioral defeminization only in those species in which expression of feminine sexual behavior normally depends on the neural action of progesterone, acting synergistically with estradiol; new data support this claim in the ferret. The possible contribution of estrogenic and 5 alpha-reduced androgenic metabolites of testosterone to the occurrence of behavioral masculinization and defeminization is considered in those mammalian species for which data are available.