Effects of early embryonic exposure to genistein on male copulatory behavior and vasotocin system of Japanese quail

Pubertal exposure to bisphenol-A affects social recognition and arginine vasopressin in the brain of male mice

Social recognition is an ability of animals to identify and distinguish conspecifics, which is essential for nearly all social species to establish social relationships. Social recognition provides the basis for a variety of social behaviors. Because of modulated by gonadal hormones, it is possible that social cognition is affected by environmental endocrine disruptors (EEDs). In the present study, after being pubertal exposed to bisphenol A (BPA, 0.04, 0.4, and 4 mg/kg) for 18 days, adult male mice did not show significant dishabituation to a novel female stimulus in habituation-dishabituation task. The capacity for discriminating the odors between familiar and novel female urine or between male and female urine was suppressed in BPA-exposed male. In addition, BPA (0.4, 4 mg/kg) decreased the number of immunoreaction of AVP (AVP-ir) neurons in both the bed nucleus of the stria terminalis (BNST) and the medial amygdala (MeA), and BPA (0.04, 0.4, 4 mg/kg) reduced the level of V1αR in the lateral septum (LS) of adult male. Further, BPA decreased the levels of testosterone (T) in the brain and androgens receptor (AR) in the LS, the amygdala, and BNST, as well the levels of estrogen receptor α and β (ERα/β) in the amygdala and BNST. These results indicate that pubertal exposure to BPA affected the actions of both androgens and estrogens in the brain and inhibited AVP system of social circuits, and these alterations may be associated with impaired social recognition of adult male mice.

RNA Expression Profile and Alternative Splicing Signatures of Genistein-Treated Breeder Hens Revealed by Hepatic Transcriptomic Analysis

Little information has been available about the influence of dietary genistein (GEN) on hepatic transcriptome of laying broiler breeder (LBB) hens. The study is aimed at broadening the understanding of RNA expression profiles and alternative splicing (AS) signatures of GEN-treated breeder hens and thereby improving laying performance and immune function of hens during the late egg-laying period. 720 LBB hens were randomly allocated into three groups with supplemental dietary GEN doses (0, 40 mg/kg, and 400 mg/kg). Each treatment has 8 replicates of 30 birds. Dietary GEN enhanced the antioxidative capability of livers, along with the increased activities of glutathione peroxidase and catalase. Furthermore, it improved lipid metabolic status and apoptotic process in the liver of hens. 40 mg/kg dietary GEN had the better effects on improving immune function and laying performance. However, transcriptome data indicated that 400 mg/kg dietary GEN did negative regulation of hormone biosynthetic process. Also, it upregulated the expressions of EDA2R and CYR61 by the Cis regulation of neighbouring genes (lncRNA_XLOC_018890 and XLOC_024242), which might activate NF-κB and immune-related signaling pathway. Furthermore, dietary GEN induced AS events in the liver, which also enriched into immune and metabolic process. Therefore, the application of 40 mg/kg GEN in the diet of breeder hens during the late egg-laying period can improve lipid metabolism and immune function. We need to pay attention to the side-effects of high-dose GEN on the immune function.

Postnatal genistein administration selectively abolishes sexual dimorphism in specific hypothalamic dopaminergic system in mice

As demonstrated in previous studies, early postnatal genistein (GEN) administration to mice pups of both sexes, at doses similar to that of infant soy-based formulas, may affect the development of some steroid-sensitive neuronal circuits (i.e. nitrergic and vasopressinergic systems), causing irreversible alterations in adults. Here, we investigated the hypothalamic and mesencephalic dopaminergic system (identified with tyrosine hydroxylase immunohistochemistry). GEN administration (50 mg/kg) to mice of both sexes during the first week of postnatal life specifically affected tyrosine hydroxylase immunohistochemistry in the hypothalamic subpopulation of neurons, abolishing their sexual dimorphism. On the contrary, we did not observe any effects in the mesencephalic groups. Due to the large involvement of dopamine in circuits controlling rodent sexual behavior and food intake, these results clearly indicate that the early postnatal administration of GEN may irreversibly alter the control of reproduction, of energetic metabolism, and other behaviors. These results suggest the need for a careful evaluation of the use of soy products in both human and animal newborns.

Effects of Phytoestrogens on the Developing Brain, Gut Microbiota, and Risk for Neurobehavioral Disorders

Many pregnant and nursing women consume high amounts of soy and other plant products that contain phytoestrogens, such as genistein (GEN) and daidzein. Infants may also be provided soy based formulas. With their ability to bind and activate estrogen receptors (ESR) in the brain, such compounds can disrupt normal brain programming and lead to later neurobehavioral disruptions. However, other studies suggest that maternal consumption of soy and soy based formulas containing such phytoestrogens might lead to beneficial behavioral effects. Select gut microbes might also convert daidzein and to a lesser extent genistein to even more potent forms, e.g., equol derivatives. Thus, infant exposure to phytoestrogens may result in contrasting effects dependent upon the gut flora. It is also becoming apparent that consumption or exposure to these xenoestrogens may lead to gut dysbiosis. Phytoestrogen-induced changes in gut bacteria might in turn affect the brain through various mechanisms. This review will consider the evidence to date in rodent and other animal models and human epidemiological data as to whether developmental exposure to phytoestrogens, in particular genistein and daidzein, adversely or beneficially impact offspring neurobehavioral programming. Consideration will be given to potential mechanisms by which such compounds might affect neurobehavioral responses. A better understanding of effects perinatal exposure to phytoestrogen can exert on brain programming will permit pregnant women and those seeking to become pregnant to make better-educated choices. If phytoestrogen-induced gut dysbiosis contributes to neurobehavioral disruptions, remediation strategies may be designed to prevent such gut microbiota alterations and thereby improve neurobehavioral outcomes.

Early genistein exposure of California mice and effects on the gut microbiota-brain axis

Human offspring encounter high amounts of phytoestrogens, such as genistein (GEN), through maternal diet and soy-based formulas. Such chemicals can exert estrogenic activity and thereby disrupt neurobehavioral programming. Besides inducing direct host effects, GEN might cause gut dysbiosis and alter gut metabolites. To determine whether exposure to GEN affects these parameters, California mice (Peromyscus californicus) dams were placed 2 weeks prior to breeding and throughout gestation and lactation on a diet supplemented with GEN (250 mg/kg feed weight) or AIN93G phytoestrogen-free control diet (AIN). At weaning, offspring socio-communicative behaviors, gut microbiota and metabolite profiles were assayed. Exposure of offspring to GEN-induced sex-dependent changes in gut microbiota and metabolites. GEN exposed females were less likely to investigate a novel female mouse when tested in a three-chamber social test. When isolated, GEN males and females exhibited increased latency to elicit their first call, suggestive of reduced motivation to communicate with other individuals. Correlation analyses revealed interactions between GEN-induced microbiome, metabolome and socio-communicative behaviors. Comparison of GEN males with AIN males revealed the fraction of calls above 20 kHz was associated with daidzein, α-tocopherol, Flexispira spp. and Odoribacter spp. Results suggest early GEN exposure disrupts normal socio-communicative behaviors in California mice, which are otherwise evident in these social rodents. Such effects may be due to GEN disruptions on neural programming but might also be attributed to GEN-induced microbiota shifts and resultant changes in gut metabolites. Findings indicate cause for concern that perinatal exposure to GEN may detrimentally affect the offspring microbiome-gut-brain axis.

Animal models of endocrine disruption

Endocrine disrupting chemicals (EDCs) are compounds that alter the structure and function of the endocrine system and may be contributing to disorders of the reproductive, metabolic, neuroendocrine and other complex systems. Typically, these outcomes cannot be modeled in cell-based or other simple systems necessitating the use of animal testing. Appropriate animal model selection is required to effectively recapitulate the human experience, including relevant dosing and windows of exposure, and ensure translational utility and reproducibility. While classical toxicology heavily relies on inbred rats and mice, and focuses on apical endpoints such as tumor formation or birth defects, EDC researchers have used a greater diversity of species to effectively model more subtle but significant outcomes such as changes in pubertal timing, mammary gland development, and social behaviors. Advances in genomics, neuroimaging and other tools are making a wider range of animal models more widely available to EDC researchers.

Hormonally active phytochemicals and vertebrate evolution

Living plants produce a diversity of chemicals that share structural and functional properties with vertebrate hormones. Wildlife species interact with these chemicals either through consumption of plant materials or aquatic exposure. Accumulating evidence shows that exposure to these hormonally active phytochemicals (HAPs) often has consequences for behavior, physiology, and fecundity. These fitness effects suggest there is potential for an evolutionary response by vertebrates to HAPs. Here, we explore the toxicological HAP-vertebrate relationship in an evolutionary framework and discuss the potential for vertebrates to adapt to or even co-opt the effects of plant-derived chemicals that influence fitness. We lay out several hypotheses about HAPs and provide a path forward to test whether plant-derived chemicals influence vertebrate reproduction and evolution. Studies of phytochemicals with direct impacts on vertebrate reproduction provide an obvious and compelling system for studying evolutionary toxicology. Furthermore, an understanding of whether animal populations evolve in response to HAPs could provide insightful context for the study of rapid evolution and how animals cope with chemical agents in the environment.

Embryonic environment and transgenerational effects in quail

Background

Environmental exposures, for instance to chemicals, are known to impact plant and animal phenotypes on the long term, sometimes across several generations. Such transgenerational phenotypes were shown to be promoted by epigenetic alterations such as DNA methylation, an epigenetic mark involved in the regulation of gene expression. However, it is yet unknown whether transgenerational epigenetic inheritance of altered phenotypes exists in birds. The purpose of this study was to develop an avian model to investigate whether changes to the embryonic environment had a transgenerational effect that could alter the phenotypes of third-generation offspring. Given its impact on the mammalian epigenome and the reproductive system in birds, genistein was used as an environment stressor.

Results

We compared several third-generation phenotypes of two quail “epilines”, which were obtained from genistein-injected eggs (Epi+) or from untreated eggs (Epi−) from the same founders. A “mirrored” crossing strategy was used to minimize between-line genetic variability by maintaining similar ancestor contributions across generations in each line. Three generations after genistein treatment, a significant difference in the sexual maturity of the females, which, after three generations, could not be attributed to direct maternal effects, was observed between the lines, with Epi+ females starting to lay eggs later. Adult body weight was significantly affected by genistein treatment applied in a previous generation, and a significant interaction between line and sex was observed for body weight at 3 weeks. Behavioral traits, such as evaluating the birds’ reaction to social isolation, were also significantly affected by genistein treatment. Yet, global methylation analyses revealed no significant difference between the epilines.

Conclusions

These findings demonstrate that embryonic environment affects the phenotype of offspring three generations later in quail. While one cannot rule out the existence of some initial genetic variability between the lines, the mirrored animal design should have minimized its effects, and thus, the observed differences in animals of the third generation may be attributed, at least partly, to transgenerational epigenetic phenomena.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-017-0292-7) contains supplementary material, which is available to authorized users.

Early postnatal genistein administration permanently affects nitrergic and vasopressinergic systems in a sex-specific way

Genistein (GEN) is a natural xenoestrogen (isoflavonoid) that may interfere with the development of estrogen-sensitive neural circuits. Due to the large and increasing use of soy-based formulas for babies (characterized by a high content of GEN), there are some concerns that this could result in an impairment of some estrogen-sensitive neural circuits and behaviors. In a previous study, we demonstrated that its oral administration to female mice during late pregnancy and early lactation induced a significant decrease of nitric oxide synthase-positive cells in the amygdala of their male offspring. In the present study, we have used a different experimental protocol mimicking, in mice, the direct precocious exposure to GEN. Mice pups of both sexes were fed either with oil, estradiol or GEN from birth to postnatal day 8. Nitric oxide synthase and vasopressin neural systems were analyzed in adult mice. Interestingly, we observed that GEN effect was time specific (when compared to our previous study), sex specific, and not always comparable to the effects of estradiol. This last observation suggests that GEN may act through different intracellular pathways. Present results indicate that the effect of natural xenoestrogens on the development of the brain may be highly variable: a plethora of neuronal circuits may be affected depending on sex, time of exposure, intracellular pathway involved, and target cells. This raises concern on the possible long-term effects of the use of soy-based formulas for babies, which may be currently underestimated.

Endocrine Disruption of Vasopressin Systems and Related Behaviors

Endocrine disrupting chemicals (EDCs) are chemicals that interfere with the organizational or activational effects of hormones. Although the vast majority of the EDC literature focuses on steroid hormone signaling related impacts, growing evidence from a myriad of species reveals that the nonapeptide hormones vasopressin (AVP) and oxytocin (OT) may also be EDC targets. EDCs shown to alter pathways and behaviors coordinated by AVP and/or OT include the plastics component bisphenol A (BPA), the soy phytoestrogen genistein (GEN), and various flame retardants. Many effects are sex specific and likely involve action at nuclear estrogen receptors. Effects include the elimination or reversal of well-characterized sexually dimorphic aspects of the AVP system, including innervation of the lateral septum and other brain regions critical for social and other non-reproductive behaviors. Disruption of magnocellular AVP function has also been reported in rats, suggesting possible effects on hemodynamics and cardiovascular function.

Perinatal exposure to genistein affects the normal development of anxiety and aggressive behaviors and nitric oxide system in CD1 male mice

Genistein is a phytoestrogen, particularly abundant in soybeans, that is able to bind estrogen receptors exerting both estrogenic and antiestrogenic activities. Genistein is largely present in the human diet even during pregnancy. Embryos and fetuses are therefore, commonly exposed to genistein during the development and after birth. In the present study, we used a murine model as a test end-point to investigate the effects of early exposure to genistein on adult male behavior and related neural circuits. Daily exposure of dams to genistein (100 μg/g of body weight) during late pregnancy and early lactation, produced in male offspring, when adults, significant changes in anxiety and aggressive behaviors. Moreover, we found statistically significant variations in the number of neuronal nitric-oxide synthase positive cells in the amygdala. In conclusions, these data indicate that early exposure to phytoestrogens may induce life-long effects on the differentiation of brain structures and behaviors.

Endocrine-disrupting chemicals: associated disorders and mechanisms of action

The incidence and/or prevalence of health problems associated with endocrine-disruption have increased. Many chemicals have endocrine-disrupting properties, including bisphenol A, some organochlorines, polybrominated flame retardants, perfluorinated substances, alkylphenols, phthalates, pesticides, polycyclic aromatic hydrocarbons, alkylphenols, solvents, and some household products including some cleaning products, air fresheners, hair dyes, cosmetics, and sunscreens. Even some metals were shown to have endocrine-disrupting properties. Many observations suggesting that endocrine disruptors do contribute to cancer, diabetes, obesity, the metabolic syndrome, and infertility are listed in this paper. An overview is presented of mechanisms contributing to endocrine disruption. Endocrine disruptors can act through classical nuclear receptors, but also through estrogen-related receptors, membrane-bound estrogen-receptors, and interaction with targets in the cytosol resulting in activation of the Src/Ras/Erk pathway or modulation of nitric oxide. In addition, changes in metabolism of endogenous hormones, cross-talk between genomic and nongenomic pathways, cross talk with estrogen receptors after binding on other receptors, interference with feedback regulation and neuroendocrine cells, changes in DNA methylation or histone modifications, and genomic instability by interference with the spindle figure can play a role. Also it was found that effects of receptor activation can differ in function of the ligand.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.

Endocrine disrupters: a review of some sources, effects, and mechanisms of actions on behaviour and neuroendocrine systems

Some environmental contaminants interact with hormones and may exert adverse consequences as a result of their actions as endocrine disrupting chemicals (EDCs). Exposure in people is typically a result of contamination of the food chain, inhalation of contaminated house dust or occupational exposure. EDCs include pesticides and herbicides (such as dichlorodiphenyl trichloroethane or its metabolites), methoxychlor, biocides, heat stabilisers and chemical catalysts (such as tributyltin), plastic contaminants (e.g. bisphenol A), pharmaceuticals (i.e. diethylstilbestrol; 17α-ethinylestradiol) or dietary components (such as phytoestrogens). The goal of this review is to address the sources, effects and actions of EDCs, with an emphasis on topics discussed at the International Congress on Steroids and the Nervous System. EDCs may alter reproductively-relevant or nonreproductive, sexually-dimorphic behaviours. In addition, EDCs may have significant effects on neurodevelopmental processes, influencing the morphology of sexually-dimorphic cerebral circuits. Exposure to EDCs is more dangerous if it occurs during specific 'critical periods' of life, such as intrauterine, perinatal, juvenile or puberty periods, when organisms are more sensitive to hormonal disruption, compared to other periods. However, exposure to EDCs in adulthood can also alter physiology. Several EDCs are xenoestrogens, which can alter serum lipid concentrations or metabolism enzymes that are necessary for converting cholesterol to steroid hormones. This can ultimately alter the production of oestradiol and/or other steroids. Finally, many EDCs may have actions via (or independent of) classic actions at cognate steroid receptors. EDCs may have effects through numerous other substrates, such as the aryl hydrocarbon receptor, the peroxisome proliferator-activated receptor and the retinoid X receptor, signal transduction pathways, calcium influx and/or neurotransmitter receptors. Thus, EDCs, from varied sources, may have organisational effects during development and/or activational effects in adulthood that influence sexually-dimorphic, reproductively-relevant processes or other functions, by mimicking, antagonising or altering steroidal actions.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Bisphenol A interferes with synaptic remodeling

The potential adverse effects of Bisphenol A (BPA), a synthetic xenoestrogen, have long been debated. Although standard toxicology tests have revealed no harmful effects, recent research highlighted what was missed so far: BPA-induced alterations in the nervous system. Since 2004, our laboratory has been investigating one of the central effects of BPA, which is interference with gonadal steroid-induced synaptogenesis and the resulting loss of spine synapses. We have shown in both rats and nonhuman primates that BPA completely negates the ∼ 70-100% increase in the number of hippocampal and prefrontal spine synapses induced by both estrogens and androgens. Synaptic loss of this magnitude may have significant consequences, potentially causing cognitive decline, depression, and schizophrenia, to mention those that our laboratory has shown to be associated with synaptic loss. Finally, we discuss why children may particularly be vulnerable to BPA, which represents future direction of research in our laboratory.

Multi-generational effects of polybrominated diphenylethers exposure: embryonic exposure of male American kestrels (Falco sparverius) to DE-71 alters reproductive success and behaviors

Polybrominated diphenylethers (PBDEs) are additive flame-retardants that are environmentally persistent and bioaccumulative compounds of particular concern to species at high trophic levels, including predatory birds. The developmental effects of in ovo exposure to male birds at environmentally relevant levels of the PBDE technical mixture, DE-71, on reproductive success and behaviors using captive American kestrels (Falco sparverius) were determined. Males were exposed in ovo by direct maternal transfer to DE-71 and unintentionally to low concentrations of hexabromocyclododecane (HBCD) at three mean +/- standard error DE-71 concentrations of 288.60 +/- 33.35 ng/g wet weight (low-exposure), 1130.59 +/- 95.34 ng/g wet weight (high-exposure), or background levels of 3.01 +/- 0.46 ng/g wet weight (control). One year following exposure, males were paired with unexposed females. Reproductive success was lower in the high exposure pairs: 43% failed to lay eggs while all other pairs laid complete clutches; they also laid smaller clutches and produced smaller eggs with reduced fertility, parameters that were negatively correlated with paternal in ovo concentrations of all PBDEs, as well as individual congeners and HBCD. Throughout courtship, there were fewer copulations by all in ovo exposed males, fewer mate-calls made by high-exposure males, and decreasing trends in pair-bonding and nest-box behaviors across treatments that continued during brood rearing. The reductions in clutch size and fertility were associated with the reduced frequencies of male courtship behaviors, and were associated with increasing concentrations of the PBDE congeners BDE-47, -99, -100, -53, -138, and HBCD. The results of the present study confirm effects noted in the F(0) generation and demonstrate that exposure to DE-71 affects multiple generations of this predatory avian species at environmentally relevant levels of exposure.

Effects on differentiation of reproductive organs and sexual behaviour in Japanese quail by excessive embryonic ERalpha activation

Exposure of Japanese quail (Coturnix japonica) embryos to oestrogenic substances disrupts sexual differentiation of the reproductive tract of both sexes and impairs the copulatory behaviour of the adult male. To examine whether these effects can be induced by selective activation of oestrogen receptor alpha (ERalpha), Japanese quail eggs were injected with various doses of the selective ERalpha agonist 16alpha-lactone-oestradiol (16alpha-LE(2)). The natural oestrogen 17beta-oestradiol (E(2)) was used as a positive control. Both 16alpha-LE(2) and E(2) induced formation of an ovary-like cortex in the left testis (ovotestis) and reduced the size of the right testis in male embryos. The asymmetry in testis size remained in sexually mature males. Both substances induced retention and malformation of the Müllerian ducts in embryos of both sexes and malformed oviducts in juveniles. Male copulatory behaviour was suppressed by embryonic exposure to E(2) and the highest dose of 16alpha-LE(2). However, the lower dose of 16alpha-LE(2), which markedly affected development of the reproductive organs, was without effects on behaviour. It can therefore not be excluded that the behavioural demasculinisation at the 100-fold higher dose involved cross-activation of oestrogen receptor beta (ERbeta). In conclusion, our results suggest that oestrogen-induced disruption of reproductive organ development in Japanese quail can be mediated via ERalpha, whereas the role of ERalpha in demasculinisation of copulatory behaviour remains to be clarified.

Genistein induces phosphorylation of cAMP response element-binding protein in neonatal hypothalamus in vivo

We investigated the effect of the phytoestrogen, genistein and 17beta-oestradiol on cAMP response element-binding protein (CREB) phosphorylation in the neonatal female rat hypothalamus in vivo using western blot analysis and immunohistochemistry. Although CREB expression was insensitive to the compounds we tested, administration of genistein and 17beta-oestradiol induced rapid CREB phosphorylation (< 15 min) in the hypothalamus and its level remained elevated at 4 h. Quantitative immunohistochemical analysis showed that genistein and 17beta-oestradiol had no effect on CREB phosphorylation in the magnocellular subdivision of paraventricular nucleus. By contrast, genistein induced a dose-dependent increase in CREB phosphorylation in the medial preoptic area (mPOA) and anteroventral periventricular nucleus (AVPV). Administration of 17beta-oestradiol also caused a rapid, dose-dependent increase in CREB phosphorylation in the hypothalamus, mPOA and AVPV. These results demonstrate that genistein induces oestrogen-like rapid action on CREB phosphorylation in the neonatal central nervous system in vivo.

Effects of estrogens on sex differentiation in Japanese quail and chicken

Estrogen production by the female avian embryo induces development of a female phenotype of the reproductive organs whereas the low estrogen concentration in the male embryo results in a male phenotype. Treatment of female embryos with exogenous estrogens disrupts Müllerian duct development resulting in malformations and impaired oviductal function. Exposure of male embryos to estrogens results in ovotestis formation and persisting Müllerian ducts in the embryos and testicular malformations, reduced semen production and partially developed oviducts in the adult bird. Furthermore, studies in Japanese quail show that the male copulatory behavior is impaired by embryonic estrogen treatment. Results from our experiments with selective agonists for ERalpha and ERbeta suggest that the effects of estrogens on the reproductive organs are mediated via activation of ERalpha. Abundant expression of ERalpha mRNA was shown in gonads and Müllerian ducts of early Japanese quail embryos. Both ERalpha and ERbeta transcripts were detected by real-time PCR in early embryo brains of Japanese quail indicating that both receptors may be involved in sex differentiation of the brain. However, in 9-day-old quail embryo brains in situ hybridization showed expression of ERbeta mRNA, but not of ERalpha mRNA, in the medial preoptic nucleus (POM) and the bed nucleus of the stria terminalis (BSTm), areas implicated in copulatory behavior of adult male quail. Furthermore, embryonic treatment with the selective ERalpha agonist propyl pyrazol triol (PPT) had no effect on the male copulatory behavior. These results suggest that ERbeta may be important for the effects of estrogens on brain differentiation.

Phytoestrogens and avian reproduction: Exploring the evolution and function of phytoestrogens and possible role of plant compounds in the breeding ecology of wild birds

Phytoestrogens are secondary plant compounds, which can act to mimic estrogen and cause the disruption of estrogenic responses in organisms. Although there is a substantial body of research studying phytoestrogens, including their mechanisms of estrogenic effects, evolution, and detection in biological systems, little is known about their ecological significance. There is evidence, however, that an ecological relationship involving phytoestrogens exists between plants and animals-plants may produce phytoestrogens to reduce fecundity of organisms that eat them. Birds and other vertebrates may also exploit phytoestrogens to regulate their own reproduction-there are well known examples of phytoestrogens inhibiting reproduction in higher vertebrates, including birds. Also, common plant stressors (e.g., high temperature) increase the production of secondary plant compounds, and, as evidence suggests, also induce phytoestrogen biosynthesis. These observations are consistent with the single study ever done on phytoestrogens and reproduction in wild birds [Leopold, A.S., Erwin, M., Oh, J., Browning, B., 1976. Phytoestrogens adverse effects on reproduction in California quail. Science 191, 98-100.], which found that drought stress correlated with increased levels of phytoestrogens in plants, and that increased phytoestrogen levels correlated with decreased young. This review discusses the hypothesis that plants may have an effect on the reproduction of avian species by producing phytoestrogens as a plant defense against herbivory, and that birds may "use" changing levels of phytoestrogens in the vegetation to ensure that food resources will support potential young produced. Evidence from our laboratory and others appear to support this hypothesis.

Organizational effects of DDE on brain vasotocin system in male Japanese quail

p,p'-DDE, or ethylene, 1,1-dichloro-2,2-bis(p-chlorophenyl), is the main metabolite of the pesticide DDT, or 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane. It is an androgen receptor antagonist and testosterone hydroxylase modulator that is also more persistent than its parent compound. In a previous study we demonstrated that embryonic exposure to different doses of p,p'-DDE accelerated onset of puberty in females and reduced male reproductive behavior. In the present study we investigated the long-term effects of the exposure to p,p'-DDE on the differentiation of male Japanese quail (Coturnix japonica) limbic circuits related to male copulatory behavior: the parvocellular vasotocin (VT) system. We observed a decrease in the density of VT-immunoreactive fibers within the medial preoptic nucleus, bed nucleus of the stria terminalis, and lateral septum in p,p'-DDE-treated birds, while no differences could be detected in the magnocellular neurons of the supraoptic nucleus. In particular the lowest dose of p,p'-DDE causes the highest decrease of VT immunoreactivity. This study provides further evidence for VT system sensitivity towards endocrine disrupting chemicals and demonstrates that the VT system may be an appropriate and sensitive biomarker for early p,p'-DDE exposure in birds.

Selective activation of estrogen receptor alpha in Japanese quail embryos affects reproductive organ differentiation but not the male sexual behavior or the parvocellular vasotocin system

Estradiol is crucial for normal female differentiation in birds. Developmental effects of estrogen are believed to be mediated by slow genomic actions through the nuclear estrogen receptors alpha (ERalpha) and/or beta (ERbeta). Consequently, exogenous compounds that interfere with the ERs may disrupt sexual differentiation of the reproductive organs and of the brain areas controlling sexual behaviors. The present study was conducted to elucidate the role of ERalpha in xenoestrogen-induced disruption of sexual differentiation in the Japanese quail (Coturnix japonica). Embryonic treatment with the synthetic estrogen, ethinylestradiol (EE(2)), and with the ERalpha-selective agonist, propyl pyrazole triol (PPT), induced oviductal malformations in females and retention of oviducts in males. Both EE(2) and PPT caused weight asymmetry between left and right testes and reduced the cloacal gland area in males. EE(2) significantly reduced the copulatory behavior in males whereas PPT had no effect on this behavior. The sexually dimorphic parvocellular vasotocin-immunoreactive (VT-ir) system in the medial preoptic nucleus (POM), the lateral septum (SL) and the medial part of the nucleus of the stria terminalis (BSTm), was not affected by EE(2) or PPT. Our results suggest that xenoestrogen-induced effects on reproductive organ differentiation are mediated by ERalpha, whereas demasculinization of male copulatory behavior and the VT-ir system appears not to be induced by activation of ERalpha alone.

Effects of xenoestrogens on the differentiation of behaviorally-relevant neural circuits

It has become increasingly clear that environmental chemicals have the capability of impacting endocrine function. Moreover, these endocrine disrupting chemicals (EDCs) have long term consequences on adult reproductive function, especially if exposure occurs during embryonic development thereby affecting sexual differentiation. Of the EDCs, most of the research has been conducted on the effects of estrogen active compounds. Although androgen active compounds are also present in the environment, much less information is available about their action. However, in the case of xenoestrogens, there is mounting evidence for long-term consequences of early exposure at a range of doses. In this review, we present data relative to two widely used animal models: the mouse and the Japanese quail. These two species long have been used to understand neural, neuroendocrine, and behavioral components of reproduction and are therefore optimal models to understand how these components are altered by precocious exposure to EDCs. In particular we discuss effects of bisphenol A and methoxychlor on the dopaminergic and noradrenergic systems in rodents and the impact of these alterations. In addition, the effects of embryonic exposure to diethylstilbestrol, genistein or ethylene,1,1-dichloro-2,2-bis(p-chlorophenyl) is reviewed relative to behavioral impairment and associated alterations in the sexually dimorphic parvocellular vasotocin system in quail. We point out how sexually dimorphic behaviors are particularly useful to verify adverse developmental consequences produced by chemicals with endocrine disrupting properties, by examining either reproductive or non-reproductive behaviors.

Neuroendocrine and behavioral effects of embryonic exposure to endocrine disrupting chemicals in birds

Endocrine disrupting chemicals (EDCs) exert hormone-like activity in vertebrates and exposure to these compounds may induce both short- and long-term deleterious effects including functional alterations that contribute to decreased reproduction and fitness. An overview of the effects of a number of EDCs, including androgenic and estrogenic compounds, will be considered. Many studies have been conducted in the precocial Japanese quail, which provides an excellent avian model for testing these compounds. Long-term impacts have also been studied by raising a subset of animals through maturation. The EDCs examined included estradiol, androgen active compounds, soy phytoestrogens, and atrazine. Effects on behavior and hypothalamic neuroendocrine systems were examined. All EDCs impaired reproduction, regardless of potential mechanism of action. Male sexual behavior proved to be a sensitive index of EDC exposure and embryonic exposure to a variety of EDCs consistently resulted in impaired male sexual behavior. Several hypothalamic neural systems proved to be EDC responsive, including arginine vasotocin (VT), catecholamines, and gonadotropin releasing hormone system (GnRH-I). Finally, EDCs are known to impact both the immune and thyroid systems; these effects are significant for assessing the overall impact of EDCs on the fitness of avian populations. Therefore, exposure to EDCs during embryonic development has consequences beyond impaired function of the reproductive axis. In conclusion, behavioral alterations have the advantage of revealing both direct and indirect effects of exposure to an EDC and in some cases can provide a valuable clue into functional deficits at different physiological levels.