Sexual differentiation in quail: conversion of androgen to estrogen mediates testosterone-induced demasculinization of copulation but not other male characteristics

Contribution of birds to the study of sexual differentiation of brain and behavior

Behavioral neuroendocrinology has largely relied on mammalian models to understand the relationship between hormones and behavior, even if this discipline has historically used a larger diversity of species than other fields. Recent advances revealed the potential of avian models in elucidating the neuroendocrine bases of behavior. This paper provides a review focused mainly on the contributions of our laboratory to the study of sexual differentiation in Japanese quail and songbirds. Quail studies have firmly established the role of embryonic estrogens in the sexual differentiation of male copulatory behavior. While most sexually differentiated features identified in brain structure and physiology result from the different endocrine milieu of adults, a few characteristics are organized by embryonic estrogens. Among them, a sex difference was identified in the number and morphology of microglia which is not associated with sex differences in the concentration/expression of neuroinflammatory molecules. The behavioral role of microglia and neuroinflammatory processes requires further investigations. Sexual differentiation of singing in zebra finches is not mediated by the same endocrine mechanisms as male copulatory behavior and "direct" genetic effect, i.e., not mediated by gonadal steroids have been identified. Epigenetic contributions have also been considered. Finally sex differences in specific aspects of singing behavior have been identified in canaries after treatment of adults with exogenous testosterone suggesting that these aspects of song are differentiated during ontogeny. Integration of quail and songbirds as alternative models has thus expanded understanding of the interplay between hormones and behavior in the control of sexual differentiation.

Key role of estrogen receptor β in the organization of brain and behavior of the Japanese quail

Estrogens play a key role in the sexual differentiation of the brain and behavior. While early estrogen actions exert masculinizing effects on the brain of male rodents, a diametrically opposite effect is observed in birds where estrogens demasculinize the brain of females. Yet, the two vertebrate classes express similar sex differences in the brain and behavior. Although ERα is thought to play a major role in these processes in rodents, the role of ERβ is still controversial. In birds, the identity of the estrogen receptor(s) underlying the demasculinization of the female brain remains unclear. The aim of the present study was thus to determine in Japanese quail the effects of specific agonists of ERα (propylpyrazole triol, PPT) and ERβ (diarylpropionitrile, DPN) administered at the beginning of the sensitive period (embryonic day 7, E7) on the sexual differentiation of male sexual behavior and on the density of vasotocin-immunoreactive (VT-ir) fibers, a known marker of the organizational action of estrogens on the quail brain. We demonstrate that estradiol benzoate and the ERβ agonist (DPN) demasculinize male sexual behavior and decrease the density of VT-ir fibers in the medial preoptic nucleus and the bed nucleus of the stria terminalis, while PPT has no effect on these measures. These results clearly indicate that ERβ, but not ERα, is involved in the estrogen-induced sexual differentiation of brain and sexual behavior in quail.

Sensitive Periods, Vasotocin-Family Peptides, and the Evolution and Development of Social Behavior

Nonapeptides, by modulating the activity of neural circuits in specific social contexts, provide an important mechanism underlying the evolution of diverse behavioral phenotypes across vertebrate taxa. Vasotocin-family nonapeptides, in particular, have been found to be involved in behavioral plasticity and diversity in social behavior, including seasonal variation, sexual dimorphism, and species differences. Although nonapeptides have been the focus of a great deal of research over the last several decades, the vast majority of this work has focused on adults. However, behavioral diversity may also be explained by the ways in which these peptides shape neural circuits and influence social processes during development. In this review, I synthesize comparative work on vasotocin-family peptides during development and classic work on early forms of social learning in developmental psychobiology. I also summarize recent work demonstrating that early life manipulations of the nonapeptide system alter attachment, affiliation, and vocal learning in zebra finches. I thus hypothesize that vasotocin-family peptides are involved in the evolution of social behaviors through their influence on learning during sensitive periods in social development.

Sex differences in brain aromatase activity: genomic and non-genomic controls

Aromatization of testosterone into estradiol in the preoptic area plays a critical role in the activation of male copulation in quail and in many other vertebrate species. Aromatase expression in quail and in other birds is higher than in rodents and other mammals, which has facilitated the study of the controls and functions of this enzyme. Over relatively long time periods (days to months), brain aromatase activity (AA), and transcription are markedly (four- to sixfold) increased by genomic actions of sex steroids. Initial work indicated that the preoptic AA is higher in males than in females and it was hypothesized that this differential production of estrogen could be a critical factor responsible for the lack of behavioral activation in females. Subsequent studies revealed, however, that this enzymatic sex difference might contribute but is not sufficient to explain the sex difference in behavior. Studies of AA, immunoreactivity, and mRNA concentrations revealed that sex differences observed when measuring enzymatic activity are not necessarily observed when one measures mRNA concentrations. Discrepancies potentially reflect post-translational controls of the enzymatic activity. AA in quail brain homogenates is rapidly inhibited by phosphorylation processes. Similar rapid inhibitions occur in hypothalamic explants maintained in vitro and exposed to agents affecting intracellular calcium concentrations or to glutamate agonists. Rapid changes in AA have also been observed in vivo following sexual interactions or exposure to short-term restraint stress and these rapid changes in estrogen production modulate expression of male sexual behaviors. These data suggest that brain estrogens display most if not all characteristics of neuromodulators if not neurotransmitters. Many questions remain however concerning the mechanisms controlling these rapid changes in estrogen production and their behavioral significance.

Japanese quail as a model system for studying the neuroendocrine control of reproductive and social behaviors

Japanese quail (Coturnix japonica; referred to simply as quail in this article) readily exhibit sexual behavior and related social behaviors in captive conditions and have therefore proven valuable for studies of how early social experience can shape adult mate preference and sexual behavior. Quail have also been used in sexual conditioning studies illustrating that natural stimuli predict successful reproduction via Pavlovian processes. In addition, they have proven to be a good model to study how variation in photoperiod regulates reproduction and how variation in gonadal steroid hormones controls sexual behavior. For example, studies have shown that testosterone activates male-typical behaviors after being metabolized into estrogenic and androgenic metabolites. A critical site of action for these metabolites is the medial preoptic nucleus (POM), which is larger in males than in females. The enzyme aromatase converts testosterone to estradiol and is enriched in the POM in a male-biased fashion. Quail studies were the first to show that this enzyme is regulated both relatively slowly via genomic actions of steroids and more quickly via phosphorylation. With this base of knowledge and the recent cloning of the entire genome of the closely related chicken, quail will be valuable for future studies connecting gene expression to sexual and social behaviors.

Embryonic and posthatching treatments with sex steroids demasculinize the motivational aspects of crowing behavior in male Japanese quail

Demasculinizing action of embryonic estrogen on crowing behavior in male Japanese quails was examined. Eggs were treated with either 20 microg of estradiol benzoate (EB) or vehicle on the 10th day of incubation. Chicks hatched from both groups of eggs were injected daily with either testosterone propionate (TP; 10 microg/g b.w.), 5alpha-dihydrotestosterone (DHT, a non-aromatizable androgen; 10 microg/g b.w.), or vehicle from 11 to 50 days after hatching, and during this period their calling behaviors were observed. Irrespective of embryonic treatments, all birds received posthatching treatment with either TP or DHT, but not with vehicle, emitted crows in place of distress calls in a stress (non-sexual) context of being isolated in a recording chamber. The posthatching TP, but not posthatching DHT, induced crowing in a sexual context (crowing in their home-cages) from much earlier age than posthatching vehicle in the birds received control embryonic treatment with vehicle. The same TP treatment, however, completely eliminated the crowing in a sexual context in the birds received EB during their embryonic life. In the birds treated with either posthatching DHT or posthatching vehicle, the crowing in a sexual context was only slightly decreased by embryonic EB treatment. These data suggest that posthatching estrogen, derived from testosterone aromatization, enhances the demasculinizing action of embryonic estrogen, and thus strongly reduces the sexual motivation for crowing behavior. This demasculinizing action, however, would not influence vocal control system which generates acoustic pattern of crowing in the presence of androgens allowing the birds to crow in a non-sexual context.

Sex- and age-related variation in neurosteroidogenic enzyme mRNA levels during quail embryonic development

Brain can synthesize steroids de novo from cholesterol and this biochemical feature is a conserved property of vertebrates. There is growing evidence indicating that neurosteroids might participate in sexual differentiation of the brain. Therefore, in this study we investigated the presence, the sex differences, and the development-dependent variation of mRNAs coding for key neurosteroidogenic enzymes, namely cytochrome P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid-dehydrogenase/Delta5-Delta4-isomerase (3beta-HSD), cytochrome P450 17alpha-hydroxylase/c17, 20-lyase (P450c17), and aromatase in embryonic prosencephali. Our results indicated that 3beta-HSD mRNA levels were sexually dimorphic and developmental age-dependent. In particular, 3beta-HSD mRNA levels were higher in females than in males at E7, whereas, this dimorphism was reversed at E9 and E15. In females, the relative levels of 3beta-HSD mRNA were highest at E7, whereas, in males they were significantly higher at E9 and E15 than at E7 and at E11. This sexual dimorphism was a peculiar feature of the prosencephalon, it could not be observed before gonadal sexual differentiation and it was not paralleled by a dimorphism in the brain content of progesterone. The level of mRNA coding for P450scc and for P450c17 did not show obvious developmental- or sex-related variation. Aromatase mRNA varied as a function of the embryonic age but not of the sex. These results, taken together, are suggestive of a potential role of some neurosteroidogenic enzymes in the development of quail brain and suggest that sexual differences in the hormonal environment may occur during brain development.

Reproductive toxicity of trenbolone acetate in embryonically exposed Japanese quail

This study was conducted to assess the effects of a one time embryonic exposure to trenbolone acetate on reproductive development and function in Japanese quail (Coturnix japonica). Embryos were exposed to either 0.05, 0.5, 5, or 50microg trenbolone or a sesame oil vehicle control at embryonic day 4. Onset of puberty, gonadal histopathology, sperm motility, cloacal gland size, and male copulatory behavior were assessed in adults. Trenbolone delayed onset of puberty in males, inhibited cloacal gland development, and reduced male reproductive behaviors. Industry laboratories have shown trenbolone acetate to be non-teratogenic in mammalian studies. Our study, however, shows that this one time in ovo exposure delayed onset of puberty in and suppressed adult copulatory behavior in quail males. These results suggest that this one time embryonic exposure to trenbolone may have disrupted development of either the central nervous system or the hypothalamic-pituitary-gonadal axis. This is the first study to demonstrate a demasculinizing effect on copulatory behavior in Japanese quail from embryonic exposure to a non-aromatizable androgenic chemical. More studies are needed to determine the mechanisms behind the observed effects.

Hypothalamic indolamines during embryonic development and effects of steroid exposure

The serotonin system has been implicated in the modulation of endocrine and behavioral components of reproduction. In this study, we examined endogenous hypothalamic indolamines during sexual differentiation and long-term effects of exogenous steroids during this time. In Experiment 1, Japanese quail were studied during the last half of embryonic development and early post-hatch. Samples were taken at embryonic day 10 (E10), E12, E14, E16, hatch (day 0), and days 3 and 5, post-hatch. Hypothalamic indolamines, including serotonin (5-HT) and its metabolite, 5-hydroxy indole acetic acid (5-HIAA) were measured by HPLC-EC detection. Females had relatively higher hypothalamic 5-HT at E14 than males, with both sexes showing increasing levels thereafter. By day 5, post-hatch, hypothalamic 5-HT content was higher in males than in females. When turnover was estimated by comparing relative concentrations of 5-HT to 5-HIAA, males were significantly higher at E12 and E14 than females. These data suggest that there are stage specific changes in the serotonin system, as well as sexually dimorphic patterns in the ontogeny and activity of this system. In Experiment 2, we investigated the effects of embryonic steroid hormone treatment on the serotonin system and on male sexual behavior. Birds were treated with either estradiol benzoate (EB), testosterone propionate (TP) or sesame oil (vehicle control) at selected embryonic days (E10, E12, E14, E16, 0, D3, and D5). At 4 weeks post-hatch, birds were transferred to short photoperiod (16D:8L) for 3 weeks to prevent photostimulated reproductive development. At 7 weeks of age, males were implanted with a 20mm silastic capsule filled with testosterone and sexual behavior was tested 1 week later. Brains were collected from both males and females, and preoptic area (POA) indolamines were measured. Steroid treatment at E10 or E12 resulted in the loss of male sexual behavior. Moreover, males treated with EB or TP on E12 also had increased POA 5-HT content as adults, compared to control males. Females treated with EB on either E10 or E 12 also had higher POA 5-HT content than control or TP treated females. These data provide evidence for sexual dimorphism in the hypothalamic 5-HT system at specific stages during embryonic development. Moreover, males were sensitive to exogenous EB and TP on E12, whereas females appeared to be affected by EB only and appeared to be sensitive to steroid effects over a longer period of time in development. Moreover, exogenous steroids at E12 in males also correlated with impaired sexual behavioral. These data suggest that long-term effects of embryonic steroid exposure may be mediated in part through effects on the serotonin neurotransmitter system.

Reproductive consequences of EDCs in birds: what do laboratory effects mean in field species?

The varied reproductive strategies of birds present a challenge in developing reliable indices for the assessment of effects of endocrine disrupting chemicals (EDCs). Precocial species, such as quail, appear to be most sensitive to EDC effects during embryonic development. Although the Japanese quail (Coturnix japonica) is a nonnative lab species, its reproductive strategy is similar to that of many free-ranging species. Because a great deal is known about the reproductive biology of this species and Japanese quail have a short generation time, this species is an ideal candidate for testing EDC effects. In this review, we present data collected in a two-generation design with embryonic exposure to estradiol benzoate (EB). This study was conducted to provide fundamental information for establishing reliable reproductive endpoints associated with estrogenic EDC exposure. Data were collected for a variety of endpoints, which were chosen as measures of reproductive capability and success. These reproductive fitness measures included fertility, hatching success, and offspring viability. Endocrine measures consisted of plasma hormone levels and gonad weight/condition. Neuroendocrine systems, such as the monoamine neurotransmitter systems, regulate hypothalamic gonadotropin releasing hormone (GnRH) and reproductive behavior. Therefore, these variables should potentially be very sensitive indicators. Behavioral measures included reproductive behavior. Results showed that embryonic estradiol exposure affected endocrine and behavioral responses in males and impacted productivity in females. Therefore, quails provide an excellent model to determine fundamental actions of EDCs. The laboratory trials then serve as a basis for the extrapolation of findings of controlled laboratory studies to effects that may be observable in free-ranging species.

Estradiol mediates effects of testosterone on vasotocin immunoreactivity in the adult quail brain

In adult male quail, the activation of sexual behavior by testosterone (T) is mediated at the cellular level by the interaction of T metabolites with intracellular steroid receptors. In particular, the aromatization of T into an estrogen plays a key limiting role. Nonaromatizable androgens such 5alpha-dihydrotestosterone (DHT) synergize with estradiol (E2) to activate the behavior. Given that the density of vasotocin (VT) immunoreactive structures is increased by T in adult male quail and that VT injections affect male behavior, we wondered whether the expression of VT is also affected by T metabolites such as E2 and DHT. We analyzed here, in castrated male quail, the effects of a treatment with T, E2, DHT, or E2 + DHT on sexual behavior and brain VT immunoreactivity. The restoration by T of the VT immunoreactivity in the medial preoptic nucleus, bed nucleus striae terminalis, and lateral septum of castrated male quail could be fully mimicked by a treatment with E2. The androgen DHT had absolutely no effect on the VT immunoreactivity in these conditions and, at the doses used here, DHT did not synergize with E2 to enhance the density of VT immunoreactive structures. These effects of T metabolites in the brain were not fully correlated with their effects on the activation of male copulatory behavior, suggesting that the increase in VT expression in the brain does not represent a necessary step for the activation of behavior. Although VT expression in the medial preoptic nucleus and bed nucleus striae terminalis is often tightly correlated with the expression of male copulatory behavior, VT presumably does not represent simply one step in the biochemical cascade of events that is induced by T in the brain and leads to the expression of male sexual behavior.

Steroid-induced plasticity in the sexually dimorphic vasotocinergic innervation of the avian brain: behavioral implications

Vasotocin (VT, the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. In addition, in male quail and in other oscine and non-oscine birds, a sexually dimorphic group of VT-immunoreactive (ir) parvocellular neurons is located in a region homologous to the mammalian nucleus of the stria terminalis, pars medialis (BSTm) and in the medial preoptic nucleus (POM). These cells are not visible in females. VT-ir fibers are present in many diencephalic and extradiencephalic locations. Quantitative morphometric analyses demonstrate that, in quail, these elements are expressed in a sexually dimorphic manner (males>females) in regions involved in the control of different aspects of reproduction: i.e., the POM (copulatory behavior), the lateral septum (secretion of gonadotropin-releasing hormone [GnRH]), the nucleus intercollicularis (control of vocalizations), and the locus coeruleus (the main noradrenergic center of the avian brain). In many of these regions, VT-ir fibers are closely related to aromatase-ir, GnRH-ir, or estrogen receptor-expressing neurons. This dimorphism has an organizational nature: administration of estradiol-benzoate to quail embryos (a treatment that abolishes male sexual behavior) results in a dramatic decrease of the VT-immunoreactivity in all sexually dimorphic regions of the male quail brain. Conversely, the inhibition of estradiol (E2) synthesis during embryonic life (a treatment that stimulates the expression of male copulatory behavior in adult testosterone (T)-treated females) results in a male-like distribution of VT-ir cells and fibers. Castration markedly decreases the immunoreactivity in both the VT-immunopositive elements of the BSTm and the innervation of the SL and POM, whereas T-replacement therapy restores the VT immunoreactivity to a level typical of intact birds. These changes reflect modifications of VT mRNA concentrations (and probably synthesis) as demonstrated by in situ hybridization and they are paralleled by similar changes in male copulatory behavior (absent in castrated male quail, fully expressed in CX+T males). The aromatization of T into estradiol (E2) also controls VT expression and, in parallel limits the activation of male sexual behavior by T. In castrated male quail, the restoration by T of the VT immunoreactivity in POM, BSTm and lateral septum could be fully mimicked by a treatment with E2, but the androgen 5alpha-dihydrotestosterone (DHT) had absolutely no effect on the VT immunoreactivity in these conditions. At the doses used in this study, DHT also did not synergize with E2 to enhance the density of VT immunoreactive structures. Systemic or i.c.v. injections of VT markedly inhibit the expression of all aspects of male sexual behavior. VT, presumably, does not simply represent one step in the biochemical cascade of events that is induced by T in the brain and leads to the expression of male sexual behavior. Androgens and estrogens presumably affect reproductive behavior both directly, by acting on steroid-sensitive neurons in the preoptic area, and indirectly, by modulating peptidergic (specifically vasotocinergic) inputs to this and other areas. The respective contribution of these two types of actions and their interaction deserves further analysis.

Neuroendocrine and behavioral implications of endocrine disrupting chemicals in quail

Studies in our laboratory have focused on endocrine, neuroendocrine, and behavioral components of reproduction in the Japanese quail. These studies considered various stages in the life cycle, including embryonic development, sexual maturation, adult reproductive function, and aging. A major focus of our research has been the role of neuroendocrine systems that appear to synchronize both endocrine and behavioral responses. These studies provide the basis for our more recent research on the impact of endocrine disrupting chemicals (EDCs) on reproductive function in the Japanese quail. These endocrine active chemicals include pesticides, herbicides, industrial products, and plant phytoestrogens. Many of these chemicals appear to mimic vertebrate steroids, often by interacting with steroid receptors. However, most EDCs have relatively weak biological activity compared to native steroid hormones. Therefore, it becomes important to understand the mode and mechanism of action of classes of these chemicals and sensitive stages in the life history of various species. Precocial birds, such as the Japanese quail, are likely to be sensitive to EDC effects during embryonic development, because sexual differentiation occurs during this period. Accordingly, adult quail may be less impacted by EDC exposure. Because there are a great many data available on normal development and reproductive function in this species, the Japanese quail provides an excellent model for examining the effects of EDCs. Thus, we have begun studies using a Japanese quail model system to study the effects of EDCs on reproductive endocrine and behavioral responses. In this review, we have two goals: first, to provide a summary of reproductive development and sexual differentiation in intact Japanese quail embryos, including ontogenetic patterns in steroid hormones in the embryonic and maturing quail. Second, we discuss some recent data from experiments in our laboratory in which EDCs have been tested in Japanese quail. The Japanese quail provides an excellent avian model for testing EDCs because this species has well-characterized reproductive endocrine and behavioral responses. Considerable research has been conducted in quail in which the effects of embryonic steroid exposure have been studied relative to reproductive behavior. Moreover, developmental processes have been studied extensively and include investigations of the reproductive axis, thyroid system, and stress and immune responses. We have conducted a number of studies, which have considered long-term neuroendocrine consequences as well as behavioral responses to steroids. Some of these studies have specifically tested the effects of embryonic steroid exposure on later reproductive function in a multigenerational context. A multigenerational exposure provides a basis for understanding potential exposure scenarios in the field. In addition, potential routes of exposure to EDCs for avian species are being considered, as well as differential effects due to stage of the life cycle at exposure to an EDC. The studies in our laboratory have used both diet and egg injection as modes of exposure for Japanese quail. In this way, birds were exposed to a specific dose of an EDC at a selected stage in development by injection. Alternatively, dietary exposure appears to be a primary route of exposure; therefore experimental exposure through the diet mimics potential field situations. Thus, experiments should consider a number of aspects of exposure when attempting to replicate field exposures to EDCs.

Steroid hormones during embryonic development in Japanese quail: plasma, gonadal, and adrenal levels

The purpose of this experiment was to measure plasma, gonad, and adrenal steroid hormones during embryonic and early posthatch development in Japanese quail. Blood plasma samples were collected from male and female Japanese quail embryos at 2-d intervals between Day 10 of incubation and Day 5 posthatch. Gonads and adrenal glands were collected from a separate set of embryos at the same ages. Concentrations of androgen (testosterone and 5alpha-dihydrotestosterone) and 17beta-estradiol (E2) were determined by RIA. Plasma androgen changed significantly (P < 0.001) with age in males and females, and there were significant differences (P < 0.001) between sexes in the hormonal patterns. Males had higher plasma androgen than females; conversely, females consistently had overall higher levels of estradiol than males. Adrenal gland steroid content remained relatively high and did not change significantly with age. In contrast, steroid content of gonads followed patterns similar to those observed for plasma levels. These results provide evidence for steroid hormone production by the gonads of both sexes, as well as for distinct differences in the patterns observed in the adrenal gland and gonads. These results provide evidence for gonadal regulation of changes in circulating hormone levels. Further, these hormonal patterns were associated with the timing of steroid-induced sexual differentiation in the Japanese quail, suggesting that plasma gonadal steroids are critical in sexual differentiation.

The behavior of the Japanese or domestic quail Coturnix japonica

This paper reviews the literature pertaining to the behavior of the Japanese or domestic quail Coturnix japonica. Details are given of the classification, characteristics, domestication and the economic and research potential of the species. Further sections deal with sensation and perception (including taste and smell, vision and hearing), maintenance behavior (including feeding and drinking, dust bathing and thermoregulation), development and aging (including vocalization, filial imprinting, sexual imprinting, fear and avoidance responses, sexual maturation and aging), adult learning (including habituation, instrumental conditioning, Pavlovian conditioning and observational learning), photoperiodism, reproductive behavior (including courtship and mating, hormonal control and ontogeny of sexual differentiation, and male and female sexual behavior), parental behavior (including nest-site selection and nest building, incubation behavior and its hormonal control, and hen-chick relationships), and aggressive behavior and dominance (including agonistic behavior and the hormonal control of aggressive behavior).

An atlas of aromatase mRNA expression in the zebra finch brain

Neural conversion of androgen to estrogen by aromatase is an important step in the development and expression of masculine behavior in mammals and birds. In contrast to the low telencephalic levels of aromatase in adult mammals and nonsongbirds, the zebra finch telencephalon possesses high aromatase activity. This study maps, by in situ hybridization, cells that express aromatase mRNA in the adult zebra finch telencephalon, diencephalon, midbrain, and pons. High aromatase mRNA expression was observed in the caudal neostriatum, limbic archistriatum, and hypothalamus. The hippocampus, parahippocampal area, and hyperstriatum accessorium contained cells expressing moderate amounts of aromatase message. Weakly labeled cells were found in the rostral neostriatum, lobus parolfactorius, and mesencephalic reticular formation. These findings are consistent with aromatase activity measurements of zebra finch tissue and document with anatomical precision both the widespread expression of aromatase mRNA in the brain and novel sites of brain aromatase. This study identifies the caudal neostriatum as a major site of telencephalic aromatase. A previous survey (Gahr et al., 1993: J. Comp. Neurol. 327:112-122) of several avian species found that the presence of estrogen receptors in parts of the caudal neostriatum is unique to songbirds, which are the only birds to possess the elaborated telencephalic song system. Together, these findings suggest that the heightened estrogen synthesis and estrogen sensitivity of the passerine caudal neostriatum may have some functional relation with the telencephalic circuits responsible for song.

Sexual differentiation of brain and behavior in quail and zebra finches: studies with a new aromatase inhibitor, R76713

In many species of vertebrates, major sex differences affect reproductive behavior and endocrinology. Most of these differences do not result from a direct genomic action but develop following early exposure to a sexually differentiated endocrine milieu. In rodents, the female reproductive phenotype mostly develops in the absence of early steroid influence and male differentiation is imposed by the early action of testosterone, acting at least in part through its central conversion into estrogens or aromatization. This pattern of differentiation does not seem to be applicable to avian species. In Japanese quail (Coturnix japonica), injection of estrogens into male embryos causes a permanent loss of the capacity to display male-type copulatory behavior when exposed to testosterone in adulthood. Based on this experimental result, it was proposed that the male reproductive phenotype is "neutral" in birds (i.e. develops in the absence of endocrine influence) and that endogenous estradiol secreted by the ovary of the female embryo is responsible for the physiological demasculinization of females. This model could be recently confirmed. Females indeed display a higher level of circulating estrogens that males during the second part of their embyronic life. In addition, treatment of female embryos with the potent aromatase inhibitor, R76713 or racemic vorozole which suppresses the endogenous secretion of estrogens maintains in females the capacity to display the full range of male copulatory behaviors. The brain mechanisms that control this sexually differentiated behavior have not been identified so far but recent data suggest that they should primarily concern a sub-population of aromatase-immunoreactive neurons located in the lateral parts of the sexually dimorphic preoptic nucleus. The zebra finch (Taeniopygia guttata) exhibits a more complex, still partly unexplained, differentiation pattern. In this species, early treatment with exogenous estrogens produces a masculinization of singing behavior in females and a demasculinization of copulatory behavior in males.(ABSTRACT TRUNCATED AT 400 WORDS)

Embryonic differentiation of sexual dimorphism in vasotocin and mesotocin levels in chickens

Chicken embryos of both sexes were injected on the tenth day of incubation with either estradiol benzoate (EB), aromatase inhibitor [1,4,6-androstatrien-3, 17-dione (ATD)], antiestrogen [tamoxifen (TAM)], antiandrogen [flutamide (FLU)], or the oil vehicle as control (C). At adulthood, at the age of 26 weeks, 10 chickens of each sex were killed and the amounts of immunoreactive arginine vasotocin (AVT) and mesotocin (MT) in the anterior hypothalamus (AHA), posterior hypothalamus (PHA), neurohypophysis (NHP), and pineal gland (PNL) were determined. Control hens had significantly more AVT in PNL and less MT in AHA and NHP than the corresponding roosters. This sexual dimorphism was affected by the embryonic treatments; TAM increased AVT in AHA of cockerels but not of hens. In both sexes, TAM and FLU increased AVT content in NYP. In males, but not in females, ATD also increased AVT content in the NHP. TAM and FLU administration to the female embryo reduced PNL AVT to the amount present in normal males. None of the treatments effected AHA MT in hens, while in cockerels TAM increased it. In females, TAM and FLU significantly increased NHP MT to the level of C males. In roosters, ATD, TAM, and FLU increased NHP MT further. In hens, but not roosters, FLU reduced MT in PNL. These results indicate that embryonic differentiation of the MT and AVT systems is affected by gonadal steroids in chickens.

Plasticity of gonadal development and protandry in fishes

Sexual differentiation in eutherian mammals follows a simple governing paradigm: development proceeds in a female direction unless a masculinizing mechanism intervenes. Sexual development in fishes is much more plastic than in mammals. It permits the intervention of environmental factors and follows several different types of sequences that produce successive hermaphrodites and alternative pathways for the development of the same final sex. In spite of this plasticity, the primacy of female development is suggested by the initial ovarian phase in the development of gonads of both sexes in some gonochoristic fishes and by protogynous sex change. One barrier to the application of this principle to fishes generally is the existence of protandric hermaphrodites. Recent evidence suggests a reinterpretation of gonadal differentiation in a protandric anemonefish and a protandric sparid. In both cases, testicular development is both preceded and followed by ovarian development. These patterns are interpreted to mean that female development is primary and that male development is a temporary phase initiated by a masculinizing mechanism and terminated by its cessation.

Effects of α-methyl-para-tyrosine on monoamine levels in the japanese quail: Sex differences and testosterone effects

Experiments were performed to obtain more information on the regulation by steroids of catecholaminergic systems in the brain of Japanese quail. Dose-response and time-response experiments were first performed to determine optimal conditions for measuring turnover in the quail brain. The norepinephrine and dopamine turnover were then estimated in microdissected brain nuclei of birds that were either sexually mature or gonadectomized or gonadectomized and treated with testosterone. Two major facts that bear direct relationship with the control of masculine reproductive behavior were demonstrated. On one hand, the dopamine turnover in the medial preoptic nucleus, a sexually dimorphic brain structure which is critically implicated in the control of copulatory behavior was much higher in male than in female quail irrespective of the hormonal condition of the birds. On the other hand, norepinephrine concentrations appeared to be higher in several nuclei of the female brain by comparison with males. These sex differences might represent part of the causal factors that underlie the sex dimorphism in reproductive behavior in quail.

Sexual differentiation of copulatory behaviour in the male chick requires gonadal steroids

1. Embryonic injections of 0.3 mg/egg of tamoxifen (TAM), 0.2 mg/egg CI-628 (both antioestrogens), 0.5 mg/egg (ATD (aromatisation inhibitor), or antibodies to oestradiol (E), all suppressed male copulatory activity (MCA) in young male chicks. 2. Embryonic injections with either flutamide (F, androgen antagonist) or high dose of antibodies to testosterone (T) only slightly suppressed MCA. 3. TAM had no effect on embryonic plasma LH levels, 24 and 48 h after injection. 4. It seems that at the embryonic stage oestradiol is required for the normal differentiation of MCA.

Inhibition of hypothalamic aromatase activity by 5 Beta-dihydrotestosterone

Abstract A variable amount of circulating testosterone that reaches brain cells is converted to biologically inactive 5beta-reduced metabolites, namely, 5beta-dihydrotestosterone (5beta-DHT) and 5beta-androstane-3alpha,17beta-diol (5beta,3alpha-diol). In avian species, the production of inactive 5beta-DHT and 5beta,3alpha-diol is highest during embryonic and post-hatching life. In the present study, we have investigated the possibility that 5beta-reduction may not only correspond to a steroid inactivation pathway, but that 5beta-reduced metabolites of testosterone may exert direct inhibitory effects on enzymatic pathways producing biologically active steroids. When added to hypothalamic homogen-ates prepared from adult male doves, 5beta-DHT but not 5beta,3alpha-diol inhibits the activity of the aromatase enzyme, which converts testosterone to 17beta-oestradiol. During the first days after hatching, when the production of 5beta-reduced metabolites is high, the hypothalamic aromatase is also inhibited by 5beta-DHT. We conclude that a high 5beta-reductase activity during sensitive periods for sexual differentiation may protect the avian brain from the differentiating effects of circulating androgens by inhibiting the production of oestrogen.

Testosterone metabolism in the avian hypothalamus

Many central actions of testosterone (T) require the transformation of T into several metabolites including 5 alpha-dihydrotestosterone (5 alpha-DHT) and estradiol (E2). In birds as in mammals, 5 alpha-DHT and E2, alone or in combination, mimic most behavioral effects of T. The avian brain is, in addition, able to transform T into 5 beta-DHT, a metabolite which seems to be devoid of any behavioral or physiological effects, at least in the context of reproduction. By in vitro product-formation assays, we have analyzed the distribution, sex differences and regulation by steroids of the 3 main T metabolizing enzymes (aromatase, 5 alpha- and 5 beta-reductases) in the brain of the Japanese quail (Coturnix c. japonica) and the zebra finch (Taeniopygia guttata castanotis). In the hypothalamus of quail and finches, aromatase activity is higher in males than in females. It is also decreased by castration and increased by T. The activity of the 5 alpha-reductase is not sexually differentiated nor controlled by T. The 5 beta-reductase activity is often higher in females than in males but this difference disappears in gonadectomized birds and no clear effect of T can be observed at this level. The zebra finch brain also contains a number of steroid-sensitive telencephalic nuclei [e.g. hyperstriatum ventrale, pars caudale (HVc) and robustus archistriatalis (RA)] which play a key role in the control of vocalizations. These nuclei also contain T-metabolizing enzymes but the regulation of their activity is substantially different from what has been observed in the hypothalamus. Aromatase activity is for example higher in females than in males in HVc and RA and the enzyme in these nuclei is not affected by castration nor T treatment. In these nuclei, the 5 alpha-reductase activity is higher in males than in females and the reverse is true for the 5 beta-reductase. These sex differences in activity are not sensitive to gonadectomy and T treatment and might therefore be organized by neonatal steroids. We have been recently able to localize aromatase-immunoreactive (AR-ir) neurons by ICC in the brain of the quail and zebra finch. Positive cells are found in the preoptic area, ventromedial and tuberal hypothalamus. AR-ir material is found in the perikarya of cells and fills the entire cellular processes including axons. At the electron microscope level, immunoreactive material can clearly be observed in the synaptic boutons. This observation raises questions concerning the mode of action of estrogens produced by central aromatization of T.

6 alpha-fluorotestosterone: a nonaromatizable androgen inhibitor of aromatase cytochrome P450

In an early survey of steroids which might serve as estrogen precursors, Gual et al. reported that 6 alpha-fluorotestosterone is not aromatized by human placental microsomes. Subsequently, 6 alpha-fluorotestosterone has been used to distinguish between androgen- and estrogen-mediated physiologic effects. We have reexamined the interaction of 6 alpha-fluorotestosterone with human placental and rat ovarian microsomes and with reconstituted purified aromatase cytochrome P450. Under conditions in which testosterone was readily aromatized, no aromatization of 6 alpha-fluorotestosterone was observed using either fluorescence detection of dansyl-estrogens separated by high-performance liquid chromatography or estrogen radioimmunoassay methods. The lack of aromatization is not due to failure of 6 alpha-fluorotestosterone to bind to P450arom, because 6 alpha-fluorotestosterone acts as a competitive inhibitor of the enzyme, and it exhibits a binding affinity similar to that of testosterone. Moreover, the addition of 6 alpha-fluorotestosterone to human placental microsomes elicits a spectral shift indicative of conversion of the heme from a low to a high spin state as observed for androgen substrates, consistent with its binding to the substrate site. The mechanism by which substitution of a fluorine at the 6 alpha-position interferes with the aromatization reaction remains to be determined, but the inhibitory action on estrogen formation may potentiate the androgenic properties of 6 alpha-fluorotestosterone in vivo due to a lowering of estrogen levels.

Sex- and age-related differences in the activity of testosterone-metabolizing enzymes in microdissected nuclei of the zebra finch brain

Many effects of testosterone (T) in the zebra finch (Taeniopygia guttata) can be mimicked by T-metabolites, mainly estradiol and 5 alpha-dihydrotestosterone. We have therefore studied the neuroanatomical distribution of testosterone-metabolizing enzymes by means of the Palkovits punch technique combined with radioenzyme assay in the brain of adult and young male and female zebra finches. The activity of these enzymes was studied by a one-point assay in 5 nuclei of the song system (X, MAN, HVc, RA, ICo), 2 nuclei of the visual system (ectostriatum, nucleus rotundus) and in limbic and hypothalamic areas. Very noticeable was the presence of a very high aromatase activity in the hippocampal and parahippocampal region and in the nucleus taeniae and the absence of this enzyme in ICo. We found a higher aromatase activity in female than male HVc and RA and a higher 5 alpha-reductase activity in MAN, HVc, RA and ICo of males compared to females. The 5 alpha-reductase was more active in the preoptic area of females. A few sex-related differences in the activity of the 5 beta-reductase were also observed (higher activity in females than in males for area X and RA, but difference in the opposite direction for the ectostriatum). The statistical significance of these differences depended, to some extent, on the statistical technique used to demonstrate them, with the sex differences in RA being by far the most robust ones. Many age-related metabolic differences were also detected but these do not have a clear interpretation since the Km of these enzymes also changes with age. Extremely low levels of 5 beta-reductase activity were found in the nuclei of the visual system in adult birds while this enzymatic activity was very high in young birds. The biological significance of this change with age remains obscure. Correlations are thus observed between the neuroanatomical distribution of T-metabolizing enzymes and of androgen and estrogen receptors with the important exception of ICo which has no aromatase but contains high concentrations of estrogen receptors. Testosterone-metabolizing enzymes are however also present in areas which are not known as steroid targets.

Correlation between the sexually dimorphic aromatase of the preoptic area and sexual behavior in quail: effects of neonatal manipulations of the hormonal milieu

The aromatase of the preoptic area is significantly more active in males than in females. This sex dimorphism in enzyme activity is still found in birds that have been gonadectomized and treated with a same dose of testosterone. This suggests that the sex difference is not the result of a differential activation by the adult hormonal environment but rather is organized neonatally by steroid hormones. As the central aromatization of testosterone is a limiting step in the activation of copulatory behavior by testosterone, the lower aromatase activity in the preoptic area of females might be responsible, at least in part, for their lower sensitivity to the activating effects of testosterone on behavior. Three experiments were carried out to determine whether early manipulations of the hormonal environment, which are known to differentiate sexual behavior, also affect in a permanent way the aromatase activity in the preoptic area. Injection of estradiol benzoate into male embryos on day 9 of incubation decreased the preoptic aromatase activity in parallel to its demasculinizing effect on behavior. Unexpectedly the same treatment tended to increase enzyme activity in females so that the physiological relevance of the observed enzymatic change remains questionable. In two independent experiments, we confirmed that neonatal ovariectomy of female quail interferes with their behavioral differentiation. Females gonadectomized at 4 days post-hatch showed significantly more male-type sexual behavior as adult in response to testosterone than females gonadectomized at the age of 5 weeks. These experiments also confirmed that the preoptic aromatase activity is higher in males than in females but no evidence for an effect of the age of gonadectomy on the enzyme activity could be obtained. The sex difference and experimental modifications observed in the aromatase activity of the preoptic area were not seen in the posterior hypothalamus demonstrating that these effects are specific. The mechanisms controlling the sex difference in aromatase activity are discussed. The difference might be organized by the action of embryonic steroids as suggested by the changes observed in males injected with estradiol benzoate in egg. Alternatively, activational mechanisms cannot be ruled out at present. In one experiment, the activity of the preoptic aromatase was positively correlated with the sexual activity of the birds.(ABSTRACT TRUNCATED AT 400 WORDS)

Contrasting effects of pre- and posthatch exposure to gonadal steroids on the development of vocal, sexual, and aggressive behavior of young domestic fowl

Prehatch treatment of domestic chicks with 17 beta-estradiol dipropionate (EDP) reduces later testosterone-facilitated sexual behavior, crowing, and suppression of peeping. Prehatch treatment with 5 alpha-dihydrotestosterone propionate (DHTP) reduces later testosterone-facilitated aggressive behavior and produces greatly enhanced avoidance that interferes with sexual behavior in some test situations. It also disturbs crowing by removing trilled call elements and increasing the number of elements/crow but has little effect on crowing posture. The majority of these results can be understood as "demasculinizing" effects of gonadal steroids on the developing male fetus, but the possibility that some result from more extreme pathological changes is also discussed. Posthatch treatment with DHTP facilitates attack and cackling but has no effect on sexual behavior or crowing; the synthetic androgen R1881 has similar effects on cackling and also has no effect on sexual behavior or crowing. Posthatch treatment with EDP enhances sexual behavior but has no effect on attack; the aromatase inhibitor 1,4,6-Androstatrien-3,17-dione (ATD) blocked the suppression of peeping by testosterone but had no effect on testosterone-facilitated sexual behavior. Combined posthatch treatment with EDP and DHTP facilitated crowing although treatment with either steroid alone was ineffective.

Distribution of estrogen receptors in the brain of the Japanese quail: an immunocytochemical study

The distribution of estrogen receptors in the quail brain was investigated by immunocytochemistry using the monoclonal antibody H222SPy raised against estrogen receptors that had been isolated from a human mammary tumor. Nuclei which contained cells labeled for estrogen receptor were identified in the telencephalon, diencephalon and mesencephalon. In particular, a high percentage of labeled cells was observed in the lateral septum, the nucleus accumbens, the preoptic medial nucleus, the supraoptic nuclei, the anterior medial hypothalamus, the paraventricular magnocellular nucleus, the caudal parts of the lateral hypothalamus and in the whole tuberal and infundibular area. A small number of weakly labeled cells was also observed in the ventromedial nucleus of the hypothalamus. Although most of the positive cells were observed in the hypothalamic and preoptic area, a few areas were also labeled in other brain regions. This was particularly the case for the nucleus taeniae, the nucleus intercollicularis and the central gray. The distribution of labeled cells in this study closely matched with the distribution of cells which accumulated radioactivity following injection of tritiated estradiol in a previous study. The distribution of cells labeled by immunocytochemistry was similar in males and females and no evidence for a quantitative dimorphism in the percentage of labeled cells could be obtained. All nuclei containing cells labeled for estrogen receptors also contain significant levels of aromatase with the exception of the ICo.

Embryonic sex steroids affect mating behavior and plasma LH in adult chickens

Chicken embryos of both sexes were treated with either antiestrogen (tamoxifen = T), antiandrogen (flutamide = F), aromatization inhibitor (ATD = A), estradiol (E), or oil (control = C). Before puberty, some males of each group were castrated. At puberty, birds were tested under the following regimes: castrated males injected daily with testosterone propionate (CAS + TP) or estradiol benzoate (CAS + EB), intact males (M-INT), intact females (F-INT), and females injected daily with TP (F-TP). In the M-INT and CAS + TP males, E treatment suppressed masculine mating behavior. The embryonic treatments with T, F, and A demasculinized only the frequency of copulations. None of the antihormone treatments caused any masculinization of the sexual activity in the F-TP birds. Untreated males had higher plasma LH than females. The embryonic treatment with E reduced (feminized) the LH levels in CAS + EB birds. This effect was less pronounced in M-INT birds. The results suggest that in chickens, estradiol plays a role in the masculinization of copulatory behavior potential in the developing male embryo. High embryonic estradiol reduces the potential for displaying male sexual behavior at puberty. Feminization of LH secretion requires a high level of estradiol in both embryonic and adult life.

Reproductive behaviour in poultry: implications for artificial insemination technology

1. Reproductive ability requires both endocrine and behavioural components. 2. Most reproductive behaviour is dependent upon the presence of sufficient circulating concentrations of the gonadal steroids, which in turn are synthesised and secreted in individuals who are in good reproductive condition. Mating behaviour patterns are thus not only essential for reproduction, but can provide excellent indices of the reproductive ability of an individual. 3. A number of factors can suppress or enhance reproductive behaviour in poultry, including management practices, flock social interactions, environmental variables, stressors, and disease. 4. Aspects of the regulation of reproductive behaviour and the endocrine control of reproductive processes in the male and in the female are reviewed in this paper. 5. An understanding of the impact of social and environmental stressors on reproductive physiology and behaviour is extremely important, both in order to improve breeding efficiency in natural mating systems and to facilitate the most effective application of artificial insemination technology.

Sexual differentiation in quail: critical period and hormonal specificity

There is a discrepancy between results showing that male quail are demasculinized by exogenous estrogens only if the treatment is given before Day 12 of egg incubation and results showing that ovariectomy of females after hatching still affects their sexual differentiation which leads to the conclusion that female demasculinization by ovarian estrogens is a continuing process extending into posthatching life. The first experiment was performed to test different models which have been proposed to reconcile these apparently contradictory results. Male and female quail were treated with 0, 5, or 25 micrograms of estradiol benzoate (EB) on either Day 9 or Day 14 of embryonic life. Birds were castrated at the age of 4 days to avoid the confounding effects of postnatal gonadal hormones and were treated as adults with testosterone (T). Whereas EB-treatment demasculizined sexual behavior and cloacal gland growth of males when administered on Day 9, it was without effect on Day 14. This result confirms the presence of a "critical period" for sexual differentiation of behavior in embryonic life. However, the time course of sexual differentiation and the sensitivity to the demasculinizing actions of estrogens were not the same for different behavioral and morphological characteristics. Some dependent variables such as plasma levels of luteinizing hormone and crowing were still affected by the EB treatment on Day 14. These results show that the whole process of demasculinization is not retricted to the "critical period" ending on Day 12 of incubation. A second experiment was performed to determine if 5 beta-dihydrotestosterone (5 beta-DHT), a metabolite of testosterone, also exerts demasculinizing effects during embryonic life. A large dose of 5 beta-DHT (2 mg/egg) had no effects on behavior and morphology in males if administered on Day 9 of egg incubation. This suggests that 5 beta-DHT, which is a steroid devoid of behavioral effects in the adult bird, is also an inactive compound as far as sexual differentiation of the quail is concerned. The high 5 beta-reductase activity which was previously identified in the hypothalamus of the embryonic quail thus probably plays a protective role. By transforming testosterone into inactive nonaromatizable androgens, it prevents male embryos from being demasculinized by their endogenous testosterone acting through aromatization.

Ontogeny of testosterone-inducible brain aromatase activity

The effects of testosterone (T) treatment on androgen-metabolizing enzymes and especially on aromatase were examined in the developing hypothalamus of quail using an in vitro microassay. Testosterone propionate (TP) injected into the pectoral muscles of one-day-old chicks had no effect on formation of 5 alpha-dihydrotestosterone (5 alpha-DHT), 5 beta-dihydrotestosterone (5 beta-DHT) and 5 beta-androstane-3 alpha, 17 beta-diol (5 beta,3 alpha-diol) in the hypothalamus. By contrast, aromatase activity was significantly enhanced in the anterior (PA) and in the posterior (HT) parts of the hypothalamus of these chicks 18-23 h after a single injection of TP. This increase was site specific as it did not occur in control non-target areas, neostriatum intermediale and hyperstriatum ventrale (VN). The increase in hypothalamic aromatase activity was accompanied by T-dependent changes in behavior and somatic development. Although aromatase activity is present as early as day 10 of embryonic life in PA and HT, it becomes inducible by circulating T only after this stage of development. There is also an important increase in basal aromatase activity during embryonic development. At day 10, when the brain is particularly sensitive to the differentiating effects of gonadal steroids, formation of 5 alpha-DHT and 5 beta-DHT in the hypothalamus is higher in females than in males. We conclude that although all important pathways of T are already present on day 10 of embryonic life, the brain metabolism of androgens continues maturing during the whole embryonic life.

Sexual differentiation and hormonal control of the sexually dimorphic medial preoptic nucleus in the quail

We recently identified a sexually dimorphic nucleus in the preoptic region of the Japanese quail, the medial preoptic nucleus (POM), which is significantly larger in males than in females. In the present study, we investigated the hormonal control of this morphological neuroanatomical difference and the possible relationships between the sexual dimorphism in POM volume and in copulatory behavior. Treatments which are known to affect sexual behavior were thus applied to different groups of birds and the POM volume was then measured. In one experiment, male and female quails were either gonadectomized, gonadectomized and treated with testosterone or left intact. The larger size of the POM in males was confirmed and treatments significantly affected the nucleus size which was decreased by gonadectomy and restored by testosterone treatment in both sexes to a level similar to that seen in intact males. In two other experiments, eggs were injected with estradiol benzoate on day 9 of incubation and the POM volume was measured in adulthood either in intact birds or in gonadectomized birds receiving a replacement therapy with testosterone. Despite the fact that estradiol benzoate treatment completely suppressed copulatory behavior, it did not affect the volume of the POM or slightly increased it. These data thus show that the POM volume is controlled by testosterone levels in adulthood and could thus be an interesting model for the study of the effects of steroids on the brain.

Plasma steroid hormone levels in free-living Wilson's phalaropes, Phalaropus tricolor

Blood samples collected from free-living Wilson's phalaropes during the reproductive season were analyzed for testosterone, dihydrotestosterone, estradiol-17 beta, and progesterone. Levels of testosterone were seven times greater in nonincubating males than in females. During incubation males underwent a reduction in testosterone and dihydrotestosterone to levels similar to those of females. Estradiol-17 beta values were higher in females than in incubating males and comparable to values reported for other avian species. Progesterone was significantly greater in females than in incubating or nonincubating males. Maximum levels of progesterone were detected in laying females. Progesterone levels increased in males during incubation while testosterone and dihydrotestosterone levels decreased. These results indicate that the greater intensity of competition for mates among females and exclusive male parental care characteristic of this species is not based upon a reversal of the typical avian levels of androgens and estrogens in males and females.

Organization and activation of behavior in quail: role of testosterone metabolism

In quail, the hypothalamus enzymatically transforms testosterone (T) into estradiol (E2), 5 alpha-dihydrotestosterone (5 alpha-DHT), and 5 beta-dihydrotestosterone (5 beta-DHT). During the embryonic life, the 5 beta-reductase activity is very high, which probably protects the brain of males from being behaviorally demasculinized by their endogenous T. 5 beta androstanes are inactive androgens. The decrease of 5 beta reductase with age during sexual maturation corresponds to a potentiation of the effects of T as shown by experiments that compared the effects of T and 5 alpha-DHT in adult and young quail. T metabolism is also involved in the activation of male behavior in the adult. T aromatization is probably essential for behavioral activation, but nonaromatizable androgens such as methyltrienolone, and to some extent 5 alpha-DHT, can also stimulate sexual behavior in castrates. These enzymatic activities show a clear neuroanatomical localization and are sexually dimorphic. Males produce more active metabolites (E2, 5 alpha-DHT) than females, which could explain the male's greater sensitivity to T treatments. It thus appears that T metabolism is involved in the differentiation and activation of behavior in quail.

Hormonal mediation of reproductive behavior

Reproductive capability requires synchronization of both endocrine and behavioral components of reproduction. The classic view of reproductive behavior was that there was simply direct stimulation of a behavioral response by the appropriate gonadal steroid. However, it has become clear with recent developments in the field of behavioral endocrinology that the relationship of hormonal and behavioral processes is complex. In addition to the complexity of the mechanisms involved, other factors, both social and environmental, influence both the endocrine and behavioral responses. This paper provides an overview of selected issues within the field of behavioral endocrinology which deal with mechanisms of hormonal induction of behavior at various stages of the life cycle and with factors that interact with these processes.